Biology - Unit 1

Open circulatory systems - blood circulates in large open spaces. Blood is pumped into cavities surrounding the animal's organs.

Closed circulatory systems - blood is enclosed within tubes. This generates higher blood pressure meaning blood travels faster and is more efficient at delivering substances around the body.

• In single circulatory systems the blood only flows through the heart once for each complete circuit of the body. (eg. fish)
• In double circulatory systems the blood flows through the heart twice for each complete circuit of the body. (eg. mammals and birds)

Blood is important in the transport of dissolved substances and cells and plays a vital role in the regulation of body temperature.

Water as a transport medium:

Water is a polar molecule as it has an unevenly distributed charge - the hydrogen end of the molecule is slightly positive and the oxygen end is slightly negative. It is its polarity that accounts for many of its biologically important properties.

The hydrogen bonding holds the water molecules together and results in it being liquid at room temperature.

Ionic molecules dissolve easily in water as they are attracted to the polar ends.

The specific heat capacity of water is very high because a large amount of energy is required to break the hydrogen bonds.

A large input of energy only causes a small increase in temperature so water warms up and cools down slowly. This is extremely useful for organisms helping them to avoid rapid changes in their internal temperature and enabling them to maintain a steady temperature when their surroundings vary considerably.

One complete cycle of the heart is called the cardiac cycle. There are three phases:

• Atrial Systole:

Blood under low pressure flows into the left and right atria from the pulmonary veins and vena cava. As the atria fill the pressure of blood against the atrioventricular valves pushes them open and blood begins to leak into the ventricles. The atria walls contract forcing more blood into the ventricles.

• Ventricular Systole:

The ventricles contract from the base upwards increasing the pressure in the ventricles. This pushes blood up and out through the arteries. The pressure against the atrioventricular valves closes them and prevents blood flowing backwards into the atria.

• Diastole:

The atria and ventricles relax. Elastic recoil lowers the pressure in the atria and ventricles. Blood under high pressure in the arteries is drawn back, closing the semi-lunar valves and preventing backflow. The coronary arteries fill during diastole. Low pressure in the atria helps draw blood into the heart from the veins.

The journey of blood:

1. Aorta → Arteries → Arterioles → Capillaries → Venules →Veins → Superior Vena Cava → Right atrium →Atrioventricular valve (Tricuspid valve) → Right ventricle → Semi-lunar valve → Pulmonary Artery → Lungs → Pulmonary Veins → Left atrium → Atrioventricular valve (Bicuspid valve) → Left ventricle → Semi-lunar valve → Aorta

• The endothelium that lines the inside artery wall becomes damaged.
• There is then an inflammatory response. White blood cells enter the artery wall and chemical such as cholesterol accumulate.
• A deposit builds up called an atheroma.
• Calcium salts and fibrous tissue accumulate resulting in a hard plaque forming. This reduces elasticity in the artery wall.
• The artery narrows and blood pressure rises. Dangerous positive feedback.
• ATHEROSCLEROSIS.
• Platelets come into contact with the damaged artery wall and become sticky forming a platelet plug.
• This causes a cascade of chemical changes.
• Prothrombin converted to thrombin.
• The enzyme thrombin catalyses the conversion of fibrinogen into fibrin.
• Fibrin causes a tangled mesh that traps blood cells to form a BLOOD CLOT.

Shortness of breath and angina are often the first signs of coronary heart disease.

Angina - narrowing of the arteries limits the amount of oxygen-rich blood reaching the heart muscle. Usually experienced during exertion as the heart is forced to respire anaerobically. Symptoms include: intense pain or discomfort in chest, heaviness, tightness, burning and pressure.

Heart attack/myocardial infarction - if the blood supply to the heart is blocked then the heart muscle will become ischaemic. If the muscle cells are starved of oxygen they will become permanently damaged. Symptoms include: sharp chest pain, pain in arms, neck and shoulders, increased or irregular heart rate, and shortness of breath.

Stroke - the blood supply to the brain is blocked. Symptoms include: numbness, dizziness, confusion, slurred speech and blurred or lost vision. Visible signs include paralysis of one side of the body opposite to the side of the brain where the stroke has occurred.

