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The Penis

External genitalia - scrotum and penis
Penis - male copulatory organ

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Male Reproductive System

Testes (within scrotum) produce sperm
Sperm delivered to exterior through system of ducts

Epididymis 🡪 ductus deferens 🡪 ejaculatory duct 🡪 urethra

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Male Reproductive System

Accessory sex glands

Seminal vesicles
Prostate
Bulbourethral glands
Empty secretions into ducts during ejaculation

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The Scrotum

Sac of skin and superficial fascia

Hangs outside abdominopelvic cavity
Contains paired testes

3°C lower than core body temperature
Lower temperature necessary for sperm production

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Seminiferous Tubules

Thick, stratified epithelium surrounding central fluid-containing lumen
Epithelium

Spheroid spermatogenic cells embedded in sustentocytes

Myoid cells surround each tubule

May squeeze sperm, testicular fluids out of testes

Tubules of each lobule form straight tubule

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The Testes

Sperm conveyed from

Seminiferous tubules 🡪
Straight tubule 🡪
Rete testis 🡪
Efferent ductules 🡪
Epididymis

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Figure 27.3a Structure of the testis.

Ductus (vas)

deferens

Head of epididymis

Efferent ductule

Rete testis

Straight tubule

Body of epididymis

Duct of epididymis

Tail of epididymis

Cavity of

tunica vaginalis

Tunica vaginalis

Tunica albuginea

Lobule

Seminiferous

tubule

Testis

Blood vessels

and nerves

Spermatic cord

Septum

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Figure 27.3c Structure of the testis.

Areolar

connective

tissue

Interstitial

endocrine

cells

Myoid cells

Spermatogenic

cells in tubule

epithelium

Sperm

Sustentocyte

Seminiferous

tubule

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Male Sexual Response

Erection

Arterioles normally constricted
Sexual excitement causes CNS activation of parasympathetic neurons
🡪 nitric oxide (NO) release 🡪 local vascular smooth muscle relaxation
🡪 arterioles dilate 🡪 corpora cavernosa expands, retards venous drainage
🡪 engorgement of erectile tissues with blood
🡪 enlargement and stiffening of penis

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Erection

Initiated by sexual stimuli

Touch; mechanical stimulation of penis; erotic sights, sounds, and smells

Can be induced or inhibited by emotions or higher mental activity
Longitudinal and circular collagen fibers around penis prevent kinking/buckling of erect penis
Corpus spongiosum keeps urethra open

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Male Sexual Response

Ejaculation

Propulsion of semen from male duct system
Sympathetic spinal reflex

Bladder sphincter muscle constricts, preventing expulsion of urine
Ducts and accessory glands contract and empty their contents
Bulbospongiosus muscles undergo rapid series of contractions 🡪 expulsion of semen at ~ 500 cm/s (close to 11 mph)

Ejaculatory event – climax (orgasm)

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Spermatogenesis

Sperm (spermatozoa) production in seminiferous tubules
Most body cells have 46 chromosomes - diploid chromosomal number (2n)

Two sets (23 pairs) of chromosomes

One maternal, one paternal – homologous chromosomes

Gametes have 23 chromosomes - haploid chromosomal number (n)

Only one member of homologous pair

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Meiosis

Gamete formation involves meiosis

Differs from mitosis
Two consecutive cell divisions (meiosis I and II); only one round of DNA replication

Produces four daughter cells

Functions of meiosis

Number of chromosomes halved (from 2n to n)
Introduces genetic diversity

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Meiosis

Random alignment of homologous pairs in meiosis I 🡪 variability of gametes
Crossover 🡪 variability of gametes
~ No two gametes exactly alike
~ All different from original mother cells

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Meiosis I

Reduction division of meiosis – reduces chromosome number from 2n 🡪 n
Prophase I events not in mitosis or meiosis II

Synapsis - homologous chromosomes pair forming tetrads of four chromatids
Crossover (chiasmata) – exchange of genetic material between male and female chromatid 🡪 unique chromosomes

