The Human Excretory System

A powerpoint on the Human Excretory System, intended for the SA Grade 11 Life Sciences Syllabus. Includes information on kidneys, osmoregulation, nephrons, excretion, etc. Hope it helps :)

1. The Human Excretory System Module One: Life Processes in Plants and Animals Paper One

2. Excretion & Homeostasis Homeostasis is the process of maintaining the ideal internal conditions (i.e. correct temperature, right amount of water and glucose & other solutes) for the body to work at it’s optimum. Excretion is the process of removing metabolic waste products and other toxins. Osmoregulation is maintaining the correct balance between water and solutes. Excretion, which includes osmoregulation, is thus extremely important in maintaining homeostasis. Secretion is the release of useful substances, e.g. hormones, from the body. Thus, it is not excretion. Egestion, i.e. defecation, is also not excretion.

3. Removal of Waste Products Certain waste products would become highly toxic if they were to accumulate. This could damage tissues. An excess of water could also lead to a number of complications. Thus, the waste products must be removed – they continually move into the bloodstream, which carries them to the excretory organs.

4. Raw Materials (Food and 0 2 ) Useful Materials Useless Materials Egested (faeces) Metabolised Metabolic Waste Products (urea and CO2) E xcreted Useful Products

5. Excretory Organs There are four main excretory organs: Lungs Colon Skin Kidneys The liver is not an excretory organ, but produces many products which are excreted elsewhere. Toxins and drugs as well as alcohol, is broken down in the liver. Hence, an excess of smoking, medication and alcohol is extremely harmful to the liver.

6. The Lungs The carbon dioxide released from cellular respiration is carried to the lungs in the blood. It then diffuses across the respiratory membrane and is exhaled. A small amount of heat and water is excreted this way. The Colon Bile pigments, from the break down of haemoglobin, and cholesterol are synthesised in the liver. They pass into the small intestine as bile and are finally excreted in the faeces as bile salts, from the colon. Mucus and bacteria are too excreted through the colon.

7. The Skin Sweat, which is excreted through the skin, contains water, salts and some urea. As the water in the sweat is excreted, heat is lost and the body is cooled. Sweat is a form of excretion as it rids the body of waste, as well as a form of secretion as it maintains the body temperature.

8. The Kidneys When amino acids and nucleic acids are broken down, nitrogenous wastes are released as ammonia, urea, uric acid and creatinine . Ammonia is toxic if it accumulates and is therefore converted to less toxic urea in the liver. The following substances are made in the liver and excreted by the kidneys: Urea , the main nitrogenous waste compound secreted. It is formed by the breakdown of excess amino acids in the process of deamination . Uric acid , the nitrogenous end product of nucleic acid metabolism. Creatinine is formed from creatinine phosphate, found in the muscle cells. Non-nitrogenous waste, e.g. CO2, excess water, ions, hormones, poisons and drugs.

9. The Urinary System The main function of the urinary system is to maintain homeostasis by regulating the volume and concentration of body fluids. It filters and reabsorbs certain materials from the blood. The urinary system is made up of the following parts: Two kidneys A bladder An urethra

10. Urinary System: Kidneys The kidneys aid in: excretion as they filter waste out of the blood regulate the water and salt balance in the body. One kidney – the right kidney – is slightly lower than the left as it is pushed down by the liver, which is larger on the right. Each kidney contains: A renal artery (a branch of the abdominal aorta), which carries waste products to the kidney and supplies the kidneys with oxygen and nutrients. A renal vein that contains the purest blood in the body. It carries CO2 to the inferior vena cava. Ureter that carries urine from the kidney to the bladder.

