Flashcards in Session 3 - Filtration Deck (95)
Outline the sequence of arteries leading into the kidney
• Renal Artery -> Segmental Arteries -> Interlobar Arteries -> Arcuate Arteries -> Interlobular Arteries -> Afferent Arterioles
Give one way in which the structure of the renal arteries increases pressure in the glomerulus
• The diameter of each afferent arteriole is slightly greater than the diameter of the associated efferent arteriole
What is the size limit and effective molecular radius for filtration?
• Size limit - 5,200
• Effective molecular radius - 1.48 nm
Why are proteins not usually filtered into the kidney?
• Basement membrane and podocyte glycocalyx have many negatively charged glycoproteins which repel protein movement
How much blood is filtered by the renal artery at any one time?
What happens to blood not filtered by the glomerulus?
• Exits via efferent arteriole
What are the two types of kidney nephron?
Why is a juxtamedullary nephron named thus?
• Glomeruli located in cortex, but next to medullary bounds
Give two differences between cortical and juxtamedullary nephrons
• Juxtamedullary has longer loops of henle
• Arrangement of peritubular capillaries around cortical nephrons messy
• Structured and organised arrangement of capillaries in juxtamedullary nephron
• Countercurrent flow in organised juxtamedullary nephron
How is filtration a selective process?
• Cells and large proteins do not get filtered through
• Water, salts and small molecules pass through
• Thanks to filtration mesh provided by podocytes
Where do the glomerula tufts always lie?
• In the cortex
Where does blood to be filtered arrive in the kidney?
• Glomerula tuft
What are the three layers in the filtration barrier?
• Capillary endothelium
○ Water, salts, glucose
• Basement membrane
○ Acellular gelatinous layer of collagen/glycoprotein
○ Permeable to small proteins
○ -'ve charge to repel protein movement
• Podocyte layer
○ Pseudopods interdigitate and form filtration slits
It is more difficult for a positive protein to pass through membrane than a negative. Do you agree?
• No, negative repelled by -vely charged basement membrane
What happens if a clinical conditions results in negative proteins being stripped of their charge?
• They will be filtered and appear in the urine
Give conc of following in plasma and ultrafiltrate
• Glucose 100
• Na+ mmol/l 140
• Urea mg/dl 15
• Creatinine umol/l 60-120
Give three physical forces involved in plasma filtration
• Hydrostatic pressure in the capillary (regulated) (capillary -> tubule)
• Hydrostatic pressure in bowman's capsule (tubule -> capillary)
• Osmotic (oncotic) pressure differences between the capillary and tubular (tubular -> Capillary)
What is the net filtration pressure in the glomerulosa?
What is the average hydrostatic pressure between capillaries and tubule?
• 50mmHG (about half of normal pressure)
What is the effect of charge on filtration?
• Neutral molecule - The bigger it is, the less likely to get through
• Anions - Negative charge also repels, more difficult to get through
• Cations - Positive charge allows slightly bigger molecules through
How is blood in afferent arteriole (going out) different to efferent (going in)?
• Oncotic (protein) pressure higher
• Blood is more concentrated
Give one cause of proteinuria involving filtration forces
• In many disease processes the negative charge is lost on the filtration barrier, so proteins are more readily filtered
What is osmotic pressure?
• Force generated because of solute within solvent
What is oncotic pressure?
• Oncotic force in generated because of protein within solute
Why is absorption in kidney called reabsorption?
• Already been absorbed once by GI tract
Give three mechanisms by which reabsorption occurs
• Active transport
What is tubular secretion?
• Substances secreted into renal tubular lumen from peritubular capillaries
By what mechanism are substances secreted into the tubular lumen?
• Active transport
What two main types of substances are secreted into the tubular lumen?
• Those present in great excess
• Natural poisons