Planet Earth and Its Environment A 5000-million year Journey

Biology in Focus, HSC CourseGlenda Childrawi, Margaret Robson and Stephanie Hollis

Maintaining a BalanceTopic 18: Hormones1DOT POINTOutline the role of the hormones, aldosterone and ADH (anti-diuretic hormone) in the regulation of water and salt levels in blood.Introduction Hormones are chemical control substances that are secreted by endocrine (ductless) glands, directly into the bloodstream. They travel via the general circulation to parts of the body and when they reach their target cells, these cells (in our case, cells within the kidney nephrons) respond. cartage.org.lb

Introduction The passage of the filtrate from Bowmans capsule to the distal parts of the nephron occurs without variation. Adjustments to the concentration of water and salts within the urine takes place mainly in the distal parts of the tubules and the collecting tubules, by alterations to the permeability of the membranes of cells lining the nephron walls. tokresource.org

Introduction These changes in permeability are brought about by two main hormones:Aldosterone: brings about retention (conservation) of salts within the body.ADH (anti-diuretic hormone): brings about water reabsorption (conservation) within the body.legacy.owensboro.kctcs.eduAldosteroneA decrease in the concentration of sodium ions in the bloodstream leads to a decrease in blood volume and this stimulates cells in the cortex of the adrenal gland (above the kidney) to secrete the hormone aldosterone. moregruel.net

AldosteroneWhen aldosterone reaches the kidney (via the bloodstream), it increases the permeability of the nephron to sodium, particularly in the ascending limb of the loop of Henle. Reabsorption of sodium ion from the nephron into the surrounding kidney tissue and capillaries occurs, resulting in the retention (conservation) of salt by the body. (less salt is lost in urine)dls.ym.edu.twAnti-diuretic hormone (ADH)When a mammal begins to dehydrate, blood volume drops and this is detected in the hypothalamus of the brain. It stimulates the pituitary gland to release the hormone ADH, which acts on the nephrons of the kidneys to increase the reabsorption of water. nsbri.org

Anti-diuretic hormone (ADH)The presence of ADH increases the permeability of the membranes of the cells lining the distal tubules and collecting tubules to water. As a result, water is reabsorbed from these tubules into the kidney tissue and bloodstream and so water is conserved within the body (less water is lost in urine). gsdhelp.info

Anti-diuretic hormone (ADH)The name of the hormone describes its function a diuretic is a substance that causes the loss of water from the body (alcohol, tea and coffee are diuretics), so anti-diuretic refers to a substance that reduces water loss. rci.rutgers.edu

OsmoregulationBoth ADH and aldosterone therefore play an important role in helping the kidney to carry out its homeostatic functions of osmoregulation:Regulation of the solute concentration of the blood: regulating the amount of sodium and other ions that are reabsorbed or secreted in urine.Regulation of blood volume: maintaining a constant fluid volume of dilute urine or a small concentration of concentrated urine. legacy.owensboro.kctcs.eduTechnology and Kidney FunctionAn understanding of how the kidney functions to remove wastes, as well as the hormonal regulation of kidney functioning to maintain homeostasis has played a key role in the development of technologies such as:Renal dialysis for people suffering from reduced kidney functionHormone replacement therapy for patients suffering from abnormally low levels of the hormone aldosterone. legacy.owensboro.kctcs.eduTechnology and Kidney FunctionThese applications of the use of biology have helped to improve the lifestyle and increase the life expectancy of people who suffer from these diseases. seymourhealth.org.au

Renal DialysisThe kidneys are responsible for filtering our blood, removing metabolic wastes so that they may be excreted via urination. If a person suffers from kidney failure, there is no natural means by which these wastes can be removed and their toxic effect eventually leads to death. actions-traitements.org

Renal DialysisThe process of renal dialysis has been developed to carry out the function of failed kidneys so that blood may be effectively filtered. There are two types of renal dialysis:Haemodialysis Peritoneal dialysistutorvista.com

Renal DialysisThe main function of a dialysis machine is to remove metabolic wastes that have built up in the persons blood. The patient is connected to a dialysis machine, which pumps their blood through a system of tubes (coiled to increase their surface area and therefore the rate of diffusion) which have artificial semi-permeable membranes. gujaratkidneyfoundation.com

Renal DialysisThe tubes are submerged in dialysis fluid (dialysate), which flows in the opposite direction to the blood in order to maximise diffusion. wordpress.as.edu.au

Renal DialysisDialysis has the same concentration as blood plasma without the metabolic wastes, and since the concentration of metabolic wastes is higher in the blood than in the dialysing fluid, the waste materials move through the semi-permeable membrane into the dialysing fluid by diffusion. webmm.ahrq.gov

Renal DialysisSince dialysis relies on passive transport for the removal of wastes from the blood, the dialysis fluid must constantly be replaced so that the concentration gradient is maintained away from the blood. imt.ie

Renal DialysisRenal dialysis must be carried out for 3 to 4 hours, two or three times per week. As well as its time-consuming nature, another disadvantage is that only limited amounts of fluid/wastes can be removed from the blood. Other substances such as sodium phosphate and potassium ions do not diffuse quickly enough and therefore may accumulate in the blood. maroondah-leader.whereilive.com.au

Renal DialysisPatients have to follow a specific diet to prevent the build up of such substances, as renal dialysis is not effective in regulating the concentration of these ions in the blood. raw-foods-diet-center.com

Hormone Replacement TherapyAldosterone increases the amount of salt reabsorbed from kidney tubules and as a result it also helps regulate blood pressure. Some people lack aldosterone. Addisons disease results from abnormally low levels of aldosterone in the body. The causes are not always known, but include:Damage to the adrenal glands that produce aldosterone, due to accident, surgery or disease (such as bacterial infections or cancer of the gland)Damage to the pituitary gland that controls the adrenal gland (for example, because of a tumor)legacy.owensboro.kctcs.edu

Hormone Replacement TherapyHormone replacement therapy involves restoring the balance of the hormones at levels that are normal for the body, by giving the patients hormones. When applied appropriately, it can increase fluid retention, raise blood pressure and remove the danger of heart failure, allowing sufferers to lead normal lives. womensvoicesforchange.orgHormone Replacement TherapySince 1927, when the first hormone replacement therapy began (using an extract from the adrenal cortex of cattle), hundreds of human lives which would have been lost to Addisons disease in the past have been saved. Modern day hormone replacement therapy involves administering a genetically engineered hormone called fludrocortisone. 1800petmeds.com

Activity-Students to complete activity 3.8 Renal Dialysis and 3.10 ADH Replacement Therapy