Transport in Human

• Veins carry deoxygenated blood back to the heart.
• Arterioles are small branches that lead into capillaries, which are tiny vessels where exchange between the blood and tissues occurs.
• The blood is pumped from the heart to all parts of the body through arteries.
• Arteries are thick-walled vessels that carry oxygenated blood away from the heart, while veins are thinner-walled vessels that carry deoxygenated blood towards the heart.
• Blood flows through the lungs to pick up oxygen and release carbon dioxide.
• The circulatory system consists of two circuits - pulmonary circuit (right side) and systemic circuit (left side).
• Capillary beds have high surface area-to-volume ratios, allowing for efficient gas exchange.
• Circulatory System


  Made up of pump, heart & a system of interconnecting tubes called blood vessels along which blood flows
• Circulatory System


  • Valves in the heart & blood vessels ensure that blood flows in 1 direction only
  • Double circulatory system
  • Blood passes through the heart twice in 1 complete turn round the body
• Pulmonary circulation


  1. Flow of blood from heart to lungs & back to heart

  2. Blood pressure is lower to prevent damage to lungs tissues & ensure efficient gas exchange in lungs
• Systemic circulation


  1. Flow of blood from heart to all body parts (except lungs) & back to heart

  2. Blood pressure is much higher to ensure that blood reach all body parts at faster rate to support metabolic rate of body
• Blood


  Liquid connective tissues containing liquid part plasma & blood cells<|>Average adult has about 5 litres of blood
• Plasma


  Pale yellow liquid composed of about 90% water & dissolved substances (10%)<|>To transport these dissolved substances as well as blood cells to all body parts
• Blood proteins or Plasma proteins

  • Fibrinogen: involved in blood clotting
  • Antibodies: involved in defense against germs
  • Albumin: involved in maintaining a suitable water potential of blood
• Components of blood and their sources and destinations

  • Water: Absorbed in small intestine & colon, to all cells, excess removed by kidneys
  • Proteins (fibrinogen & antibodies): Fibrinogen made in liver, antibodies made by lymphocytes, remain in blood
  • Lipids: Absorbed in ileum, also derived from fat reserves in the body, to liver for breakdown, to adipose tissue for storage
  • Carbohydrate (glucose): Absorbed in ileum, also produced by breakdown of glycogen in liver, to all cells, for energy release by respiration, excess converted to glycogen & stored in liver
  • Excretory substances (urea): Produce by amino acid deamination in liver, to kidneys for excretion
  • Mineral ions(Na+, Cl-): Absorbed in ileum & colon, to all cells, excess ions excreted by kidneys
  • Hormones: Secreted into blood by endocrine glands, to all parts of body, broken down by liver, remains excreted by kidneys
  • Dissolved gases (CO2): CO2 is released by cells as waste product of respiration, to lungs for excretion, most CO2 carried as hydrogencarbonate ions in bld plasma
• Red Blood Cells


  Biconcave, disc shaped without nucleus<|>Cytoplasm has a red iron containing haemoglobin<|>About 0.08 mm<|>Produced in red bone marrow of long & flat ones (rib)<|>Life span: about 4 months, they are destroyed in liver & spleen<|>Haemoglobin combines with oxygen in places where there is ↑ concentration of oxygen to form oxy-haemoglobin<|>Blood with large amount of oxyhaemoglobin = oxygenated blood<|>Blood with little oxyhaemoglobin = deoxygenated blood
• White Blood Cells


  About 0.01 mm<|>Have nucleus<|>Life span: few days only<|>Number increases during infection<|>Formed in bone marrow (lymphocytes undergo maturation in thymus glands after its formation in bone marrow)
• Types of White Blood Cells

  • Phagocytes: Irregular shape, lobed nucleus, granular cytoplasm, ingest biggest & damaged cells by phagocytosis and digest them
  • Lymphocytes: Regular shape, large spherical nucleus, clear cytoplasm, Produce antibodies that kills invading bacteria & viruses and neutralize toxins release by them, Antibodies immobilize bacteria by attaching to their flagella, Involved in tissue rejection that occurs during transplantation of tissues or organs
• Platelets


  Fragments of cells produced in bone marrow<|>No nucleus<|>About 300,000 per mm3 of blood<|>Between 5-8 days before being destroyed by phagocytes<|>Help in blood clotting preventing bleeding at wound<|>When platelets are exposed to air, they break up to release an enzyme<|>The enzymes in presence of calcium ion & vitamin K, converts soluble plasma protein fibrinogen into insoluble fibrin threads<|>The network of fibrin threads trap R.B.C to form a clot at wound to stop further bleeding & prevent entry of germs into the body
• Blood Vessels


