Transcript Chapter 42

Chapter 42
The Internal Environment: A Summary
AP Biology
Spring 2011
Gains and Losses in Water and Solutes
 Interstitial fluid: fills tissue space between cells
 Circulatory system: moves blood to and from tissues
 Interstitial fluid and blood are extracellular fluid that functions as
an internal environment for body cells
 Composition and volume must be maintained within range
body can tolerate (homeostasis)
Terms
 Urinary system: collection of
interacting organs that counter
shifts in the composition and
volume of extracellular fluid
 Paired kidneys: filter blood,
from urine, help maintain body’s
water-solute balance
 Urine: fluid excreted from the
body, contains nitrogenous wastes
and excess amounts of other
solutes and water
Challenges in Water
 In most marine invertebrates, interstitial fluid is like seawater
in its concentrations of solutes, so little water is gained or
lost by osmosis
 In vertebrates, body fluids about 1/3 as salty as seawater
Challenges in Water
 Freshwater fish and amphibians constantly gain water
and lose solutes
 Neither can drink water
 Water move in by osmosis, leaves as dilute urine
 Solute loss balanced by intake of more solutes with meals and
active pumping of sodium into cells of gills and skin at
membrane transport proteins
 Marine bony fish contain les salt and lose water by
osmosis
 Gulp in seawater, gill cells pump out excess solutes, dissolved
wastes are excreted in tiny volume of concentrated urine
Challenges on Land
 Gain and loss of water:
 Water enters gut through food or drink
 Do not lose water by way of osmosis
 Lost it in controlled ways, mainly urinary excretion
 Urinary excretion: excess water and solutes exit body as
urine
 Some water evaporates from respiratory surfaces, leaves from
sweating, small amounts leave through feces
Challenges on Land
 Gain and loss of solutes:
 Absorption of nutrients from gut, secretions from cells, and
release of carbon dioxide wastes adds solutes; air intake from
lungs adds oxygen
 Loose solutes mainly in sweat, respiration, and urinary
excretion
 All exhale carbon dioxide
 Urea: ammonia, toxic by product of
protein metabolism is converted to urea,
which is then excreted in urine
Components of Urinary System
 2 kidneys
 2 ureters
 Urinary bladder
 Urethra
Components of Urinary System
 2 kidneys: bean-shaped organs about the size of a fist,
located between peritoneal lining and abdominal cavity wall,
where they flank the backbone
Components of Urinary System
 Dense connective tissue encapsulates each kidney
 Beneath capsule is outer tissue zone, kidney cortex
 Cortex is continuous with kidney medulla, inner zone
with pyramid shaped lobes of tissue, appears striated because
of long tubes that extend down to a chamber, the renal
pelvis
Components of Urinary System
 Renal artery: transports blood to kidney
 Then flows through arterioles, capillaries, and venules in cortex
and medulla
 Venules connect with renal vein, leads out of kidney
Components of Urinary System
 Urine forms in kidneys
 Then enters one of two ureters that connect with muscular
sac, the urinary bladder
 Urinary bladder: has stretch receptors that are stimulated
when urine fills the sac
 Reflex response causes smooth muscle to contract and forces
urine into urethra
 Urethra: muscular tube that opens on to the body surface
 After age 2-3, urination can be voluntarily controlled by
neural signals that act on a sphincter of skeletal muscle at the
start of the urethra
The Nephron
 Nephron: small
functional units that are
only one cell thick all
along their length
 Each kidney contains
more than a million
The Nephron
 Nephron starts in kidney cortex
 Nephron’s wall balloons outward like a cup
 Nephron continues in cortex as a twisting tube
 Straightens as descends to kidney medulla, then ascends into
the cortex
 There, another convoluted region connects with a collecting
duct
 As many as 8 nephrons can empty into the same duct
 Duct extends through the kidney medulla and opens into
renal pelvis
The Nephron
 The cup shaped entrance = Bowman’s capsule
 At Bowman’s capsule, thin nephron wall doubles back on
itself and encloses walls of highly porous blood vessels
clustered inside
 Glomerular capillaries
 Bowman’s capsule and glomerular capillaries interact as blood
filtering unit
 Unit= renal corpuscle
The Nephron
 Bowman’s capsule collects fluid that is forced out, under
pressure, from glomerular cappilaries
 Fluid enters proximal convoluted tubule
 Proximal means region closest to start of nephron
 Loop of Henle: plunges into medulla, makes hairpin turn,
and ascends out of it
 Distal tubule: convoluted part most distant from entrance
of nephron
Nephron
A. Glomerular
B.
