Human Development

Question 1

How many chromosomes are there in a human egg once it has been fertilized?

Answer 1

A single cells contains 23 chromosomes from each parents, in total of 46 chromosomes.

Question 2

Why must the egg be fertilized within 12 to 24 hours of its release?

Answer 2

It will lose its capacity to develop further.

For a sperm and egg to join, the sperm must reach the egg during the early part of its movement through the oviduct.

Question 3

Why do so few sperm arrive the oviduct where the egg is?

Answer 3

Once they enter the female vagina, they must make their way to the cervix, then through the uterus, and finally to the oviduct into which the egg was released.

• Most sperm do not survive the journey.
• Many are destroyed by the naturally acidic environment of the vagina.
• Many goes to the “wrong way” that is - they enter the oviduct that does not have the egg.
• Only a few dozen to a few hundred survive to reach the eggs.

Question 4

Why is the first sperm that reaches the egg unlikely to be the stem that enters and joins with it?

Answer 4

A membrane (shell) surrounding the egg, the zona pellucida, has two major functions in fertilization. First, the zona pellucida contains sperm receptors which are specific for human sperm. Second, once the membrane has been penetrated by the sperm, it becomes impermeable to penetration by other sperm.

Question 5

Explain what the process of cleavage is.

Answer 5

After fertilization, the development of a multicellular organism proceeds by a process called cleavage, a series of mitotic divisions whereby the enormous volume of egg cytoplasm is divided into numerous smaller, nucleated cells.

Question 6

How does a morula differ from a blastocyst?

Answer 6

The morula reaches the uterus within three to five days after fertilization. During this time, it begins to full with fluid that diffuses from the uterus. As the fluid-filled space develops, two different groups of cells form.

Blastocyst refers as “germ pouch” which cells or tissues a develop and which new cellular structures can develop.

Question 7

From which group of cells, the trophoblast or the inner cell mass, does the embryo develop?

Answer 7

Trophoblast forms the outer layer of the blastocyst. The trophoblast will develop into a membrane called chorion.

The inner cells mass come together within the blastocyst to form, which called embryoblast.The inner cell mass develops into the embryo itself

Question 8

Explain what is implantation is.

Answer 8

Implantation is defined as the process by which the embryo attaches to the endometrial surface of the uterus and invades the epithelium and then the maternal circulation to form the placenta.

Question 9

What is hCG, and how long is it secreted?

Answer 9

hCG - Human Chorionic Gonatropin

-Has the same effects as Luteinizing Hormone (LH), so it maintains the corpus lute pas the time when it otherwise degenerate.

The Secretion of estrogen and progesterone continues, maintaining the endometrium and preventing menstruation. The secretion of hCG continue for two months.

Question 10

What is the amniotic cavity, and where does it from?

Answer 10

The amniotic cavity is the closed sac between the embryo and the amnion, containing the amniotic fluid. The amniotic cavity is formed by the fusion of the parts of the amniotic fold, which first makes its appearance at the cephalic extremity and subsequently at the caudal end and sides of the embryo.

Question 11

Name each of the three layers of embryonic disk.

Answer 11

germ layer, any of three primary cell layers, formed in the earliest stages of embryonic development, consisting of the

• endoderm (inner layer)
• the ectoderm (outer layer)
• the mesoderm (middle layer)

Question 12

Name the process that results in the formation of the primary germ layers.

Answer 12

The germ layers develop early in embryonic life, through the process of gastrulation. During gastrulation, a hollow cluster of cells called a blastula reorganizes into two primary germ layers:

• an inner layer, called endoderm
• an outer layer, called ectoderm.

Question 13

What is morphogenesis?

Answer 13

Morphogenesis - gastrulation makes the start

• The series of events that form distinct structures of the developing organism.
• Morphogenesis depends on the ability of early embryonic cells to become different types of cells - that is, too differentiate.

Question 14

Explain how the development of the primary germ layers is related to differentiation

Answer 14

Differentiation - cellular process that enables a cell to develop a particular share and to perform specific functions that different from the functions.

The development of the three primary germ layers is especially important because all the cells, tissues, and organs of the body are derived from the primary germ layers through differentiation.

Question 15

What is neurulation?

Answer 15

A process in which the neural plate bends up and later fuses to form the hollow tube that will eventually differentiate into the brain and the spinal cord of the central nervous system.

