Urinary - Weeks 1 to 5 (inc. Embryology) Flashcards
What pressures contribute to the filtration rate?
Hydrostatic pressure of capillaries and the Bowmans capsule
Oncotic pressure difference between the capillaries and the lumen of the tubule
What are the three parts of the filter?
1) capillary endothelium - fenestrated
2) basement membrane
3) podocytes - make sure large proteins etc can’t leave the capillaries, slit diaphragm
What does the Glomerulus do?
Filtration
Selective
Allow water, salts and small proteins to pass through
Makes tubule fluid the same tonicity and ion concentration etc as blood plasma, without the larger cells
What are the 2 types of nephron?
Cortical - all in the cortex
Juxtamedullary - closer to the medullary boundary, have a longer loop of Henle
What is the role of the PCT?
Reabsorption of Water, Na+, Glucose and other solutes
Isosmotic Reabsorption
Reabsorption driven by Na+ uptake
What are the Na+ transporters in the PCT?
Na-H anti porter
Na-glucose symporter
How does glucose move in the PCT?
Glucose moves with Na+ against its concentration gradient
Then moves from the lumen into the capillaries via facultative diffusion
Normally 100% reabsorbed
There is a threshold and if that goes over, you get glycosuria
Calculate the GFR…
Choose something freely filtered, non reabsorbed, non secreted.
Insulin and Creatinine
See how well the kidneys work
Conc. in urine X urine volume / plasma Conc.
What is the filtration fraction?
Proportion of substance actually filtered
GFR/RPF
What is renal clearance?
Volume of substance completely cleared by kidneys per unit time
Urine Conc. X volume / plasma Conc.
Detect glomerular damage
Follow progress of kidney disease
Describe methods of Autoregulation of the GFR
The glomerular filtration rate is kept in normal limits by
1) Myogenic response- vasoconstriction in response to stretch
2) Tubular Glomerular Feedback - macula densa detects Cl- changes. Stimulate the JGA to release vasoconstrictors (adenosine) or dilators (prostaglandins)
How do you estimate GFR?
Use Creatinine Clearance
(140 - Age) X Mass (Kg) X Constant over Serum Creatinine
Filtered Load definition
The amount of substance filtered per minute
Work out using the normal plasma concentration then times by the glomerular filtration rate (if it is freely filtered) eg glucose, creatinine.
What is the transport maximum?
The renal threshold for a substance that can be filtered, when Tm is reached, the substance starts to overflow into the urine
What is the main factor in volume control of the ECF?
Na+
Effective Osmole
What happens with an imbalance of Na+?
If less excreted, then water retention can lead to increased blood volume, then arterial pressure rises, leads to oedema.
How do we describe the changes of volume?
It is isosmotic, so we change ion concentration and water follows, so osmolarity is unchanged
Where in the Kidney do the ion and water changes occur?
Mostly in the PCT
Water then has some in the desc. loop of Henle and DCT and collecting duct
Na+ also in asc. limb and DCT and Collecting Duct
What are the 2 cell types in the late DCT/CD?
Principle Cells - Reabsorb with ENaC, creates a neg. charge
Type B intercalated cells - Active Cl- reabsorption
Describe ADH Structure
Small Peptide
9 Amino Acids long
Describe ADH’s action
ADH acts on cells in the DCT and Collecting Duct.
ADH acts on a GPCR on the basolateral membrane, releases cAMP, then PKA, which inserts Aquaporin into the apical membrane.
Increases the permeability to water and urea
What are 2 additional effects of ADH (apart from aquaporins)
Vasoconstriction in Glomerulus
Increase Ion reabsorption in the ascending limb of loop of Henle
What produces the Corticomedullary gradient?
The Juxtamedullary nephron
What 3 Parts of the Nephron create the gradient?
The active NaCl transport in the asc. limb (counter current multiplication)
The Vasa recta (maintain the gradient)
Recycling of Urea (effective osmole)
The Urea which leaves the CD does what?
It is recycled back into the ascending loop of Henle.
It increases osmotic pressure so water follows it into the interstitium (cannot follow back into the loop as it is impermiable)
Describe counter current multiplication
1) Na+ pumped out of the asc. limb. Increases osmotic pressure of interstitium and lowers the tubules
2) Water follows from the desc. limb. Makes tubule osmotic pressure back to normal
3) Cycle continues, more concentrated fluid is pushed round, creating more and more conc. fluid
4) Bottom most concentrated as it is the first to take Na+ out of the loop to create the 200mol gradient
What is the role of the Vasa Recta
Maintaining the Concentration gradient of the Kidney.
It travels in the opposite direction to the tubule and tries to match the interstitial fluid concentration, it picks up Na+ and H20
What are 2 problems with ADH secretion?
Diabetes insipidus - not enough ADH produced from the pitruitry gland or kidney is insensitive to it.
Low conc and lots of urine produced
Manage with ADH injections or nasal spray
Syndrome of Inappropriate ADH secretion (SIADH) - excessive release from pitruiry or other leads to dilutional hyponaturaemia, increase in total body fluid
Get nausea and vomiting, headache, confusion
Treat with ADH receptor antagonists
