renal Flashcards
What four systems are involved in excretion?
urinary, respiratory, digestive and integumentary
microscopic filtering units of the kidneys composed of renal corpuscle, renal tubules and a rich blood supply?
The nephron
What is the functional unit of the kidney?
The nephron
Where are the nephrons located?
mostly in the renal cortex with some tubules extending into renal pyramids of the medulla
What four processes are required for urine formation?
glomerular filtration
tubular reabsorption
tubular secretion
excretion
Define glomerular filtration.
glomerular filtration of water and solutes from the glomerular capillaries blood into Bowman’s capsular space
non-selective filter
Define tubular reabsorption.
tubular reabsorption of useful substances from renal tubules filtrate into the peritubular capillaries blood
Define tubular secretion and then excretion.
tubular secretion of waste products from the peritubular capillaries blood into the renal tubules filterate. Excretion then occurs as urine.
What is the ‘filtration membrane’ fromed from? What is the glomerular capillary hydrostatic pressure?
formed by the glomerular capillary wall and the visceral layer of Bowman capsule
60 mmHg
What does GFR stand for and what is the average L/day?
glomerular filtration rate
180 L/day
What is the equation for filtration fraction?
GFR/Renal Plasma Flow
In comparison to the glomerular capillary pressure; what is the blood capillary pressure in other parts of the body?
Ranges form 7-17 mmHg; opposed to the 60 mmHg in the glomerular capillary
What is used to calculate the net filtration pressure (NFP)?
Blood hydrostatic pressure (BHP), Colloid osmotic pressure (COP), and the capsular pressure (CP) BHP 60 mmHg OUT COP -32 mmHg IN CP -18 mmHg IN = 10 mm Hg OUT
What is fluid in the capsular space called and what does it NOT consist of?
glomerular filtrate- no blood cells, plasma proteins or fatty acids
What does glomerular filtrate contain?
metabolic wastes such as urea & uric acid
useful substances such as water, organic nutrients & electrolytes
Regulation is done by controlling the amount of glomerular blood flow. what effect does dilation of the afferent arteriole and constriction of efferent arteriole have on the GFR?
increase in GFR
Regulation is done by controlling the amount of glomerular blood flow. what effect does constriction of the afferent arteriole and dilation of efferent arteriole have on the GFR?
decrease in GFR
What 3 hormones DECREASE GFR?
NE, Epi, and endothelin
What 3 hormones INCREASE GFR?
PG, bradykinin, and enothelial-derived NO
What is autoregulation of GFR?
regulation of GFR by the juxtaglomerular/ macula densa apparatus that is found in every nephron
What is neural regulation of GFR?
sympathetic nervous system stimulation during exercise or in circulatory shock that DECREASES GFR
In tubular reabsorption, what is ultrafiltration?
Bulk flow- from the interstitial fluid through the peritubular capillary wall into the blood
In tubular reabsorption, what is transport maximum?
the amount of substance that can be transported before the transport proteins for that substance becomes fully saturated
How many liters of urine are excreted a day? How manyliters of water are reabsorbed per day?
1-2 liters of urine excreted/ day
148-178 liters of water are reabsorbed /day
Where does most of the water reabsorption take place?
- 65% in the proximal convoluted tubules (PCT)
- 15% in descending limb of loop of Henle (LOH)
- 10% in distal convoluted tubules (DCT)
- 10% in collecting ducts (CD)
How much water is reabsorped in the ascending loop of Henle?
NONE
What is passive water reabsorption coupled to?
passive water reabsorption by osmosis is coupled to sodium reabsorption
What is considered the ‘obligatory’ water reabsorption?
80%- in PCT and descending LOH
What water channel aids ‘obligatory’ water reabsorption? is it always open?
Aquaporin I
yes, it is always open
What is the ‘facultative’ water reabsorption?
20%- in DCT and CD
-this is variable depending on degree of body hydration
Facultative water reabsorption is controlled by what?
ADH activation of Aquaporin 2
What is the renal clearance of creatinine?
filtration only
What effect does ADH have on the cells of the DCT and CD?
makes their cells more permeable to water by activation of aquaporin 2
In regards to urine concentration; when is the secretion of ADH stimulated and where?
when the body water content decreases, the hypothalamic osmoreceptors are activated and secretion of ADH from the posterior pituitary is stimulated
How does urine dilution occur?
when body water content increases, the hypothalamus stops secreting ADH causing the DCT and CD to become less permeable to water reabsorption. Aldosterone secretion is also decreased and less salt and water is reaborbed this leads ton large volume of light colored urine
What is the minimum urine volume that must be excreted by the kidneys to get rid of metabolic waste and excess ions per day? Why is there a need for a minimum?
