urinary system c25

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Answer

Kidneys are major excretory organ Pg 961

though the lungs and skin do some as well

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Kidneys also react as

essential regulators of volume an chemical makeup of blood; maintaining proper balance between water and sals, and acids and bases

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Other Renal functions include

gluconeogenesis during prolonged fasting; Producing the hormones renin and erythropoietin; Metabolizing vitamin D to it's active form

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RENIN

acts as an enzyme to help regulate blood pressure and kidney funtion

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ERYTHROPOIETIN

stimulates red blood cell production

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Urinary system includes

kidneys, urinary bladder, plus 3 tubelike organs (paired ureters, and rurethra) (transportation channels)

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Renal Hilum

ureter, renal blood vessels, lymphatics, and nerves all converge here

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Three layers of supported tissue around kidney

renal fascia, perirenal fat capsule, fibrous capsule

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Renal fascia

outer layer, dense fibrous connective tissue; anchors kidney to surrounding structures

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Perirenal fat capsule

fatty mass that surrounds the kidney and cushions it against blows

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Fibrous capsule

transparent capsule that prevent infections in surrounding regions from spreading to the kidney

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Hydronephrosis

backup of urine

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3 distinct regions of the kidney

cortex, medulla and pelvis

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Renal cortex Pg 962

most superficial; light in color and has granular appearance.

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Renal Medulla Pg 962

deep to cortex; darker, reddish-brown; exhibits cone shaped tissue masses called RENAL PYRAMIDS or MEDULLARY PYRAMIDS; pyramids appear striped due to almost entirely of parallel bundles of microscopic urine collecting tubules and capillaries

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Renal columns

separate pyramids. each pyramid and its surrounding cortical tissue constitutes on of approximately eight LOBES of a kidney

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Renal Pelvis

funnel-shaped tube; continuous w/ ureter leaving the hilum;

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Major calyces

branching extensions of the pelvis form 2 or 3 major CALYCES; cup shaped area that enclose papillae

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Calyces collect urine

which drains to papillae,; empty into pelvis; the flows from pelvis to ureter; this moves it to the bladder to store;

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Walls of calyces, pelvis, and ureter contain

smooth muscle that contracts rhythmically to propel urine by PERISTALSIS

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Pyel/itis

infection of renal pelvis and calyces

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Pyel/o/nephr/itis

infections that affect entire kidney

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Kidneys have rich blood supply

true

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Renal arteries Pg 963

deliver 1/4 of total cardiac output (1200ml) to the kidneys each minute (at rest)

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Renal arteries issue at

right angles from the abdominal aorta, and the right renal artery is longer than the left because the aorta lies to the left of the midline

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Segmental arteries pg964

Renal arteries divide to 5

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Interlobar arteries

each segmental artery branches further to form these in renal sinus

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Arcuate arteries

branched from interlobar arteries, in medulla-cortex junction; arch over bases of medullary pyramids

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Cortical radiate arteries pg964

radiate outward from the arcuate arteries to supply the cortical tissue

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90% of blood entering kidney perfuses the renal cortex

true

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Afferent Arterioles

branch from cortical, radiate arteries begin a complex arrangement of microscopic blood vessels; KEY ELEMENTS of kidney function

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Veins

pretty much trace the pathway of the arterial supply in REVERSE

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Blood leaving the renal cortex Pg 964

drains into cortical radiate, arcuate, interlobar, and finally renal veins

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Renal veins issue from

kidney and empty into vena cava

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Left renal vein is almost twice as long as right

true

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Renal Plexus

network of autonomic nerve fibers and ganglia, ; provides the nerve supply of the kidney and its ureter

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Renal plexus is supplied by sympathetic fibers from the most inferior thoracic and fist lumbar splanchnic nerves

which course along w/ the renal artery to reach the nerve; the SYMPATHETIC VASOMOTOR fibers regulate renal blood flow by adjusting the diameter of renal arterioles and also influence the urine-forming role of the nephrons

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Nephrons

STRUCTURAL and FUNCTIONAL units of the kidneys

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Each kidney contains over 1 mission nephrons (blood processing units)

they carry out the process that forms urine

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1000's of collecting ducts,

each of which collects fluid from several nephrons and conveys it to the renal pelvis

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Glomerulus

in each nephron; tuft of capillaries

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Renal tubule has a

cup-shaped end which called the Glomerular capsule (or Bowman's capsule); which is blind and completely surrounds glomerulus

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Renal capsule

Glomerular capsule and the enclosed glomerulus

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Endothulium of the glomerular capillaries if FENESTRATED (penetrated by many pores)

so they are very porous

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Filtrate (plasma derived fluid)

raw material that renal tubules process to form urine

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External parietal layer of glomerular capsule

simple squamous epithelium; simply contributes to capsule structure, and plays NO PART in forming FILTRATE

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Visceral layer pg966

clings to glomerular capillaries; consists of highly modified, branching epithelial cells called PODOCYTES

