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HOMEOSTASIS XXXXXXXXXXXXXXXXXXXXXXA2.pptx
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- 2. If you werein these four environments, what would your body be having too much or too little of?
- 3. Learning Outcomes: • discussthe importance of homeostasis in mammals and explain the principles of homeostasis in terms of internal and external stimuli, receptors, central control, co-ordination systems, effectors (muscles and glands) • define the term negative feedback and explain how it is involved in homeostatic mechanisms • outline the roles of the nervous system and endocrine system in co-ordinating homeostatic mechanisms, including thermoregulation, osmoregulation and the control of blood glucose concentration • describe the deamination of amino acids and outline the formation of urea in the urea cycle (biochemical detail of the urea cycle is not required) • describe the gross structure of the kidney and the detailed structure of the nephron with its associated blood vessels using photomicrographs and electron micrographs.
- 4. • describe howthe processes of ultrafiltration and selective reabsorption are involved with the formation of urine in the nephron • describe the roles of the hypothalamus, posterior pituitary, ADH and collecting ducts in osmoregulation • explain how the blood glucose concentration is regulated by negative feedback control mechanisms, with reference to insulin and glucagon • outline the role of cyclic AMP as a second messenger with reference to the stimulation of liver cells by adrenaline and glucagon • describe the three main stages of cell signalling in the control of blood glucose by adrenaline as follows: • hormone-receptor interaction at the cell surface (see 4.1c) • formation of cyclic AMP which binds to kinase proteins • an enzyme cascade involving activation of enzymes by phosphorylation to amplify the signal
- 5. • explain theprinciples of operation of dip sticks containing glucose oxidase and peroxidase enzymes, and biosensors that can be used for quantitative measurements of glucose in blood and urine. • explain how urine analysis is used in diagnosis with reference to glucose, protein and ketones. • explain that stomata have daily rhythms of opening and closing and also respond to changes in environmental conditions to allow diffusion of carbon dioxide and regulate water loss by transpiration • describe the structure and function of guard cells and explain the mechanism by which they open and close stomata • describe the role of abscisic acid in the closure of stomata during times of water stress (the role of calcium ions as a second messenger should be emphasised)
- 11. Negative Feedback Ofhomeostasis
- 12. Role of thenervous system and endocrine system in homeostatic mechanisms • Along with the nervous system, the endocrine system coordinates the body's functions to maintain homeostasis during rest and exercise.
- 14. What does yourbody do if it becomes too warm or too cold?
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- 17. Already discussed sweating,how else is the water content in the body controlled?
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- 24. Basic Functions ofKidney • Regulation of extracellular fluid volume. The kidneys work to ensure an adequate quantity of plasma to keep blood flowing to vital organs. • Regulation of osmolarity. ... • Regulation of ion concentrations. ... • Regulation of pH. ... • Excretion of wastes and toxins. ... • Production of hormones.
- 25. Structure of thekidney • Internally, the kidney has three regions: an outer cortex, a medulla in the middle, and the renal pelvis in the region called the hilum of the kidney. The hilum is the concave part of the bean-shape where blood vessels and nerves enter and exit the kidney; it is also the point of exit for the ureters. • The kidneys are made up of millions of nephrons, which act as tiny filtering units. The cortex is the dark outer layer. This has a high density of capillaries as it is the site of blood filtration. The medulla is the lighter area inside the cortex.
- 26. Gross structure ofthe kidney
- 28. Nephrons • Blood isfiltered in the nephrons, and the majority of the filtered material returns to the blood. • It removes nitrogenous waste, and balances mineral ions and water levels in the blood. • Each nephron is about 3cm long, and there are 1.5 million per kidney. This provides the body with several kilometres for reabsorption of water, glucose, salts etc.
- 29. • There isalso a network of blood vessels associated with each nephron: • Within the Bowman’s capsule of each nephron is a structure known as the glomerulus • Each glomerulus is supplied with blood by an afferent arteriole (which carries blood from the renal artery) • The capillaries of the glomerulus rejoin to form an efferent arteriole • Blood then flows from the efferent arteriole into a network of capillaries that run closely alongside the rest of the nephron • Blood from these capillaries eventually flows into the renal vein.
