Topic 6 - Health and Physiology

Question 1

6.1.1 Explain why digestion of large food molecules is essential

Answer 1

Most food is solid and in the form of large complex molecules which are insoluble and chemically inert (not readily usable).

• As food was previously synthesised by other organisms, it contains materials not suitable for human tissue - these need to be separated and removed.
• Large molecules need to be broken down into smaller molecules that can be readily absorbed across membranes and into cells.
• Small molecules can be reassembled into new products

Question 2

6.1.2 Explain the need for enzymes in digestion

Answer 2

• Enzymes are biological catalysts which speed up the rate of a chemical reaction by lowering the activation energy.
• They allow digestive processes to occur at body temperature and at sufficient speed to meet the organism’s survival requirements
• They’re specific for a given substrate and so can allow digestion of certain molecules to occur independently of others.

Question 3

6.1.3 State the source, substrate, product and optimal pH conditions for one amylase

Answer 3

Salivary amylase:
From the salivary glands
Substrate: starch
Product: maltose
Optiumum pH: 7 (neutral)

Question 4

6.1.3 State the source, substrate, product and optimal pH conditions for one protease

Answer 4

Pepsin
Gastric juice (stomach)
Substrate: protein
Product: short polypeptides
Optimum pH: ~2 (highly acidic)

Question 5

6.1.3 State the source, substrate, product and optimal pH conditions for one lipase

Answer 5

Pancreatic lipase
Pancreas
Substrate: Lipids
Product: Glycerol, fatty acids
Optimum pH: ~8 (slightly alkaline)

Question 6

6.1.5 Outline the function of the stomach

Answer 6

Acts as a temporary storage tank and is where protein digestion begins.
Contains gastric glands which secrete digestive juices for chemical digestion.
Acids create a low pH environment (pH~1-2) that denatures proteins, while proteases like pepsin hydrolyse large proteins,
It also releases a hormone that regulates stomach secretions.
The mechanical action of the stomach also promotes digestion by mixing the food
The stomach turns food into a creamy paste called chyme

Question 7

6.1.5 Outline the function of the small intestine

Answer 7

Where usable food substances are absorbed into the bloodstream.
Pancreas and gall bladder both secrete substances into the small intestine to aid in digestion.
Lined with smooth muscle to allow for the mixing and moving of digested food products
Contains small pits that secrete intestinal juices.
Contains infolding cells called villi to increase surface area and optimise the rate of absorption.

Question 8

6.1.5 Outline the function of the large intestine

Answer 8

Absorbs water and dissolved minerals from the indigestible food residues, and by doing so converts what remains from a fluid state into a semi-sold faeces.

Question 9

6.1.6 Distinguish between absorption and assimilation

Answer 9

Absorption: Movement of a fluid or dissolved substances across a membrane.
Assimilation: Conversion of nutrients into fluid or solid parts of an organism

Absorption - taking it into something
Assimilation - making it a part of something.

Question 10

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

Answer 10

MIRCOVILLI
Greatly increase the surface area of the villus, allowing for greater rate of absorption
RICH CAPILLARY NETWORK
Help to maintain a concentration gradient for absorption by rapidly transporting absorbed products away
SINGLE EPITHELIAL LAYER
Ensures minimal diffusion distance between the intestinal lumen and capillary network
LACTEALS
Absorb lipids from the intestine into the lymphatic system
INTESTINAL CRYPTS
Located between villi and release juices that act as a carrier fluid for nutrients
MEMBRAINE PROTEINS/MITOCHONDRIA
High amounts to enable active transport into cells (contents then passively diffuse into the bloodstream)

Question 11

6.2.2 State the role of the coronary arteries

Answer 11

They supply heart muscle with oxygen and nutrients

Question 12

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

Answer 12

• Coronary arteries supply the heart muschle with oxygen and nutrients.
• Left atrium collects oxygenated blood from pulmonary vein.
• Right atrium collects deoxygenated blood from vena cava.
• Atria pump blood into ventricles.
• Ventricles contract to pump blood out of hearts into arteries.
• Right ventricle pumps deoxygenated blood to lungs via pulmonary artery.
• Left ventricle pumps oxygenated blood to body (apart from lungs) via aorta.

Question 13

6.2.4 Outline the control of the heartbeat in terms of myogenic muscle contraction, the role of the pacemaker, nerves, the medulla of the brain and adrenaline

Answer 13

• Myogenic refers to the property the heart has of contracting of its own accord.
• The pacemaker is a small patch of special muscle tissue on the wall of the right atrium near the point where the vena cava enters. It releases an electrical impulse approximately 70 per minute, the electrical impulse causes the heart muscle to contract.
• Involuntary nerves from the cardiac control center in the medulla of the brain are attached to the pacemaker.
• Impulses down the cardiac depressor nerve cause the heart rate to slow down. Impulses down the cardiac accelerator nerve cause the heart rate to speed up.
• The hormone adrenalin from the adrenal gland stimulates the pacemaker causing the heart rate to speed up.

