Human Health and Physiology

Question 1

Explain why digestion of large food molecules is essential.

Answer 1

There are two reasons why the digestion of large food molecules is vital. Firstly, the food we eat is made up of many compounds made by other organisms which are not all suitable for human tissues and therefore these have to be broken down and reassembled so that our bodies can use them. Secondly, the food molecules have to be small enough to be absorbed by the villi in the intestine through diffusion, facilitated diffusion or active transport and so large food molecules need to be broken down into smaller ones for absorption to occur.

Summary:

Food needs to be broken down and reassembled.
Large food molecules need to be broken down into smaller ones.

Question 2

Explain the need for enzymes in digestion.

Answer 2

Enzymes are needed in the process of digestion as they are the biological catalysts which break down the large food molecules into smaller ones so that these can eventually be absorbed. Digestion can occur naturally at body temperature, however this process takes a very long time as it happens at such a slow rate. For digestion to increase in these circumstances, body temperature would have to increase as well. However this is not possible as it would interfere with other body functions.This is why enzymes are vital as they speed up this process by lowering the activation energy required for the reaction to occur and they do so at body temperature.

Summary:

Enzymes break down large food molecules into smaller ones.
Speed up the process of digestion by lowering the activation energy for the reaction.
Work at body temperature.

Question 3

Outline the function of the stomach, small intestine and large intestine.

Answer 3

The stomach is an important part of the digestive system. Firstly it secretes HCL which kills bacteria and other harmful organisms preventing food poisoning and it also provides the optimum conditions for the enzyme pepsin to work in (pH 1.5 - 2). In addition, the stomach secretes pepsin which starts the digestion of proteins into polypeptides and amino acids. Theses can then be absorbed by the villi in the small intestine.

The small intestine is where the final stages of digestion occur. The intestinal wall secretes enzymes and it also receives enzymes from the pancreas. However the main function of the small intestine is the absorption of the small food particles resulting from digestion. It contains many villi which increase the surface area for absorption.

The large intestine moves the material that has not been digested from the small intestine and absorbs water. This produces solid faeces which are then egested through the anus.

Question 4

Outline the function of the stomach, small intestine and large intestine

Answer 4

Stomach:

Secretes HCL which kills bacteria.
HCL provides optimum pH for pepsin.
Secretes pepsin for protein digestion.
Small intestine:

Intestinal wall secretes enzymes
Receives enzymes from the pancreas.
Has villi for absorption of food particles.
Large intestine:

Moves material that has not been digested along.
Absorbes water.
Produces faeces.

Question 5

Distinguish between absorption and assimilation.

Answer 5

Absorption occurs when the food enters the body as the food molecules pass through a layer of cells and into the bodies tissues. This occurs in the small intestine which has many villi that are specialised for absorption. Assimilation occurs when the food molecules becomes part of the bodies tissue. Therefore, absorption is followed by assimilation.

Question 6

Explain how the structure of the villus is related to its role in absorption and transport of the products of digestion.

Answer 6

The structure of the villus is very specific. Firstly there is a great number of them so this increases the surface area for absorption in the small intestine. In addition the villi also have their own projections which are called microvilli. The many microvilli increase the surface area for absorption further. These microvilli have protein channels and pumps in their membranes to allow the rapid absorption of food by facilitated diffusion and active transport. Also, the villi contains an epithelial layer which is only one cell layer thick so that food can pass through easily and be absorbed quickly. The blood capillaries in the villus are very closely associated with the epithelium so that the distance for the diffusion of the food molecules is small. This thin layer of cells contains mitochondria to provide the ATP needed for the active transport of certain food molecules. Finally, there is a lacteal branch at the centre of the villus which carries away fats after absorption.

Question 7

Explain how the structure of the villus is related to its role in absorption and transport of the products of digestion.

