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Functions of the Kidney

• Main Function: The primary role of the kidney is to filter blood and excrete toxic metabolic waste.
  • Metabolic Waste: Refers to substances produced during metabolism that the body does not require. It encompasses two aspects of metabolism:
  • Catabolism: The breaking down of substances (e.g., proteins).
  • Anabolism: The building up of substances (e.g., synthesis of molecules).

Components of Filtration and Kidney Functionality

• The kidneys regulate several key aspects of homeostasis:
  1. Blood pressure and volume: Predominantly influenced by water volume in urine.
  • The kidneys control water loss, which helps maintain blood volume.
  1. Osmolarity: Describes the concentration of solutes in body fluids, primarily influenced by salts.
  • Electrolytes: Key components include:
    • Sodium (Na⁺)
    • Potassium (K⁺)
  1. Acid-Base Balance: The kidneys help maintain the pH balance in the body by regulating acids and bases.
  2. Erythropoiesis Regulation:
  • The kidney releases erythropoietin, a hormone that stimulates the red bone marrow to produce new red blood cells.
  1. Calcium Regulation: Through calcitriol synthesis which increases plasma calcium levels.
  2. Hormone Clearance: The kidneys detoxify substances and clear excess hormones from the bloodstream.
  3. Detoxification of Free Radicals: The kidneys help eliminate free radicals, which can cause tissue damage.
  4. Glucose Synthesis: During starvation, the kidneys can synthesize glucose from proteins, although this is not a long-term solution due to the risk of hypochrominemia.

Importance of Kidney Assessment

• Assessing kidney function is critical in clinical practice because kidney health plays a significant role in overall physiological balance.

Metabolic Waste

• Definition of Waste: Anything the body does not need or has in excess.
• Nitrogenous Waste: Waste containing nitrogen produced from the metabolism of proteins and nucleic acids.
  • Primary types of nitrogenous waste include:
  1. Urea: Product of protein catabolism.
  2. Uric Acid: Resulting from nucleic acid breakdown (includes substances like creatine phosphate).
  3. Blood Urea Nitrogen (BUN): Measurement used to assess the nitrogenous waste in blood.
     • Normal levels are usually below 20 mg/dL; levels above indicate azotemia, a sign of renal insufficiency.
  • Azotemia: Indicates elevated BUN levels but is not diagnostic on its own. Untreated azotemia can lead to Uremia, which presents a syndrome of kidney dysfunction characterized by:
  • Symptoms include diarrhea, vomiting, and dyspnea (difficulty breathing).

Excretion and Organ Systems

• The urinary system is the primary organ system responsible for excretion, along with:
  • Respiratory System: Excretes carbon dioxide.
  • Integumentary System: Also plays a role in excretion.
  • Digestive System: Eliminates waste products from digestion.

Structure of the Kidney

• Anatomical Position:
  • Located against the posterior abdominal wall, generally at the levels of T12 to L3 vertebrae. The right kidney is positioned inferior to the left to accommodate the liver.
  • Retroperitoneal: The kidneys lie behind the peritoneum, a serous membrane lining the abdominal cavity.

Protective Layers of the Kidney

1. Renal Fascia: Connects kidney to surrounding tissues.
2. Perirenal Fat: Provides cushioning.
3. Fibrous Capsule: The outermost layer protecting the kidney from pathogens.

Anatomy of the Kidney

• Kidney Dimensions: Approximate size of 150 grams, comparable to a bar of soap.
• Kidney Surfaces:
  • Lateral Surface: Convex
  • Medial Surface: Concave with a slit known as the Hilum, which receives nerves, blood vessels, lymphatics, and ureters.

Renal Parenchyma

• Refers to the functional tissue of the kidney, consisting of:
  • Cortex: The outer layer.
  • Medulla: The inner layer.
  • Corticomedullary Junction: The transition area between cortex and medulla.
  • Renal Columns: Structures separating the renal pyramids.
  • Renal Pyramids: Structures that collect urine.

Urine Flow Pathway

• Urine collection begins in the renal pyramids:
  1. Minor Calyces: Collect urine from renal pyramids.
  2. Major Calyx: Formed by the merging of minor calyces.
  3. Renal Pelvis: Formed by merging major calyces, leading to the ureter for urine transport to the urinary bladder.

Blood Supply to the Kidney

• Renal Fraction: Represents approximately 20% of the cardiac output directed to the kidneys.
• Blood Flow Pathway:
  1. enters through the Renal Artery.
  2. branches into Segmental Arteries.
  3. further branches into Interlobar Arteries.
  4. branches into Arcuate Arteries, then into Cortical Radiant Arteries.
  5. ends at the Afferent Arterioles (leading to glomeruli).
  6. Post-filtration, blood exits through Efferent Arterioles.
  7. Leads to Peritubular Capillaries for further substance exchange before returning to systemic circulation via various renal veins.