Renal Physiology

What are the primary function of the kidneys?

regulate the extracellular fluid volume and composition

How is body weight divide up?

60% water, 40% intracellular fluid, 40% extracellular (75% interstitial fluid, 25% plasma)

What is osmotic pressure?

pressure applied to prevent osmotic movement of water across membrane

What is oncotic pressure?

protein osmotic pressure, is colloid osmotic

How is water movement between intravascular and interstitial fluid compartments done?

starling's forces

How does water move between intracellular and interstitial fluid compartments?

osmosis through aquaporins

How do small molecules move through the capillary wall?

through intercellular clefts and pores; small, lipid-soluble membranes permeate cell membrane

How do mid-sized molecules move through the capillary wall?

through pores if capillary is fenestrated, large, lipid-soluble molecules might permeate the cell membrane

How do macromolecules move through the capillary wall?

retained in all capillary types; think albumin and immunoglobulins

What are the starling forces?

capillary hydrostatic pressure, interstitial fluid hydrostatic pressure, capillary colloid oncotic pressure, interstitial fluid colloid oncotic pressure that determine whether fluid will move out of capillary lumen into interstitial fluid or in opposite direction

What is capillary hydrostatic pressure?

pressure exerted by blood against the wall of a capillary; pushed fluid out of capillaries; pressure increases as water leaves plasma

What is capillary oncotic pressure?

created by proteins (albumin) and attracts water to them that keeps water in capillaries; increase in proteins in plasma increases pressure; only force that drives water back into capillaries

What is intersitial fluid oncotic pressure?

osmotic pressure generated by plasma proteins in interstitial fluid

What is interstitial fluid hydrostatic pressure?

pressure exerted by interstitial fluid against the wall of a capillary

Which of the starling forces are usually low?

interstitial fluid hydrostatic and oncotic pressure

What changes would contribute to peripheral edema?

decrease in plasma oncotic pressure, increase in IF colloid osmotic pressure, increase in capillary hydrostatic pressure, lymphatic obstruction, increase capillary wall permeability to albumin

What could cause hypoalbuminemia?

decreased production (hepatic failure, malnutrition) or increased loss (urine, feces, skin)

In health what do the net forces favor in regards to plasma filtration?

plasma into interstitium

What is the conversion from kg to lb?

1 kg = 2.2 lb

What is the difference between osmolar and osmolal?

osmolar is per liter and osmolal is per kg

What is general trend of concentrations regarding sodium and potassium in extracellular and intracellular fluid?

sodium is high in extracellular fluid and low in intracellular fluid; potassium is low in extracellular fluid and high in intracellular fluid; maintained by Na/K pump

How is water able to move across a barrier and what governs this?

by aquaporins and is governed by osmosis

Where do extracellular proteins tend to stay?

in plasma, have low concentrations in interstitial fluid; helps retain fluid in intravascular space

What is tonicity?

effect of an extracellular solution on net water movement across

What is a hypotonic solution?

hypo-osmotic compared to intracellular fluid; net movement of water from extracellular to intracellular, volume increases, cell lysis, hemolysis

What is a isotonic solution?

iso-osmotic compared to intracellular fluid; no net movement of water, cell stays same size

What is a hypertonic solution?

hyper-osmotic compared to intracellular fluid; net movement of water from cell into interstitium; cell volume decreases; rbcs crenate

Remember Taco, the chihuahua, that got lost in the desert? What is the effect on extracellular osmolarity at the end of his trek?

increase extracellular osmolarity

Remember Taco, the chihuahua, that got lost in the desert? What is the effect on intracellular osmolarity at the end of his trek?

increase intracellular osmolarity

Remember Taco, the chihuahua, that got lost in the desert? What is the effect on plasma (Na+) at the end of his trek?

high

Remember Taco, the chihuahua, that got lost in the desert? What is the effect on plasma (albumin) at the end of his trek?

high

Remember Taco, the chihuahua, that got lost in the desert? What is the effect on his brain size at the end of his trek?

low, decreased

What is the short term effect of a diffusible solute that is in a urea and NaCl solution?

hyper-osmotic, hypertonic solution, cell shrinks

What is the long term effect of a diffusible solute that is in a urea and NaCl solution?

urea would equilibrate (move down concentration gradient and diffuse into cell) and pull water in

