Anatomy of the Kidneys Quiz

The urinary system is the main excretory system, composed of several structures.
Two kidneys secrete urine.
Two ureters transport urine from kidneys to the urinary bladder.
The urinary bladder stores urine.
The urethra carries urine out of the body.
Urine is stored in the bladder and excreted through micturition.

Kidney functions include urine formation, maintaining water, electrolyte and acid-base balance.
Excretion of waste products.
Production and secretion of erythropoietin (stimulates red blood cell formation) and renin (controls blood pressure).

Kidneys lie on the posterior abdominal wall, one on each side of the vertebral column.
Located behind the peritoneum and below the diaphragm.
The 12th thoracic vertebra to the 3rd lumbar vertebra.
The right kidney is slightly lower than the left, due to the liver occupying more space on the right.

Kidney is bean-shaped; approximately 11 cm long, 6 cm wide, and 3 cm thick.
Weighs about 150 grams.
Held in place by a mass of fat.
Three areas of tissues: an outer fibrous capsule surrounding the kidney, cortex (a reddish-brown layer beneath the capsule, outside the renal pyramids) and medulla (innermost layer, made of conical-shaped renal pyramids)

Funnel-shaped tube that connects the ureter at the hilum.
Branches emerging from pelvis formed two or three major calyces.
Divided into cup-shaped minor calyces.
Urine is collected by the calyces, drained from papillae, emptied into renal pelvis and finally in the bladder.
The walls of calyces, pelvis, and ureter are smooth muscles that contract rhythmically to propel urine.

The kidney contains about one to two million functional units (nephrons) and collecting ducts
The nephron is essentially a tubule, closed at one end with the other end joining a collecting duct.
One end is a cup-shaped glomerular capsule (Bowman's capsule) which almost completely encloses a network of tiny arterial capillaries (glomerulus)
The remainder of the nephron consists of three parts: the proximal convoluted tubule, the medullary loop (Loop of Henle), and the distal convoluted tubule followed by a collecting duct
The nephron functions through ultrafiltration and reabsorption.

The kidneys receive about 20% of the cardiac output.
The renal artery branches into smaller arteries and arterioles as it enters the kidney.
The afferent arteriole enters the glomerular capsule.
The glomerular capsule subdivides into a cluster of tiny arterial capillaries.
The glomerulus is surrounded by Bowman's capsule forming a filter.
Connective tissue loops (mesangial cells) are within the capillary loops.
The blood vessel leading away from the glomerulus is the efferent arteriole.
The efferent arteriole divides into a capillary network, which wraps around the remainder of the tubule, allowing exchange between the fluid in the tubule and the blood stream.
The blood supplies oxygen and nutrients, and removes wastes.
Venous blood drains from the capillaries into the renal vein, which empties into the inferior vena cava.

The walls of the glomerulus and the glomerular capsule consist of a single layer of flattened epithelial cells.
The glomerular walls are more permeable than other capillaries.
The remainder of the nephron is lined with simple squamous epithelium.

Three processes are involved in urine formation: filtration, selective reabsorption, and secretion.

Takes place through the semipermeable walls of the glomerulus and the glomerular capsule.
Water and other small molecules readily pass through.
Blood cells, plasma proteins, and large molecules are too large to filter through therefore remain in the capillaries.
Filtration occurs because of the difference in blood pressure in the glomerulus and pressure of the filtrate in the glomerular capsule; the efferent arteriole is narrower than the afferent arteriole.

GFR is the amount of filtrate produced by the kidneys per minute.
In a healthy adult GFR is about 125 ml/min. meaning approximately 180 liters of filtrate are formed each day by the two kidneys.
A healthy adult excretes 1-1.5 liters of urine per day.
This is regulated by automatic processes known as autoregulation.

This takes place in the proximal convoluted tubule.
The walls are lined with microvilli that increase surface area for absorption of substances like water, electrolytes, and organic nutrients such as glucose.
About 60–70% of the filtrate reaches the medullary loop
Especially water, sodium, and chloride are reabsorbed.
Only about 15–20% of the original filtrate reaches the distal convoluted tubule.

Substances such as drugs, penicillin, and aspirin are cleared by secretion from the peritubular capillaries into the filtrate within the convoluted tubule

Urine is clear and amber in color due to the presence of urobilin, a bile pigment.
The specific gravity of urine is between 1020 and 1030; the pH is approximately 6-8 for healthy adults.
Typical composition: Water (95–96%), urea (2%), uric acid, creatinine, ammonia, sodium, and potassium (2%).

The Renin-angiotensin-aldosterone system (RAAS) is a crucial mechanism for regulating cardiac output and arterial pressure.
Renin (enzyme produced by the kidneys) promotes the formation of angiotensin to be used in circulating blood and tissues.
Further promoting the release of aldosterone from the adrenal cortex.

Increased sympathetic activity, decreased blood pressure; or decreased sodium delivery to distal tubules trigger the release of renin.

Reservoir for urine.
Relatively variable in size and position depending on urine volume.
Three layers: Outer layer of loose connective tissue (contains blood, lymphatic vessels, and nerves); a middle layer consisting of smooth muscle fibres and elastic tissue; inner layer (mucosa composed of transitional epithelium).
The urinary bladder wall is primarily made up of smooth muscle that is collectively called the detrusor muscle.
Empty bladder has folds (rugae) that disappear as it fills.
Total capacity is normally about 600 ml.

Canal extending from the neck of the bladder to the exterior at the external urethral orifice.
Males: about 20 cm long, associated with both urinary and reproductive systems
Females: about 4 cm long, 6 mm in diameter.
Two main layers: an outer muscle layer and an inner lining of mucosa; the external sphincter is under voluntary control.
Function: passageway for urine expulsion; in males, also for semen ejaculation.

Process by which the urinary bladder empties.
Involves the collection of 300-400ml of urine. Afferent autonomic nerve fibers send impulses to the brain. Brain send the efferent impulses to the bladder which relaxes causing the bladder muscles to contract to expel urine.