Arrhythmia - heart beat becomes irregular and can lead to heart failure.

There is a tendency to overestimate the risks of sudden imposed dangers where the consequences are severe and to underestimate a risk if it has an effect in the long-term future, even if that effect is severe.

Correlation - when an increase in one is accompanied by an increase in the other.

Causation - when a change in one is responsible for a change in the other.

Cohort studies - a group of people are followed over time to see who develops the disease.

Case-control studies - a group of people who have the disease are compared with a group who do not have the disease.

Risk factors of CVD: high blood pressure, obesity, blood cholesterol and other dietary factors, smoking, genetic inheritance.

Elevated blood pressure, known as hypertension is considered to be one of the most common factors in the development of CVD.

Blood pressure is the measure of hydrostatic force of the blood against the walls of a blood vessel.

A sphygmomanometer is a traditional device used to measure blood pressure.

Blood pressure is reported as two numbers, systolic pressure over diastolic pressure. Systolic pressure is the maximum blood pressure when the heart contracts, and diastolic pressure is the pressure when the heart is relaxed.

Peripheral resistance - contact between blood and the walls of the blood vessels causes friction which impedes the flow of blood. As peripheral resistance increases with greater total surface area, the flow of blood slows causing pressure to fall.

One sign of high blood pressure is oedema. Fluid builds up in tissues and causes swelling.

Monosaccharides are single sugar units, eg, glucose, galactose and fructose. These are know as hexose sugars. They provide a rapid source of energy and are readily absorbed.

Two single sugar units can join together to form a disaccharide in a condensation reaction. The bond that forms between the molecules is known as a glycosidic bond.

The glycosidic bond can be split by hydrolysis. Hydrolysis of carbohydrates takes place when carbs are digested in the gut and when carb stores in a cell are broken down to release sugars.

Monosaccharides are rapidly absorbed causing a sharp rise in blood sugar, but polysaccharides and disaccharides have to be digested into monosaccharides before being absorbed.

Polysaccharides are polymers made up from single sugar monomers joined by glycosidic links into long chains.

There are three main types of polysaccharide found in food: starch and cellulose in plants, and glycogen in animals.

Starch and glycogen act as storage molecules within cells. Bacteria fungi and animals store glycogen instead of starch.

Cellulose has an important function in the movement of material through the digestive tract. It helps prevent diseases such as CVD, diabetes and bowel cancer.

Lipids are organic molecules found in every type of cell. They are insoluble in water but soluble in organic solvents such as ethanol.

Triglycerides are used as energy stores in plants and animals. They are made up of three fatty acids and one glycerol molecule joined by ester bonds.

Saturated fats are straight-chained with no double carbon bonds. They are solid at room temperature as they can pack closely together with strong intermolecular bonds.

Unsaturated fats have double carbon bonds. Mono-unsaturated fats have one double bond and polyunsaturated fats have a large number of double bonds. The double bonds create kinks in the chain which prevents them packing closely together. The weaker intermolecular bonds results in oils that are liquid at room temp.

Cholesterol is a short lipid molecule. It is a vital component of cell membranes with roles in their organisation and functioning. Hormones and bile salts are formed from cholesterol.

Phospholipids are similar to triglycerides but one of the fatty acids is replaced by a negatively charged phosphate group.

You need a constant supply of energy to maintain your essential body processes. The energy needed is called the basal metabolic rate (BMR) and varies between individuals. BMR is higher in:

• males
• heavier people
• younger people
• more active people

If you eat fewer kilojoules per day than you use, you have a negative energy balance and you will lose weight. If you eat more energy than you use, you have a positive energy balance and you will gain weight.

Body Mass Index (BMI) is a conventionally used method of classifying body weight relative to a person's height.

There is evidence that waist-to-hip ratio is a better measure of obesity than BMI and shows a highly significant association with risk of heart attack.

Obesity increases your risk of coronary heart disease, stroke, and diabetes even without other risk factors being present. It can also raise your blood pressure and blood lipid levels.

Cholesterol is not soluble in water so in order to be transported in the bloodstream, insoluble cholesterol is combined with proteins to form soluble lipoproteins.