Answer 7

Many villi increase the surface area for absorption.
Epithelium is only one cell layer thick and so food is quickly absorbed.
Microvilli on the villi increase the surface area for absorption further.
Protein channels and pumps are present in the microvilli for rapid absorption.
The mitochondria in the epithelium provide ATP needed for active transport.
Blood capillaries are very close to the epithelium so diffusion distance is small.
The lacteal takes away fats after absorption.

Question 8

What do coronary arteries do?

Answer 8

The coronary arteries supply heart muscle with oxygen and nutrients.

Question 9

Explain the action of the heart in terms of collecting blood, pumping blood, and opening and closing of valves.

Answer 9

The right atrium collects blood from the superior and inferior vena cava and the left atrium collects blood from the pulmonary veins. This blood then flows into the right and left ventricle which pump the blood into the arteries. The direction of the blood flow is controlled by the atrioventricular valves and semilunar valves. When the atria contract the blood flows through the atrioventricular valves which are open, into the ventricle. At this stage the semilunar valves are closed so the ventricle fills with blood. The ventricles then contract which causes a rise in pressure. This rise in pressure first causes the atrioventricular valves to close preventing back flow of blood into the atria. Then the semilunar valves open allowing the expulsion of blood into the arteries. As this happens, the atria start to fill with blood again. The ventricles stop contracting leading to a fall in pressure which causes the semilunar valves to close, preventing back flow of blood from the arteries. When the ventricular pressure drops below the atrial pressure the atrioventricular valves open again and the cycle repeats.

Question 10

Explain the action of the heart in terms of collecting blood, pumping blood, and opening and closing of valves.

Answer 10

Atria collect blood from veins.
Atria contract, atrioventricular valves open.
Blood is pumped into ventricles.
Ventricle contracts, atrioventricular valves close and semilunar valves open.
Blood is pumped into arteries, semilunar valves close.
Cycle repeats.

Question 11

Outline the control of the heartbeat in terms of myogenic muscle contraction, the role of the pacemaker, nerves, the medulla of the brain and epinephrine (adrenaline).

Answer 11

The heart muscle can contract by itself, without the stimulation of a nerve. This is called myogenic muscle contraction. The region that initiates each contraction is found in the wall of the right atrium and is called the pacemaker. Every time the pacemaker sends out a signal, a heartbeat results. The pacemaker is under the influence of nerves and adrenaline. One nerve carries messages from the medulla of the brain to the pacemaker and speeds up the beating of the heart. Another nerve carries messages from the medulla of the brain to the pacemaker and slows down the beating of the heart. Finally, adrenaline (epinephrine) is carried by the blood and once it reaches the pacemaker it signals it to increase the beating of the heart.

Question 12

Outline the control of the heartbeat in terms of myogenic muscle contraction, the role of the pacemaker, nerves, the medulla of the brain and epinephrine (adrenaline).

Answer 12

Heart muscle can contract by itself (myogenic muscle contraction).
Pacemaker initiates contractions.
One nerve carries messages from the brain to the pacemaker to speed up the beating of the heart.
One nerve carries messages from the brain to the pacemaker to slow down the beating of the heart.
Adrenaline signals the pacemaker to increase the beating of the heart.

Question 13

Explain the relationship between the structure and function of arteries, capillaries and veins.

Answer 13

Arteries have a thick outer layer of longitudinal collagen and elastic fibers to avoid leaks and bulges. They have a thick wall which is essential to withstand the high pressures. They also have thick layers of circular elastic fibres and muscle fibres to help pump the blood through after each contraction of the heart. In addition the narrow lumen maintains the high pressure inside the arteries.

Veins are made up of thin layers with a few circular elastic fibres and muscle fibres. This is because blood does not flow in pulses and so the vein walls cannot help pump the blood on. Veins also have thin walls which allows the near by muscles to press against them so that they become flat. This helps the blood to be pushed forwards towards the heart. There is only a thin outer layer of longitudinal collagen and elastic fibres as there is low pressure inside the vein and so little chance of bursting. Finally, a wide lumen is needed to accommodate the slow flowing blood due to the low pressure.

