Unit 4.1 - Reproducton in Humans Flashcards
(232 cards)
1
Q
Is sexual reproduction different in different mammals?
A
No, it’s pretty much the same in all mammals
2
Q
What is the main purpose of sexual reproduction?
A
To promote genetic variation
3
Q
How does sexual reproduction promote genetic variation?
A
The offspring are not genetically identical or genetically identical to the parents
4
Q
Advantage of genetic variation in a species + give examples
A
Increases the chances of survival of the species (not the individuals)
e.g - disease: some will be more resistant
Climate change: some will be more able to survive
5
Q
Describe the offspring of asexual reproduction
A
Genetically identical to the parents (clones)
6
Q
Why is sexual reproduction troublesome compared with asexual reproduction?
A
Due to the need to produce gametes and to find a partner in order to combine gametes to form a zygote
7
Q
What forms when gametes combine?
A
A zygote
8
Q
Why is sexual reproduction costly?
A
Individuals can become vulnerable to predators
9
Q
How do we know that the risks taken during sexual reproduction are justified?
A
After evolution, the process still exists
10
Q
Scrotum function (male reproductive system)
A
External sac or skin containing the testes
11
Q
Testis/testes function in the male reproductive system
A
- produce gametes (sperm formed by spermatogenesis) and the sperm is used in reproduction when mature
- produce testosterone
12
Q
Where are both sperm and testosterone produces?
A
Testes
13
Q
Seminiferous tubules and epididymis function
A
Sperm are stored here and mature to become fully mobile
14
Q
Vas deferens function
A
Carries sperm towards the penis during ejaculation
15
Q
Semincal vesicle function
A
Secretes a fluid into the vas deferens that contains a mixture of chemicals which make up approximately 60% of semen
16
Q
Name all of the functions of seminal fluid, produced by the seminal vesicle
A
Provides nutrients for sperm such as fructose for respiration and amino acids
When sperm are released from the body, the seminal fluid helps to provide a source of nutrients
Seminal fluid is also alkaline which helps to neutralise the acidity of any urine remaining in the urethra and the acidity of the vaginal tract. Sperm would otherwise be killed by the acidity.
17
Q
Prostate function
A
Secretes a fluid into the vas deferens that contains a mixture of chemicals that make up approximately 30% of semen.
18
Q
What does prostate fluid do?
A
Contains zinc ions and is also alkaline which helps to neutralise the acidity of any urine remaining in the urethra and the acidity of the vaginal tract
19
Q
Urethra functions
A
Carries semen through the penis and out of the body
Carries urine from the bladder through the penis and out of the body
20
Q
Semen contents
A
Spermatozoa
Seminal fluids
Prostate fluids
21
Q
Penis function
A
Specialised organ adapted to transfer semen to the vagina during sexual intercourse
22
Q
Ovaries function
A
Production of gametes (secondary oocytes produced during oogenesis)
Produce oestrogen and progesterone
23
Q
What do we call female gametes and what don’t be call them?
A
Secondary oocytes, not “eggs”
24
Q
What are oestrogen and progesterone?
A
Hormones involved in the menstrual cycle and changes during pregnancy
25
Oviducts (fallopian tube) function
They have a lining of ciliated epithelial cells which move the secondary oocyte to the uterus
26
What adaptation do the oviducts (fallopian tubes) have in order to move the secondary oocytes to the uterus and why?
Lining of ciliated epithelial cell
The oocyte can’t propel itself like sperm can
27
Uterus function
Holds the developing foetus until birth
28
Endometrium function
Important in the early stages of pregnancy. The inner most later of the uterus wall. It has a good blood supply and builds up every month during the menstrual cycle (every month, a new endometrium is produced). If implantation of an embryo does not happen (no pregnancy), the endometrium is broken down and shed during menstruation
29
What is broken down and shed during menstruation if implantation of an embryo does not happen?
The endometrium
30
Cervix functions
A narrow ring of connective tissue and muscle
Acts as a barrier between the uterus and the outside environment during pregnancy
During pregnancy, a mucous plug forms in the cervix which helps prevent entry of pathogens.
It’s also what a baby exits the body through.
