1 Biology Teacher Notes Comes to Life Homeostasis: role of the cardiovascular, respiratory and renal systems By completing a number of common tests used in biomedical science, your students will identify how exercise influences cardiovascular, respiratory and renal responses of the human body. Students will participate in tests of jumping performance, maximal aerobic uptake (VO 2 max), and maximal power, whilst monitoring the body s physiological responses through modern technologies. Students will be given the opportunity to apply their classroom learnings about changes in the concentration of blood as it passes around the body, haemoglobin, feedback mechanisms related to blood ph and temperature, structure of blood vessels and the components of blood. Depending on the availability of time, students may also be given the opportunity to discuss the role of sweating during prolonged exercise, and consider how this will influence factors such as blood pressure and water/ electrolyte balance, in turn affecting the release of the hormones aldosterone and anti-diuretic hormone. Ref Students learn about Science Comes to Life Explain that homeostasis consists of two stages: - Detecting changes from the stable state - Counteracting changes from the stable state Identify the form(s) in which each of the following is carried in mammalian blood: CO 2, O 2, H 2 O, salts, lipids, nitrogenous waste Identify current technologies that allow measurement of oxygen saturation and carbon dioxide concentrations in blood Outline the need for oxygen in living cells and explain why removal of carbon dioxide from cells is essential Observe a maximal oxygen uptake test (VO 2 max) test of one of their classmates, and identify the role of feedback loops in maintaining homeostasis (temperature, CO 2 concentration and ph) Identify the role of each of the mentioned substances within the human body, and how they are carried in human blood Conduct experiments with pulse oximeters, and monitor the concentration of breath (O 2 and CO 2 ) before and after exercise Participate in a maximal power (30-second Wingate) test and monitor the impact that exercise has on breath concentrations Explain the adaptive advantage of haemoglobin Students will monitor oxygen uptake during exercise, and consider the importance of optimising oxygen uptake for ATP production and performance Outline the role of the hormones aldosterone and ADH (anti-diuretic hormone) in the regulation of water and salt levels in the blood Participate in an interactive vertical jump assessment, designed to demonstrate how aldosterone and ADH levels are modified to maintain homeostasis following prolonged exercise. This conceptual activity will address the impact of sweating and how it influences blood volume, blood pressure and water/electrolyte balance School of Science and Technology
2 ACTIVITIES TO BE COMPLETED DURING YOUR UNE EXPERIENCE Activity A: What impact does homeostasis have on my breath concentration? A Multiple students will be given the opportunity to complete a 30 second Wingate test, where the goal is to perform exercise with maximal power throughout the activity. Using either stationary bikes, timing gates or GPS units to monitor power or speed output, students will be able to perform breath analysis to identify what the impact of increasing metabolic processes has on O 2 uptake and CO 2 production. The homeostatic mechanisms which control breath concentration will be considered, and the impact of increasing CO 2 concentration on performance will be addressed with regard to maintaining optimal metabolic efficiency. Overall, this activity provides the opportunity for some fun competition between students and/or teachers, whilst still addressing important syllabus learning goals. Activity B: How are nutrients/gases transported in the body, and how is core temperature controlled during long duration exercise? B The VO 2 max test is generally considered the best indicator of cardiorespiratory fitness, and is performed by analysing the air inhaled and exhaled during an incremental exercise test to fatigue. The underlying principle behind the VO 2 max test is that almost every biological process in the human body is dependent on the availability of O 2 for muscle cells, and the removal of CO 2 to maintain a stable internal environment. During Activity 2, one or possibly two of your students will be given the opportunity to complete a VO 2 max test, either cycling or running. Throughout the activity, students will be able to observe and record real-time results relating to O 2 uptake, CO 2 production, heart rate and their relationship with increasing exercise intensity. The information collected will be used to re-inforce syllabus related concepts including the adaptive advantage of haemoglobin, role of blood, the changing concentration of blood as it travels around the body, and