4.2.2 Animal tissues, organs and organ systems

4.2.2.1 The human digestive system

The Digestive System

Key Terms

Digestive System – the digestive system is involved in the digestion and absorption of food

Digestion – the breakdown of food from large, insoluble molecules to small, soluble molecules

Absorption – involves the small, soluble molecules from digestion being taken into the bloodstream

Breaking Down Food

• The digestive system is responsible for the breakdown of food and absorption of nutrients
• Large, insoluble molecules cannot be absorbed into the bloodstream
• Food is broken down into small, soluble molecules, which cross cell membranes in the small intestine

Mechanical and Chemical Digestion

• There is physical breakdown of food via mechanical digestion

E.g. teeth, stomach churning

• There is also enzyme-driven breakdown via chemical digestion

E.g. lipase enzymes

• Mechanical digestion alone is not enough

Small Intestine

1. Digestion

2. Absorption of Digested Products

Large Intestine

Absorption of Water + Ions

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Food Groups

All food can be divided into carbohydrates, proteins and lipids:

• Carbohydrates are made of carbon, oxygen and hydrogen
• Lipids are made of carbon, oxygen and hydrogen
• Proteins are made of carbon, oxygen, hydrogen and nitrogen

Digestion of Carbohydrates

Function of Carbohydrases

Carbohydrates are broken down by carbohydrase enzymes into simple sugars via hydrolysis

Carbohydrates are broken down in two stages:

       Starch → Maltose

       Maltose → Smaller simple sugars e.g. glucose, fructose, galactose

Location of Carbohydrates

• Mouth: mechanical digestion via chewing, and chemical digestion via saliva

    Saliva contains amylase which hydrolyses starch

• Small Intestine (Duodenum): pancreas produces amylase that travels to duodenum via pancreatic duct

Allows for further digestion of starch

Digestion of Proteins

Function of Proteases

Proteins are broken by protease enzymes into amino acids via hydrolysis

Proteins are broken down in two stages:

1. The protein is broken down into a dipeptide (containing 2 amino acids)

2. The dipeptide is split into individual amino acids

Location of Proteases

Stomach: Protease enzyme pepsin converts proteins into amino acids. The optimum pH of the stomach is 2

Small intestine (duodenum): Pancreatic juice contains protease enzymes including trypsin

This converts proteins into amino acids, like pepsin

Function of Lipases

• Lipids are broken by lipase enzymes into fatty acids and glycerol via hydrolysis
• They are made in the pancreas and secreted into the small intestine

Location of Lipids

• Small intestine (duodenum): Pancreatic juice released contains lipase enzymes

                  Lipase converts lipids into fatty acids and glycerol

Digestion of Lipids

Bile

• Before lipids can be hydrolysed, they need to be emulsified
• Emulsification is where large lipids are broken into tiny lipid droplets
• This increases the surface area of lipids, to speed up the activity of lipase
• Bile is a substance produced by the liver and stored in the gallbladder
• During digestion, bile is released from the gallbladder and transported to the duodenum by bile ducts
• The bile then emulsifies the lipids

• Bile is alkaline and neutralises the acidic contents that have left the stomach
• It allows the trypsin, lipase and carbohydrase to act at their optimum pH

Building Carbohydrates

• Products of digestion that are absorbed into the bloodstream in the small intestine can be used to build molecules
• The simple sugars are absorbed (maltose, fructose, glucose) to build new carbohydrates

E.g. glucose can be stored as glycogen in the liver

Building Proteins

• The amino acids absorbed can be used for building protein

                 E.g. bodybuilders often eat lots of protein to increase the number of amino acids for                muscle synthesis

• The fatty acid and glycerol molecules absorbed is used to store fat

E.g. if you eat lots of high-lipid foods, you are likely to build up more and more fat stores.

Respiration

• Glucose from carbohydrate digestion can be used to release energy via respiration
• Food is so important for daily function and especially for exercise

Enzymes

Enzymes as Catalysts

• Enzymes are biological catalysts
• They increase the rates of reactions, without having to increase temperature
• When two reactants collide, they need enough energy for a reaction to happen – activation energy
• Enzymes speed up reactions by reducing activation energy
• This increases the rate at which the reaction occurs
• This also allows for reactions to occur at lower temperatures and at a greater rate

Active Sites

• The active site of an enzyme binds to a substrate (the target)
• The structure of this determines which substrates it is capable of binding to
• The unique structure of each active site means most enzymes can only bind to two substrates which “fit” into its active site
• Reactants must be complementary to the active site

Primary Structure

• The structure of the enzyme is essential for its function
• The order and number of amino acids in the chain = primary structure
• The primary structure is flat and 2D

Secondary Structure

• The secondary structure is how the protein folds or coils to make a 3D structure
• The chain of amino acids is folded into an alpha helix or coiled into beta plated sheet
• Hydrogen bonds form between amino acids

