Equine biological systems Pack 3 Circulation Pack Code: EBS3 This pack you will help you to: describe how blood circulates round the horse's body. www.lbcnc.org.uk
About this pack Objectives When you have completed this pack you should able to describe how blood circulates round the horse's body. The pack will help you to: List the components and functions of blood. Describe the structure and function of blood vessels. Identify the main vessels and arteries of an animal. Describe how the heart pumps blood round the body. The pack is also relevant to the National Diploma unit Principles of Animal Science 1, and in particular to Outcome 1: Describe the structure, function and biological systems within the animal body. Links to other packs This is one of a series of learning packs, each tackling an aspect of horse biological systems. They are: Pack 1: The skeleton Pack 2: Joints Pack 3: Circulation Pack 4: Respiration Pack 5: The digestive system of the horse Pack 6: The reproductive system Pack 7: Oestrus and hormones Pack 8: Gestation and birth Pack 9: How animal cells work Pack 10: How animal cells divide Pack 11: Connective and epithelial tissue Pack 12: Muscle and nervous tissue Pack 13: The horse s sensory organs Equine biological systems 2
Overview of the circulatory system The cells of an animal's body need to obtain nutrients (particularly oxygen) and to get rid of waste products (particularly carbon dioxide). They also need to counter threats such as temperature changes, toxins, change in ph etc. The cardiovascular system helps to meet these needs. It comprises: the blood vessels (the vascular system) in which materials travel round the body the heart which pumps blood through the blood vessels. Blood The circulatory system carries blood round the body. Functions Blood has a wide range of functions which we can group under three main headings. Transport Blood carries various materials to cells in the body: oxygen from the lungs nutrients from the intestinal tract hormones (which give messages to specific parts of the body) and antibodies (to help tackle infections) Blood also takes waste products away from the cells to various parts of the body where they are processed or eliminated, including: carbon dioxide to the lungs other metabolic wastes to the liver and kidneys other waste products to the skin Regulation Blood regulates the following aspects of cells: ph (kept slightly alkaline) temperature (heat is moved from warm active tissues to less active ones) water content. Protection Blood protects the body through: clotting agents which prevent blood loss from an injury white blood cells, which destroy foreign microbes and toxins. Equine biological systems 3
Activity Give an example of how blood acts as: a) a transport agent b) a regulating agent c) a protective agent. Check your answers with the previous section. Composition Blood accounts for about 7% of body weight. It is made up of plasma a sticky clear fluid and blood cells which are suspended in the fluid. Plasma Plasma is made of: 90% water 6% plasma proteins 1% mineral salts 3.5% nutrients, waste materials, hormones, antibodies, and gases The main functions of plasma are to: keep the water balance between cells and blood at the correct level help blood to clot provide a medium for carrying the various materials transported by the blood. Blood cells There are two main types of blood cell: Red blood cells (erthrocytes) these cells contain iron, which gives blood its red colour. They contain the protein haemoglobin, which carries oxygen to cells and carbon dioxide from the cells to the lungs. The body contains millions of these cells. White blood cells (leukocytes) there are several types of white blood cells which protect the body from invading bacteria and waste materials, by engulfing and digesting harmful substances. There are fewer white blood cells than red cells - around one white blood cell to every 700 red cells. Thrombocytes, or platelets, are a type of white blood cell which start clotting the blood when a vessel is damaged. Equine biological systems 4
Review quiz 1 1 Blood is a mix of:! a) plasma and cells! b) water and cells! c) proteins and cells 2 Plasma is composed mainly of:! a) proteins! b) water! c) platelets 3 The function of haemoglobin is to:! a) carry oxygen and carbon dioxide in the blood! b) carry iron in the blood! c) coagulate the blood Answers are given at the end of this pack. Blood vessels There are two main types of blood vessel - arteries and veins. Arteries Arteries transport oxygen rich blood from the heart. This blood leaves the heart through the aorta which branches like a tree into wide arteries, then narrow arterioles, and finally into a vast network of very narrow vessels with walls only one cell thick called capillaries. No cell is far away from a capillary. There is a particularly high density of capillaries in the liver, lungs and kidneys where much metabolic activity takes place. Oxygen rich blood is under very high pressure, so arteries have strong walls. As the blood passes from the wide main arteries into arterioles and finally capillaries it slows down and the pressure on the walls decreases. The speed reduces from around 65kph on leaving the heart to around 2cm per minute in the capillaries. Veins Veins transport blood containing waste materials including carbon dioxide from cells back to the heart. Waste materials pass from cells into the blood in a capillary. Capillaries join together to form narrow veins called venules, which then join the wide veins leading to the heart and on to the lungs. When blood reaches the lung carbon dioxide is given off, and oxygen is taken up (see the pack on respiration). Equine biological systems 5
