homeostasis and endocrine signaling

CAMPBELL BIOLOGY IN FOCUS

© 2014 Pearson Education, Inc.

Urry • Cain • Wasserman • Minorsky • Jackson • Reece

Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge

32Homeostasis and Endocrine Signaling


What is osmosis?

Why is it important in cells?


Concept 32.3: A shared system mediates osmoregulation and excretion in many animals

Osmoregulation is the general term for the processes by which animals control solute concentrations in the interstitial fluid and balance water gain and loss


Osmosis and Osmolarity

Cells require a balance between uptake and loss of water

Osmolarity, the solute concentration of a solution, determines the movement of water across a selectively permeable membrane

If two solutions are isoosmotic, the movement of water is equal in both directions

If two solutions differ in osmolarity, the net flow of water is from the hypoosmotic to the hyperosmotic solution


Figure 32.15

Gain of water andsalt ions from food

SALT WATER

Gain of waterand salt ions from drinking seawater

Excretion ofsalt ions from gills

Gain of water andsome ions in food

Excretion of salt ions andsmall amounts of water inscanty urine from kidneys

FRESH WATER

Osmotic water lossthrough gills andother parts of bodysurface

Uptake ofsalt ions by gills

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

Osmotic water gainthrough gills andother parts of bodysurface

Salt

Water

Key

(a) Osmoregulation in a marine fish

(b) Osmoregulation in a freshwater fish


Marine and freshwater organisms have opposite challenges

Marine fish drink large amounts of seawater to balance water loss and excrete salt through their gills and kidneys

Freshwater fish drink almost no water and replenish salts through eating; some also replenish salts by uptake across the gills


What do you think the difference between osmoregulators and osmoconformers might be?


Osmoregulatory Challenges and Mechanisms

Osmoconformers, consisting of some 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 or hypoosmotic environment


What are the 3 different ways you can excrete nitrogenous wastes?


Figure 32.16

Most aquaticanimals, includingmost bony fishes

Proteins Nucleic acids

Aminoacids

Nitrogenousbases

Amino groups

Mammals, mostamphibians, sharks,

some bony fishes

Many reptiles(including birds),

insects, land snails

Ammonia Urea Uric acid


Nitrogenous Wastes

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


Ammonia excretion is most common in aquatic organisms

Vertebrates excrete urea, a conversion product of ammonia, which is much less toxic

Insects, land snails, and many reptiles including birds excrete uric acid as a semisolid paste

It is less toxic than ammonia and generates very little water loss, but it is energetically more expensive to produce than urea


Figure 32.18

Tubules ofprotonephridia

Tubule

Openingin bodywall

Flamebulb Interstitial

fluid filtersthroughmembrane.

Tubulecell

Cilia

Nucleusof cap cell


Invertebrates

Flatworms have excretory systems called protonephridia, networks of dead-end tubules connected to external openings

The smallest branches of the network are capped by a cellular unit called a flame bulb

These tubules excrete a dilute fluid and function in osmoregulation


In insects and other terrestrial arthropods, Malpighian tubules remove nitrogenous wastes from hemolymph without a filtration step

Insects produce a relatively dry waste matter, mainly uric acid


Vertebrates

In vertebrates and some other chordates, the kidney functions in both osmoregulation and excretion

The kidney consists of tubules arranged in an organized array and in contact with a network of capillaries

The excretory system includes ducts and other structures that carry urine from the tubules out of the body

Animation: Nephron Introduction


In humans, how do we remove these wastes?


Figure 32.19a

Excretory Organs

Posterior vena cava

Renal artery and vein

Aorta

Ureter

Urinary bladder

Urethra

Kidney


Figure 32.19b

Kidney Structure

Renal cortex

Nephron Organization

Nephron Types

Renal medulla

Renal artery

Renal vein

Renal pelvis

Ureter

Renal cortex

Renal medulla

Cortical nephron

Juxtamedullary nephron

Collectingduct

Branch ofrenal vein

Vasarecta

Efferentarteriole

fromglomerulus

Distaltubule

Afferent arteriolefrom renal artery

Glomerulus

Bowman’scapsule

Proximaltubule

Peritubularcapillaries

Descendinglimb

Ascendinglimb

Loop of

Henle


What are the steps in urine formation?