31
Vagina function
It has muscular walls and opens at the vulva
Semen is deposited in the vagina during sexual intercourse and the foetus is able to pass out from the uterus through the vagina during birth
32
What is the production of the male gametes in mammals known as?
Spermatogenesis
33
What does spermatogenesis lead to and how?
The formation of spermatozoa after a series of cell divisions in the testis
34
What the name of the thousands of tubules that make up the tissues of the testis?
Seminiferous tubules
35
Where does spermatogenesis occur?
In the walls of the seminiferous tubules
36
Between what type of cells does spermatogenesis occur?
Sertoli cells
37
Explain briefly what spermatogenesis is
The production of male gametes by the process of mitosis and meiosis and a version of gametogenesis
38
Where does spermatogenesis occur?
In the seminiferous tubules of the testes
39
How many seminiferous tubules does each of the testes contain and what is their total length?
About 1000
600m
40
What is there a layer of in each seminiferous tubule and what does this give rise to?
Layer of germinal epithelium which gives rise to the spermtogonia by a seres of mitotic divisions
41
When does spermatogenesis start and end?
Begins at puberty and continues throughout the life of the male
42
Describe spermatogenesis
The 1st cells are spermatogonia, which are constantly dividing through mitosis
After dividing, the cells undergo differentiation
This forms primary spermtocytes, which are still diploid cells
These undergo first meiotic division to form 2 haploid cells (homologous chromosome pairs separate during 1st meiotic division) —> secondary spermatocytes
2nd meiotic division occurs and spermatids are formed (are also haploid)
Spermatids undergo differentiation to form spermatozoa (these have a more complex structure)
43
Where exactly in the seminiferous tubule does spermatogenesis occur?
When cells divide, they are pushed down towards the lumen of the seminiferous tubule. The spermatozoa are produced at the bottom.
44
Sertoli cells
Specialised cells that share the same basement membrane as the germinal epithelial cells in the testis
45
Name the functions of Sertoli cells
Believed to support the developing spermatozoa and provide nutrients to these cells as they develop by secreting a nutritive solution
Also provide protection from the male’s immune system
Spermatogenesis occurs between these cells
The heads of the spermatozoa are in these cells
46
Order of the main things to label in a seminiferous tubule
Germinal epithelium
Spermatogonia
Spermatocyte
Spermatids
Spermatozoa
47
Where are leydig cells found?
Between the seminiferous tubules
48
What do leydig cells do?
Secrete testosterone
49
Testosterone
The hormone responsible for developing male characteristics and developing spermatozoa
50
Length of spermatozoa
About 50 micrometres (small cell)
51
3 main parts of the spermatozoa
Head
Mid-section
Tail
52
What are the 2 things to label on a Spermatozoa?
Nucleus
Acrosome
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Where is the nucleus of spermatozoa found and what is its function?
Haploid nucleus formed during meiosis
Holds the DNA of the cell and so contains genetic material
54
Where is acrosome in spermatozoa and what is its function?
In the head
Contains hydrolytic enzymes that help the sperm break through the corona radiata and zona pellucida surrounding the secondary oocyte. This helps their sperm fuse with the nucleus of the female gametes.
55
What do the hydrolytic enzymes of acrosome hep sperm do?
Break through the corona radiata and zona pellucida surrounding the secondary oocyte, helping it fuse with the nucleus of the female gametes
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Surrounding of secondary oocyte that a sperm needs to break through the fuse with the nucleus of female gametes
Corona radiata and zona pellucida
57
What happens to the cell membrane of the spermatozoa during capacitation?
Becomes more permeable
58
How are the mitochondria present in the mid-section of spermatozoa?
Spiralled around microtubules
59
Describe the mid-section of spermatozoa
Packed with mitochondria. Sperm use the ATP produced by the mitochondria to move.
Contains microtubules that responsible for movement of the tail (these use the ATP).
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What do the sperm use the mitochondria in the mid-section for?
Use the ATP produced to move
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What is the tail of spermatozoa?
A long flagellum that pushes the sperm forward
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Why are spermatozoa described as being motile?
They can move (swim) towards the egg cell
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Describe the tail of spermatozoa
Microtubules from mid-section extend into axial filament in the tail
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What propels spermatozoa forward?