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Foot processes

where Podocytes terminate; intertwine as they cling to the basement membrane of the glomerus

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Filtration slits

Clefts or openings between the foot processes

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Capsular space

filtrate enter here through the slits

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remainder of Renal tubule has

3 major parts: proximal convoluted tubule (PCT); Loop of Henle; distal convoluted tubule

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Proximal convoluted tubule (PCT) Pg966

exit from glomerular capsule; elaborately coiled;

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loop of Henle (Nephron loop or Henle's loop)

hairpin loop coming from the PCT

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Distal convoluted tubule (DCT)

last part of tubule that empty into a collecting duct

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collecting ducts

receives filtrate from many nephrons; runs through pyramids(gives striped appearance); as they approach the renal pelvis, they fuse together and deliver urine into the minor calyces via papillae of the pyramids.

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Renal tubule consist of

single layer of polar epithelial cells on basement membrane; but each region has a unique cellular anatomy;

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Walls of PCT

cuboidal epithelial cells w/ large mitochondria; luminal(exposed) side bear dense microvilli

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brush border

dramatically increases the surface area and capacity for reabsorbing water and solutes

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U-shaped loop of Henle has

ascending and descending limbs

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Descending limb of loop of Henle

proximal part is continuous w/ proximal tubule and its cells are similar

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Thin segment

the rest of the descending limb, is simple squamous epithelium freely permeable to water;

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Ascending loop of Henle

becomes cuboidal or even low columnar

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Thick segment

ascending part of loop of Henle where it becomes cuboidal or columnar

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In some nephrons, the thin segment if sound only in

descending limb. In others, it extends into ascending limb as well

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Epithelial cells of the DCT

are cuboidal and confined to the cortex, but they are thinner and almost entirely lack microvilli

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Transition between DCT and collecting duct

marked by appearance of a heterogeneous collection of cells.

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Cell types in collecting ducts

INTERCALATED CELLS, (cuboidal cells w/ abundant microvilli) and more numerous PRINCIPLE CELLS which have sparse/short microvilli

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Principle cells help maintain

body's water and Na+ balance

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Nephrons; divided into two major groups

cortical nephrons and juxtamedullary nephrons

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Cortical nephrons

85% of nephrons; located entirely in cortex (except small part in the loop of Henle)

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Juxtamedullary nephrons

originate close to the cortex-medulla junction; play an important role in kidney's ability to produce concentrated urine; their loops of Henle deeply invade the medulla; their thin segment are much more extensive than those of cortical nephrons

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Nephron capillary beds Pg 966

renal tubule of every nephron is closely associated w/ 2 capillary beds; glomerulus and peritubular

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Glomerulus

in which the capillaries run in parallel, specialized for filtration; differs from all other capillary beds in the body in in that it is both fed and drained by arterioles

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Afferent arteriole

arise from cortical radiate arteries; run through renal cortex;

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BP is extremely high in glomerulus because

arterioles are high-resistance vessels; afferent arteriole has a larger diameter that the efferent

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Peritubular capillaries pg968

arise from the efferent arterioles draining the glomeruli; cling closely to adjacent renal tubules and empty into nearby venules; LOW PRESSURE, POROUS capillaries that readily absorb solutes and water from tubule cells as these substances are reclaimed

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Efferent arterioles serving the Juxtamedullary nephrons

tend not to break up into meandering particular capillaries. Instead the form bundles of straight vessels called VASA RECTA

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Vasa Recta (straight vessels)

extend deep into medulla paralleling the longer loops of Henle; thin-walled; Play important role in forming concentrated urine

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In summary

microvasculature of the nephrons consists of 2 capillary beds separated by intervening efferent arterioles; Glomerulus produces filtrate; Peritubular reclaims most of that filtrate

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Vascular resistance in Microcirulation Pg 968

Blood flow encounters high resistance

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Renal BP declines

from 95mm Hg in the renal arteries to 8mm Hg or less in the renal veins

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Resistance of the afferent arterioles

protects the glomeruli form large fluctuations in systemic BP

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Resistance in the efferent arterioles

reinforces the high glomerular pressure and reduces the hydrostatic pressure in the peritubular capillaries

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Juxtaglomerular Apparatus Pg 968

most distal portion of the ascending limb of loop of Henle lies

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JGA includes granular cells and macula densa

granular cells (also called juxtaglomerular (JG) cells)

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Granular cells

enlarged smooth muscle cells w/ prominent secretory granules contain renin; ACT AS mechanoreceptors that sense the BP in the afferent arteriole

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Macula densa

group of tall, closely packed cells of the ascending limb of the loop of Henle that lies adjacent to granular cells

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Macula densa are

chemoreceptors that respond to changes in the NaCl content of the filtrate

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Extraglomerular mesangial cells

interconnected by gap junctions and may pass signals between macula dense and granular cells

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Filtration membrane Pg 969

lies between blood and interior of glomerular capsule; porous allows free passage of water and solutes smaller that plasma proteins

