Excretory Products and their Elimination

Excretory Products and their Elimination Class XI Biology Chapter 19.
Based on NCERT Class XI Biology Text book content.
Includes flowcharts and illustrations.

1. EXCRETORY PRODUCTS AND THEIR ELIMINATION CHAPTER 19

2. WHAT IS EXCRETION Elimination of metabolic waste products from the animal body to regulate the composition of body fluids and tissues is called excretion. These waste products include ammonia, uric acid, urea, carbon dioxide and ions like Na+, Ca+, Cl-  and phosphates and sulphate.

3. Major forms of nitrogenous wastes excreted by the animals: Ammonia : most toxic form and requires large amount of water for its elimination Uric acid : least toxic , can be removed with a minimum loss of water AMMONIA UREA URIC ACID AMMONOTELISM URICOTELISM UREOTELISM

4. Modes of Excretion on basis of nature of nitrogenous waste

5. Mode 1. AMMONOTELISM The process of excreting ammonia is Ammonotelism Animals that excrete most of its nitrogen in the form  of ammonia are called  ammoniotelic Example : Many bony fishes, aquatic amphibians and aquatic insects Ammonia, as it is readily soluble, is generally excreted by diffusion across body surfaces or through gill surfaces (in fish) as ammonium ions.

6. Mode 2. UREOTELISM The process of excreting urea is called ureotelism Animals which excrete urea are called ureotelic Ammonia produced by metabolism is converted into urea in the liver of these animals and released into the blood which is filtered and excreted out by the kidneys. Example : Mammals, many terrestrial amphibians and marine fishes

7. Mode 3: URICOTELISM The process of secretion of uric acid is called uricotelism Animals which excrete nitrogenous wastes as uric acid are called uricotelic Uric acid is excreted in the form of pellet or paste with a minimum loss of water. Examples: Reptiles, birds, land snails and insects

8. Excretory structures in the Animal Kingdom Most invertebrates have a simple tubular structure in the form of primitive kidneys called  protonephridia  and  metanephridia. Vertebrates have complex tubular organs called  kidneys .

9. 1. Protonephridia or flame cells Protonephridia or flame cells are the excretory structures in Platyhelminthes (Flatworms, e.g., Planaria), rotifers, some annelids etc. Protonephridia are primarily concerned with ionic and fluid volume regulation, i.e., osmoregulation.

10. 2. Nephridia Nephridia are the tubular excretory structures of earthworms and other annelids. Nephridia help to remove nitrogenous wastes and maintain a fluid and ionic balance.

11. 3. Malpighian Tubules Malpighian tubules are the excretory structures of most of the insects including cockroaches. Malpighian tubules help in the removal of nitrogenous wastes and osmoregulation .

12. Malpighian tubules

13. 4. Antennal glands Antennal glands or green glands perform the excretory function in crustaceans like prawns.

14. Excretory organs Protonephridia Nephridia Malpighian tubules Antennal Glands Kidneys 3 1 2 4 5

15. HUMAN EXCRETORY SYSTEM

16. HUMAN EXCRETORY SYSTEM The excretory system consists of a pair of kidneys, one pair of ureters, a urinary bladder and a urethra

17. KIDNEYS HUMAN URINARY SYSTEM URETERS BLADDER URETHERA CORTEX MEDULLA NEPHRONS HILUM CALYX RENAL PELVIS Functional Unit External Internal

18. KIDNEY Kidneys are reddish brown, bean shaped structures situated between the levels of last thoracic and third lumbar vertebra close to the dorsal inner wall of the abdominal cavity. Each kidney of an adult human measures 10-12 cm in length, 5-7 cm in width, 2-3 cm in thickness with an average weight of 120- 170 g.

19. KIDNEY Towards the centre of the inner concave surface of the kidney is a notch called hilum through which ureter, blood vessels and nerves enter. Inner to the hilum is a broad funnel shaped space called the renal pelvis with projections called calyces.