The whiplash movement of the tail
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What does the whiplash movement of the tail of spermatozoa help propel the spermatozoa through?
The seminal fluid to the female gametes
66
What in spermatozoa indicates that mammals evolved from aquatic organisms?
The presence of a flagellum
67
Due to the presence of a flagellum in spermatozoa, what must be done?
Sperm must be kept in a liquid environment and be transmitted directly from inside the male mammal to inside the female —> internal fertilisation
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Internal fertilisation
Sperm is transmitted directly from inside the male mammal to inside the female
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What does internal fertilisation ensure?
That the spermatozoa are kept in an aquatic environment even though the majority of mammal live on land
70
Explain how internal fertilisation with spermatozoa is different to plants
In plants, the pollen grains (male gametes) have a waterproof outer coat so that they don’t dry out. They can therefore be released into the atmosphere and can survive outside of the organism.
71
Function of spermatozoa
To deliver male gametes to female gametes to fuse and form a zygote during fertilisation
72
What is formed when male and female gametes fuse?
A zygote
73
How many spermatozoa are produced in a male’s life?
In heir millions, constantly, throughout the adult life
74
Why are spermatozoa produced in their millions, constantly, throughout the adult life?
Increases the probability of fertilising the egg
75
Do spermatozoa know where to go to fertilise the egg? How?
Yes, they follow a chemical rail released by the oocyte
76
How does meiosis promote genetic variation?
Crossing over
Random assortment
77
When does crossing over occur during meiosis?
During prophase I
78
When does random assortment occur during meiosis?
During metaphase I and II
79
What occurs during crossing over (meiosis)?
Parts of homologous pairs of chromosomes are swapped over
Homologous pairs form bivalents during Synapsis and parts swap over. New combinations of alleles are formed on the chromatids (same genes as homologous chromosomes, different alleles)
80
Random assortment
How the homologous chromosomes arrange themselves along the spindle
81
Describe random assortment during metaphase II
The chromatids are no longer homologous, so this can lead to even more genetic variation
82
Chromosome number of cells after meiosis I and why
2 haploid nuclei (number of chromosomes per cell has halved)
83
Chromosome number throughout meiosis II + why
Haploid throughout (4 haploid cells with non-duplicated chromosomes are made)
84
Oogenesis
The production of female gametes
85
Oogenium
Stem cells in the ovaries of a foetus in the womb
86
When is there no further developments of oocytes?
Between birth and puberty
87
Describe the process of oogenesis
Before birth:
Oogenium are stem cells in the ovaries of a foetus in the womb
These undergo mitosis in order to increase in number
These grow to form the primary oocyte
Therefore, before birth there’s lots of primary oocytes
Between birth and puberty, there’s no further development of oocytes
From puberty through the menopause:
One primary oocyte develops into a secondary oocyte and is released during ovulation every month
During the first meiotic division, the secondary oocyte and the 1st polar body are formed
Both of these are haploid
The polar body is small and non-functional, whereas the secondary oocyte is functional -> the female gamete
Meiosis is then stopped and the second meiotic division doesn’t happen until a sperm cell penetrates into the egg cell
If and when this happens, the second meiotic division occurs. This forms the ovum (mature egg cell) and the 2nd polar body
The 1st polar body can divide to form more polar bodies (not always + not impotent in fertilisation anyway)
88
What is the functional female gamete?
Secondary oocyte
89
Under which circumstance does the second meiotic division occur during oogenesis?
When a sperm cell penetrates into the egg cell
90
Where do oocytes develop?
Within follicles
91
Follicles
Fluid-filled spaces that provide protection and nutrition for the developing oocyte
92
When are primary follicles formed?
Before the birth of the female child
93
What does a primary follicle contain?
A primary oocyte
94
What causes a primary follicle to mature?
When the level of follicle stimulating hormone - FSH increases
95
FSH
Follicle stimulating hormone
96
What do secondary follicles develop from?
Primary follicles
97
What do secondary follicles contain?
Secondary oocytes
98
What happens to each secondary follicle as it matures?
