2.1 Glomerulus Flashcards
(22 cards)
Osmola(l/r)ity
- Osmolality - solute per kg of solvent (mOsm/kg)
* Osmolarity - number of osmoles of solute per litre (mOsm/L)
Oncotic
• Osmotic force due to proteins
Osmotic
• Movement of water due to ions
GFR
- Glomerular filtration rate
- How much plasma filtered / min
- Usually around 125 ml/min
RBF
- Renal blood flow
- Blood arriving at kidney through renal artery / min
- Usually around 1 L/min
RPF
- Renal plasma flow
- Specifically amount of plasma arriving at kidney / min
- Usually around 600 ml/min
RPF = RBF x (1 - Hct)
- Haematocrit = proportion of blood that is RBC’s
* 1 - Hct = Proportion of blood that is plasma
Filtration fraction
- GFR/RPF
- Estimates the proportion of plasma entering the kidney that is filtered out by glomerulus
- Usually around 20%
- Around 80% of blood arriving exits efferent arteriole without being filtered
Glomerular filtrate
- Contains no blood cells or platelets
- Contains virtually no proteins (unless pathology)
- Is composed of mostly organic solutes with a low molecular weight and inorganic ions
- End product of filtration is same as plasma without large proteins and cells
Renal corpuscle
• Combination of glomerulus and Bowman’s capsule
Podocytes
- Have foot-like processes called pedicels
- They are negatively charged so do not allow negatively charged molecules to be filtered e.g. albumin
- When this negative charge is lost - it can lead to proteinuria
Body fluid compartments
- 60% of weight = TBW
- ⅔ of TBW = Intracellular fluid
- ⅓ of TBW = Extracellular fluid
- 75% of ECF = Interstitium
- 25% of ECF = Circulating volume (around 40% is red cells)
Intracellular fluid
- High K+
- Low Na+
- Many large organic ions
Extracellular fluid
- Low K+
- High Na+
- Main anions are Cl- and HCO3-
Net filtration
Pᴳᶜ - (Pᴮˢ + πᴮˢ)
50 - (12 + 25) = 13 mmHg
• Pᴳᶜ - Hydrostatic pressure exerted by the glomerular capillaries
• Pᴮˢ - Hydrostatic pressure exerted by the bowman’s space
πᴮˢ - Oncotic pressure difference from bowman’s space towards the glomerular capillaries
Autoregulation of RBF / GFR
- Myogenic mechanism
* Tubuloglomerular feedback
Myogenic mechanism
- Arterial smooth muscle responds to changes in vascular wall tension (pressure)
- Predominantly in vessels before glomerulus (e.g. arcuate, interlobular and afferent)
- Occurs rapidly (3 - 10s)
- To cause a decrease in GFR, afferent arteriole will be constricted to decrease RBF and therefore decrease GFR
Tubuloglomerular feedback
- Links Na+/Cl- concentration at the macular densa cells of the DCT
- Higher solutes = higher pressure at which plasma is being filtered
- Has 2 components
- Afferent arteriole resistance
- Efferent arteriole feedback (hormonal)
- Controls DCT solute delivery and reabsorption
Afferent arteriole resistance
- Macula densa cells detect Na+/K+ in DCT
- Solutes enter macula densa cells and then travel through ATPase into bowman’s space
- Water moves into macula densa cells due to increased osmolarity of cell which releases ATP
- ATP converted to adenosine which acts on A1 receptors at afferent arteriole to cause vasoconstriction (increases GFR)
- If GFR is low, less solutes entering cell = lower ATP = afferent arteriole remains dilated
Efferent arteriole feedback
- Macula densa cells detect Na+/K+ in DCT
- If there is lower solute delivery (low RBF), macula densa cells signal to granular cells on afferent/efferent arteriole to release renin
- Causes activation of RAAS which causes efferent arteriole constriction
- Prostaglandins release which prevent constriction of afferent arteriole
- Together, these increase RBF which increases GFR
Renin release stimuli
- Sympathetic nerve stimulation
- Decrease in stretch of afferent arteriole
- Signals generated by macula densa cells - low solute delivery to DCT
Extraglomerular mesangial cells
- In interstitium of bowman’s space
* Important for signalling, secretion and stability of the bowman’s capsule
