Primary Defences against Disease PDF

PRIMARY DEFENCES AGAINST DISEASES By Abigail,Piraarthana and Ifunanya The primary non-specific defences against pathogens in animals Pathogenic organisms need to enter the body of their host before they can cause harm Evolution has selected hosts adapted to defend themselves against...

PRIMARY DEFENCES AGAINST DISEASES By Abigail,Piraarthana and Ifunanya The primary non-specific defences against pathogens in animals Pathogenic organisms need to enter the body of their host before they can cause harm Evolution has selected hosts adapted to defend themselves against such invasions Primary defences are the mechanisms that have evolved to prevent the entry of pathogenic organisms They are non- specific as they will prevent the entry of any pathogen  CONTENTS 01 BLOOD02 03 INFLAMMATIO THE SKIN CLOTTING & N SKIN REPAIR 04 05 06 OTHER EXPULSIVE MUCOUS PRIMARY REFLEXES MEMBRANES DEFENCES 0 1 THE SKIN  The Skin The outer layer of skin is called the epidermis which consists of dead and hardened cells filled with keratin This acts as an effective physical barrier against any pathogens Keratinisation Cells at the base of the epidermis are produced via mitosis. They migrate outwards to the surface of the skin The fibrous protein keratin is produced During migration they dry out and the cell eventually dies This leaves a keratinised layer of dead skin cells (which eventually fall off)  Surface of skin covered with oily sebum produced by sebaceous glands The sebum contains fatty acids which creates an acidic layer preventing growth of harmful bacteria The surface of the skin also has harmless microorganisms which help to reduce the growth of pathogens  0 2 BLOOD CLOTTING & SKIN REPAIR  In order for the skin to be an effective barrier, it must be complete, so when it is wounded, blood clots are formed to prevent infection and excessive blood loss. This process involves platelets releasing substances that are known as clotting factors. ➔ These factors activate an enzyme cascade (a sequence of biochemical reactions where one enzyme activates another, which in turn activates another, and so on, creating a chain reaction)  SPEC POINT: blood clotting (limited to platelets releasing substances that, via a cascade of events, result in the Steps of blood formation of fibrin which itself forms a network, trapping platelets and clotting forming a clot) 1) When activated, platelets form a plug over the damaged area by sticking to the wounded area and each other 2) Platelets also release clotting factors eg thromboplastin 3) Thromboplastin and calcium ions work on a blood protein called prothrombin 4) Prothrombin is converted into an active enzyme known as thrombin 5) Thrombin acts on a soluble blood protein called fibrinogen and catalyses the formation of an insoluble protein called fibrin 6) Fibrin forms a mesh which traps platelets and red blood cells, forming a blood clot/thrombus  Skin repair - Platelets also release serotonin which causes the smooth muscle in the blood vessel walls to contract, this narrows the blood vessel and reduces blood flow to the damaged area and draws the edges of the cut together - The blood clot dries up to form a scab which prevents the entry of pathogens - Underneath the scab, stem cells in the skin’s epidermis undergo mitosis and differentiate into skin cells to replace the damaged ones. - When the new cells have all formed, the scab drops off 0 3 INFLAMMATION  Inflammation is a natural biological response to foreign stimula or tissue damage One of the signs that a tissue is infected is swelling, redness, heat and pain known as inflammation The presence of microorganisms in the tissue is detected by specialised cells called mast cells - These cellsmain ➔ The release a cell effect signalling is to substance called cause vasodilation histamine and make the capillary wall more permeable to white blood cells and some proteins ➔ Blood plasma and phagocytic white blood cells leave the blood and enter the tissue fluid ➔ This leads to increased production of tissue fluid , which causes swelling (oedema). ➔ Excess tissue fluid is drained into the lymphatic system where lymphocytes are stored ➔ This can lead to pathogens coming in contact with lymphocytes and initiating specific immune responses  EXPULSIVE REFLEXES (COUGHING AND 0 SNEEZING) Expulsive reflexes are automatic bodily responses that expel harmful substances from the body such as pathogens, helping to defend against infection and disease. Coughing - When the body is triggered by irritants, it reacts by forcefully expelling 4 air from the lungs to clear the airways and prevent them from entering the lungs, where they could cause infections like bronchitis (inflammation of the bronchi caused by exposure to irritants). Sneezing - Sneezing is primarily a defence for the nasal passages and upper respiratory tract, helping to expel irritants or pathogens from the nose and sinuses. - When foreign particles are detected in the nasal passages, it triggers sneezing which forces out mucus which removes pathogens, preventing them from causing any sinus infections ( eg acute viral sinusitis) or entering the respiratory system 0 5 MUCOUS MEMBRANES  Mucous membranes The exchange surfaces where certain substances such as oxygen and nutrients in our food enter our blood must be thinner and therefore less protected from pathogens The air and food that we take in from our environment may harbour microorganisms - Therefore, the airways, lungs and digestive system are at risk of infection Exposed parts of the body are also at risk of pathogen entry. - Such as the oral passages, nasal passages, eyes and ears. These areas are protected by mucous membranes The mucous membranes form a chemical primary defence.  The epithelial layer contains mucus-secreting cells called goblet cells Goblet cells secrete mucous, which traps pathogens These trapped organisms can be removed from the body via expulsive reflexes, which include coughing, sneezing, and vomiting. - They occur automatically when a certain part of the body is irritated e.g. sneezing occurs when the respiratory tract is irritated by dust. There are also extra mucus- secreting glands under the epithelium In the airways, the mucus lines the passages and traps any pathogen that may be in the air The epithelium also has ciliated cells. - The cilia move in a coordinated fashion to waft the layer of mucus along ➔ They move the cilia up to the top of the trachea , where it can enter the oesophagus ➔ It is swallowed and passed down the digestive system where most pathogens are killed by the acidity of the stomach which can be pH 1-2 ( this denatures the pathogen’s enzymes) 0 Other primary defences 6 Tear fluid contains antibodies and digestive enzymes which protect the eyes from pathogens The ear canal is lined with wax. The wax is responsible for trapping any pathogens The female reproductive system is protected by a mucus plug in the cervix and maintains relatively acidic conditions QUIZ - 10 multiple choice questions ACCESO A NUESTRO ESTUDIO Puedes reemplazar las imágenes en las pantallas por otras. Haz clic derecho en ellas y luego elige "Reemplazar imagen" para que puedas agregarlas