W1L4 Fri male reproductive tract and teste

Question 1

Anatomy of the male reproductive system

Answer 1

-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

Question 2

Testis structure

Answer 2

-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

Question 3

Seminiferous tubules

Answer 3

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

Question 4

Interstitial Tissue & Leydig Cells

Answer 4

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)

Question 5

Sertoli Cell

Answer 5

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

Question 6

What is the blood testis membrane

Answer 6

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)

Question 7

Retetestis & efferentducts

Answer 7

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)

Question 8

Location of testes

Answer 8

Can be scrotal or testicond (inside the body)

Question 9

Scrotum

Answer 9

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

Question 10

Spermatic cord and testicular supply

Answer 10

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

Question 11

Testis thermoregulation

Answer 11

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

Question 12

Epididymis (plural epididymides)

Answer 12

-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

Question 13

Vas Deferens

Answer 13

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

Question 14

Accessory gland- seminal vesicles

Answer 14

-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

Question 15

What does secretion contain

Answer 15

fructose (food for sperm)
* prostaglandins (communication with female immune system)
* clotting proteins
* citric acid
* mucus
* enzymes

Question 16

Accessory glands – Prostate Gland

Answer 16

-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

Question 17

Accessory glands- Bulbourethral / Cowper’s gland

Answer 17

-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

Question 18

Urethra

Answer 18

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

Question 19

The Penis (Copulatory organ)

Answer 19

3 regions: root, shaft & glans
Consists of erectile tissue & urethra
Function- Passage of semen & urine, and for penetration during intercourse

Question 20

Penile erectile tissue

Answer 20

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

Question 21

Mechanism of Penile erection

Answer 21

-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

Question 22

Diverse penis morphology and baculum

Answer 22

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