There are two major transport lipoproteins:

• low-density lipoproteins (LDL's) - the main cholesterol carrier in the blood. They circulate in the bloodstream and bind to receptor sites on cell membranes before being taken up by the cells. Excess LDL's overload the membrane receptors resulting in high blood cholesterol levels. They can also form atheromas.
• high-density lipoproteins (HDL's) - HDL's have a higher percentage of protein hence their higher density. They transport cholesterol from the body tissues to the liver where it is broken down. This lowers blood cholesterol levels and helps remove the fatty plaques of atherosclerosis.

Monounsaturated fats help in the removal of LDL's from the blood and polyunsaturated fats increase the activity of the LDL's receptor sites so they are actively removed from the blood.

Smoking - one of the major risk factors for the development of CVD. The constituents of smoke affect the circulatory system in the following ways:

• The haemoglobin in red blood cells carries carbon monoxide from the smoke instead of oxygen, reducing the supply of oxygen to cells.
• Nicotine in smoke stimulates the production of the hormone adrenaline which increases blood pressure.
• The numerous chemicals can cause damage to the lining of the arteries, triggering atherosclerosis.
• Reduces HDL cholesterol level.

Physical inactivity is considered to be one of the most common risk factors for heart disease. A person who is physically active is much more likely to survive a heart attack or stroke.

If one or other of your parents suffer or suffered from CVD you are more likely to develop it yourself and there may be inherited disposition for the disease.

During reactions in the body, unstable radicals result when an atom has an unpaired electron, eg. in the superoxide radical, oxygen.

Radicals are highly reactive and can damage many cell components including enzymes and genetic material. This type of cellular damage has been implicated in the development of some types of cancer, heart disease and premature ageing.

Some vitamins, including vitamin C and E can protect against free radical damage. They provide hydrogen atoms that stabilise the radical by pairing up with its unpaired electron.

The risk of CVD can be reduced by:

• Stopping smoking
• Maintaining resting blood pressure
• Maintaining low blood cholesterol levels
• Maintaining a normal BMI/waist-to-hip ratio
• Taking more physical exercise
• Moderate or no use of alcohol

Medications are available to reduce high blood pressure:

• ACE inhibitors - effective antihypertensive drugs which reduce the synthesis of angiotensin II. This hormone causes vasoconstriction of blood vessels to help control blood pressure. Symptoms: dry cough, dizziness, abnormal heart rhythms, and reduction in function of kidney.

• Calcium channel blockers - block calcium channels in the muscle cells in the lining of the arteries. For the muscle to contract, calcium must pass through these channels into the muscle cells.Failure of calcium to enter the cell prevents contraction of the muscle which means the blood vessels do not constrict, lowering blood pressure. Symptoms: headaches, dizziness, swollen ankles abnormal heart rhythms.
• Diurectics - increases the volume of urine produced by the kidneys and thus rid the body of excess fluids and salt. This leads to a decrease in blood plasma volume and cardiac output which lowers blood pressure. Symptoms: dizziness, nausea, muscle cramps.

Cholesterol-lowering drugs - Statins work by inhibiting an enzyme involved in the production of LDL cholesterol. They quickly reduce the risk of heart disease and stroke.

Air is drawn in to the lungs via the trachea due to low pressure in the lungs, created by movement of the ribs and diaphragm. The trachea divides into two bronchi which carry air to and from each lung. Within in each lung there are bronchioles leading to aveoli which are the site of gas exchange.

Everyone has a thin layer of mucus produced continuously from goblet cells in the walls of the airway. Any dust, debris or microorganisms become trapped in the mucus and are continually removed by the wave-like beating of cilia that cover the epithelial cells.

People with CF have mucus that is drier than usual resulting in a sticky mucus layer that the cilia find difficult to move. This increases the chances of lung infection and makes gas exchange less efficient.

White blood cells fight the infections and pathogens within the mucus but as they die they break down, releasing DNA which makes the mucus even stickier. Repeated infections can weaken the body's ability to fight the pathogens and cause damage to the gas exchange system.

Epithelial cells line the cavities and tubes and cover the surfaces of internal organs. The cells work together as a tissue, epithelium.