C.
D.
E.
F.
capillaries
Bowman’s Capsule
Proximal tubule
Distal tubule
Collecting duct
Loop of Henle
 Renal artery branches into
The Nephron
afferent arterioles, one for
each nephron
 Delivers blood to glomerular
capillaries
 Capillaires rejoin and form an
efferent arteriole, which
carries away blood that did not
get filtered into Bowman’s
capsule
 Arteriole branches to form
peritubular capillaries that
thread all around nephron
 Rejoin as venules, which join
renal vein leading out of kidney
The Nephron
 Urine forms continually by 3 processes that exchange water and
solutes between all of the nephrons, glomerular capillaries, and
peritubular capillaries
 Glomerular filtration
 Tubular reabsorption
 Tubular secretion
 Each minute nephrons in both kidneys filter close to 125
milliliters of fluid from the blood flowing past = 180 L/day
Urine Formation: Glomerular
Filtration
 Blood pressure generated by heart drives glomerular filtration,
first step of urine formation
 In glomerular capillaries inside Bowman’s capsule of each nephron,
pressure forces out 20% of volume of plasma
 Cell wall of glomerular capillaries, the inner cell wall of Bowman’s
capsule, and basement membrane between them are like a sieve
 They nonselectivly let everything (water, ions, glucose, etc.)
besides blood components
become the filtrate
Urine Formation: Glomerular
Filtration
Urine Formation: Glomerular
Filtration
 Volume of blood kidneys must handle at any time is adjusted
at afferent arterioles that deliver blood to nephron
 Will vasodilate in response to signals from sympathetic
neurons (blood pressure increases)
 Will vasoconstrict when blood pressure decreases
 If too much fluid enters body- reflex pathway overrides
sympathetic signals, vasdilates
Urine Formation: Tubular
Reabsorption
 Nephron (proximal tubule), gives back most of filtrate, in
amounts required to maintain volume and composition of
internal environment
 Tubular reabsorption: variety of substances leak or get
pumped out of nephron, diffuse through interstitial fluid, and
enter peritubuler capillary
 Returns close to 99% of filtrates water, 100% of glucose and
A.A, all but 0.5% of Na+, and 50% of urea to blood
Urine Formation: Tubular
Reabsorption
 Cotransporters span plasma membrane of cells making up
nephrons tubular walls
 As filtrate flows through proximal tubule, ions and some
nutrients are actively and passively transported outward, into
interstitial fluid
 Water follows by osmosis
 Cells making up peritubular capillaries transport them into
blood, water follows by osmosis
 Passive transporters: Na+ and glucose
 Sodium potassium pump
 Electrochemical gradient: Na+, Cl Osmosis
Urine Formation: Tubular
Reabsorption
 Occurs at
Proximal Tubule
Urine Formation: Tubular Secretion
 Urea, H+, K+, other wastes, end up in blood
 Tubular Secretion: transporters in walls of peritubular
capillaries move ions into interstitial fluid
 Transporters in tubular wall of nephrons move them from
interstitial fluid into filtrate, can be excreted in urine
 Secretion of H+ is maintaining body’s acid-base balance
Urine Formation: Concentrating the
Urine
 Kidney’s cortex, filtrate is isotonic with interstitial fluid
 No net movement of water from one to another
 Kidney’s medulla, interstitial fluid is hypertonic
 Draws water out of filtrate by osmosis, along loop of Henle’s
descending limb
 Filtrate becomes most concentrated
and attracts most water by hairpin
turn
Urine Formation: Concentrating the
Urine
 Loop of Henle’s wall after turn is impermeable to water
 Transporters in ascending limb actively pump Na+ and Cl-,
which makes interstitial fluid in medulla even saltier, which draws
out even more water before hairpin turn
 Countercurrent
mechanism: transporters
are altering composition of
filtrate that is flowing in
opposite direction inside
loop of Henle
Thirst Mechanism
