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).