Unit 10 - Kidney & Nephron Flashcards
What is the functional filtration unit of a kidney
A nephron
How many nephrons are in each kidney?
1 to 1.5 million
What does the nephron do?
Filter, reabsorb & secrete stuff that is in the blood.
What are the two basic divisions of the nephron?
Renal corpuscle and renal tubule
What is the Renal corpuscle?
Bowmans camsule - Cup-shaped portion of the renal tubule. Inner layer forms part of the filter that helps clean your blood.
Glomerulus - a small knot of capillaries tucked into bowman’s capsule. Blood enters via the afferent arteriole & exits via the efferent arteriole. Maintains relatively high pressure in glomerulus which ensures good filtration. The capillary cells are “holey” & so form the other parts of the filter.
How much of your total body blood supply passes through the kidneys every minute?
20-25%!
What is the glomerulus filtration rate?
125 mL/min
What is the proximal convoluted tubule?
Located nearest Bowman’s capsules & very twisted. Most reabsorption occurs here.
What is the Loop of Henle?
Hairpin portion of the nephron. Long descending limb, a loop, then a straight ascending limb. Water reabsorption.
What is the distal convoluted tubule?
From the ascending limb, the tubule once again gets twisty. Secretion & some reabsorption occurs.
What are the collecting tubules?
Extensions of the DCT that ultimately merge thus collecting filtered material from several nephrons & ultimately draining into the renal calyces.
What are the facts that affect the glomerular filtration rate? (GFR)
Prerenal, renal, postrenal
What are pre renal factors? Cardiac output
Normal cardiac output is about 5000 mL/min
20% or 1200 mL/min is routed through both kidneys.
Varies between 12-30%
Any decrease in cardiac output - decreased GFR
Any increase in cardiac output - increased GFR
What are pre renal factors? Arteriole pressure
Increases in blood pressure - increased glomerular pressure - increased GFR
What are pre renal factors? Blood Volume
Decreased blood volume - decreased RBF - reduced GFR
Increase in blood volume would result in renal blood flow and increased GFR
What are renal factors? Glomerular blood pressure
Pressure inside the capillaries that causes fluid to pass through the glomerular membrane into Bowman’s capsule, is about 8kPa (60 mm Hg).
What is Filtration pressure
The net pressure forcing fluid through the glomerular membrane
What is the permeability of glomerular membrane
The glomerular membrane is approximately a hundred time more porous than other capillaries found in the body.
Number of viable nephrons
The GFR is a function of the number of viable nephrons.
Not a direct relationship (there is some reserve capacity within each nephron to increase the filtration rate if the total number of nephrons declines).
what is tubular necrosis (death)
The effect of tubular necrosis is reduced GFR
Two possible causes:
Casts and cellular debris obstruct tubular lamina increasing the intratubular pressure, the net effect - decreased net filtration pressure and GFR.
Glomerular filtrate leaks back across the damaged renal tubular epithelium - “break-leak” hypothesis
What is renal calculi?
Urinary obstruction causes a significant reduction in the pressure gradient across the glomerular capillaries, which in turn reduces the GFR.
Similar to the “break leak” idea
What are post renal Factors?
Extrarenal Obstruction
Urethral occlusion can result from blasser, pelvic, or prostatic neoplasms; pro statism; surgical accidents; medications; calculi; pus; and blood clots.
The impact on the GFR is the same as in the case of renal calculi
What do the kidneys do?
Filter blood of metabolic wastes
Reabsorb any “good” stuff that was filtered
Recrete unwanted ions, drugs, hormones out of the blood into urine.
Regulate blood volume, blood pressure & composition (pH, ions)
Regulate red blood cell synthesis (erythropoietin)
Activate Vit D
What is fluid balance?
Fluid losses - Fluid gains
Water is ….
50 to 60 % of our body weight
55% is found inside our cells (ICF)
45% is in the ECF
Fluid Functions
Fluids can move between compartments relatively easily, so a change in one compartment will ultimately affect ALL compartments.
Plasma is used to..
transport nutrients & wastes throughout the body - its volume is fairly stable. A change in this fluid volume alters blood volume (& P), which impacts blood flow
Fluid balance within body compartments
Body fluids are more than just water.
The types and amounts of solutes are also important to overall homeostasis
Electrolytes (ions-charged particles) and proteins are the major solutes in the body fluids
A solute is any dissolved substance & that water follows solutes.
Factors affecting fluid balance
Pressure
If fluid pressure is higher in any one compartment, this pressure difference will cause fluids to move, until fluid pressure is equal in both compartments
Normally, blood pressure is fairly constant, so it already has little effect on fluid movements in the body.
Solute concentration and Osmosis
Electrolyte levels not only impact fluid levels, BUT also affect the functioning of all excitable cells.
So changes in electrolytes can impact blood volume and cell function.
Three categories that affect water balance
Organic compounds of low molecular weight
Organic compounds of high molecular weight
The inorganic electrolytes.
What are Organic compounds of low molecular weight?
Small molecular size compounds such as glucose, urea, amino acids, and lactate diffuse rather freely across capillary membranes but not across cell membranes.
Have little tendency to effect the movement of water. However, if present in large quantities, they cause the retention of water and thereby do influence the total body water.
what are the Organic compounds of high molecular weight?
The organic substances considered in this category are mainly the plasma proteins which are the only dissolved substances in plasma that do not diffuse readily through the capillary membranes.
It is the plasma proteins that are responsible for the osmotic gradient at the plasma capillary membranes.
What are inorganic electrolytes?
The osmolality of substances that ionize in solution is higher than that of substances that do not ionize.
The main cation in the ECF is sodium and the main cation in the intracellular fluid is potassium.
How can plasma osmolality be calculated?
Osmolality equals 2 x [Na+] + [glucose] + [urea nitrogen]
Na equation
[ ( Na+ + K+ ) ] TB
[ Na+ ]s = [ H2O ] TB
What is the tubule adjustment of water? (relation to the kidneys)
As the kidneys can only process blood, they rely on a countercurrent exchange mechanism to significantly adjust water levels.
This occurs in the Loop on Henle
What are the conditions necessary for countercurrent exchange in the kidneys?
- The flow of fluid in the tubules be in opposite directions.
- The tubules be in close proximity to one another.
- An osmotic gradient exists between the tubular fluid compartment and interstitial fluid
- there is a low medullary blood flow.
What is fluid regulation?
A balance between GFR and tubular reabsorption.
remember…
When the GFR is 125 mL/min, net tubular absorption is 124 mL/min resulting in the formation of 1.0 mL/min of urine for a 24 hr volume of 1440 mL.
At a GFR of 150 mL/min, tubular reabsorption is145 mL/min resulting in the production of 5 mL of urine each minute. The 24-hour urine output would then be 7200 mL (5 times the normal output)
What are the two major methods of controlling water levels?
ADH
When the hypothalamus detects that blood has too much solute (too salty) it releases ADH from the post. Pit. ADH opens the water channels in the collecting ducts which returns water to the blood, lowering the saltiness of the blood.
Aldosterone
When the juxtaglomerular apparatus detects low renal blood volume or changes in solute levels, they release renin. Renin activates angiotensin II which in turn does 3 things. Increases BP, releases aldosterone to cause the kidneys to absorb more Na, and stimulates the release of catecholamines from the adrenal medulla and increases sympathetic activity.