particular organs in which changes occur. Finally, students will consider how core temperature changes with prolonged exercise and consider the homeostatic mechanisms contributing to this process (eg sweating and vasodilation). This activity provides an excellent opportunity for students to monitor physiological responses, whilst collecting valuable information to assist their theoretical learning in the classroom. Activity C: What is the role of anti-diuretic hormone (ADH) and aldosterone in the human body? C Water and electrolyte balance is critical for the body to maintain metabolic efficiency. Using exercise to reflect an environmental condition which challenges the water/electrolyte balance in the body, students will be able to conceptualise the impact that sweating and fluid loss through exercise have on kidney function and the production of ADH/aldosterone. The interactive activity will require students to complete 1 minute worth of vertical jump testing, in which they are able to measure and compare their performances using digital jump mats. An interactive computer/tablet program will allow students to assess how performance, sweating, ADH, aldosterone, reabsorption, blood volume and urine volume/ concentration are inextricably linked. What can be a difficult concept for students to grasp will be made a lot easier in this fun yet competitive environment. Students and teachers alike will enjoy and benefit from this activity. Glossary Adenosine triphosphate (ATP) - energy source for all muscular contractions in the human body. Without ATP, we cannot live, let alone exercise! Carbonic Acid (H 2 CO 3 ): forms when CO 2 combines with H 2 O, causing acidity of blood [H+] Cellular respiration: process where the chemical bonds of energy-rich molecules such as glucose, are converted into ATP according to: Glucose + Oxygen Water + Carbon Dioxide + ATP Rate of ATP production - increases with increasing exercise intensity Aerobic ATP production - occurs more slowly than anaerobic, but can be sustained for long periods Anaerobic ATP production - high rate of ATP production, but less efficient and increased waste products Waste product - produced during ATP production, and has a negative effect on athlete performance. Examples include carbon dioxide, nitrogenous waste and lactic acid.
3 ANSWERS TO QUESTIONS POSED DURING THE UNE VISIT Activity A: What impact does homeostasis have on my breath concentration? 1. What change in CO 2 did you observe following the high-intensity exercise bout? Following the 30-second exercise bout, students will be able to confidently identify an increase in the concentration of CO 2 in their own breath. This will be used to discuss the increasing metabolic demands of the body to produce ATP during high-intensity exercise, leading to an increase in the use of O 2 and an increased production of CO Why must CO 2 be removed from the body, and why does this become even more important during high intensity exercise? When in the blood, CO 2 bonds with water (H 2 O) to form carbonic acid (H 2 CO 3 ) which causes the ph to fall. Homeostasis and metabolic efficiency are challenged with a fall in the ph of blood from an optimum level of 7.4. The body s defence against increasing concentrations of CO 2 in the blood is to remove it via the respiratory system, thus the varying concentration of CO 2 in breath. Increased concentration of CO 2 in the breath is reflective of increased levels of CO 2 in the blood, and is the body s attempt to modulate blood ph and homeostasis. 3. What are the two stages which contribute to a negative feedback homeostatic mechanism, such as the control of CO 2 in the blood? a) Detecting changes from the stable state b) Counteracting changes from the stable state 4. Complete the table below, with reference to the homeostatic mechanism controlling CO 2 concentration in blood during exercise (1): Stimulus Receptor organ - detects change Coordinating organ - eg hypothalamus Effector organs - bring about change Response Increased CO 2 and [H + ] Chemoreceptors- aorta & carotid a. Medulla & pons (brainstem) Lungs Heart Diaphragm Increased respiration and removal of CO 2 Decreased CO 2 and [H + ] Chemoreceptors- aorta & carotid a. Medulla & pons (brainstem) Lungs Heart Diaphragm Reduced respiration and removal of CO 2 5. What is the role of the nervous system in the process of homeostasis? CNS: consists of the brain and spinal cord and is responsible for coordinating homeostatic responses by either sending nerve impulses to effectors via the PNS or releasing hormones (eg hypothalamus releasing ADH) PNS: consists of sensory neurons (eg chemoreceptors) and motor neurons. Sensory neurons transmit information from receptor organs to the CNS, whilst motor neurons transmit information from the CNS to effector organs which activate a response
