EXCRETION 2020.pdf

1 LIFE SCIENCES GRADE 11 EXCRETION IN MAN SA 1 Learn about The structure and functioning of the kidneys The importance of the kidneys for homeostasis. Suitability...

1 LIFE SCIENCES GRADE 11 EXCRETION IN MAN SA 1 Learn about The structure and functioning of the kidneys The importance of the kidneys for homeostasis. Suitability of the nephrons for their functions The regulation of kidney activity SA 2 Learn how to Dissect a sheep’s kidney Read tables and graphs related to kidney functioning SA 3 Think about Detecting performance-enhancing drugs in athletes & discuss The ethics of using such drugs The composition of urine in diabetics Renal failure and renal dialysis Kidney stones and the treatment thereof The effect of alcohol on urine composition Different views on organ donation NOTES:  2 1. TERMS: EXCRETION is the removal of metabolic wastes, i.e. the waste products produced by the cells due to chemical reactions, such as urine, CO2 and sweat. [Don’t confuse this with SECRETION (passing out useful substance like saliva and mucus) or with EGESTION, the removal of undigested waste through the anus]. OSMOREGULATION is the control of water content. HOMEOSTASIS is the maintenance of a constant, optimal internal environment independent of changes in the external environment. Homeostatic mechanisms maintain this steady state, which is vital for survival. Excretion and osmoregulation are both homeostatic mechanisms. 2. THE NECESSITY FOR EXCRETION: Metabolism causes the formation of wastes like CO2 & nitrogenous wastes like urea, which are harmful if they accumulate. Cells only function normally if tissue fluid remains constant with respect to water, temperature, pH, waste content, ions etc. The excretory organs help to maintain this optimal internal state by the removal of metabolic wastes and by osmoregulation. The best possible internal environment is created for the survival of cells, so the excretory organs are important for homeostasis. 3. THE MAIN EXCRETORY ORGANS: 3.1 KIDNEYS: They eliminate urine (excess water, salts and nitrogenous wastes), thereby removing metabolic wastes and regulating the water and salt concentration of the body. 3.2 LUNGS: Remove CO2 by diffusion from the blood at the alveoli. 3.3 SKIN: Sweat glands eliminate sweat (also water, salts and nitrogenous wastes, but less concentrated than urine). The main salt eliminated is sodium chloride. 3.4 LIVER Removes many cellular wastes, e.g. the remains of hemoglobin from broken down red blood cells, which are excreted via bile. Proteins are deaminated and urea is formed; many ingested poisons are detoxified. 4.5 ALIMENTARY CANAL Metabolic wastes and excess inorganic substances like salts and calcium are excreted into the large intestine and eliminated with the faeces.  3 THE URINARY SYSTEM OF MAN adrenal gland inferior vena cava _______________ Excretion aorta Osmoregulation renal vein pH control renal artery ________________ Carries urine to bladder abdominal cavity _______________ Stores urine _________________ Carries urine to outside L/S KIDNEY TO SHOW INTERNAL STRUCTURE _______________ Allows accumulation of fat for ___________________ protection Oxygenated blood & _________________ wastes into kidney Dark outer region mainly for filtration of blood __________________ Deoxygenated blood _______________ Pale inner region mainly for out of kidney reabsorption of water __________________ Concave side of kidney where tubes attach _________________ Consists of large collecting ducts. Carries urine of many nephrons to pelvis. Carries urine to bladder Collects urine of all the pyramids & passes it to ureter  4 4. URINARY SYSTEM OF MAN: Kidneys, which are organs of excretion and osmoregulation. Ureters, which are tubes to carry urine from the kidneys to the _________________. Bladder, which stores urine temporarily. Urethra, which carries urine from the bladder to the ______________. It is controlled by a sphincter muscle. 4.1 KIDNEYS: On either side of the spine, with the concave side facing the spinal cord. In the posterior part of the abdominal cavity, just below the diaphragm. 4.1.1 Macroscopic structure of the kidneys: Kidneys are dark red, bean-shaped and about the size of your palm. The concave side or hilum is the place where all the tubes are attached: o RENAL ARTERY - enters kidney from the _____________ o RENAL VEIN - leads away from kidney into ________________________ o URETER - carries urine to the ___________________ The renal capsule is a thin layer of connective tissue around the kidney. It allows accumulation of __________ for protection and to holds the kidneys in position against the back of the abdominal cavity. Internally, kidneys are seen to have an outer, dark red cortex and a paler, middle medulla region. The medulla consists of triangular pyramids. The central funnel-shaped pelvis has narrower areas called calyces / calyxes collecting urine. It leads to the ureter.  