Many animal species 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: Releasing processed filtrate containing nitrogenous wastes from the body


Figure 32.17

CapillaryFiltration

Excretorytubule

Filtrate

Reabsorption

SecretionU

rine

Excretion


Concept 32.4: Hormonal circuits link kidney function, water balance, and blood pressure

The capillaries and specialized cells of Bowman’s capsule are permeable to water and small solutes but not blood cells or large molecules

The filtrate produced there contains salts, glucose, amino acids, vitamins, nitrogenous wastes, and other small molecules


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


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 all along its journey down the descending limb


Ascending limb of the loop of Henle

The ascending limb has a transport epithelium that lacks water channels

Here, salt but not water is able to move from the tubule into the interstitial fluid

The filtrate becomes increasingly dilute as it moves up to the cortex


Distal tubule

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

The controlled movement of ions contributes to pH regulation


Collecting duct The collecting duct carries filtrate through the

medulla to the renal pelvis

Most of the water and nearly all sugars, amino acids, vitamins, and other nutrients are reabsorbed into the blood

Urine is hyperosmotic to body fluids

Animation: Bowman’s Capsule

Animation: Collecting Duct

Animation: Loop of Henle


Figure 32.20

Filtrate

OUTERMEDULLA

H2OSalts (NaCI and others)

HCO3−

Glucose, amino acids

H

Some drugs

Passive transportActive transport

Key

INNERMEDULLA

CORTEX

Descending limbof loop of Henle

H2O

Interstitialfluid

NH3H

NutrientsHCO3

− K

NaCI

Proximal tubule

H2O

Thick segmentof ascending limb

H

Urea

HCO3−

K

NaCI

Distal tubule

H2O

Thin segmentof ascending limb

NaCI

H2ONaCI

NaCI

Collectingduct

1

23

5

4

3Urea


Figure 32.20a


CORTEX

Interstitialfluid

NH3H

NutrientsHCO3

− K

NaCI

Proximal tubule

H2O

H

HCO3−

K

NaCI

Distal tubule

H2O

1

Filtrate

4


Figure 32.20b

OUTERMEDULLA


INNERMEDULLA

Descending limbof loop of Henle

H2O

Thick segmentof ascending limb

Urea

Thin segmentof ascending limb

NaCI

H2ONaCI

NaCI

Collectingduct

23

3 5


Concentrating Urine in the Mammalian Kidney

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


Figure 32.21-1

Passivetransport

Activetransport

mOsm/L

CORTEX

OUTERMEDULLA

INNERMEDULLA

300

H2O

1,200

900

600

400

300

300

H2O

H2O

H2O

H2O

H2O

H2O

300

400

900

600

1,200


Figure 32.21-2

Passivetransport

Activetransport

mOsm/L

CORTEX

OUTERMEDULLA

INNERMEDULLA

300

H2O

1,200

900

600

400

300

300

H2O

H2O

H2O

H2O

H2O

H2O

NaCI

NaCI

NaCI

NaCI

NaCI

NaCI

NaCI

100

100

200

400

700

300

400

900

600

1,200


Figure 32.21-3

Passivetransport

Activetransport

H2O

mOsm/L

CORTEX

Urea

OUTERMEDULLA

INNERMEDULLA

300

NaCI

H2O

H2O

1,200

900

600

400

300

300

H2O

H2O

H2O

H2O

H2O

H2O

NaCI

NaCI

NaCI

NaCI

NaCI

NaCI

NaCI

100

100

200

400

700

300 300

400400

600

1,200

900

600

1,200

Urea

Urea

NaCI

H2O

H2O

H2O

H2O

H2O


Water and salt are reabsorbed from the filtrate passing from Bowman’s capsule to the proximal tubule

In the proximal tubule, filtrate volume decreases, but its osmolarity remains the same