  • Arteries: Carry blood away from heart to body tissues under high pressure, Smaller arteries are called arteriole, Thick layer of elastic tissue in their walls allows arteries to expand when a large volume of blood is pumped by heart into them, Thick layer of muscular tissue & collagen fibres give strength to their wall to withstand the high blood pressure and to prevent bursting of arteries, No valves (except in arteries leaving heart) as blood is under constant pressure, The narrower lumen maintains a high blood pressure
  • Veins: Elastic tissue in its wall is relatively thin as pressure along them is too low to create a recoil action, Muscular wall is relatively thin as there is no need for thick wall as pressure within veins is low, Presence of valves prevents backflow of blood, The wider lumen reduces resistance to blood flow, allowing blood to move easily through them, Has tunica
  • Capillary: Wall is one-cell thick making them extremely thin for rapid diffusion of materials between blood & body cells, Highly branched thus providing a large surface area for diffusion, Narrow diameter & can penetrate every part of body to reach body cells, Lumen is very narrow so R.B.C are squeezed against the side of capillary for easy diffusion of gases
• Comparison of Blood Vessels

  • Arteries: Carry oxygenated blood away from heat at high pressure (except pulmonary artery), Thick, strong wall contains muscles, elastic fibres & fibrous tissue, Narrow lumen, Absent valves
  • Capillaries: Supply all cells with their requirements, Very thin wall, one-cell thick, Very narrow lumen, Absent valves
  • Veins: Carry deoxygenated blood to heart at low pressure (except pulmonary vein), Thin wall, mainly fibrous, contains less muscle & elastic tissue than arteries, Wide lumen, Present valves
• Formation of Tissue Fluid

  1. The high blood pressure at the arteriole end of a capillary, forces small molecules in plasma across tiny pores in capillary wall into spaces surrounding body cells

  2. The fluid which is thus formed is called tissue fluid

  3. Contains less protein

  4. R.B.C, lymphocytes, blood platelets & plasma protein are too large to pass across capillary wall and hence are absent in tissue fluid

  5. Phagocytes can change shape & squeeze through capillary wall

  6. The nutrients & oxygen will then diffuse from tissue fluid into body cells and metabolic wastes like carbon dioxide will pass from body cells into tissue fluid

  7. At the venule end of capillary, the high osmotic pressure of blood absorbs back into the capillary, tissue fluid containing metabolic waste & other substances

  8. Most of the tissue fluid passes back into capillaries at venous end of capillary

  9. But a certain amount drains into another vessels called lymph vessel

  10. The fluid carried in these are called lymph

  11. Lymph has less protein & more fat and fatty acid

  12. The lymph vessels eventually return the lymph to blood in subclavian vein near the heart
• Heart


  Muscular organ lying behind sternum in between the 2 lungs<|>Approximately size of a clenched fist<|>Has 4 chambers: 2 upper thinner-walled chambers called atria, 2 lower thicker-walled chambers called ventricles<|>Right side of heart is separated from left by means of muscular wall called median septum<|>The 2 atria have thinner muscular walls as they have to pump blood to a very short distance to the ventricles only<|>The ventricles have to pump blood over longer distance, their thicker muscular walls allow them to produce a greater pressure on blood when they contract<|>The right ventricle has comparatively thinner muscular wall than the left one, as it has to pump blood to lungs only & these are at a short distance from heart<|>The comparative thicker wall of left ventricle enables it to exert a higher pressure on blood when it contracts as it has to pump blood over long distances to reach all body parts<|>A system of valves prevent backflow of blood & ensures that blood flows through heart in 1 direction only
• Cardiac Cycle


  1. Atrial diastole: The 2 atria relax & fill with blood

  2. Atrial systole: The 2 atria contract together to pump blood into ventricles

  3. Ventricular systole: The 2 ventricles contract at same time to pump blood out of heart

  4. Ventricular Diastole: The ventricles relax & fill with blood
• Each cardiac cycle lasts about 0.8 s
• Phases of Cardiac Cycle

  • B C: bicuspid valve close
  • S O: semi-lunar valve open
  • S C: semi-lunar valve close
  • D O: bicuspid valve open
• Electrocardiogram (ECG)


  A test that records rhythm, the rate & electrical activity of the heart during each cardiac cycle<|>Small sticky patches called electrodes are put on your arms, legs & chest, connected by wires to an ECG machine that picks up electric signal that make your heart beat
• Pulse


