Urinary System Quiz

The Urinary System

• The urinary system is responsible for excreting waste products from the body, regulating blood volume and blood pressure, and regulating plasma ion concentrations.
• It removes organic wastes from body fluids.
• It discharges waste products.
• It regulates blood plasma volume and solute concentration.
• The organs that eliminate urine are the ureters, urinary bladder, and urethra.
• The kidneys are organs that excrete urine.
• The process of eliminating urine is called urination or micturition.

Kidney Functions

• Maintain stable blood volume and blood pressure by regulating water and electrolyte excretion.
• Controlling plasma ion concentrations such as sodium, potassium, and chloride.
• Regulate levels of blood pH by controlling the loss of hydrogen and bicarbonate ions in urine.
• Preventing excretion of vital organic nutrients.
• Help the liver in detoxification.

Kidney Location and Structure

• Kidneys are positioned on either side of the vertebral column.
• The left kidney is superior to the right kidney, and their superior surfaces are capped by the adrenal glands.
• The position of the kidneys is maintained by the overlying peritoneum, contacting adjacent visceral organs, and by supporting connective tissues.
• They are protected and stabilized by three concentric layers of connective tissue: renal capsule, adipose capsule, and renal fascia.
• The renal capsule is a collagen fiber layer covering the outer surface of the entire organ.
• The adipose capsule is a thick layer of adipose tissue surrounding the renal capsule.
• The renal fascia is a dense fibrous outer layer that anchors the kidney to surrounding structures.
• A typical adult kidney is about 10 cm long, 5.5 cm wide, and 3 cm thick, weighing approximately 150 g.
• The hilum is the point of entry for the renal artery and nerves, as well as the exit point for the renal vein and ureter.
• The renal sinus is the internal cavity of the kidney lined by the fibrous renal capsule.

Kidney Internal Anatomy

• The kidney is divided into cortex (outer layer) and medulla (inner layer).
• The medulla contains renal pyramids, conical structures that base abuts the cortex and tip (renal papilla) projects into the renal sinus.
• Renal columns: Bands of cortical tissue that separate adjacent renal pyramids and extend into the medulla.
• Renal lobe: Made up of a renal pyramid, the overlying area of renal cortex, and adjacent tissues of renal columns.
• Renal papilla : Ducts discharge urine into minor calyx, which is a cup-shaped drain.
• Renal columns extend into the medulla and have a granular texture.
• The renal lobe is composed of a renal pyramid, the overlying area of cortical tissue, and adjacent portions of renal columns.

Renal Calyx

• Major calyx: Formed by 4 to 5 minor calyces, collecting urine draining from multiple renal pyramids.
• Minor calyces: Cup-shaped drainage structures collecting urine from renal papillae.

Renal Pelvis

• Is a large funnel-shaped structure made up of 2 or 3 major calyces.
• It fills most of the renal sinus.
• The renal pelvis connects to the ureter, which drains the kidney.

Blood Supply to the Kidneys

• Kidneys receive 20–25% of total cardiac output.
• Approximately 1200 mL of blood flows through each kidney each minute.
• Blood enters the kidneys via the renal artery, which branches into segmental, interlobar, arcuate, and interlobular arteries.
• Blood leaves the kidneys via the renal vein.
• Afferent arterioles branch from interlobular arteries delivering blood to capillary networks called glomeruli, supplying individual nephrons.

Nephron

• The functional unit of the kidney
• Filtration takes place in the glomerulus.
• The nephron comprises a renal corpuscle and renal tubules.
• The renal corpuscle consists of a glomerulus and Bowman’s capsule.
• It filters the blood to form filtrate, which then travels through renal tubules.

Glomerular Filtration

• Occurs in the renal corpuscle.
• Blood pressure forces water and dissolved solutes out of glomerular capillaries.
• This forms a protein-free filtrate similar to blood plasma, in the capsular space.
• Filtration depends on hydrostatic and colloid osmotic pressures.
• Hydrostatic pressure (gHP) pushes water and solutes out of the glomerulus.
• Capsular hydrostatic pressure (cHP) opposes GHP by pushing filtrate back into the capillaries.
• Blood colloid osmotic pressure (BCOP) opposes GHP by pulling water back into the glomerulus.

