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Chapter 47 ~ Animal
Development
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Menstrual Cycle
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Feedback
Positive – Enhances a process until it is complete.
– During follicular phase – Estrogen stimulates release of LH. Increased LH stimulates follicle to release more estrogen until follicle matures
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Feedback
Negative – stops a process one homeostasis has been reached
– During luteal phase, LH stimulates corpus luteum to secrete estrogen and progesterone. Once they reach sufficient levels, trigger hypothalamus and pituitary to shut off and inhibit secretion of LH and FSH
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Embryonic development/fertilization Preformation~ until 18th century; miniature infant in sperm or egg At fertilization/conception: Acrosomal reaction~ hydrolytic enzyme action on egg jelly coat…. Fast block to polyspermy~ membrane depolarization prevents multiple fertilizations…. Cortical reaction~ release of calcium causes hardening of egg outer layer and creates a... Slow block to polyspermy and... Egg activation~ increases metabolic activity; protein synthesis
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3 stages of embryonic develop:
1. Cleavage 2. Gastrulation 3. Organogenesis
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Cleavage
Depends on the amount of yolk
– Sea urchin: very little yolk, equal cleavage
– Frog: more yolk, unequal cell division, little division in yolk
– Birds: most yolk, cell division limited to nonyolky disc at top of egg
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The Fertilized Egg & Cleavage Blastomeres~ resultant cells of
cleavage/mitosis in blastula
Yolk~ nutrients stored in the egg
Vegetal pole~ side of egg with high yolk concentration
Animal pole ~ side of egg with low yolk concentration
Morula~solid ball of cells
Blastocoel~fluid-filled cavity in blastula
Blastula~hollow ball stage of development
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Gastrulation Gastrula~ 3 layered, cup-shaped embryonic
stage, rearrangement of blastula, begins with forming blastopore
3 Embryonic germ layers: Ectoderm~ outer layer; epidermis; nervous
system, etc. Endoderm~ viscera, inner layer; digestive
tract and associated organs; respiratory, etc. Mesoderm~skeletal; muscular;, blood,
excretory, etc. Invagination~ gastrula buckling process to
create the... Archenteron~ primitive gut Blastopore~ open end of archenteron, could
become mouth or anus
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Organogenesis: organ formation
Blastodisc~ cap of cells on top of yolk
Primitive streak~ invagination of blastodisc
Neural tube~ beginning of spinal cord
Somites~ vertebrae and skeletal muscles
Neural crest~ bones and muscles of skull
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Amniote embryos
Extraembryonic membranes: •yolk sac (support; circulatory function) •amnion (fluid-filled sac; protection)
•chorion (placenta formation)
•allantois (nitrogenous waste)
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Fetus and Placenta
Placenta begins to form when embryo is fully developed
Chorionic villi – extensions of chorion
Eventually disappear accept where placenta develops
Maintain lining of uterus Exchange of materials and
wastes through placenta and umbilical cord
http://www.visembryo.com/baby/index.html
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Week 3
beginning development of the brain, spinal cord, and heart
beginning development of the gastrointestinal tract
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Weeks 4 to 5
formation of tissue that develops into the vertebra and some other bones
further development of the heart which now beats at a regular rhythm
movement of rudimentary blood through the main vessels
beginning of the structures of the eye and ears
the brain develops into five areas and some cranial nerves are visible
arm and leg buds are visible
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Week 6
beginning of formation of the lungs
further development of the brain arms and legs have lengthened
with foot and hand areas distinguishable
hands and feet have digits, but may still be webbed
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Week 7
nipples and hair follicles form
elbows and toes visible
all essential organs have at least begun to form
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Week 8
rotation of intestines facial features continue to
develop the eyelids are more developed the external features of the ear
begin to take their final shape Marks end of embryonic stage and start of
fetal stage
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Weeks 9 to 12 the fetus reaches a length of
3.2 inches the head comprises nearly
half of the fetus' size the face is well formed eyelids close and will not
reopen until about the 28th week
tooth buds appear for the baby teeth
limbs are long and thin the fetus can make a fist
with its fingers genitals appear well
differentiated red blood cells are produced
in the liver
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Weeks 13 to 16 the fetus reaches a length of
about 6 inches a fine hair develops on the
head called lanugo fetal skin is almost transparent more muscle tissue and bones
have developed, and the bones become harder
the fetus makes active movements
sucking motions are made with the mouth
meconium is made in the intestinal tract
the liver and pancreas produce their appropriate fluid secretions
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Week 24 the fetus reaches a
length of 11.2 inches the fetus weighs about
1 lb. 10 oz. eyebrows and eyelashes
are well formed all the eye components
are developed the fetus has a hand
and startle reflex footprints and
fingerprints forming alveoli (air sacs)
forming in lungs
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Weeks 25 to 28 the fetus reaches a length of
15 inches the fetus weighs about 2 lbs.
11 oz. rapid brain development nervous system developed
enough to control some body functions
eyelids open and close respiratory system, while
immature, has developed to the point where gas exchange is possible
a baby born at this time may survive, but the possibilities for complications and death remain high
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Weeks 29 to 32 the fetus reaches a length
of about 15-17 inches the fetus weighs about 4
lbs. 6 oz. rapid increase in the
amount of body fat rhythmic breathing
movements occur, but lungs are not fully mature
bones are fully developed, but still soft and pliable
fetus begins storing iron, calcium, and phosphorus
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Week 36 the fetus reaches a
length of about 16-19 inches
the fetus weighs about 5 lbs. 12 oz. to 6 lbs. 12 oz.
lanugo begins to disappear
increase in body fat fingernails reach the end
of the fingertips a baby born at 36 weeks
has a high chance of survival, but may require some medical interventions
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Weeks 37 to 40
considered full-term at 37 weeks
may be 19 to 21 inches in length
lanugo is gone except for on the upper arms and shoulders
fingernails extend beyond fingertips
small breast buds are present on both sexes
head hair is now coarse and thicker
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Birth When fetal brain matures, hypothalamus causes pituitary
to stimulate adrenal cortex so androgens are released Placenta uses androgens as a precursor for estrogens
Prostaglandin and Oxytocin* Estrogen, Prostaglandin and Oxytocin all cause uterus to
contract and expel fetus Birth
– Dilation of cervix– Birth of baby– Expulsion of afterbirth (placenta and extraembryonic
membranes)