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