Renal Physiology Flashcards
the kidneys manage the outflow of ___, and the retention or expulsion of various components of the ___
- urine
- serum
the kidneys are regulators of what?
- blood pressure
- blood plasma constituents
- pH
- this regulation is provided by what is kept (returned to circulation) vs what is expelled (as urine)
what are the 4 body fluid compartments that physiological fluid is distributed across? where is the majority of the fluid?
- plasma
- intracellular fluid (majority is found here, but it can easily traverse cell membranes [tonicity])
- interstitial fluid
- transcellular fluid
generally, for alterations in the overall fluid volume, the ___ is the point of entry
plasma
how many liters of physiological fluid are in the body on average at any one time?
42 liters
how many liters per day of fluid do the kidneys dispose of?
0.5-2 liters
what ways other than renal is physiological fluid excreted from the body?
- 700 ml/day lost from skin (not sweat), insensible water loss from skin/respiratory tract
- 100 ml/day up to 1-2 L/hour in heavy exercise
- Around 100 ml/day in feces.
what is blood volume?
the fluid in the plasma and the fluid contained in RBCs
the circulatory system is a ___ system
closed
substantially increased volumes of fluid would substantially increase pressure. how do the kidneys function in managing this?
- control of urine volume can rapidly shed excess pressure
- restriction of urine volume in dehydration can conserve pressure
the kidneys regulate ___ balances and ___
- electrolyte balances and tonicity
- the kidneys control retention or excretion of these ions, thus can help regulate plasma levels
T or F:
the kidneys serve to excrete metabolic waste products an foreign chemicals
true
describe renal regulation of pH
- excretion or retention of acid or base
- so, urine can be either acidic or basic
T or F:
the kidneys deal with volatile acids
false
the kidneys deal with nonvolatile acids
the kidneys produce ___, which creates RBCs
erythropoietin
the kidneys are a site of ___, particularly during a fasting state
gluconeogenesis
what glands are located on the kidneys?
adrenal glands
the outser layer of the kidney is called the ___, and the inner layer is called the ___
- renal cortex
- renal medulla
within the ___, there are specialized regions of tissue called ___, which are composed of many individual filtration units called ___
- medulla
- renal pyramids
- nephrons
each renal pyramid is connected to the ___, or urine drainage tube, by ___
- renal pelvis
- papilla
describe the general flow through the kidneys
where does filtration occur in the kidneys?
nephrons in the renal pyramids
filtrate passes through each ___ and is modified by ___ and/or ___ of water, ions, metabolites, etc.
- nephron
- reabsorption
- secretion
what is the nephron?
the basic functional unit of the kidney where filtration occurs
about how many nephrons are in all of the renal pyramids in a single kidney?
1 million
each nephron is fed by a small cluster of ___, often referred to as a ___, which is covered by epithelial cells and encased in ___.
- glomerular capillaries
- glomerulus
- bowman’s capsule
describe the flow of plasma through the nephron
- plasma containing solutes passes out of the glomerulus and into bowman’s capsule
- proximal tubule
- loop of Henle (longer loop = more concentrated urine)
- distal tubule
- collecting duct
- renal pelvis
- ureter
describe the 2 types of nephrons
- Cortical nephrons (around 70%) are located primarily within the cortical region of the kidney, with only the loop of Henle penetrating the medulla. They are more superficial.
- Juxtamedullary nephrons (around 30%) are located primarily within the medullar region of the kidney. They have very long loops of Henle that penetrate deeply into the medulla.
describe how the blood supply differs between the two types of nephrons
- cortical nephrons - peritubular capillaries are tightly associated with the loop of henle
- juxtamedullary nephrons - the efferent arterioles extend part of the way down the loop of henle and form specialized peritubular capillaries called vasa recta; allows these nephrons to form highly concentrated urine
around what percentage of the blood plasma presented to the glomerulus enters the proximal tubule via bowman’s capsule?
20%
what is the equation for urinary excretion rate?
