Chapter 42

2. Chapter 42 The Internal Environment

3. 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

4. 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

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

6. 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

7. 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

8. 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

9. 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

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

11. 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

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

13. 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

14. 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

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

16. Urinary System • Kidneys • Paired • Cortex • Medulla • Pelvis • Only found in mammals

17. 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

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

19. 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

20. 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

21. 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

22. 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

23. 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