male reproductive Flashcards
Primary sex organs and accessory reproductive organs
Primary sex organs (gonads) - testes and ovaries
- Produce gametes (sex cells ) – sperm & ova
- Secrete steroid sex hormones
- Androgens (males)
- Estrogens and progesterone (females)
Accessory reproductive organs - ducts, glands, and external genitalia
role of sex hormones
- Development and function of reproductive organs
- Sexual behavior and drives
- Growth and development of many other organs and tissues
Testes
w/in scrotum
make sperm
sperm goes thru epididymis –> ductus deferens –> ejaculatory duct –> urethra
male accessory glands
seminal glands
prostate
bulbo-urethral
empty secretions into ducts during ejaculation
Scrotum
sac of skin and superficial fascia
-hangs outside abdominopelvic cavity
Contains paired testes
- 3 C colder than core body temp
- lower temp necessary for sperm production
Temp kept constant by:
- dartos muscle = smooth muscle which wrinkles scrotal skin and pulls scrotum close to body
- cremaster muscles = bands of skeletal muscle that elevate testes
Testes tunics and lobules
Each surrounded by two tunics
- Tunica vaginalis – outer layer derived from peritoneum
- Tunica albuginea – inner layer; fibrous capsule
Septa divide testis into ~250 lobules, each containing 1–4 seminiferous tubules - site of sperm production—about ½ mile of seminiferous tubules
Testicular Torsion
MEDICAL EMERGENCY
Must be corrected within 2 hours to save the testes
path of sperm inside the testes
sminiferous tubules –> straight tubule –> rete testis –> efferent ductules –> epididymis
Seminiferous tubules: interstitial cells
Interstitial endocrine cells (Leydig cells) in soft tissue surrounding seminiferous tubules
Produce androgens (e.g. testosterone) and secrete it into interstitial fluid
Blood supply to the testes
Testicular arteries arise from abdominal aorta
Testicular veins arise from pampiniform venous plexus surrounding each testicular artery
- Cooler; absorb heat from testicular arteries
- Keep testes cool
Spermatic cord encloses nerve fibers, blood vessels, and lymphatics that supply testes
external genitalia
scrotum and penis
Penis parts
root and shaft that ends in glans penis
prepuce/foreskin = cuff of loose skin covering glans
Crura = proximal ends of corpora cavernosa surrounded by ischiocavernosus muscle; anchors penis to pubic arch
Circumcision
Surgical removal of foreskin
60% newborn boys in US circumcised
15% in other parts of world
Some claim medically unnecessary
Studies show
- 60% reduction in HIV risk
- Reduced risk for other reproductive system infections like HPV
Penis: Internally
Spongy urethra and three cylindrical bodies of erectile tissue (spongy network of CT and smooth muscle with vascular spaces)
Corpus spongiosum surrounds urethra and expands to form glans and bulb
Corpora cavernosa = paired dorsal erectile bodies
Erection = erectile tissue fills with blood causing penis to enlarge and become rigid
Epididymis
head, body, tail
duct
sperm flow
Head - contains efferent ductules; superior aspect of testis; body and tail on posterolateral area of testis
Duct of the epididymis ~ 6 m in length
-Microvilli (stereocilia) absorb testicular fluid and pass nutrients to stored sperm
Nonmotile sperm enter, pass slowly through (~ 20 days), become motile; can be stored several months
During ejaculation epididymis contracts, expelling sperm into ductus deferens
Ductus Deferens and ejaculatory duct
Ductus deferens (vas deferens) ~ 45 cm
Passes through inguinal canal to pelvic cavity
Expands to form ampulla; joins duct of seminal vesicle to form ejaculatory duct
Smooth muscle in walls propels sperm from epididymis to urethra
Vasectomy
cutting and ligating ductus deferens; nearly 100% effective form of birth control. Must give time for any remaining sperm in the ducts to die.
