Download Homeostasis

BI 5103
FISIOLOGI TERINTEGRASI
(Integrative Physiology)
Core Principle 9: Homeostasis
(Konsep Inti 9 : Homeostasis)
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Why Homeostasis ?
Homeostasis is a process that maintains
the internal environment of living systems
in a more or less constant state.
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CONTEXT WITHIN PHYSIOLOGY
Important system parameters are measured,
and the measured values are compared with
a predetermined “set point,” or desired
values (whatever the mechanisms of these
set points).
The difference is used to generate signals
(information) that alter the functions of the
organism to return the regulated variable
toward its preset determined value.
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EXAMPLE
In mammals, body temperature is
maintained more or less constant in the
face of changes to environmental
temperature and/or changes in internal
states by manipulating heat production
and heat loss through various
mechanisms.
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EXTERNAL ENVIRONMENT
CO2
O2
Food
Mouth
ANIMAL
Respiratory
system
Digestive
system
Interstitial
fluid
Heart
Nutrients
Circulatory
system
Body
cells
Intestine
Urinary
system
Anus
Unabsorbed
matter (feces)
Metabolic waste
products (urine)

Homeostasis is the active maintenance of a
steady state within the body.
◦ External environmental conditions may
fluctuate wildly.
◦ Homeostatic mechanisms regulate internal
conditions.
© 2012 Pearson Education, Inc.
External
environment
Homeostatic
mechanisms
Large
fluctuations
Internal
environment
Small
fluctuations

Control systems
◦ detect change and
◦ direct responses.

Negative-feedback mechanisms
◦ keep internal variables steady and
◦ permit only small fluctuations around set points.
© 2012 Pearson Education, Inc.
Homeostasis:
Body temperature
approximately 37°C
Brain activates
cooling
mechanisms.
Temperature rises
above set point
Homeostasis:
Body temperature
approximately 37°C
Temperature falls
below set point
Brain
activates
warming
mechanisms.
Sweat evaporates,
cooling the body.
Brain activates
cooling
mechanisms.
Blood vessels dilate.
Temperature rises
above set point
Homeostasis:
Body temperature
approximately 37°C
Temperature falls
below set point
Blood vessels constrict.
Shivering generates
heat.
Brain
activates
warming
mechanisms.
Sweat evaporates,
cooling the body.
Brain activates
cooling
mechanisms.
Blood vessels dilate.
Temperature
decreases
Cooling mechanisms
shut off.
Temperature rises
above set point
Homeostasis:
Body temperature
approximately 37°C
Temperature
increases
Warming mechanisms
shut off.
Temperature falls
below set point
Blood vessels constrict.
Shivering generates
heat.
Brain
activates
warming
mechanisms.
Sweat glands secrete sweat that
evaporates, cooling the body.
The thermostat
in the brain
activates cooling
mechanisms.
Blood vessels in the skin dilate,
increasing heat loss.
Temperature
decreases
The thermostat shuts off
the cooling mechanisms.
Homeostasis:
Body temperature
approximately 37°C
Temperature rises
above set point
Homeostasis:
Body temperature
approximately 37°C
Temperature
increases
The thermostat shuts off
the warming mechanisms.
Temperature falls
below set point
Blood vessels in the skin constrict,
minimizing heat loss.
Skeletal muscles contract;
shivering generates heat.
The thermostat
in the brain
activates
warming
mechanisms.
Homeostasis is the maintenance of steady
internal conditions despite fluctuations in
the external environment.
Examples of homeostasis include
– thermoregulation—the maintenance of
internal temperature within narrow limits,
– osmoregulation—the control of the gain and
loss of water and solutes, and
– excretion—the disposal of nitrogen-containing
wastes.
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An animal’s regulation of body
temperature helps maintain
homeostasis
Ectothermic animals
– gain most of their heat from external sources and
– include many fish, most amphibians, lizards, and
most invertebrates.
Endothermic animals
– derive body heat mainly from their metabolism
and
– include birds, mammals, a few reptiles and fish,
and many insects.
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Heat is gained or lost in four
ways
– conduction—the transfer of heat by direct
contact,
– convection—the transfer of heat by
movement of air orliquid past a surface,
– radiation—the emission of electromagnetic
waves, or
– evaporation—the loss of heat from the
surface of a liquid that is losing some of its
molecules as a gas.
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Evaporation
Radiation
Convection
Conduction
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Thermoregulation involves adaptations that
balance heat gain and loss
 Increased metabolic heat production occurs when
– hormonal changes boost the metabolic rate in birds and
mammals,
– birds and mammals shiver,
– organisms increase their physical activity, and
– honeybees cluster and shiver.
© 2012 Pearson Education, Inc.
Thermoregulation involves adaptations that
balance heat gain and loss
 Insulation is provided by
– hair,
– feathers, and
– fat layers.
© 2012 Pearson Education, Inc.
Thermoregulation involves adaptations that
balance heat gain and loss
 Circulatory adaptations include
– increased or decreased blood flow to skin and
– countercurrent heat exchange, with warm and cold
blood flowing in opposite directions.
© 2012 Pearson Education, Inc.
Blood from
body core
in artery
Blood
returning to
body core
in vein
35°
33°C
30°
27°
20°
18°
10°
9°
Blood from
body core
in artery
Blood
returning
to body
core in vein
Thermoregulation involves adaptations that
balance heat gain and loss
 Evaporative cooling may involve
– sweating,
– panting, or
– spreading saliva on body surfaces.
© 2012 Pearson Education, Inc.
Thermoregulation involves adaptations that
balance heat gain and loss
 Behavioral responses
– are used by endotherms and ectotherms and
– include
– moving to the sun or shade,
– migrating, and
– bathing.
© 2012 Pearson Education, Inc.
Animals balance the level of water
and solutes through osmoregulation
Osmoregulation is the homeostatic control
of the uptake and loss of water and solutes
such as salt and other ions.
Osmosis is one process whereby animals
regulate their uptake and loss of fluids.
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Animals balance the level of water
and solutes through osmoregulation
Osmoconformers
– have body fluids with a solute
concentration equal to that of seawater,
– face no substantial challenges in water
balance, and
– include many marine invertebrates.
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Animals balance the level of water
and solutes through osmoregulation
Osmoregulators
– have body fluids whose solute
concentrations differ from that of their
environment,
– must actively regulate water movement,
and include
– many land animals,
– freshwater animals such as trout, and
– marine vertebrates such as sharks.
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EVOLUTION CONNECTION: A variety of
ways to dispose of nitrogenous wastes has
evolved in animals
 Uric acid is
– excreted by some land animals (insects, land snails,
and many reptiles),
– relatively nontoxic,
– largely insoluble in water,
– excreted as a semisolid paste, conserving water, but
– more energy expensive to produce.
© 2012 Pearson Education, Inc.
Proteins
Amino acids
Nitrogenous bases
Nucleic acids
NH2
(amino groups)
Most aquatic animals,
including most bony
fishes
Mammals, most
amphibians, sharks,
some bony fishes
Birds and many other
reptiles, insects, land
snails
Uric acid
Ammonia
Urea
The urinary system plays several
major roles in homeostasis
 The
urinary system
– forms and excretes urine and
– regulates water and solutes in body
fluids.
 In
humans, the kidneys are the main
processing centers of the urinary
system.
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Renal cortex
Renal medulla
Aorta
Inferior
vena cava
Renal artery (red)
and vein (blue)
Ureter
Kidney
Renal pelvis
Urinary bladder
Urethra
The urinary system
Bowman’s
capsule
Glomerulus
Arteriole
from renal
artery
1
Ureter
Proximal tubule
Capillaries
3
Arteriole
from
glomerulus
Branch of
renal vein
The kidney
Distal
tubule
Collecting
duct
Bowman’s
capsule
From
another
nephron
Branch of
renal artery
Tubule
Branch of
renal vein
Renal cortex
Collecting
duct
Renal medulla
2
Loop of Henle
with capillary
network
Detailed structure of a nephron
To
renal
pelvis
Orientation of a nephron within the kidney
Another example ?
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HORMONES
AND HOMEOSTASIS
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No inhibition
Hypothalamus
TRH
No inhibition
Anterior
pituitary
TSH
No iodine
Thyroid
Insufficient
T4 and T3
produced
Thyroid grows
to form goiter
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Hormones from the thyroid and parathyroids
maintain calcium homeostasis