20. The outer layer of the kidney is covered by three layers of supportive tissues namely, renal fascia perirenal fat capsule and fibrous capsule. KIDNEY KIDNEY

21. Inside the Kidney Inside the kidney, there are two zones: an outer cortex and an inner medulla .

22. Inside the Kidney The medulla is divided into a few conical masses (medullary pyramids) projecting into the calyces (sing.: calyx). The cortex extends in between the medullary pyramids as renal columns called Columns of Bertin .

23. NEPHRONS The functional unit of kidney is nephron . Each kidney contains about one million nephrons. Each nephron has two parts-  the glomerulus and renal tubules .

24. Structure of Nephron Glomerulus is the tuft of capillaries formed by  afferent arteriole . Blood from glomerulus is carried away by  efferent arteriole . Renal tubules starts with  Bowman’s capsule  continue with tubular parts divided into  Proximal Convoluted tubules ,  Henle’s loop  and  Distal Convoluted tubule . The Bowman’s capsule and the glomerulus together constitute the renal corpuscle .

25. NEPHRON Cortical Nephrons Juxtamedullary Nephrons Glomerulus Renal Tubule Bowman’s capsule Proximal Convoluted Tubule (PCT) Henle’s loop Distal convolutes tubule Collecting Duct TYPES Renal Corpuscle/ Malpighian body Afferent arteriole Efferent arteriole

26. The Malpighian tubules, PCT and DCT of nephron are situated in cortical region where as loops of Henle’s into medulla. TYPES OF NEPHRONS JUXTA MEDULLARY NEPHRONS CORTICAL NEPHRONS These are about 15 % of total nephrons These are about 85 % of total nephrons Glomerulus lies close to inner margin of cortex Glomerulus lie in outer cortex Loop of Henle is very long and extends into the medulla Loop of Henle is short and extends only a little into the medulla Larger in size Smaller in size

27. Juxtamedullary nephron

28. Vasa Recta The efferent arteriole emerging from glomerulus forms a capillary network around the renal tubules called peritubular capillaries . A minute vessel of peritubular capillaries runs parallel to Henle’s loop forming U shaped Vasa Recta. It plays an important role in concentration of urine through the counter current mechanisms Vasa recta is highly reduced or absent in cortical nephrons.

29. Pre knowledge: Processes SECRETION : Into the filtrate ABSORPTION/REABSORPTION : From the filtrate: back to body Active transport : Energy is consumed (ATP) Passive transport : Diffusion/ Facilitated diffusion

30. URINE FORMATION

31. 1 st Step: Glomerular filtration The first step in urine formation is the filtration of blood, which is carried out by the glomerulus and is called glomerular filtration. On an average, 1100-1200 ml of blood is filtered by the kidneys per minute which constitute roughly 1/5th of the blood pumped out by each ventricle of the heart in a minute . The glomerular capillary blood pressure causes filtration of blood through 3 layers, i.e., - The endothelium of glomerular blood vessels, - The epithelium of Bowman’s capsule ( Podocytes ) - A basement membrane between these two layers.

32. Glomerular filtration: ULTRA FILTRATION The podocytes are arranged in an intricate manner so as to form filtration slits or slit pores. Blood is filtered very finely through these membranes, that almost all the constituents of the plasma except the proteins pass onto the lumen of the Bowman’s capsule. Therefore, it is considered as a process of ultra filtration .

33. Glomerular Filtration Rate The amount of filtrate formed by kidneys per minute is called  glomerular filtration rate (GFR)  which is 125 ml/minute, i.e., 180 litres per day ! Glomerular Filtration rate  is controlled by Juxta glomerular apparatus (JGA). A fall in GFR activates the JG cells to release renin which can stimulate the glomerular blood flow and thereby the GFR back to normal. The  juxtaglomerular apparatus  = distal convoluted tubule + afferent arteriole

34. JGA

35. 2 nd Step: Reabsorption Volume of the filtrate formed per day: 180 litres per day Urine released: 1.5 litres This suggests 99% of filtrate has to be reabsorbed by renal tubules. This process is called  reabsorption.