(filtration rate - reabsorption) + (secretion)
describe the 5 possible net filtration scenarios
5th scenario is no filtration
T or F:
kidneys secrete most of what they filter out
false
they reabsorb most of what they filter out
generally, ___ are very efficiently filtered but tend not to be reabsorbed. thus, a high ___ ensures rapid removal from the blood
- waste products
- glomerular filtration rate
what is a normal total GFR?
180 L/day
we only have about 3L of blood plasma, so it is filtered about 60 times per day
for most substances, filtration rates and reabsorption rates are very ___ compared to the proportion which is ___
- high
- excreted
- thus, relatively small changes in filtration or reabsorption rates translate into relatively large changes in secretion
describe the membranes of glomerular capillaries
- slightly specialized to make it selective for relatively small positively charged molecules
- glomerular capillaries are capable of filtering several hundred times the amount of water and solutes as a normal capillary
describe the 3 layers of glomerular capillary membranes
1) Endothelium: Fenestrated, negatively charged
2) Basement membrane: Collagen/Proteoglycan mesh, negatively charged
3) Specialized epithelial cells called ‘podocytes’
describe the endothelium of glomerular capillary membranes
- has small fenestrae
- endothelial wall is negatively charged and thus repels large negatively charged albumin proteins
describe the basement membrane of glomerular capillary membranes
•The basement membrane serves to fuse the endothelium to the the podocyte cell layer
describe podocytes of the glomerular capillary membrane
- form slit pores which restrict filtrate based on size and charge
describe the glomerular filtration rate
GFR = (Kf)(net filtraiton pressure)
- Kf = glomerular capillary filtration coefficient; a measure of the surface area and hydraulic conductivity
- net filtraiton pressure = the sum of the colloid and hydrostatic pressures across the glomerular capillaries
describe the profiltration and antifiltration pressures of the glomerulus/bowman’s capsule
describe how alteration of afferent arteriole diameter alters GFR
- alteration in diameter of afferent and efferent arterioles (controlled by sympathetic nervous system)
- constriction: increase pressure on glomerulus, forcing blood out of bowman’s capsule, decreasing GFR
- dilatation: opposite effect
describe how alteration of efferent arteriole diameter alters GFR
- Minor constriction of the efferent arterioles increase resistance for blood to leave Bowman’s capsule, thereby increasing GFR.
- HOWEVER major constriction traps proteins in the Bowman’s capsule circulation, raising colloid osmotic pressure and actually decreasing GFR.
- Dilatation decreases GFR.
describe systemic regulation of GFR
in the steady state, is renal blood flow and GFR relatively constant?
yes
what is tubuloglomerular feedback?
- autonomic regulation of GFR
- links the sodium chloride concentration in the distal tubule with the constriction state of the afferent and efferent renal arterioles
describe the significance of the macula densa
- located in the distal tubule, and forms the juxtaglomerular complex with the walls of both the afferent and efferent arterioles
- can detect a decrease in NaCl concentration in the distal tubule, which indicates a decreased renal flow (GFR)
what is the role of the macula densa after a decrease in NaCl concentration in the distal tubule is detected (decreased GFR)?
- the macula densa initiated dilatation in the afferent arterioles and causes an increased release of renin
- renin increases angiotensin I and II levels, causing constriction of the efferent arterioles
- GFR is restored
describe diabetic alteration of GFR
*pay attention to blue line, not black
note the effect of antihypertensive therapy
also note that this is representing someone who has poor control of their blood sugar
once the glomerular filtrate enters the proximal tubule, it is very similar in composition to the blood plasma, minus the ___
- protein
- reabsorption is selective and quantitatively large, so filtrate will be modified
what do the relative reabsorbed amounts of water and solutes depend on?
- osmolarity (or hydration state) of the body fluid
- when osmolarity is high (body water is low), the kidney will form a more concentrated urine
- when osmolarity is low (body water is high), the kidney will form a more dilute urine
___ are generally poorly absorbed, whereas ___ and ___ are very well absorbed
- waste products
- glucose and electrolytes
the proximal tubule is heavily involved with the reabsorption of ___ through ___, which is linked to active ___ gradients
- water
- passive diffusion
- Na+
around 65% of water and Na+ are reabsorbed where?
