Human Anatomy & Physiology
Basic Anatomy & Physiology II Dr. L. Bacha
Chapter Outline (Marieb & Hoehn 6th ed)
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(The MALE REPRODUCTIVE SYSTEM
26.1 The testes are enclosed and protected by the scrotum
The Scrotum (see Fig. 26.1 and Fig. 26.2)
( what is the scrotum?
a sac of skin and superficial fascia that hangs outside the abdominopelvic cavity at the root of the penis
( what does the scrotum contain?
paired oval testes
( normal sperm production, which occurs in the testes, requires a few degrees less than core body temperature!
( there are two muscles that contract and relax reflexively to regulate the temperature of the testes by adjusting the surface area of the scrotum and the position of the testes relative to the rest of the body:
( the cremaster muscles elevate the testes
( the dartos muscle wrinkles the skin of the scrotum
- when it is cold, these muscles contract so that testes are pulled closer to the warm body wall and the scrotal skin wrinkles to reduce heat loss
- when it is warm, the scrotal skin is loose to increase the surface areal for cooling (sweating), and the testes hang lower, away from the body trunk
The Testes
( the testes (testicles) are each about the size of a plum
( they are paired oval glands that occupy the scrotum
( develop in the posterior abdomen and descend into the scrotum before birth
( produce sperm and secrete hormones
( what is the tunica albuginea?
the fibrous capsule of the testis
- connective tissue septa extend inward from the tunica albuginea to divide each testis into about 250 wedge-shaped lobules
- each lobule contains what?
one to four tightly coiled seminiferous tubules
( seminiferous tubules
∙ 1 to 4 in each lobule
∙ they are tightly coiled, but all lined up end to end would extend about ½ mile!
∙ the stratified epithelium of seminiferous tubules is formed by two groups of cells:
1. spermatogenic cells
2. sustentocytes
26.7 Spermatogenesis is the sequence of events that leads to formation of sperm
Remember there are two groups of cells of the epithelium of seminiferous tubules:
1. SPERMATOGENIC CELLS (( jump to page 900)
∙ spermatogenic cells are sperm forming cells: they include:
spermatogonia, primary spermatocytes, secondary spermatocytes, early spermatids,
late spermatids, sperm (spermatozoa)
∙ the seminiferous tubules produce sperm by a process called spermatogenesis
Spermatogenesis
∙ read about chromosomes, meiosis compared to mitosis, and meiosis I and meiosis II on pages 898 to 899 and follow the Figures
∙ spermatogenesis begins during puberty and continues throughout life
∙ examine Fig. 26.9 and the sketch on page 6 and 7 of this outline and identify the spermatogenic cells:
spermatogonia (singular = spermatogonium)
primary spermatocytes
secondary spermatocytes
early spermatids
late spermatids
sperm (spermatozoa)
Note the location of each type of cell listed above relative to the basement membrane and the lumen of the seminiferous tubule:
( which cell rests on the basement membrane?
spermatogonium (stem cell)
( which cell is in the lumen? sperm
( are spermatogonia haploid or diploid? diploid
( are primary spermatocytes haploid or diploid? diploid
( are spermatids haploid or diploid? haploid
( are spermatozoa (sperm) haploid or diploid? haploid
∙ spermiogenesis is the differentiation of spermatids into sperm
( Sperm
( about 400 million sperm (spermatozoa) are produced per day!
( locate the following parts of a sperm (described on page 900; see Fig. 26.10):
( head
- what does the head of sperm consist almost entirely of?
its flattened nucleus,
- nucleus: what does the nucleus contain?
the compacted DNA
- the acrosome is a membrane that adheres to the top of the head of the sperm
- it contains hydrolytic enzymes that enable the sperm to penetrate and enter an oocyte
( midpiece
- what does the midpiece contain? mitochondria
- what do the mitochondria provide?