Capillaries are made up of a wall that is only one cell layer thick and results in the distance for diffusion in and out of the capillary being very small so that diffusion can occur rapidly. They also contain pores within the their wall which allow some plasma to leak out and form tissue fluid. Phagocytes can also pass through these pores to help fight infections. In addition, the lumen of the capillaries is very narrow. This means that many capillaries can fit in a small space, increasing the surface area for diffusion.

Question 14

Explain the relationship between the structure and function of arteries, capillaries and veins.

Answer 14

Arteries:

Thick outer layer of longitudinal collagen and elastic fibres prevents leaks and bulges.
Thick wall withstands high pressure.
Thick layers of circular elastic fibres and muscle fibres to pump blood.
Narrow lumen to maintain high pressure.
Veins:

Thin layer with few circular elastic fibres and muscle fibres as blood does not flow in pulses.
Thin walls so that nearby muscles can help push blood towards the heart.
Thin outer layer of longitudinal collagen and elastic fibers as pressure is low.
Wide lumen to accomodate the slow flowing blood.
Capillaries:

Wall is one cell layer thick so distance for diffusion is small.
Pores allow plasma to leak out and form tissue fluid. Phagocytes can also pass through pores.
Very narrow lumen so that many can fit in a small space.

Question 15

What is blood composed of?

Answer 15

Blood is composed of plasma, erythrocytes, leucocytes (phagocytes and lymphocytes) and platelets.

Question 16

What is transported by blood?

Answer 16

Nutrients, oxygen, carbon dioxide, hormones, antibodies, urea and heat are all transported by the blood.

Question 17

Define pathogen.

Answer 17

Pathogen: an organism or virus that causes a disease.

Question 18

Explain why antibiotics are effective against bacteria but not against viruses.

Answer 18

Antibiotics are produced by microorganisms to kill or control the growth of other microorganisms by blocking specific metabolic pathways within the cell. Since bacteria are so different to human cells, antibiotics can be taken by humans to kill bacteria without harming the human cells. Viruses on the other hand are different as they do not carry out many metabolic processes themselves. Instead they rely on a host cell (a human cell) to carry out these processes for them. Therefore viruses cannot be treated with antibiotics as it is impossible to harm the virus without harming the human cells.

Summary:

Antibiotics block specific metabolic pathways in bacteria.
Bacteria are very different to human cells so human cells are not affected.
Viruses require host cell to carry metabolic processes for them and so antibiotics cannot be used to treat viruses.
Harming the virus would harm the human cells.

Question 19

Outline the role of skin and mucous membranes in defence against pathogens.

Answer 19

The skin forms a physical barrier that prevents pathogens from entering the body as the outer layer is very tough. In addition the skin contains sebaceous glands which secret lactic acid and fatty acids which creates an acidic environment on the surface of the skin preventing the growth of pathogens.

Mucous membranes form another type of barrier against pathogens. Mucous membranes are soft and moist areas of skin found in the trachea, nose, vagina and urethra. These membranes are not strong enough to create a physical barrier but they do have mucus which contain lysozyme enzymes that digest the phagocytes. Also, the mucus can be sticky such as in the trachea, and trap the pathogens which are then expelled up the trachea and out of the body by muscles within the trachea.

Summary:

Skin:

Forms a physical barrier.
Sebaceous glands secret lactic acid and fatty acids.
Mucous membranes:

Mucous contains lysozyme enzymes.
Mucous can be sticky and trap pathogens.

Question 20

Outline how phagocytic leucocytes ingest pathogens in the blood and in body tissues.

Answer 20

Phagocytes are found in the blood and ingest pathogens. They do so by recognising pathogens and engulfing them by endocytosis. Enzymes within the phagocytes called lysosomes then digest the pathogens. Phagocytes can ingest pathogens in the blood but also within body tissue as they can pass through the pores of capillaries and into these tissues.

