Concentration Mechanisms & Urine Formation - Quiz 3 Flashcards
Where in the Kidney is Renin made?
Juxtaglomerular Apparatus
What are the 4 components of the Juxtaglomerular Apparatus?
Afferent Smooth Muscle Cells
Efferent Smooth Muscle Cells
Extraglomerular Mesangial Cells
Macula Densa Cells
What is the most potent vasoconstrictor known?
Angiotensin II
What is the Renin Angiotensin Pathway?
- Renin cleaves Angiotensinogen that came from the Liver to Angiotensin I
- ACE from the Lungs converts Angiotensin I to Angiotensin II
What does Angiotensin II do?
Vasoconstriction
↑Aldosterone Synthesis & Release
↑ADH Release
↑Thirst
Feedback Renin Inhibition
Releases Prostaglandins
Along w/ Vasoconstriction, What is the purpose for Angiotensin II to release Prostaglandins?
To maintain GFR even w/ Vasoconstriction
How does Angiotensin II affect the Adrenal Gland?
Stimulates it to Release Aldosterone causing Salt & Water Reabsorption
What is Aldosterone?
Steroid made in the Zona Glomerulosa of the Adrenal Cortex that acts on the Distal Tubule & Collecting Ducts to Secrete Potassium & Hydrogen Ions, while Reabsorbing Sodium
What stimulates the release of Aldosterone?
Angiotensin II
Increased ECF Potassium
Decreased Sodium
What is the Atrial Naturetic Peptide?
Hormone made in the Atria that does the opposite of the Angiotensin Pathway by
↓Na Reabsorption
↑GFR
Inhibit Renin, Aldosterone, & ADH
What is Conn’s Syndrome?
Aldosterone Secreting Tumor that causes
HTN
Hypernatremia
Hypokalemia
What are the Concentrating & Diluting Mechanisms of the Kidney?
ADH
ANP
Countercurrent Multiplier
Urea
What dictates the Obligatory Urine Volume?
The max concentrating ability of the kidney - normally 0.5L/day
What is ADH?
An Octapeptide made in the Hypothalamus, then Stored & Release by the Posterior Pituitary to Conserve Water by Concentrating Urine
How does an increase in ECF Osmolarity affect the Osmoreceptor cells in the Anterior Hypothalamus?
Causes them to Shrink –> sends signal to Posterior Pituitary –> ADH Release
Which part of the Kidney does ADH work to Increase Water Permeability?
Late Distal Tubules
Coritcal & Medullary Collecting Ducts
What stimulates ADH release?
Osmoreceptors
Mechanoreceptors/Baroreceptors
Angiotensin II
Sympathetic Stimulation
Anesthesia
Nicotine
What Inhibits ADH Release?
Alcohol
Clonidine
Haldol
What kind of condition must the Interstitium be in for ADH to work?
Hypertonic
What is needed to form Concentrated Urine?
High ADH
Hypertonic Renal Medullary Interstitium
Water
What are the Key Features of the Kidneys that help it Concentrate Urine?
Henle’s U-Shape - Opposite Flows
Permeability of Certain Nephron Segments
ATP Energy
What’s the max amount of urine concentration can the kidney produce?
1200 - 1400 mOsm/L
What Increases the Osmolality of the Renal Interstitium?
Active Na & Cl Transport in the TAL
What is the Osmotic composition of the Fluid that enters the Descending Limb?
Enters as Iso-Osmotic, but a lot gets absorbed making it more concentrated
What are the Major Factors that contribute to the Hyperosmolarity of the Medullary Interstitium?
- Active Transport of Sodium & Co-Transport of Potassium & Chloride out the TAL
- Active Transport of ions out the Collecting Ducts
- Facilitated Diffusion of Urea out the Medullary Collecting Ducts
- Diffusion of a bit of water out the Medullary Tubules
How is the High Medullary Interstium Osmolarity preserved in the presence of ADH?
The Large amount of water is reabsorbed into the Renal Cortex rather than the Renal Medulla
Why is the Osmotic Gradient the most within the Inner Medulla even though the TAL is located in the Outer Medulla?
Urea
What is Urea?
Byproduct of amino acid metabolism produced by the liver at 25-30 g/day
What is the role of Urea?
Accounts for 40-50% of Renal Interstitium Osmolarity
How does Urea get into the Renal Interstitium?
Permeable in the Inner Medulla only w/ ADH and diffuses to the Interstitium and gets trapped there.
Where in the Kidney is some Urea Permeable w/o ADH?
Thin Ascending Loop
What is the Role of the Vasa Recta?
Preserve Medullary Hyperosmolarity by
Removing reabsorbed fluid from Interstitium
&
Minimizing Solute Uptake from Medulla
What is the Solute & Fluid movement in the Descending Vasa Recta?
Rapid Flow = More Fluid Leaving than Solute Entering
What is the Solute & Fluid movement in the Ascending Vasa Recta?
Decreased Hydrostatic Pressure & Increased Blood Osmolality
More Solute Entering than Fluid Leaving
What conditions might affect the ability to Concentrate Urine?
Too much or Too Little ADH
Impaired Countercurrent Mechanism
Inability of Distal Tubule, Collecting Tubule, & Collecting duct to Respond to ADH
What is Central Diabetes Insipidus?
Failure to Produce ADH
What is the treatment for Central Diabetes Insipidus?
Desmopressin - DDAVP
Acts on V2 Receptors to increase Water permeability in the Late Distal & Collecting Tubules
What is Nephrogenic Diabetes Insipidus?
Inability of Renal Tubular Segments to respond to ADH
