1. The Reproductive System
Chapter 53
The Reproductive System
You are not responsible for the more detailed descriptions of reproduction in fishes, amphibians, reptiles and birds on pages 1070 – 1072.
You are only responsible for the hormones we discuss in class
We will draw upon a few topics from Chapter 54 about fetal development
The Reproductive System

2. Sexual vs. asexual reproduction
Asexual reproduction: produces genetically identical cells
fission (prokaryotes)
budding
Asexual reproduction
Genetically identical cells are produced from a single parent cell through mitosis
Single-celled organisms utilize fission
Cnidarians reproduce by budding (offspring develop as a growth on the body of the parent)
The Reproductive System

3. The Reproductive System
Why sex?
Protozoa
Fish
Amphibians
Bacterial conugation
Fungi
Vertebrate sexual reproduction evolved in in the ocean before vertebrates colonized land
Marine bony fish use external fertilization
-Eggs and sperm are released into the water where union of free gametes occurs
Most other vertebrates use internal fertilization
-Sperm are introduced into the female reproductive tract
Fishes -In most species of bony fish, fertilization is external
-Thousands of eggs are fertilized, but only a few individuals grow to maturity
-In most species of cartilaginous fish, fertilization is internal
-Development of young is viviparous
Amphibians-In most species fertilization is external
-Eggs of most species develop in water -With some interesting exceptions
-Development is divided into embryonic, larval and adult stages
How does sex contribute to natural selection?
The Reproductive System

4. The Reproductive System
How is sex determined?
Environmentally controlled
Temperature
Community structure
Genetically controlled
-- e.g., Sex-determining Region of the Y chromosome)
-- Female condition is default in mammals
Humans
Embryonic gonads indifferent for first 40 days
SRY gene on Y converts gonads to testes
Testosterone promotes male development
The Reproductive System

5. Interesting “twists” to sexual determination
Hermaphroditism
One individual has both types of reproductive organs
Plants, earthworms
May be sequential
Protogyny – female-to-male change
Protandry – male-to-female change (e.g. Nemo!)
Parthenogenesis
Females produce offspring from unfertilized eggs
Nemo = protandrous hermaphrodite
The Reproductive System

6. Oviparity in male midwife toad Copyright © 2000 Michael Frede
Reproductive strategies
have evolved toward internal fertilization and development
Why is internal fertilization
better than external?
Why is internal development
Oviparity in male midwife toad
Copyright © 2000 Michael Frede
Human viviparity
The Reproductive System

7. Reproduction in mammals
Internal fertilization
All female mammals produce milk
Mammals are of three types:
Monotremes lay eggs.
Marsupials give birth to incompletely developed fetuses, which mature in mother’s pouch.
Placentals retain young in uterus for long periods of development.
The Reproductive System

8. Reproduction in Humans
Humans are Placental, genetically determined sex
Complex reproductive biology;
Hormonal regulation influences
Development & 2O sexual characteristics
Mating behavior
Gender identification
We share hormones
-- differ in quantity and effects
Female reproductive biology
particularly complicated
-- Mating receptiveness uncoupled
from Estrus
-- unlike other mammals
The Reproductive System

9. The Reproductive System
What are the characteristics of
the Male Reproductive System?
Anatomy
Erection
What are 1O and 2O sexual
characteristics?
2O characteristics
Testosterone
Androstenedione abuse
Contraception
condom
vasectomy
The Reproductive System

10. The Reproductive System
Hormonal regulation is “Endocrine”
-- Hormones move between organs
Pituitary hormones
FSH – stimulates
spermatogenesis
LH – stimulates testosterone
synthesis
Testosterone
Androstenedione abuse
The Reproductive System

11. The Reproductive System
Spermatogenesis
In the wall of the seminiferous tubule, a spermatogonium divides by mitosis to produce two diploid cells
One later undergoes meiosis, the other remains as a spermatogonium
The diploid cell that begins meiosis is called a primary spermatocyte
It undergoes meiosis I, producing two haploid secondary spermatocytes
Each secondary spermatocyte undergoes meiosis II to produce two haploid spermatids
The seminiferous tubules also contain supporting cells called Sertoli cells
Nurse developing germ cells
Help convert spermatids into spermatozoa (sperm) by engulfing their extra cytoplasm
Several developmental stages
Primary vs. secondary spermatocytes
Spermatid
Spermatozoa
The Reproductive System

12. The Reproductive System
What are the characteristics of
the Female Reproductive System?
Anatomy
Pathway of egg travel
Pregnancy
Contraception:
diaphragm
tubal ligation
spermicides
IUD
The Reproductive System

13. The Reproductive System
Hormonal control the female reproductive system
What is the ovarian cycle?
Follicle stimulating hormone (FSH)
Luteinizing hormone (LH)
Follicle & corpus luteum
What is the uterine cycle?
Estrogen & Progesterone
Endometrium & Menstruation
Other forms of contraception
Rhythm method
Chemical contraceptives
oral: (The “Pill’)
Implant (“Norplant”)
Injectable
The Reproductive System

14. The Reproductive System
What happens after fertilization?
Completion of meiosis
Implantation in endometrium
Ectopic pregnancy
The Reproductive System

15. The Reproductive System
Hormonal changes upon pregnancy
Roles of embryo and corpus luteum
Progesterone
Estrogen
Human Chorionic Gonadotropin (HCG)
What happens if the female reproductive cycle becomes disrupted?
Amenorrhia
Menopause
The Reproductive System

16. The Reproductive System
Assisted pregnancy
Artificial insemination
Gamete Intrafallopian
transfer
In-vitro fertilization
Gamete donation
Surrogate mothering
Pictures used with the permission of Dr. Clemens M. Grosskinsky, ORM, Columbus
The Reproductive System

17. The Reproductive System
What are the functions of the amnion and placenta?
Amniotic sac & fluid
Maternal and fetal
circulatory systems
-- no connection
Exchange of
nutrients
gasses
wastes
Chorionic
villi
The Reproductive System

18. The Reproductive System
What are the stages of
fetal development?
Trimesters
Embryonic stage
Fetal stage
Sensitive periods
Fetal alcohol
syndrome
4 weeks months months
The Reproductive System

19. The Reproductive System
How can
Congenital Defects
be tested for?
Amniocentesis
Chorionic villi sampling
Perform karyotype
The Reproductive System

20. The Reproductive System
Labor and Birth
Fetal position
-- why is ‘breach’ position bad
Uterine contractions
Dilation of cervix
Extraction of the placenta
The Reproductive System