inquiry into life twelfth edition

1

Chapter 21 Reproductive

System

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

21.1 Male Reproductive System

• Genital Tract

– Sperm are produced by seminiferous tubules of

testes

– Undergo maturation in the epididymis

• Maturation involves gaining of motility

– Sperm pass through vas deferens where products are

secreted by glands that contribute to semen

• Seminal vesicles

• Prostate

• Bulbourethral glands

– Semen is alkaline and contains fructose and

prostaglandins

The Male Reproductive System

urinary bladder

vas deferens

pubic bone

urethra

penis

glans penis

foreskin

scrotum

seminal vesicle

ureter (cut)

ejaculatory duct

prostate gland

bulbourethral gland

anus

epididymis

testis

vas deferens

erectile tissue

of penis



urinary bladder

ureter

prostate gland

seminal vesicle

vas deferens

urethra

bulbourethral

gland



urinary bladder

vas deferens

pubic bone

urethra

penis

glans penis

foreskin

scrotum

seminal vesicle

ureter (cut)

ejaculatory duct

prostate gland

bulbourethral gland

anus

epididymis

testis

urinary bladder

ureter

prostate gland

vas deferens

seminal vesicle

vas deferens

urethra

erectile tissue

of penis

bulbourethral

gland


Penis Anatomy

erectile tissue urethra foreskin

glans penis

skin

connective tissue

a. b.

septum

dorsal nerve

dorsal artery

dorsal vein

skin

connective

layers

external urethral

opening

erectile

tissue



• Orgasm in Males

– Sexual excitement increases blood flow to the penis

causing an erection

– Sperm enters the vas deferens, glands contribute

secretions to the semen

– Semen is ejaculated

– Ejaculation is followed by a refractory period

– Over 400 million sperm cells may be ejaculated


• Male Gonads, the Testes

– Produce sperm and hormones

– Located outside of the body cavity

• Internal body temperature is too high for sperm production

– Scrotum helps regulate temperature of the testes

Testis

• Spermatogenesis occurs

in the seminiferous

tubules

• Sertoli cells support,

nourish, and regulate

spermatogenic cells.

• Interstitial cells produce

testosterone

vas deferens

epididymis

testis

lobule

scrotal sac

uncoiled

seminiferous

tubule

a. Testis, cut to show lobules


140 µm

tails of sperm in lumen of seminiferous tubule

Sertoli cell

vas deferens

epididymis

testis

lobule

scrotal sac

MEIOSIS I MEIOSIS II

acrosome

head

middle piece

tail

end piece

b. Seminiferous tubules

c. Spermatogenesis d.

100 µm

uncoiled

seminiferous

tubule

MITOSIS

spermatogonium

(diploid)

primary

spermatocyte

secondary

spermatocyte

early

spermatid

late

spermatid

immature sperm

(haploid)

a. Testis, cut to show lobules

nucleus of

Sertoli cell


interstitial cell

b(top): © CNRI/Photo Researchers, Inc. b(bottom): © Ed Reschke

Sperm Cell

• Three Main Parts

– Head

• The acrosome contains

enzymes needed to

penetrate an egg

– Middle Piece

• Many mitochondria

– Tail

• Flagellum

acrosome

head

middle piece

tail

end piece

d.



• Hormonal Regulation in Males

– Gonadotropin Releasing Hormone (GnRH) from the

hypothalamus causes the anterior pituitary to release

Follicle-Stimulating Hormone (FSH) and Luteinizing

Hormone (LH)

• FSH targets seminiferous tubules - stimulates sperm

production

• LH stimulates interstitial cells of the testes to produce

testosterone

• All are regulated by negative feedback

– Testosterone is responsible for male secondary sex

characteristics

Hormonal Control of Testes

hypothalamus

LH

FSH

testis

GnRH

anterior

pituitary

Interstitial

cells

produce

testosterone.

Seminiferous

tubules

produce

sperm

plus inhibin.


21.2 Female Reproductive System

• Oogenesis – production of an egg or oocyte

• Ovulation – process by which oocyte burst from

ovary and enters oviduct

• Genital tract

– Oviducts have fingerlike fimbriae

– Uterus – endometrium

– Cervix

– Vagina


oviduct

ovary

uterus

urinary bladder

pubic bone

urethra

glans clitoris

labium minora

labium majora

vaginal orifice

fimbriae

cervix

rectum

vagina

anus



vagina

uterus fimbriae

ovary oviduct



oviduct

ovary

uterus

urinary bladder

pubic bone

urethra

glans clitoris

labium minora

labium majora

vaginal orifice

fimbriae

cervix

vagina

uterus fimbriae

ovary oviduct

rectum

vagina

anus



• External genitals

– Collectively known as vulva

– Labia majora

– Labia minora

• Openings for urethra and vagina

– Glans clitors

External Genitals of the Female

mons pubis

urethra

vagina

anus

labium majora

labium minora

glans clitoris



• Orgasm in Females

– Labia minora, vaginal walls,clitoris become engorged

– Erection of nipples

– Secretion of vaginal fluids, mucus for lubrication

– Vagina is the organ of intercourse, clitoris plays an

important role in excitation and orgasm

– Height of excitation - increased heart rate, blood

pressure, and smooth muscle contractions

– Females have no refractory period following orgasm

Ovarian Cycle Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

oocyte vesicular (Graafian) follicle

a.

