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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