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3 layers of filtration membrane

fenestrated endothelium of the glomerular capillaries; visceral membrane of the glomerular capsule, made of podocytes which have filtration slits between their foot processes; and between these two layers is the basement membrane composed of fused basal

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Fenestrations (capillary pores)

allow passage of plasma but not blood cells; basement membrane restricts all but smallest proteins;

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Structural makeup of basement membrane

confers electrical selectivity on the filtration process

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Urine formation Pg 969-970

3 major processes; glomerular filtration tubular reabsorption in renal tubes tubular secretion in renal tubes

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Maintain volume and chemical makeup

kidneys dump free blood into a separate container (renal tubes and collecting ducts)

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From there, the kidneys reclaim (by tubular reabsorption) everything the body needs to keep (almost everything)

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some things are selectively added to the container (by tubular secretion ) fine tuning the bodies chemical balance

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of the 1200 ml of blood that passes through the glomeruli each minute

some 650ml is plasma; about one-fifth of this (120-125) is forced into the renal tubules

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Kidneys consume 20-25% of all oxygen used by the body at rest

true

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Filtrate contains

everything found in blood plasma EXCEPT proteins

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Urine contains

mostly metabolic wastes and unneeded substances.

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The kidneys process 180L (47 gallons) of blood derived fluid daily

of this amount less than 1% typically leave the body as urine

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Glomerular Filtration Pg 970

passive process ; hydrostatic pressure forces fluids and solutes through; "simple mechanical filter", because filtrate formation doe not consume metabolic energy

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Glomerulus filtration membrane

has a large surface area and is thousands of times more permeable to water and solutes

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Glomerular BP

higher than that in other capillary beds (55mm Hg as opposed to 18 mm Hg); Resulting in a much higher net filtration pressure

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As a result of these differences, the kidneys produce

180L of filtrate daily, in contrast to the 2 to 4 L formed daily by all other capillary beds combined

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Molecules smaller than 3nm in diameter

such as water, glucose, amino acids and nitrogenous wastes; pass freely form the blood into the glomerular capsule

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Keeping plasma proteins in capillaries

due to colloid osmotic pressure of the glomerular blood

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proteins or blood cells in the urine indicates a problem with the filtration membrane

True

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Net Filtration Pressure (NFP) Pg 971

responsible for filtrate formation

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Glomerular hydrostatic pressure (HPg)

glomerular BP; chief force pushing water and solutes out of the blood and across filtration membrane.

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HPg is opposed by two forces

colloid osmotic (oncotic) pressure of glomerular blood (OP); capsular hydrostatic pressure (HP)

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Glomerular filtration Rate (GFR)

volume of filtrate formed each minute

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Factors governing filtration rate

total surface area available for filtration Filtration membrane permeability NFP (10mm Hg)

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Normal GFR ,in adults, in both kidneys is 120-125 ml/min

true

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Glomerular pressure drop of only 18%,

stops filtration altogether

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GFR is directly proportional pg972

to the NFP; any change in pressure changes both;

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Increase in arterial(and glomerular) BP in the kidneys INCREASES the GFR

in the absense of regulation

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Regulation of Glomerular filtration Pg 972

GFR is regulated by both intrinsic and extrinsic controls.

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Kidneys need constant GFR to do their job

on the other hand; the body needs constant BP and therefore a constant blood volume

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Intrinsic controls (renal autoregulation)

act locally within the kidney to maintain GFR

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Extrinsic controls (by nervous and endocrine system)

maintain BP

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In extreme changes in BP (less than 80, higher than 180)

extrinsic controls take precedence over intrinsic controls

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Intrinsic controls (Renal autoregulation)

adjusting its own resistance to blood flow; 2 types of controls- myogenic mechanism and tubuloglomerular feedback mechanism

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Myogenic mechanism

reflects tendency of vascular smooth muscle to contract when stretched

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Increasing systemic BP causes the AFFERENT arterioles to constrict

which restricts blood flow into glomerulus and prevents glomerular BP from rising to damaging levels

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Declining systemic BP causes dilation of afferent arterioles and raises glomerular hydrostatic pressure

both responses help maintain a normal GFR

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Tubuloglomerular feedback mechanism

autoregulation ; directed by the MACULA DENSE cells of the JUXTAGLOMERULAR apparatus

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When GFR increases

there is insufficient time for reabsorption and the concentration of NaCl in the filtrate remains high. This causes the macula dense to release vasoconstrictor chemical (probably ATP) that causes tense constriction of the afferent arteriole

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Extrinsic Controls; Neural and Hormonal Mechanisms Pg 972

purpose is to maintain systemic BP; sometimes to the detriment of the kidneys!

