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Cardiac Cycle

The stages in the cardiac cycle, atrial systole, ventricular systole and diastole.

Atrial Systole
 
Blood returns to the heart due to the action of skeletal and gaseous exchange (breathing) muscles as you move and breath. 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 into the ventricles.

Ventricular Systole
The ventricles contract from the base of the heart upwards, increasing the pressure in the ventricles. This pushes blood up opening the semi lunar valves and out through the arteries. The pressure of blood against the atrioventricular valves closes them and prevents blood flowing backwards into the atria.

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

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Water

Liquid at room normal biological temperature. It has an unevenly electrical charge (polar molecule). Two hydrogens are pushed towards each other making a V-shaped molecule. The hydrogen end is slightly positive and the oxygen end is slightly negative as it has more electrons. Because it is polar it has many biologically important properties.

The positive end of the molecule (hydrogen) attracts negative ends of other molecules. This is called hydrogen bonding and it holds the water molecules together.

Lots of molecules dissolve easily in water because of its polar properties. This substances are called hydrophilic, water loving. Whereas so substances do not dissolve in water (lipids) they are call hydrophobic, water hating.

Water has a very high specific heat capacity this is because a large amount of energy is needed to break the hydrogen bonds between the molecules. So, water heats up and cools down slowly.

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Ciculatory System

Open
Blood circulates in large open spaces. A simple heart pumps blood out into cavities where they take it out through diffusion. When the heart muscles relaxes blood is drawn back into the heart, through small valve openings along its length.

Closed
All vertebrates have a closed circulatory system this is where blood in enclosed in tubes generating a high blood pressure causing blood to travel faster therefor more efficient. Animals with closed systems are generally larger in size and more active than closed. Blood leaves the heart through the arteries and then arterioles to capillaries. Capillaries are the site of substance exchange between the blood and cells. Blood returns to the heart through the venules and then the veins. Valves prevent backflow.

Single E.g. fish. - Flows through the heart once
Heart -> Deoxygenated -> Gills Capillaries) -> Gaseous exchange takes place -> Diffusion-carbon dioxide from blood into water -> Diffusion- oxygen from water into blood -> Blood flows around rest fo body

Double- Flows through the heart twice
Right ventricles -> Deoxygenated blood into lungs -> Receives blood -> Oxygenated blood returns to heart -> Pumped around the body.

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The Heart

Arteries 
Narrow lumen
Thicker walls
More collagen (tough fibrous protein), elastic fibres (allow them to stretch and recoil) and smooth muscles
No valves

Veins
Wide lumen
Thinner walls
Less collagen (tough fibrous protein), elastic fibres (allow them to stretch and recoil) and smooth muscle
Valves

Blood Flow
Deoxygenated blood is received from the superior/inferior vena cava into the right atrium. It flows into the right ventricle through atrial systole. The deoxygenated blood is pumped into the lungs were it is oxygenated. The blood flows back to the heart through the pulmonary vein into the left atrium. Next it flows into the left ventricle and into the aorta where it is pumped around the body.

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Atherosclerosis/Blood clot

Atherosclerosis
Endothelium damaged (high blood pressure, toxins from cigarette smoke) -> 
Inflammatory response -> White blood cells leave blood vessel -> Move into artery wall -> Cells accumulate chemical from blood (cholesterol) -> Atheroma deposit builds up ->
Calcium salts, fibrous tissue build up (plaque) -> Artery wall loses elasticity -> 
Plaque causes artery to narrow -> Difficult for heart to pump -> Dangerous positive feedback 
-> Plaques lead to raised blood pressure -> Raised blood pressure -> Increases chance of plaques building up.

Blood Clot
Direct contact of blood with collagen -> Cascade of chemicals reactions -> Platelets stick to damaged wall of blood vessel -> Platelets stick to damaged wall and to each other, forming a platelet plug ->
Thromboplastic, calcium and potassium turns -> Prothrombin -> Thrombin (turns) -> Soluble fibrin -> insoluble fibrin -> Fibrin mesh traps blood cells, forming a clot.

Consequences
Coronary heart disease, angina, stroke.

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Risk of CvD

Perception of Risk
Involuntary, Not natural, Unfamiliar, Unfair, Very small

Risk Factors
Heredity, physical/social environment, lifestyle and behaviour choices, high blood pressure, obesity, blood cholesterol and other dietary factors, smoking, generic inheritance

Identifying Risk Factors
To determine risk factors scientists look for correlations between potential risk factors and the occurrence of the disease. Large amount of data is needed to show correlation is statistically significant. Causation is when there is a casual link between the two variables, one cause a reaction in the other.

How to Identify Risk Factors
Cohort study-When 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 compared with a group who do not have the disease. 

Features of a good study
Clear aim, representative sample, valid and reliable results. 

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Dietary Factors

Carbohydrates ‘hydrated carbon’
Sugars are either single sugar units called monosaccharides which can be joined by condensation reaction to make disaccharides. There are also polysaccharides which contain three or more sugar units.

Monosaccharides
Single sugar units. They have between 3-7 carbon atoms but the most common number is 6 e.g. Glucose, fructose, galactose. A hexose sugar molecule has a ring structure formed by 5 carbons and an oxygen atom the sixth atom projects above or below the ring. The carbons are numbered, 1 starts on the extreme right of the molecule. The side branches above or below the ring and the type of sugar molecule and its purpose.

Glucose-The main sugar used by all cells for respiration. Starch and glycogen are polymers made out of glucose subunits joined together. When starch and glycogen is digested glucose is produced. It can be absorbed and transported in the blood stream to cells.

