REGULATION AND REGULATION AND CONTROLCONTROL

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• In both animals and plants, chemical In both animals and plants, chemical messengers called messengers called hormones/plant hormones/plant growth regulatorsgrowth regulators help to transfer help to transfer information from one part to another information from one part to another and so achieve coordinationand so achieve coordination

• In many animals, In many animals, nerves nerves transfer transfer information in the form of electrical information in the form of electrical impulsesimpulses

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Importance of Importance of homeostasishomeostasis

Homeostasis Homeostasis • Maintaining a constant environment for the cells Maintaining a constant environment for the cells

within the bodywithin the body• Many features of the environment affect the Many features of the environment affect the

functioning of the cell:functioning of the cell:– TemperatureTemperature – low temperatures slow metabolic – low temperatures slow metabolic

rates/high temperatures cause denaturation of proteinsrates/high temperatures cause denaturation of proteins– Amount of waterAmount of water – lack of water in tissue fluid causes – lack of water in tissue fluid causes

water to be drawn out of cells by osmosis, causing water to be drawn out of cells by osmosis, causing metabolic reactions in the cell to slow or stop/too much metabolic reactions in the cell to slow or stop/too much water entering cell may cause it to swell or burstwater entering cell may cause it to swell or burst

– Amount of glucoseAmount of glucose – lack of it causes respiration to – lack of it causes respiration to slow or stop (no energy source)/too much glucose may slow or stop (no energy source)/too much glucose may draw water out of the cell by osmosisdraw water out of the cell by osmosis

• Homeostatic mechanisms work by controlling the Homeostatic mechanisms work by controlling the composition of blood, which controls the composition of blood, which controls the composition of tissue fluidcomposition of tissue fluid

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• Most control mechanisms use a Most control mechanisms use a negative negative feedbackfeedback control loop (involving a control loop (involving a receptorreceptor//sensorsensor and an and an effectoreffector))

• InputInput: receptor picks up information about : receptor picks up information about the parameter being regulatedthe parameter being regulated

• OutputOutput: action by the effector: action by the effector• Continuous monitoring of the parameter by Continuous monitoring of the parameter by

the receptor produces continuous the receptor produces continuous adjustments of the output, which keep the adjustments of the output, which keep the parameter oscillating around a particular parameter oscillating around a particular ‘ideal’ level, or set point. ‘ideal’ level, or set point.

• A rise in the parameter results in something A rise in the parameter results in something happening that makes the parameter fallhappening that makes the parameter fall

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Negative feedback control Negative feedback control looploop

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Excretion Excretion • The removal of toxic or excess The removal of toxic or excess

products of metabolism from the bodyproducts of metabolism from the body• Two main excretory products are Two main excretory products are

carbon dioxidecarbon dioxide and and ureaurea• Urea produced in the Urea produced in the liverliver (from (from

excess amino acids) and is excess amino acids) and is transported from the liver to the transported from the liver to the kidneys, in solution in blood plasmakidneys, in solution in blood plasma

• The kidneys remove urea from the The kidneys remove urea from the blood and excrete it, dissolved in blood and excrete it, dissolved in water, as water, as urineurine

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• DeaminationDeamination – The breakdown of excess amino acids in the liver, The breakdown of excess amino acids in the liver,

by the removal of the amine group; amine and by the removal of the amine group; amine and eventually urea are formed from the amine groupeventually urea are formed from the amine group

– UreaUrea is the main is the main nitrogenous excretory nitrogenous excretory productproduct of humans other than of humans other than creatininecreatinine and and uric aciduric acid

– Creatine is made in the liver from certain amino Creatine is made in the liver from certain amino acids, used in the muscles (creatine phosphate) acids, used in the muscles (creatine phosphate) where it acts as an energy store and some where it acts as an energy store and some converted to creatinine and excretedconverted to creatinine and excreted

– Uric acid is made from the breakdown of nucleic Uric acid is made from the breakdown of nucleic acidsacids

– Urea made in liver passes from liver cells into Urea made in liver passes from liver cells into blood plasma. As blood passes through kidneys, blood plasma. As blood passes through kidneys, the urea is extracted and excretedthe urea is extracted and excreted

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The structure of the kidneyThe structure of the kidney• Renal artery; renal veinRenal artery; renal vein• UreterUreter• UrethraUrethra• Capsule; cortex; medulla; pelvisCapsule; cortex; medulla; pelvis• NephronsNephrons• Renal (Bowman’s) capsuleRenal (Bowman’s) capsule• Proximal convulated tubuleProximal convulated tubule• Loop of HenleLoop of Henle• Distal convulated tubuleDistal convulated tubule• Collecting ductCollecting duct• Afferent arterioleAfferent arteriole• GlomerulusGlomerulus• Efferent arterioleEfferent arteriole