Tertiary Structure

• This is the final 3D structure of the protein chain
• It involves many bonds such as ionic, hydroge and hydrophobic bonds
• It determines the shape of the active site
• It can be affected by temperature and pH

Quaternary Structure

• How different chains in the protein come together
• Final structure of the protein

Optimum Conditions for Enzymes

• Enzyme tertiary structures are sensitive to environmental changes
• Changes can cause a protein to denature
• This means that it can no longer bind to its substrate as effectively

Optimal Temperature

1. Temperature rises increases the rate in two ways:

• More frequent collisions – the reactant particles move faster, and collide more often
• More successful collisions – any collision is more likely to be successful

Denaturation

2. High temperatures breaks the enzyme’s bonds

• The active site changes shape
• The rate of reaction then drops rapidly
• Very low temperatures are not ideal for successful reactions

Optimal pH

1. Most enzymes work best at a natural pH of 7.4

There are certain exceptions

E.g. the protein pepsin works best at a pH

of 2

Denaturation

2. The enzyme is affected by disruption of the bonds in the tertiary structure

• This leads to an alteration in the specific shape of the active site

Lock and Key Model

• The lock and key have to have complementary shapes
• The enzyme is the lock, and substrate the key
• The substrate must have the correct shape which allows it to “fit” into the active site
• This model assumes that the enzyme active site and substrate have the exact same shape
• Enzymes can bind to many different substrates
• They may change their active site slightly to bind to a new substrate – induced fit model

Rate of Reactions

Calculating the Rate of Reactions

Calculating Rates from Graphs

1. Check the graph’s axes
2. Pick two points on the graph
3. Gradient = Rise/Run
4. Check your gradient

4.2.2.2 The heart and blood vessels

Structure of the Heart

Chambers of the Heart

• The tricuspid valve: Lies between the right atrium and theright ventricle
  • It prevents blood flowing back into the right atrium

• The bicuspid valve: The lies between the left atrium and the left ventricle
  • It prevents blood flowing back into the left atrium
• The pulmonary valve: This lies between the right ventricle and the pulmonary artery
  • It prevents blood flowing back into the right ventricle from the artery
• The aortic valve: This lies between the left ventricle and the aorta
  • It prevents blood flowing back into the left ventricle from the artery

Muscle Tissue of the Heart

• Special muscle tissue is present in the heart walls – cardiac muscle
• It helps to pump blood around the body
• The muscle is myogenic, which means that it does not tire
• The left ventricle has the most cardiac muscle as it is responsible for pumping blood to the whole body

Double Circulatory System

• The circulatory system involves three components:

• The heart uses a double circulatory system: blood passes through the heart twice for every complete circuit of the body

Pulmonary Circuit

• Deoxygenated blood begins in the right atrium
• The deoxygenated blood is pumped out the right atrium into the right ventricle, then into the pulmonary artery
• The pulmonary circuit carries the blood to the lungs where it is oxygenated
• The oxygenated blood returns to the left atrium via the pulmonary vein

Systemic Circuit

• The oxygenated blood returns from the pulmonary circuit, and passes into the left atrium, then into the left ventricle
• The oxygenated blood is pumped out of the left ventricle into the aorta, and is carried around the body
• The blood unloads oxygen and gives it to the body’s cells.
• The vena cava (veins) carry the blood (now deoxygenated) back to the heart

Route of Blood in Vessels

Structure of Arteries

The arteries carry blood quickly away from the heart

Structure of Arteries

• The arteries have the thickest walls to withstand the high pressure of blood
• Their walls are elastic, helping to maintain a high blood pressure
• There is no need for valves as blood is flowing so fast that there will not be backflow

Structure of Veins

The veins carry blood slowly back to the heart

• The veins carry blood slowly back to the heart
• Valves are needed to prevent backflow of blood
• The veins have thin walls and large lumens

Structure of Capillaries

The capillaries carry blood within organs for gas exchange

• The capillaries carry blood within organs for gas exchange
• They are very thin to allow diffusion of oxygen in blood to body cells
• They do not need valves

Pacemakers: Natural

• Special cells in the right atrium act as a natural pacemaker
• They keep a resting rhythm in adults of ~ 70 bpm
• They send electrical nerve impulses through the heart muscle, causing contraction

Pacemakers: Artificial

Artificial pacemakers can be inserted into the body for conditions with irregular rhythms

Pulmonary Vessels

• Blood passes from the heart into the pulmonary artery, and then into pulmonary capillaries

• The pulmonary capillaries come into contact with alveoli, where gas exchange takes place

• Oxygenated blood travels back to the heart via pulmonary veins

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Function of the Lungs

• Ventilation: air needs to be moved in and out of the lungs
  • Oxygenated air is moved in, and deoxygenated air is moved out after gas exchange

