Homeostasis

Homeostasis

� Homeostasis refers to maintaining internal stability within an organism and returning to a particular stable state after a fluctuation.a fluctuation.

Homeostasis

� Changes to the internal environment come from:� Metabolic activities require a supply of

materials (oxygen, nutrients, salts, etc) that materials (oxygen, nutrients, salts, etc) that must be replenished.�Waste products are produced that must be

expelled.

Homeostasis

� Systems within an organism function in an integrated way to maintain a constant internal environment around a setpoint.� Small deviations in pH, temperature, � Small deviations in pH, temperature,

osmotic pressure, glucose levels, & oxygen levels activate physiological mechanisms to return that variable to its setpoint.� Negative feedback

Osmoregulation & Excretion

� Osmoregulation regulates solute concentrations and balances the gain and loss of water.� Excretion gets rid of metabolic wastes.� Excretion gets rid of metabolic wastes.

Osmosis

� Cells require a balance between osmotic gain and loss of water.�Water uptake and loss are balanced by

various mechanisms of osmoregulation various mechanisms of osmoregulation in different environments.

Osmosis

� Osmosis is the movement of water across a selectively permeable membrane.� If two solutions that are separated by a � If two solutions that are separated by a

membrane differ in their osmolarity, water will cross the membrane to bring the osmolarity into balance (equal solute concentrations on both sides).

Osmotic Challenges

� Osmoconformers , which are only marine animals, are isoosmotic with their surroundings and do not regulate their osmolarity.their osmolarity.� Osmoregulators expend energy to

control water uptake and loss in a hyperosmotic or hypoosmoticenvironment.

Osmotic Regulation

�Most marine invertebrates are osmotic conformers – their bodies have the same salt concentration as the seawater.� The sea is highly stable, so most marine � The sea is highly stable, so most marine

invertebrates are not exposed to osmotic fluctuations.� These organisms are restricted to a narrow

range of salinity – stenohaline .� Marine spider crab

Osmotic Regulation

� Conditions along the coasts and in estuaries are often more variable than the open ocean.� Animals must be able to

handle large, often abrupt handle large, often abrupt changes in salinity.

� Euryhaline animals can survive a wide range of salinity changes by using osmotic regulation .� Hyperosmotic regulator

(body fluids saltier than water)

� Shore crab.

Osmotic Regulation

� The problem of dilution is solved by pumping out the excess water as dilute urine.� The problem of salt loss is compensated � The problem of salt loss is compensated

for by salt secreting cells in the gills the actively remove ions from the water and move them into the blood.� Requires energy.

Osmotic Regulation - Freshwater

� Freshwater animals face an even more extreme osmotic difference than those that inhabit estuaries.

Osmotic Regulation - Freshwater

� Freshwater fishes have skin covered with scales and mucous to keep excess water out.� Water that enters the body is pumped out by the

kidney as very dilute urine.� Salt absorbing cells in the gills transport salt ions into

the blood.Salt absorbing cells in the gills transport salt ions into the blood.

Osmotic Regulation - Freshwater

� Invertebrates and amphibians also solve these problems in a similar way.way.� Amphibians actively

absorb salt from the water through their skin.

Osmotic Regulation – Marine

� Marine bony fishes are hypoosmotic regulators .� Maintain salt concentration at 1/3 that of seawater.� Marine fishes drink seawater to replace water lost by

diffusion.� Excess salt is carried to the gills where salt-secreting cells � Excess salt is carried to the gills where salt-secreting cells

transport it out to the sea.� More ions voided in feces or urine.

Osmotic Regulation – Marine

� Sharks and rays retain urea (a metabolic waste usually excreted in the urine) in their tissues and blood.� This makes osmolarity of the shark’s � This makes osmolarity of the shark’s

blood equal to that of seawater, so water balance is not a problem.

Osmotic Regulation – Terrestrial

� Terrestrial animals lose water by evaporation from respiratory and body surfaces, excretion surfaces, excretion (urine), and elimination (feces).� Water is replaced by

drinking water, water in food, and retaining metabolic water.

Osmotic Regulation – Terrestrial

� The end-product of protein metabolism is ammonia, which is highly toxic.� Fishes can excrete ammonia directly

because there is plenty of water to wash it because there is plenty of water to wash it away.

Osmotic Regulation – Terrestrial

� Terrestrial animals must convert ammonia to uric acid.� Semi-solid urine – little water loss.� In birds & reptiles, the wastes of developing � In birds & reptiles, the wastes of developing

embryos are stored as harmless solid crystals.

Osmotic Regulation – Terrestrial

� Marine birds and turtles have a salt gland capable of excreting highly concentrated salt concentrated salt solution.

Excretory Processes

� Most excretory systems produce urine by refining a filtrate derived from body fluids (blood, body fluids (blood, hemolymph, or coelomic fluid).

