Controlling the Internal Controlling the Internal EnvironmentEnvironment

Chapter 40Chapter 40

The Big PictureThe Big Picture

• The excretory system is a regulatory The excretory system is a regulatory system that helps to maintain homeostasis system that helps to maintain homeostasis within the bodywithin the body

• Homeostasis = the dynamic constancy of Homeostasis = the dynamic constancy of the internal environmentthe internal environment

• The excretory system eliminates wastes The excretory system eliminates wastes and functions in osmoregulation. and functions in osmoregulation.

• OsmoregulationOsmoregulation= the control of salt and = the control of salt and water balancewater balance

Osmoconformers vs. Osmoconformers vs. OsmoregulatorsOsmoregulators

• OsmoconformersOsmoconformers– Do not actively adjust their internal Do not actively adjust their internal

osmolarityosmolarity

• OsmoregulatorsOsmoregulators– Animals whose body fluids are not isotonic Animals whose body fluids are not isotonic

with the external environment must with the external environment must manipulate solute concentrations in their manipulate solute concentrations in their body fluidsbody fluids

• Which one are we??Which one are we??

Passive vs. Active TransportPassive vs. Active Transport

• Passive transport = does not require Passive transport = does not require an input of energy by the cellan input of energy by the cell

• Active transport = requires an input Active transport = requires an input of energy by the cellof energy by the cell

The Vertebrate Excretory The Vertebrate Excretory SystemSystem

• Kidneys, ureters, urinary bladder, Kidneys, ureters, urinary bladder, urethra, renal artery, renal veinurethra, renal artery, renal vein

• Also…Also…– Lungs: excrete carbon dioxideLungs: excrete carbon dioxide– Skin: excretes water, salts, and a small Skin: excretes water, salts, and a small

amount of urea (in sweat)amount of urea (in sweat)

Anatomy of the Vertebrate Anatomy of the Vertebrate Excretory SystemExcretory System

• Kidneys = bean-shaped organs, about the Kidneys = bean-shaped organs, about the size of your fist in humanssize of your fist in humans

• Blood enters the kidney through the renal Blood enters the kidney through the renal artery, and exits the kidney through the artery, and exits the kidney through the renal veinrenal vein

• Urine exits the kidney through the ureterUrine exits the kidney through the ureter• The ureter from each kidney goes to the The ureter from each kidney goes to the

urinary bladderurinary bladder• Urine leaves the body through the urethraUrine leaves the body through the urethra

Human Excretory SystemHuman Excretory System

Blood Supply to the KidneyBlood Supply to the Kidney

• Into the kidney: Into the kidney: – Renal artery to afferent arteriole to capillaries Renal artery to afferent arteriole to capillaries

of the glomerulusof the glomerulus• Capillaries converge into efferent arteriole, Capillaries converge into efferent arteriole,

which subdivides into peritubular which subdivides into peritubular capillariescapillaries

• Vasa recta = looped capillary system that Vasa recta = looped capillary system that serves the loop of Henleserves the loop of Henle

• Out of the Kidney: renal veinOut of the Kidney: renal vein• Kidneys receive ~20% of the blood Kidneys receive ~20% of the blood

pumped with each heartbeatpumped with each heartbeat

Kidney Structure Kidney Structure

• Divided into renal cortex (outer Divided into renal cortex (outer portion) and renal medulla (inner portion) and renal medulla (inner portion)portion)

• Renal pelvis: where the ureter meets Renal pelvis: where the ureter meets the kidneythe kidney

The NephronThe Nephron

• The functional unit of the kidney (ie. The The functional unit of the kidney (ie. The smallest part of the kidney that can still smallest part of the kidney that can still perform all the tasks associated with it)perform all the tasks associated with it)

• There are approximately 1 million There are approximately 1 million nephrons in each kidneynephrons in each kidney

• Nephron consists of a single long tubule Nephron consists of a single long tubule and a ball of capillaries (glomerulus)and a ball of capillaries (glomerulus)

• Made up of Bowman’s Capsule, Proximal Made up of Bowman’s Capsule, Proximal Tubule, Loop of Henle, Distal Tubule, Tubule, Loop of Henle, Distal Tubule, (Collecting Duct)(Collecting Duct)

The NephronThe Nephron

The NephronThe Nephron

• 80% of nephrons are cortical 80% of nephrons are cortical nephrons (located in the renal nephrons (located in the renal cortex)cortex)– Have reduced loops of HenleHave reduced loops of Henle

• 20% of nephrons are juxtamedullary 20% of nephrons are juxtamedullary nephrons (extend into renal medulla)nephrons (extend into renal medulla)– Have well-developed loops of HenleHave well-developed loops of Henle– Allow for the conservation of waterAllow for the conservation of water

The Nephron: An OverviewThe Nephron: An Overview

44-21-NephronIntroduction.mov

Regulation of Blood Regulation of Blood CompositionComposition

• Filtration:Filtration:– Blood pressure forces fluid from the Blood pressure forces fluid from the

capillaries of the glomerulus into capillaries of the glomerulus into Bowman’s CapsuleBowman’s Capsule•Capillaries function as a filter: permeable to Capillaries function as a filter: permeable to

water and small solutes but not to blood water and small solutes but not to blood cells or large molecules like plasma proteinscells or large molecules like plasma proteins