  Pulse rate: number of times an artery expands & recoils in 1 minute<|>When the ventricles contract to pump blood into arteries, the latter dilate. After each dilation, the elastic walls of the arteries recoil & force blood along as a series of waves. Each expansion of arteries can be felt as a pulse & it is produced after every ventricular systole<|>During physical activities pulse rate increases as the heart pumps blood faster to lungs to provide all muscles with oxygen more quickly
• Coronary Heart Disease (CHD)

  Occurs when coronary arteries that supply the heart with nutrients & oxygen is blocked with fatty deposits and blood clots<|>Fats & cholesterol carried in blood can be deposited on inner wall of major arteries such as coronary arteries, narrowing their lumen<|>Such deposit (atheroma) reduces blood supply to heart<|>Can cause pain in chest (angina)<|>Rough surface of atheroma increases risk of formation of blood clot in coronary arteries (coronary thrombosis)<|>This may completely block blood supply to heart muscle, resulting it to not being able to contract causing a heart attack
• Risk Factors of CHD

  • Eating food rich in saturated fat & cholesterol: these will be deposited inside arteries lining forming an atheroma
  • Cigarette smoking: carbon monoxide may damage the lining of arteries, increasing risk of formation of atheroma, nicotine increases the tendency for blood to clot
  • Stress: causes release of adrenaline that constricts artery wall leading to rise in blood pressure, high blood pressure damage the lining of arteries leading to formation of atheroma inside them
  • Lack of exercise: a sluggish blood flow (resulting from lack of exercise) may allow atheroma to form in arterial lining
  • Age: heart diseases can happen at any age, but the risk goes up as we age
  • Gender: men have a higher risk of getting heart attacks
  • Heredity: children with parents with heart disease are more likely to develop heart diseases themselves
• Preventive measures for CHD

  • Eat a healthy diet: can help to lower blood pressure & cholesterol
  • Get regular exercise: help to maintain a healthy weight, lower cholesterol and blood pressure
  • Stay at a healthy weight: Being overweight can increase risk for heart diseases
  • Keep cholesterol & triglyceride level under control: high levels of cholesterol & triglyceride can clog your arteries and increase risk of coronary artery disease
  • Limit alcohol: drinking too much can increase blood pressure
  • Don't smoke: raises your blood pressure
  • Manage stress
• Blood circulation


  1. Through blood vessels

  2. Closed circulation

  3. Blood flows by pumping action of heart

  4. Closed system of blood vessels

  5. Blood is kept moving
• Blood vessels


  Arteries, veins and capillaries
• Arteries


  • Carry oxygenated blood away from heart
  • Large artery leaving left side of heart is aorta
  • Arteries branch to form smaller arteries
  • Arterioles divide to form capillaries
  • Total cross-sectional area increases, lowering blood pressure in capillaries
  • Blood flow slowed down, allowing more time for exchange of substances
• Arteries


  • Thick outer wall
  • Narrow lumen
  • Wavy elastic membrane
  • Thick layer of muscles and elastic fibres
  • Thick muscular walls resist high pressure from heart
  • Elastic layer maintains high blood pressure
  • Contraction and relaxation of muscles allows constriction and dilation
  • Blood under high pressure
  • Rapid blood flow in spurts
  • Absence of valves
  • Carry oxygenated blood except pulmonary arteries
• Veins


  • Carry deoxygenated blood from body to heart except pulmonary veins
  • Thin layer of muscles and elastic fibres
  • Blood flows slowly under low pressure
  • Absence of pulse
  • Presence of valves to prevent backflow
  • Movement assisted by skeletal muscle action
• Capillaries


  • Thin-walled (one cell thick)
  • Carry blood from arterioles to venules
  • Endothelium is selectively permeable
  • Divide repeatedly to provide large surface area for exchange
  • Thin walls and large surface area allow more time for exchange of substances
  • Absence of pulse
  • Absence of valves
• Heart


  • Pumping organ made of cardiac muscle
  • Protected by ribs and sternum
  • Has 4 chambers - 2 atria and 2 ventricles
  • Atria have thin walls, ventricles have thick walls
  • Right atrium receives deoxygenated blood, left atrium receives oxygenated blood
  • Right ventricle pumps blood to lungs, left ventricle pumps blood to body
  • Valves prevent backflow of blood
  • Chordae tendinae attach valves to ventricle walls
  • Median septum separates right and left sides
• Cardiac cycle


  1. Atria relax to receive blood

  2. Atria contract to force blood into ventricles

  3. Ventricles contract to pump blood out

  4. Ventricles relax to receive blood

  5. Cycle repeats
• Cardiac cycle lasts about 0.8 seconds, average heart rate is 72 beats per minute