Biology in Focus - Chapter 31
Transcript of Biology in Focus - Chapter 31
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CAMPBELL BIOLOGY IN FOCUS
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Urry • Cain • Wasserman • Minorsky • Jackson • Reece
Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge
32Homeostasis and Endocrine Signaling
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Overview: Diverse Forms, Common Challenges
Anatomy is the study of the biological form of an organism
Physiology is the study of the biological functions an organism performs
Form and function are closely correlated
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Figure 32.1
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Concept 32.1: Feedback control maintains the internal environment in many animals
Multicellularity allows for cellular specialization with particular cells devoted to specific activities
Specialization requires organization and results in an internal environment that differs from the external environment
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Hierarchical Organization of Animal Bodies
Cells form a functional animal body through emergent properties that arise from levels of structural and functional organization
Cells are organized into Tissues, groups of cells with similar appearance and
common function Organs, different types of tissues organized into
functional units Organ systems, groups of organs that work together
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Table 32.1
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The specialized, complex organ systems of animals are built from a limited set of cell and tissue types
Animal tissues can be grouped into four categories Epithelial Connective Muscle Nervous
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Figure 32.2
Axons of neurons
Skeletal muscle tissue
Bloodvessel
Looseconnectivetissue
Blood
Epithelial tissue
Collagenousfiber
Epithelial tissue
Lumen 10 m
Basal surface
Apical surfaceNervous tissue
Glia 20 m
PlasmaWhiteblood cells
(Con
foca
l LM
)
50
m
Red blood cells
100 mElastic fiber
Nuclei
Musclecell
100 m
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Figure 32.2a
Epithelial tissue
Lumen 10 m
Basal surface
Apical surface
Epithelial tissue
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Figure 32.2b
Axons of neurons
Bloodvessel
Nervous tissueGlia 20 m
(Con
foca
l LM
)
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Figure 32.2c
Loose connective tissue
Collagenousfiber
100 mElastic fiber
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Figure 32.2d
Blood
PlasmaWhiteblood cells
50
m
Red blood cells
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Figure 32.2e
Skeletal muscle tissue
Nuclei
Musclecell
100 m
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Regulating and Conforming
Faced with environmental fluctuations, animals manage their internal environment by either regulating or conforming
An animal that is a regulator uses internal mechanisms to control internal change despite external fluctuation
An animal that is a conformer allows its internal condition to change in accordance with external changes
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Figure 32.3
River otter (temperature regulator)40
Largemouth bass (temperature conformer)
Ambient (environmental) temperature (C)
30
20
10
00 40302010
Bod
y te
mpe
ratu
re (
C)
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An animal may regulate some internal conditions and not others
For example, a fish may conform to surrounding temperature in the water, but it regulates solute concentrations in its blood and interstitial fluid (the fluid surrounding body cells)
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Homeostasis
Organisms use homeostasis to maintain a “steady state” or internal balance regardless of external environment
In humans, body temperature, blood pH, and glucose concentration are each maintained at a constant level
Regulation of room temperature by a thermostat is analogous to homeostasis
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Figure 32.4
Sensor/control center:Thermostatturns heater off.
Sensor/control center:Thermostatturns heater on.
Stimulus:Room
temperatureincreases.
Stimulus:Room
temperaturedecreases.
Roomtemperatureincreases.
Roomtemperaturedecreases.
Set point:Room temperature
at 20C
Response:Heating stops.
Response:Heating starts.
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Figure 32.4a
Sensor/control center:Thermostatturns heater off.
Stimulus:Room
temperatureincreases.
Roomtemperaturedecreases.
Set point:Room temperature
at 20C
Response:Heating stops.
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Figure 32.4b
Sensor/control center:Thermostatturns heater on.
Stimulus:Room
temperaturedecreases.
Roomtemperatureincreases.
Set point:Room temperature
at 20C
Response:Heating starts.
