Understanding the Excretory and Urinary Systems: Functions and Anatomy
The Excretory System: An Overview
The excretory system comprises the urinary system and other organs and systems that aid in waste product excretion.
Other Components of the Excretory System
- Respiratory System: Removes carbon dioxide from the blood and expels it from the body.
- Sweat Glands: Located in the skin, these glands produce sweat, which evaporates to cool the skin. Some excretory substances are also eliminated through sweat.
- Liver: Eliminates products from the breakdown of hemoglobin from old red blood cells. These products are added to bile, which drains into the intestine and is eventually expelled. The liver also eliminates small amounts of cholesterol and some toxic substances.
The Urinary System: The Primary Excretory System
The urinary system is the most crucial part of the excretory system, eliminating waste products in the form of urine.
In addition to waste removal, the excretory system helps maintain the body’s vital systems in balance. It regulates water levels in tissues, mineral concentrations in the blood, and the blood’s pH level.
The Urinary System: Components and Functions
The urinary system consists of:
- A pair of kidneys that remove waste from the blood and produce urine.
- Two ureters that carry urine from the kidneys.
- A bladder for urine storage.
- A urethra through which urine exits the body.
The Kidneys: Structure and Function
The kidneys are located at the back of the abdomen, one on each side. Each kidney has:
- An external part (the renal cortex).
- An internal part (the renal medulla).
- A hollow chamber (the renal pelvis).
Urine forms in the renal cortex and renal medulla, containing excretory substances that drain into the renal pelvis.
Nephrons: The Functional Units of the Kidneys
Each kidney contains over a million nephrons, small tubes with one open end surrounded by a capillary. Nephrons filter the blood to produce urine. Key parts of a nephron include:
- Bowman’s Capsule: The initial part of the nephron, a round sac containing a curled-up capillary called the glomerulus.
- Convoluted Tubule: A long, twisted tube with two sections: proximal and distal.
- Loop of Henle: A U-shaped portion between the proximal and distal convoluted tubules.
Nephrons connect to collecting ducts, which drain into the renal pelvis.
Ureters, Bladder, and Urethra: Urine Collection and Excretion
Urine is collected from the kidneys, stored, and then expelled from the body through urination. Different organs facilitate these functions.
Ureters: Transporting Urine
The ureters are two narrow tubes, approximately 28 cm long, connecting the renal pelvis of the kidney to the bladder. The bladder is an elastic sac where urine collects before excretion.
When the bladder fills, a nervous stimulus (the micturition reflex) causes the bladder to contract and push urine out via the urethra.
Urethra: Urine Excretion
The urethra is the duct that leads to the outside of the body. At the beginning of the urethra, a sphincter remains closed until the micturition reflex occurs.
In men, the urethra is connected to the reproductive system, allowing both urine and semen to pass through it (at different times). In women, the urethra…