Biology excretion

There is no factory which can manufacture a product without generating any waste. This is true of our body which is a cellular factory too. And for other organisms as well. Wastes are generated at regular intervals from the bodies of most organisms. This raise questions like. Where are the wastes produced? How are they produced? What are the substances present in them? Does the composition vary in the same organism in different situations? Let us understand such kind of questions. Living beings need energy for their survival and to perform activities either building up of body material (anabolism) or its breakdown (catabolism), collectively called metabolic activities. Organisms use different substances for metabolic activities. Different products are generated as a result of these metabolic activities. Can you name different products generated by the following life processes?
We have already learnt that different kinds of materials are produced out of various metabolic activities. Some of these may be harmful for the organism are removed from their body or packed and stored in some other forms. These are all the wastes produced in the body of an organism. We have already discussed how organisms get rid of gaseous wastes generated during photosynthesis or respiration. Other metabolic activities generate nitrogenous wastes have to be removed along with salts, excess water and several other materials. Excretion is the term coined for all the biological process involved in separation and removal of wastes or non useful products from the body. (In latin ex means out, crenere means shift.) Now let us study how excretion takes place in human being.
Excretion in Human Beings A number of reactions take place during various metabolic activities. Many useful substances and energy are produced. At the same time many other things happen such as, toxic wastes may be produced, water content may increase, ionic balance (homeostasis) in the body may be disturbed. The waste products include carbon dioxide, water, nitrogenous compounds like ammonia, urea, uric acid, bile pigments, excess salts etc. The most poisonous of all waste products of metabolism is Ammonia. Where are these waste materials produced? How does the body manage them. Is there a way to detect their presence in our body? Now let us observe the test reports of Blood and Urine of a person given in table-2, 3 and find out the components present in both Blood and Urine. (For 24 hours urine test urine is collected for 24 hours From that, 100-150 ml sample will be tested.) observe the reports in the next page and answer the following questions.
TEST NAME RESULT UNITS RANGE GLUCOSE FASTING 82 mg/dl 60-100 SODIUM 137 mmoles/L 135-145 POTASSIUM 4.10 mmoles/L 3.5-5.0 CHLORIDES 101 mmoles/L 95-106 UREA 29 mg/dl 15-40 CREATININE 2.8. mg/dl 0.6-1.5 URIC ACID 7.50 mg/dl 3.0-5.0 TOTAL CHOLESTEROL 221 mg/dl 150-200 TRIGLYCERIDES 167 mg/dl 60-200 CALCIUM 9.40 mg/dl 8.0-10.5 PHOSPHORUS 4.50 mg/dl 3-4.5 BILIRUBIN (TOTAL) 0.70 mg/dl 0.1-0.8 TOTAL PROTEINS 7.20 g/dl 6.0-7.5 ALBUMIN 4.60 g/dl 3.0-5.0 Table-3: DEPARTMENT OF BIOCHEMISTRY REPORT ON URINE ANALYSIS TEST/METHOD RESULT UNITS RANGE 24 hrs.Protein 90 mg/day <100 mg 24 hrs Creatinine 2.7 mg/day 1-2 24 hrs.Calcium 305 mg/day Up to 200 24hrs.phosphorous 0.8 mg/day upto 1g 24hrs.uric Acid 800 mg/day upto 600 ELECTROLYTES : Sodium 140 mmoles/L 125-250 potassium 50 mmoles/L 25-100 Osmolality (calculated) 180 mmoles/L 100-600 Glucose 65 mg/dl 50-80 Chlorides 128 mmoles/L 120-130 Urea 35 gm/day 20-30 m moles / L means millimoles per litre, mg/dl means milligram per deci litre.