Question 21

Distinguish between antigens and antibodies.

Answer 21

Antibodies are proteins that defend the body against pathogens by binding to antigens on the surface of these pathogens and stimulating their destruction. Antigens are foreign substances which stimulate the production of antibodies. Antibodies usually only bind to one specific antigen.

Question 22

Explain antibody production.

Answer 22

Lymphocytes are a type of leukocyte which make antibodies. Each lymphocyte makes only one specific antibody. A large amount of different lymphocytes are needed so that the body can produce different types of antibodies. The antibodies are found on the surface of the plasma membrane of these lymphocytes with the antigen-combining site projecting outwards. Pathogens have antigens on their surface which bind to the antigen-combining site of the antibodies of a specific lymphocyte. When this happens the lymphocyte becomes active and starts to make clones of itself by dividing by mitosis. These clones then start to make more of this specific antibody needed to defend the body against the pathogen.

Summary:

Each lymphocyte makes one type of antibody.
Antibodies are found on the surface of the lymphocyte.
Pathogen have antigens on their surface.
The antigens bind to the antibodies.
Lymphocyte becomes active and makes clones of itself.
The clones make more of the specific antibody.

Question 23

Outline the effects of HIV on the immune system.

Answer 23

The HIV virus (which causes AIDS) destroys a type of lymphocyte which has a vital role in antibody production. Over the years this results in a reduced amount of active lymphocytes. Therefore, less antibodies are produced which makes the body very vulnerable to pathogens. A pathogen that could easily be controlled by the body in a healthy individual can cause serious consequences and eventually lead to death for patients affected by HIV.

Question 24

What causes AIDs?

Answer 24

Cause: HIV causes AIDS (acquired immunodeficiency syndrome). A syndrome is a group of symptoms that are found together. HIV destroys a type of lymphocyte which is vital for antibody production. Over the years, less active lymphocytes are produced which leads to a fall in the amount of antibodies. Pathogens that would normally be easily controlled by the body in healthy individuals can cause serious consequences and eventually lead to death for patients affected by HIV. The immune system is considerably weakened.

Question 25

How does AIDs transmit?

Answer 25

Transmission: HIV is transmitted through body fluids from an infected person to an uninfected one. This can occur through vaginal and anal intercourse as well as oral sex if there are cuts or tears in the vagina, penis, mouth or intestine. It can also be transmitted by hypodermic needles that are shared by intravenous drug abusers. The small amount of blood present on these needles after their use may contain the virus and is enough to infect another person. Another way of transmission is through the placenta from mother to child, or through cuts during childbirth or in milk during breast feeding. Finally there is a risk of transmission in transfused blood or with blood products such as Factor VIII used to treat hemophiliacs.

Question 26

What are the social implications of AIDs?

Answer 26

Social implications: Relatives and friends suffer grief. Families can also suffer from a loss of income as the person infected by HIV can lose their wage if they are unable to work and are refused life insurance. Also, HIV patients may find it hard to find partners, employment and even housing. Finally, AIDS can cause fear in a population and reduce sexual activity.

Question 27

Distinguish between ventilation, gas exchange and cell respiration.

Answer 27

Ventilation is the process of bringing fresh air into the alveoli and removing the stale air. It maintains the concentration gradient of carbon dioxide and oxygen between the alveoli and the blood in the capillaries (vital for oxygen to diffuse into the blood from the alveoli and carbon dioxide out of the blood into the alveoli).

Gas exchange is the process of swapping one gas for another. It occurs in the alveoli of the lungs. Oxygen diffuses into the capillaries from the air in the alveoli and carbon dioxide diffuses out of the capillaries and into the air in the alveoli.

Cell respiration releases energy in the form of ATP so that this energy can be used inside the cell. Cell respiration occurs in the mitochondria and cytoplasm of cells. Oxygen is used in this process and carbon dioxide is produced.

