Human development

Biol- L 112 IU

Fertilization

The fusion of egg and sperm cells that forms a zygote, happens in the fallopian tubes b4 implantation

Polyspermy

is the fertilization of an egg by multiple sperm cells, which can lead to abnormal development.

Prevented after the first sperm fertilizes the egg

Zygote

(Day 1-4) Ball of cells that divides after fertilization and begins the process of cleavage as it travels toward the uterus for implantation.

A stage of embryonic development

Morula

(Day 4-5) A solid ball of 16-32 cells formed from the zygote that undergoes further division before developing into a blastocyst.

A stage of embryonic development

Blastocyte

(Day 5-6) A hollow ball of cells with an inner cell mass eventually develops into the embryo and an outer layer that becomes the placenta.

Implants in the endometrium, around 100 cells

A stage of embryonic development

Cleavage

The series of rapid cell divisions that occur immediately following fertilization, resulting in the formation of a multicellular embryo without significant growth.

Gastrula

(forms ~ day 9) A stage of embryonic development characterized by the formation of three distinct germ layers: ectoderm, mesoderm, and endoderm, which later give rise to all body tissues.

Ectoderm

(stage of gastrula) The outer layer that forms the nervous system and retinas, as well as skin and hair.

Mesoderm

(stage of gastrula) The middle layer that develops the heart, kidneys, and muscles, as well as blood and connective tissues.

Endoderm

(stage of gastrula) The inner layer that forms the lining of the digestive tract and associated organs, such as the liver and pancreas.

Embryo

from week 2 - ~ week 8

The developing human organism from the blastocyst stage until the end of the eighth week of pregnancy, during which major organs and structures begin to form.

Fetus

from week 8 until birth The developing human organism from the end of the eighth week until birth, characterized by continued growth and maturation of organs and systems.

First trimester (8-9 weeks after fertilization)

embryonic

embryo (called a fetus) has all its major organs, and its limb buds develop into tiny arms and legs with fingers and toes

genitals are rapidly developing

secondary sex determination characteristics like breast, hair, body types, and voice begin to appear. (determined by testosterone/ estrogen)

SRY

(8-9 weeks) protein on the Y gene initiates male sex differentiation

• Embryos develop sperm production testies

DAX1

a gene that produces an anti-testis factor (maleness inhibitor factor) that developed ovaries and eggs.

present when SRY is absent

First trimester (week 10)

embryonic

placenta is fully formed producing estrogen and progesterone

Antibody (IgG) crosses the placenta

Second trimester

(week 13-27)

14 weeks: fetus is ~6cm (2.4 inches) long and starting to look distinctly human

20 weeks: fetus is ~19cm (7.6 inches) long and weighs roughly 1lb (half a kilogram) and has the face of an infant

Months 5-7:

• 12in and 3lb

• Langugo - body covered by “downy hair”

• kicking

• eyes open

• Venix caseosa - white cheesy substance

28 weeks (7 months): fetus can survive outside the womb (age of viability)

Third trimester

(week 28-40) The fetus continues to grow rapidly, gaining weight and maturing organs and systems. By the end, the fetus averages around 20 inches and 7.5 pounds, preparing for birth.

Oxytocin

• A hormone produced by the hypothalamus and released by the posterior pituitary gland

• stimulates the smooth muscle walls in the uterus, which is important for inducing labor,

• Returns the uterus to normal size

• forces breast tissue to contract and forces milk to the ducts

• used for the treatment of anxiety, schizophrenia, and social bonding

Low levels of Oxytocin

the cervix does not dilate during labor, C-section will be recommended

little breast milk is produced

Prostaglandins

produced by the placenta

induces labor- contraction of the uterine smooth muscles and cervical ripening. 12-16 hours of contractions getting closer, stronger, and more painful

Dilation

stage 1 of labor

Longest stage of labor, increases the opening of the cervix to 10 cm

Amniotic sac ruptures, expulsion of mucus plug, and contractions become more intense and frequent

Expulsion

stage 2 of labor

the baby is delivered through the birth canal.

Delivery

the final stage of labor

the placenta is expelled after the baby has been born.

~15 minutes after birth

Estrogen and Progesterone in lactation

contribute to the growth of mammary glands and ducts in the breast and regulate milk production after childbirth.

Secrets prolactin and oxytocin

Prolactin

a hormone produced by the pituitary gland that stimulates milk production in breastfeeding mothers.

Colostrum

the first form of milk produced by mammals after giving birth, rich in antibodies and nutrients for newborns.

Low fat, high IgA, anti-microbial factors, growth factors, protein rich

what happens when a Rh- mother has a Rh+ fetus

The mother's immune system may produce antibodies against the Rh factor, leading to hemolytic disease of the newborn in future pregnancies.