11.4 Sexual Reproduction Flashcards
(148 cards)
1
Q
What is gametogenesis?
A
Gametogenesis is the process by which diploid precursor cells undergo meiotic division to become haploid gametes (sex cells)
2
Q
What is the male version of gametogenesis?
A
In males, this process is called spermatogenesis and produce spermatozoa (sperm)
3
Q
What is the female version of gametogenesis?
A
In females, this process is called oogenesis and produce ova (eggs)
4
Q
What are the 3 general steps of gametogenesis?
A
The process of gametogenesis occurs in the gonads and involves the following steps:
Multiple mitotic divisions and cell growth of precursor germ cells
Two meiotic divisions (meiosis I and II) to produce haploid daughter cells
Differentiation of the haploid daughter cells to produce functional gametes
5
Q
What does spermatogenesis describe?
A
Spermatogenesis describes the producton of spermatozoa (sperm) in the seminiferous tubules of the testes
6
Q
When does spermatogenesis start?
A
The process begins at puberty when the germline epithelium of the seminiferous tubules divides by mitosis
7
Q
What do the spermatogonia undergo to form?
A
The spermatocytes undergo two meiotic divisions to form four haploid daughter cells (spermatids)
8
Q
What do spermatids undertake to become functional sperm cells?
A
The spermatids then undertake a process of differentiation in order to become functional sperm cells (spermatozoa)
9
Q
What is oogenesis?
A
Oogenesis describes the production of female gametes (ova) within the ovaries (and, to a lesser extent, the oviduct)
10
Q
When does oogenesis begin?
A
The process begins during foetal development, when a large number of primordial cells are formed by mitosis (~40,000)
11
Q
What happens to oogonia?
A
These cells (oogonia) undergo cell growth until they are large enough to undergo meiosis (becoming primary oocytes)
12
Q
What process do primary oocytes begin and what occurs?
A
The primary oocytes remain arrested in prophase I until puberty, when a girl begins her menstrual cycle
13
Q
What is the role of FSH in oogenesis?
A
Each month, hormones (FSH) will trigger the continued division of some of the primary oocytes
14
Q
What process do primary oocytes undergo?
A
These cells will complete the first meiotic division to form two cells of unequal size
15
Q
What are the 2 products of the first meiotic division in oogenesis?
A
One cell retains the entirety of the cytoplasm to form a secondary oocyte, while the other cell forms a polar body
16
Q
What happens to the primary oocyte after the first meiotic division?
A
The polar body remains trapped within the follicle until it eventually degenerates
17
Q
What does the secondary oocyte begin and when is it arrested?
A
The secondary oocyte begins the second meiotic division but is arrested in metaphase II
18
Q
Where does the secondary oocyte travel?
A
The secondary oocyte is released from the ovary (ovulation) and enters into the oviduct (or fallopian tube)
19
Q
What is the role of the follicular cells in oogenesis?
A
The follicular cells surrounding the oocyte form a corona radiata and function to nourish the secondary oocyte
20
Q
What will happen if the oocyte is fertilised by a sperm?
A
If the oocyte is fertilised by a sperm, chemical changes will trigger the completion of meiosis II and the formation of another polar body (the first polar body may also undergo a second division to form a third polar body)
21
Q
What happens when meiosis II is complete?
A
Once meiosis II is complete the mature egg forms a ovum, before fusing its nucleus with the sperm nucleus to form a zygote
22
Q
What are the 3 key differences of spermatogenesis and oogenesis?
A
- number of cells produced
- size of cells produced
- timing of the process
23
Q
How do oogenesis and spermatogenesis differ in terms of the number of cells produced?
A
In spermatogenesis, the cells divide equally during meiosis to produce four functional gametes
In oogenesis, the cells do not divide equally and as a result only one functional gamete is formed (plus 2 – 3 polar bodies)
24
Q
How do oogenesis and spermatogenesis differ in terms of the size of cells produced?
A
In spermatogenesis, the cells that are formed following differentiation are all of equal size with equal amounts of cytoplasm
In oogenesis, one daughter cell (the ovum) retains all of the cytoplasm, while the other daughter cells form polar bodies
The polar bodies remain trapped within the surrounding layer of follicle cells until they eventually degenerate
25
How do oogenesis and spermatogenesis differ in terms of the timing of the process?
