Male Reproduction Flashcards
1
Q
male reproduction responsibilities
A
- production, nourishment, storage of haploid gametes
- ejaculation of semen into the female reproductive tract
- generation of male sex hormones = androgens
2
Q
how do testes develop
A
- PGCs become incorporated in epithelial-like sex cords
- when SRY is produced by the primitive sex cords within the primitive gonad, the male reproductuve system is stimulated
- many components of the embryonic kidney that will degenerate become parts of reproductive system
3
Q
developmental sequence of the testes
A
- testicular components then become interconnected
- paramesonephric duct begins to degenerate under the direct influence of anti-mullerian hormone produced by cells that have formed in the developing testis
4
Q
development of seminiferous cords
A
- sex cords grow into seminiferous cords that are solid tubules containing germ cells
- In cross-section, these tubules contain a peripheral layer of 15-20 mesonephric-derived cells that will become Sertoli cells, they surround a central core of 4 spermatogonia
- mesenchymal cells, between the cords develop into leydig or interstitial cells
- connective tissue septa form to divid the testis into several lobules that will contain the cords (well developed in the testes of pigs, dogs and cats but less developed in ruminants in horses the septa contains smooth muscle cells)
5
Q
development of the sequence of testies
A
- mesonephric duct develops into epididymis and the ductus deferens
- in total, efferent ducts, epididymis and ductus deferens are part of excurrent extragonadal duct system that will carry sperm through to the urethra
- subsequently, at puberty the seminiferous cords become seminiferous tubules ( with a lumen) and there is continuity between rete testes and efferent ducts
6
Q
scrotom
A
- hold the testes
- so they can regulate temperature (normal temperature should be 2-4 C below the core body temperature)
7
Q
cryptorchidism
A
- undescended testes
- one(unilateral) or two(bilateral) failed to descend
- bilateral result in sterality
- testosterone still produced in both cases, but spermatogenesis does not occur. males still exhibit intact characteristics
- can remain in abdomen or inguinal canal itself
8
Q
where does spermatogenesis take place
A
- seminiferous tubules
9
Q
where is testosterone secreted
A
leydig cells
10
Q
testicular descent
A
- in most mammals, and in all domestic species, the testes descend into the scrotum
- this is a peculiar event in that it involves two largely different processes
- testies must move a great distance from retroperitoneal position in the body cavity to the scrotum
- requires rapid growth and then rapid regression of a ligamentous structure called gubernaculum
11
Q
effects of testosterone reproductive system before birth
A
- masculinizes the reproductive tract and external genitalia
- descent of testes into the scrotum
12
Q
effects of testosterone sex-specific tissues after birth
A
- growth and maturation of the reproductive system at puberty
- essential for spermatogenesis
- maintains the reproductive tract throughout adulthood
13
Q
effects of testosterone on other reproductive effects
A
- develops the sex drive (libido) at puberty
- controls gonadotropic hormone secretion
14
Q
effects of testosterone on secondary sex characteristics
A
- male pattern of hair, antler or feather growth
- deepening of the voice
- muscle growth and masculine body configuration
15
Q
the effects of testosterone on non-reproductive actions
A
- protein anabolic effect
- bone growth at puberty
- closes the epiphyseal plates
- aggressive behaviour
16
Q
puberty
A
- the achievement by the gonads of their complete hormonal and gametogenic capability for reproduction = results in GnRH secretion
- mechanisms regulating its timing are still being studied (can be gradual or rapid ) variety of morphological features can result
- involves activation of the hypothalamic pituitary gonadal (HPG)
- can also stimulate other organs such as adrenals
- adrenal androgen production assists in stimulating adolescent growth
17
Q
pubery pathway
A
- signals markedly increase GnRH secretion and frequency of the secretion from the hypothalamus
- stimulates increased pulses of gonadotropins in the pituitary ( LH and FSH)
- activates gonadal steroidogenesis and gametogenesis
18
Q
female puberty
A
- occurs before the development of physical maturity
- capable of reproducing, but number of offspring not maximal yet
19
Q
male puberty
A
- younger males entering puberty can show behavioural characteristics
- reduced sperm production capacity, reduced fertilization rates
- quality of ejaculate can be used as puberty index
- secretions from the HPG axis become consistent but with daily and even seasonal fluctuations
- GnRH pulsatile releases would precede the LH which would be before testosterone
- with distinct seasonal breeding, active spermatogenesis would be limited to a few months of the year or less
20
Q
spermatogenesis
A
- germ cells in various stages of sperm development
- Sertoli cells provide support for spermatogenesis
- spermatozoa are the mature male gametes
- basic pattern of this process is similar amongst all animals
- a layer of germ cells (spermagonia ) are on the periphery of each seminiferous tubule
- differentiation proceeds inwardly with most mature cells (sperm) in the lumen
- spermatogenesis duration can vary (bulls 64 days )
- large quantitys are produced (6x10^9 per days in bulls) ( 17x10^9 in boars)
- along the length of the tubules, stages present can vary
21
Q
spermazoa
A
mature male gametes
- head - nucleus capped with an acrosome for penetrating the ovum
