27

PowerPoint® Lecture Slides

prepared by

Janice Meeking,

Mount Royal College

C H A P T E R

TheReproductiveSystem: Part A

Reproductive System

•Primary sex organs (gonads): testes andovaries

•Produce sex cells (gametes)

•Secrete steroid sex hormones

•Androgens (males)

•Estrogens and progesterone (females)

•Accessory reproductive organs: ducts, glands,and external genitalia

Reproductive System

•Sex hormones play roles in

•Development and function of the reproductiveorgans

•Sexual behavior and drives

•Growth and development of many otherorgans and tissues

Male Reproductive System

•Testes (within the scrotum) produce sperm

•Sperm are delivered to the exterior through asystem of ducts

•Epididymis, ductus deferens, ejaculatory duct,and the urethra

Male Reproductive System

•Accessory sex glands: seminal vesicles,prostate, and bulbourethral glands

•Empty secretions into the ducts duringejaculation

Figure 27.1

Peritoneum

Seminal

vesicle

Ampulla of

ductus

deferens

Ejaculatory

duct

Rectum

Prostate

Bulbourethral

gland

Anus

Bulb of penis

Epididymis

Ureter

Urinary bladder

Prostatic

urethra

Pubis

Membranous

urethra

Urogenital

diaphragm

Corpus

cavernosum

Corpus

spongiosum

Glans penis

Prepuce

External

urethral orifice

Spongy urethra

Testis

Scrotum

Ductus (vas)

deferens

The Scrotum

•Sac of skin and superficial fascia

•Hangs outside the abdominopelvic cavity

•Contains paired testes

• 3C lower than core body temperature(temperature necessary for spermproduction)

The Scrotum

•Temperature is kept constant by two sets ofmuscles

•Smooth muscle that wrinkles scrotal skin(dartos muscle)

•Bands of skeletal muscle that elevate thetestes (cremaster muscles)

Figure 27.2

Penis

Internal spermatic

fascia

Superficial inguinal

ring (end of inguinal

canal)

Urinary bladder

Spermatic cord

Ductus (vas)

deferens

Autonomic

nerve fibers

Testicular artery

Epididymis

Pampiniform

venous plexus

Tunica vaginalis

(from peritoneum)

Tunica albuginea

of testis

Middle septum

of scrotum

Cremaster muscle

External spermatic

fascia

Superficial fascia

containing dartos

muscle

Skin

Scrotum

The Testes

•Each is surrounded by two tunics

•Tunica vaginalis, derived from peritoneum

•Tunica albuginea, the fibrous capsule

•Septa divide the testis into 250–300 lobules,each containing 1–4 seminiferous tubules(site of sperm production)

The Testes

•Sperm are conveyed through

•Seminiferous tubules

•Tubulus rectus

•Rete testis

•Efferent ductules

•Epididymis

The Testes

•Blood supply comes from the testiculararteries and testicular veins

•Spermatic cord encloses nerve fibers, bloodvessels, and lymphatics that supply the testes

Figure 27.3a

Head of epididymis

Body of epididymis

Tail of epididymis

Efferent ductule

Rete testis

Straight tubule

Duct of epididymis

Ductus (vas)

deferens

Lobule

Testis

Septum

Tunica albuginea

Tunica vaginalis

Cavity of

tunica vaginalis

Spermatic cord

Seminiferous

tubule

Blood vessels

and nerves

(a)

The Testes

•Interstitial (Leydig) cells outside theseminiferous tubules produce androgens

Figure 27.3c

Spermatogenic

cells in tubule

epithelium

Interstitial cells

Areolar

connective

tissue

Sperm

Myoid

cells

(c)

Seminiferous

tubule

The Penis

•External genitalia are the scrotum and thepenis

•Penis is the male copulatory organ

The Penis

•Penis consists of

•Root and shaft that ends in the glans penis

•Prepuce, or foreskin—the cuff of loose skincovering the glans

•Circumcision is the surgical removal of theforeskin

•Crura

•The proximal end surrounded byischiocavernosus muscle; anchors penis tothe pubic arch

The Penis

•Spongy urethra and three cylindrical bodies oferectile tissue (spongy network of connectivetissue and smooth muscle with vascularspaces)

•Corpus spongiosum surrounds the urethra andexpands to form the glans and bulb

•Corpora cavernosa are paired dorsal erectilebodies

•Erection: erectile tissue fills with blood,causing the penis to enlarge and become rigid

Figure 27.4

Urinary bladder

Dorsal vessels

and nerves

Skin

Deep arteries

(b)

(a)

Bulbourethral gland and duct

Urogenital diaphragm

Bulb of penis

Corpora cavernosa

Corpus spongiosum

Section of (b)

