NOVA- Anesthesia Physiology Exam 3- Renal

K, Ca, and Mg

What three electrolytes should be excreted by the kidney?

ECF

What is the main homeostatic variable for the renal system?

Nephron

What is the functional unit of the kidney?

-kidney failure= loss of these

Glomerulus

-primary urine formation

-enveloped by bowman's capsule

-hydrostatic pressure is strongest here to push the fluid into the capsule

Six

How many different distal tubules converge with a single collecting duct?

Cortical nephrons

What nephron type makes up 85% of all nephrons?

-glomeruli is in outer cortex and loop of henle are short

Juxtameduallry nephrons

What nephron type makes up 15% of all nephrons?

-glomeruli deep in cortex and loops of henle are long

-important for urine concentration

-reabsorb a higher proportion of glomerular filtrate (salt conserving)

Juxtameduallry

When effective circulating blood volume is low, higher proportion of renal blood flow is directed to _______ nephrons to help conserve ECF

150-200L

Glomerular filtration of plasma occurs at a rate of _____ daily

-98% is reabsorbed

Renal insufficiency

What occurs when GFR is low?

60

Magic number for GFR?

-any lower suggests different stages of chronic kidney disease

Proximal tubule

Rate of reabsorption for most substances is highest where?

-first site for reabsorption of Na+, K+, H2O, and other nutrients and secretion of H+

Distal tubule

Where does fine control of excretion usually occur?

-site of reabsorption of Na+ and H2O and secretion of H+ and K+

Filtration

What ONLY occurs at Bowman's capsule?

Loop of Henle

Functions to dilute or concentrate the urine

Descending limb

Where in the loop of Henle is water reabsorbed?

Ascending limb

Where in the loop of Henle is NaCl reabsorbed?

1/4

How much CO goes to the kidneys?

Renal blood flow

High rate of _____ _____ _____ is needed to supply enough plasma for glomerular filtration

-this is autoregulated across a wide range of MAP

Sympathetic vasoconstriction

RBF can be reduced by what if ECF needs to be conserved?

Peritubular capillary bed

What receives reabsorbed H2O and solutes?

-is supplied by efferent arterioles in series with glomerular capillaries

Vasa recta

What travels with the loop of Henle and is involved in urine- concentrating mechanisms?

Afferent and efferent arterioles

Where is the site of greatest vascular resistance located in the kidney?

-these are altered to change GFR

-changes in these alter vascular resistance and glomerular capillary hydrostatic pressure (changes in RBF and GFR)

Acute renal failure

Decrease in GFR occurring over hours to days

Chronic renal failure

GFR is persistently low for more than 3 months

Prerenal ARF

-most common cause of acute renal failure

-any condition that results in renal hypoperfusion (hypovolemina)

Renal ARF

Directly results in damage to the renal parenchyma

Postrenal ARF

Causes obstruction of urinary tract

-e.g. kidney stones

Macula densa

What senses effective circulating blood volume?

Renin

Hormone secreted by the kidney to raise blood pressure by influencing vasoconstriction when blood volume is low

-released by juxtaglomerular apparatus in response to a decrease in effective circulating blood volume

Atherosclerosis

What can cause a false low BP read by the macula densa, ultimately causing the release of renin and aldosterone for no reason

Renin angiotensin II aldosterone cascade

What is the most important endocrine axis in control of ECF?

Paraythyroid hormone

The liver produces the inactive form of vitamin D which is then converted into the active form by the kidney under control of what hormone?

-this is also the most important regulator of phosphate

Vitamin D

Promotes Ca2+ conservation by increasing intestinal Ca2+ absorption and by reducing urinary Ca2+ loss

Blood cells and plasma proteins

What two things should never be in the filtrate?

Nephrotic syndrome

Severe proteinuria, hypoalbuminemia, generalized edema, and hyperlipidemia

Nephritic syndrome

Hematuria, HTN, oliguria, and axotemia (inc. BUN/Cr concentration)

Albumin

What protein is about 70kDa and is almost small enough to be filtered but isnt because it is negatively charged?

-largest contributor to plasma oncotic pressure

Negative charges

At pH 7.4, proteins carry _____ _____, further reducing filtration

Glomerular capillary endothelial cell layer, glomerular basement membrane, and podocytes

What three factors make up the glomerular filtration barrier?

Glomerular capillary endothelial cell layer

-large fenestrations

-only excludes blood cells

Glomerular basement membrane

-fiber meshwork

-acts like a sieve for macromolecules

-negatively charged (proteins are stopped here)

Podocytes

Specialized endothelial cells provide narrow filtration slits that are bridged by a protein called nephrin

-negatively charged

60mmHg

What is the hydrostatic pressure in the glomerular capillary?

29mmHg

What is the oncotic pressure in the glomerular capillary?

15mmHg

What is the hydrostatic pressure in Bowman's space?

0mmHg

What is the oncotic pressure in Bowman's space?

Oncotic pressure in the glomerular capillary

What is the main factor that opposes filtration?

Hydrostatic pressure of glomerular capillary and oncotic pressure of bowmans capsule

What two factors favor filtration?

Hydrostatic pressure of bowmans capsule and oncotic pressure of the glomerular capillary

What two factors oppose filtration?

The filtrate that comes out

GFR= Puf x Kf

Puf= Pgc - (πgc + Pbc)

What is Puf?

