Male and Female Reproductive Physiology: Control of Testicular and Ovarian Function Flashcards
What cells are contained in the seminiferous tubules?
Germ cells
Sertoli cells
What cells are contained in the interstitial space?
Leydig cells - secrete testosterone
Do sertoli cells regenerate?
No, they have a constant number throughout adult life.
What do sertoli cells do?
They regulate and support function of germ cells
What regulates sertoli cell function?
Function dependent on Follicle Stimulating Hormone (FSH) and Testosterone.
How are sertoli cells joined to each other?
Via tight junctions, this creates what is known as a blood testes barrier.
What is the function of sertoli cells?
Protect spermatocyte/spermatids from autoimmune response; prevents toxins from entering tubules (blood-testes barrier and tight junctions between sertoli cells)
Support and nourish developing germ cells
Phagocytosis of residual cytoplasm during spermiogenesis
Release of spermatids into lumen of tubule (spermiation)
Secretory - >100 proteins including androgen binding protein (ABP), antimullerian hormone (AMH), and inhibin
What is AMH important for?
Sexual differentiation
What is ABP important for?
Transport and storage of androgens.
How does spermatogenesis take place?
Rounds of mitosis form multiple stem cells from which to start producing sperm. (spermatogonium)
Rounds of meiosis to reduce chromosome number.
Cytoplasmic remodelling.
What are the products of the mitotic phase of spermatogenesis?
Spermatogonium produce type A and type B spermatogonia. Type A stay as stem cells and keep forming more spermatogonia.
Type B spermatogonia become primary spermatocytes and undergo 1st meiotic division to form secondary spermatocytes then a 2nd.meiotic division to form spermatids
Are primary spermatocytes diploid or haploid?
Diploid
Are secondary spermatocytes diploid or haploid?
Haploid with homologous chromosomes next to each other.
Are spermatids diploid or haploid?
Haploid with the chromosome number half of the secondary spermatocytes
What does spermiogenesis produce?
It converts spermatids into spermatozoa
How often is spermatogenesis undergone?
Stem cells enter into spermatogenesis approximately every 16 days and spermatogenesis takes approximately 64 days to complete..
Why is it that males are often fertile all the time?
Because of the spermatogenic wave: Adjacent tubules are at different stages of the seminiferous cycle
How is spermatogenesis controlled?
Via the hypothalamus - pituitary - gonadal axis.
GnRH -> FSH +LH:
FSH acts on sertoli cells to produce androgen receptors
LH acts on Leydig cells which produce androgens which act on sertoli cells by binding to androgen receptors.
Both of these together regulate spermatogenesis.
What are the actions of testosterone?
Acts on sertoli cells to make sperm
Produces 5alphaDHT which is more potent than testosterone
Acts on pituitary and hypothalamus as negative feedback for LH secretion (reducing LH production)
Forms oestradiol which also acts as negative feedback
What does inhibin B do?
It is produced by sertoli cells as negative feedback on the anterior pituitary which reduces FSH secretion.
What are the stages of oogenesis?
Oogonium undergoes mitosis to produce more oogonia.
primary oocytes are produced during prophase of the first meiotic division but it stops there until just prior to ovulation.
Meiosis reduces number of chromosomes to form secondary oocyte. Meiosis forms 1 polar body and 1 viable secondary oocyte. Secondary oocyte is also arrested. This time at metaphase 2.
Second meiotic division results in ovum and 2 more polar bodies.
Ovum finishes meiosis after fertilization.
When do oogonia normally first form?
Early in foetal life (first 20 weeks)
When do follicles first develop?
Follicles and oocytes develop during embryonic life.
When do oogonia undergo mitosis?
Maximum numbers at approximately 20 weeks of gestation.
When does follicular atresia occur?
At any stage of follicular development.
What is follicular atresia?
Hormonally controlled apoptosis.
Why do follicles undergo apoptosis?
Due to absence of essential trophic factors during formation or maturation.
Which stage of follicular growth and maturation is gonadotropin-independent?
The preantral stage. (first 270 days)
What stage of follicle formation requires gonadotropins?
Conversion of a pre-antral follicle to an antral follicle.
What are the stages of follicle maturation?
Primordial follicles are the first to develop during gestation.
Pre-antral follicles form when oocyte starts growing and this occurs over 270 days.
In response to gonadotropins antral follicles are formed
More oestrogen stimulates antral expansion of one of the follicles and this is the dominant follicle. (dominant follicle increases in size from 7 - 25mm)
Which cells produce androgens in follicles?
Granulosa cells cooperate with thecal cells to produce androgens.
What surrounds a primordial follicle?
Single layer of squamous-like granulosa cells
What surrounds pre-antral follicle.
It is also known as multi-laminar follicle due to presence of several layers of granulosa and thecal cells around the follicle.
What forms the corpus luteum?
Formed from ruptured follicle - granulosa and thecal cells (after ovulation)
Granulosa lutein and theca lutein cells.
What happens when the corpus luteum is formed?
LH and angiogenic factors stimulate a rich vascular network that surrounds it.
Cholesterol is sequestered within these cells to create progesterone.
What does the corpus luteum secrete?
Progesterone
Oestradiol
Inhibin A
What happens to corpus luteum in the absence of pregnancy?
It regresses after 12 - 14 days and forms scar tissue (Corpus albicans)
What causes luteolysis?
Human Chorionic Gonadotropin stimulation.
In primates it is not caused by decrease in LH or LH receptors
What triggers endometrium buildup?
Oestrogen increase after ovulation.
This is then maintained by progesterone which is produced from the corpus luteum
How is the ovarian cycle controlled?
Via the hypothalamus - pituitary - gonadal axis.
GnRH is produced -> FSH + LH produced
FSH acts on granulosa cells to stimulate growth of the follicle.
LH acts on thecal cells to produce androstenedione which go to granulosa cells to be converted to oestradiol which is then converted into oestrogen.
Oestrogen acts autocrinally resulting in lots of oestrogen production which exerts a positive feedback loop of LH production increase
What does oestradiol do?
It acts as negative feedback for the hypothalamus and the anterior pituitary gland.
Decreases FSH and LH levels.
Acts on granulosa cells to further stimulate growth of follicles. This results in an oestrogen surge.
How do the thecal and granulosa cells produce oestradiol?
Thecal cell:
LH stimulates cAMP
cAMP increases cholesterol
Cholesterol forms androstenedione
Androstenedione goes to granulosa cell
Granulosa cell:
FSH activates cAMP which upregulates aromatase
Androstenedione is converted by aromatase into 17beta oestradiol
17beta oestradiol is released into blood
What 2 hormones stimulate granulosa cell proliferation?
Androgen + FSH
What causes the oestradiol surge?
Aromatase activity increases E2 synthesis which results in granulosa cell proliferation which results in more E2 synthesis.
