Renal function, urine formation, and Micturition Flashcards
Which hormoes does the kidney produce
EPO, Renin
Which waste products are excreted from the kidneys
Ammonia from oxidation that is converted to urea, proteins and nucleic acids are excreted
How do kidneys maintain long-term acid-base balance
Secrete or reabsorb H+ or HCO3
What is the pathway of urine production
Cortex–> medulla–> minor calyx–> major calyx–> renal pelvis–> ureter
Which artery suplies the kidneys and where does it arise from
Renal artery (branch off abdminal aorta)
Very short with large diameter, which creates low resistance for filtration
What is the key vascular structure in the kidneys
Glomerulus, capillary bed that is continuous fenestrated for blood filtration
Is afferent or efferent arteriole smaller in kidneys
Efferent is smaller
Renal vein function
return blood back to IVC
What causes constriction of kidney blood vessils
norepinephrine and angiotensin 2
- Sympathetic
Are sympathetic effects stronger on afferent or efferent arterioles
Afferent are stronger- decrease filtration rate so we conserve fluid. Don’t create as much filtrate, in sympathetic so constricting vessils
What causes dialation of blood vessels in kidneys
Dopamine, Ach
- Parasympathetic activation
Function of nephrons
Filter blood and concentrate neuron
Site of exchange between blood and urine
How many nephrons do we have
1.3 million in each kidney (2.5 million total)
Function of podocytes
form filtration slits
Function of bowman’s capsule
start filtrate production
What type of cells are in the collecting duct and what are thier functions
P cells- ->Na+ reabsorbtion
I cells–> H+ and HCO3- secretion and reabsorbtion
What do RMICs secrete
prostaglandins
Which nephrons have vasa recta
In Juxtamedullary nephrons
Function of renorenal reflex
maintains kidney balanced in their output. If one ureter senses pressure, decreases efferent nerve activity in other kidney too.
Which types of nephrons have vasa recta on them
Medullary nephrons
Where does Filtrate production begin
Bowman’s capsule (glomerulus capsule)
What type of capillary bed is the Glomerulus? What is its function?
Continuous fenestrated
Filter blood
Vasa recta are alongside _____ nephrons and Peritubular capillaries are alongside ____ nephrons
Longer ( Juxtamedullary)
Both (Juxtamedullary and cortical)
Constriction in the kidneys occurs via which 2 hormones
Norepinephrine and Angiotensin 2
Dialation in the kidneys occurs via which neurotransmitters
Dopamine and Ach
Norepinephrine and Angiotensin 2 have the strongest effect on which arterioles
Afferent arterioles
What is the primary site for reabsorbtion in the kidneys, and what special feature does this site have?
Proximal Tubule
Has lots of brush border enzymes with lots of microvilli(increases surface area and absorbtion)
Which part of the loop of henle is thick and which is thin
Thick: Ascending– Has lots of mitochondira for the active transport of Na
Thin: Descending (very permiable cells to H2O)
What are P cells and what are their function
Princapal cells- For Na reabsorbtion
What are I cells and what are their function
Intercalated cells, have microvilli and mitochondria, H+ and HCO3- Ion Transport
What are the 2 types of nephrons and what percent does each category make up of the total number ?
Cortical- 85% (reabsorb and secrete things)
Juxtamedullary nephrons- 15% (concentrate urine– very long loops of henle).
Is the glomerulus closer to cortical or juxtamedullary nephrons
Glomerulus is closer to cortex- medulla junction in juxtamedullary nephrons
What is the main role of RMICs (Renal Medullary Interstitial cells)
Secrete Prostaglandins
The Juxtaglomerular apparatus is a junction of
Bowman’s capsule, distal tubule, and afferent and efferent arterioles
Where are the granular cells in the juxtamedullary apparatus and what is their significance
Are sensing the blood and blood pressure.
All around the afferent arteriole to sense blood pressure and moniter BP. When they detect low BP, they release renin. They have mechanoreceptors.