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Meiosis I

End of meiosis I each daughter cell

Two copies of one member of each homologous pair (either maternal or paternal); none of the other
Haploid chromosomal number; still-united sister chromatids one chromosome (twice amount DNA in each chromosome)

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Meiosis II

Equational division of meiosis

Sister chromatids from meiosis I separated, one per cell

Like mitosis except no chromosome replication before begins

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Spermatogenesis

Spermatogenic cells give rise to sperm

Mitosis of spermatogonia (stem cell) forms two spermatocytes
Meiosis

Spermatocytes 🡪 secondary spermatocytes 🡪 spermatids

Spermiogenesis

Spermatids become sperm

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Figure 27.8a Spermatogenesis.

Scanning electron micrograph of a

cross-sectional view of a seminiferous

tubule (165x)

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Mitosis of Spermatogonia

Spermatogenesis begins at puberty
Spermatogonia

Stem cells in contact with epithelial basal lamina
Each mitotic division → one type A daughter cell and one type B daughter cell

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Mitosis of Spermatogonia

Type A cells maintain germ cell line at basal lamina
Type B cells move toward lumen and develop into primary spermatocytes

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Meiosis: Spermatocytes to Spermatids

Meiosis I

Primary spermatocyte (2n) → two secondary spermatocytes (n)

Meiosis II

Each secondary spermatocyte (n) → two spermatids (n)
Spermatid – small, nonmotile cells close to lumen of tubule

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Figure 27.8b Spermatogenesis.

Spermatogonium

(stem cell)

Mitosis

Growth

Enters

meiosis I and

moves to

adluminal

compartment

Meiosis I

completed

Meiosis ll

Type A daughter cell

remains at basal lamina

as a precursor cell

Type B daughter cell

Primary

spermatocyte

Secondary

spermatocytes

Early

spermatids

Late spermatids

Spermatogenesis

Spermiogenesis (late

spermatogenesis)

Meiosis (early

spermatogenesis)

Events of spermatogenesis, showing the relative

position of various spermatogenic cells

Spermatozoa

Basal lamina

2n

n

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Spermiogenesis: Spermatids to Sperm

Spermatids

Correct chromosome number (n)
Nonmotile

Spermiogenesis

Spermatids elongate; lose excess cytoplasm; form a tail 🡪 spermatozoon (sperm)

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Sperm

Major regions

Head - genetic region; nucleus and helmetlike acrosome containing hydrolytic enzymes that enable sperm to penetrate egg
Midpiece - metabolic region; mitochondria 🡪 ATP to move tail
Tail - locomotor region; flagellum

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Role of Sustentocytes

Large supporting cells (Sertoli cells)

Extend through wall of tubule and surround developing cells
Provide nutrients and signals to dividing cells
Move cells along to lumen
Secrete testicular fluid into lumen for sperm transport
Phagocytize faulty germ cells and excess cytoplasm
Produce chemical mediators to regulate spermatogenesis

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Role of Sustentacular Cells

Tight junctions divide tubule into two compartments

Basal compartment—spermatogonia and primary spermatocytes
Adluminal compartment—meiotically active cells and tubule lumen

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Hormonal Regulation of Male Reproductive Function

Sequence of hormonal regulatory events involving hypothalamus, anterior pituitary gland, and testes

Hypothalamic-pituitary-gonadal (HPG) axis
Regulates production of gametes and sex hormones through 3 interacting sets of hormones

GnRH indirectly stimulates testes via FSH & LH
FSH & LH directly stimulate testes
Testosterone & inhibin – negative feedback on hypothalamus and anterior pituitary

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HPG Axis

Sequence of regulatory events

Hypothalamus releases gonadotropin-releasing hormone (GnRH) 🡪 anterior pituitary to secrete FSH and LH
FSH causes sustentocytes to release androgen-binding protein (ABP) 🡪 high concentration of testosterone near spermatogenic cells 🡪 spermatogenesis
LH prods interstitial endocrine cells 🡪 testosterone 🡪 spermatogenesis

