Learning Objectives EXCRETION Recall the origin of CO 2 and O 2 as waste products of metabolism. Recall that the lungs, kidneys and skin are organs of excretion. Understand how the kidney carries out its roles of excretion. STRUCTURE OF URINARY SYSTEM AND THE KIDNEYS Describe the structure of the urinary system. Describe the structure of a nephron.

Excretion Some products of chemical reactions that occur within cells are poisonous and so must be removed. Excretion is the removal from the body of: The ______ products of its chemical reactions. The excess ______ and _____ taken in with the diet. Spent __________. D____. Any other foreign substances taken into the alimentary canal and absorbed by the blood. waste watersalts hormones rugs

Excretory Organs – Lungs _________ (the breakdown of glucose) produces ______ ______, which is carried away from the cells by the _____, and removed in the _____. The loss of water vapour from the lungs is unavoidable, and not a method of controlling the water content of the body. carbon dioxide bloodlungs Respiration

Excretory Organs – Skin When we ______, we expel water, sodium chloride (____) and traces of urea. The skin is not a true example of an excretory organ though, as sweating is a response to a rise in temperature, not a change in the blood composition. sweat salt

Excretory Organs – Kidneys Excess amino acids are broken down in the ____, to form glycogen and ____. The ____ is removed from tissues by the _____, and expelled by the kidneys. Urea and uric acid from the breakdown of protein contain nitrogen – nitrogenous waste products. When hormones have done their job, they are modified in the liver and excreted. _____ is the watery solution excreted by the kidneys which contains the nitrogenous waste products, excess salts and ______, drugs, toxins and spent hormones. blood urea Urine water liver

Structure of the Kidneys Two kidneys. Fairly solid, oval-shaped structures. Red-brown in colour. Enclosed in a transparent membrane. Attached to the back of the abdominal cavity. Renal artery branches off from the aorta and supplies the kidneys with oxygenated blood. The renal vein takes deoxygenated blood back to the vena cava.

Ureter – a tube that connects each kidney to the bladder. Renal tubules – many capillaries and tiny tubes in the kidney tissue, held together with connective tissue. Cortex – dark outer region of kidney. Medulla – lighter, inner zone. Pelvis – space where the ureter joins the kidney. Glomerulus – a divided and coiled capillary leading from each arteriole. The renal artery divides up into many arterioles and capillaries in the cortex.

Renal capsule (Bowman’s capsule) – a cup-shaped organ almost entirely surrounding the glomerulus. It is a smooth semi-transparent membrane. The renal capsule leads to the renal tubule. Collecting duct – the coiled and looped renal tubule leads to the collecting duct. The collecting duct passes through the medulla and opens into the pelvis. Nephron – a single glomerulus with its renal capsule, renal tubule and capillaries. There are thousands of glomeruli in the cortex, and the surface area of their capillaries is very large.

A NEPHRON Renal capsule (Bowman’s) Glomerulus (capillaries) Renal artery (blood with waste) Renal vein (blood without waste) Loop of Henle Renal tubule Collecting duct

YOUR TURN LABEL KIDNEY AND NEPHRON WORKSHEET : ‘19: matchmaker – removing wastes’ QUESTIONS

Learning Objectives ULTRAFILTRATION Describe ultrafiltration in the Bowman’s capsule and the composition of the glomerular filtrate. SELECTIVE REABSORPTION Understand that water is reabsorbed into the blood from the collecting duct. Understand that selective reabsorption of glucose occurs at the proximal convoluted tubule.

Ultrafiltration The process by which fluid is filtered out of the blood by the glomerulus into the Bowman’s capsule. This allows the body to remove waste products and regulate the amount of water in the blood. The blood pressure in the glomerulus is very high. This causes small molecules like water with dissolved salts, glucose, urea and uric acid to leak out of the blood plasma through the capillary walls. Red blood cells and proteins are too large to filter out (similar to tissue fluid).

Selective Reabsorption This filtrate from the glomerulus (glomerular filtrate) collects in Bowman’s capsule and trickles down to the renal tubule and collecting duct. The surrounding capillaries absorb back into the blood those substances that the body needs: All the glucose (occurs in the proximal convoluted tubule) Much of the water Some of the salts All other substances not needed by the body (rest of salts, urea, uric acid, water) continue down the renal tubule into the pelvis, then onto the ureter to bladder.

Learning Objectives OSMOREGULATION AND ADH Understand how the kidney carries out its roles of osmoregulation. Describe the role of ADH in regulating the water content of the blood.

Osmoregulation The regulatory processes that keep the blood at a steady concentration. The body gains and loses a lot of water all the time. How/where? The kidneys keep the concentration of body fluids within very narrow limits. If the blood concentration is too dilute (too much water): Less water is reabsorbed by the renal tubules So more enters the bladder So a large volume of dilute urine is produced.

If the blood is too concentrated, more water is reabsorbed from the renal tubules. If the body is short of water (e.g. after sweating profusely), only a small amount of urine is produced. The ‘thirst’ centre in the brain is stimulated, to return the blood to its correct concentration. Because these processes regulate the osmotic strength of the blood, it is called osmoregulation. It is an example of homeostasis – keeping the composition of the tissue fluid within narrow limits.

ADH (anti-diuretic hormone) Detected by the hypothalamus in the brain, and produced by the pituitary gland. ADH is secreted into the blood if the concentration is too high. ADH causes the kidneys to reabsorb more water from the glomerular filtrate back into the blood. The urine then becomes more concentrated, and less water is lost from the blood. The opposite will happen if the blood passing through the brain is too dilute.