Male Reproductive System

Question 1

Outline the H-AP-Gonad axis

(Hypothalamus - Anterior pituitary - Gonadal)

Answer 1

Hypothalamus secretes GnRH which acts on the Anterior Pituitary

Anterior Pituitary then secretes FSH and LH.

FSH acts on the seminiferous tubules and LH acts on the Interstitial (leydig) cells

Question 2

where are the stem cells located and what are they called?

Answer 2

called Spermatogonia, they are located at the outermost region of the seminiferous tubules, right against the basement membrane

as they develop into spermatozoa, they move towards the lumen of the seminiferous tubules

Question 3

Describe Spermatogenesis

Answer 3

Spermatogonis are DIPLOID stem cells that give rise to 2 daughter cells.

One remains are the basement membrane as a stem cell

A second daughter cell (primary spermatocyte) that moves towards the tubule lumen.

>this daughter cell undergoes 2 meiotic divisions to form 4 HAPLOID cells

Question 4

Outline the divisions of spermatogonia

Answer 4

Primary spermatocyte undergoes first meiotic division and becomes secondary spermatocyte.

Secondary spermatocyte undergoes secondary meiotic division and becomes halpoid spermatids.

Via spermiogenesis the spermatids become spermatozoa

Question 5

why would the immune system attack developing sperm

Answer 5

Left alone, the immune system can attack developing sperm

Immunological Infertility in Men

Sertoli Cells help seminiferous tubules as an immunologically privileged site by :

1. Blood-testis barrier (tight junctions, basement membrane)
2. Sertoli cells produce FAS-ligand; this binds to FAS-receptor on T-cells triggering apoptosis of the T-cells and preventing immune attack on developing sperm

Question 6

Survival of Spermatozoa

Answer 6

Once ejaculation has occured sperm has limited life span - approx 80 hrs

>cervical mucus helps in maintaining metabolic requirements of spermatozoa

>when migrating in the genital tract, they are rapidly separated from the seminal plasma and resuspended in the female genital fluid

>spermatozoa undergo “capacitation” during their passage through the reproductive tract

Question 7

Loss of Spermatozoa

Answer 7

• Although millions of sperm are deposited into the female reproductive tract only few can reach the site of fertilization
• Most spermatozoa are eliminated at the selective barriers: cerviz and uterotubal junction
• Majority of sperm are removed by phagocytosis
• Damaged or immotile spermatozoa are carried back to the cervix by ciliated cells

Question 8

What is capacitation

Answer 8

Physiological changes occuring in the mammalian spermatozoa during passage through the female reproductive tract that enables them to penetrate the egg membrane

> the alteration of the glycoprotein surface of spermatozoa under the influence of secretion of the tissues of the female reproductive tract

**non-mammalian spermatozoa do not require this capacitation step

Question 9

Describe the condition of the sperm throughout capacitation

Answer 9

Epididymal : surface of epididymal spermatozoa contain proteins and carbohydrates

Ejaculated : these surface proteins are coated with seminal plasma proteins

Capacitated : when sperms are exposed to female tract environment, the surface proteins are removed exposing the molecules that can bind the zona pellucida of the oocyte

Question 10

What is fertilization ?

Answer 10

Series of processes beginning with the spermatozoa penetrating the corona radiata and ending with the intermingling of maternal and paternal chromosomes after the spermatozoon entered the egg

Question 11

How do you get an erection

Answer 11

Parasympathetic nerve induced vasodilation of arterioles allows blood flow into the corpora cavernosa

>Corpus-cavernosum compresses

Neurotransmitter that mediates this is nitric oxide

• arterioles vasodilate - blood goes into corpus cavernosa
• Vein contracts - less blood outflow
• Increased intracavernosal pressure
• erection

Question 12

describe the role of nitric oxide in erection of the penis

Answer 12

1. Nitric Oxide acts on Vascular Smooth Muscle Cell (VSMC) and activates GTP (guanylate cyclase), producing cGMP
2. cGMP causes Ca2+ channels in VSMC to close (cytoplasmic [Ca2+] decreases)
3. VSMC relaxes from decrease in [Ca2+], causing vasodilation of penis and engorgement of the erectile tissue (promotes erection)

Question 13

How does viagara work?

Answer 13

Viagara inhibits Phosphodiesterase

1. Viagara inhibits PDE that catalyzes the breakdown of cGMP
2. this INCREASES the availability of cGMP
3. Promotes erection