CHAPTER 25 Control of the Internal Environment

Bears don’t technically hibernate Let Sleeping Bears Lie Bears don’t technically hibernate They do enter a dormant state, when their body temperature drops by several degrees Bears are endotherms Endothermic animals derive most of their body heat from metabolism Ectothermic animals warm themselves mainly by absorbing heat from their surroundings

Dormant bears have internal homeostatic mechanisms that compensate for fluctuations in the external environment Thermoregulation maintains the body temperature within a tolerable range Osmoregulation controls the gain and loss of water and dissolved solutes Excretion is the disposal of metabolic wastes

25.1 Heat is gained or lost in four ways THERMOREGULATION 25.1 Heat is gained or lost in four ways Body temperature regulation requires adjustment to heat gained from or lost to an animal’s environment Convection Radiation Evaporation Conduction Figure 25.1

25.2 Thermoregulation depends on both heat production and heat gain or lost Both endotherms and ectotherms may change their rate of heat loss

Hormonal changes may increase heat production by raising the metabolic rate Fur and feathers help the body retain heat Shivering, as these honeybees are doing, also increases metabolic heat production Figure 25.2A

Blood flow to the skin affects heat loss Top view of shark Skin Blood vessels of gills Artery Vein Capillary network within muscle Heart Artery and vein under the skin Dorsal aorta Figure 25.2B

Body surface (cool) In a countercurrent heat exchanger, blood from the core body warms cooler blood returning from the gills or limbs 18˚ C 20˚ C 20˚ 22˚ This process conserves body heat Blood flow 22˚ 24˚ Heat transfer 24˚ 26˚ Inner body (warm) Figure 25.2C

25.3 Behavior often affects body temperature Basking in the sun Sitting in the shade Bathing Burrowing or huddling Migrating Figure 25.3

25.4 Reducing the metabolic rate saves energy Torpor is a state of reduced activity and lowered metabolic rate Hibernation in cold weather Estivation in warm weather Figure 25.4

OSMOREGULATION AND EXCRETION 25.5 Osmoregulation: All animals balance the gain and loss of water and dissolved solutes Many marine animals are osmoconformers Their body fluids have the same concentration of solutes as sea water

Osmoregulators control water and solute concentrations Freshwater fishes gain water by osmosis and tend to lose solutes Osmotic water gain through gills and other parts of body surface Uptake of water and some ions in food Excretion of large amounts of water in dilute urine from kidneys Uptake of salt ions by gills Figure 25.5A

Many marine fishes lose water by osmosis, drink seawater, and excrete excess salts Gain of water and salt ions from food and by drinking seawater Osmotic water loss through gills and other parts of body surface Excretion of salt ions and small amounts of water in scanty urine from kidneys Excretion of salt ions from gills Figure 25.5B

Land animals gain water by drinking and eating They lose water and solutes by evaporation and waste disposal Their kidneys, behavior, and waterproof skin conserve water

25.6 Connection: Sweating can produce serious water loss Water lost in thermoregulation can cause osmoregulatory problems Drinking water is the best way to prevent dehydration during exercise Figure 25.6

25.7 Some animals face seasonal dehydration Many small invertebrates can dehydrate and become dormant when their environment dries up Figure 25.7

25.8 Animals must dispose of nitrogenous wastes Nitrogen-containing wastes are toxic by-products of protein and nucleic acid breakdown Ammonia is poisonous but soluble and easily disposed of Urea is less toxic and easy to store and excrete Some land animals save water by excreting a virtually dry waste

Proteins Nucleic acids Amino acids Nitrogenous bases –NH2 Amino groups Most aquatic animals, including many fishes Mammals, amphibians, sharks, some bony fishes Birds, insects, many reptiles, land snails Ammonia Urea Uric acid Figure 25.8

25.9 The excretory system plays several major roles in homeostasis expels wastes regulates water and salt balance (Inferior vena cava) Renal artery and vein Kidney (Aorta) Ureter Bladder Urethra A. THE EXCRETORY SYSTEM Figure 25.9A

Urine leaves the kidneys via the ureters The two human kidneys each contain about a million functional units called nephrons Urine leaves the kidneys via the ureters It is stored in the urinary bladder

Bowman’s capsule Nephron tubule Renal medulla Renal cortex Renal artery Renal cortex Renal vein Collecting duct Renal pelvis Renal medulla Ureter To renal pelvis B. THE KIDNEY C. ORIENTATION OF A NEPHRON WITHIN THE KIDNEY Figure 25.9B, C

Each nephron consists of a folded tubule and associated blood vessels 1 Proximal tubule Bowman’s capsule Glomerulus Arteriole from renal artery Capillaries Arteriole from glomerulus 3 Distal tubule Branch of renal vein From another nephron The nephrons extract a filtrate from the blood They refine the filtrate into a much smaller amount of urine Collecting duct 2 Loop of Henle with capillary network D. DETAILED STRUCTURE OF A NEPHRON Figure 25.9D

25.10 Overview: The key functions of the excretory system are filtration, reabsorption, secretion, and excretion Filtration Blood pressure forces water and many solutes from the blood into the nephron Reabsorption The nephron tubule reclaims valuable solutes

H2O, other small molecules Secretion The nephron removes substances and adds them to the filtrate The product of all of the above processes is urine, which is excreted Nephron tubule FILTRATION REABSORPTION EXCRETION SECRETION H2O, other small molecules Urine Capillary Figure 25.10

25.11 From blood to filtrate to urine: A closer look The proximal tubule reabsorbs nutrients salts water Antidiuretic hormone and other hormones regulate the amount of salt and water the kidneys excrete

Controlled secretion of H+ and reabsorption of bicarbonate ions help regulate blood pH Secretion also includes the active transport of drugs and poisons Reabsorption of salts and urea promote the osmotic reabsorption of water

Proximal tubule Distal tubule Bowman’s capsule NaCl H2O Glucose and amino acids H2O HCO3– NaCl HCO3– Blood Some drugs and poisons NH3 H+ K+ H+ Filtrate Collecting duct H2O CORTEX Salts (NaCl, etc.) MEDULLA HCO3– H+ Loop of Henle Urea NaCl Glucose Amino acids NaCl Some drugs H2O Reabsorption Urea Active transport NaCl H2O Passive transport Secretion (active transport) Urine (to renal pelvis) Figure 25.11

25.12 Connection: Kidney dialysis can be a lifesaver A dialysis machine compensates for kidney failure It performs the function of the nephrons by removing wastes from the blood and maintaining its solute concentration

Tubing made of a selectively permeable membrane Line from artery to apparatus Pump Tubing made of a selectively permeable membrane Dialyzing solution Line from apparatus to vein Fresh dialyzing solution Used dialyzing solution (with urea and excess salts) Figure 25.12

25.13 The liver is vital in homeostasis HOMEOSTATIC FUNCTIONS OF THE LIVER 25.13 The liver is vital in homeostasis It assists the kidneys by making urea from ammonia breaking down toxic chemicals

Blood from the intestines flows through the liver before distribution to the rest of the body Inferior vena cava Hepatic vein Liver This allows the liver to adjust the blood’s chemical content Hepatic portal vessel Intestines Figure 25.13