• Gas Exchange: the movement of oxygen from the air into the blood and carbon dioxide away the blood into the air

Structure of the Lungs

• Air enters the lungs through the mouth and nose and passes into the trachea
• The trachea splits into two bronchi
• Each bronchus splits into lots of smaller bronchioles
• Each bronchiole ends in lots of small alveoli, which are specialised for gas exchange

Adaptations of Alveoli

• Large surface area: speeds us rate of gas exchange
• Thin walls: reduced diffusion distance
• Constant blood supply: closely associated with capillaries
• Constant ventilation: new air always arriving

Adaptations of the Lungs

• Trachea have cartilage to keep it open
• Trachea and bronchi have mucus and epithelia to trap dust and bacteria

Rate Calculations

4.2.2.3 Blood

Composition of Blood

Plasma: 

Function

• Plasma is a watery fluid where all the components of blood flow
• It carries platelets, red and white blood cells, carbon dioxide, glucose, amino acids, urea, hormones, antibodies, antitoxins and proteins
• Some oxygen is dissolved in plasma

Plasma: Structure

• Plasma is clear and watery
• Different things are transported to different places in plasma:

Red Blood Cells

Function

RBCs transport oxygen around the body

• They contain a pigment called haemoglobin, which binds to oxygen, forming oxyhemoglobin
• Oxyhaemoglobin remains in this form until it reaches the respiring tissues, where it splits back
  • Oxygen + Haemoglobin ⇌ Oxyhaemoglobin

RBCs: Structure

• RBCs have a biconcave disk shape to increase their surface area
  • The shape helps RBCs quickly take up and release oxygen
• RBCs also have no nucleus
  • They have more space to pack in as much haemoglobin

White Blood Cells

Function

• WBCs help protect against infection and foreign pathogens
• There are two types: Phagocytes and Lymphocytes

• Phagocytes engulf and eat pathogens in phagocytosis.

• Lymphocytes produce antibodies to fight against pathogens

WBCs: Structure

• WBCs have flexible cell membranes, which form pseudopodia, to help engulf
• They also have lysozyme enzymes in their cytoplasm, or digesting foreign pathogens
• Sometimes WBCs have a lobed nucleus

Platelets: Function

• Platelets are used to clot the blood and reduce blood flow around cuts and wounds

Platelets: Structure

• Platelets have no nucleus
• They have cell surface proteins, which allow them t clump and close up a broken blood vessel
• They also have stored proteins, to initiate a sequence of reactions – a clotting cascade.

4.2.2.4 Coronary heart disease: a non-communicable disease

Coronary Heart Disease

Coronary arteries are found on the surface of the heart, and they supply it with oxygen

Fatty deposits (plaques) can build up inside these arteries

This occludes the blood supply to the heart. This is Coronary Heart Disease.

1. Treatment of CHD
2. Stents
3. Statins
4. Heart Transplant

1. Stents (Mechanical Device)

• To restore the blood supply to the heart, the coronary arteries must be reopened
• Stents are placed inside the artery in order to keep it open

2. Statins (Drugs)

• Statins reduce the amount of Low Density Lipoprotein cholesterol (LDLs)
  • LDLs increase the amount of fatty deposits forming in the bloodstream
• Statins reduce the formation of fatty deposits in the arteries as there is less cholesterol in the bloodstream

3. Heart Transplants

• Sometimes CHD can lead to heart failure…
  • …the heart is unable to pump enough blood around the body to meet the demands for oxygen
• In this case, heart transplants can be used

Donor Transplants

• Donor hearts can be transplanted into those with heart failure
• People often donate their heart after death
• However, suitable hearts are not that common to find

Artificial Transplants

• This is a man made device that temporarily pumps blood in the patient
• This can give the heart time to rest or heal, or help the patient as they wait for a transplant

Immunosuppressants

• These are drugs which suppress the immune system
• They reduce the risk of an immune response against the transplanted heart
• If there is any infection from surgery, immunosuppressants can make things worse by weakening the body’s natural defences

Treatment of Faulty Valves

Valves

• Damage to the heart valves can make them more leaky, causing the back flow of blood
• It can also make them more stiff, stopping the valves opening properly
• When the valves are severely damaged, valves must be replaced:
  • Biological valves are made from humans or other animals such as cows or pigs
  • Mechanical valves require surgery, and carries risks of thrombosis or complication

4.2.2.5 Health issues

Defining Health

• Health is the state of well-being. It involves:
  • Physical well-being – fitness, BMI, and lack of disease
  • Mental well-being – stress, mental illness and psychology

Defining Disease

• Disease is often caused by presence of pathogens or foreign agents in the body
• Health is therefore affected heavily by disease
• A lack of disease does not necessarily mean good health

Viruses and Cancer

• Viruses can increase risk of certain diseases, such as cancer
  • Infection by the human papilloma virus can lead to an increased risk of cervical cancer
  • Infection by the hepatitis virus could lead to suffering from liver cancer

Immune System

• Those with a weakened immune system have a greater risk of suffering from diseases
  • HIV can weaken a patient’s immune system, leaving them susceptible to other diseases
• Immune reactions can lead to allergic reactions by the body
  • These can manifest as skin rashes and exacerbation of asthma

Mental Health

Physical Health and Mental Health are interlinked

Types of Disease

Communicable Disease

• Communicable diseases spread from one organism to another.
• They are contagious or infectious diseases.

