Chapter 20: Urinary Part 2

What is GFR?

the amount of fluid filtered by the glomeruli over time

Kidneys receive 25% of cardiac output which means 25% of the blood pumped by the heart is?

going to kidneys

20% of the blood is filtered by glomerular capillaries which means?

20% of the blood is entering the glomeruli is filtered

Average adult GFR is?

125 mL/min or 180L/day

Blood plasma is filtered about?

60x/day

Only a small percentage of the filtrate is excreted as urine the rest is?

reabsorbed back into blood

Factors affecting GFR is?

GFR is directly proportional to net filtration NFP when NFP increases GFR does too and same for decreasing.

Changes in glomerular or capsular hydrostatic pressure, colloid osmotic pressure and changes in diameter (afferent or efferent)

Regulation of glomerular filtration rate GFR:

autoregualtion, JGA, tubuloglomerular feedback

Autoregulation keeps GFR constant:

increased blood pressure causes vasoconstriction of afferent arterioles this reduces blood flow to the glomerulus and decreases GFR

Juxtaglomerular appartus (JGA) and tubularglomerular feedback:

increased GFR increases filtrate in renal tubules, excess NaCl reaches macula densa in distal tubule, afferent arterioles constrict, and GFR decreases toward normal range

Hormonal control by cardiac hormones:

heart releases ANP and BNP when blood volume and pressure increase, hormones increase sodium and water excretion

Your body controls GFR in two main ways:

sympathetic nervous system (neurol control) and hormonal control (renin AA system)

Sympathetic nervous system helps control GFR when blood pressure does what?

change (affect kidneys)

When blood pressure or volume decreases sympathetic stimulation causes?

afferent and efferent arterioles to constrict and helps GFR maintain normal range

Hormonal control (renin AA system) is also called?

renin angiotensin system

Hormonal renin AA system becomes activated when?

BP decreases, sympathetic stimulation, macula densa

Steps for hormonal renin AA system:

secretion of renin, renin convert of angiotensinogen to angiotensin I then to angiotensin II by ACE, vasoconstriction, increase blood pressure

Tubular reabsorption is what?

movement of useful substances from the renal tubules back into the blood of peritubular capillaries

Most tubular reabsorption 70% occurs where?

proximal tubule which is lined with microvilli

Different parts of the renal tubule reabsorb?

specific substances

Substances are transported by various methods of transport:

diffusion and osmosis

Diffusion:

passive transport of lipd-soluable substances

Osmosis:

passive transport of water sometimes containing solutes

Active transport is?

movement of substances against their concentration gradients

Active transport has a limited transport capacity because of?

number of carrier proteins

With active transport each substance has a transport maximun Tm meaning?

there is a limit to how much can be transported in a certain amount of time

Renal plasma threshold is reached when there is more transported substance in the plasma than the?

active transport mechanisms can handle and the excess spills forming urine

Substances that are reabsorbed by active transport is?

glucose, amino acids, lactic acid, phosphate, sulfate, calcium, potassium, and sodium ions

70% of Na ions are reabsorbed in proximal tubule by?

active transport

Na+ active transport provides energy and method for reabsorption of many nutrients:

glucose, amino acids, ions, vitamins, and H2O

Na+/K+ pumps create gradient that provides for reabsorption by?

secondary active transport

Secondary active transport:

Na+ moves down concentration gradient

other substances move with Na+ into renal tubule cells

Glucose and ions (Cl- and HCO3-) are reabsorbed this way

proces continues through renal tubules

97 to 99% Na and H2O are reabsorbed before?

excretion of urine

ADH = increases water reabsorption and what does Aldosterone do?

increases sodium reabsorption

What is tubular secretion?

the movement of substances from the blood into the renal tubules

What is tubular secretion the reverse of?

tubular reabsorption

What does tubular secretion remove?

wastes and large molecules that were not filtered by the glomeruli

Active transport mechanisms function in tubular secretion but do what?

work in opposite direction as tubular reabsorption

Substances secreted into forming urine are?

drugs, ions like K+ and H+

What is the purpose of secreting H+ ions?

to regulate the pH of body fluids

What happens to K+ ions as Na+ ions are reabsorbed?

K+ ions are secreted in the distal tubule

What is the difference between reabsorption and secretion?

reabsorption is renal tubules to blood and secretion is blood to renal tubules

What two hormones affect the solute concentration of urine?

aldosterone and cardiac natriurtic peptides

What does aldosterone stimulate?

sodium reabsorption

How do kidneys concentrate urine?

by reabsorbing large amounts of water

What happens to the distal tubule and collecting duct without ADH?

they are impermeable to water

What type of urine is produced without ADH?

dilute urine

What happens to the distal tubule and collecting duct when ADH is present?

they become permeable to water

How is water reabsorbed when ADH is present?

by osmosis

What happens to urine concentration when ADH is present?

urine becomes more concentrated

What happens to urine volume when ADH is present?

urine volume decreases

Which nephrons are more important for water reabsorption?

juxtamedullary nephrons

What does ADH stand for?

antidiuretic hormone

What happens when the body reabsorbs large amounts of water?

urine becomes more concentrated

What is the difference between urine with ADH and without ADH?

with ADH is less concentrated urine and without is more dilute urine

What is the purpose of the countercurrent multiplier?

keeps the medullary interstitial fluid hypertonic so concentrated urine can be produced

Which nephrons use the countercurrent multiplier?

juxtamedullary nephrons

What happens in the thick ascending limb?

it is impermeable to water and actively reabsorbs Na+ and Cl-

What happens to the interstitial fluid in the ascending limb?

it becomes hypertonic

What happens to water in the descending limb?

water leaves by osmosis because it is permeable to water

What happens to the tubular fluid in the descending limb?

it becomes hypertonic more concentrated

Why is it called countercurrent multiplier?

because each cycle increases the NaCl concentration in the ascending limb

What is the countercurrent exchanger and where does it occur?

it occurs in the vasa reacts of juxtamedullary nephrons, and no active transport occurs

What is urea?

a by product of amino acid catabolism

What does plasma urea concentration reflect?

The amount of protein in the diet

How does urea enter the renal tubules?

through glomerular filtration

What happens to urea in the renal tubules?

it undergoes tubular reabsorption and tubular secretion

How much urea is reabsorbed what percentage?

up to 80% the rest is excreted in urine

What is uric acid?

a product of nucleic acid metabolism

How does uric acid enter the renal tubules?

through glomerular filtration

What happens to filtered uric acid?

active transport completely reabsorbs it

How much uric acid enters the urine through tubular secretion?

10%

What can excess uric acid cause and what happens during it?

gout; uric acid forms crystals in the joints that causes pain

objective 10