Testes Development and Function

Describe the development of the fetal testis.

• Begin as a gonocyte - (precursor) germ cells in the center, surrounded by sertoli cells

• Later the cell is lined by peritubular myoid cells

  • Germ cells migrate to the side

  • Leydig cells lie in the interstitium between the tubules, containing blood vessels and lymph

Describe how the testis descend into the scrotum.

Occuring before birth!

• Androgens cause the suspensory ligament to degenerate

• A factor called INSL3 causes the shortening of the gubernaculum

  • Testosterone and INSL3 made by the leydig cells

• Androgens act to complete the shortening of the gubernaculum and movement of the testes into the sctroum

In the center or lumen of the tubules we see ____, and surrounding the tubules we see ______ ____.

sperm, interstitial tissue

What specific cell type is found in the interstitial tissue?

• Leydig cells

  • Which secrete the Testosterone

Where are the peritubular myoid cells located?

• Flattened cell types surrounding the individual tubules

Where are the sertoli cells found?

In the periphery of the tubules

What are the somatic cells of the testis?

• Leydig cell

• Sertoli cell

• Peritubular myoid cell

Describe where the leydig cells are found and the populations found in the testes.

• What is their main function?

• Found in the interstitial tissue between tubules

• In mammals there appear to be 2 different population of Leydig cells. One fetal and one adult.

• The Leydig cells function to make androgens, primarily testosterone, under the control of LH release from the anterior pituitary

Describe the two different peaks of androgen production, occurring fetal + postnatal.

Two peaks of androgen production -

1) in fetus (ensures masculinisation)

2) adult (necessary for fertility, sex drive and maintenance of secondary sex characteristics)

• Puberty - causing massive increase

What hormones control the action of the sertoli cells?

Controlled by FSH release from the anterior pituitary and androgen release from Leydig cells

What are the main functions of the sertoli cells?

Essential regulator of testis development

• SRY acts to form SC. SC regulate development of other cell types

Forms the blood testis barrier

• Tight junctions between SC "seal off" the lumen of the tubule

Secrete AMH

• Prevents paramesonephric duct development

In the adult, maintains the Leydig cells

• Mechanism unknown

Describe key features of theperitubular myoid cell.

• Contractile Cell

• Androgen dependent

• Essential for normal spermatogenesis

The testis are ___ cooler than core body temperature.

~3° C

Describe how testicular thermoregulation occurs, considering the vasculature.

Pampiniform Plexus

• Allows countercurrent exchange in the testis, blood from the body warms the returning blood, but is cooled by the cold veinous blood as it enters the testis

Other than the counter-current exchange, what other anatomical features aid in testicular thermoregulation.

Other aids to thermoregulation:

• Tunica dartos: smooth muscle in the scrotum -Capable of sustained contraction, elevating testes in cold environmental temperatures

• Cremaster muscle is continuous with internal abdominal oblique muscle- Capable of short-term contraction, Short term elevation of testes during fear or excitement

What may happen if the testes fail to descend into the scrotum?

• What may cause this condition?

• The affected animal is known as a cryptorchid

• The condition may be unilateral or bilateral

• May be caused by problems with AMH, androgens, CGRP or other factors

Why is cryptorchidism “important” or something that should be noted?

• It is important because…

• It increases the risk of testicular cancer (esp germ cell carcinoma)

• May be inherited.

• It may cause infertility (Why?)

  • (Spermatogenesis cannot occur here)

What breeds are susceptible to retained testes?

• Dogs eg Boxer, Chihuahua, Bulldog, Shetland sheepdog, Yorkshire terrier

• Horses (known as a Rig or a ridgling)

• Persian cats

• Humans - may be linked to endocrine disruptors

What endocrine hormones primarily control output by the testes?

• Testes are controlled primarily by endocrine regulation through LH and FSH secretion from the anterior pituitary

• Also some input from ACTH, GH and thyroid hormones

Why is paracrine regulation of the testis important? (Furthermore what is paracrine regulation?)

• A system called “paracrine signaling” allows cells to communicate with each other by releasing signaling molecules that bind to and activate surrounding cells.

• e.g. Sertoli cells + Myoid cells affect the Leydig cell

Describe the spermatogenesis pathway.

Proliferation

• 1 cell produces 64

Meiosis

• 64 generates 256

Spermiogenesis

• Differentiation process

• Cell differentiation must occur to generate a motile DNA package

How long does spermatogenesis usually take?

Spermatogenesis takes…

56-93 days in dog

64d in human

60d bull

49d ram

Why can we think of spermatogenesis like a conveyer belt?

Once a spermatogonium develops to meiosis (red arrow) then the next spermatogonium starts maturing behind it (green arrow)

Describe the steps involved in the proliferation stage of spermatogenesis.

• Also note where this is taking place.

Proliferation takes place on the basement membrane inside the tubule, and moves to the center of the lumen as they become more mature.

• Spermatogonia Divide by Mitosis: Spermatogonia (the stem cells) undergo mitotic division to produce more spermatogonia or primary spermatocytes.

• Formation of Primary Spermatocytes: Some spermatogonia become primary spermatocytes, which are diploid cells ready for meiosis. (2n)

• Meiosis I – Secondary Spermatocytes: Each primary spermatocyte undergoes Meiosis I, dividing into two secondary spermatocytes, which are haploid (half the original chromosome number). (n - double chromatids)

• Meiosis II – Spermatids: Secondary spermatocytes then undergo Meiosis II, resulting in four haploid spermatids, each with a single set of chromosomes. (n - single chromatids)

• Spermiogenesis: Spermatids undergo differentiation and maturation in a process called spermiogenesis, transforming into mature sperm cells capable of fertilization. (Spermatozoa) (n)

What feature of the sertoli cell allows continious sperm production?

To ensure there is continuous sperm production each Sertoli cell (SC) supports 20-30 germ cells at different stages of cycle.

The hormonal control of spermatogenesis is largely controlled by the _____ cells.

sertoli

What is the main function of the epididymis?

• Functions to induce sperm maturation

How do sperm move inside the epididymis?

• Non-motile, non-fertile sperm enter at the head and then become fertile and motile as they travel down the epidiymis

• The tail acts as a sperm storage area.

What cell structure makes up the epididmis?

• Pseudostratified, columnar epithelium with stereolcilia

• Epithelium gets smaller towards the tail

• Androgen sensitive structure

• How it functions to induce fertility/motility not known