Where are macula densa cells in the juxtaglomerular apparatus and what is their function here
Are sensing Filtrate.
Embedded in the edge of the distal tubule– Have chemoreceptors that measure solute concentration (mostly Na concentration)
Which type of nephrons is the juxtaglomerular apparatus found in
Both Medullary and juxtamedullary nephrons
Which parts of the nephron are in the cortex of the kidney
Bowman’s capsule
PCT and DCT
Glomerulus
Peritubular capillaries/start of collecting duct
What parts of the nephron are in the medulla of a kidney
Vasa recta
Loop of Henle
Most of Collecting duct
What are the 4 steps of the renorenal reflex
- Increased pressure in ureter in one kidney causes stretch on the ureter
- sends afferent signal to spinal cord
- Decreased efferent nerve signals to the other kidney, which causes vasodialation of afferent and efferent arterioles.
- Increased excretion of Na and water
General function of renorenal reflex
Balance kidney output
If one kidney starts to increase urine production, what occurs with the other?
It will also increase urine production (renorenal reflex)
Norepinephrine stimulation on tubule cells and granular cells cause what 3 changes
- Increased sensitivity by granular cells
- Increased Na reabsorption
- Renal vasoconstriction, which causes Decreased GFR and renal blood flow
Decreases urine production overall–> part of SNS activity
How much urine production is there per day and what percentage of total filtrate is this?
1.8 L per day
1% of total filtrate–> 99% is brought back into the body
What are the 3 anatomical contributions to filtration
- Large diameter, short renal arteries
- Larger afferent arteriole vs efferent
- Very leaky fenestrated capillaries
Give the role for each Anatomical contributions to filtration:
1) Large diameter, short renal arteries
2) Larger afferent arteriole vs. efferent
3) Very leaky fenestrated capillaries
1) increase hydrostatic pressure, increase flow
2) increases hydrostatic pressure
3) high permeability
What is the normal rate of filtration at the glomerulus and at which GFR do kidney filtration problems begin?
Normal GFR is 125 ml/min
Kidney problems begin if GFR is <60 ml/min
How do 1. Increased systemic BP and 2. Decreased systemic BP impact GFR?
- Increased GFR when systemic BP increases
- Decreased BP with decreased GFR
When Systemic BP increases, what adjustment is made that causes GFR to go back to normal?
Myogenic response- Stretch causes reaction
Afferent arteriole constricts, which sends less blood into the glomerulus
When Systemic BP decreases, what adjustment is made that causes GFR to go back to normal?
Afferent arteriole dialates, sending more blood back into glomerulus
Regulation of GFR occurs via the permiability of ___. This permiability changes based on the contraction or relaxation of ____ cells. What causes this contraction, and what happens to GFR?
- Glomerular capillaries
- Mesangial cells
- Angiotensin 2 causes contraction of Mesangial cells, which decreases GFR (decreased permiability)
How do neutral substances between 4 and 8 nm pass through glomerular capillaries
freely
What charge are on the glomerular capillary walls?
Negatively charged proteins
This blocks negatively charged things like albumin from entering into filtrate. Albumin would stay in the blood and then go out through renal vein after supplying nutrients to vasa recta with the rest of the blood and peritubular capillaries.
Only small or neutral or positively charged molecules enter filtrate- others stay in the blood and don’t pass into the filtrate
Outline the flow of blood through the kidneys
Renal artery–> afferent arteriole–> glomerulus–>efferent arteriole–> renal vein
Or, if not becoming filtrate
Renal artery–> peritubular capillaries or vasa recta–> renal vein
What is the role of Mesangial cells
Change permeability of afferent arterioles (contraction decreases, dilation increases)
What is the role of Granular Cells
monitor and measure blood pressure via mechanoreceptors. Releases renin when BP is low
What is the role of Macula Densa Cells
Monitor filtrate and measure solute concentration in filtrate via chemoreceptors (mostly in terms of Na+ conc.)
