w.g. Igcse Transport in Humans (2)

7/31/2019 w.g. Igcse Transport in Humans (2)

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TRANSPORT IN HUMANS

7.2.Transport in humans

Core Describe the circulatory system as a system of tubes with a pump and valves to ensure one -way flow of

blood Describe the double circulation in terms of a low pressure circulation to the lungs and a high pressure

circulation to the body tissues and relate these differences to the different functions of the two circuits

7.2.1 Heart

Core Describe the structure of the heart including the muscular wall and septum, chambers, valves and

associated blood vessels Describe the function of the heart in terms of muscular contraction and the working of the valves Investigate, state and explain the effect of physical activity on pulse rate Describe coronary heart disease in terms of the blockage of coronary arteries and state the

possible causes (diet, stress and smoking) and preventive measures.

7.2.2 Arteries, veins and capillaries

Core Name the main blood vessels to and from theheart, lungs, liver and kidney Describe the structure and functions of arteries, veins and capillariesSupplement Explain how structure and function are related in arteries, veins and capillaries Describe the transfer ofmaterials between capillaries and tissue fluid

7.2.3 Blood

Core Identify red and white blood cells as seen under the light microscope on prepared slides, and in

diagrams and photomicrographs List the components of blood as red blood cells, white blood cells, platelets and plasma State the functions of blood: red blood cells haemoglobin and oxygen transport white blood cells phagocytosis and antibody formation platelets causing clotting (no details) plasma transport of blood cells, ions, soluble nutrients, hormones, carbon dioxide, urea and plasma-

Proteins

Supplement

Describe the immune system in terms ofantibody production, tissue rejection and phagocytosis Describe the function of the lymphatic system in circulation of body fluids, and the production of-

lymphocytes Describe the process of clotting (fibrinogen to fibrin only)


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Transport in humans

The main transport system of humans is the blood system, also known as the

circulatory system.

Human circulatory system is made up of a pump called the heart, a net work of tubes

called blood vessels, and the blood.

Functions of circulatory system:

It transports useful things like oxygen from the lungs to the cells and digested food from

the small intestine to the cells.

It removes waste chemicals like carbon dioxide from the cells to the lungs and other

wastes from cells to the kidneys.

It transports hormones, antibodies and blood proteins.

Blood circulation:

The heart is the pump which circulates the blood through the blood vessels. Blood flows in arteries away from the heart to the different organs of the body. Blood

flows back to the hearty in veins.

Arteries are connected to veins by means of the smallest blood vessels called capillaries.


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The circulatory system allows a one-way flow of blood around the body.

The heart pumps blood giving it pressure so that it flows inside arteries and this helps to

maintain a one-way flow. This is good for getting blood to the capillaries.

We have valves called semi-lunar valves in our veins to make sure blood does not flow

backwards away from the heart. If this happened, blood would collect in veins, which

would swell, preventing proper circulation. These valves open when the pressure of theblood pushes against them, but they close when blood flows back to fill the pockets.

Double circulation:

Humans have a double circulatory system because the blood travels through the heart twice

during one complete circuit around the body. It includes a low pressure circulation to the lungs

and a high pressure circulation to the body tissues.

The heart is divided into two halves: right and left. The two halves are separated by a thick wall

of muscle called septum. It stops blood in the right side of the heart mixing with blood in the

left side.

The right side of the heart pumps blood to the lungs and back to the heart again. The pressure

need to force blood to the lungs is not very high because there is little resistance to flow in the

lungs as there is a spongy tissue filled with air. As blood flows through the capillaries in the


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lungs, gas exchange occurs. Blood absorbs oxygen and loses carbon dioxide. The blood that

flows through the lungs is rich in oxygen so it is called oxygenated blood and it is bright red in

color.

The left side of the heart pumps blood to the rest of the body and back to the heart again. The

pressure of blood leaving the left side is much greater than on the right side because there ismuch more resistance to flow than there is through the lungs. Gas exchange occurs as blood

flows through capillaries in organs such as muscles, the gut, liver and kidneys. Oxygen leaves

the blood and carbon dioxide enters. Blood that leaves capillaries and flows through veins

contains less oxygen and is called deoxygenated blood. It is dark red in color but is always

shown as blue in diagrams.

The double circulatory system helps to maintain blood pressure and making circulation

efficient

Structure of the heart:

It is a pump made of a special type of muscle called cardiac muscle. This muscle

contracts and relaxes regularly throughout life.


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The muscle is constantly active, so it needs its own blood supply, through the coronary

arteryto provide it with oxygen and glucose. Coronary arteries are present on the

surface of the heart.

