in this lecture we reviewed renal anatomy and started to look at some filtration physiology. most of the renal anatomy was covered in the urinary system lecture from histology. some random facts that weren't:
-there are 1 million nephrons in each kidney, and over time, the number of functional nephrons decreases gradually, 10% every 10 years, such that only 40% are functional by age 80.
-within the nephron, loops of henle are sites for urine concentration and proximal/distal tubules are sites for reabsorption/secretion.
-cortical nephrons, nephrons located in the cortex of the kidneys, have shorter loops of henle and therefore are involved in reabsorption / secretion.
-juxtamedullary nephrons, nephrons in the medulla of the kidneys, have longer loops of henle and are involved in urine concentration.
-the vasa recta are blood vessels that are aligned with the loops of henle and are involved in urine concentration.
we then look briefly at renal innervation. the preganglionic efferent neurons originate at the T12/L1 level and synapse with postganglionic neurons at the renal plexus. the post ganglionic neurons innervate the kidney and are involved in stimulation of vasoconstriction and hormone secretion. the afferent sensory neurons bring signals from pain and baroreceptors on the kidney, routing to the solitary nucleus in the medulla (same as the baroreceptors for blood pressure regulation).
next was the beginning of renal physiology. the four basic processes of urine formation are introduced: filtration is the flow from the glomerulus to the bowman's capsule, reabsorption is the flow from the nephritic tubule to the peritubular capillaries, secretion is the opposite of reabsorption, and excretion is the flow of waste out of the tubules into the urine. we looked more in depth at the structure of the glomerular filtration mechanism, which consists of fenestrated endothelium, a basement membrane, and podocytes. podocytes have large foot processes which wrap around the capillaries, and between these foot processes lies a filtration sheath called the slit diaphragm. these slit diaphragms are made of nephrin and are anchored to the actin cytoskeleton of the podocyte foot processes. these three layers work to filter proteins by size: the endothelium blocks blood cells but allows large proteins. the basement membrane blocks large proteins but allows medium sized ones. the podocyte slit diaphragm blocks the rest of the proteins and allows water, electrolytes, etc. to flow through.
the filtration rate can be expressed by the equation GFR=Kf*NFP. Kf is the glomerular filtration coefficient and can be affected by the contraction of the mesangial cells (which surround the glomerular capillaries), decreasing the surface area available for filtration. NFP is the net filtration pressure and is a measure of the force available to push fluid from the glomerulus to the bowman's capsule. it is further broken down into 3 components: hydrostatic pressure of the glomerular capillaries (Pgc), oncotic pressure (∏gc), and hydrostatic pressure of the bowman's capsule (Pbc). Pgc is related to mean arterial pressure and is intricately regulated by constriction of the afferent arteriole, which decreases bloodflow into the glomerulus and thus lowers Pgc, or constriction of the efferent arteriole, which increases backpressure in the glomerulus and thus increases Pgc. oncotic pressure is caused by the higher concentration of proteins inside the glomerular capillaries, which induces water to flow inward. finally, Pbc is the hydrostatic pressure in the bowman's capsule, which can be increased by blockages in the urinary tract, lowering NFP and thus reducing glomerular filtration.
questions
1. describe the position of the kidneys.
2. renal arteries stem from... and renal veins drain into...
3. where are the medullary pyramids and what do they do?
4. what do minor calyces do?
5. what do major calyces do?
6. what is the renal pelvis?
7. what are the main functions of the kidney?
8. what are some examples of waste excreted by the kidney?
9. how many nephrons are in each kidney?
10. after 40, number decreases ... % every 10 years
11. only ... % are functional by age 80
12. what is the function of the proximal convoluted tubule?
13. what is the function of the loop of henle?
14. what is the function of the distal convoluted tubule?
15. what are the differences between the cortical and juxtamedullary nephrons?
16. what % of cardiac output goes to the kidneys? what is the flow rate of blood through the kidneys?
17. afferent arterioles...