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Ultrafiltration Ultrafiltration • Involves filtering small molecules (urea) out of Involves filtering small molecules (urea) out of

the blood and into the renal capsule, from the blood and into the renal capsule, from here they flow along the nephron towards the here they flow along the nephron towards the ureterureter

• Blood in the glomerular capillaries is Blood in the glomerular capillaries is separated from the lumen of the renal capsule separated from the lumen of the renal capsule by two cell layers and a basement membraneby two cell layers and a basement membrane

• Capillary Capillary endotheliumendothelium – more gaps than – more gaps than other capillariesother capillaries

• Basement membraneBasement membrane – made up of a – made up of a network of collagen and glycoproteins; stops network of collagen and glycoproteins; stops large protein molecules and blood cells from large protein molecules and blood cells from getting through (filter)getting through (filter)

• Epithelial cellsEpithelial cells – make up the wall of the – make up the wall of the renal capsule; have renal capsule; have podocytespodocytes

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• Factors affecting glomerular filtration rateFactors affecting glomerular filtration rate– Glomerular filtration rateGlomerular filtration rate: rate at which fluid : rate at which fluid

seeps from the blood in the glomerular capillaries seeps from the blood in the glomerular capillaries into the renal capsule(125 cminto the renal capsule(125 cm33minmin-1-1 in humans) in humans)

– Determined by the differences in Determined by the differences in water water potentialpotential between contents of the glomerular between contents of the glomerular capillaries and the renal capsulecapillaries and the renal capsule

– Afferent arteriole is wider than the efferent Afferent arteriole is wider than the efferent arteriole causing a ‘traffic jam’ inside the arteriole causing a ‘traffic jam’ inside the glomerulus; blood pressure rises and so raising glomerulus; blood pressure rises and so raising the water potential as wellthe water potential as well

– Concentration of solutes in blood plasma in the Concentration of solutes in blood plasma in the capillaries is higher than the concentration of capillaries is higher than the concentration of solutes inside the renal capsule (plasma protein solutes inside the renal capsule (plasma protein still remain)still remain)

– Overall, the effect of difference in pressure Overall, the effect of difference in pressure outweighs the effect of the differences in solute outweighs the effect of the differences in solute concentration so water move down water concentration so water move down water potential gradient from the blood into capsulepotential gradient from the blood into capsule

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ReabsorptionReabsorption• Involves taking back any useful molecules from the Involves taking back any useful molecules from the

fluid in the nephron as it flows alongfluid in the nephron as it flows along• Reabsorption in the proximal convoluted Reabsorption in the proximal convoluted

tubuletubule– Many of the substances in the filtrate (identical to blood Many of the substances in the filtrate (identical to blood

plasma except large protein molecules) need to be kept in plasma except large protein molecules) need to be kept in the body, so they are reabsorbed into the blood as the fluid the body, so they are reabsorbed into the blood as the fluid passes along the nephron (passes along the nephron (selective reabsorptionselective reabsorption))

– NaNa++ transport transport– All All glucoseglucose in glomerular filtrate is transported out of the in glomerular filtrate is transported out of the

proximal convulated tubule and into blood (proximal convulated tubule and into blood (amino acidsamino acids, , vitaminsvitamins, , sodiumsodium and and chloride ionschloride ions are actively are actively reabsorbed)reabsorbed)

– 65% of 65% of waterwater in the filtrate is reabsorbed as water can in the filtrate is reabsorbed as water can move freely out of the filtrate, through the walls of the move freely out of the filtrate, through the walls of the tubule and into the blood by osmosistubule and into the blood by osmosis

– About half the urea in the filtrate is reabsorbed by diffusing About half the urea in the filtrate is reabsorbed by diffusing passively through the wall into the bloodpassively through the wall into the blood

– Uric acid and creatinine are not reabsorbedUric acid and creatinine are not reabsorbed– Creatinine is actively Creatinine is actively secretedsecreted by the cells of the proximal by the cells of the proximal

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• Reabsorption in the loop of Henle and Reabsorption in the loop of Henle and collecting ductcollecting duct– The function of the The function of the loop of Henleloop of Henle is to create a very high is to create a very high

concentration of salts in the tissue fluid in the medulla of concentration of salts in the tissue fluid in the medulla of the kidneythe kidney

– This allows a lot of water to be reabsorbed from the fluid in This allows a lot of water to be reabsorbed from the fluid in the collecting duct as it flows through the medullathe collecting duct as it flows through the medulla

– The loop of Henle allows water to be conserved in the body The loop of Henle allows water to be conserved in the body rather than lost in urinerather than lost in urine

– Counter-current multiplierCounter-current multiplier: an arrangement in which : an arrangement in which fluid in adjacent tubes flows in opposite directions, fluid in adjacent tubes flows in opposite directions, allowing relatively large differences in concentration to be allowing relatively large differences in concentration to be built upbuilt up