Excretory System in Human being In human beings excretion mainly occurs through a urinary or excretory system consisting of a pair of kidneys, a pair of ureters, urinary bladder and urethra, as shown in the fig-4. Now let us observe external and internal features of a kidney in goat / sheep, which is similar to Human kidney in function. Lab Activity Aim: Studying the external and internal features of a kidney Materials required: Freshly collected specimen of sheep/goat’s kidney from the butcher or 3D Model of a kidney, sharp blade/scalpel, tray and a jug of water. fig-1: Kidney of goat fig-2: LS of Kidney of goat Procedure for observation: Before coming to the class wash the kidney thoroughly so that, blood is completely drained from it. Put the kidney in the tray and observe it carefully. Note your observations in the observation book. With the help of sharp blade take a longitudinal section here you are advised to do this activity under the guidance of your teacher and observe the internal structure. Draw what you have observed and compare it with fig-1,2. What is the shape of kidneys? What is the colour of kidney? Do you find any attachments on upper portion of kidney? Is the Internal structures similar to fig-2 What is the colour of the outer part in L.S of kidney? In L.S of kidney where do you find dark brown colour portion? How many tubes are coming out from kidney fissure? Don’t forget to wash your hands with antibacterial lotion after completing dissection. Now let us know the structure of human excretory system and its functions.
Kidneys In Human beings there is a pair of bean shaped, reddish brown structures in the abdominal cavity attached to dorsal body wall (fig-3) one on either side of the back bone they are kidneys. The right kidney is placed slightly lower than the left kidney. Think why it is so? The size of the kidney is 10 cm in length, 5-6 cm in breadth, and 4 cm in thickness. Each kidney is convex on the outer side and concave on the inner side. The position of the right kidney is lower than the left kidney due to the presence of liver above. Let us recall the last question in your lab activity. The inner side of each kidney has a fissure or hilum for the entry of a renal artery, exit of a renal vein and an ureter. Renal artery brings oxygenated blood loaded with waste products and renal vein carries deoxygenated blood. The waste products generated in various organs of the body are filtered and removed by the kidney.
Internal structure of the kidney: Let us observe L.S of the kidney to know more about internal structure. It shows two distinct regions. Dark coloured outer zone called the cortex and pale inner zone called medulla. Each kidney is made up of approximately more than one million (1.3 to 1.8 million) microscopic and thin tubular functional units called nephrons or uriniferous tubule.
Structure of nephron Each nephron has basically two parts. 1) Malpighian body and 2) Renal tubule. Malpighian body: It consists of a blind cup shaped broader end of nephron called Bowman’s capsule and bunch of fine blood capillaries called glomerulus. The Bowman’s capsule and glomerulus together called malpighian capsule or renal capsule. Glomerulus develops from afferent arteriole. It gives rise to an efferent arteriole. Think why the diameter of the efferent arteriole is less than that of afferent arteriole? Because of the narrower out let (efferent arteriole) pressure exerts in the glomerulus.It functions as a filtration unit. Bowmans capsule which accommodates one glomerulus,is lined by a single layer of squamous epithelial cells called podocyte cells. There are fine pores between podocyte cells to allow passage of materials filtered out of glomerulus.
Renal tubule: It has three parts. First or proximal convoluted tubule (PCT), loop of Henle, which is U shaped, second or distal convoluted tubule (DCT). Distal convoluted tubules open into a collecting tube. Collecting tube form pyramids and calyces which open into the pelvis. Pelvis leads into the ureter. All the parts of the renal tubule are covered by a network of peritubular (around tube) capillaries formed from efferent arteriole. The peritubular capillaries join to form renal venule, which joins the other venules to form finally the renal vein. Why the nephron is considered to be the structural and functional unit of the kidney.

Mechanisms of urine formation Formation of urine involves four stages i. Glomerular filtration, ii.Tubular reabsorption, iii. Tubular secretion, iv.Concentration of urine i) Glomerular filtration Blood flows from renal artery to glomerulus through afferent arteriole. Observe the fig-7 of glomerular filtration in nephron and try to answer the following questions. Which arteriole has more diameter, afferent or efferent? What are the substances that are filtered into the glomerular capsule? ii) Tubular Re-absorption Filtrate from glomerular is also called primary urine which almost equal to blood in chemical composition except the presence of blood cells. It passes into proximal convoluted tubule. Useful substances in primary urine are reabsorbed into peritubular net work. If you drink more water will you pass more urine? What are the substances reabsorbed into peritubular net work from proximal convoluted tubule (PCT)? iii) Tubular secretion After reabsorption in PCT region, the urine travels through the loop of Henle into DCT. Here some other wastes like extra salts ions of K+ Na+ Cl – and H+ secretes from peritubular capillaries in to DCT. It occurs mostly in the distal convoluted tubule, which is also surrounded by peritubular capillaries. This maintains a proper concentration and pH of the urine. Smaller amount of tubular secretion also takes place in the area of proximal convoluted tubule. Observe tubular secretion in fig-7. What are the substances that secretes into DCT?