Question 14

6.2.5 Explain how the arteries are adapted to their function

Answer 14

Collagen fibers:
Tough inelastic fibres protect and prevent the wall from being overstreched.

Endothelium:
Smooth lining

Thick Muscular Wall
Withstands high pressure, contracts to increase blood pressure.

Elastic fibres:
Stretched by pulse and when contracted helps to maintain steady blood flow.

Question 15

6.2.5 Explain how the capillaries are adapted to their function

Answer 15

Wall of single layer of flattened cells:
Reduced distance for diffusion between blood and tissues

Narrow lumen:
Increased surface area

No muscle, elastic of fibrous tissue; Gaps between cells:
Facilitate diffusion as substances only have to pass through the basement membrane.

Question 16

6.2.5 Explain how veins are adapted to their function

Answer 16

Endothelium:
Smooth lining

Thin walls:
Allows vein to be squashed between muscle blocks which pumps blood

Large lumen:
Reduces resistance to flow

Valves:
Prevent backflow when pressure very low

Collagen fibres:
Protection

Question 17

6.2.6 State the components of the blood

Answer 17

Plasma
Erythrocytes - red blood cells (involved in oxygen transport)
Leukocytes - white blood cells, such as phagocytes (non-specific immunity) and lymphocytes (specific immunity)
Platelets - responsible for blood clotting (haemostasis)

Question 18

6.2.7 What is transported by the blood?

Answer 18

Nutrients (e.g. glucose)
Antibodies
Carbon dioxide
Hormones
Oxygen
Urea
Heat

Question 19

6.3.1 Define pathogen

Answer 19

Disease-causing micro-organism, virus or prion

Question 20

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

Answer 20

They target the metabolic pathways of prokaryotes (targeting specofoc features).
As eukaryotic cells do not have features such as key enzymes, 70S ribosomes and the bacterial cell wall antibiotics can kill bacterial cells without harming humans or viruses.

Viruses do not carry out metabolic reactions themselves, but they infect a host cell.

Question 21

6.3.3 Outline the role of skin in defence against pathogens

Answer 21

Protects external structures.

Contains biochemical defence agents

The skin also releases acidic secretions to lower pH and prevent bacteria from growing

Question 22

6.3.3 Outline the role of mucous membranes in defence against pathogens

Answer 22

Protect internal structures (externally accessable cavities and tubes, such as trachea, vagina and urethra)

A thin region containing living surface cells that release fluids to wash away pathogens (mucus, tears, saliva, etc.)

Contains biochemical defence agents (secretions contain lysozyme, which can destroy cell walls and cause cell lysis)

Mucous membranes may be ciliated to aid in the removal of pathogens (along with physical actions such as coughing or sneezing)

Question 23

6.3.4 Outline how phagocytic leucocytes ingest pathogens in the blood and in body tissue

Answer 23

Phagocytic leucocytes (macrophages) circulate in the blood but may move into body tissue (extravasation) in response to infection

They concentrate at sites of infection due to the release of chemicals (such as histamine) from damaged body cells

Pathogens are engulfed when cellular extensions (pseudopodia) surround the pathogen and then fuse, sequestering it in an internal vesicle

The vesicle may then fuse with the lysosome to digest the pathogen

Some of the pathogens antigenic fragments may be presented on the surface of the macrophage, in order to help stimulate antibody production

This mechanism of endocytosis is called phagocytosis (‘cell-eating’)

Question 24

6.3.5 Define antigen

Answer 24

A foreign chemical to the body, which brings about an immune response

Question 25

6.3.4 Define antibody

Answer 25

Specific protein produced by lymphocytes in response to an antigen. An antibody binds to its antigen and brings about its destruction.

Question 26

6.3.6 Explain antibody production

Answer 26

B lymphocytes (B cells) are antibody-producing cells that develop in the bone marrow to produce a highly specific antibody that recognises one type of antigen

When wandering macrophages encounter a pathogen, they digest it and present the antigenic fragments on their surface to helper T lymphocytes (TH cells)

These cells activate the appropriate B cell which divides and differentiates into short-lived plasma cells that produce massive quantities of antibody (~2,000 molecules per second for ~4 - 5 days)

A small proportion of B cell clones develop into memory cells, which may survive for years providing long-term immunity

Question 27

6.3.7 Outline the effect of HIV on the immune system

Answer 27

The human immunodeficiency virus (HIV) is a retrovirus that infects helper T lymphcytes (TH cells)