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Animals achieve homeostasis by maintaining a variable at or near a particular value, or set point
Fluctuations above or below the set point serve as a stimulus; these are detected by a sensor and trigger a response
The response returns the variable to the set point
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Homeostasis in animals relies largely on negative feedback, a control mechanism that reduces the stimulus
Homeostasis moderates, but does not eliminate, changes in the internal environment
Set points and normal ranges for homeostasis are usually stable, but certain regulated changes in the internal environment are essential
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Thermoregulation: A Closer Look
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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Endotherms can maintain a stable body temperature in the face of large fluctuations in environmental temperature
Ectotherms may regulate temperature by behavioral means
Ectotherms generally need to consume less food than endotherms, because their heat source is largely environmental
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Figure 32.5
(a) A walrus, an endotherm
(b) A lizard, an ectotherm
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Figure 32.5a
(a) A walrus, an endotherm
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Figure 32.5b
(b) A lizard, an ectotherm
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Balancing Heat Loss and Gain
Organisms exchange heat by four physical processes Radiation Evaporation Convection Conduction
Heat is always transferred from an object of higher temperature to one of lower temperature
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Figure 32.6Radiation
Convection
Evaporation
Conduction
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In response to changes in environmental temperature, animals can alter blood (and heat) flow between their body core and their skin
Vasodilation, the widening of the diameter of superficial blood vessels, promotes heat loss
Vasoconstriction, the narrowing of the diameter of superficial blood vessels, reduces heat loss
Circulatory Adaptations for Thermoregulation
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The arrangement of blood vessels in many marine mammals and birds allows for countercurrent exchange
Countercurrent heat exchangers transfer heat between fluids flowing in opposite directions and reduce heat loss
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Figure 32.7
Canada goose
Blood flow
Artery Vein
Heat transfer
Cool bloodWarm blood
Key
30
35C
9
20
10
18
27
33
2
31
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Birds and mammals can vary their insulation to acclimatize to seasonal temperature changes
Acclimatization in ectotherms often includes adjustments at the cellular level
Some ectotherms that experience subzero temperatures can produce “antifreeze” compounds to prevent ice formation in their cells
Acclimatization in Thermoregulation
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Physiological Thermostats and Fever
Thermoregulation in mammals is controlled by a region of the brain called the hypothalamus
The hypothalamus triggers heat loss or heat-generating mechanisms
Fever is the result of a change to the set point for a biological thermostat
Animation: Negative Feedback
Animation: Positive Feedback
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Figure 32.8Sensor/controlcenter: Thermostatin hypothalamus
Stimulus:Decreased body
temperature
Bodytemperatureincreases.
Bodytemperaturedecreases.
Homeostasis:Internal body
temperature ofapproximately
36–38C
Response:Blood vesselsin skin dilate.
Response: Shivering
Sensor/controlcenter: Thermostatin hypothalamus
Response:Blood vesselsin skin constrict.
Stimulus:Increased body
temperature
Response: Sweat
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Figure 32.8a
Sensor/controlcenter: Thermostatin hypothalamus
Bodytemperaturedecreases.
Homeostasis:Internal body
temperature ofapproximately
36–38C
Response:Blood vesselsin skin dilate.
Stimulus:Increased body
temperature
Response: Sweat
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Figure 32.8b
Stimulus:Decreased body
temperature
Bodytemperatureincreases.
Homeostasis:Internal body
temperature ofapproximately
36–38C
Response: Shivering
Sensor/controlcenter: Thermostatin hypothalamus
Response:Blood vesselsin skin constrict.
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Concept 32.2: Endocrine signals trigger homeostatic mechanisms in target tissues
There are two major systems for controlling and coordinating responses to stimuli: the endocrine and nervous systems
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Coordination and Control Functions of the Endocrine and Nervous Systems
In the endocrine system, signaling molecules released into the bloodstream by endocrine cells reach all locations in the body
In the nervous system, neurons transmit signals along dedicated routes, connecting specific locations in the body
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Signaling molecules sent out by the endocrine system are called hormones
Hormones may have effects in a single location or throughout the body
Only cells with receptors for a certain hormone can respond to it
The endocrine system is well adapted for coordinating gradual changes that affect the entire body
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Figure 32.9
Cellbody ofneuron
Response
Hormone
Nerveimpulse
Signaltravelseverywhere.
Signaltravels toa specificlocation.
Response
Stimulus Stimulus
Nerveimpulse
Blood vessel
Endocrinecell
(a) Signaling by hormones
Axons
Axon
(b) Signaling by neurons
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Figure 32.9a
Cellbody ofneuron
Hormone
Signaltravelseverywhere.
Signaltravels toa specificlocation.
