Transcript Document

Maintaining the Internal Environment
Chapter 49
1
Outline
•
•
•
•
•
•
•
•
•
Need to Maintain Homeostasis
Antagonistic Effectors and Positive
Feedback
Osmolality and Osmotic Balance
Osmoregulatory Organs
Evolution of the Vertebrate Kidney
The Mammalian Kidney
Transport Processes in Mammalian Nephron
Ammonia, Urea, and Uric Acid
Hormones Control Homeostatic Functions
2
Need to Maintain Homeostasis
•
•
Homeostasis may be defined as dynamic
constancy of the internal environment.
Negative feedback loops
– The vertebrate body must have sensors to
measure conditions of the internal
environment.
 information relayed to integrating center
 When a deviation occurs, the
integrating center sends a message
to increase or decrease the activity of
particular effectors.
3
Negative Feedback Loop
4
Need to Maintain Homeostasis
•
Regulating body temperature
– Hypothalamus responds to increased
body temperature by promoting the
dissipation of heat through sweating,
dilation of blood vessels, and other
mechanisms.
 Coordinates a different set of responses
such as shivering and blood vessel
constriction for decreased body
temperature.
5
Need to Maintain Homeostasis
•
Regulating blood glucose
– Glucose levels are constantly monitored
by the islets of Langerhans in the
pancreas.
 When levels increase, the islets secrete
insulin which stimulate blood glucose
uptake.
 In this case, the islets are the sensor
and the integrating center.
6
Antagonistic Effectors and Positive Feedback
•
•
Antagonistic effectors
– Increasing activity of one effector is
accompanied by decreasing activity of an
antagonistic effector.
Positive feedback loops
– feedback loops that accentuate a
disturbance
 Deviations cause the effector to drive
the value of the controlled variable even
farther from the set point.
7
Positive Feedback During Childbirth
8
Osmolality and Osmotic Balance
•
Osmolality and osmotic pressure
– Because the total solute concentration of a
solution determines its osmotic behavior,
the total moles of solute per kilogram is
expressed as osmolality of the solution.
– Osmotic pressure of a solution is a
measure of its tendency to take in water
by osmosis.
 hypertonic, hypotonic, isotonic
9
Osmolality and Osmotic Balance
•
Osmoconformers and osmoregulators
– osmoconformers - Osmolality of body fluid
is same as that of surroundings.
 no osmotic gradient
 most marine invertebrates
– osmoregulators - Maintain a relatively
constant blood osmolality despite different
concentrations in the surrounding
environment.
10
Osmolality and Osmotic Balance
•
•
Freshwater vertebrates are hypertonic to
their environment.
– Water tends to enter their bodies.
 Must actively transport ions back into
their bodies.
Most marine vertebrates are hypotonic to
their environment.
– in danger of losing water by osmosis
 drink seawater and eliminate excess
ions through kidneys and gills
11
Osmoregulatory Organs
•
In many animals, removal of water or salts is
coupled with removal of metabolic wastes
through the excretory system.
– flatworms - flame cells
– earthworms - nephridia
12
Osmoregulatory Organs
•
•
Insects - Malpighian tubules
+
– Create an excretory fluid by secreting K
into tubules.
 Creates an osmotic gradient.
Vertebrates - Kidneys create a fluid (urine)
by filtration of the blood under pressure.
13
Malpighian Tubules of Insects
14
Evolution of the Vertebrate Kidney
•
Kidney is made up of thousands of repeating
units (nephrons), each with the structure of a
bent tube.
– Blood pressure forces the fluid in blood
past a filter, glomerulus, at the top of each
nephron.
 Water and small molecules pass
through filter and into the nephron tube.
 Sugars and ions are removed by
active transport.
15
Vertebrate Nephron Organization
16
Evolution of the Vertebrate Kidney
•
Freshwater fish
– Body fluids have greater osmotic
concentration than surrounding water.
– Water enters body from environment.
 They do not drink water and excrete
large amounts of dilute urine.
– Solutes tend to leave the body.
 reabsorb ions across nephron tubules
17
Evolution of the Vertebrate Kidney
•
Marine bony fish
– Body fluids are hypotonic to surrounding
seawater.
 Water tends to leave body via osmosis.
 drink large amounts of seawater
 Actively transport ions out of the
blood across the gill surfaces.
 Excrete urine isotonic to body
fluids.
18
Evolution of the Vertebrate Kidney
•
Cartilaginous fish
– Reabsorb urea from nephron tubules and
maintain a blood urea concentration 100
times higher than that of mammals.
 Blood is approximately isotonic to
surrounding sea.
