Copyright 2010, John Wiley & Sons, Inc. Chapter 9 The Urinary System.

Copyright 2010, John Wiley & Sons, Inc.

Chapter 9

The Urinary System


Urinary System Two kidneys and two ureters Urinary bladder & urethra Effector organ for

1. Regulation of Plasma ion composition2. Regulation of Body water Volume (BP)3. Regulation of blood pH (with lung)4. Production of Hormones5. Excretion of waste


Urinary System


Kidney Divided into cortex –outer portion Medulla- inner portion

Contain renal pyramids & renal columns Urine goes into renal pelvis

Edges are made of major & minor calyces Then out ureter


Kidney


Renal Blood Supply 20-25% resting CO goes through kidneys L. & R. renal arteries then

Segmental interlobar arcuate interlobular afferent arterioles glomerulus (capillary network) efferent arterioles peritubular capillaries veins renal vein Capillaris Units –nephrons grouped at pyramids


Renal Blood Supply


Renal Blood Supply


Nephron Unit of renal function: corpuscle & tubule Corpuscle: forms filtrate Glomerulus & Glomerular capsule (cortex) Proximal convoluted tubule (cortex) Descending Loop of Henle (into medulla) ascending Loop of Henle (into medulla) Distal convoluted tubule (cortex) Collecting duct minor calyx


Nephron


Basic Operation Glomerular filtration-filter plasma Tubular reabsorption

Reabsorb needed compounds & water from filtrate Tubular Secretion

Secrete some materials into filtrate


Glomerular Filtration Two layers of capsule surround glomerulus Between is capsular space Podocytes support capillary epithelium Form filtration membrane Permeable to water & solute but not most proteins & blood cells


Filtration Pressure Blood pressure for filtration Opposed by colloid osmotic pressure and

capsular pressure Efferent and afferent arteriole diameters

adjust to maintain a net filtration pressure Even with small changes in blood pressure


Glomerular Filtration Rate = GFR 105-125 ml/min Determines net reabsorption because it

determines filtrate flow ANP(Atrial natriuretic peptide) increases

GFR Responds to increased blood volume

Sympathetic stimulation vasoconstriction decreased GFR

Urine production


Glomerular Filtration


Tubular Reabsorption Proximal tubule

~65% Na+ & H2O Normally 100% nutrients ~100% HCO3

- (depends on blood pH) Active transport of solutes Osmosis moves water Cells distal to proximal tubule fine tune

reabsorption under control


Tubular Secretion Takes place all along tubule Major substances : H+, K+, ammonia, urea,

creatine, drugs like penicillin Helps regulate plasma pH 7.35-7.45 Diet is acid urine is typically acidic


Urine Route Collecting ducts to calyces Calyces to ureter Ureter to bladder Bladder to urethra


Filtration, Reabsorption,Secretion


Hormonal Regulation Angiotensin II & aldosterone

Angiotensin II- stimulates NaCl in proximal tube Aldosterone- increases Na+ reabsorption & K+

secretion in DCT & CD More ions reabsorbed more water

ANP-increases GFR & inhibits aldosterone action less Na+ reabsorbed

ADH- responds to increased concentration of solute in blood + fall in BP


Hormonal Regulation ADH: important to body water balance Increased concentration of solute in blood +

fall in BP ADH With no ADH: DCT & CD walls are

impermeable to water dilute urine With ADH: water reabsorption occurs

concentrated urine


Components of Urine Urine = 1-2 l /day 95% water + urea, creatine, K+, ammonia, uric acid, Na+,

Cl-, Mg2+, sulfate, phosphate & Ca2+

Depends on diet and state of health See table 21.3


Regulation of Water Reabsorption


Urine Route Collecting ducts calyces Ureter

Lined with mucus & transitional epithelium Pass under bladder Full bladder prevents backflow

Bladder- directly in front of rectum Can stretch (700-800 ml) Smaller in females because of uterus Three layers of detrussor muscle

Urethra- internal urethral sphincter External urethral sphincter (voluntary)


Urine Route


Micturition = Urination Autonomic reflex- internal sphincter

Responds to stretch like rectum Parasympathetic detrusor muscle

contraction Conscious control-external sphincter


Aging Kidneys shrink- decrease in capacity Thirst decreases dehydration urinary tract infections Males: prostate enlargement frequent

urination & slow flow Females: more prone to leakage of external

sphincter (incontinence) Both: nocturia


Fluid, Electrolyte and Acid-Base Balance


Fluid Compartments Total body water = 55-60% of lean body

mass Remainder: solid parts of bone, muscles, tendons

Major compartments (3): ICF, IF, plasma Intracellular fluid (ICF): inside cells= 2/3 Extracellular Fluid (ECF): outside cells = 1/3