36. Reabsorption Done by: tubular epithelial cells in different segments of nephron Mechanisms: Active : like glucose, amino acids, Na+ , etc., Passive : nitrogenous wastes, water

37. 3 rd Step: Secretion The tubular cells secrete substances like H+ , K + and ammonia into the filtrate. Tubular secretion helps in the maintenance of ionic and acid base balance of body fluids.

38. JUXTA MEDULLARY NEPHRONS One of the two types of nephrons JUXTAGLOMERULAR APPARATUS (JGA) = Afferent arteriole + DCT RENAL CORPUSCLE/MALPIGHIAN BODY = Glomerulus +Bowman’s Capsule TUBULES = PCT + Henle’s Loop + DCT + CD

39. FUNCTION OF THE TUBULES Proximal Convoluted Tubules (PCT) Henle’s Loop Distal convolutes Tubule (DCT) Collecting Duct (CD)

40. ( i ) Proximal Convoluted Tubules (PCT) L ined by simple cuboidal brush border epithelium which increases the surface area for reabsorption. A ll the important nutrients, 70-80% electrolytes and water are reabsorbed. H elps to maintain the pH and ionic balance of the body fluids by selective secretion of H + , NH 3 , and K+ ions into the filtrate and by absorption of HCO 3 – from it.

41. (ii) Henle’s Loop Two regions: Descending and ascending limb The descending limb of loop of Henle is permeable to water but almost impermeable to electrolytes. This concentrates the filtrate as it moves down. The ascending limb is impermeable to water but allows transport of electrolytes actively or passively. maintenance of high osmolarity of medullary interstitial fluid. Therefore, as the concentrated filtrate pass upward, it gets diluted due to the passage of electrolytes to the medullary fluid.

42. (iii) Distal convolutes Tubule (DCT) Conditional reabsorption of Na+ and water. C apable of reabsorption of HCO 3 – . Selective secretion of H + and K + ions and NH 3 to maintain the pH and sodium-potassium balance in blood.

43. (iv) Collecting Duct (CD) This long duct extends from the cortex of the kidney to the inner parts of the medulla. Large amounts of water is reabsorbed from this region to produce a concentrated urine. This segment allows passage of small amounts of urea into the medullary interstitium to keep up the osmolarity. It also plays a role in the maintenance of pH and ionic balance of blood by the selective secretion

44. OSMOREGULATION

45. MECHANISM OF CONCENTRATION OF THE FILTRATE Mammals have the ability to produce a concentrated urine. Significant role of : Henle’s loop and vasa recta he flow of filtrate in two limbs of Henle’s loop is in opposite direction to form counter current. The flow of blood in two limbs of vasa recta increase the osmolarity towards the inner medullary interstitium in the inner medulla. The transport of substance facilitated by special arrangement of Henle’s loop and vasa recta is called  counter current mechanism.

46. Osmolarity

47. Counter current mechanism The proximity between the loop of Henle’s and vasa recta , as well as the counter current in them help in maintaining an increasing osmolarity towards the inner medullary interstitial fluid i.e. from 300 mOsmol /L in the cortex to about 1200 mOsmol /L in the inner medulla. This gradient is mainly caused by NaCl and urea.

48. Counter current mechanism NaCl is transported by the ascending limb of loop of Henle which is exchanged with the descending capillary of vasa recta . NaCl is returned to the medullary interstitial fluid by the ascending capillary of vasa recta. Similarly, small amounts of urea enter the thin segment of the ascending limb of loop of Henle which is transported back to the medullary interstitial fluid by the collecting duct .

49. NaCl Descending capillary Loop of Henle Ascending limb Ascending Capillary Vasa Recta Medullary Interstitial Fluid

50. Urea Loop of Henle Ascending limb (THIN) Collecting Duct Medullary Interstitial Fluid Loop of Henle Ascending limb (THIN) Collecting Duct

51. NaCl Urea Descending capillary Loop of Henle Ascending limb Ascending Capillary Vasa Recta Medullary Interstitial Fluid Loop of Henle Ascending limb (THIN) Collecting Duct

52. Counter current mechanism The counter current mechanism helps to maintain a concentration gradient in the medullary interstitial fluid which helps in an easy absorption of water from the filtrate present in the collecting duct so that the concentration of the filtrate (urine) is increased. Human kidneys can produce about four times concentrated urine than the initial filtrate formed. The overall function of counter current mechanism is to concentrate sodium chloride in the interstitial fluid and thereby cause water to diffuse out of collecting ducts and concentrate the urine.

