Exercise 40 - Part A, Part 1

Human Development

fertilization

the process by which the nuclei of an ovum and a sperm, each with 23 chromosomes. fuse to form a single cell with 46 chromosomes

zygote

fertilized ovum, the beginning stage of human life, single cell

fetus

name for after 9 weeks after fertilization, when the developing human is referred to as _____

embryonic period

the time from fertilization through the 8th week of development

fertilization, cleavage, blastocyst formation, implantation, formation of the three primary germ layers, and formation of embryonic membranes

major events during the embryonic period

corona radiata, zona pellucida

The secondary oocyte is surrounded by two layers, the ______ and _____

corona radiata

is the outer layer of cells

zona pellucida

is the translucent layer of glycoprotein just beneath the corona radiata and exterior to the plasma membrane

sperm

must break through both of these layers (corona radiata and zona pellucida) to reach the oocyte

hardened

After one sperm penetrates the plasma membrane, the zona pellucida is enzymatically ______ so other sperm may not enter.

ovum

name for the secondary oocyte after it completes the second meiotic division

zygote

[In fertilization] The 26-chromosome sperm then fertilizes the 26-chromosome ovum, and the two fuse to form a one-celled ______ with 46 chromosomes

ampulla of the uterine tube

Fertilization usually occurs within the _______.

cleavage

The rapid series of early mitotic divisions of the zygote are referred to as ______.

blastomeres

The one-celled zygote divides into two cells that are called _____ 24 to 30 hours after fertilization

smaller, same

[In cleavage] Although there is an increase in the number of cells because of rapid mitosis, each cell becomes increasingly ____ in size so that the entire ball of cells remains approximately the _____ size as the original zygote.

morula

[In cleavage] By the 4th day, the 16 to 32-cell stage, is a solid ball of cells called a _____ that passes through the isthmus of the uterine tube and into the uterine cavity.

blastocyst cavity (blastocele), blastocyst

[In blastocyst formation] By the 5th day, the solid morula develops a hollow cavity called the _____, and the developing zygote is now called a _____.

embryoblast (inner cell mass)

Blastocyst cells begin the process of differentiation by forming two different cell regions, the _____ and the trophoblast.

embryoblast

a group of cells in the interior of the blastocyst that will develop into the embryo and form the developing human body

trophoblast

the superficial layer of cells that form the wall of the blastocyst, and develops into the outer chorionic sac

chorionic sac

surrounds the fetus and develops into the fetal portion of the placenta

blastocyte, enzymes, zona pellucida

[In blastocyst formation] Around the fifth day, the ______ secretes _____ that produce a small hole in the _______.