Download Development: Life Before Birth & Aging

Unit V: Development
Life Before Birth & Aging
Chapter 26
Pgs. – 173, 269, 274, 306, 464-465,
638-639, 715, 754
Definitions
• Pregnancy – presence of a developing offspring in the uterus
• Fertilization – union of a haploid sperm cell and a haploid
secondary oocyte
• Zygote – a fertilized egg; diploid #
Prenatal Development
Fetal development
Embryological
development
4 weeks
8 weeks
16 weeks
Fertilization
Fertilization
• Egg survival
– fertilization within 12-24 hours after ovulation
• Obstacles:
– vagina
– leukocytes of uterus
– wrong uterine tube
• 5-10 minutes from ejaculation  uterine tube
• 10 hours for fertilization
• 72 hours for zygote to reach uterus
Pre-embryonic Stage - First 2 Weeks
• Cleavage - mitotic divisions that occur for 3 days after fertilization
– within 30 hrs –
• zygote splits into 2 blastomeres
– within 72 hrs – morula
• Morula free in uterine cavity for 4-5 days
• Zona pellucida disintegrates to release blastocyst
– trophoblast - helps to form placenta
– inner cell mass - develops into embryo
– blastocoele – internal cavity
From Ovulation to Implantation
Pre-embryonic
Implantation
Day 9: Formation of Amniotic Cavity
ENDOMETRIUM
Blastodisc
Trophoblast cells divide rapidly
Amniotic cavity
Blastocoele
Amnion
Cellular trophoblast
Day 10: Yolk Sac Formation
Syncytial trophoblast
Cellular trophoblast
Yolk sac
Lacuna
Embryogenesis:
Day 12: Gastrulation
Migrating cells leave the surface
and move between the two existing
layers to create:
(1) the ectoderm
(2) the endoderm
(3) the mesoderm
Amnion
Yolk sac
Ectoderm
Mesoderm
Primitive
streak
Blastodisc
Endoderm
Embryonic disc
Embryonic Stage or Weeks 2 to 9
Endometrium
• Begins when all 3 primary
germ layers present
• Embryo begins receiving its
nutrients from placenta
• Germ layers differentiate
into organs and organ
systems
– presence of organs
marks the beginning of
fetal stage
Yolk
sac
Amniotic
cavity
Embryo
Uterine
lumen
Blastocoele
Syncytial
trophoblast
Week 3
Umbilical stalk
Amniotic
cavity
Blastocoele
Embryo
Uterus
Uterine
lumen
Yolk sac
Week 5
Placenta and Embryonic Membranes
Fetal Development and Circulation
• Fetus = from 8 weeks until birth
– organs mature to support external life
• Fetal circulation
– umbilical-placental circuit via umbilical cord
– circulatory shunts
• ductus venosus connects to inferior vena cava
• foramen ovale connecting right and left atria
• ductus arteriosus connects pulmonary trunk to aorta
Prenatal Nutrition
1. Uterine Milk (5 days)
• glycogen rich secretion
2. Trophoblastic nutrition (week 1  8)
3. Placental nutrition (week 9  birth)
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Placental nutrition
Trophoblastic
nutrition
0
4
8
Trophoblastic
phase
12 16 20 24 28
Weeks after implantation
Placental phase
32
36
40
Physiological Strains on Maternal Systems
•
Weight gain (6–7 kg or ~13–15 lb)
•
•
Weight not aligned with body axis
Requiring more energy to maintain balance
•
Location of some maternal organs
•
Respiratory rate and TV increase
•
Mammary glands mature/activate
•
GFR in kidneys increases ~50%
•
Frequency of urination increases
Physiological Strains on Maternal Systems
• Maternal blood volume increases ~50%
• Nutrient requirements increase by up to ~30%
• Uterus expands through cell hypertrophy
• 3” length to 12”
• 30–40 g ( 1–1.4 oz) to 1100 g (2.4 lb) in weight
• 2L of fluid + fetus + placenta = 15lbs total
Hormones of Pregnancy
• Cells of embryo produce HCG (human chorionic gonadotropin)
– prevent degeneration of corpus luteum
• Placenta produces estrogens and progesterone
– progesterone: suppress pituitary secretion of FSH and LH
– inhibits uterine contractions
– estrogen: tissue growth of fetus and mother
Hormones of Pregnancy
Placental Factors
Placental estrogens
↑ sensitivity of myometrium
Stimulates contractions
Fetal Factors
Relaxin
relaxes the
pelvis
Growth
of fetus
Fetal
pituitary
releases
oxytocin
Distortion of
Myometrium
↑ the sensitivity of the
smooth muscle layers
Maternal
Oxytocin
Release
Prostaglandin Production
Occurs in the endometrium
further stimulate smooth muscle
contractions.