Decreases

As blood passes from afferent to efferent arterioles, hydrostatic pressure _______ to allow blood to flow

Increases

Plasma oncotic pressure _______ along glomerular capillaries because fluid being filtered by proteins remains in the blood

-proteins exert a stronger pressure along the length because were losing H2O due to hydrostatic pressure

Hydrostatic pressure in bowmans space

What pressure NEVER CHANGES along the length?

Norepinephrine

What preferentially constricts afferent arterioles ultimately reducing RBF, GFR, and Na+ excretion?

Angiotensin II

What preferentially constricts efferent arterioles to reduce RBF but maintain GFR?

GFR

Whenever you alter the hydrostatic pressure of the glomerular capillaries, what factor will be proportionally altered?

RBF = Pgc = GFR

What three factors should be equal at baseline (in regard to the arterioles)?

Decrease in RBF, Pgc, and GFR

What happens when norepinephrine constricts the afferent arteriole?

Increase in RBF, Pgc, and GFR

What happens when the afferent arteriole is dilated?

Decrease in RBF, and increase in Pgc and GFR

What happens when angiotensin II causes mild constriction in the efferent arteriole?

Decrease in RBF, increase in πgc, and decrease in GFR

What happens when angiotension II causes extreme constriction in the efferent arteriole?

Increase in RBF and decrease in Pgc and GFR

What happens when efferent arteriole is dilated?

NSAIDs

What are vasodilators of the afferent arterioles?

ACE inhibitors and ARBs

What are vasodilators of the efferent arterioles?

Clearance

The volume of plasma rendered free of a given substance in one minute

-used to estimate GFR and RBF

Plasma creatinine

What is a direct index of GFR because its production is constant and excretion rate varies with GFR?

GFR

As creatinine increases, what decreases?

Filtered load

Amount of a substance filtered by unit time

Excretion rate

Amount excreted per unit time

Rate of net tubular transport

What is the difference between filtered load and excretion rate?

Reabsorption

ER

Secretion

ER>FL

Fractional excretion

-solute concentration as a percentage of filtered load

-useful because changes show altered tubular transport rather than changes in GFR

Clearance ratio

Ratio of solute clearance to creatinine clearance

-CrC should be normal, so we compare other values to this

Glucose in the urine

What happens in diabetics with poor glucose control?

-if plasma glucose increases, the filtered load increases and reabsorption mechanisms are saturated

Filtration and reabsorption

What are the only two significant processes affecting NaCl and H2O excretion?

Diuretics

What drugs inhibit tubular Na+ reabsorption?

Proximal tubule

What area of the nephron reabsorbs 70% of filtered Na+?

Loop of Henle

What area of the nephron reabsorbs 20% of filtered Na+?

Distal tubule/ common collecting duct

What area of the nephron reabsorbs 10% of filtered Na+?

Co-transporters

These are located in the early proximal tuble

-concentration gradients kept stable by Na+/K+ pump

-allows for reabsorption of glucose, amino acids, acids, and HCO3-

Na/ H

What is the only antiporter in the early proximal tubule?

Na/ H and Cl/ Formate

What are the two antiporters in the late proximal tubule?

Na/ K/ 2Cl

What is the triple transporter in the thick ascending limb of the loop of henle?

-all three must be present for this transporter to work!

Loop diuretics

What diuretics work in the thick ascending limb of the loop of henle by blocking Cl- from binding to the triple transporter?

-it prevents Na+ reabsorption, causing Na+ and water excretion in the filtration

-cause loss of Mg2+ and Ca2+

-lasix/ furosemide, bumetanide, torsemide

Thiazide diuretics

What diuretics work in the early distal tubule by blocking Cl- from binding to the Na+ Cl- co transporter?

Spirinolactone

-antagonist to aldosterone

-K+ sparing

-Na+ channel inhibition in cortical collecting duct

-K+ stays in the blood, and Na+ stays in the filtrate against their normal simple diffusion gradients kept up by the sodium potassium pump

Glomerular filtration, Na+ reabsorption without water reabsorption, and variable water permeability in collecting duct

What three processes are required for water balance over a wide range of plasma osmolarity to exist?

NaCl and H2O

Adequate glomerular filtration delivers what to the loop of Henle?

Na reabsorption without water reabsorption

What happens in the ascending limb of the loop of Henle to dilute tubular fluid (dilution of urine)

-causes meduallary interstitial fluid to become hypertonic--> potential to concentrate urine in the collecting ducts

Antidiuretic hormone

What controls water permeability in collecting duct?

-is under the influence of plasma osmolarity

-affects the kidney: formation of concentrated urine and retention of solute-free H2O in the body

-synthesized in hypothalamus and secreted from nerve terminals in the posterior pituitary

-determines where or not the kidney produces concentrated or dilute urine

increases; decreases

Large increases in ADH secretion occurs if osmolarity _____ and/ or blood volume ______

V1 receptors

Which receptors for ADH cause vasoconstriction?

V2 receptors

Which receptors for ADH cause renal water retention?

Stimuli for ADH secretion

-reduction in plasma volume of more than 10

-low pressure baroreceptors in atria/ lungs

-high pressure carotid baroreceptors

Nicotine

Increases secretion of ADH

Ethanol

Inhibits secretion of ADH

Increased plasma osmolarity

Why would the body produce urine that is more concentrated than the plasma?

Decreased plasma osmolarity

Why would the body produce urine that is more dilute than plasma?