12

Question 1

insemination

Answer 1

When the male ejaculates, the sperm are released in the vagina at the entrance to the uterus

Question 2

sperm mortality

Answer 2

The death rate of sperm, is high, and is one reason why a large number of sperm are required if fertilisation is to occur.

Question 3

the secondary oocyte has two layers

Answer 3

• The outer corona radiata consists of follicle cells held together by cementing materials that contain acid.
• The inner zona pellucida is a glycoprotein matrix surrounding the plasma membrane of the oocyte.

Question 4

The outer surface of the acrosome on the head of the sperm contains …….

Answer 4

an enzyme. This enzyme can break down the acid in the cementing material that holds the cells of the corona radiata together. When several thousand sperm surround the oocyte, there is enough enzyme to loosen the cells of the corona, allowing one sperm to penetrate the corona radiata.

Question 5

What happens when sperm encounters the zona pellucida

Answer 5

This initiates the acrosomal reaction, causing digestive enzymes from the acrosome to be released. These enzymes break down the glycoprotein matrix of the zona pellucida, giving the sperm access to the plasma membrane of the oocyte. When the plasma membranes of the oocyte and spermatozoa fuse, the nucleus of the sperm enters the ovum. The entrance of one sperm into the secondary oocyte stimulates the formation of a fertilisation membrane around the oocyte, which prevents the entrance of any more sperm.

Question 6

By about six days after fertilisation what happens

Answer 6

the original zygote has reached the uterus and has developed into a blastocyst.

Question 7

What is the blastocyst

Answer 7

is a hollow ball of cells that surround a cavity filled with fluid.

At one side of the cavity is a group of about 30 cells called the inner cell mass. The inner cell mass is composed of stem cells that will differentiate into the different body cells to form the embryo.

Question 8

implantation

Answer 8

The blastocyst remains free within the cavity of the uterus for two to three days, and then sinks into the soft endometrium (uterine lining) to become firmly attached to the wall of the uterus.

Question 9

it is the corpus luteum that produces

Answer 9

High levels of oestrogen and progesterone in the blood stop the endometrium from breaking down, and so the menstrual cycle ceases. until the developing placenta can take over the role after approximately 8–12 weeks

Question 10

fertilised oocyte is a totipotent stem cell which means..

Answer 10

that it has the potential to create any type of cell necessary for embryonic development

Question 11

inner and outer cells of the blastocyst

Answer 11

The outer layer of cells will eventually form the placenta and other tissues that are needed for the support and development of the foetus.
The inner cell mass will form all the tissues of the human body; therefore, these are the cells that develop into the foetus

Question 12

during the third week of development, the inner cell mass of the blastocyst undergoes

Answer 12

changes as the cells change to multipotent. This process results in the formation of three layers of cells, the primary germ layers. These layers, called the ectoderm, mesoderm and endoderm,

Question 13

Ectoderm

Answer 13

is the outermost germ layer. This will form the outer layers of the body, such as the skin, hair and mammary glands, as well as the nervous system.

Question 14

Mesoderm

Answer 14

is the middle germ layer. The skeleton, muscles, connective tissue, heart, blood and urogenital tract form from the mesoderm. The mesoderm also allows the formation of the stomach and intestines.

Question 15

Endoderm

Answer 15

is the innermost germ layer. It forms the lining of the digestive system as well as the lungs and thyroid

Question 16

Amnion

Answer 16

secretes amniotic fluid. This fluid serves to protect the embryo against physical injury by acting as a shock absorber. It also helps to maintain a constant temperature and allows the developing embryo, and later the foetus, to move freely.

Question 17

breaking of the waters.

Answer 17

It usually ruptures just before childbirth, releasing the amniotic fluid

Question 18

Chorion

Answer 18

formed from the outer cells of the blastocyst together with a layer of mesodermal cells

As the amnion enlarges, it fuses with the inner layer of the chorion. Eventually, the chorion becomes the main part of the foetal portion of the placenta.

Question 19

Yolk sac and allantois

Answer 19

These are not as important in humans as they are in the development of many other animals; however, they do form the outer structure of the umbilical cord.

Question 20

Placenta

Answer 20

forms from both foetal and maternal tissues during the first three months of gestation, with the foetal portion developing from part of the chorion
The placenta is attached to the foetus by the umbilical cord.

Question 21

chorionic villi

Answer 21

Small, branching, finger-like projections, called chorionic villi, develop from the chorion and contain numerous blood vessels. They grow into the endometrium, much like the root of a tree penetrating the soil.

Question 22

5 placenta roles

Answer 22

endocrine- hormones
excretory- waste
immune- antibodies
nutritional- nutrients
Respiratory -oxygen

Question 23

gestation

Answer 23

The period of pregnancy, the time that the embryo or foetus is carried in the uterus

takes about 280 days, measured from the beginning of the last menstrual period

Question 24

3 months growth

Answer 24

Forelimbs well developed; eyelids closed; outer ear completed; bone marrow formed; blood cells formed in bone marrow; sex distinguishable

Question 25

4 months growth

Answer 25

Arms and hands fully shaped; skeleton completed; exercising of muscles evident; ears stand out from head

Question 26

5 months growth

Answer 26

Fine hair covers body; gripping reflexes are developed; increased growth

Question 27

6 months growth

Answer 27

Respiratory movements; digestive glands begin to function; tooth buds evident; eyebrows and eyelashes

Question 28

7 months growth

Answer 28

Period of greatest growth; all systems functional except respiratory system

Question 29

8 months growth

Answer 29

Accumulation of fat beneath skin; growth slowed

Question 30

9 months growth

Answer 30

Eyes open; nose well formed; sucking and grasping reflexes apparent; fine body hair is shed

Question 31

changes of the mother during pregnancy

Answer 31

There is an increase in the size of the heart and in blood volume

The greater blood volume results in an increased blood flow to the kidneys and, therefore, increased urine production

The emotional state of the mother may be affected due to the changes in hormonal balance and as a result of natural fears accompanying pregnancy

enlargement of the breasts

Question 32

Parturition

Answer 32

The process by which the foetus is expelled from the mother’s body at the end of gestation is called birth, or parturition. Parturition is preceded by a sequence of events commonly called labour.

