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PowerPoint® Lecture Slides prepared by Janice Meeking, Mount Royal College

C H A P T E R

Copyright © 2010 Pearson Education, Inc.

27

The Reproductive System: Part C


Establishing the Ovarian Cycle

• During childhood, until puberty

• Ovaries secrete small amounts of estrogens

• Estrogen inhibits release of GnRH


Establishing the Ovarian Cycle

• At puberty

• Leptin from adipose tissue decreases the estrogen inhibition

• GnRH, FSH, and LH are released

• In about four years, an adult cyclic pattern is achieved and menarche occurs


Hormonal Interactions During a 28-Day Ovarian Cycle

• Day 1: GnRH release of FSH and LH

• FSH and LH growth of several follicles, and estrogen release

• estrogen levels

• Inhibit the release of FSH and LH

• Stimulate synthesis and storage of FSH and LH

• Enhance further estrogen output



• Estrogen output by the vesicular follicle increases

• High estrogen levels have a positive feedback effect on the pituitary at midcycle

• Sudden LH surge at day 14



• Effects of LH surge

• Completion of meiosis I (secondary oocyte continues on to metaphase II)

• Triggers ovulation

• Transforms ruptured follicle into corpus luteum



• Functions of corpus luteum

• Produces inhibin, progesterone, and estrogen

• These hormones inhibit FSH and LH release

• Declining LH and FSH ends luteal activity and inhibits follicle development



• Days 26–28: corpus luteum degenerates and ovarian hormone levels drop sharply

• Ends the blockade of FSH and LH

• The cycle starts anew

Copyright © 2010 Pearson Education, Inc. Figure 27.19

Hypothalamus

Late follicular andluteal phases

1

1

2 2

2

3

4

5

5

6

8

8

7 Slightlyelevated estrogen and rising inhibin levels.

Positivefeedback exerted by large inestrogen output.

Mature follicleCorpus luteum

Ovulatedsecondaryoocyte

Rupturedfollicle

LH surgeProgesteroneEstrogenInhibin

Hypothalamus

Early and midfollicular phases

Travels viaportal blood

Granulosacells

Inhibin

Androgens

Convertandrogens toestrogens

Thecalcells

Anterior pituitary

GnRH

FSH LH

Copyright © 2010 Pearson Education, Inc. Figure 27.20a

(a) 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.

FSH

LH

Copyright © 2010 Pearson Education, Inc. Figure 27.20b

(b) 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.

Primaryfollicle

Secondaryfollicle

Vesicularfollicle

Ovulation

Corpusluteum Degenerating

corpus luteum

Follicularphase

Ovulation(Day 14)

Lutealphase


Uterine (Menstrual) Cycle

• Cyclic changes in endometrium in response to ovarian hormones

• Three phases

1. Days 1–5: menstrual phase

2. Days 6–14: proliferative (preovulatory) phase

3. Days 15–28: secretory (postovulatory) phase (constant 14-day length)


Uterine Cycle

• Menstrual phase

• Ovarian hormones are at their lowest levels

• Gonadotropins are beginning to rise

• Stratum functionalis is shed and the menstrual flow occurs


Uterine Cycle

• Proliferative phase

• Estrogen levels prompt generation of new functional layer and increased synthesis of progesterone receptors in endometrium

• Glands enlarge and spiral arteries increase in number


Uterine Cycle

• Secretory phase

• Progesterone levels prompt

• Further development of endometrium

• Glandular secretion of glycogen

• Formation of the cervical mucus plug

Copyright © 2010 Pearson Education, Inc. Figure 27.20c

(c) 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).

Progesterone

Estrogens

Copyright © 2010 Pearson Education, Inc. Figure 27.20d

(d) The three phases of the uterine cycle: • Menstrual: Shedding of the functional layer of the endometrium. • Proliferative: Rebuilding of the functional layer of the endometrium. • 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. Thesecretory phase corresponds in time to the luteal phase of the ovarian cycle.

Menstrualphase

Menstrualflow

Endometrialglands

Blood vessels

Functional layer

Basal layer

Proliferativephase

Secretoryphase

Days


Uterine Cycle

• If fertilization does not occur

• Corpus luteum degenerates

• Progesterone levels fall

• Spiral arteries kink and spasm

• Endometrial cells begin to die

• Spiral arteries constrict again, then relax and open wide

• Rush of blood fragments weakened capillary beds and the functional layer sloughs


Effects of Estrogens

• Promote oogenesis and follicle growth in the ovary

• Exert anabolic effects on the female reproductive tract

• Support the rapid but short-lived growth spurt at puberty



• Induce secondary sex characteristics

• Growth of the breasts

• Increased deposit of subcutaneous fat (hips and breasts)

• Widening and lightening of the pelvis



• Metabolic effects

• Maintain low total blood cholesterol and high HDL levels

• Facilitates calcium uptake


Effects of Progesterone

• Progesterone works with estrogen to establish and regulate the uterine cycle

• Effects of placental progesterone during pregnancy

• Inhibits uterine motility

• Helps prepare the breasts for lactation


Female Sexual Response

• Initiated by touch and psychological stimuli

• The clitoris, vaginal mucosa, and breasts engorge with blood

• Vestibular gland secretions lubricate the vestibule

• Orgasm is accompanied by muscle tension, increase in pulse rate and blood pressure, and rhythmic contractions of the uterus


Female Sexual Response

• Females do not have a refractory period after orgasm and can experience multiple orgasms in a single sexual experience

