Revision 7.pptx this is a biology course aimed at high schoolers

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1. Revision notes

2. Homeostasis, temperature regulation & excretion Key understanding: The internal environment of an organism is kept constant so that it can carry on its life processes. Homeostasis is achieved through receptors, effectors and negative feedback. Waste products are produced in our body all the time. There is a need to remove these waste products and all other substances in excess in order to maintain a constant internal environment. Temperature , water and blood glucose regulation is an important homeostatic mechanism.

3. Learner’s Outcomes State that homeostasis is the maintenance of a constant internal environment . Understand that homeostasis involves receptors, effectors and the negative feedback mechanism. State that thermoregulation is the process of temperature regulation, involving the skin, blood and the brain. Explain the process of thermoregulation. State that osmoregulation is the regulation of salt and water in the body, involving the kidneys and skin. Explain the process of osmoregulation. Define excretion. Name the products excreted from the body and explain why they must be excreted (nitrogenous waste products, excess water, salts, heat). Describe the removal of carbon dioxide from the lungs. Explain that a unicellular or simple organism excretes by the diffusion of waste products out of its surface. Explain why an excretory system is essential for a multi-cellular organism . Relate the structure of the kidney to its functions of producing urine through ultra-filtration and selective reabsorption . Describe the role of ADH in the formation of urine through the negative feedback reaction. List the causes of kidney failure and ways to prevent it. Describe dialysis as the diffusion of waste products and salts through a semi-permeable membrane Compare the two different forms of dialysis - haemodialysis and peritoneal dialysis.

4. LO1: State that homeostasis is the maintenance of a constant internal environment. LO2: Understand that homeostasis involves receptors, effectors and the negative feedback mechanism. A conformer allows its internal condition to vary with external change . --- NO homeostasis A regulator controls its internal condition in the face of fluctuating external conditions. --- Homeostasis Homeostasis --- the maintenance of a constant internal environment despite changes in the external environment. Receptors – detects stimulus (deviation from set point) Messengers – to coordinate a corrective mechanism that reduces the stimulus i.e. negative feedback Chemical molecule or nerve impulse Effectors – carries out corrective mechanism

5. LO2: Understand that homeostasis involves receptors, effectors and the negative feedback mechanism . Set point Stimulus Stimulus Smaller value Larger value Negative feedback Negative feedback

6. LO3: State that thermoregulation is the process of temperature regulation, involving the skin, blood and the brain. The process by which animals maintain an internal temperature within a tolerable range . Body temperature >37 o C or <37 o C Thermoreceptors Hypothalamus (Brain) Nerve impulse Skin – sweat glands, hair erector muscles, arterioles Skeletal muscles

7. Erector muscle Sweat gland Nerves Sweat pore Arterioles Hair follicle

8. LO4: Explain the process of thermoregulation. Internal & external factors both can cause  in body temperature : hot external environment increased muscular activities Infection etc External factor can cause  in body temperature Change in body temperature = change in blood temperature

9. LO3: State that thermoregulation is the process of temperature regulation, involving the skin, blood and the brain. Radiation Convection Conduction Hot Cold Insulating Layer of air Evaporative heat loss Cold Hot Hot: Arterioles near skin surface dilate Cold: Arterioles near skin surface constrict

10. LO4: Explain the process of thermoregulation.

11. LO4: Explain the process of thermoregulation. Thermoregulatory adaptation Example Endotherm Ectotherm Insulation Fur / hairs trap an insulating layer of air that traps heat. In humans, hairs are raised via action of hair erector muscles. Insulating layer of fats  Not common Circulatory adaptation Constriction of arterioles near the skin surface (via smooth muscle contraction in response to nerve signals) ↓ blood flow  ↓ heat loss by conduction, convection & radiation   Cooling by evaporative heat loss Evaporation of sweat produced by sweat glands. Evaporation of moisture from tongue (e.g. dogs) or other exposed body surfaces   Adjusting metabolic heat production Increase rate of metabolic reactions throughout body to release heat instead of storing as ATP Shivering due to involuntary skeletal muscle contraction.  (source of body heat) Mostly X (body heat from external sources) Behavioral adaptation Migration (into cooler shades/ orient towards heat source/ to colder or hotter climate)   (Major) Regulators

