| Question | Answer |
| Kidney Functions | - Removal of toxins, metabolic waste, and excess ions from the
blood
- Regulation of blood volume, chemical composition, and pH
- Gluconeogenesis during prolonged fasting
- Activation of vitamin D
- Endocrine functions (renin and erythropoietin) |
| Renin | regulation of blood pressure and kidney function |
| Erythropoietin | regulation of RBC production |
| Vascular Resistance in Microcirculation | High resistance in afferent and efferent arterioles
Causes blood pressure to decline from ~95 mm Hg to ~8 mm Hg in kidneys |
| Mechanisms of Urine Formation | Glomerular filtration
Tubular reabsorption
Tubular Secretion |
| Tubular Reabsorption | Returns all glucose and amino acids, 99% of water, salt, and other components to the blood |
| Tubular Secretion | Reverse of reabsoprtion: selective addition to urine |
| Glomerular Filtration | Passive process driven by hydrostatic pressure
Molecules >5 nm are not filtered (e.g., plasma proteins) and function to maintain colloid osmotic pressure of the blood |
| Why is the glomerulus an efficient filter | -Its filtration membrane is very permeable and it has a large
surface area
- Glomerular blood pressure is higher (55 mm Hg) than other
capillaries |
| Net Filtration Pressure (NFP) | The pressure responsible for filtrate formation (10 mm Hg) |
| Net Filtration Equation | NFP = HPg – (OPg + HPc)
net filtration pressure = glomular hydrostatic pressure - (Colloid osmotic pressure of glomerular blood - capsular pressure) |
| NFP determined by... | Glomerular hydrostatic pressure (HPg) the chief force
Two opposing forces:
Colloid osmotic pressure of glomerular blood (OPg)
Capsular pressure (HPc) |
| Glomerular Filtration Rate (GFR) | Volume of filtrate formed per minute by the kidneys (120–125 ml/min) |
| GFR determined by... | - Total surface area available for filtration
- Filtration membrane permeability
- NFP |
| GFR mechanisms | Intrinsic controls (renal autoregulation)
Extrinsic controls |
| Intrinsic control of GFR | Act locally within the kidney
Maintains a nearly constant GFR
Two types of renal autoregulation
- myogenic mechanism
- Tubuloglomerylar feedback mechanism, which senses changes
in the juxtaglomerular apparatus |
| Extrinsic control of GFR | Nervous and endocrine mechanisms that maintain blood pressure, but affect kidney function |
| Myogenic Mechanism | increased BP: contraction of afferent arterioles
- Helps maintain normal GFR
- Protects glomeruli from damaging high BP
decreased BP: dilation of afferent arterioles
- Helps maintain normal GFR |
| tubular reabsoprtion routes | transcellular
paracellular |
| transcellular route (tubular reabsorption) | Apical membrane of tubule cells ->
Cytosol of tubule cells ->
Basolateral membranes of tubule cells ->
Endothelium of peritubular capillaries |
| paracellular route (tubular reabsorption) | Between cells
- Movement through the interstitial fluid and into the capillary
- Limited by tight junctions, but leaky in proximal nephron
- Water, Ca2+, Mg2+, K+, and some Na+ in the PCT |
| What gets reabsorbed in tubular reabsoption | - all nutrients -> glucose & amino acids
- Ions: Na+, Ca2+, Mg2+, K+
- water |
| urinary bladder function | - temporary urine reservoir |
| paired ureters | - transport urine from the kidneys to the bladder |
| urethra | - transports urine from the bladder out of the body |
| kidney anatomy | - Retroperitoneal and in superior lumbar region
- Right kidney is lower than the left
- Convex lateral surface, concave medial surface
- Renal hilum ->renal sinus
- Ureters, renal blood vessels, lymphatics, and nerves enter and
exit at the hilum |
| kidney layers | - renal fascia
- perirenal fat capsule
- fibrous capsule |
| Renal fascia | - The anchoring outer layer of dense fibrous connective tissue |
| Perirenal fat capsule | - A fatty cushion |
| Fibrous capsule | - Prevents spread of infection to kidney |
| Renal cortex | - A granular superficial region |
| Renal capsule | - The cone-shaped medullary (renal) pyramids separated by renal
columns |
| Lobe | - A medullary pyramid and its surrounding cortical tissue |
| Papillary | - Tip of pyramid; releases urine into minor calyx |
| Renal Pelvis | - The funnel-shaped tube within the renal sinus |
| regions of internal kidney | - renal cortex
- renal medulla
- renal pelvis |
| Renal cortex | - granular-appearing superficial region |
| Renal medulla | - medullary renal pyramids: cone shaped
- pyramids separated by renal columns (made of cortical tissue)
- Lobe: medullary pyramid and its surrounding cortical tissue;
about eight lobes per kidney |
| Renal pelvis | - Funnel-shaped tube continuous with ureter
-minor calyces
- Cup-shaped areas that collect urine draining from pyramidal
papillae
-major calyces
- Areas that collect urine from minor calyces + Empty urine
into renal pelvis |
| Flow of urine | - Renal pyramid -> minor calyx -> major calyx -> renal pelvis ->
ureter |
| Blood and Nerve supply | - 1/4 (1200 ml) of cardiac output to the kidneys each minute
- Arterial flow into and venous flow out of the kidneys follow
similar paths
- Nerve supply is via sympathetic fibers from the renal plexus |
| Nephrons | - Structural and functional units that form urine
- 1 mill. per kidney
- 2 main parts
- renal corpuscle
- glomerulus
- bowman's capsule (surrounds glomerulus)
- renal tubule: tube |
| Glomerular capsule | - Parietal layer: simple squamous epithelium
- Visceral layer: branching epithelial podocytes |
| Renal Tubule | - single layer of epithelial cells
- Proximal convoluted tubule (PCT)
- Proximal, closest to renal corpuscle
- Nephron loop
- ascending and descending loops
- Distal convoluted tubule (DCT)
- Distal, farthest from renal corpuscl |
| PCT histology | - Cuboidal cells
- Functions in reabsorption and secretion
- Confined to the cortex |
| Loop of Henle histology | - Thin segment usually in descending limb
- Simple squamous epithelium
- Freely permeable to water
Thick segment of ascending limb
- Cuboidal to columnar cells |
| DCT histology | - Cuboidal cells with very few microvilli
- Function more in secretion than reabsorption
- Confined to the cortex |
| Collecting ducts | - receive filtrate from many nephrons
- Fuse together to deliver urine through papillae into minor
calyces
- 2 types of cells
- intercalated cells
- principal cells |
| intercalated cells | - Cuboidal cells with microvilli
- Function in maintaining the acid base balance of the body |
| principal cells | - Cuboidal cells without microvilli
- Help maintain the body’s water and salt balance |
| types of nephrons | - cortical nephrons
- juxtamedullary nephrons |
| Cortical nephrons | - 85% of nephrons; almost entirely in the cortex |
| Juxtamedullary nephrons | - Long loops of Henle deeply invade the medulla
- Extensive thin segments
- Important in the production of concentrated urine |
