Module 11: Human Health and Physiology II 11.3 The Kidney

Assessment Statements Define excretion. Draw and label the structure of the kidney. Annotate a diagram of a glomerulus and associated nephron to show the function of each part. Explain the process of ultrafiltration, including blood pressure, fenestrated blood capillaries and basement membrane. Define osmoregulation. Explain the reabsorption of glucose, water and salts in the proximal convoluted tubule, including the roles of microvilli, osmosis and active transport. Explain the roles of the loop of Henle, medulla, collecting duct and ADH in maintaining the water balance of the blood. Explain the differences in the concentration of proteins, glucose and urea between blood plasma, glomerular filtrate and urine. Explain the presence of glucose in the urine of untreated diabetic patients.

Define excretion. Excretion is the removal of waste products of cell reactions/metabolic pathways

Draw and label the structure of the kidney Renal pelvis Renal

Annotate a diagram of a glomerulus and associated nephron to show the function of each part. The functional unit of the kidneys is the nephron

Explain the process of ultrafiltration, including blood pressure, fenestrated blood capillaries and basement membrane. The afferent arteriole brings in unfiltered blood into the glomerulus. Unlike other capillary beds, it has fenestrations that open when blood pressure is high. The pressure is maintained due to the fact that the efferent arteriole has a smaller diameter than the afferent arteriole. This is called ultrafiltration. Basement membrane

Explain the process of ultrafiltration [2 marks] blood (in the glomerulus) under high pressure caused by difference in diameter of (afferent and efferent) arterioles; fluid plasma and small molecules forced into kidney tubule/ Bowman’s capsule/through fenestrations/basal membrane; which prevent larger molecules/blood cells from passing through;

Define osmoregulation. Osmoregulation is the homeostatic control of the water balance of the blood, tissue or cytoplasm of a living cell/organism

Quick review… What structure is responsible for ultrafiltration? How is the high blood pressure generated in the glomerulus? What are fenestrations? What kind of molecules cannot pass through the basement/basal membrane? What happens to these molecules?

Explain the reabsorption of glucose, water and salts in the proximal convoluted tubule, including the roles of microvilli, osmosis and active transport. There are many useful substances left in the filtrate once it enters the proximal convoluted tubule. This is where reabsorption occurs. These substances are returned back to the blood using the peritublar capillary bed.

Explain the reabsorption of glucose, water and salts in the proximal convoluted tubule, including the roles of microvilli, osmosis and active transport.. 1)Glucose is actively transported from the filtrate into the cells of the proximal convoluted tubule wall to the peritubular capillary bed 2)Salt ions (Na +, K -, Cl - ) are actively transported into tubule cells and then to the intercellular fluid outside the tubule before entering the peritublar capillary bed 3)Water follows the flow of salt ions and leaves the filtrate to enter the tubule cells  intercellular fluid  peritubular capillary bed through osmosis

Explain the roles of the loop of Henle, medulla, collecting duct and ADH in maintaining the water balance of the blood. Descending portion: permeable to water; impermeable to salt Ascending portion: permeable to salt; impermeable to water The loop of Henle makes a hypertonic environment in the medulla

Explain the roles of the loop of Henle, medulla, collecting duct and ADH in maintaining the water balance of the blood. The hypertonic environment of the medulla draws out water from the collecting duct via osmosis. ADH increases the permeability of the DCT and the collecting duct by opening pores called aquaporins. If there is no ADH, water content in filtrate remains high and is excreted in urine

Explain the differences in the concentration of proteins, glucose and urea between blood plasma, glomerular filtrate and urine. Proteins are too large to pass through the basement membrane into the filtrate Glucose is actively transported back into the peritubular capillary (even though it makes it to the filtrate) High concentration of urea is due to reabsorption of water MoleculeAmount in blood plasma (mg 100 ml -1 ) Amount in glomerular filtrate (mg 100 ml -1 ) Amount in urine (mg 100 ml -1 ) Proteins>70000 Glucose>90 0 Urea30 >1800

Explain the presence of glucose in the urine of untreated diabetic patients. Blood glucose is so high that the maximum rate of active transport of glucose is exceeded. As a result, glucose is left in the filtrate.

Explain why diabetes could be detected through the analysis of urine [8 marks] urine of diabetics contains glucose; whereas urine of non-diabetics contains no glucose; glomerular filtrate contains glucose / glucose filtered out; glucose (normally) reabsorbed from filtrate/into blood; through wall of / in the proximal convoluted tubules; blood glucose concentration higher than normal in diabetics; reabsorption not completed / pumps cannot reabsorb all glucose in diabetics; glucose in urine can be detected using test strips; type I diabetes is lack of insulin secretion / lack of β cells; type II diabetes is body cells not responding to insulin / not absorbing glucose;8 max