Chapter 27— The Male Reproductive System
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Ch. 27 Study Guide
1. Read pp. 1048-1050 of section 27.1 before prenatal hormones and sexual differentiation section; also read sections 27.2-27.4 (pp.1053-1067)
2. Comprehend Terminology (those in bold)3. Study-- Figure questions, Think About It
questions, and Before You Go On (section-ending) questions
4. Do end-of-chapter questions:– Testing Your Recall— 2-20– True or False– 1-9– Testing Your Comprehension– 3, 4
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Said an ovum one night to a sperm, “You’re a very attractive young germ.
Come join me, my sweet, let our nuclei meet
And in nine months we’ll both come to term.”
--Isaac Asimov
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27.2. Male Reproductive Anatomy—A. The Spermatic Ducts and the
Accessory Glands
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§ A. Sperm’s journey
1. Testes– sperm-producing organs; inside the scrotum (skin-covered sac)
2. Routes (spermatic ducts) the sperm travel: A-Testes B-Efferent ductules C-Epididymis D-Ductus deferens E-Ejaculatory duct F-Urethra Exterior
Fig. 27.11b27-5
Urinary bladder
DF
Glans penis A
C
3. Bulbourethral gland
E
1. Seminal vesicle
Ureter2. Prostate gland
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B
Penis
Anterior/posterior view?
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§ Spermatic Ducts Include--• Efferent ductules
– 12 small ciliated ducts collecting sperm from rete testes and transporting it to epididymis
• Epididymis (head, body and tail)– 6 m long coiled duct adhering to posterior of testis– site of sperm maturation and storage (fertile for 60 days)
• Ductus (vas) deferens (peristalsis during orgasm)– muscular tube 45 cm long passing up from scrotum
through inguinal canal to posterior surface of bladder
• Ejaculatory duct– 2 cm duct formed from ductus deferens and seminal
vesicle and passing through prostate to empty into urethraFig. 27.9, 27.11
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§ Male Urethra
1. Three Regions: prostatic, membranous and penile urethra--- totals 20 cm long (Fig. 20.11b)
2. Function– It serves both urinary and reproductive
roles– It cannot pass urine and semen
simultaneously
Ampulla
Ductus deferens
Epididymis
Prostate gland
A
B
Efferent ductules
C
Seminal vesicle
Ejaculatory duct
Bulbourethral gland
Testis
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1. Sperm is supported by semen from accessory sex glands--
– including the seminal vesicles, prostate gland, and bulbourethral glands
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§ Accessory Glands-A
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§ Accessory Glands-B• Seminal vesicles (paired)
– posterior to bladder– Yellowish alkaline secretion empties into ejaculatory
duct; constitute 60% of the semen– Containing fructose, sugars, ascorbic acid, a
coagulating enzyme, prostaglandins, proseminogelin
• Prostate gland (single)– below bladder, surrounds urethra and ejaculatory
duct; digital rectal examination– 2 x 4 x 3 cm; thin, acidic milky secretion; 30% of the
semen– Plays a role in activating sperm, containing citrate (a
nutrient), serine protease
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§ Accessory Glands-C• Bulbourethral glands (paired; Cowper’s
glands)– near bulb of penis– empty into penile urethra – neutralize urine – lubricating fluid secreted during sexual
arousal
27.2. Male Reproductive Anatomy—
B. The Scrotum & Testicular Thermoregulation
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§ Scrotum1. Perineum–
Fig. 27.6
2. Pouch (scrotum) holding testes– divided into 2 compartments by ______ which is
external marked by perineal raphe3. Spermatic cords– paired structures
consisting of layers of CT and muscle enclosing ductus deferens, blood and lymphatic vessels, and testicular nerves.– Location– each spermatic cord begins at the
entrance to the In-________ canal
Fig. 27.7
Fig. 27.6--The male perineum
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§ Testicular Thermoregulation• Sperm cannot be produced at core body
temperature (too warm): – 1. pampiniform plexus = near testicular
artery, a network of veins– forming countercurrent heat exchanger that cools arterial blood entering testis by 1-2 degree Celsius (Fig. 27.8)
• When Cold:– 2. cremaster muscle = pulls testes close to
body when cold– 3. dartos muscle--
• Contracts and scrotum becomes taut• wrinkles skin reducing surface area of scrotum
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27.2. Male Reproductive Anatomy—C. Testes
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§ Testes (Fig. 27.10 a-b)-ADimension-- Oval organ; 3 cm (anterior to
posterior) x 2.5 cm (wide) x 4 cm (long)
Each testis is surrounded by two tunics: (From outermost and moving in)
1.Its anterior and lateral surfaces are covered by tunica vaginalis
2.Tunica albuginea– testis itself has a white fibrous capsule
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Review spermatic
ducts
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§ Testes (Fig. 27.10 a-b)-B3. Septa divide testes into 250-300 wedge-
shaped lobules containing seminiferous tubules (where sperm are produced)– each tubule lined with a thick germinal epithelium
(several layers of germ cells) for sperm production– Tall Sertoli (sustentacular) cells; function?