the metabolic energy (ATP) needed for the whiplike movements of the tail that will propel the sperm along its way in the female reproductive tract
( tail
- the tail is a typical what? flagellum
- it is mostly formed by microtubules
See the second column on p. 902 to answer the following:
( are the sperm released into the lumen of the seminiferous tubule mature or immature?
immature
( are the sperm in the lumen of the seminiferous tubule able to “swim”? no
( are they capable of fertilizing an oocyte? no
( what pushes them into the epididymis?
the pressure of the testicular fluid
2. SUSTENTOCYTES (p. 900)
( they are large columnar cells that extend from the basement membrane to the lumen of the seminiferous tubules
the tubule lumen
( spermatogenic cells develop in pockets of the cytoplasm of sustentocytes cells
( the tight junctions between the sustentacular cells form what barrier?
the blood testis barrier
- the tight junctions (see Fig. 26.9b) join the cell membranes of adjacent sustentocytes together just above the level of the spermatogonia, so that the other spermatogenic cells, which develop antigens on their surface that the person’s immune system detects as foreign, are isolated from the blood
( other functions of sustentocytes, in addition to forming the blood-testis barrier:
∙ sustentocytes provide what to the dividing cells?
nutrients and essential signals to the dividing cells, even telling them to live or die
∙ they also move the spermatocytes and spermatids along to what? the lumen
∙ they secrete what fluid?
testicular fluid
- what does testicular fluid provide?
the transport medium for sperm in the lumen
∙ what do sustentocytes phagocytize?
faulty spermatogenic cells and the excess cytoplasm sloughed off as the spermatids transform into sperm
∙ they also produce what two chemical mediators that help regulate spermatogenesis?
androgen-binding protein and inhibin
( Interstitial Endocrine Cells
( interstitial endocrine cells, also called interstitial cells or Leydig cells are in the interstitial connective tissue between seminiferous tubules of the testes
( they secrete testosterone
26.7 Male reproductive function is regulated by hypothalamic, anterior pituitary, and testicular hormones
The Hypothalamic-Pituitary-Gonadal Axis (p. 903)
Read the information on pages 903, and follow the 7 steps in Fig. 26.11; we will cover the same information next:
Now for another version (mine) of hormonal regulation of the testes:
A. REGULATION OF BLOOD LEVELS OF TESTOSTERONE
- locally rising testosterone levels serve as the final trigger for spermatogenesis
- testosterone also stimulates maturation of sex organs, development and maintenance of secondary sex characteristics, and libido (sex drive)
The amount of testosterone secreted by the interstitial cells of the testes is regulated by a negative feedback system involving the hypothalamus, the pituitary gland, and the testes:
1A. As the blood levels of testosterone drop, the hypothalamus secretes GnRH.
2A. GnRH stimulates the anterior pituitary gland to release LH and FSH into the blood.
3A. The increased secretion of LH stimulates the interstitial cells of the testes to release more testosterone, and the blood level of testosterone rises.
4A. As the blood level of testosterone rises, the hypothalamus becomes inhibited and its stimulation of the anterior pituitary by GnRH is decreased. As the secretion of LH by the anterior pituitary decreases, the amount of testosterone released by the interstitial cells is reduced, and the blood level of testosterone drops (back to #1A.)
B. REGULATION OF SPERMATOGENESIS
1B. GnRH also stimulates the anterior pituitary to secrete FSH.
2B. The main target of FSH is the sustentacular cells (Sertoli cells) of the seminiferous tubules.
3B. FSH stimulates spermatogenesis indirectly by causing the Sertoli cells to release androgen-binding protein (ABP). ABP keeps the concentration of testosterone in the vicinity of the spermatogenic cells high, which stimulates spermatogenesis.
4B. Once the appropriate level of spermatogenesis is achieved, the sustentacular cells release a hormone called Inhibin.
5B. An increase in blood levels of inhibin inhibit the release of FSH, and spermatogenesis decreases. If spermatogenesis proceeds too slowly, the release of inhibin will decrease, causing an increase in the release of FSH, which promotes spermatogenesis.
