Urinary System and ExcretionUrinary System and Excretion

OrgansOrgansUrine FormationUrine Formation

Homeostatic MechanismsHomeostatic Mechanisms

Path of Urine through the Urinary SystemPath of Urine through the Urinary System

Kidneysproduce urine

Urinary bladderstores urine Urethra

passes urineto outside

Ureterstransport urine

Applying Your KnowledgeApplying Your Knowledge

A.A. Where is urine stored? Where is urine stored? B.B. Which structure passes urine to the outside Which structure passes urine to the outside

of the body?of the body?C.C. Which structure transports urine to the Which structure transports urine to the

bladder?bladder?D.D. Where is urine produced? Where is urine produced?

1.1. UretersUreters

2.2. BladderBladder

3.3. KidneyKidney

4.4. UrethraUrethra

Functions of the Urinary SystemFunctions of the Urinary System

• Excretion: removal of metabolic wastesExcretion: removal of metabolic wastes– Urea: breakdown product of amino acidsUrea: breakdown product of amino acids– Creatinine: breakdown product of creatine Creatinine: breakdown product of creatine

phosphate, a high energy molecule in musclesphosphate, a high energy molecule in muscles– Uric acid: breakdown product of nucleotidesUric acid: breakdown product of nucleotides

Ammonium from amino acids used for

energy

Structure of the KidneyStructure of the Kidney

• Renal Cortex: outer layerRenal Cortex: outer layer

• Renal Medulla: inner layerRenal Medulla: inner layer

• Renal Pelvis: central spaceRenal Pelvis: central space

Nephrons are Nephrons are microscopic tubulesmicroscopic tubulesthat produce urinethat produce urine

Structure of the NephronStructure of the Nephron

Glomerularcapsule

Glomerulus(capillaries)

Proximal convoluted

tubule

Descending limb Ascending

limb

Loop of the nephron

Collecting Duct

Peritubular capillary network

Distal convoluted

tubule

Urine Formation: Glomerular FiltrationUrine Formation: Glomerular Filtration

• Formation of a Formation of a filtrate containing filtrate containing some components some components from whole blood from whole blood

• Water and small Water and small molecules enter molecules enter glomerular capsule glomerular capsule from the glomerulusfrom the glomerulus

• Proteins, cell Proteins, cell fragments and cells fragments and cells are excluded from are excluded from the filtratethe filtrate

Water, nutrients, salts, nitrogenous wastes

enter nephron

Cells, cell fragments and proteins remain in

the bloodstream

Urine Formation: Tubular ReabsorptionUrine Formation: Tubular Reabsorption

• Molecules and ions Molecules and ions are reabsorbed into are reabsorbed into the blood, either the blood, either actively or passively actively or passively

• Reabsorption occurs Reabsorption occurs from the proximal from the proximal convoluted tubule convoluted tubule into the peritubular into the peritubular capillary networkcapillary network

• Water, nutrients and Water, nutrients and salts are reabsorbed salts are reabsorbed into the bloodstreaminto the bloodstream

Peritubular capillary network

Water, nutrients, salt reenter the bloodstream

Nitrogenous waste, excess salts, some water

remain in nephron

Urine Formation: Tubular SecretionUrine Formation: Tubular Secretion

• Substances are Substances are actively transported actively transported from the blood from the blood (peritubular capillary (peritubular capillary network) into the network) into the kidney tubulekidney tubule

• Involves transport of Involves transport of hydrogen ions, hydrogen ions, creatinine, penicillin creatinine, penicillin and other drugsand other drugs

Peritubular capillary network

H+, creatinine, drugs enter the nephron

Urine Formation: Urine Formation: Water ReabsorptionWater Reabsorption

• Water is reabsorbed into Water is reabsorbed into the bloodstream from all the bloodstream from all parts of the nephron, parts of the nephron, and the collecting ductand the collecting duct

• Occurs by osmosis Occurs by osmosis through aquaporins, through aquaporins, membrane channel membrane channel proteinsproteins

• Controlled by Controlled by – Reabsorption of saltReabsorption of salt– Gradient of NaCl in Gradient of NaCl in

medulla tissue medulla tissue surrounding the loopsurrounding the loop

– ADH, antidiuretic ADH, antidiuretic hormone, released from hormone, released from pituitary when water pituitary when water intake is low, stimulates intake is low, stimulates aquaporin activity in distal aquaporin activity in distal convoluted tubule and convoluted tubule and collecting ductcollecting duct

rele

ase

is in

hib

ited

by

alco

ho

l

Urine has a lower water concentration

than blood

Applying Your KnowledgeApplying Your Knowledge

A.A. Where is glucose returned to the bloodstream? Where is glucose returned to the bloodstream? B.B. Which structures does ADH influence? Which structures does ADH influence? (two answers)(two answers)

C.C. Which structure forms a NaCl gradient to influence Which structure forms a NaCl gradient to influence water reabsorption? water reabsorption?

D.D. Which structure produces a blood filtrate that Which structure produces a blood filtrate that contains water, nutrients and waste?contains water, nutrients and waste?

