deck_17046748 Flashcards
Male reprodutive system
..
functions of male reproductive system
1) gonads produce gametes
2) gonads produce hormones
male gametes are
sperm
male reproductive structure include
external genitalia
internal genitalia
external genitalia
1) penis
2) urethra
3) scrotum
penis contains
erectile tissue
penis is responsible for depositing ___ into ___
deposits sperm into vaigna
urethra, conducts ___ to ___
conducts SEMEN to exterior
urine(?)
scrotum function
surrounds and supports the testes
IMPORTANT NOTE ABOUT SCROTUM:
—> scrotum
= SKIN
= DARTOS mm
= SUPERFICIAL FASCIA
NOT PART OF SCROTUM:
= cremaster mm
= tunica vaginalis
= tunica albuginea
ANOTHER IMPORTANT NOTE:
epididymis is distinct from TESTES
internal genitalia
1) testes
2) epididymis
3) ductus deferens (vas deferens)
4) seminal gland (seminal vesicles)
5) prostate
6) bulbo-urethral glands
testes function
produce sperm and hormones
epididymis function
the site of sperm MATURATION
vas deferens
passage that conducts sperm between…
A) EPIDIDYMIS
and c) PROSTATE
via B) EJACULATORY DUCT
(vas deferens and seminal vesicle merge into the ejaculatory duct)
—- NOTE THAT vas deferens doesn’t really go through seminal vesicle
—-> RATHER, the seminal vesicle JOINS with the AMPULLA of the Vas deferens to go to the PROSTATE, via the EJACULATORY DUCT
seminal gland/vesicle funciton
secretes fluids that make up majority (90%) of semen
prostate function
fluids and enzymes
fluids from prostate vs fluids from seminal vesicles
Secretions from the seminal vesicles make up about 60 percent of the volume of the semen
with most of the remainder coming from the prostate gland.
The sperm and secretions from the bulbourethral gland contribute only a small volume.
chemical properties of seminal vesicle fluids vs prostate fluids
Prostatic fluid is slightly acidic, but other components of semen make it alkaline overall.
This is to counteract the acidity of the vagina and protect the sperm from damage.
bulbourethral glands function
secretes fluids that lubricate the tip of the penis
glans etymology
acorn
bulbourethral glands also known as
Cowper’s glands
where does pre-ejaculate (pre-cum) primarily come from?
The Cowper’s gland is the main source of the pre-ejaculate fluid.
It is situated below the prostate and is also called the bulbourethral gland.
what is the function of pre-ejaculate?
It produces an alkaline, mucus-like fluid during sexual stimulation.
Pre-ejaculation fluid neutralizes the acidity in the urethra.
PATH OF SPERM
..
where sperm made?
Made in the testes (in LOBULES OF TESTES)
Moved to the epididymis
Then along the ductus (vas) deferens
Then along the ejaculatory duct to the urethra
SCROTUM
Cutaneous outpouching of the abdomen that houses and supports the testes
scrotal septum
Scrotal septum separates right and left cavities
—> Marked by a raised thickening (RAPHE OF SCROTUM) in the scrotal surface
the perineal raphe (raphe of scrotum) – function
The perineal raphe joins your internal septum with your scrotum.
(The scrotal septum divides the scrotal sac into two parts.)
Dartos etymology
Derived from the Greek δέρνω/derno (beat, flog) and/or δέρμα/derma (skin), meaning “that which is skinned or flayed”, possibly due to its appearance.
dartos muscle vs dartos fascia
The dartos muscle is the thin rugated fascial muscle of the scrotum made of smooth muscle. Hence it is also referred to as dartos fascia or simply the dartos.
It forms from the subcutaneous tissue of the scrotum and base of the penis and attaches to the scrotal skin and fibrous midline septum between the testes.