In spermatogenesis, the production of gametes is a continuous process that begins at puberty and continues until death
In oogenesis, the production of gametes is a staggered and finite process:
It begins before birth (prenatally) with the formation of a fixed number of primary oocytes (~40,000)
It continues with the onset of puberty according to a monthly menstrual cycle
It ends when hormonal changes prevent the further continuance of the menstrual cycle (menopause)
26
Where does gametogenesis occur in males?
In males, the gametes are produced within the seminiferous tubules of the testes
27
Where does gametogenesis occur in females?
In females, the gametes are produced by the ovaries
28
What are the testes composed of?
The testes are composed of seminiferous tubules which produce sperm
29
What is each seminiferous tubule surrounded by?
Each tubule is surrounded by a basement membrane which is lined by germline epithelium
30
What is the role of the germline epithelium?
The germline epithelium will divide by mitosis to make spermatogonia (which divide by meiosis to make spermatids)
31
What do the spermatids differentiate into?
The spermatids differentiate into functional spermatozoa, which are then released into the lumen of the tubule
32
What are the developing spermatozoa nourished by?
These developing spermatozoa are nourished by Sertoli cells, which reside in the tubule lining
33
What is outside of the tubules?
Outside of the tubules are blood capillaries and interstitial cells (Leydig cells) which produce testosterone
34
What does the ovary contain (in general)?
The ovary contains follicles in various stages of development
35
When will these follicles develop over?
These follicles will develop over the course of a menstrual cycle and hence will not always be apparent upon inspection
36
What do primordial follicles contain?
Primordial follicles contain egg cells that have been arrested in prophase I (primary oocytes)
37
What will these follicles develop into each month?
Some of these follicles will develop each month into primary follicles and then secondary follicles
38
What will one follicle become each month?
Each cycle, one follicle will become a dominant Graafian follicle and rupture to release the secondary oocyte
39
What will the ruptured follicle develop into?
The ruptured follicle will then develop into a short-lived corpus luteum, which secretes key ovarian hormones
40
What will the corpus luteum degenerate into?
Eventually the corpus luteum will degenerate to form a corpus albicans
41
Where does spermatogenesis start?
Spermatogenesis in the seminiferous tubules starts at the outer lining of the tubule (germline epithelium)
42
Where do germ cells move in spermatogenesis?
As the germ cells divide by meiosis they move towards the inner lining before being released into the lumen as sperm
43
What represents the sertoli cells?
Non-dividing cells within the tubule lining will represent the Sertoli cells, which nourish and support the spermatocytes
44
What will cells located externally to the tubule represent?
Cells located externally to the tubule will likely represent interstitial cells (Leydig cells), which produce testosterone
45
Is oogenesis a continuous process?
Oogenesis in the ovaries is not a continuous process and proceeds according to a monthly menstrual cycle
46
Due to oogenesis being monthly, when will certain follicles be present?
Consequently, certain developing follicles will only be visible at particular stages in the cycle
47
When can comparison between primary and secondary follicles be possible?
As a follicle matures it will grow larger in size, allowing for comparisons to be made between primary and secondary follicles
48
What is the difference between oo and spermatogenesis in terms of other germline epithelium?
Unlike in spermatogenesis, the outer germline epithelium of the ovaries does not directly contribute to gamete formation
49
What do the male and female gametes have in order to fulfil their function?
The male and female reproductive gametes (sperm and egg) have specialised structures which reflect their functions
50
How is the male gamete adapted to its function?
The male gamete (sperm) is small and motile and only contributes the male’s haploid nucleus to the zygote
51
How is the female gamete adapted to its function?
The female gamete (egg) is large and non-motile and contributes all the organelles and cytoplasm to the zygote
52
What 3 sections can typical human spermatozoa be divided into?
A typical human spermatozoa can be divided into three sections – head, mid-piece and tail
53
What 3 structures does the head region contain?
The head region contains three structures – a haploid nucleus, an acrosome cap and paired centrioles
54
What does the haploid nucleus of the sperm cell contain?
The haploid nucleus contains the paternal DNA (this will combine with maternal DNA if fertilisation is successful)
55
What does the acrosome cap contain?
The acrosome cap contains hydrolytic enzymes which help the sperm to penetrate the jelly coat of the egg
56
What are the centrioles needed by?
The centrioles are needed by a zygote in order to divide (egg cells expel their centrioles within their polar bodies)
57
WHat does the midpiece contain and why?