- 30. Structure of theNephron • Bowerman's capsule: a cup shaped structure containing the glomerulus where ultrafiltration takes place. • Glomerulus: a tangle of capillaries in which the pressure forces all solutes in the blood plasma to be forced through the capillary walls. This includes ions, amino acids, glucose, urea, water. Proteins and erythrocytes do not pass through as they are too large. • Proximal Convoluted Tubule: First coiled region of the tubule, where products needed in the blood (ions, glucose, amino acids etc) are reabsorbed into the blood. • Loop of Henle: A long loop of tubule which spans the cortex and medulla, used to concentrate the urine. A salty environment is created in the medulla in order to cause water to osmose of water out of the nephron on the falling limb, and the impermeable rising limb allows salts to diffuse out maintaining salty conditions. • Distal Convoluted Tubule: Second coiled region of the tubule, where osmosis and diffusion of solutes occurs in order to fine tune the water potential and pH of the blood. Antidiuretic Hormone (ADH) affects the permeability of the distal convoluted tubule. • Collecting Duct: Urine travels through the collecting duct down to the pelvis. More fine tuning occurs, as ADH creates aquaporins to allow the exit of excess water.
- 31. Formation of Urinein the Nephron • The nephron is the functional unit of the kidney. • The nephrons are responsible for the formation of urine • The process of urine formation in the kidneys occurs in two stages: • Ultra filtration • Selective reabsorption
- 34. Ultra-filtration • Arterioles branchoff the renal artery and lead to each nephron, where they form a knot of capillaries (the glomerulus) sitting inside the cup shaped Bowman’s capsule • The capillaries get narrower as they get further into the glomerulus which increases the pressure on the blood moving through them (which is already at high pressure because it is coming directly from the renal artery which is connected to the aorta) • This eventually causes the smaller molecules being carried in the blood to be forced out of the capillaries and into the Bowman’s capsule, where they form what is known as the filtrate • The blood in the glomerular capillaries is separated from the lumen of the Bowman’s capsule by two cell layers with a basement membrane in between them: • The first cell layer is the endothelium of the capillary – each capillary endothelial cell is perforated by thousands of tiny membrane-lined circular holes • The next layer is the basement membrane – this is made up of a network of collagen and glycoproteins • The second cell layer is the epithelium of the Bowman’s capsule – these epithelial cells have many tiny finger-like projections with gaps in between them and are known as podocytes
- 35. • As bloodpasses through the glomerular capillaries, the holes in the capillary endothelial cells and the gaps between the podocytes allows substances dissolved in the blood plasma to pass into the Bowman’s capsule ▫ The fluid that filters through from the blood into the Bowman’s capsule is known as the glomerular filtrate ▫ The main substances that pass out of the capillaries and form the glomerular filtrate are: amino acids, water, glucose, urea and inorganic ions (mainly Na+ , K+ and Cl- ) • Red and white blood cells and platelets remain in the blood as they are too large to pass through the holes in the capillary endothelial cells • The basement membrane acts as a filter as it stops large protein molecules from getting through
- 40. Glomerular filtration rate(GFR) • Glomerular filtration rate (GFR) is a test used to check how well the kidneys are working. Specifically, it estimates how much blood passes through the glomeruli each minute. • Factors affecting GFR: 1.Solute Potential 2.Hydrostatic potential
- 41. Factors Affecting WaterPotential
- 43. Selective Reabsorption • Manyof the substances that end up in the glomerular filtrate actually need to be kept by the body • These substances are reabsorbed into the blood as the filtrate passes along the nephron • This process is known as selective reabsorption as only certain substances are reabsorbed • Glucose reabsorption occurs in the proximal convoluted tubule • The lining of the proximal convoluted tubule is composed of a single layer of epithelial cells, which are adapted to carry out reabsorption in several ways: ▫ Microvilli ▫ Co-transporter proteins ▫ A high number of mitochondria ▫ Tightly packed cells • Water and salts are reabsorbed via the Loop of Henle and collecting duct
- 44. Proximal Convoluted Tubule •The function of the proximal tubule is essentially reabsorption of filtrate in accordance with the needs of homeostasis (equilibrium), whereas the distal part of the nephron and collecting duct are mainly concerned with the detailed regulation of water, electrolyte, and hydrogen-ion balance.