4 Activity B: How are nutrients/gases transported in the body, and how is core temperature controlled during long duration exercise? 1. Complete the equation to demonstrate cellular respiration (ATP production) in the body? Glucose + OXYGEN Water + CO 2 + ATP 2. What is the role of blood in the human body? Blood is the link between the heart/lungs and the rest of the body. All processes within the human body rely on O 2 being available for ATP production, and the removal of CO 2 to maintain blood ph at a consistent level. Blood has the capacity to carry both O 2 and CO 2, along with other products required for or produced during metabolic reactions (eg nitrogenous waste, lactic acid, glucose, salts, lipids and water). One very important component of blood is haemoglobin, which significantly increases the carrying capacity of O 2 and CO 2 in the blood. 3. What did you notice about the use of oxygen by the body as the intensity of exercise increased? During increasing exercise intensity, there is a corresponding increase in the rate of cellular respiration to meet the demand of ATP of the muscles. With an increase in the demand for ATP, the body will increase the speed of cellular respiration thereby increasing the use of reactants (oxygen and glucose), whilst increasing accumulation of products (ie ATP, CO 2 and water). This will be visible in the real-time analyses of O 2 uptake (VO 2 ). 4. What happened to the CO 2 concentration of breath with the commencement of exercise? An increase in the rate of cellular respiration causes an increase in the concentration of CO 2 produced in cells. This MUST be removed concurrently so it doesn t cause the concentration of H+ ions to rise significantly as a result of carbonic acid (H 2 CO 3 ) accumulation. In order to modulate the levels of CO 2 in the blood, the body will increase its removal of CO 2 in the breath, which students will identify as an increase in the %CO 2 of breath during and after exercise. 5. Why do you think heart rate increases with the intensity of exercise? Increasing exercise intensity requires greater quantities of O 2 and glucose to be transported to cells, whilst larger quantities of CO 2 are produced in the cells and must be removed. Each of these substances is carried in the blood. During exercise, the heart increases its cardiac output predominantly through an increase in heart rate, to meet each of the requirements listed above. 6. What carrier molecule, containing iron, is considered an adaptive advantage in the human body and why? Haemoglobin; is a protein molecule which has a high affinity for O 2. As a result, it significantly increases the O 2 carrying capacity of blood leading to a survival advantage allowing more ATP to be produced aerobically. Haemoglobin also carries CO 2 from working muscles to the lungs allowing for removal via respiration. Not only does this help in maintaining correct gas concentration in the body, but it takes CO 2 out of solution, meaning that it doesn t impact upon ph (advantage of haemoglobin as a buffer system). 7. The concentration of CO 2 gas, in the blood, triggers an increase in the respiratory rate of the body. This is identified by chemoreceptors which respond primarily to changes in blood ph. 8. Complete the table by choosing from the following options (CO 2, O 2, nitrogenous waste, water, fats, salts and products of digestion) (1) : Substance What it is carried by... Coordinating organ - eg hypothalamus O 2 Red blood cells Oxyhaemoglobin CO 2 Plasma Red blood cells Water Plasma Water molecules Salts Plasma Ions Lipids Plasma Nitrogenous waste Plasma Mostly urea Mostly as bicarbonate ions, with a small percentage dissolved directly in plasma Carbamate (combination of CO 2 and haemoglobin) Chylomicron (a package of digested lipids, phospholipids and cholesterol wrapped in protein) Other products of digestion Plasma Whole molecules: eg glucose
5 9. Draw an arrow to demonstrate how substances follow a concentration gradient: HIGH LOW 10. How do the concentrations of blood gasses and nutrients (e.g. glucose) change as blood passes around the body? What are the particular organs in which blood concentration changes? A continuous exchange of substances between cells and the blood means that the composition of blood is constantly changing. The levels of physical activity and other metabolic processes influence the rate at which these changes are occurring, primarily determined by the concentration gradients present. The larger the concentration gradient, the faster the substances will pass across the permeable membrane. The changes in blood composition occur according to the following: Substances transported to cells: Glucose, O 2 Substances removed from cells: CO 2 and other waste products (eg nitrogenous waste) Small intestine: glucose is transported from the gut into the blood stream Kidney: nitrogenous waste and [H+] are removed from blood, which is excreted as urine 