– Collecting ductCollecting duct runs down into medulla where the solute runs down into medulla where the solute concentration of the tissue fluid is very highconcentration of the tissue fluid is very high

– Water moves out of collecting duct by osmosis until the Water moves out of collecting duct by osmosis until the water potential of urine is the same as the water potential water potential of urine is the same as the water potential of the tissue fluid in the medullaof the tissue fluid in the medulla

– The degree to which this happens is controlled by The degree to which this happens is controlled by antidiuretic hormoneantidiuretic hormone ( (ADHADH))

– The longer the loop of Henle, the greater the concentration The longer the loop of Henle, the greater the concentration that can be built up in the medulla and the greater the that can be built up in the medulla and the greater the concentration of the urine which can be produced concentration of the urine which can be produced

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• Reabsorption in the distal Reabsorption in the distal convoluted tubule and collecting convoluted tubule and collecting ductduct– First part behaves in the same way as the First part behaves in the same way as the

ascending limb of the loop of Henle and ascending limb of the loop of Henle and second part as the collecting ductsecond part as the collecting duct

– In distal convoluted tubule and collecting In distal convoluted tubule and collecting duct, duct, sodium ionssodium ions are actively pumped are actively pumped from the fluid in the tubule into the tissue from the fluid in the tubule into the tissue fluid, from where they pass into the bloodfluid, from where they pass into the blood

– Potassium ionsPotassium ions are actively transported are actively transported into the tubuleinto the tubule

– The rate at which these 2 ions are moved The rate at which these 2 ions are moved into and out of the fluid in nephron can be into and out of the fluid in nephron can be varied and helps regulate the amount of varied and helps regulate the amount of these ions in the bloodthese ions in the blood

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Control of water and Control of water and metabolic wastesmetabolic wastes

• Osmoreceptor, the hypothalamus and Osmoreceptor, the hypothalamus and ADHADH– OsmoregulationOsmoregulation: the control of the water content : the control of the water content

of the fluids in the body/regulating the of the fluids in the body/regulating the concentration of water in body fluids (kidney)concentration of water in body fluids (kidney)

– In osmoregulation in mammals, the receptor is cells In osmoregulation in mammals, the receptor is cells in the in the hypothalamushypothalamus ( (osmoreceptorsosmoreceptors), and the ), and the effectors are the effectors are the pituitary glandpituitary gland and the walls of and the walls of the distal convulated tubulesthe distal convulated tubules

– Nerve cells produce a chemical called Nerve cells produce a chemical called antidiuretic antidiuretic hormonehormone ( (ADHADH – polypeptide of 9 amino acids) – polypeptide of 9 amino acids)

– ADH passed along to the endings in the posterior ADH passed along to the endings in the posterior lobe of the pituitary glandlobe of the pituitary gland

– Action potentialsAction potentials from stimulation by from stimulation by osmoreceptor cells causes ADH to be released from osmoreceptor cells causes ADH to be released from endings into blood in capillaries in the posterior endings into blood in capillaries in the posterior pituitary glandpituitary gland

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• How ADH affects the kidneysHow ADH affects the kidneys– ADH acts on the plasma membranes of the cells ADH acts on the plasma membranes of the cells

making up the walls of the collecting ducts, making up the walls of the collecting ducts, making them more permeable to water than usualmaking them more permeable to water than usual

– This change in permeability is brought about by This change in permeability is brought about by increasing the number of water-permeable increasing the number of water-permeable channels in the plasma membranechannels in the plasma membrane

– As the fluid flows down through the collecting As the fluid flows down through the collecting duct, water is free to move out of the tubule and duct, water is free to move out of the tubule and into the tissue fluid and it does so because this into the tissue fluid and it does so because this region of the kidney contains a high concentration region of the kidney contains a high concentration of saltsof salts

– Secretion of ADH caused the increased Secretion of ADH caused the increased reabsorption of water into the bloodreabsorption of water into the blood

– Diuresis: production of dilute urine (antidiuretic Diuresis: production of dilute urine (antidiuretic hormone stops production of dilute urine)hormone stops production of dilute urine)

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• Negative feedback in the control Negative feedback in the control of water contentof water content– When blood water content rises, the When blood water content rises, the

osmoreceptor are no longer stimulated osmoreceptor are no longer stimulated and stop stimulating their neighboring and stop stimulating their neighboring nerve cells. So ADH secretion slows nerve cells. So ADH secretion slows downdown

– The collecting duct cells do not respond The collecting duct cells do not respond immediately to the reduction in ADH immediately to the reduction in ADH secretion by the posterior pituitary glandsecretion by the posterior pituitary gland

– It takes some time for the ADH already It takes some time for the ADH already in the blood to be broken downin the blood to be broken down

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