NST shared lectures Flashcards
(330 cards)
1
Q
Parthenogenesis
A
Asexual reproduction
- offspring are genetically identical, or very similar, to the single parent
- offspring generated entirely by mitosis
- rapid and efficient method of propagation
- some fish and reptiles
2
Q
Sexual reproduction
A
- offspring are genetically novel due to mixing of genes from two parents
- offspring generated by fusion of haploid gametes produced by meiosis
- genetic diversity to enable natural selection in different environments
3
Q
Sexual differentiation of mammals
A
- XX homogametic oocytes
- XY heterogametic sperm
- genotype identified by the sperm at fertilisation
- Sry gene is the sex determining region of the Y chromosome
4
Q
Sexual differentiation of birds
A
- ZZ homogametic sperm
- ZW heterogametic oocyte
- genotype determined by oocyte at fertilisation
- Dmrt1 gene on the Z chromosome induces testes development
5
Q
Sexual differentiation of reptiles
A
- no sex chromosomes
- temperature sensitive sex determining genes
- turtle eggs>32degrees = females, <28degrees = male
- temperature may alter levels of aromatase activity: testosterone to oestrogen
6
Q
Migration of primordial germ cells
A
They arise at the base of the allantois. Migrate via the hindgut to the genital ridges. Genital ridges then develop into testes or ovaries
7
Q
Differential localization of primordial germ cells in the genital ridge
A
Female germ cells move to the cortex. This is where they initiate meiosis and arrest in the 1st meiotic division.
Male germ cells line up along the cords in the medulla. They arrest in mitosis.
8
Q
Specific genes that promote testicular development.
A
Sry- triggers Sertoli cell differentiation, suppresses dax1 gene expression (sex determining region of the Y chromosome
sox9- maintains sertoli cell differentiation and function, activates Mullerian inhibiting hormone (MIH)
9
Q
Anti-testes genes that promote ovarian development
A
dax1- inhibits activity of sox9 and other male-determining genes
wnt4- suppresses the production of androgens
10
Q
General genes that promote gonadal development
A
sf1- activates MIH gene and genes involved in steroid biosynthesis
wt1- promotes early gonadal development
11
Q
Sexual differentiation of internal genitalia
A
Mesonephric Wolffian duct persists in males (induced).
Paramesonephric Mullerian duct persist in females (default).
12
Q
Experimental animals with Mullerian duct
A
Normal female, ovariectomised female, castrated male, castrated male with androgens, knockout-MIH male.
13
Q
Testicular hormones
A
Testosterone maintains the Wolffian duct.
Mullerian inhibiting hormone causes regression of the Müllerian duct.
14
Q
Developmental control of male gonads (testis)
A
Y chromosome- sry gene
15
Q
Developmental control of female gonads (ovaries)
A
No Y chromosome- no sry gene
16
Q
Developmental control of male internal genitalia (epididymis, vas deferents, seminal vesicles, prostate gland)
A
Androgens, MIH
17
Q
Developmental control of female internal genitalia (oviducts, uterus, cervix, upper vagina)
A
Lack of MIH
18
Q
Developmental control of male external genitalia (penis, scrotum) (testicular descent)
A
Androgens
Androgens, MIH, INSL3 (gubernaculum)
19
Q
Developmental control of female external genitalia (labia, clitoris)
A
Lack of androgens
20
Q
Brain sex experiments
A
Female + testes at birth = no ovarian cycles (can’t support LH surge)
Male + remove testes at birth + ovaries in adulthood = ovarian cycles
Male + remove testes in adulthood + ovaries in adulthood =no ovarian cycles
Brain is masculinised but exposure to androgens over perinatal period
21
Q
Abnormalities in chromosome sex
A
Klinefelter’s syndrome: XXY, impaired testicular development, infertile
Turners syndrome: XO, impaired ovarian development, infertile
Super female: XXX, fertile
Super male: XYY, fertile
Sex reversed: XX but with sry gene, infertile
22
Q
Other abnormalities in sexual differentiation
A
Failure to respond to gonadal hormones
Testicular feminisation/ androgen hypersensitivity syndrome: XY, mutation in androgen receptor, abdominal testes, no male or female internal tracts, female external genitalia and breast development
Inappropriate
23
Q
Functions of sertoIi cells
A
Sexual differentiation of male phenotype
Control of spermatogenesis
Mechanical support
Production of seminiferous fluid and androgen binding proteins
Formation of blood-testis barrier
24
Q
Functions of blood testis barrier
A
Prevent auto-antibody production- spermatogenesis only starts at puberty so no immunological tolerance
Prevent entry of toxic substances
Create a special tubular environment
25
Stages of spermatogenesis
Stem cells (A0 spermatogonia)
More levels of spermatogonia(A1-4), intermediate, B- mitosis
Primary and secondary spermatocytes- meiosis
Spermatids- meiosis and spermiogenesis
Sperm and residual bodies- spermiogenesis
26
Structure of spermatogenesis
Seminiferous tubules are composed of Sertoli cells and spermatogonia cells.
The Sertoli cells form tight junctions next to each other- the blood test is barrier.
The spermatogenic cells migrate from the basal compartment to the adluminal compartment as they develop.
Leydig cells are found in the interstitial space- they produce testosterone.
27
Temperature and spermatogenesis
Scrotal testes:
- 4-7 degrees lower than body temperature
- sweat glands
- counter current heat exchanger
Intra abdominal testes:
- at core temperature
- species that have this still produce sperm
- e.g. elephants, dolphins, whales etc
28
Stages of spermiogenesis
Micro structural adaptations that take place in the developing haploid sperm.
Formation of the acrosome, flagellum and mitochondrial sheath.
Condensation of nucleus and removal of the residual cytoplasm.
29
Structure of mature sperm
Head- contains DNA
Midspace- contains lots of mitochondria
Tail
30
Spermatogenic cycle
The time between reinitiation of successive rounds of spermatogenesis. Helps to ensure continuous sperm production in the seminiferous tubules. It results in specific associations of cell types in the seminiferous tubules.
31
Spermatogenic wave
The cell associations change progressively along the length of the seminiferous tubule.
32
Mechanisms to ensure continuous sperm production
Renewable A0 spermatogonia
Spermatogenic cycle
Spermatogenic wave
33
Hormonal control of testicular function
Hypothalamus—GnRH—> anterior pituitary
Anterior pituitary —LH—> leydig cells
Leydig cells —testosterone—> Sertoli cells
Anterior pituitary —FSH—> Sertoli cells
Sertoli cells germ cells
Leydig cells —Testosterone—I hypothalamus and anterior pituitary
Sertoli cells —inhibin—I anterior pituitary
34
Tubular structure of the male gonad and reproductive tract
Seminiferous tubules—>rete testis—> efferent ducts—>epididymis—> vas deferens
35
Maturational changes that take place in the epididymis
Develop capacity to swim
Changes to surface of sperm head
- EPPIN: epididymal peptidase inhibitor, inhibits motility
- LIPOCALINS: prevent premature acrosome release
Changes in metabolism from use of endogenous glucose to external fructose. Express fructose transporter GLUT5
Changes of sperm structure and loss of cytoplasmic droplet
36
Composition of seminal fluid (what do the accessory glands add?)
Seminiferous tubules: spermatozoa, salts, ions
Seminal vesicles: fructose, prostaglandins, fibrinogen-like proteins
Prostate gland: coagulating enzymes, proteolytic enzymes
Bulbourethral gland: mucus
37
Nervous control of erections and what it causes
Parasympathetic:
ACh—> nitric oxide—> cGMP—> smooth muscle relaxation
Causes vasodilation in penis: increased blood flow to sinuses (corpus cavernosus and corpus spongiosum)
38
Ejaculation
Smooth muscle contraction in bad deferens and accessory glands.
Sympathetic control.
39
pH of semen
7.2-7.8
40
Which domestic animal produces the highest volume of sperm?
Boar
41
Obstacles faced by sperm
```
Distance
General losses
Unfavourable vaginal pH (5.0-6.0)
Female immune system
Cervical mucus
Oviductal fluid movement
```
42
Oviductal fluid movement overcome by:
Rheotaxis (head on to prevent resistance)
Oviduct sphincter muscle
Cilia movement (free ride)
43
Stages of fertilisation
Spermatozoa penetrate the layer of cumulus oophorus cells surrounding the ovum.
Release of enzymes, hyaluronidase and acrosin and bind to the ZP3 protein in the zona pellucida.
Sperm entry causes release of Ca2+ in the pocket.
This leads to secretion of cortical granules.
Enzymes of the cortical granules cleave the binding site of ZP3 preventing further attachment (polyspermy).