Spongy urethra

Glans penis

Prepuce (foreskin)

External urethral orifice

Corpora cavernosa

Urethra

Tunica albuginea of erectile bodies

Corpus spongiosum

Crus of penis

Bulbourethral duct opening

Ductus deferens

Ampulla of ductus deferens

Prostatic urethra

Orifices of prostatic ducts

Prostate

Membranous urethra

Root of penis

Shaft (body) of penis

Ejaculatory duct

Seminal vesicle

Epididymis

Testis

Ureter

The Male Duct System

•Epididymis

•Ductus deferens

•Ejaculatory duct

•Urethra

Epididymis

•Head: contains the efferent ductules

•Duct of the epididymis

•Microvilli (stereocilia) absorb testicular fluidand pass nutrients to stored sperm

•Nonmotile sperm enter, pass slowly through,and become motile

•During ejaculation the epididymis contracts,expelling sperm into the ductus deferens

Ductus Deferens and Ejaculatory Duct

•Ductus deferens

•Passes through the inguinal canal

•Expands to form the ampulla and then joinsthe duct of the seminal vesicle to form theejaculatory duct

•Propels sperm from the epididymis to theurethra

•Vasectomy: cutting and ligating the ductusdeferens, which is a nearly 100% effectiveform of birth control

Urethra

•Conveys both urine and semen (at differenttimes)

•Has three regions

1.Prostatic urethra

2.Membranous urethra

3.Spongy (penile) urethra

Figure 27.4

Urinary bladder

Dorsal vessels

and nerves

Skin

Deep arteries

(b)

(a)

Bulbourethral gland and duct

Urogenital diaphragm

Bulb of penis

Corpora cavernosa

Corpus spongiosum

Section of (b)

Spongy urethra

Glans penis

Prepuce (foreskin)

External urethral orifice

Corpora cavernosa

Urethra

Tunica albuginea of erectile bodies

Corpus spongiosum

Crus of penis

Bulbourethral duct opening

Ductus deferens

Ampulla of ductus deferens

Prostatic urethra

Orifices of prostatic ducts

Prostate

Membranous urethra

Root of penis

Shaft (body) of penis

Ejaculatory duct

Seminal vesicle

Epididymis

Testis

Ureter

Accessory Glands: Seminal Vesicles

•Produces viscous alkaline seminal fluid

•Fructose, ascorbic acid, coagulating enzyme(vesiculase), and prostaglandins

•70% of the volume of semen

•Duct of seminal vesicle joins the ductusdeferens to form the ejaculatory duct

Accessory Glands: Prostate

•Encircles part of the urethra inferior to thebladder

•Secretes milky, slightly acid fluid:

•Contains citrate, enzymes, and prostate-specific antigen (PSA)

•Plays a role in the activation of sperm

•Enters the prostatic urethra during ejaculation

Accessory Glands: Bulbourethral Glands(Cowper’s Glands)

•Pea-sized glands inferior to the prostate

•Prior to ejaculation, produce thick, clearmucus

•Lubricates the glans penis

•Neutralizes traces of acidic urine in the urethra

Figure 27.4

Urinary bladder

Dorsal vessels

and nerves

Skin

Deep arteries

(b)

(a)

Bulbourethral gland and duct

Urogenital diaphragm

Bulb of penis

Corpora cavernosa

Corpus spongiosum

Section of (b)

Spongy urethra

Glans penis

Prepuce (foreskin)

External urethral orifice

Corpora cavernosa

Urethra

Tunica albuginea of erectile bodies

Corpus spongiosum

Crus of penis

Bulbourethral duct opening

Ductus deferens

Ampulla of ductus deferens

Prostatic urethra

Orifices of prostatic ducts

Prostate

Membranous urethra

Root of penis

Shaft (body) of penis

Ejaculatory duct

Seminal vesicle

Epididymis

Testis

Ureter

Semen

•Mixture of sperm and accessory glandsecretions

•Contains nutrients (fructose), protects andactivates sperm, and facilitates theirmovement (e.g., relaxin)

•Prostaglandins in semen

•Decrease the viscosity of mucus in the cervix

•Stimulate reverse peristalsis in the uterus

Semen

•Alkalinity neutralizes the acid in the maleurethra and female vagina

•Antibiotic chemicals destroy certain bacteria

•Clotting factors coagulate semen just afterejaculation, then fibrinolysin liquefies it

•Only 2–5 ml of semen are ejaculated,containing 20–150 million sperm/ml

Male Sexual Response

•Erection

•Enlargement and stiffening of the penis fromengorgement of erectile tissue with blood

