Session 3 Flashcards
(74 cards)
1
Q
What is the general overview of puberty?
A
- Accelerated somatic
- Maturation of primary sexual characteristics
- Appearance of secondary sexual characteristics
- Menstruation and spermatogenesis
2
Q
What are environmental inferences on puberty?
A
- Triggered by changes in day length
- Involvement of pineal gland
- Secretion of melatonin
3
Q
What is the critical weight for girls to begin puberty?
A
47kg
4
Q
What is the effect of significant weight loss in women?
A
The reproductive cycle ceases
5
Q
What are the sequence of changes girls follow in puberty?
A
9-13
- Breast bud appears
- Pubic hair growth
- Growth spurt
- Onset of menstrual
- Pubic hair becomes adult like
- Breast become adult like
6
Q
Why does pubic hair grow?
A
It is a response to oestrogen and testosterone levels
7
Q
What are the sequence of changes boys follow in puberty?
A
10-14 years of age
- Genital develpment
- Pubic hair growth
- Spermatogenesis
- Growth spurt
- Genitalia becomes adult like
- Pubic hair becomes adult like
8
Q
What does genital development in boys depend on?
A
Testosterone
9
Q
What is accelerated somatic growth?
A
Period of growth that pepends on growth hormone and sex steroids in both sexes
- It is earlier and shorter in girls
- It is longer and faster in men so larger growth spurt
10
Q
How does accelerated osmotic growth stop?
A
Epiphyseal fusion in response to oestrogen
-Ended earlier in girls
11
Q
What triggers the onset of puberty?
A
Switching on the HPG axis. Done by:
- Increased stimulation of hypothalamus-pituitary-gonadal axis
- Gradual activation of GnRH
- Increases frequency and amplitude of LH pulses
- Gonadotropins stimulate secretion of sexual steroids
- Extragonadal hormonal changes
12
Q
What is the GnRH-1 gene?
A
- Repsosnible for mammalian GnRh
- Exclusive expressed in a discrete population of neutrons in the hypothalamus
13
Q
What is the effect of treating prepubertal primates with pulsatile GnRH alone?
A
Induces puberty
14
Q
What happens if GnRH secretion is blocked?
A
Lack of gonadotrophin synthesis and secretion and reproductive development
15
Q
What hormone plays a critical role in reproductive maturation?
A
GnRH
16
Q
What are the characteristics of hypothermic releasing hormones?
A
- Secretion in pulse tied to the internal biological clock
- Act on specific membrane receptors
- Transduce signals via secondary messengers
- Stimulate release of stored pituitary hormones
- Stimulate synthesis of pituitary hormones
- Stimulates hyperplasia and hypertrophy of target cells
- Regulates it own receptor
17
Q
What does the GnRH stimulate in the anterior pituitary gonadotrophs?
A
Stimulates production of
- Luteinizing hormone
- Follicle Stimulating hormone
from
18
Q
What is leptin?
A
Adipocyte derived protein hormone that signal information about energy stores to the CNS and plays an important role in regulating neuroendocrine function.
19
Q
How can leptin affect the reproductive cycle?
A
- If deficient, associated with reproductive dysfunction
- Leptin can accelerate the onset of reproductive function
20
Q
How is leptin released?
A
Pulsatile release pattern significantly associated with the variations in LH
21
Q
What the effects of growth hormone secretion fro the pituitary?
A
- Increases TSH
- Increased metabolic rate
- Promote tissue growth
- Increases androgens so retention of minerals in body to support bone and muscle growth
Growth spurt
22
Q
How is the anterior pituitary connected to the hypothalamus?
A
Superior hypophyseal artery
23
Q
What are the 6 hormones produced in the anterior pituitary?
A
- Growth hormone
- Thyroid stimulation hormone
- Adrenocorticotropic hormone
- Follicle stimulating hormone
- Lutenizing hormone
24
Q
How does the hypothalamus exert control on release of FSH and LH?
A
GnRH
-Released every 1.3 hours
25
Describe the sleep dependant nocturnal rise in LH
- Increase in sleep related LH
- Stimulates a nocturnal rise in Testosterone
- Could account of early pubertal changes seen in males
26
Describe the hormonal control of puberty in an overview.