12. LO5: State that osmoregulation is the regulation of salt and water in the body, involving the kidneys and skin. LO6: Explain the process of osmoregulation. Osmoconformers – organisms whose internal and external environments have similar solute concentrations. ( No homeostasis of water potential ) Osmoregulation – control of the content of Water Mineral salts Other dissolved substances e.g. metabolic wastes i n body fluid to maintain osmotic (or water potential) balance relative to the external environment Osmoregulators actively regulate their water loss or gain Removal of soluble metabolic wastes contribute to osmoregulation Build-up will  osmotic pressure of body fluids  can cause dehydration Toxic to cells  even osmoconformers have to remove them (but not for purpose of regulating osmotic pressure) Terrestrial animals need to guard against dehydration while removing excess water from body.

13. LO10: Explain that a unicellular or simple organism excretes by the diffusion of waste products out of its surface. Unicellular organisms Exchange of substances by simple diffusion Water Gases Mineral salts Metabolic waste products Concentration gradient  diffusion gradient  rate of diffusion All living cells must be bathed in a watery solution so that exchange of materials can occur. Changes in osmotic pressure in blood Changes in osmotic pressure in interstitial fluid Changes in osmotic pressure in cell

14. LO11: Explain why an excretory system is essential for a multi-cellular organism . With  complexity of organism direct exchange with environment is not possible for most cells Amount of excretory products to be removed   inadequacy of diffusion to cope with demands Extensively folded or branched internal surfaces to maximize surface area for exchange (  SA:volume ratio) Simple multicellular organisms exchange metabolic wastes by simple diffusion.

15. LO7: Define excretion. Excretion The process by which metabolic waste products are removed from the body What is metabolism ? The chemical reactions that takes place within the body to maintain life Egestion The process by which undigested food materials are removed from the body. These substances have never been absorbed into the cells and are not produced as a result of metabolic changes.

16. LO8: Name the products excreted from the body and explain why they must be excreted (nitrogenous waste products, excess water, salts, heat). carbon dioxide Product of cellular respiration Excreted by lungs (excretory organ) as a gas in expired air If allowed to accumulate  blood pH drops Solubility of substances in plasma will change  osmotic pressure change Eventually affects cellular pH and thus rate of metabolic reactions excess water Product of cellular respiration Excreted by kidney (in urine), skin (in sweat) and lungs (in expired air)

17. LO8: Name the products excreted from the body and explain why they must be excreted (nitrogenous waste products, excess water, salts, heat). bile pigments - Excreted by liver (excretory organ) - Excreted via the intestines - Formed from breakdown of haemoglobin (*FYI: bilirubin) - If not excreted  cause the condition, jaundice, that can be dangerous (*FYI: bilirubin is neurotoxic) mineral salts - Excreted by kidney and skin (excretory organs) - A constituent of urine and sweat Help in digestion of lipids and than excreted together with feces  NOT Egestion

18. LO8: Name the products excreted from the body and explain why they must be excreted ( nitrogenous waste products , excess water, salts, heat). Nitrogenous waste products Ammonia Urea Uric acid Formation Deamination of proteins Deamination of proteins Breakdown of nucleic acid Solubility in water (Most soluble) Ammonia > Urea > Uric acid (Least soluble) Toxicity (Most toxic) Ammonia > Urea > Uric acid (Least toxic) Toxic effects if not excreted Toxic base that disrupts blood (or cellular) pH At high conc., denatures proteins Forms crystals  inflammation (e.g. gout), kidney stones Amount of water used for elimination (Highest) Ammonia > Urea > Uric acid (Lowest) Energy expenditure (Lowest energy to produce ) Ammonia > Urea > Uric acid (Highest energy to produce ) Main excretory product of: Marine animals Mammals Reptiles, birds, insects Excretion in humans Little Nitrogenous waste mainly excreted in this form Excretory organ (humans) Kidney (urine) and skin (sweat)

19. LO8: Name the products excreted from the body and explain why they must be excreted (nitrogenous waste products, excess water, salts, heat). Excretory product Main excretory organs Kidney Skin Liver Lungs Carbon dioxide  Excess water    Mineral salts   Nitrogenous waste   Bile pigments  Followed by intestines