4. Between the seminiferous tubules are interstitial (Leydig) cells, the source of testosteroneFig. 27.10 and X
See next slide for details of germ and sustentacular cells
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Lumen of seminiferous tubule
Spermatozoon
Spermatids
SecondaryspermatocytePrimaryspermatocyte
Tight junctions --see next slide
Spermatogonium
Sertoli cell
Stages of sperm maturation:
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§ Blood-testis barrier of testes• (Structures) Formed by tight junctions
between sustentacular (Sertoli) cells -- separating sperm from blood and immune systems
• (Functions) Prevents proteins and other large molecules in the blood and intercellular fluid from getting to the germ cells
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§ Blood circulation to/from the testis1. Sperm’s transportation inside the testes--
Seminiferous tubules drain into rete testis which is embedded in the capsule on the posterior side
2. Testicular arteries– arise from the abdominal aorta; low BP of testicular artery results in poor O2 supply– sperm develop very large __________ helping
them also survive hypoxic environment of female reproductive tract
3. Pampiniform plexus of veins and then testicular veins-- the right one drains to inferior vena cava; the left one drains into the left renal vein
27.2. Male Reproductive Anatomy—
D. The Penis
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§ Penis (Fig. 27.11, 27.12)• Internal root; visible (external)-- shaft, and glans
– external portion 4 in. long when flaccid– skin over shaft loosely attached allows expansion
• extends over glans as prepuce (foreskin)• 3 cylindrical bodies of erectile tissue
– corpus spongiosum (1) along ventral side of penis• encloses penile urethra• at distal end, fill the entire glans
– corpora cavernosa (2)• On each side; separated by a median septum• Each is ensheathed in a fibrous tunica albuginea• diverge like arms of a Y• each arm, called crus, attaches to pubic arch
covered with ischiocavernosus muscle
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27.3. Sperm and Semen—A. Spermatogenesis
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§ Spermatogenesis--A
1. Def. of spermatogenesis– The production of sperm cells through a series of mitotic and meiotic cell divisions• Location?• How long does it take?• Microscopic examination– two important
cell types (see next slide)
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§ Spermatogenesis--B
2. Two important cell types in seminiferous tubulesA. Germ cells– • In various stages of sperm development,
such as spermatogonia, primary spermatocytes, secondary spermatocytes
B. Sustentacular (Sertoli) cells– these cells provide crucial support for spermatogenesis
Figure 27.15
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§ Spermatogenesis--C
3.Three major stages—A. Mitotic proliferation—• Spermatogonia located in the outermost
layer of the seminiferous tubule, outside the blood-testis barrier (BTB)
• One of the daughter cells (Type A spermatogonium) remain at the outer edge of the tubule; importance?
• The other daughter cell (Type B spermatogonium) starts moving toward lumen forming 4 identical primary spermatocytes (2N) 27-36
§ Spermatogenesis--D
B. Meiosis—• Each primary spermatocyte (2N) must pass
through BTB (tight junction) and ultimately yield 4 spermatids (1N)
C. Spermiogenesis—
• Spermatids become extremely specialized and motile spermatozoa
• Sperm travel lightly
Figure x&y, 27.16
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Meiosis
A.
B.
C.
SpermatogenesisStages:
Mitosis
Meiosis
Spermio-genesis
Spermatids
Secondaryspermatocyte
Primaryspermatocyte
Spermatozoa
First meioticdivision
Second meioticdivision
One daughter cell remainsat the outer edge of theseminiferous tubule tomaintain the germ cell line
One daughter cell movestoward the lumen to produce spermatozoa
Chromosomes:46; 2n (diploid number;single strands)
46; 2n(diploid number;single strands)
46; 2n (diploid number;doubled strands)
23; n(haploid number;Single strands)
23; n(haploid number;double strands)
23; n(haploid number;single strands)
Spermatogonia
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Figure 27.16
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27.3. Sperm and Semen—B. Spermatozoon
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§ The Spermatozoon--A
• Two parts– the head and the tail
1.Head contains three structures:A. A nucleus– with a haploid set of
chromosomes
B. Acrosome– a lysosome vesicle in a thin cap; in the apical half of the head
C. Flagellar basal body– is nestled in an indentation at the basal end of the nucleus
Fig. 27.17
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§ The Spermatozoon--B
• Two parts– the head and the tail
2.Tail contains three regions:A. Midpiece– many large mitochondria coil
around the axoneme (center of the sperm) and they provide the ATP needed for the tail
B. Principal piece– constitutes most of the tail and provides motility for the spermatozoon
C. Endpiece– axoneme only; the narrowest part of the sperm
Fig. 27.1727-44
Figure 27.17b
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27.3. Sperm and Semen—C. Semen
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§ Semen (2-5 ml)--A1. Def.– milky white mixture of sperm and
accessory gland secretions expelled during orgasm
2. Functions– A. provides a transport medium and nutrients
(fructose mainly and also citrate and sugars)
B. protects and activates the sperm• overall alkalinity helps neutralize the acid
environment• prostaglandins– decrease the viscosity of
mucus guarding the entry of the uterus 27-47
§ Semen--B– The clotting enzyme from the prostate
activates proseminogelin (from the seminal vesicles) into seminogelin
– Seminogelin sticks to the walls of the vagina, ensuring the semen doe not drain back
– 20-30 minutes after ejaculation: serine protease of the prostatic fluid breaks down seminogelin and liquefies the semen (sperm now very active)
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§ Semen—C; Low sperm count?
• 2-5 ml semen per ejaculation
• 200 million sperm per ejaculation
• 50-130 million sperm per ml
• Low sperm count is < 20 million sperm per ml of semen (less than the minimal jackpot of the Powerball)
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