19
Osmotic Problems
20
Evolution of the Vertebrate Kidney
•
Amphibians and reptiles
– Amphibian kidney is identical to that of
freshwater fish.
– Reptile kidneys are very diverse.
 Marine species eliminate excess salt
through salt glands.
 Terrestrial reptiles reabsorb much of salt
and water in nephron tubules.
21
Evolution of the Vertebrate Kidney
•
Mammals and birds
– Only vertebrates able to produce urine with
a higher osmotic concentration than their
body fluids.
 Hypertonic urine accomplished by loop of
Henle portion of the nephron.
– Birds have relatively few or no loops, and
thus cannot produce urine as concentrated
as that in mammals.
 Marine birds excrete excess salt from salt
glands.
22
Ammonia, Urea, and Uric Acid
•
When amino acids and nucleic acids are
catabolized, they produce nitrogenous wastes
that must be eliminated from the body.
– First step is the removal of the amino
(-NH2) group and its combination with H+ to
form ammonia (NH3) in the liver.
 toxic to cells
23
Ammonia, Urea, and Uric Acid
•
•
Elasmobranchs, adult amphibians, and
mammals eliminate nitrogenous wastes in the
form of urea.
Reptiles, birds, and insects excrete
nitrogenous wastes in the form of uric acid.
– Most mammals have enzyme uricase
which converts uric acid into a more
soluble derivative, allantoin.
24
Nitrogenous Wastes
25
The Mammalian Kidney
•
Each kidney receives blood from a renal
artery, and produces urine.
– Urine drains from each kidney through a
ureter which carries urine to urinary
bladder.
– Within the kidney, mouth of ureter flares to
form renal pelvis.
 Divided into renal cortex and renal
medulla.
26
Urinary System of a Human Female
27
The Mammalian Kidney
•
Nephron structure and function
– Blood is carried by an afferent arteriole to
the glomerulus.
 Blood is filtered as it is forced through
porous capillary walls.
 Glomerular filtrate enters Bowman’s
capsule.
 Moves to the proximal convoluted
tubule.
28
The Mammalian Kidney
•
Fluid then moves down the medulla and
back into the cortex in a loop of Henle.
– After leaving the loop, the fluid is delivered
to a distal convoluted tubule in the cortex
that drains to a collecting duct.
 merges with other collecting ducts to
empty its contents into the renal pelvis
29
Mammalian Kidney Nephron
30
The Mammalian Kidney
•
•
Reabsorption and secretion
– Most of the water and dissolved solutes
that enter the glomerular filtrate must be
returned to the blood.
– Reabsorption of glucose and amino acids,
is driven by active transport carriers.
– Secretion of waste products involves
transport across capillary membranes and
kidney tubules.
Excretion
31
Transport Processes in the Mammalian Nephron
•
•
Some mechanism is needed to create an
osmotic gradient between the glomerular
filtrate and the blood, allowing reabsorption.
Proximal convoluted tubule
– Approximately two-thirds of NaCl and
water filtered in Bowman’s capsule is
immediately reabsorbed across the walls
of the proximal convoluted tube.
32
Transport Processes in the Mammalian Nephron
•
Loop of Henle
– Descending limb is permeable to water, thus
water leaves via osmosis.
– Water loss in the descending limb multiples
concentration achieved at each loop.
+
– Ascending limb actively extrudes N and Cl
follows.
– NaCl pumped out of ascending limb is
trapped within surrounding interstitial fluid.
– countercurrent multiplier system
33
Transport Processes in the Mammalian Nephron
•
Distal tubule and collecting duct
– Permeability of the collecting duct to water
is adjusted by antidiuretic hormone (ADH vasopressin).
 Kidneys also regulate the balance of
electrolytes in the blood by reabsorption
and secretion.
34
Reabsorption of Salt and Water
35
Hormones Control Homeostatic Functions
•
Antidiuretic hormone
– Stimulates reabsorption of water by the
kidneys.
36
Hormones Control Homeostatic Functions
•
•
Aldosterone
– Promotes reabsorption of NaCl and water
across the distal convoluted tubule and
the secretion of K+ into the tubule.
Atrial natriuretic hormone
– decreases NaCl reabsorption
37
Summary
•
•
•
•
•
•
•
•
•
Need to Maintain Homeostasis
Antagonistic Effectors and Positive
Feedback
Osmolality and Osmotic Balance
Osmoregulatory Organs
Evolution of the Vertebrate Kidney
The Mammalian Kidney
Transport Processes in Mammalian Nephron
Ammonia, Urea, and Uric Acid
Hormones Control Homeostatic Functions
38
39