NOTE:
THIS MAY BE INCORRECT AS OTHER DIAGRAMS INDICATE THAT DARTOS FASCIA IS IN THE PENIS (SUPERFICIAL FASCIA OF PENIS) AND IS DIFFERENT FROM DARTOS MM IN SCROTUM
dartos fascia is continuous with
scrotal septum
—> continuous in the sense that they are the same tissue (?)
—-> appears that way in diagram
IMPORTANT NOTE ABOUT SCROTUM:
—> scrotum
= SKIN
= DARTOS mm
= SUPERFICIAL FASCIA
NOT PART OF SCROTUM:
= cremaster mm
= tunica vaginalis
= tunica albuginea
ANOTHER IMPORTANT NOTE:
epididymis is distinct from TESTES
dartos muscle
part of or interchangeable term vs dartos fascia (?)
Smooth muscle in the skin of the scrotum
dartos muscle function
Elevates testes and contracts the scrotum (reduces heat loss)
CREMASTER MUSCLE
Contracts to pull testes closer to body during sexual arousal or when exposed to cold temperature
DARTOS mm vs CREMASTER mm:
“The Cremaster and Dartos muscles work together to maintain the temperature of the testicles which is responsible for spermatogenesis. The Cremaster Muscle also prevents injuries during sex, and moments of fear and flight. The Dartos Muscle is responsible for mobility, and blood supply to penile skin.”
why do the testicles need to be pulled closer to body during sexual arousal?
The cremaster muscle is an involuntary muscle and contraction can occur during arousal which can prevent injury to the testicles during sexual intercourse.
(Contraction also occurs during orgasm and ejaculation.)
chatgpt’s logic about why testicles need to be closer to body during sexual arousal
(could have errors)
“This reflex helps regulate the temperature of the testicles, keeping them at an optimal temperature for sperm production and health. The closer position during arousal can also enhance sensitivity and may help prepare the body for ejaculation. This physiological response is part of the overall changes that occur in the body during sexual excitement.”
scrotuma nd associated structures
..
spermatic cord
a bundle of nerves, ducts, and blood vessels connecting the testicles to the abdominal cavity.
Extend through the inguinal canals between testes and abdominopelvic cavity
spermatic cord contains layers of fascia and muscle enclosing …
ductus deferens
blood vessels (testicular artery and veins)
Nerves
lymphatic vessels
superficial (external) inguinal ring
Entrance to the INGUINAL CANAL
The superficial or external ring is the terminal end of the inguinal canal. It is located just superior to the pubic tubercle.
The superficial ring has a triangular shape that is made by fibers of the external oblique muscle.
the testes (sing. testis/testicle)
5 cm long; 3 cm wide; 2.5 cm thick
Each weighs 10 – 15 g
testes formation during fetal development
Form inside the body cavity adjacent to the kidneys
Late in fetal development (~ 7 months), connective tissue band contracts
Pulls each testis through abdominal musculature into the scrotum
tunica vaginalis of the testes
1) parietal layer of the tunica vaginalis
2) visceral layer of the tunica vaginalis
3) tunica albuginea of the testes
about the tunica vaginalis of the testes
serous membrane derived from peritoneum partially covers testes
recall – what do all serous membranes have in common?
(which also occurs at the tunica vaginalis)
Just like other serous membrances, fluid can collect here
what is it called when fluid (excess fluid?) forms in the tunica vaginalis of the testes
Called a HYDROCELE
“Hydrocele is the type of scrotal swelling that occurs when fluid collects in the thin sheath that surrounds the testicle.”
hydrocele prognosis
Simple hydroceles in children often go away without surgery. In adults, hydroceles usually do not go away on their own. If surgery is needed, it is an easy procedure with very good outcomes. After surgery, a hydrocele can sometimes reoccur.
tunica albuginea of the testes
dense, white, irregular CT capsule, deep to tunica vaginalis
Extends inward to form many septa, which form 200-300 LOBULES
each (of the 200-300) lobules of the testes are filled with …
2 or 3 SEMINIFEROUS TUBULES
seminiferous etymology
semen – seed
iferous – “having, bearing, or containing (a specified thing).” (ferous)
what is the function of the SEMINIFEROUS TUBULES
This is where spermatogenesis happens
**
“Seminiferous tubules are structures located inside the male testes. They consist of a network of tubes composed of unique cells known as sertoli cells. The seminiferous tubules are the site where meiosis, or the production of sex cells, takes place.”