Question 16

Other an neurulation, identify two events that occur during the third week of development

Answer 16

-A thickened band of mesoderm cells develops along the back of the embryonic disk. The cell lie along what will become the baby’s back and come together to form a rod-like structure called the “Notochord”.

The notochord will form the basic framework of the skeleton. The NS develops from ectoderm that is located just above the notochord. First, cells along the surface above the notochord begin to thicken.

Question 17

Identify three events that occur during the fourth week of development

Answer 17

-The fourth week of prenatal development and on is a time of rapid growth and differentiation.

• Blood cells start tp form and fill developing blood vessel
• Lungs and kidney take shape
• Small buds, which will develop into arms, and legs, appear.
• A distinct head is visible, as well as early evidence of eyes, ears, and nose.
• The embryo is about 0.6cm long at this long.

The mother might now suspect that she is pregnant, because her menstrual period is about two weeks later.

Question 18

Identify four events that occur between the fifth and eighth week and when they occur.

Answer 18

Fifth Week

• The embryo is very large compared with its body.
• The eye open, but they do not yet have eyelids or irises
• Cells in the brain are differentiating very quickly.
• The embryo is about 1.3 cm long now.

Sixth Week

• The brain continues its rapid development.
• The limbs length and flex slightly
• The gonads are starting to produce hormones that will influence the development of the external genitalia

Seventh & Eighth Week

• Distinct Human Characteristics.
• The organs are formed , and the NS is starting to coordinate body activity
• A skeleton cartilage has formed. (Bone will not begin to replace the cartilage until about the ninth week)
• Eyes are well developed, but the lids are now closed, stuck together to protect them against random movement of fingers form the still-elongating arms.
• The nostrils are developed, but plugged with mucus. (Breathing will not be required until the baby emerges from the uterus.)
• The external genitalia are still forming, but they are undifferentiated.
• The physical sex of the embryo is not yet apparent, even though its genetic sex has been determined.
• The end of the eighth week of prenatal development. the embryo is about the size and mass of a paper clip.

Question 19

What is the point of the embryo termed fetus?

Answer 19

• 90% pf the organs and other structure that make up the adult human body are established.
• The organs enlarge and mature, until birth, the developing life is called a fetus.

Question 20

Name the extra-embryonic membranes.

Answer 20

Amnion: A transparents sac that develops from cell of the embryonic disk, it grows to enclose the embryo completely. It is a penetrated only by the umbilical cord. The amnion becomes filled with fluid (amniotic fluid), which protects the embryo from trauma and temperature fluctuations, allows freedom of movements, and prevents limbs from sticking to the body.

Yolk Sac: A smalls that is suspended from the abdominal area if the embryo. It contributes to the formation of the digestive tract and produces the first blood cells and the future egg or sperm cells. Unlike the yolk sac in many other vertebrates, the yolk sac in humans serves no nutritive functions.

Allantois: forms the foundation for the umbilical cord. During the second month, most of the allantois degenerates. the remainder becomes part of the urinary bladder.

Chorion: the outermost membrane. it encloses all the other extra-embryonic membranes, as well as the embryo. The chorion forms the fetal portion of the placenta.

Question 21

From which extra-embryonic membranes do the placenta and umbilical cord?

Answer 21

Chorion - forms the fetal portion of placenta

Amnion - It grows to enclose the embryo completely. It is penetrated only by the umbilical cord. The amnion becomes filled with fluid ( amniotic fluid), and

Question 22

Summarize the role of placenta.

Answer 22

The placenta is an organ that develops in the uterus during pregnancy. This structure provides oxygen and nutrients to a growing baby. It also removes waste products from the baby’s blood. The placenta attaches to the wall of the uterus, and the baby’s umbilical cord arises from it.

Question 23

Summarize the role of the umbilical cord.

Answer 23

The cord is sometimes called the baby’s “supply line” because it carries the baby’s blood back and forth, between the baby and the placenta. It delivers nutrients and oxygen to the baby and removes the baby’s waste products.

Question 24

What is the main difference between the embryonic and fetal periods of development?

Answer 24

The embryonic period is all about the formation of important systems of the body. Think of it as your baby’s basic foundation and framework.

The fetal period, on the other hand, is more about growth and development so your baby can survive in the outside world.

Question 25

Identify three events or characteristics of fetal development during the second trimester.

