BIOLOGY FORM 5 NOTES CHAPTER 1 : TRANSPORT

CHAPTER 1: TRANSPORT

1.1  THE IMPORTANCE OF HAVING A TRANSPORT SYSTEM IN SOME MULTICELLULAR ORGANISMS

1.    The distribution of food and oxygen throughout the body of all living organisms and the removal of waste products such as carbon dioxide is performed by a transport system.

2.    The rate of exchange of substances in an organism depends on:

(a)  The total area to volume (TSA/V) ratio

-          The larger the TSA/V ratio, the faster the diffusion of substances

(b)  The distance between the source of substances and the body cells

-          The smaller the distance between the source of substances and the body cells, the faster the diffusion of substances

(c)  The concentration gradient between the source and the body cells

-          The higher the concentration gradient between the source and the body cells, the faster the diffusion of substances

3.    In unicellular organisms with large TSA/V ratio, oxygen can diffuse through the cell surface and reach the center of the cell easily. Similarly, waste products can be rapidly removed from the cell by simple diffusion.

4.    Why the large multicellular organisms cannot depend on simple diffusion through the body surface alone to supply the oxygen and nutrients needed by the cells?

(a)  The total area to volume (TSA/V) ratio is smaller

(b)  The cells are situated far away from the external environment

1.2  THE CIRCULATORY SYSTEM

1.    The role of the circulatory system:

(a)  to transport nutrient and oxygen to cells

(b)  to carry the waste materials away from cells

(c)  to protect the body against infection

2.    Three major components of the circulatory system:

(a)  Blood – a type of connective tissue made up of liquid plasma, suspended blood cells and platelets

(b)  Heart – a muscular pump that circulates blood throughout the body

(c)  Blood vessels –branched vessels consisting of arteries, capillaries and veins.

1.2.1      Blood and Haemolymph

1.    Blood – is the medium of transport in humans and animals

2.    Haemolymph is the blood-like nutritive fluid fills the entire body cavity (haemocoel) of arthropods such as insects, and surrounds all cells

3.    The functions of blood:

(a)     transports oxygen from lungs to the cells throughout the body, and carbon dioxide from the cells to the lungs

(b)     transports nutrients, hormone and waste products

(c)     helps to regulate the pH of body fluid, the body temperature and the water content of cells

(d)     blood clots to protect the body against excessive blood loss following in injury

(e)     protects the body against diseases

4.    The functions of haemolymph:

(a)     transports water, inorganic salts and organic compounds throughout the haemocoel

~ unlike blood, haemolymph does not transport respiratory gases.

5.    The composition of human blood

Constituents	Major Function
Water
Ions -          sodium, potassium, magnesium, calcium, chloride, and bicarbonate
Plasma proteins: Albumin Fibrinogen Immunoglobulins
Hormones
Dissolved substances -          nutrients such as glucose, vitamins, waste products and respiratory gases
Erythrocytes
Leucocytes
Platelets

Erythrocytes (Red blood cells)

-          It is shaped like biconcave disc. It is thinner at the center than its edges. It is small, about 7.5 micrometre in diameters.

(to provide a large surface area to volume ratio for gases exchange)

-          It does not have nucleus.

(to contain more haemoglobin, about 250 million haemoglobin in each erythrocytes)

-          Haemoglobin is an oxygen-carrying pigment which gives the erythrocytes red colour.

-          It is elastic, it can squeeze through capillaries smaller than itself in diameter.

-          There are about 5,000,000 red blood cells in each cubic millimeter of blood

-          The life span of an erythrocyte is only 120 days. When they are worn out, they are destroyed in the spleen and the liver.

-          Erythrocytes are produced by the bone marrow of the long bones, ribs, skull and vertebrae.

Leucocytes (White blood cells)

-          Leucocytes are colourless and do not contain haemoglobin.

-          Each Leucocyte is irregular in shape and contains a nucleus.

-          It can move. It can change its shape and squeeze through the wall of the fine blood capillaries into the spaces among the tissue cells.

-          They are larger than erythrocytes and fewer in number.