The mid-piece contains high numbers of mitochondria which provide the energy (ATP) needed for the tail to move
58
What does the tail contain and why?
The tail (flagellum) is composed of a microtubule structure called the axoneme, which bends to facilitate movement
59
What two layers is a typical egg surrounded by?
A typical egg cell is surrounded by two distinct layers – the zone pellucida (jelly coat) and corona radiata
60
What is the zona pellucida?
The zona pellucida is a glycoprotein matrix which acts as a barrier to sperm entry
61
What is the corona radiata?
The corona radiata is an external layer of follicular cells which provide support and nourishment to the egg cell
62
What is within the egg cell?
Within the egg cell are numerous cortical granules, which release their contents upon fertilisation to prevent polyspermy
63
Does an egg cell have a haploid nucleus?
Although diagrams of egg cells commonly include a haploid nucleus, no nucleus will form within the egg until after fertilisation has occurred (the egg cell is arrested in metaphase II until it becomes fertilised by a sperm)
64
What does external fertilisation involve?
External fertilization involves the fusion of gametes (egg and sperm) outside of the body of a parent
65
When is external fertilisation most common?
It is most common in aquatic animals, where the water acts as a medium via which the gametes can travel
66
What is external fertilisation susceptible to?
This method of fertilization is susceptible to environmental influences, such as predators and pH changes
67
Therefore what quantity of gametes are released when organisms reproduce via external fertilisation?
Consequently, species that reproduce this way usually release large quantities of gametes to compensate for losses
The process of releasing gametes into the water is called spawning
68
What is internal fertilisation?
Internal fertilization involves the fusion of gametes (egg and sperm) inside of the body of a parent
69
What method does internal fertilisation require?
This requires a method by which the gamete of one parent can be introduced inside the body of another (e.g. copulation)
70
What type of animals use internal fertilisation and why?
Internal fertilization offers more protection to the gametes and embryos, but at a potential survival cost to the parent
71
What are the 3 processes involved in fertilisation in humans?
capacitation
acrosome reaction
cortical reaction
72
What is a brief description of capacitation?
biochemical changes which occur post ejaculation to improve sperm motility
73
What is a brief description of acrosome reaction?
the release of hydrolytic enzymes which softens the zona pellucida (jelly coat)
74
What is a brief description of cortical reaction?
hardening of the jelly coat post fertilization to prevent potential polyspermy
75
When does capacitation occur?
Capacitation occurs after ejaculation, when chemicals released by the uterus dissolve the sperm’s cholesterol coat
76
What does capacitation improve?
This improves sperm motility (hyperactivity), meaning sperm is more likely to reach the egg (in the oviduct)
77
What does capacitation destabilise?
It also destabilises the acrosome cap, which is necessary for the acrosome reaction to occur upon egg and sperm contact
78
What is the role of the acrosome reaction?
When the sperm reaches an egg, the acrosome reaction allows the sperm to break through the surrounding jelly coat
79
Where does the sperm bind to?
The sperm pushes through the follicular cells of the corona radiata and binds to the zona pellucida (jelly coat)
80
What does the acrosome vesicle fuse with?
The acrosome vesicle fuses with the jelly coat and releases digestive enzymes which soften the glycoprotein matrix
81
What does the softening of the zona pellucida allow for?
The sperm then pushes its way through the softened jelly coat and binds to exposed docking proteins on the egg membrane
82
What membranes fuse in the acrosome reaction?
The membrane of the egg and sperm then fuse and the sperm nucleus (and centriole) enters the egg
83
WHen does the cortical reaction occur?
The cortical reaction occurs once a sperm has successfully penetrated an egg in order to prevent polyspermy
84
What is released during the cortical reaction?
Cortical granules within the egg’s cytoplasm release enzymes (via exocytosis) into the zona pellucida (jelly coat)
85
What do these enzymes destroy?
These enzymes destroy sperm binding sites and also thicken and harden the glycoprotein matrix of the jelly coat
86
What is the role of destroying sperm binding sites?
This prevents other sperm from being able to penetrate the egg (polyspermy), ensuring the zygote formed is diploid
87
What is the role of destroying sperm binding sites?
This prevents other sperm from being able to penetrate the egg (polyspermy), ensuring the zygote formed is diploid
88
What prompts the completion of meiosis II after fertilisation?
Following the fusion of an egg and sperm (fertilization), an influx of Ca2+ into the ova prompts the completion of meiosis II
89
What are the fused sperm and egg called?