Reverse transciptase allows viral DNA to be produced from its RNA code, which is integrated into the host cells genome

After a number of years of inactivity (during which infected TH cells have continually reproduced), the virus becomes active and begins to spread, destroying the TH cells in the process (known as the lysogenic cycle)

This results in lower immunity as antibody production is compromised - the individual is now susceptible to opportunistic infections

Question 28

6.3.8 Discuss the cause, transmission and social implications of AIDS

Answer 28

Cause

Acquired Immunodeficieny Syndrome (AIDS) is a collection of symptoms and infections caused by the destruction of the immune system by HIV

While HIV infection results in a lowering in immunity over a number of years, AIDS describes the final stages when observable symptoms develop

Transmission

HIV is transmitted through the exchange of bodily fluids (including unprotected sex, blood transfusions, breast feeding, child birth, etc.)

The risk of exposure to HIV through sexual contact can be reduced by using latex protection (condoms)

A minority of people are immune to HIV infection (they do not have the CD4+ T cell receptor that HIV needs to infect the cell)

Social Implications

People with HIV may be stigmatised and discriminated against, potentially leading to unemployment and poverty

Majority of people who die from AIDS are at a productive age, which may cripple a country’s workforce and economic growth

It can result in an increased number of orphans, taxing a country’s welfare resources

Poverty may increase transmission of AIDS (due to poor education and high cost of treatments), creating a moral obligation for assistance from wealthier countries

Question 29

6.4.1 Distinguish between ventilation, gas exchange and cell respiration

Answer 29

Ventilation: The exchange of air between the lungs and the atmosphere; it is achieved by the physical act of breathing

Gas exchange: The exchange of oxygen and carbon dioxide in the alveoli and the bloodstream; it occurs passively via diffusion

Cell Respiration: The release of ATP from organic molecules; it is greatly enhanced by the presence of oxygen (aerobic respiration)

Question 30

6.4.2 Explain the need for a ventilation system

Answer 30

Because gas exchange is a passive process, a ventilation system is needed to maintain a concentration gradient within the alveoli

Oxygen is needed by cells to make ATP via aerobic respiration, while carbon dioxide is a waste product of this process and must be removed

Therefore, oxygen must diffuse from the lungs into the blood, while carbon dioxide must diffuse from the blood into the lungs

This requires a high concentration of oxygen - and a low concentration of carbon dioxide - in the lungs

A ventilation system maintains this concentration gradient by continually cycling the air in the lungs with the atmosphere

Question 31

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

Answer 31

Thin wall: Made of a single layer of flattened cells so that diffusion distance is small

Rich capillary network: Alveoli are covered by a dense network of capillaries that help to maintain a concentration gradient

Increased SA:Vol ratio: High numbers of spherically-shaped alveoli optimise surface area for gas exchange (600 million alveoli = 80 m2)

Moist: Some cells in the lining secrete fluid to allow gases to dissolve and to prevent alveoli from collapsing (through cohesion)

Question 32

6.4.5 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 32

Breathing is the active movement of respiratory muscles that enable the passage of air to and from the lungs
The mechanism of breathing is described as negative pressure breathing as it is driven by the creation of a negative pressure vacuum within the lungs, according to Boyle’s Law (pressure is inversely proportional to volume)

Inspiration

Diaphragm muscles contract and flatten downwards
External intercostal muscles contract, pulling ribs upwards and outwards
This increases the volume of the thoracic cavity (and therefore lung volume)
The pressure of air in the lungs is decreased below atmospheric pressure
Air flows into the lungs to equalise the pressure

Expiration

Diaphragm muscles relax and diphragm curves upwards
Abdominal muscles contract, pushing diaphragm upwards
External intercostal muscles relax, allowing the ribs to fall
Internal intercostal muscles contract, pulling ribs downwards
This decreases the volume of the thoracic cavity (and therefore lung volume)
The pressure of air in the lungs is increased above atmospheric pressure
Air flows out of the lungs to equalise the pressure

Question 33

6.5.1 What is the nervous system composed of?

Answer 33

Central Nervous System (CNS), made up of the brain and spinal cord.

Peripheral Nervous System (PNS) - Link the CND with the body’s receptors and effectors.

Composed of cells caulled neurons that are specially adapted for the conduction of nerve impulses and serve as the fundamental unit of the nervous system.

Question 34

6.5.3 Recall the three main neurons in the nervous system and their function

Answer 34

Sensory Neurons: Conduct nerve impulses from receptors to the CNS (afferent pathway)
Relay Neurons: Conduct nerve impulses within the CNS (also called interneurons or connector neurons)
Motor Neurons: Conduct nerve impulses from the CNS to effectors (efferent pathway)

Question 35

6.5.4 Define resting potential and action potential (depolarisation and repolarisation)

Answer 35

Resting Potential: The charge difference across the membrane when a neuron is not firing (-70 mV), as maintained by the sodium-potassium pump

Action Potential: The charge difference across the membrane when a neuron is firing (about 30 mV)

Depolarisation: The change from a negative resting potential to a positive action potential (caused by opening of sodium channels)

Repolarisation: The change from a positive action potential back to a negative resting potential (caused by opening of potassium channels)

Question 36

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

Answer 36

Resting potential rises above threshold level.