26.3 Sperm travel from the testes to the body exterior through ducts
The Male Duct System (page 893)
( see Fig. 27.5 and 27.7 as you study the parts of the male duct system; Here is my summary:
1. immature, nonmotile sperm pass from the seminiferous tubules and eventually enter
2. efferent ductules – emerge from each testis and lead into the duct of the epididymis
3. duct of the epididymis
* a single, highly convoluted 20 feet long passageway inside of the epididymis
* storage site of sperm
* site of maturation of sperm (where they gain the ability to swim)
4. ductus deferens (vas deferens)
* ~18 inches long
* the ductus deferens is inside of the spermatic cord
- the spermatic cord contains: the ductus deferens; testicular artery and veins; lymphatic vessels; nerves; cremaster muscle, etc. are all enclosed in a CT sheath
Each ductus deferens ascends within the spermatic cord from the testis in the scrotum
( through the external (superficial) inguinal ring
( through the inguinal canal (a passageway through the anterior abdominal wall)
( the ductus deferens emerges through the internal (deep) inguinal ring into the pelvic cavity, where it separates from the other components of the spermatic cord
( loops over the ureter and posterior surface of the urinary bladder
( passes into the prostate gland, where it is continuous with the ejaculatory duct
5. ejaculatory duct
6. prostatic urethra - the portion surrounded by the prostate gland
7. intermediate part of the urethra (membranous urethra)
8. spongy urethra (penile urethra), which runs through the
penis and opens to the outside at the
9. external urethral orifice (urethral opening)
26.4 The male accessory glands produce the bulk of semen
The Male Accessory Glands (page 894)
( the male accessory glands included the seminal vesicles, the prostate gland, and the bulbourethral glands
( they secrete most of the liquid portion of semen
( locate the three types of glands in Fig. 26.1
( The Seminal Glands (Seminal Vesicles)
( describe the location, size and shape of the seminal vesicles:
- lie on the posterior bladder surface
- fairy large, hollow gland is about the shape and length of a little finger
( the seminal vesicles are enclosed in a thick layer of smooth muscle that does what?
contracts during ejaculation to empty the gland
( the secretion of the seminal vesicles is a viscous alkaline fluid containing what?
fructose sugar, citric acid, a coagulating enzyme, and prostaglandins, as well as other substances that enhance sperm motility or fertilizing ability
( The Prostate
( describe the size and shape of the prostate gland:
a single doughnut-shaped gland about the size of a peach pit
( what does it encircle?
encircles the urethra just inferior to the bladder
( during ejaculation, prostatic smooth muscle contracts, squeezing the prostatic secretion into the prostatic urethra through several ducts
( the secretion from the prostate gland plays a role in activating sperm and contains nutrient sources for the sperm
( The Bulbo-Urethral Glands
( pea-sized and located inferior to the prostate gland
( they produce a mucus that drains into the spongy urethra; what are the functions of this mucus?
- neutralizes traces of acidic urine
- lubricates the glans penis when a man becomes sexually excited
Semen (page 895)
( semen is a mixture of sperm, testicular fluid, and accessory gland secretions
( the accessory gland secretions of semen provide what?
a transport medium and nutrients
- it contains chemicals that do what?
that protect and activate the sperm and facilitate their movement
( what is the function of fructose in semen?
provides nearly all the fuel needed for sperm ATP synthesis
( clotting factors in semen coagulate it just after it is ejaculated; coagulation causes and prevents what?
causes the sperm to stick to the walls of the vagina and
prevents the initially immobile sperm fro draining out of the vagina
- soon after semen coagulates, what do enzymes in semen do?
liquefy the sticky mass and the sperm swim out and begin their journey through the female duct system
( what is the pH of semen ? alkaline (pH 7.2 to 8.0)
- what is the function of the relative alkalinity of semen as a whole?
helps neutralize the acid environment of the male’s urethra and the female’s vagina, protecting the delicate sperm and enhancing their motility
( what is the typical volume of semen in an ejaculation? 2 – 5 ml
( how many sperm are in a milliliter of semen?!
