MALE Reproductive system - slides

Somatic cells

also known as diploid cells (2n)

• 23 chromosomes (homologous pairs-very similar)

• 22 autosomes & 1 pair of sex chromosomes

• XX and XY

• in males sex cells are not homologous

• in females all homologous

Gametes

also known as haploid cells (n)

• single set of chromosomes

• produced by special type of division: meiosis

siter chromatids

are identical

Meiosis

sexual reproduction

• reduce chromosome number by half ( 2n → n)

• 2 stages- Meiosis I and II

• Diploid- 2N (homologous chromosomes(pair)

• Haploid - N

DNA synthesis

occurs in S phase of interphase

During prophase I

• synapsis of homologous chromosomes

• cross over

During metaphase I

homologous chromosomes line up at the metaphase plate

During metaphase II

sister chromatids line up at the metaphase plate

Outcome of Meiosis

Four haploid cells at the end of meiosis II

Gonads

testes

System of ducts

• epididymis

• ductus deferens

• ejaculatory duct

• urethra

Accessory sex glands

• seminal vesicles

• prostate

• bulbourethral glands

Supporting structures

• scrotum

• penis

Scrotum

• support structure for testes

• sac of loose skin, fascia & smooth muscle divided into 2 pouches by septum

• Raphe a ridge running along the midline.

Scrotum muscles

cremaster (smooth muscle) and Dartos (smooth)

• regulate position of testes and temperature for optimal sperm production.

• cold/arousal: contract

• hot: relax

• testes are located outside of the body (regulate temp, external position keeps them 2-3 degrees lower than core body temp)

Testes

paired, oval glands in the scrotum

surrounded by two tunics

• tunica albuginea (inner tough layer)

• tunica vaginalis (outer)

Mediastinum testis (house rete testis- about 250 lobules)

Seminiferous tubules

• ¼ tubules per lobe

• produce sperm

Seminiferous tubules

Site of sperm production

• formed sperm are transferred to epididymis (where sperm matures) and sperm leaves epididymis during ejaculation via the ductus deferens

Cryptorchidism

one or both testes fail to descend normally

• about 3% of full term babies

• about 30% premature babies

Support cells of the seminiferous tubule

• Sertoli cells (sustentacular)

• Leydig cells (interstitial)

Sertoli (sustentacular) cells

Somatic cells

• form blood-testis barrier (sperms are antigenic)

• support, protect & nourish spermatogenic cells

• produce fluids

• control release of sperm into lumen

• secrete inhibin (when sperm production is high)- regulate effects of FSH and testosterone

Leydig (interstitial) cells

• arise from dividing stem cells

• produce androgens (testosterone)

Spermatogenesis

• begins at puberty

• takes 2.5 months

• Stimulated by FSH & LH

• Spermatogonia(2n) → Primary Spermatocyte(2n) → Secondary spermatocyte(n) → spermatids(n) → spermatozoa/sperm(n)

Spermiogenesis

spermatids → sperm cells

Spermiation

the release of mature sperm cells from Sertoli cells into the seminiferous tubules

Sperm head

• contain 23 chromosomes

• DNA

• acrosome (hyaluronidase & proteinase enzyme) pushes sperm out

Mid piece of sperm

• mitochondria (does not enter egg cell)

Tail (flagellum) of sperm

• movement (locomotion)

Sperm production and viability

• about 100-300 million sperm produced each day

• once ejaculated, sperm remain viable for up to 5 days within the female reproductive tract

Testosterone production

• stimulate sperm production (spermatogenesis)

• stimulate libido

• sex characteristics

Regulation of Testosterone Production

Hypothalamus releases GnRH that stimulates the pituitary gland to release LH and FSH, which in turn promote testosterone production in the testes.

• LH release → targets Leydig cells → testosterone release

• FSH release → target Sertoli cells → inhibin release (in response to rising sperm count levels)which stops release of FSH → negative feedback of hypothalamus and pituitary → inhibits release of FSH, LH and GnRH

• FSH release → target Sertoli cells → androgen binding protein release → testosterone release (ADP binds to testosterone keeping the latter at a high concentration)

Epididymis

store sperm until fully mature

Pathway of sperm flow through Ductus of Testis

1. seminiferous tubules

2. straight tubules

3. rete testis

4. efferent ducts

5. epididymis

6. ductus (vas) deferens

Spermatic cord

• ductus deferens

• testicular artery

• plexus of testicular veins

• autonomic nerves

• lymphatic vessels

• cremaster muscle

Seminal vesicles (accessory glands)

• viscous, whitish-yellow, alkaline fluid

• fructose, prostaglandins, clotting proteins, seminal plasmin

prostate (accessory gland)

• slightly milky fluid, weakly acidic

• citric acid, proteolytic enzymes

Bulbourethral or Cowper’s gland

• clear, viscous mucin (alkaline)

Accessory glands

seminal vesicles, prostate, bulbourethral glands

Semen

• made of sperm and seminal fluid

• pH 7.2-7.7

• coagulates & reliquefies on ejaculation (clotting factors and fibro myosin)

• average ejaculate contains 50-150 million sperm/ml

Sperm analysis

• motility

• count (normal- 200-500 million sperm/ml)

• shape

Penis

Forms external genitalia with scrotum

• passageway for semen & urine(urethra)

• root: bulb and crus, body, glans penis, prepuce

Body composed of 3 erectile tissue masses filled with blood sinuses

• 2 corpora cevernosa

• 1 corpus spongiosum

Erection

Parasympathetic fibers release & cause local production of NO (nitric oxide) → smooth muscle in arterioles to relax and dilate allowing large amounts of blood to enter penis

• blood enters penis compressing drainage veins → blood being trapped (retards blood outflow and maintain engorgement)

• erectile dysfunction = impotence

Ejaculation

Due to Sympathetic stimulation

• muscle contractions close sphincter at base of bladder

• move fluids through ductus deferens, seminal vesicle & ejaculatory ducts

• contraction of muscles in ischiocavernosus & bulbospongiosus → completes ejaculation(the job)

Men with decreased testosterone levels in the 50s

• due to decreased number of interstitial cells

• decline more gradually than women’s hormone drop

• most men with few symptoms

• some with mood swings, decreased sex drive, hot flashes

Prostate enlargement

• experienced by most men with age

• can interfere with sexual and urinary functions

Erectile dysfunction

• inability to achieve or maintain erection

• associated with aging, other risk factors

• MEN can reproduce until 80-90