The heart has two sides-the right side receives deoxygenated bloodfrom the body and

pumps it to the lungs for oxygenation while the left side receives oxygenated blood

from the lungs and pump it to the body. The heart is divided into 4 chambers-the two upper chambers are called atria and the

two lower chambers are called ventricles.

The chambers on the left side are completely separated from the ones on the right side

by the septum which prevents deoxygenated blood on the right side mixing with

oxygenated blood on the left side.

Both of the atria receive blood. The left atrium receives blood from the pulmonary

veins, which comes from the lungs. The right atrium receives blood from the rest of the

body, arriving through the vena cavae.

When the atria contract, they pump blood into ventricles.

When the ventricles contract, they pump blood out into arteries at higher pressure. Theblood in the left ventricle is pumped into the aorta, which takes blood around the body


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The right ventricle pumps blood into thepulmonary artery, which takes it to the lungs.

The ventricles have much thicker, more muscular walls than the atria. It helps them to

pump blood out of the heart and all around the body.

The wall of the left ventricle is much thicker than that of the right ventricle. This is

because the right ventricle pumps blood to the lungs, which are very close to the heart

But the left ventricle pumps blood all around the body and has to overcome more

resistance to flow. The thick wall helps to generate greater pressure to pump blood all

around the body.

Between each atrium and ventricle is a valve called AV valves, which prevent the blood

flowing back in to the right and left atrium when the right and left ventricles contract.

The AV valve between the right atrium and the right ventricle is called tricuspid valve

and that between the left atrium and left ventricle is called bicuspid valve or mitralvalve. There are tendons attached to the valves which stop the valves from going up too

far as the ventricles contract.

The place where the pulmonary artery and aorta opens in to the ventricles, there are

valves called semilunar valves which prevent the back flow of blood from these arteries

back to the ventricles.

Working of human heart (pumping of blood by the heart):

The heart pumps blood when its muscles contract. Contraction of the heart muscles is

called systole. When they contract, the heart becomes smaller and squeezes the bloodout.

After contraction, the heart muscles relax. When they relax, the heart becomes larger,

allowing blood to flow into the atria and ventricles. Relaxation of the heart muscles is

called diastole.

One systole and one diastole together called a heartbeat.

The normal healthy heart beats 70 times per minute.


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The rate at which the heart beats is controlled by a patch of muscle in the right atrium

calledpace maker. It sends electrical through the walls of the heart at regular intervals

which make the muscle contract.

Cardiac cycle: the changes that occur in the heart during one heart beat. It involves three

changes-diastole, atrial systole and ventricular systole.

Diastole: During this process:

All muscles of the heart chambers are relaxed. Blood flows into the heart.

The muscles of the atria relax allowing blood to flow into the heart from the veins- from

the body to the right atrium via vena cava and from the lungs to the left atrium via

pulmonary vein.

The AV valves open

The semilunar valves shut, preventing blood from flowing into the ventricles

Atrial systole:

The muscles of the atria contract. The muscles of the ventricles remain relaxed. Blood is forced from the atria into the ventricles through the open AV valves.

The semilunar valves remain shut.

The valves in the veins are forced to shut by the pressure of the blood, stopping the

blood from flowing back into the veins.


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Ventricular systole:

The muscles of the atria relax. The muscles of the ventricles contract.

Blood is forced out of the ventricles into the arteries- from the right atrium into the

pulmonary artery and from the left ventricle into the aorta.

The AV valves are forced shut by the pressure of the blood.

The semilunar valves are forces open by the pressure of the blood.

Investigate, state and explain the effect of physical activity on pulse rate.Describe coronary heart disease in terms of the blockage of coronary arteries and state thepossible causes (diet, stress and smoking) and preventive measures.

Effect of physical exercise on pulse rate:

The heart beats about 70 times a minute.

During exercise the heart rate increases to supply the muscles with more oxygen and

glucose and removing carbon dioxide quicker. These are needed to allow the muscles to

respire aerobically, so they have sufficient energy to contract.

Regular exercise is important to keep the heart muscle in good tone. This results in the

heart being more efficient in maintaining blood pressure and reduces the risk of coronary

heart disease and stroke.

How to measure the rate of heart beat:

The best way to measure the rate of heart beat is to take the pulse.

Use the first two fingers of your right hand and rest them on the inside of your wrist.

Feel for the tendon near the outside of your wrist.

If you rest your fingers lightly just over this tendon, you can feel the artery in your wrist

pulsing as your heart pumps blood through it.

Coronary heart disease:

Heart disease caused by blockage of coronary arteries that supply heart muscles with

blood.

Heart muscles need oxygen and glucose to keep it contracting. These are transported to

the heart in the coronary arteries.