- 45. How the selectivereabsorption of solutes occurs • Blood capillaries are located very close to the outer surface of the proximal convoluted tubule ▫ As the blood in these capillaries comes straight from the glomerulus, it has very little plasma and has lost much of its water, inorganic ions and other small solutes • The basal membranes (of the proximal convoluted tubule epithelial cells) are the sections of the cell membrane that are closest to the blood capillaries • Sodium-potassium pumps in these basal membranes move sodium ions out of the epithelial cells and into the blood, where they are carried away • This lowers the concentration of sodium ions inside the epithelial cells, causing sodium ions in the filtrate to diffuse down their concentration gradient through the luminal membranes (of the epithelial cells) • These sodium ions do not diffuse freely through the luminal membranes – they must pass through co-transporter proteins in the membrane • There are several types of these co-transporter proteins – each type transports a sodium ion and another solute from the filtrate (eg. glucose or a particular amino acid) • Once inside the epithelial cells these solutes diffuse down their concentration gradients, passing through transport proteins in the basal membranes (of the epithelial cells) into the blood
- 46. Molecules reabsorbed fromthe PCT during selective reabsorption • All glucose in the glomerular filtrate is reabsorbed into the blood ▫ This means no glucose should be present in the urine • Amino acids, vitamins and inorganic ions are reabsorbed • The movement of all these solutes from the proximal convoluted tubule into the capillaries increases the water potential of the filtrate and decreases the water potential of the blood in the capillaries ▫ This creates a steep water potential gradient and causes water to move into the blood by osmosis • A significant amount of urea is reabsorbed too ▫ The concentration of urea in the filtrate is higher than in the capillaries, causing urea to diffuse from the filtrate back into the blood
- 47. Adaptations for SelectiveReabsorption
- 51. Reabsorption of waterand salts • As the filtrate drips through the Loop of Henle necessary salts are reabsorbed back into the blood by diffusion • As salts are reabsorbed back into the blood, water follows by osmosis • Water is also reabsorbed from the collecting duct in different amounts depending on how much water the body needs at that time
- 52. Loop of Henle •Loop of Henle, long U-shaped portion of the tubule that conducts urine within each nephron of the kidney of reptiles, birds, and mammals. The principal function of the loop of Henle is in the recovery of water and sodium chloride from urine. This function allows production of urine that is far more concentrated than blood, limiting the amount of water needed as intake for survival. Many species that live in arid environments such as deserts have highly efficient loops of Henle. Anatomically, the loop of Henle can be divided into three main segments: the thin descending limb, the thin ascending limb, and the thick ascending limb (sometimes also called the diluting segment).
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- 54. The distal convolutedtubule (DCT) and collecting duct (CD) • The DCT is located in the cortex and corticomedullary junction. The functions of this segment include fine- tuning ion concentrations and acid-base balance to maintain homeostasis. The epithelium of the DCT is also involved in reabsorption or excretion of bicarbonate and hydrogen ions to maintain blood pH. • The last part of a long, twisting tube that collects urine from the nephrons (cellular structures in the kidney that filter blood and form urine) and moves it into the renal pelvis and ureters. Also called renal collecting tubule.
