Lecture #19 Date________ Chapter 44 ~ Regulating the Internal Environment

Homeostasis: regulation of internal environment Thermoregulation internal temperature Osmoregulation solute and water balance Excretion nitrogen containing waste

Regulation of body temperature Thermoregulation 4 physical processes: Conduction~transfer of heat between molecules of body and environment Convection~transfer of heat as water/air move across body surface Radiation~transfer of heat produced by organisms Evaporation~loss of heat from liquid to gas Sources of body heat: Ectothermic: determined by environment Endothermic: high metabolic rate generates high body heat

Regulation during environmental extremes Torpor ~ low activity; decrease in metabolic rate 1- Hibernation long term or winter torpor (winter cold and food scarcity); bears, squirrels 2- Estivation short term or summer torpor (high temperatures and water scarcity); fish, amphibians, reptiles Both often triggered by length of daylight

Water balance and waste disposal Osmoregulation: management of the body’s water content and solute composition Nitrogenous wastes: breakdown products of proteins and nucleic acids; ammonia-very toxic Deamination~ Ammonia: most aquatic animals, many fish Urea: mammals, most amphibians, sharks, bony fish (in liver; combo of NH 3 and CO 2 ) Uric acid: birds, insects, many reptiles, land snails

Osmoregulators Osmoconformer: no active adjustment of internal osmolarity (marine animals); isoosmotic to environment Osmoregulator: adjust internal osmolarity (freshwater, marine, terrestrial) Freshwater fishes (hyperosmotic)- gains water, loses; excretes large amounts of urine salt vs. marine fishes (hypoosmotic)- loses water, gains salt; drinks large amount of saltwater

Water Loss in Land Animals Terrestrial organisms must also regulate their water levels Adaptations include: –Waxy cuticle in plants –Shells of land snails –Waxy layers of insect exoskeleton –Layers of dead skin –Being nocturnal Most loose water from moist surface areas of gas exchange, urine, feces, and skin Must gain water from diet or through metabolism

Excretory Systems Production of urine by 2 steps: Filtration (nonselective) and Selective Reabsorption (secretion of solutes) Protonephridia ~ flatworms (“flame-bulb” systems) Metanephridia ~ annelids (ciliated funnel system) Malpighian tubules ~ insects (tubes in digestive tract) Kidneys ~ vertebrates

Kidney Functional Units Renal artery/vein: kidney blood flow Ureter: urine excretory duct Urinary bladder: urine storage Urethra: urine elimination tube Renal cortex (outer region) Renal medulla (inner region) Nephron: functional unit of kidney, approx. 1 million per kidney) Cortical nephrons (confined to renal cortex; 80%) Juxtamedullary nephrons (extend into renal medulla; 20%; only in mammals and birds, important in water conservation – hyperosmotic urine)

Nephron Structure Afferent arteriole: supplies blood to nephron from renal artery Glomerulus: ball of capillaries Efferent arteriole: blood from glomerulus Bowman’s capsule: surrounds glomerulus Proximal tubule: secretion & reabsorption Peritubular capillaries: from efferent arteriole; surround proximal & distal tubules Loop of Henle: water & salt balance Distal tubule: secretion & reabsorption Collecting duct: carries filtrate to renal pelvis

Basic Nephron Function

Proximal Tubule, Loop of Henle, Distal Tubule PT – reabsorb HCO 3 -, NaCl, water, nutrients, and K + ions; secrete H + and NH 3 Decending L of H – reabsorb water Ascending L of H – reabsorb NaCl DT – reabsorb NaCl, water, and HCO 3 - ; secrete K + and H +

Collecting Duct Carries filtrate through the medulla to the renal pelvis Reabsorbs NaCl, urea, and water

Water Conservation in Kidney Creates hyperosmotic urine Conserves water through both active and passive processes

Kidney regulation: hormones Antidiuretic hormone (ADH) ~ secretion increases permeability of distal tubules and collecting ducts to water (H2O back to body); inhibited by alcohol and coffee Juxtaglomerular apparatus (JGA) ~ reduced salt intake--->enzyme renin initiates conversion of angiotensin (plasma protein) to angiotensin II (peptide); increase blood pressure and blood volume by constricting capillaries Angiotensin II also stimulates adrenal glands to secrete aldosterone; acts on distal tubules to reabsorb more sodium, thereby increasing blood pressure (renin- angiotension-aldosterone system; RAAS) Atrial natriuretic factor (ANF) ~ walls of atria; inhibits release of renin, salt reabsorption, and aldosterone release