urinary system Flashcards
what does the urinary system do
the urinarysystem filters urinary waste from the blood and helps regulatewater,electrolyte and acid base balances.
how does the urinary do that
the kidney filters blood in nephrons and secrete or reasorb electrolytes under the direction of hormones.
why oes the kidney do these things
to maintain blood preasure.
the kidneys act like a garbage cleaner for blood
The kidneys, which maintain the purity and constancy of our internal fluids, are perfect examples of homeostatic organs. Like sanitation workers who keep a city’s water supply drinkable and dispose of its waste, the kidneys are usually unappreciated until there is a malfunction and “internal garbage” piles up. Every day, the kidneys filter gallons of fluid from the bloodstream. They then process this filtrate, allowing wastes and excess ions to leave the body in urine while returning needed substances to the blood in just the right proportions. Although the lungs and the skin also play roles in excretion, the kidneys bear the major responsibility for eliminating nitrogenous (nitrogen-containing) wastes, toxins, and drugs from the body.Disposing of wastes and excess ions is only part of the kidneys’ work. As they perform these excretory functions, the kidneys also regulate blood volume and maintain the proper balance between water and salts, and between acids and bases.
The kidneys have other regulatory functions, too:
By producing the enzyme renin, they help regulate blood pressure.
The hormone erythropoietin, released by the kidneys, stimulates red blood cell production in bone marrow (see Chapter 10).
Kidney cells convert vitamin D produced in the skin to its active form.The kidneys alone perform the functions just described and manufacture urine in the process. The other organs of the urinary system—the paired ureters and the single urinary bladder and urethra (Figure 15.1a)—provide temporary storage for urine or serve as transportation channels to carry it from the kidneys to the outside of the body.
kidney position
Although many people believe the kidneys are located in the lower back, this is not the case. These small, dark red organs with a kidney-bean shape lie against the dorsal body wall in a retroperitoneal position (behind the parietal peritoneum) in the superior lumbar region (Figure 15.1b). The kidneys extend from the T12 to the L3 vertebra; thus they receive some protection from the lower part of the rib cage. Because it is crowded by the liver, the right kidney is slightly lower than the left.
Kidney Structure
An adult kidney is about 12 cm (5 inches) long, 6 cm (2.5 inches) wide, and 3 cm (1 inch) thick, or about the size of a large bar of soap. It is convex laterally and has a medial indentation called the renal hilum. Several structures, including the ureters, the renal blood vessels, and nerves, enter or exit the kidney at the hilum (Figure 15.2). Sitting atop each kidney is an adrenal gland, which is part of the endocrine system and is a separate organ.
The kidney has three protective layers. Deep to superficial, they are as follows:
A transparent fibrous capsule encloses each kidney and gives it a glistening appearance.
A fatty mass, the perirenal fat capsule, surrounds each kidney and cushions it against blows.
The renal fascia, the most superficial layer made of dense fibrous connective tissue, anchors the kidney and adrenal gland to surrounding structures.
if the fat around the kidney is ruined
The fat surrounding the kidneys is important in holding them in their normal body position. If the amount of fatty tissue dwindles (as with rapid weight loss), the kidneys may drop to a lower position, a condition called ptosis (to′sis; “a fall”). Ptosis creates problems if the ureters, which drain urine from the kidneys, become kinked. When this happens, urine that can no longer pass through the ureters backs up and exerts pressure on the kidney tissue. This condition, called hydronephrosis (hi″dro-nĕ-fro′sis), can severely damage the kidney.
When a kidney is cut lengthwise, three distinct regions become apparent (see Figure 15.2).
outer region, which is light in color, is the renal cortex (cortex = bark). Deep to the cortex is a darker reddish brown area, the renal medulla. The medulla has triangular regions with a striped appearance, the renal pyramids, or medullary (med′u-lar″e), pyramids. The broad base of each pyramid faces toward the cortex; its tip, the apex, points toward the inner region of the kidney. The pyramids are separated by extensions of cortexlike tissue, called renal columns.
Lateral to the hilum is a flat, funnel-shaped tube, the renal pelvis. The pelvis is continuous with the ureter leaving the hilum (see Figure 15.2b). Extensions of the pelvis, calyces (kal′ĭ-sēz; singular calyx), form cup-shaped “drains” that enclose the tips of the pyramids. The calyces collect urine, which continuously drains from the tips of the pyramids into the renal pelvis. Urine then flows from the pelvis into the ureter, which transports it to the bladder for temporary storage until it leaves the body.
Blood Supply
The kidneys continuously cleanse the blood and adjust its composition, so it is not surprising that they have a rich blood supply (see Figure 15.2b and c). Approximately one-quarter of the total blood supply of the body passes through the kidneys each minute. The artery supplying each kidney is the renal artery. As the renal artery approaches the hilum, it divides into segmental arteries, each of which gives off several branches called interlobar arteries, which travel through the renal columns to reach the cortex. At the cortex-medulla junction, interlobar arteries give off the arcuate (ar′ku-at) arteries, which arch over the medullary pyramids. Small cortical radiate arteries then branch off the arcuate arteries to supply the renal cortex. Venous blood draining from the kidney flows through veins that trace the pathway of the arterial supply but in a reverse direction—cortical radiate veins to arcuate veins to interlobar veins to the renal vein, which emerges from the kidney hilum and empties into the inferior vena cava. (There are no segmental veins.)