The two pro nuclei fuse to form the zygotes nucleus.
44
Capacitation
Freshly ejaculated sperm cannot fertilise.
Capacitation is required for sperm binding to egg via ZP3 protein.
Removal of glycoproteins coating sperm (CRISPR- inhibits CATSPER)
Increased motility
Increased permeability and sensitivity to Ca2+
45
Zona pellucida proteins
ZP1- structural cross link between ZP2 and ZP3
ZP2- binds acrosome-reacted sperm. Facilitates spermatogenic passage through zona pellucida.
ZP3- binds transiently to acrosome-intact sperm. Stimulates Ca2+ influx and acrosome reaction.
46
Acrosome reaction
Release of digestive enzymes from acrosome- acrosin and hyaluronidase (digests hyaluronic acid in zona pellucida).
Fusion of acrosome membrane with plasma membrane of the egg.
47
Changes to oocyte at fertilisation
Completion of second meiotic division- 2nd polar body
Ca2+ release from intracellular stores
Cortical reaction: exocytosis of cortical granules
Hardening of zona pellucida
Prevention of polyspermy (not compatible with life)
48
Functions of the ovaries
Production of oocytes
Synthesis and secretion of sex hormones (oestrogen and progesterone)
49
Stages of oogenesis
Before birth: pogo is are found in large numbers in cortex of feral ovary.
By birth: all the oogonia have become primary oocytes arrested in the first meiotic division.
After birth: atresia occurs of most follicles (failure to develop to ovulate and release an egg)
At ovulation: completion of the first meiotic division
After fertilisation: completion of the second meiotic division
50
Stages of follicular growth of the ovum
Primordial follicle becomes surrounded with granulosa cells (squamous granulosa).
Multilayered is a pre-antral follicle (cuboidal granulosa).
After puberty some of the preantral follicles develop into Antral or Graafian follicles under the influence of LH and FSH.
51
Ovulation and uptake of ovum into oviduct
Fluid in antrum increases in volume. Enzymes thin the wall of the follicle at the stigma. The wall bursts to release follicular fluid and the ovum surrounded by cumulus cells.
Uptake is occurred by wafting movement of the folds or fimbria, at the opening of the oviduct.
52
Ectopic pregnancy
If the egg gets out into the peritoneal cavity instead of into the oviductal infundibulum it can cause ectopic pregnancy.
53
Antral follicle
If a pre-antral follicle reaches critical size when there are appropriate levels of gonadotrophic hormones in the circulation it can become an antral follicle. LH and FSH control its development.
54
Hormonal control of ovarian functions
Hypothalamus --GnRH--> anterior pituitary
Anterior pituitary --LH--> Theca cells
Theca cells --testosterone--> granulosa cells (aromatase)
Anterior pituitary --FSH--> Granulosa cells
Granulosa cells I--> oocytes
Granulosa cells --inhibin--I anterior pituitary
Granulosa cells --low oestrogens --I anterior pituitary and hypothalamus
Granulosa cells --high oestrogens--> anterior pituitary and hypothalamus
55
Kisspeptin neurons- where are they? what do the mediate?
Found in the female hypothalamus.
Mediates both the positive and negative feedback responses.
56
Negative feedback on Kiss1 neurons
Negative feedback by oestrogen on Kiss1 neurons in the arcuate nucleus of the hypothalamus.
Regulates the basal production of GnRH.
57
Positive feedback on Kiss1 neurons
Positive feedback on the Kiss1 neurons in the anteroventral periventricular (AVPV) region mediates the GnRH/LH surge required for ovulation
58
Kiss1 neurons
Sexually dimorphic with very few neurons in the AVPV region of males.
59
Effect of the LH surge on oocyte
- Completion of first meiotic division (primary oocyte --> secondary oocyte and first polar body)
- Arrest in metaphase of second meiotic division
- Withdrawal of granulosa cell processes
- Formation of cortical granules
- Increase in collagenase activity, especially in stigma region of follicle
60
Ovarian cycle of most species
A period of oestrogen dominance, an LH surge prior to ovulation, and a subsequent period of progesterone dominance.
61
When does oestrus behaviour occur?
Around the time of ovulation
62
Follicular/ proliferative phase
Oestrogen dominance.
| Changes to reproductive tract to prepare for the transport of the gametes.
63
Luteal/ secretory phase
Progesterone dominance.
| Changes to the reproductive tract to prepare of implantation.
64
Why do we have periods?
Build up of uterine wall is too great to be reabsorbed so must be shed.
65
Repeated ovarian cycles
Not a common feature of normal reproduction.
Increased risk of certain diseases:
- endometriosis
- uterine fibroids
- ovarian, endometrial and breast cancers
66
Manipulation of ovarian cycles
Prevention of pregnancy in women:
- steroidal contraceptives (high dose progesterone with/without low does oestrogen)
- inhibition of ovulation via negative feedback
- increased viscosity of cervical and uterine secretions
Induction of synchronous cycling in animal husbandry:
- progesterone vaginal sponges
- prostaglandin analogous to induce luteolysis in some species and more rapid entry into the next cycle e.g regumate
67
Changes at oestrus: bitches
A few times a year
A bit of blood discharge (not menstruation)
Anxious, grumpy
Pheromones
68
Changes at oestrus: sows
Standing behaviour
69
Changes at oestrus: camels
Induced ovulators so
Always ready to mate
Mating very long time so sat down
70
Changes to cervix during the menstrual cycle
Cervical mucus: in the follicular phase it is aqueous with protein filament channels. In the luteal phase it is mucous with protein filament mesh.
Cervical muscle tone: relaxed in the follicular phase and constricted in the luteal phase.
71
Ovarian cycle of the rat
A peak of progesterone from the adrenal gland occurs around the LH surge. This is essential for the normal expression of oestrus behaviour.
72
Changes at oestrus: cows
Stimulate other cows to mount them
73
Changes at oestrus: ewes
Will stand for mounting
Females don’t mount each other so use sterile rams
74
Changes at oestrus: mares
Raise tail and urinate
Vulva winks
75
Neuroendocrine reflex where mating maintains the corpus luteum e.g. rodents
Mechanical stimulation of cervix
Decreased dopamine release from hypothalamic neurones
Increased prolactin release from anterior pituitary
Maintenance of the corpus luteum
76
Neuroendocrine reflex where mating triggers ovulation e.g. cats, rabbits, camels, koala, hedgehogs
Mechanical stimulation of cervix at mating
Increased GnRH release from hypothalamic neurones
Increased FSH and LH release from anterior pituitary
Ovulation
77
Mechanisms of luteolysis in sheep
Corpus luteum produces progesterone and oxytocin
Oxytocin stimulates uterus to produce prostaglandin and F2alpha (luteolysis factor)
78
What effect does a hysterectomy have on the corpus luteum
Prevents corpus luteum breakdown as it is the uterus that produces F2alpha
79
What effect does an embryo have on the corpus luteum
Embryo prevents production of F2alpha so maintains the corpus luteum
80
Structure of the uterus (internal to external)
Endometrium- inner strolls, glandular, and epithelial layer
Myometrium- circular and longitudinal smooth muscle layers
Serosa- outer connective tissue layer
81
Male contraceptives
Hormonal:
- long acting progesterone analogue to suppress GnRH
Non-hormonal:
- vasagel- blocks vas with the injection of a gel, allows solute movement but not sperm
- gendarussa- herbal extract in phase II clinical trials
- anti-EPPIN- located on surface of sperm. Antibodies can prevent sperm motility
- clean sheets pill (ejaculation inhibitor)- inhibits smooth muscle contraction of vas, no sperm in ejaculate
82
Factors effecting fertility (5)
- age (puberty and menopause)
- genetic and developmental factors
- pathological factors
- environmental factors
- physiological factors
83
Changes at puberty
- onset of fertility
- appearance of secondary sexual characteristics
- changes in body composition
- growth spurt
- psychological effects
84
How is puberty initiated?
- reactivation of hypothalamic-pituitary-gonad axis
- increase in frequency and amplitude of GnRH pulses
- increase in pulsative release of LH and FSH, first at night and then in day
- increase in adrenal and gonadal production of sex steroids
85
Importance of HPG axis in puberty
Delay or prevention of puberty by suppression of HPG axis
Precocious puberty of HPG axis is stimulated prematurely
86
Gonadostat theory
Circulating concentrations of the gonadotrophins, LH and FSH, may be increased by changes in the sensitivity of the anterior pituitary to the gonadal sex steroids
87
Hypothalamic maturation theory
- increase in GnRH neuronal activity
- decrease in inhibitory input: GABA
- increase in stimulatory input: glutamate, kisspeptins
88
Which theory was shown to not apply using castrated monkeys?