11. The 3 different types of blood vessels have different roles within the body. Their structure dictates what their function is and viceversa. Can you identify the structural differences between arteries, veins and capillaries, and suggest how these contribute to function? The primary role of the blood vessels is to transport molecules to and from the cells of the body. The structure of the blood vessels varies according to their function, and the mechanical pressure that is placed on them. There are 3 different types of blood vessel. Arteries: carry blood away from the heart which is pumped under high pressure. They have thick/muscular walls designed to withstand this pressure, and also have the capacity to influence blood pressure by vasodilating/constricting. Arteries also expand and relax with the heart, to aid transport of blood around the body Veins: carry blood towards the heart under low pressure. As a result of low pressure, the veins only have thin walls. Moving against gravity whilst people are in an upright posture, blood is mechanically pumped by muscles back towards the heart. A functional characteristic of veins is the presence of valves to stop back flow of blood, meaning that any muscle contraction around the structure will cause forward movement of blood in veins towards the heart. In the absence of valves, the return of blood back to the heart (venous return) would be ineffective. Capillaries: the primary role of capillaries is to allow the transfer of substances from within the blood stream, into the cells of the body (and vice-versa). Thick walls would make this transfer more difficult, therefore capillaries are made of a single layer of cells, allowing the transfer of gases, nutrients and wastes between blood cells and tissue cells. 12. Complete the table from the following options (Kidney, small intestine, lungs, and other body tissues) (1): Tissue Main change Lungs Removal of CO 2 ; Oxygenation of blood Other body tissues Kidneys Small intestine Deoxygenation of blood; removal of glucose; increase in carbon dioxide Removal of nitrogenous waste Increase in digestive products (ie glucose) 13. How do concentration gradients influence the transfer of substances in the human body? How would this change with exercise? Concentration gradients are important for the transfer of the majority of substances within the body. Passive diffusion occurs when substances flow from a high concentration to a low concentration, and applies to O 2, CO 2, glucose and some salts. The rate of diffusion is heavily influenced by the concentration gradient present (ie a greater difference between the concentration of the two compartments will cause an increase in the rate of diffusion). During exercise, the body uses more oxygen and glucose whilst producing more CO 2. In effect this increases the concentration gradient between tissue cells and the blood, therefore causing an increase in the rate of diffusion down the concentration gradient.
6 14. Can you identify why exercise is so important for diabetic patients, and why it is so effective in controlling blood sugar levels? Exercising muscles require more ATP to perform, and therefore muscle cells have an increased rate of glucose usage. An increase in the rate of glucose used within the cell leads to an increase in the concentration gradient between the blood and muscle cells. As a result, there is an increased uptake of glucose from the blood into the muscle cells, which is the treatment priority for diabetic patients. This process occurs independently of insulin, therefore is still effective when patients don t produce insulin or are desensitised to it, as in diabetic patients. 15. Prolonged exercise causes an increase in core temperature. Can you complete the following table, demonstrating the role of the homeostatic control mechanism under prolonged exercise? (1) Stimulus Receptor organ - detects change Increased temperature Thermoreceptors (in skin) Coordinating organ - eg hypothalamus Hypothalamus Effector organs - bring about change Blood vessels Response Vasodilation- heat removal via skin Skin/sweat glands Increased sweat production (evaporation of heat in sweat) 16. Does temperature follow a concentration gradient? Why might people fatigue earlier in hot conditions, and why would this impact upon performance? Heat also flows down a concentration gradient (from high to low). If the ambient temperature is higher than the temperature of the body (37 C), then the body will not be able to remove heat via sweating mechanisms, and will therefore fatigue very quickly due to an increase in core temperature. An increase in core temperature will have a negative impact on the function of enzymes involved in ATP synthesis. It is important to understand that the greater the gradient between the body and the ambient temperature, the greater the rate of heat loss/gain between the two compartments. 