Urinary System Components Quiz

Urinary System Components

• The urinary system consists of the kidney, ureters, bladder, and urethra.

Kidney Structure

• The kidney has two main parts: the parenchyma and the medulla.
• The medulla has 10-18 medullary pyramids, and the renal column is located between them.
• The cortex has medullary rays and cortical labyrinth.

Renal Lobe and Renal Lobule

• A renal lobe is a medullary pyramid and the associated cortical tissue.
• A renal lobule is a medullary ray and the surrounding cortical labyrinth.

Renal Corpuscle (Nephron)

• The renal corpuscle is spherical, approximately 200mm in diameter.
• It has a glomerulus (a tuft of capillaries) and a glomerular capsule (a double-walled epithelial capsule).
• The renal corpuscle has two poles: the vascular pole (where the afferent arteriole enters and the efferent arteriole leaves) and the urinary pole (where the proximal convoluted tubule begins).

Glomerulus

• The glomerulus is a fenestrated capillary and arterial capillary.
• Blood flow through the glomerulus is very fast (1.2-1.3L/min) with high hydrostatic pressure (about 45mmHg).

Capillaries of Glomerulus

• The capillaries are fenestrated, with openings of about 70-90 nm in diameter.
• The cell coat contains negatively charged proteoglycan.

Glomerular Capsule

• The glomerular capsule is a double-walled epithelial chamber.
• It has a parietal layer (simple squamous epithelium) and a visceral layer (podocytes).

Podocyte

• Podocytes have secondary processes that interdigitate with each other and embrace the capillaries.
• The filtration slits are narrow spaces between the secondary processes, approximately 25nm wide.

Filtration Barrier

• The filtration barrier consists of fenestrated endothelial cells, a fused basal lamina, and slit membrane.

Basal Lamina

• The basal lamina has two electron-lucent layers (laminae rara) and a central electron-dense layer (laminae densa).
• The central electron-dense layer is a meshwork of type IV collagen and laminin.

Filtration Membrane

• The filtration membrane is a selective macromolecular filter.
• It has a physical filter, allowing molecules less than 10nm in diameter to pass through.
• It also has a charge barrier, allowing negatively charged proteins with a molecular mass of less than 69kD to pass through sparingly.

Renal Tubule

• The renal tubule is simple epithelium.
• It has proximal convoluted tubule, proximal straight tubule, thin segment, distal convoluted tubule, distal straight tubule, and collecting tubule.

Proximal Convoluted Tubule

• The proximal convoluted tubule is approximately 14 mm long and 50-60um in diameter.
• It has a cuboidal shape with a round nucleus, a small lumen, and a brush-like border.

Function of Proximal Tubule

• The proximal tubule absorbs 85% of sodium chloride, phosphate, and calcium, as well as all of glucose, amino acid, polypeptide, proteins, and vitamins.
• It excretes creatinine and foreign substances.

Thin Segment

• The thin segment is 10-15 um in diameter, with a simple squamous epithelium.
• It absorbs sodium and chloride and 5% of water.

Distal Convoluted Tubule

• The distal convoluted tubule has a lumen that is larger than the proximal convoluted tubule.
• It has a cuboidal shape with a round nucleus, and no brush-like border.

Function of Distal Tubule

• The distal tubule is regulated by aldosterone (adrenal gland).
• It absorbs sodium and secretes potassium ions, influencing the total salt and water content of the body.
• It maintains the acid-base balance in the blood.

Collecting Tubule and Duct

• The collecting tubule and duct have a simple epithelium with cuboidal to columnar cells.
• They are controlled by arginine vasopressin (ADH) or antidiuretic hormone.

Function of Collecting Tubule

• The collecting tubule absorbs sodium and water and secretes potassium ions.
• It is controlled by the arginine vasopressin (ADH) or antidiuretic hormone.

Juxtaglomerular Complex

• The juxtaglomerular complex consists of juxtaglomerular cells (JG cells) and macula densa cells.

Juxtaglomerular Cells (JG Cells)

• JG cells are modified smooth muscle cells of afferent arterioles.
• They have a larger, cuboidal shape with round nuclei and contain secretory granules.
• They secrete renin, which increases blood pressure.

Macula Densa

• Macula densa cells are derived from the epithelium of the distal tubule.
• They have a taller, narrower shape with round nuclei and apical processes connecting with other cells.
• They are chemoreceptors, sensing the sodium concentration.

Extraglomerular Mesangial Cell

• Extraglomerular mesangial cells are located between the macula densa and Bowman's capsule at the entry of the afferent arteriole.
• They produce ground substance, endocytose normal and pathologic molecules, give structural support to the glomerulus, and secrete chemical mediators.