-          There are only 5,000 to 10,000 white blood cells in each cubic millimeter of blood. The ratio of erythrocytes to Leucocytes is 700:1

-          The life span is only a few days in the blood stream

-          They are made from stem cells in bone marrow

-          Leucocytes are classified into:

(a)  Granular leucocytes

-          include neutrophils, easinophils, basophils

-          neutrophils: are phagocytes, which engulf and digest bacteria and dead cells

-          easinophils: release enzymes that combat inflammation in allergic reaction, and kill parasitic worms

-          basophils: involve in combating inflammatory and allergic reactions

(b)  Agranular leucocytes:

-          include lymphocytes and monocytes

-          lymphocytes: produce immune response against foreign substances. Lymphocytes are produced by the lymph glands or lymph nodes

-          monoscytes: are phagocytes

Platelets

-          Platelets are cells fragments from bone marrow

-          They have no nucleus

-          They are involved in the process of blood clotting.

The differences between erythrocytes and leucocytes

Erythrocytes	Leucocytes

1.1.1      Human Blood Vessels

1.    There are 3 types of human blood vessels:

(a)  Arteries

-          Arteries are blood vessels that carry blood away from the heart.

-          The function of arteries is to transport blood quickly and at high pressure to the tissue

-          The wall of arteries consists of epithelial, smooth muscle and connective tissue.

-          Arteries have walls that are thick, muscular and elastic.

·         The thick elastic walls help to maintain the high blood pressure in the artery

·         The elasticity permits stretching and recoiling of the artery wall. These help to push the blood along.

·         The elastic walls of the arteries also prevent the arteries from bursting as blood under high pressure surges through them.

-          The elastic layer is much thicker in the great arteries near the heart, such as aorta (the main artery leaving the heart)

-          Arteries branch into smaller vessels called arterioles as they reach the tissue to which they are transporting blood.

-          The arterioles continue to branch and eventually form a network of capillaries.

(b)  Capillaries

-          Capillaries are thin-walled (one-cell thick) blood vessels which allow rapid gaseous exchange to occur between the blood and cells via diffusion.

-          They carry blood from a small artery (arteriole) to a small vein (venule)

(c)  Veins

-          Veins are blood vessels which convey blood towards the heart

-          The walls of veins also consist of epithelial, smooth muscle and connective tissue. However, the smooth muscle layer in veins is thinner than in arteries.

-          The blood in veins flows under low pressure

-          The veins have large lumen and valves that maintain the one-way flow of blood and to prevent backflow of blood.

-          The movement of blood along the veins is assisted by the action of the skeletal muscles on the veins. Muscular exercise increases the pressure exerted on the veins and moves the blood along more quickly.

1.    The differences between arteries, veins and capillaries

Arteries	Veins	Capillaries

AMAZING FACTS:

• One drop of blood contains a half a drop of plasma, 5 MILLION Red Blood Cells, 10 Thousand White Blood Cells and 250 Thousand Platelets.
• You have thousands of miles of blood vessels in your body. "Bill Nye the Science Guy" claims that you could wrap your blood vessels around the equator TWICE!
• Keep your heart healthy...it's going to have to beat about 3 BILLION times during your lifetime!

1.1.1      The Human Heart

1.    The heart is situated between the two lungs in the thoracic cavity.

2.    The heart weighs between 7 and 15 ounces (200 to 425 grams) and is a little larger than the size of your fist.

3.    The function of the heart:

~ to pump blood, which carries all the vital material that help the body function and to pump blood, which carries waste products that the body does not need.

4.    It usually beats from 60 to 100 times per minute, but can go much faster when it needs to. It beats about 100,000 times a day, more than 30 million times per year, and about 2.5 billion times in a 70-year lifetime.

5.    With each heartbeat, blood is sent throughout our bodies, carrying oxygen and nutrients to all of our cells. Each day, 2,000 gallons (more than 7,570 liters) of blood travel many times through about 60,000 miles (96,560 kilometers) of blood vessels that branch and cross, linking the cells of our organs and body parts.

1.    The human heart contains 4 chambers.

-          The two upper chambers are atria and the lower chambers are ventricles.

-          Atria receive blood returning to the heart while the ventricles pump blood out of the heart.

2.    The flow of blood through heart:

-          The superior vena cava and the inferior vena cava carry deoxygenated blood to the right atrium.

-          As blood fills the right atrium, the right atrium contracts and pushes the blood into the right ventricles through tricuspid valve.

-          When the right ventricle contracts, the tricuspid valve is closed, and blood is pushed out through semi-lunar valve into the pulmonary arteries.

-          Deoxygenated blood is pumped to the lungs.

-          Oxygenated blood from the lungs is brought back to the heart by way of the pulmonary veins which open to the left atrium.

