Chapter 25. Control of the Internal Environment 2018 Biology2 Chapter 25. Control of the Internal Environment

25.2 Heat is gained or lost in four ways THERMOREGULATION 25.2 Heat is gained or lost in four ways Body temperature regulation requires adjustment to heat gained from or lost to an animal’s environment

25.3 Thermoregulation involves adaptations that balance heat gain or lost Endotherms and many ectotherms maintain a fairly constant internal temperature as the external temperature fluctuates Thermoregulatory adaptation Metabolic heat production Insulation Circulatory adaptation (constriction and dilation of blood vessels) Evaporative cooling Behavioral responses

Behavioral responses Basking in the sun Sitting in the shade Bathing Burrowing or huddling Migrating

OSMOREGULATION AND EXCRETION 25.4 Animals balance the gain and loss of water and solutes through osmoregulation Osmoregulation: regulation of the chemical composition of the body fluids of an organism Precise balance of water and dissolved solutes e.g., amino acids, proteins, ions such as Na+, Cl-, K+, Ca2+, HCO3-

Many marine animals are osmoconformers Their body fluids have the same concentration of solutes as sea water Such animals do not undergo a net gain or loss of water e.g., many marine invertebrates (jellyfish, scallop, lobster…)

Osmoregulators have body fluids whose solute concentration is different from that of their environment -Such animals control water and solute concentrations -Freshwater fishes gain water by osmosis and tend to lose solutes It does not drink water

Many marine fishes lose water by osmosis, drink seawater, and excrete excess salts

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

25.5 A variety of ways to dispose of nitrogenous wastes have evolved in animals Nitrogen-containing wastes are toxic by-products of protein and nucleic acid breakdown Ammonia -Too toxic to be stored in the body -Highly soluble in water and diffuse rapidly across the cell membrane e.g., aquatic animals

2. Urea -Ammonia is converted to urea in the liver -Urea is highly soluble in water and much less toxic than ammonia -Water is required for disposing of it e.g., mammals, adult amphibians, some fishes 3. Uric acid -Ammonia is converted to uric acid in birds, insects, many reptiles -Uric acid is largely insoluble in water -In most cases, it is excreted as a paste or dry powder, combined with feces

25.6 The urinary system plays several major roles in homeostasis The excretory system expels wastes regulates water and salt balance Controls blood pH and blood pressure

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

Juxtamedullary nephron Cortical nephron: major (85%)

Each nephron consists of a folded tubule and associated blood vessels 1 Proximal tubule Bowman’s capsule Glomerulus peritubular Arteriole from renal artery Capillaries Arteriole from glomerulus 3 Distal tubule The nephrons extract a filtrate from the blood They refine the filtrate into a much smaller amount of urine 0.8-1.5 millions/kidney Branch of renal vein From another nephron Collecting duct 2 Loop of Henle with capillary network Vasa recta D. DETAILED STRUCTURE OF A NEPHRON

25.7 Overview: The key processes of the urinary 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 from the filtrate and returns them to the body fluids

The product of all of the above processes is urine, which is excreted Secretion Toxins and excess ions are extracted from body fluids and added to the contents of the tubule The product of all of the above processes is urine, which is excreted

25.8 Blood filtrate is refined to urine through reabsorption and secretion The proximal and distal tubules reabsorb Nutrients (e.g., glucose, amino acid etc.) Salts (NaCl, HCO3-) water (by osmosis) Water reabsorption is the major function of the loop of Henle and the collecting duct Antidiuretic hormone, aldosterone, atrial natriuretic hormone, and parathyroid hormone regulate the amount of salt and water the kidneys excrete

Increase in the osmolarity In blood Low blood volume or Low blood pressure Osmoreceptors in hypothalamus Secretion of renin from juxtaglomerular apparatus Thirst Release of ADH from posterior pituitary gland Angiotensinogen  angiotensin Constriction of arteriole Increase in water reabsorption at collecting duct Secretion of aldosterone Increase in Na+ and H2O reabsorption and K+ secretion at distal tubule

COLLECTING DUCT LUMEN INTERSTITIAL FLUID Osmoreceptors in hypothalamus trigger release of ADH. Thirst Hypothalamus COLLECTING DUCT CELL ADH ADH receptor Drinking reduces blood osmolarity to set point. cAMP ADH Second messenger signaling molecule Pituitary gland Increased permeability Storage vesicle Distal tubule Exocytosis Aquaporin water channels H2O H2O reab- sorption helps prevent further osmolarity increase. H2O STIMULUS: Increase in blood osmolarity Collecting duct (b) The collecting duct is normally impermeable to water and permeable in the presence of ADH Homeostasis: Blood osmolarity (300 mOsm/L)

Liver Distal tubule Renin Angiotensin I Juxtaglomerular Angiotensinogen Renin Angiotensin I Juxtaglomerular apparatus (JGA) ACE Angiotensin II STIMULUS: Low blood volume or blood pressure Adrenal gland Aldosterone Increased Na+ and H2O reab- sorption in distal tubules Arteriole constriction Homeostasis: Blood pressure, volume

Atrial natriuretic hormone - High blood pressure - Produced at the wall of the atria of the heart - Secrete more Na+ at distal tubule, dilation of blood vessels Parathyroid hormone - Reabsorption of more Ca2+ and secretion of more phosphate at distal tubule

Controlled secretion of H+ and NH3 and reabsorption of bicarbonate ions help regulate blood pH Secretion also includes the active transport of drugs and poisons in the proximal tubule Reabsorption of salts and urea promote the osmotic reabsorption of water

NH3 Impermeable to water