It becomes fluid-filled (the fluid filled area is called the antrum) and the secondary oocyte becomes surrounded by small follicular cells known as the corona radiata
99
Antrum
Fluid filled area of a secondary follicle
100
Corona radiata
Small follicular cells surrounding the secondary oocyte
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Small follicular cells surrounding the secondary oocyte
Corona radiata
102
Fluid-filled space of a secondary follicle
Antrum
103
What is a fully mature follicle called?
A Graafian follicle
104
Graafian follicle
Fully mature follicle
105
When is the Graafian follicle formed?
When the secondary oocyte is ready to be released at ovulation
106
Where do all of the processes of oogenesis occur?
In the ovary
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What does the Graafian follicle stay in the ovary as after ovulation and why?
As the corpus luteum
Helps control hormone levels during pregnancy
108
What does the corpus luteum do?
Controls hormone levels during pregnancy
109
Other word for Graafian follicle
Ovarian follicle
110
What are the different things to label on a Graafian follicle?
Theca
Antrum
Secondary oocyte
Cumulus cells (cells of corona radiata)
111
When are cumulus cells released (present in a Graafian follicle)?
With the oocyte from the Graafian follicle
112
1epu at 40x magnification
0.025mm
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1epu at 100x magnification
0.01mm
114
1 epu at 400x magnification
0.0025mm
115
Things to label on a secondary oocyte
Corona radiata
Plasma membrane
Nucleus (haploid)
Cytoplasm
Zona pellucida
116
Zona pellucida of a secondary oocyte
Protective layer
117
Protective layer of a seondary oocyte
Zona pellucida
118
Type of nucleus of a secondary oocyte
Haploid
119
Why is the cytoplasm of a secondary oocyte very large?
Contains nutrients that will feed the embryo in the early stages of developments
120
Why would one secondary follicles have different appearances under the microscope to others?
May have been cut in a different plane or is in an earlier stage of development
121
Fertilisation definition
The fusion of the male and female gametes
122
What is fertilisation the same for?
All organisms that undergo sexual reproduction
123
What is *not* fertilisation?
The penetration of the sperm into the egg
124
When exactly is fertilisation occurring?
When the nuclei of both the sperm and the egg fuse in the oocyte
125
When can the second meiotic division of the oocyte occur?
After the sperm cell penetrates into the oocyte
126
Describe the size different between the oocyte and spermatozoa
Oocyte is much bigger
127
How many male gametes should fuse with the male gamete in the oocyte?
Only 1
128
Why does it have to be ensured that only 1 male gamete fuses with the female gamete in the oocyte?
If not, will lead to mutations and the embryo won’t develop
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Explain the stages of fertilisation
1. Following sexual intercourse, spermatozoa move into the oviducts and approach the secondary oocyte
2. Capacitation increases the permeability of he cell membrane in the head of the sperm above the acrosome. When the sperm approached the egg, an acrosome reaction occurs. This is where hydrolase enzymes from the acrosome are released from the head of the sperm. These enzymes digest through the zona pellucida. This enables the membrane of the sperm cell to reach the membrane of the oocyte.
3. When the sperm cell reaches the oocyte membrane, there are receptor proteins on the oocyte membrane and the proteins on the sperm’s head attract to these receptors
4. Fusion of sperm and secondary oocyte membranes. The sperm now moves into the cytoplasm of the oocyte and now fertilisation can occur. Genetic material of sperm cell enters the secondary oocyte triggering completion of meiosis II and formation of ovum and second polar body.
5. Only one male nucleus can fertilise the female nucleus. The cortical reaction ensures this. During this reaction, cortical granules fuse with the cell membrane and modify the zone pellucida to form the fertilisation membrane. This ensues that only 1 sperm can fertilise and prevents polyspermy.
6. Nuclei of the sperm and ovum fuse to form a zygotic nucleus. 2 haploid nuclei form a diploid zygote nucleus.
130
Capacitation
How the enzymes are released from the acrosome
131
Describe the acrosome reaction during fertilisation
Hydrolase enzymes from the acrosome are released from the head of the sperm. These enzymes digest through the zona pellucida.
132
Describe the cortical reaction during fertilisation
Cortical granules fuse with the cell membrane and modify the zona pellucida to form the fertilisation membrane. This ensures that only 1 sperm can fertilise and prevents polyspermy
133
Where does fertilisation happen?