-          When the left atrium contracts, the blood enters the left ventricle via bicuspid valve.

-          When the left ventricle contracts, blood leaves by way of a large artery, the aorta through another semi-lunar valve.

-          From aorta, blood is distributed to all parts of the body (expect lungs).

3.    The muscular wall of the left ventricle is thicker than the wall of the right ventricle

-          because left ventricle needs to pump blood to all parts of the body. The right ventricle only needs to pump blood to the lungs.

4.    The heart has valves that allow blood to flow in only one direction.

-          The valve between the right atrium and right ventricle is called tricuspid valve; the valve between the left atrium and left ventricle is called bicuspid valve. These valves prevent blood from flowing back into the atria.

-          The semi-lunar valves are located at the point where the pulmonary artery and aorta leave the heart. These valves prevent blood from flowing back into the ventricles when the ventricles relax.

5.    The blood in the pulmonary arteries is at a lower pressure than the blood in the aorta.

-          This gives sufficient time for gaseous exchange to occur in the lungs.

6.    The right side of the heart is completely separated from the left side of the heart by a muscular wall called median septum which runs down the middle of the heart.

-          In this way, deoxygenated blood in the right side is unable to mix with the oxygenated blood in the left side of the heart.

7.    Mode of action of the heart

-          The two atria of the heart work simultaneously. They relax at the same time to receive the blood from the veins. The right atrium receives blood from the two vena cavae while the left atrium receives blood from the pulmonary veins.

-          The two atria the contract at the same time, forcing the blood into the relaxed ventricles.

-          After a slight pause, the two ventricles contract simultaneously, forcing the blood from the left and right ventricles into aorta and pulmonary arteries respectively.

-          Meanwhile the backflow of blood into the atria is prevented by the sudden closing of the tricuspid and the bicuspid valves.

-          The closing of these valves produces a loud “lub” sound which we can hear in a heartbeat.

-          After the ventricles have fully contracted, they start to relax. As they relax, the blood in the arteries tends to flow back into the ventricles, but this is prevented by the sudden closing of the semi-lunar valves. The closure of these valves produces a soft “dup” sound.

-          Therefore, ventricular contraction or systole makes a “lub” sound and the ventricular relaxation or diastole makes a “dup” sound.

-          A systole and a diastole make up one heartbeat.

-          The average normal heartbeat of an adult is about 72 times per minute.

-          Notice that the atria and the ventricles work alternately. When the atria contract, the ventricles relax and vice versa.

1.1.1      The Circulation Of Blood In Human

The pumping of the heart

1.    The heart is made up of strong muscle, called cardiac muscle.

-          The cardiac muscle cells are interconnected. This allows electrical signals to be conducted rapidly through the heart, and the same time stimulate the cardiac muscle cells to contract in a coordinated way.

-          Cardiac muscle is myogenic – it contracts and relaxes without the need to receive impulses from the nervous system.

2.    The contraction of the heart is initiated and coordinated by a pacemaker.

-          The pacemaker is a cluster of specialized heart muscle cells that sets the rate at which the heart contracts.

-          The pacemaker is located in the wall of the right atrium.

-          It generates electrical impulses which spread rapidly over walls of both atria casing the atria to contract in a rhythmical pattern.

-          The heart’s primary pacemaker is called the sinoatrial (SA) node.

3.    From the SA node, the impulses reach the atrioventricular (AV) node.

-     The AV node is located at the floor of the right atrium.

4.    From the AV node, specialized muscle fibres called bundle of His fibres, bundle branches and Purkinje fibres conduct the signals to the apex of the heart and throughout the wall of the ventricles, causing the ventricals to contracts and push blood out to the lungs and body.

5.    The pacemaker is regulated by

(a)  parasympathetic nerve – slows down the pacemaker

(b)  sympathetic nerve – speeds up the pacemaker

6.    The pacemaker also controlled by hormone adrenaline – increases heartbeat rate during moment of fear or threat.

1.1.1      How Blood Pressure Is Regulated

1.    Blood pressure is the force of the blood exerted on the walls of the blood vessels

2.    At rest, a healthy adult will have a blood pressure of 120/80 mm Hg. The upper figure, 120 refers to the systolic (ventricular contraction) pressure while the lower figure, 80 refers to the diastolic (ventricular relaxation) pressure.

