W1L4 Fri male reproductive tract and teste Flashcards
Anatomy of the male reproductive system
-Components vary in different species
In human:
Gonads - testis x 2 (1)
Excretory / conductive tracts
- epididymis x 2 (2)
- vas deferens x 2 (3)
ejaculatory duct x 2 (4)
urethra x 1 (5)
Accessory glands:
- seminal vesicle x 2
- prostate x 1
- bulbourethral/ cowper gland x 2
External genitalia:
- scrotum x 1
- penis x 1
Related structures :spermatic cord and inguinal canal
Testis structure
-Develop from posterior abdominal wall (gonadal ridges)
-Descend to scrotum via inguinal canal (human 7th month gestation)
-Contain germ cells
-Dual function- sperm and hormone production
-Comprise of 250-300 lobules, each lobule has
1-4 seminiferous tubules
Seminiferous tubules
Contain germ cells & Sertoli cells
Surrounded by a basement membrane & an outer layer of myoid cells. Single layer of muscle to squeeze the sperm
Looped tubules- both ends open into rete testis
Interstitial Tissue & Leydig Cells
contains BVs, lymph vessels , connective tissue, nerves + macrophages
Ø Leydig cells: influenced by LH binding (pituitary) to convert cholesterol to androgens (testosterone)
§Testosterone receptors on surface for negative feedback (enough=stop production)
Sertoli Cell
nurse cells’ in seminiferous tubules that help produce/develop sperm
§ Bind FSH to stimulate production of testosterone (Leydigcells) +sperm
§ Secretes Anti-Mullerian Hormone (AMH) during virilisation which regresses Mullerian duct to prevent development of uterus, cervix + vagina
§ Produces androgen binding protein (ABP) which holds androgens (for conversion into oestrogen)
§ Conversion of androgens to oestrogens (control testis fluid regulation + balances T/oestrogen levels) via aromatase
§Inhibin production :negative feedback on FSH to regulate amount of sperm + steroid production
What is the blood testis membrane
tight junction b/w Sertoli cells dividing seminiferous tubule into 2 compartments
* Basal compartment: outer side of tubule, in contact with blood + lymph
* Adluminal compartment: inner side of tubule, isolated from blood + lymph
* Stops toxic substances + autoimmune response to germ cells (haploid)
Retetestis & efferentducts
concentrate sperm by fluid resorption(assisted by oestrogen)
Ø Sperm pushed from seminiferous tubules to rete testis by myoid cells
Ø ST → rete testis → efferent ducts → epididymis (stored) → vas deferens (ejaculation)
Location of testes
Can be scrotal or testicond (inside the body)
Scrotum
Sac of loose skin, fascia plus dartos smooth muscle
Numerous sweat glands
Considerable variation in size and position relative to penis
Role - protection and thermo-regulation
Spermatic cord and testicular supply
Connective tissues sheath that suspends testes in scrotum+passes through inguinal canal
§Contains vas deferens, pampiniform plexus, cremaster muscle, arteries, nerves, lymphatic vessels
§Sperm are susceptible to oxidative damage+ stress=↓temperature stops/slows metabolic reactions
Testis thermoregulation
Ø Cremaster skeletal muscle: contract to raise testes if cold/during ejaculation, relax to lower testes if hot
Ø Pampiniform plexus: intricate arrangement of testicular arterial supply + venous drainage
§ Counter current heat exchange:cooling in coming arterial blood via cool out going venous blood
Ø High temperature stops spermatogenesis + increases cancer risk
§ Absent in animals with abdominal testes
Epididymis (plural epididymides)
-Comma-shaped, highly convoluted tube:
-Caput (head), with multiple efferent ducts connected to seminiferous tubules - fluid resorption
-Corpus (body), highly coiled, up to 6m long tube (~86m in stallion)- secretory tissue
-Cauda (tail), continues with vas deferens -sperm storage and maturation
-Takes ~20 days for immature sperm to swim through the epididymis – maturation process
-have smooth muscle walls, peristalsis promote sperm movements
Vas Deferens
Long tube that travels behind bladder+ receives input from seminal vesicles+ prostate then opens into urethra
-Part of the spermatic cord that passes through inguinal canal
-Thick smooth muscle – peristalsis to move sperm, muscle contraction at ejaculation
-Site of sperm storage
-Vasectomy- vas deferentia are cut
Accessory gland- seminal vesicles
-Paired, elongated gland posterior to bladder (absent in some species)
-Opens into vas deferentia or urethra
-Stores and secretes seminal (~70% of the fluid volume – humans)
-segregation are sticky, alkaline to neutralize vaginal acidity
What does secretion contain
fructose (food for sperm)
* prostaglandins (communication with female immune system)
* clotting proteins
* citric acid
* mucus
* enzymes
Accessory glands – Prostate Gland
-Single walnut-size and -shape organ. Can be lobule, disseminated or a mixture.
*Prostate depends on dihydrotestosterone (DHT), Testosterone from testes convert to DHT locally via 5a-reductase
-Under bladder surrounds ejaculatory ducts & urethra
*Secretes milky fluid ~30% semen volume (humans)
* proteins, bicarbonate, citric acid
* prostate acid phosphatase (PAP)
* proteolytic and clotting enzymes : prostate specific antigen (PSA) , diagnostic marker for prostate disease
Accessory glands- Bulbourethral / Cowper’s gland
-Paired, pea-size gland within the urogenital diaphragm at the base of penis
-Absent in some species
-At sexual arousal secretes clear salty, viscous alkaline mucus into the urethra (pre-ejaculate)
-Cleans urethra, neutralizes vaginal acidity and lubricates the glans penis before penetration
Urethra
3 regions: prostatic, membranous & cavernous
-prostatic urethra –receives sperm from vas deferentia & fluid from seminal vesicles & prostate
-membranous- forms external sphincter of the bladder
-cavernous (penile)- runs the length of the penis
The Penis (Copulatory organ)
3 regions: root, shaft & glans
Consists of erectile tissue & urethra
Function- Passage of semen & urine, and for penetration during intercourse
Penile erectile tissue
3 cylinders of erectile tissue:
-A single, ventral cylinder, the corpus spongiosum - Surrounds the urethra
-Paired dorsal corpora cavernosa. Both have a large central artery and are enclosed by a dense, fibroelastic tunica albuginea
Mechanism of Penile erection
-Autonomic nervous system (ANS) releases nitric oxide (NO) in the walls of penile arteries to increase cyclic GMP
-A large deep artery runs along the centre of each corpus cavernosum will dilate – supply more blood for erection
-Superficial and deep dorsal veins are located between a dense fibrous tunica albuginia and skin –will close while penis extends, allowing erection
Diverse penis morphology and baculum
Species variation of penis morphology
-Can be prehensile- dolphin, tapir, echinda
-Baculum - bone develops in the penis between the paired corpora cavernosa, above the urethra, May permit longer bouts of intercourse, retractor muscle
-Prepuce/foreskin is a retractable fold of skin that covers the pre-scrotal part of non-erect penis
-Sheath, a layer of skin that protects the non-erect penis