Blood in veins is at low pressure, so the vein wall does not need to be so strong. Artery Vein The diagram shows that arteries and veins are made up of the same three layers: tunica intima - inner layer of epithelium tunica media - middle layer of smooth muscle and elastic tissue which works with the heart to move the blood along tunica adventitia - outer layer of fibrous tissue The big difference between them is that the middle layer of muscle is much thicker in arteries to cope with the high pressure of the oxygen rich blood. When cut a vein collapses, whereas an artery with its thicker wall stays open. The thickness of the middle layer in arteries decreases as the blood pressure decreases. Some veins in the limbs have valves to prevent the deoxygenated blood, which is under low pressure, from flowing back down the limb. Blood passes up through the valve, which closes until the next valve opens and so on. Muscles next to the vein in the limb also help the blood to move up the vein. Equine biological systems 6
Review quiz 2 1 Match the following vessels and functions Veins Arteries Capillaries carry oxygenated blood carry oxygenated or deoxygenated blood carry deoxygenated blood 2 Are the following statements true or false? a) Arteries have valves! True! False b) The tunica media is thicker in arteries than in veins! True! False c) Veins are narrower than venules! True! False Answers are given at the end of this pack. Circulation systems While the blood flows round the body continuously it is possible to describe three aspects of this circulation. Systemic circulation This is the main circulation of blood between the heart and the cells throughout the body. Oxygenated blood leaves the heart (the left ventricle) via the aorta which divides into a number of artery branches. Deoxygenated blood returns from the body by the most direct route into two main veins: the inferior and superior venae cavae which take it back to the heart (the right atrium). Pulmonary circulation This is the circulation of blood between the heart and the lungs. De-oxygenated blood Heart Lungs Oxygenated blood The pulmonary artery carries deoxygenated blood from the heart (from the right ventricle) to the lungs. Note this is the one exception to the rule that arteries normally carry oxygenated blood. Equine biological systems 7
Pulmonary veins carry oxygenated blood from the lungs to the heart (the left atrium). Similarly this is the exception to the rule that veins normally carry deoxygenated blood. Portal circulation This is the detour deoxygenated blood takes from the digestive system through the liver before being returned to the heart. Blood from the digestive system, the spleen and pancreas, first passes to the liver where nutrients are regulated before rejoining the veins of the systemic circulation. De-oxygenated blood Digestive system Liver Veins Heart The next diagram shows the three circulation systems. Equine biological systems 8
Review quiz 3 Match the following circulation systems and their functions: Systemic circulation carries blood between the heart and lungs Portal circulation carries blood between the heart and cells throughout the body Pulmonary circulation carries deoxygenated blood from the digestive system through the liver Answers are given at the end of this pack. The heart The function of the heart is to keep blood circulating round the body at all times, so cells are continually supplied with oxygen and nutrients and waste products are removed. If the heart stops the animal will quickly die as cells become starved of oxygen. The heart is a muscular pump situated between the lungs and well protected by the ribcage, breastbone (sternum) and spinal column. The heart is formed of three layers of tissue: pericardium: a protective covering anchored to the diaphragm myocardium: (heart muscle) a specialised muscle forming the walls of the four chambers of the heart endocardium: the smooth lining inside the heart The heart has two distinct pumps, separated by the septum. The pumps are powered by contractions of the heart muscle. These contractions open and close a series of valves to allow blood to flow in and out of the heart chambers. The following diagram shows the main chambers of the heart, the vessels in which blood enters and leaves the heart, and the direction of blood flow. Equine biological systems 9
