Urinary System

Kidney Location

• Located in the retroperitoneal space, behind the stomach and pancreas.
• At the level of the 12th thoracic vertebrae (T12) to the 3rd lumbar vertebrae (L3).

Nephron Function

• Functional unit of the urinary system, responsible for filtering nitrogenous waste from the blood and forming urine.
• Approximately 2.2 million nephrons per kidney.
• Renal arteries bring blood into the kidneys, and renal veins carry blood away from the kidneys.
• Afferent arterioles carry blood into individual glomeruli, the filtering units within the nephrons.
• Efferent arterioles carry blood away from the glomeruli.

Glomerular Filtration

• Glomerulus: A ball of capillaries where filtration takes place, separating substances from blood into Bowman's capsule.
• Filtrate then travels through the proximal convoluted tubule (PCT), loop of Henle, distal convoluted tubule (DCT), and collecting duct.
• Most water and ions are reabsorbed along the way.
• Red blood cells (RBCs), white blood cells (WBCs), platelets, and plasma proteins (like albumin) do not filter out of the glomerulus.
• These larger molecules remain in the blood and shouldn't be found in urine.

Nephron Tubule Stages - Reabsorption

• Proximal Convoluted Tubule (PCT): Reabsorbs 65% of water, ions (like sodium), bicarbonate, and hydrogen ions (H+). Also reabsorbs 100% of glucose and amino acids (these should not be present in urine).
• Descending Loop of Henle: Primarily responsible for water reabsorption.
• Ascending Loop of Henle & Early Distal Convoluted Tubule (DCT): Primarily responsible for solute (like sodium) reabsorption.
• Late DCT & Collecting Duct: Fine-tuning for reabsorption of water and solutes based on the body's needs.

Hormonal Regulation

• Antidiuretic Hormone (ADH): Increases water reabsorption in the late DCT and collecting duct.
• Aldosterone: Increases sodium reabsorption in the late DCT and collecting duct.

Urine Pathway

• After the collecting duct, urine flows into the renal pelvis, then into the ureters, bladder, and finally out through the urethra.

Urinary System Anatomy and Function

• Kidneys are located retroperitoneally, at the level of T12-L3, posterior to the stomach and pancreas.
• Nephrons are the functional units of the urinary system (about 2.2 million per kidney).
• Each nephron filters nitrogenous waste from blood, forms urine, and removes excess water and electrolytes.
• Renal arteries carry blood into the kidneys, while renal veins carry blood out.

Nephron Structure and Function

• Afferent arterioles carry blood into individual nephrons, specifically into the glomeruli.
• Efferent arterioles carry blood out of individual nephrons, specifically away from the glomeruli.
• The glomerulus is a ball of capillaries that filters substances out of blood and into Bowman's capsule.
• The glomerulus filters out water, ions, glucose, and amino acids, but not red blood cells, white blood cells, platelets, or plasma proteins.
• Filtered substances pass through the proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct.

Nephron Processes

• Proximal convoluted tubule (PCT): Approximately 65% of water, ions, bicarbonate, and H+ are reabsorbed. 100% of glucose and amino acids are reabsorbed.
• Descending Loop of Henle: Water reabsorption only.
• Ascending Loop of Henle/Early DCT: Solute (e.g., sodium) reabsorption only.
• Late DCT/Collecting Duct: Fine-tuning of reabsorption based on bodily needs.

Hormones Involved

• Antidiuretic hormone (ADH): Causes increased water reabsorption in the late DCT/collecting duct.
• Aldosterone: Causes increased sodium reabsorption in the late DCT/collecting duct.

Urine Flow

• Urine flows from the collecting duct into the renal pelvis, then to the ureters, the urinary bladder, and finally out the urethra.

Kidney Location

• Located in the retroperitoneal space, behind the stomach and pancreas
• Positioned between the levels of T12 and L3 vertebrae

Nephron: The Functional Unit

• Each kidney contains approximately 2.2 million nephrons, the filtering units of the urinary system.
• Nephrons filter nitrogenous waste from the blood, regulate water balance, and remove excess electrolytes.
• Blood enters the kidneys through the renal arteries and leaves through the renal veins.

Nephron Blood Flow

• Afferent arterioles carry blood into individual nephrons, specifically into the glomeruli.
• Efferent arterioles carry blood away from individual nephrons, specifically away from the glomeruli.

Glomerular Filtration

• The glomerulus, a ball of capillaries, filters substances from the blood into Bowman's capsule.
• Filtrate then passes through the:
  • Proximal convoluted tubule (PCT)
  • Loop of Henle
  • Distal convoluted tubule (DCT)
  • Collecting duct
• Reabsorption: Most water, ions, glucose, and amino acids are reabsorbed back into the bloodstream.
• Non-filterable substances: Large molecules like red blood cells, white blood cells, platelets, and plasma proteins (albumin) do not filter out. These are too big and remain in the blood.

Nephron Tubule Function

• Proximal Convoluted Tubule (PCT):
  • Reabsorbs 65% of water, ions, bicarbonate, and H+
  • Reabsorbs 100% of glucose and amino acids (these should not be present in urine)
• Descending Loop of Henle:
  • Only reabsorbs water.
• Ascending Loop of Henle/Early DCT:
  • Only reabsorbs solutes, particularly sodium.
• Late DCT/Collecting Duct:
  • Fine-tunes reabsorption based on the body's needs.

Hormone Regulation

• Antidiuretic Hormone (ADH): Increases water reabsorption in the late DCT and collecting duct.
• Aldosterone: Increases sodium reabsorption in the late DCT and collecting duct.

Urine Flow

• After the collecting duct, urine passes through:
  • Renal pelvis
  • Ureters
  • Urinary bladder (UB)
  • Urethra
  • Finally excreted from the body.