Homeostasis –Maintenance of steady internal conditions despite fluctuations in the external...

Homeostasis

– Maintenance of steady internal conditions despite fluctuations in the external environment

Examples of homeostasis

– Thermoregulation—the maintenance of internal temperature within narrow limits

– Osmoregulation—the control of the gain and loss of water and solutes

– Excretion—the disposal of nitrogen-containing wastes

Copyright © 2009 Pearson Education, Inc.

Introduction: Chilling Out

THERMOREGULATION


Thermoregulation

– The process by which animals maintain an internal temperature within a tolerable range

25.1 An animal’s regulation of body temperature helps maintain homeostasis


Ectothermic animals

– Absorb heat from their surroundings

– Many fish, most amphibians, lizards, most invertebrates

Endothermic animals

– Derive body heat mainly from their metabolism

– Birds, mammals, a few reptiles and fish, many insects


25.1 An animal’s regulation of body temperature helps maintain homeostasis

Heat exchange with the environment may occur by

– Conduction

– Convection

– Radiation

– Evaporation

25.2 Heat is gained or lost in four ways


Convection

Conduction

Evaporation

Radiation

25.3 Thermoregulation involves adaptations that balance heat gain and loss

Five general categories of adaptations promote thermoregulation


Increased metabolic heat production

– Hormonal changes boost metabolic rate in birds and mammals

– Shivering

– Increased physical activity

– Honeybees cluster and shiver



Insulation

– Hair

– Feathers

– Fat layers



Circulatory adaptations

– Increased or decreased blood flow to skin

– Large ears in elephants

– Countercurrent heat exchange



Blood frombody corein artery

33°C

Blood frombody corein artery

Blood returningto body corein vein

Blood returning tobody corein vein

27°

18°

9°

35°

30°

20°

10°

Evaporative cooling

– Sweating

– Panting



Behavioral responses

– Used by endotherms and ectotherms

– Examples

– Moving to the sun or shade

– Migrating

– Bathing



OSMOREGULATION AND EXCRETION


25.4 Animals balance the gain and loss of water and solutes through osmoregulation

Osmoconformers

– Have the same internal solute concentration as seawater

– Many marine invertebrates are osmoconformers


Osmoregulators control their solute concentrations

Freshwater fishes

– Gain water by osmosis

– Excrete excess water

– Pump salt across their gills



Osmotic water gain through gillsand other parts of body surface

Uptake ofsalt bygills

Uptake ofsome ionsin food

Excretion oflarge amounts ofwater in diluteurine from kidneys

Saltwater fish

– Lose water by osmosis

– Drink seawater

– Pump out excess salt



Osmotic water loss through gills and other parts of body surface

Excretion of saltfrom gills

Gain of water andsalt from foodand by drinkingseawater

Excretion of excessions and small amounts of water in scanty urine from kidneys

Land animals

– Gain water by drinking and eating

– Lose water by evaporation and waste disposal

– Conserve water using

– Kidneys

– Behavior adaptations

– Waterproof skin



25.5 EVOLUTION CONNECTION: A variety of ways to dispose of nitrogenous wastes have evolved in animals

Nitrogenous wastes are toxic breakdown products of protein

Animals dispose of nitrogenous wastes in different ways


Ammonia (NH3)

