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Form Fits Function

Coordination of Body Systems

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Concept 40.3: Homeostatic processes for thermoregulation involve form, function, and behavior

Thermoregulation is the process by which

animals maintain an internal temperature within a tolerable range

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Endothermic animals generate heat by

metabolism; birds and mammals are endotherms

Ectothermic animals gain heat from external

sources; ectotherms include most invertebrates, fishes, amphibians, and nonavian reptiles

Endothermy and Ectothermy

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• In general, ectotherms tolerate greater variation in internal temperature, while endotherms are

active at a greater range of external temperatures

• Endothermy is more energetically expensive than ectothermy

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• Heat regulation in mammals often involves the integumentary system: skin, hair, and nails

• Five adaptations help animals thermoregulate:

– Insulation

– Circulatory adaptations

– Cooling by evaporative heat loss – Behavioral responses

– Adjusting metabolic heat production

© 2011 Pearson Education, Inc.

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Size and Metabolic Rate

• Metabolic rate is proportional to body mass to the power of three quarters (m3/4)

• Smaller animals have higher metabolic rates per gram than larger animals

• The higher metabolic rate of smaller animals

leads to a higher oxygen delivery rate, breathing rate, heart rate, and greater (relative) blood

volume, compared with a larger animal

© 2011 Pearson Education, Inc.

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Torpor and Energy Conservation

Torpor is a physiological state in which activity is low and metabolism decreases

• Torpor enables animals to save energy while avoiding difficult and dangerous conditions

Hibernation is long-term torpor that is an adaptation to winter cold and food scarcity

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Countercurrent heat exchange

Many birds, mammals, and some fish have

countercurrent heat exchangers, circulatory adaptations that allow heat to be transferred

from blood vessels containing warmer blood to those containing cooler blood. The arteries of their arms and legs run parallel to a set of deep veins.

To see how this works, let's look at an example

of a sea bird whose legs are wading in cold sea

water.

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Parallel pipes that flow in the opposite direction are called countercurrent.

Countercurrent heat exchangers transfer heat between fluids flowing in opposite directions and reduce heat loss.

Parallel pipes that flow in the same direction are called concurrent, and are not as efficient as countercurrent flow in retaining energy.

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External environment Food

Mouth

Animal body

Respiratory system CO2 O2

Lung tissue (SEM)

Cells

Interstitial fluid

Excretory system Circulatory

system

Nutrients

Digestive system

Heart

Blood vessels in kidney (SEM) Lining of small

intestine (SEM)

Anus

100 m

Unabsorbed matter (feces)

50 m250 m

Metabolic waste products (nitrogenous waste)

Figure 40.4

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Figure 40.6

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Chemical digestion of duodenum can be summarized as follow:

• 1. Carbohydrates – pancreatic amylases break starch, glycogen, and small polysaccharides into the disaccharide maltose. The breakdown of

maltose and other disaccharides (sucrose and lactose) into their monomers occurs at the wall of the duodenal epithelium.

• 2. Proteins: Pepsin begins breakdown of protein in stomach. In

duodenum, they are broken down into smaller chains of polypeptides and then into amino acids.

• 3. Nucleic Acids: Most of the enzymes responsible for nucleic acid

digestion enter the duodenum from the pancreas. The breakdown starts with hydrolysis of DNA and RNA into their respective nucleotides. The nucleotides are then broken down to nitrogenous bases, sugars, and phosphate groups.

• 4. Fats : Fats are emulsified by bile secreted by liver in the small intestine. The enzyme lipase, which is produced in the pancreas, hydrolyzes the small fat droplets into fatty acids and glycerol.

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Transport System for Nutrients

• The epithelial lining of small intestine has folds called villi, which in turn bear projections called microvilli-both of which radically increase the surface area available for absorption.

• In each villus are capillaries for the absorption of monomers, including monosaccharides and amino acids.

• Each villus also has a lymph vessel, termed a lacteal, which absorbs small fatty acids.

• Passive facilitated diffusion and active transport are used to move monomers across the intestinal membrane and into blood vessels.

• The capillaries and veins that drain the nutrients away from the villi flow into hepatic portal vein, a blood vessel that goes to the liver. The liver then regulates the distribution of nutrients to the body.