 When you do not drink enough water
 Solute concentration in blood is high, which
slows saliva secretions into mouth
 Drier mouth stimulates nerve endings that signal
thirst center
 Region of hypothalamus
 Thirst center also receives signals from
osmoreceptors that detect rise of blood level of
sodium inside brain
 Thirst center notifies other centres in cerebral
cortex, which compel you to search for and drink
fluid
 Hormonal controls act to conserve water already
inside body
Effect of ADH
 ADH: antidiuretic hormone
 When signaled by osmoreceptors, hypothalamus stimulates the
pituitary gland to secrete ADH
 Promotes water conservation
 ADH makes walls of distal tubules and collecting ducts more
permeable to water, thus urine becomes more concentrated
 As volume of extracellular fluid rises and solute
concentration declines, ADH secretion slows
Effect of ADH
 Loss of blood pressure or nausea and vomiting can also
trigger ADH secretions
 Aquaporines selectively allow water to diffuse rapidly across
plasma membrane
 ADH alters reabsorption in target cells by affecting these
passive transporters
Effect of Aldosterone
 Aldosterone: hormone stimulates production of sodium-
potassium pumps and their insertion into the plasma
membrane of cells in collecting ducts walls
 Cells in arterioles release the enzyme rennin in response to a
decline in the volume of extracellular fluid
 Renin starts chain of reactions that results in secretion of
aldosterone by adrenal glands located above each kidney
Effect of Aldosterone
 Aldosterone stimulates production and placement of sodium-
potassium pumps into the plasma membrane of cells in
collecting duct wall
 Urine becomes more concentrated
 Atrial natruitec peptide (ANP) makes urine more dilute by
inhibiting the secretion of aldosterone and also by indirectly
inhibiting rennin secretion
Abnormalities in Hormonal Control
 Diabetes insipidus occurs when pituitary gland secreted
too little ADH, when receptors do not respond to ADH, or
when the aquaporin proteins are missing or modified and do
not work
 Symptoms: large volumes of highly dilute urine and insatiable
thirst
Abnormalities in Hormonal Control
 Oversecretion of ADH causes kidneys to retain too much
water, allowing solute concentrations in interstitial fluid to
decline
 Solutes move out of body cells into interstitial fluid while water
in the interstitial fluid move out and into body cells
 In brain cells this process can be deadly
 Hyperaldosteronism occurs when adrenal gland tumors
cause over secretion of aldosterone, leading to fluid retention
and high blood pressure
Acid-Base Balance
 Maintained by controlling hydrogen ions through buffer
systems, respiration, and excretion by kidneys
 Buffers can neutralize hydrogen ions by bicarbonate-carbon
dioxide buffer system; the lungs can eliminate carbon dioxide
Acid-Base Balance
 Only urinary system can eliminate excess hydrogen ions
 The HCO3- that forms in nephron cells is moved to capillaries
where it neutralizes excess acid
 The H+ that forms in cells is secreted into tubular fluid where
it combines with bicarbonate ions to form carbon dioxide
(which is returned to blood and excreted by the lungs) and
water (which is excreted in urine)
 Hydrogen ions are permanently removed from extracellular
fluid
 Life-threatening metabolic acidosis develops when kidneys
cannot excrete enough of the H+ released during metabolism
Renal Failure
 Most kidney problems are outcomes of diabetes mellitus and
high blood pressure
 While some people are genetically predisposed to kidney
problems, toxins (lead, arsenic, pesticides) may accumulate
in kidney tissues, causing them to fail
 High protein diets increase the risk of for kidney stones and
cause kidneys to work hard to dispose of nitrogen-rich
breakdown products
 Renal failure occurs when rate of filtration through
glomerular capillaries drops by half
