Urinary System: Anatomy, Function, and Pathology
Anatomy of the Urinary System
The urinary system is composed of two kidneys, two ureters, the bladder, and the urethra.
Composition of the Nephron
The kidney is made up of multiple nephrons. The nephron is the structural and functional unit of the kidney. It is composed of:
- Glomerulus: A network of capillaries that receive blood from an afferent arteriole and drain through an efferent arteriole.
- Bowman’s capsule: Surrounds the glomerulus and has an open portion for collecting urine filtered in the glomerulus.
- Proximal convoluted tubule: The first part of the tubular system.
- Loop of Henle: A U-shaped portion of the proximal tubule, consisting of:
- Descending limb: Thin portion.
- Ascending limb: Thicker portion.
- Distal convoluted tubule: Located next to the glomerulus.
- Collecting tubule: Formed by the confluence of the distal tubules of several nephrons.
Main Functions of the Urinary Tract
The main function of the urinary tract is to filter the blood to remove waste products from the body through the urine. The kidneys are involved in the regulation of fluid and electrolyte balance and acid-base balance, as well as the control of blood pressure.
Mechanisms Involved in Urine Formation
These include glomerular filtration, tubular secretion, and tubular reabsorption.
Antidiuretic Hormone (ADH) regulates the absorption and elimination of water according to the body’s needs, and aldosterone causes sodium reabsorption and potassium secretion.
Mechanism of Blood Pressure Regulation
- Renin-Angiotensin System: When blood pressure drops, the kidneys release renin, which stimulates the activation of angiotensin, which raises blood pressure.
- Aldosterone: When blood pressure decreases, the adrenal glands increase the secretion of aldosterone. This hormone causes the kidneys to retain salt, which stimulates water retention. The increased water and salt lead to an increase in blood volume, elevating blood pressure.
- Kidneys and Body Fluids: When blood pressure decreases, the secretion of water and salts in the kidneys decreases. This causes them to retain water and salts, which increases blood volume and, as a result, increases blood pressure.
Principal Regulatory Mechanisms
- Antidiuretic Hormone: Works as a feedback system that controls osmolarity, sodium concentration in extracellular fluid, and urine formation.
- Aldosterone: This hormone regulates extracellular fluid volume by regulating the amount of sodium reabsorbed into the blood from the renal tubules and the amount of potassium excreted.
Pathology
- Renal Insufficiency: A kidney disorder in which the kidneys cannot eliminate metabolic wastes or perform their regulatory functions. As a result, water, electrolytes, and metabolic waste products accumulate in body fluids, altering endocrine function and metabolism, as well as hydroelectric and acid-base balance.
- Pyelonephritis: Bacterial infection of the kidney.
- Cystitis: Inflammation of the bladder due to urinary infections.
- Lithiasis: Presence of kidney stones (nephrolithiasis) and urinary tract stones (urolithiasis).
- Dehydration: An imbalance between sodium and water, leading to a decrease in extracellular fluid volume. Caused by kidney disease, digestive alterations (vomiting, diarrhea, fistulas), or skin alterations (increased sweating and burns).
- Hyperkalemia: Increased blood potassium levels.
- Hypokalemia: Decreased blood potassium levels.
- Respiratory Acidosis: A disorder caused by the alteration of carbonic acid in the blood. The main clinical signs are hypoventilation, shallow breathing, and drowsiness, which may progress to stupor and coma.