What is the role of I cells
Regulate acid-base balance. Intercalated cells that have more microvilli and more mitochondria -> H+ ion and HCO3- ion transport
What is the role of P cells
Na Reabsorption
Overall purpose of Tubuloglomerular feedback
Decrease GFR
What is glomerular filtration
Pull substances out of the blood and into filtrate
What is tubular reabsorption
Bring substances back into the body that were in the filtrate
Filtrate starts with what kind of osmolarity in relation to the blood.
Isoosmotic.
Must use active transport via membrane proteins to reabsorb (this creates a gradient)
What osmolarity is the medulla
Hyperosmotic
In the descending loop, water is reabsorbed (not secreted!) into the surrounding interstitial space of the kidney’s medulla. Water is picked up by the vasa recta to return to blood
In the Ascending loop, Sodium (Na⁺), along with potassium (K⁺) and chloride (Cl⁻), is reabsorbed into the interstitial space of the medulla.
The deeper in the medulla, the more concentrated the filtrate is.
What is tubular secretion vs tubular reabsorbtion
In Tubular secretion, substances are added to the filtrate
In Tubular reabsorbtion, Substances are removed from the filtrate and added back into the bloodstream
Tubular secretion is usually what substances?
Waste products! Also, pH balance (i.e. H+ ions or HCO3- ions)
Sodium is reabsorbed into the kidney tubule cells via co-transport with which 6 ions/electrolytes?
Glucose, Phosphate, Amino Acids, lactate, Hydrogen, Cl
Sodium is moved out of the cell that lines the kidney tubules and back into the blood via what mecahnism, and what percent of sodium reabsorbtion occurs in which parts of the nephron?
Na/K atpase
60% occurs in proximal tubule
30% occurs in ascending limb of loop of henle
7% occurs in distal tubule
3% occurs in collecting duct
What is the primary driver of water reabsorbtion
Na reabsorbtion
In the Proximal Tubule, What is reabsorbed? Which channels or mecahnisms allow this? What is the effect on osmotic pressure?
- Sodium(Via active transport) ; Nutrients like glucose (Via SGLT2 transporter) and amino acids (Via cotransport with sodium); water(Via aquaporins)
Osmotic pressure does not change
How are sodium and water reabsorbed in the proximal tubule?
Via active transport
Water follows Na
How are glucose and amino acids reabsorbed in the proximal tubule?
Glucose: via SGLT1 cotransporter with sodium
Amino Acids: Via cotransport with sodium
Descending limb - Loop of Henle
* Highly permeable to:
* Doesn’t transport:
Water
Na
Ascending limb - Loop of Henle
* Active transport of: _____________ into interstitial space
* Impermeable to:
Na
Water
What is the result of filtrate modification in the loop of henle
Interstitial fluid around the bottom of the loop of henle is hyperosmotic
Counter-Current Multiplier Mechanism
Ascending loop:
* What happens?
* Role of vasa recta?
- Na Reabsorption ( Na pumped into vasa recta)
- Vasa recta picks up some Na
Counter-Current Multiplier Mechanism
Descending loop:
* What happens?
* Role of vasa recta?
- Water reabsorbed by osmotic pressure created by Na reabsorption on the other side
- Vasa recta picks up water
What are the 2 goals of the countercurrent multiplier mechanism
- Reabsorb water
- Set up strong concentration gradient next to collecting duct
The descending limb secretes what product to help concentrate the interstitial space, and what hormone increases this action
Secretes urea
ADH increases this
High protein diet leads to → increased ______________ production and increased ability to _______________ urine = __________ urine production
- Urea
-Concentrate
-Decreased
Filtrate Modification: Distal Tubule
- What is reabsorbed?
- Relatively impermeable to ______________
-Na (as much as the body needs
- Water
Filtrate Modification: Distal Tubule
- What is secreted? Why?
