biology - homeostasis presentation

7/29/2019 Biology - Homeostasis presentation

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Homeostasis

Chapter 30


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Homeostasis

Homeostasis refers to maintaining

internal stability within an organism and

returning to a particular stable state after

a fluctuation.


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Homeostasis

Changes to the internal environment

come from:

Metabolic activities require a supply of

materials (oxygen, nutrients, salts, etc) that

must be replenished.

Waste products are produced that must be

expelled.


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Homeostasis

Systems within an organism function in

an integrated way to maintain a constant

internal environment around a setpoint.

Small deviations in pH, temperature,

osmotic pressure, glucose levels, & oxygen

levels activate physiological mechanisms to

return that variable to its setpoint. Negative feedback


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Osmoregulation & Excretion

Osmoregulation regulates solute

concentrations and balances the gain

and loss of water.

Excretion gets rid of metabolic wastes.


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Osmosis

Cells require a balance between osmotic

gain and loss of water.

Water uptake and loss are balanced by

various mechanisms of osmoregulation

in different environments.


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Osmosis

Osmosis is the movement of water

across a selectively permeable

membrane.

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 soluteconcentrations on both sides).


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Osmotic Challenges

Osmoconformers, which are only

marine animals, are isoosmotic with

their surroundings and do not regulate

their osmolarity.

Osmoregulators expend energy to

control water uptake and loss in a

hyperosmotic orhypoosmoticenvironment.


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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

invertebrates are not exposed to osmotic

fluctuations.

These organisms are restricted to a narrowrange of salinitystenohaline.

Marine spider crab


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Osmotic Regulation

Conditions along thecoasts and in estuariesare often more variablethan the open ocean.

Animals must be able tohandle large, often abruptchanges in salinity.

Euryhaline animals cansurvive a wide range ofsalinity changes by using

osmotic regulation. Hyperosmotic regulator

(body fluids saltier thanwater)

Shore crab.


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Osmotic Regulation

The problem of dilution is solved by

pumping out the excess water as dilute

urine.

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.


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Osmotic Regulation - Freshwater

Freshwater animals face an even more

extreme osmotic difference than those

that inhabit estuaries.


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Freshwater fishes have skin covered with scales andmucous to keep excess water out.

Water that enters the body is pumped out by thekidney as very dilute urine.

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


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Invertebrates and

amphibians also

solve these

problems in a similarway.

Amphibians actively

absorb salt from the

water through theirskin.


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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

transport it out to the sea.

More ions voided in feces or urine.


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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 sharks

blood equal to that of seawater, so water

balance is not a problem.


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Osmotic Regulation Terrestrial

Terrestrial animalslose water byevaporation fromrespiratory and bodysurfaces, excretion(urine), andelimination (feces).

Water is replaced bydrinking water, waterin food, and retainingmetabolic water.


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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 itaway.


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Terrestrial animals must convert

ammonia to uric acid.

Semi-solid urine little water loss.

In birds & reptiles, the wastes of developing

embryos are stored as harmless solid

crystals.


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Marine birds and

turtles have a salt

gland capable of

excreting highlyconcentrated salt

solution.


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Excretory Processes

Most excretory

systems produce

urine by refining a

filtrate derived frombody fluids (blood,

hemolymph, or

coelomic fluid).


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Excretory Processes

Key functions of most excretory systems

are:

Filtration, pressure-filtering of body fluids

producing a filtrate.

Reabsorption, reclaiming valuable solutes

from the filtrate.

Secretion, addition of toxins and othersolutes from the body fluids to the filtrate.

Excretion, the filtrate leaves the system.


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Invertebrate Excretory Structures

Contractile vacuoles are found in

protozoans and freshwater sponges.

An organ of water balance expels excess

water gained by osmosis.


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The most common type ofinvertebrate excretory organis the nephridium. The simplest arrangement

is the protonephridium of

acoelomates and somepseudocoelomates.

Fluid enters through flamecells, moves through thetubules, water andmetabolites are recoveredand wastes are excretedthrough pores that openalong the body surface. Highly branched due to

lack of circulatory system.


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The metanephridium isan open system found inannelids, molluscs, andsome smaller phyla.

Tubules are open atboth ends.

Water enters throughthe ciliated, funnelshaped nephrostome.

The metanephridium issurrounded by bloodvessels that assist inreclaiming water andvaluable solutes.


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In arthropods,antennal glands arean advanced form ofthe nephridial organ. No open

nephrostomes,hydrostatic pressureof the blood formsan ultrafiltrate in theend sac.

In the tubule,selective resorptionof some salts andactive secretion ofothers occurs.


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Insects and spiders haveMalpighian tubules thatare closed and lack anarterial supply.

Salts (especially

potassium) are secretedinto the tubules from thehemolymph (blood). Water & other solutes

(including uric acid)

follow. Water & potassium are

reabsorbed.

Uric acid is expelled infeces.


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Vertebrate Kidneys

Kidneys, the excretory organs of

vertebrates, function in both excretion

and osmoregulation.


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Vertebrate Kidneys

Nephrons and associated blood vessels

are the functional unit of the mammalian

kidney.

The mammalian excretory system

centers on paired kidneys which are also

the principal site of water balance and

salt regulation.


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Vertebrate Kidneys

Each kidney is

supplied with

blood by a renal

artery anddrained by a

renal vein.


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Vertebrate Kidneys

Urine exits each kidney through a duct

called the ureter.