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Villi in Small Intestine

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• Air passes through the pharynx, larynx, trachea, bronchi, and bronchioles to the alveoli, where gas exchange occurs

• Exhaled air passes over the vocal cords in the larynx to create sounds

• Cilia and mucus line the epithelium of the air ducts and move particles up to the pharynx

• This “mucus escalator” cleans the respiratory system and allows particles to be swallowed into the

esophagus

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• Gas exchange takes place in alveoli, air sacs at the tips of bronchioles

• Oxygen diffuses through the moist film of the epithelium and into capillaries

• Carbon dioxide diffuses from the capillaries across the epithelium and into the air space

© 2011 Pearson Education, Inc.

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Bohr Effect

Carbon dioxide is carried in blood in the form of carbonic acid. Carbon dioxide reacts with water as shown in the following equation:

CO2+ H2O <---> H+ + HCO3-

As the amount of carbon dioxide increases, more H+ are formed and the pH will decrease. According to Bohr, the lower pH will cause Haemoglobin to

deliver more oxygen! The H+ displace the oxygen from hemoglobin.

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Haemoglobin

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Figure 42.32 Body tissue

Capillary wall Interstitial

fluid

Plasma within capillary

CO2 transport from tissues CO2 produced

CO2

CO2

CO2 H2O

H2CO3 Hb Red

blood

cell Carbonic acid

Hemoglobin (Hb) picks up CO2 and H+.

H+ HCO3 Bicarbonate

HCO3

HCO3

To lungs

CO2 transport to lungs

HCO3

H2CO3

H2O CO2

H+

Hb

Hemoglobin releases CO2 and H+.

CO2

CO2

CO2

Alveolar space in lung

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Open and Closed Circulatory Systems

• In insects, other arthropods, and most molluscs, blood bathes the organs directly in an open

circulatory system

• In an open circulatory system, there is no

distinction between blood and interstitial fluid, and this general body fluid is called hemolymph

© 2011 Pearson Education, Inc.

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Figure 42.3

(a) An open circulatory system Heart

Hemolymph in sinuses surrounding organs

Pores

Tubular heart

Dorsal vessel (main heart)

Auxiliary hearts Small branch vessels in each organ

Ventral vessels Blood

Interstitial fluid Heart

(b) A closed circulatory system

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In a closed circulatory system, blood is confined to vessels and is distinct from the interstitial fluid

• Closed systems are more efficient at transporting circulatory fluids to tissues and cells

• Annelids, cephalopods, and vertebrates have closed circulatory systems

© 2011 Pearson Education, Inc.

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Single Circulation

• Bony fishes, rays, and sharks have single circulation with a two-chambered heart

In single circulation, blood leaving the heart passes through two capillary beds before

returning

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Figure 42.4a

Bony fishes, rays, and sharks have single circulation with a two-chambered heart Blood leaving the heart passes through two capillary beds before returning.

Artery

Heart:

Atrium (A) Ventricle (V)

Vein

Gill

capillaries

Body

capillaries Key

Oxygen-rich blood Oxygen-poor blood

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Evolution of heart is evident by number of Heart Chambers

• Amphibians and reptile have a three-

chambered heart: two atria and one ventricle

• Mammals and birds have a four-chambered heart with two atria and two ventricles. The

left side of the heart pumps and receives only oxygen-rich blood, while the right side

receives and pumps only oxygen-poor blood Mammals and birds are endotherms and

require more O

2

than ectotherms

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Figure 42.4b

(b) Double circulation

Systemic circuit

Systemic capillaries Right Left

A A

V V

Lung

capillaries Pulmonary circuit

Key

Oxygen-rich blood Oxygen-poor blood

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Respiratory Surfaces Adaptation

• Animals require large, moist respiratory surfaces for exchange of gases between their cells and the respiratory medium, either air or water

• Gas exchange across respiratory surfaces takes place by diffusion

• Respiratory surfaces vary by animal and can

include the outer surface, skin, gills, tracheae, and lungs

© 2011 Pearson Education, Inc.

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Gills in Aquatic Animals

• Gills are outfoldings of the body that create a large surface area for gas exchange

© 2011 Pearson Education, Inc.