-K + , exchanged with Na+ (high levels of aldosterone - causes K+ secretion)
- H+ (as needed for pH control)
Filtrate Modification: Distal Tubule
What is the overall effect on concentration/volume?
- Minor volume reduction
- Slight dilution of urine
FINE TUNING OF NA+ LEVELS
Reabsorption in the collecting duct is controlled by what
ADH–> ADH in collecting duct increases H2O reabsorbtion
What increases reabsorption in the collecting duct?
ADH increases reabsorbtion of water via aquaporin 2 channels
What are the 3 effects of aldosterone (what does it increase including channels and ion exchange)
- Increases the number of ENaC’s (Endothelial Na channels)
- Increases Na/K exchange
- Increases H/Na exchange
What is the effect of caffine on filtration?
Caffeine blocks aldosterone action (diuretic effect)
Lasix (furosemide) is a loop diuretic → blocks _______________ reabsorption in the ___________________
* How would this make you lose more water?
- Na
- Ascending loop of Henle
- You lose more water because there is less of an osmotic gradient, so you don’t pull as much water back into the blood, which causes a greater volume of urine
How does ethanol increase water loss
Inhibits ADH release from the posterior pituitary
What are the effects of alcohol on electrolyte balance?
No impact on electrolyte balance, only causes dehydration because more fluid is lost
Equation:
RC = UV/P
What does each letter mean?
RC = renal clearance
U = concentration of substance in urine
V = flow rate of urine formation
P = concentration of substance in plasma
If: RC = GFR
How is filtration, secretion, and reabsorption affected? Examples?
- Freely filtered, not secreted, not reabsorbed
- Examples: inulin, creatinine
What molecules are both good for calculating kidney function?
Inulin
Creatinine
Both typically have a RC=GFR
If: RC < GFR
How is filtration and reabsorption affected? Examples?
- Freely filtered and reabsorbed (less filtrate in urine)
- Examples: Na+ ; Glucose, amino acids
- We don’t want to lose these– want to retain
If: RC < GFR
How is filtration and reabsorption affected? Examples?
- Freely filtered and secreted (more filtrate in urine)
- Examples: K+ , mostly all drug metabolites
Clinical application: pharmacists must know the ____________________ for drugs in order to determine correct dosage. Explain how this affects dosage?
Renal Clearance
- High Renal Clerance–> Higher dose needed
- Low Renal Clearance–> Lower Dose needed
Kidneys funnel urine into ______ _________ from ____________ _____________. It then goes into the _____________ for excretion
- Renal Pelvis
- Collecting Ducts
- Ureter
How does the ureter move urine
Peristaltic contractions
What affects the Peristaltic contractions of the ureters? (SNS vs. PNS)
- Parasympathetic: increases contraction of smooth muscle
- Sympathetic: decreases contraction of smooth muscle
Bladder pressure increases _____________ with low volumes less than 500 ml. When above 500ml, pressure increases ________________
Slowly
Quickly
1) Which urethral sphincter is under voluntary control?
2) Which is involuntary?
3) Detrusor muscle function
1) External urethral sphincter
2) Internal urethral sphincter
3) contracts to release urine
Micturition reflex purpose and receptors
Purpose: Eliminate urine from the bladder
Receptors: Stretch receptors in bladder wall
What are the afferent nerves in the micturition reflex
Pelvic nerves
What are the afferent nerves in the micturition reflex and where do these send signals to?
Pelvic nerves are afferent that send signals to sacral region of spinal cord.
After the micturition reflex reaches the sacral region of the spinal cord, what efferent nerve then causes an action?
The sacral parasympathetic nerves
NOT the vagus nerve
Describe the voluntary portion of the micturition reflex
External urethral sphincter is voluntary
Motor neurons are inhibited, which relaxes the sphincter, opening it.
External urinary sphincter:
______________ (Inhibit or activate) motor neurons → relax → open
Inhibit