iv) Formation of hypertonic Urine 75% of water content of nephric filtrate is reabsorbed in the region of proximal convoluted tubule. 10% of water passes out of filtrate through osmosis in the area of loop of Henle. Further concentration of urine takes place in the area of collecting tubes in the presence of hormone called vasopressin. The hormone is secreted only when concentrated urine is to be passed out. Think why is it not secreted when a person drinks a lot of water? Absence of vasopressin hormone produces dilute urine. Hormone action maintains osmotic concentration of body fluids. Deficiency of vasopressin causes excessive, repeated, dilute urination called diabetes insipidus. Why more urine is produced in winter? What happens if reabsorption of water does not takes place? Now let us discuss remaining parts of excretory system. 2. Ureters There are a pair of whitish, narrow distensible and muscular tubes of 30cm length. Each ureter arises from hilus of the kidney. It moves downward and obliquely opens into the urinary bladder. Ureter carries urine from the kidney to the urinary bladder. The movement of urine in the ureter is through peristalysis.
3. Urinary bladder It is a median, pear shaped and distensible sac. It is situated in the pelvic region on the ventral side of the rectum in the abdomen. It stores urine brought by two ureters. The storage capacity of urinary bladder is 300 - 800ml. 4. Urethra It is a tube that takes urine from urinary bladder to outside. The opening of urinary bladder into urethra is guarded by a ring of muscles or sphincter. Urethra is 4 cm long in females open to vestibule and in males it is about 20cm long. Its opening is separate in females but is in common with the reproductive tract in males (urino-genital duct). Micturition The urine is temporarily stored in the bladder. There are two sets of circular sphincter muscles in the bladder. When the bladder is filling up both these sets of muscles are constricted, so the exit is closed. However as the pressure of the urine increases the walls of the bladder are stretched and this triggers off an automatic reflex action which causes the upper sphincter to relax. But the lower sphincter is under the control of brain. So urine can still be retained until this muscle is relaxed too. Control of urination is not possessed by very young children but is gradually learned. Urge for micturition occurs when urinary bladder is filled with 300 - 400 ml of urine. The stretched bladder stimulates nerve endings to develop the reflex. However, urine can be retained in the urinary bladder till it gets filled up to the maximum capacity of 700 - 800ml. At this time the urge becomes painful and leads to voluntary micturition. Total amount of urine excreted per day is about 1.6-1.8 litres. It’s quantity increases with larger intake of fluids like water, fruit juices and decreases with lesser intake.
Composition of urine It is a transparent fluid produced by urinary system. Urine has amber color due to presence of urochrome.Composition of normal urine varies considerably depending on several factors for instance taking a protein.
rich diet will result in more formation of urea in the urine. This is because the proteins get de-aminated in the liver with subsequent formation of urea. Even sugar can appear in a normal person after a heavy intake. If other conditions are constant, a large intake of liquids or water - rich food increases the volume of water in the blood, hence more urine is excreted. Urine contains 96% of water 2.5% of organic substances (urea, uric acid, creatine, creatinine, water soluble vitamins, hormones, and oxalates etc) and 1.5% of inorganic solutes (sodium, chloride, phosphate, sulphate, magnesium, calcium, iodine). It is acidic (pH=6.0)in the beginning but becomes alkaline on standing due to decomposition of urea to form ammonia. What happens if both kidneys fail completely? Complete and irreversible kidney failure is called End Stage Renal Disease (ESRD). If kidneys stop working completely, our body is filled with extra water and waste products. This condition is called uremia. Our hands or feet may swell. You feel tired and weak because your body needs clean blood to function properly. Is there any solution to this problem? Let us know about artificial kidney. Dialysis Machine (Artificial kidney) Kidneys are vital organs for survival. Several factors like infections, injury, very high blood pressure, very high blood sugar or restricted blood flow to kidneys. This leads to accumulation of poisonous wastes in the body and leads to death. Dialysis machine is used to filter the blood of a person when both kidneys are damaged. The process is called ‘haemodialysis’. In this process blood is taken out from the main artery, mixed with an anticoagulant, such as heparin, and then pumped into the apparatus called dialyzer. In this apparatus blood flows through channels or tubes which are madeup of cellophane. These tubes are embedded in the dialyzing fluid. The membrane separates the blood flowing inside the tube and dialyzing fluid (dialysis), which has the same composition as that of plasma, except the nitrogenous wastes. As nitrogenous wastes are absent in dialyzing fluids, these substances from the blood move out freely, there by cleaning the blood of its wastes. This process is called dialysis. This is similar to function of the kidney but is different as there is no reabsorption involved .The cleaned blood is pumped back to the body through a vein after adding anti-coagulant (heparin). Each dialysis session lasts for 3 to 6 hours. This method has been using for thousands of uremic / kidney failure patients all over the world. Is there any long term solution for kidney failure patients?