Gonadostat theory
89
Age at puberty: humans
Male: 12-14
Female: 12-14
90
Age at puberty: sheep
Male: 9-12 months
Female: 6-7 months
91
Age at puberty: cattle
Male: 7-12 months
Female: 12 months
92
Age at puberty: pigs
Male: 6-8 months
Female: 6-7 months
93
Age at puberty: rabbit
Male: 4-12 months
Female: 3-4 months
94
Age at puberty: rats
Male: 45-60 days
Female: 35-45 days
95
Factors affecting age at onset of puberty
Genetic factors: 50% of variation
Size at birth: earlier puberty in small babies with rapid catch up growth
Heath and nutrition: age in Western Europe fallen 2-3 months per decade in the last 150 years
Body mass and composition: critical body weight, body fat and lepton also important
Pheromones
96
Effect of introducing a boar on the age of reaching puberty in a group of juvenile sows
They reach puberty earlier
97
Neuroendocrine pathway for the effect of photoperiod on reproductive function
Retina (photoreceptor) --> suprachiasmatic nucleus (biological clock) --> pineal gland (transducer) --> hypothalamus and pituitary (effector) --> GnRH, LH and FSH
98
When is melatonin secreted?
During hours of darkness
99
Short day breeders e.g. sheep
Increase reproductive activity in response to decreasing day length.
Mate in autumn and give birth in spring.
Melatonin stimulates HPG
100
Long day breeders e.g. horses
Increase reproductive activity in response to increasing day length.
Mate in spring/summer, give birth in following spring/summer.
Melatonin supresses HPG.
101
Lactational inhibition of implantation in rodents
Lactation is not sufficient to prevent LH surge/ ovulation
102
Lactational inhibition of implantation in other species
Uterus must be appropriately stimulated with oestrogen.
Lactational suckling decreases hypothalamic dopamine and increases prolactin.
Prolactin inhibits oestrogen production required for implantation.
103
Diapause
The embryo does not implant and so is held in the uterus at the blastocyst stage.
104
How many species can diapause be found in?
130
105
Neuroendocrine reflex where lactation inhibits ovulation
Mechanical stimulation of mammary teat at suckling --> decreased dopamine and GnRH release from hypothalamic neurones
Decreased dopamine increases prolactin release.
Decreased GnRH and increased Prolactin decreases LH and FSH release from anterior pituitary- this causes the cessation of ovarian cycles.
106
Oviduct
The reproductive tract that connects the ovary to the uterus and where fertilization occurs. The fertilized zygote will travel through the oviduct into the uterus.
107
Pronucleus
The haploid nucleus in a sperm or egg after completion of meiosis II.
108
Zygote
The one-cell embryo after fertilisation and prior to cleavage divisions.
109
Syngamy
The coming together of gametic chromosomes (i.e. the germ cell pronuclei) in the zygote after fertilisation.
110
Conceptus
Total product of the fertilised oocyte during the pre-implantation period; this term is interchangeable with embryo during early development.
111
Embryo
Similar to conceptus in pre-implantation development; after implantation, the part of the conceptus that will form the fetus.
112
Totipotent
A cell capable of giving rise to any cell type or a complete embryo.
113
Blastomere
One cell within the early multicellular embryo (pre-implantation).
114
Epigenetics
Heritable changes in gene expression that occur without changes in the DNA base sequence (e.g. DNA and histone methylation, non-coding RNA)
115
Epigenetic reprogramming
Erasure of epigenetic marks (e.g. DNA methylation) during mammalian development to erase gametic epigenetics.
116
Genomic imprinting
Epigenetic phenomenon whereby certain genes are expressed in a parent-of-origin specific manner according to epigenetic marks inherited from mother or father.
117
What do oocytes contribute?
```
Majority of the cellular material:
- Cell membrane
- Cytoplasm
- Proteins and RNAs
- Organelles- incl. mitochondria
- DNA
(Maternal cytoplasmic inheritance)
```
118
What do spermatozoa contribute?
- DNA (pronucleus)
- Centriole, pericentriolar material
- Small non-coding RNAs
(No proteins or mitochondria because they degrade)
119
How long does it take a fertilised egg to travel along the oviduct to the uterine cavity?
3-8 days
120
How does the fertilised egg travel along the oviduct?
Ciliary cells respond to pregnancy hormones (e.g progesterone and oestrogen) secreted by the mother and true cumulus cells to enable movement of sperm and the fertilised egg.
In horses muscular contraction is also very important.
121
How does the zona pellucida aid tubular transport?
ZP3 is helpful for sperm binding but also for tubular transport of the oocyte.
122
How do the cumulus cells aid tubular transport?
Prevent adhesion of the embryo to the oviduct wall and by secreting progesterone to act as a beacon to the cilia and to influence ciliary beating in the oviduct.
123
What is the role of the mothers progesterone in aiding the entry of the conceptus into the uterus?
It relaxes the isthmus sphincter.
124
The main point in tubular transport of the conceptus
Ciliary and smooth muscle cells in oviduct respond to hormones to help developing embryo move towards the uterus.
125
Morphological changes in the conceptus (5)
- Fertilisation and syngamy
- Cleavage divisions
- Compaction
- Cavitation
- Blastocyst
126
What does the sperm contribute to a embryo?
Centrioles and a haploid pronucleus.
127
What is nuclear membrane breakdown in sperm?
Protamines (sperm specific proteins around which DNA is wrapped) are replaced with histones to cause chromatin decondensation.
128
What happens at syngamy?
The germ cell pronuclei come together along the mitotic plate to form the zygotic nucleus.
The first mitotic anaphase and telophase are completed. The cleavage furrow forms and the first cleavage division occurs to generate a two-cell embryo.
129
How frequently do cell divisions occur?
Initially cell divisions occur at regular intervals, generally 12-24 hours in mammals.
130
How large is the human oocyte?
100micrometers.
131
What is compaction?
The initiation of cell polarity and specialisations (cell adhesions). The cells become closely packed by forming tight junctions.
132
What is polarisation of a blastomere?
The formation of apical and basal subcellar regions. The apical portion of the cell contains endosomes and microvilli whereas the basal portion contains the nuclei and relatively few organelles.
133
What is cavitation?
The formation of a fluid filled cavity within the embryo called the blastocoel.
134
What cell types is the blastocoel composed of?
The outer cells called the trophectoderm are extra-embryonic and will contribute to the formation of the placenta. The inner cells comprise the inner cell mass (ICM), which will eventually form the fetus as well as other extra-embryonic membranes. In most species the ICM becomes located at one side of the blastocoel. A few species do not show a distinct separation of trophoblast and ICM. Instead the ICM is a group of cells with trophoblast extending to either side but forming strings of cells rather than an encompassing layer.
135
What makes up the blastocyst?
Trophectoderm and inner cell mass
136
What makes up the trophectoderm?
Placental trophoblast placenta
137
What makes up the inner cell mass?
Embryo proper and placental mesoderm
138
How is the blastocoel cavity formed?
Tight junctions in outer cells create diffusional ion gradient which causes influx of water to form blastocoel cavity.
139
Early transcriptional milestones
- Maternal (and paternal) RNA activity and degradation.
| - Zygotic genome activation
140
How is cell fate specification initiation?
Different gene expression pathways.
141
Species specific initiation of transcription from the embryonic genome (mouse, pig, human, rabbit, sheep, cow)
```
Mouse- 2 cell
Pig- 4 cell
Human- 4- to 8- cell
Rabbit- 8 cell
Sheep- 8- to 16- cell
Cow- 8- to 16- cell
```
142
Which cells express the oct4 gene?
All cells in a four cell conceptus, at the blastocyst stage it is restricted to the ICM.
143
Where is the gene Nanog expressed?
The epiblast (presumptive embryonic tissue) but not the hypoblast (presumptive extra-embryonic endoderm).
144
Where is the gene Gatao expressed?
The hypoblast.
145
What genes do the trophectoderm cell express?
Cdx2 and Eomes
146
What is epigenetic regulation?
Heritable changes in gene expression that occur without changes in the DNA base sequence.
147
What epigenetic factors can influence the expression of a gene?
- DNA methylation
- Histone modifications
- Non-coding RNAs
- Chromatin remodelers
- Higher order chromatin structure
148
What does DNA methylation do?
Alters gene dosage to effect cell lineage.
149
Epigenetic reprogramming
Germ cell epigenetic marks are removed or replaced with embryonic epigenetic marks required for the maintenance of totipotent cells or for defining specific cell lineages in the developing embryo.