b.

zygote

sperm

meiosis I meiosis II

2. The secondary follicle

contains a primary

oocyte and produces the

sex hormones estrogen

and some progesterone. 3. Vesicular (Graafian)

follicle develops.

secondary

follicle

primary

follicles

1. A primary follicle contains

an oocyte and begins

producing the sex

hormone estrogen.

4. Ovulation: The

secondary oocyte is

released.

Sperm nucleus and

egg nucleus fuse;

zygote with 46

chromosomes results.

Second polar

body

secondary oocyte

(23 chromosomes)

First polar

body

primary oocyte

(46 chromosomes)

5. Corpus luteum produces

the sex hormones

progesterone and some

estrogen.

secondary

oocyte

6. Corpus luteum

degenerates.

corpus

luteum

(oocyte): © Ed Reschke/Peter Arnold

Hormonal Control of the Ovaries

• The hypothalamus,

anterior pituitary and

ovaries all function to

control female

hormone levels.

• Like other hormones,

female hormones are

regulated by feedback

mechanisms.


LH

FSH

GnRH

oocyte

hypothalamus

anterior

pituitary

follicle

estrogen

corpus

luteum

progesterone

21.3 Female Hormone Levels

• Female cycles are studied based on an average

of 28 days

The Ovarian Cycle The Uterine Cycle

Two Phases Three Phases

Follicular Phase Menstruation

Luteal Phase Proliferative Phase

Secretory Phase


En

do

me

triu

m

endometrium

GnRH

1 3 5 7 9 11 13 15 17 19 21 23 25 27 30

FSH LH

1 3 5 7 9 11 13 15 17 19 21 23 25 27 1

anterior

pituitary

Days

Ho

rmo

ne

Le

ve

ls

Menstruation Proliferative Phase Secretory Phase

Days

Ovarian cycle ovulation

early

corpus luteum

regressing

corpus luteum

maturefollicle developing follicle

Follicular Phase Ovulation Luteal Phase

ovulation Uterine cycle

estrogen

menstruation

progesterone

Ova

ria

n

Eve

nts

Ho

rmo

ne

Le

ve

ls

ovary

Ovarian and Uterine Cycles

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• Menstruation

– Arteries that supply the endometrium (uterine lining)

constrict thereby weakening the capillaries

– The endometrium detaches in random patches

– Tissue, blood, and mucus are lost in the menstrual

flow

– Menstruation lasts 3-10 days


• Fertilization and Pregnancy

– An embryo begins development in the oviduct

– Implantation occurs when embryo migrates into uterus

– Embryo begins to produce human chorionic

gonadotropin (hCG)

• hCG maintains the corpus luteum to prevent a drop in levels

and estrogen and progesterone

• Pregnancy tests detect hCG

– Later, the placenta will secrete estrogen and

progesterone

– Estrogen and progesterone prevent ovulation and help

to maintain the endometrium

Implantation Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

endometrium

uterine tube

a. b.

ovary

embryo

(not drawn

to scale)

b: © Bettman/Corbis


• Estrogen and Progesterone

– Both have effects other than those in the ovarian and

uterine cycles

– Estrogen

• Maintains female secondary sex characteristics

– Breast development, axillary and pubic hair, subcutaneous fat

deposition

– Wider pelvis

– Progesterone

• Also needed for breast development


• Menopause

– Generally occurs between the ages of 45-55

– Ovaries become unresponsive to FSH and LH

– At the onset of menopause, the menstrual cycle

becomes irregular. Other characteristics include hot

flashes, dizziness, headaches, insomnia, and

depression.

– Menopause is complete when menstruation has not

occurred for one year

– Hormone replacement therapy has advantages and

disadvantages

Various Methods of Birth Control

21.4 Control of Reproduction

• Morning-After Pills

– Emergency contraception

– Taken after unprotected intercourse has occurred

– Two types, both disrupt uterine environment

• Preven - series of progesterone pills that disrupts normal

cycle making implantation difficult

• RU-486 (mifepristone) - blocks progesterone receptors in the

uterus so that the endometrium is sloughed off

inquiry into life twelfth edition

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