11. Urinary System: Bladder Stores urine Is stimulated by impulses from a motor nerve, to contract to expel the urine. Has sphincter muscles at the base to control the flow of urine Urinary System: Urethra Carries urine from the bladder to outside the body

12. Aorta Carries oxygenated blood, food and waste from the heart Inferior vena cava Carries deoxygenated blood and other substances back to the heart Renal Artery Carries blood from body to kidneys Kidney Excretory and osmoregulatory organ. Motor Nerve Stimulates bladder nerve Renal Vein Carries blood from kidneys to inferior vena cava Ureter Carries urine from kidneys to bladder Bladder Stores urine Urethra Carries urine from bladder to outside the body Adrenal Gland Regulates Salt

13. The Kidneys Found in abdominal cavity below the diaphragm, near the posterior, on either side of the vertebral column. Kept in position with connective tissue, the peritoneum, as well as renal blood vessels. They are wedged in with other organs. Externally they are bean-shaped, dark red and the size of a large bar of soap. The inner, concave border is called the hilum. Surrounded by three layers of protective tissue: A tough, fibrous renal capsule on the surface protects them from disease. A middle layer of adipose tissue cushions them against blows. An outer layer of fibrous connective tissue, the renal fascia, anchors the kidneys to surrounding structures.

14. Renal Capsule Protects kidney Nephron Medulla Made up of pyramids Pyramid Made up of collecting ducts Calyx Collects urine from collecting ducts Papilla Tips of each pyramid, fits into calyx Renal artery Carries blood to kidneys Renal vein Carries blood fromkidneys Ureter Carries urine from pelvis to bladder for storage

15. Blood Supply of Kidney The kidney needs to have a constant supply of blood in order to control the composition of body fluids. The renal artery, a branch from the aorta, enters the kidney at the hilum. It supplies blood rich in nitrogenous waste, oxygen and nutrients. The renal vein carries purified, deoxygenated blood to the inferior vena cava, and then to the heart.

16. Glomerular Filtration The fluid part of the blood is filtered from the glomerulus into the cavity of the Bowman’s capsule. Tubular Reabsorption As the fluid flows along the renal tubule, useful substances are reabsorbed back into the bloodstream according to the body’s needs. Tubular Excretion In addition, certain unwanted substances in the blood are actively excreted into the tubules. How the Kidneys Function

17. A passive, non selective process. Fluids and solutes are forced through the glomerular membrane by hydrostatic pressure. The glomerular filtrate has the same composition as blood, without the blood cells and plasma proteins. These are too large to fit through the glomerular membrane . Substances in glomerular filtration: Blood plasma without protein molecules which includes: Useful substances – water, glucose, amino acids, vitamins, hormones, and ions. Waste substances – e.g. nitrogenous waste such as urea, uric acid and creatinine . Glomerular Filtration

18. Occurs in the loop of Henle . Substances are reabsorbed in the following ways: Active reabsorption Passive reabsorption Tubular Reabsorption

19. This is the process by which substances are reabsorbed. Carrier molecules on the microvilli join up with certain molecules from the filtrate and actively transport them through the epithelial cells to the blood. Energy from ATP is used to join the molecule to the carrier molecule. The following are actively reabsorbed: All organic nutrients such as glucose, amino acids and water soluble vitamins are completely reabsorbed. Sodium ions and fat soluble vitamins are selectively reabsorbed, according to the needs of the body. Active Reabsorption

20. Passively = no energy needed. About 65% of the water is passively reabsorbed from the filtrate in the proximal convoluted tubule by osmosis. Chloride ions passively follow the path of sodium ions. Urea, uric acid and creatinine is not reabsorbed. Passive Reabsorption

21. Takes place in proximal and distal tubules and is reabsorption in reverse. The following molecules and ions are taken from the blood and deposited into the filtrate: Hydrogen and potassium ions (secreted directly) Creatinine and uric acid Drugs, preserves and colourants (actively excreted) Tubular Excretion

22. About 96% of urine is water. 1.5% is salts, mainly sodium chloride. Urea makes up 2% Small quantities of drugs, colourants , hormones and preservatives. About 1.5 litres of urine is produced daily. Composition of Urine

23. Maintain homeostasis in the following ways: Excreting nitrogenous waste Osmoregulation – water and salts Maintain pH of body fluids Maintain electrolytic (salt) balance of body fluids by absorbing and/or secreting ions. Key Functions of Kidneys