7. Coitus & fertilisation (lecture)

Question 1

what do spermatogonia (2n) mature to?

Answer 1

spermatozoa (sperm)

Question 2

how long does it take spermatogonia to mature to spermatozoa?

Answer 2

up to 74 days

50 days in testis, 12-24 days in epididymis

Question 3

where are spermatozoa produced?

Answer 3

in the seminiferous tubules of the testis

Question 4

when does sperm production begin?

Answer 4

puberty and continues until death

Question 5

how many sperm is produced per day?

Answer 5

200-300 million sperm

only 1/2 become viable sperm

Question 6

where is sperm produced?

Answer 6

in testis (Sertoli cells of seminiferous tubules)

Question 7

how does sperm production change with age?

Answer 7

slight decrease in quantity and quality with age

Question 8

describe the process of spermatogenesis: spermatogonium to spermatocyte (step 1)

Answer 8

spermatogonium (2n) –(mitosis)–> primary spermatocyte (2 x 2n)
1 stays in basal lamina and continue to divide (type A)
type B: pushed towards lumen (primary spermatocyte)

Question 9

describe the process of spermatogenesis: primary spermatocyte (step 2)

Answer 9

primary spermatocyte (2n) –(meiosis I)–> secondary spermatocyte (2 x 1n)

Question 10

describe the process of spermatogenesis: secondary spermatocyte (step 3)

Answer 10

2 x secondary spermatocyte (1n) –(meiosis II)–> 4 x 1n spermatid

Question 11

describe the process of spermatogenesis: spermatid (step 4)

Answer 11

4 x spermatid (1n) –(spermiogenesis)–> spermatozoa (4 sperm)

Question 12

what happens as sperm matures through the seminiferous tubules?

Answer 12

it migrates from the periphery of the seminiferous tubule in towards the centre (lumen)

Question 13

what are the hormones controlling spermatogenesis?

Answer 13

during puberty, hypothalamus triggered to release GnRH, stimulating anterior pituitary to release LH and FSH

Question 14

how does release of LH trigger spermatogenesis?

Answer 14

LH (anterior pituitary) –> Leydig cells (testis) –> testosterone (steroidogenesis) –> spermatogenesis
(testosterone diffuse into seminiferous tubules to bind to ABP)
Leydig cells produce testosterone (steroidogenesis)

Question 15

how does release of FSH trigger spermatogenesis?

Answer 15

FSH produced triggers Sertoli cells to release androgen binding protein (ABP) - which binds to testosterone (diffused in) and triggers sperm production (control gamete production)
(FSH maintains Sertoli cells sensitivity to testosterone via release of ABP, requires testosterone)

Question 16

aside from ABP, what else do Sertoli cells release?

Answer 16

inhibin: negative feedback on FSH (Sertoli cells)

Question 17

what effect does testosterone have on Sertoli cells?

Answer 17

positive feedback

Question 18

if pituitary gland is removed, how can spermatogenesis be initiated?

Answer 18

with FSH and testosterone alone

LH was only to produce testosterone from Leydig cells, to bind to ABP released by FSH

Question 19

what is the function of testosterone released from Leydig cells

Answer 19

increase sperm viability

Question 20

effect of testosterone on the feedback loop? (HPG axis)

Answer 20

negative feedback on hypothalamus release GnRH and there ant pit release LH/FSH

Question 21

structurally, what happens to the HEAD of the spermatid in order to mature to a spermatozoon (spermatozoa) in spermiogenesis?

Answer 21

nuclear condensation

Question 22

structurally, what happens to the ACROSOME of the spermatid in order to mature to a spermatozoon (spermatozoa) in spermiogenesis?

Answer 22

(acrosome: covering on tip of sperm - degraded by female secretions)
contains golgi apparatus
lysoosome-like (hydrolytic enzymes released to breakdown coroner radiata of oocyte)
enable sperm to penetrate ovum

Question 23

structurally, what happens to the BODY (midpiece) of the spermatid in order to mature to a spermatozoon (spermatozoa) in spermiogenesis?

Answer 23

mitochondria packed around contractile filaments

provide energy for the sperm to swim up the vaginal canal –> cervix –> uterus –> fallopian tube

Question 24

structurally, what happens to the TAIL of the spermatid in order to mature to a spermatozoon (spermatozoa) in spermiogenesis?

Answer 24

flagellum produced by microtubules growing from centriole to form axoneme (flagellum made up of many microtubules)
(centrioles –> microtubules –> flagellum –> axoneme)

Question 25

what happens to the spermatozoa under the influence of testosterone?

Answer 25

cytoplasm and organelles stripped

Question 26

what happens to spermatozoa?

Answer 26

they are now mature, but still lack motility (infertile)

Question 27

what is spermation?

Answer 27

spermatozoa released from Sertoli cells into lumen of seminiferous tubule

Question 28

after the spermatozoa released into the lumen of seminiferous tubule, what happens?

Answer 28

transported to epididymis in testicular fluid (produced by Sertoli cells) by peristaltic contractions

Question 29

what happens to the spermatozoa within the epididymis?

Answer 29

gain motility and become ‘fertile’ in epididymis

Question 30

how long can spermatozoa be stored within the epididymis?

Answer 30

stored for several months, no loss of fertility

Question 31

what does sexual arousal lead to?

Answer 31

contraction of epididymal wall muscle –> expels spermatozoa into ductus (vas) deferens

Question 32

what happens to the spermatozoa eventually if it is not expelled into the vas deferens?

Answer 32

eventually phagocytosed by epididymal epithelial cells