3.    Blood pressure varies in different parts of the body, being highest near the aorta and becoming weaker the further away the arteries are from the heart. It is low in veins and it reaches almost 0 mm Hg in the vena cavae, just before the vena cavae open into the right atrium of the heart.

4.    A person’s blood pressure can be measured by sphygmomanometer.

5.    Blood pressure is regulated by a negative feedback mechanism. Baroreceptors located in the arch of aorta and carotid arteries ( arteries in the neck that supply blood to the brain), detect blood pressure flowing through them. They send impulses continuously to the cardiovascular center in the medulla oblongata in the brain to help regulate blood pressure.

1.1.1      The Circulatory System In Human, Fish And Amphibians

1.    The circulatory system of large multicellular organisms can be divided into two types:

(a)  The open circulatory system

-          Example: The circulatory system in insects

-          One or more hearts pump the haemolymph through vessels into the haemocoel.

-          The haemocoel contains soft internal organs and is filled with haemolymph.

-          Chemical exchange occurs between the haemolymph and the body cells.

-          Haemolymph flows out from the hearts into the haemocoel when the hearts contract. When the heart relax, haemolymph is drawn back into the hearts through a poses called ostia.

(b)  The closed circulatory system

-          Example: The circulatory system in all vertebrates, includes human, mollusks (e.g. squid and snails), and annelid (e.g. earthworm)

-          Blood is confined in vessels.

-          One or more hearts pump blood into major vessels that branch into smaller vessels in organs.

-          Chemical exchange occurs between the blood and the interstitial fluid and the body cells, and between the interstitial fluid and the body cells.

2.    The closed circulatory system can be divided into two types:

(a)  Single circulatory system

-          Blood flows through the heart only once in each complete circulation of the body

(b)  Double circulatory system

-          Blood flows through the heart twice in each complete circulation of the body

3.    There are two ways blood circulation:

(a)  Systematic circulation

-          Blood circulation from heart to all parts of the body except lungs.

-          The oxygenated blood is pumped to the body tissues through left ventricle to aorta and arteries.

-          In capillaries, chemical exchange occurs between the blood and the interstitial fluid and the body cells.

-          Then deoxygenated blood is carried back to the heart through veins and vena cavae to the right atrium.

(b)  Pulmonary circulation

-          Blood circulation from heart to the lungs and back to the heart.

-          The deoxygenated blood is pumped from the right ventricle through the pulmonary arteries to the lungs.

-          In the lungs, carbon dioxide is released and the oxygen is taken in from the air.

-          Then, the oxygenated blood is carried back to the heart through pulmonary vein to the left atrium.

4.    The circulatory system in fish

-          A fish has a heart with two main chambers, one atrium and one ventricle.

-          Blood leaving the ventricle will travel to the gills capillaries where gaseous exchange occurs.

-          The gill capillaries converge into a vessel that caries the oxygenated blood to the systemic capillaries.

-          In the systemic capillaries, oxygen diffuses into the tissues while the carbon dioxide diffuses out of the tissue and into the capillaries.

-          The deoxygenated blood then returns to the atrium of the heart via veins.

-          In the circulatory system in fish, blood flows in only one circuit, hence, it is called a single circulatory system.

5.    The circulatory system in frogs and amphibian

-          Frogs and other amphibians have a three-chambered heart, with two atria and one ventricle.

-          Deoxygenated blood from the body is delivered into the right atrium and oxygenated blood from the lung is delivered into the left atrium.

-          Blood form the both atria then enters a single ventricle.

-          The ventricle then pumps blood through the pulmocutaneous circulation and the systemic circulation.

-          The pulmocutaneous circulation leads to the lungs and skin where the gaseous exchange occurs. Oxygenated blood returns the left atrium of the heart.

-          The systemic circulation carries oxygenated blood to body tissues and then returns deoxygenated blood to the right atrium.

-          Bloods in the in frogs and amphibian flows in two separate circulations: the pulmocutaneous circulation and the systemic circulation, it is called a double circulatory system.

6.    The circulatory system in humans and other mammals

-          Humans have a four-chambered heart, two atria and two completely separated ventricles.

-          Deoxygenated blood and oxygenated blood do not mix:

~ to ensure efficient and rapid movement of the highly oxygenated blood to the organs of the body.

