Transport in Humans
Transport in Humans
Transport in Humans
In large organisms, diffusion is too slow for the efficient exchange of materials
needed for survival.
Transport system in mammals consists of the blood system and the lymphatic
system.
Blood is a fluid tissue made up of 55% plasma and 45% blood cells and platelets.
Plasma
Contains dissolved substances including some protein, mineral salts, food substances,
hormones (eg insulin) and excretory products (eg urea).
Does not have a nucleus and has a biconcave shape which increases surface area
to volume ratio, allowing absorption and release of oxygen at a faster rate.
Elastic and bell-shaped in or to squeeze through blood vessels smaller than itself.
Produced in the bone marrow and broken down in the spleen, releasing
haemoglobin which is broken down in the liver into iron (stored in liver) and bile
pigments (excreted into the gut in bile).
Features
• Colourless and does not contain haemoglobin
• Irregular in shape and contains nucleus
• Can change its shape and move
They play a vital role in keeping the body healthy by fighting diseases.
Blood groups
Functions of blood
Blood transports
• Oxygen and digested food to all parts of the body
• Excretory products to excretory organs
• Hormones to parts of the body where they are needed
• Distributes heat
In higher altitudes, oxygen levels are lower than at sea level. The body increases the
number of red blood cells and hence the haemoglobin content in the body to allow
more oxygen intake.
Clotting
An enzyme known as thrombokinase is released by damaged tissue and platelets
when blood vessels are damaged.
Immune system
Consists of white blood cells and their products.
Tissue rejection will not be a problem if the tissue to be transplanted comes form
the same person.
The heart
Muscular organ which drives blood
around the whole body.
Arterioles
Arteries branch to form tiny vessels
called arterioles which branch into
tinier blood vessels called
capillaries.
Venules
Before capillaries leave an organ or
tissue, they unite to form small
veins called venules.
Walls are one cell thick called the endothelium. The endothelium is partially
permeable, enabling selected substances to diffuse through quickly.
Capillaries branch repeatedly, lowering the blood pressure in the capillaries in order
to slow down the flow of blood, giving more time for the exchange of substances.
Arteries Veins
Carry blood away from the heart Carry blood towards the heart
High blood pressure, hence blood flows Low blood pressure, hence blood flows
in spurts more slowly and smoothly
Have think and elastic muscular walls Have thin and slightly muscular walls
Have a smaller lumen when compared Have a larger lumen when compared
to a vein of similar external diameter to an artery of similar external
diameter
Pulmonary circulation
From the heart, the pulmonary arteries carry the
blood to the lungs.
Systemic circulation
Oxygenated blood leaves the left side of the heart
and is distributed by arteries to all parts of the
body (except the lungs).
The heart
Structure
Four chambers
• Left atrium
• Left ventricle
• Right atrium
• Right ventricle
Path taken by blood through the heart a brief summary to prevent insane boredom
Deoxygenated blood from various parts of the body is returned to the right atrium.
When the right atrium contracts, blood flows into the right ventricle.
Oxygenated blood from the lungs is brought back to the left atrium by the
pulmonary arteries.
Both the atria and ventricles are relaxed. The left atrium receives blood from the
pulmonary arteries while the right atrium receives blood from the venae cavae.
The ventricles then relax, which is called the ventricular diastole. The drop in
pressure in the ventricles causes the semi-lunar valves in the two arches to close,
preventing back-flow of blood into the ventricles. The produces the softer ‘dub’ sound.
The drop in pressure in the ventricles also causes the bicuspid and the tricuspid valves
to open. The whole cycle then repeats.
Veins
• The hepatic vein returns blood from the liver to the heart
• The renal veins return blood from the kidneys to the heart
• The pulmonary veins return blood from the lungs to the heart
• The hepatic portal vein delivers blood from
the gut to the liver
Blood pressure is the force exerted by blood on the walls of blood vessels.
If the coronary arteries become blocked, blood supply to the heart is reduced,
resulting in either angina (chest pains usually in women) or heart attack.
A diet consisting mainly of saturated fats, smoking and stress can increases risks of
atherosclerosis and coronary heart disease.
Cutting down on the aforementioned activities and exercising regularly can reduce the
risk of coronary heart disease.
Chapter 8 - Transport in humans
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