developmental and inheritance

Germinal period

• fertilization and ends about 1- 2 weeks of development

• cells are forming (morula, blastocysts) and implants in the lining (endometrium)

• The placenta will form as soon as it’s implanted

Embryonic period

• 14-56 days after fertilization

• development of primitive germ layers (endoderm, ectoderm and mesoderm) which develops the structures for the embryo development of major organ systems (heart, liver, brain, etc.)

Fetal period

• 56 days after fertilization to birth

• maturation of organ systems grows and mature; developing human is called a fetus

Neonatal period

first 42 days after birth

infancy

1 month to 2 years of age and ends when the child begins to walk

childhood

age 1-2 to puberty; developing emotional characteristics

adolescence

puberty to about 20 years; developing secondary sexual characteristics

adult

20 to death, female stature is about 17 or 18, 19 or 20 in males

oocyte transported towards uterus

• peristalsis of uterine tube

• movement of cilia

• oocyte releases chemical attractants

sperm swims toward oocyte

• Flagella is used to propel the sperm cells

• prostaglandins (within semen) stimulate uterine contractions that help propel sperm

final maturation of sperm occurs within female

• acrosomal reaction occurs: acrosomes of sperm cells release digestive enzymes. This breaks down the zona pellucida allowing the sperm cell to penetrate the oocyte

• The head/midpiece makes contact, the tail is removed

cleavage

• Zygote goes through multiple cell division; embryonic cell reaches morula when about 16 clusters of cells have formed

• called Blastula/blastocysts, once 32 or more embryonic cells have formed

• blastula cells arranged in two layers (inner cell mass/embryoblast and trophoblast); inner cell mass forms the embryo, and trophoblast layers will form the placenta, which nourishes the embryo

implantation

• blastula (embryo) migrate to the uterus, specifically the endometrium lining where implantation will occur 7days after fertilization

• trophoblast will eventually develop to form the placenta

cytotropholast

divided trophoblast, not fused together yet

synctiotrophoblast

• divided cytotropholast cells that fuse together and get bigger

• will grow and form the fetal blood vessel, eventually this forms into the placenta

placenta forming

• forms during 3rd month

• diffusion of O2, nutrients, wastes; stores nutrients & produces hormones

• barrier to microorganisms, except some viruses, AIDS, measles, chickenpox

• not a barrier to drugs or alcohol

Amniotic sac formation

• amniotic cavity forms within the inner cell mass, providing a protective environment for the developing embryo

• the inner cell mass aka the embryoblast will flatten out and be called embryonic disk

epiblast

gives rise to the three germ layers (endoderm, ectoderm and mesoderm)

hypoblast

forms the yolk sac which provides nutrient and gas exchange between the mother and the embryo

Amnion

inner membrane which protect the embryo from mechanical shock; nourishment

Chorion

layer that surrounds the amnion, which aids in gas exchange

amniocentesis

• usually done at 14-16 weeks gestation to detect suspected genetic abnormalities

• Fetal cells from 10 ml sample of amniotic fluid are examined

• Needle through abdominal wall & uterus

endoderm

• epithelial lining of GI & respiratory

• gives rise to lining of lungs, lining of GI, urinary bladder, thymus, thyroid, tonsil

mesoderm

• muscle, bone & other connective tissues (process called somites)

• cardiovascular, muscles, bones(except for facial), kidneys, microglia, dermis of skin

ectoderm

• epidermis of skin & nervous system (process called neurulation)

• gives rise to tooth enamel, epidermis of skin, lens of the eye, cornea of the eye, nasal cavity, CNS: brain, spinal cord, glial cells, melanocytes, sensory neurons

Neural tube formation

• process of developing the CNS (brain & spinal cord)

• Approx 18 days after fertilization: The cells in the ectoderm will also form notochord

Notochord

secrete growth factor which stimulate the ectoderm cells to thicken and form a neural plate and at the edge you find neural folds

neural fold

fold and bud inwards below the ectoderm and mesoderm forming a neural tube

neuroectoderm

cells inside the neural tubes; these cells become the brain, spinal cord and peripheral NS

somites

• series of paired, cube-shaped structures, develop from the mesoderm

• separated into dermato-myotome and sclerotome which then eventually breaks into three chunks

• give rise to the skull, head muscles, vertebral column, and some skeletal muscles

Myotome

Forms most of the skeletal muscle

Dermatome

Forms connective tissues

Sclerotome

Forms the vertebrae

Fore gut

pharynx, esophagus, stomach, duodenum

Mid gut

jejunum, ileum, Cecum, ascending colon, part of the transverse colon

Hind gut

rest of the transverse colon, descending colon, sigmoid colon, rectum, anus

fifth week development

rapid brain development and considerable head growth

sixth week development

• head grows even larger in relation to the trunk

• there is substantial limb growth

• the neck and trunk begin to straighten

• the heart is now four chambered

seventh week development

various regions of the limbs become distinct, and the beginnings of the digits appear

eighth week development

• all regions of the limbs are apparent, the digits are distinct

• the eyelids come together, the tail disappears

• the external genitals begin to differentiate

Parturition

giving birth

labor

• the process of expelling the fetus

• begins when progesterone is overcome by an increase in the levels of estrogen

1st stage - labor and parturition

• Stretching of the cervix signals the hypothalamus and pituitary gland to release oxytocin via the blood

• Uterine walls contract and stimulate the placenta to release prostaglandin; prostaglandin allow continuous contraction
  of the uterine

• cervix stretch to about 3cm and dilates to 10cm

• Crowning of cervix occurs and the baby’s head is visible

2nd stage - labor and parturition

The cervix is fully at 10 and delivery takes place

3rd stage - labor and parturition

• Delivery of the placenta needs to occur which means the placenta needs to detach from the uterine lining, at this point the uterus is still contracting

• umbilical cords are clamped and cut

lactation

• Production of milk by the mammary glands

• Prolactin increase due to the increase in estrogen and progesterone before delivery

• after delivery, decrease in estrogen and progesterone causing the blocking of the prolactin receptors to release

• Suckling stimulates prolactin (milk production) and oxytocin (release of milk)