The egg and sperm nuclei combine to form a diploid nuclei and the fertilized cell is now called a zygote
90
What will the dividing zygote undergo? What does it form?
The zygote will undergo several mitotic divisions to form a solid ball of cells called a morula
91
What processes must a morula undergo to form a blastocyst?
As the morula continues to divide, it undergoes differentiation and cavitation (cavity formation) to form a blastocyst
92
What 3 distinct sections is a blastocyst composed of?
An inner cell mass (that will develop into the embryo)
A surrounding outer layer called the trophoblast (this will develop into the placenta)
A fluid filled cavity called the blastocoele
93
What is the final stage of early embryo development?
The final stage of early embryo development is the implantation of the blastocyst into the endometrial lining of the uterus
94
What does the blastocyst breach? (final stage)
The blastocyst breaches the jelly coat that was surrounding it and preventing its attachment to the endometrium
95
What is released from the embedded blastocyst?
Digestive enzymes are released which degrade the endometrial lining, while autocrine hormones released from the blastocyst trigger its implantation into the uterine wall
96
What can occur once the blastocyst is embedded?
Only once the blastocyst is embedded within the uterine wall can the next stage of embryogenesis occur
97
What sustains the embryos development?
The growing embryo will gain oxygen and nutrients from the endometrial tissue fluid, ensuring its continued development
98
How long does embryogenesis take?
The entire process (from fertilization to implantation) takes roughly 6 – 8 days
99
What hormone does the embedded blastocyst begin to secrete?
When a blastocyst becomes implanted in the endometrial lining it begins to secrete human chorionic gonadotropin (hCG)
100
What does hCG promote?
hCG promotes the maintenance of the corpus luteum within the ovary and prevents its degeneration
101
What is the effect of hCG in terms of maintaining pregnancy?
As a consequence of this, the corpus luteum survives and continues to produce both oestrogen and progesterone
102
How does oestrogen maintain pregnancy?
Oestrogen inhibits FSH and LH production by the pituitary gland, preventing the release of more eggs from the ovaries
103
How does progesterone maintain pregnancy?
Progesterone also functions to maintain the endometrium (which is nourishing the embryo) and thicken the cervix
104
How long are the levels of hCG maintained for?
The levels of hCG are maintained for roughly 8 – 10 weeks while the placenta is being developed
105
How is pregnancy maintained once the blastocyst no longer secretes hCG?
After this time, the placenta becomes responsible for progesterone secretion and nourishing the embryo
106
What happens to the corpus luteum once the blastocyst no longer secretes hCG?
At this point the corpus luteum is no longer required and begins to degenerate as hCG levels drop
107
What is the v. general function of the placenta?
The placenta functions as the life support system for the foetus
108
What are the two key functions of the placenta?
It facilitates the exchange of materials between the mother and foetus
It secretes hormones to maintain the pregnancy after the corpus luteum has degenerated
109
What is the general structure of the placenta?
The placenta is a disc-shaped structure that nourishes the developing foetus
110
WHat is the placenta formed from and what does it eventually invade?
It is formed from the development of the trophoblast upon implantation and eventually invades the uterine wall
111
What allows the maternal blood to pool?
Maternal blood pools via open ended arterioles into intervillous spaces within the placenta called lacunae
112
What is the role of the chorionic villi?
Chorionic villi extend into these pools of blood and mediate the exchange of materials between the foetus and the mother
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How is exchanged material transported from mother to foetus?
Exchanged material is transported from the villi to the foetus via an umbilical cord, which connects the foetus to the placenta
114
What happens to the placenta after birth?
Upon birth, the placenta is expelled from the uterus with the infant – it is then separated from the infant by severing the umbilical cord (the point of separation becomes the belly button)
115
Where do the chorionic villi extend to allow for material exchange?
The chorionic villi extend into the intervillous space (lacuna) and exchange materials between the mother and foetus
116
What are chorionic villi lined by and why?
Chorionic villi are lined by microvilli to increase the available surface area for material exchange
117
What helps minimise diffusion distance in placental material exchange?
Foetal capillaries within the chorionic villi lie close to the surface to minimise diffusion distance from blood in the lacunae
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What will diffuse FROM the lacunae INTO foetal capillaries?