20. LO9: Describe the removal of carbon dioxide from the lungs . Carbon dioxide from cells diffuse into blood Carried as hydrogen carbonate ion (HCO 3 - + H+) in red blood cells and blood plasma Carried by blood to the lungs HCO 3 -  CO 2 in the capillaries in the lungs CO 2 diffuses into the alveoli

21. LO9: Describe the removal of carbon dioxide from the lungs . (Recap on transport in blood) Form Blood Plasma Red blood cell Dissolved CO 2 ~ 5% of total CO 2 transported Yes, little amounts in the cytoplasm H 2 CO 3 Yes, little amounts (due to absence of carbonic anhydrase) Yes. > plasma. Catalysed by carbonic anhydrase HCO 3 - ~ 80% of total CO 2 transported Yes, but mostly transported out to plasma Bound to amino groups on polypeptide chains of Hb ( Carbaminohemoglobin ) X ~ 15% of total CO 2 transported Dissociation

22. LO12: Relate the structure of the kidney to its functions of producing urine through ultra-filtration and selective reabsorption . Structure of Urinary system Function Kidney (x2) Filters blood of toxins, excretory waste and excess water and mineral salts, forming urine Renal artery delivers waste to kidney Renal vein transports ‘cleaned’ blood away from kidney Ureter (x2) Transports urine from kidney to bladder Urinary Bladder (x1) Stores urine temporarily before it is discharged from the body A ring of muscle controls the exit of urine from the bladder Urethra (x1) Transports urine from the urinary bladder to the exterior Direction of flow of urine

23. LO12: Relate the structure of the kidney to its functions of producing urine through ultra-filtration and selective reabsorption. Structure of kidney Characteristics (Outer) Renal cortex Packed with ~ 1 million nephrons. Site of Urine formation Renal corpuscle, proximal convoluted tubule, distal convoluted tubule and part of collecting duct and loop of Henle located here Richest supply of blood vessels (Inner ) Renal medulla Collecting duct and main part of loop of Henle located here. Rich in blood vessels. Renal papilla Collection of urine, which eventually is directed into the ureter. Each collects urine from the collecting ducts in each renal medulla region Renal calyx Collects urine from multiple renal papillae. Multiple calyces join to form the renal pelvis. Renal pelvis Urine from all collecting ducts eventually collects in renal pelvis that leads into the ureter. Outermost Innermost

24. LO12: Relate the structure of the kidney to its functions of producing urine through ultra-filtration and selective reabsorption. Working unit of kidney is nephron A system of tubes that act as a filter Each nephron weaves back and fro between renal cortex & medulla Blood enters the kidney by renal artery Renal artery branch extensively to form afferent arterioles that brings blood to each nephron

25. LO12: Relate the structure of the kidney to its functions of producing urine through ultra-filtration and selective reabsorption. Parts of a nephron Remarks Structure –to- Function Renal corpuscle Glomerulus A ball of capillaries branched from afferent arteriole (V. impt .) Afferent arteriole via which blood enters has larger diameter than efferent arteriole via which blood leaves  high capillary blood pressure  push fluid out of glomerulus into Bowman’s capsule i.e. Physical force for Ultrafiltration Capillary wall consists of only a single layer of endothelial cells with pores in between i.e. sieve-like  allow fluid and small solutes, but not proteins and cells, to pass through Bowman’s capsule (BC) Formed from blind end of long kidney tubule Wall of Bowman’s capsule is sieve-like  allow only particles of a certain small size to pass through. RBC, WBC & proteins can’t pass throigh *** Surface in contact with glomerular capillaries consists of cells with foot-like processes ( podocytes ) that interdigitate to form narrow slits Proximal convoluted tubule (PCT) Continues from BC Wall consists of a single layer of epithelial cells + near to capillaries ( peritubular capillaries *** )  short distance for exchange of substances between filtrate and plasma (i.e. for reabsorption & secretion). Not venule !!! *** indicate FYI