order of layers of scrotum
1) SKIN
2) DARTOS mm
3) SUPERFICIAL FASCIA
= AKA SCROTUM
4) CREMASTER mm
5) TUNICA VAGINALIS
6) TUNICA ALBUGINEA (forming septa testis)
7) seminiferous tubules (within the septa tesis of tunica albuginea)
—> which join via/w/ RETE TESIS –> efferent ductules –> Epididymis
rete testis etymology
rete = netwrok
rete testis function
A network of small tubes in the testicle that helps move sperm cells (male reproductive cells) from the testicle to the epididymis.
cells of the seminiferous tubules
3 cell types
The seminiferous epithelium that lines the tubules consists of three cell types:
1) spermatogonia, which are stem cells
2) spermatocytes, which are in the process of becoming mature sperm cells (after becoming spermatids)
(also technically a fourth type? –> spermatids)
3) Sertoli cells, which nurture developing sperm and secrete a variety of products into the blood and the lumina of seminiferous tubules.
what about the spaces between the seminiferous tubules
Spaces between tubules contain:
1) Areolar tissue
2) Blood vessels
3) Leydig cells (Large interstitial endocrine)
1) areolar tissue (between seminiferous tubules)
FUNCTION
Provides a protective framework that keeps major structures in place and offers support. Contains mast cells that help prevent infection. The areolar tissue is also dense with collagen fibres, which makes it strong and rigid.
3) Leydig cells (interstitial endocrine cells) function
Produce androgens, such as testosterone and androstenedione (dominant sex hormones in males)
Sertoli cells of seminiferous tububles
aka
Nurse cells
or Sustentacular cells
function of sustentacular cells
extend from basement membrane to lumen of seminiferous tubule
protect, support, nourish developing sperm
phagocytize excess SPERMATID cytoplasm
produce fluid for sperm transport (probably small amount compared to seminal vesicles & prostate)
spermatids
“one of the haploid cells that are formed by the second meiotic division of a spermatocyte and that differentiate into spermatozoa compare ootid”
sustentacular (Sertoli or nurse) cells also …
release sperm into lumen
release INHIBIN (hormone)
form BLOOD-TESTIS BARRIER
inhibin function
Inhibin is a protein secreted by the Sertoli cells in men and by the granulosa cells in women.
It inhibits the synthesis and release of the follicle-stimulating hormone in the pituitary gland and reduces the hypothalamic LH - releasing hormone content.
“a gonadal hormone which inhibits the secretion of follicle-stimulating hormone, under consideration as a potential male contraceptive.”
follicle stimulating hormone (FSH) function
It triggers the growth of eggs in the ovaries and gets the eggs ready for ovulation. Ovulation is when an ovary releases an egg so it can travel down a fallopian tube where it can be fertilized by sperm. In men, FSH helps control the amount of sperm that the testicles (testes) make.
blood testis barrier function
isolate developing gametes from blood
prevents immune response from developing against spermatogenic cells’ surface antigens b/c they are “foreign”
three other cell types of the seminiferous tubules (technically just sperm cells at various stages of development)
The walls of the seminiferous tubules also contains the developing sperm cell at different stages of development:
A) Spermatogonia (stem cells)
B) Spermatocytes (undergoing meiosis)
C) Spermatids (undergoing spermiogenesis)
—> Develop into mature sperm
what is SPERMIATION
Process in which a sperm loses attachment to the nurse cell (sustentacular cell) and enters the tubule lumen
spermatogenesis
The development of sperm
Complete maturation takes 65-75 days
Millions of sperm produced per day
4 basic steps of spermatogenesis
1) Creation of many SPERMATOGONIUM through mitosis
2) MEIOSIS to create gametes
3) SPERMIOGENESIS to create functional sperm
4) SPERMIATION
1) Creation of many spermatogonium through mitosis
Primordial germ cells migrate from yolk sac to testes in 5th week gestation (fetus)
Differentiate into spermatogonia & remain dormant until puberty
At puberty, spermatogonium undergo mitosis
spermatogonia cell features
diploid cells
stem cells that undergo mitosis
where can spermatogonia stay?
