Renal Tubular Mechanisms Flashcards
What are 2 ways for Tubular Reabsorption?
- Paracellular -> through tight junctions
- Transcellular -> through the cell
What are the 5 barriers that a substance must traverse through in Transcellular Reabsorption?
- Luminal cell membrane
- Cytosol
- Basolateral membrane
- Interstitial fluid
- Peritubular capillaries
Percentage of Na and H2O reabsorbed in the Renal Tubules
What is the Transport Maximum?
- Limit for the rate that a solute can be transported into the Peritubular capillaries due to saturation of available carrier proteins
- If limit is reached, rest gets excreted in urine
What is the relationship of Filtration of Glucose with plasma Glucose levels?
directly proportional
What is the relationship between reabsorption of glucose and plasma glucose?
directly proportional until Transport Maximum is reached. After Transport Maximum is reached, glucose gets excreted
If arterial pressure increases and nothing else changes, what happens to the GFR?
- GFR increases
If we constrict the afferent arteriole, what happens to glomerular pressure (Pgc) and GFR?
Pgc is decreased
GFR is decreased
If we constrict the efferent arteriole, what happens to glomerular pressure (Pgc) and GFR?
Pgc is increased
GFRis increased
If we dilate the efferent arteriole, what happens to glomerular pressure (Pgc) and GFR?
Pgc is decreased
GFC is decreased
If we dilate the afferent arteriole, what happens to glomerular pressure (Pgc) and GFR?
Pgc is increased
GFR is increased
What happens if GFR is increased? (think about reabsorption)
Inadequate reabsorption occurs because not enough time for substances to be reabsorbed therefore substances lost in the urine
What happens if GFR is decreased? (think about reabsorption)
Reabsorption is increased because more time for substances to be reabsorbed so not excreted in urine
Are renal blood flow and GFR maintained relatively constant?
Yes they are autoregulated
What does autoregulation mean?
Organ maintains constant blood flow despite changes in arteriole pressure
Is urine flow regualted?
No
What is the relationship between urine flow and arterial pressure?
directly proportional
What are the two mechanism that allow for autoregulation?
- Myogenic Mechanism
- Tubuloglomerular feedback
How does the Myogenic Mechanism work?
- increase in blood pressure causes afferent arterioles to constrict which decreases blood flow to the glomerulus -> normalises glomerular pressure -> keeps GFR constant
- Arterioles constrict bc due to shear stress and stretch, calcium channels open -> calcium influx -> Vascular smooth muscle cells contstrict
How does Tubuloglomerular Feedback work?
- GFR increases
- Flow through tubule increases
- Flow past macula densa increases
- Paracrine from macula densa to afferent arteriole
- Afferent arteriole constricts -> resistance in afferent arteriole increases -> hydrostatic pressure in glomerulus decreases -> GFR decreases
What happens when you ingest NaCl tablets?
- increased Na+ in ECF
- H2O moves into ECF
- When H20 moves out of ICF, some Na+ moved into ICF to balance it
- will be increased osmolarity in ICF and ECF
- increased ECF vol, and decreased ICF vol.
- Cell chrinks
What is Pressure Natriuresis?
Natriuresis = excretion of sodium in urine
- When BP is high, Na+ is secreted -> reduction is plasma vol -> reduction in plasma volume -> bring arterial pressure back down
How does body sense changes in Na+ Levels?
- Cardiovascular stretch-sensitive and baroreceptors (atria, veins, arteries)
- Renal sensors (intrarenal baroreceptors, macula densa)
What happens when theres more Na+ and H2O loss? (for eg in Diarrhoea)
- decreased plasma vol
- decreased venous pressure & arterial pressure
- decreased arterial blood pressure
- increased activity of renal sympathetic nerves
- constriction of afferent arteriole
- decreased net Pgc & GFR
- More time for Na+ and H2O to be reabsorbed -> less is excreted in the urine
Describe the control of Na+ reabsorption in Distal tubule and Collecting ducts
Describe how Aldosterone affects absorption of Na+. also where is it secreted from?
- By variations in Aldosterone, Na+ reabsorption can be finely controlled
- secreted from the zona glomerulosa
Describe the action of Aldosterone on distal tubule and collecting ducts
- Aldosterone gets secreted from Peritubular capillaries
- diffuses through cell membrane and goes to nucleus of DT and CD cells bia binding to mineralocorticoid receptor
- induces gene transcription of proteins (P1, P2, P3, P4) involved in sodium reabsorption
- increased synthesis of sodium channels, Na+/K+ ATPase pumps, etc -> increase sodium reabsorption
How long does it take for body to excrete excess sodium
days
What is Addison’s Disease and what are some symptoms?
= Adrenal glands don’t produce sufficient aldosterone
- Low BP
- Salt cravings bc low Na+
- Muscle weakness bc of high K+
What is Aldosteronism and what are some symptoms?
= Adrenal glands produce excessive Aldosterone
- High Na+
- Low K+
What leads to Aldosterone secretion?
RAAS System
What are ACE inhibitors used to treat?
Hypertension
What does activation of RAAS lead to
- Increased Na+ reabsorption
- decreased Na+ excretion
What is Renin and where is it released from?
= enzyme that forms Angiotensin 1 from Angiotensinogen
- synthesised, stored and released from granular cells in Juxtaglomerular region of afferent renal arteriole
- involved in increased reabsorption of Na+ via RAAS
Whats the relationship bw Renin secretion and renal arterial pressure?
Inversely related
- decreased plasma vol -> decreased renal arterial pressure -> decreased stretch of juxtaglomerular cells -> less Ca2+ -> increased renin secretion
Summary of Renin and RAAS
