HSC4555 Dr.Ferdowsi UCF Pathophysiology Test 4

kidneys responsible for

Maintaining fluid and electrolyte homeostasis

Ridding the body of water-soluble wastes

functional unit of kidney

nephron

nephrons can

regulate their own function

Each kidney contains how many nephron

one million

nephrons perform

all filtration, reabsorption, and secretory functions

nephrons filter how much

more than 7 L of fluid per hour

kidneys reabsorb what percentage of water

99%

how highly concentrated is urine

very highly concentrated

if 50% of nephrons are removed

No significant impairment of renal function

renal reserve is reduced

Serious renal impairment occurs when

75% and 90% of the total nephrons have been damaged

Clinical findings of chronic kidney disease may not be evident until

late in the course of chronic kidney disease

Urinary system structures

Kidneys

Ureters

Urinary bladder

Urethra

Kidneys Located in

the retroperitoneal space, under the diaphragm

Right kidney is slightly lower

than the left

external landmark useful for locating the kidneys

Costovertebral angle

kidney shaped like

a red kidney bean

kidney hilum faces

the vertebral column

Lymphatic vessels, blood vessels, and nerves enter and exit the kidney through

the hilum

what covers each kidney

thin, fibrous capsule

Renal parenchyma Divided into three main areas

Pelvis

Medulla

Cortex

renal pelvis

composed of urinary collecting structures called calyces

renal medulla

middle portion; contains the renal pyramids

renal cortex

outer portion; contains glomeruli and nephron tubules

nephron major functions

Filters water-soluble substances from blood

Reabsorbs filtered nutrients, water, electrolytes

Secretes wastes or excess substances into the filtrate

nephron composed of

Glomerulus

Tubule

Glomerulus composed of

Includes the capillary tuft and Bowman capsule

Tubule composed of

Proximal convoluted tubule

Loop of Henle

Distal convoluted tubule

Epithelial cells in each segment of the tubule are

specialized for certain functions

Nearly all cells in the nephron have a

single cilium

Mechanoreceptors and chemoreceptors

sense flow rate and composition of the tubular filtrate

Proximal convoluted tubule

Provides bigger surface areas for reabsorption

Proximal convoluted tubule Made up of

cuboidal epithelium

Proximal convoluted tubule Reabsorbs

2/3 of the filtered water and electrolytes

all of the glucose, amino acids, proteins, and vitamins

Water is reabsorbed passively in

Proximal convoluted tubule

Loop of Henle comprised of

Thin descending limb

Thick ascending limb

Thin descending limb of Loop of Henle

Receives filtrate from proximal convoluted tubules and delivers to ascending limb

Permeable to water

Thick ascending limb of Loop of Henle

Contains powerful Na+-K+-2Cl− cotransporters that pump ions into the interstitium

Impermeable to water

Which part of the loop of Henle is impermeable to water?

Thick ascending limb

Which part of the loop of Henle is permeable to water?

Thin descending limb

Distal convoluted tubule

makes hypo-osmotic Filtrate because of removal of electrolytes in the ascending loop of Henle.

Further reabsorption in Distal convoluted tubule

Aldosterone and angiotensin II

Atrial natriuretic peptide and urodilatin

Aldosterone and angiotensin II

stimulate distal convoluted tubule cells to reabsorb sodium and water

Atrial natriuretic peptide and urodilatin

Inhibit reabsorption in distal convoluted tubule

Collecting duct

Form the medullary pyramids

have Two cell types

cell types in collecting duct

Principal Cells (majority)

Intercalated Cells

Principal (P) cells

respond to antidiuretic hormone

majority type

Intercalated (I) cells

participate in acid-base balance by regulating secretion of acid

Glomerulus

Filters fluid from the blood into Bowman capsule; prevents the passage of blood cells and proteins

Proximal convoluted tubule

Transports two thirds of the filtered water and electrolytes and all of the filtered bicarbonate, glucose, amino acids, and vitamins from filtrate to interstitium

Ascending loop of Henle

Actively transports Na+, K+, Cl- to produce a hypo-osmotic filtrate and

a high interstitial osmolality

Distal convoluted tubule

Transports Na+, CI-, water, and urea; responsive to aldosterone; site of macula densa regulation of

GFR; secretes H+ and K+

Collecting tubule

Passive transport of water under the influence of ADH; secretes H+ and K*

normal Glomerular Filtration rate

125 mL/min

GFR determined by

filtration pressure in the glomeruli

the permeable surface of the glomerular membrane

what pressure factors favor filtration in GFR

Capillary hydrostatic pressure

Bowman capsule oncotic pressure

what pressure factors oppose filtration in GFR

Plasma/capillary oncotic pressure

Bowman capsule hydrostatic pressure

Filtration pressure varies from

the afferent end of the glomerulus to the efferent end

Factors affecting filtration pressure

blood volume

Pressure within Bowman capsule

plasma oncotic pressure

mesangial cells in the glomerulus

blood volume affects filtration pressure

if blood volume rises or falls, there is a change

if Blood volume increases gfr does what?

