Renal Blood flow and Filtration Flashcards
What rate does blood flow through the glomerulus and how much is filtered?
All blood coming in through the renal artery flows through the glomeruli in the cortex usually at a rate of about 1.1L/min, not all of this is filtered, only about 20%.
What is the plasma flow rate through the glomerulus?
Renal plasma is what is actually filtered (as cells are too big to fit). 45% of blood is plasma (Haematocrit, Ht or HCT = ratio of plasma to cell) so the plasma flow is about 605ml/min.
Describe the different vascular structures that lead from a renal artery to a renal vein.
There are 5 segmental arteries within a kidney. The renal artery splits into the segmental arteries, these split into Interlobar arteries which flow between renal pyramids, these split into arcuate arteries flow horizontally at the medullary/cortical boundary these branch off interlobular arteries which produce afferent arterioles.
Leaving the glomerulus is the efferent arteriole that feed into a complicated network of peritubular capillaries into venules and then interlobular veins, then arcuate veins, interlobar veins, segmental veins and then renal veins etc. etc.
How is pressure in the afferent arteriole kept high?
Efferent arteriole narrower than afferent arteriole so pressure is high in afferent arteriole.
What are vasa recta?
Vasa recta are a type of peritubular capillary associated with a specific type of nephrons. (juxtamedullary nephrons) these are specialised for concentrating urine (20% of nephrons).
What’s different between vasa recta and normal peritubular capillaries?
The vasa recta in Juxtamedullary nephrons are much more ordered in their location surrounding the loop of the Henle.
What’s the main differences between Cortical Nephrons and Juxtamedullary Nephrons?
Cortical Nephrons: located in outer part of cortex, have a small glomerulus, AA diameter > EA diameter, Rich sympathetic innervation and a high concentration of renin.
Juxtamedullary Nephrons: located in inner part of cortex, have a large glomerulus, AA diameter = EA diameter, Poor sympathetic innervation and a low concentration of renin.
Why does the efferent arteriole have an increased oncotic pressure?
Efferent arteriole has a higher viscosity and proportionally more albumin and so increased oncotic potential.
How does charge effect how well a molecule is filtered?
Positive molecules filter more easily than neutral molecules and negative molecules do not filter at all well. All of these decrease with increasing effective molecular radius. This is because of the negative charge pf all the glycoproteins in the basement membrane shared by the capillary endothelium and podocyte cells.
What’s the largest know protein to be filtered?
Inulin is the largest known molecule that can pass through the fenestrations of the endothelium and podocytes.
What three forces influence filtration a the glomerulus?
- Hydrostatic pressure within the capillary.
- Hydrostatic pressure within the bowman’s capsule (less than arteriole)
- Oncotic pressure force opposing the direction of filtration (due to high protein content in capillary)
Describe how Myogenic Autoregulation takes place?
Change in afferent arteriole diameter in response to changes in blood pressure to maintain GFR at the same rate. This control mechanism only works between the physiological limits of 80-180mmHg.
Describe Tubular Glomerular Feedback?
If GFR increases then there is an increase in (Na)Cl which is detected by the MD (macula densa) cells in the distal tubule, they stimulate the juxtaglomerular apparatus to release adenosine which is a vasodilator of the EA and if (Na)Cl decreases then they release prostaglandins which is a vasodilator of the AA. This is moment to moment short term regulation.
Generally describe PCT reabsorption
Bulk transport driven by Na reuptake. Other ion accompanies this such as Cl, glucose and water.PCT reabsorption is described as being Isosmotic as the Osmolarity doesn’t change as we move down the tubules so at the end of the PCT the filtrate is still isosmotic to plasma.
How can solutes move between the lumen of the PCT and the capillaries?
Reabsorption can be transcellular or paracellular (i.e. between the cells in the gap). The solutes move into the PCT cells, the into interstitium and from there into the capillaries.
