5 GFR and Filtration Flashcards
What are the functions of the kidney? (4)
- Regulation
- Conc of ECF
- Excretion
- eg urea
- Endocrine
- Renin, EPO, prostaglandins
- Metabolism
- active form of Vitamin D, insulin catabolism, calcitonin
Describe the path taken by blood from the renal artery to the afferent arterioles.
Renal artery
5 Segmental arteries
Interlobar arteries
Arcuate arteries
Interlobular arteries
Afferent arterioles
What causes the (relatively) higher hydrostatic pressure of blood in the glomerulus?
Diameter of afferent arteriole is slightly greater than diameter of efferent arteriole
The increased hydrostatic pressure in the blood in the glomerulus helps to force what components out of the blood?
Water, salts, glucose, urea
(NOT blood cells and plasma proteins as larger)
What is ultrafiltrate and how much of it does the body produce in a day?
Ultrafiltrate: (of plasma) plasma without cells and large organic molecules
180L per day
What is a normal GFR?
125 mL/min
Describe the glomerular capillaries.What is their function?
Small tuft of inter-connecting capillaries with fenestrated endothelium and specialised basement membrane
Function:
Selective filtration of blood
What is a podocyte and what is its function?
Specialised epithelial cell
Have ‘foot processes’ (pedicels)–> connect to basement membrane
Gaps between pedicels= filtration slits
Filtration slits= critical for selective permeability
Describe bowman’s capsule.
Layer of epithelial cells- surround glomerular capillaries- continuous with epithelium of proximal tubule so fluid directed into proximal tubule
What is the name for the cells that maintain the basement membrane in which the glomerular capillaries are embedded (providing them with structural support). What is the basement membrane made up of?
Mesangial cells (connected together by gap junctions)
What makes up the juxtaglomerular apparatus?
- Macula densa cells (salt sensors)
- Mesangial cells
- Afferent and efferent glomerular arterioles
What do the macula densa cells do?
Sensitive to changes in NaCl conc
–> affects renin release by juxtaglomerular cells
What % of blood arriving at the glomerulus exits via the efferent arteriole unfiltered?
80%
(Only 20% filtered)
Name some solutes which may be symported (active transport) back from the tubules with sodium.
Lactate
Acetate
Ketones
Glucose
Amino acids
Vitamin C
What is ‘tubular secretion’?
Substances- added to glomerular filtrate in nephron tubule- from epithelial cells lining renal tubules and collecting ducts - to remove excessive quatities from body eg:
- H+
- K+
- NH4+
Name the 2 mechanisms used to autoregulate renal blood flow to the glomerulus (and therefore GFR).
(Protects glomerular capillaries against increased perfusion pressure that could cause structural damage)
Myogenic (faster) (smooth muscle)
Tubuloglomerular (TG-F) (slower)
Describe how the myogenic response works. (will reference to glomerulus)
Opening of stretch activated cation channels in vascualr smooth muscle
Depolarisation: influx of Ca2+ stimulates contraction
Describe how the tubuloglomerular feedback works.
Macula densa cells- sense increase in glomerula filtration rate
BECAUSE increase in NaCl concentration increases NaCl
Causes vasoconstriction
More detail:
NaCl delivered to distal convoluted
Causes more Na and Cl ions to move into Macula densa
Increase intracellular conc of NaCl in macula densa–> triggers release of ATP
ATP exits macula densa
ATP converted to AMP
Adenosine binds to mesangial cells
Activation of GPCRs
Rise in intracellular calcium- vasoconstriction of afferent arteriole
Differentiate between osmolarity and osmolality.
Osmolality= solute per kg of solvent
Osmolarity= number of osmoles of solute per litre
What is the filtration fraction?
% volume of fluid reaching kidneys that passes into renal tubules (= about 20%)
In which type of nephron (cortical or juxtamedullary) does autoregulation take place?
Cortical
Fill in the missing labels:
What is highlighted in pink on this image?
The selectivity of the barrier in the glomerulus means that inulin is the largest molecule that can pass through. Why is it that smaller, negative molecules may not be able to pass through the barrier?
Basement membrane contains glycoproteins
Glycoproteins= negative
What is PGC?
Hydrostatic pressure in glomerular capillary
What forces oppose the PGC?
What is the immediate response in the glomerulus if the GFR drops?
Prostaglandin release
-strong vasodilators- to increase GFR
Why is it very important to ask a patient about their kidneys before prescribing NSAIDs?
NSAIDs inhibit prostaglandins
So patient won’t be able to recover from sudden drop in GFR
Explain how blocking the effect of angiotensin II (eg ACE inhibitors) cause acute renal failure in elderly patients.
Angiotensin II helps to maintain GFR when renal perfusion low
Major determinant of efferent vasoconstriction
Neural regulation of the GFR occurs in situations such as:
Fight of flight
Ischaemia
Haemorrhage
Describe the neural regulation of GFR.
Sympathetic nerve fibres- innervate Afferent and Efferent arterioles
Vasoconstriction occurs