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Ventilation moves the respiratory medium over the respiratory surface

• Aquatic animals move through water or move water over their gills for ventilation

Fish gills use a countercurrent exchange system, where blood flows in the opposite

direction to water passing over the gills; blood is always less saturated with O2 than the water it meets

© 2011 Pearson Education, Inc.

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Figure 42.23

Gill arch

O2-poor blood O2-rich blood

Blood vessels Gill arch Operculum

Water flow

Water flow

Blood flow

Countercurrent exchange PO (mm Hg) in water

2 150

PO (mm Hg) in blood 2

120 90 60 30 140 110 80 50 20

Net diffu- sion of O2

Lamella

Gill filaments

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Energetics of Osmoregulation

• Osmoregulators must expend energy to maintain osmotic gradients

• The amount of energy differs based on

– How different the animal’s osmolarity is from its surroundings

– How easily water and solutes move across the animal’s surface

– The work required to pump solutes across the membrane

© 2011 Pearson Education, Inc.

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Figure 44.3

(a) Osmoregulation in a marine fish (b) Osmoregulation in a freshwater fish Gain of water

and salt ions from food

Excretion of salt ions from gills

Osmotic water loss through gills and other parts of body surface

Gain of water and salt ions from drinking seawater

Excretion of salt ions and small amounts of water in scanty urine from kidneys

Gain of water and some ions in food

Uptake of salt ions by gills

Osmotic water gain through gills and other parts of body surface

Excretion of salt ions and large amounts of water in dilute urine from kidneys Key

Water Salt

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Concept 44.2: An animal’s nitrogenous wastes reflect its phylogeny and habitat

• The type and quantity of an animal’s waste products may greatly affect its water balance

• Among the most significant wastes are

nitrogenous breakdown products of proteins and nucleic acids

Some animals convert toxic ammonia (NH3) to less toxic compounds prior to excretion

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Figure 44.8

Proteins Nucleic acids

Amino acids

Nitrogenous bases

—NH2 Amino groups

Most aquatic animals, including

most bony fishes

Mammals, most amphibians, sharks,

some bony fishes

Many reptiles (including birds), insects, land snails

Ammonia Urea Uric acid

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Urea

• The liver of mammals and most adult

amphibians converts ammonia to the less toxic urea

• The circulatory system carries urea to the kidneys, where it is excreted

• Conversion of ammonia to urea is energetically expensive; excretion of urea requires less

water than ammonia

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Uric Acid

• Insects, land snails, and many reptiles, including birds, mainly excrete uric acid

• Uric acid is relatively nontoxic and does not dissolve readily in water

• It can be secreted as a paste with little water loss

• Uric acid is more energetically expensive to produce than urea

© 2011 Pearson Education, Inc.

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The Influence of Evolution and

Environment on Nitrogenous Wastes

• The kinds of nitrogenous wastes excreted

depend on an animal’s evolutionary history and habitat, especially water availability

• Another factor is the immediate environment of the animal egg

• The amount of nitrogenous waste is coupled to the animal’s energy budget

© 2011 Pearson Education, Inc.

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Excretory Processes

• Most excretory systems produce urine by refining a filtrate derived from body fluids

• Key functions of most excretory systems – Filtration: Filtering of body fluids

– Reabsorption: Reclaiming valuable solutes – Secretion: Adding nonessential solutes and

wastes from the body fluids to the filtrate – Excretion: Processed filtrate containing

nitrogenous wastes, released from the body

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Figure 44.10

Capillary

Filtration

Excretory tubule

Reabsorption

Secretion

Excretion

FiltrateUrine

2 1

3

4

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Malpighian Tubules

• In insects and other terrestrial arthropods, Malpighian tubules remove nitrogenous wastes from hemolymph and function in osmoregulation

• Insects produce a relatively dry waste matter, mainly uric acid, an important adaptation to terrestrial life

• Some terrestrial insects can also take up water from the air

© 2011 Pearson Education, Inc.

