Human Reproduction Flashcards
1
Q
What is the function of the testes?
A
A pair of organs that contain seminiferous tubules and epididymis, crucial for sperm production
2
Q
What is the function of the scrotum?
A
An external sac that protects the testes and maintains them at a temperature lower than the body’s core temperature
3
Q
What is the function of the penis?
A
Intromittent organ that is responsible for delivering sperm into the female reproductive system
4
Q
What is the function of the seminiferous tubules?
A
These structures within the testes are where spermatozoa are produced
5
Q
What is the function of the epididymis?
A
Where spermatozoa mature and are stored until ejaculation
6
Q
What is the function of the vas deferens?
A
Spermatozoa travel along this tube from the epididymis to the urethra during ejaculation
7
Q
What is the function of the seminal vesicle?
A
This gland produces a mucus secretion that enhances sperm motility
8
Q
What is the function of the prostate gland?
A
These glands produce an alkaline fluid that neutralises urine and supports sperm motility
9
Q
What is the function of the urethra?
A
Tube carries urine from the bladder to the outside of the body
10
Q
What is the function of the ureter?
A
Tubes connect the kidneys to the bladder
11
Q
What is spermatogenesis?
A
The formation of sperm in the testes
12
Q
What is oogenesis?
A
The formation of ova in the ovaries
13
Q
Why is it important that the gametes are haploid?
A
So that on fertilisation the diploid number is restored and the zygote has a full set of homologous chromosomes
14
Q
What leads to the genetic variation in the gametes?
A
Crossing over during prophase I
Independent assortment of homologous chromosomes during metaphase I and II
15
Q
Where are spermatozoa produced?
A
Within the seminiferous tubules of the testes
16
Q
Which hormones are required for the development of spermatozoa?
A
FSH and testosterone
17
Q
Describe spermatogenesis
A
- Diploid spermatogonia (2n) divide many times by mitosis to produce diploid primary spermatocytes
- Primary spermatocytes (2n) undergo meiosis I to form haploid secondary spermatocytes (n)
- Secondary spermatocytes (2n) undergo meiosis II to form spermatids (n)
- Spermatids mature and differentiate into spermatozoa (n)
18
Q
What is a Sertoli cell?
A
A type of somatic cell around which spermatids develop. Located in the seminiferous tubules.
19
Q
What is the role of the Sertoli cells?
A
- To secrete a fluid which nourishes the spermatids and protects them from the immune system of the male
- To provide oxygen and remove waste products
20
Q
What are interstitial cells?
A
A type of somatic cell that is stimulated by the hormone LH. Located outside the seminiferous tubules.
21
Q
What is the role of interstitial cells?
A
Secrete testosterone
Testosterone stimulates spermatogenesis and causes male secondary sex characteristics to develop
22
Q
What are the contents and function of the head of a spermatozoon?
A
Contains a haploid nucleus and is covered at the end by a structure called the acrosome, a large lysosome which contains enzymes used in fertilisation
23
Q
What are the contents and function of the mid piece of a spermatozoon?
A
Packed with mitochondria which provide ATP for movement
24
Q
What is the function of the tail of a spermatozoon?
A
Makes lashing movements that propel the sperm, enabling its motility
25
What is the importance of mitosis in spermatozoon production?
Mitosis produces large numbers of primary spermatocytes. This leads to large numbers of spermatocytes, which increases the chances of fertilisation.
26
What is the importance of meiosis in spermatozoon production?
Meiosis produces haploid spermatozoa and leads to genetic variation
27
Describe oogenesis
- Cells of the germinal epithelium divide by mitosis to make diploid oogonia
- The oogonia undergo mitosis many times and enlarge to form diploid primary oocytes
- The primary oocytes begin meiosis I but stop during prophase I
- Before each ovulation, a primary oocyte matures, completing the first meiotic division to form a haploid secondary oocyte and a polar body
- The secondary oocyte is released from the ovary during ovulation and begins meiosis II. It pauses at metaphase II until fertilisation takes place
- On fertilisation, meiosis II completes, resulting in the formation of a large ovum and a second polar body
28
The polar bodies contain much less cytoplasm than the oocyte. What is the benefit of this?
