87. Male genitals, hormone regulation in the male reproductive system, spermatogenesis

Question 1

Reproductive activity of male animals can be characterized with ;

Answer 1

continuity.

The testis produces sperm cells with a nearly regular speed throughout adult (fertile) life, and the transmission of them to the female sexual ducts is possible at any time.
• Male animals are able to produce virtually unlimited number of offspring. This is utilized by modern animal husbandry by using previously collected and stored semen, which was taken from male animals in the most advantageous time and circumstances.

Question 2

Internal male genitals

Answer 2

 The two testes sit in the scrotum. They are oval- shaped and it is here that the sperm and male sex hormones are produced. They are very sensitive to touch and pressure.
 The epididymes are the two coiled tubes attached to the testes. This is where the sperm matures and is stored until released during ejaculation.
 The deferent ducts are the paired tubes that carry the mature sperm from the epididymes to the urethra.

Question 3

Sertoli cells

Answer 3

FSH stimulates their activity
Major function:
• Spermiocytogenesis
• Spermio(morpho)genesis
Hormones and other factors • Estrogen
• Inhibin
• Dihydrotestosterone (DHT)
• Androgen Binding Protein (ABP) • Müllerian Inhibitory Factor (MIF)

Question 4

Leydig cells

Answer 4

LH stimulates their activity Major function:

• Testosterone production

Question 5

The external genitals

Answer 5

consist of the penis surrounded by the prepuce, with glands in the wall of it in certain species (horse, goat), also muscles for protrusion, erection and ejaculation.

Question 6

Male genitals

Answer 6

The male genitals are present in the body at birth, but they are not sexually active until adolescence. The genitals are mature when the testes produce functional sperm. Every day a man makes between 50 and 500 million sperm.
 Puberty is the time when males start to produce sperm, and females start to release eggs. Usually puberty occurs a few years earlier in females than males (in human).
 Menopause (in human) is the time when females stop releasing eggs. This usually occurs between 45 to 55
years of age in human. However, males produce sperm all their lives after puberty.

Question 7

Spermatogenesis

Answer 7

-Spermatogenesis can only be completed when both FSH and testosterone can reach the layer of germ cells.
• Testosterone is produced in the interstitial cells of Leydig and controlled by LH.
• Most steps of spermatogenesis, especially the part of meiotic division, require a continuous supply with androgens.
• Sertoli cells have a role in this process: they intake androgens with their high affinity androgen-receptors and they pass them directly to the germinal epithelium and germ cells. This direct mechanism makes possible for the testosterone concentration in the testis to be many times higher than that in the peripheral blood.

Question 8

Spermatogenesis

Answer 8

1. Spermiocytogenesis
2. Mitosis
    Type A spermatogonium  Type B spermatogonium
3. Meiosis
    Spermatocytes
4. Spermiomorphogenesis
    Spermatides
    Sperms (spermatozoa)

Question 9

Phases of Spermiomorphogenesis

Answer 9

Spermatids → Spermatozoa • Golgi phase
• Cap phase
• Acrosome phase
• Maturational phase
Release of spermatozoa Final maturation

Question 10

Golgi phase:

Answer 10

development of the acrosomal granule from the
Golgi complex forming the acrosomal vesicle at the anterior of the cell, the centrioles move to the opposit of flagella. Here is the formation of axoneme, which is the central portion of sperm tail (flagellum).

Question 11

Cap phase:

Answer 11

development of acrosomal cap over nucleus and
condensation of chromatin, development of
flagellum from axonemal complex
• acrosome contains hydrolases (proteases,
hyaluronidase, neuramidase, acid phosphatase)
important in penetration of the oocyte membrane
during fertilization

Question 12

Acrosome phase:

Answer 12

spermatid re-orients so that tail (flagellum)
projects into the lumen of the tubule and the acrosome towards the base of the epithelium, further condensation of chromatin, flattening and elongating of nucleus at the anterior of the cell, movement of cytoplasm to the posterior of cell, further development of flagellum, linkage of flagellum to nucleus via the connecting piece developed from a centriole