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Digestive tract

Midgut (stomach)

Malpighian tubules

Rectum

Intestine Hindgut

Salt, water, and nitrogenous

wastes

Feces and urine Malpighian

tubule

To anus

Rectum

Reabsorption

HEMOLYMPH

Figure 44.13

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Birds and Other Reptiles

• Birds have shorter loops of Henle but

conserve water by excreting uric acid instead of urea

• Other reptiles have only cortical nephrons but also excrete nitrogenous waste as uric acid

© 2011 Pearson Education, Inc.

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Figure 44.14a

Human Excretory Organs

Posterior vena cava

Renal artery and vein

Aorta Ureter Urinary bladder

Urethra

Kidney

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Figure 44.14b

Kidney Structure

Renal cortex Renal medulla Renal artery Renal vein

Ureter

Renal pelvis

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Nephron – Functional unit of Kidney

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Concept 44.4: The nephron is organized for stepwise processing of blood filtrate

• The filtrate produced in Bowman’s capsule

contains salts, glucose, amino acids, vitamins, nitrogenous wastes, and other small molecules

© 2011 Pearson Education, Inc.

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From Blood Filtrate to Urine: A Closer Look

Proximal Tubule

• Reabsorption of ions, water, and nutrients takes place in the proximal tubule

• Molecules are transported actively and passively from the filtrate into the interstitial fluid and then capillaries

• Some toxic materials are actively secreted into the filtrate

• As the filtrate passes through the proximal tubule, materials to be excreted become concentrated

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Proximal tubule Distal tubule

Filtrate CORTEX

Loop of Henle

OUTER MEDULLA

INNER MEDULLA Key

Active transport Passive transport

Collecting duct

Nutrients NaCl

NH3 HCO3 H2O K

H

NaCl H2O

HCO3

K H

H2O

NaCl

NaCl

NaCl H2O

Urea Figure 44.15

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Descending Limb of the Loop of Henle

• Reabsorption of water continues through channels formed by aquaporin proteins

• Movement is driven by the high osmolarity of

the interstitial fluid, which is hyperosmotic to the filtrate

• The filtrate becomes increasingly concentrated

© 2011 Pearson Education, Inc.

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Ascending Limb of the Loop of Henle

• In the ascending limb of the loop of Henle, salt but not water is able to diffuse from the tubule into the interstitial fluid

• The filtrate becomes increasingly dilute

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Distal Tubule

• The distal tubule regulates the K+ and NaCl concentrations of body fluids

• The controlled movement of ions contributes to pH regulation

© 2011 Pearson Education, Inc.

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Collecting Duct

• The collecting duct carries filtrate through the medulla to the renal pelvis

• One of the most important tasks is reabsorption of solutes and water

• Urine is hyperosmotic to body fluids

© 2011 Pearson Education, Inc.

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Solute Gradients and Water Conservation

• The mammalian kidney’s ability to conserve water is a key terrestrial adaptation

• Hyperosmotic urine can be produced only

because considerable energy is expended to transport solutes against concentration

gradients

• The two primary solutes affecting osmolarity are NaCl and urea

© 2011 Pearson Education, Inc.

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Antidiuretic Hormone

• The osmolarity of the urine is regulated by nervous and hormonal control

Antidiuretic hormone (ADH) makes the

collecting duct epithelium more permeable to water

• An increase in osmolarity triggers the release of ADH, which helps to conserve water

© 2011 Pearson Education, Inc.

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Figure 44.19-2

Thirst

Hypothalamus

ADH

Pituitary gland Osmoreceptors in hypothalamus trigger

release of ADH.

STIMULUS:

Increase in blood osmolarity (for

instance, after sweating profusely)

Homeostasis:

Blood osmolarity (300 mOsm/L) Drinking reduces

blood osmolarity to set point.

H2O reab- sorption helps prevent further

osmolarity increase.

Increased permeability Distal

tubule

Collecting duct

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• Binding of ADH to receptor molecules leads to a temporary increase in the number of

aquaporin proteins in the membrane of collecting duct cells

© 2011 Pearson Education, Inc.

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Collecting duct

ADH receptor

COLLECTING DUCT CELL

LUMEN

Second-messenger signaling molecule Storage

vesicle

Aquaporin water

channel

Exocytosis

H2O

H2O

ADH

cAMP

Figure 44.20

References

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