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4. NUTRITION: THE CIRCULATORY AND EXCRETORY SYSTEMS. INTRODUCTION. DISCUSS THE FOLLOWING QUESTIONS. Why is blood so important? What is the relationship between blood and the heart? How does the body get rid of waste products? 1. THE INTERNAL ENVIRONMENT AND BLOOD. Blood is a viscous fluid with a salty taste which flows inside the vessels of the circulatory system. The human body contains around 5.5 litres of blood. 1. THE INTERNAL ENVIRONMENT AND BLOOD. 1.1 COMPOSITION OF BLOOD. 1.1 COMPOSITION OF BLOOD. BLOOD PLASMA: is a yellowish substance made up of water containing various dissolved molecules: minerals, nutrients, waste products (urea, uric acid, CO2), proteins and hormones. 1.1 COMPOSITION OF BLOOD. •THERE ARE THREE TYPES OF CELLS: ERYTHROCYTES or red blood cells: -Most common. 99% -Haemoglobin. -120 days living. 1.1 COMPOSITION OF BLOOD. •THERE ARE THREE TYPES OF CELLS: LEUCOCITES or white blood cells: -There are fewer white blood cells than red ones -Neutrophils, eosinophils, basophils, lymphocytes and monocytes. -Protect the body from infections. 1.1 COMPOSITION OF BLOOD. •THERE ARE THREE TYPES OF CELLS: TROMBOCYTES: -Not true cells but cell fragments. -They contain enzymes that allow the blood to coagulate preventing hemorrhage 1.2 THE FUNCTIONS OF BLOOD. •TRANSPORT. •COLLECT WASTE PRODUCTS (UREA, CO2…) •REGULATE TEMPERATURE. •PROTECTION. •HEMOSTASIS. 12 2.1 THE BLOOD VESSELS. As arteries get further away from the heart, they gradually branch out into narrower vessels leading to the different organs. These vessels then divide into even smaller ones called arterioles. 2. THE BLOOD VESSELS. 3. THE HEART. In order for the blood to move around the circulatory system, it needs to be pumped by the heart. Cells depend on the heart to receive a constant supply of nutrients and oxygen. Poor heart function can have fatal consequences. 3. THE HEART. The heart is a hollow organ made of muscle tissue. It is divided into two halves, right and left, by an internal wall. The two halves are not connected in any way. 3. THE HEART. Each half is then divided again into a small upper chamber, the atrium, and a larger lower chamber, the ventricle. Between the atrium and the ventricle on each side, there is a valve: the atrioventricular valve. This allows blood to flow from the atrium to the ventricle, but not vice versa. 3. THE HEART. Several veins lead to the atria: two venae cavae on the right and four pulmonary veins on the left. Two arteries lead away from the ventricles: the pulmonary artery (on the right) and the aorta (on the left). The semilunar valves prevent blood from flowing back to the heart after it has left. 3. THE HEART. 3. THE HEART. 21 2.2.1 HEARTBEAT. Each heartbeat has three phases: atrial systole, ventricular systole and diastole. ATRIAL SYSTOLE: the atria contract and the blood is pumped into the ventricles via the open atrioventricular valves. 2.2.1 HEARTBEAT. VENTICULAR SYSTOLE. The ventricles contract, the semilunar valves open, and the blood flows out into the pulmonary artery and the aorta. At the same time, the atrioventricular valves close. 2.2.1 HEARTBEAT. DIASTOLE. The heart relaxes and draws flood from the venae cavae and pulmonary veins. This blood flows into the atria. 2.3. BLOOD CIRCUITS. Blood is constantly pumped around a circuit of blood vessels (arteries, capillaries and veins) by the heart. In humans, this circuit has two parts: pulmonary circulation and systemic circulation. Pulmonary artery leads away from the heart and splits into two arteries which each lead to a lung. The blood starts in the left ventricle and flows along the aorta, which splits into arteries, arterioles and capillaries. These lead to all body tissues and organs except the lungs. 