Excretory Processes

� Key functions of most excretory systems are:� Filtration , pressure-filtering of body fluids

producing a filtrate.producing a filtrate.� Reabsorption , reclaiming valuable solutes

from the filtrate.� Secretion , addition of toxins and other

solutes from the body fluids to the filtrate.� Excretion , the filtrate leaves the system.

Invertebrate Excretory Structures

� Contractile vacuoles are found in protozoans and freshwater sponges.� An organ of water balance – expels excess

water gained by osmosis.water gained by osmosis.

Invertebrate Excretory Structures

� The most common type of invertebrate excretory organ is the nephridium .� The simplest arrangement

is the protonephridium of acoelomates and some pseudocoelomates.pseudocoelomates.� Fluid enters through flame

cells , moves through the tubules, water and metabolites are recovered and wastes are excreted through pores that open along the body surface.� Highly branched due to

lack of circulatory system.

Invertebrate Excretory Structures

� The metanephridium is an open system found in annelids, molluscs, and some smaller phyla.� Tubules are open at

both ends.both ends.� Water enters through

the ciliated, funnel shaped nephrostome .

� The metanephridium is surrounded by blood vessels that assist in reclaiming water and valuable solutes.

Invertebrate Excretory Structures

� In arthropods, antennal glands are an advanced form of the nephridial organ.� No open

nephrostomes, hydrostatic pressure hydrostatic pressure of the blood forms an ultrafiltrate in the end sac.� In the tubule,

selective resorption of some salts and active secretion of others occurs.

Invertebrate Excretory Structures

� Insects and spiders have Malpighian tubules that are closed and lack an arterial supply.� Salts (especially

potassium) are secreted into the tubules from the potassium) are secreted into the tubules from the hemolymph (blood). � Water & other solutes

(including uric acid) follow.� Water & potassium are

reabsorbed.� Uric acid is expelled in

feces.

Vertebrate Kidneys

� Kidneys , the excretory organs of vertebrates, function in both excretion and osmoregulation.

Vertebrate Kidneys

� Nephrons and associated blood vessels are the functional unit of the mammalian kidney.� The mammalian excretory system � The mammalian excretory system

centers on paired kidneys which are also the principal site of water balance and salt regulation.

Vertebrate Kidneys

� Each kidney is supplied with blood by a renal artery and drained by a drained by a renal vein .

Vertebrate Kidneys

� Urine exits each kidney through a duct called the ureter .� Both ureters drain into a common urinary

bladder.bladder.

Structure and Function of the Nephron and Associated Structures

� The mammalian kidney has two distinct regions:� An outer renal cortex� An inner renal medullaAn inner renal medulla

(b) Kidney structure

UreterSection of kidney from a rat

Renalmedulla

Renalcortex

Renalpelvis

Structure and Function of the Nephron and Associated Structures

� The nephron , the functional unit of the vertebrate kidney consists of a single long a single long tubule and a ball of capillaries called the glomerulus .

Filtration of the Blood

� Filtration occurs as blood pressure forces fluid from the blood in the glomerulus into the glomerulus into the lumen of Bowman’s capsule .

Pathway of the Filtrate

� From Bowman’s capsule, the filtrate passes through three regions of the nephron:� Proximal tubule� Proximal tubule� Loop of Henle � Distal tubule

� Fluid from several nephrons flows into a collecting duct .

From Blood Filtrate to Urine: A Closer Look

� Filtrate becomes urine as it flows through the mammalian nephron and collecting duct.� The composition of the filtrate is modified � The composition of the filtrate is modified

through tubular reabsorption and secretion.� Changes in the total osmotic concentration

of urine through regulation of water excretion.

From Blood Filtrate to Urine: A Closer Look

� Secretion and reabsorption in the proximal tubule substantially alter the volume and composition of filtrate.� Reabsorption of water continues as the filtrate

moves into the descending limb of the loop of moves into the descending limb of the loop of Henle .

From Blood Filtrate to Urine: A Closer Look

� As filtrate travels through the ascending limb of the loop of Henle salt diffuses out of the permeable tubule into the interstitial fluid.The distal tubule plays a key role in � The distal tubule plays a key role in regulating the K+ and NaCl concentration of body fluids.� The collecting duct carries the filtrate

through the medulla to the renal pelvis and reabsorbs NaCl.

Conserving Water

� The mammalian kidney’s ability to conserve water is a key terrestrial adaptation.� The mammalian kidney can produce � The mammalian kidney can produce

urine much more concentrated than body fluids, thus conserving water.

Solute Gradients and Water Conservation

� In a mammalian kidney, the cooperative action and precise arrangement of the loops of Henle and the collecting ducts are largely responsible for the osmotic are largely responsible for the osmotic gradient that concentrates the urine.

