Transcript Inquiry into Life Twelfth Edition

Lecture PowerPoint to accompany
Inquiry into Life
Twelfth Edition
Sylvia S. Mader
Chapter 22
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
22.1 Principles of Animal Development
• Fertilization
• Sperm squeezes through follicle cells
• Sperm releases acrosomal enzymes so it can
penetrate the zona pellucida
• Sperm cell membrane fuses with egg cell
membrane
• Sperm enters egg, nucleus is released
• Egg nucleus and sperm nucleus fuse forming a
zygote
Fertilization
22.1 Principles of Animal Development
• Early Stages of Animal Development
– Cleavage: first mitotic divisions resulting in a
multicellular embryo
• Cell divisions without growth in size
• Increases number of cells but not the total volume of
cytoplasm
– Cleavage Divisions
• Divisions of zygote are equal
• Forms a multicellular stage called a morula (ball of cells)
• The next stage is the Blastula (a hollow ball of cells)
– The fluid-filled cavity is called a blastocoel
Lancelet Early Development
22.1 Principles of Animal Development
• Early Stages of Animal Development
– All vertebrates have a blastula stage, but the
appearance may be different
– Human blastulas resemble chick blastulas
even though we have little yolk
22.1 Principles of Animal Development
• Tissue stages of Development
– Gastrulation: The invagination of cells into the
blastocoel
• Cells migrate to specific destinations
• Form distinct cell layers- “germ” layers
• Pore created by invagination is the blastopore
– Early Gastrula has two layers of cells
• Ectoderm- outer layer of cells
• Endoderm- inner layer of cells
– Lines the archenteron
– Late gastrula- has three layers of cells
• A middle mesoderm layer is formed
Comparative Development
of Mesoderm
22.1 Principles of Animal Development
• Organ Stages of Development
– Mesodermal cells along longitudinal axis of the embryo form the
notochord
• Notochord persists in the lancelet but is replaced by the vertebral
column in vertebrates
– The nervous system develops from the ectoderm
• Neural plate stage-thickening of ectoderm above notochord forms
neural plate
• Neural folds form moving upward and joining to form a neural tube
– Anterior end becomes the brain, the rest becomes spinal cord
• Neural crest cells form where tube pinches off from ectoderm– Cells migrate to contribute to skin, muscles, adrenal medulla, ganglia
Development of Neural Tube and
Coelom in a Frog Embryo
Vertebrate Embryo
(Cross Section)
22.1 Principles of Animal Development
• Processes of Animal Development
– Cellular Differentiation
• Cells become specialized in structure and function
– Morphogenesis
• Produces the shape and form of the body
– Pattern Formation
• How tissues and organs are arranged in the body
22.1 Principles of Animal Development
• Processes of Animal Development
– Cellular Differentiation
• Due to differential gene expression
• Frogs: egg cytoplasm is different in different regions
– Gray crescent is visible after fertilization
– Egg has polarity- both a dorsal/ventral and anterior/posterior
axis
– A classic experiment
» If egg is divided so both halves get gray crescent, then two
complete tadpoles develop
» If egg is divided so only half gets gray crescent, then that
half develops into a tadpole and the other half stops
developing
Experimental Determination of
Cytoplasmic Influence on Development
22.1 Principles of Animal Development
• Processes of Animal Development
– Cellular Differentiation Continued
• Cytoplasmic Segregation
– Frog experiment shows egg contains substances called
maternal determinants- influence development
– Parceling out of maternal determinants (like the gray
crescent) during mitosis
– Determines how cells of morula will develop
– Specialization of cells is influenced by maternal
determinants and signals from surrounding cells
• Induction
– Ability of one embryonic tissue to influence another by
chemical signals
22.1 Principles of Animal Development
• Processes of Animal Development
– Cellular Differentiation Continued
• Dorsal blastopore lip in the frog is the primary organizer
– Contains gray crescent
– Cells closest to dorsal lip become endoderm, those farthest
become ectoderm, those in the middle become mesoderm
– Location of the gray crescent indicates the dorsal surface
» Mesoderm here forms the notochord
» Notochord induces ectoderm to become the neural plate
• Another Example of Induction
– Vertebrate eye- optic vesicle induces overlying ectoderm to
become the lens
– Lens then induces the optic vesicle to form retina
22.1 Principles of Animal Development
• Processes of Animal Development
– Morphogenesis
• Processes by which specific body plan develops
• Morphogen genes- determine relationship of
individual parts
– Some genes control which end becomes the head and
which the tail
» These genes code for proteins in a morphogen
gradient
» Cells at one end have high levels, at the other end
they have low levels
– Other morphogen genes determine how many segments
the body will have
– Determines shape of organism
22.1 Principles of Animal Development
• Processes of Animal Development
– Morphogenesis Continued
• Sequential sets of master genes code for morphogen
gradients that activate the next set of master genes, etc.
• Homeotic genes-control the organization of differentiated
cells into 3 dimensional structures like wings, legs, etc.
