Lecture #17, Biology 115
Human Development and Aging
T. Irving 01/07/97; revised 03/25/00 A.Howard

Goals of this Section:

1. Describe the process of fertilization, where it occurs and how it takes place
2. Explain the basis of pregnancy tests, and what are symptoms of pregnancy
3. Name the extraembryonic membranes and state the function of each
4. Describe structure and function of the placenta
   • Trace the path of blood in the fetus
   • Describe weekly events of embryonic development and monthly events of fetal development
5. Describe general effects of pregnancy on the mother
6. Describe processes occurring during birth
7. Describe the anatomy of the female breast. What hormones effect it and what do they do?
8. State 3 theories of aging. effect of aging on bodily systems and ways to prevent a decline in body functions.

Stages in development before implantation:

• Secondary oocyte --> Fertilization --->
• cleavage (2,4, 8 cell stage) --->morula ---> early & late blastocysts
• transported down the oviduct into the uterus where it embeds itself in the prepared endometrium 2-3 days after fertilization
• A membrane surrounding the developing embryo secretes human chorionic gonadotropic hormone (HCG)
• HCG Prevents degeneration of the Corpus Luteum
• CL produces greater quantities of progesterone
• Maintains endometrium & inhibits motility of the uterus

Placenta

• Starts forming soon after implantation
• Fully formed by 10th week of pregnancy
• Placenta has components of both maternal and fetal tissue
• Location of exchange of gases & nutrients between maternal and fetal blood
• Once formed, placenta produces HCG,
• estrogen and progesterone
• Shuts down AP - no new follicles produced
• Uterine lining maintained Corpus Luteum no longer needed
• Menstruation ceases for duration of pregnancy

Embryonic Development

1. Cleavage: cells divide but do not increase in size initially
2. Growth: Cells enlarge
3. Morphogenesis: embryo changes shape
4. Differentiation: Cells specialize for various kinds of tissues

First Week

• Cleavage main event during first week up to implantation and formation of the morula;
• even the formation of the blastocyst can be considered pre-embryonic stage.

Second week: true embryonic development begins

• Wall amniotic cavity called amnion , filled with amniotic fluid
• yolk sac appears, will be source of blood cells
• differentiates eventually into intestines and reproductive system
• Placenta begins to form
• Chorionic villae begin to digest away part of the endometrium which fills with maternal blood. Chorionic villae contain the embryonic blood vessels

Third week

• Placenta well formed. Nervous system begins to differentiate, Allantois and blood vessels start to appear.
• Allantois will eventually differentiate into the umbilical cord and the urinary bladder.

Fourth week

• Heart starts beating, nervous system prominent, embryo has tail, limb buds
• Liver, heart start to form
• HCG production can maintain CL and uterine lining

Second month

• Tail disappears, arms, legs, fingers, toes appear
• All major organs present

Fetal Development

Third and fourth month

• Head growth slows down, body increases in length, hair, fingernails, nipples etc. form
• Cartilage starts to ossify
• Third month possible to distinguish sex
• Testes release androgens required for male development
• female - default state
• Testes descent fourth trimester
• Fetal heartbeat detectable fourth month

Fifth through seventh months

• Fetal movement
• eyes open
• covered fine down called lanugo
• Seventh month babies frequently survive

Eighth and ninth months

• Fetus rotates so head points towards cervix
• Fetus grows and gains weight
• Fat accumulates beneath skin
• Increased chance of survival for full term babies

Maternal changes during pregnancy

• Morning sickness appears to be caused by HCG
• Expansion of the uterus makes breathing, urination, defecation and movement difficult
• Malnutrition in the mother may lead to fetal nervous system defects and low birth weight
• Mother's blood volume, cardiac output, and respiration increase during pregnancy

Birth

• Labor: Initiated by both maternal and fetal hormones
• Fetus moves from uterus through the birth canal
• Stage 1 includes dilation of the cervix, tearing of the amnion, release of amniotic fluid, expulsion mucus plug cervix
• Stage 2 Contractions every one - two minutes
• Positive feedback - pressure on cervix causes more contractions
• Expulsion and delivery of the newborn by powerful uterine contractions
• Episiotomy is a surgical incision to prevent tearing of the opening to the vagina.
• Stage 3 - delivery of the afterbirth about 15 min after parturition- placenta, extraembryonic membranes, umbilical cord
• Cesarean ( C-section) birth is surgical removal of the baby from the uterus.
• Shortly after birth, respiratory center in infants brain detects CO₂ rise in blood causing breathing to start
• Three fetal shunts, ductus venosus, foramen ovale, and ductus arteriosus close causing normal blood circulation