Increased Excitability of the Myometrium
the smooth muscle in a later-term uterus is 100 times more
sensitive to oxytocin than the smooth muscle in a nonpregnant uterus.
LABOR CONTRACTIONS OCCUR
Positive
Feedback
loop
Aging and Senescence
• Aging is all changes occurring with the passage of time -- growth,
development and degeneration
• Senescence is the degeneration that occurs after the age of peak
functional efficiency
– leading causes of death from 18 to 34 is accidents, homicides,
suicides and AIDS
– leading causes of death after 55 is senescence related
• cancer, stroke, diabetes, heart and lung disease
Exercise and Senescence
• Good nutrition and exercise are best ways to slow aging
– exercise improves quality of life
• Resistance exercise reduces bone fractures
• Endurance exercises reduce body fat, and increase cardiac output
and oxygen uptake
Theories of Senescence
• Limit to number of times cells can replicate
• Failure of polymerase to replicate terminal genes of DNA on older
chromosomes
• Collagen molecules become cross-linked (less soluble and more
stiff)
• Proteins become abnormal due to improper folding or links to
other molecules
• Free radicals damage macromolecules (due to lack of antioxidants)
• Lymphocytes mount an attack against own tissues
Death
• Life expectancy is average length of life in a given population
– average boy can expect to live to 75
– average girl can expect to live to 81
• Life span is maximum attainable (122 record)
• No definable instant of biological death because some organs
function for an hour after heart stops
– clinical death is lack of cerebral activity, reflexes, heartbeat and
respiration
• Death usually occurs as a failure of a particular organ followed by
a cascade of other organ failures
Senescence of Integumentary System
Becomes noticeable in late 40s
• Decrease in activity of melanocytes 
• Decline in mitosis 
• Decline in sebaceous gland activity 
• Loss of elastic fibers 
• Less antigen-presenting cells (<40%) 
• Thermoregulation 
− atrophy of cutaneous vessels, sweat glands and
subcutaneous fat
•  vitamin D production  Ca2+ deficiency 
Photoaging is degeneration in proportion to UV exposure -- skin spots,
skin cancer, wrinkling
Senescence of Skeletal System
• Osteopenia - Osteoporosis
• Joint diseases
– Osteoarthritis is most common cause of physical disability
Senescence of Muscular System
• Muscular atrophy causes replacement of lean body mass (muscle)
with fat
– by 80, we have half as much strength and endurance
• fast-twitch fibers exhibit earliest and most severe atrophy
• Reasons for loss of strength
– fibers have fewer myofibrils, smaller mitochondria, less
enzymes, glycogen and myoglobin 
– fewer motor neurons in spinal cord with less efficient synaptic
transmission of acetylcholine 
– sympathetic nervous system is less efficient so less efficient
blood flow to muscles causes fatigue
Senescence of Nervous System
• Cerebral and neuronal atrophy
– from age 35 on, 100,000 brain cells die every day
– brain weight 50% less by age 75
– cortex thinner, gyri narrower, fewer synapses and neuroglia,
less neurotransmitter and receptors
– degeneration of myelin slows down signal
– neurons contain less ER and Golgi as their metabolism slows
• Motor coordination, intellectual function and short-term memory
suffer the most
• Autonomic nervous system is less efficient at regulating body
temperature and BP
Senescence of Circulatory System
• Anemia results from 
Effects on body 
• Coronary atherosclerosis leads to infarction, arrhythmia and heart
block
Effects on heart 
• Atherosclerosis of other vessels increases BP
• Varicose veins due to weaker valves
Senescence of Immune System
• Amounts of lymphatic tissue and red bone marrow decline
• Both types of immune responses are less efficient
Senescence of Respiratory System
• Declining pulmonary ventilation
• Elderly less able to clear lungs of irritants and pathogens
• Chronic obstructive pulmonary diseases (emphysema and chronic
bronchitis)
Senescence of Urinary System
• Renal atrophy (40% smaller by age 90)
– loss of nephrons and atherosclerotic glomeruli
– filtration rate decreases leaving little reserve capacity
• can not clear drugs as rapidly
• Fluid balance
– less responsive to antidiuretic hormone and sense of thirst is
sharply reduced (dehydration is common)
Test V
• Unit V Test:
Lecture: Chapters 25 & 26
• Cumulative: (same amount of points)
Lecture: First 4 units tests and quizzes
Unit V
Same lab for everyone:
•Identify organs/structures/cells
•Slides, models
•Role of organ/structure to the system