26. LO12: Relate the structure of the kidney to its functions of producing urine through ultra-filtration and selective reabsorption. Proximal convoluted tubule Capsule space Efferent arteriole (smaller) Endothelium of glomerulus Afferent arteriole (larger) Bowman’s capsule Podocyte

27. LO12: Relate the structure of the kidney to its functions of producing urine through ultra-filtration and selective reabsorption. Caution: Ultrafiltration is NOT diffusion In ultrafiltration , substances move via pores between cells (microscopic pores between capillary endothelial cells and slits between podocytes of Bowman’s Capsule). Relies on size of pores to change permeability to substances . Diffusion involves movement of molecules directly across cell membranes (e.g. O 2 ) or through microscopic pores in the capillary wall, down the concentration (hence, diffusion) gradient of the molecule . Ultrafiltration relies on high hydrostatic pressure to cause the flow of f luids, along with dissolved substances (amino acids, glucose, urea etc.) except for large molecules, across the sieve-like capillary and Bowman’s capsule wall into the Bowman’s capsule. Sieve-like with capillary pores Sieve-like with slits between podocytes Filtration Diffusion Conc. gradient Pressure

28. LO12: Relate the structure of the kidney to its functions of producing urine through ultra-filtration and selective reabsorption. Parts of a nephron Remarks Structure –to- Function Loop of Henle (LOH) Continues from PCT Wall consists of a single layer of epithelial cells + near to capillaries (vasa recta *** )  short distance for re-absorption of water and NaCl *** Countercurrent flow of filtrate in LOH where d escending limb is permeable to water but not Na + , while ascending limb is permeable to Na + but not water. *** Countercurrent flow of blood in vasa recta  Creates and maintains a high salt concentration in the medulla, enabling water-reabsorption to form concentrated urine. Distal convoluted tubule (DCT) Continues after LOH *** Same as for PCT Collecting duct (CD) Continues from DCT Multiple nephrons share 1 CD Wall consists of a single layer of epithelial cells  short distance for re-absorption of water and NaCl Contains ADH-responsive water channels ( *** aquaporins )  regulate amount of water reabsorbed into plasma  regulate plasma volume/ blood pressure and blood osmotic concentration (osmolality) *** indicate FYI

29. LO12: Relate the structure of the kidney to its functions of producing urine through ultra-filtration and selective reabsorption. Cleaning of blood of waste products in kidney Ultrafiltration Adjust composition of filtrate Starts with Selective Reabsorption Selective Secretion Filtrate  Blood Blood  Filtrate Urine Blood  Filtrate

30. LO12: Relate the structure of the kidney to its functions of producing urine through ultra-filtration and selective reabsorption. Kidney region Part of nephron Process Out of plasma Into the plasma Resultant fluid Renal cortex Glomerulus & Bowman’s capsule Ultrafiltration Water, glucose, amino acids, urea, uric acid, mineral salts, HCO 3 - None Glomerular Filtrate Proximal convoluted tubule Selective reabsorption into blood --- Water, mineral salts (e.g. NaCl ), glucose, amino acids, HCO 3 - Selective secretion *** H + (blood more acidic = more secreted) --- Renal medulla Loop of Henle Selective reabsorption *** --- Water, NaCl Renal cortex Distal convoluted tubule Selective reabsorption *** --- NaCl , HCO 3 - , some water Selective secretion *** H + --- Cortex + medulla Collecting duct Selective reabsorption into blood --- Water, NaCl Renal papilla None Urine *** indicate FYI

31. LO12: Relate the structure of the kidney to its functions of producing urine through ultra-filtration and selective reabsorption. Urine (100cm3) consists mainly of Water 96.0 g Mineral salts 1.8 g Urea 2.0 g Other nitrogenous substances 0.2 g Varies with diet Reabsorbed Main Site(s) Water ~ 99% PCT, LOH, CD NaCl Large % PCT, LOH, CD Amino acids Nearly all PCT Glucose Nearly all PCT HCO 3 - Depends on blood pH PCT, DCT Urea, Uric acid None None Blood entering glomerulus < 20% ultrafiltrated > 80% pass on unfiltrated ~ 1% of volume as urine In red indicate FYI