The epithelium consists of one or more layers of cells sitting on a basement membrane. There are several types of epithelia:

• Squamous - in the walls of the alveoli and capillaries. Very thin flattened cells.
• Columnar - the epithelial cells extend out from the basement membrane. They are covered in microvilli which greatly increase the surface area.

There are many features that increase gas exchange:

• large surface area of the alveoli
• numerous capillaries around the alveoli
• thin walls of the alveoli and capillaries meaning a short distance between the alveolar air and blood in the capillaries

The rate of diffusion depends on:

• Surface area - as the surface area increases the rate of diffusion increases.
• Concentration gradient - the greater the concentration gradient the faster the diffusion.
• Thickness of gas exchange surface - the thicker the surface the slower the diffusion.

Fick's Law:

The sticky mucus layer in the bronchioles of a person with CF tends to block these narrow airways, preventing ventilation of the alveoli below the blockage. This reduces the number of alveoli available for gas exchange.

People with CF find it difficult to take part in physical exercise because their gas exchange system cannot deliver enough oxygen to their muscle cells. This makes them very short of breath but is very beneficial to them.

The mucus layer is stickier as it contains less water than normal. The reduced water level is due to abnormal salt and water transport across the cell surface membranes caused by a faulty transport channel in the membrane.

In a phospholipid there are only two fatty acids as a negatively charged phosphate group replaces the third fatty acid.

The phosphate head of the molecule is slightly polar; one end is slightly positive and the rest is slightly negative. This makes the phosphate head attract other polar molecules like water as it is hydrophillic. The fatty acid tails are hydrophobic so when phospholipids are added to water they arrange themselves so that the tails are pointed inwards away from the water and the heads are pointing out towards the water.

CF sufferers have difficulty maintaining body mass because of problems with the digestion and absorption of nutrients.The also have a high basal metabolic rate. They have to eat more food than most people including high energy food to make sure they are getting suffiecient nutrients and energy.

They take digestive enzymes to help break down food.

The pancreatic duct becomes blocked by sticky mucus, impairing the release of digestive enzymes. The lower concentration of enzymes within the small intestine reduces the rate of digestion so food is not fully digested and nutrients cannot be absorbed.

When the enzymes become blocked they can damage the pancreas itself. They form cysts of hard, damaged or fibrosed tissue within the pancreas.

Enzymes are globular proteins that act as biological catalysts. The precise three dimensional shape adopted by an enzyme includes a depression on the surface of the molecule called the active site.

Lock and key theory

• Substrate molecules with a complementary shape form temporary bonds with the amino acids on the active site to produce an enzyme-substrate complex. Only catalyse one specific reaction.

Induced fit theory

• The enzyme molecule changes shape slightly fitting more closely around the substrate. Only a specific substrate will induce the change in shape.

The convert substrates into products bonds must change within and between molecules. The energy needed to break bonds and start the chemical reaction is known as the activation energy.

In cells, enzymes reduce the amount of energy needed to bring about the reaction; this allows reactions to occur without raising the temperature of the cell.

Females have a reduced chance of becoming pregnant because a mucus plug develops in the cervix. This stops sperm from reaching the egg.

Males with CF commonly lack the vas deferens (sperm duct) on both sides, which means sperm cannot leave the testes. Where the vas deferens is present it can become partially blocked by a thick sticky mucus layer. This means fewer sperm are present in each ***********.

DNA is found in every cell nucleus. It contains the genetic code which dictates all the inherited characteristics of an organism. It does this by controlling the manufacture of proteins.

Gene - a sequence of bases on a DNA molecule coding for a sequence of amino acids in a polypeptide chain. All the genes in an individual are known as the genome.

Bases:

• Adenine
• Cytosine
• Guanine
• Thymine

In a DNA molecule there are two long strands of nucleotides twisted around each other to form a double helix. The sugars and phosphates form a backbone. The two strands are antiparallel as they run in opposite directions and are held together by hydrogen bonds.

Triplet code - three bases that code for an amino acid.

RNA - single strand instead of a double helix that contains ribose sugar instead of deoxyribose. Uracil replaces thymine. There are three types; mRNA, tRNA and rRNA.

There are two stages in protein synthesis:

• Transcription - takes place in nucleus.