between 20 and 150 million sperm/milliliter
26.2 The penis is the copulatory organ of the male
The Penis (page 891)
( what is the penis designed to deliver?
sperm into the female reproductive tract
( the penis and the scrotum, which hang suspended from the perineum, make up what?
the external genitalia of the male
( the penis consists of what?
an attached root and a free body (shaft) that ends in an enlarged tip, the glans penis
( the raised ridge that separates the glans penis from the body of the penis is called the corona
( the glans penis contains the external urethral orifice
( the prepuce is a retractable fold of skin that covers the glans penis
- what is another name for the prepuce? foreskin
- what is surgical removal of the prepuce called? circumcision
( erectile tissue:
( internally, the penis contains erectile tissue; describe erectile tissue:
is a spongy network of CT and smooth muscle riddled with vascular spaces
( during sexual excitement, what happens to the vascular spaces that leads to erection?
fill with blood, causing the penis to enlarge and become rigid
( there are three long, cylindrical bodies of erectile tissue:
- the midventral mass is the corpus spongiosum
( what does the corpus spongiosum surround? the urethra
( the corpus spongiosum expands distally to form the glans penis
- the paired dorsal masses are the corpora cavernosa
The Male Perineum (page 892)
( what does the male perineum (Fig. 26.5) suspend and contain?
- suspends the scrotum
- contains the root of the penis, and the anus
26.5 The male sexual response includes erection and ejaculation (page 896)
Erection
∙ what is erection?
enlargement and stiffening of the penis
∙ what does it result from?
engorgement of the erectile bodies with blood
∙ sexual excitement triggers a parasympathetic reflex that promotes the release of what?
nitric oxide (NO) locally;
- nitric oxide relaxes smooth muscle of blood vessels so that more blood flows to the penis, filling the vascular spaces and leading to an erection
∙ also, nerve impulses cause the mucous glands of the penile urethra and the bulbourethral glands to secrete mucus, which lubricates the glans penis
Ejaculation
∙ what is ejaculation?
the propulsion of semen from the male duct system
∙ the nervous system causes:
- the internal sphincter of the urinary bladder to constrict
- the reproductive ducts and accessory glands to contract:
∙ contractions of the seminal vesicles and prostate gland cause their secretions to move into the urethra
∙ peristalsis of the reproductive ducts cause the passage of sperm from the ductus epididymis through the ductus deferens and ejaculatory duct into the urethra
( rhythmic muscular contractions force semen out of the urethra through the urethral orifice
The End!
-----------------------
First, some background information:
( function of reproductive systems:
1) production of gametes (egg and sperm) by the gonads (ovaries and testes)
2) maintenance and transport of gametes
3) production and secretion of hormones
( review of human chromosomes:
DIPLOID CELL (2N = 46):
( most cells of the body are diploid
( each diploid cell has 23 pairs of chromosomes in the nucleus (total of 46 chromosomes):
22 pairs of au has 23 pairs of chromosomes in the nucleus (total of 46 chromosomes):
22 pairs of autosomes
1 pair of sex chromosomes
∙ the pair of sex chromosomes in males is designated XY
∙ the pair of sex chromosomes in females is designated XX
HAPLOID CELL (N = 23):
( the gametes (eggs and sperm) are haploid cells; they form as a result of meiosis
( each haploid cell has one member of each of the 23 pairs of chromosomes (total of 23 chromosomes)
( Review the information on mitosis and meiosis on p. 898 to 899, and see Fig. 26.6 and 26.7!!!
Spermatogenesis:
First, a summary of some hormones…
GnRH = gonadotropin releasing hormone
produced by neurons of the hypothalamus of the brain
stimulates the release of the gonadotropins (LH and FSH) from the anterior pituitary
gonadotropins = hormones produced by the cells of the anterior pituitary gland that stimulate the gonads to produce their hormones:
LH = luteinizing hormone (or ICSH =interstitial cell stimulating hormone)
FSH = follicle stimulating hormone
Did somebody say sponge?!
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