Question 28

Explain the need for a ventilation system.

Answer 28

A ventilation system is needed to maintain the concentration gradients of gases in the alveoli. Diffusion of gases occurs due to the concentration gradient of oxygen and carbon dioxide between the alveoli and the blood. The body needs to get rid of carbon dioxide which is a product of cell respiration and needs to take in oxygen as it is needed for cell respiration to make ATP. There must be a low concentration of carbon dioxide in the alveoli so that carbon dioxide can diffuse out of the blood in the capillaries and into the alveoli. Also there must be a high concentration of oxygen in the in the alveoli so that oxygen can diffuse into the blood in the capillaries from the alveoli. The ventilation system makes this possible by getting rid of the carbon dioxide in the alveoli and bringing in more oxygen.

Question 29

Describe the features of alveoli that adapt them to gas exchange.

Answer 29

Even though alveoli are so small there are huge numbers of them which results in a large surface area for gas exchange. Also the wall of the alveoli is made up of a single layer of thin cells and so are the capillaries, this creates a short diffusion distance for the gases. Therefore this allows rapid gas exchange. The alveoli are covered by a dense network of blood capillaries which have a low oxygen and high carbon dioxide concentrations. This allows oxygen to diffuse into the blood and carbon dioxide to diffuse out of the blood. Finally, there are cells in the alveolar walls which secrete a fluid that keeps the inner surface of the alveoli moist, allowing gases to dissolve. This fluid also contains a natural detergent that prevents the sides of the alveoli from sticking together.

Question 30

Explain the mechanism of ventilation of the lungs in terms of volume and pressure changes caused by the internal and external intercostal muscles, the diaphragm and abdominal muscles.

Answer 30

Inhalation:

• The external intercostal muscles contract. This moves the ribcage up and out.
• The diaphragm contracts. As it does so it moves down and becomes relatively flat.
• Both of these muscle contractions result in an increase in the volume of the thorax which in turn results in a drop in pressure inside the thorax.
• Pressure eventually drops below atmospheric pressure.
• Air then flow into the lungs from outside the body, through the mouth or nose, trachea, bronchi and bronchioles.
• Air continues to enter the lungs until the pressure inside the lungs rises to the atmospheric pressure.

Exhalation:

• The internal intercostal muscles contract. This moves the ribcage down and in.
• The abdominal muscles contract. This pushes the diaphragm up, back into a dome shape.
• Both of these muscle contractions result in a decrease in the volume of the thorax.
• As a result of the decrease in volume, the pressure inside the thorax increases.
• Eventually the pressure rises above atmospheric pressure.
• Air then flows out of the lungs to outside of the body through the nose or mouth.
• Air continues to flow out of the lungs until the pressure in the lungs has fallen back to atmospheric pressure.

Question 31

What does the nervous system consist of?

Answer 31

The nervous system consists of the central nervous system (CNS) and peripheral nerves, and is composed of cells called neurons which carry rapid electrical impulses.

Question 32

Where do nerve impulses come from?

Answer 32

Nerve impulses are conducted from receptors to the CNS by sensory neurons, within the CNS by relay neurons, and from the CNS to effectors by motor neurons.

Question 33

Define resting potential and action potential (depolarization and repolarization).

Answer 33

Resting potential: the electrical potential across the plasma membrane of a cell that is not conducting an impulse.

Action potential: the reversal and restoration of the electrical potential across the plasma membrane of a cell, as an electrical impulse passes along it (depolarization and repolarization).

Question 34

Define resting potential and action potential (depolarization and repolarization).

Answer 34

Resting potential: the electrical potential across the plasma membrane of a cell that is not conducting an impulse.

Action potential: the reversal and restoration of the electrical potential across the plasma membrane of a cell, as an electrical impulse passes along it (depolarization and repolarization).

Question 35

Explain how a nerve impulse passes along a non-myelinated neuron.

