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Homeostatic Mechanisms 1 (function) Example 3: Osmoregulation Big Questions: How do the physiological systems of organisms help the organism maintain homeostasis? How have the physiological systems of organisms been adapted to the constraints of the environments that organisms live in? What does an organism need to do? Stay alive (at least until reproduction)! The physiological systems that an organism has are adapted to this purpose. Generalized Animal Body Plan: How does each system contribute to homeostasis? Generalized Plant Body Plan What do each of the following do to maintain homeostasis? • root root tip/root hairs • shoot (stem) Nodes/internodes Buds Terminal/apical/axillary buds Flower buds & flowers • leaves mesophyll tissue/veins (vascular bundles) How does the environment influence an organism’s physiology? Tremendously! Natural selection will tend to drive the adaptation of physiology to environmental contstraints. This has resulted in a variety of mechanisms for maintaining homeostasis A Note About Plants: Plants have it a bit different: • They release almost no Nitrogenous waste. – Nitrogen is a limiting factor for plant growth in most soils. • They regulate osmolarity through transpiration. • Nitrogenous waste is an “animals only” problem. • Animals couple Nitrogenous waste excretion to osmolarity regulation. Conformers vs. Regulators • Two evolutionary paths for organisms – regulate internal environment • maintain relatively constant internal conditions – conform to external environment • allow internal conditions to fluctuate along with external changes osmoregulation thermoregulation regulator regulator conformer conformer Homeostasis • Keeping the balance – animal body needs to coordinate many systems all at once • • • • • • • temperature blood sugar levels energy production water balance & intracellular waste disposal nutrients ion balance cell growth – maintaining a “steady state” condition Animal systems evolved to support multicellular life aa O2 CH CHO CO2 aa NH3 CHO O2 O2 CH aa CO2 aa NH3 CO2 NH3 CO2 CO2 NH3 NH3 CO2 CH NH3 NH3 CO2 CO2 aa O2 NH3 NH3 CO2 O2 intracellular waste CO2 CHO CO2 aa Diffusion too slow! extracellular waste Overcoming limitations of diffusion • Evolution of exchange systems for – distributing nutrients • circulatory system – removing wastes • excretory system CO2 CO2 aa CO2 CO2 O2 NH3 CO2 systems to support multicellular organisms NH3 CO2 CO2 NH3 NH3 CO2 CH NH3 NH3 CO2 aa O2 NH3 NH3 CHO CO2 aa Osmoregulation hypotonic • Water balance – freshwater • hypotonic • water flow into cells & salt loss – saltwater • hypertonic • water loss from cells hypertonic – land • dry environment • need to conserve water • may also need to conserve salt Why do all land animals have to conserve water? always lose water (breathing & waste) may lose life while searching for water Intracellular Waste • What waste products? Animals poison themselves from the inside by digesting proteins! – what do we digest our food into… • • • • CO2 + H2O carbohydrates = CHO lipids = CHO CO2 + H2O proteins = CHON CO2 + H2O + N nucleic acids = CHOPN cellular digestion… cellular waste NH2 = ammonia lots! very little CO2 + H2O + P + N H| O || H N –C– C–OH | H R CO2 + H2O Nitrogenous waste disposal • Ammonia (NH3) – very toxic • carcinogenic – very soluble • easily crosses membranes – must dilute it & get rid of it… fast! • How you get rid of nitrogenous wastes depends on – who you are (evolutionary relationship) – where you live (habitat) aquatic terrestrial terrestrial egg layer Nitrogen waste Aquatic organisms can afford to lose water Ammonia: most toxic Terrestrial need to conserve water Urea: less toxic Terrestrial egg layers need to conserve water need to protect embryo in egg uric acid: least toxic Freshwater animals • Water removal & nitrogen waste disposal – remove surplus water • use surplus water to dilute ammonia & excrete it – need to excrete a lot of water so dilute ammonia & excrete it as very dilute urine • also diffuse ammonia continuously through gills or through any moist membrane – overcome loss of salts • reabsorb in kidneys or active transport across gills Land animals H • Nitrogen waste disposal on land H H – need to conserve water – must process ammonia so less toxic N C N H • urea = larger molecule = less soluble = less toxic – 2NH2 + CO2 = urea – produced in liver Urea – kidney costs energy to synthesize, but it’s worth it! • filter solutes out of blood • reabsorb H2O (+ any useful solutes) • excrete waste – urine = urea, salts, excess sugar & H2O » urine is very concentrated » concentrated NH3 would be too toxic mammals O Egg-laying land animals • Nitrogen waste disposal in egg – no place to get rid of waste in egg – need even less soluble molecule • uric acid = BIGGER = less soluble = less toxic – birds, reptiles, insects itty bitty living space! Uric acid • Polymerized urea – large molecule – precipitates out of solution And that folks, is why most male birds don’t have a penis! • doesn’t harm embryo in egg – white dust in egg • adults still excrete N waste as white paste – no liquid waste – uric acid = white bird “poop”! O H H N N O O N N H H Mammalian System • Filter solutes out of blood & reabsorb H2O + desirable solutes • Key functions blood filtrate – Filtration: fluids (water & solutes) filtered out of blood – Reabsorption: selectively reabsorb (diffusion) needed water + solutes back to blood – Secretion: pump out any other unwanted solutes to urine – Excretion: expel concentrated urine (N waste + solutes + toxins) from body concentrated urine Mammalian Kidney inferior vena cava aorta adrenal gland kidney ureter bladder urethra nephro n renal vein & artery epithelial cells Nephron Functional units of kidney 1 million nephrons per kidney Function filter out urea & other solutes (salt, sugar…) blood plasma filtered into nephron high pressure flow selective reabsorption of valuable solutes & H2O back into bloodstream greater flexibility & control why selective reabsorption & not selective filtration? “counter current exchange system” Mammalian kidney • Interaction of circulatory & excretory systems • Circulatory system – glomerulus = ball of capillaries • Excretory system – nephron – Bowman’s capsule – loop of Henle • proximal tubule • descending limb • ascending limb • distal tubule – collecting duct How can different sections allow the diffusion of different molecules? Bowman’s capsule Proximal tubule Distal tubule Glomerulus Glucose Amino acids H2O Mg++ Ca++ H2O Na+ ClH2O H2O Na+ Cl- H2O H2O Loop of Henle Collecting duct Nephron: Filtration • At glomerulus – filtered out of blood • • • • H2O glucose salts / ions urea – not filtered out • cells • proteins high blood pressure in kidneys force to push (filter) H2O & solutes out of blood vessel BIG problems when you start out with high blood pressure in system hypertension = kidney damage Nephron: Re-absorption • Proximal tubule – reabsorbed back into blood • NaCl – active transport of Na+ – Cl– follows by diffusion • H2O • glucose • HCO3– bicarbonate – buffer for blood pH Nephron: Re-absorption Loop of Henle descending limb high permeability to H2O many aquaporins in cell membranes low permeability to salt few Na+ or Cl– channels reabsorbed H2O structure fits function! Nephron: Re-absorption Loop of Henle ascending limb low permeability to H2O Cl- pump Na+ follows by diffusion different membrane proteins reabsorbed salts maintains osmotic gradient structure fits function! Nephron: Re-absorption Distal tubule reabsorbed salts H2O HCO3- bicarbonate Nephron: Reabsorption & Excretion Collecting duct reabsorbed H2O excretion concentrated urine passed to bladder impermeable lining Osmotic control in nephron • How is all this re-absorption achieved? – tight osmotic control to reduce the energy cost of excretion – use diffusion instead of active transport wherever possible the value of a counter current exchange system Summary • Not filtered out – Cells, proteins – remain in blood (too big) why selective reabsorption & not selective filtration? • Reabsorbed: active transport – Na+ Cl-, amino acids, glucose • Reabsorbed: diffusion – Na+, Cl–, H2O • Excreted – Urea, excess H2O, excess solutes (glucose, salts), toxins, drugs, “unknowns” Negative Feedback Loop hormone or nerve signal lowers body condition gland or nervous system (return to set point) high sensor specific body condition sensor raises body condition low gland or nervous system (return to set point) hormone or nerve signal Nervous System Control Controlling Body Temperature nerve signals brain sweat high body temperature low brain constricts surface shiver blood vessels nerve signals dilates surface blood vessels Endocrine System Control Blood Osmolarity ADH pituitary increased water reabsorption increase thirst nephron high blood osmolarity blood pressure low ADH = AntiDiuretic Hormone Maintaining Water Balance • High blood osmolarity level Get more water into blood fast – too many solutes in blood • dehydration, high salt diet – stimulates thirst = drink more – release ADH from pituitary gland • antidiuretic hormone – increases permeability of collecting duct & reabsorption of water in kidneys • increase water absorption back into blood • decrease urination Alcohol suppresses ADH… makes you urinate a lot! H2O H2O H2O Endocrine System Control Blood Osmolarity Oooooh, zymogen! JGA = JuxtaGlomerular Apparatus high blood osmolarity blood pressure adrenal gland low increased water & salt reabsorption in kidney JGA nephron renin aldosterone angiotensinogen angiotensin Maintaining Water Balance • Low blood osmolarity level or low blood pressure Get more water & salt into blood fast! – JGA releases renin in kidney – renin converts angiotensinogen to angiotensin – angiotensin causes arterioles to constrict • increase blood pressure – angiotensin triggers release of aldosterone from adrenal gland – increases reabsorption of NaCl & H2O in kidneys • puts more water & salts back in blood Why such a rapid response system? Spring a leak? adrenal gland Endocrine System Control Blood Osmolarity ADH increased water reabsorption pituitary increase thirst nephron high blood osmolarity blood pressure adrenal gland low increased water & salt reabsorption JuxtaGlomerular Apparatus nephron renin aldosterone angiotensinogen angiotensin Don’t get batty… Ask Questions!! Quick Check: Make Sure You Can 1. Explain the role of animal excretory systems in osmoregulation. 2. Compare the osmoregulatory approaches taken by conformers and regulators. 3. Label/Identify all organs that play major roles in the Excretory system. 4. Diagram all important parts of a nephron and explain their functions. 5. Diagram the feedback loops that function in regulating blood osmolarity. 6. Explain the causes of excretory system disruptions and how disruptions of the excretory system can lead to disruptions of homeostasis.
