Lecture 57: Male Reproductive Physiology Flashcards
1
Q
what is the function of the testes
A
production of male gametes (spermatozoa) and the male sex hormone testosterone
2
Q
where do spermatogenesis and spermiogenesis take place
A
in convoluted seminiferous tubules of testes
3
Q
where does testosterone production take place
A
interstitial cells of Leydig in between seminiferous tubule coils
4
Q
what glands secrete fluid medium for spermatozoa transportation
A
accessory glands:
- seminal vesicle
- prostate gland
- cowpers (bulbourethral gland)
5
Q
describe testicular descent before birth
A
- testes develop in abdomen of fetus
- descend down inguinal canal
- at birth lie within scrotum
6
Q
what is cryptorchidism and why is it a problem
A
undescended testes (occurs in 3% full term and 30% premature babies)
- can lead to infertility
- ^ risk of cancer
7
Q
outline the temp regulation of testes
A
- spermatic arteries and paminiform plexus of spermatic veins (running parallel but in opposite directions) helps remove heat from testes in counter current exchange mechanism
- cremaster muscle acts to alter distance that scrotum hangs from abdomen conserving heat in cold conditions and allowing ventilation and cooling in warm conditions
8
Q
what are the 4 stages of sperm formation
A
- spermatogenesis (prod of haploid gametes from diploid precursors)
- spermiogenesis (spermatids change to become motile)
- spermiation (release of spermatocytes into the lumen of seminiferous tubules where they swim in seminiferous fluid)
- capacitation ( in epididymis and female genital tract; final step rendering spermatocytes capable of fertilising ovum)
9
Q
outline spermatogenesis
A
- sperm production begins at puberty and continues throughout rest of life
- spermatozoa develop from progenitor cells called spermatogonia next to BM
- these divide by mitosis w/ one of the resulting cells maturing to become spermatozoa (other left behind to form permanent reserve)
- after initial differentiation, daughter cell undergoes meiosis
- involves 2 divisions
- initially genetic material in cell duplicates giving primary spermatocyte w/ 2 copies of each 23 chromosome pairs (2n+2n)
- gene pairs (homologous chromosomes) line up and undergo genetic recombination
- these then split and cell division occurs (meiosis I) to form 2nd spermatocytes –> haploid cells, each chromosome now unpaired (n+n in each cell)
- meiosis II occurs, final division w/ each cell (spermatid) containing unduplicated haploid number of chromosomes (n)
- spermatids must undergo further maturation to become fully motile spermatozoa
10
Q
outline spermiogenesis and describe role of Sertoli cell
A
- cells resulting from spermatogenesis have correct genetic material but need to differentiate into motile gametes
- happens within folds of Sertoli cell
- Sertoli cell nourishes developing sperm cells, phagocytoses old or defunct cells, protects sperm from blood borne toxins
- b/c of tight junctions between Sertoli cell and BM, any substance has to pass through it to get sperm, forming a —— barrier
- final function of Sertoli cell is to secrete sperm into lumen (spermiation) along w/ seminiferous tubule fluid
11
Q
what is present in seminiferous tubule fluid
A
high in:
- K+
- androgens
- oestrogens
- inositol
- glutamic acids
12
Q
describe the structure of sperm
A
- mature spermatozoon is highly differentiated cell
- head contains genetic material and enzymatic cap (acrosome)
- mid section contains centrioles (progenitors of all centrioles in fetal cells), and many mitochondria (provide energy for tail ‘flagellum’)
- tail makes sperm motile by rotating in corkscrew motion
- micro tubular core of spermatozoon formed from centrioles
- spermatozoon not considered fully mature until exposed to female environment
13
Q
outline the hormonal control of male reproduction
A
- concerned w/ maintaining turnover of spermatozoon production and ensuring appropriate level of testosterone to maintain spermatogenesis and secondary sexual characteristics of male
- GnRH released from hypothalamus daily, keeping processes of gametogenesis and testosterone formation ongoing
- carried in hypophyseal circulation to ant. pit.
- stimulates release of FSH and LH which are carried to target cells in testes
- LH exerts effects on interstitial cells of leydig causing them to release testosterone
- FSH promotes spermatogenesis by acting (along w/ locally prod testosterone) on sertoli cells
- feedback control exerted by testosterone directly on LH prod in ant. pit. and GnRH prod in hypothalamus, and by hormone inhibin on FSH prod in ant. pit.
14
Q
outline the function of testosterone
A
- dominant male sex steroid
- local source of testosterone necessary for spermatogenesis to proceed
- gives male phenotype in utero
- causes pre natal structural changes resulting in male external genitalia
- develops and maintains male reproductive system in young and mature male adult, responsible for changes in 2ndary sexual characteristics at puberty
- promotes adolescent growth spurt and subsequent fusion of epiphyses
- anabolic hormone promoting muscle deposition and ^ metabolic rate
- behavioural effects w/ characteristic effects on male libido and aggression
15
Q
describe the process of erection
A
- dilation of penile arterioles fills erectile tissue of penis (paired corpus cavernosa and corpus spongiosum) w/ blood
- gives efficient turgidity for penetration of female
- may be initiated by erotic cognitive stimuli and is strongly reinforced by stimulation of sensory receptors on glans and anterior penis
- further reinforced when veins draining penis are compressed
- erection reflex involves activation of parasympathetic dilator nerves and inactivation of sympathetic constrictor nerves