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HPG Axis

Testosterone 🡪 sex organ maturation, development/maintenance secondary sex characteristics, libido
Rising testosterone levels 🡪 feedback inhibition on hypothalamus to inhibit GnRH and on pituitary to inhibit gonadotropin release
Inhibin (released when sperm count high) – inhibits GnRH and FSH release

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Figure 27.10 Hormonal regulation of testicular function, the hypothalamic-pituitary-gonadal (HPG) axis.

Slide 1

GnRH

Inhibin

Via portal

blood

Interstitial

endocrine

cells

Testosterone

Somatic and

psychological

effects at other

body sites;

maintenance

of secondary sex

characteristics

Spermatogenic

cells

Seminiferous

tubule

Stimulates

Inhibits

Sustentocyte

FSH

LH

7

3

7

6

5

2

3

4

1

Spermatogenesis

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Figure 27.10 Hormonal regulation of testicular function, the hypothalamic-pituitary-gonadal (HPG) axis.

Slide 2

GnRH

Interstitial

endocrine

cells

Spermatogenic

cells

Sustentocyte

1

Stimulates

Inhibits

Spermatogenesis

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Figure 27.10 Hormonal regulation of testicular function, the hypothalamic-pituitary-gonadal (HPG) axis.

Slide 3

GnRH

Interstitial

endocrine

cells

Spermatogenic

cells

Sustentocyte

1

Stimulates

Inhibits

LH

2

FSH

Seminiferous

tubule

Via portal

blood

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Figure 27.10 Hormonal regulation of testicular function, the hypothalamic-pituitary-gonadal (HPG) axis.

Slide 4

GnRH

Interstitial

endocrine

cells

Spermatogenic

cells

Sustentocyte

1

Stimulates

Inhibits

LH

2

FSH

Seminiferous

tubule

Via portal

blood

3

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Figure 27.10 Hormonal regulation of testicular function, the hypothalamic-pituitary-gonadal (HPG) axis.

Slide 5

GnRH

Interstitial

endocrine

cells

Spermatogenic

cells

Sustentocyte

1

Stimulates

Inhibits

LH

2

FSH

Seminiferous

tubule

Via portal

blood

3

4

Testosterone

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Figure 27.10 Hormonal regulation of testicular function, the hypothalamic-pituitary-gonadal (HPG) axis.

Slide 6

GnRH

Interstitial

endocrine

cells

Spermatogenic

cells

Sustentocyte

1

Stimulates

Inhibits

LH

2

FSH

Seminiferous

tubule

Via portal

blood

3

4

Somatic and

psychological

effects at other

body sites;

maintenance

of secondary sex

characteristics

5

Testosterone

Spermatogenesis

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Figure 27.10 Hormonal regulation of testicular function, the hypothalamic-pituitary-gonadal (HPG) axis.

Slide 7

GnRH

Interstitial

endocrine

cells

Spermatogenic

cells

Sustentocyte

1

Stimulates

Inhibits

LH

2

FSH

Seminiferous

tubule

Via portal

blood

3

4

Somatic and

psychological

effects at other

body sites;

maintenance

of secondary sex

characteristics

5

6

Testosterone

Spermatogenesis

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Figure 27.10 Hormonal regulation of testicular function, the hypothalamic-pituitary-gonadal (HPG) axis.

