Urinary System

Functions of Urinary System Secrete waste Regulate blood volume and composition Ph, excrete H+, conserve bicarbonate ions Ions like Na, K, Ca, Cl, and phosphate Help regulate blood pressure Synthesize glucose Release erythropoietin Participate in vitamin D synthesis Gets rid of urine

KIDNEYS AND NEPHRONS

NEPHRON

Nephrons 2 main structures – glomerulus=knot of capillaries and a renal tubule The renal tubule surrounds the glomerulus This portion of the tubule is called the glomerular or bowman’s capsule Podocytes make up the inner layer of the capsule. They have long branching processes that intertwine and cling to the glomerulus They produce a porous membrane around the glomerulus

Collecting Ducts Proximal convoluted tubule, loop of Henle, distal convoluted tubule Lumen of proximal contains microvilli for SA

Nephrons continued Most nephrons are called “cortical” because they are located in the cortex Some are denoted “juxtamedullary nephrons” b/c they are situated between the cortex/medulla junction Collecting ducts run from the pyramids which give the kidney its striped appearance They deliver final urine product into calyces and renal pelvis

Figure 3. Kidney tubules, transverse section (2) (Formalin, H&E, Bar = 16.7 µm). 1. first proximal tubule; 2. second proximal tubule; 3. intermediate tubule segment; 4. distal tubule; 5. collecting duct; 6. brush border; 7. mitotic epithelial cell; 8. melanomacrophage; 9. red blood cells.  

Nephron capillaries Each nephron has a glomerulus and a peritubular capillary bed Fed (afferent arteriole) and drained (efferent arteriole) by arterioles

Glomerulus capillary bed Specialized for filtration Fed and drained by arterioles (high resistance vessels) blood pressure is high The high pressure forces fluid and solutes out of the blood into glomerular capsule

Peritubular Capillary Bed Arises from efferent arteriole that drains the glomerulus Low pressure and porous for absorption Found clinging to length of renal tubules where they can receive solutes and water These peritubular capillaries drain into interlobular veins leaving the cortex

Blood Supply The kidneys continuously cleanse the blood (1/4 of total blood supply passes through the kidney per minute) Arterial blood supply Renal Artery@ hilus divides into segmental arteriesin pelvis break up into lobar arteriesinterlobar arteries which travel through the renal columns to reach the cortex

Artery branching continued @ medulla-cortex junction, interlobar arteries give off arcuate arteries Curve over medullary pyramids Interlobular arteries branch off the arcuate arteries and run outward to supply the cortex tissue

Venous system in the kidney Venous blood drains from the kidney in the same pattern as the arterial blood flow but in the opposite direction Interlobular veinsarcuate veinsinterlobar veinsrenal vein which emerges at the hilus NOTICE: no lobar or segmental veins