•Initiated by sexual stimuli, including:

•Touch and mechanical stimulation of thepenis

•Erotic sights, sounds, and smells

•Can be induced or inhibited by emotions orhigher mental activity

Male Sexual Response

•Erection:

•Parasympathetic reflex promotes release ofnitric oxide (NO)

•NO causes erectile tissue to fill with blood

•Expansion of the corpora cavernosa

•Compresses drainage veins and maintainsengorgement

•Corpus spongiosum keeps the urethra open

•Impotence: the inability to attain erection

Male Sexual Response

•Ejaculation

•Propulsion of semen from the male ductsystem

•Sympathetic spinal reflex causes

•Ducts and accessory glands to contract andempty their contents

•Bladder sphincter muscle to constrict,preventing the expulsion of urine

•Bulbospongiosus muscles to undergo arapid series of contractions

Spermatogenesis

•Sequence of events that produces sperm inthe seminiferous tubules of the testes

•Most body cells are diploid (2n) and contain

•Two sets of chromosomes (one maternal, onepaternal)

•23 pairs of homologous chromosomes

•Gametes are haploid (n) and contain

•23 chromosomes

Meiosis

• Gamete formation involves meiosis

•Nuclear division in the gonads in which thenumber of chromosomes is halved (from 2nto n)

•Two consecutive cell divisions (meiosis Iand II) following one round of DNA replication

•Produces four daughter cells

•Introduces genetic variation

Figure 27.6 (1 of 2)

MEIOSIS I

Prophase I

Prophase events occur, as in mitosis. Additionally,

synapsis occurs: Homologous chromosomes come

together along their length to form tetrads. During

synapsis, the “arms” of homologous chromatids wrap

around each other, forming several crossovers. The

nonsister chromatids trade segments at points of

crossover. Crossover is followed through the diagrams

below.

Anaphase I

Unlike anaphase of mitosis, the centromeres do not

separate during anaphase I of meiosis, so the sister

chromatids (dyads) remain firmly attached. However, the

homologous chromosomes do separate from each other

and the dyads move toward opposite poles of the cell.

Telophase I

The nuclear membranes re-form around the

chromosomal masses, the spindle breaks down, and

the chromatin reappears as telophase and cytokinesis

are completed. The 2 daughter cells (now haploid)

enter a second interphase-like period, called

interkinesis, before meiosis II occurs. There is no

second replication of DNA before meiosis II.

Metaphase I

The tetrads align randomly on the spindle

equator in preparation for anaphase.

Crossover

Interphase cell

Centriole

pairs

Nuclear

envelope

Chromatin

2n = 4

Spindle

Sister

chromatids

Nuclear envelope

fragments late

in prophase I

Tetrad

Dyad

Chromosomes

uncoil

Nuclear

envelopes

re-form

Cleavage

furrow

Centromere

Interphase events

As in mitosis, meiosis is preceded

by DNA replication and other

preparations for cell division.

Figure 27.6 (2 of 2)

MEIOSIS II

Meiosis II begins with the

products of meiosis I (2

haploid daughter cells) and

undergoes a mitosis-like

nuclear division process

referred to as the equational

division of meiosis.

Prophase II

After progressing through the

phases of meiosis and

cytokinesis, the product is 4

haploid cells, each genetically

different from the original

mother cell. (During human

spermatogenesis, the daughter

cells remain interconnected by

cytoplasmic extensions during

the meiotic phases.)

Metaphase II

Anaphase II

Telophase II

and cytokinesis

Products of

meiosis:

haploid

daughter cells

Figure 27.5 (1 of 2)

Mother cell

(before chromosome replication)

Chromosome

replication

Chromosome

replication

2n = 4

MITOSIS

Replicated

chromosome

Prophase

Chromosomes

align at the

metaphase plate

Sister chromatids

separate during

anaphase

Metaphase

Daughter

cells of

mitosis

Tetrad formed by

synapsis of replicated

homologous

chromosomes

Tetrads align at the

metaphase plate

Homologous chromosomes

separate but sister

chromatids remain together

during anaphase I

No further chromosomal

replication; sister chromatids

separate during

anaphase II

Daughter cells of meiosis II

(usually gametes)

Prophase I

Metaphase I

Daughter cells

of meiosis I

Meiosis II

MEIOSIS

Figure 27.5 (2 of 2)

MITOSIS

MEIOSIS

One, consisting of prophase, metaphase,

anaphase, and telophase.

Number of

divisions

Synapsis of

homologous

chromosomes

Daughter cell

number and

genetic

composition

Roles in the body

Two, each consisting of prophase, metaphase,

anaphase, and telophase. DNA replication does

not occur between the two nuclear divisions.