26 3. THE LYMPHATIC SYSTEM. Water and solutes from blood plasma filter out the capillaries into the spaces between the cells in the body tissue. These spaces are filled with a fluid known as the interstitial fluid. Excess interstitial fluid is collected, and then returned to the bloodstream, by the lymphatic system. 3. THE LYMPHATIC SYSTEM. 3. THE LYMPHATIC SYSTEM. This system is made up of lymphatic vessels and lymph nodes. •Lymphatic vessels. These include lymphatic capillaries in the body tissues. They join together to form progressively larger ducts called lymph-collecting vessels, which lead back to the veins of the circulatory system. •Lymphatic nodes. These organs are located along the route followed by some lymphatic vessels. They produce lymphocytes, release them into the vessels and filter waste substances out from the vessels. 3.1. FUNCTIONS OF THE LYMPHATIC SYSTEM. FUNCTIONS OF THE LYMPHATIC SYSTEM. •It maintains the fluid balance between the interstitial fluid and the blood plasma. •It helps protect the body from infection. •It collects the products of fat digestion in the small intestine. 31 4. THE EXCRETORY SYSTEM. The excretory system is made up of the urinary system and a number of other organs and systems that contribute to the excretion of waste products. •Respiratory system. This removes carbon dioxide from the blood and expels it from the body. 4. THE EXCRETORY SYSTEM. •Sweat glands. They produce sweat, which evaporates to cool the skin. Some excretory substances are also expelled from the body in sweat. 4. THE EXCRETORY SYSTEM. •Liver. This organ eliminates products resulting from the breakdown of haemoglobin from old red blood cells. It is also eliminates a small amount of cholesterol and some toxic substances. 4. THE EXCRETORY SYSTEM. •Urinary system. This is the most important part of the excretory system. It eliminates waste products in the form of urine. 4.1 The Urinary system. THE KIDNEYS. These two organs are at the back of the abdomen (one on each side). Each kidney has an external part (cortex) and an internal part (medulla), and a hollow chamber (renal pelvis). URINE is formed in the cortex and medulla. It contains excretory substances and drains into the renal pelvis. 4.1 The Urinary system. THE KIDNEYS. Each kidney is made up of over a million nephrons, small tubes with an open end surrounded by a capillary. They filter the blood to produce urine. 4.1 The Urinary system. THE KIDNEYS. Nephrons are made up of several parts: 39 4.1.2 Urinary tract. THE URETERS, THE BLADDER AND THE URETHRA. Urine is collected from the kidneys, stored, and then expelled from the body. There are different organs for these functions. •URETERS. There are two narrow tubes, around 28 cm long, connecting the renal pelvis of the kidney to the bladder. 4.1.2 Urinary tract. THE URETERS, THE BLADDER AND THE URETHRA. •BLADDER. An elastic sac where urine collects before it is expelled from the body. When the bladder fills up with urine, a nervous stimulus makes the bladder contract and push the urine out (via urethra). 4.1.2 Urinary tract. THE URETERS, THE BLADDER AND THE URETHRA. •URETHRA. This duct leads to the outside of the body. In men, the urethra is connected to the reproductive system. This means that urine and semen pass through it (at different times). In women, the urethra is separate form the reproductive system. 4.2 Urine formation. PRODUCTION OF URINE. Urine is a liquid obtained from the blood and made up of water, various minerals, and different waste products (mainly urea and uric acid). Urine is produced in two phases: GLOMERULAR FILTRATION: this process filters the water and most of the solutes circulating in the blood plasma. The liquid that enters Bowman´s capsule is similar to blood plasma but does not contain proteins. TUBULAR REABSORPTION: as they travel through the nephron´s tubule, a lot of filtered substances are reabsorbed, including nutrients, vitamins, amino acids, etc. Water is reabsorbed in the loop of Henle, and the other substances are reabsorbed in the proximal tube. Waste substances are nor reabsorbed. 44