53. Summary The concentrated urine is formed in the following ways: NaCl is transported from the ascending limb of the Henle’s loop to the descending limb of the vasa recta. The ascending limb of the vasa recta, in turn, transports NaCl to the interstitium (the tissue between the loop of Henle and the vasa recta). Thus, a concentration gradient of 300 mm in the cortex to 1200 mm in the medulla is created (milliosmoles or mOsm is a unit of osmolarity i.e. the concentration of osmotically active substances). Urea contributes to this process by being transported to the descending limb of the loop of Henle from the interstitium , and then back to the interstitium by the collecting tubule. As urine flows downwards in the collecting tubule, it encounters higher and higher concentrations of solutes in the interstitium . Hence it goes on losing water due to osmosis. This is how urine is concentrated.

54. REGULATION OF KIDNEY FUNCTION Functioning of kidney is monitored by hormonal feedback mechanism of hypothalamus and JGA, and the heart. 1. Hypothalamus: ADH/Vasopressin 2. JGA: Renin Angiotensin System 3. Heart: Atrial Natriuretic factor Diuresis : increased or excessive production of urine.

55. 1. Hypothalamus: ADH

56. Changes detected by Osmoreceptors Blood Volume Body Fluid Volume Ionic Concentrations Excessive Loss of Body fluid ADH Hypothalamus Increase in Body Fluid Switch off Stimulates activate Pituitary activates Release of OSMORECEPTORS Increased absorption of water from tubules Decreased Diuresis Constriction of blood vessels BP increases GFR increases

57. 2. JGA: Renin/Angiotensin system

58. Fall in- Glomerular Blood Flow Glomerular Blood Pressure GFR JGA Cells activates Renin Angiotensin I Angiotensin II Adrenal Cortex Reabsorption of Na+ and Water from distal parts of tubule BP increases GFR increases RENIN-ANGIOTENSIN MECHANISM ALDOSTERONE releases Angiotensinogen ACE

59. 3. Heart: Atrial Natriuretic Factor (ANF)

60. CARDIAC ATRIA VASODILATION Increase in BP/BV Renin Atrial Natriuretic Factor Blood Pressure decreases Renin angiotensin mechanism is kept in CHECK Secretes a peptide

61. REGULATION OF KIDNEY FUNCTION HYPOTHALAMUS JUXTAGLOMERULAR APPARATUS HEART Secretion of ADH Renin-angiotensin system Secretion of ANF (Atrial Natriuretic Factor) Vasodilation and decrease in blood pressure Reabsorption of water by DCT and CD Constriction of Blood Vessels to increase GFR and Blood pressure Increase in blood pressure

62. MICTURITION Micturition – The process of expulsion of urine from the urinary bladder is called micturition. The neural mechanism that causes it is called micturition reflex. Urine formed in nephron is stored in urinary bladder till a voluntary signal is given by CNS . This initiates the contraction of smooth muscles of the bladder and simultaneous relaxation of the urethral sphincter causing the release of urine.

63. MICTURITUON REFLEX Urinary Bladder URINE NEPHRON CNS VOLUNTARY SIGNAL Contraction of smooth muscles of the bladder R elaxation of the urethral sphincter RELEASE OF URINE

64. URINE An adult human on an average excretes 1 to 1.5 L of urine per day. The urine formed is a yellow coloured watery fluid which is slightly acidic in nature (pH 6.0), and has a characteristic odour. Changes in diet may cause pH to vary between 4.5 to 8.0 The yellow colour of the urine is due to the presence of a pigment, urochrome . On an average, 25- 30 gms of urea is excreted per day.