some stay near BASEMENT MEMBRANE of seminiferous tubule for future cell divisions and sperm production
some squeeze through tight junctions to other side of blood-testes border and differentiate into PRIMARY SPERMATOCYTES
blood testis barrier location
The blood-testis barrier (BTB) is located at the border between BASAL and APICAL compartments of the seminiferous epithelium.
2) MEIOSIS to create gametes
Primary spermatocytes
—> Diploid
—> Undergo meiosis I
—> Results in 2 secondary spermatocytes
Secondary spermatocytes
—> Haploid
—> Undergo meiosis II
—> Results in 4 spermatids
recall haploid vs diploid cells
A haploid cell has only a single set of chromosomes. Most cells in humans are diploid rather than haploid, meaning they have two copies of each chromosome.
3) Spermiogenesis to create functional sperm
Spermatids undergo spermiogenesis
no cell division, spermatid changes into sperm
cell changes shape from spherical to elongated
forms acrosome (cap) & flagellum (tail)
mitochondria multiply
Takes 24 days for spermatids to mature
4) SPERMIATION
Spermiation is when sperm cells are released from sustentacular cell connections into the lumen of seminiferous tubules
how do the newly formed sperm move?
sperm are not yet able to swim, so fluid in tubule pushes them toward ducts of testes
which fluid?
sustentacular cells produce fluid for sperm transport
structure of sperm
60µm (micrometres)
Specialized to deliver chromosomes to female gamete
—> Lacks most organelles and intracellular structures in order to reduce size and mass
sperm head
4-5µm long
nucleus with 23 chromosomes
ACROSOME:
cap filled w proteins (hyaluronidase & proteases) to penetrate ovum
sperm neck
Contains both centrioles of the original spermatid
Microtubules of distal centriole are continuous with those of the middle piece and tail
sperm middle piece
Contains mitochondria to provide ATP for tail movement
sperm tail (flagellum)
Whiplike organelle that moves the sperm
capacitation
Sperm released from testes are physically mature
—> But immobile and incapable of fertilizing an oocyte
Other parts of male reproductive system are responsible for functional maturation, nourishment, storage, and transport of spermatozoa
capacitation is
Capacitation is the process enabling sperm to become motile and fully functional
capacitation usually occurs in two steps
1) Sperm become motile when mixed with SEMINAL GLAND secretions
2) Sperm become capable of fertilization when exposed to the female reproductive tract
when do sperm become motile
when mixed with SEMINAL GLAND secretions
when do sperm become capable of fertilization?
when exposed to the female reproductive tract
recap of sperm
Sperm moves to the penis through the reproductive tract:
1) Epididymis
2) Ductus deferens
3) Ejaculatory duct
4) Urethra
Along the way, three glands add to moving sperm:
1) Seminal glands (vesicles)
2) Prostate gland
3) Bulbo-urethral glands
EPIDIDYMIS
…
epididymis is considered the start of…
Start of the male reproductive tract
epididymis is a …
Coiled tube bound to posterior border of each testis
epididymis is lined with
Lined with PSEUDOSTRATIFIED COLUMNAR EPITHELIUM
STEREOCILIA of pseudostratified columnar epithelium
long stereocilia that increase surface area
“branching microvilli that increase surface area for reabsorption of degenerated sperm that were stored & not ejaculated”
are stereocilia actually cilia?
no
more closely related to microvilli (but still distinct):
“They are distinct from cilia and microvilli, but are closely related to microvilli.”
what do sperm do in the epididymis?