Materials such as oxygen, nutrients, vitamins, antibodies and water will diffuse from the lacunae into foetal capillaries
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What will diffuse FROM the lacunae INTO MATERNAL blood vessels?
Foetal waste (such as carbon dioxide, urea and hormones) will diffuse from the lacunae into the maternal blood vessels
120
What is the general hormonal role of the placenta?
The placenta takes over the hormonal role of the ovaries (at ~12 weeks) and begins producing estrogen and progesterone
121
What does estrogen stimulate? (placenta)
Estrogen stimulates the growth of uterine muscles (myometrium) and the development of the mammary glands
122
What does progesterone maintain? (placenta)
Progesterone maintains the endometrium, as well as reducing uterine contractions and potential maternal immune responses
123
When do progesterone and estrogen levels drop?
Both estrogen and progesterone levels drop near the time of birth
124
What is the process of childbirth called and by what mechanism does it occur by?
The process of childbirth is called parturition and occurs via positive feedback under hormonal control
125
What does positive feedback involve?
Positive feedback involves a response that reinforces the change detected (it functions to amplify the change)
126
WHat does fetal growth cause? birth 1
In the case of childbirth, fetal growth eventually causes stretching of the uterine walls, which is detected by stretch receptors
127
What does the stretching of uterine walls trigger? birth 2
This triggers the release of hormones (oxytocin) that induce uterine muscles to contract, further reducing space in the womb
128
What does oxytocin trigger? birth 3
This causes more stretching and hence more contraction until the origin stimulus (the foetus) is removed (i.e. birth)
129
What 4 hormones regulate the birthing process?
The chemical regulators of the birthing process include oxytocin, oestrogen, progesterone and prostaglandin
130
1. what happens to trigger the birth process after 9 months?
After 9 months, the baby is fully grown and stretches the walls of the uterus – placing a strain on both mother and infant
131
2. what does this stress induce?
This stress induces the release of chemicals which trigger a rise in the levels of estrogen (estriol in particular)
132
3. What does estriol prepare?
Estriol prepares the smooth muscle of the uterus for hormonal stimulation by increasing its sensitivity to oxytocin
133
4. What does estriol inhibit?
Estriol also inhibits progesterone, which was preventing uterine contractions from occurring while the foetus developed
134
5. Once the uterus is prepared for childbirth, what is released?
Now that the uterus is primed for childbirth, the brain triggers the release of oxytocin from the posterior pituitary gland
135
6. What is the role of oxytocin? (+what does it inhibit)
Oxytocin stimulates the uterine muscles to contract, initiating the birthing process (it also inhibits progesterone secretion)
136
7. What does the foetus release in response to uterine contractions?
The foetus responds to this uterine contraction by releasing prostaglandins, which triggers further uterine contractions
137
8. What loop is created due to the cycle of contractions?
As the uterine contractions trigger the release of chemicals that cause further contractions, a positive feedback loop ensues
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9. When will contractions stop?
Contractions will stop when labour is complete and the baby is birthed (no more stretching of the uterine wall)
139
What is the gestation period (for mammals)?
For mammals, the gestation period is the time taken for a foetus to develop – beginning with fertilization and ending with birth
140
Will the duration of the gestation period differ between species?
YES
The duration of the gestation period will differ markedly between different species of animal
141
What are the two main factors that contribute to the length of the gestation period?
animal size/mass
level of development at birth
142
How does animal size/mass affect the length of the gestation period?
Animal size / mass – larger animals tend to have longer gestation periods (as they tend to produce larger offspring)
143
How does level of development at birth affect the length of the gestation period?
The level of development at birth – more developed infants will typically require a longer gestation period
144
How can the level of development at birth be described for mammalian infants?
The level of development at birth for mammalian infants can be described as either atricial or precocial
145
What does it mean if an infant is altricial?
Altricial mammals give birth to relatively helpless, undeveloped offspring that need extended rearing
146
What does it mean if an infant is precocial?
Precocial mammals give birth to more developed offspring that are mobile and independent and require minimal rearing
147
Do altricial or precocial mammals require shorter gestation periods?
Generally, altricial mammals (e.g. marsupials and rodents) require shorter gestation periods than precocial mammals (e.g. ungulates such as cows, pigs and rhinoceroses)
148
Are size/mass and level of development the only factors affecting the gestation period?
While the length of a gestation period does appear to positively correlate with size and development, other factors also exist
Some mammal species may have similar gestation periods despite having significantly different body masses
