Male reproductive system Flashcards
The Y chromosome contains which gene that codes for the production of Testis-Determining Factor (TDF)?
SRY (Sex-Determining Region of the Y)
permits differentiation into male sex organs
lack of gene permits differentiation into female sex organs
What happens in male (XY) gender differentiation?
testes develop
testosterone from Leydig cells
Wolffian ducts develop into male genitalia
Müllerian inhibiting factor from Leydig cells
Müllerian ducts degenerate
What are the male reproductive organs?
gonads - testes
internal genitalia - epididymis, vas deferens, accessory glands (seminal vesicles, prostate gland, bulbourethral glands)
external genitalia - scrotum, penis
During the third to fifth months, the cells in the testes differentiate into which three main types of cell?
spermatogonia, Leydig cells, Sertoli cells
What are spermatogonia?
germ cells for sperm formation
What are Leydig cells?
outside seminiferous tubules
produce testosterone which develops male reproductive system by differentiation of Wolffian ducts and common primordial genital tissue
What are Sertoli cells?
produce anti-Müllerian hormone
immature Sertoli cells secrete testosterone and Müllerian-Inhibiting Factor (MIF) to inhibit differentiation of Müllerian ducts into female reproductive system
act as ‘nurse’ cells for germ cells (foetal spermatogonia)
When does the male external genitalia develop?
third and fourth months of gestation
When do the testes begin to descend through the inguinal canal?
6-10 weeks
When do the testes enter the scrotum?
around 28 weeks
What are the functions of the male reproductive system?
testes - to produce the male gametes (sperm) and male hormones (testosterone)
spermatic ducts and accessory glands - to carry sperm through the tubules for activation
penis - to penetrate the female and deposit sperm within the female reproductive system
What are the testes?
reproductive glands which produce sperm
oval in shape
4-5 cm long and 2.5 cm in diameter
produced in abdomen and descend into scrotum
suspended in scrotum by spermatic cord
scrotum hangs outside the body to maintain testes at a temperature 1-2°C lower than core body temperature (optimal temperature for sperm production) and to ensure they are not exposed to intra-abdominal pressure causing sperm to be squeezed out of the testes before maturation
testicular artery, vein and nerve supply enter testes via spermatic cord
What is cryptorchidism?
failure of testes to descend into scrotum
results in infertility if uncorrected
What are the three layers of tissue within the testis?
tunica vaginalis, tunica albuginea, tunica vasculosa
What is the tunica vaginalis?
covers anterior and lateral surfaces of testis
derived from peritoneum with descent of testis
fluid in cavity prevents friction within scrotum
What is the tunica albuginea?
fibrous tissue
covers and creates partitions between seminiferous tubules
connected to the tunica vaginalis and epididymis
What is the tunica vasculosa?
innermost layer of connective tissue
contains blood supply to testis
How many lobules does each testis contain?
200-300
How many seminiferous tubules does each lobule contain?
1-4
Sperm are composed of which three sections?
head, mid-piece, tail (flagellum)
What is the structure and function of the head?
nucleus contains 23 chromosomes
acrosome contains enzymes to penetrate ovum for fertilisation
What is the structure and function of the mid-piece?
contains mitochondria for energy
What is the function of the tail (flagellum)?
to propel sperm through female reproductive tract
How do Sertoli cells support maturation?
provide nutrients to germ cells
remove waste material from germ cells
How are Sertoli cells activated?
by FSH and testosterone
Sertoli cells produce which peptide hormone?
inhibin
What is the function of inhibin?
to inhibit FSH production
to increase spermatogenesis
Why are Sertoli cells stacked tightly together?
to form the blood-testis barrier
germ cells would be attacked by immune system if barrier did not exist as they are genetically different
How do Sertoli cells move sperm cells before ejaculation?
bath them in fluid
this moves sperm cells through the seminiferous tubules to the rete testis (a network of tubules in the testis that carries sperm to the efferent ducts)
in this area, sperm become concentrated and other fluids are reabsorbed
results in infertility if not carried out effectively
What are the functions of testosterone?
promotes male sex organ development
influences libido and sexual behaviour
stimulates metabolism, protein synthesis and muscle growth
stimulates growth of pubic hair, chest hair and reduces scalp hair
increases bone calcium retention and strength
What are the three spermatic ducts?
epididymis, ductus (vas) deferens, ejaculatory ducts
What is the epididymis?
six metre coiled and convoluted tube on the posterior border of the testis
receives sperm entering the head of the epididymis from efferent ducts
sperm are still immature and incapable of fertilising ova at this stage
sperm travel through length of epididymis over 20 days
sperm are stored, protected and remain fertile for 40-60 days in the tail
once fertile, they disintegrate and are reabsorbed by epididymis
What is the ductus (vas) deferens?