150
Examples of epigenetic regulation in development
- Different DNA methylation patterns in cell lineages (e.g. ICM v trophectoderm)
- Unequal genetic contribution of sperm and egg to zygote (e.g. imprinted genes)
- Dosage compensation by X-inactivation
151
Horse + donkey mixes
Male horse + female donkey --> Hinny
| Female horse + male donkey --> Mule
152
Parthenogenic embryos
Diploid embryos with alleles inherited from only the father or only the mother.
153
Gynogenic embryos
Development of a diploid oocyte without fertilisation by sperm.
154
When do gynogenic embryos stop developing in mice?
They can implant into the uterus but fail to develop a placenta so development fails.
155
Androgenic embryos
Development of embryos without a female pronucleus and with two male pronuclei. They form extraembryonic tissue but no embryonic tissue.
156
Genomic imprinting
When genes are expressed in a parent of origin specific manner. It represses gene expression from one parental allele usually by DNA methylation. The allele that is repressed depends on which parent it is inherited from.
157
Genomic imprinting of insulin growth factor 2 (Igf2) and H19 gene locus
Igf2 expression enhances growth and H19 represses growth. Maternally inherited Igf2/H19 gene locus is unmethylated at the imprinted control region (ICR). The ICR of the paternally inherited Igf2/H19 allele is methylated. Methylation prevents the CTCF protein from binding. As a result the Igf2 gene is expressed only from the paternal allele and the H19 gene is expressed only from the maternal allele.
158
X inactivation
Female mammals must compensate for the extra X chromosome by a method of dosage condensation. One is chosen at random for silencing and is coated with non coding RNA called Xist.
159
What is a Barr body?
The inactivated X chromosome that appears as a blob adjacent to the nuclear membrane.
160
How do tortoiseshell cats exist?
They are all female and so X chromosomes are inactivated but the process is random at the level of the cell so different cells inactivate different chromosomes.
161
What is the first cell fate decision?
Totipotency
162
Why do mammalian embryos implant into the uterus?
- The blastocyst cannot self sustain growth
- Requires direct interaction with the uterus
- The goal is to form a placenta for exchange of oxygen, nutrients and waste
163
Length of diapause in the horse
24-30 days
164
Facultative delayed implantation
Implantation is only delayed for a few days and is induced by suckling (e.g. marsupials, bank vole, mice, gerbils etc.)
165
Obligatory delayed implantation
Implantation is delayed for weeks and months. It is induced by the length of day (i.e. seasonal). (e.g. Roe deer, badger, fruit bat, mink, etc.)
166
Hormonal control of diapause
Suckling stimulus or decreased daylight (increased melotonin) leads to increased prolactin. No corpus luteum formation (luteal suppressive effect), decreased progesterone and so embryonic diapause.
167
The hormonal profile of the mother in the implantation window
In humans it is the period of progesterone dominance with superimposed oestrogen.
168
When is oestrogen secreted from the ovary? What does this stimulate?
The luteal phase. It stimulates uterine glandular secretions which in turn stimulates the blastocyst.
169
In which species does the conceptus synthesize oestrogen if the ovary has insufficient levels?
Pigs
170
Does an ovariectomised rat secrete oestrogen, progesterone, both or neither?
Neither
171
Ovariectomy --> ?
Ovariectomy + progesterone --> ?
Ovariectomy + progesterone + oestrogen --> ?
Free floating blastocyst (eventual death)
Free floating blastocyst (eventual death)
Implantation
172
Uterus pre-receptive phase
Embryo repulsion
173
Uterus implantation window
Embryo apposition --> adhesion
174
Uterus refractory phase
Embryo 'invasion'
175
Unreceptive uterine phases to blastocyst attachment
Pre-receptive phase and post-receptive phase (refractory). Mucin (MUC1), a cell surface glycoprotein is highly expressed and acts as a go away signal.
176
Uterine receptive phase to blastocyst attachment
The microvilli on the apical surface of the uterine epithelial cells shorten and MUC1 expression decreases in the immediate vicinity of the blastocyst (in rabbits and humans) and across the entire epithelial surface (in mice). Increased expression of maternally derived growth factors like LIF is also observed.
177
What is LIF?
Leukaemia inhibitory factor- it is secreted by the uterine glands in response to oestrogen and promotes endometrial receptivity to blastocyst attachment.
178
What do trophoblast cells express? What happens when these are stimulated?
EGF receptors and heparin sulphate proteoglycans. When these are stimulated by EGF and heparin binding EGF-like GF these receptors undergo phosphorylation and a 2nd messenger cascade is initiated in the blastocyst. This is followed by hatching from the zona pellucida.
179
Blastocyst hatching
Involves the production of a proteolytic enzyme called strypsin by the blastocyst to dissolve a hole in the zona pellucida. As the blastocyst expands it squeezes out of the hole and is now ready to attach to the uterine wall.
180
What does the Zona pellucida prevent?
Early implantation- ectopic pregnancy.
181
LIF secretion
- Secreted from uterine glands
- Acts on trophectoderm and uterine epithelium
- Increases HB-EGF (uterine epithelium)which binds to ErbB (trophoblast)
182
ErbB + HB-EGF --> ?
Prostaglandins --> decidualisation
183
OPN (osteopontin) secretion
- Secreted from uterine glands
| - Induces integrin expression for adhesion (trophoblast)
184
Embryo spacing
Very important in species that have litters to allow them access to nutrients etc.
- Uterine muscle contractions ?
- Molecular signalling between conceptuses ?
- Fluid level in uterus (pinopodes)?
185
The two phases of blastocyst attachment to the uterine wall
Apposition and adherence
186
What composes the extracellular matrix that catches the blastocyst?
Complex sugars, collagen, laminin and fibronectin.
187
Adhesion molecules
Integrins and cadherins
188
Types of implantation
Invasive implantation: the conceptus breaks through the surface epithelium to invade into the underlying stroma and newly formed decidua. (humans, most primates, dogs, cats, mice and rabbits).
Non-invasive implantation: the epithelial integrity of the endometrium is maintained or only breached locally, transiently or later in gestation. The epithelium becomes incorporated into the placenta (e.g. pigs, sheep, cows and horses).
189
Decidualisation
The uterine stroma differentiates into decidua, this results from a series of changes to the stromal cells including inflammatory responses.
190
What responses are involved in invasive implantation?
Inflammatory response (hyperaemia, oedema, angiogenesis).
Influx of uNK cells to restrain invasion.
LIF, prostaglandins, growth factors (VEGF).
191
Species specific invasion depths:
Humans, chimpanzees and mice:
Rhesus monkeys, dogs, cats and rats:
Interstitial implantation- deep stromal invasion.
Eccentric invasion- only partial invasion of the stroma.
192
What type of placenta do humans and mice have?
Haemochorial placenta- the extensive invasion leads to the breakdown of the walls of the maternal blood vessels, such that fetally-derived trophoblast cells are bathed in maternal blood.
193
What type of placenta do cats have?
Endothelialchorial placenta- the trophoblast cells that are less invasive and only break down the maternal epithelium.
194
When does blastocyst attachment occur in the pig?
About 16 days after the blastocyst has entered the uterus.
195
What type of placenta does non-invasive implantation lead to?
Epitheliochorial placenta- the extraembryonic tissue of the developing fetus lies against the maternal epithelium.
196
Recognition of pregnancy in dogs
There is no special mechanism to maintain progesterone levels as the ovarian cycle is long enough that the normal period of progesterone dominance is similar to the length of gestation.
197
Recognition of pregnancy in induced ovulators e.g. cats and ferrets
Neuro-endocrine link: maternal progesterone levels always increase following mating. Coitus initiates a signal to the hypothalamus to produce GnRH which causes an increase in LH. LH initiates ovulation, which results in the formation of the corpus luteum. The corpus luteum secretes sufficient levels of progesterone to maintain pregnancy.
198
Recognition of pregnancy in mice and rats
Neuro-endocrine link: mechanical stimulation of mating initiates a neuro-endocrine link to the hypothalamus, resulting in increased prolactin secretion by the anterior pituitary. Prolactin in this case prevents luteal regression. The advantage to this is that if the animal has not mated, it rapidly enters the next oestrus cycle.
199
Recognition of pregnancy in large domestic animals (pigs, cows, sheep)
Maintenance of progesterone by the inhibition of a luteolytic factor: the normal regression of the corpus lutea is dependent on the action of prostaglandin F2alpha produced by uterine tissue.