– Poisonous

– Soluble in water

– Easily disposed of by aquatic animals



Urea

– Less toxic

– Easier to store

– Some land animals save water by excreting uric acid

– A virtually dry waste

– Urea and uric acid take energy to produce



Nitrogenous bases

—NH2

Amino groups

Amino acids

Uric acid

Birds and many otherreptiles, insects, landsnails

Nucleic acidsProteins

Ammonia Urea

Mammals, amphibians,sharks, some bonyfishes

Most aquatic animals,including most fishes

25.6 The urinary system plays several major roles in homeostasis

The excretory system

– Expels wastes

– Regulates water balance

– Regulates ion balance


Aorta

Inferiorvena cava

Renal artery and vein

Urinary bladder

Kidney

Ureter

Urethra

Aorta

Inferiorvena cava

Renal pelvis

Ureter

Renal cortex

Renal artery and vein

Urinary bladder

KidneyUreter

Urethra

A The urinary system

Renal medulla

D Detailed structure of a nephron C Orientation of a nephron within the kidney

B The kidney

Renal cortex

Bowman’scapsule

To renalpelvis

Collectingduct

Renal artery

Renal vein

Tubule

Renal medulla

Bowman’scapsule

Arteriolefrom renalartery

Arteriolefromglomerulus

Glomerulus

Distaltubule

Proximal tubule

Branch ofrenal vein

Capillaries

Fromanothernephron

1

3

Loop of Henlewith capillarynetwork

2

Collectingduct

Nephrons

– Functional units of the kidneys

– Extract a filtrate from the blood

– Refine the filtrate to produce urine

Urine

– Ureters drain the kidneys

– Stored in the urinary bladder

– Expelled through the urethra


25.6 The urinary system plays several major roles in homeostasis

Animation: Nephron Introduction

Bowman’scapsule

Arteriolefrom renalartery

Arteriolefromglomerulus

Glomerulus

Distaltubule

Proximal tubule

Branch ofrenal vein

Capillaries

Fromanothernephron

Loop of Henlewith capillarynetwork

Collectingduct

3

1

2

25.7 Overview: The key processes of the urinary system are filtration, reabsorption, secretion, and excretion

Filtration

– Blood pressure forces water and many small solutes into the nephron

Reabsorption

– Valuable solutes are reclaimed from the filtrate


Secretion

– Excess H+ and toxins are added to the filtrate

Excretion

– The final product, urine, is excreted


25.7 Overview: The key processes of the urinary system are filtration, reabsorption, secretion, and excretion

Filtration

H2O, other small molecules

Capillary

Nephron tubuleReabsorption Secretion

Urine

Interstitial fluid

Excretion

Reabsorption in the proximal and distal tubules removes

– Nutrients

– Salt

– Water

pH is regulated by

– Reabsorption of HCO3–

– Secretion of H+

25.8 Blood filtrate is refined to urine through reabsorption and secretion


High NaCl concentration in the medulla promotes reabsorption of water

Antidiuretic hormone (ADH) regulates the amount of water excreted by the kidneys


25.8 Blood filtrate is refined to urine through reabsorption and secretion

Animation: Bowman’s Capsule and Proximal Tubule

Animation: Collecting Duct

Animation: Effect of ADH

Animation: Loop of Henle and Distal Tubule

Blood

Proximal tubule

Somedrugsand poisons

HCO3–

Nutrients

Medulla

Bowman’scapsule

Cortex

H+

NaClH2O

H2O

NaCl

HCO3–

H+

UreaGlucoseAmino acidsSome drugs

Filtrate composition

NaCl

H2O

NaCl

NaCl H2O

NaClH2O

HCO3–

H+K+

Distal tubule1

2

3

Reabsorption

Secretion

Filtrate movement

Loop ofHenle

Collectingduct

Urea

Urine (to renal pelvis)

Compensating for kidney failure

A dialysis machine

– Removes wastes from the blood

– Maintains its solute concentration

25.9 CONNECTION: Kidney dialysis can be a lifesaver


Line from arteryto apparatus

Pump Tubing made of aselectively permeablemembrane

DialyzingsolutionLine from

apparatusto vein

Fresh dialyzingsolution

Used dialyzingsolution(with urea andexcess ions)

FreshwaterFish

Land Animal

Saltwater Fish

Osmosis

Gain water Lose water

Excretion Pump in

Salt

Drinking Osmosis Excrete,pump out

Drinking,eating

Evaporation,urinary system

(a) (b) (c)

(d)(e)

(f)

(g)

(h)(i)

water andsolutes

endotherm

involves processes of

humankidney

Homeostasis

animal maybe

maintainsbalance of

both done by

requirementsdepend on

mechanismsmostly mechanisms

include

heat production,insulation,

countercurrentheat exchange

may be

ocean, fresh water,land

reproduction(where embryo

develops)

depends on

nitrogenouswastes

involvesremoval of

form may be

Bowman’scapsule

To renalvein

From renalartery

(a) (b)

Loop of Henle

Glomerulus

Tubule

Capillaries

Collecting duct

(d)

(c)

1. Describe four ways that heat is gained or lost by an animal

2. Describe five categories of adaptations that help animals thermoregulate

3. Compare the osmoregulatory problems of freshwater fish, saltwater fish, and terrestrial animals

You should now be able to


5. Compare the three ways that animals eliminate nitrogenous wastes

6. Describe the structure of the human kidney

7. Explain how the kidney promotes homeostasis

8. Describe four major processes that produce urine

9. Describe the key events in the conversion of filtrate into urine


You should now be able to

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