- the proximal tubule
- a significant amount of Cl- is reabsorbed along with the Na+
describe the cells bordering the proximal tubule
- have a huge capacity for active transport and passive reabsorption
- lots of mitochondria
- brush border with large membrane surface area
what is preferentially reabsorbed at the more proximal end of the proximal tubule? distal end?
- proximal end: glucose, amino acids, HCO3-, and Na+
- distal end: glucose and amino acids are depleted, so it is mainly Cl- that is reabsorbed
why are waste products not well reabsorbed?
- due to tubule permeability
- drugs/drug metabolites are often the same
what happens to the amount and concentration of Na+ as you proceed along the proximal tubule?
- amount decreases
- concentration stays the same
describe the thin descending segment of the loop of henle
- highly permeable to water (aquaporins)
- not very many active transporters
- about 20% of filtered water is reabsorbed here
describe the thick ascending segment of the loop of henle
- not permeable to water
- lots of active transporters
- reabsorption of Na+, Cl-, K+ (around 25% of these ions are reabsorbed here)*
- Ca2+, Mg2+, and HCO3- are also reabsorbed here
*in contrast to the proximal tubule, Na+ primarily moves out of the lumen via Na+, Cl-, and K+ co-transporter, because there is not much glucose/amino acids left
what is the main function of the loop of henle?
control the concentration of the urine
describe the general mechanism of renal counter-current exchange
water permeability of the thin descending segment works in conjunction with the active transporter capabilities of the thick ascending segment
describe osmolarity of the interstitial fluid in deep tissues of the renal medulla
- osmolarity is maintained at a very high level compared to that in the rest of the body
- around 1200-1400 mOsm/L vs 300 mOsm/L
- this gradient allows more water to be drawn out of the descending limb, while the structural nature of the ascending limb prevents it from getting back in, thus concentrating the urine
- **the transporters in the thick ascending segment only have a capacity to maintain a 200 mOsm/L difference
the distal tubule contains the ___ and thus, the ___
- macula densa
- juxtaglomerular apparatus
T or F:
the kidneys are involved in the metabolism and excretion and secretion of systemic hormones
true
what are 4 common metabolic waste products that the kidneys serve to excrete?
- urea (protein metabolism)
- uric acid (nucleic acid metabolism)
- creatinine (muscle metabolism)
- bilirubin (hemoglobin metabolism)
what are 4 common foreign substances excreted by the kidney?
- pesticides
- food additives
- toxins
- drugs
is the retention of HCO3- more or less important than H+ excretion in terms of renal control of pH?
- it is more important
- excreting 1HCO3- is basically the same as adding 1H+
- the kidneys can also produce “new” HCO3- by metabolizing glutamine, which makes ammonium and bicarbonate
describe the blood supply of the kidneys
- supplied by renal artery which enters via the hilum
- branches into afferent arterioles
- branch into glomerular capillaries (supply nephrons, site of filtration)
- glomerular capillaries feed into efferent arterioles
- form peritubular capillaries (reabsorption/secretion occurs)
- these ultimately return to the renal vein which passes back out of the hilum
describe the hydrostatic pressure in the glomerular capillaries
- it is much higher than in the peritubular capillaries (60 mmHg vs. 13 mmHg)
- this is regulated by changes in the afferent/efferent arterioles
describe filtration in the different segments of the nephron loop
describe the transporters in the tubules
- Na/K ATPase - primary active transporter
- sets up gradients for secondary active transport
- active transport of Na+ is linked to the reabsorption of many things, including glucose and H+ ions
- co-transporter
- brings glucose into the cell from the tubule with Na+ and it can diffuse out the other side back into the blood
- counter-transport
- H+ ions are excreted with Na+
how does water traverse the proximal tubules?
- it traverses the proximal tubule tight junctions in response to the osmotic force generated by Na+ and can drag some small solutes along with it
T or F:
Na+ reabsorption is independent of the reabsorption of other things
false:
Na+ reabsorption is highly linked to the reabsorption of many other things
