The Urinary System Kidney

The urinary system The urinary system provides temporary storage reservoirs for urine or serve as transportation channels The organs involved in the urinary system are: Kidney Ureter Bladder Urethra

Kidneys Locations: The kidneys extend from T12 to L3 Because it is crowded by the liver, the right kidney is positioned slight lower than the left An adult kidney is about the size of a large bar of soap

Kidney Structure A fibrous, transparent renal capsule encloses each kidney: In a living person, a fatty mass, the adipose capsule, surrounds each kidney and helps hold it in place against the muscles of the trunk wall

Kidney Structure The kidney has 3 distinct regions: 1. Renal cortex: The outer region, light in color 2. Renal medulla: Deep to the cortex, darker reddish-brown area It is made of many triangular regions with a striped appearance, the medullary pyramids The pyramids are separated by extensions of cortical tissue, the renal columns

Kidney Structure 3. Renal pelvis: medial to the cortex, a basin-like cavity Extensions of the pelvis, calyces, form cup shaped areas that enclose the tips of the pyramid

Blood Supply The kidneys continuously cleanse the blood and adjust its composition: Approximately ¼ of the total blood supply of the body passes through the kidneys each minute

Renal Arteries Renal Arteries (from large to small): Renal artery Segmental artery Lobar artery Interlobar artery Arcuate artery Interlobular artery

Renal Veins Venous blood draining from the kidney flows through veins that trace the pathway of the arterial supply but in a reverse direction: Interlobular veins  arcuate viens interlobar veins  renal veins There are no lobar or segmental veins

Nephrons Nephrons: the structural and functional units of the kidneys and are responsible for forming the urine product Each nephron consists of two main structures: Glomerulus: knot of capillaries Renal tubule

Tubules Bowman’s capsule: the closed end of the renal tubule that is enlarged and cup-shaped and completely surrounds the glomerulus Tubules (from bowman’s capsule to renal pelvis): Proximal convoluted tubule Loop and Henle  Distal convoluted tubule  Collecting ducts

Tubules The lumen surfaces of the tubule cells in the proximal convoluted tubules are covered with dense microvilli Microvilli also occur on the tubule cells in other parts of the tubule but in much reduced numbers

Types of nephrons Most nephrons are called cortical nephrons because they are located almost entirely within the cortex Some nephrons are called juxtamedullary (juxta- nearby) nephrons because they are situated close to the cortex-medulla junction and their loops of Henle dip deep into the medulla

Capillaries Each and every nephron is associated with 2 capillary beds: The glomerulus Peritubular capillaries (peri- around) The glomerulus is both fed and drained by arterioles: The afferent arteriole: feeder vessel The effector arteriole: receives blood that has passed through the glomerulus

Capillaries The peritubular capillaries: Arise from the efferent arteriole that drains the glomerulus Drain into interlobular veins leaving the cortex

Urine Formation Urine formation is a result of 3 processes: Filtration Reabsorption Secretion Filtration: non-selective, passive process Water and solutes smaller than proteins are forced through the capillary walls and pores of the glomerular capsule into the renal tubule

Urine Formation Reabsorption: Water, glucose, amino acids and needed ions are transported out of the filtrate into the tubule cells and then enter the capillary blood

Urine Formation Secretion: It is essentially reabsorption in reverse H+ , K+, and breakdown product of the body are removed from the peritubular capillaries to the tubules https://www.youtube.com/watch?feature=player_embedded&v=AdlfxBooqIA#!