Kidney transplantation The best long term solution for kidney failure (acute renal failure) is Kidney transplantation. A functioning kidney is used in transplantation from a donor preferably a close relative. The kidney that is received by a recipient must be a good match to his body, to minimize the chances of rejection of transplanted kidney by the immune system of the recipient. Modern clinical procedures have increased the success rate of such complicated technique. fig-9: Kidney transplantation Where is the transplanted kidney fixed in the body of a kidney failure patient? What about the failed kidneys? Can donor lead normal life with a single kidney without any complications? Now a days the process of organ donation helps a lot for kidney failure patients. Organs are collected from brain dead patients, then transplanted to the recepient. To know more about organ donation see in annexure. Other pathways of excretion (accessory excretory organs) You have learnt about kidney, chief excretory organ of our body. What are the other excretory organs of human body? Lungs, skin, liver have their own specific functions but carry out excretion as a secondary function. Lungs: In respiratory process lungs remove carbon dioxide and water. Skin: It consists of large number of sweat glands richly supplied with blood capillaries, from which they extract sweat and some metabolic wastes.
Since the skin sends out plenty of water and small amount of salts, it serves as an excretory organ. Sebaceous glands in skin eliminate sebum which contains waxes, sterols, hydrocarbons and fatty acids. Collect information on sebum and prepare a news bulletin, display it on bulletin board? People in cold countries get very less/no sweat. What changes occur in their skin and in other excretory organs? Liver: It produces bile pigments (bilirubin ,biliverdin and urochrome) which are metabolic wastes of haemoglobin of dead R.B.Cs. The life span of RBC is 120 days. They are destroyed in the liver. Urochrome is eliminated through urine. Biliverdin and bilirubin are excreted through bile along with cholesterol and derivatives of steroid hormones, extra drug, vitamins and alkaline salts. Liver is also involved in urea formation. Large intestine: Excess salts of calcium magnesium and iron are excreted by epithelial cells of colon (large intestine) for elimination along with the faeces. fig-11: Liver, intestine Table-4 Name of the phylum/ Excretory system/ organism organ Protozoa Simple diffusion from the body surface in to the surrounding water Porifera and coelenterates Water bathes almost all their cells Platyhelminthes Flame cells Nematoda Renette cells Annelids Nephridia Arthropoda Green glands, Malpighian tubules Mollusca Meta nephridia Echinodermata Water vascular system Reptiles, Aves and Mammals Kidneys Small amount of nitrogenous wastes are also eliminated through saliva and tears. Excretion in other organisms Different organisms use varied strategies in excretion. Specific excretory organs are absent in unicellular organisms. These organisms remove waste products by simple diffusion from the body surface into the surrounding water. Fresh water organisms like Amoeba, Paramoecium possess osmoregulatory organelle called contractile vacuole. It collects water and waste from the body, swells up, reaches the surface and bursts to release its content to outside. The main excretion takes place through body surface (Diffusion).