Stimulus Stimulus
Nerveimpulse
Blood vessel
Endocrinecell
(a) Signaling by hormones
Axon
(b) Signaling by neurons
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In the nervous system, signals called nerve impulses travel along communication lines consisting mainly of axons
Other neurons, muscle cells, and endocrine and exocrine cells can all receive nerve impulses
Nervous system communication usually involves more than one type of signal
The nervous system is well suited for directing immediate and rapid responses to the environment
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Figure 32.9b
Response
Nerveimpulse
Response
Blood vessel
(a) Signaling by hormones
Axons
(b) Signaling by neurons
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Simple Endocrine Pathways
Digestive juices in the stomach are extremely acidic and must be neutralized before the remaining steps of digestion take place
Coordination of pH control in the duodenum relies on an endocrine pathway
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Figure 32.10
Response
Hormone
Low pH induodenum
S cells of duodenumsecrete the hormonesecretin ( ).
Pancreas
Stimulus
Blood vessel
Endocrinecell
Pathway Example
Bicarbonate release
Targetcells
Neg
ativ
e fe
edba
ck
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The release of acidic stomach contents into the duodenum stimulates endocrine cells there to secrete the hormone secretin
This causes target cells in the pancreas to raise the pH in the duodenum
The pancreas can act as an exocrine gland, secreting substances through a duct, or as an endocrine gland, secreting hormones directly into interstitial fluid
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Neuroendocrine Pathways
Hormone pathways that respond to stimuli from the external environment rely on a sensor in the nervous system
In vertebrates, the hypothalamus integrates endocrine and nervous systems
Signals from the hypothalamus travel to a gland located at its base, called the pituitary gland
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Figure 32.11a
PancreasInsulinGlucagon
Testes(in males)Androgens
Parathyroid glandsParathyroid hormone (PTH)
Ovaries (in females)EstrogensProgestins
Thyroid glandThyroid hormone(T3 and T4)Calcitonin
Pineal glandMelatonin
Major Endocrine Glandsand Their Hormones
Hypothalamus
Pituitary gland Anterior pituitary
Posterior pituitaryOxytocinVasopressin(antidiuretichormone, ADH)
Adrenal glands(atop kidneys)
Adrenal medullaEpinephrine and norepinephrine Adrenal cortexGlucocorticoids Mineralocorticoids
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Figure 32.11b
Posteriorpituitary
Neurosecretorycells of the hypothalamus
Hypothalamichormones
Hypothalamus
Testes orovaries
Portal vessels
Pituitary hormones
Anterior pituitaryEndocrine cells
Thyroidgland
Adrenalcortex
Mammaryglands
Melanocytes Liver, bones,other tissues
HORMONE
TARGET
ProlactinFSH TSH ACTH MSH GH
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Figure 32.11ba
Posteriorpituitary
Neurosecretorycells of the hypothalamus
Hypothalamichormones
Hypothalamus
Portal vessels
Pituitary hormones
Anterior pituitaryEndocrine cells
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Figure 32.11bb
Adrenocorticotropichormone
Follicle-stimulating hormoneLuteinizing hormone
Testes orovaries
Melanocyte- stimulating hormone
Thyroidgland
Adrenalcortex
Mammaryglands
Melanocytes Liver, bones,other tissues
HORMONE
TARGET
Prolactin Growthhormone
Thyroid-stimulatinghormone
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Figure 32.11c
TSH circulationthroughout body
Anteriorpituitary
Thyroidgland
Stimulus
Response
Thyroidhormone
Thyroid hormonecirculationthroughoutbody
TSH
−
TRH
Neurosecretory cell
Neg
ativ
e fe
edba
ck
Hypothalamus−
Sensoryneuron
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Figure 32.11d
Thyroid scan
Low level ofiodine uptake
High level ofiodine uptake
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Hormonal signals from the hypothalamus trigger synthesis and release of hormones from the anterior pituitary
The posterior pituitary is an extension of the hypothalamus and secretes oxytocin, which regulates release of milk during nursing in mammals
It also secretes antidiuretic hormone (ADH)
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Figure 32.12Pathway
Sensoryneuron
Posi
tive
feed
back
Hypothalamus/posterior pituitary
Example
SucklingStimulus
Neuro-secretory cell
Smoothmuscle inbreasts
Neuro-hormone
BloodvesselTarget
cells
Response Milk release
Posteriorpituitarysecretes theneurohormoneoxytocin ( ).
