Urinary SystemUrinary SystemA. KidneysA. Kidneys 1. External anatomy1. External anatomy 2. Internal anatomy2. Internal anatomy 3. Nephron3. Nephron a. Parts of the nephrona. Parts of the nephron b. Cortical and juxtamedullary b. Cortical and juxtamedullary

nephrons nephrons c. Histology of the nephronc. Histology of the nephron 4. Blood and nerve supply4. Blood and nerve supplyB. Physiology of urine formationB. Physiology of urine formation 1. Glomerular filtration1. Glomerular filtration a. Net filtration pressurea. Net filtration pressure b. Glomerular filtration rateb. Glomerular filtration rate c. Regulation of GFRc. Regulation of GFR 2. Tubular reabsorption2. Tubular reabsorption 3. Countercurrent multiplier and 3. Countercurrent multiplier and

exchange system exchange system 4. Tubular secretion4. Tubular secretion 5. Renal clearance5. Renal clearance

C. UretersC. Ureters 1. Structure1. Structure 2. Histology2. Histology 3. Physiology3. PhysiologyD. Urinary bladderD. Urinary bladder 1. Structure1. Structure 2. Histology2. Histology 3. Physiology3. PhysiologyE. UrethraE. Urethra 1. Histology1. Histology 2. Physiology2. Physiology

What is excretion? What is excretion? How is it different from secretion?How is it different from secretion?Why do we need a urinary system?Why do we need a urinary system?

1. protein catabolism yields toxic 1. protein catabolism yields toxic nitrogenous wastes nitrogenous wastes

(ammonia and urea)(ammonia and urea)

2. water and essential ions tend to 2. water and essential ions tend to accumulateaccumulate

Organs that contribute to the function of Organs that contribute to the function of waste elimination from the body include:waste elimination from the body include:

1. kidneys1. kidneys

2. lungs2. lungs

3. sudoriferous glands3. sudoriferous glands

4. gastrointestinal tract4. gastrointestinal tract

The urinary system consists of:The urinary system consists of:

1. kidneys (2)1. kidneys (2)

2. ureters (2)2. ureters (2)

3. urinary bladder3. urinary bladder

4. urethra4. urethra

The kidneys have several The kidneys have several general functions:general functions:

1. regulate blood volume and 1. regulate blood volume and compositioncomposition

2. regulate blood pressure (renin)2. regulate blood pressure (renin)

3. secrete erythropoietin3. secrete erythropoietin

4. vitamin D synthesis4. vitamin D synthesis

Kidney-externalKidney-external

1. location1. location a. T12 - L3a. T12 - L3 b. retroperitonealb. retroperitoneal2. gross appearance2. gross appearance3. hilus3. hilus4. coverings4. coverings a. renal fasciaa. renal fascia b. adipose capsuleb. adipose capsule c. renal capsulec. renal capsule

Kidney-internalKidney-internal1. medulla1. medulla a. renal pyramidsa. renal pyramids b. renal papillaeb. renal papillae2. cortex2. cortex a. renal columnsa. renal columns b. cortical b. cortical vsvs

juxtamedullary nephronsjuxtamedullary nephrons3. renal pelvis and calyces3. renal pelvis and calyces

Nephrons, the functional units of the Nephrons, the functional units of the kidneys, have three basic functions:kidneys, have three basic functions:

1. filtration1. filtration

2. reabsorption2. reabsorption

3. secretion3. secretion

Types of NephronsTypes of Nephrons

1. cortical (85%)1. cortical (85%)

2. juxtamedullary (15%)2. juxtamedullary (15%)

juxtamedullary nephron(with very long loop of Henle)

cortical nephron(with relatively short loop of Henle)

Parts of a NephronParts of a Nephron

1. renal corpuscle1. renal corpuscle a. glomerulusa. glomerulus b. Bowman's capsuleb. Bowman's capsule (parietal vs visceral)(parietal vs visceral)2. renal tubule2. renal tubule a. proximal convoluteda. proximal convoluted b. loop of Henleb. loop of Henle c. distal convolutedc. distal convoluted

Bowman's capsule and the endothelial-Bowman's capsule and the endothelial-capsular membranecapsular membrane

1. parietal vs. visceral layers1. parietal vs. visceral layers2. fenestrated endothelial cells2. fenestrated endothelial cells (restrict formed elements)(restrict formed elements)3. fused basement membranes3. fused basement membranes (restrict plasma proteins)(restrict plasma proteins)4. visceral layer = podocytes4. visceral layer = podocytes a. pedicelsa. pedicels b. filtration slitsb. filtration slits