Milk Production

• During pregnancy no milk is produced
• Breasts enlarge as ducts and alveoli increase in number and size
• Estrogen and progesterone from the placenta inhibit AP from secreting prolactin inhibiting milk production
• Mammary glands form milk after birth
• First two days - called colustrum, an antibody rich fluid.
• Continued milk production requires suckling
• Stimulates areolar nerve endings
• Hypothalamus stimulates AP to release oxytocin
• Oxytocin allows milk "let down"

Human Development

• Infancy is considered to last up to two years
• Rapid growth and sensorimotor development
• Childhood years two - through puberty
• Growth slows down, changes in body proportions
• Adolescence begins with puberty:
• Acceleration in growth
• Secondary sex characteristics appear
• Functional sex organs
• Physical peak appears in late teens or early adulthood
• Downhill from there!

Aging & Health

Study of aging called gerontology

Maximum life span about 115 years - why?

• Genetic effects:
• # times a cell can divide is species specific
• humans about 50 times
• Studies of cells in tissue culture show accumulation of deleterious mutations with number of divisions
• Accumulation of non-functional or cancerous cells
• Genes that protect against free radicals may enhance longevity

Whole body Processes:

• Decline in hormonal system function
• cell receptors to insulin no longer respond in type II diabetes
• ovaries no longer respond to FSH after menopause
• decline estrogen, progesterone
• uterus contracts
• male androgen levels decline ages 50 - 90
• Immune system breaks down
• increased incidence of cancer
• autoimmune diseases
• Collagenous tissue becomes increasingly crosslinked with age
• AGES - advanced glycosylation end products
• cataracts
• atherosclerosis

Extrinsic Factors

Diet and Exercise (or lack thereof), alcohol, smoking, toxins in environment can influence:

• Osteoporosis
• cancer
• heart disease
• stroke
• more?

Effects of aging

• Skin thinner and less elastic (collagen X-linking)
• Hair follicles diminish
• Melanocytes decrease - gray hair, pale skin
• Cardiovascular disorders
• Reduction cardiac muscle mass (not always a problem)
• Elastic fibers in arteries become more rigid
• Reduced blood flow to liver, kidneys
• Lungs become less elastic
• Prostate enlargement in males
• Nerve and muscle system degeneration
• New nerve and muscle cells not normally formed in adults
• With age cognitive skills do not necessarily decline
• Short term memory declines, learning slower but
• other functions may be just fine
• Other:
• Reduced blood flow can lead to neuronal death
• lens accommodation function reduced - presbyopia (farsightedness)
• high frequency hearing goes
• bone density often declines (osteoporosis)
• osteoarthritis (loss of cartilage end of bones)
• weight gain - basal metabolism decreases,
• muscle replaced by fat and fluid

What can you do?

• Modify diet
• Reduce dietary fat especially saturated fat
• Reduce sodium intake:
  
  • hypertension associated with high sodium
  • not everybody susceptible but no way to tell
• Reduce cholesterol and chosterol-producing saturated fats
• avoid possible carcinogens in food
• Nitrites and nitrates:found in bacon, sausages, ham;
  chemically converted to nitrosamines by stomach acid
• Charbroiled foods: fats + charcoal = various carcinogens
• Increase dietary fiber
• Soluble fiber helps control cholesterol,
• moderate insulin response
• Insoluble fiber prevents constipation,
  helps irritable bowel syndrome, colon cancer
• prevention:
  • Eat a wide variety of foods
  • essential minerals K, Ca, Fe and vitamins
• Manage liquor consumption carefully:
  • Moderate Alcohol Consumption is okay for some people;
    Heavy drinking - throat cancer, high blood pressure, other heart problems
  • Liver damage begins immediately and continues with heavy alcohol use
  • Final stage liver cells die and turn orange - Cirrhosis of the liver
  • Synergistic effect of smoking and alcohol
  • Decreased HDL ("good cholesterol") levels
  • More serious health risk from drunk driving and other accidents
• Exercise:
  • Large improvements in life expectancy can be realized for moderate increases in activity
  • Can slow weight gain due to aging
  • Increase bone density post-menopausal women
  • Aerobic capacity can be maintained into old age
  • Mental agility can be improved by regular exercise
  • "Use it or lose it"