Interstitial fluid (IF): 80% of ECF Includes: lymph; cerebrospinal, synovial, pericardial,

pleural and peritoneal fluids; fluid in eyes and ears Blood plasma: 20% ECF


Fluid Compartments


Barriers Between Compartments Plasma membrane: between ECF and ICF

Blood vessel walls: between plasma and interstitial fluid

Fluid balance correct distribution of water & solutes

Water redistributes rapidly by osmosis Thus fluid balance depends on solute

(electrolyte) balance


Fluid Balance Fluid balance requires

Appropriate total volume of body fluid Appropriate distribution of water and solutes

Fluid balance depends on solute (electrolyte and nonelectrolyte) balance Fluids and electrolytes are closely linked

Water redistributes rapidly by osmosis


Fluid BalanceInteractions Animations

Water and Fluid Flow

You must be connected to the internet to run this animation.

http://www.wiley.com/college/tortora/0470230169/interactions_animations/anim_fluid_flow/anim_fluid_flow/screen0.swf


Water Gain and Loss Gain: ingestion + metabolic reactions

Ingestion (food and drink): 2300 mL/day Metabolism: 200 mL/day

Gain should = loss Daily intake = daily output. Both 2500 mL/day

Loss: skin, lungs, kidneys, GI tract Kidneys: ~1500 mL/day Skin: sweat evaporates ~600 mL/day Lungs: 300 mL/day; more if fever GI tract: ~100 mL/day; more if diarrhea


Water Balance


Regulation of Gain Thirst center in hypothalamus ~2% dehydration will cause BP

Increase in body osmolality dry mouth thirst Hormonal responses

High osmolality hypothalamus releases ADH water retention by kidneys

BP renin released from kidney angiotensin II aldosterone water retention by kidneys

Sensation of thirst may be decreased, especially in elderly


Regulation of Gain


Regulation of Salt and Water Loss Urinary NaCl loss mainly determines body fluid volume

Na+ = main solute in ECF determining osmosis Fluid intake varies so loss must vary also

ANP, angiotensin II and aldosterone regulate ADH regulates water loss


Regulation of Salt and Water Loss


Movement of Fluid ICF and ECF are normally at the same

osmolality Water moves freely interstitial fluid osmolality cell swelling

and vice versa Most often due to Na+ change ADH responds rapidly: prevents significant

cell change


Electrolytes in Body Fluids Functions of electrolytes

1. Confined to compartments; control osmosis

2. Help maintain acid-base balance

3. Carry electrical currents

4. Serve as cofactors for enzymes


Electrolyte Distribution Electrolyte content of ICF and ECF differ

significantly ICF: K+ major cation; protein, HPO4

2-: anions ECF: Na+ major cation; Cl- major anion

Na+/K+ pump maintains the cation difference The two ECF fluids are similar

Electrolytes in plasma similar to those in IF One difference: plasma contains more protein

than interstitial fluid (IF) Colloid osmotic pressure (due largely to plasma

proteins) “holds onto” fluid in capillaries


Electrolyte Distribution


Other Electrolytes K+ high in ICF, low in ECF

Regulated by aldosterone Mg2+ and SO4

2- high in ICF, low in ECF Ca2+ high in ECF, low in ICF

Regulated in plasma (PTH, calcitriol, and calcitonin)

Bones serve as Ca2+ reservoir


Acid- Base Balance Input: diet, products of metabolism

Such as lactic acid, ketones Output

Lungs: exhale CO2

Kidney: can eliminate H+ or HCO3-

Regulatory mechanisms1.Buffers: fastest but incomplete

2.Respiratory responses: fast but incomplete

3.Renal responses: slowest but complete elimination


1: Buffer Systems Protein in cells or plasma

Carboxyl and amino groups of amino acids Hemoglobin (protein) in red blood cells

Carbonic acid-bicarbonate Especially important in plasma CO2 + H2O H2CO3 ↔ HCO3

- + H+

Phosphate H2PO4

- H+ + HPO42-


2: Exhalation of Carbon Dioxide H+ + HCO3

- ↔ H2CO3 ↔ CO2 + H2O

Decrease of CO2 ↔ decrease of H+

Increase of CO2 ↔ increase of H+

Change of rate and depth of ventilation rapidly alters plasma pH

Negative feedback loop regulates


2: Exhalation of Carbon Dioxide


3. Renal Responses Kidney Excretion of H+

Slow but only way to actually eliminate acid or base

Secrete H+ and replace with HCO3-


Imbalances Acidosis: arterial blood pH < 7.35

Depresses CNS Below pH 7.0 can be fatal

Alkalosis: arterial blood pH > 7.45 Overexcitation of CNS Muscle spasms, convulsions

Compensation Respiratory or renal mechanisms Respiratory very rapid; renal slower


Aging Decrease in control of water and electrolyte

balance can lead to pH problems Decreases in respiratory and renal

functioning Decreased capacity to sweat

Copyright 2010, John Wiley & Sons, Inc. Chapter 9 The Urinary System.

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blood pressure slide

filtrate slide

glomerular filtration

renal blood supply slide

nephron slide

kidney slide

control slide