Equine biological systems Pack 20 The lymphatic system Pack Code: EBS20 This pack will help you to: List the functions of the lymphatic system. Describe the components of the lymphatic system.. www.lbcnc.org.uk
About this pack Objectives When you have completed this pack you should be able to describe how the horse s lymphatic system works. The pack will help you to: List the functions of the lymphatic system. Describe the components of the lymphatic system. The pack is also relevant to the level 3 unit Understand Animal Anatomy and Physiology, and in particular: Outcome 1: Know the structure and functions of biological systems in animals. 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 20: The lymphatic system Pack 21: The endocrine system Pack 22: The nervous system There are also packs on: Reproduction Cells, tissues and sensory organs Breeding and genetics Equine biological systems 2
Introduction The lymphatic system is closely linked to the circulatory system, as it contains a network of capillaries and vessels that collect excess fluid and return it to the bloodstream. However, it also contains a number of tissues and organs, including the spleen and bone marrow, and plays a crucial role both in the immune system, and in fat digestion. Functions of the lymphatic system The lymphatic system has a number of important functions: Draining excess fluid. 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. Immune response. Lymph also collects foreign materials (including bacteria, viruses and other dangerous materials such as cancerous cells) and transports them to lymph nodes where they can be destroyed. Absorbing nutrients. The lymph system collects the products of fat digestion from the small intestine and transports these to the bloodstream. Transport. The lymph also transports cells used in the immune response and waste materials. This diagram shows some of the main parts of a horse s lymphatic system that we shall describe in this pack including some superficial lymph nodes those that you can feel. There are many more lymph nodes deeper in the body and many capillaries and vessels. Superficial lymph nodes: Parotid Submanibular Prescapular Axillary Inguinal Popliteal Tonsils Thymus Bronchial lymphatic tissue Lymphatic duct Spleen Lymphatic tissue in intestine Equine biological systems 3
How the lymphatic system works We will now look at the main parts of the lymphatic system in turn. Lymphatic capillaries and vessels The lymphatic capillaries are thin-walled tubes which collect the excess fluid that has leaked into the interstitial fluid of body tissues. This fluid becomes lymph and is passed to lymphatic vessels (rather like veins in the blood system), via one or more lymph nodes. Vessels before a lymph node are called afferent while those after a node are called efferent. From the lymphatic vessels lymph is passed to one of the two lymph ducts: The right lymph duct drains the right forelimb, shoulder and right side of the head and neck. The left lymph duct (also called the thoracic duct) drains other parts of the body left forelimb, shoulder and left side of the head and neck as well as the hind limbs and abdomen. From the lymph ducts lymph drains into the jugular vein or the cranial vena cava and is returned to the heart. Valves regulate the flow of lymph Interstitial fluid Lymphatic capillaries Afferent lymphatic vessels Lymph nodes Efferent lymphatic vessels Lymph ducts Veins Activity Suggest: a) One way in which the lymphatic system is similar to the blood circulation system b) One way in which the lymphatic system is different from the blood circulation system Check your answers with those at the end of the pack. Equine biological systems 4
Lymph nodes As lymph travels through the lymphatic vessels it passes through small organs called lymph nodes. There are many lymph nodes throughout the body, especially in areas where lymphatic vessels converge. The lymph fluid enters the node via a valve and flows through the sinuses. Within the cortex of the node nodules supply two types of white blood cells called lymphocytes which are vital for the immune response: B lymphocytes in the lymph nodes produce antibodies which lock on to bacteria and other antigens. T lymphocytes (sometimes called killer cells) locate the bacteria, cells infected with viruses, and cancer cells, and destroy them Bone marrow and the thymus Two other parts of the system, bone marrow and the thymus, are crucial for the development of lymphocytes. B lymphocytes are produced in the bone marrow. T lymphocytes grow to maturity in the thymus. The thymus is found in the front part of the chest and is especially important in foals and other young animals. Equine biological systems 5