• Orgasm is not essential for conception


Sexually Transmitted Infections (STIs)

• Also called sexually transmitted diseases (STDs) or venereal diseases (VDs)

• The single most important cause of reproductive disorders


Gonorrhea

• Bacterial infection of mucosae of reproductive and urinary tracts

• Spread by contact with genital, anal, and pharyngeal mucosae


Gonorrhea

• Signs and symptoms

• Males

• Urethritis, painful urination, discharge of pus

• Females

• 20% display no signs or symptoms

• Abdominal discomfort, vaginal discharge, or abnormal uterine bleeding

• Can result in pelvic inflammatory disease and sterility

• Treatment: antibiotics, but resistant strains are becoming prevalent


Syphilis

• Bacterial infection transmitted sexually or contracted congenitally

• Infected fetuses are stillborn or die shortly after birth

• Infection is asymptomatic for 2–3 weeks

• A painless chancre appears at the site of infection and disappears in a few weeks


Syphilis

• If untreated, secondary signs appear several weeks later for 3–12 weeks, and then disappear: pink skin rash, fever, and joint pain

• The latent period may or may not progress to tertiary syphilis, characterized by gummas (lesions of the CNS, blood vessels, bones, and skin)

• Treatment: penicillin


Chlamydia

• Most common bacterial STI in the United States

• Responsible for 25–50% of all diagnosed cases of pelvic inflammatory disease

• Symptoms: urethritis; penile and vaginal discharges; abdominal, rectal, or testicular pain; painful intercourse; irregular menses

• Can cause arthritis and urinary tract infections in men, and sterility in women

• Treatment: tetracycline


Viral Infections

• Genital warts

• Caused by human papillomavirus (HPV)

• Second most common STI in the United States

• Increase the risk of cancers in infected body regions


Viral Infections

• Genital herpes

• Caused by human herpes virus type 2

• Characterized by latent periods and flare-ups

• Congenital herpes can cause malformations of a fetus

• Treatment: acyclovir and other antiviral drugs


Developmental Aspects: Determination of Genetic Sex

• One of the 23 pairs of chromosomes in body cells are sex chromosomes: X and Y

• Females are XX and each egg has an X chromosome

• Males are XY, so ~50% of sperm contain X, ~50% contain Y


Developmental Aspects: Determination of Genetic Sex

X egg + X sperm XX (female offspring)

X egg + Y sperm XY (male offspring)

• The SRY gene on the Y chromosome initiates testes development and maleness


Developmental Aspects: Sexual Differentiation

• Sexually indifferent stage

• Gonads begin development in fifth week as gonadal ridges

• Paramesonephric (Müllerian) ducts (future female ducts) form lateral to the mesonephric (Wolffian) ducts (future male ducts)

• Primordial germ cells migrate to the gonadal ridges to provide germ cells destined to become spermatogonia or oogonia

• Gonads begin development in seventh week in males, eighth week in females

Copyright © 2010 Pearson Education, Inc. Figure 27.21 (1 of 5)

Mesonephros

Gonadal ridge

Metanephros(kidney)

5- to 6-week embryo:sexually indifferent stage

Mesonephric(Wolffian) ductParamesonephric(Müllerian) duct

Cloaca


Paramesonephricduct (degenerating)

Testes

Mesonephric ductforming the ductusdeferensUrinary bladder

Seminal vesicle

Urogenital sinusforming the urethra

Epididymis

Efferent ductules

7- to 8-week male embryo


Ovaries

8- to 9-week female fetus

Paramesonephricduct forming theuterine tubeMesonephric duct(degenerating)Fusedparamesonephricducts forming the uterusUrinary bladder(moved aside)Urogenital sinusforming the urethraand lower vagina


Developmental Aspects: Development of External Genitalia

• Genital tubercle penis of male; clitoris of female

• Urethral fold urethra of male; labia minora of female

• Labioscrotal folds scrotum of male: labia majora of female


Urethral fold

LabioscrotalswellingUrethral groove

Genitaltubercle

Anus

Tail (cut)

(a) Indifferent

Copyright © 2010 Pearson Education, Inc. Figure 27.22c

(c) Female development

Anus

Labia majora

Glans clitoris

Labiaminora

Anus

Labioscrotalswellings(labia majora)

Glans clitorisUrogenitalsinusUrethralfolds(labiaminora)

Approximately 5 weeks


Development Aspects: Descent of the Gonads

• About two months before birth

• Testosterone stimulates the migration of the testes toward the scrotum

• Ovaries also descend, but are stopped by the broad ligament at the pelvic brim

• Gubernaculum: fibrous cord from each testis to the scrotum or from ovary to labium majus; guides the descent


TestisPenis

Urinary bladder

Seminal vesicle

Epididymis

Urethra

Ductus deferens

Bulbourethral glandProstate

Efferent ductules

At birth: male development


At birth: Female development

Uterine tube

Ovary

Uterus

Urinary bladder(moved aside)Vagina

HymenVestibule

Urethra


Development Aspects: Puberty

• In response to rising levels of gonadal hormones

• Reproductive organs grow to adult size and become functional

• Secondary sex characteristics appear

• Earliest time that reproduction is possible


Menopause

• Has occurred when menses have ceased for an entire year

• There is no equivalent to menopause in males


Menopause

• Declining estrogen levels

• Atrophy of reproductive organs and breasts

• Irritability and depression in some

• Hot flashes as skin blood vessels undergo intense vasodilation

• Gradual thinning of the skin and bone loss

• Increased total blood cholesterol levels and falling HDL

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