If a coronary artery gets blocked-for example, by a blood clot-the cardiac muscles run

short of oxygen and glucose. They cannot obtain energy to allow them to contract. The

heart therefore stops beating. This is called a heart attack or cardiac arrest.


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Risk factors for CHD (Factors that increase a persons risk of getting coronary heart disease):

Cause Explanation Preventive measure

Diet: eating a diet with too

much saturated(animal) fat

Leads to cholesterol which

deposit in arteries, finally

blocking the blood vessel orallowing a blood clot to form

Eat a diet containing a very

wide variety of foods with

little fat in it. Use oils fromplants, and fish. Eat more

fresh fruits and vegetables.

Eat less red meat. Reduce

fried foods

Smoking Nicotine present in the cigarette

smoke cause damage to the

heart and blood vessels.

Stop smoking

Obesity Being overweight puts extra

strain on the heart and makes it

more difficult for the person toexercise.

Go on a controlled diet and

take regular exercise

Stress Tends to increase blood

pressure, which can result in

deposition of fatty materials in

the arteries.

Find ways of relaxing. Identify

the causes of stress and avoid

them.

Inherited factors (genes) Heart disease appears to be

passed from one generation to

the next in some families.

Make sure other factors do

not increase the risk of heart

disease. Monitor health.

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The main blood vessels to and from the heart, lungs, liver and kidney:

Vessel Organs

heart lungs liver kidneys

Bringing blood to

organ

Venacava to

right atrium;pulmonary vein

to left atrium

Pulmonary

artery

Hepatic artery;

hepatic vein

Renal artery

Taking blood

away from organ

Pulmonary

artery from right

ventricle; aorta

from left

ventricle

Pulmonary vein Hepatic vein Renal vein


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Structure and functions of arteries, veins and capillaries:

Arteries carry blood at high pressure, away from the heart to organs of the body.

They divide again and again and finally form very tiny vessels called capillaries.

Capillaries supply all cells with requirements like oxygen, glucose etc. and take away

waste products like carbon dioxide (exchange of materials). The capillaries gradually join up with one another to form large vessels called veins.

Veins return blood at low pressure from organs towards the heart.

Arteries:

Wall is thick and strong containing muscles and elastic fibres.

Narrow lumen

Smooth lining

Valves absent

Capillaries:

Permeable wall, one cell thick, with no muscle or elastic tissue.

Very narrow lumen, just wide enough for a red blood cell to pass through.

Presence of pores between the cells in the wall.

Valves absent.


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Veins:

Thin wall, containing very less muscle and elastic tissue than arteries.

Wide lumen.

Valves present

How the structure and functions are related in arteries, veins and capillaries

Blood vessel structure How structure is related to function

Artery 1. Thick and strong wallcontaining

muscles and elastic fibres.

2. Lumen very narrow, but

increases as a pulse of blood

passes through.3.Valves absent

1.Helps to carries blood at high

pressure.

1. Prevent bursting and maintain

pressure wave.

2. helps to maintain blood pressure.

3. high pressure prevents bloodflowing back.

Vein 1. Thin wall containing very less

muscle and elastic tissue than

arteries.

2. wide lumen

3. valves present

1. carries blood at low pressure.

2. reduce resistance to blood flow.

3. prevent back flow of blood

Capillary 1. very thin, permeable, one cell thick

wall with no muscle or elastic fibres.

2. very narrow lumen, one red blood

cell wide.

3. valves absent

4.pores present between cells in the

wall

1. allows diffusion of materials

between capillary and surrounding

tissues.

2. white blood cells can squeeze

between cells of the wall.

3. blood cells pass through slowly to

diffusion of materials and tissue

fluid.

4. allows easy diffusion of materials.


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Transfer of materials between capillaries and tissue fluid:

Tissue fluid: it is the fluid that surrounds all the cells in the body, formed from blood plasma

that leaks out of capillaries.

Formation of tissue fluid: When blood at high pressure flowing through the capillaries reach

body tissues, some of the constituents of the blood plasma and some white blood cells move

out through the small gaps in the capillary walls. The fluid formed in this way is called tissuefluid. It surrounds all the cells in the body. Red blood cells cannot get out because they are too

large and cannot change their shape to pass through the wall.

Function of tissue fluid: It helps substances to diffuse into and out of cells. Useful substances

like glucose,amino acids, fatty acids, vitamins, ions and oxygen pass from tissue fluid into

cells. Carbon dioxide and waste chemicals like urea and excess ions pass out of the cells intothe tissue fluid.