32. LO12: Relate the structure of the kidney to its functions of producing urine through ultra-filtration and selective reabsorption. Functions of Kidney Elimination of waste substances Removal of toxic substances ( eg metabolites of drugs ) Salvage of essential ions such as Na+, K+ and Cl - Regulation of blood pH by removing / reabsorbing H+ and HCO3- Regulation of plasma volume / blood pressure Regulation of blood osmotic concentration Production of hormones – erythropoietin and renin Influenced by ADH

33. LO13: Describe the role of antidiuretic hormone (ADH) in the formation of urine through the negative feedback reaction . Homeostasis of blood osmolality ( or water potential ) ADH – chemical message Main effector: collecting ducts in kidney Effect of ADH:  permeability of collecting duct to water   water reabsorption from glomerular filtrate into blood  more urine Other non-ADH responses triggered by osmoreceptor  thirst Control center Set-point Main effector ADH: Increased/ decreased secretion NOT all-or-none (baseline secretion always present)

34. LO14: List the causes of kidney failure and ways to prevent it. Top 2 causes: High blood pressure (Hypertension) Diabetes mellitus Others: Alcoholism – long time over-consumption of alcohol Alcohol inhibits ADH secretion Kidney inflammation e.g. due to infection Kidney cysts Rare cases of kidney failure after surgery Some over-the counter painkillers – toxicity to kidney tubule cells Prevention Healthy lifestyle Drink more water Avoid alcohol over-consumption Reduce salt intake in diet

35. LO15: Describe dialysis as the diffusion of waste products and salts through a semi-permeable membrane Hemodialysis Peritoneal dialysis Engineering feature Property Function Similar feature Tubing Made of cellophane that is semi-permeable (Note: tubing is NOT selectively permeable) Ensure that blood cells and plasma proteins remain in the blood as they are too large to pass through the pores of the tubing membrane Peritoneal membrane in the body’s peritoneal cavity Coiled  surface area in contact with the dialysis fluid for more rapid diffusion of metabolic waste from the blood into dialysis fluid --- Dialysis fluid composition Contains essential salts for the body and glucose at normal blood glucose concentration; and isotonic Prevents essential salts and glucose from diffusing out of blood and lost with the dialysis fluid Same as hemodialysis Changed regularly (continuously) To remove metabolic waste products so as to maintain a diffusion gradient between blood and dialysis fluid Changed regularly Fluid flow direction Direction of flow of blood in the tubing is opposite to the direction of flow of the dialysis fluid (counter-current flow) To always maintain a diffusion gradient between the patient’s blood and the dialysis fluid for diffusion of substances --- Others Temperature sensor Bubble trap Pressure sensor To maintain patient’s body temperature so that he/she does not need to expend energy to increase body temperature Prevent bubbles from forming in patient’s blood To ensure efficiency of dialysis by maintain patient’s blood pressure ---

36. LO16: Compare the two different forms of dialysis - haemodialysis and peritoneal dialysis. Peritoneal Dialysis Hemodialysis Method Uses peritoneal membrane to filter blood Uses partially permeable cellophane tubing to filter blood. Blood is cleaned inside the body Blood is cleaned outside the body Dialysis fluid is drained and replaced in batches. Dialysis fluid is constantly drained and replaced. Removal of waste products and salts via diffusion through a partially permeable membrane

37. LO16: Compare the two different forms of dialysis - haemodialysis and peritoneal dialysis . Peritoneal Dialysis Hemodialysis Advantage Blood is continuously purified and adjusted. Blood is purified after every few days (variable) Freedom of movement. Patient is free to move around and engage in normal activities while dialysis ( *** CAPD) is performed. Patient has to be stationed at the dialysis machine in one place for long periods of time. More freedom of time as it can be performed at home and when sleeping ( *** CCPD). Less freedom of time as dialysis is performed for 6 – 8 hours at a dialysis center during the day. Does not use needles – psychological barrier and source of contamination Uses disposable needles that need to be properly sterilized Patient can self-administer dialysis. Requires professional medical help. Disadvantage Needs to be performed daily. Performed about 3-4 times per week. Increased risk of peritoneal infection due to catheter exposed to external environment Low risk of infection if needles and tubing are properly sterilized. Limitation Cannot replace kidneys in the production of hormones such as renin *** indicate FYI