Lecture 21
Male Reproductive System
 Testes
o Male __________ – combined endocrine and exocrine glands that produce
sex hormones and sperm
o Oval-shaped and slightly flattened
o Divided into 200 to 300 wedge-shaped lobules
o Each lobule contains one to three _____________________ tubules
 Seminiferous tubules are slender ducts up to 1 meter long in which
sperm are produced
 Between the seminiferous tubules are clusters of interstitial cells,
the source of _____________________
o The epithelium of the seminiferous tubules consists of:
 several layers of germ cells in the process of becoming sperm
 a smaller number of sustentacular cells which protect the germ
cells and promote their development
 germ cells depend on sustentacular cells for
_____________, waste removal, growth factors, and other
needs
 the rate of sperm production depends on a hormone called
inhibin, secreted by sustentacular cells
 Scrotum
o The pouch in which the _______________ are contained is the scrotum
o It is separated into left and right compartments by an internal median
septum
 It prevents infection of one of the testes from spreading to the other
o The spermatic cord is a cord of connective tissue that passes upward
behind the testis, across the anterior side of the pubis, and through an
opening called the inguinal ring in the muscles of the groin
 It contains the ________________ deferens (vas deferens), blood
and lymphatic vessels, and the testicular nerves
o The testes must be held at 35 degrees Celsius to produce viable sperm
 The core body temperature is 37, so the scrotum holds the testes
away from the core of the body
 There are three mechanisms for regulating the temperature of the
testes
 The ____________________ muscle contracts and draws
the testes closer if external temperatures are cold
 The dartos muscle contracts when cold, making the
scrotum taught and wrinkled, and reducing surface area
 The pampiniform plexus is an extensive network of veins.
o They help to prevent the testes from warming as
blood is carried into the testes by the testicular
arteries
 Spermatogenesis and Sperm

o Spermatogenesis is the process of ______________ production
 Three events:
 Remodeling a relatively large germ cell into a small,
mobile cell with a flagellum
 Reduction of the chromosome number by ½ so that when
an egg cell and sperm cell combine they do not get a
____________________ of the chromosome number with
each generation
 A shuffling of the genes so that each chromosome of the
sperm carries new gene combinations that did not exist in
the chromosomes received from one’s parents
 The reduction in chromosome number and shuffling of
genes occur as a result of meiosis
o Meiosis produces four _____________ daughter
cells that subsequently differentiate into sperm
o Spermatozoon
 Two parts:
 Head
o Contains 3 structures:
 Nucleus – fills most of the head and contains
a _________________ set of condensed,
genetically inactive chromosomes
 Acrosome – lysome in the form of a thin cap
covering the apical half of the nucleus
 It contains enzymes that are later
used to penetrate the egg if the sperm
is successful
 Basal body of the flagellum – nestled in an
indentation at the posterior end of the
nucleus
 Tail
o Divided into 3 regions:
 Midpiece – a cylinder about 5 to 9
micrometers long and half as wide as the
head
 Contains numerous
________________ that produce
ATP needed for the beating of the
tail
 Principal piece – 40 to 45 micrometers long
and constitutes most of the tail
 Endpiece - 4 to 5 micrometers long
Spermatic Ducts
o After leaving the testes, the sperm travel through a series of spermatic
ducts



__________________ ductules – small tubes that carry sperm to
the epididymis
 Epididymis – site of sperm maturation and storage
 Adheres to the posterior side of the testis
 Reabsorbs about 90% of the fluid secreted by the testis
 Sperm are physiologically immature when they leave the
testis, but mature as they travel through the epididymis
 Sperm are stored here and are reabsorbed if they become to
old without being ejaculated
 Ductus (vas) deferens – This tube carries sperm from the
__________________ upward into the pelvic cavity, where it turns
medially and approaches the urinary bladder
 Where it passes between the bladder and ureter, it turns
downward behind the bladder and widens into a terminal
ampulla
 Ejaculatory duct – This tube runs from the ampulla through the
prostate gland and empties into the urethra
Accessory Glands
o Seminal vesicles
 These are a pair of glands dorsal to the urinary bladder
 One is associated with each ductus deferens
 The duct empties into the ___________________ duct
 The secretion constitutes about 60% of the semen
o Prostate
 This is a structure immediately below the urinary bladder
 It surrounds the _______________ and ejaculatory duct
 The milky secretion contributes about 30% of the semen
o Bulbourethral gland
 These are brownish, spherical glands about 1 cm in diameter
 They are found at the inner end of the penis
 During sexual arousal, they produce a clear slippery fluid that
lubricates the head of the ______________ in preparation for
coitus
 It neutralizes the acidity of residual urine in the urethra
Semen
o This is a complex mixture of sperm and glandular secretions
o A typical ejaculation discharges 2 to 5 m of ________________
 10% consists of sperm and fluid from the spermatic ducts
 30% is from the prostate
 60% is from the seminal vesicles
 sperm count is normally 50 to 120 million sperm/mL
o Ejaculation:
 Peristalsis of the ductus deferens drives sperm from the epididymis
to the ___________________



Contraction of the ampulla then discharges the sperm into the
prostatic urethra, where they mix the secretions with the accessory
glands
Semen in the urethra triggers a reflex contraction of the
bulbospongiosus muscle which ___________________ the root of
the penis
 Rhythmic compression of the urethra by this muscle expels
the semen from the penis
 Most of the sperm are contained in the first 1 mL of
ejaculate, followed by prostatic fluid and seminal fluid
Penis
o The function of the penis is to deposit ________________ in the vagina
o About half is the internal root
o The other half is externally visible, including shaft and glans
 The glans is the expanded head at the distal end of the penis
 The prepuce, or foreskin, is skin that is loosely attached to the skin
continues over the _________________
 The glans and prepuce have sebaceous glands that produce a
secretion called smegma
o The penis consists of three cylindrical bodies called ______________
tissues
 These fill with blood during sexual arousal
 They cause enlargement of the penis and an erection
 Corpus spongiosum – single erectile body that encloses the urethra
in the penis
 It passes along the ventral side of the penis
 It expands at the ________________ end to fill the entire
glans
 Corpus cavernosum – Pair of erectile bodies on each side of the
dorsal surface of the penis
 All three cylinders are spongy in appearance and contain blood
sinuses called lacunae
o The penis receives blood from a pair of internal pudental arteries
 The dorsal artery supplies blood to the skin, fascia, and corpus
spongiosum
 The deep artery travels through the core of the corpus cavernosum
 When the deep arteries dilate, the ________________ fills with
blood and the erectile tissues swell.
 When the penis is flaccid, most of its blood comes from the dorsal
arteries
 The deep dorsal vein is the blood vessel that drains blood from the
penis
o Nerves
 The penis is richly innervated by sensory and motor nerve fibers


Parasympathetic fibers extend from S2 to S4 of the spinal cord and
are involved in an autonomic reflex arc that causes erection in
response to direct stimulation of the penis
__________________ fibers from T12 to L2 dilate penile arteries
and can induce erection in response to input from special senses
and sexual thoughts