-          In the pulmonary circulation, the deoxygenated blood is pumped from the right ventricle through the pulmonary arteries to the lungs where it passes through the blood capillaries. Carbon dioxide is released and the oxygen is taken in from the air. Then, the oxygenated blood is carried back to the heart through pulmonary vein to the left atrium

-          In the systemic circulation, The oxygenated blood is pumped to the body tissues through left ventricle to aorta and arteries. In capillaries, chemical and gaseous exchange occur between the blood and the body tissues. Then deoxygenated blood is carried back to the heart through veins and vena cavae to the right atrium.

-          Blood in humans flows in two separate circulations: the pulmonary circulation and the systemic circulation, it is called a double circulatory system

7.    The advantages of a double circulation:

(a)  Blood entering the lungs is at a low pressure. This ensures that the blood is well oxygenated before it returns to the heart.

(b)  Blood leaving the heart for the systemic circulation is at high pressure. This ensures that oxygenated blood is distributed to the body tissues at a faster rate. (This help to maintain the high metabolic rate in mammals).

1.2  THE MECHANISM OF BLOOD CLOTTING

1.2.1      The necessity of blood clotting

-          Blood clotting stops or minimizes blood loss at the site of damaged blood vessels to prevent excessive bleeding after injury.

1.2.2      Blood clotting

1.    In the case when the damage of the vessel is small

-          When a blood vessel is damaged, the connective tissue in the vessel wall is exposed to blood. Platelets stick rapidly to form platelet plug (an aggregation of sticky platelets) to stop blood loss completely if the damage to the vessel is small.

2.    In the case when the damage of the vessel is severe

-          The clumped platelets, the damaged cells and clotting factors in the plasma will form activators, thromboplastins.

-          Thromboplastins, together with the help of calcium and vitamin K, convert prothrombin (an inactive plasma protein) to thrombin (an active plasma protein).

-          Thrombin catalyses the conversion of the soluble protein fibrinogen present in the blood plasma into the insoluble protein fibrin.

-          Fibrin is a fibrous protein which forms a mesh over the wound trapping red blood cells and sealing the wound.

-          The resulting clot hardens on exposure to air to form a scab.

1.1.1      Problems related to blood clotting

1.    Haemophilia

-          An inherited disease caused by a lack of particular clotting factors in the blood

-          A person with this disease may die due to excessive bleeding from minor cuts and bruises. He may also experience spontaneous internal bleeding.

2.    Thrombosis

-          Blood does not normally clot in intact blood vessels. This is because of the action of a number of anticoagulants such as heparin circulating in the bloodstream.

-          But sometimes, blood clots may form within the blood vessels due to various factors such as:

·         Defects in the vessel walls

·         Blood flows to slowly

Causing clotting factors to accumulate and initiate a clot.

-          Clot formation inside an unbroken blood vessel is called Thrombosis.

-          The clot is called thrombus. Sometimes, the thrombus may become dislodged and travel in the bloodstream.

-          A blood clot that ravels in the bloodstream is called an embolus. The embolus is swept along until it becomes lodged in artery which is too small to pass. When this happens, blood flow in the blood vessel is stopped.

-          If the clot occurs in a coronary artery, an area of heart muscle may die or be permanently damaged because of an inadequate supply of oxygen to that area. This can lead to a heart attack.

-          If the clot blocks blood flow to the brain, it can result in a stroke.

1.1  THE LYMPHATIC SYSTEM

1.1.1      Formation And Composition Of Interstitial Fluid

1.    Blood that enters the arterial end of a capillary is under high pressure which cause fluid to leak continuously from the blood into the spaces between the cells. This fluid is known as interstitial fluid.

2.    Interstitial fluid is important to cells because it is through this fluid that the exchange of materials between blood capillaries and cells occurs. Nutrients and oxygen diffuse from the blood through the interstitial fluid into body cells. Waste products and carbon dioxide diffuse from the body cells through the interstitial fluid into the blood.

3.    Interstitial fluid consists of:

·         Water

·         Dissolve nutrients

·        Water

From the blood

Hormones

·         Waste products

·         Gases

·         Small proteins

4.    It does not contain

·         The plasma proteins: albumin, globulin and fibrinogen

·         The erythrocytes

·         Platelets

~ because they are too large to pass through the capillaries.

5.    It contains leucocytes which can ooze through the openings between the capillaries.

1.    The blood pressure at the arterial end of the capillaries is high, so blood plasma (without plasma protein, erythrocytes and platelets) is forced out through the capillaries walls into the spaces between the cells (intercellular spaces).