urethra
Conveys both urine and semen (at different times)
Has three regions
- Prostatic urethra – surrounded by prostate
- Intermediate part of the urethra (membranous urethra) – in urogenital diaphragm
- Spongy urethra – runs through penis; opens at external urethral orifice
Seminal Glands
On posterior bladder surface; smooth muscle contracts during ejaculation
Produces viscous alkaline seminal fluid
- Fructose, citric acid, coagulating enzyme (vesiculase), and prostaglandins
- Yellow pigment fluoresces with UV light
- 70% volume of semen
Duct of seminal gland joins ductus deferens to form ejaculatory duct
Prostate
Encircles urethra inferior to bladder; size of peach pit; smooth muscle contracts during ejaculation
Secretes milky, slightly acid fluid
- Contains citrate, enzymes, and prostate-specific antigen (PSA)
- Role in sperm activation
- Enters prostatic urethra during ejaculation
1/3 semen volume
Bulbo-urethral glands (cowper’s glands)
pea-sized glands inferior to prostate
make thick, clear mucus during sexual arousal
- lubricate glans penis
- neutralize traces of acidic urine in urethra
Semen contents
Milky-white mixture of sperm and accessory gland secretions
2–5 ml semen ejaculated, contains 20–150 million sperm/ml
Contains fructose for ATP production; protects and activates sperm; facilitates sperm movement
Alkaline neutralizes acidity of male urethra and female vagina enhanced motility
Semen functions
Prostaglandins decrease viscosity of mucus in cervix; stimulate reverse peristalsis in uterus
Contains ATP for energy
Suppresses female immune response
Antibacterial action
Clotting factors coagulate semen initially to prevent draining out; then liquefied by fibrinolysin sperm begin journey
Erection: what happens
Arterioles normally constricted
Sexual excitement causes CNS activation of parasympathetic neurons
nitric oxide (NO) release local vascular smooth muscle relaxation
arterioles dilate corpora cavernosa expands, retards venous drainage
engorgement of erectile tissues with blood
enlargement and stiffening of penis
Initiation of erection
and protection of penis during
Initiated by sexual stimuli
-Touch; mechanical stimulation of penis; erotic sights, sounds, and smells
Can be induced or inhibited by emotions or higher mental activity
Longitudinal and circular collagen fibers around penis prevent kinking/buckling of erect penis
Corpus spongiosum keeps urethra open
Ejaculation
Propulsion of semen from male duct system
Sympathetic spinal reflex
- Bladder sphincter muscle constricts, preventing expulsion of urine
- Ducts and accessory glands contract and empty their contents
- Bulbospongiosus muscles undergo rapid series of contractions expulsion of semen at ~ 500 cm/s (close to 11 mph)
Ejaculatory event – orgasm
HTG axis
Hypothalamus: Gonadotropin releasing hormone (GnRH)
- Simulates release of hormones from anterior pituitary that regulate function of testes
- Pulsatile release to produce stable FSH + LH levels
Anterior pituitary:
Follicle stimulating hormone (FSH)
Luteinizing hormone (LH)
Testes:
Testosterone (T)
Inhibin
-both have negative feedback on hypothalamus and ant. pituit.
Actions of FSH and LH
FSH causes sustenocytes (sustenacular cells/ Sertoli cells) to release androgen binding protein (ABP) –> binds testosterone and keeps it near spermatogenic cells for spermatogenesis
LH prods interstitial endocrine cells (Leydig) to secrete testosterone for spermatogenesis
Testosterone and Inhibin
- when is inhibin released?
Testosterone = sex organ maturation, development/maintenance secondary sex characteristics, libido
Rising testosterone levels –> feedback inhibition on hypothalamus
Inhibin released when sperm count is high –> inhibits GnRH and FSH
Development of HPG axis
takes 3 years to achieve balance, then testosterone and sperm porduction is fairly stable throughout life
Without GnRH and gonadotropins, testes atrophy; sperm and testosterone production cease
Male secondary sex characteristics
Features induced in NONREPRODUCTIVE organs by male sex hormones
- pubic, axillary, and facial heair
- chest hair
- deep voice
- skin thickens and becomes oily
- skeletal muscles increase in size and mass
- bones grow and increase in density
- boosts BMR
- basis of sex drive in males
Testosterone in embryo
masculinizes embryonic brain
continues to exert effect well into adulthood
adrenal glands produce androgens in small amounts– insufficient to maintain normal testosterone-mediated functions
spermatogenesis
sperm (spermatozoa) production in seminiferous tubules
Spermatogenic cells give rise to sperm
- mitosis of spermatogonia (stem cells) forms 2 spermatocytes
- meiosis: spermatocytes –> secondary spermatocytes –> spermatids
- spermiogenesis = spermatids become sperm
functions of meiosis
halve the number of chromosomes
introduce genetic diversity
Mitosis of spermatogonia
Spermatogenesis begins at puberty
Spermatogonia = stem cells in contact with epithelial basal lamina
-each mitotic division = one type A daughter cell and one type B daughter cell
Type A cells maintain germ cell line at basal lamina
Type B cells move toward lumen and develop into primary spermatocytes
Meiosis: spermatocytes to spermatids
Meiosis I
-primary spermatocytes (2n) –> two secondary spermatocytes (n)
Meiosis II
- each secondary spermatocyte (n) –> two spermatids (n)
- Spermatid = small, nonmotile cells close to lumen of tubule
Spermatids to sperm
Spermatids
-correct chromosome number (n), but nonmotie
Spermiogenesis
-spermatids elongate; lose excess cytoplasm; form a tail –> spermatozoon (sperm)
Sperm major regions
Head = genetic region; nucleus and helmet-like acrosome containing hydrolytic enzymes that enable sperm to penetrate egg
Midpiece = metabolic region; mitochondria –> ATP to move tail
Tail = locomotor region; flagellum
Role of sustentocytes (sertoli cells)
Extend through wall of tubule and surround developing cells
Provide nutrients and signals to dividing cells
Move cells along to lumen
Secrete testicular fluid into lumen for sperm transport
Phagocytize faulty germ cells and excess cytoplasm
Produce chemical mediators to regulate spermatogenesis
two compartments of sustentocytes
Tight junctions divide tubule into two compartments:
Basal compartment: spermatogonia and early primary spermatocytes
Adluminal compartment: meiotically active cells and tubule lumen
Blood testis barrier
tight junction bt sustentocytes form this barrier
- prevents sperm antigens from escaping into blood –> activation of immune system
- important: sperm not formed until puberty - absent during immune system development, would not be recognized as self
How long does spermatogenesis take?
What pushes immotile sperm into epididymis?
takes 64-72 days if conditions are hospitible
Pressure of testicular fluid pushes the sperm –> THEN they get their motility and fertilizing power