As filtrate flows down the descending limb of the loop of Henle, water leaves the tubule, increasing osmolarity of the filtrate

Salt diffusing from the ascending limb maintains a high osmolarity in the interstitial fluid of the renal medulla


The loop of Henle and surrounding capillaries act as a type of countercurrent system

This system involves active transport and thus an expenditure of energy

Such a system is called a countercurrent multiplier system


The filtrate in the ascending limb of the loop of Henle is hypoosmotic to the body fluids by the time it reaches the distal tubule

The filtrate descends to the collecting duct, which is permeable to water but not to salt

Osmosis extracts water from the filtrate to concentrate salts, urea, and other solutes in the filtrate


Adaptations of the Vertebrate Kidney to Diverse Environments

Variations in nephron structure and function equip the kidneys of different vertebrates for osmoregulation in their various habitats


Desert-dwelling mammals excrete the most hyperosmotic urine and have long loops of Henle

Birds have shorter loops of Henle but conserve water by excreting uric acid instead of urea


Mammals control the volume and osmolarity of urine

The kidneys of the South American vampire bat can produce either very dilute or very concentrated urine

This allows the bats to reduce their body weight rapidly or digest large amounts of protein while conserving water


Figure 32.22


Homeostatic Regulation of the Kidney

A combination of nervous and hormonal inputs regulates the osmoregulatory function of the kidney

These inputs contribute to homeostasis for blood pressure and volume through their effect on amount and osmoregulatory of urine


Antidiuretic Hormone

Antidiuretic hormone (ADH) makes the collecting duct epithelium temporarily more permeable to water

An increase in blood osmolarity above a set point triggers the release of ADH, which helps to conserve water

Decreased osmolarity causes a drop in ADH secretion and a corresponding decrease in permeability of collecting ducts

Animation: Effect of ADH


Figure 32.23-1

STIMULUS:Increasein blood

osmolarity

Osmoreceptorstrigger release

of ADH.

ADH


Figure 32.23-2

Distaltubule STIMULUS:

Increasein blood

osmolarity

Increasedpermeability


of ADH.Thirst

ADH

Collecting duct


Figure 32.23-3

Distaltubule

H2Oreabsorption

STIMULUS:Increasein blood

osmolarity

Drinkingof fluids

Increasedpermeability


of ADH.Thirst

ADH

Collecting duct

Homeostasis


The Renin-Angiotensin-Aldosterone System

The renin-angiotensin-aldosterone system (RAAS) also regulates kidney function

A drop in blood pressure near the glomerulus causes the juxtaglomerular apparatus (JGA) to release the enzyme renin

Renin triggers the formation of the peptide angiotensin II


Figure 32.24-1

STIMULUS: Low blood

pressure

JGA releasesrenin.

Distaltubule

Juxtaglomerularapparatus (JGA)

Renin


Figure 32.24-2

ACE

STIMULUS: Low blood

pressure

JGA releasesrenin.

Distaltubule


Renin

Angiotensin II

Angiotensin I

Angiotensinogen

Liver


Figure 32.24-3

ACE

STIMULUS: Low blood

pressure

JGA releasesrenin.

Distaltubule


Renin

Arteriolesconstrict.

Angiotensin II

Angiotensin I

Angiotensinogen

Liver


Figure 32.24-4

ACE

Na and H2O reabsorbed.

STIMULUS: Low blood

pressure

JGA releasesrenin.

Distaltubule


Renin

Aldosterone

Homeostasis

Arteriolesconstrict.

Adrenal gland

Angiotensin II

Angiotensin I

Angiotensinogen

Liver


Angiotensin II

Raises blood pressure and decreases blood flow to capillaries in the kidney

Stimulates the release of the hormone aldosterone, which increases blood volume and pressure


Coordination of ADH and RAAS Activity

ADH and RAAS both increase water reabsorption

ADH responds to changes in blood osmolarity

RAAS responds to changes in blood volume and pressure

Thus, ADH and RAAS are partners in homeostasis

homeostasis and endocrine signaling

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