Urinary (o10)

• Nearly 21% of the blood pumped out of the heart each minute is routed to the kidneys.
• Some of the plasma is filtered and separated from the blood cells in the kidneys.
• Descending pathways facilitate the reflex when stretch of the urinary bladder produces the conscious urge to urinate.
• The brain voluntarily controls the external urethral sphincter through the somatic motor nerves, causing the sphincter to relax or constrict.
• The kidneys play a major role in controlling the extracellular fluid volume in the body by producing either a large volume of dilute urine or a small volume of concentrated urine, depending on the hydration level of the body.
• The kidneys help regulate the concentration of primarily the major ions—Na+, Cl−, K+, Ca2+ , HCO3 −, and HPO4 2−; they also regulate other solute concentration, such as urea.
• The kidneys secrete variable amounts of H+ to help regulate the extracellular fluid acidity.
• The kidneys secrete the hormone erythropoietin, which stimulates the synthesis of red blood cells in red bone marrow.
• The kidneys play an important role in controlling blood levels of Ca2+ by activating vitamin D.
• The kidneys are retroperitoneal and are located on each side of the vertebral column near the psoas major muscles.
• The liver is superior to the right kidney, causing the right kidney to be slightly lower than the left.
• Each kidney measures about 11 cm long, 5 cm wide, and 3 cm thick, which is about the size of a clenched fist and weighs about 130 grams, approximately the weight of 1 cup of flour.
• Each kidney is surrounded by an outer layer of connective tissue called renal capsule.
• Filtration is the movement of materials across the filtration membrane into the Bowman capsule to form filtrate.
• Branches from the interlobar arteries diverge near the base of each pyramid and arch over the bases of the pyramids to form arcuate arteries.
• Water is reabsorbed across the wall of the renal tubule by osmosis.
• After each efferent arteriole exits the glomerulus, it gives rise to a plexus of capillaries, called the peritubular capillaries, around the proximal and distal convoluted tubules.
• Efferent arterioles arise from the glomerular capillaries and carry blood away from the glomeruli.
• The primary function of the kidney is regulation of body fluid composition.
• There are three major steps in urine production: filtration, tubular reabsorption, and tubular secretion.
• A renal artery branches off the abdominal aorta and enters the renal sinus of each kidney.
• Water and solutes pass from the interstitial fluid into the peritubular capillaries.
• Interlobular arteries project from the arcuate arteries to the cortex, and afferent arterioles are derived from the interlobular arteries or branches.
• Segmental arteries diverge from the renal artery to form interlobar arteries, which ascend within the renal columns toward the renal cortex.
• The afferent arterioles supply the blood to the glomerular capillaries of the renal corpuscles.
• The kidney is the organ that sorts the substances from the blood for either removal in the urine or return to the blood.
• Tubular Reabsorption is the reabsorption of solutes across the wall of the renal tubule to the interstitial fluid by transport processes, such as active transport and cotransport.
• Every loop of Henle has two limbs: the descending limb and the ascending limb.
• Surrounding the outside of the capsule is a thick layer of adipose tissue, which cushions and protects the kidneys.
• A thin layer of connective tissue, the renal fascia, surrounds the adipose tissue and helps anchor the kidneys to the abdominal wall.
• Some of these solutes may not have been filtered by the filtration membrane.
• Renal plasma flow is 55% of renal blood flow.
• Glomerular Filtration Rate (GFR) is the amount of plasma that enters the Bowman's capsule per minute; equals renal plasma flow times the percentage (19% filtration fraction) of the plasma that enters the renal capsule.
• Health professionals use standard measures of blood flow through the kidney to determine whether the kidney is functioning properly.
• Renal blood flow rate is calculated using the following formula: Cardiac Output x Renal Fraction = Renal Blood Flow Rate (5,600 x 0.21 = 1,176 mL/min).
• Filtration is a nonspecific process whereby materials are separated based on size or charge.
• One standard measure is the renal blood flow rate.
• Filtration Membrane is a specialized structure that filters blood in the kidneys.
• Urine is the non-reabsorbed filtrate that leaves the kidneys per minute; equals glomerular filtration rate times percentage (0.8%) of filtrate that is not reabsorbed into the blood.
• Health professionals also use the renal plasma flow rate, which is equal to the renal blood flow rate multiplied by 55% (percentage of whole blood that is plasma) and its formula is: 1,176 mL/min x 0.55 = 646.8 mL plasma/min, or approximately 650 mL/min (0.650 L).