In pigs the developing embryo secretes oestrogen to inhibit PGF2alpha synthesis, so the corpus lutea are not degraded and progesterone secretion is maintained.
In sheep and cows the breakdown of the corpus lutea is dependent on PGF2alpha production stimulated by maternal oxytocin. The developing blastocyst produces trophoblast interferon, which downregulates the oxytocin receptors in the uterine epithelium, ultimately blocking the oxytocin-stimulated rise in PGF2alpha.
200
Recognition of pregnancy in primates.
Maintenance of progesterone by secretion of a luteotrophic factor. The developing blastocyst produces a luteotrophic substance (e.g. human chorionic gonadotrophin hCG). These molecules have a similar structure to LH and act on LH receptors in the corpus luteum to prolong its life and maintain progesterone levels.
201
Recognition of pregnancy in horses.
Maintenance of progesterone by the formation of an accessory corpus luteum. Following fertilisation the equine embryo produces pregnant mare serum gonadotrophin (PMSG), which stimulates receptors of the ovarian follicles to initiate the ovulation of a second oocyte to produce an accessory corpus luteum. This augments ovarian progesterone secretion.
202
What is the placenta?
Apposition of parental and foetal tissue for the purposes of physiological exchange- Mossman 1937
There is little mixing of maternal and foetal blood, and for most purposes can be considered separate.
203
Origins of viviparity
- Oophagy
- Embryophagy
- Epitheliophagy
- Lecitrophic and transfer
- Placentrophic
204
Oophagy
- Many sharks (teeth/ faeces in gut), alpine salamander
- Eggs retained in the maternal body
- Fertilised eggs feed on the unfertilised eggs around them
205
Embryophagy
- Sandtiger sharks, fire salamander
- Embryos hatch from the eggs inside the mothers reproductive tract
- Embryos survive by eating their siblings
206
Epitheliophagy
- Alpine salamander (later)
| - Embryos eat from a specialised uterine region
207
Lecitrophic and transfer
- Spiny dogfish, many squamates
| - Nutrients from yolk sac, but also water, ions and oxygen from mother
208
Placentrophic (two types)
- Cartilaginous fish, amphibians, squamates, marsupials, eutherians
- Absorption across fetal membranes
Histiotrophic:
- Absorb uterine secretions/ cells. 'Uterine milk', often maintained by progesterone.
- Long period in ungulates since implantation is so late (day 35 in horses, 20-30 in ruminants)
- Phagocytosis persists in pig/horse/carnivores via areolae, and in sheep/carnivores via haemophagous zones
Haemotrophic
- Direct transfer between bloodstreams by 'definitive' placenta
209
The four fetal membranes found in reptiles, birds and mammals
Amnion
Chorion (trophoblast)
Allantois
Yolk sac
210
What are the fetal membranes derived from?
The zygote
211
What are the main functions of the fetal membranes?
To isolate and protect the fetus, and to form the fetal side of the placenta.
212
The four main roles of the placenta
- Exchange of nutrients and waste
- Protection
- Immunological
- Endocrine/ paracrine
213
Placenta- Exchange of nutrients and waste- simple diffusion
- Very small molecules (water sol. <100Da, lipid sol. <600Da). Ions, fatty acids, cholesterol, fat soluble vitamins, steroids, urea, O2 and CO2
- Down concentration gradient/ no energy needed
- Oxygen is a special case as it diffuses freely across the placenta and rapidly reaches an equilibrium between maternal and fetal Hb. Oxygen use by the placenta takes precedence over fetal use.
214
Placenta- Exchange of nutrients and waste- facilitated diffusion
- Larger/ less fat soluble molecules, often needed in large quantities. Lactate, glucose
- Down concentration gradient/ no energy required
215
Placenta- Exchange of nutrients and waste- active transport carrier molecules
- Most other molecules, which are either: potentially toxic (Cu2+, I-, Ca2+, PO43-), lipid insoluble (amino acids, water soluble vitamins), or needed to maintain gradients (Na+, K+, Cl-)
- Concentration can be higher on either side
- Process requires energy
216
Placenta- Exchange of nutrients and waste- Receptor mediated endocytosis phagocytosis
- Fe2+: very important but very toxic
- IgG: humans>> carnivores > ungulates
- Concentration can be higher on either side, process requires energy
217
Placenta- Physical protection
The fetal membranes, especially the amnion
218
Placenta- Protection against teratogens
- Teratogens are external influences that induce developmental abnormalities
- They can either interfere with developmental processes or damage fetal DNA
- Teratogens include radiation, hyperthermia, physical trauma, microorganisms, nutritional deficiencies, hyperglycaemia, chemicals
219
Non-iatrogenic (environmental) chemical teratogens
Pollutants, plants, ethanol, cocaine, LSD
220
Iatrogenic (medical) chemical teratogens
Thalidomide, grisefulvin, tetracyclines, many chemotherapies
221
Placenta- immunological barrier
- The fetus is semi allogenic (semi foreign)- so how does it avoid maternal attack
- There are three different methods, used by different species
222
Placenta- immunological barrier- the fetal trophoblast may downregulate expression of MHC class 1
- However MHC class 1 has a crucial role in the immune response so cannot just be switched off.
- Some invasive trophoblasts 're-upregulate' class 1 MHC
- Most invasive cells in horses are chorionic girdle cells
- Most invasive cells in cattle are binucleate cells
- In humans the most invasive fetal cells (extravillous cytotrophoblasts) express non classical MHC class 1, HLA is non-polymorphic in the population
223
Placenta- immunological barrier- The fetus may 'modulate' maternal immune responses
- Locally: progesterone-induced uterine milk proteins suppress lymphocyte proliferation in the ruminant uterus. HLA-G suppresses T-lymphocyte proliferation.
- Systemically: human fetus may induce a 'Th1 --> Th2' (cell mediated --> antibody mediated) shift in maternal immunity. Most graft rejection is cell mediated.
224
Placenta- immunological barrier- the placenta may act as an immunological barrier to immune detection or attack
- Reduces access of maternal cells to the fetus and vice versa, but some do leak through in some species
- Humans and rodents: maternal immune stem cells colonise the fetal bone marrow permanently
- The placental fetal stroma can act as an immunosorbent maternal which binds anti-fetal antibodies
225
Placenta- endocrine/ paracrine
a. Support pregnancy: IFN-t, hCG, steroids, eCG
b. Prepare for lactation: placental lactogens
c. Initiate birth: steroids, relaxin, prostaglandins
d. ? promote uterine involution when eaten
226
What are steroids?
A group of cholesterol- derived lipid hormones
- bind nuclear receptors (like eicosanoids)
- Profound effect on gene expression
- Affect many different tissue
- Wide taxonomic distribution
Fall into functional subsets- defined by receptors.
227
Steroid formation (origins)
Cholesterol--> pregnenolone --> progesterone-->
- mineralocorticoids
- androgens --> oestrogens
- glucocorticoids
228
What is the difference between PMSG and eCG?
Equine chorionic gonadotrophin (eCG) is the biological name for the highly glycosylated form of LH made by the endometrial cups.
Pregnant mare serum gonadotrophin (PMSG) is the commercial pharmaceutical product, purified from pregnant mare serum.
The terms are however used interchangeably.
229
Weight gain/ internal compression
Pregnant animals gain weight: gravid uterus, stored nutrients, blood and tissue fluid.
This impinges on other structures- esp. hollow ones like veins, lungs, urinary tract and gut.
230
Cardiovascular changes in pregnant animals
Vasodilation --> venous pooling --> arterial 'underfilling' --> baroreceptor activation -->
- ADH secretion --> renal water reabsorption --> increased plasma volume
- renin-angiotensin-aldosterone --> water and Na+ reabsorption --> increased plasma volume
231
Cardiovascular- cardiac output
Dramatic increase in CO, mainly due to increased stroke volume.
1. Chamber dilation may lead to: murmur number 1 due to atrioventricular regurgitation
2. Increased wall thickness may lead to: murmur number 2 due to increased blood velocity; exacerbate dysrhythmias.
Also a lesser effect due to increased heart rate.
232
Cardiovascular- vasodilation
It was once thought that systemic vascular resistance decreases because uterine vasculature is added in parallel but it is now known to be mainly due to vasodilation induced by oestrogens and other hormones/ factors. Pulmonary resistance also decreases.
233
Cardiovascular- blood pressure
Changes in blood pressure are unpredictable and species variable, since there is an increase in cardiac output and systemic vascular resistance. Many species show early declines in BP, e.g. early 'dip' in women around the time of the first midwife visit to measure 'baseline' BP
234
Cardiovascular- postural/ compression
Positional occlusion of caudal/ inferior vena cava may cause dramatic fluctuations in VR --> CO.
