• The heart organ is a?double pump
  • Oxygenated blood?from the lungs enters the?left?side of the heart and is pumped?to the rest of the body (the systemic circuit)
    • The left ventricle has a thicker muscle wall than the right ventricle?as it has to pump blood at high pressure around the?entire body,

     

  • Deoxygenated blood?from the body enters the?right?side of the heart and is pumped?to the lungs (the pulmonary circuit)
    • The right ventricle is pumping blood at lower pressure to the?lungs

     

  • A muscle wall called the?septum?separates the two sides of the heart 

   

• Blood is pumped?towards?the heart in?veins?and?away?from the heart in?arteries
• The?coronary?arteries?supply the?cardiac muscle tissue?of the heart with oxygenated blood
  • As the heart is a muscle it needs a constant supply of oxygen (and glucose) for aerobic respiration to release energy to allow continued muscle contraction

   

• Valves?are present to?prevent blood flowing backwards

Structure of the Heart

The pathway of blood through the heart

• Deoxygenated blood?coming from the body flows through the?vena cava?and into the?right atrium
• The?atrium?contracts?and the blood is forced through the?tricuspid (atrioventricular) valve?into the?right ventricle
• The ventricle?contracts?and the blood is pushed through the?semilunar valve?into the?pulmonary artery
• The blood travels to the?lungs?and moves through the capillaries past the alveoli where?gas exchange?takes place
  • Low pressure?blood flow on this side of the heart prevents damage to the capillaries in the lungs

   

• Oxygenated blood?returns?via the?pulmonary vein?to the?left atrium
• The?atrium contracts?and forces the blood through the?bicuspid (atrioventricular) valve?into the?left ventricle
• The ventricle?contracts?and the blood is forced through the?semilunar valve?and out through the?aorta
  • Thicker muscle walls of the left ventricle produce a?high enough pressure?for the blood to travel around the whole body

   

Control of the heart rate

• A heart rate is measured by counting the number of times a heart beats in a minute (bpm)
• The natural resting heart rate is controlled by a group of cells located in the right atrium called the?pacemaker
  • The role of the pacemaker is to?coordinate?the contraction of the heart muscle and regulate the heart rate
  • Pacemaker cells send out?electrical?impulses?which initiate a contraction in the cardiac muscle

   

• Other factors can also influence the heart rate, such as the? hormone?adrenaline 

Exercise and heart rate

• The heart pumps blood around the body in order to supply?oxygen and glucose?to?respiring cells
• The blood also removes?waste products?from the respiring cells
• During?exercise, the cells of the muscles?respire more?rapidly in order to provide energy for?muscle contraction
  • Respiration may be?aerobic?if exercise is moderate, or?anaerobic?is exercise is more intense

   

• An increase in respiration means an increase in requirement for oxygen and glucose as well as an increase in production of waste products that need to be removed
• The nervous system responds to this requirement by stimulating the following changes
  • Heart rate increases?to deliver oxygen and glucose and remove waste more frequently
  • The volume of blood pumped out?of the heart also increases to deliver bigger quantities of oxygen and glucose

   

• Production of the hormone?adrenaline?increases heart rate as part of a 'fight or flight' response
• At the end of a period of exercise, the heart rate may remain high for a period of time as?oxygen?is required in the muscles to break down the?lactic acid?from anaerobic respiration
  • This is how the?oxygen debt?is paid off

   

• The time taken for the heart rate to return to the resting rate is called the?recovery time
  • A physically fit person will have a?lower resting heart rate?and a?shorter recovery time?compared to an unfit person

   

Causes of coronary heart disease

• Like all cells in the body, cardiac?muscle cells?need a supply of blood to deliver?oxygen?and?glucose?and to remove waste products such as?carbon dioxide
• The blood is supplied to the heart by the?coronary arteries?which branch off directly from the aorta
  • The heart needs to constantly respire, so it is vital that it receives oxygen

   

The coronary arteries supply the heart with oxygenated blood

• In coronary heart disease?(CHD), layers of fatty material (plaque) build up inside the?coronary arteries
• These fatty deposits are mainly formed from?cholesterol
• There are two sources of cholesterol in the body:
  • Dietary cholesterol (from animal products eaten)
  • Cholesterol synthesised by the liver

   

Buildup of plaque in the coronary arteries narrows the lumen

• If a coronary artery becomes partially or completely blocked by these fatty deposits, it loses its?elasticity?and cannot stretch to accommodate the blood which is being forced through every time the heart contracts
• The flow of blood through the arteries is reduced, resulting in a lack of oxygen for the heart muscle
  • Partial blockage?of the coronary arteries creates a restricted blood flow to the cardiac muscle cells and results in severe chest pains called?angina
  • Complete blockage?means cells in that area of the heart will not be able to respire aerobically, leading to a?heart attack

   

• Treatment of CHD involves either increasing the width of the lumen of the coronary arteries using a stent, or prescribing statins to lower blood cholesterol

The effect of a narrowed lumen in a coronary artery is reduced blood flow to the heart

Risk factors of coronary heart disease

• There are several?risk factors?which will increase the chances of coronary heart disease:
• Obesity
  • Carrying extra weight puts a strain on the heart
  • Increased weight can lead to diabetes which further damages your blood vessels

   

• High blood pressure
  • This increases the force of the blood against the artery walls and consequently leads to damage of the vessels

   

• High cholesterol
  • Speeds up the build up of fatty plaques in the arteries leading to blockages

   

• Smoking
  • Chemicals in smoke cause an increase in plaque build up and an increase in blood pressure
  • Carbon monoxide also reduces the oxygen carrying capacity of the red blood cells

轉(zhuǎn)載自savemyexam