What is the effect of placing a cell into a hyperosmotic solution (mannitol and NaCl solution)?

hyper-osmotic, hypertonic solution, cell shrinks

What is the use of a isotonic crystalloid fluid?

replace extracellular fluid volume with dehydration, blood loss and provide maintenance fluid to animals that can't hydrate orally (normal saline, LRS)

What is the use of a hypotonic crystalloid fluid?

reduce osmolarity in severely dehydration animal with marked acute hypernatremia and provide fluid support for salt-sensitive animals (half-strength saline)

What is the use of a hypertonic crystalloid fluid?

replace extracellular fluid volume when blood loss or dehydration causes severe hypotension (low bp), treat acute hyponatremia or brain swelling (hypertonic saline)

What is the use of a colloid solution?

treat hypoalbuminemia where low capillary oncotic pressure, cause edema as fluid exits plasma and enters interstitium, improve blood volume (hetastarch)

What is the effect on ECFV, ICFV, and total protein in blood if you administer normal saline solution IV?

ECFV (IF and plasma volume) increase, no effect on ICFV, reduced total protein, dilutes plasma protein

What is the effect on ECFV, ICFV, and total protein in blood if you administer half strength saline solution IV?

ICFV increased, ECFV (IF and plasma volume) increases, total protein reduced, dilutes plasma protein

What is the effect on ECFV, ICFV, and total protein in blood if you administer hypertonic saline solution IV?

ICFV decreased, ECFV (IF and plasma volume) increased, total protein reduced, plasma protein diluted

What is the effect on ECFV, ICFV, and total protein in blood if you administer 20% mannitol IV?

ICFV decreased, ECFV (plasma and IF volume) increased, total protein reduced, plasma protein diluted

What is the initial effect of isotonic saline infusion?

ECF volume increases

What is the long term effect of isotonic saline infusion?

ECF volume is increased; no water flow

What is the initial effect of hypertonic saline infusion?

ECF volume and osmolarity increases

What is the long term effect of hypertonic saline infusion?

ECF volume and osmolarity increases; ICF volume decreases and osmolarity increases; water flows from ICF to ECF

What is the initial effect of hypotonic saline infusion?

ECF volume increases and osmolarity decreases

What is the long term effect of hypotonic saline infusion?

ECF volume increases and osmolarity decreases; ICF volume increases and osmolarity decreases; water flows from ECF to ICF

What is the effect of administering dextrose solution infusion?

initial increases ECF volume; glucose/dextrose metabolized so ECF volume increases and osmolarity decreases; in the end water flows from ECF to ICF, ECF and ICF volume high and osmolarity decreases

What are the functions of the kidneys?

regulate water and electrolyte balance, ECF volume and systemic bp, acid-base balance, excrete metabolic waste and foreign substances, regulate rbc production, regulate vitamin D production and Ca and P balance, gluconeogenesis

What is unique about bovine kidneys?

lobulated cortex and medulla

What kind of kidneys do primates and pigs have?

fused cortex and lobulated medulla

What kind of kidneys do dogs, cats, sheep, goats, and horses have?

fused cortex and medulla

What is the functional unit of the kidney?

nephron; kidney size, function and nephron number are proportional to body mass

What does the cortex contain?

renal corpuscles, coiled blood vessels, coiled tubules

What does the medulla contain?

straight blood vessels and straight tubules

What does the glomerular capillary network favor?

high capillary hydrostatic pressure and favors filtration

What does the post-glomerular capillaries favor?

low capillary hydrostatic pressure and favors reabsorption

What is unique about the feline kidney?

outer cortical venous drainage (nephrons drain into stellate veins that drain into renal veins at the renal hilum and are visible on capsular surface)

What is unique about the avian urinary system?

2 kidneys with 3 divisions, no distinct cortex and medulla, vessels/nerves go through kidneys, no renal pelvis, no urinary bladder (to cloaca)

What is true about nephrons in avians?

mammalian and reptilian nephrons (intermittent function, no loops of henle)

What is the function of the glomerulus?

massive filtration of water and small molecules

What are the special attributes of the glomerular capillaries?

high capillary hydrostatic pressure, highly permeable and highly selective barrier; prevent filtration of cells and large molecules

What is the filtration fraction?

