Cecie Starr
Christine Evers
Lisa Starr
www.cengage.com/biology/starr
Chapter 37
The Internal Environment
(Sections 37.4 - 37.7)
Albia Dugger • Miami Dade College
37.4 Urine Formation
• Urine consists of water and solutes filtered from blood and not
returned to it, along with solutes secreted from blood into the
nephron’s tubular regions
• Urine is formed by three processes:
• Glomerular filtration
• Tubular reabsorption
• Tubular secretion
Glomerular Filtration
• Blood pressure drives glomerular filtration
• 20% of blood fluid entering a glomerulus is forced out
through gaps in capillary walls into Bowman’s capsule
• Plasma proteins, blood cells, and platelets remain in blood
• Protein-free plasma in Bowman’s capsule becomes filtrate
that enters the proximal tubule
• glomerular filtration
• Protein-free plasma forced out of glomerular capillaries by
blood pressure enters Bowman’s capsule
Glomerular Filtration
Glomerular Filtration
glomerulus inside
Bowman’s capsule
outer wall of
Bowman’s capsule
efferent arteriole
(to peritubular
capillaries)
afferent arteriole
(from renal artery)
filtrate (to
proximal
tubule)
Fig. 37.9, p. 620
Tubular Reabsorption
• Tubular reabsorption returns water, glucose, amino acids,
most Na+, Cl–, K+, and bicarbonate ions to the blood
• In the proximal tubule, transport proteins move ions and
other nutrients into peritubular capillaries
• Water follows solutes by osmosis
• tubular reabsorption
• Substances move from the filtrate inside a kidney tubule
into the peritubular capillaries
Tubular Secretion
• Tubular secretion moves H+, K+ and breakdown products of
foreign organic molecules (drugs, food additives, pesticides)
from blood in peritubular capillaries into the filtrate
• Membrane proteins in peritubular capillaries actively
transport substances into interstitial fluid
• Substances cross tubule epithelium and enter the filtrate
• tubular secretion
• Substances move out of peritubular capillaries and into the
filtrate in kidney tubules
Concentrating the Urine
• Active transport of ions at the ascending loop of Henle, and
urea pumped out of the collecting tubule, contribute to high
solute concentration in interstitial fluid of the renal medulla
• High solute concentration draws water out of filtrate in the
descending loop of Henle, and again as urine descends
through the collecting tubule
• The body adjusts how much water is reabsorbed at distal
tubules and collecting tubules
Hormonal Effects on Urine Formation
• Hormones alter permeability of distal and collecting tubules to
adjust urine concentration
• A rise in Na+ concentration causes the hypothalamus to tell
the pituitary gland to secrete antidiuretic hormone
• When blood pressure declines, cells in nephron arterioles
release renin, which (through a series of reactions) results in
secretion of aldosterone by adrenal glands
Key Terms
• antidiuretic hormone (ADH)
• Pituitary hormone that encourages water reabsorption
• Makes distal tubules and collecting tubules more
permeable to water
• aldosterone
• Adrenal hormone that makes distal tubules and collecting
tubules more permeable to Na+
• Encourages sodium reabsorption
• Leads to more water reabsorption
Hormonal Effects on Urine (cont.)
• Atrial natriuretic peptide (ANP) makes urine more dilute by
inhibiting aldosterone secretion
• Muscle cells in the heart’s atria release ANP when high
blood volume causes atrial walls to stretch
• Parathyroid hormone (PTH) affects urine composition
• When blood calcium level declines, PTH acts on the
kidney to increase reabsorption of calcium
Urine Formation
Urine Formation
proximal tubule
collecting tubule
distal tubule
protein-free
plasma
Glomerular 2 Tubular 3 Tubular
1 filtration reabsorption secretion
Bowman’s
capsule
Na+, Cl–, K+,
nutrients, H2O
Na+, Cl–,
H2O
H+, K+
H+
4
peritubular capillary
renal cortex
renal medulla
descending arm
of loop of Henle
increasing solute
concentration in
interstitial fluid
1 Glomerular
filtration Proteinfree plasma
forced out of
glomerular
capillaries by
blood pressure
enters Bowman’s
capsule.
Na+
H2O
2 Tubular
reabsorption
Essential ions,
nutrients, water,
and some urea in
the filtrate return to
the blood. Green
arrows indicate
reabsorption.