2.    The fluid is called interstitial fluid.

3.    If the blood plasma continuously moved out of the blood capillaries, the blood would lose far too much liquid. To prevent this, some of the interstitial fluid is absorbed into the blood capillaries at the venous end of capillaries.

4.    Blood plasma at the venous end of capillaries is hypertonic compared to the surrounding interstitial fluid. Blood pressure is also much lower at the venous end of capillaries.

5.    As a result, 85% of interstitial fluid that contains water, mineral salts and waste products flow back into the capillaries. The fluid must be returned to the circulatory system to maintain normal blood volume.

6.    The 15% of interstitial fluid is collected as lymph and returns to the blood through a network of vessels known as the lymphatic system.

1.1.1      The Structure Of Lymphatic System

1.    The lymphatic system is a network of lymph capillaries and larger vessels.

2.    The lymph capillaries are blind-ended tubes or closed at one end. They are located in the spaces between the cells.

3.    Main functions of lymphatic system:  

·         to collect and return interstitial fluid, including plasma protein to the blood,
and thus help maintain fluid balance

·         to defend the body against disease by producing lymphocytes

·         to absorb lipids from the intestine and transport them to the blood

4.    The Lymphatic System includes

·         Lymph nodes located along the paths of collecting vessels

·         Isolated nodules of lymphatic patches in the intestinal wall

·         Specialized lymphatic organs such as the bone marrow, thymus, and spleen

-          The spleen serves as a reservoir for blood, and filters or purifies the blood and lymph fluid that flows through it. If the spleen is damaged or removed, the individual is more susceptible to infections.

-          The thymus secretes a hormone, thymosin, that causes pre-T-cells to mature (in the thymus) into T-cells.

5.    The interstitial fluid which is not absorbed into the bloodstream drains into the lymph capillaries. It is known as lymph. Lymph is a transparent yellowish fluid within the lymphatic system that is composed primarily of interstitial fluid and lymphocytes.

6.    The lymph capillaries unite to form larger lymphatic vessels. Within the lymphatic vessels, there are one-way valves that

·         ensure the continuous flow of the lymph away from the tissues.

·         prevent the back flow of the lymph

7.    The lymph nodes located at intervals along the lymphatic vessels. The functions of lymph nodes are:

(a)  Defense functions--filtration and phagocytosis

-          The structure of the sinus channels within the lymph nodes slows the lymph flow through them.

-          This gives the reticuloendothelial cells that line the channels time to remove microorganisms and other injurious particles (soot) from the lymph and phagocytose them.

-          Sometimes such large numbers of microorganisms enter the node that the phagocytes cannot destroy enough of them to prevent their injuring the node. An infection of the node, adenitis, then results.

(b)  produce and store lymphocytes that help to defend the body against infection.

8.    From the lymphatic vessels, lymph eventually passes into one of two main channels:

·         The thoracic duct

-          receives lymph from the left head, neck and chest, the left upper limb and the entire body below the ribs.

·         The right lymphatic duct

-          receives lymph from the right arm, shoulder area, and the right side of the head and neck.

9.    The thoracic duct empties its lymph into the left subclavian vein and the right lymphatic duct empties its lymph into the right subclavian vein. Hence, lymph drains back into the blood.

10.  Lymph moves toward the subclavian vein with the help of:

·         One-way valves

·         Muscular contraction

·         Intestinal movements

·         Pressure changes that occur during inhalation and exhalation.

1.1.2      The Role Of Lymphatic System In Transport

1.    The lymphatic system collects and returns interstitial fluid, including plasma protein to the blood, and thus help maintain fluid balance.

-          This is crucial because water, nutrients and other molecules continuously leak our of the blood capillaries into the surrounding body tissues. If excess fluid is not returned to the bloodstream, body tissue will become swollen because too much fluid is retained.

-          An excessive accumulation of interstitial fluid in the spaces between the body cells will result in a condition known as oedema.

-          Oedema may be caused by a blocked lymphatic vessel.

2.    The lymphatic system collects lipids from the intestine and transport them to the blood via lacteals in the villi of small intestine-    

-          Lacteals are lymph capillaries in which droplets of lipids and fat-soluble vitamins are transported to the bloodstream.

1.2  THE ROLE OF THE CIRCULAORY SYSTEM IN THE BODY’S DEFENCE MECHANISM

Definitions:

·         Pathogens are disease-causing microorganisms.

