Maintenance of internal environment within tolerable limits - steady state physiological condition

Thermoregulation - internal temperature

Osmoregulation - solute balance and gain/loss of water

Excretion - elimination of nitrogen-containing products of metabolism

Regulators - use homeostatic mechanisms to moderate internal change in presence of external fluctuations - e.g., endothermy in birds, mammals and others

Conformers - allow internal conditions to vary with external changes - tend to live in relatively stable environment - e.g., ectothermic oceanic fish

Regulation of body temperature - maintenance of temperature within tolerable range - allows cells to function efficiently

Important because metabolism and other processes temperature-sensitive

Q₁₀ effect - rates of enzymatic-mediated reactions increase 2- to 3-fold for each 10^oC increase in temperature, until temperature high enough to cause enzyme denaturation

Conduction - direct transfer of thermal motion (heat) between body surface and environment

Convection - transfer of heat via movement of air

Radiation - emission of electromagnetic waves

Evaporation - absorption of heat due to evaporation

Distinction based on method of obtaining body heat

Ectotherm - body temperature regulated primarily through use of environmental energy and behavioral adaptations - most invertebrates, fishes, reptiles, amphibians

Endotherm - regulates body temperate primarily through metabolism (metabolic heat) - some invertebrates, reptiles and fishes; all mammals and birds

Adjusting rate of heat exchange between animal and its environment

Cooling by evaporative heat loss

Behavioral responses

Changing rate of metabolic heat production

Body insulation - hair, feathers & fat - reduce heat loss

Circulatory system - alterations in amount of blood flowing to skin - vasodilation (increase in diameter of superficial blood vessels) & vasoconstriction (contraction of vessels)

Countercurrent heat exchanger(s) - blood in arteries & veins of extremities flows in opposite direction - facilitates heat transfer along entire vein - common in birds and marine mammals

Energy absorbed as water evaporates - latent heat of evaporation

Cooling achieved by evaporation from cutaneous and respiratory systems - sweat glands, water loss through breathing which may be accentuated by panting

Relocation to suitable location - i.e., orientation of body to absorb maximum incoming radiation under cold conditions - hiding or burrowing in soil to avoid high temperatures

Migration - movement of individuals or populations to avoid environmental extremes - common in birds & mammals

Applies only to endotherms

Muscle contractions (e.g., shivering) increases heat production - vertebrates and invertebrates

Nonshivering therogenesis (NST) - hormones cause mitochondria to increase metabolic activity - produces heat rather than ATP

Brown fat - occurs in some mammals - specialized for rapid heat production

Certain moths and bees endothermic

Preflight "warm-up" - generate heat by contracting flight muscle

Countercurrent heat exchanger - common in bees and moths - maintains high temperature of thorax

Huddling - common in social bees - shift positions frequently to distribute heat

Most reptiles and amphibians ectothermic - regulate body temperature by behavioral adaptations - e.g., sunning (cold conditions) or evasion of excessive heat (hot conditions)

Some reptiles endothermic under certain conditions - e.g., vasoconstriction in marine iguanas - shivering in pythons - both conserve or generate heat

In most fishes, metabolic heat lost through gills and dorsal aorta from gills

Several species endothermic - e.g., bluefin tuna, swordfish & great white shark

In endothermic fishes, swimming muscles generate metabolic heat near core & adaptations of circulatory system retain heat - vessels in core arranged to form a countercurrent heat exchanger

Adaptation for foraging in cold seas

Hormonal effects - increases metabolic rate and production of heat rather than ATP - "nonshivering thermogenesis" - brown fat in certain mammals specialized for rapid heat production

Heat generated by muscle contractions - shivering

Other factors involved in thermoregulation - vasodilation and vasoconstriction, insulating fat, position of hair & feathers, perspiration, saliva (kangaroos), urine (bats)

Complex homeostatic system - nerve cells involved in thermoregulation concentrated in hypothalamus - system’s thermostat

Nerve sensors that sense temperatures located in various areas of body - respond to changes in temperature by activating mechanisms that promote heat loss or gain

In response to elevated temperatures, shuts down heat-saving mechanisms & promotes body cooling

Depressed temperatures - opposite effects

Acclimatization - adjustment to new new range of environmental temperatures over a period of days or weeks - often involves adjusting amount of insulation (e.g., fur) or varying metabolic heat production

At cellular level - increases in production of enzymes that function well under new conditions -changes in lipid composition of membranes

Stress-induced and heat-shock proteins - response to rapid change in temperature - maintain integrity of proteins that would otherwise by denatured

Physiological state in which metabolism and activity decreases

Estivation - summer torpor - reduced metabolism and activity due to summer heat or water scarcity

Hibernation - long term torpor - metabolism decreases & body temperature lowered for extended period of time - response to winter conditions (cold temperatures; food shortage)

Both processes may be triggered by changes in photoperiod (day length)

In most animals, cells not in direct contact with environment - bathed in internal body fluid - hemolymph in animals with open circulatory systems - interstitial fluid in those with closed circulatory systems

Transport epithelium - layer(s) of epithelial cells that regulate solute movement - essential components of osmotic regulation and metabolic waste disposal

Form a selectively permeable barrier at tissue-environment boundary - regulate movement of solutes

In most animals, transport epithelia arranged into tubular networks with extensive surface areas

Molecular structure of plasma membranes determines permeability to various solutes - may involve diffusion (no energy requirement) or active transport (requires energy)

By-products of metabolism resulting from breakdown of proteins and nucleic acids - nitrogen removed when broken apart for energy or when converted to carbohydrates or fats