In the oviduct (Fallopian tube)
134
What has to be true for fertilisation to lead to a pregnancy?
Has to happen early after ovulation
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At which stage would it be unlikely that fertilisation will occur?
If fertilisation happens later on after ovulation
136
List the stages before, including and after fertilisation
Ovulation
Fertilisation
Cleavage
Morula
Early blastocyst
Late blastocyst
137
Explain how everything is still contained within the same structure after fertilisation
Still a zona pellucida
The same oocyte
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What type of divisions does the zygote undergo as it moves down the oviduct?
Mitotic
139
When does the zygote undergo repeated mitotic divisions?
As it moves down the oviduct
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What can a blastocyst be described as?
A hollow ball of cells
141
List the stages from the zygote to the blastocyst
Zygote
2 cell stage
4 cell stage
8 cell stage
Morula
Blastocyst
142
How long does a morula last?
72 hours
143
How long does a blastocyst last?
4 days
144
What is the morula?
A solid ball of cells
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Which part of the oocyte undergoes divisions to room more cells in the oocyte?
The cytoplasm
146
What is the morula?
A cluster of undifferentiated cells
147
Which stage of development of the zygote are embryonic stem cells?
Morula
148
Why are the cells of the morula used as embryonic stem cells?
No differentiation has occurred so the cells are genetically identical
149
How can we use the cells of the morula as embryonic stem cells?
We’ able to remove one of these cells and all of the others can form a new embryo. The cell can be used for embryo splitting for cloning.
150
From which stage of development of the zygote can identical twins form?
Morula
(Get 2 genetically identical embryos)
151
3 things to label on a blastocyst
Inner cell mass
Trophoblast
Blastocoel (fluid-filled cavity)
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Between which cells is there a difference in nature in them in the blastocyst?
Between the cells of the trophoblast and the inner cell mass
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What is the first stage in the zygote development where cells differentiate and specialise?
Blastocyst stage
154
Which part of a blastocyst will form the placenta?
Trophoblast (outer layer)
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What does the trophoblast of a blastocyst go on to form?
The placenta
156
What does the inner cell mass of a blastocyst form?
The foetus
157
Which part of a blastocyst will form the foetus ?
The inner cell mass
158
What happens during implantation?
The blastocyst moves into the uterus where it attaches and sinks into the endometrium (the lining of the uterus)
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What does the blastocyst attach and sink into in the uterus during implantation?
The endometrium (the lining of the uterus)
160
What is the endometrium in the uterus?
A layer of tissue that develops during the menstrual cycle
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How is it ensured that implantation is successful?
Everything is timed so that the endometrium is in the right condition to receive the embryo in the uterus
162
Describe how implantation occurs
The blastocyst sinks into the endometrium
Cells on the outside of the blastocyst, the trophoblast cells, form trophoblastic villi that will penetrate the endometrium
The villi increase the surface area for the absorption of nutrients from the endometrium
The embryo now realised on nutrients from the mother’s blood supply - the early embryo was completely dependent on what was inside of the cytoplasm of the oocyte for nutrition
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What does the placenta begin to develop from after implantation?
The trophoblast cells
164
What do trophoblastic villi do?
Increase the surface a for the absorption of nutrients from the endometrium
165
From when onwards does the embryo rely on the nutrients from the mother’s blood supply?
After the trophoblastic villi penetrate the endometrium
166
Before the trophoblastic villi penetrate the endometrium and the embryo could rely on nutrients from the mother’s blood supply, how did the early embryo obtain nutrients?
Was completely dependent on what was inside of the cytoplasm of the oocyte for nutrition
167
What do the trophoblast cells develop into after implantation?
The placenta
168
How does the foetus get nutrients from its mother during pregnancy as it develops?
Via the placenta
169
How does the uterus grow as the embryo develops?
Is controlled by changing hormone levels
170
What is the foetus surrounded by in the womb?
Amniotic fluid
171
Where is amniotic fluid in the womb?
Contained within the amniotic sack in the womb
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In which part of the womb does the placenta grow?
In the uterine wall
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How is the placenta connected to the foetus?