Both ureters drain into a common urinary

bladder.


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Structure and Function of the Nephron

and Associated Structures

The mammalian kidney has two distinct

regions:

An outerrenal cortex

An innerrenal medulla

(b) Kidney structure

Ureter

Section of kidney from a rat

Renal

medulla

Renal

cortex

Renal

pelvis


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Structure and Function of the Nephron

and Associated Structures

The nephron, the

functional unit of

the vertebrate

kidney consists ofa single long

tubule and a ball

of capillaries

called theglomerulus.


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Filtration of the Blood

Filtration occurs as

blood pressure

forces fluid from the

blood in theglomerulus into the

lumen ofBowmans

capsule.


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Pathway of the Filtrate

From Bowmans

capsule, the filtrate

passes through three

regions of the nephron:

Proximal tubule

Loop of Henle

Distal tubule

Fluid from severalnephrons flows into a

collecting duct.

F Bl d Filt t t U i A


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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

through tubular reabsorption and secretion.

Changes in the total osmotic concentration

of urine through regulation of waterexcretion.



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Closer Look

Secretion and reabsorption in the proximal

tubule substantially alter the volume and

composition of filtrate.

Reabsorption of water continues as the filtratemoves into the descending limb of the loop of

Henle.



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Closer Look

As filtrate travels through the ascendinglimb of theloop of Henle salt diffuses outof the permeable tubule into the interstitial

fluid. The distal tubule plays a key role in

regulating the K+ and NaCl concentration ofbody fluids.

The collecting duct carries the filtratethrough the medulla to the renal pelvis andreabsorbs NaCl.


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Conserving Water

The mammalian kidneys ability to

conserve water is a key terrestrial

adaptation.

The mammalian kidney can produce

urine much more concentrated than body

fluids, thus conserving water.

Solute Gradients and Water


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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 osmoticgradient that concentrates the urine.



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Conservation

The collecting duct, permeable to water

but not salt conducts the filtrate through

the kidneys osmolarity gradient, and

more water exits the filtrate by osmosis.



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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 is hyperosmotic to the blood.


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Regulation of Kidney Function

The osmolarity of the urine is regulated

by nervous and hormonal control of

water and salt reabsorption in the

kidneys.


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Regulation of Kidney Function

Antidiuretic

hormone (ADH)

increases water

reabsorption in thedistal tubules and

collecting ducts of

the kidney.


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Temperature Regulation

Animals must keep their bodies within a

range of temperatures that allows for

normal cell function.

Each enzyme has an optimum

temperature.

Too low and metabolism slows.

Too high and metabolic reactions becomeunbalanced. Enzymes may be destroyed.


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Poikilothermicanimals body

temperatures fluctuate with

environmental temperatures.

Homeothermicanimals body

temperatures are constant.


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All animals produce heat from cellularmetabolism, but in most this heat is lostquickly.

Ectotherms lose metabolic heat quickly,so body temperature is determined by theenvironment. Body temp may be regulated environmentally.

Endotherms retain metabolic heat andcan maintain a constant internal bodytemperature.

Ectothermic Temperature


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Regulation

Many ectotherms regulate body temperature

behaviorally.

Basking to increase temperature.

Shelter in shade or coolness of a burrow todecrease temperature.



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Regulation

Most ectotherms can also adjust their

metabolic rates to the environmental

temperature.

Activity levels can remain unchanged over awider range of temperatures.

Endothermic Temperature


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Regulation

Constant temperature in endotherms is

maintained by a delicate balance

between heat production and heat loss.

Heat is produced by the animalsmetabolism.

Producing heat requires energy supplied

by food. Endotherms must eat more in cold weather.



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Regulation

If an animal is toocool, it cangenerate heat byincreasingmuscular activity

(exercise orshivering). Heat isretained throughinsulation.

If an animal is too

warm it decreasesheat productionand increases heatloss.


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Adaptations for Hot Environments

Small desert mammals are mostly

fossorial (living underground) or

nocturnal.

Burrows are cool and moist.

Adaptations to derive water from

metabolism and produce concentrated

urine & dry feces.


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Adaptations for Hot Environments

Larger desert mammals(camels, desertantelopes) have differentadaptations. Glossy, pallid color

reflects sunlight. Fat tissue is

concentrated in ahump, rather thanbeing evenly distributedin an insulating layer.

Sweating and pantingare ways of dumpingheat.


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Adaptations for Cold Environments

In cold environments,mammals reduce heatloss by having a thickinsulating layer of fat,fur, or both.

Heat production isincreased.

Extremities are allowedto cool.

Heat loss is preventedthroughcountercurrent heatexchange.


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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. Subnivean environment.

This is where food is located.


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Adaptive Hypothermia

Endothermy is energetically expensive.

Ectotherms can survive weeks without

eating.

Endotherms must always have energysupplies.


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Some very small

mammals & birds

(bats or

hummingbirds)maintain high body

temperatures when

active, but allow

temperatures to dropwhen sleeping.

Daily torpor


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Hibernation is a way to solve

the problem of low

temperatures and the scarcity

of food.

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.


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Other mammals, such as bears,

badgers, raccoons and opossums enter

a state of prolonged sleep, but body

temperature does not decrease.

Ad i H h i


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Adverse conditions can also occur during

the summer.

Drought, high temperatures.

Some animals enter a state of dormancy

called estivation.

Breathing rates and metabolism decrease.

African lungfish, desert tortoise, pigmymouse, ground squirrels.

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