5 INVESTIGATION 1: DISSECTION OF A KIDNEY: (Groups) Work in groups of about 5 and follow the instructions from your teacher about how to proceed with the kidney dissection. It will be necessary to remove some of the kidney material above the calyces after the initial longitudinal cut, since sheep kidneys have a slightly different structure from the human kidney. The calyces and pyramids will be more visible then. Make a neat, labeled drawing of the kidney L/S in the space below:  6 ARRANGEMENT OF NEPHRONS WITHIN THE KIDNEYS cortex medulla  7 4.1.2 Microscopic structure of the kidneys: Kidneys consist of about 1 million tiny nephrons, which are very narrow, folded tubules that are not visible to the naked eye. Each nephron has a tubule and a capillary network. Bowman’s capsule is the closed, expanded end of the nephron. It is indented to form a cup- shape enclosing a capillary network called the ______________________. Both Bowman’s capsule and the glomerulus consist of a single layer of squamous epithelium. Together, Bowman’s capsule & the glomerulus form the Malpighian body in the renal cortex. The proximal convoluted tubule of ________________ epithelium is just below Bowman’s capsule in the cortex. The loop of Henle extends into the medulla. The ascending limb consists of cuboidal epithelium, while the descending limb has __________________ epithelium. The distal convoluted tubule of ___________________ epithelium is again in the cortex. Several nephrons open into collecting ducts that lead to the calyxes and then into the pelvis. 4.2 BLOOD SUPPLY: Branches of the renal artery form renal arterioles in the kidney. They divide to form the _____________ arteriole going to the glomerulus at each nephron. Capillaries re-unite after the glomerulus to form the ________________ arteriole leading away from the glomerulus. It is NARROWER than the afferent arteriole, causing pressure in the glomerulus. The efferent arteriole re-divides to form a capillary network around the proximal and distal tubules and the loop of Henle. The capillary network re-unites to form renal venules that ultimately form the renal vein, which leaves the kidney at the hilum.  8 STRUCTURE OF ONE NEPHRON: ENLARGEMENT OF THE MALPIGHIAN BODY (renal corpuscle)  9 PODOCYTES ON THE INNER WALL OF BOWMAN’S CAPSULE: DETAIL OF PODOCYTES FORMING THE INNER WALL OF THE CAPSULE:  10 THE FORMATION OF URINE (General functioning of the kidneys)  11 4.3 THE FUNCTIONING OF THE NEPHRON: URINE FORMATION: The nephrons are the functional units of the kidneys. They remove wastes, regulate the pH, salt and water content of the blood by 3 processes, namely Glomerular filtration / Ultra-filtration Selective reabsorption Tubular excretion 4.3.1 Glomerular filtration / Ultra-filtration This is made faster by ______________the glomerulus, as the afferent arteriole is wider than the efferent arteriole. Pressure is also increased by the pumping of the heart (blood pressure). Ultra-filtration is caused by hydrostatic pressure and cannot be called diffusion. Small molecules like water, salts, glucose, vitamins and urea filter out of the glomerulus into the capsular space. They pass through narrow pores between specialized star-shaped cells in the inner wall of the capsule, called _____________________. They have major processes and minor processes, the latter to keep the cells attached to the capillary network. Large molecules like _________________ and blood cells do not pass into the capsule. The liquid that enters the capsule is an ultra-filtrate of blood plasma. It is mainly water and has useful substances like amino acids, glucose, salts and vitamins, but also wastes like urea, uric acid and excess minerals. The liquid is called ‘the filtrate’. The filtrate is not yet urine. Much selective reabsorption and excretion needs to be done before it can pass out of the body.  12 Structural suitability of the Malpighian body for ultra-filtration: PART STRUCTURE SUITABILITY Glomerulus Network of ____________________ increase _______________________ for ultra-filtration. Capillaries are__________________ to ________________ pressure & slow down the movement of blood. Walls have ____________________ to allow ________________________ to pass through. Arterioles __________________ arteriole has a wider to create _____________________ in the lumen than the efferent arteriole glomerulus for rapid ultra-filtration. Bowman’s Is ___________ shaped to increase ______________________ capsule for ultra-filtration. Walls consist of a single layer of to allow __________________ passage of _________________ epithelium substances. Special cells called ______________ to _____________________________ have pores between cells _______________________________ 4.3.2 Selective reabsorption: Useful substances are selectively reabsorbed from the proximal convoluted tubules into the surrounding __________________ network. This process is partly active and partly passive. Active reabsorption involves carrier molecules and often occurs against the concentration gradient, to ensure that all useful substances can re reabsorbed into blood. The cuboidal cells thus have many __________________________ to supply energy. The cells also have a brush border / microvilli to increase the surface area for reabsorption. Passive reabsorption occurs by diffusion and/or ______________ and needs no energy, as it always occurs with the concentration gradient. Much water is reabsorbed here by osmosis.  13 Capillaries reabsorb all ______________ and amino acids here, also any vitamins & minerals the body needs. Excess vitamins / minerals won’t be reabsorbed, e.g. if the person has more vitamin C in the blood than needed (we can’t store water-soluble vitamins). The loop of Henle is specifically concerned with water reabsorption. __________ are pumped into the medulla on the ascending side, so that water is easily reabsorbed into the capillaries around the descending side. This always occurs by osmosis. In desert animals like camels and kangaroo rats, the loop of Henle is very long, so water is conserved easily. Their renal medulla is thus wider than that of other animals. 