Urinary System

What is the function of podocytes?

- The podocytes and their projections wrap around the capillaries, and leave slits between them. - Blood filter through these slits. - They are also involved in regulating glomerular filtration rate (GFR) via contraction.

Describe the portal system of the kidney. Is this arterial or venous portal system?

- The two capillary beds are the glomerulus (proximal) and the peritubular capillaries (distal). Blood ultimately enters the renal portal system by the renal artery, and blood is ultimately drained from the renal portal system by the renal vein. - Arterial

Where is the vasa recta capillary bed located? What vessel delivers blood to these capillaries?

- Vasa recta - long straight bundles of capillaries that branch off from efferent arteriole and extend deep into the medulla paralleling the courses of the longest loops of Henle - Function in helping to concentrate the filtrate

What comprises a renal lobe?

a medullary pyramid and its overlying cortex

What are the three layers of the GBM?

- Lamina rara interna (LRI): next to endothelial cell - Lamina densa (LD): central electron dense layer - Lamina rara externa (LRE): next to epithelial cell

How and why does the composition of the ultrafiltrate changes as it flows through the following uriniferous tubules?

- Proximal convoluted tubule: reabsorbs protein, glucose, aa and most water - Proximal straight tubule: reabsorbs protein, glucose, aa and most water - Descending thin limb: permeable to water; in hypertonic medulla, H2O out, urea & Na+ in - Ascending thin limb: impermeable to water, permeable to salts; Na out - Ascending thick limb: active resorption of Na from lumen to interstitium - Distal convoluted tubule: impermeable to water. Under influence of aldosterone, resorption of water and Na from lumen to interstitium

What are functions of Intraglomerular and extraglomerular mesangial cells?

- extraglomerular mesangial cells are part of juxtaglomerular apparatus -> regulate blood pressure - intraglomerular mesangial cells are located among the glomerular capillaries within a renal corpuscle of a kidney -> filtration, structural support, and phagocytosis

Where is peritubular capillary bed located and what vessel delivers blood to these capillaries?

- peritubular capillaries are tiny blood vessels that travel alongside nephrons allowing reabsorption and secretion between blood and the inner lumen of the nephron. - Receive blood from efferent arteriole

How do glomerular basement membrane relate the formation of ultrafiltrate in the glomerulus?

GBM retards molecules greater than >69kDa (hemoglobins, globulins and most albumins). Polyanionic GBM (heparan sulfate PG) retards most negatively charged molecular complexes.

How does ADH affect the formation of urine? What is the target of ADH?

ADH increases the water reabsorption at distal tubule and collecting duct in the kidney through insertion of water channels -> increase urine osmolarity

How do afferent arteriolar pressure relate the formation of ultrafiltrate in the glomerulus?

Afferent arteriolar pressure is 4.5-6 times greater than the efferent pressure -> providing the net hydrostatic pressure that drive the filtration of plasma.

How do endothelial fenestrae relate the formation of ultrafiltrate in the glomerulus?

Endothelial fenestrae retard cells, platelets, chylomicrons and large complexes.

Why is anemia common in people with kidney disease?

Kidney produce erythropoietin which promote red blood cell production.

What triggers the release of renin from Juxtaglomerular cells

Macular densa cells detect low level of Na in the distal tubule and signal JG to release renin.

Describe the flow of blood into the kidney through the renal corpuscles and out of the kidney. How does the flow differ for cortical versus juxtamedullary glomeruli?

Renal a. -> segmental a. -> interlobar a. -> arcuate a. -> cortical radiate a. -> afferent arteriole -> glomerulus -> efferent arteriole -> peritubular capillaries -> cortical radiate v. -> arcuate v. -> interlobar v. -> segmental v. -> renal v.

How is urine osmolality (and sodium homeostasis) and blood pressure regulated by the release of renin from JG cells?

Renin elevates aldosterone and antidiuresis -> promote reabsorption of Na and water at the distal tubule and proximal collecting duct -> increase blood pressure

Where are JG cells located?

at the Juxtaglomerular apparatus

What comprises a renal lobule? What structure is in the center of a lobule? Identify structures of a nephron.

consisting of all renal corpuscles that drain into a common set of collecting ducts (and later into a Duct of Bellini) with a medullary ray at the center of each lobule

What comprises a renal pyramid?

straight parallel segments of nephrons