Compression of veins in pelvis may cause leg oedema in women.
235
Cardiovascular- haemodynamics at birth
Contractions and uterine involution lead to an autotransfusion of blood from the uterus --> VR, CO and BP increase.
This birth stress and the relief of the compression leads to increased heart rate and so increased cardiac output.
This lasts for about 1 hour after birth.
236
Cardiovascular effects of oestrogen in non-pregnant sheep
Increased body weight, increased whole body weight, increased plasma volume, slightly increased erythrocyte volume, decreased blood pressure, much increased heart rate
237
Haematology of pregnancy
- Increased erythropoiesis does not keep pace with blood volume so [RBC] is decreased. This is makes them not pathologically anaemic but still with a lower [Hb].
- This physiological anaemia reduces blood viscosity, may lead to 'haemic' murmur number 3 (the less viscous the blood the more likely it is to become turbulent).
- Demand for iron increases 2-3x, for use in Hb and enzymes, but iron deficiency is very rare as menstruation has stopped.
- [Platelet] is decreased, but a rebalancing of clotting factor proteins renders mother hypercoagulable in advance of birth
238
ECG changes in pregnancy
Upward pressure of uterus deviates QRS axis of ECG leftwards
239
Urinary changes in pregnancy
As well as increased CO, progesterone specifically drives renal blood flow and so glomerular filtration increases, as does urine output.
In humans, also a relaxin/ NO vasodilation of afferent and efferent arterioles:
- GFR increases so reduced plasma urea and creatine
- reduced reabsorption so glycosuria
Progesterone dilates hollow urinary tract --> backflow, infections
240
Metabolic (sequelae) changes in pregnancy
Maternal insulin resistance:
glucose increases, insulin increases, beta-cell proliferation (signs of insulin resistance).
Also fetuses of diabetic mothers are larger and may become hypoglycaemic after delivery.
The equivalent in ruminants is twin lamb/ kid disease. Diversion of glucose to fetus --> mobilisation of lipid for energy --> hepatic lipidosis --> ketone body production increases, clearance decreases--> toxicity, especially of the CNS
241
Metabolic (gastrointestinal) changes in pregnancy
Species variable:
- intestinal hypertrophy- small mammals/ ruminants
- liver hypertrophy- mice/ ruminants
Progesterone causes smooth muscle contraction in their gut (gut hypotonia). This induces the oesophageal sphincter tone to decrease, which along with compression-induced increased intragastric pressure leads to reflux.
242
Calcium mobilisation
PTH secretion increases to:
- Increase reabsorption of Ca2+ in renal DCT and CD
- Increased activation of vitamin D to its active dihydroxy form, increased gut Ca2+ uptake
- Mobilisation of bone Ca2+ by osteoclast if necessary
Increased uptake precedes demand (formation of fetal bones), so mother is generating skeletal store.
243
Thyroid/ iodine changes in pregnancy
Oestrogens increase thyroid binding globulins, total T3 and T4 is increased but free T3 and T4 may not have.
Hyperthyroid state may also be due to cross-stimulation of TSHR by hCG (TSH, hCG, LH, FSH, eCG all have similar alphabeta heterodimer glycoproteins).
Dietary iodine requirement increases due to fetal use and increased renal loss as GFR increases.
244
Morning sickness
Many women have nausea and vomiting in early pregnancy (can be sever, life threatening hyper-emesis gravidarum).
Might be adaptive to stop mothers eating toxic plants? but only occurs in humans and is very variable.
245
Respiratory changes in pregnancy
Oxygen demand increases 20%
Tidal volume increases, respiratory rate slightly increases.
Ribcage expands to counter uterine pressure on diaphragm- so vital capacity stays exactly the same.
PO2 increases for most pregnancy, though later may fail to keep pace as metabolic demands increase.
Pregnant women often feel breathless although, unusually this is relieved by mild exercise.
246
How do we measure fetal growth in humans?
Ultrasound- poor/ user variable at detecting intra-uterine growth retardation (IUGR): leads to unnecessary caesareans/ treatments.
- Head/ abdominal circumference
- Biparietal diameter
- Body length
- Femur length
247
How do we measure fetal growth in animals?
Direct, post mortem.
| Indwelling methods: crown-rump length, limb lengths, blood volume.
248
Growth and proportion- the fetus
Fetal weight often follows a sigmoid curve- but weight is not the full story.
- Proportionate/ 'symmetrical' size- environmental?
- Non-proportionate/ 'asymmetrical' size- genetic?
249
Growth and proportion- the placenta
The placenta is relatively small, and weight seems a poor indicator of function- may sometimes decrease in some species.
250
Why is fetal growth important?
- Affects chances of fetus at the time of birth
- There is a range of birth weights at which the death rate is extremely low
- 'Fetal programming': low birth weight associated with increased rates of cardiovascular and metabolic disease; a stimulus at a critical, sensitive period of early life can have permanent effects
251
Potential mechanisms of fetal growth impairments
- Gene expression and epigenetics
- Anatomical changes
- Resetting of hormonal axes
252
Fetal influences on growth
Genome:
- Ethnicity/ breed
- Genetic disease e.g. trisomy and osteogenesis imperfecta
Endocrine:
- [insulin] has positive correlation with bodyweight
- [thyroid hormones] have positive correlation with body weight
- [glucocorticoids] have negative correlation with body weight
- Effect of GH varies between species
253
Maternal influences on growth
Uterus:
- Size of uterus
- Epigenetics
Nutrition:
- Calorie restriction reduces growth
- Famine can have complex effects in humans e.g. dutch hunger
Parity:
- How many offspring the mother has had before
- Maternal size/ resources/ health?
- Uterine 'remodelling'
Socio-economic (humans):
- Nutrition? Behaviour? Disease?
- Age at which mother left education
Disease:
- Not all disease reduces fetal growth e.g. diabetes
254
Placental influences on growth
Weight:
- Sheep have 'cotyledonary' placenta that permits experimental excision of parts of the placenta, the lower mass leads to lower fetal body weight
Vascular:
- ligation of a subset of placental vessels on day 11/165
- 'Brain sparing' non-proportionate IUGR, despite this being 'environmental'
Transport:
- Diffusion, facilitated diffusion or active transport
- The members of transporter molecules can be correlated with fetal growth
Compensation:
- Proliferation of fetal villi
- Decreased exchange distance
- Capillary proliferation
- Dilation and reduced vascular resistance
- Upregulation of transport genes
255
Fetal homeostasis- nutrition/ metbolism
- The fetus is catabolic and energy-demanding rather than storing, so it uses glucose more than lipids and amino acids
- Lipids are mainly used for storage for neonatal use (rabbit, guinea pig, human)
- Liver gradually transitions from haemopoietic to metabolic organ
- Liver and pancreas are secretory, but perhaps to prevent sloughed epithelium/ hair blocking the epithelium
- Meconium accumulated in the colon, and is the first 'faeces' released
- Fetal stress may cause its release into the amniotic fluid - inhalation pneumonia
256
Fetal homeostasis- fluid balance
- Fetus is in aquatic environment, kidneys receive only 2% of cardiac output and it produces hypotonic urine
- It is in dynamic interaction with the fluid spaces around it
257
Fetal homeostasis- Cardiovascular: heart, volume
- The heart is functioning near the top end of its range- increased venous return does not increase cardiac output much
- About half the contractile protein machinery of adult myocardial cells- fewer myofibrils, less regularly oriented
- Heart more constrained by chest wall and fluid filled lungs
- Blood volume is 10-12% of body volume (7-8% in adult) mainly due to placenta
258
Fetal homeostasis- cardiovascular: circulation
Circulation is 'in parallel' rather than 'in series'
259
Fetal homeostasis- cardiovascular: stress
- If CO decreases, flow to CNS, adrenal and heart are maintained; lungs and lower body are impacted
- Hypoxia --> chemoreceptors --> vagal bradycardia, sympathetic vasoconstriction
- Long term hypoxia --> reduced growth (particularly lower body) --> 'fetal programming' of adult disease
260
Fetal homeostasis- haemopoiesis
Intraembryonic haemopoiesis starts when cortisol --> stem cell budding from the aortic endothelium in the 'aorta-gonad-mesonephros' region
261
Fetal homeostasis- gas transfer
- Fetal haemoglobin has higher oxygen affinity- not inhibited by 2,3-bisphosphatoglycerate ('DPG') due to his --> ser change in O2-binding pocket
- Adult Hb is alpha,alpha,beta,beta, fetal is alpha,alpha,gamma,gamma, embryonic is alpha,alpha,epsilon,epsilon
- Fetal blood has higher Hb concentration
- Fetus-to-mother loss of CO2 enhances O2 transfer
262
Fluid fluxes in ovine conceptuses
```
Swallow 700ml/day in
Urethra 800ml/day out
Lungs 300ml/day out
Skin/glands 15ml/day in
Intra-membranes 500ml/day in
Urachus 100ml/day out
Placenta 22ml/day in
```
263
Fluid fluxes in human conceptuses
```
Swallow 700ml/day in
Urethra 1000ml/day out
Lungs 170ml/day out
Skin/glands 25ml/day out
Intra-membranes 380ml/day in
Placenta 10ml/day in
```
Allantois regresses in humans so no urine flow via urachus.