Review quiz 1 Lymph enters a lymph node from:! a) an afferent vessel! b) an efferent vessel 2 Lymph leaves a lymph node into:! a) an afferent vessel! b) an efferent vessel 3 The left lymph duct is also called:! a) the cervical duct! b) the thoracic duct! c) the spleen duct 4 Antibodies are produced by:! a) B lymphocytes! b) T lymphocytes 5 Which of the following grows to maturity in the thymus?! a) B lymphocytes! b) T lymphocytes 6 Give three functions of the lymphatic system: a) b) c) Check your answers at the end of this pack. Equine biological systems 6
The spleen The spleen is the largest organ of the lymphatic system, and is found close to the stomach. It also has an important role in filtering abnormal cells out of the blood and contains lymphocytes for attacking antigens. The spleen also destroys old red blood cells Other lymphatic tissue Away from the spleen, thymus and lymph nodes there are several other areas of lymphatic tissue in the horse s body: Lymphatic tissue in the small intestine (gut associated lymphoid tissue or GALT) collects the nutrients from fat digestion. The tonsils help to prevent antigens from entering the body via the mouth. Other lymphatic tissue associated with the nose, bronchus, larynx and skin (mucosa associated lymphoid tissue or MALT) also contains lymphocytes. Disorders of the lymphatic system Because the lymphatic system is so important to the immune response, problems with the system often indicate another problem. Inflamation of the lymph nodes can occur when a horse is fighting off disease, or after a vaccination. The term lymphadenopathy is used to describe swelling of the lymph nodes resulting from infection while lymphadenitis describes inflammation of the lymph nodes. Inflamation of the lymph vessels is lymphangitis. Lymphosarcoma is a cancer of the lymphocytes and lymphatic tissue. Although cancer in horses is quite rare, this is one of the more common cancers to affect horses. Equine lymphedema is a condition sometimes found particularly in certain breeds such as friesian horses. It happens when the lymphatic system fails to absorb interstitial fluid so that fluid bulds up in tissues leading to swollen limbs. Metastasis: the lymphatic system transports cancerous cells and lymph nodes collect them. If the lymphocytes fail to destroy them, secondary cancers can develop. Equine biological systems 7
Further reading Glossary Reece, W. O., 2009. Functional Anatomy and Physiology of Domestic Animals (4 rd Ed) Wiley-Blackwell Lane, D. R. and Cooper, B., 2003. Veterinary Nursing (formerly Jones s Animal Nursing, 3 rd Revised Ed). Butterworth Heinemann Afferent vessel Efferent vessel GALT Interstitial fluid Lymphocytes MALT Superficial lymph nodes Lymphatic vessel before a lymph node Lymphatic vessel after a lymph node Gut associated lymphoid tissue Fluid found in body tissues Types of white blood cells which are vital for the immune response Mucosa associated lymphoid tissue Nodes that you can feel Answers to activities Activity on page 4 The lymphatic system is similar to the blood circulation system in that it transports a fluid round the body and contains capillaries and vessels. Differences include the fact that the lymphatic system transports lymph rather than blood although the two fluid have similarities, they The lymphatic system only transports lymph towards the heart while blood is transported both to and from the heart. Review quiz on page 6 1 Lymph enters a lymph node from (a) an afferent vessel 2 Lymph leaves a lymph node into (b) an efferent vessel 3 The left lymph duct is also called (b) the thoracic duct 4 Antibodies are produced by (a) B lymphocytes 5 Which of the following grows to maturity in the thymus? (b) T lymphocytes 6 The main functions of the lymphatic system are: Draining excess fluid Immune response Absorbing nutrients Transport Equine biological systems 8
Knowledge quiz Check your knowledge with the following questions. 1 Give three functions of the lymphatic system: a) b) c) 2 What is the main function of: a) the spleen? b) lymph nodes? c) the thymus? 3 What are the two types of lymphocytes? a) b) 4 What is the role of the gut associated lymphoid tissue? 5 List two disorders of the lymphatic system: a) b) Equine biological systems 9
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. Critical review Lorna Cameron, Sparsholt College Jackie Irving, Barony College Cover photograph: Steve Watson, Riseholme College Developed and produced for LBCNC by Learners First Revised in September 2013 2013 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 10