– All share a sequence of nucleotides called a homeobox
» Codes for a sequence of 60 amino acids called a
homeodomain
» Homeodomain protein binds to DNA and determines which
genes are turned on
– Homeodomain protein from one homeotic gene binds to the
next homeotic gene and turns it on, etc.
Morphogen Gradients in the Fruit Fly
22.1 Principles of Animal Development
• Morphogenesis Continued
– Homeotic genes of many different organisms contain
the same homeodomain- indicates this sequence
originated early in evolutionary history
– Apoptosis-plays role in morphogenesis
• Hands and feet of humans are shaped by apoptosis
• Cell receives a death signal
– An inhibiting protein becomes inactivated
– Cell-death cascade proceeds
– Enzymes destroy cell
Pattern Formation in Drosophila
22.2 Human Embryonic and Fetal
Development
• Human Development
– From conception to birth is approximately nine
months
– Embryonic Development- Months 1 and 2
• Development of all organ systems
– Fetal Development- Months 3-9
• Refinement of organ systems
Extraembryonic Membranes
22.2 Human Embryonic and Fetal
Development
• Extraembryonic Membranes
– In the Chick
•
•
•
•
Chorion: lies next to the shell and functions in gas exchange
Amnion: contains amniotic fluid which bathes embryo
Allantois: collects nitrogenous wastes
Yolk sac: surrounds yolk which provides nourishment
– Humans
•
•
•
•
Chorion: develops into the fetal side of the placenta
Yolk sac: the earliest site of blood cell formation
Allantoic vessels: become the umbilical vessels
Amnion: contains the amniotic fluid
22.2 Human Embryonic and Fetal
Development
• Embryonic Development - The First Week
– Fertilization occurs within the first 1/3 of the oviduct
– Zygote undergoes the first cleavage divisions as it
migrates through the oviduct toward the uterus
– After about three days it is in the morula stage
• Morula enters the uterus
• At day five it has become a blastocyst
– Outer layer of trophoblast cells becomes the chorion
– The inner cell mass becomes the embryo
Human Development Before
Implantation
22.2 Human Embryonic and Fetal
Development
• Embryonic Development - The Second Week
– Implantation- trophoblast cells secrete digestive enzymes to
burrow into the endometrium
– Trophoblast cells begin to secrete human chorionic gonadotropin
– Inner cell mass detaches itself from the trophoblast
– Amnion and yolk sac develop
– Gastrulation occurs- inner cell mass now becomes the flattened
embryonic disk
• At this stage ectoderm and endoderm differentiate
– Embryonic disk elongates to form primitive streak and mesoderm
develops
Human Embryonic Development
22.2 Human Embryonic and Fetal
Development
• Embryonic Development
• The Third Week
– The nervous system becomes visually evident
– Development of the heart begins
• The Fourth and Fifth Weeks
– The body stalk (mesoderm) connects the tail end of the embryo
with the chorion
• Allantois is contained within this stalk
– Limb buds appear
– Sense organs are distinguishable
Human Embryonic Development
Human Embryo at the Beginning
of the Fifth Week
22.2 Human Embryonic and Fetal
Development
• Embryonic Development
• The Sixth Through Eighth Weeks
• The embryo becomes recognizable as human
• Nervous system continues to develop
– Reflexes are present
• All organ systems are now established
22.2 Human Embryonic and Fetal
Development
• Fetal Development
– The Third and Fourth Months
• The head is large, nose is flat, eyes are far apart
• Epidermal structures develop
– Eyelashes, hair on head, eyebrows, fingernails, and nipples
• Cartilage begins to be replaced by bones
• Sex of the individual may be determined
• In the fourth month, the heartbeat can be heard
Three to Four Month Old Fetus
22.2 Human Embryonic and Fetal
Development
• Fetal Development
– The Fifth Through Seventh Months
• The mother begins to feel movement
• Fetal skin is covered by fine hair called lanugo
• The skin is also covered with a thick, cheesy coating called
the vernix caseosa
• Eyelids are open
• Survival is now possible if birth occurs prematurely
22.2 Human Embryonic and Fetal
Development
• Fetal Development
– Features of Fetal Circulation
• A fetus does not use its lungs for gas exchange
• Blood entering the right atrium is shunted through the left
atrium through the oval opening (foramen ovale)
• Any blood that enters the right ventricle ends up being
shunted into the aorta by way of the arterial duct (ductus
arteriosus)
• Blood in the aorta is distributed to iliac arteries leading to the
placenta
22.2 Human Embryonic and Fetal
Development
• Fetal Development
– Features of Fetal Circulation continued
• Exchange of gases and nutrients between the fetus and
mother occur in the placenta
• Blood leaves the placenta via the umbilical vein
• Blood enters the fetal liver and joins the venous duct which
merges with the inferior vena cava
• The inferior vena cava returns blood to the heart
Fetal Circulation and the Placenta
22.2 Human Embryonic and Fetal
Development
• Fetal Development
– Features of Fetal Circulation continued
• At birth blood in the left atrium should cause a flap to close
off oval opening
• Arterial duct closes as endothelial cells proliferate. Remains
of the arterial duct and umbilical vessels are converted to
connective tissue
• The most common cardiac defects in newborns is that the
oval opening fails to close.
