Transcript Reproductive System

Reproductive System
Getting Genes Into
The Next Generation
Fertilization brings together
a haploid sperm and a haploid egg (ovum) to
form a diploid zygote and embryo.
Haploid
Diploid
Haploid
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
Basic Male Anatomy
Ureter
Urinary bladder
Seminal Vesicles
seminal fluid
Prostate gland
seminal fluid
Penis
erectile tissue
semen delivery
Glans
sensitive nerve endings
Epididymis
store sperm
sperm mature/motile
Testis (Testes)
spermatogenesis
endocrine tissue
Basic Female Anatomy
Uterus
Site of embryological development
Ureter
Urinary Bladder
Urethra
Clitoris
sensitive nerve
endings
Oviduct (uterine tube)
site of fertilization
carries sperm to ovum
carries embryo to uterus
Ovary
Oogenesis
Endocrine tissue
Cervix
Vagina
separates the uterus
accommodates
and the vagina
the penis
Development of Reproductive Organs
1. 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 embryos
begin 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 as
a 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
Epididymis
D
C
Seminiferous
Tubules
Testis
Spermatogenesis
B
A
Interstitial Cells
Of Leydig
A and B = Spermatogonia
D = Spermatids
C= Spermatocyte
• Interstitial Cells of
Leydig = produce
Testosterone.
• Sertoli Cells
(Sustenacular Cells)
Surround spermatocytes
and 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)
Inhibits GnRH
Secretion
Gonadotropic
Releasing Hormone
GnRH
LH
+ FSH
Inhibits FSH
secretion
Inhibin
Physiological
Effects
Testosterone
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 Scrotum
Temperature regulation
Female Reproductive System
Uterine Tube (oviduct)
Myometrium
Fimbriae
Ovary
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
Pre-ovulation
Positive Feedback
LH +
FSH
GnRH = gonadotropin
Releasing hormone
FSH = follicle stimulating
hormone
LH = luteinizing hormone
Low levels
of LH and FSH
E
E
1. The positive feedback of
Estrogen at the hypoThalamus causes a surge
in GnRH release.
GnRH
surge
2. The GnRH release causes
a surge in FSH and LH
FSH and LH
Surge
3. The LH surge causes ovulation
and the formation of the
corpus luteum
4. The Corpus luteum continues
to release E and high
levels of P
5. The E and P provide
negative feedback
to the hypothalamus
E and P
Rising levels
of estrogen
over several
days.
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 and
subcutaneous fat layer
(secondary sex traits)
Physiological Effects of
Progesterone
• 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)
If Fertilization Does Not Occur
Without 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.”