1.1. Distal Convoluted TubuleDistal Convoluted Tubule2.2. Glomerular CapsuleGlomerular Capsule3.3. Loop of the NephronLoop of the Nephron4.4. Proximal Convoluted TubuleProximal Convoluted Tubule

5.5. Collecting DuctCollecting Duct

Urine Formation: Salt ReabsorptionUrine Formation: Salt Reabsorption

• Sodium: Sodium: >99% reabsorbed>99% reabsorbed

– reabsorption in PCT, reabsorption in PCT, DCT, collecting ductDCT, collecting duct

– active transport in active transport in ascending limb of loop ascending limb of loop of nephronof nephron

• Other reabsorbed or Other reabsorbed or excreted ionsexcreted ions– potassium ionspotassium ions– bicarbonate ionsbicarbonate ions– magnesium ions magnesium ions

Hormonal Control of Sodium ReabsorptionHormonal Control of Sodium Reabsorption

AngiotensinogenAngiotensinogen

Angiotensin IAngiotensin I

Angiotensin IIAngiotensin II

If blood pressure decreasesIf blood pressure decreases

ReninRenin

secr

ete

secr

ete

ss

Stimulates sodium Stimulates sodium reabsorption from DCT,reabsorption from DCT,

water follows sodiumwater follows sodiumAldosteroneAldosterone

(from adrenal glands)(from adrenal glands)

stim

ulat

es

stim

ulat

es

secr

etio

n of

secr

etio

n of

constrictsconstrictsblood vesselsblood vessels

Hormonal Control of Sodium ExcretionHormonal Control of Sodium Excretion

AngiotensinogenAngiotensinogen

Angiotensin IAngiotensin I

Angiotensin IIAngiotensin II

If blood pressure If blood pressure increasesincreases

ReninRenin

secretesecrete

ss

AldosteroneAldosterone(from adrenal glands)(from adrenal glands)

Heart atrial cellsHeart atrial cells

Atrial Natriuretic Atrial Natriuretic Hormone (ANH)Hormone (ANH)

secretesecrete

prevents renin prevents renin secretionsecretion

XX

inhi

bitio

n of

inhi

bitio

n of

secr

etio

n

secr

etio

n

XX

XX

XXSodium is excreted in urine, Sodium is excreted in urine, water followswater follows

Functions of the Urinary SystemFunctions of the Urinary System

• Maintenance of Water-Salt Balance Maintenance of Water-Salt Balance important for blood pressure and blood important for blood pressure and blood volumevolume– Water reabsorption Water reabsorption

• Loop of the NephronLoop of the Nephron• Collecting DuctCollecting Duct

– Sodium reabsorption Sodium reabsorption or excretionor excretion• Proximal convoluted tubuleProximal convoluted tubule• Distal convoluted tubuleDistal convoluted tubule

Functions of the Urinary SystemFunctions of the Urinary System• Maintenance of Acid-Base BalanceMaintenance of Acid-Base Balance

– Blood pH is controlled by the Blood pH is controlled by the bicarbonate buffering systembicarbonate buffering system• Buffer: substance that resists pH changeBuffer: substance that resists pH change

– When lungs release carbon dioxide, When lungs release carbon dioxide, HH+ + has been used to produce water, has been used to produce water, so pH remains about neutral (7.4)so pH remains about neutral (7.4)

bicarbonate ion

hydrogen ion

carbonic acid carbon dioxide

water

Functions of the Urinary SystemFunctions of the Urinary System

• Maintenance of Acid-Base BalanceMaintenance of Acid-Base Balance– KidneyKidney

• excretes excess hydrogen ions (Hexcretes excess hydrogen ions (H++))

• reabsorbs bicarbonate ions (HCOreabsorbs bicarbonate ions (HCO33--))

Functions of the Urinary SystemFunctions of the Urinary System

• Assistance with Hormone Release and Assistance with Hormone Release and Secretion of HormonesSecretion of Hormones– Renin (enzyme) influences secretion of Renin (enzyme) influences secretion of

aldosterone from adrenal glands aldosterone from adrenal glands located at top of kidneyslocated at top of kidneys

– Aldosterone regulates water/salt Aldosterone regulates water/salt balance of blood by influencing ion balance of blood by influencing ion exchange at the distal convoluted exchange at the distal convoluted tubuletubule

– Erythropoietin: stimulates red blood Erythropoietin: stimulates red blood cell productioncell production

Functions of the Urinary SystemFunctions of the Urinary System

• Assisting other body systemsAssisting other body systems– Kidneys regulate the level of calcium Kidneys regulate the level of calcium

ions in bloodions in blood• Convert Vitamin D to a form that assists Convert Vitamin D to a form that assists

with calcium absorptionwith calcium absorption• Regulate the excretion of calciumRegulate the excretion of calcium

– Kidneys regulate the sodium and Kidneys regulate the sodium and potassium ions in blood, important for potassium ions in blood, important for nerve conduction, heart and skeletal nerve conduction, heart and skeletal muscle contractionmuscle contraction

Applying Your KnowledgeApplying Your Knowledge

A.A. Which one affects activity of aquaporins? Which one affects activity of aquaporins? B.B. Which one is made by the kidney in response to Which one is made by the kidney in response to

decreased blood pressure?decreased blood pressure?C.C. Which one stimulates red blood cell production?Which one stimulates red blood cell production?D.D. Which one stimulates reabsorption of sodium?Which one stimulates reabsorption of sodium?

1.1. AldosteroneAldosterone2.2. Antidiuretic Hormone (ADH)Antidiuretic Hormone (ADH)3.3. ReninRenin4.4. Angiotensin IIAngiotensin II5.5. ErythropoietinErythropoietin