Solute Gradients and Water Conservation

� The collecting duct, permeable to water but not salt conducts the filtrate through the kidney’s osmolarity gradient, and more water exits the filtrate by osmosis.more water exits the filtrate by osmosis.

Solute Gradients and Water Conservation

� Urea diffuses out of the collecting duct as it traverses the inner medulla.� Urea and NaCl form the osmotic gradient

that enables the kidney to produce urine that enables the kidney to produce urine that is hyperosmotic to the blood.

Regulation of Kidney Function

� The osmolarity of the urine is regulated by nervous and hormonal control of water and salt reabsorption in the kidneys.kidneys.

Regulation of Kidney Function

� Antidiuretic hormone (ADH)increases water reabsorption in the distal tubules and distal tubules and collecting ducts of the kidney.

Temperature Regulation

� Animals must keep their bodies within a range of temperatures that allows for normal cell function.� Each enzyme has an optimum � Each enzyme has an optimum

temperature.� Too low and metabolism slows.� Too high and metabolic reactions become

unbalanced. Enzymes may be destroyed.

Temperature Regulation

� Poikilothermic animals’ body temperatures fluctuate with environmental temperatures.� Homeothermic animals’ body � Homeothermic animals’ body

temperatures are constant.

Temperature Regulation

� All animals produce heat from cellular metabolism, but in most this heat is lost quickly.� Ectotherms – lose metabolic heat quickly,

so body temperature is determined by the so body temperature is determined by the environment.� Body temp may be regulated environmentally.

� Endotherms – retain metabolic heat and can maintain a constant internal body temperature.

Ectothermic Temperature Regulation

� Many ectotherms regulate body temperature behaviorally.� Basking to increase temperature.� Shelter in shade or coolness of a burrow to Shelter in shade or coolness of a burrow to

decrease temperature.

Ectothermic Temperature Regulation

�Most ectotherms can also adjust their metabolic rates to the environmental temperature.� Activity levels can remain unchanged over a � Activity levels can remain unchanged over a

wider range of temperatures.

Endothermic Temperature Regulation

� Constant temperature in endotherms is maintained by a delicate balance between heat production and heat loss.� Heat is produced by the animal’s � Heat is produced by the animal’s

metabolism.� Producing heat requires energy – supplied

by food.� Endotherms must eat more in cold weather.

Endothermic Temperature Regulation

� If an animal is too cool, it can generate heat by increasing muscular activity (exercise or shivering). Heat is shivering). Heat is retained through insulation.� If an animal is too

warm it decreases heat production and increases heat loss.

Adaptations for Hot Environments

� Small desert mammals are mostly fossorial (living underground) or nocturnal .� Burrows are cool and moist.� Burrows are cool and moist.

� Adaptations to derive water from metabolism and produce concentrated urine & dry feces.

Adaptations for Hot Environments

� Larger desert mammals (camels, desert antelopes) have different adaptations.� Glossy, pallid color

reflects sunlight.� Fat tissue is

concentrated in a hump, rather than being evenly distributed in an insulating layer.� Sweating and panting

are ways of dumping heat.

Adaptations for Cold Environments

� In cold environments, mammals reduce heat loss by having a thick insulating layer of fat, fur, or both.� Heat production is � Heat production is

increased.� Extremities are allowed

to cool.� Heat loss is prevented

through countercurrent heat exchange .

Adaptations for Cold Environments

� Small mammals are not as well insulated.� Many avoid direct exposure to the cold by

living in tunnels under the snow.living in tunnels under the snow.� Subnivean environment.� This is where food is located.

Adaptive Hypothermia

� Endothermy is energetically expensive.� Ectotherms can survive weeks without

eating.� Endotherms must always have energy � Endotherms must always have energy

supplies.

Adaptive Hypothermia

� Some very small mammals & birds (bats or hummingbirds) maintain high body maintain high body temperatures when active, but allow temperatures to drop when sleeping.� Daily torpor

Adaptive Hypothermia

� Hibernation is a way to solve the problem of low temperatures and the scarcity of food.� True hibernators store fat, � True hibernators store fat,

then enter hibernation gradually.� Metabolism & body slows to a

fraction of normal.� Body temperature decreases.� Shivering helps increase

temperatures when they are waking up.

Adaptive Hypothermia

� Other mammals, such as bears, badgers, raccoons and opossums enter a state of prolonged sleep, but body temperature does not decrease.temperature does not decrease.

Adaptive Hypothermia

� Adverse conditions can also occur during the summer.� Drought, high temperatures.

� Some animals enter a state of dormancy � Some animals enter a state of dormancy called estivation .� Breathing rates and metabolism decrease.� African lungfish, desert tortoise, pigmy

mouse, ground squirrels.