Reproductive system Flashcards
1
Q
What are the 3 main roles of the male reproductive system?
A
- sperm production
- hormone synthesis
- the sexual act
2
Q
What are the parts of the male anatomy?
A
- urethra (common passage for semen and urine)
- scrotum (temperature regulation)
- testis (es) (spermatogenesis + hormones - testosterone) - outside body for temp regulation
- epididymus (sperm storage - has head, body and tail which feeds into the vas deferens)
- seminal vesicles*
- prostate gland*
- bulbourethral glands*
- vas deferens (transports sperm)
- denotes accessory glands
3
Q
Describe the role of the accessory glands in the composition of the fluid ejaculated
A
- seminal vesicles, volume 60% (alkaline), composition = fructose, semenogelin, prostaglandins. For ATP (energy), coagulation (keep sperm together), smooth muscle contraction (along vas deferens)
- Prostate, volume 25% (acidic), composition = citric acid, prostate specific antigen (PSA). For ATP, and disrupt clot (allow sperm to become free on their own)
- Bulbourethral gland, volume 5% (alkaline), composition = mucus. For lubrication
4
Q
Describe the testis anatomy + cell types
A
- located inside the scrotum (external)
- conditions + temp (2 degrees C below normal body temp) v important (for propre cell division and maturation - spermatogenesis)
- testicular temp regulated through the contraction and relaxation of the cremaster muscles to elevate or lower the position of the testes
- epididymis comes into testis -> efferent ductules -> rete testis -> eventually to seminiferous tubule
- 2 main cell types: Sertoli cells (inside), and Leydig cells (outside) - both play a key role in spermatogenesis
- contain blood testes barrier (BTB) - barrier between genetic makeups - seperation between mitotic cells and meoitic cells (mitosis above, meiosis below) - unzips to let cells pass through
5
Q
Describe spermatogenesis
A
- mitosis gives rise to a pool of genetically identical germ cells called spermatogenia (diploid)
- spermatogenia remain close to basement membrane to maintain a population that the developping spermatocytes are recruited from to undergo meioisis
- mature sperm, known as spermatozoa, are located closest to the lumen, generated only after completing meiosis I and II (haploid) (secondary spermatocytes -> spermatids) - generate genetically distinct cells
- poses potential problem since the immune system is effective at destroying “foreign” or non-self cells, but the presence of tight junctions between sertoli dells forms the blood-testes barrier to maintain an immunologically privileged environment for these cells
- in any given section of the seminiferous tubule, spermatogenesis proceeds in a regular sequence (~1500/sec)
- needs testosterone and time to generate spermatazoa from spermatogenic stem cells ~ 30-40 days
- all starts in puberty and spermatogenesis requires temperatures < 37 degrees C
6
Q
What are the stages of spermatogenesis
A
- spermatogenia - undergo mitosis - produce primary spermatocytes
- primary spermatocytes - undergo meiosis I to generate secondary spermatocyte containing chromosomes with two unique chromatids
- secondary spermatocytes - complete meiosis II to give rise to spermatids containing single chromatid
- spermatids - differentiate through process called spermiogenesis to produce spermatozoa with tail and head structures
- spermatozoa - mature sperm which undergo further alterations to acquire motility and fertilization capacity
7
Q
Describe spermatozoa
A
- spermatids appear as rounded cells -> through spermiogenesis, the spermatozoa gain an acrosome, flagellum, undergo nuclear condensation and numerous mitochondria organize in the midpiece
- head contains genetic material - has an acrosome (membranous organelle) at its tip and contains a haploid set of chromosome in a compact inactive state
- acrosome contains digestive enzymes including hyaluronidase and acrosin which break down the outer membrane of the ovum called the zona pellucida during fertilization
- mid-piece contains mitochondria and a single centriole, a tail or flagella
- spermiation, shedding residual cytoplasm and then release into the lumen - mature spermatozoa are released from the Sertoli cell into the tubule lumen and travel to the epididymus
- head and tail develop polarity
8
Q
Describe the regulation of spermatogenesis - steroidogenesis
A
- steroidogenesis provides hormonal control (production of testosterone, etc, from cholesterol)
- Leydig cells play important role through hormone synthesis
- spermatogonia are present at birth but the process of spermatogenesis is initiated at puberty when sufficient levels of testosterone begin to be synthesized
- testosterone is a steroid hormone derived from cholesterol - testosterone one of the most abundant androgens here
- first step of steroidogenesis = conversion of cholesterol to pregnenolone (by action of StAR - transport protein - and cytochrome P450scc - cleavage - rate limiting if not present, etc)
- after pregnenolone is produced in mitochondrial, transported to the endoplasmic reticulum
- precursor to testosterone is androstenedione - converted to testosterone via the action of 17-B-hydroxy-steroid dehydrogenase (rate limiting step)
- testosterone can be converted to DHT (Dihydro-testosterone) by the action of 5a-reductase - DHT is more potent form
- testosterone can also be converted to estradiol via aromatase
9
Q
Describe the gonadotropin regulation for steroidogenesis
A
- FSH and LH are released (in pulsatile fashion - pulse generator) in response to gonadotropin releasing hormone (GnRH) from the hypothalamus, and regulation of these hormones occur through negative feedback - testosterone acts back on anterior pituitary and hypothalamus
- LH and FSH both have alpha and beta subunits - beta more important for both
10
Q
Describe the pulse mechanism of LH + FSH regulation?
A
- pulsatile regulation
- the pulse generator of GnRH has different speeds
- fast pulses = higher levels of output of LH, less FSH
- slow pulses = more FSH, less LH
11
Q
Describe the action of LH and FSH
A
- Leydig cells produce testosterone in response to luteinizing hormone (LH) released from anterior pituitary gland
- LH binds to receptor on Leydig cell and leads to GPCR activation to increases steroidogenesis (cholesterol - testosterone)
- testosterone has 2 fates -> can go into circulation or -> can diffuse across membrane and move into the Sertoli cell
- follicle-stimulating hormone (FSH) also released from anterior pituitary, acts mostly on Sertoli cells
- will activate GPCR, which increases ABP levels (androgen binding protein), and androgen receptor levels
- ABP binds testosterone to hold onto it
- need to maintain high levels of testosterone in Sertoli cells (for spermatogenesis) and ABP is one of the ways to maintain this
- AR increase will also lead to increased transcription, more genes for fluid production, etc
12
Q
What is another method of negative feedback?
A
- inhibin (peptide hormone) produced by the Sertoli cells inhibits FSH synthesis
13
Q
Describe puberty and the hormonal changes in boys
A
- testosterone levels have a large wave in younger fetus, then goes low
- another large wave at a couple of months
- then low until testosterone levels increase lots at puberty (switched on by pulse generator)
- growth action increases lots with testosterone
14
Q
Describe the systemic effects of testosterone
A
- in utero + development
- larynx development (thickening of vocal cords)
- required for muscle and bone growth (growth plate closure generally requires estrogen)
- more red blood cells - helps to produce
15
Q
What are the sites of specific testosterone or DHT action?
A
- Testosterone:
- in-utero: embryonic development
- post-pubertal secretory activity
- pubertal growth of larynx and bone
- anabolic effects on muscle
- stimulation of spermatogenesis and libido - DHT
- in-utero: embryonic development (prostate) and descent of the testes
- phallic growth
- development of pubic hair and underarm hair
- activity of sebaceous glands