Question 13

Maturational phase:

Answer 13

residual body of cytoplasm shed (cell linkages
lost) and the cells released by Sertoli cells into
lumen of tubule (Willi are free but cannot move
himself yet)

Question 14

Released spermatid

Answer 14

move with fluid via peristaltic action of myoid cells transporting it to the straight tubule- straight tubule lined solely with Sertoli cells

Question 15

Final maturation

Answer 15

(gain motility in flagellum) occurs downstream in the epididymis (stimulated by steroids + phosphoglycerin) They also gain here a lecithin cover (electric charge, ensuring organized movement of spermatozoa).

Question 16

Hormonal regulation

Answer 16

Basic role of the male reproductive
system
• spermatogenesis,
• storage of spermatozoa
• transport of them into the genital tracts of females.
 Androgens
• Most important male hormones (synthesized in the
testes)
• The secretion of androgens are under the control of
hypothalamo-pituitary control: GnRH, LH, FSH
Neural control:
• related to copulation: the formation of reflexes
resulting in erection and ejaculation.

Question 17

Hormones

Answer 17

 GnRH
Hypophyseal hormones • FSH
• LH (ICSH)
Peripheral hormones • Testosterone
• Other androgens • Inhibin
 Pheromonok

Question 18

Testosterone in the tubules

Answer 18

ABP binding
• Higher-than- blood-level testosterone cc.
In Sertoli cells • Converting to
DHT
(highly potent androgen)

Question 19

Paracrine effects

Answer 19

 Testosterone:
• Stimulates ABP production in the tubules
 (The ABP binds the Testosterone and increases its cc in
the seminiferous tubule and also carries it directly to the epididymes, so the tesotserone cc is higher in the testis than in the blood.)
Inhibin
•Activates aromatase enzymes in Sertoli cells
Testosterone estrogen conversion ↑ •Increases spermatogenesis

Question 20

FSH effects on Sertoli cells

Answer 20

Production of ABP (Androgen Binding Protein; testosterone further stimulates it in paracrine manner; ABP binds testosterone and helps its transport to epididymis)
 Conversion of testosterone to dihydrotestosterone (DHT) and estrogen
 Stimulation of spermiocytogenesis
• conversion of primary spermatocytes to secondary ones. It happens
only if FSH is present). Completion of spermatogenesis, however needs (LH) + testosterone as well.
 Completion of sperm release
 Secretion of inhibin
• Negative feedback action on FSH release (GnRH),
• Paracrine effect: Increasing spermatogenesis; activation of
Aromatase enzyme system stimulating conversion of testosterone to Estrogen in male horse and swine).

Question 21

LH (ICSH)

Answer 21

 Other name: ICSH (interstitial cell-stimulating hormone)
 Results in hypertrophy of Leydig cells.
 Stimulates production of testosterone by
Leydig cells.
 If administered, LH (or hCG) or GnRH stimulate endogenous testosterone production.

Question 22

Testosterone

Answer 22

Testosterone is the biologically important product of the Leydig cell.
Testosterone passes freely across cell membranes.
• rapidly enters the blood and lymph
Causes negative feedback mostly at hypothalamus (via a long feedback loop, on the GnRH production) which inhibits LH release.
• some hormone enters the adluminal compartment (seminiferous tubules)
Relatively high level of testosterone (compared to systemic circulation) required for spermatid migration.
Upon entering the adluminal compartment (crossing
the basal membrane), testosterone bounds to ABP • thelocaltestosteroneconcentrationismuchhigherthanin
the blood
 Testosterone-ABP complex serves to carry
testosterone to the accessory sex glands of the male
tract as well which are androgen dependent tissues.  Some testosterone entering the Sertoli cells may be
metabolized to the more potent DHT (di-hydro-
testosterone).
• It bounds to very high affinity androgen receptor, thereby
maintains the spermatogenesis.
• DHT has two-fold more poten cythan testosterone in
epididymis, prostate, seminal vesicle, penis, kidney, certain
hypothalamic neurons and some skeletal muscles.