Development

 

1.        Early development

  1. Fertilization is the union of sperm and egg.
  2. Once an egg is fertilized it is called a zygote (diploid).
  3. Cleavage is rapid mitotic divisions.
  4. Gastrulation is the migration of cells.
  5. Germ layers are formed.

i.                     Ectoderm : all nervous tissue, skin, eyes, ears, hair, feathers, pituitary gland, adrenal medulla.

ii.                    Endoderm:  linings of digestive, respiratory, reproductive tracts.

iii.                  Mesoderm:  muscle, bone, blood, kidney and gonads.

  1. Notochord comes from the mesoderm and induces the ectoderm to make the spinal cord.

2.        Control of Development

  1. The sequence of development is strictly controlled.
  2. Specialization increases during development.
  3. Genetic control.
  4. Induction is when one tissue influences another tissue (notochord).

3.        Eggs

  1. 3 types of animal eggs.
  2. Differ by amount of yolk (food).

4.        Frog Development

  1. Animal pole
  2. Vegetal pole
  3. Morula
  4. Blastula

i.                     Blastocoel

       E.  Gastrulation

5.        Chicken Development

  1. Germinal disk
  2. Blastoderm
  3. Blastocoel

i.                     Ectoderm

ii.                    Endoderm

 

  1. Yolk sac
  2. Allantois
  3. Amnion
  4. Chorion

6.        Fertilization

  1. 150-350 sperm deposited.
  2. Only a few 100 make it to oviduct.
  3. Only one sperm will enter the cytoplasm of the oocyte using digestive enzymes.
  4. The arrival of the successful sperm stimulates the completion of Meiosis 11 followed by the fusion of the egg and sperm’s nuclear material.
  5. Females have 2 million follicles, reduced to 300-400K at puberty, only 400 mature.

7.  Human Development

  1. Takes 266 days (10 months)
  2. Fertilization takes place in the oviduct. Cilia in the oviduct
  3. Tubular pregnancy is in oviduct. Ectopic pregnancy is anywhere outside of uterus.
  4. Eggs can get lost and enter the abdominal cavity.
  5. Uterus: strongest muscle pound for pound. About the size of a pear.
  6. First trimester ( All or none period) exposure to hazardous chemical will kill the embryo or cause it no harm.

i.                     During the first few days the zygote undergoes repeated cleavages as it travels down the oviduct.

ii.                    By the time it reaches the uterus( 5 days),  it is a solid ballof cells called a morula which is transformed into a blastocyst

iii.                  Before the first week ends, the balstocyst contacts and adheres to the uterine lining and is tranformed into an embyonic disk that will develop into the embryo proper within the next week.

iv.                  Implants in uterus at blastocyst stage.

v.                   The trophoblast is the embryonic membrane.

vi.                  The embryo is called the inner cell mass.

vii.                Around the embryo and part of the placenta is the Chorionic villi.

viii.               The placenta is the place of exchange of wastes and nutrients.

ix.                   Embryo is smaller than a pea at one month.

x.                    By the third week many organ systems have begun to form including the nervous system, heart, blood vessels, esphagus, stomach, liver, panceas and intestines.

xi.                   All the major organ systems are formed at 2 months and will merely increase in size for the remainder of the pregnancy.

xii.                 Heart pulses at 3-4 weeks.

xiii.                Buds appear for arms and legs

xiv.               1st 6 weeks crucial for normal development.

 

  1. Membranes around the embryo

i.                     yolk sac gives rise to the digestive tube

ii.                    the allantois does not function in waste storage as in bird eggs but is active in oxygen transport

iii.                  The amnion is a fluid filled sac that keeps the embryo from drying out and acts as a shock absorber.

iv.                  The chorion is a protective membrane around the embryo and forms a portion of the placenta  It secretes a hormone that maintains the uterine lining after implantation.

v.                   The umbilical cord connects the growing embryo to parts of the yolk sac, allantois and chorion.

vi.                  The placenta (formed at about day 17) is a combination of endometrial tissue and embryonic chorion.

vii.                Materials are exchanged from the blood capillaries of mother to fetus and vice versa by diffusion. The maternal blood and the fetal blood do not mix.

