Anatomy Lesson 2 - Embryology

When is the prenatal period

first 38 wks of human development

breakdown the first 38 wks of human development in 3 phases

1. pre-embyronic phase wks 1-2

2. embryonic phase wks 3-8

3. fetal phase. wks 9-38

What are the three germ layers?

ectoderm, mesoderm, endoderm

what is the derivative of ectoderm?

[**on the actual lesson slides it only says skin and nervous tissue]

• skin, epidermal derivatives(hair, nail, sweat glands, mammary glands)

• nervous tissue

• sense organs

• pituitary gland

• adrenal medulla

• enamel of teeth

• lens of eye

what is the derivative of mesoderm

[**on actual lesson slide it says: muscle tissue, heart, kidneys, reproductive organs, connective tissue]

• dermis of skin

• epithelial lining of blood vessels

• lymph vessels

• serous membranes

• muscle tissue

• connective tissue

• adrenal cortex

• heart

• kidneys

• ureters

• internal reproductive organs

• spleen

what is the derivative of endoderm

[**on actual lesson slide it says: digestive systems, respiratory systems]

• epithelial lining of respiratory

• GI tract

• urinary tract

• reproductive tract

• lymphatic cavity

• auditory tube

• liver

• gallbladder

• pancreas

• palatine tonsils

• thyroid gland

• parathyroid gland

• thymus

what are the three germ layers collectively called

trilaminar embryonic disc

What are the steps of cleavage?

2 to 4 to 8 cells then to 16cells (morula)

When morula enters the lumen of the uterus, fluid leaks to make a fluid filled cavity called blasticyst cavity w/in the morula.

Morula becomes blastocyst (blastula)

Blastocyst has 2 components: trophoblast(forms chorion, fetal half of placenta) and embryoblast(aka inner cell mass; forms embryo)

what happens after cleavage?

implantation of blastocyst

on what day does implantation begin?

day 7

the cells of embryoblast are _______.

pluripotent

by day ___ blastocyst is completely embedded inthe uterine wall

9

how long does implantation take in total

2 weeks

describe the steps of implantation

Blastocyst invades the inner lining of uterine wall called endometrium. Simultaneous w/ implantation, trophoblast (one of the 2 components of blastocyst) begins to divide into two layers (cytotrophoblast, the inner layer of trophoblast, and syncytiotrophoblast, the outer layer that allows burrowing of blastocyst) (*the two layers later form the chorion and the placenta)

during implantation what happens to embryoblast

it separates into two components: hypoblast and epiblast, the two forms bilaminar germinal disc (aks blastodisc)

hypoblast: surrounds yolk sac

epiblast: surrounds amniotic cavity

what forms the chorion?

by both cytotrophoblast and syncytiotrophoblast (which are the two components of trophoblast)

what forms the amnion?

epiblast of embryoblast

define and describe gastrulation

definition: the formation of 3 germ layers that later produce everything in a human body

First, the primitive streak forms. Some epiblast cells invaginates between the hypo and epiblast to form the mesoderm and some go to form the endoderm. The rest of the epiblast cells become the ectoderm.

what is the folding of the head and tail region of the embryo called and why does this happen

cephalocaudal folding

this happens bc the embryonic disc and amnion grow very quickly while the yolk sac doesn’t which leads the head and tail region to folding on themselves

what is the folding of the left and right side of the embryo called

transverse folding or lateral folding > this forms the torso/trunk region of the embryo while pinching off the yolk sac

what are the steps of neurulation

a cylindrical mass of mesoderm called notochord, formed parallel and deep to the primitive streak, induces the formation of neural plate on the ectoderm. The edges of the neural plate rises to form neural folds that have a neural groove in b/t them. The fold fuse together to form the neural tube which later forms the brain and spinal cord.

neurulation is complete by wk ___ of development

4

what is organogenesis

it is the period of organ making, which follows after gastrulation and body folding

all organs are developed by wk ___ of development

8

define premature birth

any birth that takes before the full 38 wks of development

infants born as early as ___ weeks can survive w/o lifesaving measures and survive as early as ___ weeks

30; 22

anything that causes a birth defect is called a

teratogen

___% of babies are born w/ serious structural birth defect. ___% of cause is unknown, ___% is multifactoral, ____% is chromosomal, ___% is monogenic and ___% is major environmental factor

50; 25; 10; 8; 7