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Feedback Regulation in Endocrine Pathways
A feedback loop links the response back to the original stimulus in an endocrine pathway
While negative feedback dampens a stimulus, positive feedback reinforces a stimulus to increase the response
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Pathways of Water-Soluble and Lipid-Soluble Hormones
The hormones discussed thus far are proteins that bind to cell-surface receptors and that trigger events leading to a cellular response
The intracellular response is called signal transduction
A signal transduction pathway typically has multiple steps
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Lipid-soluble hormones have receptors inside cells When bound by the hormone, the hormone-
receptor complex moves into the nucleus There, the receptor alters transcription of particular
genes
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Multiple Effects of Hormones
Many hormones elicit more than one type of response
For example, epinephrine is secreted by the adrenal glands and can raise blood glucose levels, increase blood flow to muscles, and decrease blood flow to the digestive system
Target cells vary in their response to a hormone because they differ in their receptor types or in the molecules that produce the response
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Figure 32.13
Different cellular responses
Same receptors but differentintracellular proteins (not shown)
Glycogenbreaks downand glucoseis releasedfrom cell.
Different cellular responses
Different receptors
Glycogendeposits
Vesseldilates.
Vesselconstricts.
(c) Intestinal bloodvessel
(b) Skeletal muscle blood vessel
(a) Liver cell
Epinephrine
receptor
Epinephrine
receptor
Epinephrine
receptor
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Evolution of Hormone Function
Over the course of evolution the function of a given hormone may diverge between species
For example, thyroid hormone plays a role in metabolism across many lineages, but in frogs it has taken on a unique function: stimulating the resorption of the tadpole tail during metamorphosis
Prolactin also has a broad range of activities in vertebrates
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Figure 32.14
Tadpole
Adult frog
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Figure 32.14a
Tadpole
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Figure 32.14b
Adult frog
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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
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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
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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
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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
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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
SaltWater
Key
(a) Osmoregulation in a marine fish
(b) Osmoregulation in a freshwater fish
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Figure 32.15a
Gain of water andsalt ions from food
SALT WATER
Gain of waterand salt ions from drinking seawater
Excretion ofsalt ions from gills
Excretion of salt ions andsmall amounts of water inscanty urine from kidneys
Osmotic water lossthrough gills andother parts of bodysurface
SaltWater
(a) Osmoregulation in a marine fish
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Figure 32.15b
Gain of water andsome ions in food
FRESH WATER
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
SaltWater
(b) Osmoregulation in a freshwater fish
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Land animals have mechanisms to prevent dehydration
Most have body coverings that help reduce water loss
They drink water and eat moist foods, and they produce water metabolically
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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
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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
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Figure 32.16a
Most aquaticanimals, includingmost bony fishes
Mammals, mostamphibians, sharks,
some bony fishes
Many reptiles(including birds),
insects, land snails
Ammonia Urea Uric acid
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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
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Excretory Processes
In most animals, osmoregulation and metabolic waste disposal rely on transport epithelia
These layers of epithelial cells are specialized for moving solutes in controlled amounts in specific directions
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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
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Figure 32.17
CapillaryFiltration
Excretorytubule
Filtrate
Reabsorption
SecretionU
rine
Excretion
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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
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Figure 32.18
Tubules ofprotonephridia
TubuleOpeningin bodywall
Flamebulb Interstitial
fluid filtersthroughmembrane.
Tubulecell
Cilia
Nucleusof cap cell
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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
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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
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Figure 32.19a
Excretory Organs
Posterior vena cavaRenal artery and vein
Aorta
Ureter
Urinary bladder
Urethra
Kidney
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Figure 32.19b
Kidney StructureRenal 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
GlomerulusBowman’scapsule
Proximaltubule
Peritubularcapillaries
Descendinglimb
Ascendinglimb
Loop of
Henle
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Figure 32.19ba
Kidney Structure
Renal cortex
Renal medulla
Renal artery
Renal vein
Renal pelvis
Ureter
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Figure 32.19bb