H2O
3 Tubular secretion
Wastes and excess
ions are moved from
the blood into the
filtrate for
elimination in urine.
Blue arrows indicate
secretion.
ascending arm
of loop of Henle
Na+
urea
H2O
4 Hormones that alter
permeability of distal and
collecting tubules adjust
urine concentration.
Aldosterone increases Na+
reabsorption, and water
follows by osmosis.
Antidiuretic hormone directly
increases water reabsorption.
urine to
renal pelvis
Fig. 37.10, p. 621
Urine Formation
collecting tubule
proximal tubule
distal tubule
protein-free
plasma
2 Tubular
1 Glomerular reabsorption
Bowman’s filtration
capsule
Na+, Cl–, K+,
nutrients, H2O
3 Tubular
secretion
Na+, Cl–,
H2O
H+, K+
H+
4
renal cortex
renal medulla
peritubular capillary
descending arm
of loop of Henle
increasing solute
concentration in
interstitial fluid
Na+
H2O
H2O
ascending arm
of loop of Henle
Na+
urea
H2O
urine to
renal pelvis
Stepped Art
Fig. 37.10, p. 621
ANIMATION: Urine formation
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Key Concepts
• What Kidneys Do
• Urine begins forming when protein-free plasma filters
across capillary walls into kidney tubules
• Reabsorption returns most water, solutes, and nutrients to
the blood
• Unabsorbed filtrate and secreted substances become the
urine
• Hormones adjust urine concentration
ANIMATION: Formation of urine
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ANIMATION: Tubular reabsorption
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Animation: Reabsorption and Secretion
37.5 Kidney Disease
• Kidney function is measured in terms of the filtration rate
through glomerular capillaries
• Kidney failure occurs when the filtration rate falls by half
• Failure of both kidneys can be fatal: Wastes build up in blood
and interstitial fluid, pH rises, and changes in ion
concentrations (Na+, K+) interfere with metabolism
Causes of Kidney Failure
• Most kidney problems arise as complications of diabetes
mellitus or high blood pressure, which damage capillaries that
interact with nephrons
• Kidneys also fail after filtering toxins (lead, arsenic,
pesticides), high doses of drugs (aspirin), or other dangerous
substances from the blood
• High-protein diets force kidneys to work harder, and increase
the risk for kidney stones
Treating Kidney Failure
• Kidney dialysis can restore proper solute balances in a
person with kidney failure
• With hemodialysis, a patient’s blood is pumped through
semipermeable tubes submerged in a solution that draws out
wastes, and cleansed blood is returned to the patient’s body
• With peritoneal dialysis, dialysis solution is pumped into a
patient’s abdominal cavity at night, and drained in the morning
Two Types of Kidney Dialysis
filter where blood flows
through semipermeable
tubes and exchanges
substances with dialysis
solution
Two Types of
Kidney Dialysis
abdominal
cavity, lined
with peritoneum
(green)
patient’s blood
inside tubing
A Hemodialysis
Tubes carry blood from a
patient’s body through a filter
with dialysis solution that
contains the proper
concentrations of salts.
Wastes diffuse from the
blood into the solution and
cleansed, solute-balanced
blood returns to the body.
dialysis solution
flowing into
abdominal cavity
dialysis solution
with unwanted
wastes and
solutes draining
out
B Peritoneal dialysis
Dialysis solution is pumped
into a patient’s abdominal
cavity. Wastes diffuse across
the lining of the cavity into
the solution, which is then
drained out.
Fig. 37.11, p. 622
filter where blood flows
through semipermeable
tubes and exchanges
substances with dialysis
solution
Two Types of
Kidney Dialysis
abdominal
cavity, lined
with peritoneum
(green)
patient’s blood
inside tubing
A Hemodialysis
Tubes carry blood from a
patient’s body through a filter
with dialysis solution that
contains the proper
concentrations of salts.
Wastes diffuse from the
blood into the solution and
cleansed, solute-balanced
blood returns to the body.
dialysis solution
flowing into
abdominal cavity
dialysis solution
with unwanted
wastes and
solutes draining
out
B Peritoneal dialysis
Dialysis solution is pumped
into a patient’s abdominal
cavity. Wastes diffuse across
the lining of the cavity into
the solution, which is then
drained out.