18. glomerular capillaries...
19. efferent arterioles...
20. peritubular capillaries
21. vasa recta...
22. where do the preganglionic neurons that innervate the kidney originate?
23. what do the postganglionic neurons do and where are cell bodies located?
24. what sort of sensory neurons innervate the kidney and where do they project?
25. describe the four basic processes of urine formation
26. what is an average filtration rate per day?
27. how much of this filtrate is reabsorbed into the peritubular capillaries?
28. what is it that provides the force to filter material from the glomerulus to the bowman's capsule?
29. describe what constitutes the glomerular filtration layer, starting from the endothelium.
30. what are slit diaphragms mostly composed of?
31. what does nephrin connect to?
32. what are the signalling sources that the actin cytoskeleton responds to?
33. describe the different layers of glomerular filtration mechanism according to what they can filter.
34. how is polarity related to glomerular filtration?
35. what is the formula for glomerular filtration rate?
36. what is Kf and what is it affected by?
37. what is NFP?
38. what is the glomerular capillary pressure affected by?
39. what is the plasma oncotic pressure caused by?
40. what affects the bowman's capsule hydrostatic pressure?
answers
1. deep to the 12th rib, right kidney is slightly lower due to downward projection of liver.
2. aorta, inferior vena cava.
3. in the medulla of the kidneys, excrete urine through papillae into calyces.
4. collect urine from one pyramid
5. collect urine from multiple minor calyces
6. convergence of major calyces into the ureter
7. excretion of metabolic waste, regulation of volume and composition of extracellular fluids, hormone secretion, gluconeogenesis. extracellular excretion hormones gluconeo
8. urea, creatinine
9. 1 million
10. 10
11. 40
12. bulk reabsorption of water, electrolytes, glucose, etc.
13. urine concentration
14. fine tuning of reabsorption via ADH and aldosterone
15. cortical nephrons have shorter loops of henle and are involved in reabsorption and secretion, whereas juxtamedullary nephrons have long loops of henle and are involved in urine concentration.
16. 21%, 1200mL/min
17. regulate blood flow into the glomerulus
18. have high hydrostatic pressure and porosity for filtration
19. connects glomerular and peritubular capillaries. major site for control of filtration and reabsorption
20. surrounds nephritic tubules, major site for reabsorption
21. lie parallel to loops of henle, major sites for concentration / dilution
22. ventral horn of T12, L1
23. in the renal plexus, involved in stimulating vasoconstriction and hormone secretion.
24. baroreceptor and pain neurons, project to solitary nucleus in brainstem
25. filtration is flow from glomerular capillaries to bowman's capsule. reabsorption is flow from tubular lumen into peritubular capillaries. secretion is flow from peritubular capillaries to tubular lumen. excretion is flow out of collecting ducts.
26. 180L
27. 99%
28. hydrostatic blood pressure
29. endothelium, endothelium basement membrane, podocyte basement membrane, podocyte foot processes and slit diaphrams between foot processes.
30. nephrin
31. the actin cytoskeleton of the foot processes.
32. glomerular basement membrane, slit diaphragms, or cell surface.
33. endothelium doesn't allow blood cells, but lets larger proteins through. basement membrane doesn't allow large proteins through, but lets intermediate proteins through. slit diaphragms block the rest of the proteins.
34. negative charge on the glomerular filtration layers makes it more difficult for negatively charged molecules (as in, molecules bound with proteins) to pass through.
35. GFR=Kf *NFP
36. glomerular capillary filtration coefficient, affected by constriction/dilation of mesangial cells which increases / decreases capillary surface area available for filtration.
37. net filtration pressure. NFP=Pgc-Pbc-∏gc
38. depends on arterial pressure. also, constriction of afferent arteriole decreases Pgc, and constriction of efferent arteriole increases Pgc.
39. the backflow of water into the glomerular capillaries due to higher protein concentration
40. obstruction of urinary tract can increase Pbc and lower filtration.
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