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Reproduction &
Development
Chp 21
GAMETE FORMATION
Meiotic division produces Haploid Gametes
• Egg
• Sperm
Anatomy Of A Sperm Cell
• Arcosome
• head
• Midpiece
• tail
Anatomy Of Egg Cell
• Jelly coat
• Membrane
• Organelles
Fertilization
• Sperm and egg unite: 6-24 hours after intercourse,
sperm survives days
• One sperm fertilizes one egg
• Acrosome: rich in digestive enzymes
• Sperm penetrates corona radiata and zona pellucida
• Sperm proteins lock with egg membrane receptors
• Zona pellucida made impermeable to other sperm
Arcosomal Reaction
• Arcosome opens & releases digestive
enzyme
• Fertilization tube forms
• DNA moves into egg & joins w/Egg DNA
Prevention of Polyspermy
• Wave of depolarization - Fast block to
polyspermy
• Cortical reaction - fertilization membrane
Twins
1. Fraternal: more than one oocyte fertilized by
different sperm, may be different sex
2. Identical: one oocyte fertilized, split before 16
cell stage, same sex
3. Conjoined twins: separation not complete
Developmental Processes
1. Cell division or mitosis - cell division
without cell growth
2. Differentiation - individual cells take on
specialized forms and functions
3. Morphogenesis - physical development of
organism, ongoing
4. Growth - at implantation, growth in size
Summary Early Developmental Events
1. Cleavage 2. Blastulation 3. Gastrulation 4. Organogenesis/Nerulation -
Pre-embryonic Development:
The First Two Weeks
Process
• Travels through oviduct
• Implantation into uterine lining
• Growth, differentiation, and morphogenesis
begins
• Morula to blastocyst to embryonic disk
• Ectopic pregnancy possible
Embryonic Development: Weeks
Three to Eight, Embryo
Tissues and organs: derived from three germ layers
• Ectoderm: body covering & neural structures brain, spinal cord, & nerves.
• Mesoderm: skeleton, muscles, blood vessels,
heart, kidneys, gonads, & dermis.
• Endoderm: primitive gut, lungs, liver &
pancreas [+ most organs]
Placenta and Umbilical Cord
Figure 21.8
Placenta
• Development
• Chorion digests into endometrium, creating pool
of blood
• Placenta seals off the pool and projects chorionic
villi into blood
• Villi contain blood capillaries connected through
the umbilical vessels to the fetus
Placenta
(cont.)
• Functions
• Filters nutrients, waste, and antibodies for fetus
without mixing mother or fetal circulations
• Some toxins or viruses may pass through
• Hormonal: produce estrogen and progesterone
Embryo Development: Third and
Early Fourth Week
Figure 21.9
Rapid Embryo Development
• Day 15
• Primitive streak: appears in embryonic disk,
elongates along one axis
• Day 19-24
• Neural groove: brain and spinal cord
• Somites: bone, muscle, skin
• Pharyngeal arches: part of face, neck, and mouth
• Limb buds: arms and legs
Fetal Development: Eight Weeks to
Birth
• Months three and four: organ development,
beginnings of organ function
• Months five and six: fetal movement begins,
responds to external sounds, survival possible
outside mother
• Months seven through nine (third trimester):
growth and maturation
Stages of Birth
Figure 21.13A
Stages of Birth
(cont.)
Figure 21.13B, C
Birth
Labor & delivery
• Stages of labor:
• Stage 1: dilation
• Stage 2: expulsion
• Stage 3: afterbirth
• Cesarean delivery: surgical delivery of baby
Early Postnatal Period
• Transition from fetus to newborn
• Taking the first breath: pulmonary surfactants
necessary
• Changes in cardiovascular system
• Umbilical circulation cut off
• Ductus venosus regresses to connective tissue
• Foramen ovale and ductus arteriosus close in
days/weeks
• All blood from the digestive tract goes to liver
• Lactation: colostrum to milk
Birth to Adulthood
• Neonatal period: helpless period, movement by
reflex
• Infancy; rapid development and maturation of
organ systems
• Childhood: continued development and growth
• Adolescence: transition to adulthood
Aging: Change Over Time
• Causes of aging: theories
• Internal cellular program that counts finite
number of cell divisions, thus determining cell
death
• Cell DNA damaged beyond repair
• Aging a whole body process; all systems
interdependent
Aging: Change Over Time
(cont.)
• Body systems: age at different rates;
musculoskeletal, skin, cardiovascular, respiratory,
immune, nervous, sensory, reproductive, endocrine,
digestion and nutrition, urinary
• Aging well: life style, exercise, diet
Death: Final Transition
• Legal and medical criteria
• Irreversible cessation of circulatory and
respiratory functions
• Irreversible cessation of all functions of the entire
brain, including the brain stem