Renal Functions (Part 1) Flashcards
List 9 normal renal functions
1) Excretion of waste products & urine
2) Regulation of BP
3) RBC production → erythropoietin
4) Breakdown of drugs
5) Metabolism of hormones
6) Regulation of electrolytes & acid-base balance
7) Synthesis of vitamin D
8) Fluid balance
9) Balance pH of blood stream
What happens to vitamin D without proper kidney function?
Vitamin D becomes inactive; & plays a role with calcium absorption
How many lobes are there per kidney?
8-18 lobes
Where are the kidneys located?
Retroperitoneally on the posterior wall of the abdomen
What is each lobe of the kidney composed of?
Nephrons → functional units of the kidneys
What does the renal cortex contain? Hint: 3
Glomeruli, convoluted tubules, blood vessels
What does the inner medulla contain?
Renal pyramids
Which kidney is positioned slightly lower than the other?
The right → because of the liver
Why is it harder for kidneys to get injured?
They are semi protected by the ribs & other organs
What is considered the collection system of the urine?
Renal pelvis
How much of the body’s cardiac output do the kidneys take?
20-25%
Describe the renal artery Hint: 2
1) Divides into 5 segmental arteries that enter the hilus
2) Segmental artery inside kidney branches into lobular arteries, then interlobular arteries
Renal function begins with BF to the ____ ____
Renal vasculature
Kidneys filter ~ ___-___ mL of blood per minute
90-120 mL
What is the main functional unit of the kidney?
Nephron!!
Can the kidneys regenerate nephrons?
NO → therefore, there’s a generalized decrease in functioning nephrons w/ aging
Approx. what % of nephrons do adults lose for each decade? What age does this begin at?
~ 10% of nephrons for each decade; beginning at 40 yrs
Which capillary structure/ system of a nephron is responsible for filtration?
Glomerulus
Which capillary structure/ system of a nephron is responsible for reabsorption?
Peritubular capillaries
List 4 parts that make up the nephron?
1) Proximal convoluted tubule
2) Loop of Henle
3) Distal convoluted tubule
3) Collecting duct
List the 2 categories of nephrons
1) Cortical
2) Juxtamedullary nephrons
What category nephrons make up ~ 85% of the nephrons & where do they originate?
Cortical nephrons → Originate in the superficial part of the cortex
Describe cortical nephrons
They have short, thick loops of Henle that penetrate only a short distance into the medulla
Describe juxtamedullary nephrons
Originate deeper in the cortex & have longer, thinner loops of Henle that penetrate the entire length of the medulla
What category nephrons are the primary site of urine concentration?
Juxtamedullary nephrons
What is the glomerulus?
Capillaries enclosed in thin, double – walled capsule (Bowman capsule)
Describe the flow of blood in a nephron
Afferent arteriole → glomerular capillaries → efferent arteriole → peritubular capillaries
List the 3 layers of glomerular capillary membrane
1) Capillary endothelial layer
2) Basement membrane
3) Single-celled capsular epithelial layer
Approx how many L of filtrates do we filter each day & what do they consist of?
~ 180 L per day
→ consists of water, electrolytes, creatinine, etc
What % of filtrates are reabsorbed into the bloodstream? What does this result in pertaining to urine?
90% of filtrates are reabsorbed
→ Results in ~ 1-2 L of urine per day
What does amount of urine output depend on?
The actual amount of fluid we drink
i.e. Drink 2 L = Urinate 2 L
What happens to flow of blood & filtration if there are renal/ kidney stones?
Causes obstruction; & can lead to increased pressure & obstructed BF
What happens to flow of blood & filtration in someone with hypotension?
Slows things down!!
Average GFR for an adult
125 mL/ min or 180 L/day
What is filtration pressure & GFR regulate by?
1) Constriction/ relaxation of the afferent & efferent arterioles
→ Arterioles innervated by SNS
→ Arterioles sensitive vasoactive hormones
By age 70, what does renal function look like?
Renal function will be down by 30 mL/min so their avg GFR will be 95 mL/min
In healthy adults, decline in renal function has little impact until what age?
Age 90
Where does tubular reabsorption occur?
In the renal tubules (primarily proximal convoluted tubule)
The higher the # for GFR the…
Better it is!! → indicates better renal function
What will GFR look like in patients with ESRD?
GFR of 15 mL/min of less
ALL blood circulates through the ____
Kidneys
Why is it important that GFR is adequate?
In order to remove waste products
List 3 mechanisms for regulation of renal BF
1) Neural & humoral control mechanisms
2) Autoregulatory mechanisms
3) Effect of increased protein & glucose load
Neural & humoral control mechanisms:
What does an ↑ in SNS activity lead to?
Leads to constriction of arterioles which leads to ↓ in renal BF
Neural & humoral control mechanisms:
List the 3 humoral substances
1) Angiotensin II
2) Endothelin
3) Endothelial-derived nitric oxide
Neural & humoral control mechanisms:
What does angiotensin II do?
Preferentially constricts efferent arterioles (we do NOT like)
Neural & humoral control mechanisms:
What is endothelin?
Peptides released from damaged endothelial cells in the kidney & other tissues
Vasoconstrictor
Neural & humoral control mechanisms:
Endothelial-derived nitric oxide allows..