Answer 35

Sodium is found in greater concentrations outside of the cell while potassium is found in greater concentrations inside the cell. Sodium-potassium pumps exist in the plasma membrane to maintain the the concentration gradients and the membrane potential. Nerve impulses have a domino effect. An action potential in one part of the neuron causes another action potential in the adjacent part and so on. This is due to the diffusion of sodium ions between the region of the action potential and the resting potential. It is the movement of sodium and potassium that reduce the resting potential.

If the resting potential rises above the threshold level, voltage gated channels open. Voltage gated sodium channels open very fast so that sodium can diffuse into the cell down its concentration gradient. This reduces the membrane potential and results in more sodium channels opening. Sodium ions are positively charged and so the inside of the cell develops a net positive charge compared to the outside of the cell. This results in depolarization as the potential across the membrane is reversed.

A short while after this, voltage gated potassium channels open and potassium ions flow out of the cell down the concentration gradient. Since potassium ions are positively charged, their diffusion out of the cell causes a net negative charge to develop again inside the cell compared to the outside. The potential across the membrane is restored. This is called repolarization.

Finally, the concentration gradients of both ions are restored by the sodium-potassium pump. Sodium is pumped out of the cell while potassium is pumped in. The resting potential is restored and the neuron is ready to conduct another nerve impulse.

Question 36

Explain the principles of synaptic transmission.

Answer 36

A synapse is a junction that permits a neuron to pass an electrical or chemical signal to another cell. At a synapse, the plasma membrane of the signal passing neuron (presynaptic neuron) is closely related to the plasma membrane of the target cell (postsynaptic neuron). Between the two there is a narrow fluid filled space called the synaptic cleft. Chemical signals called neurotransmitters pass from the presynaptic neuron to the post synaptic neuron.

This is how a synaptic transmission occurs:
An action potential travels along the neuron and reaches the end of the pre-synaptic neuron. The depolarization of the pre-synaptic membrane results in the opening of voltage gated calcium channels. Calcium ions flow into the presynaptic neuron and cause vesicles with neurotransmitters inside the neuron to fuse with the plasma membrane and release the neurotransmitters into the synaptic cleft via exocytosis. These neurotransmitters then diffuse within the synaptic cleft and some will bind to specific receptors located on the postsynaptic plasma membrane. The receptors are transmitted-gated ion channels which open and let sodium and other positively charged ions into the postsynaptic neuron when the neurotransmitters bind. As these positively charged ions enter the postsynaptic neuron they cause its membrane to depolarize. This depolarization results in an action potential which passes down the postsynaptic neuron. The neurotransmitters in the synaptic cleft are then quickly degraded and the calcium ions are pumped back into the synaptic cleft from inside the presynaptic neuron.

Question 37

What does the endocrine system consist of?

Answer 37

The endocrine system consists of glands that release hormones that are transported in the blood.

Question 38

What does homeostasis cause?

Answer 38

Homeostasis involves maintaining the internal environment between limits, including blood pH, carbon dioxide concentration, blood glucose concentration, body temperature and water balance.

Question 39

Explain that homeostasis involves monitoring levels of variables and correcting changes in levels by negative feedback mechanisms.

Answer 39

Homeostasis involves maintaining the internal environment between limits, including blood pH, carbon dioxide concentration, blood glucose concentration, body temperature and water balance. Blood and tissue fluid (derived from blood) make up the internal environment. This internal environment varies very little compared to the external environment which varies greatly. Negative feed back is used to keep the internal environment between limits. It uses the nervous and endocrine system to do so. It has a stabilising effect as any change from a set point level will result in an opposite change. The levels of production of for example blood glucose, feed back to affect the rate of production. If blood glucose levels rise above the set point, this will feed back to decrease production and reduce the level back around the set point. A decrease in blood glucose levels below the set point will result in an increase in production so that the levels increase back to the set point. Small fluctuations around the set point will not cause any response. Negative feed back is only triggered when there are significant increases or decreases from the set point.