- 55. Osmoregulation • The controlof the water potential of body fluids is known as osmoregulation • Osmoregulation is a key part of homeostasis • Specialized sensory neurones, known as osmoreceptors, monitor the water potential of the blood (these osmoreceptors are found in an area of the brain known as the hypothalamus) • If the osmoreceptors detect a decrease in the water potential of the blood, nerve impulses are sent along these sensory neurones to the posterior pituitary gland (another part of the brain just below the hypothalamus) • These nerve impulses stimulate the posterior pituitary gland to release ant diuretic hormone (ADH) • ADH molecules enter the blood and travel throughout the body • ADH causes the kidneys to reabsorb more water • This reduces the loss of water in the urine
- 58. The effect ofADH on the kidneys • Water is reabsorbed by osmosis from the filtrate in the nephron • This reabsorption occurs as the filtrate passes through structures known as collecting ducts • ADH causes the luminal membranes (ie. those facing the lumen of the nephron) of the collecting duct cells to become more permeable to water • ADH does this by causing an increase in the number of aquaporins (water-permeable channels) in the luminal membranes of the collecting duct cells. This occurs in the following way: ▫ Collecting duct cells contain vesicles, the membranes of which contain many aquaporins ▫ ADH molecules bind to receptor proteins, activating a signalling cascade that leads to the phosphorylation of the aquaporin molecules ▫ This activates the aquaporins, causing the vesicles to fuse with the luminal membranes of the collecting duct cells ▫ This increases the permeability of the membrane to water • As the filtrate in the nephron travels along the collecting duct, water molecules move from the collecting duct (high water potential), through the aquaporins, and into the tissue fluid and blood plasma in the medulla (low water potential) • As the filtrate in the collecting duct loses water it becomes more concentrated • As a result, a small volume of concentrated urine is produced. This flows from the kidneys, through the ureters and into the bladder
- 65. The Control ofBlood Glucose ● If the concentration of glucose in the blood decreases below a certain level, cells may not have enough glucose for respiration and may not be able to function normally ● If the concentration of glucose in the blood increases above a certain level, this can also disrupt the normal function of cells, potentially causing major problems ● The control of blood glucose concentration is a key part of homeostasis ● Blood glucose concentration is controlled by two hormones secreted by endocrine tissue in the pancreas ● This tissue is made up of groups of cells known as the islets of Langerhans ● The islets of Langerhans contain two cell types: ○ α cells that secrete the hormone glucagon ○ β cells that secrete the hormone insulin ● These α and β cells act as the receptors and initiate the response for controlling blood glucose concentration ● The control of blood glucose concentration by glucagon can be used to demonstrate the principles of cell signalling
- 66. Decrease in bloodglucose concentration ● If a decrease in blood glucose concentration occurs, it is detected by the α and β cells in the pancreas: ○ The α cells respond by secreting glucagon ○ The β cells respond by stopping the secretion of insulin ● The decrease in blood insulin concentration reduces the use of glucose by liver and muscle cells ● Glucagon binds to receptors in the cell surface membranes of liver cells ● This binding causes a conformational change in the receptor protein that activates a G protein ● This activated G protein activates the enzyme adenylyl cyclase ● Active adenylyl cyclase catalyses the conversion of ATP to the second messenger, cyclic AMP (cAMP) ● cAMP binds to protein kinase A enzymes, activating them ● Active protein kinase A enzymes activate phosphorylase kinase enzymes by adding phosphate groups to them ● Active phosphorylase kinase enzymes activate glycogen phosphorylase enzymes ● Active glycogen phosphorylase enzymes catalyse the breakdown of glycogen to glucose ○ This process is known as glycogenolysis ● The enzyme cascade described above amplifies the original signal from glucagon and results in the releasing of extra glucose by the liver to increase the blood glucose concentration back to a normal level
- 69. Increase in bloodglucose concentration ● When the blood glucose concentration increases to above the normal range it is detected by the β cells in the pancreas ● When the concentration of glucose is high glucose molecules enter the β cells by facilitated diffusion ● The cells respire this glucose and produce ATP ● High concentrations of ATP causes the potassium channels in the β cells to close, producing a change in the membrane potential ● This change in the membrane potential causes the voltage-gated calcium channels to open ● In response to the influx of calcium ions, the β cells secrete the hormone insulin ○ Insulin-containing vesicles move towards the cell-surface membrane where they release insulin into the capillaries ● Once in the bloodstream, insulin circulates around the body ● It stimulates the uptake of glucose by muscles cells, fat cells and the liver