Sperm undergo functional maturation here and storage (up to a month)
epididymis regions
A) head
B) body
C) tail
head of epididymis
Receives spermatozoa from EFFERENT DUCTULES
efferent ductules define
Efferent ductules (ductuli efferentes) are small, highly convoluted and delicate tubules that connect RETE TESTIS cavities with the head of the epididymis
body of the epididymis
Extends inferiorly along the posterior surface of the testis
tail of the epididymis
Starts near the inferior border of the testis
Number of coils decreases here
tail of the epididymis connects with the
with the ductus deferens (VAS DEFERENS)
epididymis histology
1) lined with pseudostratified ciliated columnar epithelium
2) layer of smooth muscle
pseudostratified ciliated (?) columnar epithelium
–> not actually ciliated (?)
—-> just stereocilia (?) – I.e. similar to structure of micovilli
what does layer of smooth muscle in the epididymis do?
propels sperm onward w peristaltic contractions during sexual arousal
the Ductus (Vas) deferens function
Stores sperm and propels them toward the urethra during ejaculation
how long can epididymis store sperm?
Can store sperm for several months before they degenerate
pathway of VAS DEFERENS
ascends along posterior border of epididymis
passes up through spermatic cord and inguinal ligament (goes above inguinal lig)
reaches posterior surface of urinary bladder
—> Joins ducts of seminal vesicles to form ejaculatory duct
where does the ejaculatory duct deposit?
empties into prostatic urethra
(portion of the urethra inside the prostate)
vas deferens histology
1) lined with pseudostratified columnar epithelium
—> (same as epididymis?)
2) covered with heavy coating of muscle
what does vas deferens do?
convey sperm through peristaltic contractions
—> seems to have same function as epididymis
ejaculatory ducts
union of seminal vesicle ducts & ducti deferens
eject spermatozoa into the prostatic urethra
Urethra
shared terminal duct of the reproductive and urinary systems
passageway for semen and urine
portions of urethra (3)
1) prostatic urethra
2) membranous urethra
3) spongy (cavernous)
membranous vs spongy urethra
The second part, a short region that penetrates the pelvic floor and enters the penis, is called the membranous urethra.
The third part, the spongy urethra, is the longest region.
seminal glands (vesicles) –> position
Sandwiched between the posterior wall of the urinary bladder and the rectum
(same position as AMPULLA of VAS DEFERENS)
how is fluid secreted from seminal vesicles?
what is secreted?
Secretion ejected by smooth muscle lining gland
—> alkaline: neutralizes vaginal & male urethral acid
—> fructose: sperm ATP production
—> Prostaglandins: motility and viability
—> Stimulates flagellum movement in sperm
sperm contact with seminal vesicles secretions is the first step in …
First step of capacitation
###
recall steps:
1) Sperm become motile when mixed with SEMINAL GLAND secretions
2) Sperm become capable of fertilization when exposed to the female reproductive tract
seminal vesicles fluid produce __% of semen volume
60 % of semen volume
PROSTATE GLAND
Encircles the proximal urethra as it leaves the bladder
Roughly the size of a golf ball
prostate gland secretions contain:
1) seminalplasmin
2) proteolytic enzymes to liquefy semen:
3) citric acid
1) seminalplasmin
Antibiotic that may help prevent urinary tract infections in males
2) proteolytic enzymes to liquefy semen:
prostate-specific antigen (PSA), pepsinogen, lysozyme, amylase, and hyaluronidase
3) citric acid
sperm ATP production
proteolysis
Proteolysis is the breakdown of proteins into smaller polypeptides or amino acids.
prostate gland produces what percentage of remaining semen volume?
