cell differentiation

the mechanism by which different sorts of cells arise. Deals with the way genes are activated or repressed and how the activity of the genes is susequently maintained.


the process of generating pattern in a previously similar population of cells. Involves the intercellular mechanisms collectively called induction.

4 types of tissue

epithelial, connective, muscular, nervous

epithelial cells

lining of surface or body cavities, glandular secretion, absorption (the intestines), contractility (myoepithelial cells)

what do the cells of connective tissue look like?

several types of fixed and wandering cells

what are the main functions of connective tissue?

support and protection

what type of tissue has the most extracellular material produced by its cells?

connective tissue


organ cells responsible for the main functions typical of the organ


supporting tissue of an organ

where is the stroma NOT made of connective tissue?

the brain and spinal cord

lamina propria

the connective tissue supporting the epithelia lining of internal organs that provides nutrition to the epithelum and binds it to underlying structures

basal pole

the region of the epithelial cells that faces connective tissue

apical pole

the region of the epithelial cells that faces a space, not the connective tissue

where does fertilization usually occur?

ampulla of fallopian tube

where does the sperm bind to the oocyte?

corona radiata

zona pellucida

glycoprotein membrane surrounding the plasma membrane of an oocyte

what are the steps of embryonic development involved in the first week following fertilization?

fertilization, cleavage, compaction, differentiation, cavitation, zona hatching, implantation

what is a fertilized egg called?



symmetrical cell divisions of the zygote

does the zygote size increase as its cells divide?

no, cells are compacted


16 cells in 3 days contained by the zona pellucida

what happens in the morula stage?

cells increase their adhesion to one another to form an impenetrable barrier (compaction), differentiation into the inner cell mass and trophoblasts begins

when does differentiation begin?

day 4

when does the embryo travel to the uterus?

day 3-4


58-107 cells in 4 days

what happens in the blastocyst stage?

cells excrete fluid forming a cavity (a blastocoele), zona pellucida is shed, ICM and trophoblasts further differentiated

early blastocyst

58 cells in 4 days

when does implantation begin?

day 6-12

when does cavitation begin?

day 4

when does zona hatching begin?

day 5


cells forming the outer layer of a blastocyst, which provide nutrients to the embryo and develop into a large part of the placenta

inner cell mass

mass of cells inside the primordial embryo that will eventually give rise to the definite structures of the fetus

monozygotic twins

identical twins developed from one zygote that splits and forms two embryos

dizygotic twins

fraternal twins that develop when two separate eggs are fertilized by two separate sperm

what happens to make twins conjoined?

inner cell mass division is incomplete


when the embryo adheres to the wall of the uterus

what stage is an embryo at implantation?

a blastocyst


when the endometrium of the uterus increases in thickness and becomes vascularized and its glands grow and increase secretions


the very first, albeit loose, connection between the blastocyst and the endometrium. The inner cell mass rotates inside the trophoblast to align closest to the endometrium


trophoblasts that penetrate the endometrium become a multi-nucleated single mass called the syncytiotrophoblasts, they form the outermost fetal component of the placenta and secrete progesterone


the inner layer of the trophoblast, interior to the syncytiotrophoblasts

what types of tissues does the inner cell mass develop into?

epiblast and hypoblast


the primary ectoderm that differentiates into the endoderm, mesoderm, and ectoderm during gastrulation


lies beneath the epiblast and differentiates ino the yolk sac


a glycoprotein located on the exposed trophectoderm involved in the adhesion between the trophectoderm and the endometrium

bilaminar embryo

consists of epiblast and hypoblast that turn into the amnion and yolk sac

trilaminar embryo

consists of three germ layers - ectoderm, mesoderm, and endoderm

where do most ectopic pregnancies occur in the body?

ampulla (fallopian tube)

yolk sac

a membranous sac attached to an embryo, providing early nourishment and functioning as the developmental circulatory system of the embryo


a membrane building the amniotic sac that surrounds and protects an embryo


a phase of the development of the embryo in which the morphology of the embryo is reorganized to form three germ layers: ectoderm, mesoderm, and endoderm; epiblasts migrate through the primitive streak to form the three layers

when does gastrulation occur?

week 3

what does the ectoderm give rise to?

epidermis (skin, nails, and hair) and neural tissues

what does the mesoderm give rise to?

muscle, cartilage, notochord, blood, blood vessels, bone, connective tissue

what does the endoderm give rise to?

epithelium of the digestive and respiratory systems, organs in the digestive system

primitive streak

the structure that will establish bilateral symmetry, determine the site of gastrulation, and initiate germ layer formation; it is formed by mesenchyma cells that are arranged at the midline


a flexible, rod-shaped body composed of cells derived from the mesoderm that defines the primitive axis of the embryo; eventually replaced by the vertebral column


development of the notochord by the epiblasts that make up the floor of the amnion cavity


masses of mesoderm distributed along the two sides of the neural tube that will eventually become the dermis, skeletal muscle, and vertebrae