1. Chapter 42 BIOL 1000 Dr. Mohamad H. Termos
Development and Aging
Chapter 42
BIOL 1000
Dr. Mohamad H. Termos

2. Early Developmental Stages
Biology, 9th ed, Sylvia Mader
Chapter 44
Early Developmental Stages
Fertilization - sperm and egg unite to form a zygote
A human sperm cell has three parts:
The head
Haploid nucleus
Acrosome
A middle piece
The tail
Animal Development

3. Early Developmental Stages
Biology, 9th ed, Sylvia Mader
Chapter 44
Early Developmental Stages
An egg
Actually a secondary oocyte
Surrounded by layers of adhering follicular cells termed the corona radiata
Surrounded by the zona pellucida
Between the plasma membrane and the corona radiata
Animal Development

4. Biology, 9th ed, Sylvia Mader
Fertilization
Chapter 44
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
microvilli of oocyte plasma membrane
2. Acrosomal enzymes
digest a portion of
zona pellucida.
tail
3. Sperm binds to and
fuses with oocyte
plasma membrane.
sperm
1. Sperm makes its
way through the
corona radiata.
corona radiata
4. Sperm nucleus enters
cytoplasm of oocyte.
5. Cortical granules
release enzymes;
zona pellucida
becomes fertilization
membrane.
plasma
membrane
nucleus
middle
piece
head
acrosome
fertilization membrane
6. Sperm and egg
pronuclei are enclosed
in a nuclear envelope.
cortical granule
sperm pronucleus
oocyte plasma membrane
zona pellucida
egg pronucleus
© David M. Phillips/Visuals Unlimited; (Chick, p. 779): © Photodisc/Getty Images
Animal Development

5. Early Developmental Stages
Biology, 9th ed, Sylvia Mader
Chapter 44
Early Developmental Stages
Several hundred sperm reach the oocyte
Sperm secrete enzymes to weaken the corona radiata and bind to the zona pellucida
Acrosome releases digestive enzymes to allow the sperm to pass through the zona pellucida to the plasma membrane of the oocyte
Animal Development

6. Early Developmental Stages
Biology, 9th ed, Sylvia Mader
Early Developmental Stages
Chapter 44
One sperm enters the egg
Prevent polyspermy
Fertilization membrane forms
The secondary oocyte completes meiosis
A single nuclear envelope surrounds the egg and sperm pronuclei
Zygote
First cell division occurs
Animal Development

7. Biology, 9th ed, Sylvia Mader
Fertilization
Chapter 44
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
microvilli of oocyte plasma membrane
2. Acrosomal enzymes
digest a portion of
zona pellucida.
tail
3. Sperm binds to and
fuses with oocyte
plasma membrane.
sperm
1. Sperm makes its
way through the
corona radiata.
corona radiata
4. Sperm nucleus enters
cytoplasm of oocyte.
5. Cortical granules
release enzymes;
zona pellucida
becomes fertilization
membrane.
plasma
membrane
nucleus
middle
piece
head
acrosome
fertilization membrane
6. Sperm and egg
pronuclei are enclosed
in a nuclear envelope.
cortical granule
sperm pronucleus
oocyte plasma membrane
zona pellucida
egg pronucleus
© David M. Phillips/Visuals Unlimited; (Chick, p. 779): © Photodisc/Getty Images
Animal Development

8. Biology, 9th ed,Sylvia Mader
Chapter 09
The Cell Cycle

9. Early Developmental Stages
Biology, 9th ed, Sylvia Mader
Chapter 44
Early Developmental Stages
Embryonic Development
Development: all the changes that occur during the life cycle of an organism
Embryo: first stages of development
Cleavage: Cell division without growth
Animal Development

10. Embryonic Development
Biology, 9th ed, Sylvia Mader
Chapter 44
Embryonic Development
Cellular stages
Morula –ball of cells resulting from cleavage
Blastula- hollow ball of cells
results from the morula continuing to divide and cells releasing sodium into center of ball of cells
Fluid filled center
Hollow center is called blastocoel
Animal Development

11. Early Developmental Stages: Tissues
Biology, 9th ed, Sylvia Mader
Chapter 44
Early Developmental Stages: Tissues
Gastrulation
Germ layer formation and differentiation
Ectoderm – outer layer
Mesoderm – middle layer of cells
Endoderm – inner layer
Blastopore
Pore created by the inward folding of cells
Eventually becomes the anus
Archenteron- opening created by inward folding (primitive gut)
Animal Development

12. Biology, 9th ed, Sylvia Mader
Germ Layers
Chapter 44
Ectoderm: Outer layer. Gives rise to:
epidermis and related structures
nervous system
lining of oral cavity and rectum
Mesoderm: Middle layer. Gives rise to: muscles, cardiovascular system, urinary system, reproductive system and outer layers of systems
also the notochord which becomes the backbone
Endoderm: Inner layer. Gives rise to: linings of digestive system, respiratory system, and glands
Animal Development

13. Biology, 9th ed, Sylvia Mader
Chapter 44
Embryonic Germ Layers
Animal Development

14. Early Developmental Stages: Organs
Biology, 9th ed, Sylvia Mader
Chapter 44
Early Developmental Stages: Organs
Organ Stages of Development
Nervous system
Develops from midline ectoderm located just above the notochord
Notochord = dorsal supporting rod
Neural grove becomes the neural tube
Animal Development

15. Developmental Processes
Biology, 9th ed, Sylvia Mader
Chapter 44
Developmental Processes
Development requires:
Growth
Cellular Differentiation
Cells become specialized in structure and function
Morphogenesis
Produces the shape and form of the body
Includes pattern formation
Arrangement of tissues and organs within the body
Involves apoptosis
Animal Development