Brain > Hypothalamus > Pituitary > Increase in LH and FSH levels > Gonadal development > Androgens and oestrogen
27
Describe the HPG axis in a male
- LH stimulates Leydig cells in testis
- Production of steroid hormone testosterone (mostly testes)
- Testosterone levels remain constant in the medium long term
- Circadian rhythm and environmental stimuli have an effect
28
Where is the location of spermatogenesis?
Seminiferous tubules
29
Which cells can be found in the interstitial tissue?
Leydig cells which produce testosterone. They function independently of the seminiferous tubules
30
What do the seminefrous tubules require?
Testosterone (functioning leydig cells)
31
What is the structure of seminiferous tubules?
Lined by complex epithelium made up of 2 cells types
- Support cells which are the sertoli cells
- Spermatogenic cells
32
What is the function and control of the Sertoli cells?
- Provide nutrition and hormonal support to the germ cells allowing sperm formation
- Sensitive to FSH
- Inhibin negatively feeds back on the anterior pituitary to decrease FSH
33
Which cells reduce a tight unction in the seminiferous tubules and why?
Sertoli cells
| -Prevent blood and sperm mixing to prevent an immune reaction
34
What is the primary target cells of FSH and LH in the female and the effect?
- Ovarian granulose cells
- Theca interna
Stimulate sex hormone synthesis and control gamete production
35
What is the effect of moderate and high levels of oestrogen on GnRH secretion?
- Moderate amounts of oestrogen reduce GnRH secretion by negative feedback
- High amounts of oestrogen alone promotes GnRH secretion by positive feedback causing an LH surge
36
What is the effect of progesterone on oestrogen?
- Increases the inhibitory effects of moderate oestrogen
| - Prevents positive feedback of high oestrogen so no LH surge
37
Where is inhibin realised from?
Granulosa cells of corpus luteum
38
What is the function of inhibin?
- Inhibits the secretion of FSH
| - Has a small inhibitory effect on LH
39
What do germ cells do after colonising the gonad?
- Proliferate by mitosis
- Reshuffle genetically and reduce haploid by meiosis
- Cytodifferentiate into mature gametes
40
What are the features of oogenesis?
- Usually 1 ovum per 28 day menstrual cycle
- One ovum with unequal division of cytoplasm and 3 polar bodies formed
- Starts in the foetus
- Ends at menopause
- Non motile gametes
- Last stage of meiosis 2 occurs in the oviduct
41
What are the features of spermatogenesis?
- Huge number of sperm reduced (200 million)
- 4 spermatids formed with no polar body formation and equal division of cytoplasm
- Starts at puberty
- Continuous production from puberty throughout adult life
- Motile gametes
- All stages are completed in the testes
42
What are the main functions of meiosis?
- Reduction of chromosome number to 23
- Ensures gametes is genetically unique
- Used only in production of sperm and eggs
- 2 successive cell divisions
- Production of 4 daughter cells
43
How many mature oocytes are formed in the female?
1
| The rest are polar bodies
44
What does genetic variation arise from?
- Crossing over (exchange of DNA between 2 homologous chromosomes)
- Independent assortment (random orientation of each bivalent along the metaphase plate with respect to other bivalents)
- Random segregation (random distribution o alleles among four gametes)
45
Where do the seminiferous tubules concentrate the sperm?
Ductile differentes
46
Describe spermatogenesis
- Spermatogonia fide by mitosis to give Ad spermatogonium(resting) and Ap spermatogonium(active)
- Ap spermatogonium maintain stock and from puberty onwards produce type B spermatogonia which give rise to primary spermatocyte
- Primary spermatocyte divide by meiosis giving rise to secondary spermatocytes then spermatids
- Each primary spermatocyte divides to form 4 haploid spermatids which differentiate into spermatozoa
47
What is the definition of the spermatogenic cycle?
The time it take for the appearance of the same stage within a segment of the tubule
48
What is the definition of the spermatogenic wave?
Distance between the same stag is called the spermatogenic wave
49
Describe the process that results in the differentiation of the spermatids to spermatozoa.
- Spermatids are related into the lumen of seminiferous tubules
- They remodel as the pass down seminiferous tubules. through the rete testis and ductile efferentes and into epididymis to finally form spermatozoa
50
Where do the spermatids become motile?
When they reach the epididymis
51
Where are secretions for semen released from?
- Seminal vesicle secretions (about 70%)
- Secretion of prostate (about 25%)
- Sperm (about 2-5%)
- Bulbourethral gland (less than 1%)
52
What is secreted form seminal vesicle?