- 70. Action of insulin ●Insulin increase the uptake of glucose into target cells ○ The target cells of insulin include muscle cells, fat storage cells, adipose tissue and liver cells; all of these cells have specific insulin receptors on their cell surface membranes ○ Insulin binds to specific receptors on the membranes of these target cells ○ The binding of insulin to receptors on target cells stimulates the cells to add more glucose transporter proteins to their cell surface membranes, increasing the permeability of the cells to glucose ■ These glucose transporter proteins are known as GLUT proteins ■ When blood glucose levels are low GLUT proteins are stored inside the cell in the membranes of vesicles, but when insulin binds to the surface receptors the vesicles move to the cell surface membrane and fuse with it, adding GLUT proteins to the membrane ○ The rate of facilitated diffusion of glucose into the target cells increases as a result of the increase in GLUT proteins ● Insulin causes activation of an enzyme known as glucokinase ○ Glucokinase phosphorylates glucose, trapping it inside cells ● Insulin causes activation of another enzyme; glycogen synthase ● Glycogen synthase converts glucose into glycogen in a process known as glycogenesis
- 71. Negative Feedback Controlof Blood Glucose ● Blood glucose concentration is regulated by negative feedback control mechanisms ● In negative feedback systems: ○ Receptors detect whether a specific level is too low or too high ○ This information is communicated through the hormonal or nervous system to effectors ○ Effectors react to counteract the change by bringing the level back to normal ● In the control of blood glucose concentration: ○ α and β cells in the pancreas act as the receptors ○ They release the hormones glucagon (secreted by α cells) and insulin (secreted by β cells) ○ Liver cells act as the effectors in response to glucagon and liver, muscle and fat cells act as the effectors in response to insulin
- 73. Test Strips &Biosensors Measuring urine glucose concentration ● People with diabetes cannot control their blood glucose concentration so that it remains within normal, safe limits ● The presence of glucose in urine is an indicator that a person may have diabetes ○ If blood glucose concentration increases above a value known as the renal threshold, not all of the glucose from the filtrate in the proximal convoluted tubule is reabsorbed and some will be left in the urine ● Test strips can be used to test urine for the presence and concentration of glucose ● Two enzymes are immobilised on a small pad at one end of the test strip. These are: ○ glucose oxidase ○ peroxidase ● The pad is immersed in the urine sample for a short time ● If glucose is present: ○ Glucose oxidase catalyses a reaction in which glucose is oxidised to form gluconic acid and hydrogen peroxide ○ Peroxidase then catalyses a reaction between the hydrogen peroxide and a colourless chemical in the pad to form a brown compound and water
- 74. ● The colourof the pad is compared to a colour chart – different colours represent different concentrations of glucose (the higher the concentration of glucose present, the darker the colour) ● Urine tests only show whether or not the blood glucose concentration was above the renal threshold whilst urine was collecting in the bladder – they do not indicate the current blood glucose concentration.
- 75. Measuring blood glucoseconcentration ● A biosensor can be used by people with diabetes to show their current blood glucose concentration ● Similar to the test strips, a biosensor uses glucose oxidase (but no peroxidase) immobilised on a recognition layer ● Covering the recognition layer is a partially permeable membrane that only allows small molecules from the blood to reach the immobilised enzymes ● When a small sample of blood is tested, glucose oxidase catalyses a reaction in which any glucose in the blood sample is oxidised to form gluconic acid and hydrogen peroxide ● The hydrogen peroxide produced is oxidised at an electrode that detects electron transfers ● The electron flow is proportional to the glucose concentration of the blood sample ● The biosensor amplifies the current, which is then read by a processor to produce a digital reading for blood glucose concentration ● This process is complete within a matter of seconds
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- 83. Opening and Closingof Stomata
- 86. Homeostasis in plants Stomatahave daily rhythms of opening and closing and also respond to changes in environmental conditions to • - allow diffusion of CO2 • - regulate water loss by transpiration Stomata open due to : • high light intensity • low concentration of CO2 Stomata close due to: • darkness • high concentration of CO 2 • low humidity • high temperature • water stress
- 87. • ATP powersproton pumps to actively transport H+ out of cell • There is a low concentration of H+ and negative charge inside the cell --> K+ channels open --> K+ diffuse in • High concentration of K+ inside the cell decreases water potential • Water moves in via osmosis • Water entry increases the volume of the guard cell, causing it to expand --> open
- 88. Abscisic acid andstomatal closure • Abscisic acid (ABA) is a stress hormone that is secreted in response to difficult environmental conditions such as very high temperatures or much reduced water supplies. ABA triggers the closure of stomata to reduce transpiration and prevent water loss. • ABA binds to cell surface receptors • inhibits proton pumps: stop H+ pumped out • stimulates movement of Ca2+ through the cell surface membrane and tonoplast • Ca2+ acts as a 2nd messenger to activate channel proteins to open that allow negatively charged ions to leave the guard cell. This in turn • opens channel proteins that allow K+ to leave the cell • closes channel proteins that allow K+ to enter the cell • --> net movement: K+ leaves cell • Loss of ions = higher water potential inside cell = water passes out by osmosis = guard cells become flaccid --> stomata close