Gas Exchange & Transport

Gas Exchange & Transport


Using hand drawn diagrams explain the structure and function of the respiratory system.


1. Using diagrams explain the mechanism of breathing and gas exchange

2. Using diagrams explain how breathing is regulated


Go through all the disorders of the respiratory system and explain:

1. What are their causes?

2. What are their symptoms?

3. What kind of medical interventions can be used to help to either cure or alleviate the disease?

4. What is the prognosis for the future on each of the disorders?

Biology 1 – Level 3



Write a short essay explaining the composition and functions of the heart and blood vessels


Research into the disorders of the circulatory system. Explain what these disorders are, their causes, how they can be prevented and how they can be treated.


The blood is one of the two fluid tissues found within the body. The bloods main function is to transport substances to different parts of the body, for example it transports food and oxygen to respiring tissues; it takes carbon dioxide and waste products away from respiring cells to the various organs that remove them and it carries hormones that are secreted by the endocrine glands to the target organs. The blood has many other functions such as, it helps to maintain constant body temperature, it provides pressure that many organs depend on to enable them to carry out their functions, it acts as a buffer by keeping the pH constant and it defends the body against infection.

The four main components that make up the blood are the plasma, erythrocytes (red blood cells), leucocytes (white blood cells) and thrombocytes (platelets). All of these components perform different functions which allow bodily processes to take place i.e. respiration, digestion, and immunisation.

The plasma is a pale, straw-coloured liquid, of which 90% of the composition is water and the other 10% is composed of dissolved substances. The plasma makes up 55% of the blood and the dissolved substances which are present in plasma include protein, glucose, amino acids, vitamins, hormones, oxygen, carbon dioxide, antibodies, anti-toxins and other nutrients.

Carbon dioxide is a by-product which is produced through respiration and is dissolved in the plasma after the cells have respired aerobically. It is then transported to the lungs where it is exhaled, forming the 4% of exhaled carbon dioxide in exhalation. Urea is another waste product that circulates in the plasma until it reaches the excretory organ which will remove it.

The plasma is also responsible for the transportation of hormones, which have been secreted by the endocrine glands, to the target organs. Hormones like erythropoietin, which are responsible for stimulating the production of erythrocytes, are transported in plasma. Other hormones like testosterone, oestrogen, ADH, thyroxin, adrenaline, insulin, FSH and LH are also transported in the plasma.

The red blood cells are produced in a complex process called erythropoiesis. This is where the red blood cells are formed as stem cells, which are synthesised in the bone marrow, and then develop into erythrocytes. This process is stimulated by the hormone erythropoietin, which is usually produced by the kidneys.

The primary function of erythrocytes is to deliver oxygen around the body to aerobically respiring cells. Red blood cells are suited to this function as they contain pigmentations called haemoglobin, which bind to oxygen to form oxyhaemoglobin. This allows for oxygen to be transported around the body. In addition to this is the biconcave shape of the red blood cells, which allows for maximum oxygen absorption. Also erythrocytes are characterised by the absence of a nucleus, which also allows for maximum oxygen absorption.

Haemoglobin in the blood is comprised of globular proteins with the addition of a prosthetic group (iron), which binds to oxygen in the process of diffusion. In correlation to this, is the erythrocytes ability to take on carbon dioxide in deoxygenated blood to the lungs for exhalation. This is a shared ability in which the plasma shares this function with red blood cells.

The main role of white blood cells is to defend against disease. They destroy micro-organisms and produce anti-bodies to fight bacteria. Anti-toxins are produced to neutralise the toxins produced by bacteria. In order to assist this function there are five different types of white blood cells, each leucocyte interlinks with another to enable a compatible eradication of pathogens. The five different types include: neutrophils, basophils, eosinphils, lymphocytes and monocytes.

Neutrophils destroy invading pathogens by releasing highly toxic substances and carry out phagocytosis. Basophils are mainly responsible for the inflammation which acts to remove injurious stimuli. Lymphocytes contain receptors that stimulate the production of antibodies and also perform phagocytosis. Monocytes circulate in the blood where they mature into macrophages in bodily tissue and share the same ability as Neutrophils and lymphocytes and eosinophils combat infections caused by parasites

Platelets or thrombocytes are small fragments of cells, that have no nucleus, which are used to clot the blood when a wound or cut is present to prevent severe blood loss. Together with leucocytes they form one percent of the total composition of blood. The thrombocytes don't actually transport any substances around the body.

The primary function of the platelets is to assist in blood clotting. The formation of blood clots is the started by the process of haemostasis. This intrinsic process involves vasoconstriction, which is the narrowing of the blood vessels resulting from the contracting of the muscular wall of the vessels, to slow and eventually stop the bleeding.




The Lymphatic System

The lymphatic system can be described as an extensive drainage system that is made up of a vast network of vessels. It is closely connected to both the circulatory and immune systems and has the responsibility for keeping bodily fluids in balance and defending the body against infections. The huge network of vessels that make up the lymphatic system are known as lymphatic vessels. The lymphatic vessels carry tissue fluid known as lymph, which is a colourless fluid that contains a high number of white blood cells and resembles plasma, throughout the body. There are different parts that are found within the lymphatic system these include: the spleen; thymus gland; lymph nodes; tonsils and bone marrow, in which major parts of the lymph tissue are located.