Slide 8

GnRH

Inhibin

Via portal

blood

Interstitial

endocrine

cells

Testosterone

Somatic and

psychological

effects at other

body sites;

maintenance

of secondary sex

characteristics

Spermatogenic

cells

Seminiferous

tubule

Stimulates

Inhibits

Sustentocyte

FSH

LH

7

3

7

6

5

2

3

4

1

Spermatogenesis

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Female Reproductive Anatomy

Ovaries - female gonads

Produce female gametes (ova)
Secrete female sex hormones, estrogen (estradiol, estrone, estriol) and progesterone

Accessory ducts include

Uterine tubes
Uterus
Vagina

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Female Reproductive Anatomy

Internal genitalia – in pelvic cavity

Ovaries
Uterine tubes
Uterus
Vagina

External genitalia

External sex organs

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Uterus

Hollow, thick-walled, muscular organ
Function

Receive, retain, nourish fertilized ovum

Anteverted – inclined forward; retroverted – inclined backward
Body - major portion
Fundus - rounded superior region
Isthmus - narrowed inferior region

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Uterus

Cervix - narrow neck, or outlet; projects into vagina
Cervical canal communicates with

Vagina via external os
Uterine body via internal os

Cervical glands secrete mucus that blocks sperm entry except during midcycle

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Ovaries

Blood supply - ovarian arteries and ovarian branch of the uterine arteries
Surrounded by fibrous tunica albuginea
Germinal epithelium - outer layer
Two poorly defined regions

Outer cortex – houses forming gametes
Inner medulla - large blood vessels and nerves

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Ovaries

Embedded in cortex

Ovarian follicles

Immature egg (oocyte) surrounded by

Follicle cells (one cell layer thick)
Granulosa cells (more than one layer present)

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Follicles

Several stages of development

Primordial follicle – single layer of follicle cells + oocyte
More mature follicles – several layers of granulosa cells

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Ovaries

Vesicular (antral or tertiary) follicle – fully mature follicle

Fluid-filled antrum forms; follicle bulges from ovary surface

Ovulation

Ejection of oocyte from ripening follicle

Corpus luteum develops from ruptured follicle after ovulation

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Female Duct System

Ducts have no contact with ovary

Oocyte cast into peritoneal cavity; some lost there

Uterine (fallopian) tubes or oviducts
Uterus
Vagina

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Physiology of the Female Reproductive System

Always assumed females total supply of eggs determined at birth
New evidence stem cells can arise from epithelial cells at ovary surface
May overturn previous assumption

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Oogenesis

Production of female gametes

Takes years to complete

Begins in fetal period

Oogonia (2n ovarian stem cells) multiply by mitosis and store nutrients
Primary oocytes develop in primordial follicles
Primary oocytes begin meiosis; stall in prophase I

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Oogenesis

At birth female presumed to have lifetime supply of primary oocytes
Each month after puberty, a few primary oocytes activated
One "selected" each month to resume meiosis I
Result is two haploid cells of different sizes

Secondary oocyte – large cell with ~ all cytoplasm and organelles of original cell
First polar body – small cell

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Oogenesis

Secondary oocyte arrests in metaphase II; ovulated ovum
If not penetrated by sperm - deteriorates
If penetrated by sperm second oocyte completes meiosis II, yielding

Ovum (functional gamete)
Second polar body

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Comparison of Oogenesis and Spermatogenesis

Spermatogenesis 🡪 4 viable sperm
Spermatogenesis – error rate of 3-4%
Oogenesis 🡪 1 viable gamete; 3 polar bodies
Oogenesis – error rate of 20%
Unequal divisions ensure oocyte has ample nutrients for 6-7 day journey to uterus
Polar bodies degenerate and die

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Ovarian Cycle

Monthly series of events associated with maturation of egg
Two consecutive phases (in 28-day cycle)

Follicular phase - period of follicle growth (days 1–14)
Ovulation occurs midcycle
Luteal phase - period of corpus luteum activity (days 14–28)

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Ovarian Cycle

Only 10 – 15% women have 28-day cycle
Follicular phase varies
Luteal phase constant – always 14 days from ovulation to end of cycle

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Follicular Phase

Primordial follicle becomes primary follicle

Squamouslike cells become cuboidal; oocyte enlarges

Primary follicle becomes secondary follicle

Stratified epithelium (granulosa cells) forms around oocyte
Granulosa cells and oocyte guide one another's development via gap junctions

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Follicular Phase

Secondary follicle becomes late secondary follicle

Connective tissue (theca folliculi) and granulosa cells cooperate to produce estrogens
Inner thecal cells produce androgens in response to LH
Zona pellucida forms around oocyte
Fluid accumulates between granulosa cells

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Figure 27.20 Schematic and microscopic views of the ovarian cycle: development and fate of ovarian follicles.