Question 40

Explain the control of body temperature, including the transfer of heat in blood, and the roles of the hypothalamus, sweat glands, skin arterioles and shivering.

Answer 40

The hypothalamus is responsible for monitoring the temperature of the blood which is normally close to 37 degrees. If there are significant fluctuations from this set point, the hypothalamus sends signals (messages carried by neurons) to different parts of the body to restore the temperature back to the set point. This is done through negative feedback.

Question 41

Explain the control of blood glucose concentration, including the roles of glucagon, insulin and α and β cells in the pancreatic islets.

Answer 41

Blood glucose concentration does not have a specific set point like blood temperature. Blood glucose levels drop and rise through the day and so the body usually tries to keep blood glucose levels around 4 to 8 millimoles per dm3 of blood. Once again, negative feedback is used to do so. There are responses by target organs which affect the rate at which glucose is taken up from the blood or loaded into the blood.

Question 42

Distinguish between type I and type II diabetes.

Answer 42

Type I diabetes
The onset is usually early, sometime during childhood.
β cells do not produce enough insulin.
Diet by itself cannot be used to control the condition. Insulin injections are needed to control glucose levels.
Type II diabetes
The onset is usually late, sometime after childhood.
Target cells become insensitive to insulin.
Insulin injections are not usually needed. Low carbohydrate diet can control the condition.

Question 43

Outline the role of hormones in the menstrual cycle, including FSH (follicle stimulating hormone), LH (luteinizing hormone), estrogen and progesterone.

Answer 43

The menstrual cycle:

FSH is secreted by the pituitary gland and its levels start to rise. This stimulates the follicle to develop and the follicle cells to secret estrogen.
Estrogen then causes the follicle cells to make more FSH receptors so that these can respond more strongly to the FSH.
This is positive feedback and causes the estrogen levels to increase and stimulate the thickening of the endometrium (uterus lining).
Estrogen levels increase to a peak and by doing so it stimulates LH secretion from the pituitary gland.
LH then increases to its peak and causes ovulation (release of egg from the follicle).
LH then stimulates the follicle cells to secrete less estrogen and more progesterone. Once ovulation has occurred, LH stimulated the follicle to develop into the corpus luteum.
The corpus luteum then starts to secrete high amounts of progesterone. This prepares the uterine lining for an embryo.
The high levels of estrogen and progesterone then start to inhibit FSH and LH.
If no embryo develops the levels of estrogen and progesterone fall. This stimulates menstruation (break down of the uterine lining). When the levels of these two hormones are low enough FSH and LH start to be secreted again.
FSH levels rise once again and a new menstrual cycle begins.

Question 44

List three roles of testosterone in males.

Answer 44

Stimulates the development of prenatal genitalia.
Stimulates the development of the male secondary sexual characteristics such as growth of the skeletal muscle and pubic hair.
During adulthood it maintains the sex drive.

Question 45

Outline the process of in vitro fertilization (IVF).

Answer 45

Process:

For a period of three weeks, the women has to have a drug injected to stop her normal menstrual cycle.
After these three weeks, high doses of FSH are injected once a day for 10-12 days so that many follicles develop in the ovaries of the women.
HCG (another hormone) is injected 36 hours before the collection of the eggs. HCG loosens the eggs in the follicles and makes them mature.
The man needs to ejaculate into a jar so that sperm can be collected from the semen. The sperm are processed to concentrate the healthiest ones.
A device that is inserted through the wall of the vagina is used to extract the eggs from the follicles.
Each egg is then mixed with sperm in a shallow dish. The dishes are then put into an incubator overnight.
The next day the dishes are looked at to see if fertilization has happened.
If fertilization has been successful, two or three of the embryos are chosen to be placed in the uterus by the use of a long plastic tube.
A pregnancy test is done a few weeks later to find out if any of the embryos have implanted.
A scan is done a few weeks later to find out if the pregnancy is progressing normally.