Question 33

1. The first stage of labour

Answer 33

the dilation of the cervix is the time from the onset of labour to the complete dilation (or opening) of the cervix. With each contraction, the muscle fibres making up the uterus shorten a small amount, pulling on the cervix. This pull on the cervix shortens it so that it no longer projects down into the vagina. At the same time, the cervix is opened. This cervical dilation allows the foetus to move more deeply into the pelvis. As the contractions become more frequent and stronger, the head of the foetus is pushed more forcefully against the slowly dilating cervix.

Complete dilation of the cervix marks the end of the first stage of labour

Question 34

the birth canal

Answer 34

the uterus, cervix and vagina form a single, curved passage. This passage, termed the birth canal, is the route through which the foetus will pass, aided by the contractions of the uterus and voluntary contractions of the abdominal muscles of the mother.

Question 35

The second stage of labour

Answer 35

involves the delivery of the foetus and is often called the stage of expulsion. It frequently begins with the bursting of the membrane surrounding the foetus and a gush of fluid from the vagina.This distension of the vagina stimulates the woman to contract her abdominal muscles. These contractions, together with the contractions of the uterus, push the foetus through the vagina. Her pulse rate increases, and she usually begins to sweat from the effort required. Once the head has emerged, it turns sideways again to face the mother’s hips. This rotation allows the shoulders and the rest of the body to move more easily through the birth canal.

Question 36

3. Third stage of labour

Answer 36

Once born, the baby begins to breathe with its own lungs, even though it is still connected to the placenta by the umbilical cord. The amnion, chorion and placenta are still inside the uterus at this stage. The umbilical cord is clamped, tied in two places, and then cut between the ties The uterus continues to contract, and about five minutes after delivery the placenta, other membranes and the remains of the umbilical cord are expelled. Together these are called afterbirth. Little blood is lost during this stage as the placental blood vessels constrict and contractions of the uterus squeeze shut the uterine vessels that supply blood to the placenta

Question 37

Ductus venosus

Answer 37

The ductus venosus is a shunt that allows oxygenated blood in the umbilical vein to bypass the liver and is essential for normal fetal circulation

The remainder, approximately 30%, bypasses the liver by flowing through a vessel called the ductus venosus, and then into the inferior vena cava. The fact that much of the blood does not pass through the liver causes no problems at this stage, as the mother’s liver is serving the needs of the foetus.

Question 38

Blood returning to the foetal heart enters the right atrium. From there it can follow several pathways:

Answer 38

• Blood may flow into the right ventricle and then to the lungs in the usual way. However, the lungs are collapsed and not functioning at this stage, so they offer considerable resistance to blood flow and little blood reaches the lungs.
• Most of the blood from the right ventricle flows through the ductus arteriosus to the aorta. The ductus arteriosus is a vessel that bypasses the lung, allowing blood in the pulmonary artery to flow directly into the aorta.
• Blood in the right atrium of the heart may flow directly into the left atrium through an oval opening between the two chambers. This opening is called the foramen ovale. The foramen ovale is located so that most of the blood entering the right atrium goes through it. This is beneficial, as the blood coming from the placenta is highly oxygenated and can flow to the developing foetal tissues via the aorta very quickly.

Question 39

a gradual increase in what…..

mother during pregnancy

Answer 39

the volume of the mother’s blood and a faster rate of circulation through her blood vessels. This results from an increase in both the rate at which the heartbeats and the amount of blood pumped with each beat. By the end of pregnancy, the mother’s blood volume will have increased by 40%.

Question 40

listeriosis,

Answer 40

is a very mild illness caused by eating food contaminated with the bacterium Listeria monocytogenes. Infection in pregnant women has the potential to cause miscarriages or stillbirths

pregnant women should eat food that has been freshly prepared or cooked. Foods to avoid are salads from salad bars, pre-packaged salads, soft cheeses, pâté, and raw or smoked seafoods

Question 41

The hormonal changes involved in pregnancy promote the conversion of ……

Answer 41

energy to fat and the retention of water in the body, both contributing to an increase in weight.

Question 42

teratogen

Answer 42

is one that causes physical defects in the developing embryo. Teratogens are usually identified after an increased prevalence of a certain birth defect. For example, the increased prevalence of cerebral palsy in babies born to mothers living around Minamata Bay in Japan led to researchers identifying methyl mercury as the offending agent

Question 43

Foetal alcohol syndrome (FAS)

Answer 43

… is the term used to describe the effects of foetal exposure to alcohol.

The most obvious effect is a lower than normal birth weight. Other symptoms include slow growth before and after birth, a small head, irregularities of the face such as narrow eye slits and sunken nasal bridge, defects of the heart and other organs, malformed arms and legs, and intellectual disabilities.