AQA AS Biology - C5

Structure - BASIC

• Two seperate pumps - side by side
  • The left deals with OXYGENATED blood
  • The right deals with DEOXYGENATED blood

• Each pump has 2 chambers
  • ATRIUM: ~ thin walled, stretches as it collects blood, thin muscular wall as the blood only has to be pumped a small distance.
  • VENTRICLE: ~ thicker muscular walls as the blood has to be pumped a longer distance (lungs or rest of body)
• Ventricles: pump blood AWAY from the heart, into the ARTERIES
• Atria: recieve blood from the VEINS

• VALVES:
  • Left Atroventricular (BICUSPID) valves: two cup-shaped flaps on the LEFT side
  • Right Atroventricular (TRICUSPID) valves: three cup-shaped flaps on the RIGHT side
• VESSELS:
  • Connecting heart to lungs: PULMONARY VESSELS
  • Vessels conncted:
    • Aorta connected: LEFT ventricle, carries oxygenated blood to all parts of body except lungs
    • Vena Cava connected: RIGHT atrium, brings deoxygenated blood back from tissues of body
    • Pulmonary Artery connected: RIGHT ventricle, carries deoxygenated blood to lungs (Unusual for artery to carry deoxygenated blood)
    • Pulmonary Vein connected: LEFT atrium, brings oxygenated blood back from lungs (Unusual for vein carry oxygenated blood)

Supplying the heart muscles with oxygen

• Oxygenated blood in the LEFT side of the heart is not used for the hearts own respartitory needs
• INSTEAD:
  • Heart muscle supplied by OWN blood vessels
    • Coronary Arteries: branch off aorta shortly after it leaves heart
    • Blockage of these arteries leads to myocardial infraction (heart attack)
      • As area of heart muscle is deprived of oxyge it dies = heart attack.

Extra

• Although left ventricl has thicker walls than right, their internal volumes are the same.

• The left and right side of the heart contract together

Cardiac Cycle (BASIC)

• TWO phases of the beating of the heart:
  • Contraction (SYSTOLE)
  • Relaxation (DIASTOLE)
• Contraction:
  • Atria: Atrial Systole
  • Ventricle: Ventricular Systole
• Valves:
  • Atrioventricular Valves
  • Semi-lunar Valves
  • Pocket Valves

 Cardiac Output = Heart Rate * Stroke Volume

Realxation of the heart (DIASTOLE)

• Blood returnes to atria of heart through pulmonary vein (from lungs) & vena cava (from body).
• As atria fills the pressure in them rises
  • Pushing open the atrioventricular valves & allowing blood to pass into ventricles
• Muscular walls of BOTH atria & ventricles relaxed at this stage
• The relaxation of the ventricle wall reduces the pressure within the ventricle
  • Causes pressure to be lower than that of the aorta anf pulmonary artery so the semi-lunar valves in aorta & pulmonary artery colses

Contraction of atria (ATRIAL SYSTOLE)

• Muscles of atrial walls contracts, forcing remaining blood into the ventricles
• Blood only has to be pushed a short distance
  • Therefore muscular walls of atria thin
• During this stage the ventricle walls remain RELAXED

Contraction of the ventricles (VENTRICULAR SYSTOLE)

• After short delay to allow ventricles to fill with blood, their walls contract simultaniously, increasing blood pressure within them
  • Forces atrioventricular valves shut preventing backflow of blood
• With atrioventricular valves closed the pressure rises further, forcing semi-lunar valves open, forcing blood into the pulmonary artery & aorta
  • Walls of ventricles are much thicker as they have to pump blood much further
• Left ventricle walls are thicker as they have to pump blood to the extremerties of the body compared to the right (only has to pump blood to lungs)

Valves & control of blood flow

• IMPORTANT to keep blood flowing in the right direction around the heart & body

• Are instances in circulartitory system when pressure difference would result in blood flowing in the wrong direction
  • Valves are used to prevent this

• Valves are designed so that they open whenever the difference in blood pressure either side of them favours the movement of blood in the requiered direction
  • When pressure difference is reversed the valves are designed to close

Examples of Valves

• Atrioventricular Valves: between the atriums & ventricles, these prevent backflow of blood when contraction of ventricles means that ventricular pressure is greater than the atrial pressure.
  • Closure of valves ensures that when the ventricles contract blood moves into the aorta & pulmonary arteries rather than back to the atria
• Semi-lunar Valves: In the aorta & pulmonary artery.
  • Prevents backflow of blood into ventricles when recoil of elastic walls of vessels create greater pressure in vessels than ventricles
• Pocket Valves: In veins that occur throughout system
  • Ensure when veins are squeezed (e.g. muscles contract) blood flows back to the heart rather than away from it

Designs of valves = basically the same, made up of number of flaps of tissue that is cusp-shaped (when blood collects within the 'bowls' they are pushed together to form a tight fit & prevent to flow of blood

Cardiac Output

• Volume of blood pumped by one ventricle of the heart in one minute
• It depends on two factors:
  • The heart rate
  • The Stroke volume (volume of blood pumped out at each beat)