20-30% of plasma entering glomerulus is filtered into bowman's space; = glomerular filtration rate/ renal plasma flow

What is the glomerular filtration rate?

how much kidneys are filtering

What is true about the tubules?

cells are polarized, proteins on basolateral side are different from the ones on the apical side; cells connected by tight junctions

What happens to water and small solutes entering the renal artery?

all blood goes through glomerulus, 20-30% of plasma water and small solutes are filtered by highly selective filtration barrier

What are the 3 key nephron processes and where do they occur?

filtration through glomerular capsule, reabsorption and secretion between renal tubule and peritubular capillaries

What substances are handled by filtration in renal system?

creatinine

What substances are handled by filtration and partial reabsorption in renal system?

water and electrolytes

What substances are handled by filtration and complete reabsorption in renal system?

glucose and amino acids

What substances are handled by filtration and secretion in renal system?

some metabolic waste products and drugs

What is the role of the glomerulus?

massive filtration of water and small molecules

What is the role of the proximal tubule?

bulk (2/3) reabsorption of filtrate without regard to body needs, complete reabsorption of glucose and amino acids, secretion of organic acids and bases

What is the role of the loop of henle?

reabsorption of Na+ and Cl- than water leading to hyperosmolarity of medullary interstitial fluid

What is the role of the distal tubule?

fine tuning, Na+, K+, and H+ homeostasis

What is the role of the collecting duct?

fine tuning; Na+, K+, H+ homeostasis, urine concentration; reabsorb water

What is the role of the lower urinary tract?

storage and controlled elimination of urine

What is true about blood flow in the medulla?

flow is low and slow

What does Poiseuille's law indicate?

resistance and radius are indirectly related

What is true regarding interlobular arteries?

radiate to surface; branches into multiple afferent arterioles with respective glomeruli, are parallel so less resistance to flow

What are cortical nephrons?

short loops of henle, don't reach inner medulla, short peritubular capillaries

What are juxtamedullary nephrons?

specialized peritubular capillaries called vasa recta that lie next to long loops of henle; role in formation of concentrated or diluted urine; centermost vasa recta supply capillaries in renal medulla (little blood flow into papilla) to maintain hyperosmolar medullary interstitium

What is the effect of the low and slow blood flow rate to medulla?

maintains high concentration of solutes in medullary interstitium and ability to produce concentrated urine

What are the attributes of glomerular capillaries?

high capillary hydrostatic pressure to favor filtration; highly permeable with highly selective barrier; massive filtration of small molecules

What is happening to hydrostatic pressures between afferent and efferent arterioles?

afferent arteriole is wide and short so hydrostatic pressure in glomerular capillaries are higher than peripheral capillaries and increases filtration rate, efferent arterioles offer resistance to blood flow

What is the glomerular filtration barrier made of?

glycocalyx is a negatively charged gel of glycoproteins

What is the filtration fraction?

= glomerular filtration rate/renal plasma flow; normal is 20-30% so that amount of water and small molecules entering glomerulus will be filtered into bowman's space

What is the glomerular filtration rate?

main determinant of renal function; excrete large amount of waste product, regulate internal environment; regulated by starling forces

How do you calculate filtration rate?

= filtration coefficient x net filtration pressure

What is filtration coefficient?

Kf; = hydraulic permeability x surface area

How do you calculate net filtration pressure?

glomerular capillary hydrostatic pressure (high) - bowman's space hydrostatic pressure - bowman's space oncotic pressure

What is renal autoregulation?

intrinsic renal feedback mechanisms can keep renal blood flow and GFR constant despite marked changes in arterial bp; constrict and dilate

How is GFR regulated?

modulating diameter and resistance of afferent and efferent arterioles

What is the effect of dilated afferent arterioles?

increase renal blood flow, increase GFR; L-type calcium channel blocker

What is the effect of constricted afferent arterioles?

decrease renal blood flow, decrease GFR; sympathetic nervous stimulation

What is the effect of constricted efferent?

decrease renal blood flow, increase GFR; angiotensin 2

What is the effect of dilated efferent?

increase renal blood flow, decrease GFR; inhibition of angiotensin 2

What are the transport mechanisms regarding the tubular cells?

transcellular path through cell membrane, channels, or transporters or paracellular path between tubular cells