Voltage gated sodium channels open.

Sodium ions flow into the cell, more sodium channels open.

Inside of cell develops a net positive charge compared to the outside and results in depolarization.

Voltage gated potassium channels open.

Potassium ions flow out of the cell.

Cell develops a net negative charge compared to the outside and results in repolarization.

Concentration gradients restored by sodium-
potassium pumps.

Resting potential is restored.

Question 37

6.5.6 Explain the principles of synaptic transmission.

Answer 37

Action potential reaches the end of a presynaptic neuron.
Voltage gated calcium channels open.
Calcium ions flow into the presynaptic neuron.
Vesicles with neurotransmitters inside the presynaptic neuron fuse with the plasma membrane.
Neurotransmitters diffuse in the synaptic cleft and bind to receptors on the postsynaptic neuron.
The receptors are channels which open and let sodium ions into the postsynaptic neuron.
The sodium ions cause the postsynaptic membrane to depolarize.
This causes an action potential which passes down the postsynaptic neuron.
Neurotransmitters in the synaptic cleft are degraded and the calcium ions are pumped back into the synaptic cleft.

Question 38

6.5.7 What is the endocrine system made up of?

Answer 38

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

Question 39

6.5.8 What does homeostasis involve?

Answer 39

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

Question 40

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

Answer 40

Most homeostatic control mechanisms operate through a negative feedback loop

When specialised receptors detect a change in an internal condition, the response generated will be the opposite of the change that occurred

When levels have returned to equilibrium, the effector ceases to generate a response

If levels go too far in the opposite direction, antagonistic pathways will be activated to restore the internal balance

Question 41

6.5.10 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 41

IF BLOOD TEMPERATURE INCREASES:
Skin arterioles increase in diameter so that more blood flows to the skin. By doing so it transfers heat from the core of the body to the skin and this heat is then lost to the external environment, cooling down the body in the process.

Skeletal muscle stays relaxed so that more heat is not generated.

Sweat glands secrete large amounts of sweat which makes the surface of the skin moist. When water evaporates from the moist skin it cools down the body.

IF BLOOD TEMPERATURE DROPS
Skin arterioles decrease in diameter so that less blood flows to the skin. The diameter of the capillaries in the skin cannot change but less blood flows through them. This prevents heat loss to the external environment as the temperature of the skin falls.

Shivering occurs. This is when the skeletal muscle does many small rapid contractions to generate heat.

Sweat glands to not secrete sweat and so no water evaporation can occur as skin stays dry.

Question 42

6.5.11 Explain the control of blood glucose concentration

Answer 42

GLUCOSE LEVELS ABOVE SET POINT:
β cells in the pancreatic islets produce insulin. Insulin stimulates muscle cells and the liver cells to take up glucose from the blood and convert it into glycogen. These are then stored in the form of granules in the cytoplasm of cells. Also, other types of cells are stimulated to take up glucose and use it for cell respiration instead of fat. All of these processes lower the levels of glucose in the blood.

BELOW SET POINT
α cells in the pancreatic islets produce glucagon. Glucagon stimulates the liver cells to convert glycogen back into glucose and release this glucose into the blood. This raises the glucose levels in the blood.

Question 43

6.5.12 Distinguish between type I and type II diabetes.

Answer 43

TYPE 1
Onset is usually early, 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 2
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 44

6.6.2 Outline the roles of the hormones in the menstrual cycle.

Answer 44

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 45

6.6.4 List three roles of testosterone in males.

Answer 45

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 46

6.6.5 Outline the process of in vitro fertilization (IVF).

Answer 46

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.

Question 47

6.6.6 Discuss the ethical issues associated with IVF

Answer 47

Advantages of IVF

Chance for infertile couples to have children
Genetic screening of embryos could decrease suffering from genetic diseases
Spare embryos can be stored for future pregnancies or used for stem cell research

Disadvantages of IVF

IVF is expensive and might not be equally accessible to all
Success rate is low (~15%) and therefore stressful for couples
It could lead to eugenics (e.g. gender choice)
Often leads to multiple pregnancies which may be unwanted, unable to be budgeted for and involves extra birth risks
Issues concerning storage and disposal of unused embryos (right to life concerns)
There are cultural and religious objections to embryo creation by such means
Inherited forms of infertility may be passed on to children