Lymphatic System

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One of the lymphatic system's major roles is to collect extra lymph fluid from body tissues and return it to the blood. This process is crucial because, during the course of the day, around 21 litres of fluid from the plasma, carrying dissolved substances and some plasma protein, escapes from the capillaries of the circulatory system and into the tissues. Most of this fluid is returned directly to the blood stream via the capillary, but 3-4 litres of fluid are drained away by the lymphatic vessels. If the lymphatic system didn't drain the excess fluid from the tissues, the lymph fluid would build up in the body's tissues and would cause them to swell.

The other role that the lymphatic system plays is to help defend the body against germs like viruses, bacteria and fungi (micro-organisms) that can cause illnesses. These germs are filtered out in the lymph nodes, which are small masses of tissue that are located along the network of lymph vessels. Most of the lymph nodes are found in clusters in the neck, armpit, and groin area. Lymph nodes are also located along the lymphatic pathways in the chest, abdomen, and pelvis, where they filter the blood.

Section through a lymph node

Arrows indicate the direction of lymph flow

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The lymph nodes are oval, bean shaped organs that are located, often in groups along the length of the lymph vessels. The lymph nodes are surrounded by outer layer of fibrous tissue that immerses itself downwards into the node substance forming divisions within the node. The main substance of the node consists of reticular and lymphatic tissue which contains concentrated areas of lymphocytes, a type of white blood cell, and macrophages. The lymphocytes produce chemicals called antibodies, which are special proteins that fight off germs and prevent infections from spreading, which kill micro-organisms in various ways, either by surrounding the micro-organisms and destroying them directly or by destroying the toxins that they release.

The origin of a lymph capillary

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The lymphatic flow begins in the areas round the blood capillaries, where the excess tissue fluid drains into a system of tiny, blind-ending tubes, the lymphatic capillaries. The cells which form the walls of the lymph capillaries are loosely fitted together, making it permeable, to allow lipids and large molecules, such as proteins, to flow through them. This fluid, now called lymph, is collected by a series of larger lymph vessels that run throughout the body and are surrounded by the skeletal muscles that allow movement. When these muscles contract, it compresses the lymph vessels and rhythmically moves the lymph along.

A lymph vessel cut open to show valves.

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The lymph flow is quite slow and is one directional, as there are valves located within the vessels which prevent back flow. The lymph is moved along the vessels in the direction of the heart and passes through numerous lymph nodes, along the way, which filter out cell debris and micro-organisms. Micro-organisms can cause harm by either damaging the cells around them or by releasing toxins that make you ill, if they do manage to enter your body, they are attacked by the white blood cells when the lymph enters the lymph nodes. After these micro-organisms have been filtered out, the lymph fluid leaves the lymph nodes and re-enters the lymph vessels.

The lymph vessels become larger as they join together, eventually forming two large ducts called the thoracic duct and the right lymphatic duct. The thoracic and right lymphatic ducts are major lymphatic vessels. The thoracic duct, which begins near the lower part of the spine and collects lymph from the pelvis, abdomen, and lower chest, runs up through the chest and empties into the blood through a large vein near the left side of the neck. The right lymphatic duct collects lymph from the right side of the neck, chest, and arm, and empties into a large vein near the right side of the neck. In each case, the lymph is returned to the veins where it re-enters the blood stream.

A section through the Spleen

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The spleen, which lies below the ribs and near the stomach, contains reticular and lymphatic tissue and is the largest of the lymph organs. It plays an important part in a person's immune system by helping the body fight off infection. Like the lymph nodes, the spleen contains antibody-producing lymphocytes. These antibodies weaken or kill the micro-organisms that cause infection and illness. Also, if the blood passing through the spleen carries damaged cells, white blood cells called macrophages in the spleen will destroy them and clear them from the bloodstream. Unlike the lymph nodes, the spleen does not filter lymph and it is therefore not exposed to the diseases spread by lymph.

The thymus gland in the adult, and related structures.

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The thymus, which is situated in the chest behind the sternum, is also an important lymphocyte producing gland. It weighs about 10 to 15g at birth and continues to grow until puberty, when it begins to waste away. The thymus consists of two lobes which are connected together by areolar tissue. The lobes are surrounded by a fibrous capsule which immerses into their substance, separating them into lobules that consist of an irregular branching structure of epithelial cells and lymphocytes. The lymphocytes that enter the thymus build up into T-lymphocytes. As these T-lymphocytes mature, they are able to discriminate between ‘self' tissue and foreign tissue and also each mature T-lymphocyte gains the ability to react to the antigens it will encounter. The T-lymphocytes then leave the thymus and enter the blood.

Throughout the body, at strategically placed locations, are groups of lymphoid tissue which, unlike the spleen and thymus, are not enclosed within a capsule. These groups of lymphoid tissue contain B- and T-lymphocytes which are important in the early detection of antigens. Lymph is not filtered through these groups of tissue, as they have no afferent lymphatic vessels, and therefore they are not exposed to the diseases spread by the lymph fluid. The tonsils, one of the main groups of lymphoid tissue, are located in the mouth and throat and produce antibiotics. The tonsils are therefore equipped to destroy any swallowed and inhaled antigens.

In conclusion, the lymphatic system is an important part of the mammalian body and is often overlooked. By absorbing fats and trapping antigens, it helps to keep the body healthy and disease-free. Also, the role of maintaining proper fluid balances is essential. Truly, a healthy lymphatic system is necessary to the survival of the animal.


All Illustrations:

Waugh, A., Grant, A., (2006) Anatomy and Physiology in Health and Illness. 10th ed. USA: Elsevier (from the online image bank)

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