Kidney Dialysis
 A kidney dialysis machine is used to restore proper solute
balances after renal failure
 Hemodialysis connects machine to vein or artery and pumps
blood through semipermeable tubes soaked in solutes; as
patients blood flows through the tube, the wastes diffuse out
and solute concentrations are restored as the cleansed,
balanced blood flows back to patient
 Peritoneal dialysis pumps a fluid of a specific composition
into a patient’s abdominal cavity, allowing the peritoneum
(lining of the abdominal cavity) to function as the membrane
for dialysis
Kidney Dialysis
Kidney Transplants
 About 12,000 people are recipients of kidney transplants
annually in US
 Shortage of suitable donors; 40,000 remain on waiting list
 Most are available after donors death or from relatives or
friends; kidney’s from living donors have a higher success rate
in transplants than a kidney from a dead person
 Potential alternative to donors is use of genetically modified
pigs as organ factories
Core Temperature Change
 The core temperature of an animal body rises when heat
from surrounding or metabolism builds up
Core Temperature Change
 4 processes drive exchange of heat
 Thermal radiation: gain of heat from some source, or loss of
heat from the body to the surroundings, depending on
temperatures of environment
 Conduction: transfer of heat from one object to another
when they are in direct contact, as when a human sits on cold or
hot concrete
 Convection: transfer of heat by way of a moving fluid such as
air or water
 Evaporation: process whereby heated substance changes from
a liquid to a gaseous state with a loss of heat to the surroundings
Core Temperature Change
Endotherm, Ectotherm,
Heterotherm
 Ectotherms: (lizards) have low metabolic rates; therefore
they must gain their heat from their environment in
behavioral temperature regulation
Endotherm, Ectotherm,
Heterotherm
 Endotherm: (birds, mammals) generate heat from
metabolic activity and exercise controls over heat
conservation and dissipation by means of adaptations such as
feathers, fur, or fat, which reduce heat loss
Endotherm, Ectotherm,
Heterotherm
 Heterotherm: (hummingbird) generate body heat during
their active periods but resemble ecototherms during
inactive times
Endotherm, Ectotherm,
Heterotherm
 Warmer climates favor ectotherms since they conserve
energy as they maintain the core temperature
 Cold climates favor endotherms
Temperature Regulation in
Mammals: Responses to Heat Stress
 When mammals become too hot the hypothalamus send
signals to widen diameter of blood vessels to allow greater
volumes of blood to reach the skin and dissipate the heat
 Evaporative heat loss by sweating is cooling mechanism
 Sweating to dissipate heat can only be effective when the
external temperatures are high enough to cause evaporation
 Nearly all mammals (except marine species) sweat; many pant
or lick fur to assist evaporative cooling
Temperature Regulation in
Mammals: Responses to Heat Stress
 Hyperthermia is rise in core temperature, with devastating
effects
 Fever is defensive response against pathogens that occurs
with a rise in core temperature above normal set point
Temperature Regulation in
Mammals: Responses to Cold Stress
 Mammals respond to cold by redistributing blood flow,
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fluffing hair and fur, and shivering
In some responses hairs or feathers become more erect to
create a layer of still air that reduces convection and radiative
heat losses
Shivering responses are common response to cold but are not
effective for very long and come at high metabolic cost
Nonshivering responses include release of thyroid hormones
that bind to brown adipose tissue increasing metabolism
Hypothermia is condition in which the core temperature
drops below normal; may lead to brain damage and death