264
Shunts in fetal circulation
```
Ductus arteriosus (PA-->Ao)
Foramen ovale (LA-->RA)
Ductus venosus (umbilical vein --> vena cava)
```
265
Fetal preparations- endocrine: the cortisol rise
- Prepartum rise in fetal plasma cortisol concentrations
- Fetal adrenal is the main source, stimulated by fetal pituitary ACTH
- Cortisol is central to maturation of many organs and in many species it also induces birth
- Cortisol is secreted late in gestation
266
Fetal preparations- respiratory
All mammals (except Julia Crelk dunnart) must breathe as soon as they are born. In preparation there is intermittent fetal 'breathing' of amniotic fluid
267
Fetal preparations- respiratory: compliance
- Elastin content is increased
- Surfactant synthesis upregulated by cortisol, adrenaline, thyroids (lack of surfactant is often a major problem for premature babies)
- Adrenaline --> increases water reabsorption in advance of labour
- Androgens inhibit lung maturation, more problems in males
268
Fetal preparations- excretory
The final metanephric kidney is active throughout most of pregnancy, towards term, cortisol --> GFR increases and tubular Na+/K+ATPase activity increases.
269
Fetal preparations- nutritional/ metabolic
- At birth the fetus will transition from continuous placental nutrition to more intermittent central nutrition
1. The gut must mature
2. The fetus must develop the ability to generate glucose between meals
3. The pancreas develops alpha- and sigma- cells first and then beta-cells
270
Fetal preparations- positional
- Near birth fetuses (esp. in monotocous species) reposition themselves so that they are in the correct position for birth
- In the domestic species this is back- dorsal, belly- ventral and head and forelimbs towards the cervix (headfirst and rotated 180 degrees in humans)
271
What is parturition?
Birth canal remodelling --> uterine contractions --> cervical dilation --> uterine and abdominal contractions
272
Labour stages
1. Uterine contractions press fetus onto cervix, which dilates
2. Abdominal straining, membrane rupture and expulsion of fetus
3. Expulsion of placenta
273
What causes birth?
Either linear cause and effect story (over simplification), or re-balance of anti- and pro- birth influences.
Best understood in sheep; evidence that humans are different in some ways.
274
Progesterone decline after pregnancy
Pregnancy is a time of progesterone dominance in most species. It inhibits myometrial gap junction formation and hyperpolarises the myometrium so suppresses contraction. Progesterone also inhibits PG and OTR synthesis.
275
Oestrogen increase
There is an activation of enzymes converting P into E in the placenta (aromatase).
In contrast to progesterone, oestrogen 'activates' the myometrium.
- Oestrogen induces birth in pregnant sheep, but without cervical dilation
- Myometrial gap junction proteins increases, ion channels especially Ca2+ increases
- This prepares for coordinated contractile activity
- Activates prostaglandin and oxytocin systems
276
Remodelling of the cervix
Phase 1: P --> slow 'softening'
- matrix reorganisation and loss of collagen cross-linking
- P inhibits collagenolysis
Phase 2: E --> rapid 'ripening'
- Fibrous organisation decreases, cross linking decreases, elastin increases
- Hyaluronic acid increases (lubricant)
- In pigs and mice, CL produces relaxin which also leads to ripening
Phase 3: Rapid dilation, once contractions started
Phase 4: E, relaxin --> post partum repair
277
Prostaglandins
- Semen caused contraction of myometrium from pregnant women, but relaxation in non-pregnant women
- PGs often act locally --> diverse, and often mutually antagonistic effects
- In late pregnancy E increases uterine cyclooxygenase-2 which increases PGF2alpha; and it increases expression of PG receptors
- Contractions occur when when PGF causes action potentials to propagate across uterus--> Ca2+ influx --> contractions
- In species in which the CL is still a significant source of P the PGF2alpha also induces luteolysis, this decreases progesterone further
278
Oxytocin and its role in birth
- Posterior pituitary nonapeptide which causes uterine contraction
- E drives upregulates oxytocin receptors in late pregnancy
- As the fetus starts to press on the cervix it activates the neuroendocrine Ferguson reflex
- Sensory nn. --> spinal cord --> hypothalamus --> posterior pituitary oxytocin secretion
- Synergistic with PGF2alpha to cause increased contractions
- Positive feedback interaction that leads to birth
279
Fetal hypothalamo-pituitary-adrenal axis
Fetal pituitary or adrenal ablation delays birth.
Infusion of CRH, ACTH or cortisol hastens birth.
Fetal cortisol changes steroidogenic enzyme expression to increase maternal E/P.
The placenta may also make its own CRH; E, P and may be prostaglandins, may reduce HPA negative feedback.
280
Fine tuning of parturition
- Some mammals have evolved mechanisms to control time of actual fetal expulsion
- Maternal CNS mediated birth delay in Andean camelids- give birth in the morning, and can delay if the weather is bad
- In pigs, the regressing CL secretes relaxin, which delays contractility, perhaps for the cervix to ripen- allows time for maturation of all fetuses in this polycotous species
281
Artificial induction/ hastening of birth
Requires an understanding of the natural initiation
- glucocorticoids
- progesterone inhibitors (e.g. epostane)
- PGF analogues or sex (PGs in semen?)
- oxytocin
Choice of agent is often for practical reasons or reduction of side effects.
282
Hormonal sequence of parturition
Mature fetal hypothalamic CRH --> fetal pituitary ACTH --> fetal adrenal cortisol --> placental adrenal cortisol --> maternal circulating E/P increases...
... --> PGF2alpha (--> luteolysis, if necessary --> P decreases) --> myometrial contractions --> fetal pressure on cervix --> maternal hypothalamus oxytocin --> myometrial contractions
... --> reduces negative feedback within HPA?
... --> cervical remodelling
... --> P induced quiescence ends --> myometrial contractions
... --> E induced myometrial activation --> myometrial contractions
--> fetal size stretches myometrium --> E induced myometrial activation --> myometrial contractions
283
Evolution of lactation
It define mammals, it evolved from apocrine sweat glands. All mammalian species lactate. There are no teats in monotremes: young lap milk from a pool on the mothers belly.
284
What are some clinical relevancies of lactation?
Agalactia (absence of milk production), neoplasia, infection, dairy industry, paediatrics
285
Microscopic anatomy of the mammary gland
- Conserved between species- ducts lead to milk-secreting cuboidal-cell lined alveoli, surrounded by a mesh of myoepithelial cells (ectoderm).
- Glandular lobules among fibrous and adipose tissue
- Only ducts when 'resting' --> the alveoli only form during pregnancy --> very dilated during lactation
286
Biochemistry- composition of milk
Change as the physiological and environmental needs change in different species
287
Biochemistry of milk- lactose
Disaccharide present only in milk and some plants- dissolved. It may be used to stop bacterial overgrowth as it is so specific. It collects in the golgi.
288
Biochemistry of milk- protein
As milk production starts, the ER and golgi enlarge and RNA/DNA ratio increases. It is also secreted by the golgi/ exocytosis route. 20-80% are caseins- a group of related phosphoproteins. Mainly as a colloid suspension of calcium caseinate aggregates. The rest is dissolved albumins and globulins, 'whey proteins'
289
Biochemistry of milk- lipids
Lipids are secreted in the ER, but via separate droplets. Fat globules present as an emulsion. Bilayer surface charge charge prevents coalescence.
290
Biochemistry of milk- ions, tonicity
High K+, low Na+- ICF-like- tight junctions prevent plasma and milk paracellular flux.
Milk is isotonic, although half of the osmotic pressure is due to lactose rather than ions.
Iron is low in milk, but neonates have hepatic stores- oral iron can cause bacterial proliferation. Often pigs are injected with iron as in the wild they would ingest in soil.
291
What does milk being isotonic mean for milk replacers?
They should not be overconcentrated for infants as it can dehydrate them.
292
What is fore milk for?
