Urinary System Overview

The Excretory System

• The excretory system is a complex group of systems designed to eliminate waste products generated by cellular respiration.
• The lungs excrete carbon dioxide.
• The liver breaks down toxins from ingested substances.
• The kidneys eliminate toxins and maintain blood pH and water balance.
• The urinary tract, also known as the renal system, is responsible for excreting toxins from the kidneys.

Urinary Tract (Renal System)

• The urinary tract consists of the bladder, kidneys, ureters, and urethra.
• The kidneys filter waste from the blood.
• Ureters transport urine from the kidneys to the bladder.
• Urine is stored in the bladder.
• Urine exits the body through the urethra.

Anatomy of the Urinary Tract

• The aorta carries oxygenated blood to the kidneys through renal arteries.
• Renal arteries transport unfiltered, but oxygenated blood to the kidneys.
• Kidneys filter waste and excess water.
• The ureters transport the waste and excess water to the bladder.
• The bladder stores urine.
• The urethra allows urine to exit the body.
• Renal veins carry filtered blood back to the heart,
• Vena Cava - brings clean and deoxygenated blood to the heart

Anatomy of the Kidney

• The kidney has three layers: Cortex, Medulla, Renal pelvis.
• The cortex is an outer layer of connective tissue.
• The medulla is the inner layer that lies below the cortex.
• The renal pelvis is a hollow chamber that connects the kidney to the ureter.
• Nephrons are tubes that filter waste from the blood, span the cortex and medulla of each kidney.

The Nephron

• Kidneys contain nephrons, slender tubules that filter blood.
• Nephrons remove waste and other substances from the blood.
• Nephrons help reabsorb water and substances into the bloodstream.

Kidney Composition: Movement of Blood through Nephrons

• Small branches from the renal artery help supply the nephrons with blood (afferent arterioles).
• The afferent arterioles branch into small capillaries called glomerulus.
• Blood leaves the glomerulus via efferent arterioles.
• Efferent arterioles branch into peritubular capillaries.
• Filtered blood exits the kidney through the renal vein.

Bowman's Capsule

• The Bowman's capsule surrounds the glomerulus.
• Afferent, and efferent arterioles and Bowman's Capsule are located in the Kidney cortex.

Formation of Urine

• Urine formation involves three steps: filtration, reabsorption, and secretion.
• Filtration removes materials from the blood into the Bowman's capsule.
• Reabsorption returns essential components to the bloodstream.
• Secretion adds materials to the urine.

Filtrate

• Substances that can pass through the glomerulus: water, salts, glucose, amino acids, and hydrogen ions,
• Substances that cannot pass: blood plasma proteins, erythrocytes and platelets.
• The activity of the glomerulus explains why red blood cells are not found in healthy urine.

Urine Formation

• Urine gets its distinct smell from urea, a byproduct of excess amino acids.
• When the body gains more protein than needed, proteins break down to ammonia, and in the liver, ammonia combines with CO2 to form urea, which is eventually excreted through the kidneys in urine.

Reabsorption

• Reabsorption begins in the proximal tubule, where reabsorption of water, glucose, salts, potassium, amino acids, and urea occur.
• Majority water reabsorption occurs in the descending limb of the Loop of Henle (osmosis).
• The ascending limb of the loop of Henle reabsorbs salt via diffusion and active transport.
• Additional water and salt can be reabsorbed in the distal tubule, controlled by hormones

Secretion

• Secretion is the movement of wastes from the blood to the proximal tubule, distal tubule, or collecting duct of a nephron.
• Ammonia and excess H+ Ions, minerals are examples of secreted substances.
• pH of the blood is regulated by the secretion of excess H+ ions and the restoration of bicarbonate ions.

How Can We Influence This? Hormones

• Direct reabsorption of water is aided by the hormone antidiuretic hormone (ADH).
• ADH increases the permeability of collecting ducts to H₂O.

Aldosterone

• Reabsorption of sodium is aided by aldosterone.
• Aldosterone makes distal tubules more permeable to NaCl.
• Water is also reabsorbed to maintain osmotic gradient.

Kidney Dysfunction

• Kidney disorders are diagnosed using urine samples.
• Diabetes mellitus occurs due to inadequate insulin secretion.
• Blood glucose levels are too high.
• Body cannot reabsorb water.
• Diabetes insipidus results from a problem with antidiuretic hormone (ADH).
• Body cannot reabsorb water.
• Nephritis is inflammation of the nephrons.
• Usually due to a Urinary tract infection
• Toxins destroy vessels, proteins pass into nephrons.
• Kidney stones are mineral precipitates in urine due to imbalance in diet or reduced water intake.

Kidney Dialysis

• Dialysis is used for people whose kidneys cannot process waste properly.
• A machine removes excess waste, salts, and water from the blood.