L18: Male anatomy/spermatogenesis

Male reproductive organs diagram

Main function of male reproductive organs

to produce and deliver spermatozoa tothe female

Temperature control in male reproductive organs

• Testes need to be kept 4-6 C below temperature for spermatogenesis

• During late part of gestation or early life: testicular descent via the inguinal canal is required, or else infertility or tumour can occur. Can be surgically moved down

• Later in life: temperature controlled by the veins of the “pampiniform plexus” (in the spermatic cord) forming a countercurrent heat exchanger; cools down arterial blood in the testes. Heat exchange between blood in arteries and veins.

Testes location

Located in the scrotum = skin sac from the abdominal cavity with a layer of smooth muscle (tunica dartos)

• When tunic dartos contracts, its moves the testis closer to the abdominal cavity if external environment is cold, or relax if hot. Another mechanism to regulate the testis

Compositions of outside the testes

• On the inside of the scrotum: layers of connective tissue (scrotal fascia and parietal vaginal tunic)

• Covering the testes is a layer of vascularized connective tissue (tunica albuginae + visceral vaginal tunic) that projects septa in the testis. Smooth muscle cover the septa (help moving immature sperms)

• Between the parietal and visceral vaginal tunic, there is fluid (vaginal cavity), allowing testis to move up and down without friction

• Tunica albuginae is where all the blood vessels coming from the periphery of the testes inter the testes itself

Composition of inside the testes

2 major parts:

• Seminiferous tubules (S.T.): site of sperm production. Ducts collect sperm to rete testis in the center = tubes that bring the sperm to the epididymis. Contains sertoli cells that control spermatogenesis.

• Interstitium (between S.T.): composed of connective tissue, nerve, blood vessels, and Leydig cells which produce testosterone

What provides strict separation between seminiferous tubles and interstitial

The basal lamina and the sertoli cells closely attached to one another

• the sertoli cells which have contact with the basal lamina and all spermatogenic cells play a critical role in supporting the differentiation of the spermatogonia, providing nutrients and regulating the multiplications of the cells

Boar reproductive tract characteristics

• Testis structure similar to bull – more pronounced interstitium [Leydig cells produce wider array of androgens, C16, C19 steroids (16- androstenes) plus estrogens], reason for boar taint

• Testis location against the abdominal cavity reduces efficiency of heat exchange

• Large seminal vesicles = large volume

• Large bulbo-urethral glands = gel

• Copious ejaculate/prolonged ejaculation (large volume)

• Smaller sperm “reserves” v/v bull

Spermatogenesis diagram

Steps of Meiosis

1. Interphase

2. Prophase I

3. Metaphase I

4. Anaphase I

5. Telophase I

6. Prophase II

7. Metaphase II

8. Anaphase II

9. Telophase II

Interphase

replication of DNA (4c-2n)

Prophase I

1. Leptotene: condensation of chromatin

2. Zygotene: pairing of homologues (forming a tetrade)

3. Pachytene: crossing-over and recombination

4. Diplotene: synaptonemal complexes dissociate

5. Diakinesis: chiasma disappear and homologues begin to repel

Metaphase I

homologue centromere binds to spindle fiber

Anaphase I

homologous pairs separate and begin to move

Telophase I

hromosomes migrate to each pole, cell division. 1 chromosome of pair in each cell = (2c – 1n)

Prophase II

spindle fibers rearrange and chromosomes recondense

Metaphase II

chromosomes align along spindle equator

Anaphase II

sister chromatids separate and move to opposite poles

Telophase II

daughter cell nucleus has one set of chromosomes (1c – 1n)

Sertoli cells function

• Blood testis barrier; separates spermatogenic cells from the blood

• Controls what moves in and out of the seminiferous tubules including bringing in nutrients and removing waste

• Basal/luminal and adluminal compartments

• Provide nutrients and several factors to control spermatogenesis

• “Fluid pumping” during final maturation if sperm

• Produce androgen-binding protein and inhibin (short-loop negative feedback)

• Express FSH receptors (regulated by FSH)

Spermatogenesis function

• In contact with Sertoli cells

• Nuclear condensation

• Formation of the acrosomal cap (derived from Golgi); enzymes accumulate in the acrosome which drill a hole into the oocyte allow sperm to penetrate

• Development of a tail; helps swim

• The distal centriole provides a template for accretion of cytoskeletal elements comprising the contractile lattice of the tail

• Mitochondria become concentrated into the sheath of the middle piece.

Final structure of sperm diagram

Leydig cell characteristics and composition

• Interstitial cells – located in the spaces between tubules

• Highly perfused (blood vessels/capillaries)

• Synthesize androgens – testosterone

• Express LH receptors

Passage through the epididymis

• go from testis upward via smooth muscle toward head of epididymis

• the sperm goes through the convoluted spool tubule first entering the head of the epididymis (caput) where they are still immotile and infertile

• they then move into the body where they acquire motility and fertility

• Tail of epididymis is where they acquire their final maturation and are stored

Accessory sex glands includes

• Ampular gland (ampullae, absent in boar and dogs)

• Vesicular (absent in dogs)

• Prostate

• Bulbourethral

Overall purpose of accessory sex glands

Provide nutrition for sperm and some protection

Ampular gland purpose

enlargement of the ductus defferent

Vesicular purpose

Secretes

• Fructose: sperm energy pack

• Vitamins and prostaglandins important for mobility and survival

• Proteins for coagulation

Prostate purpose

alkaline substance to enhance motility

Bulbourethral purpose

lkaline substances to neutralize acidity and mucus to lubricate vagina during copulation

Epididymis diagram

Arousal diagram

Ejaculatory process diagram

Innervation of the male genital diagram

Extender for cryopreservation

Nutrient

• egg yolk

• whole homogenized milk

Buffer

• citrate

• sodium phosphate

Antimicrobials

• penicillion/streptomycin (bacteria)

• minosin (myocoplasma)

Cryoprotectant

• 6-12% glycerol (if to be frozen)

Most popular are egg yolk-citrate (clear) and whole homogenized milk (opaque)

Endocrine control in the male diagram