[3] Overview of Renal Physiology and Glomerular Filtration Flashcards
3 Options of ERSD
Transplant
Dialysis
Death
A man contains about what % of body weight in water?
60%
Specifically what part of the kidney produces renin?
Granular cells in the Juxtaglomerular Apparatus
Function: Renin
Converts Angiotensinogen -> Angiotensin I
What is the rate limiting step of the Renin-Angiotensin-Aldosterone System?
Renin conversion of Antiotensinogen to Angiotensin I
What converts Angiotensin I to Angiotensin II?
Angiotensin Converting Enzyme
What produces Angiotensin Converting Enzyme?
Mostly by the lungs and some by the kidneys
Function: Angiotensin II
- Stimulation of sympathetic activity
- Formation of aldosterone
- Arteriolar vasoconstriction causing increase in BP
- Stimulation of ADH secretion from posterior lobe of pituitary gland causing water absorption
- Cardiac and vascular hypertrophy
What stimulates thirst?
Angiotensin II
Angiotensin is stimulated by?
Low BP
Decreased sodium delivery to the macula densa
Sympathetic Stimulation
Where is Erythropoietin produced?
Peritubular Capillary and Endothelial Cells in the Kidney
Main stimulus of erythropoietin
Hypoxia
Stages of Erythropoiesis
- Stem and Progenitor Stage
2. Precursor Stage
Steps of Erythropoiesis
Pluripotential Stem Cell -> Unipotential Stem Cell -> Burst Forming Colonies -> Colony Forming Units -> Precursor Cells
What do precursor cells need to mature?
Folic Acid
Iron
Vitamin B
If a patient has a kidney problem what do you need to do before administering erythropoietin?
Give iron and vitamin B to ensure maturation of RBCs
What happens to stem cells without erythropoietin?
Apoptosis
What is Calcitriol
Active metabolite of Vitamin D
What is Vitamin D important in the absorption of?
Calcium
What happens to Vitamin D in the presence of sunlight?
Activates 7-dehydrocholesterol -> cholecalciferol (Vitamin D3)
Composition: Renal Corpuscle
Glomerulus
Bowman’s Capsule
What epithelial cells cover the Glomerulus?
Podocytes
Composition: Renal Tubule
Proximal Tubule
Loop of Henle
Juxtaglomerular Apparatus
Distal Convoluted Tubule
Types of Nephrons
Cortical
Juxtamedullary
Characteristics of the Cortical Nephron
Short Loop of Henle
Almost Absent Thing Ascending Limb
Network of Peritubular Capillaries and Series of Vascular Loops
Vasa Recta
Where do you find the vasa recta?
Juxtaglomerular Nephron
Vasa Recta receives how much of the renal blood flow?
0.7%
[Cortical Nephron vs. Juxtamedullary Nephron]
Location
CN: Near Cortex
JN: Reaches Medulla
[Cortical Nephron vs. Juxtamedullary Nephron]
Source of Afferent Arterioles
CN: Interlobular Artery
JN: Interlobular Artery/Arcuate Artery
[Cortical Nephron vs. Juxtamedullary Nephron]
2nd Set of Capillaries
CN: Peritubular Capillary
JN: Vasa Recta
Pathway of Vitamin D Metabolism
Sunlight -> 7-dehydrocholesterol -> Cholecalciferol (Vitamin D3) -> 25-hydroxyvitamin D3 -> 1,25-dihydroxyvitamin D3
3 Basic Renal Processes
- Glomerular Filtration
- Tubular Reabsorption
- Tubular Secretion
Define: Glomerular Filtration
Filtration of the plasma in the glomerulus
Ultrafiltrate collects in the urinary space of Bowman’s capsule and flows to the tubular lumen
Differentiate Tubular Secretion vs. Tubular Excretion
Excretion: Elimination through urine
Secretion: Peritubular capillary into the lumen
Components of GFR
Blood
Filtration Membrane
Ultrafiltrate Formation
Comparison of Blood Flow to Different Organs
- Kidney
- Heart
- Brain
- Liver
- Resting Muscles
- Kidney: 4.0 mL/g/min.
- Heart: 0.9
- Brain: 0.6
- Liver: 0.2
- Resting Muscles: 0.1
Most blood flow to the kidney goes to?
Renal Cortex
70% of the Kidney’s Weight but 92% of Blood Flow
Parts of a Renal Corpuscle
- Endothelial Fenestration
- Basement Membrane
- SM Membrane between Pedicels
Parts of the Basement Membrane
- Lamina Dense: Central Layer
2. Lamina Rara Interna and Externa
Most important factor for filterability
Size
What passes easier, positively or negatively charged molecules?
Negative
Normal GFR
125ml/minute
Starling Hypothesis Equation
Jv = Kf [(Pcap – PIF) – σ(πcap – πIF)] = Kf (∆P - ∆π)
Define: Mesangial Cell
Supports the glomerular capillary and secretes the extracellular matrix
Secretes prostaglandins and cytokines
Has contractile properties (most important for GFR)
Sample problem:
What is the net filtration pressure if the glomerular capillary hydrostatic pressure (Pcap) is 55mmHg, plasma oncotic pressure (πcap) is 30 mmHg and hydrostatic pressure at Bowmann’s capsule (Pif) is 15 mmHg? (Oncotic pressure in the Bowman’s capsule (πif)) = 0)
NFP = [(Pcap – Pif) – (πcap– πif)]
= (ΔP) – (Δπ)
= (55-15)-(30)
= 10 mmHg
[Skeletal Muscle Capillary]
Where is hydrostatic pressure high?
Where is it low?
High: Arterial End
Low: Venous End
[Renal Capillary]
Where is hydrostatic pressure high?
Where is it low?
Generally higher than extracapillary and does not decline significantly with distance
[Renal Capillary]
Where is oncotic pressure high?
Where is it low?
Oncotic pressure increases due to filtration of protein-free fluid
Effect of Angiotensin on GFR
Angiotensin vasoconstricts the efferent arteriole
Increases GFR
Tubuloglomerular Feedback Mechanism is a function of?
Juxtaglomerular Apparatus
Explain: Myogenic Reflex Theory
If vascular wall tension is to maintain the constancy of blood flow, the radius is forced to increase when pressure drops or the radius is forced to decrease as pressure increases
Formula for Vascular Wall Tension
T = P x R
P: Pressure Gradient
R: Radius of the Vessel
What is the autoregulatory range?
100 mmHg - 200 mmHg
What does the autoregulation mechanism autoregulate?
Constancy of RBF and GFR
