Male reproductive physiology

Question 1

Spermatogonia

Answer 1

Immature germ cells in seminiferous tubules which begin to proliferate and differentiate at puberty and continues for the rest of life.

Question 2

Blood-testis barrier

Answer 2

Tight junctions between adjacent sertoli cells make an impermeable barrier separating the basal compartment from the adluminal compartment.

This is important so that maturing sperm are hidden from the immune system.

Question 3

Spermatogenesis

Answer 3

Process of cell division of mitosis and then meiosis which starts with spermatogonia and ends with mature spermatozoa.

Takes ~ 74 days but the volume is so high that there is still 120 million sperm made per days.

Question 4

Parts of the mature sperm

Answer 4

Head (condensed nucleus within thin cytoplasmic later

Acrosome (formed by golgi which contains enzymes similar to lysosomes)

Tail (flagellum) Microtubules skeleton that causes movement. Mitochondria in the body provide ATP.

Question 5

Control of male sexual function by hypothalamus and pituitary

Answer 5

GnRH from arcuate nuclei of the hypothalamus –> LH and FSH from the gonadotropes of anterior pituitary.

Significant levels of GnRH begin to be released at the onset of puberty and is released cyclically. LH closely follows the pattern of GnRH while FSH responds only to long term changes.

Question 6

Luteinizing Hormone (LH)

Answer 6

Released from the anterior pituitary and causes testosterone release from Leydig cells of testes.

Testosterone has a negative feedback mechanism with GnRH and AP to inhibit secretions.

Question 7

Follicle-stimulating hormone (FSH)

Answer 7

Initiates spermatogenesis with testosterone (both are required)

Stimulates sertoli cells to secrete spermatogenic substances needed. Sertoli cells secrete inhibin –> inhibit FSH

Question 8

Estrogen

Answer 8

Formed from testosterone by sertoli cells when stimulated by FSH. Also essential for spermatogenesis

Question 9

Growth hormone

Answer 9

Secreted from the anterior pituitary and promotes early division of spermatogonia.

Question 10

Sperm maturation in the epididymis

Answer 10

Sperm spend several days passing through 6 meter long epididymis

Gain capability of motility, but are not motile due to presence of inhibitory proteins in epididymal fluid

Question 11

Sperm storage

Answer 11

Most sperm are stored in the epididymis

In a nutrient fluid made by Sertoli cells and epithelium of epididymis. Contains hormones (testosterone and estrogen), enzymes, and nutrients necessary for sperm maturation

Question 12

Seminal vesicles

Answer 12

Secrete a mucoid substance containing: Fructose, citric acid, prostaglandins, and fibrinogen

During emission it empties contents into the combined ejaculatory duct shortly after vas deterens empties sperm.

Question 13

Prostate gland

Answer 13

Secretes a thin, milky alkaline fluid containing calcium, citrate ion, phosphate ion, clotting enzyme, and profibrinolysin.

It is alkaline to help neutralize the acid from vas deferents fluid and vaginal secretions.

During emission the prostate capsule contracts to add its secretion to the posterior urethra via prostatic ductule opening.

Question 14

Sperm composition

Answer 14

Sperm/vas deferens fluid= 10% volume

Prostate fluid= 30%

Seminal vesicle fluid = 60%

Question 15

Capacitation of sperm in the female genital tract

Answer 15

1. Uterine and fallopian tube fluids wash away inhibitory factors from the male genital tract.
2. Acrosomal membrane becomes weaker.
3. Sperm become more permeable to calcium (drives whiplash motion of the flagellum and allows for release of acrosomal enzymes upon contact with ovum)

Question 16

Acrosome reation

Answer 16

Acrosome releases hyalinuronidase (which depolymerizes hyaluronic acid holding the ovarian granulosa together) and proteolytic enzymes (which digest proteins of tissue cells adhering to ovum)

Allows the sperm to pass through many layers of granulosa cells and the zona pellucida of the egg –> fertilization

Question 17

Male sex hormones

Answer 17

Testosterone (most abundant)
Dihydroxytestosterone (DHT) (most active)
Androstenedione

Question 18

Testosterone development

Answer 18

Testosterone is high during fetal development (thought to promote development of male sexual organs)

Also significant in first 10 weeks after birth.

Low until puberty when it then rises to max and diminishes later in life.

Question 19

Testosterone effects

Answer 19

Penis, scrotum, and testes enlarge after puberty.
Body hair growth, deep voice, thickness of skin, acne.
Decreases growth of hair on top of head. Only occurs significantly in those with genetic background
Increases protein formation and muscle development
Increases bone matrix and calcium retention
Increases basal metabolic rate
Increases red blood cells

Question 20

Mechanism of testosterone effects

Answer 20

1. Testerone enters the cells and most often is converted to DHT by 5-alpha-reductase
2. DHT binds androgen receptor
3. DHT-AR complex moves to the nucleus to promote gene transcription.
4. Most effects result form an increased rate of protein formation in cells