Heart and Heart Disease
Anatomy
Heart consists of 4 chambers
o Right atrium (RA)
o Right ventricle (RV)
o Left atrium (LA)
o Left ventricle (LV)
Blood flow
o Right atrium receives blood from
- Superior vena cava (SVC) - carries blood from upper body (head, arms)
- Inferior vena cava (IVC) - carries blood from lower body (chest, abdomen, legs)
o Blood flows from right atrium, across a/v valve, into right ventricle
o Blood leaves right ventricle and enters pulmonary artery
- Backflow into RV prevented by semilunar valve
- Deoxygenated blood arrives at lungs via pulmonary artery
- Oxygenated blood leaves lungs via pulmonary vein
o Blood from pulmonary vein enters left atrium
o Blood flows from left atrium, across a/v valve, into left ventricle
o Left ventricle has a thick muscular wall / generates high pressures during contraction
o Blood from LV is ejected, across semi-lunar valve, into aorta
Muscle of left ventricle is thicker than right ventricle
o Pressure in aorta is higher than pulmonary artery
o Left ventricle must generate more pressure to overcome pressure of aorta
o Therefore, thicker muscle required in left ventricle
Atrioventricular (AV) valves
o Have fibrous strands (cordae tendinae) that attach to papillary muscles
o Papillary muscles contract during ventricular contraction
o Generate tension on valve via cordae tendinae to prevent AV valves from flapping back into atria
Semilunar valves do not have these attachments
Cardiac Cycle
Atria receive blood from veins and store it prior to each heart beat
Systole: period of contraction by heart muscle
Diastole: period of relaxation by heart muscle
Atrial systole
o Both atria contract and move blood across AV valves into ventricles
o This reduces volume of atria but increases pressure
- Pressure in Atria > Ventricle - forces A/V valve to open
Ventricular systole
o Contraction of ventricles increases pressure
o AV valves close as blood is forced against them → 1st heart sound
o This prevents backflow into atria
o Instead, blood is ejected into arteries through aortic and pulmonary valves
Ventricular diastole
o End of cardiac cycle, all chambers relax
o Aortic and pulmonary valves close → 2nd heart sound
o This prevents backflow into ventricles
o Atria fill up again to start next cycle
o Volume increases while pressure decreases
Electrical Activity
Heart has unique ability to beat (contract) on its own
Assisted by nerves and hormones in blood but can function without them
Sinoatrial (SA) node
o Located at the top right atrium
o Also known as the "natural pacemaker" controlling heart rate
o Increases with physical activity and decreases when relaxing
o Sends impulses across the atria to the AV node
o Cause contraction of atria
Atrioventricular (AV) node
o Located between atrium and ventricle
o Ventricles are isolated from atria
o Impulse must pass through AV node to travel across ventricles
AV node is connected to the Bundle of His
o Branches into a right bundle (to right ventricle) and left bundle (to left ventricle)
o Fibres that branch out to distant ventricles are called Purkinje Fibers
o Cause contraction of ventricles
Pressure Changes
Ventricular contraction
o Ventricles start to contract
o Intraventricular pressure rises and causes AV valves to close
o Ventricles are no longer filled with blood and volume says the same
o Pressure is not high enough to open semilunar valves
Pressure in LV > aorta
o Semilunar valves open
o Ventricular volume decreases
o Blood is ejected into aorta
Pressure in LV < aorta
o Back pressure causes blood to move back and semilunar valves to shut
Ventricular relaxation
o AV and semilunar valves are closed
o Lasts until pressure in atria > ventricles
Pressure atria > ventricles
o Ventricles are filled
o Atrial contraction/systole - final amount of blood is emptied into ventricles immediately prior to next phase of isovolumetric contraction of ventricles
Heart Disease
Atherosclerosis
· Hardening of arteries
o Tunica intima thickens with deposits of
- Cholesterol
- Fibrous (scar) tissue
- Dead muscle cells
- Blood platelets
o Arteries become less elastic and partially narrowed
- ↑BP which in turn accelerates atherosclerosis
- Leads to endothelium damage and weak walls
Mechanism
o Excess cholesterol leaks from lipoproteins (LDLs)
o Deposited on arterial walls
o Macrophages (white blood cells) are trapped within cholesterol
o Release free radicals which damage the arterial wall
o Activates blood platelets which stick to damaged areas releasing clotting factors (thromboxanes)
o Forms a plaque which may rupture to produce a thrombus
o Circulating thrombus is called an embolus
o Embolus may lodge elsewhere in the circulation (brain, heart arteries)
o NB: healthy arteries produce anti-clotting factors (prostaglandins) → don't form clots
Factors that aggravate atheroma formation / atherosclerosis:
o Hypertension (↑BP)
o Smoking (release of free radicals)
o High LDL and low HDL
o NB: they all cause endothelial damage
