The Internal Environment

Maintaining Internal Balance Internal environment maintained in narrow range Homeostasis Extracellular fluid Interstitial—between cells of body tissues Blood Stays stable because of exchanges substances w/ environment Fluids & solutes enter by osmosis, digestive system, metabolism Minerals & water lost through respiratory system, skin, kidneys

Osmosis Diffusion—movement of substance from high to low concentration Osmosis—diffusion of water across a selectively permeable membrane Isotonic solution—concentration of solutes equal in and out of cell, no net movement of water Hypertonic solution— concentration of solutes greater outside of cell than inside; water moves out of cell Hypotonic—concentration of solutes greater inside of cell than outside; water moves into cell

Aquatic Animals Mollusks, arthropods, cartilaginous fish Body fluids nearly isotonic to seawater No movement of salt or water No difficulty maintaining salt/water balance

Aquatic Animals Marine bony fish Seawater is hypertonic Prone to water loss Drink seawater constantly to take in enough water Excess salt excreted by gills Scant, highly concentrated urine retains water

Aquatic Animals Freshwater bony fish Freshwater is hypotonic Prone to water gain Never drink water Produce large amount of dilute urine Must actively take salt through gills and food

Land Animals Bigger risk of dehydration since not surrounded by water Water gain—food, drink, metabolic reactions Water loss Do not loose through osmosis Urinary excretion Evaporation from respiratory surfaces Sweating in mammals

Land Animals Balance Birds & reptiles have glands to eliminate salt Marine iguanas specialized Reptiles dry, scaly skin to prevent water loss Desert mammals (camel, kangaroo rat, etc.) Reabsorb moisture from exhaled air Limited amount of urine, highly concentrated No sweat glands More absorption of water from feces More active in cooler parts of day

Nitrogen Waste Produced by breakdown of nucleic acids & amino acids Ingestion Metabolic processes Ammonia produced Very toxic Must be eliminated

Nitrogen Waste Aquatic animals Excrete ammonia directly in urine Need large amounts of water Insects, reptiles, birds Excrete uric acid Low toxicity Poorly soluble in water Therefore highly concentrated Large amount of water conserved Mammals, terrestrial amphibians Excrete urea Less toxic than ammonia Excreted in moderately concentrated solution

Excretory Organs Flame cell Nematodes, platyhelminthes, flatworms, rotifers Cilia in cells move water through Tubules remove excess water

Excretory Organs Nephridium Many invertebrates, mostly annelids Cilliated cells move fluid from coelom into nephridium Capillaries around tubule reabsorbs solutes Dilute urine expelled through external pore

Excretory Organs Malpighian tubules Insects, myriapods, arachnids Absorb water, solutes, wastes from surrounding hemolymph Wastes excreted through gut Amount of fluid absorbed dependent on environment

Excretory Organs Kidney Most vertebrates Filter blood Produce urine Urea & uric acid Often other functions Regulate blood pressure Glucose metabolism RBC production

Urinary System Kidneys Paired Cortex Medulla Pelvis Only found in mammals

Urinary System Ureter—kidney to bladder Bladder—urine storage Only in mammals Urethra—bladder to outside Part of reproductive tract in males Separate in females

Nephron Functional unit of kidney Renal Corpuscle Non-selective filtration Glomerulus Blood vessels enter kidney Glomerular capsule Filtrate collected

Nephron Renal Tubules 99% of filtered products reabsorbed Proximal convoluted tubule Organic Solutes (amino acids, glucose) 2/3 of salt & water Loop of Henle Concentrates salt (absorbs water) Distal convoluted tubule Reabsorb calcium, excrete potassium

Nephron 1 million nephrons in human kidney 25% must be functional for homeostasis Maintain blood pH Release erythropoeitin for RBC production Stimulate ADH release when dehydrated Maintain blood pressure Chronic renal failure irreversible Dialysis—pump blood through machine that allows diffusion of wastes, then pump blood back into body

Temperature Regulation Heat gain & loss Thermal radiation Sun, warm object Warmth produced by metabolism Conduction Transferred between two objects in direct contact Convection Moving air or water “Wind chill” Evaporation Water on surface converts to gas Draws heat from body

Temperature Regulation Heat stress Peripheral vasodilation— diameter of skin blood vessels increases Evaporation Sweat—most mammals, no other animals Licking fur Panting Move to shaded, cooled area Under surface of ground, rocks Design adaptations Desert animals usually smaller (greater surface area per body size), less body fat, thinner hair coats

Temperature Regulation Cold stress Peripheral vasoconstriction Pilomotor response—hairs stand up Layer of still air next to skin Reduce convective and radiative heat loss Shivering Muscles contract 10-20x per second Generates internal heat Nonshivering heat production Long-term (hibernating animals) Brown adipose tissue Move to warmer area Reptile basking Design adaptations Thicker coat, larger size (smaller surface area), increased fat for insulation