Renal Tubule Segments

• Proximal convoluted tubule (PCT): Is the first segment, absorbs water and nutrients.
• Loop of Henle (Loop of Henle): U-shaped structure responsible for establishing a concentration gradient. Consists of descending and ascending limbs separated by thin segment and thick segment.
• Distal convoluted tubule (DCT): Active reabsorption of ions (sodium and chloride ions), and secretion of other substances.

Reabsorption and Secretion at the PCT

• The PCT (proximal convoluted tubule) is responsible for reabsorbing 60-70% of filtrate.
• Active reabsorption of ions (Sodium, potassium, bicarbonate, magnesium and phosphate)
• Reabsorption of organic nutrients (glucose, amino acids), and water by osmosis.
• Secretion of hydrogen ions in exchange for sodium, helping regulate blood pH.

Reabsorption and Secretion at the Loop of Henle

• The thick descending limb of the loop of Henle plays a vital functional role comparable to the DCT.

• It pumps sodium and chloride ions out of tubular fluid.

• The thin segment of the loop of Henle, is permeable to water.

• Water flows out, concentrating the tubular fluid.

• The thick ascending limb of the loop of Henle actively excretes sodium chloride.

Countercurrent Multiplication System

• A mechanism in the loop of Henle that generates high interstitial fluid osmolarity, enabling efficient water reabsorption in the collecting ducts.
• Sodium chloride moves into the interstitial fluid due to the active transport from the thick ascending limb of the loop.
• This establishes a concentration gradient between the thick ascending limb and the peritubular fluid.
• Water moves passively from the thin descending limb into the interstitial fluid due to osmosis. This happens because the sodium chloride and urea in the interstitial fluid of the medulla creates a higher concentration than the tubular fluid in the thin descending limb.
• Fluid entering the thick ascending limb is highly concentrated compared to the thin descending limb, and sodium chloride is actively excreted.

The Collecting System

• The distal convoluted tubule empties into the collecting system.
• Individual nephrons drain into nearby collecting ducts.
• Collecting ducts converge into larger papillary ducts from several collecting ducts.
• Papillary ducts empty urine into minor calyces.
• The collecting system transports tubular fluid from nephrons to the renal pelvis and adjusts its fluid composition.
• It determines the final osmotic concentration and volume of urine.
• In the collecting ducts, sodium reabsorption is controlled by aldosterone, bicarbonate reabsorption exchanges chloride ions, and urea reabsorption concentrates the medulla. The collecting ducts also secrete hydrogen ions or bicarbonate ions.

The Urinary Tract

• The urinary system also comprises the ureters, urinary bladder, and urethra.
• Urine travels from kidneys through the ureters to the urinary bladder, a temporary storage reservoir.
• From the bladder, urine is excreted via the urethra
• The ureters are a pair of muscular tubes transporting urine from the kidneys to the urinary bladder.
• Smooth muscle contraction (peristaltic) moves urine.
• The urinary bladder is a hollow, muscular organ that stores urine.
• It is stabilized by folds of peritoneum and ligamentous bands.
• The urethral opening is at the apex of the trigone, the most inferior point of the urinary bladder.
• The neck of the bladder contains the internal urethral sphincter, which regulates urine discharge.
• The urethra carries urine from the bladder to the exterior.
• The male urethra is longer than the female urethra and has three parts: prostatic, membranous, and spongy (penile).
• The external sphincter is located where the urethra passes through the urogenital diaphragm and is involved in voluntary control of urination.

The Female Urethra

• The female urethra is shorter, extending from the bladder to the vestibule near the anterior wall of the vagina.

Other terms in the context

• The Filtration Membrane: Includes fenestrated endothelium (no RBCs pass), lamina densa (inhibits large plasma proteins), and filtration slits (no small plasma proteins).
• ADH (antidiuretic hormone): Hormone that increases water permeability in the DCT and collecting system.
• Diuretics: Drugs that promote water loss in urine, decreasing blood volume, blood pressure, and extracellular fluid volume.
• Buffering of Urine: Cells in the PCT and DCT use the NH2 group from amino acids to bind to hydrogen ions to produce NH4 that passes into the tubular fluid.