Theca

folliculi

Forming

antrum

Late

secondary

follicle

Slide 5

Corona

radiata

Secondary

oocyte

Antrum

Primary

oocyte

Theca folliculi

3a

2

7

6

5

3b

Zona pellucida

Secondary

oocyte

4

3b

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Follicular Phase

Late secondary follicle becomes vesicular follicle

Antrum forms; expands to isolate oocyte with corona radiata on stalk
Vesicular follicle bulges from external surface of ovary
Primary oocyte completes meiosis I 🡪 secondary oocyte and first polar body

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Ovulation

Ovary wall ruptures, expels secondary oocyte with its corona radiata to peritoneal cavity
Mittelschmerz - twinge of pain sometimes felt at ovulation
1–2% of ovulations release more than one secondary oocyte, which, if fertilized, results in fraternal twins
Identical twins result from fertilization of one oocyte, then separation of daughter cells

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Luteal Phase of the Ovarian Cycle

Ruptured follicle collapses; antrum fills with clotted blood – corpus hemorrhagicum
Granulosa cells and internal thecal cells form corpus luteum
Corpus luteum secretes progesterone and some estrogen

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Luteal Phase

If no pregnancy, corpus luteum degenerates into corpus albicans (scar) in 10 days
If pregnancy occurs, corpus luteum produces hormones that sustain pregnancy until placenta takes over at about 3 months

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Establishing the Ovarian Cycle

During childhood, ovaries grow and secrete small amounts of estrogens that inhibit hypothalamic release of GnRH
As puberty nears, GnRH released; FSH and LH released by pituitary, and act on ovaries
These events continue until an adult cyclic pattern achieved and menarche occurs

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Hormonal Regulation of the Ovarian Cycle

Hormone interaction produces cyclic events in ovaries

Gonadotropin-releasing hormone (GnRH)
Pituitary gonadotropins
Ovarian estrogen
Ovarian progesterone

Onset of puberty linked to amount of adipose tissue via hormone leptin

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Establishing the Ovarian Cycle

During childhood, until puberty

Ovaries secrete small amounts of estrogens
Estrogen inhibits release of GnRH
If leptin levels adequate hypothalamus less sensitive to estrogen as puberty nears; releases GnRH in rhythmic pulse-like manner 🡪 FSH and LH release 🡪 ovarian hormone release

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Hormonal Interactions During a 28-Day Ovarian Cycle

1. GnRH → release of FSH and LH
2. FSH and LH → growth of several follicles, and hormone release
3. ↑plasma estrogen levels inhibit release of FSH and LH

↑estrogen levels enhance further estrogen output
Inhibin from granulosa cells also inhibits FSH release

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Hormonal Interactions During a 28-Day Ovarian Cycle

4. When estrogen levels high 🡪 brief positive feedback on brain and anterior pituitary
5. Stored LH, and some FSH, suddenly released by anterior pituitary at midcycle 🡪 surge triggers ovulation
🡪 primary oocyte to complete meiosis I 🡪 secondary oocyte
Secondary oocyte 🡪 meiosis II

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Figure 27.21 Regulation of the ovarian cycle.

Slide 7

3

Hypothalamus

GnRH

Travels via

portal blood

Anterior pituitary

FSH

LH

Thecal cells

Androgens

Granulosa

cells

Convert androgens

to estrogens

Mature vesicular

follicle

Ovulated

secondary

oocyte

Corpus luteum

Ruptured

follicle

LH surge

Stimulates

Inhibits

Early and

midfollicular phases

Late follicular and

luteal phases

Positive feedback exerted by large in

estrogen output by maturing follicle.