Produces 20–30 % of semen volume
bulbo-urethral glands (Cowper’s glands)
Located at the base of the penis
–> inferior/adjacent to prostate
Duct of each gland empties into the urethra
bulbo-urethral glands release …
Secrete thick, alkaline mucus (PRE-EJACULATE)
—> Helps neutralize acids in the urethra
—> Also lubricates the tip of the penis
semen contains
contains sperm and seminal fluid
seminal fluid is from
Seminal fluid is from accessory glands
—> seminal vesicles
—> prostate
—> Cowper’s gland
Semen is
slightly alkaline, milky appearance
2.5 to 5 ml released per ejaculation
normal sperm count is 50 to 150 million/ml
how long does it take semen to coagulate after ejaculating
does it re-liquify
Once ejaculated, semen coagulates w/in 5 minutes
—> (via) clotting proteins from seminal vesicles
after 10-20 mins, semen re-liquifies
—> (via) PSA (prostate specific antigen) and proteolytic enzymes from prostate gland
why does coagulation/re-liquification occur?
This occursto protect sperm cells from the acidic vaginal environment
Functions of the penis (two functions)
1) Conducts urine to the exterior
2) Introduces semen into the vagina during sexual intercourse
regions/structures of the penis
Root of the penis
Body (shaft) of penis
Glans (head) of penis
root of penis
Fixed portion that attaches the penis to the body wall just inferior to the pubic symphysis
—> CRURA attach to pubo-ischial junction (ischiopubic rami)
—> BULBS “attached to the perineal membrane that extends from the perineum, the area between the scrotum and anus.”
Bulb of root of penis
expanded, posterior continuation of corpus spongiosum
crura of root of penis
2 separated, tapered portions of corpora cavernosa
body (shaft) of penis
Tubular, movable
portion of the organ
Glans penis (head)
Expanded distal end that surrounds the external urethral orifice
Neck of glans
Narrow portion between the shaft and the glans
Erectile tissue
..
The body is composed of three erectile tissue masses:
Corpora cavernosa
Two cylindrical masses on the dorsal surface of the penis
Corpus spongiosum
Surrounds the penile urethra
Expands at the tip of the penis to form the glans
erectile tissue is…
Three-dimensional network with vascular spaces (sinusoidal spaces)
sinusoidal spaces
The substance of the corpora cavernosa (erectile tissue) consists of numerous sinusoids (lacunar spaces) among interwoven trabeculae of smooth muscles and supporting connective tissue.
The corpora cavernosa sinusoids are widely communicative and larger in the center of the corpora, having a Swiss-cheese appearance.
corpus spongiosum sinusoidal spaces
The structure of the corpus spongiosum is similar to that of the corpora cavernosa, except that the sinusoids are larger and a much thinner …
in resting non aroused state…
In the resting state, arterial branches are constricted, and muscular partitions are tense (restricts blood flow into the erectile tissue)
erection
“Each sinusoid contains endothelial cells, smooth muscle cells and blood flow into the sinusoids leads to their expansion which is necessary for erection.
Subsequently to the erection, the sinusoidal blood flows through tunica albuginea to venous system and to the dorsal vein which leads to the penile flaccid status.”
helicine arteries
“The cavernous artery supplies the corpora cavernosa and branches into helicine arteries throughout the length of each corporal body. The helicine arteries supply the trabecular tissue and sinusoids of the erectile chambers. In the flaccid state, the helicine arteries are tortuous and constricted.”
emissary veins
“Emissary veins begin within the erectile tissue of the corpora cavernosa and course through the tunica albuginea and drain into the circumflex or deep dorsal veins. The circumflex veins arise from the spongiosum, ventrum of the penis, and often, the emissary veins drain into them.”
emissary = from Latin emissarius ‘scout, spy’, from emittere ‘send out’ (see emit).
does corpus spongiosum also have a tunica albuginea of its own?
note that one diagram didn’t show a tunica albuginea on the corpus spongiosum, whereas another one did.
ANOTHER SOURCE:
“The corpus spongiosum possesses a much thinner and more elastic tunica albuginea to allow for distention of the corpus spongiosum for passage of …”
Phases in the male sexual response
Arousal
Erotic thoughts or stimulation of sensory nerves in the genital region increase parasympathetic stimulation through pelvic nerves
what causes arterial dilation?