Nephron Types
Renal cortex
Renal medulla
Cortical nephron
Juxtamedullary nephron
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Figure 32.19bc Nephron Organization
Collectingduct
Branch ofrenal vein
Vasarecta
Efferentarteriole
fromglomerulus
Distaltubule
Afferent arteriolefrom renal artery
GlomerulusBowman’scapsule
Proximaltubule
Peritubularcapillaries
Descendinglimb
Ascendinglimb
Loop of
Henle
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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
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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
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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 all
along its journey down the descending limb
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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
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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
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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 fluidsAnimation: Bowman’s Capsule
Animation: Collecting Duct
Animation: Loop of Henle
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Figure 32.20
Filtrate
OUTERMEDULLA
H2OSalts (NaCI and others)HCO3
−
Glucose, amino acids
H
Some drugs
Passive transportActive transport
KeyINNERMEDULLA
CORTEX
Descending limbof loop of Henle
H2O
Interstitialfluid
NH3H
NutrientsHCO3
− K
NaCIProximal tubule
H2O
Thick segmentof ascending limb
H
Urea
HCO3−
K
NaCI
Distal tubuleH2O
Thin segmentof ascending limb
NaCI
H2ONaCI
NaCI
Collectingduct
1
23
5
4
3Urea
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Figure 32.20a
Passive transportActive transport
CORTEXInterstitialfluid
NH3H
NutrientsHCO3
− K
NaCIProximal tubule
H2O
H
HCO3−
K
NaCI
Distal tubuleH2O
1
Filtrate
4
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Figure 32.20b
OUTERMEDULLA
Passive transportActive transport
INNERMEDULLA
Descending limbof loop of Henle
H2O
Thick segmentof ascending limb
Urea
Thin segmentof ascending limb
NaCI
H2ONaCI
NaCI
Collectingduct
23
3 5
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Concentrating Urine in the Mammalian Kidney
The mammalian kidney’s ability to conserve water is a key terrestrial adaptation
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Figure 32.21-1
Passivetransport
Activetransport
mOsm/L
CORTEX
OUTERMEDULLA
INNERMEDULLA
300
H2O
1,200
900
600
400
300300
H2O
H2O
H2O
H2O
H2O
H2O
300
400
900
600
1,200
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Figure 32.21-2
Passivetransport
Activetransport
mOsm/L
CORTEX
OUTERMEDULLA
INNERMEDULLA
300
H2O
1,200
900
600
400
300300
H2O
H2O
H2O
H2O
H2O
H2O
NaCI
NaCI
NaCI
NaCI
NaCI
NaCI
NaCI
100100
200
400
700
300
400
900
600
1,200
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Figure 32.21-3
Passivetransport
Activetransport
H2O
mOsm/L
CORTEX
Urea
OUTERMEDULLA
INNERMEDULLA
300
NaCI
H2O
H2O
1,200
900
600
400
300300
H2O
H2O
H2O
H2O
H2O
H2O
NaCI
NaCI
NaCI
NaCI
NaCI
NaCI
NaCI
100100
200
400
700
300 300
400400
600
1,200
900
600
1,200
Urea
Urea
NaCI
H2O
H2O
H2O
H2O
H2O
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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
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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
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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
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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
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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
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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
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Figure 32.22
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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
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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
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Figure 32.23-1
STIMULUS:Increasein blood
osmolarity
Osmoreceptorstrigger release
of ADH.
ADH
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Figure 32.23-2
Distaltubule STIMULUS:
Increasein blood
osmolarity
Increasedpermeability
Osmoreceptorstrigger release
of ADH.Thirst
ADH
Collecting duct
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Figure 32.23-3
Distaltubule
H2Oreabsorption
STIMULUS:Increasein blood
osmolarity
Drinkingof fluids
Increasedpermeability
Osmoreceptorstrigger release
of ADH.Thirst
ADH
Collecting duct
Homeostasis
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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
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Figure 32.24-1
STIMULUS: Low blood
pressure
JGA releasesrenin.
Distaltubule
Juxtaglomerularapparatus (JGA)
Renin
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Figure 32.24-2
ACE
STIMULUS: Low blood
pressure
JGA releasesrenin.
Distaltubule
Juxtaglomerularapparatus (JGA)
Renin
Angiotensin II
Angiotensin I
Angiotensinogen
Liver
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Figure 32.24-3
ACE
STIMULUS: Low blood
pressure
JGA releasesrenin.
Distaltubule
Juxtaglomerularapparatus (JGA)
Renin
Arteriolesconstrict.
Angiotensin II
Angiotensin I
Angiotensinogen
Liver
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Figure 32.24-4
ACE
Na and H2O reabsorbed.
STIMULUS: Low blood
pressure
JGA releasesrenin.
Distaltubule
Juxtaglomerularapparatus (JGA)
Renin
Aldosterone
Homeostasis
Arteriolesconstrict.
Adrenal gland
Angiotensin II
Angiotensin I
Angiotensinogen
Liver
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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
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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
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Figure 32.UN01
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Figure 32.UN02
Stimulus: Change in internal variable
Homeostasis
Response/effector
Control center
Sensor/receptor