Reproductive System

Getting Genes IntoThe Next Generation

Fertilization brings togethera haploid sperm and a haploid egg (ovum) to

form a diploid zygote and embryo.

Haploid

Haploid

Diploid Diploid

Overall Strategies of Reproduction

Males Produce haploid gametes (sperm - testes) Produce lubricants and nutrients for sperm (seminal fluids) Deliver semen to female reproductive system (penis) Provide hormones to coordinate system

Females Produce haploid gametes (ovaries) Produce lubricants for intercourse Receive semen from male (vagina) Provide for development of embryo (uterus and placenta) Provide nutrients for growth of enfant (breasts – lactation) Provide hormones to coordinate system

Ureter

Urinary bladder

Testis (Testes) spermatogenesis endocrine tissue

Epididymis store sperm sperm mature/motile

Penis erectile tissue semen delivery

Prostate gland seminal fluid

Seminal Vesicles seminal fluid

Glans sensitive nerve endings

Basic Male Anatomy

Basic Female Anatomy

Ovary Oogenesis Endocrine tissue

Oviduct (uterine tube) site of fertilization carries sperm to ovum carries embryo to uterus

Uterus Site of embryological development

Cervix separates the uterus and the vagina

Vagina accommodates the penis

Clitoris sensitive nerve endings

Ureter

Urinary Bladder

Urethra

Development of Reproductive Organs1. Undifferentiated gonad

2. Wolffian ducts

3. Mulerian Ducts

4. Ureter

5. Genital tubercle

6. Cloaca

7. and 8. Labioscrotal fold

9. Anus

Genetics of Sex

• Normally humans have two complete sets of chromosomes: pairs of 23 different chromosomes.

• Normally females have two “X” chromosomes and males have a mismatched pair: one “X” and one “Y”.

• The Y chromosome carries genes that will help to regulate the normal development of a male embryo/fetus.

At 10 weeks of development, visible differences in male and female embryosbegin to occur. Genes from the Y chromosome (only present in males) activate the production of testosterone and Mullerian Inhibiting Substance (MIS). These Substances sustain the development of the Wolffian Ducts and inhibit the development of the Mullerian ducts.

In the absence of testosterone and MIS, the reproductive tract will develop asa normal female phenotype.

Reproductive Tracts at Birth

Androgen Insensitivity Syndrome(Testicular Feminizing Syndrome)

• Normal XY genotype• Have a mutated gene that codes for the testosterone receptor, and

sometimes the MIS receptor as well.• Produce normal levels of testosterone, but the target tissues are unable

to respond.• Wolffian ducts do not persist and Mullerian ducts may develop.• If MIS is present, then no uterus will develop and the vagina is small.• Normal female phenotype develops - except, testes are located where

the ovaries belong.• Often undetected prior to puberty.• Externally puberty proceeds as normal, but no menstruation occurs.

Three Siblings with Androgen Insensitivity Syndrome

Male Reproduction

Testis

SeminiferousTubules

Epididymis

Spermato-genesis

D

C

B

A

A and B = Spermatogonia C= SpermatocyteD = Spermatids

Interstitial Cells Of Leydig

• Interstitial Cells ofLeydig = produceTestosterone.

• Sertoli Cells(Sustenacular Cells)Surround spermatocytesand spermatids.Produce Inhibin

What Effects Does Testosterone Have?

• Normal Embryological Development in Males• Stimulates growth and development of the

male reproductive tract at puberty• Stimulates spermatogenesis• Male secondary sex traits (Height, muscle

mass, larger larynx, facial and body hair)

GnRHGonadotropicReleasing HormoneGnRH

LH+ FSHLH+ FSH

InhibinInhibin

Inhibits FSHsecretion

TestosteroneTestosteronePhysiologicalEffects

Inhibits GnRHSecretion

Role of the Accessory Glands• Seminal Vesicles – fructose (energy source) and

prostaglandins that stimulate contractions of female repro. Tract.

• Prostate Gland – High pH fluid that neutralizes the acidic environment of the vagina and increases the motility of the sperm.

• Bulbourethral gland (Cowper’s Gland)

Role of the ScrotumTemperature regulation

Female Reproductive System

Ovary

Fimbriae

Uterine Tube (oviduct)Myometrium

Endometrium

Cervix

Vagina

Overview of the Menstrual Cycle• Approximately 28 days (may be highly variable)• Day one is counted as the first day after menstrual bleeding

stops.• Days 1-14 - Ovum enlargess inside a growing follicle and the

endometrial lining of the uterus thickens in preparation to receive a fertilized egg

• Day 14 - Ovulation (release of egg from ovary) occurs and the ovum enters the uterine tube.

• Days 15-20 – Ovum (or fertilized egg) moves to uterus.• Days 18-21 – If embryo exists, it begins to implant in

endometrium• Days 25-28 – If embryo does not implant, endometrial lining

as lost in menstrual bleeding.

Stages of the Ovarian Cycle

GnRH

LH +FSH

E E

Positive Feedback

Low levelsof LH and FSHGnRH = gonadotropin

Releasing hormone

FSH = follicle stimulatinghormone

LH = luteinizing hormone

Pre-ovulation

1. The positive feedback ofEstrogen at the hypo-Thalamus causes a surgein GnRH release.

2.The GnRH release causes a surge in FSH and LH

3.The LH surge causes ovulationand the formation of thecorpus luteum

4.The Corpus luteum continuesto release E and highlevels of P

5.The E and P providenegative feedbackto the hypothalamus

Rising levelsof estrogenover severaldays.

GnRHsurge

FSH and LHSurge

E and P

Physiological Effects of Estrogen

• Estrogen - steroid produced by the ovary*growth of the female reproductive tract*stimulates growth of endometrial lining during each menstrual cycle*stimulates the production of a watery secretion at the cervix.*stimulates breast and hip development andsubcutaneous fat layer (secondary sex traits)

• Progesterone* Increases endometrial lining and maintains the endometrial lining.* Causes a thick mucous secretion from the cervix.* Increases the basal metabolic rate (increase in resting body temperature by about 1 degree)

Physiological Effects of Progesterone

If Fertilization Does Not OccurWithout additional LH or some other source of hormonal stimulation, the corpus luteum has a limited life; typically around 10 days. After 10 days the corpus luteum will degenerate and turn into scar tissue (corpus albicans). At this point the levels of estrogen and progesterone decline very rapidly. Without estrogen and progesterone, the endometrial lining is lost.

Chemical Contraception

Birth control pills, Depoprovera (injected 2-4 times per year), and “patches”

All contain relatively high levels of estrogen and lower amounts of progesterone.

Provides negative feedback to hypothalamus.

Interferes with normal secretions of cervix.

Fertilization

Signaling by the Embryo• Blastocyst• Trophoblast releases Human Chorionic

Gonadotropin (HCG)• HCG acts like LH and stimulates the ovary to

maintain the corpus luteum• Ovary continues to make progesterone and

estrogen.• Endometrial lining is retained - woman

“misses her period.”