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7.2.3 BloodCore Identify red and white blood cells as seen under the light microscope on prepared slides, and in

diagrams and photomicrographs List the components of blood as red blood cells, white blood cells, platelets and plasma

State the functions of blood: red blood cells haemoglobin and oxygen transport white blood cells phagocytosis and antibody formation platelets causing clotting (no details) plasma transport of blood cells, ions, soluble nutrients, hormones, carbon dioxide, urea and plasma

Proteins.Supplement Describe the immune system in terms of antibody production, tissue rejection and phagocytosis Describe the function of the lymphatic system in circulation of body fluids, and the production of

lymphocytes Describe the process of clotting (fibrinogen to fibrin only)----------------------------------------------------------------------------------------------------------------------------- ---------------

Blood:

Composition of blood: Blood is made of a liquid called plasmain which 3 types of blood cells-red blood cells, white blood cells and platelets- are suspended.


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Functions of blood:

1. Blood plasma: It is the liquid part of the blood which forms 50% of blood volume.

Its functionis transportof blood cells, mineral ions like sodium and chloride ions, solublenutrients like amino acids, glucose, lipids and vitamins, hormones like insulin, glucagon etc.,carbon dioxide, urea and plasma proteins. It acts as a pool for amino acidsand containsblood proteins that are important in blood clotting.

Main substances carried by plasma:

Substances carried inplasma

from to

Amino acids Small intestine Sites of growth and repair

Carbon dioxide Respiring tissues lungs

Glucose Small intestine All tissues

Heat Liver, muscles All tissues

Hormones eg. Insulin Endocrine glands, eg.pancreas

Target organ, eg.liver

urea liver kidneys

2. Red blood cells: Their cytoplasm contains haemoglobin which transport oxygen from thelungs to the respiring tissues.

3. White blood cells:phagocytosis (fight diseases by surrounding bacteria and engulfing

them), and antibody production.


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4.platelets:form blood clots, which stop blood loss at a wound and prevents the entry of

germs into the blood.

Process of blood clotting:

When a blood vessel is cut, the blood platelets bump into the rough edges of the cut,

and react by releasing a chemical.

The chemicals released by the platelets and the damaged tissues set off a chain ofreactions which cause the fibrinogen, a soluble protein in the blood plasma, to change

into insoluble fibrin.

Fibrin forms fibres which form a mesh across the wound.

Red blood cells and platelets get trapped in the tangle of fibrin fibres, forming a blood

clot.

Advantages of blood clotting:

stops too much blood loss at a wound.

Stops pathogens getting into the body through breaks in the skin.

Differences between red blood cells and white blood cells:

Red blood cells White blood cells

More in number (5 million in every mm3) than

WBCs.

Very less in number than RBCs

Contain the pigment haemoglobin Haemoglobin absent

nucleus absent Nucleus present

Biconcave disc shaped No definite shape

Live only for 120 days as they have no nucleus Can live more than 120 days

Only one type of cells Two types-phagocytes and lymphocytes

Transport oxygen Fight pathogen, and clear up dead body cells


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Structural adaptations of RBCs for oxygen transport:

Contain haemoglobin which carries oxygen. Nucleus absent so more space for packing in haemoglobin.

Biconcave disc shape and small size give them large surface area compared with

their volume which speeds up rate of diffusion of oxygen.

IMMUNE SYSTEM

The function of WBCs is to fight pathogens (disease-causing bacteria and

viruses), and to clear up any dead body cells. There are many different kinds of WBCs. They all have the function of destroying

pathogens in our body, but they do it in different ways.

Generally there are two types of WBCs present in the blood; they are phagocytes

and lymphocytes.

Phagocytes:

A phagocyte cell

- larger than lymphocytes

- have lobed nucleus

- can move around the body, engulfing and destroying pathogens by a process

called phagocytosis.

Phagocytosis:


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Lymphocytes:

A lymphocyte cell

- smaller than phagocytes.

- have large spherical nucleus.

- function is to produce chemicals called antibodies, which are carried in the

blood to every part of the body which can destroy pathogens.

Function of lymphocytes:


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In our body, we have 1000s of different kinds of lymphocytes. Each kind is able

to produce a different type of antibody.

An antibody is a protein molecule with a particular shape and this shape is just

right to fit into another molecule on the outside of the pathogen. These

pathogen molecules are called antigens. When a pathogen enters the body, its antigen is recognized by one particular

type of lymphocyte.

This lymphocyte will start to divide repeatedly by mitosis, making a clone of the

same type.

These lymphocytes then produce their antibody, destroying the pathogen.

Antibodies attack the pathogens in a number of ways:

They make them stick together (agglutinate).

They dissolve their cell membranes.

They neutralize the toxins (poisons) that some pathogens produce.

Alert phagocytes to the presence of pathogens so that phagocytes will come anddestroy them.


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The fig. 4.2 shows the action of WBCs when bacteria enters the body.

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w.g. Igcse Transport in Humans (2)