L27 2024 - Homeostasis - An Introduction to the Kidney PDF

Homeostasis and the Kidney Dr Ashley Le Vin [email protected]  Outline Define homeostasis Example of temperature regulation Function of the kidney Structure of the kidney How the kidneys work Bowman’s capsule Filtration forces ...

Homeostasis and the Kidney Dr Ashley Le Vin [email protected]  Outline Define homeostasis Example of temperature regulation Function of the kidney Structure of the kidney How the kidneys work Bowman’s capsule Filtration forces  Homeostasis In 1857 Claude Bernard stated: “A constant internal environment is a necessary condition for life under varying external conditions” Our body functions properly when the fluid surrounding our cells are maintained within narrow limits Small fluctuations can disrupt biochemical activities and large fluctuations can kill the cells The maintenance of a constant internal environment is known as Homeostasis Greek for ‘Staying the same’  Homeostasis The most important features of our internal environment that must be kept constant are: 1. Chemical composition - e.g. ions, glucose 2. Blood pH – (range 7.35 to 7.45): CO2 + H2O = H2CO3 H2CO3 = H+ + HCO3- 3. Osmotic pressure = osmoregualtion 4.Temperature - regulated in birds and mammals (endotherms) - not regulated in most fish & amphibia (ectotherms) - Although some ectotherms use behavioural mechanisms to regulate temperature  Temperature regulation Regulation and conforming Regional heterothermy in tuna 19.3oC 31.4oC Red muscle Rete mirabile Campbell 9th ed. Fig 40.7 Behavioural regulation in an ectotherm Pre-flight warm-up in moths Campbell 9th ed. Fig 40.15 Campbell 9th ed. Fig 40.11  Control system for thermoregulation Stimulus Temperature change Receptors Skin and Hypothalamus Control Centre (Set Point) Hypothalamus Effectors Skin blood vessels Sweat glands Hair (fur) Muscles Response mechanisms Blood vessels constrict or dilate Sweat produced or not Piloerection Shivering thermogenesis See also Campbell 9th ed. Fig 40.16  Some basics If one solution is Hyperosmotic to another = contains more solutes than the other solution. It therefore contains less water If one solution is Hypo-osmotic to another = contains less solutes than the other solution. It therefore contains more water Water will move by osmosis from a high to a low concentration. So water will move in to a hyperosmotic solution and out of a hypo-osmotic solution. A solution with few solutes in it will have lower osmotic pressure than one with many solutes. Water will move from a low to a high osmotic pressure solution. Osmolarity/solute conc. = no. of osmoles solute per litre of solution  Functions of the Kidney Important regulatory functions 1. Removal of nitrogenous waste (products of protein /nucleic acid metabolism) 2. Regulation of water content of body (osmoregulation) 3. Regulation of salt balance (body concentration of Na+, K+, Cl-, Ca2 , Mg2+ etc.) (ionic regulation) http://calibermag.org/?attachment_id=17743 http://www.health.com/health/gallery/0,,20365078,00.html http://www.phase1clinicaldevelopment.com/always-checks-drugs-side-effects/  Removal of nitrogenous wastes When amino acids are metabolised, the amino (-NH2) group is removed and forms ammonia (NH3). Ammonia may be excreted as: Ammonia/ Urea Uric acid/Guano Ammonium The particular waste excreted depends on the animal’s group, habitat and the stage of development http://www.chemistryviews.org/details/news/2778521/Electride_Ammonia.html http://www.sodahead.com/fun http://www.motifake.com/bird-poo-demotivational-posters-7070.html  Forms of nitrogenous waste Ammonia Urea Uric acid Toxicity High Low Very Low Solubility 500 50 1 (ml for 1g N) Metabolic None Some High cost Examples Fish Mammals Birds Aquatic Amphibia Adult Terrestrial Insects (& tadpoles) Amphibia Aquatic Aquatic Terrestrial Turtles Turtles Reptiles Crocodiles Sharks Eggs (allantois)  Structure of the kidneys Two bean-shaped organs, each the size of a clenched fist They are located against the back wall of the abdomen on either side of the body The kidneys are 1% body weight, but receive 25% of cardiac output (1.25 litres per min) Reason: they control the chemical composition of blood in our body  Structure of the kidneys Renal Pelvis Cortex Nephron Medulla Cortex Renal Ureter pelvis Ureter Medulla Bladder Campbell 9th ed. Fig 44.14  The Nephron Cortical nephron There are approx. 2 million nephrons in the body Each nephron is Juxta-medullary nephron 30-60 mm long In total ~60 km of nephrons Two kinds of nephrons ; juxta-medullary = very concentrated urine cortical = less concentrated urine  Parts of a Nephron Campbell 9th ed. Fig 44.14 Afferent arteriole Peritubular capillaries Humans ~85% are cortical and ~15% are Efferent arteriole juxta-medullary Only birds and mammals have juxta- medullary nephrons = very conc. urine Reptiles and amphibians have only Vasa recta cortical nephrons (blood vessels)  Bowman’s capsule 20 µm Fluid moves by process of ultrafiltration. The hydrostatic pressure of the blood plasma (blood pressure) forces fluid and solutes through the glomerular capillaries into Bowman’s capsule. Passive process – no energy  What passes through in to Bowman’s space? Oil What is passed through? Micropipette Studies by Richards in the late 1930’s on nephrons of South American Salamander - Mudpuppy http://quizlet.com/22363034/urinary-em-images-flash-cards/  What passes into Bowman’s space? MW filtrate/plasma % passing conc through Myoglobin 17,000 0.75 75% Egg albumin 43,500 0.22 22% Haemoglobin 68,000 0.03 3% Serum albumin 69,000