For normal excretion of sodium as well as water (We like it)
Neural & humoral control mechanisms:
What kind of role do prostaglandins (PGE2 & PGI2) play?
Protective role against vasoconstricting effects of sympathetic stimulation & angiotensin II
Why do we like COX1?
It is an enzyme that plays a role in production of prostaglandins & helps protect the kidneys
What role do otc NSAIDs play in neural & humoral control mechanisms?
They inhibt prostaglandin synthesis; they ↓ renal BF & ↓ GFR
What types of patients should definitely avoid NSAIDs? Why?
Pts Dx with HTN → double whammy HTN already causes vasoconstriction & taking an NSAID on top of that will ↑ vasoconstriction & impair BF to kidneys
Autoregulatory mechanisms
Exact mechanisms responsible for renal BF regulation are unclear
Proposed mechanisms:
→ Mechanism #1
→ Mechanism #2
Autoregulatory mechanisms:
Proposed mechanism #1: Hint: 3
1) Direct effect on vascular smooth muscle
2) ↑ in BP causes vessels to relax
3) ↓ in BP causes vessels to constrict
Autoregulatory mechanisms:
Proposed mechanism #2:
Juxtaglomerular complex
→ Feedback control system that links RBF to GFR & composition of distal tubular fluid
List the 2 types of cells involved in the juxtaglomerular complex
1) Macula densa cells
2) Juxtaglomerular cells
What are the macula densa cells?
Specialized group of epithelial cells in distal tubule in close contact w/ afferent & efferent arterioles
List 2 things the macula densa cells monitor
1) BP by sensing the stretch of afferent arteriole (changes in volume delivery)
2) Sodium concentration in filtrate as it flows through
What do the juxtaglomerular cells contain?
Contains granules of inactive renin
How is renin release determined in the juxtaglomerular cells?
Information from macula densa is used to determine the renin release
What happens when there is decreased renal perfusion?
The RAAS will be triggered
Tubular reabsorption & secretion:
~ ____ % of reabsorption & secretory processes occur in proximal tubule
Highly permeable to _____
~65%
Permeable to water
List 7 things the proximal tubules reabsorb
1) Na+
2) Cl-
3) HCO3-
4) K+
5) H2O
6) Glucose
7) Amino acids
List 2 things proximal tubules secrete
1) H+
2) Organic acids & bases
Tubular reabsorption & secretion:
What happens at the descending loop of Henle (Loop elbow)?
Osmolality increases & is maximum here
List 1 thing the descending loop of Henle reabsorbs
1) H2O
Which loop of Henle is impermeable to water?
Ascending loop → as filtrate ascends it becomes more dilute
List 6 things the ascending loop of Henle reabsorbs
1) Na+
2) Cl-
3) K+
4) Ca++
5) HCO3-
6) Mg++
List 1 thing the ascending loop of Henle secretes
1) H+
Tubular reabsorption & secretion:
Distal convoluted tubule Hint: 2
1) Relatively impermeable to water
2) Thiazide diuretics work here by inhibiting NaCl reabsorption in this segment
List 4 things reabsorbed in the early distal tubule
1) Na+
2) Cl-
3) Ca++
4) Mg++
Tubular reabsorption & secretion:
What type of diuretics work in the late distal tubule?
Potassium sparing diuretics
List 2 things the principle cells in the late distal tubule reabsorb
1) Na+
2) Cl-
List 2 things the principle cells in the late distal tubule secrete
1) K+
2) ADH-mediated H2O reabsorption
List 2 things the intercalated cells of the late distal tubule reabsorb
1) HCO3-
2) K+
List 1 thing the intercalated cells of the late distal tubule secrete
1) H+
List the 3 factors that determine how the kidneys concentrate urine
1) Osmolarity of interstitial fluids in the urine-concentrating part of the kidney
2) Antidiuretic hormone (ADH)
3) Action of ADH on the cells in the collecting tubules of the kidney
Elimination function of the kidney:
Kidneys help remove what 4 things
1) Water
2) Waste products
3) Excess electrolytes
4) Unwanted substances
Diuretics & where they work in the kidneys:
Osmotic diuretics
Proximal tubule
→ accounts for 65% of filtered Na+ reabsorption
Diuretics & where they work in the kidneys:
Loop diuretics
Thick ascending loop of Henle
→ Accounts for 20% of filtered Na+ reabsorption
Diuretics & where they work in the kidneys:
Thiazide diuretics
Early distal tubule
→ Accounts for 10% of filtered Na+ reabsorption
Diuretics & where they work in the kidneys:
Potassium-sparing diuretics
Late distal tubule
→ Accounts for 2-5% of filtered Na+ reabsorption
List 4 endocrine functions of the kidneys
1) Assists w/ BP regulation through renin-angiotensin-aldosterone mechanism
2) Regulation of RBCs through synthesis of erythropoietin
3) Assists w Ca++ homeostasis by activating vit. D
4) Glucose homeostasis
List 4 things that decrease in the GU system as we age
1) BF to kidneys
2) # of functioning nephrons
3) GFR (most reliable indicator)
4) Tubular secretion
What do all the age related GU changes impact?
The elimination of medications!!
Why is GFR a better indicator of kidney function than BUN/Cr?
B/c it tells about kidney function & the kidneys ability to excrete wastes!!