Cardiac Output = Heart Rate * Stroke Volume

Pressure & Volume changes of heart

• Mammals have closed circulatitory system (bloos confined to vessels)
  • This allows pressure witin them to be mantained & regulated

How the Cardiac Cycel is controlled

• Cardiac muscles myogenic (contraction initiated from muscle)
• Within wall of right atrium = group of cells Sinostrial Node (SAN) often referd to as peacemaker
• Sequence of events=
  • Wave of electrical activity spreads from SAN across both atria causing them to CONTRACT
  • Layer of non-conductive tissue (atrioventricular septum) prevents waves crossing to ventricles
  • Wave of electrical activity allowed to pass through 2nd group of cells atrioventricular node (AVN) which lies between the atria
  • AVN after short delay conveys wave of electrical activity between ventricles along series of specialist muscle fibre = bundle of His
  • Bundle of His conducts wave through atrioventricular septum to base of ventricles where bundle branches into smaller fibres
  • Wave of electrical activity released from fibres causing ventricles to contact quickly at the same time, from apex upwards

Examples of Heart Disease

• Coronary Heart Disease (CHD)
• Atheroma
• Thrombosis
• Aneurysm
• Myicardial Infraction

Risk factors associated with CHD

• Smoking
• High Blood Pressure
• Blood Cholesteral
• Diet

CHD

• Affects pair of blood vessels, the coronary arteries, which supply the heart with the products it needs for respiration
• Blood flow through these vessels may be impared by the build up of fatty deposits known as atheroma
• If blood flow to heart muscles interupted, it can lead to myocardial infraction (heart attack)

Atheroma

• Fatty deposit that forms within the walls of an artery, begins as fatty streaks that are accumulations of white blood cells that have taken up LDL's
• Streaks enlarge to form irregular patch (atheromatous plaque), are deposits of cholesterol, fibers & dead muscle cells
• Buldge into lumen, causing artery to narrow so blood flow reduced

Thrombosis

• If atheroma breaks through lining of blood vessel it forms a rough surface that interupts otherwise smooth flow of blood
• May result in formation of blood clot ot thrombus, in condition known as thrombosis
• Thrombosis may block blood vessel, reducing or preventing flow of blood to tissues beyond
• The region of tissue deprived of blood often dies due to lack of oxygen & other products that the blood normally supplies
• Sometime thrombus is carried from origin and loges (&blocks) another artery.

Aneurysm

• Atheromas that lead to thrombus also weaken artery walls
• Weakened points swell to form balloon like, blood filled structure, known as aneurysm
• Aneurysms frequently burst leading to haemorrhage & loss of blood to the region of the body surved by that artery
• A brain aneurysm is known as a cerebrovascular accident (CVA) or stroke.

Myocardial Infraction

• Refers to reduced supply of oxygen to the heart (myocardium) muscles
• Results from blockage of coronary arteries
• If occurs close to junction of coronary artery & aorta the heart will stop beating as the blood supply will be completely blocked
• If blockage further along coronary artery then symptoms = less severe
  • Smaller area suffering from lack of oxygen

Risk Factors associated with CHD

Smoking

• Two main products in tabacco that increase likelyhood of developing CHD:
  • Carbon Monoxide: conbines easily (& irreversably) with haemoglobin to form carboxyhaemoglobin. Reducing oxygen-carrying capacity of blood. This leads to heart needing to wokr harder to supply the same amount of oxygen. This can lead to
    • Raised blood pressure, which increases risk of CHD & strokes
    • Insufficiant supply of Oxygen to heart during exercise, this can lead to chest pains (anguna) or in sever cases myocardial infraction
  • Nicotine: stimulated production of adrenaline, increasing the heart rate & blood pressure
    • Greater risk of suffering CHD or a stroke
    • Nicotine leads to red blood cells becomming more 'sticky', leading to a higher risk of thrombosis & hence strokes & myocardial infraction.

High Blood Pressure

• DNA can cause high blood pressure
• BUT lifestyle choices e.g excessice prolonged stress, certain diets, lack of exercise, can alos incereas risk of high blood pressure
• Increases risk of CHD due to following factors:
  • Higher pressure in the arteries, heart muscles must therefore work harder to pump blood around the them
  • Higher blood pressure within arteries means that they are more likely to develope an aneurysm (& burst causing) haemorrhage
  • To resist higher pressure within them, walls of blood vessels may thicken & harden restricting flow of blood

Blood Cholesteral

• Cholesteral essentail component of membranes, an esentail biochemical that must be transported in the blood
• Carried in plasma as tiny spheres of lipoproteins, there are two main types:
  • High-Density (HDL's): remove cholesteral from tissues & transport to liver for excretin, help protect arteries against heart disease
  • Low-Density (LDL's): transport cholesteral from liver to tissues, including artery walls, which they infultrate, leading to the development of atheroma & hence heart disease.

Diet

• High levels of salt: raise blood pressure
• High levels of saturated fat: increase LDL's & hence blood level concentration
• Food that act as antioxidants reduce chance of heart disease, so does non-starch polysaccharide (dietary fibre)