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Sympathetic nervous system controls

volume of extracellular fluid is normal-sympathetic nervous system is at rest-the renal blood vessels are DIALATED and renal auto regulation mechanisms prevail

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During extreme stress or emergency , neural controls may overcome renal autoregulatory mechanisms

true

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Renin-angiotensin Mechanism

triggered when various stimuli cause the granular cells to release the hormone RENIN

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Renin

acts enzymatically on ANGIOTENSINOGEN; converting it to ANGIOTENSIN I; this, in turn, is converted to ANGIOTENSIN II by ANGIOTENSIN CONVERTING ENZYME(ACE)

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Angiotensinogen

plasma globuloin made by the liver

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Angiotensin II acts to;

potentent vasoconstrictor; activates smooth muscle of arterioles throughout the body, raising mean arterial BP

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Angiotensin II acts to

stimulate hypothalamus to release hormone and activate the hypothalamic thirst center, both of which increase blood volume

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Angiotensin II acts to

stimulate reabsorption of Na+. Both directly by acting on renal tubules and indirectly by triggering the release of aldosterone from the adrenal cortex; Because water follows Na+, blood volume and BP rise

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Angiotensin II acts to pg973

increases fluid reabsorption by decreasing peritubular capillary hydrostatic pressure; this pressure drop occurs because the efferent arterioles constrict and the downstream drop in hydrostatic pressure allows more fluid to move back into the peritubula

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Angiotensin II acts to

targets the glomerular mesangial cells, causing them to contract and reduce the GFR by decreasing the total surface area of tglomerular capillaries available for filtration

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REMEMBER: ALL of the effects of Angiotensin II are aimed at RESTORING blood volume and BP!

The vasoconstrictor and stimulating reabsorption of Na+ are most important

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Triggers for RENIN release Pg 974

Reduced stretch of the granular cells; Stimulation of the granular cells by input from activated macula densa cells: Direct stimulation of granular cells via B1-adrenergic receptors by renal sympathetic nerves

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Other factors affecting GFR

Prostaglandin E2 (PGE2); Intrarenal angiotensin II; Adenosine

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Prostaglandin E2 (PGE2)

vasodialatory paracrine counteracts vasoconstriction by norepinephrine and angiotensin II within the kidney. The adaptive value of these opposing action is to prevent renal damage while responding to body demands to increase peripheral resistance

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Intrarenal angiotensinII

Although we think of angiotensin II as a hormone; the kidney makes it's own, locally acting angiotensin IIthat reinforces effects of hormonal angiotensin II. Dampens resulting renal vasoconstriction by causing PGE release

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Adenosine

released as such or produced extracellularly form ATPreleased by macula dense cells. Although it functions as a vasodilator systemically, adenosine CONSTRICTS the renal vasculature

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anuria

low urinary output (less than 50ml/day); may indicate that glomerular BP is too low to cause filtration

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Renal failure and anuria can also result from

nephrons cease to function; acute nephritis, transfusion reactions, crush injuries

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Tubular Reabsorption (reclamation process) pg974

Selective trans/epitheilial process.;

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Reabsorbed sustances follow

either the Trans/cellular or Para/cellular route

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Trans/cellular Route

substances move through the LUMINAL MEMBRANE, the CYTOSOL, and BASOLATERAL MEMBRANE; then to the endo/thelium of the peritubular capillaries

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Movement in paracellular route between the tubule cells is

limited due to tight junctions.

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In Proximal Nephron

tight junctions are "leaky" and allow some important ions through (Ca, Mg, K, and some Na)

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Virtually all Organic nutrients are completely reabsorbed

REABSORPTION of WATER and many ions is continuously regulated and adjusted in response to hormonal signals

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Reabsorption Process is either

passive(no ATP) or active(at least one step driven by ATP directly or indirectly)

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Sodium Reabsorption Pg 974

SODIUM IONS are single most ABUNDANT CATION 80% of energy used for active transport is devoted to their reabsorption.

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Sodium reabsorption is

ACTIVE and via TRANS/CELLULAR route

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2 basic processes that promote active Na reabsorption

occur in each tubule segment; 1. Na actively transoported OUT of tubule cell by PRIMARY ACTIVE transport (a Na -K ATPase pump present in basalateral membrane)

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From there;

Na is swept by bulk flow of water into adjacent peritubular capillaries; Flow is RAPID due to low hydrostatic pressure and high osmotic pressure

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Most PROTEINS remain IN blood instead of being filtered out into the tubule

True

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SECONDARY active transport (symport or antiport carriers)

ACTIVE PUMPING of Na+ from tubule cells results in a strong ELECTROCHEMICAL gradient that favors its passive entry at the luminal face via secondary active transport or;

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via FACILITATED DIFFUSION through channels, this occurs

because 1) pump maintains the intracellular Na concentration at low levels, and 2) the K pumped into the tublu cells almost immediately diffuses out into the interstitial fluid via leakage channels, leaving interior tubule cell w/ NET NEGATIVE charge

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Reabsorption of Nutrients, Water, and Ions Pg 975

Reabsorption of Na by primary active transport provides energy and means for reabsorbing almost every other substance, even WATER