17. What impact does sweating have on blood volume and blood pressure? Sweating is a natural response to remove heat from the body. Sweat consists of water and electrolytes, therefore prolonged sweating can lead to a fall in blood volume, and a change in the fluid/electrolyte concentration of blood. It is important to recognise that sweat consists of relatively more water than salts, therefore causes an increase in the electrolyte concentration of blood. 18. Can you think of an example of when an endurance athlete may demonstrate extreme fatigue as a result of homeostasis not being maintained? Can you explain? Ultra-endurance athletes can perform moderate intensity exercise for up to 24 hours. At the completion of these sorts of competitions, it is not uncommon to see an athlete stumbling across the finish line to collapse. Homeostasis is a likely contributor, with the athlete most likely depleted of glucose and glycogen stores, and high concentrations of metabolic waste products such as nitrogenous waste, carbon dioxide (ph) and lactic acid. Core temperature may be high and water/electrolyte balance (dehydration) may be influencing the capacity of muscles to contract.
7 Activity C: What is the role of anti-diuretic hormone (ADH) and aldosterone in the human body? 1. Complete the following table to identify the main metabolic waste products produced in the body and how they are excreted (1): Metabolic Waste Product Carbon dioxide Excess water Excess salts Nitrogenous waste (urea, ammonia, uric acid) Exhaled in breath Urine excreted from kidney Urine excreted from kidney Urine excreted from kidney Excreted in For optimal functioning of the human body, the concentration of water and electrolytes in cells should be maintained at the same (isotonic) levels as it is outside the cell. If cells are hypertonic or hypotonic, then the diffusion of water will occur to achieve the isotonic balance. What happens during exercise when water and electrolytes are lost as sweat from outside of cells, and how does this affect the constant internal environment? Both water and electrolytes flow across the semi-permeable membrane of the cell according to concentration gradients. When sweat is produced as a defence against overheating during exercise, this causes a reduction in the concentration of water outside cells, and a corresponding increase in the concentration of electrolytes. As a result of heightened concentration gradients, water flows from within the cell into the interstitial fluid (ie from high to low), in an attempt to balance the concentrations within and surrounding the cell. Continued sweating will contribute to ongoing loss of fluid from within cells, which also effects the concentration of electrolytes within cells. Each of these factors contributes to a change in the constant internal environment, thereby having a detrimental impact on the efficiency of metabolic processes. 3. What is the underlying role of the kidney, and what is the functional unit of the kidney which allows this process to occur? The underlying role of the kidney is to remove nitrogenous waste from the blood, which if otherwise accumulates is toxic to the body. This nitrogenous waste is removed as urea by the nephron, which is the functional unit of the kidney. 4. What is the defining characteristic of substances which are filtered out of the blood as glomerular filtrate? All substances within the glomerular filtrate are small and must be able to fit through the capillary walls in the glomerulus. These substances include water, sodium, chloride, potassium, urea, glucose, amino acids, vitamins and minerals. This filtration process is fairly effective at sorting the components of blood into waste and non-waste products; however reabsorption is still required to remove substances from the glomerular filtrate which are required by the body. 5. What molecules are too large to be filtered through the glomerular capillaries, and therefore remain in the blood stream? Red and white blood cells and large proteins such as hormones 6. What components are filtered out of the blood into the glomerular filtrate? Water, sodium, chloride, potassium, urea, glucose, amino acids, vitamins and minerals 7. What components are actively reabsorbed from the glomerular filtrate for recirculation around the body? Glucose, sodium, potassium 8. Explain why water is passively reabsorbed back into the blood stream following active reabsorption of sodium (Na+)? Sodium is actively reabsorbed from out of the nephron, into the blood stream. This creates a concentration gradient in which the concentration of sodium in the blood is higher than in the nephron. As a result, the water is passively reabsorbed into the blood stream, passing from a high concentration to a low concentration. This in turn causes an increase in the blood volume, and blood pressure to rise.