4.3.3 Tubular excretion: At the distal convoluted tubule, large wastes like creatinine are actively excreted from the ________________ into the tubules, as such molecules are too big to filter into the capsule. Smaller wastes like urea & uric acid are also passed out of the blood, as many of them may not have come close to the podocytes during ultra-filtration. Drugs like penicillin and aspirin are excreted into the distal convoluted tubule after they have circulated through the body and done their work. The walls of the distal tubule do not have microvilli. The distal tubule also regulates the ______ of blood by regulating the excretion of H+ ions and bicarbonate ions. More H+ ions are excreted if the blood is too acidic and more bicarbonate ions are excreted if the blood is too alkaline. Much water passes from the distal tubule and collecting duct into the blood stream. This is regulated by the hormone ________ from the pituitary gland and is the chief mechanism responsible for osmoregulation.  14 The distal convoluted tubule: Consider the functioning of the distal convoluted tubule. Why is it that athletes at most high-level events are asked to submit urine samples? What are organizers looking for and why are they confident of finding “the cheats”? ___________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ 4.3.4 The composition of urine: Urine composition varies depending on diet, activity, fluid intake and environmental temperature. Factors affecting urine composition: How will each of the factors mentioned above influence the composition of urine and why? Diet ____________________________________________________________________________ ________________________________________________________________________________ Activity __________________________________________________________________________ ________________________________________________________________________________ Fluid intake _______________________________________________________________________ ________________________________________________________________________________ Environmental temperature ___________________________________________________________ ________________________________________________________________________________________ The average person’s urine may contain the following: Water 96 % Urea 2 % Inorganic salts (mainly NaCl) 1,5 % Other substances* 0,5 % * These include bile pigments (which give urine the typically yellow colour), as well as bile salts (which gives urine a bitter taste) [No, the staff have not tasted urine to find out… J] The smell of urine is due to urea. The pH of urine is usually slightly acidic (pH 6,5), but it may be neutral or slightly alkaline, depending on diet.  OSMOREGULATION IN THE KIDNEYS 15  16 4.4 THE REGULATION OF KIDNEY ACTIVITY: The hormone _______is released by the pituitary gland & reaches the kidneys via the blood. It controls the permeability of the walls of the _________ convoluted tubules and __________________ ducts of the nephrons. The amount of water in the blood is detected by osmorecepetors in the brain If there is too little water in the blood, e.g. due to __________________________________: MORE ADH is released, making the walls of the distal tubule & collecting ducts more permeable to water. More water is reabsorbed into the blood by osmosis, so water is conserved. A __________ volume of concentrated urine is excreted. If there is too much water in the blood, e.g. due to _________________________________: LESS ADH is released, making the walls of the distal tubule and collecting ducts less permeable to water. Less water is reabsorbed into the blood by osmosis, so more water is released via urine. A ____________ volume of dilute urine is excreted. So the kidneys and pituitary gland together maintain the correct water content in the blood. 4.5 FUNCTIONS OF THE KIDNEYS: Excretion Eliminate nitrogenous wastes like __________ and uric acid. Osmoregulation Maintain normal __________ content of the blood by elimination of salts and excess water. pH control H+ or bicarbonate ions are excreted to maintain the blood pH at a slightly alkaline level. Toxin control Some ingested poisons may be excreted by the kidneys. 5. IMPLICATIONS FOR HOMEOSTASIS The kidneys are the ultimate CONTROLLERS OF CHEMICAL BALANCE between the body and environment. Osmoregulation causes the retention / elimination of water to maintain the volume of blood and intercellular fluid at levels optimal for the functioning of the cells. DISCUSSION TOPIC: Organ donation: See Worksheet Question 6. Discuss in class. This need not be a formal debate, but must be done.  17 WORKSHEET: QUESTION 5 IS ESSENTIAL, THE REST ARE OPTIONAL ACTIVITIES QUESTION 1: Differentiate between: Ureter & urethra ____________________________________________________________ __________________________________________________________________________ Renal artery & renal vein _____________________________________________________ __________________________________________________________________________ Cortex & medulla ___________________________________________________________ __________________________________________________________________________ Nephron & Malpighian body __________________________________________________ _________________________________________________________________________ Afferent & efferent arteriole _________________________________________________ _________________________________________________________________________ Active & passive reabsorption ________________________________________________ _________________________________________________________________________ QUESTION 2: List the following parts in their correct order and briefly give the function of each: Collecting duct; Proximal convoluted tubule; Distal convoluted tubule; Loop of Henle; Bowman’s capsule. PART FUNCTION  18 QUESTION 3: Fill in the following flow diagram on the functioning of ADH. _______ ADH secreted Kidney tubules ________ permeable Blood water content Is too low _________ water reabsorbed CORRECT A. Blood Eatingwater salty food / much sweating potential WATER Blood water content BALANCE ________________ Blood water content B. Drinking water / not sweating _________________ __________ water reabsorbed Blood water content is too high Kidney tubules ________ ________ ADH secreted permeable QUESTION 4: (1) What is “oedema” and why is it associated with renal failure? ______________________ __________________________________________________________________________ (2) Why is a “selectively permeable” membrane used in a dialysis machine? __________________________________________________________________________ __________________________________________________________________________ __________________________________________________________________________ __________________________________________________________________________ __________________________________________________________________________ __________________________________________________________________________  19 QUESTION 5: Interpreting data in a table and making deductions: The table below compares the concentrations of selected substances in normal blood plasma, the glomerular filtrate and urine of a healthy person: Substance (A) Blood (B) Filtrate (C) Urine g/100 ml g/100 ml g/100 ml Glucose 0,1 0,1 0 Protein 7 0 0 Urea 0,03 0,03 2 Ammonia 0 0 0,04 Water 92 98 96 5.1 Briefly explain the differences in concentrations of (1) glucose in B and C __________________________________________________________________________ __________________________________________________________________________ (2) protein in A and B __________________________________________________________________________ __________________________________________________________________________ (3) urea in B and C __________________________________________________________________________ __________________________________________________________________________ (4) ammonia in A and C __________________________________________________________________________ __________________________________________________________________________ 5.2 The intake of alcohol inhibits the release of ADH. Explain how the composition of urine would differ from normal if a person has had a fair amount of alcohol to drink. __________________________________________________________________________ __________________________________________________________________________ __________________________________________________________________________ __________________________________________________________________________ 5.3 The concentration of which of the substances on the table, if any, would be affected if a person ate a meal with a very high protein content? _______________________________ __________________________________________________________________________ __________________________________________________________________________  20 QUESTION 6: Discussion topic: ORGAN DONATION Read the viewpoints of different people regarding organ donation and have a class discussion. Our religion prevents us from donating any It was so fortunate that I was compatible with my organs – we have to be buried with all our husband. I donated one of my kidneys to him more organs intact. than 2 years ago. Today, you would never know that he had ever been sick. We had a beautiful little girl two months ago. If I hadn’t donated my kidney, I wouldn’t have my husband or my daughter. My mom is really sick. She needs a new I’ve heard that you can get quite a lot of kidney. I don’t know what I’ll do if she dies. money for selling one of your kidneys. I’d like She is the only person who cares about me. Is to find out more about this – I’m struggling to there someone who can help us? find enough money to feed my family. I’ll do anything it takes. We have such a long waiting list of patients My twin sister needs a kidney transplant, but needing a kidney transplant. It’s not so bad there is no way I’m giving up one of my kidneys. It for private patients, but there are so many is just not done in our culture. Even if I decided to poor people who need a donor. Many will do it, what would happen if my other kidney die before one becomes available. stopped working? And what about the scar? She’s been on the waiting list for a while and I’m sure she will get a donor soon. --------------------------------------------------------