0.5 liters/ day
kidneys cannot get rid of excess metbolites and ions without water
‘we would be like a salt shaker’
Why can we control (to some extent) when we pee?
The external urethral sphincter is made of skeletal muscle and is controlled by the punendal nerve
what is the process for the micturition reflex?
singlas from sensory stretch receptors in bladder–> pelvic nerve afferent fibers–>n sacral spinal cord–> pelvic nerve motor fibers–> detrusor mucles contraction and internal urethral sphincter relaxtion–>’feeling you need to pee’
What is atonic bladder?
also called overflow incontinence, destruction of sensory nerve fibers abolish the micturition reflex contractions, this causes the bladder to fill and start dripping
usually caused by syphilis and sacral nerve injury
What is automatic bladder?
loss of conscious control of urination due to spinal cord injury above the sacral region
What is uninhibited neurogenic bladder?
The loss of inhibitory signals to the bladder promote frequent urination can be due to nerve damage, UTIs, pregnancy
urge to go never goes away
Potassium secretion is increased by what 4 factors?
increased extracellular potassium, increased tubular flow rate, aldosterone, alkalosis
How much filtered calcium is reabsorbed? where does most of the reabsorption occur?
99%
65% proximal convoluted tubule
30% LOH
How is phosphate reulated in the renal system?
by an overflow mechanism
80% is reabsorbed in the proximal convoluted tubules
How is magnesium excretion increased and how is it regulated?
inc Mg+ conc, inc Ca2+ conc, inc extracellular fluid
regulated by changing tubular reabsorption: 65% reabsorption in LOH
25% in PCT
In what sceraios might blood AND ECF volumes be increased?
CHF and increased vascular capacity
In what scenarios would ECF be increased but not blood volume?
liver cirrhosis (decreased plasma proteins synthesis), nephrotic syndrome (loss of plasma proteins in the urine)
What three systems regulate acid-base balance in the body fluids?
the buffer system
the respiratory system
the kidneys
What is the bicarbonate buffer system equation?
CO2+ H2O H2CO3 H+ + HCO3
NaHCO3 Na+ HCO3
What is the phosphate buffer system?
NaH2PO4 NaHPO4 + H+
What is the protein buffer system?
Hb+ H+ HHb
What is the cause of respiratory acidosis?
respiratory center damage, respiratory obstruction, lung tissue destruction, gas exchange impairment
What is the cause of respiratory alkalosis?
hyperventilation, high altitude
What is metabolic acidosis and what are the causes of it?
decreased ECF bicarb concentration
can be caused by kidney failure, diarrhea, diabetes mellitus, ingestion of acids
What is metabolic alkalosis? What can the causes be?
Increased ECF bicarb conc
can be caused by diuretics treament, alkaline, drugs ingetion, excess aldosterone secretion, gastric acid loss with vomiting
How is acidosis corrected?
Renal commpensation– excrete acidic urine, reabsorb and make new bicarb
respiratory- inc rate of breathing
How is alkalosis corrected?
renal- decreased H+ excretion, increased bicarb excretion
respiratory- decreased rate of breathing
treatment for acidosis?
sodium bicarb, sodium lactate, or sodium gluconate
treatment for alkalosis?
ammonium chloride
when are diuretics used?
alleviate vascualr hypervolemia, edema, CHF, hypertension
What is the mechanism of action for diuretics?
osmotic effects, interference with membrane protein transporters, enzyme inhibition or hormone receptor blockage
Central diabetes insipidus is a kidney disease where what occurs?
failure of hypothalamus to priduce ADH or posterior pituitary to release ADH
What is nephronic diabetes insipidus?
inability of kidney tubules to respond to ADH stimulation
Azotemia/ Uremia definition?
retention of water, eletrolytes and waste products into the blood
What is nephrotic syndrome?
protein excretion in the urine
In regards to acute kidney injury; what is the difference between prerenal, intrarenal and postrenal?
prerenal- caused by decreased blood supply
intrarenal- caused by kidney diseases and tissue abnormalities
postrenal- caused by any urine outflow obstruction
What is chronic kidney disease?
irreversible loos of functional nephrons to less than 25% of normal due to blood, kidneys or urinary tract disorders
What is end-stage renal failure?
kidney transplant or dialysis is required for life
