Unit V: DevelopmentSex Hormones

Chapter 26: pp. 966-967

Chapter 16: pp. 569

Essence of Sex

• Reproduction

– great variety of methods

asexual vs. sexual

• Sexual reproduction

– each offspring has 2 parents

– provides genetic diversity

Functions of Reproductive System

1. Produce and nurture sex cells

2. Transport gametes to site of fertilization

3. Secrete hormones

– Secondary sex characteristics

– Reproductive physiology

Two Sexes

• Gametes combine to form a zygote

1. Motility to achieve contact

• has Y chromosome

2. contains nutrients for developing embryo

• lacks Y chromosome

• in mammals female also provides shelter for developing embryo (uterus and placenta)

Role of Sex Chromosomes

• Somatic cells contain 23 pairs of chromosomes

– 22 pairs of autosomes

– 1 pair of sex chromosomes (XY males: XX females)

• 50% sperm carry Y; 50% X

• all eggs carry the X chromosome

• Sex of child determined by type of sperm that fertilizes mother’s egg

• Meiosis – series of two cell divisions that cut chromosome number in half

– diploid haploid fertilization diploid

Hormones and Sex Differentiation

• Gonads begin to develop at 6 weeks• Gonadal ridges

– mesonephric ducts vas deferens– paramesonephric ducts (müllerian ducts) oviduct

• SRY gene– in males, codes for a protein (TDF) that causes development of

testes • secrete testosterone • secrete müllerian-inhibiting factor degenerates

paramesonephric ducts• Female development occurs in absence of androgens

Fig. 27.3-2

Ovaries

Efferent ductules

Epididymis

Urinary bladder

Seminal vesicle

Mesonephros

Gonadal ridge

Kidney

Mesonephric duct

7 to 8 weeks 8 to 9 weeks

Cloaca

Male Female

Paramesonephric(müllerian) duct

5- to 6-week embryo;sexually indifferent stage

Testes

Paramesonephricduct (degenerating)

Mesonephric ductforming theductus deferens

Urogenital sinusforming the urethra

Paramesonephricduct forming theuterine tube

Mesonephric duct(degenerating)

Fused paramesonephricducts formingthe uterus

Urinary bladder(moved aside)

Urogenital sinusforming the urethraand lower vagina

Adrenal Gland

Adrenal Cortex:

–sex steroids

• Skeletal growth and sustain adult bone mass

• Development of pubic, axillary hair, apocrine glands

• Sustain sex drive

•androgen – male sex hormones

DHEA testosterone

Meets 50% requirement in women

•estrogen (estradiol)

Important after menopause

Adrenogenital Syndrome (AGS)

•Hypersecretion of androgens

•In children:

–Causes enlargement

–Premature onset of puberty

•In women and fetus:

–Masculinizing effects

Female Sex Hormones

• Estrogens – estradiol, estrone, and estriol

• Progesterone– changes in uterus during menstrual cycle (pregnancy)– affects mammary glands– regulates secretion of LH and FSH

• Androgens– development of female skeleton

• Inhibin

Responses to Estrogens in FemalesIntegumentary System

Produce vellus hairs, terminal hair in axillae and genital areaInitial development of the mammary glands

Skeletal System

Muscular System

Cardiovascular System

Respiratory System

More rapid epiphyseal closure Thus skeletal growth is brief

Growth of skeletal muscle fibersThus increasing strength and endurance

At puberty, activates CNS centers involved in female sexual drive and sexual behaviors

Reproductive System

Menstrual cycle ↑ risk of iron-deficiency anemiaEstrogens ↓ plasma cholesterol levels and slow the formation of plaque within arteries.

Less growth of the larynx and vocal cordsThus females have higher-pitched voices

Thicken of the myometrium↑ blood flow to the endometriumDevelopment of accessory reproductive structures

Nervous System

Female Sex Hormones

Release of Gonadotropin-Releasing Hormone (GnRH)Stimulates the production andsecretion of FSH and the production—but not the secretion—of LH.

HYPOTHALAMUS

GnRH

FSHProduction of LHSecretion of LH

Negative feedback

OVARY• Follicle development

• Inhibin• Estradiol

• Ovulation

• Corpus luteum

Progesterone

Beforeday 10

Afterday 10

KEYStimulationInhibition

Secondary Sexcharacteristics

ReproductiveSystem

Stimulation ofendometrial growth and secretion

ANTERIOR LOBE OFPITUITARY GLAND

The Gonads:Ovaries

Responses to Testosterone in MalesIntegumentary SystemTerminal hairs on the face and chest, axillae and genital areaAdipose tissues respond differently totestosterone than to estrogens

Skeletal System

Muscular System

Nervous System

Cardiovascular System

Accelerates bone deposition and skeletal growthPromotes closure of the epiphyseal cartilages

Stimulates the growth of skeletal muscle fibers

A t puberty, activates the CNS centers concerned with male sexual drive and sexual behaviors.

Stimulates erythropoiesis, thereby increasing bloodvolume and the hematocrit.

Respiratory System

Reproductive System

Stimulates disproportionate growth of the larynxThickening and lengthening of the vocal cordsGradual deepening of the voice

Development of the accessory reproductive glandsHelps promote spermatogenesis.

Male Sex Hormones

The Gonads:Testes

GnRHHYPOTHALAMUS

Negative feedback

Released relatively steady.

ANTERIOR LOBE OF THE PITUITARY

GLAND

LH

FSHTargets seminiferous tubules.

KEYStimulationInhibition

Negative feedback

Sustenacular Cells

Inhibin

Interstitial CellTestosteroneTESTES

Respond to factors released by developing spermatozoa

Androgen-binding protein (ABP)binds androgens ofseminiferous tubulesMaturation ofspermatids.

Spermatogenesis and spermiogenesis.

Peripheral Effects

Nervous System

Skeletal System

Secondary sex characteristics

Reproductivesystem

The Gonads:Testes

Androgen-Insensitivity Syndrome(Testicular Feminization)

•Genetically male

•Target cells lack receptors for testosterone

•Female anatomy

–no menstruation or uterus

–presence of testes in abdomen

Overview of Reproductive System

• Primary sex organs

– produce gametes

• Secondary sex organs

– male - ducts, glands, penis

– female - uterine tubes, uterus and vagina

• Secondary sex characteristics

– develop at puberty to attract a mate

• pubic, axillary and facial hair, scent glands, body morphology and low-pitched voice in males