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Secondary active transport ("push" comes from gradient created by Na+ -K+ pumping at basolateral membrane) pg975

glucose, amino acids, lactate, and vitamins; Luminal carrier moves Na DOWN concentration gradient as it co transports (SYMPORTS) another solute

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Cotransported (SYMPORTED) solutes diffuse across

basolateral memebrane before moving into the peritubular capps

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Transport Maximum (Tm) (reported in mg/min)

reflects number of transport proteins in the renal tubules available to ferry each substance; Generally plenty of transporters; Tm high for glucose and few for substance of no use

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when Transport are saturated (all bound to substances)

the excess is excreted in urine; that is what happens to someone HYPERGLYCEMIC because of DM

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Passive tubular reabsorption Pg 975

encompasses osmosis, diffusion, and facilitated diffusion; substances move DOWN electrochemical gradients WITHOUT ATP.; establishes strong osmotic gradient, and water moves by osmosis into peritubular capps

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Aquaporins

transmembrane proteins; form water channels across cell membranes

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Aquaporins in continuously water-permeable regions

such as PCT, constant components of tubule cell membranes; makes body "obliged" to absorb water in the proximal NEPHRON regardless of its state of over- or under hydration.

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this water flow is called Obligatory water reabsorption

true

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Aquaporins are virtually absent

in luminal membranes of collecting duct UNLESS antidiuretic hormone is present

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as Water leaves tubules

concentration of solutes in filtrate increases and begin to follow gradients into peritubullar capps

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Solute following solvent

phenomenon ; explains the passive reabsorption of a number of solutes present in the filtrate; also explains in part why lipid-soluble drugs and environmental toxins are difficult to excrete;

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since lipid-soluble compounds can generally pass through membranes

they will follow their concentration gradients and be reabsorbed, even if this is "not desirable"

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Reabsorption capabilities of Renal Tubules and Collecting Ducts pg976 Pg976

PROXIMAL CONVOLUTED TUBULE, LOOP OF HENLE, DISTAL CONVOLUTED TUBULE

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Proximal convoluted tubule

PCT cells most active in reabsorption; Normally absorb all glucose, lactate, and amino acids and 65% of Na and water; 80% of bicarbonate, 60% of Cl, and 55% of K.

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Bulk of reabsorption of electrolytes is accomplished by the time filtrate reaches loop of Henle

nearly ALL uric acid and 1/2 of urea are reabsorbed in PCT, BUT, both are later secreted back into filtrate

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Loop of Henle

permeability changes dramatically; here, for the 1st time water reabsorption IS NOT coupled to solute reabsorption.

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Water can leave the DESCENDING loop but not ASCENDING loop

where aquaporins are scarce or absent in the tubule membrane.

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Permeability differences play a vital role in kidney ability to form dilute and concentrated urine

True

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Rule of water is

it leaves descending (but not ascending) limb of Henle and OPPOSITE is true for SOLUTES

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Virtually NO solute reabsorption occurs in the descending limb, but

both active and passive reabsorption of solute occus in the ascending limb.

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In THIN PORTION of ascending limb

Na moves passively down gradient created by water reabsorption

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Na+ -K+ -2Cl symporter is main means of Na entry at lumina surface in THICK PORTION of ascending limb

true

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Na -K ATPase operates

at basolateral membrane to create ionic gradient that drives the symporter.

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Thick ascending limb also

has Na -H antiporters

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50% of sodium passes via paracellular route in thick region

true

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Distal Convuluted tubule and Collecting ducts pg978 Pg978

by time DCT is reached only 10% of originally filtered NaCl and 25% of water remain in tubule

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Most reabsorption from this point on depends on the bodies needs

and is regulated by hormones (mainly aldosterone for Na, ADH for water, and PTH for Ca

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In absence of ADH, the collecting duct is relatively impermeable to water

so reabsorption of more water depends on presence of ADH, which insert aquaporins

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Aldosterone "fine tunes" reabsorption of remaining Na

decreased BV or BP, low extracellular Na concentration (hyponatremia), or high extracellular K concentration (hyperkalemia) can cause adrenal cortex to release aldosterone to the blood

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Except for hyperkalemia (which directly stimulates the adrenal cortex to secrete aldosterone)

these conditions promote the renin-angiotensisn mechanism,w which in turn prompts the release of aldosteone

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little or no Na leaves the body in urine w/ aldosterone

without aldosterone, much less Na is is reabsorbed , resulting in Na losses of about 2% of Na filtered daily an amount IMCOMPATIBLE WITH LIFE

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Aldosterone's Role (conserve Na)

increase BV , and therefor BP, by enhancing Na reabsorption. Also reduces K concentrations because it induced reabsorption of Na is couple to K secretion in principal cells. That is Na enters K moved into lumen

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Atrial natriuretic peptide (ANP) reduces

Na, thereby decreasing BV and BP; Released by cardiac atrialcells when BV or BP is elevated, ANP exerts sever effects that lower Na content

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Failure of tubule cells to reabsorb some solutes is an important way of clearing plasma of unwanted substances

another way is TUBULAR SECRETION

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Tubular Secretion

essentially reabsorption in reverse; H, K NH, creatinine and certain organic acids either move into the filtrate from the peritubular capps through the tubule cells or are synthesized in the tubule cells and secreted.