Release of nitric oxide causes arterial dilation
what happens with NO release
Blood flow increases, engorging vascular channels
veins become compressed, and blood is trapped
Erection of the penis occurs
Emission or ejaculation caused by
Caused by sympathetic activation
ejaculation begins with
Begins with peristaltic contractions in the ampullae of the ductus deferens
—> Pushes sperm into the prostatic urethra
Contractions continue in the seminal glands and prostate
Secretions from these glands mix with sperm to form semen
Impotence, or erectile dysfunction (ED)
Inability to achieve or maintain an erection
various causes of ED
Vascular changes (e.g., low blood pressure)
Interference with neural commands
Psychological factors (depression, anxiety)
how do medications that facilitate erection work?
Medications (e.g., Viagra and Cialis) temporarily inactivate enzymes that oppose nitric oxide (NO)
—> Small amounts of NO can then produce erection
Hormones and the Male Reproductive System
..
Hormonal Regulation via
Hypothalamus
Anterior lobe of the pituitary
hypothalamus
Secretes gonadotropin-releasing hormone (GnRH)
—> Released at a steady rate and pace
Targets the anterior lobe of the pituitary gland
Anterior lobe of the pituitary
Responds by producing two gonadotropins:
–> Luteinizing hormone (LH)
–> Follicle-stimulating hormone (FSH)
Luteinizing hormone (LH)
Targets the interstitial cells of the testes (Leydig Cells)
—> Interstitial cells secrete testosterone and other androgens
how are testosterone levels regulated
Testosterone levels are regulated by negative feedback
—> High testosterone level inhibits release of GnRH
Follicle-stimulating hormone (FSH)
Targets nurse cells of seminiferous tubules
recall nurse cells (Sertoli/Sustentacular cells)
Promote spermatogenesis and spermiogenesis
Secrete androgen-binding protein (ABP)
—> Binds testosterone and keeps in area of developing sperm
—> Stimulates maturation of spermatids
Secrete inhibin
—> Inhibits FSH
—> Provides feedback control of spermatogenesis
Testosterone
principal androgen
synthesized from cholesterol
Released by interstitial cells (Leydig cells)
lipid soluble
—> moves from interstitial cells, to interstitial fluid, to blood
testosterone is controlled by
Controlled by negative feedback
—> suppresses GnRH & LH
—> recall
GnRH –> LH –> Leydig cells –> T
How is DHT made?
external genitalia & prostate transform testosterone to DHT (dihydrotestosterone)
Effects of Testosterone
(Prenatally)
testosterone stimulates development of male reproductive system & descent of testes
DHT stimulated development of external genitals
in brain testosterone converted to estrogens, which support some parts of brain development
Effects of Testosterone
(Puberty)
enlarge male sex organs, spermatogenesis, sex drive
secondary sex characteristics
—> facial & chest hair
—> muscle/bone enlargement
—> increase sebaceous gland secretion
—> laryngeal enlargement
testosterone is
anabolic – ie: stimulates protein production
Effects of Testosterone
(After puberty)
Maintains libido (sexual drive) and related behaviors
Stimulates bone and muscle growth
Maintains male secondary sexual characteristics
Maintains accessory glands and organs of the male reproductive system
Effects of Dihydrotestosterone (DHT)
Testosterone is converted to DHT in some tissues
Comprises ~10 percent circulating levels of testosterone
Can bind to same receptors as testosterone
what tissue responds to DHT instead of T
Some tissues respond to DHT instead of testosterone
E.g.
—> EXTERNAL GENITALIA
what tissue is more sensitive to DHT instead of T
Other tissues are more sensitive to DHT than testosterone
E.g.
—> Prostate and hair follicles
what percentage of circulating T is DHT
Comprises ~10 percent circulating levels of testosterone
what tissues transform T to DHT
external genitalia
& prostate
transform testosterone to DHT (dihydrotestosterone)