Renal Tubule HistologyRenal Tubule Histology1. 1. PCT = simple cuboidal + brush borderPCT = simple cuboidal + brush border

2. loop of Henle = simple squamous2. loop of Henle = simple squamous

3. DCT = simple cuboidal + hormone receptors3. DCT = simple cuboidal + hormone receptors

4. Collecting Ducts= Simple cuboidal4. Collecting Ducts= Simple cuboidal

Renal Blood SupplyRenal Blood Supply

1. ~25% of CO (1,250 ml/min)1. ~25% of CO (1,250 ml/min)

via the renal arteriesvia the renal arteries

segmental arteries interlobar arteries arcuate arteries

2. afferent arteriole --->2. afferent arteriole --->

glomerulus --->glomerulus --->

efferent arteriole--->efferent arteriole--->

3. peritubular capillaries3. peritubular capillaries

and vasa rectaand vasa recta

Renal Blood SupplyRenal Blood Supply

1. ~25% of CO (1,250 ml/min)1. ~25% of CO (1,250 ml/min)

via the renal arteriesvia the renal arteries

segmental arteries interlobar arteries arcuate arteries

2. afferent arteriole --->2. afferent arteriole --->

glomerulus --->glomerulus --->

efferent arteriole--->efferent arteriole--->

3. peritubular capillaries3. peritubular capillaries

and vasa rectaand vasa recta

Juxtaglomerular ApparatusJuxtaglomerular Apparatus

11. location. location2. macula densa cells2. macula densa cells3. juxtaglomerular cells3. juxtaglomerular cells

______________________________________4. decreased BP =4. decreased BP =

renin secretionrenin secretion5. vasoconstrictor substance5. vasoconstrictor substance

Filtrate formation high-increasedFiltrate formation high-increasedFiltrate formation low-decreasedFiltrate formation low-decreased

Nerve supply of the kidneysNerve supply of the kidneys

Renal nerves arise from the superior Renal nerves arise from the superior mesenteric ganglion- mostly mesenteric ganglion- mostly sympathetic fiberssympathetic fibers

Regulate blood flow and stimulate Regulate blood flow and stimulate secretion of reninsecretion of renin

Nephrons carry out three Nephrons carry out three important functions:important functions:

1. control blood concentration and 1. control blood concentration and volumevolume

2. regulate blood pH2. regulate blood pH

3. remove toxic wastes from the blood3. remove toxic wastes from the blood

What do nephrons accomplish?What do nephrons accomplish?

Urine formation requires three Urine formation requires three processes:processes:

1. glomerular filtration by the renal corpuscle1. glomerular filtration by the renal corpuscle

2. tubular reabsorption by the renal tubule2. tubular reabsorption by the renal tubule

3. tubular secretion by the renal tubule3. tubular secretion by the renal tubule

Glomerular filtration is the first Glomerular filtration is the first step in urine formation.step in urine formation.

1. principle of filtration1. principle of filtration

2. endothelial-capsular membrane2. endothelial-capsular membrane

3. blood hydrostatic pressure is the driving force3. blood hydrostatic pressure is the driving force

4. filtrate = all blood components except formed4. filtrate = all blood components except formed

elements and plasma proteinselements and plasma proteins

5. filtrate = 180 L/day5. filtrate = 180 L/day

urine = 1 - 2 L/dayurine = 1 - 2 L/day

filtrate reabsorbed = 178 - 179 L/dayfiltrate reabsorbed = 178 - 179 L/day

Features of the renal corpuscle that Features of the renal corpuscle that enhance its blood-filtering capacity:enhance its blood-filtering capacity:

1. glomerular capillaries are long1. glomerular capillaries are long

2. endothelial-capsular membrane is 2. endothelial-capsular membrane is porous and thinporous and thin

3. glomerular blood hydrostatic 3. glomerular blood hydrostatic pressure is high due to relationship pressure is high due to relationship between afferent and efferent arteriolesbetween afferent and efferent arterioles

Net filtration pressure (NFP)Net filtration pressure (NFP)

1. glomerular blood hydrostatic pr.1. glomerular blood hydrostatic pr.2. capsular hydrostatic pr.2. capsular hydrostatic pr.3. blood colloid osmotic pr.3. blood colloid osmotic pr.

