The Internal Environment: A Summary

Chapter 42

AP BiologySpring 2011

Gains and Losses in Water and SolutesInterstitial fluid: fills tissue space

between cells Circulatory system: moves blood to and

from tissuesInterstitial fluid and blood are extracellular

fluid that functions as an internal environment for body cellsComposition and volume must be maintained

within range body can tolerate (homeostasis)

TermsUrinary 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 WaterIn 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 WaterFreshwater fish and amphibians constantly

gain water and lose solutes Neither can drink water Water move in by osmosis, leaves as dilute urineSolute 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 osmosisGulp in seawater, gill cells pump out excess

solutes, dissolved wastes are excreted in tiny volume of concentrated urine

Challenges on LandGain 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 urineSome water evaporates from respiratory

surfaces, leaves from sweating, small amounts leave through feces

Challenges on LandGain 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 excretionAll exhale carbon dioxide Urea: ammonia, toxic by product of protein metabolism is converted to urea, which is then excreted in urine

Components of Urinary System2 kidneys2 ureters Urinary bladderUrethra

Components of Urinary System2 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 SystemDense connective tissue encapsulates each

kidney Beneath capsule is outer tissue zone,

kidney cortexCortex 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 SystemRenal 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 SystemUrine 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 cortexNephron’s wall balloons outward like a cupNephron 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 ductAs many as 8 nephrons can empty into the

same ductDuct 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 insideGlomerular 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 capillaries

B. Bowman’s Capsule

C. Proximal tubuleD. Distal tubule E. Collecting ductF. Loop of Henle

The Nephron Renal artery branches into

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 nephronRejoin 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 capillariesGlomerular filtrationTubular 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 FiltrationVolume 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 capillaryReturns 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 osmosisCells 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

bloodTubular 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 fluidNo 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 limbFiltrate 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 MechanismWhen you do not drink enough

waterSolute concentration in blood is high,

which slows saliva secretions into mouthDrier mouth stimulates nerve endings

that signal thirst centerRegion 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 ADHADH: antidiuretic hormone

When signaled by osmoreceptors, hypothalamus stimulates the pituitary gland to secrete ADH

Promotes water conservationADH 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 ADHLoss of blood pressure or nausea and

vomiting can also trigger ADH secretions Aquaporines selectively allow water to

diffuse rapidly across plasma membraneADH alters reabsorption in target cells by

affecting these passive transporters

Effect of AldosteroneAldosterone: 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 AldosteroneAldosterone stimulates production and

placement of sodium-potassium pumps into the plasma membrane of cells in collecting duct wallUrine 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 ControlDiabetes 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 ControlOversecretion of ADH causes kidneys to

retain too much water, allowing solute concentrations in interstitial fluid to declineSolutes 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 BalanceMaintained 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 BalanceOnly urinary system can eliminate excess

hydrogen ionsThe HCO3- that forms in nephron cells is moved to

capillaries where it neutralizes excess acidThe 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 FailureMost kidney problems are outcomes of

diabetes mellitus and high blood pressureWhile 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 TransplantsAbout 12,000 people are recipients of

kidney transplants annually in USShortage of suitable donors; 40,000 remain

on waiting listMost 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 ChangeThe core temperature of an animal body

rises when heat from surrounding or metabolism builds up

Core Temperature Change4 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, HeterothermEctotherms: (lizards) have low metabolic

rates; therefore they must gain their heat from their environment in behavioral temperature regulation

Endotherm, Ectotherm, HeterothermEndotherm: (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, HeterothermHeterotherm: (hummingbird) generate

body heat during their active periods but resemble ecototherms during inactive times

Endotherm, Ectotherm, HeterothermWarmer 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 mechanismSweating 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 StressMammals respond to cold by redistributing blood flow,

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