Slightly elevated estrogen and rising inhibin levels inhibit FSH

secretion.

GnRH

1

2

Estrogens

4

6

4

5

6

5

Progesterone

Estrogens

Inhibin

Hypothalamus

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Figure 27.22a Correlation of anterior pituitary and ovarian hormones with structural changes of the ovary and uterus.

Fluctuation of gonadotropin levels: Fluctuating levels of pituitary �gonadotropins (follicle-stimulating hormone and luteinizing hormone) �in the blood regulate the events of the ovarian cycle.

Plasma hormone level

LH

FSH

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Figure 27.22b Correlation of anterior pituitary and ovarian hormones with structural changes of the ovary and uterus.

Ovarian cycle: Structural changes in the ovarian follicles during the �ovarian cycle are correlated with (d) changes in the endometrium of the �uterus during the uterine cycle.

Primary

follicle

Secondary

follicle

Vesicular

follicle

Ovulation

Corpus

luteum

Degenerating

corpus luteum

Follicular

phase

Ovulation

(Day 14)

Luteal

phase

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The Uterine (Menstrual) Cycle

Cyclic changes in endometrium in response to fluctuating ovarian hormone levels
Three phases

Days 1–5 - menstrual phase
Days 6–14 - proliferative (preovulatory) phase
Days 15–28 - secretory (postovulatory) phase (constant 14-day length)

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Uterine Cycle

Menstrual phase (Days 1 - 5)

Ovarian hormones at lowest levels
Gonadotropins beginning to rise
Stratum functionalis shed; menstrual flow (blood and tissue) 3 - 5 days
By day 5 growing ovarian follicles produce more estrogen

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Uterine Cycle

Proliferative phase (Days 6 - 14)

Rising estrogen levels prompt generation of new stratum functionalis layer; increased synthesis of progesterone receptors in endometrium; glands enlarge and spiral arteries increase in number
Normally thick, sticky cervical mucus thins in response to rising estrogen (allows sperm passage)
Ovulation occurs at end of proliferative phase

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Uterine Cycle

Secretory phase (Days 15 – 28)

Most constant timewise
Endometrium propares for embryo
Rising progesterone levels prompt

Functional layer 🡪 secretory mucosa
Endometrial glands secrete nutrients
Formation of cervical mucus plug

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Uterine Cycle

If fertilization does not occur

Corpus luteum degenerates toward end of secretory phase
Progesterone levels fall
Spiral arteries kink and spasm
Endometrial cells begin to die; glands regress
Spiral arteries constrict again, then relax and open wide
Rush of blood fragments weakened capillary beds and functional layer sloughs

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Figure 27.22c Correlation of anterior pituitary and ovarian hormones with structural changes of the ovary and uterus.

Fluctuation of ovarian hormone levels: Fluctuating levels of ovarian �hormones (estrogens and progesterone) cause the endometrial changes

of the uterine cycle. The high estrogen levels are also responsible for the �LH/FSH surge in (a).

Estrogens

Progesterone

Plasma hormone level

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Figure 27.22d Correlation of anterior pituitary and ovarian hormones with structural changes of the ovary and uterus.

Endometrial

glands

Blood vessels

Menstrual

flow

Functional

layer

Basal layer

Days

5

10

15

20

25

28

Menstrual

phase

Proliferative

phase

Secretory

phase

1

The three phases of the uterine cycle:

• Menstrual: The functional layer of the endometrium is shed.

• Proliferative: The functional layer of the endometrium is rebuilt.

• Secretory: Begins immediately after ovulation. Enrichment of the blood

supply and glandular secretion of nutrients prepare the endometrium to

receive an embryo.

Both the menstrual and proliferative phases occur before ovulation, and

together they correspond to the follicular phase of the ovarian cycle. The

secretory phase corresponds in time to the luteal phase of the ovarian cycle.