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Urine eventually exerted contains both filtered and secreted substances.

with one major exception, (K) the PCT is the MAIN site of SECRETION, but the cortical parts of the COLLECTING DUCTS are also active

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Tubular secretion is important for; Pg 978

Disposing of substances Eliminating undesirable substances Ridding the body of excess K Controlling blood pH

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Regulation of Urine Concentration and volume pg979 Pg 979

crucial renal function is to keep the solute concentration of body fluids constant

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Osmolality is

number of solute particles dissolved in 1 kg of water and reflects solution's ability to cause osmosis

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1 osmol (equivalent to 1 mole of particles)

because this is a fairly large unit, the milliosmol (mOsm) equal to 0.00l osmol, is generally used

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Kidneys keep the solute load of body fluids constant at 300 mOsm

the osmotic concentration of blood plasma, by regulating urine concentration and volume

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Countercurrent mechanisms

fluid flows in opposite direction through adjacent segments of the same tube connected by a hairpin turn

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Countercurrent mechanisms are

1) the interaction between flow of filtrate through ascending and descending limbs of long loops of Henle of juxtameduallary nephrons (the COUNTER CURRENT MULTIPLIER. 2) the flow of blood through the ascending and descending portions of the vasa recta

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Vasa Recta blood vessels are

the countercurrent exchanger

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Osmolality of filtrate entering PCT is identical to plasma, 300 mOsm

because of PCT reabsorption of water and solutes, filtrate is still iomotic w/ plasma by the time it reaches the descending limb.

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Osmolality increases from 300 to 1200 mOsm in the deepest part of the medulla

true

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filtrate in the loops of Henle and blood in the vasa recta - first descend an then ascend through parallel limbs

true

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Countercurrent multiplier functions because of two factors Pg979

1)descending limb of loop is relatively impermeable to solutes and freely permeable to water 2) ascending limb is permeable to solutes, but not to water

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Uria recycling and the Medullary Osmotic Gradient pg981 Pg 981

Urea enters the filtrate by facilitated diffusion in ascending thin limb; water reabsorbed; now highly concentrated is transpired by facilited diffusion out of tubule into IF of the medulla, forming pool of urea; recycles back into thin limb

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ADH, stimulates exertion of urine,

enhances urea transport in medullary collecting duct. When ADH is present, urea recycling is enhanced, medullary osmotic gradient is enhanced and more concentrated urine can be formed

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Countercurrent Exchanger (vasa recta function as this) Pg 981

maintaining gradient ; blood flow is sluggish;passive exchanges w/ IF. as blog flows into medullary depths, it LOSES water and GAINS sal (hypersonic). as it emerges from medulla to cortex, it picks up water and loses salt

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Water picked up by ascending vasa includes not only water lost from descending vasa, but water reabsorbed form loop

As a result, volume of blood at the end of the vasa recta is GREATER than at the beginning

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Vessels of the vasa recta act as

countercurrent exchangers; this system does not create the medullary gradient, but it protects it by preventing rapid removal of sal an removing reabsorbed water

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Formation of Dilute or Concentrated Urine Pg 981

w/o gradient you would not be able to raise the concentration of urine above 300 mOsm; as a result you would not be able to EXCRETE excess solutes to lower your body's osmolality

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ADH ( Inhibits diuresis, or urine output)

controlling reabsorption of water from filtrate order to adjust the body's osmalality

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Dilute Urine

When ADH is not ring released; the collecting ducts remain essentially impermeable to water du to absence of aquaporins in luminal cell membranes, and no further water reabsorption occurs

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Na and selected other ions can be removed from the filtrate by DCT and collecting duct cells so that urine becomes even more dilute before entering the renal pelvis

osmolality of urine can plunge as low as 50 mOsm about one sixth the concentration of glomerular filtrate or blood plasma

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Concentrated Urine

formation of concentrated urine depends on medullary osmotic gradient and the presence of ADH

🗑

In distal tubules filtrate osmolality is 100 mOsm

as filtrate flows through the collecting ducts and is subjected to hyperosmolar conditions, water rapidly leaves followed by urea

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Depending on amount of ADH released

urine concentration my rise as high as 1200 mOsm, the concentration of IF in the deepest part of the medulla

🗑

Maximal ADH secretion,

up to 99% of water is reabsorbed and returned to blood, half a liter per day of highly concentrated urine is excreted

🗑

Ability of our kidneys to produce such concentrated urine is

critically tied to our ability to survive w/o water

🗑

Facultative water reabsorption

Water reabsorption that depends on the presences of ADH

🗑

ADH release is enhanced by

any event that raises plasma osmolality above 300 mOsm, such as sweating diarrhea, or reduced BV or BP

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Release of ADH is the "signal" to produce concentrated urine that opens the door for water reabsorption (through aquaporins)

Kidneys ability to respond to signal depends on the high medullary osmotic gradient

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Diuretics Pg 982

several types; chemicals that enhance urinary output

🗑

osmotic diuretic

substance that is not reabsorbed and that carries water out with it

🗑

Alcohol, essentially a sedative, encourages diuresis by inhibiting release of ADH

other diuretics increase urine flow by inhibiting Na reabsorption and the obligatory water reabsorption that normally follows.

