12.05.11+-+Urinary+System


 * 12.05.11 - Urinary System**


 * 1. At the gross and microscopic levels, describe the different anatomical regions of the kidney and the structures found in these regions: cortex, medulla, medullary rays, cortical labyrinths, vasa recta, pyramids, renal columns, papilla, and calyces.**

Cortex Medulla Medullary rays: only in cortex; bundles of tubules going to collecting duct/tubule Cortical labyrinths: only in cortex; the mixed region of the cortex formed by glomeruli and distal and proximal tubules Vasa recta: bundles of capillaries in the outer medulla encircling tubules (w/in renal columns) Pyramids: medullary structures interdigitated with renal columns; formed from many Loops of Henle Renal columns: extensions of cortical tissue (filled with col Papilla: the point of the renal pyramid where collecting ducts merge into a minor calyx Calyces: the collecting tubes merge into minor and then major calyces that become the renal pelvis and ureter
 * Gross: external portion of kidney; formed of lobes composed outer medullary rays
 * Microscopic: composed of proximal and distal convoluted tubules, renal corpuscles (bowman's capsule and glomerulus), and the upper portion of the collecting tubule; divided into cortical labyrinth and medullary rays.
 * Gross: Composed of interdigitated cortical extensions called renal columns and renal pyramids
 * Microscopic: composed of loop of Henle including thin segment and lower collecting tubule. Divided into renal pyramids and renal columns.


 * 2. Describe a renal lobe and renal lobule.**

A renal lobe is formed from the cortical tissue adjacent to a single renal pyramid.

A renal lobule is formed from the cortical tissue adjacent to a single medullary ray.


 * 3. Describe the histological and cytological features of the nephron and the regions of the kidney in which the different portions of the nephron are found.**


 * Regions of the Kidney:**

Cortex Medulla (divided inner and outer) Medulla (divided side by side)
 * Cortical labyrinth
 * Medullary ray
 * Inner medulla
 * Outer medulla
 * Renal pyramid
 * Renal column


 * Regions of the Nephron:**

Renal corpuscle: Proximal convoluted tubule: Proximal (Descending) tubule: Thin loop: Distal (Ascending) tubule: Distal convoluted tubule: Collecting tubule:
 * cortical labyrinth
 * distinctive circle of capillaries with capsule
 * formed from glomerulus (ball of capillaries; filtrate exits glomeruli into urinary space) and Bowman's capsule (barrier between urinary space rest of tissue);
 * 2 poles: vascular pole with afferent and efferent arterioles and urinary pole with exiting proximal convoluted tubule
 * cortical labyrinth:
 * dark, pink staining, interspersed with renal corpuscles, with brush border, more common (6:1)
 * highly permeable to water; pumps out sodium, water follows (concentrates filtrate); tight junctions; absorb/endocytose valuables (glucose, amino acids, bicarbonate)
 * medullary ray, outer medulla, and renal pyramid:
 * dark, pink staining, brush border on cells
 * Similar function to proximal convoluted tubule
 * inner medulla and renal pyramid:
 * narrow, like fat capillaries
 * either similar function to proximal or distal depending on whether it is ascending or descending; can't tell in slide
 * outer medulla and renal pyramid:
 * lateral interdigitations between epithelial cells
 * not permeable to water, but now pumps sodium back into filtrate if excess
 * cortical labyrinth:
 * interspersed with renal corpuscles, ligher staining, less common (1:6)
 * not permeable to water, but now pumps sodium back into filtrate if excess
 * Medullary ray:
 * no brush border and also very distinct cell margins
 * responsive to renin -> angiotensin I -> angiotensin II -> Aldosterone and Vasopressin (ADH). Tight junctions are still present, but the cells themselves are made porous with aquaporins (AQP 2, 3, and 4). AQP 3/4 are present on the basolateral side; they receive signal from aldosterone; they send cAMP second messenger to exocytose vesicles on apical side that lodge AQP 2 in plasma membrane. This opens channel for water to flow down osmotic gradient out of urine and into tissue.


 * 4. Describe the primary function of each of the glomerulus, Bowman's capsule, collecting tubules and ducts, and the named tubular parts of the nephron.**

See question above


 * 5. Name the various cell types that comprise the juxtaglomerular apparatus and describe the functions and structure of each cell type.**

There are two cell types in the juxtaglomerular apparatus: the juxtaglomerular (jg) cells and the macula densa. The jg cells are modified smooth muscle cells of the afferent arteriole and the macula densa are modified epithelial cells of the distal tubule. The jg cells store and secrete renin, which sets off the angiotensin loop. The function of the macula densa cells is unknown.


 * 6. Describe where renin is produced.**

Renin is produced in the juxtaglomerular cells (modified smooth muscle cells) of the afferent arteriole of the glomerulus.


 * 7. Describe the function of aquaporins in the kidney and describe the cellular and tissue distributions of the different aquaporin species.**

AQP 1 is unregulated (constitutive) and present in the proximal tubules. Always open. Always allowing water to exit the tubule following the Na+ being pumped out.

AQP 2 is on the apical side of the collecting tubule. Stored in vesicles in the epithelial lining of the collecting tubule, activated by aldosterone and ADH via cAMP to exocytose on apical side in response to low blood pressure, low water levels.

AQP 3/4 are on the baso-lateral side of the collecting tubule. Have receptor for aldosterone and ADH. Send signal via cAMP to AQP 2 vesicles to exocytose


 * 8. Describe the cellular mechanism by which aldosterone exerts its action in the kidney.**

Aldosterone is activated through several steps by the renin produced by jg cells, which activates angiotensin I to be secreted by the liver. Angiotensin I is cleaved into angiotensin II by endothelial cells of lung, which signal aldosterone to release from adrenal cortex. Once released, aldosterone hits AQP 3/4 on the baso-lateral side of the endothelial lining of the collecting tubules. They trigger a cAMP 2nd messenger system which sends off the AQP 2 vesicles.


 * 9. Describe the microscopic organization and functions of the ureter and bladder.**

Ureter: transitional epithelium; muscular star shaped epithelium

Bladder: transitional epithelium; multiple crossing layers of smooth muscle