Non Communicable Disease

• Non-communicable diseases cannot be passed on to another organism.
• They are often chronic – e.g. Coronary Heart Disease.

Disease Incidence

Sampling

Populations are too large to individual take data

You must take an accurate, random, representative sample of the population

For example…

2 of the 6 people have CHD

The whole population is 21

So 7 people probably have CHD

The incidence is 33%

4.2.2.6 The effect of lifestyle on some non-communicable diseases

Human Costs

• There is great suffering to those with diseases
• Their life expectancy and quality of life is lowered
• Disease can affect their mental health

Financial Costs

• Much of the NHS’s budget is spent on chronic illness
• Families often give up jobs or move in to provide the necessary healthcare for these patients

Factors Affecting Incidence

1. Lifestyle Factors
2. Environmental Factors

Lifestyle Factors: Diet

Lifestyle Factors: Smoking

Lifestyle Factors: Alcohol

Lifestyle Factors

• Lifestyle factors increase your risk of non-communicable diseases on a local level
• An impoverished area may have increased alcohol intake and smoking, leading to a greater incidence of these diseases on a national level
• If a country is less economically developed, it may have a worse lifestyle, leading to higher rate of these diseases on a global level

Environmental Factors

• There are some environmental factors that can affect risk
  • E.g. at a local level we see asbestos in buildings, whilst at a national level we may see poor air pollution

Causal mechanism

• A causal mechanism means there is a link between two factors
• A correlation does not always prove causation

• Most diseases are caused by a combination of factors

Diet and Cardiovascular Disease

• Poor diet increases the risk of obesity
• It could lead to a higher cholesterol level
• This can increase the chance of the blocking the arteries

Smoking and Cardiovascular Disease

• Artery walls can be damaged by smoke tar chemicals
• The nicotine can lead to an increase in heart rate
• This leads to a greater incidence of cardiovascular disease

Exercise and Cardiovascular Disease

• Exercise increases blood supply to the heart
• It can also reduce cholesterol level
• This reduces the cardiovascular disease risk

Obesity and Type 2 diabetes

• Obesity makes the body less sensitive to insulin
• It can lead to an increased incidence of Type 2 Diabetes
• Limiting the number of high-sugar foods can reduce this

Alcohol and the Liver / Brain Function

• Long term drinking of large volumes of alcohol can damage the liver
• This can cause cirrhosis (scarring of the liver) and cancer
• Alcohol damages the nervous system, affecting brain function

Smoking and Lung Disease and Lung Cancer

• Tobacco contains many chemicals that can affect the body, which can increase the risk of lung disease
• Tar damages the alveoli, leading to Chronic Obstructive Pulmonary Disease (COPD) and can also cause cancer
• Other chemicals also flatten the cilia in the trachea, so they can no longer move the mucus

Smoking and Alcohol and Unborn Babies

• A pregnant lady smoking starves the baby of oxygen – causing stillbirths, premature birth or reduced birth weight
• Alcohol can cross the placenta and lead to deformities and heart problems, which can lead to developmental problems

Carcinogens and Cancer

• Carcinogens are factors that predispose cancer
• Ionising radiation, smoking, viruses
• Lab workers may wear radiation detectors to reduce exposure

Risk Factors

Sampling for Risk Factors

• The general principles of sampling include taking a random, large, unbiased group
• Samples can be used to look for people with risk factors
• Risk factors can be plotted on graphs and tables
• Correlations can be seen if you can draw a line through the data points

Risk Factors

• These can be plotted on graphs and in tables
• On a graph, if there is a link, there is a correlation.
• This will be clear when you can draw a straight line through the data

4.2.2.7 Cancer

Mutations and Cancer

Mutations and Cancer

• Cancer involves the uncontrolled growth and division of cells – tumour
• There can be a change in the genetic material – mutation
• This makes a cell divide very fast and out of control

Benign Tumours

• Benign tumours can form from uncontrolled cell divisions
• These tumours do not move from their site of origin
• Benign tumours are not normally dangerous

Malignant Tumours

• Malignant tumours spread from their site of origin
• They can spread through the blood and form secondary tumours – metastasis
• They also invade the tissues near to them

Risk Factors