Chapter 44:Internal Regulation!
By Juliana Wiele and Emily Vancor
Thermoregulation- maintenance of internal temperature within a tolerable range
Osmoregulation- maintenance of solute balance
Excretion- release of nitrogenous waste products of metabolism
Regulators vs. Conformers
Regulator- uses mechanisms of homeostasis to moderate internal change in response to external changes
Conformer- allows internal conditions to vary with external changes
Ex. Salmon osmoregulate in response to changes in external salinity, but spider crabs do not. They lose or gain water to conform to the external environment.
Evaporative Cooling
As water evaporates, it requires energy to break the hydrogen bonds holding it together. This energy is released as heat. When water evaporates from a body in sweat or in the respiratory tract, heat is released, cooling the organism.
Endothermy
Endothermy is coupled with an active lifestyle. Endothermic animals also have highly elaborate circulatory and respiratory systems.
Mechanisms for Lowering Body Temperature
Evaporative cooling Vasodilation Behavior
– Increasing surface area– Moving to cool, damp areas– Migrating
Mechanisms for Raising Body Temperature
Vasoconstriction Insulation Countercurrent heat exchange Muscle movement Non-shivering Thermogenesis (using
hormones to increase metabolic rate)
Endotherms: Birds and mammals
Ectotherms: invertebrates, fish, amphibians, reptiles
Countercurrent Heat Exchange
Arteries and veins are arranged so that most heat lost from arteries is transferred to veins instead of to the external environment. This minimizes heat loss and directs heat back toward the core.
Many mammals and birds use it, including geese, dolphins, and wolves.
Cellular Homeostasis!
Rapid changes in temperature cause mammalian cells to synthesize heat-shock proteins, a type of stress-induced protein, that protect other proteins from being denatured by heat.
Torpor & Hibernation
Torpor is a physiological state in which activity is low and metabolism decreases. Hibernation is a long-term torpor that some mammals and birds enter in the winter. Estivation is a summer torpor in which animals have a very slow metabolism to survive on scarce water supplies. Some small mammals and birds undergo a daily torpor to conserve energy.
Nitrogenous Wastes
Nitrogenous wastes are produced in the form of ammonia during the breakdown of proteins and nucleic acids for energy or conversion to carbohydrates. Ammonia is a small and very toxic molecule that is safe to most animals only when very dilute. Some animals use the enzyme ATPase to convert it to less toxic forms including urea or uric acid.
Nitrogenous Wastes
Advantage Disadvantage Example Animal
Ammonia Small, soluble, no energy needed
Toxic at high concentrations, requires much water
Invertebrates, freshwater fish
Urea
Lower toxicity, easily stored, less water needed than for ammonia
Requires energy to produce from ammonia
Mammals, Amphibians, sharks, bony fish
Uric Acid
Less toxic than urea, insoluble in water, can be excreted with only a small amount of water
Requires more energy to produce from ammonia than urea does
Birds, insects, reptiles, land snails
Cow feces vs. lion feces
A lion’s feces would have more nitrogen than a cow’s because lions are carnivores and consume more protein (so more nitrogen) than cows.
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A tropical fish in freshwater is in a hypotonic environment and will have the problem of taking in water.
Excretory Organs
Animal Excretory organ
Planarian Protonephridium
Earthworm Metanephridium
Insect Malpighian Tubules
Human Kidneys
Juxtamedullary Nephrons
Juxtamedullary nephrons extend deep into the renal medulla and allow for the production of urine that is hyperosmotic to body fluids.
Mammals and birds have them. 20% of nephrons in the human kidney are
juxtamedullary.
Events of the Kidney
Bowman’s Capsule Solutes including salts, glucose, and vitamins filter from the blood in the glomerulus.
Proximal Tubule
The epithelial lining of the tubule buffers the fluid with hydrogen ions and ammonia and reabsorbs bicarbonate. Drugs and toxins are secreted from capillaries into the lumen, and glucose, amino acids, and potassium, salt, and water are reabsorbed.
Descending Limb Water is reabsorbed by the hyperosmotic interstitial fluid bathing the tubule.
Ascending Limb Salt is secreted from the tubule as its membrane becomes permeable to salt but not water.
Distal Convoluted Tubule
Potassium is secreted and salt is reabsorbed. Hydrogen ions are secreted and bicarbonate is reabsorbed.
Collecting TubuleFiltrate is carried to renal pelvis. Salt is actively reabsorbed, and water follows through osmosis. Some urea also is reabsorbed, contributing to the high osmolarity in the medulla of the kidney.
Antidiuretic Hormone
Produced by hypothalamus and released by pituitary gland
Osmoreceptors in hypothalamus monitor osmolarity of blood, release ADH by negative feedback
Targets of ADH are distal tubules and collecting ducts of kidneys
ADH increases permeability of ducts, increasing water reabsorption
Aldosterone
Released by adrenal glands in response to angiotensin II
Acts on distal tubules, causing reabsorption of sodium and water
Increases blood volume and pressure
Renin and Angiotensin
When blood pressure or volume in the afferent arteriole (supplies blood to the glomerulus) drops, the enzyme renin initiates reactions to convert angiotensinogen to angiotensin II.
Angiotensin II constricts artierioles, decreasing blood flow to the capillaries of the kidney, increasing pressure
Angiotensin II stimulates the proximal tubules to reabsorb more salt and water, increasing the blood volume and stimulates the adrenal glands to secrete aldosterone
With aldosterone, these proteins form the renin-angiotensin-aldosterone system (RAAS).
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