🗑

also, caffeine and many prescribed drug for hypertension or edema of congestive heart failure

common diuretics inhibit Na associated symporters.

🗑

Loop diuretics (like furosemide(lasix)

are powerful because they inhibit formation of the medullary gradient by acting as the ascending limb of Henle's loop. THIAZIDES are less potent and act at the DCT

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Renal Clearance Pg 984

refers to volume of plasma that is cleared of a particular substance in a given time(usually 1 min)

🗑

Renal Clearance Test are done

to determine the GFR which allows us to detect glomerular damage and followw the progress of renal disease

🗑

Renal clearance rate (RC)

in ml/min is calculated RC = UV/P where U = concentration of the substance in urine V = flow rate of urine formation P=concentration of the substance in plasma

🗑

Insulin

freely filtered and neither reabsorbed nor secreted by the kidneys; is standard used to determine the GFR

🗑

Inulin (polysaccharid w/ a molecular weight of 5000

has a renal clearance value equal to GFR; when inulin is fused such that its plasma concentration is 1mg/ml(P = 1mg/ml), then generally U =125 mg/ml, and V = 1 ml/min. Therefor RC = (125 x 1)/1 = 125 ml/min

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Meaning that

in 1 minute the kidneys have removed (cleared) all inulin present in 125 ml of plasma

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chronic renal disease

GFR of less than 60 ml/min for at least three months

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Renal failure

GFR <15 ml/min; filtrate formation decreases or stops completely

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Urine Pg 984

color and transparency; UROCHROME, a pigment that results from the body's destruction of hemoglobin

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More concentrate the urine, the deeper the yellow color

abnormal color (pink or brown) eating certain foods or presence in the urine of bile pigments or blood

🗑

cloudy urine

indicated a urinary tract infection

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odor in urine

fresh is slightly aromatic, but let stand it develops ammonia odor as bacteria metabolize its urea solutes

🗑

uncontrolled DM urine smells fruity

because of its acetone content

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pH of urine

usually slightly acidic (pH 6) changes in body metabolism or diet may cause the pH to vary form 4.5 to 8.0.

🗑

A predominantly acidic diet that contains large amount of protein and whole wheat products produces acidic urine

Vegetarian (alkaline) diet, prolonged vomiting, and bacterial infection of the urinary tract all cause the urine to become alkaline

🗑

Specific gravity

urine is water plus solutes, a given volume has a greater mass than the same volume of distilled water; ratio of mass to mass of equal volueme of distilled water is SPECIFIC GRAVITY; distilled water 1.0; Urine ranges from 1.001 to 1.035

🗑

Chemical Composition Pg 985

95% water; 5% solutes;

🗑

largest component of urine by weight, apart form water, is UREA

derived from the normal breakdown of amino acids

🗑

Nitrogenous wastes

in urea, include uric acid (end product of nucleic acid metabolism) and creatinine (metabolite of creatine phosphate which stores energy for regeneration of ATP. Found in large amounts in skeletal muscle tissue

🗑

Normal solute constituents of urine (order of decreasing concentration)

urea, Na, K, PO, SO, creatinine, and uric acid; much smaller but highly variable amounts of Ca, Mg, and HCO are also present

🗑

High concentrations of any solute or the presence of abnormal substances such as blood proteins, WBCs(pus), or bile pigments may indicate pathology

true

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Ureters Pg 985

Slender tubes that convey urine from kidney to bladder; begins at L2 as continuation of renal pelvis

🗑

Any increase in bladder pressure

compresses and closes the distal ends of the ureters

🗑

Ureter wall has three layers

transitional epithelium of its lining MUCOSA is continuous w/ that of kidney pelvis superiorly and bladder medially; Middle MUSCULARIS two smooth muscle sheets (internal longitudinal layer, external circular layer)cont'd

🗑

An additional smooth muscle layer, the extrnal longitudial layer, arrears in lower third of ureter. The ADVENTITIA covering the ureter's external surface is typical fibrous connective tissue

true

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Ureter plays an active role in transporting urine;

incoming urine distends ureter and stimulates muscularis to contract, propelling urine into bladder

🗑

Urine DOES NOT reach the bladder through gravity alone

strength and frequency of peristaltic waves are adjusted to the rate of urine formation

