Human Transport


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Transport in Humans

(Credits to Mustafa Asif)


Animal cells exchange material across the cell membrane

    • nutrients

    • fuels for energy

    • oxygen

    • waste (urea, CO2)

Importance of circulatory system

    • carries fluids and dissolved material throughout the body

    • cells are never far from body fluid

    • only a few cells away from blood

Circulatory system consists of

    • circulatory fluid = blood

    • tubes = blood vessels

    • muscular pump = heart

What substances are transported

    • nutrients

      • products from digestive sysem

    • respiratory

      • waste products from cells

      • water, salts, nitrogenous waste products (urea)

    • protection

      • blood clotting

      • immune defenses

      • white blood cells etc

    • regulation

      • hormones

Heart Valves

    • prevent backflow of blood as it circulates

    • comprises

      • right and left AV valves

      • semilunar valves

        • close as blood leaves the ventricles and enters the arteries

Blood pathway in body

    • Right side of heart

      • right ventricle pumps deoxygenated blood to lungs

    • Left side of heart

      • left ventricle pumps oxygenated blood to body

Blood pathway

Veins --> Vena cava --> Right atrium --> Right ventricle --> Pulmonary artery

Left atrium --> left ventricle --> Aorta --> Arteries --> Capillaries --> Veins

Cardiac cycle

    • about every 0.8sec

    • Diastole: heart relaxes and blood flows into chambers (0.4s)

    • Systole: Heart contracts

      • first atria (0.1s)

      • then ventricles (0.3s)


    • controls heart rate

    • regulated by nervous and endocrine systems

Heart Beat

    • two heart beat sounds: lub-dup

Structured Question Worked Solutions

1. Compare and contrast the structure of arteries and veins with reference to their functions.


    • Arteries carry blood away from the heart while veins carry blood back to the heart.

    • Arteries have thick muscular walls to withstand the high pressure of the blood being pumped out of the heart.

    • The walls are also elastic so that they can stretch and recoil, helping to push blood along the artery in spurts.

    • The blood pressure in the veins is much lower than in the arteries, and blood flows more slowly and smoothly in veins.

    • Hence the walls of veins are not as thick and muscular as those of arteries of about the same size. Veins also contain less elastic tissue.

    • Most veins have interval valves along their length to prevent backflow of blood. Arteries do not contain internal valves.

2. Describe the route taken by the blood from the intestine to the kidney. List all major blood vessels and organs involved.


Blood flows from the intestine via the hepatic portal vein to the liver, then via the hepatic vein and the posterior vena cava to the heart, then via the pulmonary artery to the lungs, then via the pulmonary vein back to the heart, and finally via the aortic arch and the dorsal aorta and the renal artery to the kidney.

3. The diagram below shows the transfer of materials between capillaries, lymph capillaries and tissue fluid. Describe what happens at points A and B.


    • Walls of capillaries are selectively permeable.

    • At A, plasma is driven out of the blood capillary by hydrostatic pressure.

    • Red blood cells and blood proteins are retained in the capillary.

    • Tissue fluid is formed from plasma.

    • Tissue fluid delivers nutrients to cells and removes waste products.

    • Soluble substances, for example, glucose, diffuse into cells. Cells give out waste products, for example, carbon dioxide, to the capillary at B.