•Nonselective with regard to small moleculesNonselective with regard to small molecules

Regulation of Blood Regulation of Blood CompositionComposition• Secretion:Secretion:

– Substances are transported into the tubule Substances are transported into the tubule from the surrounding interstitial fluid (ISF)from the surrounding interstitial fluid (ISF)

– Occurs mostly in the proximal and distal Occurs mostly in the proximal and distal tubulestubules

– Net effect is the addition of plasma solutes to Net effect is the addition of plasma solutes to the filtrate within the tubulethe filtrate within the tubule

– A very selective process involving both passive A very selective process involving both passive and active transportand active transport

– Responsible for maintenance of a constant pH Responsible for maintenance of a constant pH level (secretion of H+ ions)level (secretion of H+ ions)

Regulation of Blood Regulation of Blood CompositionComposition• Reabsorption:Reabsorption:

– The selective transport of substances across The selective transport of substances across the epithelium of the excretory tubule from the the epithelium of the excretory tubule from the filtrate to the ISFfiltrate to the ISF

– Because filtration is nonselective, it’s Because filtration is nonselective, it’s important that small molecules essential to the important that small molecules essential to the body be returned to the ISF and blood plasmabody be returned to the ISF and blood plasma

– Occurs in the Occurs in the proximal tubuleproximal tubule, loop of Henle, , loop of Henle, distal tubule, and collecting ductdistal tubule, and collecting duct

– Involves both passive and active transportInvolves both passive and active transport

Bowman’s CapsuleBowman’s Capsule

• Tube of nephron that surrounds the Tube of nephron that surrounds the glomerulus, which is a ball of glomerulus, which is a ball of capillariescapillaries

• Blood pressure forces water, urea, Blood pressure forces water, urea, salts and other small solutes from salts and other small solutes from blood in the glomerulus into blood in the glomerulus into Bowman’s Capsule; this fluid is now Bowman’s Capsule; this fluid is now called called filtratefiltrate

Proximal TubuleProximal Tubule• Reabsorption and secretionReabsorption and secretion• Reabsorption:Reabsorption:

– Nutrients (glucose, amino acids)Nutrients (glucose, amino acids)– WaterWater **– NaClNaCl **

• Secretion:Secretion:– Drugs and other poisons from the liverDrugs and other poisons from the liver– Ammonia Ammonia

• Maintains a constant pH: H+ and HCOMaintains a constant pH: H+ and HCO33

Descending Loop of HenleDescending Loop of Henle

• Permeable to water but not to saltPermeable to water but not to salt

• ISF is hypertonic to filtrate, and ISF is hypertonic to filtrate, and water moves out of the tubule by water moves out of the tubule by osmosisosmosis

• NaCl becomes more and more NaCl becomes more and more concentrated in the tubuleconcentrated in the tubule

Ascending Loop of HenleAscending Loop of Henle

• Permeable to salt, but impermeable to Permeable to salt, but impermeable to waterwater

• Two regions:Two regions:– Thin: NaCl diffuses out into the ISFThin: NaCl diffuses out into the ISF– Thick: NaCl is actively transported into the Thick: NaCl is actively transported into the

ISFISF

• Result: filtrate becomes more and more Result: filtrate becomes more and more dilute because it loses salt without losing dilute because it loses salt without losing water (ie. salt concentration decreases)water (ie. salt concentration decreases)

Distal TubuleDistal Tubule

• Site of selective secretion and absorptionSite of selective secretion and absorption– Secretion:Secretion:

• K+K+

– Reabsorption:Reabsorption:• WaterWater

• NaClNaCl

• Regulates pH levelsRegulates pH levels– Secretion of H+Secretion of H+

– Reabsorption of HCOReabsorption of HCO33--

Collecting DuctCollecting Duct

• Shared by many nephronsShared by many nephrons• Carries the filtrate back towards the Carries the filtrate back towards the

medulla and renal pelvismedulla and renal pelvis• Permeable to water but impermeable Permeable to water but impermeable

to saltto salt• Filtrate becomes more and more Filtrate becomes more and more

concentrated again as water is lost concentrated again as water is lost by osmosis to the hypertonic ISFby osmosis to the hypertonic ISF

The NephronThe Nephron

An Overview ofAn Overview of Kidney Function Kidney Function

Why do animals have to get rid Why do animals have to get rid of nitrogen?of nitrogen?

• The metabolism of proteins and nucleic acids The metabolism of proteins and nucleic acids produces toxic by-products ammoniaproduces toxic by-products ammonia

• Ammonia:Ammonia:– a small and very toxic moleculea small and very toxic molecule– can be transported and excreted only in a very can be transported and excreted only in a very

dilute solutiondilute solution

• Many animals convert ammonia to urea or Many animals convert ammonia to urea or uric acid, which are much less toxic, but uric acid, which are much less toxic, but require ATP to producerequire ATP to produce