Does not occur.

Occurs during mitosis I; tetrads formed,

allowing crossovers.

Two. Each diploid (2n) cell is identical to

the mother cell.

Four. Each haploid (n) cell contains half as many

chromosomes as the mother cell and is

genetically different from the mother cell.

For development of multicellular adult

from zygote. Produces cells for growth

and tissue repair. Ensures constancy of

genetic makeup of all body cells.

Produces cells for reproduction (gametes).

Introduces genetic variability in the gametes and

reduces chromosomal number by half so that when

fertilization occurs, the normal diploid chromosomal

number is restored (in humans, 2n = 46).

Spermatogenesis

•Spermatic cells give rise to sperm

•Mitosis

•Spermatogonia form spermatocytes

•Meiosis

•Spermatocytes form spermatids

•Spermiogenesis

•Spermatids become sperm

Figure 27.7a

Figure 27.7c

Basal lamina

Spermatogonium

(stem cell)

Cytoplasm of adjacent

sustentacular cells

Sustentacular

cell nucleus

Tight junction between

sustentacular cells

Lumen of

seminifer-

ous tubule

Late spermatids

Early

spermatids

Secondary

spermatocytes

Cytoplasmic

bridge

Primary

spermatocyte

Spermatozoa

Type B daughter cell

Type A daughter cell

remains at basal lamina

as a stem cell

genic cells surrounded by sustentacular cells (colored gold)

Mitosis of Spermatogonia

•Begins at puberty

•Spermatogonia

•Stem cells in contact with the epithelial basallamina

•Each mitotic division  a type A daughter celland a type B daughter cell

Mitosis of Spermatogonia

•Type A cells maintain the germ cell line at thebasal lamina

•Type B cells move toward the lumen anddevelop into primary spermatocytes

Meiosis: Spermatocytes to Spermatids

•Meiosis I

•Primary spermatocyte (2n)  two secondaryspermatocytes (n)

•Meiosis II

•Each secondary spermatocyte (n)  twospermatids (n)

•Spermatid: small nonmotile cells close to thelumen of the tubule

Figure 27.7b

Basal lamina

Spermatogonium

(stem cell)

Mitosis

Growth

Late spermatids

Early

spermatids

Secondary

spermatocytes

Primary

spermatocyte

Spermatozoa

Type B daughter cell

Enters meiosis I

and moves to

adluminal

compartment

Meiosis I

completed

Meiosis II

Type A daughter cell

remains at basal lamina

as a stem cell

(b) Events of spermatogenesis,

showing the relative position

of various spermatogenic cells

Spermiogenesis: Spermatids to Sperm

•Spermatids lose excess cytoplasm and form atail, becoming spermatozoa (sperm)

Sperm

•Major regions

1.Head: genetic region; nucleus and helmetlikeacrosome containing hydrolytic enzymes thatenable the sperm to penetrate an egg

2.Midpiece: metabolic region; mitochondria

3.Tail: locomotor region; flagellum

Figure 27.8a, b

Centrioles

Spermatid

nucleus

Golgi

apparatus

Acrosomal

vesicle

Mitochondria

Approximately 24 days

Excess

cytoplasm

Nucleus

Acrosome

Microtubules

Flagellum

Tail

Midpiece

Head

(a)

(b)

Role of Sustentacular Cells

•Large supporting cells (Sertoli cells)

•Extend through the wall of the tubule andsurround developing cells

•Provide nutrients and signals to dividing cells

•Dispose of excess cytoplasm sloughed offduring spermiogenesis

•Secrete testicular fluid into lumen for transportof sperm

Role of Sustentacular Cells

•Tight junctions divide the wall into twocompartments

1.Basal compartment—spermatogonia andprimary spermatocytes

2.Adluminal compartment—meiotically activecells and the tubule lumen

Figure 27.7c

Basal lamina

Spermatogonium

(stem cell)

Cytoplasm of adjacent

sustentacular cells

Sustentacular

cell nucleus

Tight junction between

sustentacular cells

Lumen of

seminifer-

ous tubule

Late spermatids

Early

spermatids

Secondary

spermatocytes

Cytoplasmic

bridge

Primary

spermatocyte

Spermatozoa

Type B daughter cell

Type A daughter cell

remains at basal lamina

as a stem cell

genic cells surrounded by sustentacular cells (colored gold)

Role of Sustentacular Cells

•Tight junctions form a blood-testis barrier

•Prevents sperm antigens from escaping intothe blood where they would activate theimmune system

•Because sperm are not formed until puberty,they are absent during immune systemdevelopment, and would not be recognized as“self”