The left side of the heart pumps blood which has been enriched with oxygen from the lungs to cells throughout the body. Oxygenated blood from the lungs enters the left auricle via the right and left pulmonary veins, passes through the left ventricle, and leaves via the aorta to the body. The right side of the heart pumps blood carrying waste materials, particularly carbon dioxide, from cells throughout the body back to the heart and on to the lungs. Deoxygenated blood from the body enters the right atrium via the inferior and superior venae cavae, passes through the right ventricle, back to the right auricle, and leaves for the lungs via the pulmonary artery. Equine biological systems 10
Review quiz 5 1 Label the following parts of the heart on the diagram. Right auricle, left auricle, right ventricle, left ventricle, septum, valves. 2 Label the passage of deoxygenated blood into, through and out of the heart. 3 Label the passage of oxygenated blood into, through and out of the heart. Refer back to the diagram on the previous page to check your answers. The lymphatic system Blood capillaries have very thin walls, so some plasma fluid seeps out into the surrounding tissue. The lymphatic system collects this fluid in small capillaries, transporting it through larger and larger vessels until it reaches the chest where it is returned to the blood stream. Besides removing excess tissue fluid the lymph system also: transports waste materials has lymph nodes which filter foreign materials (such as cancerous cells) out of the lymph. Equine biological systems 11
Further reading William O Reece, Physiology of Domestic Animals (3 rd Wilkins, 2004 Ed) Williams and D.R. Lane and B Cooper, Veterinary Nursing (formerly Jones s Animal Nursing, 3 rd Revised Ed). Pergamon Press, 2003 Answers to review quizes Review quiz 1 1 a) Blood is a mix of plasma and cells. 2 b) Plasma is composed mainly of water. 3 a) The function of haemoglobin is to carry oxygen and carbon dioxide in the blood Review quiz 2 1 Veins carry deoxygenated blood. Arteries carry oxygenated blood. Capillaries carry oxygenated or deoxygenated blood. 2 a) False b) True c) False Review quiz 3 Pulmonary circulation carries blood between the heart and lungs Systemic circulation carries blood between the heart and cells throughout the body Portal circulation carries deoxygenated blood from the digestive system through the liver Equine biological systems 12
Knowledge quiz Check your knowledge with the following questions. 1 Give three functions of blood. 2 what is the main function of: a) red blood cells? b) white blood cells? 3 What is the name of the vessels which carry: a) oxygenated blood? b) deoxygenated blood? 4 What is the main difference in the structure between arteries and veins? 5 What is the role of: a) the left side of the heart? b) the right side of the heart? Equine biological systems 13
Glossary Aorta Arterial blood Arteriole Artery Atrium Capillary Endocardium Erthrocyte Haemoglobin Leukocyte Lymph Lymph node Myocardium Pericardium Plasma Portal circulation Pulmonary artery Pulmonary circulation Pulmonary vein Septum Systemic circulation Vascular system Vein Vena cava Venous blood Ventricle artery carrying arterial blood from the heart oxygenated blood narrow artery blood vessel carrying blood away from the heart one of the chambers of the heart very narrow blood vessel inner lining of the heart red blood cell protein in blood to which O 2 and CO 2 become attached white blood cell excess tissue fluid structures in the lymph system which filter out foreign materials heart muscle outer protective layer of the heart liquid component of blood circulation of blood from the abdominal part of the digestive system, the spleen and the pancreas to the liver vessel carrying blood from the heart to the lungs circulation of blood between the heart and lungs vessel carrying blood from the lungs to the heart division between the left and right side of the heart circulation of blood between the heart and the rest of the body, excluding the lungs closed system of blood vessels (veins and arteries) blood vessel carrying blood to the heart vein carrying venous blood into the heart deoxygenated blood one of the chambers of the heart Equine biological systems 14
Acknowledgements This learning pack has been produced by the Land Based Colleges National Consortium Ltd. The LBCNC is a consortium of colleges working in the land-based sector which cooperate in the development and production of quality flexible learning materials which encourage independent learning. We would like to acknowledge the contributions made by the following individuals and colleges in the development of this learning pack. Cover photograph: Steve Watson, Riseholme College, University of Lincoln Developed and produced for LBCNC by Learners First Written by May Johnstone Illustrations: Shevanthi De-Silva Graphic design: Eat Cake Design, Bristol Revised in November 2008 2008 The Land Based Colleges National Consortium Ltd. All rights reserved. Permission to photocopy or adapt the material in this learning pack is granted to members of the Land Based Colleges National Consortium Ltd. only. For further information please contact the LBCNC project management team at 7 Tyne Road, Bishopston, Bristol BS7 8EE. Tel 0117 942 3504 Equine biological systems 15