Male Reproductive System Flashcards
Epididymis
Structure within the scrotum attached to the backside of the testes
Store, mature and transport spermatozoa between the testis and the vas deferens
Ductus (vas) deferens
Tube begins at epididymis, enters abdominal cavity behind bladder, dilate to form ampulla, outside the prostate, unite with the seminal duct to form an ejaculatory duct, which pass thru prostate and end in urethra (the tube carries urine & semen)
Bulbourethral glands (Cowper’s gland) (Accessory glands)
Below prostate produce alkaline fluid
Secrete lubricating mucus
Seminal vesicles
Accessory glands
Produce lubricating alkaline– fructose, prostaglandins (PG), and clotting pr
PG (active lipid molecule): lowers female immune response to semen
Prostate
Accessory glands
Exocrine gland, store and secrete a milky, acidic fluid
Citric acid used for ATP production
Enzymes to liquefy semen
Scrotum
Supporting structures
Scrotal location and muscle contraction regulate temp of testes
Normal sperm production occurs 2-3 °C lower than core body temp
Response to cool temp;
- Cremaster muscles contract to pull testes close to body
- Dartos muscles contract to tighten scrotum
Response to warm temp: Reverse of above actions
Penis
Supporting structures
External sex organ of male through which both urine and semen pass
Contains urethra
Passage of sperm and urine
Masses of erectile tissue (smooth muscles and connective tissue that contains blood sinuses)
Distal end forms glans penis: covered with fold of skin (prepuce), removed by circumcision
Testes
Primary sex organs
Develop initially in abdominal cavity
Descend into scrotum: begins in 6/7th month of gestation, should be in scrotum by birth
Cryptorchidism
Condition in which testes do not descend into the scrotum (undescended testicle)
Untreated bilateral cryptorchidism results in sterility
Cells involved in spermatogenesis are destroyed by the higher temp of the pelvic cavity
Male gonads
Pair of small egg-shaped organs
Encapsulated in a layer of fibrous connective tissue
Divided into 200-300 lobules
Each containing set of highly coiled tubes called -Seminiferous tubules: site of sperm production -contain single layer of Sertoli cells
Interstitial cells- Leydig (spaces between tubules): secrete testosterone
The wall of seminiferous tubule
Basement membrane
Inner layer of epithelial cells called Sertoli cells: nourish spermatogenic cells, carry out phagocytosis, control spermatogenic movement, produce fluid for transport, secrete hormone inhibit-B (controls FSH secretion via neg feedback mech)
Sperm cells in various stages of development are located in spaces between Sertoli cells
Mature sperm are located in the lumen
Spermatogenesis
Starts near basement membrane with germ cells called spermatogonia –undifferentiated (reserve stem cells)
Undergo cell division repeatedly
Therefore, total number of spermatogonia does not change, ensuring that the pool of sperm is never depleted
To become a mature sperm:
- Spermatogonium
- Meiosis I
- Meiosis II
Spermatogonium differentiates to become primary spermatocyte, contains 46 chromosomes (diploid)
Meiosis I: results in two secondary spermatocytes, each with 23 chromosomes (haploid)
Meiosis II: results in four spermatids (haploid), mature sperm’s characteristics have not developed
Transformation of spherical spermatids into elongated sperm
Human Sperm
- head
- neck
- tail
Head: consists of acrosome: (caplike, membrane-bound structure covering the anterior portion of head of sperm; it contains enzyme called spermlysin for penetrating oocyte)
Neck: has a proximal centriole and distal centriole
- Proximal centriole enters into egg during fertilization and starts first cleavage division
- Distal centriole gives rise to the axial filament which forms the tail
Middle piece: has mitochondria
Tail: flagellum - longest part, developed from the distal centriole
Spermatogenesis is initiated through hormonal controls in hypothalamus
(3 hormones)
GnRH (from hypothalamus): increased production at puberty, stimulates secretion of LH and FSH
LH (pituitary gland): stim interstitial cells (Leydig cells) -secrete testosterone (androgens)
FSH (pituitary gland): stim Sertoli cells (secrete inhibit-B) to aid with developmental stages of spermatogenesis
Testosterone
Principal androgen, suppresses LH and GnRH secretion, produces several effects:
Prenatal development
Development of male sexual characteristics
Development of sexual function
Stimulation of anabolism
Released from Leydig cells
Secrete testosterone in abundance during the first trimester of embryonic life (for sexual differentiation of male reproductive structures)
At puberty, testosterone rises again and then declines gradually after middle age
Semen
Combination of sperm and seminal fluid
Alkaline pH – protection from the hostile acidic environment
Survival 48 hrs in female reproductive system
Penile Erection
- spongy tissue
- NO effects
- responses
The penis is composed of 3 spongy cylinders consisting of paired corpora cavernosa and a single corpus spongiosum
Shaft of the human penis filled by components of spongy tissue that expand with blood to make penis stiff
Erotic thoughts/stimuli =release NO (vasodilator—relax smooth muscle in the arteries)
NO from nerve endings initiate erection/moving blood
Flux of moving blood causes further release of NO from endothelial cells
Erection of penis results from flow of the blood into spongy tissue, controlled by (NO)
Sexual stimulation → (NO) from parasympathetic nerves and endothelial cells directly into the penis
NO enters smooth muscle cells and binds to guanylyl cyclase → forming (cGMP)
cGMP → stimulating PKG → decrease Ca2+ influx → relaxes arteries and smooth muscle fibers and dilates of the corpus cavernosum → blood flow =erection
NO released from two principal sources:
erection
- directly from non-cholinergic parasympathetic nerves
- indirectly from the endothelium lining sinusoids and blood vessels in response to cholinergic stimulation
Ejaculation & Emission
Sympathetic impulses leave the spinal cord and pass to genital organs
Two effects:
1) emission begins with contraction of vas deferens and ampulla to release sperm
2) contraction of prostate gland and seminal vesicles expel fluids into the urethra
Fluids mix in urethra with mucus to form semen
Role of testosterone in fetal development
-SRY
SRY on Y chromosome initiates genital ridge cells to differentiate into cells that secrete testosterone
Testosterone stim development of penis, scrotum, prostate gland, seminal vesicles and male genital ducts
Also involved with descent of testes into scrotum
Adult primary & secondary sex characteristics
Distribution of body hair
Baldness
Effect on voice
Increases thickness of skin and contribute to acne
Increases protein formation and muscle development
Increases bone matrix and causes calcium retention
Increased metabolic rate
Increased red blood cells
Effects on electrolyte and water balance
Dihydrotestosterone (DHT)
Made from testosterone by an enzyme called 5-alpha-reductase
DHT plays role in prostate, skin, and hair follicles
DHT can bind to receptors on hair follicles on scalp causing them to shrink which causes hair loss
With too much DHT, a man can develop benign prostate hypertrophy (BPH), aka an enlarged prostate
Medication can treat male pattern hair loss and BPH by inhibiting 5-alpha-reductase