Rehydration
293
What is later milk for?
Higher in lipids
294
What is the 'curds' part of milk?
Gastric renin, a complex mix of enzymes (e.g. protease chymosin) which coagulates casein.
295
What do the peptides in milk aid in the infant?
Decreased blood pressure, decreased blood clotting, increased immune system, decreased gut motility
296
Physiology of lactational anoestrus
Species variable and poorly understood but mainly induced by suckling. Lactating tends to inhibit ovarian cycles but this is pretty ineffective in mares.
297
When does mammary development start?
By birth- 'witches' milk in baby girls. Mammary growth starts earlier than expected and is then hastened by ovarian cycles (lactiferous duct system).
298
When do alveoli develop?
Lobules of alveoli start to develop mid pregnancy.
299
Which hormones aid development of different parts of the lactational system?
Oestrogens, GH, PRL --> ducts, blood vessels, adipose tissue
Progesterone, oestrogen, GH, PRL, PL --> alveoli
300
What are somatomammotrophins?
A group of related peptide hormones with just under 200 amino acids- can cross-bind to each others receptors. They are wither pituitary in origin (GH, PRL) or placental (PLs).
301
Species variable effects of placental lactogens.
Body growth, 'anti-insulin' metabolic, mammary growth/lactation, luteotrophic, especially carnivores, rodents, marsupials
302
Physiology of lactogenesis
Birth, stress --> glucocorticoids --> lactogenesis
Increased E, decreased P, suckling --> Prolactin --> lactogenesis
Placental lactogens, progesterone (both decreased at birth --I lactogenesis
303
Local (autocrine) route for maintenance of lactation
Increased frequency --> decreased pressure atrophy and decreased specific inhibitory protein --> increased milk secretion
304
Neuroendocrine reflex for maintenance of lactation
Suckling stimulus --> spinal cord --> hypothalamus --> dopamine secretion decreased --> increased PRL secretion
305
Endocrine route for maintenance of lactation
Regulated by an array of hormones which are also responsible for controlling the dramatic repartitioning of nutrients in the body.
GH predominates in ruminants
PRL predominates in most others
306
Physiology of milk ejection
Myoepithelial milk-ejection reflux.
Suckling etc. --> spinal cord -> hypothalamus --> oxytocin secretion --> myoepithelial contraction
307
Physiology of mammary involution
As suckling by the infant decreases, all the local, endocrine drives to lactation also decrease. Many ducts remain, but alveolar cells degenerate while remaining in place. Some epithelial cells act as 'non-professional phagocytes'- ingesting milk and cell debris, then macrophages take over.
308
Respiration of the neonate
Tying/ breakage of umbilical cord and factors from the external environment stimulate the nervous system to initiate first breath.
Initial breaths require high inspiratory and expiratory pressures to force out the amniotic fluid and overcome high surface tension.
309
What regulates the maturation of the surfactant system?
Plasma cortisol, it also regulates the expression of genes controlling lung liquid reabsorption.
310
Why is respiration harder for premature neonates?
They would miss out on the prepartum cortisol surge so there is an absence of sufficient surfactant.
311
Stimuli that induce first breath
- Neonate grunts against closed glottis (increases trans-pulmonary pressure to establish FRC)
- Generalised arousal and cold (increased sensory output)
- Tying up/ breaking of the umbilical cord (promotes hypoxia and hypercapnia)
312
Fetal lung development
During lung growth, distal pulmonary epithelial cells actively secrete Cl- rich fluid into the bronchial tree.
This leads to accumulation of fluid in fetal airways.
Hyperexpanded fetal lungs- increased pulmonary vascular resistance.
Fetal breathing starts at 10 weeks gestation and is associated with REM sleep (inhibited by hypoxaemia).
Breathing movements are important to pulmonary development.
313
Lung liquid secretion
By active chloride transport. The composition of fetal lung fluid is distinct from both amniotic fluid and plasma- increased chloride content (CLC-2/CLCN2). Chloride ions are co-transported into cells with Na+/K+ pump.
The secretion of the lung liquid contributes to amniotic fluid and creates a pressure that contributes to lung growth.
314
Lung liquid reabsorption
In sheep spontaneous labour LL reabsorption began with the appearance of the forelimbs and becomes very rapid after delivery.
Plasma adrenaline concentrations increase dramatically just before birth which promotes LL reabsorption.
Active Na+ transport in the direction lung lumen to plasma and an associated decrease in active Cl- transport in the opposite direction.
315
Neonatal lung fluid transport
Adrenaline stimulates beta-adrenoreceptors on the apical membrane of the type II epithelial cells around the time of birth
Na+ ions extruded by basolateral Na+/K+ ATPase pump into the interstitium, brings Cl- and water passively along with it through the paracellular and intracellular pathways
Activation of cAMP inserts Na+ channels in apical membrane
Na+ enters cells due to steep electrochemical gradient
Most interstitial lung liquid moves into the pulmonary circulation; some drains via the lung lymphatics
316
Neonatal fluid clearance summary
Clearance of fetal lung fluid begins before birth, is augmented by labour
During spontaneous labour and immediately after birth, the respiratory epithelium changes from active fluid secretion (with active Cl- transport into the intraluminal space) to active fluid absorption (with active Na+ transport into the interstitium)
The Na+ mediated active absorption process is believed to be initiated even before labour, with regulation by increased cortisol levels
Beta-receptor agonist stimulation promotes this respiratory epithelium transition during spontaneous labour
Increased oxygenation after birth helps to maintain the expression of these Na+ mediated channels
317
Lung inflation of neonates
Dependent on adequate levels of pulmonary surfactants.
318
What is surfactant?
A mixture of lipids and proteins that reduces tension within airways by forming a monolayer at the liquid-air interface, allowing for inflation at lower pressure.
Secreted by type II pneumocytes
319
Antenatal glucocorticoid therapy
Women suspected of having preterm delivery are given synthetic glucocorticoids (dexamethasone or betamethasone) that are able to cross the placenta, to accelerate fetal maturation, in particular surfactant in the lungs.
320
Neonatal circulatory changes
Two shunts:
- Foramen ovale
- Ductus arteriosus
At birth there is:
- Decreased pulmonary vascular resistance
- Increased pulmonary blood flow
- Closure of foramen ovale and initiation of closure of ductus arteriosus
321
Obliteration of the placenta (effects on circulation)
Increased systemic vascular resistance, decreased blood flow through DV (passive closure)
322
Effects of O2 on ductus arteriosus
- Closure of DA depends on contraction of the ductal smooth muscle wall
- Ventilation of fetal sheep lungs with oxygen caused a rise in arterial O2 saturation, constriction of the DA and development of an audible murmur.
- Decreased O2 saturation (N2) --> dilation of DA, murmur disappearance
323
Fuel reserves in the newborn
Main neonatal reserves are liver glycogen, muscle glycogen and fat.
Lactate concentrations rise prior to birth (decrease in pH levels).
Fructose levels decline slowly.
FFA levels rapidly increase after birth
324
Stimuli for mobilising hepatic glycogen
- Increased catecholamine levels at birth and direct splanchnic innervation
- Changes in the insulin/ glucagon ratio
- After birth, the depressed serum insulin and elevated glucagon and adrenaline levels, elevated GH levels at birth, favour glycogenolysis, lipolysis and glycogenolysis.
325
Gluconeogenesis in the neonate
Activity of gluconeogenic enzymes increases before birth. Maturation of glucogenic capacity occurs late in gestation so premature offspring are affected negatively.
326
Lipids in neonates
Species variable. Fat reserve around 16% in humans but 1% in piglets.
327
Gastric digestion in neonates
There is minimal digestive activity in the first 24hrs of life in many species due to the need to absorb macromolecules from the colostrum.
328
Thermoregulation of neonates
Vary heat production by varying metabolic rate, although this requires energy and thus adequate nutrition and O2 for respiration.
Shivering is limited but they can also produce heat through non-shivering thermogenesis (brown fat).
329
Neural regulatory mechanisms in neonates
Changes to ANS and CNS around time of birth.
Innervation to some tissues like adrenal medulla may not be fully developed by birth.
There is also a central plasticity of synaptic connections in many altricial species.
330
Endocrine regulatory mechanisms in neonates
Most endocrine glands are functional in utero, but may alter their set point/ sensitivity.
- Pituitary-adrenal axis: prepartum activation essential for neonatal adaptation.
- Thyroid gland: Prepartum increases in T3 with resetting of the axis after birth in association with the need for thermoregulation
- Pancreas: becomes important in the control of glycaemia. Large changes in the insulin and glucagon concentrations.