- midpiece contains mitochondria
- tail motility
22
Q
spermatogenesis mitosis
A
- spermatogonia (germ cells with 2n chromosomes), divide, forming primary spermatocytes (2n)
- mitotic proliferation of spermatogonia happening near tubuke periphery gives a continual supply of new diploid germ cells
- after division, one daughter cell stays to maintain germ line
- second daughter cell divides to produce a possible total of 4 primary spermatocytes
23
Q
spermatogenesis meiosis I
A
the primary spermatocytes enter a resting state and duplicate their DNA content ( chromosomes appear double stranded)
- chromosomes pair up - homologous chromosomes
- each primary spermatocyte divides into two secondary spermatocytes
- each secondary spermatocyte is haploid (meiosis = reduction division)
24
Q
spermatogenesis meiosis II
A
- each seconday spermatocyte divides into two spermatids
- each spermatid still haploid ( doubled chromosome strands in each chromosome split maintaining haploid state)
- in total each primary spermatocyte has produced a total of 4 spermatids
25
Q
spermatogenesis packaging
A
- spermatids need to be reorganized into spermatozoa
- cytosol stripped down to bare minimum
- organelles removed
- add capabilirt to be potentially highly motile
- known as spermiogenesis
- following meiosis I division, developing sperm have remained connected by cytoplasmic bridges
- cytoplasm exchanged between cells
- criminal in mammals X vs Y carrying cells
26
Q
why are sertoli cells important
A
- sertoli cells create a ring around the entire inner area of the seminiferous tubule
- surround the developing sperm
- attach to one another with juntions (developing sperm will move from periphery to the lumen - junctions will open to allow passage)
- sertoli cells form a blood testes barrier
- blood cannot enter the seminiferous tubule
- sertoli cells can regulate what enters
- intratubular fluid very different than the blood ( key to sperm development)
27
Q
functions of sertoli cells
A
- nourish developing sperm = produce lactate for use by sperm as energy source
- phagoctose (eat) cytoplasm from spermatids during packing
- destroy defective germ cells throughout spermatogenesis - quality control
- secrete tubule fluid to flush sperm towards epididymis for storage
- produce androgen - binding protein (a testosterone collector so testosterone remains high to induce sperm production )
28
Q
feedback regulation of testicular function
A
- vertebrate testes are controlled by two gonadotrophic hormones secreted by anterior pituitary
- LH acts on leydig (interstitial) cells to regulate testosterone secretion
- FSH acts on sertoli cells to stimulate spermatogenesis
- secretion of both LH and FSH is stimulated by hypothalamic GnRH or inhibited by GNIH
29
Q
negative feedback of testicular function
A
- Testosterone inhibits LH secretion in a negative feedback manner ( decreasing GnRH secretion, reduces responsiveness of LH secretory cells to GnRH)
- inhibin, secreted by sertoli cells, acts on the ant pit to inhibit FSH secretion
- both testosterone and FSH are required for spermatogenesis ( testosterone induces mitosis and meiosis, FSH initiates spermatogenesis and spermatid remodelling)
- some testosterone is converted to estradiol by aromatase ( estradiol is responsible for sealing of epiphyseal plates in males and females)
30
Q
reproductive tract
A
- in sequence of sperm movement
- vasa efferentia, epididymis, ductus deferens, ejaculatory duct and urethra
31
Q
efferent ducts
A
- how sperm leaves the testes
32
Q
epididymous
A
- a long coiled tube
- sperm gain abilities to fertilize as well as move from this portion of the tract
- will absorb the vast majority of the seminiferous tubule fluid
- during breeding season will produce own fluid for sperm movement into ductus deferens
33
Q
ductus deferens
A
muscular tube that passes out of the scrotom and into pelvic cavity
- for sperm storage
- muscular contractions push sperm into the urethra
34
Q
ampulla
A
- of ductus deferens is an enlarged portion o this duct just before entrance to urethra
- meets up with seminal vesicle ducts to form ejaculatory duct that merges with urethra
35
Q
accessory sex glands
A
- secretions from the male accessory sex glands provide the bulk of seminal fluid
36
Q
seminal vesicles
A
supply fructose for ejaculated sperm
- secrete prostaglandins, which stimulate smooth muscles contractions in the male and female reproductive tracts
- secrete fibrinogen to help form clots (plugs) such as in rodents, boas and stallions
- secretions make up more than half semen volume
37
Q
prostate gland
A
- secretes an alkaline fluid that neutralizes the acidic vaginal secretions
- provides clotting enzymes to reduce semen loss during withdrawl of the penis
- releases prostate specific antigen which breaks down the seminal clot after entering female tract so sperm can move towards the oocyte
38
Q
bulbourethral glands
A
- provides lubrication by secreting a mucous like substance
- mucous neutralizes acidic pH of urethra
39
Q
anatomy of penis
A
root
- body or shaft ( erectile tissue consists of the three columns of spongy vascular spaces extending the length of the penis)
- glans - richly supplied with nerves
40
Q
sigmoid flexor
A
- boars bulls and rams
- penis extends during erection with little change in diamter
- controlled by retractor penis muscle
- contains a lof of connective tissue compared to erectile tissue = fibroelastic penis
41
Q
musculocavernous penis
A
- horse
- large cavernous spaces of erectile tissue surrounded by smooth muscle
- increase length by vascular engorgement
42
Q
osteomusculocavernous
A
- dog
