Chapter 20 Pt 2 -- Male Reproductive Physiology -- VTPP 434

Chapter 20 Pt 2 -- Male Reproductive Physiology -- VTPP 434

Components of Male Reproductive System

-Testis
-Epididymis & Ductus (Vas) Deferens
-Seminal Vesicle
-Prostate Gland
-Bulbourethral Gland

Testis

-a pair of skin covered sac
-located in scrotum suspended between legs
-produce sperm & secrete testosterone

Epididymis & Ductus (Vas) Deferens

-a pair
-Epididymis -- 1 attached to rear of each testis
-Ductus Deferens -- 1 travels from each epididymis up out of scrotal sac through inguinal canal & empties into urethra at neck of bladder
-serve as sperm's exit route from testis
-serve as site for maturation fo sperm for motility & fertility
-concentrate & store sperm

Seminal Vesicle

-a pair
-empty into last portion of ductus deferens, one on each side
-supply fructose to nourish ejaculated sperm
secrete prostaglandins -- stimulate motility to help transport sperm within male & female
-provide bulk of semen
-provide precursors for clotting of semen

Prostate Gland

-single
-completely surrounds urethra at neck of bladder
-secretes an alkaline fluid that neutralizes acidic vaginal secretions
-triggers clotting of semen to keep sperm in vagina during penis withdrawal

Bulbourethral Gland

-a pair
-both emptying into urethra, one on each side, just before urethra enters penis
-secrete mucus for lubrication

Seminiferous tubules

-where spermatogenesis
-highly coiled
-next to Leydig cells in testes

Leydig Cells (interstitial cells)

-produce and secrete testosterone
-located in connective tissue between seminiferous tubules

Testosterone Effects Reproductive Changes During Puberty

1) Enlargement & Maturation of Gonads
2) Development of 2ndary sex characteristics
3) Gamete Production
4) Growth & Maturation of Reproductive Tract
5) Gives Libido

Effects on Sex-Specific Tissues After Brith

1) Growth & Metabolism of Reproductive System at Puberty
2) essential for spermatogenesis
3) maintains reproductive tract in adulthood

Testosterone Non Reproductive Actions

1) exerts protein anabolic effect
2) prootes bone growth at puberty
3) closes epiphyseal plate after being converted to estrogen
4) may induce aggressive behavior

Spermatogenesis

-64 days for maturation
-Spermatogonia -- male germ cells
-3 stages: Mitotic Proliferation, Meiosis, Packaging

Mitotic Proliferation

• in outer layer
  1) Spermatogonia divide by mitosis
  2) Half of germ cells remain, other half move to undergo steps to form sperm released into lumen
  3) Sperm-forming daughter cell divides by mitosis twice to make -- 4 identical Primary Spermatocytes
  4) enter a resting phase and prepare for meiosis

Meiosis

1) Each primary spermatocyte makes 2 Secondary Spermatocytes
2) each 2ndary spermatocyte makes 4 Spermatids

Packaging (spermiogenesis)

-spermatids resemble germ cells, but are the finalized product
-remodeling of cell elements of spermatids to make spermatozoa
-need FSH

Spermatozoon

-Head, Acrosome Cap, Midpiece, Tail
-sperm

Sertoli Cells

-in the seminiferous tubules
-form a ring around tubule lumen
-joined by tight junctions
-help Spermiation -- process of releasing mature sperm from Sertoli cells

Sertoli Cells Functions for Spermatogenesis

1) Tight junctions between Sertoli cells form a Blood-testes barrier
2) Sertoli cells nourish sperm cells by metabolizing glucose to lactate for food for sperm
3) Destroy defective germ cells that fail to complete spermatogenesis
4) Secrete seminiferous tubule fluid into lumen
5) Secrete Androgen-binding protein
6) Site of action for control of spermatogenesis by testosterone & FSH
7) Secrete Mullerian inhibiting factor during fetal development

Inhibin

-peptide hormone
-secreted by Sertoli cells
-acts directly on anterior pituitary to stop FSH

Kisspeptins

-peptide neurotransmitters
-released by Kiss1 Neurons in Arcuate (ARC) nucleus
-stimulate GnRH secretion

Testosterone

-acts on Kisspeptins to inhibit GnRH
-acts on anterior pituitary to inhibit LH
-needed for mitosis and meiosis

FSH

-needed for spermatid remodeling
-acts on Sertoli cells to enhance spermatogenesis
-low-level during puberty

LH

-LH acts on Leydig cells to regulate testosterone secretion
-inhibited by decrease GnRH
-low level during pre-puberty

Capacitation

-enhancement of sperm's capacity in male and female reproductive tract
-epididymis enhances sperm for motility & fertilization

Male Embryonic Development

1) SRY gene produces Testis Determining SRY Protein
2) Testis Determining Protein initiates production of proteins that cause gonad medulla to differentiate into testis
3a) Interstitial Cells (Leydig) secretes testosterone to control:
-development of wolffian duct into accessory structures
-development of male external genitalia (via DHT)
3b) Sertoli cells secrete anti Mullerian Hormone that causes regression of Mullerian duct

Gametogenesis

1) Mitosis
-germ cell (Spermatogonium) proliferation
-Spermatogonium divide into Spermatogonia
2) Meiosis
-DNA replicates but no cell division
-46 chromosomes (4n)
-Spermatogonia becomes Primary Spermatocyte (4n) & are Sister Chromatids
3) 1st Meiotic Division -- Primary Spermatocyte divides into 2 (23) (2n) Secondary Spermatocytes
4) 2nd Meiotic Division -- Secondary Spermatocytes becomes Spermatids (23 haploid)