16. Human Embryonic and Fetal Development
Biology, 9th ed, Sylvia Mader
Chapter 44
Human Embryonic and Fetal Development
Human gestation time - time from conception to birth - is approximately nine months
Embryonic Development - Months 1-2
Formation of major organs
Fetal Development - Months 3-9
Major organs become larger and refined
Animal Development

17. Human Embryonic and Fetal Development
Biology, 9th ed, Sylvia Mader
Chapter 44
Human Embryonic and Fetal Development
Extraembryonic Membranes
Chorion – responsible for gas exchange
Amnion – contains the protective amniotic fluid, which functions to bathe the developing embryo
Allantois – collects nitrogenous wastes
Yolk sac – provides nourishment
Presence of embryonic membranes in humans demonstrates our evolutionary relationship to reptiles
Animal Development

18. Human Embryonic Development
Biology, 9th ed, Sylvia Mader
Chapter 44
Human Embryonic Development
First Week
Morula transformed into blastocyst
Blastocyst consists of: 1- A fluid-filled cavity, 2- A single layer of outer cells called the trophoblast, which gives rise to chorion. The inner cell mass - develops into a fetus
Second Week
Implantation begins
Trophoblast secretes human chorionic gonadotropin (HCG)
Maintains corpus luteum, therefore maintaining the endometrium and preventing menstruation
Hormone that is the basis of the pregnancy test
Gastrulation occurs
Inner cell mass flattened into embryonic disk
Ectoderm, mesoderm, and endoderm differentiate
Animal Development

19. Human Development Before Implantation
Biology, 9th ed, Sylvia Mader
Chapter 44
Human Development Before Implantation
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
egg nucleus
2. Fertilization
sperm nucleus
secondary oocyte
secondary oocyte
zona pellucida
corona radiata
5. Early blastocyst
single cell =
zygote
1. Ovulation
fimbriae
inner cell
mass
ovary
oviduct
2-cell
stage
6. Implantation
4-cell
stage
3. Cleavage
8-cell
stage
early chorion
4. Morula
(fertilization): © Don W. Fawcett/Photo Researchers,Inc.; (2-cell): © Rawlins-CMSP/GettyImages;(morula): © RBM Online/epa/Corbis; (implantation): © Bettmann/Corbis
Animal Development

20. Human Embryonic Development
Biology, 9th ed, Sylvia Mader
Chapter 44
Human Embryonic Development
Third Week
Nervous system and circulatory system appear
Fourth and Fifth Weeks
Umbilical cord is fully formed
Limb buds appear
Head enlarges
Sense organs more apparent
Sixth Through Eighth Weeks
Head achieves normal relationship with the body as a neck region develops
Nervous system is developed enough to permit reflex actions
Animal Development

21. Human Embryo at Beginning of Fifth Week
Biology, 9th ed, Sylvia Mader
Chapter 44
Human Embryo at Beginning of Fifth Week
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
brain
tail
brain
optic
vesicle
optic
vesicle
pharyngeal
pouch
tail
pharyngeal
pouch
heart
region of
heart, liver
liver
limb bud
limb bud
umbilical
vessel
umbilical
vessel
somite
limb bud a. b.
gastrointestinal tract
a: © Lennart Nilsson, A Child is Born, Dell Publishing
Animal Development

22. Human Embryonic and Fetal Development
Biology, 9th ed, Sylvia Mader
Chapter 44
Human Embryonic and Fetal Development
The Structure and Function of the Placenta
Placenta
a mammalian structure that functions in gas, nutrient, and waste exchange between embryonic and maternal cardiovascular systems.
Begins formation once the embryo is fully planted
Chorionic villi
Project into the maternal tissues
Surrounded by maternal blood sinuses
The maternal and fetal blood do not mix
Exchange between the fetal and maternal blood takes place across the walls of the chorionic villi
Animal Development

23. Fetal Development and Birth
Biology, 9th ed, Sylvia Mader
Chapter 44
Fetal Development and Birth
Fetal development (months 3–9) involves:
Extreme increase in size
The genitalia appear in the third month
A fetus soon acquires hair, eyebrows, eyelashes, and nails
A fetus at first only flexes its limbs and nods its head
Later it moves its limbs vigorously
A mother feels movements from the fourth month on
After 16 weeks, a fetal heartbeat is heard through a stethoscope.
A fetus born at 24 weeks may survive
Animal Development

24. Preventing and Testing for Birth Defects
Biology, 9th ed, Sylvia Mader
Chapter 44
Preventing and Testing for Birth Defects
Have good health habits
Nutritious diet
Avoid potentially harmful substances, radiation, and pathogens
Avoid alcohol, smoking, and drugs of abuse
Alcohol consumption during pregnancy is a leading cause of birth defects
Many preventable birth defects are caused by cigarette smoking
Avoid certain medications and supplements
Avoid having X-rays
Penetrating forms of radiation such as X-rays can hinder cell division and damage DNA
Animal Development

25. Biology, 9th ed, Sylvia Mader
Stages of Birth
Chapter 44
When the fetal brain matures, the hypothalamus causes the pituitary to stimulate the adrenal cortex so that androgens are released.
The placenta uses androgens as precursors for estrogens that stimulate the production of prostaglandin and oxytocin
The hormones estrogen, prostaglandin, and oxytocin all cause the uterus to contract and expel the fetus
The process of birth (parturition) has three stages: dilation of the cervix, birth of the baby, and expulsion of the placenta
Animal Development