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Excretion
The Kidney, Excretion and Osmoregulation
| Question | Answer |
|---|---|
| This is the removal of the waste products of metabolism from the body. | Excretion |
| This is the removal of substances such as dietary fibre that has not been involved in the metabolic activity of cells. | Egestion (elimination) |
| This is the process by which animals control solute concentrations inside their bodies by balancing water gain and loss. | Osmoregulation |
| This is any compound produced from the chemical reactions of the catabolic or anabolic pathways of an organism. | Metabolite |
| The 4 main organic elements in organic compounds and how they are excreted. | CHON Excreted as CO2, H20 and urea |
| The 3 main stages in urea production | 1) Amino groups are removed from amino acids (deamination) and made into NH3. 2) Remainder of amino acid can be respired to give ATP 3) NH3 is actively converted to urea by addition of CO2 in the ornithine cycle. |
| Formula for urea | CO (NH2)2 |
| An outer membrane that protects the kidney | fibrous capsule |
| A lighter coloured outer region made up of renal (Bowman's) capsules, convoluted tubules and blood vessels | cortex |
| A darker coloured inner region made up of loops of Henle, collecting ducts and blood vessels | medulla |
| A funnel-shaped cavity that collects urine into the ureter | renal pelvis |
| A tube that carries urine to the bladder | ureter |
| Blood vessel which supplies the kidney with blood from the heart via the aorta | renal artery |
| Blood vessel which returns blood to the heart from the kidney via the vena cava | renal vein |
| The basic structural and functional unit of the kidney | nephron |
| The closed end at the start of the nephron; cup-shaped and contains the mass of blood capillaries known as the glomerulus. Its inner layer is made up of specialised cells called podocytes. | Renal (Bowman's ) capsule |
| Specialized cells which make up the inner layer of the renal capsule. | Podocytes |
| A series of loops surrounded by blood capillaries. Walls are made up of cuboidal epithelial cells with microvilli. | Proximal convoluted tubule (PCT) |
| A long, hairpin loop that extends from the cortex into the medulla of the kidney and back again. It is surrounded by blood capillaries. | Loop of Henle |
| A series of loops surrounded by blood capillaries. Its walls are made of cuboidal epithelial cells, but is surrounded by fewer capillaries than the proximal tubule. | Distal convoluted tubule (DCT) |
| A tube into which a number of distal convoluted tubules empty. It is lined by cuboidal epithelial cells and becomes increasingly wide as it empties into the pelvis of the kidney. | Collecting duct |
| A tiny vessel that is a branch of the renal artery and supplies the nephron with blood. | Afferent arteriole |
| A many-branched knot of capillaries from which fluid is forced out of the blood. | Glomerulus |
| A tiny vessel that leaves the renal capsule. | Efferent arteriole |
| A concentrated network of capillaries that surrounds the nephron and merge together to form the renal vein. | Peritubular capillaries |
| State 4 functions of the kidneys. | 1) Regulation of the composition of the blood and maintaining a constant water potential 2) Regulating blood pressure 3) Maintaining the body's calcium level 4) Stimulating the production of red blood cells |
| State 3 ways in which the kidneys regulate the composition of blood. | 1) Maintain a constant volume of water 2) Remove waste such as urea 3) Maintain the concentration of mineral ions and other substances |
| State the 3 basic steps in the production of urine. | 1) Glomerular filtration of the blood 2) Reabsorption of water and nutrients at the proximal tubule 3) Tubular secretion of substances to be excreted (e.g. urea) at the distal tubule |
| What is ultrafiltration/glomerular filtration? | The movement of substances due to high pressure across the glomerular wall into the lumen of the Bowman's capsule. Substances are water, inorganic ions, urea, uric acid, glucose and amino acids. |
| T or F. Glomerular filtrate is identical to blood plasma minus most proteins. | T |
| What happens in selective reabsorption? | Useful substances within the glomerular filtrate are returned to the blood by passing through the walls of the nephron. |
| Where does most (85%) of the selective reabsorption occur? | Proximal convoluted tubule |
| How are the cells of the proximal convoluted tubule specifically adapted for selective reabsorption? | 1) Microvilli - many microvilli present to give large surface area 2) Mitochondria - to supply ATP for active transport of sodium ions |
| Outline the transport mechanisms involved in the selective reabsorption of sodium ions from the PCT. | 1) Na+ are actively transported out of the PCT into the blood capillaries by Na+/K+ carrier protein pump. 2) Na+ ions then diffuse through co-transport carrier proteins which carry other molecules such as glucose, amino acids, Cl- ions etc. |
| How is water reabsorbed? | By osmosis down the water potential gradient created by transport of Na+ ions. |
| How are all the glucose ions reabsorbed? | By co-transport as Na+ ions are reabsorbed followed by diffusion down the concentration gradient into the blood. |
| What is the significance of the length of the loop of Henle? | To create a very high concentration of sodium ions and chloride ions in the tissue fluid in the medulla. This allows a lot of water to be reabsorbed from the contents of the nephron as they pass through the collecting duct. This conserves water. |
| What happens in the descending limb of the loop of Henle? | Water diffuses out by osmosis. |
| What happens in the ascending limb of the loop of Henle? | Na+ and Cl- leaves by diffusion in the lower part and by active transport in the upper part. Water cannot pass out of the ascending limb. |
| What happens in the distal convoluted tubule (DCT)? | Active transport of Na+ ions out and K+ ions in. |
| What happens in the collecting duct? | Water diffuses out by osmosis into the blood capillaries (vasa recta) |
| What is the site of urea formation? | Liver |
| What is the site of urine formation? | Kidney (nephron) |
| This is the term for the presence of protein in urine. | Proteinuria |
| What is the significance of protein in the urine? | It indicated that a person may have or be at risk for renal disease and cardiovascular disease complications especially for patients with hypertension and diabetes mellitus. |
| T or F. High blood pressure has a major role in the development of proteinuria. | T |
| What can patients with proteinuria do as a preventative measure? | Maintain a blood pressure at less than 130/80 mmHg to maintain health and achieve maximal renal and cardiovascular protection. |
| This part of the brain contains sensory neurones called osmoreceptors. | Hypothalamus |
| ADH stands for | anti-diuretic hormone |
| What happens when the water potential of the blood rises above normal (increased water potential/blood too dilute)? | 1) Osmoreceptors in the hypothalamus detect the increased water potential. 2) Pituitary gland releases less ADH 3) Wall of DCT and collecting duct become LESS permeable to water 4) Large volume of dilute urine produced |
| What happens when the water potential of the blood falls below normal (decreased water potential/blood too concentrated)? | 1) Osmoreceptors in the hypothalamus detect the decreased water potential. 2) Pituitary gland releases more ADH 3) Wall of DCT and collecting duct become MORE permeable to water 4) Small volume of concentrated urine produced |
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CAPE Biology Unit 2
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