Kidney Functions and Anatomy Quiz

Kidney Functions

• Six functions of the kidney include regulating extracellular fluid volume, blood pressure, osmolarity, ion balance, waste excretion, and hormone production.

Anatomic Path of Water from Bowman's Capsule to Urine

• Bowman's Capsule: Plasma is filtered from the glomerulus, forming a filtrate containing water and small molecules.
• Proximal Convoluted Tubule: Most water, salts, and nutrients are reabsorbed.
• Loop of Henle:
  • Descending Limb: Water is reabsorbed, concentrating the filtrate due to high osmolarity in the medulla.
  • Ascending Limb: Water is retained while salts are actively transported out, diluting the filtrate.
• Distal Convoluted Tubule: Hormones, like aldosterone, adjust water and salt reabsorption.
• Collecting Duct: Antidiuretic hormone (ADH) fine-tunes urine concentration.
• Renal Pelvis: Urine drains from multiple nephrons.
• Ureters: Urine travels via peristalsis to the bladder.
• Urinary Bladder: Urine is stored.
• Urethra: Urine exits the body during micturition.

Tubular and Vascular Elements of the Nephron

• Glomerulus and Bowman's Capsule: The glomerulus (capillary tuft) is encased by Bowman's capsule facilitating plasma filtration into the nephron tubular system.
• Peritubular Capillaries and Tubules: Peritubular capillaries surround tubules enabling efficient exchange of substances—reabsorption of water, ions, and nutrients, and secretion of waste.
• Loop of Henle and Vasa Recta: Vasa recta closely follows the Loop of Henle in juxtamedullary nephrons helping maintain the medullary osmotic gradient for urine concentration.
• Distal Tubule and Collecting Duct: Peritubular capillaries surrounding these tubules allow further reabsorption and secretion of substances like ions.

Efferent and Afferent Arterioles, Peritubular Capillaries, Glomerulus, and Vasa Recta

• Afferent Arteriole: Brings blood into the glomerulus, regulating blood flow.
• Glomerulus (Capillaries): High hydrostatic pressure and fenestrated endothelium facilitate initial filtration of blood.
• Efferent Arteriole: Carries blood away from the glomerulus.
• Peritubular Capillaries: Surround distal and proximal tubules, taking up reabsorbed substances.
• Vasa Recta: In juxtamedullary nephrons, assists in the medullary osmotic gradient maintenance.

Vasa Recta

• Found in juxtamedullary nephrons, are long, straight capillaries that follow the Loop of Henle, maintaining the medullary osmotic gradient.
• Efficient process of reabsorbing water and solutes essential for urine concentration.

Anatomy of the Urinary System

• Portal System: Glomerulus forms a capillary bed within Bowman's capsule.
• Renal Blood Flow: Blood flows from afferent arteriole to glomerulus to efferent arteriole and then to peritubular capillaries/vasa recta.

Overview of Kidney Function

• Filtration: Blood filtration and entry into the tubule.
• Primarily occurs at the renal corpuscles of the Bowman's capsule.

Filtration Barrier

• Consists of glomerular capillary endothelium, basement membrane, and podocytes of Bowman's capsule.
• Allows small molecules to pass while retaining blood cells and large proteins.

Glomerular Filtration Rate (GFR)

• The volume of fluid filtered into Bowman's capsule per unit time.
• Primarily regulated by regulating blood flow through renal arterioles.

Reabsorption and Secretion

• Active Reabsorption: The active transport(sodium pump) drives the reabsorption of other substances like water, glucose, amino acids, and ions.

• Passive Reabsorption: Water follows the reabsorption of solutes through osmosis, moving down the concentration gradient.

• Tubular secretion: Substances may be moved from the blood into the tubular fluid.

Excretion

• The amount of a substance excreted through the urine.
• Determined by filtration, reabsorption, and secretion.
• Calculated using clearance.

Micturition (Urination)

• The involuntary reflex for emptying of the bladder, Subject to voluntary control by higher brain centers.
• Parasympathetic neurons trigger bladder contraction and somatic neurons relax the external sphincter muscles.