141 - Kidney Function I Flashcards
Kidney functions 1 2 3 4 5 6
1) Water, sodium homeostasis 2) Control of ECF ion concentration (K, Ca, Mg, Cl, HPO4) 3) Acid-base balance 4) Excretion of waste products and xenobiotics 5) Endocrine functions 6) Formation of concentrated/dilute urine
Most important function of the kidneys
Water and sodium balance
Why do the kidneys regulate ECF ion concentration?
All can kill if not maintained within a tight band; High[K+] sudden death; high P or low Ca++ cause fractures, Mg++ critical in nerve, muscle and brain
Which organ, in tandem with the kidneys, regulate acid-base balance?
Lungs
Breakdown of what leads to urea formation?
Protein
Role of vitamin D3
Calcium absorption
Examples of renal endocrine functions 1 2 3 4
EPO, renin, Vitamin D3, PGI2 (prostacyclin)
*Structure of a nephron
Where is the initial filtrate formed in the kidneys?
Bowman’s capsule
Size of fenustrations in Bowman’s capsule capillaries?
2nM
Why mightn’t all molecules under 2nM be filterable in the kidneys?
Bowman’s capsule capillary fenestrations are negatively-charged, so negatively-charged molecules are less-likely to fit through (EG: serum albumin), positively-charged molecules over 2nM can fit through.
Average GFR in humans
180L/day (60mL/minute/single kidney)
Average length of loop of Henle
Only very shallowly enters medulla of kidney (85% of nephrons). 15% go very deep (long loops of Henle)
Significance of junction between thick ascending limb and distal tubule
Where the nephron makes contact with the home glomerulus and the afferent arteriole. Contact point is the macula densa.
Arrangement of collecting ducts
Often several distal tubules (from different nephrons) feed into collecting duct. Collecting ducts fuse, until they form the renal pelvis that feeds into the bladder
Sequential segments of the nephron 1 2 3 4 5 6 7
- Bowman’s capsule 2. Proximal Tubule – pars recta and PCT ( convoluted tubule) 3. Thin descending limb of Henle’s Loop – tDLH 4. Thin ascending limb of Henle’s Loop – tALH this is very short in superficial cortical nephrons It is long in JM nephrons 5. Thick Ascending limb – TAL 6. Distal Tubule –DT 7. Collecting Duct – CD
Role of proximal tubule
Reabsorbs ~65% of water, NaCl, most solutes. Absorbs 100% of very important molecules (EG: glucose, amino acids, lactic acid) using active transport.
Role of the loop of Henle (thin descending limb)
Concentrating (1200 miliosmolar/L at tip of loop of Henle)
Role of thick ascending loop of Henle
Dilutes filtrate
Macula densa
Part of the juxta-glomerular apparatus At junction between ascending limb and distal tubule
Distal tubule role
Fine-tunes water/ion balance of filtrate. Alters concentration of urine according to the body’s needs.
Collecting duct role
Aldosterone-dependent equillibrator. Surrounded by fluid of a high osmolarity. How much water escapes collecting duct is contingent on permeability of collecting duct to water (aquaporins).
Role of aldosterone in the collecting duct
Induces aquaporin expression, which increases water loss from collecting duct (increases urine concentration)
Superficial cortical glomeruli
~90% of glomeruli. Loop of Henle penetrates a short distance into the medulla Efferent arterioles give rise to cortical capillaries surrounding the proximal and distal convuluted tubules
Juxtamedullary glomeruli
Loop of Henle penetrates deep into the medulla Efferent arterioles become the vasa recta that also penetrate deep into the medulla, parallel to the loops of Henle
Role of juxtamedullary glomeruli
They account for the medullary concentration gradient; osmolarity increases from 300 at the C-M junction to 1200 in the deepest part (papilla) of the medulla
Blood vessels that surround nephron path
Peritubular capillaries
Name for capillaries accompanying loops of Henle
Vasa recta
*Arrangement of vasculature of nephron
Parts of nephron where reabsorption occurs
All parts
Things that can occur in the nephron SERF
F= Filtration R = Reabsorption S = Secretion E = Excretion
Part of nephron where filtration occurs
Bowman’s capsule
Where does secretion occur?
Proximal, distal tubules, collecting duct
Is secretion active or passive?
Active
Role of secretion
Takes substances that couldn’t be passively filtered out of the nephron by active transport
*Areas in nephron where filtration, reabsorption, secretion and excretion occur
Does reabsorption or filtration account for the reuptake of more products?
Reabsorption
Example of a situation where excretion = filtration - reabsorption + secretion doesn’t apply
Proteins (a few grams are excreted each day) are filtered and not reabsorbed, but aren’t excreted, as they are broken down in the proximal tubule (in health)
*Glomerulus diagram
Things that aren’t filtered in health 1 2 3 4 5 6 7 8
1) RBC 2) WBC 3) Platelets 4) Albumin (a very small amount is filtered) 5) IgG 6) Small peptides (partially filtered) 7) Organic solutes bound to proteins 8) Protein-bound drugs
Things that are filtered in health 1 2 3 4
1) Albumin (very small amount) 2) Small ions 3) Organic solutes (free) 4) Drugs (free)
Why can albumin filtration rate increase in disease?
Bowman’s capsule fenestrations can lose their negative charge
What forms the filtration mechanism in Bowman’s capsule?
Fenestrations in capillary endothelium and podocyte foot processes.
*Bowman’s capsule filtration apparatus
Part of Bowman’s capsule that responds to angiotensin II
Mesangial cells
Name for space between podocyte foot processes
Filtration slits
Common filtration rate
125mL/minute
Normal filtration fraction
20% of renal plasma flow
Forces that affect GFR 1 2 3 4
1) Hydrostatic pressure in the glomerular capillary (50mmHg) 2) Hydrostatic pressure in Bowman’s capsule (10mmHg) 3) Oncotic pressure in the glomerular capillary (25->40mmHg) 4) Oncotic pressure in Bowman’s capsule (0mmHg)
What determine oncotic pressure?
Plasma proteins that can’t be filtered
Driving force of hydrostatic pressure between glomerular capillary and Bowman’s capsule
40mmHg (50mmHg in glomerular capillary, 10mmHg in Bowman’s capsule)
Driving force of oncotic pressure between glomerular capillary and Bowman’s capsule
25-40mmHg (25-40mmHg in glomerular capillary, 0mmHg in Bowman’s capsule)