Multicellular organisms possess different excretory organs for removal of waste materials from the body. Structural and functional complexity of excretory organs increases from sponges to humans. Sponges and coelenterates do not have specific excretory organs as water bathes almost all their cells. Excretory structures appear for the first time in Flatworms (Platyhelminthes) are known as flame cells. Now let us see how this vital process takes place in plants Excretion and release of substance in plants Do plants excrete like animals? We are amazed to answer such type of questions. You are aware that a variety of end products are formed during metabolism and these nitrogenous wastes are important. Plants does not have specific organs to excrete these wastes. Plants break down waste substances at much slower rate than in animals. Hence accumulation of waste is also much slower. Green plants in darkness and plants that do not possess chlorophyll produce carbon dioxide and water as respiratory waste products. Oxygen itself can be considered as a waste product generated during photosynthesis, that exits out side through stomata of leaves and lenticels of stem. How do the plants manage or send out waste products from its body? Plants can get rid of excess water by a process like transpiration and guttation. Waste products may be stored in leaves, bark, and fruits. When these dead leaves, bark, and ripe fruits fall off from the tree then waste products in them are get rid off. Waste gets stored in the fruits in the form of solid bodies called Raphides. However several compounds are synthesized by the plants for their own use especially for defence. Many plants synthesize chemicals and store them in roots, leaves, seeds, etc., for protection against herbivores. Most of the chemicals are unpleasant to taste. Hence, herbivores usually do not prefer to eat such plants. Some of the chemicals are toxic and may even kill the animal that eats them Some of the plants secrete chemicals when injured. These chemicals seal the wound and help the plant to recover from an injury. Some of the plants release attractants for other organisms which will help the plants for pollination, seed dispersal or even in their nutrition. For example, plants. having root nodules secrete chemicals to attract rhizobia into the surroundings of the roots and form a symbiotic relationship with the rhizobium. These compounds are called secondary metabolites. Why plants shed their leaves and bark periodically? The biochemical substances produced in plants are of two types, primary metabolites and secondary metabolites. The materials like carbohydrates, fats and proteins are primary metabolites. The materials which do not require for normal growth and development are secondary metabolites. e.g.: Alkaloids, Tannins, Resins, Gums, and Latex etc. Though plants produce these chemical for their own use. Man found the usage of these chemicals for own benefits. They are generally coloured and fragrant. Alkaloids: These are nitrogenous by- products and poisonous. These are stored in different parts of the plants. Common alkaloids in plants and their uses are given below.

Tannins: Tannins are carbon compounds. These are stored in different parts of the plant and are deep brown in colour. Tannins are used in tanning of leather and in medicines e.g. Cassia, Acacia. Resin: Occur mostly in Gymnosperms in specialized passages called resin passages. These are used in varnishes- e.g.Pinus. fig-13(a): Cassia fig-13(b): Acacia fig-13(c): Pinus fig-14(a): Neem fig-14(b): Jatropa fig-14(c): Rubber plant Do you know? Chewing gum is a type of sticky for chewing made dates back 5000 years. Modern chewing gum originally made of natural latex from plants like chicle, sapota etc. Whenever pollen grains enter in our body they cause allergy due to the presence of nitrogenous substances. These allergens cause skin allergy and asthma. Ex: Parthenium. Gums: Plants like Neem, Acacia oozes out a sticky substance called gum when branches are cut. The gum swells by absorbing water and helps in the healing of damaged parts of a plant. Gums are economically valuable and used as adhesives and binding agents, in the preparation of the medicines, food, etc. Latex: Latex is a sticky, milky white substance secreted by plants. Latex is stored in latex cells or latex vessels. From the latex of Hevea braziliensis (Rubber plant) rubber is prepared. Latex from Jatropa is the source of bio-diesel. Do you know which part of jatropa used in production of bio diesel. SCERT fig-14(a): Neem of bio diesel. TELANGA. Brugman’ a botanist proved from his experiments that the roots not only absorb fluid from soil, but returns a portion of their peculiar secretions back into it. We can see such instances in plants like apple where a single apple crop for 4 or 5 years continuously in the same soil, that fail to produce fruits. It will not give proper yield even if you use lot of fertilizers. Do you think there is any relation between reduction in yielding and root secretions? Why do we get peculiar smell when you shift the potted plants? Excretion Vs Secretion Excretion and secretion are the same in nature. Since both are involved in passage or movement of materials. Both processes move and eliminate unwanted components from the body. Excretion is the removal of materials from a living being, while secretion is movement of material from one point to other point. So secretion is active while excretion is passive in nature. Humans excrete materials such as tears, urine, Carbon dioxide, and sweat while secretion on other hand, includes enzymes, hormones, and saliva. In plants too we find excretion through roots into its surroundings and falling off leaves and bark. Secretions occur in the plant body in form of latex, resins, gums etc