Maintaining a Balance Topic 16: The Kidneys

1. Maintaining a BalanceTopic 16: The Kidneys Biology in Focus, HSC Course Glenda Childrawi, Margaret Robson and Stephanie Hollis

2. DOT POINT • Explain why the removal of wastes is essential for continued metabolic activity • Distinguish between active and passive transport and relate these to processes occurring in the mammalian kidney • Explain why the processes of diffusion and osmosis are inadequate in removing dissolved nitrogenous wastes in some organisms

3. Removing Wastes Any accumulation of wastes may be toxic to cells and so metabolic wastes must be removed from the body to maintain homeostasis. If wastes are not continuously removed, their levels in the body will increase and alter the conditions in the internal environment. This in turn inhibits enzyme functioning and prevents cells from undergoing normal metabolic activity. pettalk.com.au

4. Removing Wastes The build up of nitrogenous wastes such as ammonia causes an increase in pH in cells. This results in them becoming more alkaline. The build up of carbon dioxide lowers pH which results in the internal environment becoming more acidic. These changes can slow down or inhibit enzyme functioning in metabolism. students.cis.uab.edu

5. The Excretory System The excretory system is a group of organs that function together to remove metabolic wastes from the tissues of an organism and expel them to the outside. The kidneys are the main excretory organs responsible for removing nitrogenous wastes from the bodies of vertebrate animals, including fish and mammals. Handout 16.1.2 Excretory System Diagram emc.maricopa.edu

6. The Excretory System The function of the kidney in excretion is to filter the blood that enters it, removing wastes (in solution) from the bloodstream so that they can be excreted from the body. This filtration is carried out in millions of tiny units called nephrons. emc.maricopa.edu

7. The Excretory System Urine is the excretory solution finally produced by these microscopic tubules and it drains out of the kidneys, carrying wastes out of the kidney via ducts, the ureters. In vertebrates, the ureters lead to a urine storage organ, the bladder, which passes urine via the urethra to the outside. lurvely.com

8. The Excretory System In other vertebrates, the ureters carry urine directly to a chamber, the cloaca (the common opening of the urinary, digestive and reproductive tracts), which empties to the outside. backyardchickens.com

9. The Excretory System Oxygenated blood arrives at the kidney via the renal artery and carries nitrogenous wastes. These, together with water and other solutes are filtered to form urine. The kidney is then drained of its fluids by two vessels: • The renal vein, which carries purified blood back into the general circulation • The ureter, which carries urine out of the kidney. kidney.org.au

10. The Excretory System Animals use water to flush metabolic wastes out of the body. Excretion therefore brings with it the problem of regulating the amount of water lost, while ensuring that wastes are removed. The role of the kidney includes both the excretion of nitrogenous wastes and osmoregulation – maintaining the water and salt (electrolyte) balance in animals. flickrhivemind.net

11. The Excretory System The maintenance of a stable blood volume, blood pressure and pH depends upon a stable water balance within a narrow range in the body. The importance of conserving water varies in different animals, depending on the environment which each inhabits. abc.net.au

12. The Excretory System The main environments inhabited by living organisms are freshwater, marine and terrestrial habitats. Each habitat presents its own problems for organisms in terms of maintaining their internal water and salt balance. tolweb.org

13. The Excretory System The kidneys of animals have evolved to function in both excretion and the removal or conservation of water and salts, maintaining optimal levels of these substances within the bodies of animals that live in different environments. fanpop.com

14. Active and Passive Transport (Diffusion and Osmosis) Movement of materials into and out of cells takes place either passively or actively. • Passive movement includes the processes of diffusion and osmosis. These types of movement require no energy input from the cell, since molecules move along a concentration gradient. • Active transport requires an input of cellular energy to actively move molecules against a concentration gradient. cumbavac.org

15. Passive Transport in the Kidney Diffusion and osmosis results from the random movement of particles, called Brownian motion, whereby particles continually collide and move randomly. When they are in higher concentration in one region, this constant movement slowly results in an overall spreading out from the most concentrated point, finally brining about their even distribution within a space. okc.cc.ok.us

16. Passive Transport in the Kidney The main limitations of passive movement are: • it depends on the presence of a difference in concentration of substances (a concentration gradient) between two regions • it is relatively slow, especially when the concentration gradient is not steep bbc.co.uk

17. Passive Transport in the Kidney Diffusion is the movement of any molecule from a region of high concentration to a region of low concentration of that substance, until equilibrium is reached. This does not require an energy input. notesforpakistan.blogspot.com

18. Passive Transport in the Kidney Osmosis is the movement of water molecules from a region of high water concentration to a region of low water concentration through a selectively permeable membrane. This also does not require energy. hartnell.edu

19. Passive Transport in the Kidney Within the kidney, the movement of substances between the bloodstream and excretory fluid in the microscopic tubules (called nephrons) involves both active and passive transport. umm.edu