Aneurysm
· Weak arterial walls may burst leading to severe loss of blood (haemorrhaging)
· Brain aneurysm is called a stroke
Deep Vein Thrombosis
· Clots are formed by
o Endothelial damage (see atherosclerosis)
o Altered blood components (dehydration, too many platelets)
o Altered blood flow (stasis of veins) → this is what causes DVT
- Prolonged immobility
- Such as paralysis, long-distance flights, lying down for weeks after surgery
Thrombus often originates in calf veins
Inflammation of vein walls → destroys vein valves
Causes leg pain, swelling, and redness
Elastic support stockings required for life
Prevented by taking aspirin or warfarin which inhibit blood clotting
Coronary Heart Disease
Atherosclerosis causes arteries to become narrowed
o More force required to move blood through narrowed vessels
o Blood pressure increases
Stable angina
o ↑exercise leads to ↑oxygen requirements by heart
o Narrowed arteries prevent more blood to pass through
o Shortage of blood to heart muscle causes chest pain
o Cells do not die as some blood can still pass through
o Pain only occurs during activity but not at rest
Myocardial infarction (MI)
o Coronary artery is totally blocked by a thrombus/embolus
o No blood supply to heart muscle and cells die
o Irreversible if not treated within 90min
Heart failure
o Prolonged blockage of artery causes damage to heart muscle
o ↓contractions / ↓cardiac output / ↓pressure generated / less blood leaves heart
o More blood is stored:
- on the right side of the heart → enlarged heart
- in veins → swollen legs and enlarged liver
Lifestyle Cholesterol
Needed for
o Vitamin D production in skin
o Sex hormone production in gonads and adrenal glands
o Making cell membranes
o Produce bile acid (salts)
Has properties similar to fats → soft, waxy, and insoluble (difficult to remove if deposits form)
Transported in blood from liver to tissues
o Safe transport is needed due to its insolubility
o Achieved by lipoproteins, which are soluble fatty proteins
o These are wrapped around cholesterol
o Normally, only small amounts of free cholesterol escape
LDL
· Low density lipoproteins
· Carries cholesterol from liver to tissues
· Normally, some cholesterol 'leaks' from the lipoprotein and is absorbed to build cell membranes
· Excess LDL/cholesterol → too much cholesterol leaks out and causes atherosclerosis
HDL
· High density lipoprotein
· Picks up cholesterol from arterial walls and carries it away from tissues
· Travels to liver where cholesterol is removed with bile
Smoking
· ↓antitoxidants (vitamins), more damage due to release of free radicals by phagocytes
· [exam] Nicotine constricts arteries causing platelets to stick together → vasoconstriction → heart must work harder to force blood through → increases BP
· [exam] ↑BP causes damage to blood vessel lining / endothelium / collagen
o Leads to rise on blood platelets and makes them more sticky / form a plug / adhere to collagen fibres
o Release of thromboplastin/thrombokinase
o Fibrinogen converted to insoluble fibrin
o Platelet plug trapped by fibrin mesh
Raises conc. of fibrinogen (in blood) → increased risk of clotting
↑LDL causes more cholesterol to leak out in blood
Carbon monoxide reduces the efficiency of the blood in terms of carrying oxygen
o Haemoglobin combines with CO more readily than with oxygen → forms carboxyheamoglobin
o Associated with plaque formation
Principle CHD = heart muscle receives inadequate amount of blood or oxygen/(coronary) blood supply reduced
Treatment
Medication
o Beta blockers reduce heart rate and reduce oxygen required by heart
o Aspirin prevents blood clotting and thrombosis formation
o ACE inhibitors stabilize plaques → prevent thrombus to break off
o Statins reduce LDL and increase HDL
Angioplasty
o Deflated balloon-like device is passed up to the heart via the aorta
o Guided into damaged coronary artery and inflated to stretch the artery
Heart by-pass graft
o Leg veins and arteries from chest are used to by-pass the blocked region of the coronary artery
o Involves open heart surgery
Reperfusion therapy after a myocardial infarction
o Angioplasty done within 90 minutes of onset of chest pain
o May prevent irreversible damage to the heart muscle
Prevention
1. Screen population for
o High BP
o High cholesterol
o Uncontrolled diabetes
o Smoking? Unhealthy diet? No exercises?
o Men over 55 and women over 65 are at highest risk
2. Monitor the behaviour of the heart during exercise
o Difficult but encouraging the population to adopt a more healthy lifestyle from an early age is important
o Often leads to changes in diet and weight management
3. Giving up smoking and reducing alcohol intake
o Reduces blood pressure
o Coronary heart disease is a long-term degenerative disease, starts at birth
The Control Of the Heart Rate
Carbon Dioxide and Oxygen Transport
The Chemistry Society - Oxygen Transport
An Overview of the HeartHow the Heart works - an interactive lesson