8 9. Why does some urea get reabsorbed from the collecting duct into the blood, when the primary function of the kidney is to remove nitrogenous waste? Urea is another substance that flows down a concentration gradient. Some urea may be transported back into the blood, in order to create a concentration gradient for water to follow. The impact of this will be to re-establish water balance and blood pressure in the body. 10. What happens to the concentration of urine as the loop of Henle increases in length? The loop of Henle allows active and passive reabsorption of substances from the glomerular filtrate, most importantly sodium and water. The longer the loop of Henle is, the greater the time available for reabsorption to occur, therefore seeing a reduction in the volume of urine produced and a corresponding increase in concentration. Animals that live in the desert with limited access to water have long loops of Henle, meaning that they produce a small amount of very concentrated urine so to conserve water. 11. How does the concentration of blood influence the rate of reabsorption of substances in the nephron? The concentration of blood influences reabsorption processes due to the concentration gradient present. As the magnitude of the concentration gradient increases, the rate of diffusion between the nephron and blood also increases. For example, when a person is dehydrated such as following prolonged exercise, the concentration of salts in the blood will be higher causing an increase in the rate of passive reabsorption of water from the nephron into the blood stream. As such, following prolonged exercise we would expect to see only a small volume of highly concentrated urine produced. 12. The rate of reabsorption is dependent not only on concentration gradients, but also on the permeability of nephron walls. What are the two main hormones produced in the body which influence permeability of the nephron walls to water and salts? Anti-diuretic hormone (ADH): increases permeability of nephron walls to water causing an increased reabsorption of water into the blood stream, and a corresponding fall in the production of urine. An increase in production of ADH by the brain is stimulated by an increased solute concentration in blood, reflecting dehydration. Aldosterone: increases permeability of the nephron walls to sodium, allowing more sodium to be actively reabsorbed from in the nephron back into the blood. This causes a concentration gradient to be established, which causes a passive reabsorption of water back into the blood stream. Aldosterone is produced by the adrenal glands (kidney) in response to a fall in blood pressure. As a result of increased passive water reabsorption in response to aldosterone and sodium reabsorption, there is an increase in blood pressure. 13. Prolonged and high-intensity exercise causes an increase in sweating in order to control body temperature. Can you explain the results demonstrated by the jumping activity? As the volume of sweat increased, there was an anticipated reduction in blood volume. This would be recognised by the body as a fall in blood pressure (causing an increase in aldosterone concentration) and an increase in the concentration of solutes within the blood (leading to an increase in the release of ADH. As a result of aldosterone and ADH concentrations increasing, the permeability of the nephron walls would increase to both sodium and water. The rate of active sodium reabsorption would increase, creating a concentration gradient, which contributes to an increase in the rate of passive reabsorption of water back into the blood stream. As the reabsorption of sodium and water increased, we would expect a reduction in the volume and an increase in the concentration of urine. Blood volume and blood pressure would increase, whilst the concentration of solutes in the blood would fall. 14. A high concentration of aldosterone and ADH was associated with an INCREASED rate of reabsorption from the nephron. 15. A sports scientist was asked to analyse a urine sample from an athlete immediately following a 42km marathon. Would you expect that they would have a high or low concentration of ADH and aldosterone, and describe their urine in terms of volume and concentration? The athlete would have been profusely sweating, therefore have a reduced blood volume. Aldosterone and ADH levels would be high in an attempt to increase reabsorption of water back into the blood stream. Increased rates of reabsorption will contribute to a low volume of urine, of very high concentration (coloured). Reference: Jeffery, C. and Ross, P. (2007) NSW BIOLOGY- Maintaining a balance, Macmillan Education Australia, South Yarra, Australia.