Early Developmental Stages

Question 1

Where does fertilization usually occur

Answer 1

The widest part of the fallopian tube: the ampulla

Question 2

Acrosomal apparatus

Answer 2

Tubelike structure that forms when the first sperm comees into direct contact with the secondary oocyte’s cell membrane

Question 3

Cortical reaction

Answer 3

A release of calcium ions that occurs after penetration of the sperm through the cell membrane. These calcium ions depolarize the membrane of the ovum

Question 4

What is the purpose of the cortical reaction

Answer 4

1. depolarization prevents fertilization of the ovum by multiple sperm cells
2. increased calcium concentration increases the metabolic rate of the newly formed diploid zygote

Question 5

Fertilization membrane

Answer 5

The depolarized and impenetrable membrane

Question 6

Indeterminate cleavage

Answer 6

Results in cells that can still develop into complete organisms

Question 7

Determinate cleavage

Answer 7

Results in cells with fates that are already determined,

Question 8

Stages of blastulation

Answer 8

1. Embryo becomes a solid mass of cells: morula

2. Forms blastula, hollow ball of cells with fluid-filled inner cavity known as blastocoel

Question 9

What does the trophoblast in a blastocyst give rise to

Answer 9

The chorion and later the placenta

Question 10

What does the inner cell mass in a blastocyst give rise to

Answer 10

It gives rise to the organism itself.

Question 11

Chorion

Answer 11

An extraembyronic membrane that develops into the placenta

Question 12

Chorionic villi

Answer 12

Microscopic fingerlike projections that penetrate the endometrium

Question 13

What does the umbilical cord consist of

Answer 13

Two arteries and one vein encased in a gelationous substance.

Question 14

Yolk sac

Answer 14

Until placenta is functional, embryo is supported by the yolk sac –> also the site of early blood development.

Question 15

Allantois

Answer 15

Involved in early fluid exchange between the embryo and the yolk sac.

Question 16

What does the umbilical cord originate from

Answer 16

it originates from the remnants of the yolk sac and allantois

Question 17

Amnion

Answer 17

surrounds allantois and is a thin, tough membrane filled with amniotic fluid, which serves as a shock absorber during pregancy, lessening the impact of maternal motion on the developing embryo

Question 18

Archenteron

Answer 18

Membrane invagination into the blastocoel –> later develops into the gut

Question 19

Blastopore

Answer 19

Opening of the archenteron

Question 20

Deuterostomes

Answer 20

Blastospore develops into the anus

Question 21

Protostomes

Answer 21

Blastospore develops into the mouth

Question 22

Ectoderm

Answer 22

Gives rise to the integument, including epidermis, hair, ails, and epithelia of nose, mouth, and lower anal canal
Also lens of eye, nervous system (including adrenal medulla) and inner ear

Question 23

Mesoderm

Answer 23

Musculoskeletal, circulatory, and most of the excretory sytems.
Mesoderm also gives rise to the gonads, muscular and connective tissue layers of the digestive and respiratory systems, and adrenal cortex

Question 24

Endoderm

Answer 24

Forms epithelial linings of digestive and respiratory tracts, including lungs.
Pancrease, thyroid, bladder, and distal urinary tracts, as well as parts of the liver.

Question 25

How does differentiation occur

Answer 25

Selective transcription: only the genes needed for that particular cell type are transcribed.

Question 26

Induction

Answer 26

Ability of one group of cells to influence the fate of nearby cells.

Question 27

Steps of neurulation

Answer 27

1. Notochord induces a group of overlying ectodermal cells to slide inward to form neural fold
2. Neural fold surrounds neural groove
3. Neural folds grow toward one another until they fuse into a neural tube (gives rise to CNS)
4. Tip of each neural fold are neural crest cells: these cells migrate outward to form PNS.

Question 28

Morphogens

Answer 28

Specific molecules that may cause neighbouring cells to follow a particular developmental pathway.

Question 29

Paracrine signals

Answer 29

Act on cells in the local area

Question 30

Juxtacrine signals

Answer 30

Involve a cell directly stimulating receptors of an adjacent cell.

Question 31

Growth factors

Answer 31

Peptides that promote differentiation and mitosis in certain tissues –> often inducers

Question 32

Fetal hemoglobin (HbF)

Answer 32

Has a greater affinity for oxygen than maternal (adult) hemoglobin. Assists with transfer (and retention) of oxygen into the fetal circulatory system.

Question 33

Foramen ovale

Answer 33

A one-way valve that connects the right atrium to the left atrium.

Question 34

Difference in pressure in heart in fetuses vs adults

Answer 34

In fetuses, the right side of the heart is at a higher pressure in the developing fetus than the left side, which pushes blood through the opening. after birth, this pressure differential reverses, shutting the foramen ovale.

Question 35

Ductus arteriosus

Answer 35

Shunts leftover blood from the pulmonary artery to the aorta.

Question 36

Ductus venous

Answer 36

Bypasses liver –> shunts blood returning from the placenta via the umbilical vein directly into the inferior vena cava.

Question 37

Characteristics of first trimester

Answer 37

By the end of 8 weeks most of the organs have formed, the brain is fairly developed, and the embryo is called a fetus.
At the end, fetus is about 9 cm long

Question 38

Characteristics of second trimester

Answer 38

Tremendous amount of growth
Fetus begins to move within amniotic fluid,
Its face takes on human appearance, and its toes and fingers elongate

Question 39

Characteristics of third trimester

Answer 39

Continued rapid growth and brain development

Antibodies in fetus highest in ninth month just before birth

Question 40

What hormones coordinate parturition

Answer 40

Prostaglandins and the peptide hormone oxytocin.