______________________________________________________4. NFP = GBHP - (CHP + BCOP)4. NFP = GBHP - (CHP + BCOP) = 60 - (18 + 32) or = 60 - (18 + 32) or (15 + 27)(15 + 27) = +10 mm Hg= +10 mm Hg

______________________________________________________5. filtration fraction = 10%5. filtration fraction = 10% (1,250 ml/min x 0.1=(1,250 ml/min x 0.1=6. GFR = 125 ml/min)6. GFR = 125 ml/min)

Glomerular filtration rate (GFR)Glomerular filtration rate (GFR)

1. GFR = 125 ml filtrate produced every 1. GFR = 125 ml filtrate produced every minuteminute

2. GFR is directly related to the NFP.2. GFR is directly related to the NFP.

3. Homeostasis requires a relatively 3. Homeostasis requires a relatively constant GFR:constant GFR:

a. if GFR is too high, then...a. if GFR is too high, then...

b. if GFR is too low, then...b. if GFR is too low, then...

Regulation of GFRRegulation of GFR

1. glomerular blood flow depends on 2 factors:1. glomerular blood flow depends on 2 factors:

a. systemic blood pressurea. systemic blood pressure

b. afferent and efferent arteriolar diametersb. afferent and efferent arteriolar diameters

2. factors regulated by three mechanisms2. factors regulated by three mechanisms

a. renal autoregulationa. renal autoregulation

b. hormonal regulationb. hormonal regulation

c. neural regulationc. neural regulation

Renal AutoregulationRenal Autoregulation1. myogenic mechanism1. myogenic mechanism

Tendency of smooth muscle of afferent arteriole to contract Tendency of smooth muscle of afferent arteriole to contract

when arterial BP is high, relaxes when arterial BP is lowwhen arterial BP is high, relaxes when arterial BP is low

2. tubuloglomerular feedback2. tubuloglomerular feedback

(vasoconstrictor substance)(vasoconstrictor substance)

Renal Autoregulation

increased blood pressure

stretch of afferent arteriole

arteriolar vasoconstriction

decreased glomerular blood pressure

decreased filtration

decreased NFP

MYOGENIC MECHANISM

works the opposite way with decreased BP

increased GFR

increased flow of tubular fluid

macula densa cells secrete vasoconstrictor substance onto juxtaglomerular cells

vasoconstriction of afferent arteriole

decreased NFP

decreased glomerular blood pressure

TUBULOGLOMERULAR FEEDBACK

works the opposite way with decreased GFR

decreased filtration

Renin-Angiotensin SystemRenin-Angiotensin System

Atrial Natriuretic Peptide (ANP)Atrial Natriuretic Peptide (ANP)

When BP is too high, ANP is produced When BP is too high, ANP is produced by the heart which inhibits sodium and by the heart which inhibits sodium and water reaborption and the secretion of water reaborption and the secretion of renin and ADH. Kidneys eliminate renin and ADH. Kidneys eliminate more sodium and water and lower more sodium and water and lower blood pressureblood pressure

Neural Regulation of GFRNeural Regulation of GFR

Sympathetic Nervous SystemSympathetic Nervous System

Tubular Reabsorption of SolutesTubular Reabsorption of Solutes1. tubular maximum (TM)1. tubular maximum (TM)2. active transport2. active transport a. receptors (carriers)a. receptors (carriers) b. glucose and amino acidsb. glucose and amino acids (100% of the time)(100% of the time) c. Na+ and K+c. Na+ and K+ (aldosterone controlled)(aldosterone controlled) d. Ca++d. Ca++ (PTH and CT controlled)(PTH and CT controlled)3. passive transport (diffusion)3. passive transport (diffusion) a. diffusion or electricala. diffusion or electrical b. Cl-, PO4--b. Cl-, PO4--

Tubular Reabsorption of WaterTubular Reabsorption of Water

1. obligatory reabsorption (90%)1. obligatory reabsorption (90%)

a. osmosis related to solutesa. osmosis related to solutes

b. Na+ has major effectsb. Na+ has major effects

2. facultative reabsorption (10%)2. facultative reabsorption (10%)

(controlled by ADH)(controlled by ADH)

Negative Feedback Control of ADH

CONTROLLED CONDITION

RECEPTORHypothalamic osmoreceptors respond to increased blood osmotic pressure and

send nerve impulses to appropriate neurons in hypothalamus

CONTROL CENTERHypothalamic neurons, via the posterior pituitary gland, secrete ADH in the blood