– Failure to close can usually be corrected by surgery
22.2 Human Embryonic and Fetal
Development
• Fetal Development
– Structure and Function of the Placenta
• The placenta is attached to the uterine wall by the allantois
and chorionic villi
• Placenta is fully formed by the tenth week
– Produces progesterone and estrogen
– Functions in gas, nutrient, and waste exchange between the
fetal and maternal circulatory systems
– Fetal and maternal blood do not mix
Anatomy of the Placenta in a Fetus
at Six to Seven Months
22.2 Human Embryonic and Fetal
Development
• Fetal Development
– Structure and Function of the Placenta
• The umbilical cord functions to take fetal blood to and from
the placenta.
• Harmful substances (ex: alcohol, some medications) can
cross the placenta and cause irreversible birth defects
22.2 Human Embryonic and Fetal
Development
• Birth
– Contractions occur throughout the third trimester and
become stronger and more frequent toward the end
of pregnancy.
– A positive feedback mechanism is involved.
• Stretching of the uterus causes oxytocin release
– Oxytocin causes further contractions which causes the
uterus to be stretched further.
– More oxytocin is then released
22.2 Human Embryonic and Fetal
Development
• Birth
– Events That Occur Shortly Before Birth
• Strong uterine contractions occur about every five
minutes
• The “water breaks”, meaning the amnion has
ruptured and the amniotic fluid is released
• A mucus plug (from the cervix) is expelled
– The plug prevents bacteria and sperm from entering the
vagina during pregnancy
Three Stages of Parturition (birth)
22.2 Human Embryonic and Fetal
Development
• Female Breast and Lactation
– Each contains 15-25 lobules
• Lobule has a milk duct which branches from the nipple into
numerous smaller ducts that terminate in alveoli
• During pregnancy the number of ducts and alveoli increase
• Prolactin stimulates milk synthesis
– Inhibited by estrogen and progesterone during pregnancy
– When placenta is delivered, the anterior pituitary produces
prolactin
• First secretions are colostrum which is rich in protein and
antibodies
– Suckling stimulus-causes oxytocin release
• Oxytocin causes milk let-down into the ducts
Female Breast Anatomy
22.2 Human Embryonic and Fetal
Development
• Benefits of Breast Feeding
– Breast milk contains antibodies
– Breast-fed babies are less likely to develop stomach
and intestinal illnesses in the first 13 weeks of life
– Suckling by the baby helps return the uterus to
normal size
– Breast-feeding burns calories helping the mother to
return to her normal weight
22.3 Human Development After Birth
• Development continues throughout the stages of
life.
•
•
•
•
Infancy
Childhood
Adolescence
Adulthood
• Gerontology is the study of aging.
22.3 Human Development After Birth
• Hypotheses About Aging
– Genetic in Origin
• Cells divide a specific number of times
– This is species specific
• Some cell lines become nonfunctional before the maximum
number of divisions occurs
– Mutations may accumulate and affect function
• Children of long-lived parents tend to live longer than children
of shorter-lived parents
22.3 Human Development After Birth
• Hypotheses About Aging
– Whole-Body Process
• Decline in hormonal systems affect many different organs
• Could also be due to a change in a specific tissue type that
affects many organs
– Cross-linkages in collagen lead to stiffness, decreased
elasticity
– Extrinsic Factors
• Could be that what we view as aging is actually the result of
poor life choices in nutrition, habits
• Sensible diet and exercise may prevent many signs of aging
22.3 Human Development After Birth
• Effect of Age on Body Systems
– Skin
•
•
•
•
Thinner, less elastic, less subcutaneous fat
Causes wrinkles, decreased insulation
Number of oil glands reduced, skin is dry
Pigmented blotches may appear
22.3 Human Development After Birth
• Effect of Age on Body Systems
– Processing and Transport
• Cardiovascular disorders are the leading cause of
death
– Heart shrinks because of reduction in cardiac muscle cell
size
– Arteries become more rigid; plaque buildup may narrow
lumen of vessels
– Blood pressure increases with age
22.3 Human Development After Birth
• Effect of Age on Body Systems
– Processing and Transport
• Cardiovascular disorders are the leading cause of
death
– Blood flow to the liver is reduced, and the liver does not
metabolize drugs as efficiently.
» Smaller doses of medications are needed
– Blood supply to the kidneys is also reduced
» Salt and water balance are difficult to maintain
» The elderly dehydrate easier than young people
22.3 Human Development After Birth
• Effect of Age on Body Systems
– Integration and Coordination
•
•
•
•
•
Brain and muscle cells do not replace lost cells
Few neurons in cerebral cortex are lost.
Cognitive functions are not affected in normal aging
Short-term memory skills may decrease
If neurons do die, may be due to decreased oxygen
availability and not from aging
• Loss of skeletal muscle mass may prevented by exercise
• Osteoporosis may be prevented by calcium intake and
exercise
22.3 Human Development After Birth
• Effect of Age on Body Systems
– The Reproductive System
• Females undergo menopause
• Males produce less androgens
– Still produce sperm until death
• Females tend to live longer than males