65. Urine test in diagnostics Various metabolic disorders can affect the composition of urine. Analysis of urine helps in clinical diagnosis of various metabolic disorders and the malfunctioning of the kidneys. For example the presence of glucose (glucosuria ) and ketone bodies (ketonuria) in the urine are indications of diabetes mellitus.

66. Role of other organs in excretion LUNGS: Lungs remove large amounts of CO2 (approximately 200mL/minute) and also significant quantities of water every day LIVER: Secrets bile containing bilirubin, biliverdin, cholesterol, degraded steroid hormones, drugs, certain vitamins etc These enter alimentary canal and pass out along with fecal matter

67. Role of other organs in excretion SKIN : Skin has two types of glands: Sweat Glands : Sweat is a watery fluid containing sodium chloride, small amounts of urea and lactic acid. IT also produces a cooling effect on the body. Sebaceous Glands : They eliminate sterols, hydrocarbons and waxes through sebum.

68. Haemodialysis Artificial kidney is a machine used to filter the blood (to remove urea and other nitrogenous wastes) of a person whose kidneys are damaged. This process is called haemodialysis PRINCIPLE: DIALYSIS PROCESS: A dialyzing machine or an artificial kidney is connected to the patient’s body. A dialyzing machine consists of a long cellulose tube surrounded by the dialysing fluid in a water bath. The patient’s blood is drawn from a conveinent artery and pumped into the dialysing unit after adding an anticoagulant like heparin . The tiny pores in the dialysis tube allows small molecules such as glucose, salts and urea to enter into the water bath, whereas blood cells and protein molecules do not enter these pores. This stage is similar to the filtration process in the glomerulus. The cleared blood is then pumped back to the body through a vein.

69. KIDNEY TRANSPLANT It is the ultimate method for correction of acute renal failures. This involves transfer of healthy kidney from one person (donor) to another person with kidney failure. The donated kidney may be taken from a healthy person who is declared brain dead or from sibling or close relatives to minimise the chances of rejection by the immune system of the host. Immunosuppressive drugs are usually administered to the patient to avoid tissue rejection.

70. Disorders of Excretory System Uremia – there is high concentration of non-protein nitrogen (urea, uric acid, creatinine). Urea can be removed by hemodialysis . Renal failure – also known as kidney failure where glomerular filtration is ceased and both kidney stops working. Kidney transplant is the ultimate method in correction of acute kidney failure. Renal Calculi – formation of stone or insoluble mass of crystallized salts formed within the kidney. Glomerulonephritis ( Bright’s Disease ) -inflammation of glomeruli of kidney due to entry of protein or red blood corpuscles in to filtrate due to injury.

71. TOPICS DISCUSSED! Types of nitrogenous wastes Excretory organs across animal kingdom Human excretory system Nephron Urine formation (GFR) Functions of tubules Concentration of Filtrate (Counter current mechanism) Regulation of kidney function Micturition Role of other organs in excretion Disorders Haemodialysis and kidney transplant

72. THANKYOU 

73. 1. The following substances are the excretory products in animals. Choose the least toxic form among them? a. Urea b. Uric acid c. Ammonia d. Carbon dioxide 2. Filtration of the blood takes place at a. PCT b. DCT c. Collecting ducts d. Malpighian body

74. Which of the following is removed from our body by lungs? a. CO2 only b. H2O only c. CO2 and H2O d. Ammonia

75. The pH of human urine is approximately a. 6.5 b. 7 c. 6 d. 7.5

76. Which one of the following statements is incorrect? a. The medullary zone of kidney is divided into a few conical masses called medullary pyramids projecting into the calyces. b. Inside the kidney the cortical region extends in between the medullary pyramids as renal pelvis. c. Glomerulus along with Bowman’s capsule is called the renal corpuscle. d. Renal corpuscle, proximal convoluted tabule (PCT) and distal convoluted tubule (DCT) of the nephron are situated in the cortical region of kidney.

77. The condition of accumulation of urea in the blood is termed as a. Renal Calculi b. Glomerulonephritis c. Uremia d. Ketonuria Which one of the following is also known as antidiuretic hormone? Oxytocin b. Vasopressin c. Adrenaline d. Calcitonin