Flashcards in Reproductive Physiology Deck (27)
What are the 2 main functions of the male reproductive system?
1. The provision of androgens (primarily testosterone) to initiate and sustain the necessary male phenotype
2. The production of mature sperm.
Where is testosterone produced?
Leydig (interstitial) cells, which are stimulated by LH to produced androgens.
Where are sperm produced?
Describe the path of the sperm during ejaculation.
Before ejaculation, sperm are stored in the epididymis. They pass through the vas deferens and mix with fluid from the seminal vesicles. This fluid leaves the ejaculatory duct and mixes with secretions from the prostate gland in the urethra.
Where is GnRH produced and what does it give rise to in males?
Produced in the hypothalamus and gives rise to LH and FSH. Testosterone (acts on anterior pituitary and hypothalamus) and inhibin have a negative feedback effect on GnRH.
What is the function of Sertoli cells?
They support the process of spermatogenesis, which is stimulated by FSH and testosterone together.
They also produce inhibin, which acts to inhibit GnRH production (negative feedback).
Describe male reproductive function.
1. Begins at puberty
2. Functions continually
3. Continues throughout lifetime
4. Sperm quantity AND quality decrease with age
Outline the process of spermatogenesis.
Begin with primordial germ cells, which convert to spermatogonia in the seminiferous tubules. These then differentiate further to produce sperm in a complex process.
Up to how many sperm may be produced in a day?
Describe female reproductive function.
1. Begins at puberty
2. Functions cyclically (menstruation)
3. Only operates until menopause (roughly 45 years old)
4. Egg quality decreases with age
Where do LH and FSH act in females?
- LH gives rise to progesterone (LH release is pulsatile)
- FSH stimulates development of ovarian follicles and 17-beta oestradiol synthesis
Which cells in the ovarian follicles produce oestrogens and progesterone?
Thecal cells produce oestrogens.
Granulosa-luteal cells produce oestrogens/progesterone during the luteal phase of the cycle.
Describe the feedback changes that occur during the menstrual cycle.
During the first half (follicular phase), oestradiol exerts a negative feedback effect on the hypothalamus and pituitary gland.
Mid-cycle, there is an oestrogen peak and it begins to exert a positive feedback effect, causing an LH surge (stimulating ovulation) and a small peak in FSH.
During the second half (luteal phase), LH and FSH levels fall. Oestrogen and progesterone begin to rise again and there is a negative feedback effect, but it involves progesterone as the main steroid.
What feedback changes occur during pregnancy?
Progesterone levels rise and continue to rise throughout the whole of pregnancy. The negative feedback from progesterone halts the menstrual cycle.
What is the normal range for the length of a menstrual cycle?
21-35 days, but up to 45 days in younger teens.
Describe the changes occurring in the endometrium during the first half of the menstrual cycle.
During the first half (proliferative phase), oestrogen produced by developing follicles causes the endometrium to thicken; this is the perfect environment for implantation.
Describe the process of oogenesis.
Begins with a primordial germ cell, which gives rise to an oogonium. By the point of birth, there are no germ cells left in the ovary (all cells are at least oogonia).
The oogonium produces a primary oocyte, which differentiates to produce a secondary oocyte and the first polar body. The secondary oocyte differentiates to produce an ovum and a second polar body.
Describe the process of folliculogenesis.
It begins with a primary oocyte living inside a primordial follicle. This follicle begins to grow independently of sex steroids. One follicle becomes dominant and grows more quickly; it enters the second stage of development and becomes the antral follicle (this gives rise to the release egg). Other follicles break down in the process of atresia.
Describe how the sperm's nucleus reaches the egg during fertilisation.
The sperm swims to the egg in the fallopian tube. Coronal cells of the follicle surround the egg. The sperm binds to the zona pellucida and produces digestive enzymes to digest its way through. The sperm releases its nucleus into the egg's cytoplasm.
Describe the production of 2n cells during fertilisation.
The sperm's nucleus expands rapidly in size and converts itself into a pro-nucleus (n). The egg completes meiosis and also converts into a pro-nucleus (n). The two pro-nuclei merge to form a group of 2n chromosomes. At this point, they both duplicate again and immediately after fertilisation, the chromosomes merge to form a single nucleus (4n). This then cleaves to form 2 identical 2n cells.
What is the evolutionary purpose of sexual intercourse?
The continuation of the human race through production of genetically different offspring. It also provides sexual pleasure and human bonding (activation of pleasure pathways in the brain encourage intercourse).
What are the two pathways for regulation of penile erection?
- the brain -> via the spinal cord and efferent nervous system
- the spinal cord -> via the afferent system (pudendal nerve)
How is erection initiated?
Erection is initiated by increased parasympathetic activity to smooth muscle of the pudendal artery.
This increases activity of nitric oxide synthase (NOS) and therefore NO.
NO -> increases cGMP -> dilation of arterial smooth muscle
How does the dilation of arterial smooth muscle cause erection?
Blood flow in the corpus cavernosum increases, compressing the dorsal vein and reducing outflow of blood. The urethra is protected by corpus spongiosum,
What is the mechanism of action of Viagra?
cGMP is deactivated by a phosphodiesterase enzyme. Viagra inhibits this enzyme, potentiating cGMP effects.
What is the mechanism of female erectile tissue?
Female erectile tissue -> clitoris
Same mechanism as male erectile tissue.