Urinary System Overview

Urinary System

• Functions:
  • Produces erythropoietin and renin, crucial for red blood cell production and blood pressure regulation.
  • Converts vitamin D to its active form.
  • Carries out gluconeogenesis during prolonged fasting.
• Urine-forming kidneys:
  • Ureters: Transport urine from the kidneys to the bladder.
  • Urinary Bladder: Temporary storage for urine.
  • Urethra: Carries urine from the bladder to the exterior.
• External Anatomy of kidneys:
  • Renal Hilum: A vertical cleft, entrance for structures like ureters, renal blood vessels, and nerves.
  • Renal Sinus: Internal space within the kidney
  • Ribcage: Protects lower part of the kidneys;
  • Adrenal gland: Located atop the kidneys, but functionally distinct.
• Layers of supportive tissue surrounding each kidney:
  • Renal Fascia: Superficial layer, anchors the kidney.
  • Perirenal Fat Capsule: Fatty cushion for protection.
  • Fibrous Capsule: Transparent capsule enclosing the kidney.
• Distinct regions of the kidney (superficial to deep):
  • Renal Cortex: Light-colored with granular appearance, outermost region.
  • Renal Medulla: Deeper region, reddish-brown, contains triangular regions (pyramids).
• Renal Pelvis: Flat, medullary tube connecting the hilum and ureters.
• Sections of the Urinary System:
  • Components of a nephron:
    • Renal corpuscle: Glomerulus and glomerular capsule; filters blood.
    • Renal tubule: Proximal convoluted tubule, Loop of Henle (descending & ascending limbs), Distal convoluted tubule, Collecting duct; processes filtrate.
  • Classes of nephrons:
    • Cortical nephrons: 85% of nephrons, located predominantly in the cortex.
    • Juxtamedullary nephrons: 15% of nephrons, located near the cortex-medulla junction, important for concentrating urine.
• Glomerular filtration: Formation of a protein-free filtrate using the glomerulus, specialized for blood filtering and filtrate production. Crucial components: Fenestrated endothelium, basement membrane, filtration slits, filtration membrane. The process ensures waste products are excreted without losing essential proteins.
• Tubular reabsorption & secretion: Kidney tubules reabsorb necessary materials (water, glucose, ions) back into the bloodstream. Simultaneously, some substances are secreted into the filtrate for excretion.

Flow of Blood Supply in the Kidneys

• Renal arteries branch & divide into smaller arteries to the kidneys.
• Blood flows through the glomeruli (capillaries)
• Blood filtered in the glomeruli.
• Water and essential components reabsorbed into the bloodstream.
• Waste products excreted in the urine.
• Blood exits the kidney through veins.

Routes of Reabsorbed Substances

• Transcellular route: Substance passes through the cell membrane.
• Paracellular route: Substance passes between cells, particularly in the proximal convoluted tubule (PCT).

Tubular Secretion

• Selective process, adding solutes to the filtrate (e.g., urea, uric acid). Helps maintain the proper pH of the blood and excrete wastes.

Urine Transportation, Storage, and Elimination

• Incoming urine triggers peristaltic waves in the ureters to move it to the bladder.
• Urine accumulates in the expanding bladder.
• Internal and external urethral sphincters control urine release.

Micturition (urination):

• Reflex actions control urination under automatic control.
• Conscious brain control takes over later.

Urinary System Osmolality

• Rise in osmolality: Triggers ADH release for water conservation.
• Decrease in osmolality: Inhibits ADH release leading to increased urine output.
• The renin-angiotensin mechanism regulates water, blood pressure, and electrolyte balance, involving hormones such as renin and aldosterone.

Diseases of the Urinary System

• Renal Ptosis/Nephroptosis or "wandering kidney" - Kidney displaced from its normal position
• Renal calculi/Kidney stones: Solid masses of minerals and salts created from concentrated urine, can lead to pain and blockages.
• Urinary tract infections (UTIs): Bacteria infections in the urinary system.
• Diabetes insipidus: Imbalance in water retention due to insufficient ADH in the body.

Physical Characteristics of Urine

• Color: Varies from pale yellow to dark yellow, depending on concentration.
• Transparency: Usually clear
• Odor: Can vary based on diet, presence of disease, etc.
• Specific gravity: Measures the density.

Test your knowledge of the Urinary System, including its functions, anatomy, and the structures involved in urine formation. This quiz covers the kidneys, ureters, bladder, and the role of supportive tissue. Dive into the essential functions like hormone production and urine transport in this crucial body system.