20. Passive Transport in the Kidney A balance in the optimal concentrations of blood chemicals is maintained by the selective excretion of wastes, as well as any excess water and salts in urine. Therefore the ability of the kidney to alter the urine concentration plays a vital role in homeostasis. urologyhealth.org

21. Passive Transport in the Kidney Within the kidney tubules, there is a two-way movement of substances: • Waste substances pass from the bloodstream into the kidney tubules, to be excreted in urine (filtration and secretion) • Substances required by the body are removed from the urine in the kidney tubules (before it is excreted) and returned to the bloodstream (reabsorption) cumbavac.org

22. Passive Transport in the Kidney Passive transport moves water (by osmosis), and some nitrogenous wastes such as urea and ammonia(by diffusion) in the kidneys of mammals. lupusqld.org.au

23. Passive Transport in the Kidney In the kidney, only excess water and salts are excreted. Homeostasis requires that sometimes water and salts should be conserved to maintain the required levels within the body and at other times they should be excreted. Salt movement is via active transport and this in turn draws water by osmosis. naturalguidetohealth.com

24. Active Transport in the Kidney Active transport is the movement of molecules from an area of low concentration to a region of high concentration, requiring an input of energy. cumbavac.oraustincc.edug

25. Active Transport in the Kidney Sometimes in living organisms there is a need to move a chemical against the concentration gradient, and to do this, active transport occurs. This involves a carrier protein that spans the membrane and this carrier molecule can actively move chemicals from low to high concentration, utilising cellular energy. hyperphysics.phy-astr.gsu.edu

26. Active Transport in the Kidney Active transport moves mainly sodium ions, glucose, amino acids and hydrogen ions across the wall of the nephron. • All glucose and amino acids are reabsorbed by kidney cells so that they are not lost in urine and so they move against a concentration gradient. • Additional nitrogenous wastes (eg: uric acid) and hydrogen ions (H⁺) are added to urine (from blood capillaries) in the kidney tubules

27. Active Transport in the Kidney • Additional nitrogenous wastes (eg: uric acid) and hydrogen ions (H⁺) are added to urine (from blood capillaries) in the kidney tubules wikis.lib.ncsu.edu

28. Active Transport in the Kidney • A ‘sodium pump’ mechanism operates in the tubules of the kidneys, actively transporting ions (salts) from the urine back into the kidney cells. Besides conserving salts, this process also brings about the conservation of water within the body – the active transport of salts draws water out of the urine, because water follows by osmosis (passive transport). Water is drawn by the osmotic pull of the salts in solution. cumbavac.org

29. How Effective are These Processes? Diffusion: The rate of movement is to slow to just rely on diffusion. Nitrogenous wastes and toxins such as drugs and alcohol must be dissolved in water to be removed. If their removal by the kidney was dependent on diffusion only, wastes would be able to move only if they were concentrated inside the cells or the bloodstream than in the fluids outside. As their concentrations begin to equalise, their movement would slow down and eventually stop. guardian.co.uk

30. How Effective are These Processes? Diffusion: Not all wastes can be removed by diffusion. Since nitrogenous wastes are toxic, it is essential they are all removed. If concentrations within the blood and urine equalised and no further wastes were removed, their accumulation would change the pH of cells and become toxic. leavingbio.net

31. How Effective are These Processes? Osmosis: Too much water may be lost in urine. If urine contains a large number of nitrogenous wastes in solution, water will be drawn into the urine by osmosis to dilute the wastes and try to equalise the concentration of fluid inside the urine and in the surrounding kidney. Excretion of dilute urine means the loss of large amounts of water from the body – something many terrestrial animals cannot afford. modernmom.com

32. How Effective are These Processes? Osmosis: Movement of water may make waste too dilute for excretion by diffusion. Organisms that live in freshwater environments have a different problem. Osmosis results in water moving into the body tissues from the surrounding environment. Although this dilutes the toxic wastes in the body, it slows down their excretion by diffusion (lowers the concentration gradient). Therefore a mechanism is essential to remove wastes against a concentration gradient. australian-animals.net

33. Solution to the Problems Active transport, which requires energy is quicker and more effective than diffusion as it removes most wastes, even against a concentration gradient. It can also be used to pump salts from urine back into the kidney tissue and these in turn will draw water with them (by osmosis), ensuring in this way that the amount of water lost in urine does not affect the body’s water balance. humanphisiology.wikispaces.com

34. Activity -Students to use ALARM to answer the following DOT Points: • Explain why the removal of wastes is essential for continued metabolic activity • Distinguish between active and passive transport and relate these to processes occurring in the mammalian kidney • Explain why the processes of diffusion and osmosis are inadequate in removing dissolved nitrogenous wastes in some organisms