40-45 cm long tube
ascends out of scrotum into pelvic cavity via inguinal canal
sperm moves through tube by peristalsis
terminates behind bladder, widens and joins duct of seminal vesicles to become ejaculatory duct
What is the ejaculatory duct?
a short 2 cm duct
passes through prostate gland and merges with urethra
What are the three accessory glands?
seminal vesicles, prostate gland, bulbourethral gland
What are the seminal vesicles?
two blind-ended tubular glands of smooth muscle lined by stratified columnar epithelium
each merge with vas deferens on same side to form ejaculatory duct
secretions (stimulated by testosterone) are stored in lumen of seminal vesicles
during ejaculation, fluid from seminal vesicles is expelled and mixes with fluid from testes and other accessory glands to form semen
What are seminal vesicle secretions?
comprise 60% of semen
alkaline and neutralise acidic pH of vaginal tract in sexual intercourse
What is the prostate gland?
4 cm in diameter
surrounds urethra and ejaculatory duct adjacent to bladder
contains 30-50 tubuloacinar glands inside a fibrous capsule with 20 pores to empty prostatic fluid into urethra
smooth muscles of prostate help expel semen in ejaculation
What is the bulbourethral gland?
produce 10% of seminal fluid to provide lubrication for the head of the penis
protect sperm by alkaline pH which neutralises any acidity of the urethra from residual urine
What is testicular cancer?
one of the most common forms of cancer in younger men
usually affects men between 15 and 49 years
men are encouraged to perform testicular self-examination (TSE) monthly to promote early detection
What is testicular cancer?
one of the most common forms of cancer in younger men
usually affects men between 15 and 49 years
men are encouraged to perform testicular self-examination (TSE) monthly to promote early detection
What are the two functions of the penis?
passage for urine
male sexual organ specialised to deliver sperm into the vagina
urethra carries urine from bladder and transports seminal fluid from ejaculatory duct through penis into vagina
What are the two halves of the penis called?
root - internal attachment to body wall
shaft and glans - external visible components of penis, urethra exits at glans through urethral meatus
What is the function of the loose skin surrounding the shaft?
it permits expansion as an erection occurs during arousal
What is the prepuce (foreskin)?
the skin over the glans where it is attached by a fold of tissue called the frenulum
What is the name of the waxy substance produced from sebaceous glands by the glans and enclosing skin?
smegma
What is the structure of the shaft?
three cylindrical bodies of erectile tissue surrounded by a fibrous sheath (tunica albuginea) and separated by a median septum
corpus spongiosum contains urethra and expands at distal end of penis which fills glans
erectile tissue is highly vascular and contains lacunae that fill with blood in sexual arousal which expands penis
lacunae separated by connective tissue and smooth trabecular muscle (provides muscle tone in erect penis)
What is the structure of the root?
corpus spongiosum attaches to perineal membrane (surrounding muscle of perineum) at the bulb
corpora cavernosa diverge (crura) and attach to pubic arch
Gonadotrophin-releasing hormone (GnRH) from the hypothalamus stimulates the secretion of which two hormones from the anterior pituitary gland?
follicle-stimulating hormone (FSH) and luteinising hormone (LH)
What is the function of FSH in males?
to act on Sertoli cells and stimulate spermatogenesis and secretion of inhibin which acts via negative feedback to reduce FSH secretion from anterior pituitary
this maintains FSH at relatively constant level
What is the function of LH in males?
to stimulate Leydig cells to secrete testosterone
testosterone inhibits secretion of hypothalamic and pituitary hormones via negative feedback which initially cause testosterone secretion
What are the three modes of sexual arousal leading to an erection in males?
psychogenic, reflexogenic, REM sleep induced
What is the psychogenic mode of arousal?