Answer 25

Second Trimester - Weeks 13 to 24

Fourth Months

• The heartbeat of the fetus is strong enough to hear with a stethoscope.
• The bones of the skeleton begins to form
• The brain grows rapidly and the NS starts to function.
• As the fetal legs grow and develop, the mother begins to feel movement.

Fifth Months

• The fetus becomes covered with fine, soft hair, and an oily substance to protect the still-developing skin.
• The hair, called language is usually shed before birth.

Sixth Month

• The skin appears wrinkled because there is very little far beneath it.
• The skin becomes more pink as blood-filled capillaries extend into it.
• If the fetus is born at this stage, it is unlikely to survive, it certainly would not survive without medical intervention.

Question 26

Identify three events or characteristics of fetal development during the third trimester

Answer 26

Third Trimester - Weeks 25 to 38

• Connecting to form more and more intricate networks.
• The testes of males descend into the scrotum.
• A layer of fat develops beneath the skin
• The digestive and respiratory systems are usually the last to mature, which is why infants that are born prematurely often have difficulty digesting milk and breathing.
• Proper nutrition is important during all of pregnancy, for both the mother and the fetus.
• Nutrition is especially important during the third trimester.
• Poor nutrition damages the placenta, which can lead to low birth weight, short stature, delayed sexual development, and learning disabilities.
• About 266 days (approximately 40 weeks) after the formation of a single fertilized cell, a multi-trillion celled being is ready to be born.

Question 27

What are teratogens?

Answer 27

Teratogens are substances that may produce physical or functional defects in the human embryo or fetus after the pregnant woman is exposed to the substance.

Question 28

Give three examples of dangers that teratogens pose to the developing baby.

Answer 28

1. Cigarette smoke
2. Alcohol
3. Prescription Drugs with teratogenic effects is thalidomide, which was first prescribe in the 1950s to reduce morning sickness.

Question 29

What hormones are involved during parturition (birth)?

Answer 29

Here we discuss four hormones that are important for reproduction: oxytocin, endorphins, adrenaline and related stress hormones, and prolactin. These hormones play a major role in regulating labor and birth.

Question 30

What is a Caesarean section?

Answer 30

A cesarean section, also called a c-section, is a surgical procedure performed when a vaginal delivery is not possible or safe, or when the health of the mother or the baby is at risk. During this procedure, the baby is delivered through surgical incisions made in the abdomen and the uterus.

Question 31

What is lactation?

Answer 31

Lactation is the process of making human milk. Human milk is secreted through your mammary glands, which are located in your breasts. Lactation is hormonally driven and occurs naturally in people who are pregnant.

Question 32

Describe the role of oxytocin in lactation.

Answer 32

The nerve impulses travel to the hypothalamus which, in turn, stimulates the posterior pituitary to release oxytocin. Oxytocin causes contractions within the mammary lobules. The mammary lobules contain alveoli, which are sacs with cells that produce milk. The lobules end in mammary ducts at the nipple. Contractions within the lobules cause milk to flow to the ducts, where the infant can draw it out by sucking. If suckling does not occur, or if it stops, milk production stops within a few days. Conversely, increased suckling stimulates increased milk production which can continue for several years.

Question 33

Give two reasons that a man might be infertile or sterile, and identify two productive technologies that could help.

Answer 33

• Low Sperm Count
• Obstruction in the ductus deferent or epididymis, which may be caused by complications arising from STIs or from other blockages in the testicles
• High proportion of abnormal or non-viable sperm. caused by factors including overheated restyles, exposure to toxic chemicals or radiation
• Ejaculation caused by factors including vascular disease, NS injury, stress, hormonal balance, medication, smoking, and alcohol intake.

Question 34

Give two reason that a woman might be infertile or sterile, and identify two productive technologies that could help.

Answer 34

• Blocked oviduct, often an effect of STIs
• Failure to ovulate, caused by hormonal imbalances that occur for a variety of reason, including being malnourished
• Endometriosis, a painful condition in which endometrial tissues grow outside the uterus.
• Damaged eggs, which may be caused by environmental factors such as exposure to toxic chemicals or radiations.

Question 35

What is the most effective method to avoid conceiving a child?

Answer 35

Abstinence - not sexual relationship

Tubal Ligation - oviducts and tying of cut ends.