Stepped Art
Fig. 37.11, p. 622
ANIMATION: Kidney dialysis
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37.6 Heat Gains and Losses
• Maintaining the temperature of the internal environment within
a tolerable range is another major aspect of homeostasis
• The heat content of any complex animal depends on a
balance between gains (from metabolism and the
environment) and losses (to the environment):
Heat change = heat produced + heat gained - heat lost
Changes to Core Temperature
• Heat is gained or lost at body surfaces by processes of
radiation, conduction, convection, and evaporation
• Thermal radiation is emission of heat into space around a
warm object
• Conduction transfers heat between objects in direct
contact with each other
• In convection, moving air or water transfers heat
• In evaporation, converting water on a body surface from
liquid to gas cools the body
Endotherm? Ectotherm? Heterotherm?
• Fishes, amphibians, and nonbird reptiles are ectotherms,
which are “heated from outside” by the environment
• Most birds and mammals are endotherms, which are
“heated from within” by metabolism
• Some birds and mammals are heterotherms, which maintain
a constant core temperature some of the time but allow their
temperature to shift at other times
Key Terms
• ectotherm
• Animal that controls its internal temperature by altering its
behavior; for example, a fish or a lizard
• endotherm
• Animal that controls its internal temperature by adjusting
its metabolism; for example, a bird or a mammal
• heterotherm
• Animal that maintains its temperature by production of
metabolic heat sometimes, and allows its temperature to
fluctuate with the environment at other times
Ectotherm and Endotherm
Key Concepts
• Adjusting the Core Temperature
• Heat losses to the environment and heat gains from the
environment and from metabolic activity determine an
animal’s body temperature
• Ectotherms adjust their temperature behaviorally
• Endotherms can adjust production of metabolic heat
37.7 Temperature Regulation
in Mammals
• The hypothalamus maintains body temperature through
negative feedback response
• The hypothalamus receives input from thermoreceptors
• When the temperature deviates, the hypothalamus calls for
responses that return temperature to the set point
Responses to Heat Stress
• When a mammal is too hot, the hypothalamus issues
commands for peripheral vasodilation (increases radiation)
• Sweat increases evaporative heat loss across skin; mammals
that don’t sweat may drool, lick fur, or pant to speed cooling
• Dangerous overheating (hyperthermia) occurs when the body
gets too hot – above 41.5°C (105°F)
Evaporative Cooling
• Sweat only cools if it
evaporates from skin
• On humid days,
evaporation rate slows,
so sweating is less
effective at cooling
ANIMATION: Control of human body
temperature
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Responses to Cold Stress
• The hypothalamus can cause arterioles in skin to contract,
reducing radiation; fluffing up hair or fur reduces convection;
and shivering produces metabolic heat
• shivering response
• In response to cold, rhythmic muscle contractions
generate metabolic heat
Responses to Cold Stress (cont.)
• Exposure to cold increases secretion of thyroid hormone,
which binds to metabolically active fat (brown adipose
tissue) and encourages nonshivering heat production
• brown adipose tissue
• Adipose tissue that responds to cold by releasing energy
as heat, rather than using it to make ATP
• nonshivering heat production
• Heat-generating mechanism of brown adipose tissue;
energy is released as heat, rather than stored in ATP
Hypothermia
• Hypothermia occurs when a drop in core body temperature
disrupts normal function
• In humans, body temperature of 95°F (35°C) impairs brain
activity
• Severe hypothermia causes loss of consciousness, disrupts
heart rhythm, and can be fatal
Impact of Cold Stress
Titanic: Death by Hypothermia
Heat and Cold Stress Compared
Key Concepts
• Regulation
• Mammals react to heat stress by moving blood to the skin
and increasing evaporation by sweating or panting
• They react to cold stress by moving blood to their core,
fluffing up fur or hair, and increasing metabolic heat
production
Truth in a Test Tube (revisited)
• Water-soluble drugs and toxins are generally not reabsorbed
from filtrate in kidney tubules, and end up in the urine
• How fast kidneys remove substances from blood varies with
age and health
• A healthy 35-year-old eliminates drugs twice as fast as a
healthy 85-year-old
ANIMATION: Feedback control of
temperature
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ANIMATION: Human thermoregulation
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