Homeostasis - Biology Chapter 9 PDF

Okay, here is the converted text from the images into a structured markdown format. ### CHAPTER 9 ### HOMEOSTASIS (4 HOURS) **Learning Outcomes:** (a) describe homeostasis and its importance. (b) explain negative feedback mechanisms using thermoregulation and blood glucose regulation as examples. (...

Okay, here is the converted text from the images into a structured markdown format. ### CHAPTER 9 ### HOMEOSTASIS (4 HOURS) **Learning Outcomes:** (a) describe homeostasis and its importance. (b) explain negative feedback mechanisms using thermoregulation and blood glucose regulation as examples. (c) describe the urinary tract and excretion. (d) describe the kidney structure. (e) describe the structure of the nephron and related blood vessels. (f) explain the process of ultrafiltration, reabsorption, and secretion in the formation of urine. (g) describe the hormonal regulation of fluid and electrolyte balance by antidiuretic hormone (ADH). (h) apply the knowledge gained in this section in new situations or to solve related problems. ## 9.1 CONCEPT OF HOMEOSTASIS ### 9.1.1 DEFINITION AND IMPORTANCE * Homeostasis, which means the maintenance of internal balance. * In achieving homeostasis, humans maintain a relatively constant internal environment even when the external environment changes significantly. * Humans exhibit homeostasis for a range of physical and chemical properties. For example, * humans maintain a fairly constant body temperature of about $37^\circ C$ * blood pH within 0.1 pH unit of 7.4, and * blood glucose concentration that is predominantly in the range of 70-110 mg of glucose per 100 mL of blood. * Homeostatic control system in humans maintains a variable at or near a particular value or set point. * A fluctuation in the variable above or below the set point serves as the stimulus detected by a sensor. * The sensor signals a control center, which triggers a response, a physiological activity that helps return the variable to the set point. The image shows the homeostasis regulation loop. The loop has Normal Range for Internal Variable in the center. The loop proceeds as stimulus changes in the internal variable detected by a sensor which then affects the controlled center, leading to a response. ### 9.1.2 NEGATIVE FEEDBACK MECHANISM * A control mechanism that reduces the stimulus * `Negative` = act opposite to stimulus * `Feedback` = response towards the stimulus * An increase in some substances or activity; negative feedback mechanism will inhibit the process by decreasing the substance or activity. #### Examples of negative feedback mechanism: * Thermoregulation * Blood Glucose regulation ## 9.1.2.1 THERMOREGULATION * Process by which animals maintain body temperature within a normal range. * Thermostat in hypothalamus - activate mechanism that promote heat loss or heat gain * Body temperature decrease: * Thermostat inhibits heat loss mechanism * Activate mechanism heat gain (shivering, constriction of vessels in skin) * Body temperature increase * Body temperature increase: * Thermostat shuts down heat retention mechanism * Promote cooling by dilation of vessels in the skin, sweating or panting * Body temperature decrease The image shows the thermoregulation and its control loop The loop contains `NORMAL BODY TEMPERATURE(approximately 36-38°C)` in the center. The response is blood vessels in the skin dilate when the body increase. The response is sweat when body temperature increase The response is Shivering when the body temperature decreases. The response is vasoconstriction when the body temperature decreases. ## 9.1.2.1 BLOOD GLUCOSE REGULATION * After a meal, high blood glucose level * Beta cells of the pancreas secrete insulin * Insulin * trigger the transport of glucose into body cells * stimulates the liver to store glucose as glycogen. * Blood glucose decreases * Between meals, and when blood glucose decreases * Alpha cells of the pancreas secrete glucagon * Glucagon promote breakdown of glycogen into glucose in the liver and release into blood * Blood glucose increases The image shows the blood glucose regulation by insulin and glucagon. The loop contains the `NORMAL BLOOD GLUCOSE (70-110 mg glucose/100 mL)` in the center. When the blood glucose level rises, the beta cells of the pancreas secrete insulin, which enhances the transport of glucose into body cells and stimulates the liver to store glucose as glycogen. When blood glucose level falls, the alpha cells of the pancreas secrete glucagon, which promotes the breakdown of