-          Examples: bacteria, viruses and parasites.

·         Antigens are molecules carried or produced by microorganisms that initiate antibody production

·         Antibodies are proteins produced by immune system cells that bind to foreign molecules and microorganisms, and inactivate them.

·         Immunity is the body's capability to repel foreign substances and cells.

·         Immune response is the interactive between antibody and antigen which result in the antigen being eliminated from the body

The circulatory system also defends the body against foreign bodies, especially disease- causing microorganisms.

There are 3 lines of defence mechanisms:

                      i.        The first line of defence

                     ii.        The second line of defence

                    iii.        The third line of defence

The first and second lines of defence are non-specific defences – they do not differentiate one pathogen from another.

The third line of defence is a specific defence – it recognizes specific pathogen and defens the body against them.

The First Line of Defence

1.    The first line of defence consists of physical and chemical barriers that prevent pathogens from entering the body.

2.    Barriers to entry are

(a)  Skin

-          The skin is a passive barrier to infectious agents such as bacteria and viruses.

-          The outer layer of the skin is tough and provides a physical barrier that is impermeable to bacteria and viruses.

-          The continual shedding of dead skin cells makes it difficult of bacteria to grow on the skin

-          The skin also acts as chemical barrier as it secretes sebum. Sebum forms a protective film over the skin.

-          In addiction, sweat excreted by the skin contains lysozyme, an enzyme capable of breaking down the cell walls of certain bacteria.

(b)  Mucous membranes

-          Mucus membranes lining the respiratory, digestive, urinary, and reproductive tracts secrete mucus that contain lysozyme which traps and destroy bacteria.

-          Example: the mucous membrane of the nose has mucus-coated hairs that trap and filter microorganisms, dust and pollutants from inhaled air.

(c)  Tears and saliva

-          Tears and saliva also secrete lysozyme which helps protect the eyes and mouth from bacterial invasion

(d)  Hydrochloric acid secreted by the stomach

-          Pathogens that gain entry into the body via food and drinks consumed are destroyed by the hydrochloric acid secreted by the stomach

The Second Line of Defence

1.    Despite the physical and chemical barriers, pathogens may still able to gain entry into our body. To fight against these pathogens, the body has a second line of defence, called phagocytosis.

2.    Phogocytosis is the process by which phagocytic white blood cells (phagocytes) engulf and ingest microorganisms or other particles such as cellular debris.

3.    The two main types of phagocytes are:

(a)  Neutrophils

-    found in the blood

(b)  Monocytes / macrophages

-    found in the interstitial fluid

4.    When an infection occurs, neutrophils and monocytes migrate to the infected area. During migration, monocytes enlarge and develop into macrophages.

5.    The stages of phagocytosis:

(i)    When a phagocyte encounters an invading pathogen, the phagocyte engulfs the pathogen.

(ii)   After the pathogen is engulfed and drawn inside the phagocyte, the enzyme lysozyme kills the pathogen.

The Third Line of Defence

1. The third line of defence is immune system. It is a specific or targeted defence.

2. During an infection, the immune system identifies the antigens invading the body.

3. The antigens induce the lymphocytes to release antibodies into the bloodstream to destroy a particular antigen.

4. The mechanism used by antibodies to destroy antigens:

The Various Type of Immunity

1.    There are two types of immunity:

(a)  Active immunity

-          the body makes its own antibodies in response to stimulation by an antigen.

(b)  Passive immunity

-          the body receives antibodies from an outside source.

AIDS

1. The human immunodeficiency virus (HIV) is a virus that attacks the immune system.
2. Infection by the HIV Virus results in acquired immunodeficiency syndrome (AIDS).
3. The virus reproduces inside the lymphocytes and kill them in process. Since the immune system of a person is weakened, the body is prone to infections. Eventually, the immune system collapse and the victim dies of an infection.

1.1  APPRECIATING A HEALTY CARDIOVASCULAR SYSTEM

Diseases linked to the cardiovascular system	Syndromes	Factors that contribute the disease	Prevention and cure
Coronary thrombosis
Atherosclerosis
Arteriosclerosis
Hypertension
Diseases linked to the cardiovascular system	Syndromes	Factors that contribute the disease	Prevention and cure
Heart attack
Stroke

1.1  THE TRANSPORT OF SUBSTANECS IN PLANTS