 

H.  Miscarriage is loss of embryo or fetus before 20 weeks.  Occurs in more than 30 % of pregnancies (50%?).  Most occur before 12 weeks.  50-60 % due to chromosomal damage so severe that the fetus would not develop anyways.

 

  1.   The second trimester

i.                     Sensitive to light

ii.                    Movements felt by mother.

iii.                  Moves at 4 months and some body systems start to function.

iv.                  Embryo now called a fetus will undergo a major increase in size (600 x).

  1. The third trimester

i.                     Finishing touches

ii.                    Mother is uncomfortable

 

 

  1. Maternal physiologic changes

i.                     uterus grows to contain more than 5 liters, enlarges 500-1000x.

ii.                    Ovaries less active, secrete relaxin, a hormone that relaxes ligaments.

iii.                  Skin changes in pigment, mask of pregnancy, dark line on abdomen, increased oil production on face, vacular spiders.

iv.                  Blood volume increased by more than 50 %.

v.                   Urinary system , kidneys filter 50-60 % more urine.

vi.                  Heartburn, bloating, constipation, bums enlarge and bleed, hemorrhoids.

  1. Birth

i.                     Lightening is when fetal head drops into woman’s pelvis. A couple of weeks before labor.

ii.                    Braxton-Hicks contractions (false labor)

iii.                  Passing of mucus plug occurs up to 2 weeks before birth.

iv.                  Contractions are caused by oxytocin.

v.                   Early labor can last minute-days. Cervix is less than 4 cm dilated.

vi.                  Stage one: active labor 4-10 cm dilated. Contractions are 3-5 minutes apart.

vii.                Transition: 7-10 cm dilated. Contractions one right on top of the other.

viii.               Stage Two: Pushing, 1-2 hours

ix.                   Stage three; expulsion of placenta.

 

7.        Breastfeeding

  1. Today 60 % of women try. Only 20 % continue past 6 months.
  2. Our parent’s generation: 20 % of women tried.
  3. Historically princes have breastfed for 15 years.
  4. Worldwide 5 years is the average length of time.
  5. In Egypt the number of child mortality increases at 3 years, about the time of weaning.
  6. Breast milk contains antibodies, all the immunities that the mother has which protect the babie.
  7. Formula.  Costs 1500 a year, and is bad for the environment, and not as good for human babies.  Packaging, water use for cows is a burden on the environment.
  8. Breast milk is free and contains nutrients not found elsewhere.  Staves of allergic reactions, allergies, and asthma.
  9. Formula fed babies see doctor 2 x as often as breastfed babies.
  10. Formula fed babies are hospitalized  for bacterial infections, SIDS, cancer, dermatitis, ear infections, diarrhea, diabetes, and liver disease 4 x more often as breastfed babies.
  11. Breast milk is sterile and always the right temperature.
  12. Breastfed babies have less diaper rash and diarrhea.
  13. Breastfed babies have less colic, gas, and spit up.

i.                     Breast milk contains lipase, an enzyme that breaks down fats.

ii.                    300 components in breast milk.

  1. Breast milk has lower sodium and protein than formula, so there is less kidney stress.
  2. Ca and iron in breast milk is in a form that is easily absorbed.
  3. Breast milk helps to avoid childhood weight problems.

i.                     The composition of breast milk changes in the am vs. pm.

ii.                    The composition of breast milk changes between the 1st month and the 7th. Goes from whole milk to lowfat.

iii.                  The fat composition changes during a feeding. 1st milk is lowfat, the longer the infant nurses the more fat is added to the milk.

iv.                  Increasing the number of feeding increases the fat content of the milk.

  1. Breast milk increases IQ scores 5-10 pts.

i.                     Breast milk contains essential fats that are parts of the myelin sheath( insulation on nerve cells). If the mom does not eat the correct fats, the breast will make these fats.

ii.                    There is a lot of cholesterol in human milk, little in cows milk and none in formula. Cholesterol is needed in brain development.

iii.                  Human milk has more lactose than any other mammalian milk. The more lactose in the milk the larger the mammals brain is.

  1. Breastfed babies are 40 % less likely to have misaligned teeth.
  2. Breastfed babies have better eyesight.
  3. ADD may be related to the overabundance of magnesium in formula.
  4. Breastfeeding decreases the risk of breast cancer in the mom and infant.