glycogen in the liver and the release of glucose into the blood. ## 9.2 OSMOREGULATION * Process to control solute concentration and balance of water in the internal environment * Importance: Balance the water and solute in the internal environment * Ex: Sodium ($Na^+$) and Calcium ($Ca^{2+}$) must be maintained to permit normal activities of muscles, neurons and other body cells. ### 9.2.1 THE URINARY SYSTEM IN HUMAN * The human urinary system consists of kidneys, as well as organs for transporting and storing urine. * Urine produced by each kidney exits through a duct called the ureter which drains into a common sac called the urinary bladder. * During urination, urine is expelled from the bladder through a tube called the urethra. **Organs of the Excretory System** * Posterior vena cava * Renal artery and vein * Kidney * Aorta * Ureter * Urinary bladder * Urethra **Structures of the Kidney:** * Renal cortex * Renal medulla * Renal artery * Renal vein * Ureter * Renal pelvis **Nephron Types** * Cortical nephron * Juxtamedullary nephron **Kidney Structure** * The outer portion of the kidney is the **cortex**; the inner is the **medulla**. * Kidneys are supplied with blood by the renal artery and drained by the renal vein. * Within the cortex and medulla lie renal tubules and associated blood vessels. * Renal tubules carry and process filtrate (produce from blood entering kidneys). * Fluids in the filtrate are reabsorbed into surrounding blood vessels and exit kidneys in the renal vein. * The remaining fluid becomes urine collected in the renal pelvis and exits via the ureter then drains to the urinary bladder. ### 9.2.2 STRUCTURE AND FUNCTION OF THE NEPHRON * The nephron is the functional unit of the kidney, found within the cortex and medulla. * Components of the nephron: * Glomerulus (ball of capillaries) * Renal tubule (Bowman's capsule, proximal tubule, loop of Henle and distal tubule) **Nephron Organization:** * Afferent arteriole from the renal artery * Glomerulus * Bowman's capsule * Proximal tubule * Distal tubule * Efferent arteriole from glomerulus * Branch of the renal vein * Peritubular capillaries * Descending limb * Ascending limb * Loop of Henle * Collecting duct * Vasa recta * Filtrate is formed when blood pressure forces fluid from the blood in the glomerulus into the lumen of Bowman's capsule. * Processing of the filtrate occurs as it passes through: * The proximal tubule * The loop of Henle * The distal tubule * A collecting duct receives the processed filtrate from many nephrons and transports it to the renal pelvis. * Each nephron is supplied with blood by an afferent arteriole that branches and forms the capillaries of the glomerulus * The capillaries converge as they leave the glomerulus and form an efferent arteriole. * Efferent arteriole branches forming the peritubular capillary (surround proximal and distal tubule) and vasa recta (serve renal medulla) ### 9.2.3 URINE FORMATION * There are four steps of excretory system function: * Filtration * Reabsorption * Secretion * Excretion * **Filtration** * The renal/ excretory tubule collects a filtrate from the blood. * Water and solutes are forced by blood pressure across the selectively permeable membranes of a cluster of capillaries and into the excretory tubule. * **Reabsorption** * The transport epithelium reclaims/reabsorbs valuable substances from the filtrate and returns them to the body fluids. * **Secretion** * Other substances, such as toxins and excess ions, are extracted from body fluids and added to the contents of the excretory tubule. * **Excretion** * The altered/ processed filtrate (urine) leaves the system and the body. The image shows the Capillary, Excretory tubule, and urine formation steps. The steps of urine formatin is as follows: Filtration, Reabsorption, Secretion, and Excretion * **Bowman's Capsule** * Ultrafiltration occurs at Bowman's capsule. * This occurs due to high pressure in the glomerulus (a ball of capillaries). * The pressure is due to the difference in diameter between afferent and efferent arterioles. * Diameter of afferent arteriole > efferent arteriole * Fluid and small molecules move from the capillaries through the fenestrations of glomerular endothelium, glomerular basement membrane and between the filtration slits of podocytes. Glomerulus (Blood plasma) → Bowman's capsule (Renal filtrate) The filtrate produced in Bowman's capsule contains salts, glucose, amino acids, vitamins, nitrogenous wastes, and other small molecules. Blood cells and large molecules, such as plasma proteins