Chapter 29: Development and Inheritance

Differentiation

The changes that occur in a single cell to become specialized.

Three stages of development

Fertilization, prenatal development, and postnatal development.

State of the oocyte at ovulation

Arrested in meiosis II, metabolically arrested, surrounded by zona pellucida and corona radiata.

Prevention of polyspermy

Exocytosis of cortical granules, which changes sperm receptor conformation after one sperm fuses.

Location of fertilization

The ampulla of the fallopian tube.

Cleavage

Division of a zygote without increasing overall size, producing blastomeres.

Blastocyst components

Trophoblast (becomes placenta) and inner cell mass (becomes embryo).

Implantation timing

Around day 6 or 7 after fertilization (day 22 of the uterine cycle).

Human chorionic gonadotropin (HCG)

Hormone secreted by the placenta that maintains the corpus luteum for about 2 months.

Relaxin

Placental hormone that loosens maternal joints and ligaments during childbirth.

Ectopic pregnancy

Implantation of the embryo at a site other than the uterine endometrium.

Hydatidiform mole

A molar pregnancy where only the placenta develops with no or a small embryo.

Gastrulation

Process where the bilaminar germ disk becomes a trilaminar germ disk.

Three germ layers

Ectoderm (epidermis/CNS), mesoderm (muscles/bones/blood), and endoderm (digestive/respiratory linings).

Critical period for organogenesis

Weeks 3 to 8, when the embryo is most susceptible to teratogens.

Spina bifida (meningomyelocele)

Neural tube defect where neural tissue and meninges protrude from the lumbar vertebra.

Prevention of neural tube defects

Folic acid supplementation taken before pregnancy.

Hormones stimulating uterine contractions

Estrogen, oxytocin, and prostaglandins (inhibited by progesterone).

Three stages of childbirth

Cervical dilation, expulsion of the baby, and placental delivery.

Monozygotic vs. dizygotic twins

Monozygotic: one egg splits (identical). Dizygotic: two fertilized eggs (fraternal).

Colostrum

Low-fat, high-protein early breast secretion containing antibodies, growth factors, and a laxative.

Milk let-down reflex hormone

Oxytocin (stimulates contraction of myoepithelial cells to squeeze out milk).

Puberty initiation trigger

GnRH release from the hypothalamus, which requires leptin to stimulate puberty.