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Each ureter is INNERVATED by both SYMPATHETIC and PARASYMPATHETIC fibers

BUT neural control of peristalsis appears to be insignificant compared to the way ureteral smooth muscle responds to stretch

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Bladder Pg 986

smooth, collapsible, muscular sac; stores urine temporarily;

🗑

interior of the bladder has openings for

both ureters and urethra

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Trigone

smooth, triangular region of the bladder base outlined by these three openings; Important clinically because INFECTIONS tend to persist here

🗑

Bladder wall has 3 layers

mucosa(transitional epithelium) Thick muscular layer Fibrous adventitia (except on its superior surface)

🗑

Detrusor muscle

muscular layer; consists of intermingled smooth muscle fibers arranged in inner and outer longitudinal layers and a middle circular layer

🗑

Rugae

bladder folds

🗑

Moderately full bladder

12cm (5inches); holds 500 ml (1 pint); Can hold double; When tense w/ urine it can be palpated well above the pubi symphysis; MAX capacity 800-1000ml

🗑

Urethra Pg 987

thin-walled muscular tube; drains urine from bladder to outside body; epithelium of mucosal linin is pseudostratified columnar;but Near the bladder it becomes transitional epithelium; near external opening changes to stratified squamous

🗑

Internal urethral sphincter

at bladder-urethra junction; thickened detrusor smooth muscle; involuntary; UNUASUAL in that contraction OPENS, relaxation CLOSES it

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External urethral sphincter

surrounds urethra as it passes through the UROGENITAL DIAPHRAGM; skeletal muscle; voluntarily controlled

🗑

Levator ani muscle of pelvic floor

also serves as a voluntary constrictor of the urethra

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Female urethra

Female urethra 3-4cm(1.5 in); tightly bound to anterior vaginal wall by figrous connective tissue

🗑

External urethral orifice

external opening; lies anterior to vaginal opening and post to clit

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Male urethra

20cm(8in); 3 regions

🗑

Prostatic urethra (1inch)

runs w/in prostate

🗑

Membranous urethra

runs through the urogenital diaphragm, extends about 2cm from prostate to beginning of penis

🗑

Spongy urethra (15cm)

passes through the penis and opens at the tip via EXTERNAL URETHRAL orfice

🗑

Micturition (urinate) Pg 988

In order for this to occur; detrusor muscle must contract, internal urethral sphincter must open, external urethral sphincter must open

🗑

Detrusor muscle and its internal urethral sphincter

composed of smooth muscle; innervated by both Para and Sympathetic nervous systems, which have opposing actions

🗑

External urethral sphincter is

skeletal muscle; is innervated by the somatic nervous system

🗑

Spinal reflex coordinate the process of micturition

urine accumulates, bladder distends activating stretch receptors; impulses travel vi avisceral afferent fibers to sacral region of spinal cord; cont'd

🗑

Visceral afferent impulses, relayed by sets of interneurons, excite parasym neurons and inhibit symp neurons

as a result, detrusor muscle contracts nad internal sphincter opens; Visceral afferent impulses also inhibit tonically active somatic effernts that keep the external urethral sphincter closed

🗑

by age 2 descending circuits have matured enought to begin to override relexive urination

Pons has two centers that participate in control of urination; PONTINE STORAGE center inhibits, PONTINE MICTURITION center promotes this reflex

🗑

lower bladder volumes activate the pontine storage center

which acts to inhibit urination by suppressing parasym and enhancing symp output to bladder

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Choose not to void

reflex bladder contractions subside

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Developmental Aspects Pg 988

3 different sets of kidneys develop from the UROGENITAL rigdges, paired elevations of the intermediate mesoderm that give rise to both urinary organs and reproductive organs

🗑

Pronephros

(4th week)first tubule system forms then quickly degenerate as second, lower set apprears; NEVER function; gone by 6th week

🗑

Pronephric duct

connects pronephros to cloaca; it is retained and used by later developing kidneys

🗑

The cloaca is the terminal part of the gut that opens to the body exterior

true

🗑

Mesonephros (middle kidney)

2nd renal system claims the pronephric duct (now called mesonephric duct); these degenate once the 3rd set makes their apperance

🗑

Metanephros (after Kidneys)

3rd set; 5th week; URETERIC BUDS push superiorly from mesonephric duct

🗑

Ureteric ducts

become ureters

🗑

Mestanephric kidneys excrete urine by 3rd month

true

🗑

as metanephros develope

cloaca subdivides to form the future rectum and anal canal and the UROGENITAL SINUS, into which urinary and genital ducts empty

🗑

Urinary bladder and the Urethra develope

from urogenital sinus

🗑

Hypospadias

male infants only; orifice is located on the ventral surface of the penis

🗑

Polycystic kidney disease (PKD)

disorder; presence of many fluid filled cysts in kidneys; cause renal failure

🗑

adult urine output

1500 ml/day

🗑

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