are retained in the blood vessels. Efferent arteriole, Afferent arteriole, Proximal tubule, Bowman's space, Epithelial Prodocytes, Filtration slit, Glomerular basement membrane, Glycocalyx, capillary lumen. **Proximal Tubule** * **Reabsorption:** * Reabsorption of ions, water, and nutrients takes place in the proximal tubule * Molecules are transported actively and passively from the filtrate into the interstitial fluid and then capillaries * **Secretion:** * As the filtrate passes through the proximal tubule, materials to be excreted become concentrated * Some toxic materials are actively secreted into the filtrate **Descending Limb of the Loop of Henle** * Reabsorption of water continues through channels formed by aquaporin proteins * Movement is driven by the high osmolarity of the interstitial fluid, which is hyperosmotic to the filtrate * The filtrate becomes increasingly concentrated **Ascending Limb of the Loop of Henle** * In the ascending limb of the loop of Henle, salt but not water is able to diffuse from the tubule into the interstitial fluid * The filtrate becomes increasingly dilute **Distal Tubule - Reabsorption & Secretion** * The distal tubule regulates the $K^+$ and NaCl concentrations of body fluids * The controlled movement of ions ($H^+$ and $HCO_3^−$) contributes to pH regulation **Collecting Duct** * The collecting duct carries filtrate through the medulla to the renal pelvis * One of the most important tasks is reabsorption of solutes and water * Urine is hyperosmotic to body fluids #### 9.2.4.1 ANTIDIURETIC HORMONE (ADH) * Osmoreceptor cells in the hypothalamus monitor blood osmolarity and regulate the release of ADH from the posterior pituitary. * When osmolarity rises above its set point, ADH release into the bloodstream increases, leading to concentrated urine. * When osmolarity drops below a set point, it causes a reduction in ADH secretion, and leads to more dilute urine. The image shows water absorption in the collecting duct. The Osmoreceptors in hypothalamus monitor blood osmolarity. When blood osmolarity is increased, the hypothalamus triggers the release of ADH, which allows the collecting duct to absorb more water into the blood through kidney reabsorption. The Specific neurons of the hypothalamus also trigger drinking. Drinking water reduces blood osmolarity. \ **Explain how your body regulates water content on a hot day.** * Hot day, solute concentration increases in blood due to excessive sweating (increase of blood osmolarity). * Osmoreceptors in the hypothalamus detects the changes - trigger release of ADH from the posterior pituitary. * ADH binds to the receptor on the collecting duct. * The increase of aquaporin in the collecting duct increases the permeability of water. * Water diffuses out into the medulla by osmosis and is reabsorbed into the blood vessel. * Blood osmolarity drops to normal level. **Explain how your body regulates water when you drink a lot of fluid.** * Blood osmolarity decreases. * Osmoreceptors in the hypothalamus detects the changes - inhibit the release of ADH from the posterior pituitary. * The number of aquaporin in the collecting duct is less and has lower permeability of water. * Water is retained in the renal tubule. * Blood osmolarity increases to normal level. #### 9.2.4.2 RENIN-ANGIOTENSIN-ALDOSTERONE SYSTEM (RAAS) * The renin-angiotensin-aldosterone system (RAAS) responds to the drop in blood pressure and reduction of blood volume (without increasing osmolarity) * Example: major wound, severe diarrhea * A drop in blood pressure near the glomerulus causes the juxtaglomerular apparatus (JGA) to release the enzyme renin * Renin triggers the formation of the peptide angiotensin II. * Angiotensin II: * raises blood pressure by triggering vasoconstriction and decreases blood flow to the kidneys. * stimulates the release of the hormone aldosterone from the adrenal gland, which increases blood volume and pressure. * Aldosterone: * Increases the permeability of $Na^+$ at the distal tubule. * This will cause more $Na^+$ reabsorption and more water diffuse out of the tubule by osmosis into the blood vessel. * Blood pressure and volume increase back to normal. The image shows the Renin-Angiotensin-Aldosterone System (RAAS) and its control loop. Sensors in JGA detect decrease of blood pressure or blood volume drop. The JGA then releases renin, which is converted into Angiotensin II. Adrenal glands then release Aldosterone and Arterioles constrict. Sodium and Water reabsorption increases to return `NORMAL BLOOD PRESSURE AND VOLUME`.