By the umbilical cord
174
What transport materials between the foetus and the mother?
Umbilical arteries
175
Functions of the placenta
Gas and nutrient exchange
Acts as a barrier between the mother’s blood and fetal blood
Protects the foetus from the mother’s immune system and the difference in blood pressure
Secretes hormones
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Why does the foetus need to be protected for the difference in blood pressure of the mother by the placenta?
The look pressure of the mother’s blood is much higher
177
Which part of the placenta has features which aid the exchange of gases and nutrients between the blood of the mother and fetus?
The surface between the placenta and the lining of the uterus
178
What are the placenta’s adaptations for exchange?
Chorionic villi
Barrier between the blood of the mother and the fetal blood is very thin
The blood of the mother and the fetal blood flow in the opposite direction (counter-current flow)
179
What does fetal blood flow through?
Chorionic villi
180
The surface area for the exchange of what is increased by the placenta having chorionic villi?
Gas
Nutrients
Waste products in the blood
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Why is the barrier between the blood of the mother and the fetal blood very thin in the placenta?
To provide a short diffusion pathway
182
Why does the blood of the mother and fetal blood flow in the opposite direction (counter-current flow)?
To maintain a concentration gradient across the whole exchange surface
183
How are hormones carried throughout the body?
In the bloodstream
184
What all need to coincide with the development of the endometrium?
Follicle development, ovulation, fertilisation and implantation
185
What do Follicle development, ovulation, fertilisation and implantation all need to coincide with? Why?
The development of the endometrium
Ensures that the uterus is prepared for the foetus to implant
186
Can cilia move?
Ywa
187
Where are the pituitary glands?
In the brain
188
Explain all of hormonal control during the menstrual cycle
1. Anterior pituitary gland secretes follicle stimulating hormone (FSH)
2. FSH stimulates maturation of primary follicle to secondary follicle
3. Maturing follicle secretes oestrogen
4. Oestrogen:
-stimulates lutenising hormone (LH) production by anterior pituitary gland
-inhibits secretion of FSH (to stop another follicle from developing)
-triggers rebuilding of endometrium
5. LH:
-stimulates secretion of FSH
-induces ovulation on day 14 (this is the population average and can vary)
-stimulates conversion of Graafian follicle into corpus luteum
6. FSH inhibits oestrogen production (which has been rising until ovulation)
7. Corpus luteum secretes progesterone that:
-maintains endometrium
-inhibits section of FSH
-inhibits secretion of LH
(The corpus lutetum also releases oestrogen. However, during the latter half of the menstrual cycle, oestrogen does not stimulate LH sections because of the effects of progesterone)
8. When no pregnancy occurs, falling levels of FSH and LH cause corpus luteum to degenerate
9. Progesterone (and oestrogen) levels decrease as secretions from degenerating corpus luteum decline
10. Low levels of progesterone and oestrogen cause endometrium to breakdown and be shed during menstruation
189
List what the hormone oestrogen does
-stimulates lutenising hormone (LH) production by anterior pituitary gland
-inhibits section of FSH (to stop another follicle form developing)
-triggers rebuilding of endometrium
190
Why does oestrogen inhibit the section of FSH?
To stop another follicle from developing
191
What does the hormone LH do?
-stimulates section of FSH
-induces ovulation on day 14 (average)
-stimulates conversion of Graafian follicle into corpus luteum
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What does corpus luteum do?
Secretes progesterone
193
What does progesterone do?
-maintains the endometrium
-inhibits secretion of FSH
-inhibits secretion of LH
194
Trimester
3 months
195
Explain all of the hormonal changes that occur during pregnancy
Just before and following implantation, the developing embryo secretes HCG (Human Chorionic Gonadotrophin) which maintains the corpus luteum for the first 16 weeks of pregnancy (so HCG levels rise before other hormone levels do)
The placenta then secretes progesterone and oestrogen which rise to high levels in he plasma
FHS and LH section are inhibits due to these high levels
Progesterone suppresses the uterine wall’s ability to contract
Oestrogen stimulates the growth of the uterus to accommodate the growing foetus and stimulates the growth and development of the mammary glands during pregnancy
196
HCG
Human chorionic gonadotrophin
197
When does the developing embryo secrete HCG and why?