Galactose- In out diet mainly as part of the disaccharide sugar lactose in milk.

Fructose-Occurs naturally in fruit, honey and some vegetables. Sweetness attracts animals to eat the fruit and help with seed dispersal.

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Dietary Factors

Disaccharides
Two single sugar units join together to make a disaccharide in a condensation reaction. It's a condensation reaction because a water molecule is released as the two sugar molecules combine. Bond between the two sugars is a glycosidic bond. The glycosidic bond can be broken down through hydrolysis this is where water is added to the molecule causing ti to split in two. This usually happens in the gut and when carbohydrates stores in a cell are broken down to release sugars. Disaccharides have to digest into monosaccharide before being absorbed. This takes time so they are not the cause swings in blood sugar levels. Common disaccharides in food are sucrose, maltose and lactose.

Sucrose- Formed from glucose and fructose, it is the usual form which sugar is transported around the plant.

Maltose- Formed from two glucose molecules. Produced when amylase breaks down starch. Found in germinating seeds such as barley as they break down their starch to use for food.

Lactose-Formed from galactose and glucose. Found in milk. 

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Dietary Factors

Polysaccharides
Polymers made from simple sugar monomers joined by glycosidic bonds into long chains. Three main types of pol
ysaccharides found in food, starch and cellulose in plants and glycogen in animals. They do not dissolve easily and do no taste sweet although they're polymers of glucose molecules.

Starch- Energy storage within the cells. Suitable because compact and low soluble in water. Does not affect concentration of water in cytoplasm and does not affect osmosis. Does not diffuse across cell membranes. Found naturally in fruit, vegetables and cereals. Added to many foods as a replacement of fat. Made from a mixture of amylose and amylopectin. 

Cellulose- Dietary fibre. Indigestible in the human gut. Important function in the movement of material through the digestive tract.

Glycogen- Energy storage within the cells. Suitable because compact and low soluble in water. Does not affect concentration of water in cytoplasm and does not affect osmosis. Bacteria, fungi and animals store glycogen instead of starch. Made from glucose molecules. Numerous side branches so it can be rapidly hydrolysed, giving easy access to stored energy. In humans glycogen stored in liver and muscles.

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Dietary Factors

Lipids
Enhance the flavour and palatability of food making it feel smoother and creamier. Supply over twice the energy of carbohydrates. Large amount of energy can be stored in small mass e.g. Seeds. Organic molecules, insoluble in water but soluble in organic solvents such as ethanol.

Triglycerides- Lipids that we eat. Used as energy store in plants and animals. Made up of three fatty acids and a glycerol linked by condensation reactions. Bond between each fatty acid and glycerol is called an ester bond (3 are formed). Glycerol is CH2OH, fatty acid is HOOC - Charley has 2 orange hairs, Emi is a hooc-er!

Saturated fats (bad)-Maximum number of hydrogen bonds. Hydrocarbon chain is long and straight. No carbon to carbon double bonds and no more hydrogens can be added to it. Animal fats from meat and dairy products are major sources. Pack together closely strong intermolecular bonds between triglycerides made up of saturated fatty acids results in fats that are solid in room temperature. 

Unsaturated fats (good)- Monosaturated fats have one double bond between two of the carbon atoms in each fatty acid chain. Polysaturated have a larger number of double bonds. Double bond causes a kink in hydrocarbon chain. Kinks prevent unsaturated hydrocarbons packing closely together. Weaker intermolecular bonds result in oils that are liquid at room temperature.

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Dietary Factors

Cholesterol
A short lipid molecule. Vital component of cell membranes with roles of their organisation and functioning. Steroid sex hormones, some growth hormones, bile salts are produced and formed from cholesterol. Associated with saturate fats. Made in the liver from saturated fats and obtained in out diet. The higher your blood cholesterol level the greater the risk of CHD. Cholesterol is not soluble in water so combines with proteins to form soluble lipoproteins.

LDLs (Low density lipoproteins) - The main cholesterol collector in the blood. Made up of triglycerides from saturated fats, protein and cholesterol. Circulate in the bloodstream and bind to receptor site on the cell membrane before being taken up by cells. Excess LDLs in diet overload receptors resulting in high blood cholesterol levels. Saturated fats may reduce the activity of LDL receptors so the LDLs are not removed from the blood. This cholesterol may be deposited in the artery walls resulting in an atheroma.

HDLs (High density lipoproteins) - Higher percentage of proteins then LDLs. Made up of triglycerides from unsaturated fats, cholesterol and protein. They transport cholesterol from the body tissue to the liver where it is broken down. This lower blood cholesterol levels and helps remove the fatty plaques of atherosclerosis.

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Reducing The Risk of CVD

ACE inhibitors
Block your body from producing a chemical called angiotensin II. When angiotensin II enters your blood stream your blood vessels ­become narrower. Giving your blood less space to move in, which raises your blood pressure. CE inhibitors lower your blood pressure by reducing angiotensin II in your body. This allows your blood vessels to relax and widen, making it easier for blood to flow through. Side effects can be dry cough, dizziness, and abnormal heart rhythms.

Calcium Channel Blockers
Antihypertensive drug that block the 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. The failure of calcium entering the cells prevents contraction of the muscle, the blood vessels do not constrict this lowers blood pressure. Side effect can be headaches, dizziness, swollen ankles and constipation.

Diet
Energy balanced, reduced saturated fat, more polyunsaturated fats, reduced cholesterol, reduced salt, include oily fish, more fruit and vegetables. 

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