At fertilisation the resulting zygote will have sufficient cytoplasm to provide nutrients for rapid cell division
29
Describe the ovarian cycle
During oogenesis, the germinal epithelial cells divide to form follicle cells, which surround the primary oocytes to form primary follicles
Hormones stimulate these follicles to develop further. Each month one or more follicles will mature into a Graafian follicle containing the secondary ooctye
The mature Graafian follicle migrates to to the surface of the ovary where it bursts to release the secondary oocyte (ovulation)
After ovulation, the Graafian follicle becomes the corpus luteum which (if fertilisation occurs) secretes hormones for pregnancy
If fertilisation does not occur, the corpus luteum degenerates into the corpus albicans
30
A clear glycoprotein layer called the _____ _________ surrounds the cell membrane of the secondary oocyte. The chromosomes of the secondary oocyte are in ____________ __
Zona pellucida, metaphase II
31
____________ ______________ cells surround the secondary oocyte and provide nutrients
Corona radiata
32
What is secreted and from where at the the start of the menstrual cycle?
FSH is secreted by the anterior pituitary gland
33
What does FSH trigger at the start of the menstrual cycle?
The development of a follicle in the ovary (will mature into a Graafian follicle). FSH stimulates the production of oestrogen
34
Following menstruation, the levels of _____________ (secreted by the _____________ ____________) increases in the blood. What does this result in?
Oestrogen, developing follicle
- Inhibition of further production of FSH by negative feedback so no new follicles develop
- Stimulation of the anterior pituitary gland to secrete luteinising hormone (LH) by positive feedback
- Growth and repair of the endometrium
35
What happens at high levels of luteinising hormone (LH)?
A high level of LH, secreted by the anterior pituitary gland, initiates ovulation. This also causes the Graafian follicle to develop into a corpus luteum.
36
What does the corpus luteum secrete and what does this lead to?
Progesterone which causes further development of the endometrium. Progesterone also inhibits further production and release of LH and increases the level of mucus in the cervix to block the entry of sperm
37
What happens if implantation does not occur?
- Falling FSH and LH levels cause the corpus luteum to degenerate
- Progesterone levels fall
- The endometrium breaks down and is lost during menstruation
- FSH is no longer inhibited, and another menstrual cycle in initiated
38
Summarise the menstrual cycle
- FSH secreted by the anterior pituitary gland stimulates the maturation of a follicle, stimulating the production of oestrogen
- As a result, oestrogen increases in the blood which triggers the repair of the endometrium, inhibits FSH production and stimulates LH production
- A high level of LH initiates ovulation and causes the Graafian follicle to develop into a corpus luteum
- Progesterone secreted by the corpus luteum causes further development of the endometrium prior to menstruation
- If implantation does not occur, falling FSH and LH levels cause the corpus luteum to degenerate, progesterone levels fall, the endometrium breaks down and is lost during menstruation
39
Explain how oestrogen can be used as a contraceptive pill (3)
- Oestrogen inhibits production of FSH
- Without FSH, follicles won't develop
- Without a Graafian follicle, ovulation and subsequent fertilisation cannot occur
40
Explain how progesterone can be used as a contraceptive pill (3)
- Progesterone inhibits LH secretion so no ovulation
- Progesterone increases the level of mucus in the cervix so blocks entry of sperm
- No ovulation or no sperm means no fertilisation can take place
41
IVF involves the maturation of a large number of follicles which can then be retrieved from the ovary. Suggest the hormone that would be provided to patients and explain why
FSH
Responsible for primary follicles developing into Graafian follicles
42
Describe sexual intercourse (copulation)
- Arterioles entering the penis dilate while the venules leaving the penis constrict
- This leads to a build up of blood in spaces in the penis, causing it to become erect
- The penis is then inserted into the vagina, and movement result in the ejaculation of semen
- The force of ejaculation is sufficient to propel some sperm through the cervix into the uterus, with the remainder being deposited at the top of the vagina
- The sperm respond to chemoattractants released by the secondary oocyte and swim to the oviduct
43
How long will sperm remain viable for after ejaculation?
2-5 days but are most fertile 12-24 hours after ejaculation
44
How long will a secondary oocyte remain viable in the oviduct?
24 hours unless fertilised
45
What are the 3 reactions that occur in fertilisation?
1. Capacitation
2. Acrosome reaction
3. Cortical reaction
46
Describe capacitation
Capacitation involves changes to the cell membrane covering the acrosome, removing cholesterol and glycoproteins
This increases the permeability of the acrosome membrane to calcium ions and enhances the spermatozoon's motility
47
Describe the acrosome reaction
- The spermatozoa push their way through the cells of the corona radiata
- On contact with the zona pellucida, the acrosome membrane ruptures, releasing hydrolase enzymes which digest a path through the zona pellucida
- The membranes of the spermatozoon and secondary oocyte then fuse, allowing the genetic material of the spermatozoon to enter the secondary oocyte
48
Describe the cortical reaction
Once a spermatozoon has successfully penetrated the secondary oocyte, the oocytes smooth endoplasmic reticulum releases calcium ions into the cytoplasm
These calcium ions cause cortical granules to fuse with the cell membrane and release their contents, modifying the zona pellucida
The zona pellucida hardens to form the fertilisation membrane, which prevents other sperm from penetrating the egg (polyspermy)
49
Why is preventing polyspermy important?