Just before and following implantation
Maintains he corpus luteum for the first 16 weeks of pregnancy
198
Which hormone suppresses the uterine wall’s ability to contract?
Progesterone
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What does progesterone do to the uterine wall?
Suppresses its ability to contract
200
Which hormone stimulates the growth of the uterus?
Oestrogen
201
What does oestrogen do the uterus?
Stimulates its growth to accommodate the growing foetus
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What does oestrogen stimulate the growth of?
The uterus
The mammary glands
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Which hormone is tested for in a pregnancy test?
HCG
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How do you know if you’re pregnant after a pregnancy test?
If there’s HCG in the blood, the individual is pregnant
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Describe the increase in oestrogen and progesterone during the last 3 months of a pregnancy
The increase in oestrogen is greater than the increase of progesterone but just prior to birth, the progesterone concentration in the plasma decreases
206
What is in the mother’s interests during a pregnancy and what is in the foetus’ interest and what happens eventually?
It is in the mothers’ interest to give birth as soon as the foetus can live independently
Whereas, he foetus ants to delay birth as long as possible
They both release hormones supporting their conflicting needs but at 39 weeks, the mothers’ prevail
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What are foetal hormones that are transferred to the mother’s bloodstream at 39 weeks doing?
Transferred across the placenta and decrease decrease her plasma concentrations of progesterone
208
What have the high levels of progesterone throughout a pregnancy inhibited?
The secretion of oxytocin and prolactin
209
What are the main two hormonal increases and decreases just before birth?
Oestrogen levels increase
Progesterone levels decrease
210
When is oxytocin secretion no longer inhibited?
When progesterone levels decrease
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What happens during birth when oxytocin secretion is no longer inhibited by progesterone?
Oxytocin is secreted by the posterior pituitary gland
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What do secretions of oxytocin during birth lead to?
Contractions of the myometrium in the uterus wall
213
Explain how a positive feedback occurs with oxytocin during birth
Secretions of oxytocin causes contractions of the myometrium in the uterus wall
The contractions are mild initially but they stimulate the section of more oxytocin by positive feedback and so the oxytocin concentration in the blood increases and the contractions get stronger throughout the birth
214
Why do contractions get stronger throughout a birth?
Secretions of oxytocin causes contractions of the myometrium in the uterus wall
The contractions are mild initially but they stimulate the section of more oxytocin by positive feedback and so the oxytocin concentration in the blood increases and the contractions get stronger throughout the birth
215
How do contractions become as time passes and more oxytocin is secreted?
Contractions become stronger and more frequent
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How does the myometrium contract? Why?
From the top down so that the foetus can be pushed out through the cervix
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What is prolactin secreted by?
The anterior pituitary gland
218
What does prolactin do?
Stimulates the glandular tissue in the mammary glands to synthesise milk
219
Where synthesises milk when stimulated by prolactin?
The glandular tissue in the mammary glands
220
When is milk released from the glandular tissue in the mammary glands?
When oxytocin causes the muscles around the milk ducts to contract
221
When does prolactin section happen?
During and continues after birth, as long as the milk is needed
222
Copuaiton
Sexual intercourse
223
What does copulation increase production of?
LH and FSH and also progesterone levels
224
Can humans ovulate with no copulation?
Yes
225
Compare the differences between umbilical arteries and umbilical veins
(Arteries first, then veins)
Less O2, more O2
More CO2, less CO2
More urea, less urea
Less nutrients, more nutrients
Less antibodies, more antibodies
226
What does a pressure difference in the placenta do?
It forces materials through capillaries
227
Describe the rate of exchange in the placenta + explain this
Fast
Maintains concentration gradients
228
What does the nucleus of spermatozoa do?
Fuses with oocyte to form 2n zygote
229
Why does the placenta secrete hormones?
To maintain pregnancy
230
Why is it important to have a higher number of of blood vessels in the ovary after ovulation?
The hormones can be transported
231
where in a spermatozoa is the acrosone found?
at the very tip of the head
232
What does amniotic fluid do?
Acts as a shock absorber to protect from physical damage