EFFECTORSIn response to ADH, aquaporins in distal

tubules and collecting ducts become more permeable to water

RETURN TO HOMEOSTASISIn response, there is increased water

reabsorption, and blood osmotic pressure decreases

Blood osmotic pressure (decreased water concentration) is increased in response to

some stressor

The concentration gradient in The concentration gradient in interstitial fluidinterstitial fluid

Contributing factors:Contributing factors:

1.1.The nephron loop via the countercurrent multiplierThe nephron loop via the countercurrent multiplier

2.2.The Vasa recta via the countercurrent exchange systemThe Vasa recta via the countercurrent exchange system

3.3.Urea RecyclingUrea Recycling

The countercurrent multiplier-Responsible for The countercurrent multiplier-Responsible for establishing the salt concentration gradient with the establishing the salt concentration gradient with the interstitial fluid.interstitial fluid.

Countercurrent- tubular fluid reversing directionsCountercurrent- tubular fluid reversing directions

Multiplier- positive feedback loop that increases Multiplier- positive feedback loop that increases concentration of salts.concentration of salts.

Blood flows in opposite direction to nephron loopBlood flows in opposite direction to nephron loop

Exchanges salts for waterExchanges salts for water

Countercurrent Exchange SystemCountercurrent Exchange System(Loop of Henle and Vasa Recta) (Loop of Henle and Vasa Recta)

Blood flows in opposite directionsTo Loop of Henle.

As blood flows down alongsideAscending loop of Henle, water is lost and salt gained.

As blood flows up alongsideDescending loop of Henle, wateris gained and salt lost.

Overall, vessels absorb morewater on the way out than theyGave up on the way in.

Osmolarity of medulla maintainedAnd water and solutes maintained.

The Loop of Henle acts as a Countercurrent multiplierThe Loop of Henle acts as a Countercurrent multiplier

Tubular secretionTubular secretion

1. cells secrete directly into filtrate1. cells secrete directly into filtrate

2. two principal effects2. two principal effects

a. directly excrete substancesa. directly excrete substances

(H+, NH3, K+, creatinine)(H+, NH3, K+, creatinine)

b. control body fluid pHb. control body fluid pH

(H+, NH4+)(H+, NH4+)

If H+ secretion = HCO3- filtration then no change occurs in extracellular fluid pH.

If H+ secretion > HCO3- filtration, then extracellular fluid (blood)pH increases.

If H+ secretion < HCO3- filtration, then extracellular fluid(blood) pH decreases.

Secretion and Neutralization of Secretion and Neutralization of H+ ions in KidneyH+ ions in Kidney

Renal ClearanceRenal Clearance

Renal clearance is the volume of blood Renal clearance is the volume of blood plasma from which a particular waste is plasma from which a particular waste is completely removed in 1 minute.completely removed in 1 minute.

What would you expect the renal What would you expect the renal clearance of glucose to be in a normal clearance of glucose to be in a normal individual?individual?

Summary of Nephron FunctionsSummary of Nephron Functions

Urine DrainageUrine Drainage

1. papillary ducts --->1. papillary ducts ---> minor calyces --->minor calyces ---> major calyces --->major calyces ---> renal pelvis --->renal pelvis --->2. ureters2. ureters a. locationa. location b. anatomyb. anatomy c. functionc. function

Urinary BladderUrinary Bladder

1. location1. location

2. anatomy2. anatomy

3. histology3. histology

a. detrusor musclea. detrusor muscle

b. sphinctersb. sphincters

4. micturition reflex4. micturition reflex

UrethraUrethra

1. anatomy1. anatomy

2. location2. location

a. femalea. female

b. maleb. male

(1) prostatic(1) prostatic

(2) membranous(2) membranous

(3) penile(3) penile

Micturition reflex (in the adult)Micturition reflex (in the adult)

1. stretch of the bladder (1/2 full) stimulates stretch 1. stretch of the bladder (1/2 full) stimulates stretch receptors receptors 2. sacral parasympathetic area output, causing:2. sacral parasympathetic area output, causing: a. contraction of the detrusor muscle; anda. contraction of the detrusor muscle; and b. reflex relaxation of the internal urethral sphincterb. reflex relaxation of the internal urethral sphincter3. association neuron carries information to cerebrum 3. association neuron carries information to cerebrum for conscious awareness for conscious awareness4. voluntary relaxation of the external urethral 4. voluntary relaxation of the external urethral sphinctersphincter

(in the infant, this is also reflexive)(in the infant, this is also reflexive)5. expulsion of urine through urethra5. expulsion of urine through urethra

Neural Control of MicturitionNeural Control of Micturition