To prevent the oocyte receiving too many chromosomes, resulting in an unviable zygote
50
What triggers the continuation of meiosis II, forming an ovum and a polar body?
Entry of the spermatozoon’s genetic material
51
The nuclei and the ovum fuse to form a _________ ___________. The fertilised ovum, now called a _________ is diploid (2n)
Zygotic nucleus, zygote
52
Describe implantation
- The zygote undergoes repeated mitotic divisions, forming a ball of cells. This process is known as **cleavage**
- By day 7, cleavage has resulted in the production of a hollow ball of cells called a **blastocyst**
- The blastocyst moves into the uterus where it attaches and embeds into the endometrium, **(implantation)**
53
What is the role of the amniotic fluid?
- Maintains the foetal temperature
- Acts as a shock absorber, protecting the foetus from injury outside the uterus
54
Prenatal diagnosis can take place to identify any chromosomal abnormalities. Suggest 4 concerns that some people may have about the ethics of prenatal diagnosis
- Selective abortion may become more common
- Foetus has right to live
- May cause harm to foetus
- Could result in a false positive/negative result
55
The _________ forms between the maternal and foetal tissues and is connected to the foetus by the __________ ______
Placenta, umbilical cord
56
What is the role of the unbilical vein?
Carries oxygenated blood and nutrients such as glucose to the foetus
57
What is the role of the umbilical artery?
Carries deoxygenated blood and waste products such as carbon dioxide away from the foetus
58
Where are foetal capillaries located?
Within chorionic villi, which will form the boundary between maternal and foetal blood
59
Describe exchange of materials between the mother and the foetus
Blood from maternal arterioles empties into an intervillous space. The absence of maternal capillaries between the maternal arteriole and maternal venuole reduces the number of cell laters to be crossed, providing a shorter diffusion pathway for materials.
Foetal capillaries are immersed in this intervillous space, allowing the exchange of materials to occur. Blood containing waste materials then returns to maternal venues from the intervillous space.
Maternal and foetal blood flow in opposite directions to maintain a concentration gradient.
60
What are the 4 roles of the placenta?
1. Facilitates the exchange of materials across a thin barrier which separates maternal and foetal blood (into foetal blood: glucose, oxygen, amino acids salts. Out of foetal blood: carbon dioxide, nitrogenous waste)
2. Provides protection from the immune system of the mother
3. Protects the foetus from differences in maternal and foetal blood pressures (mothers is much higher and could cause damage to foetus)
4. Allows the passage of maternal antibodies into the foetus to provide short term immunity (passive)
61
What does the developing embryo secrete just before and following implantation and what does it do?
**hCG** which maintains the corpus luteum for the first 16 weeks of pregnancy
62
Which hormones are secreted by the placenta during pregnancy?
Progesterone and oestrogen which rise to high levels in the blood plasma. These hormones suppress the secretion of FSH and LH
63
Why are LH, FSH and oxytocin suppressed during pregnancy?
LH: so ovulation isn’t possible
FSH: so no more follicles mature
Oxytocin: so no uterine contractions
64
What does progesterone do during pregnancy?
Suppresses the uterine wall’s ability to contract and maintains the endometrium
65
What does oestrogen do during pregnancy?
Stimulates the growth of the uterus to accommodate the growing foetus and stimulates the growth and development of the mammary glands
66
Which hormones increase and decrease just before birth?
Oestrogen levels increase, progesterone levels decrease
67
What 2 hormones are secretes just before birth?
Oxytocin and prolactin
68
What does oxytocin do during birth and where is it secreted from?
Secreted by the posterior pituitary gland. Stimulates the contraction of the myometrium. This contractions stimulate the release of more oxytocin (positive feedback). As oxytocin levels increase, contractions become stronger and more frequent.
69
What is the role of prolactin and where is it released?
Released from the anterior lobe of the pituitary gland during and after birth to stimulate the production of milk by the mammary glands
70
What releases milk for the current feed and helps the baby to get the milk easily?
Oxytocin