- Amino acids
- Citrate (better than glucose as less completion from bacteria)
- Fructose
- Prostagladins
53
What is released from the prostate?
Proteolytic enzymes
54
What is released for the bulbourethral gland?
Mucoproteins which help lubricates and neutralised acidic urine in distal urethra
55
What is sperm capacitation?
Conditions in the female genital tract stimulate:
- Removal of glycoproteins and cholesterol from sperm membrane
- Activation of sperm signalling pathways
- Allow sperm to bind to the bona pellucida of oocyte and initiate acrosome reaction
56
When does maturate of oocytes begin?
Before birth
57
Describe the maturation of germ cells before birth
- Germ cells colonise the gonadal codex and differentiate oogonia
- Oogonia then proliferate rapidly by mitosis
- By end of the 3rd month oogonia are arranged inc clusters surrounded by flat epithelial cells
- Majority then continue to divide by mitosis but some enter meiosis and these arrest in prophase of meiosis 1 and are called primary oocytes
- Max number f germ cells reached mid gestation
- Cell death then begins and oogonia and primary oocytes begin to degenerate. by 7th moth most oogonia degenerated
- All surviving primary ones have now entered meiosis 1 and are individually surrounded by layer of flat epithelial cells called follicular cells.
- Follicular cells are now called primordial follicle cells
58
Describe maturation of oocytes at puberty
15-20 oocytes start to mature each month passing through 3 stages
1. Preantral
2. Antral
3. Preovulatory
59
What is the preantral stage?
As Primordial follicles begin to grow
- Surrounding follicular cells change from flat to cuboidal and proliferate to produce a stratified epithelium of granulosa cells
- Granulosa cells secrete layer of glycoprotein on oocyte forming the bona pellucida
60
What is the antral stage?
As development continues
- Fluid filled spaces appear between the granulosa cells and these come together to form the antrum
- Several follicles begin to develop with each ovarian cycle and usually one will reach maturity
61
Describe the features of the preovulatory phase
- Surge in LH induces this stage
- Meiosis 1 is complete resulting in 2 haploid daughter cells of unequal size due to one cells revving most of the cytoplasm and the other (1st polar body) receiving none.
- Each daughter cells now has 23 chromosomes and 46 chromatids
- Cell enters meiosis 2 but arrest in metaphase 2
- Meiosis 2 is only completed if the oocyte is fertilised otherwise the cell degenerates
62
What stimulates growth of the follicle during ovulation
FSH and LH
63
What is the mature follicle called when it is 2.5cm in diameter
Graafin follicle
64
What stimulate collagenase activity
LH surge
65
What is the function of prostaglandins in relation to LH.
Increase response to LH and cause local muscular contractions in ovarian wall
66
Give an overview of ovulation
- Rapid growth of follicle several hours before ovulation occurs
- Graffin follicle formation
- Local muscular contractions in ovarian wall and increase in collagenase activity
- Oocyte is extruded and breaks free from ovary
67
How is the corpus leteum formed.
-Remaining granulosa and theca internal cells become vascularised and develop yellowish pigment and change into lutein cells which form the corpus luteum
68
What does the corpus luteum secrete?
Oestrogens and progesterone
69
What is the function of the corpus luteum?
-Stimulates the uterine mucos to enter secondary stage in preparation for the embryo implantation
70
What happens to the corpus luteum if fertilisation doesn't occur?
Dies
71
How is the oocyte transported?
- Fimbriae sweep over surface of ovary shortly before ovulation
- Uterine tube begins to contract rhythmically
- Oocyte carried into tube by sweeping movement s of fimbriae and by motion of cilia on epithelial lining
- Oocyte is then propelled by peristaltic muscular contractions of the tube and by cilia in the mucosa
- If fertilised, oocyte reaches uterine lumen in 3 to 4 days
72
What forms the corpus albicans?
-If fertilisation does not occur corpus luteum degenerates and forms mass of fibrotic scar tissue which is the corpus albicans.
73
Why does menstrual bleeding occur?
Progesterone production decreases
74
What happens in the event of fertilization?
- HCG secreted boy the embryo prevent corpus luteum from degenerating
- Corpus luteum continues to grom ad form the corpus luteum of pregnancy
- Cells contine to secrete progesterone until the 4th month when the secretion from the placenta is adequate