GFR increases, extra fluid is excreted

if Blood volume decreases gfr does what?

GFR decreases, fluid is conserved

Autoregulation protects

the glomerular capillary in GFR

Pressure within Bowman capsule can be caused by

obstruction in the tubules

Pressure within Bowman capsule can

can affect GFR

what factors affect plasma oncotic pressure and therefore GFR

plasma proteins,

ex low albumin increases gfr

Specialized mesangial cells in the glomerulus affect gfr how

if they contract, decrease gfr

if they relax, increase gfr

Each nephron can regulate

its own GFR

nephron autoregulation controlled by

Juxtaglomerular apparatus

Afferent constriction and efferent dilation of glomerulus affects gfr how

decrease GFR

Afferent dilation and efferent constriction of glomerulus affects gfr how

increase GFR

Macula densa

the Less sodium transported to macula densa cells in the distal tubule, the more it increases GFR

Effects of glucose and amino acids on GFR

an increase in tubular glucose and amino acids results in an increased amount of sodium reabsorbed by the proximal tubule, which causes an increased GFR

Specialized juxtaglomerular cells produce and release

renin

Reabsorption and secretion Across Renal Tubules Accomplished by

two routes:

Transcellular

Paracellular

Transcellular movement Across Renal Tubules

specific transporter proteins in the membranes of the tubular epithelial cells move substances between the tubular filtrate and the interstitial fluid.

Dependent on Na+ reabsorption

Possible by Na+-K+ pump in the basolateral membrane

Paracellular movement Across Renal Tubules

moves substrates through the tight junctions that hold the tubular epithelial cells together

Passive movement

Reabsorption of glucose Across Renal Tubules

Glucose filtered freely across the glomerular membrane

Normally all filtered glucose is reabsorbed in proximal tubule

glucose Transporters in Renal Tubules can be overwhelmed by

excessive tubular loads of glucose

results in Glycosuria

glucose is normally transported across renal tubules by

sodium-dependent cotransporter, SGLT2.

glucose renal threshold

Point at which glucose begins to spill into the urine

300 mg/dl

Serum glucose level of 300 mg/dl results in

significant glycosuria

Regulation of acid-base balance by kidneys

Kidneys excrete excess H+ and regulate the concentration of bicarbonate

HCO3− is filtered where in kidney

filtered freely through the glomerulus and must be efficiently reabsorbed to maintain acid-base balance

HCO3− is not directly reabsorbed across

the renal epithelium.

HCO3− Combines with H+ in the tubule to form

H2CO3

which dissociates into CO2 and water

Carbonic anhydrase catalyzes the reaction

intracellular carbonic anhydrase catalyzes

reverse reaction

forms HCO3− and H from H2CO3

HCO3− is transported out through the

basolateral membrane

Secretion of potassium across renal tubule

Promoted by activity of the Na+-K+ pump on the basolateral cell membrane

sodium potassium pumps in distal tubule regulated by

Aldosterone, which increases potassium excretion

Secretion of potassium Also affected by

activity of the K+-H+ exchanger

plasma K+ concentration

Kidneys regulate blood volume and osmolality by

altering GFR

reabsorption from the urinary filtrate

Antidiuretic hormone

Increases the permeability of the collecting tubule to water

increased reabsorption and reduced blood osmolality

Antidiuretic hormone is aka

vasopressin

which hormones Alter blood volume without affecting blood osmolality?

Aldosterone, angiotensin II, natriuretic peptides, urodilatin, uroguanylin, and guanylin

Aldosterone and angiotensin II increase

sodium and water reabsorption

natriuretic peptides and urodilatin inhibit

sodium and water reabsorption

Diuretic agents

Drugs that alter the osmolality of the urinary filtrate and oppose the reabsorption of water, resulting in an increase in urine volume

Osmotic diuretics increase

osmolality of the filtrate by causing more water to remain in the tubule

Osmotic diuretics

Increase solute load in tubule

ACE inhibitors

Block production of aldosterone and angiotensin II