Renal: Renal Filtration 1 Flashcards
three functions of the kidney (brief)
- primarily an excretory organ
- maintenance of ECF volume and blood pressure (fluid balance)
- endocrine functions
details about the kidney being an excretory organ
Eliminates byproducts of protein and nucleic acid metabolism (dietary, muscle), drugs, toxins, metabolites.
- BUN - Blood Urea Nitrogen: product of amino acid degradation
- Cr (Creatinine), SDMA (Symmetric Dimethyl Arginine) - Products of muscle and cellular metabolism etc.
- Many other molecules excreted
-toxins and drugs
-ketones, sulphates, etc
endocrine functions of the kidneys
- Vitamin D metabolism
- Erythropoietin (EPO) production
- Renin-Angiotensin-Aldosterone system (Renin production)
what are the vascular components of the kidney
- Glomerulus
- Afferent arteriole
- Glomerular capillaries
- Efferent arteriole
- Peritubular capillary
- Vasa recta
what are the tubular components of the kidney
- Bowman’s capsule
- Proximal tubule
- Loop of Henle
- Distal tubule
- Collecting tubule/duct
whats part of the juxtaglomerular apparatus
- JGA – afferent and efferent arterioles, mesangial and JG cells, and macula densa – renin release
what is the macula densa
is a specialized portion of distal tubular epithelial cells adjacent to JG cells
what are the JGA and macula densa important for
Important for control of both systemic and local vascular resistance
(regulation of BP as well as single nephron glomerular filtration rate)
what happens in the course of normal metabolism
and why is this important
In the course of normal metabolism, the body generates nitrogenous wastes (urea (BUN), creatinine, SDMA), primarily from protein and nucleic acid metabolism.
Kidneys remove nitrogenous wastes from plasma in direct proportion to the level of renal function – when normal function is present, wastes are rapidly and efficiently removed. When they are sub-functional (disease, injury, lack of blood flow) then clearance is impaired
This is important because:
1) The molecules that accumulate when the kidney is failing are toxic to cells and tissues – leading to clinical disease.
2) The level of these molecules in the blood can be used to assess renal function.
what happens in glomerular filtration, what does the glomerulus allow, whats its production, what is estimation of GFR important for
Nitrogenous wastes are removed from plasma by filtration in a structure called the glomerulus.
The glomerulus is a specialized capillary bed which has evolved to allow
– Complete retention of plasma proteins
– Vascular control that permits GFR and renal blood flow to be maintained over wide range of perfusion pressures
Glomerular filtration is the production of a protein-free filtrate of plasma
Estimation/assessment of glomerular filtration rate (GFR) is one of the key steps in the clinical assessment of renal function
what is glomerular filtration rate, examples for species
The volume of plasma filtered by all glomeruli in a given time period
* Normal ranges of 2-4 ml/kg/min in a 10 kg dog and 1-3 ml/kg/ min in a 500 kg horse
* 10 kg dog produces 30-60 liters of filtrate every day
* 500 kg horse produces 720-1440 litres of filtrate every day!
what do epithelial podocytes do
they put different levels of tension on the filter membrane to let thing pass out or not
they are the most important cell type in glomerular filtration
what is glomerular ultrafiltrate
water and small molecules (<2nm) pass freely, cells and larger (<4nm) molecules (proteins) retained = glomerular ultrafiltrate
selective permeability of glomerular membrane
- <2 nm (water and small molecules) pass freely
- > 4 nm (larger proteins) retained
- 2-4 nm variable filtration, dependent on electrical charge
and deformability (-ve charge pass easier than +ve charge)
what is glomerulonephritis
- Clinical condition affecting the glomerulus.
- Causes a protein-losing nephropathy of dogs associated with immune-mediated glomerular pathology (immune system damages glomerular membrane)
– Marked proteinuria (+/- blood)
– Hypoalbuminemia
– Peripheral edema
– Progression to chronic renal failure
three factors determining GFR
- Renal blood flow (RBF) and renal perfusion pressure (PGC ).
- The net pressure difference between the tubule lumen and the capillaries (balance between blood pressure (“out” of vascular system) and colloidal oncotic pressure (“in” to vascular system).
- The surface area available for ultrafiltration and the “ultrafiltration
coefficient” (KUF) of the glomerular membrane
what happens to glomerular pressure, renal blood flow and GFR when there is increased resistance in afferent arteriole
all decreased
what happens to glomerular pressure, renal blood flow and GFR when there is increased resistance to efferent arteriole
glomerular pressure and GFR increases
RBF decreases
what happens to glomerular pressure, renal blood flow and GFR when there is decreased resistance in efferent arteriole
RBF increases
GFR and glomerular pressure decreases
what happens to glomerular pressure, renal blood flow and GFR when there is decreased resistance in afferent arteriole
RBF, GFR and glomerular pressure increases
what does autoregulation maintain
autoregulation maintains a nearly constant GFR when mean arterial blood pressure is between 80-180mmHg
when blood pressure drops, GFR drops and vice versa
what is a myogenic response, and what leads to vasoconstriction vs vasodilation and what is it mediated by
Myogenic response - vascular smooth muscle responses to factors such as adenosine, local hypoxia etc.
* Similar to autoregulation in other systemic arterioles
-increased arterial wall tension = vasoconstriction
-decreased arterial wall tension = vasodilation
Mediated by stretch receptors that open and close ion channels. Modulates blood flow and pressure in the glomerulus and therefore influences GFR. Modulated by local factors (prostaglandins, NO etc.) that are present
what are the mechanisms of renal autoregulation (brief)
1- myogenic response
2- hormones and autonomic neurons
hormones and autonomic neurons for renal autoregulation… how does it work
what are the hormones for dilation vs constriction
what are the neural factors
Hormones and autonomic neurons - eg. sympathetic vascular responses
* By changing resistance in arterioles (eg. adrenergic receptors)
* By altering the filtration coefficient (tension on the glomerular membrane)
Hormones:
* Vasoconstrictors - Renin-angiotensin-aldosterone system (Angiotensin II), Endothelin
* Vasodilators - Dopamine, Atrial Naturiuretic Peptide/Factor Prostaglandins (PGE2, PGI2)
Neural (ANS) Factors:
* Sympathetic stimulation: Increased vascular resistance
and increased renin release.
renin angiotensin aldosterone system (how it affects BP, ADH secretion, tubular reabsorption, sympathetic activity)
a decrease in renal perfusion (decreased blood pressure), leads to release of renin which immediately activates angiotensinogen to angiotensin. angiotensin converting enzyme then activates it into angiotensin 2 which has many effects:
1= effects on arteriole vasoconstriction that would increase blood pressure
2 = angiotensin 2 stimulates the pituitary gland and causes ADH secretion which stimulates the collecting duct for water absorption
3 = stimulate adrenal gland to secrete aldosterone
4 = directly increase tubular Na, Cl reabsorption and K excretion, water retention (aldosteron also does this)
*** if BP is too high, the opposite happens