occurs following audiovisual stimuli or sexual thought/fantasy and a resulting emotional reaction
these primarily lead to activation of the bilateral inferior temporal and frontal cortex and the limbic system (insula and cingulate gyrus)
signals are then sent through the spinal cord to spinal nerves (T11-L2 and S2-S4) to the penis via the cavernous nerve where the erectile process is activated
What is the reflexogenic mode of arousal?
stimulation of the male genitalia results in a spinal reflex arc response (bulbocavernosus reflex)
sensory input is sent to the spinal erection centres (T11-L2 and S2-S4)
signals then ascend to the cerebral cortex (sensory perception) and autonomic signals relaying to the cavernous nerve where the erectile process is activated
What is the REM sleep induced mode of arousal?
REM sleep induces increased activity in the pontine reticular formation
this activates cholinergic neurons in the lateral pontine tegmentum
this is thought to initiate signals to the spinal erection centres to induce an erection
What happens during an erection?
smooth muscle of the corpora cavernosa relax
arterioles dilate and arterial blood flow increases
blood is trapped in lacunae, causing erectile tissue to become engorged
penile veins are compressed by the engorged erectile tissue, reducing venous outflow
engorged tissue creates an erection, enhanced by high PO2 and contraction of ischiocavernosus muscles
What are the four stages of sexual response in males and females?
arousal, plateau, orgasm (and male ejaculation), resolution
What happens during the arousal stage in males?
physical or psychological stimulation causes an erection
blood flows into the corpora in penis
penis grows in size
scrotum becomes tighter and testes drawn up towards the body
What happens during the plateau stage in males?
glans of penis widens
blood vessels in and around penis fill, penis grows <50% larger
testes continue to rise
pulse and blood pressure rise, breathing gets faster, thighs and buttocks tighten
What happens during the orgasm stage in males?
contractions in pelvic floor and ductus deferens move sperm, and seminal vesicles and prostate gland add fluid to sperm
semen consists of 5% sperm and 95% fluid
contractions are part of orgasm, and are followed by ejaculation of semen out of penis
What happens during the resolution stage in males?
recovery phase: penis and testes return to normal size
breathing heavily and fast, pulse rate high, sweating
recovery period of minutes to hours before another orgasm - gets longer with increasing age
What happens during intercourse?
the male inserts his erect penis into the woman’s vagina
arousal continues in both sexes to orgasm and ejaculation of semen into the vagina
contractions of pelvic and vaginal muscles help sperm to enter uterus from where some will enter Fallopian tube and one will fertilise an ovum
What is an orgasm?
a psychophysiological response
connected with rhythmic bodily contractions, erogenous stimulation, and emotional response to the sexual experience
provides the pleasurable, whole-body sensation that makes sexual experiences attractive to people
coordination of simultaneous orgasm and ejaculation in the male is central to effective reproduction
What happens when an erection subsides (detumescence)?
smooth muscle of corpus cavernosa contract, reducing arterial flow
this initially slowly reduces pressure in erectile tissue and venous outflow is slowly restored
this is followed by a rapid reduction in pressure and full restoration of venous return
What happens during ejaculation?
glans contains encapsulated receptors (Krause-finger corpuscles) and free nerve endings that are stimulated by sensations in the penile shaft, perineum and testes
these peripheral sensory inputs relay to the spinal cord where spinal thoracolumbar and lumbosacral nuclei are innervated
this leads to efferent stimulation of the accessory sexual glands, smooth muscles of the spermatic ducts, and striated muscles of the urethral sphincter
the intensity of the stimuli causes ejaculation
What are the two phases of ejaculation?
emission and expulsion
What happens during the emission phase?
an autonomic reflex contraction occurs in the spermatic ducts, seminal vesicles and prostate
this results in semen being collected in the prostatic urethra
the urethral bulb expands which increases intra-urethral pressure
some seminal fluid is released prior to expulsion, particularly from the bulbourethral glands and prostate
What happens during the expulsion phase?
the striated sphincter muscle of the urethra relaxes
semen is propelled along the urethra by the cyclic contraction of the urethral smooth muscle and the muscles at the base of the penis
What happens after ejaculation?
recovery period occurs
this prevents any further ejaculation for minutes to hours