Many - especially ammonia - highly toxic

Kind of nitrogenous waste dependent on evolutionary history and habitat

Principal nitrogenous waste of most aquatic animals

Very soluable in water - passes through cell membranes readily

Extremely toxic - can only be transported and excreted in very dilute solution - requires large amounts of water for storage & excretion - unsuitable for disposal of nitrogenous wastes on land

Relatively nontoxic - 100,000x less toxic than ammonia - most animals can tolerate high concentrations of ammonia

Produced by vertebrate liver by metabolic cycle that combines ammonia with carbon dioxide - transported to (and released by) kidneys

Excreted in concentrated form - water conservation adaptation - requires energy

Relatively nontoxic - energy required

Insoluable - excreted in paste- like form

Principal waste product of vertebrates with shelled eggs - precipitates within egg and left behind when young emerges from egg

In many groups of animals, excretion of urea vs uric acid dependent on habitat - e.g., aquatic turtles excrete urea or ammonia while terrestrial forms excrete uric acid

Osmolarity - solute concentration expressed as molarity

Hypertonic solution - concentration of solute in solution greater than within cell

Hypotonic - concentration of solute in solution less than within cell

Isotonic - concentration of solution and cell same

Diffusion of water across selectively-permeable membrane

Water will move across membrane in direction that tends to equalize concentration(s) of solute on both sides of membrane - "water dilutes"

Important concept in water balance

Adaptations to control water balance of organisms living in hypertonic, hopotonic or terrestrial environments

Osmoregulators - body fluids have different osmolarity than environment - must adjust internal osmolarity - requires energy

Osmoconformers - body fluids isoosmotic with environment - do not actively adjust internal osmolarity

Most marine invertebrates osmoconformers

Marine fishes hypoosmotic to seawater - lose water (by osmosis) and gain salt (by diffusion) - replenish water by drinking large quantities - excrete salt in urine (low quantities)

Sharks and other cartilaginous fishes maintain high concentrations of urea in blood - become slightly hyperosmotic to seawater - do not experience constant water loss

Most freshwater animals hyperosmotic to water - constantly gain water through osmosis

Most excrete large amounts of very dilute urine - regain lost salts by uptake from surroundings via gills

Adaptations to minimize desiccation key to survival on land - only two major groups of animals (Arthropods and Vertebrates) have colonized land with great success

Adaptations - waxy exoskeletons of arthropods - dead keratinized skin cells in vertebrates - reduce water loss

Use of metabolic water (from cellular respiration)and nocturnal activity patterns -common in many desert animals

Anhydrobiosis - adaptation that allows certain organisms to lose nearly all of their body water and survive extended periods - up to 10 years in desiccated state - common in tardigrades, nematodes and others

In dehydrated individuals, trehalose (disaccharide) replaces water in cell membrane & proteins - prevents damage

Filtration - blood filtered by selectively permeable transport epithelia - proteins & other large molecules retained - water and small solutes moved into excretory system

Reabsorption - selective transport of water and valuable solutes back into body fluids

Secretion - solutes from body fluids added to filtrate

Excretion - wastes voided in urine

Protonephridia - also known as flame-bulb systems - mainly osmoregulatory - flatworms

Metanephridia - excretory and osmoregulatory functions - annelids

Malpighian tubules - excretory and osmoregulatory functions - arthropods

Vertebrate kidney - excretory and osmoregulatory functions - vertebrates

Occur in flatworms (Platyhelminthes)

System of branching internal tubes that function mainly in osmoregulation - also known as "flame-bulb" systems

Cilia draws interstitial fluid into lumen of tubule (flame-bulb) - very dilute urine excreted through nephridiopore

Occurs in segmented worms (Anellida)

Involved in both osmoregulation and excretory functions

Pair of metanephridia occurs in each segment of worm - nephrostome collects coelomic fluid from adjacent anterior segment - passes through coiled tubule - dilute urine excreted through nephridiopore

Occurs in insects and other arthropods (Arthropoda)

Involved in both osmoregulatory and excretory functions

Tubules extend into hemolymph - salt, water, and nitrogenous wastes enter tubules and digestive tract - water and certain organic molecules reabsorbed in rectum

Functions in both osmoregulation and excretion

Bean-shaped - occur in pairs (abdominal cavity

Consists of outer region (renal cortex) and inner region (renal medulla)

Nephron - functional unit of kidney

Urine drained via ureter > urinary bladder > urethra

Blood enters Bowman’s capsule via afferent arterioles - absorption of water and ions in proximal tubule - hydrogen ions, ammonia enter tube - pH regulation

Water reabsorption in descending loop of Henle and absorption of salt in ascending loop of Henle - creates concentration gradient in medulla

Reabsorption of water in proximal tubule and collection duct due to concentration gradient - concentrated (hyperosmotic) urine - efficient water conservation mechanism in mammals

Antidiuretic hormone - secreted by hypothalamus - responds to blood osmolarity - enhances fluid retention by making kidneys reclaim more water

Renin-angiotensin-aldosterone-system (RAAS) - responds to blood volume and pressure - stimulates resorption of salt and water - leads to increase in blood volume and pressure

Atrial natriuretic factor (ANF) - opposes RAAS - tends to lower blood volume and pressure

One of most important functions is to adjust both volume and osmolarity of urine - dependent on animal’s salt and water balance and rate of urea production

In situations of high salt intake and low water availability, animal can excrete urea and salt with minimal water loss

In situations of high fluid intake and scarcity of salt, can excrete excess water with little salt loss by producing large volumes of dilute (hypoosmotic) urine