Blood calcium level is regulated by a
tightly balanced antagonism between
Calcitonin from the thyroid
 Parathyroid hormone (PTH) from
the parathyroid glands

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8
7
Calcitonin
Thyroid
gland
releases
calcitonin
Stimulates
Reduces
Ca2+ deposition Ca2+ uptake
in bones
in kidneys
9
6
Stimulus:
Rising
blood Ca2+
level
(imbalance)
Blood Ca2+ falls
Ca2+
level
Homeostasis: Normal blood
calcium level (about 10 mg/100 mL)
Ca2+
level
Stimulus:
Falling
blood Ca2+
level
(imbalance)
1
Blood Ca2+ rises
5
Parathyroid
glands
release parathyroid
hormone (PTH)
Stimulates
Ca2+ release
from bones
2
3
PTH
Parathyroid
gland
Increases
Active
Ca2+ uptake
vitamin D in kidneys
Increases
Ca2+ uptake
in intestines
4
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Pancreatic hormones regulate
blood glucose levels

The pancreas secretes two
hormones that control blood glucose
Insulin—signals cells to use and
store glucose
 Glucagon—causes cells to release
stored glucose into the blood

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Body
cells
take up more
glucose
Insulin
3
2
Beta cells
of pancreas stimulated
to release insulin into
the blood
4
Blood glucose level
declines to a set point;
stimulus for insulin
release diminishes
Liver takes
up glucose
and stores it as
glycogen
1 High blood
glucose level
Stimulus:
Rising blood glucose
level (e.g., after eating
a carbohydrate-rich
meal)
Glucose
level
Homeostasis: Normal blood glucose level
(about 90 mg/100 mL)
Glucose
level
Stimulus:
Declining blood
glucose level
(e.g., after
skipping a meal)
5 Low blood
glucose level
Blood glucose level
rises to set point;
stimulus for glucagon
release diminishes
6
Alpha
cells of
pancreas stimulated
to release glucagon
into the blood
8
Liver
breaks down
glycogen and
releases glucose
to the blood
7
Glucagon
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