Circulatory and Excretory Systems: Structure and Function

Circulatory System Elements

The circulatory system includes:

• Veins, arteries, and capillaries: These vessels transport blood throughout the body.
• Heart: This organ pumps the blood.

Arteries vs. Veins

Arteries and veins differ in structure and function:

• Arteries: Have thick, elastic walls that stretch and spring back, propelling blood forward. They carry blood away from the heart.
• Veins: Have thinner walls that cannot stretch as much. They often have valves to prevent the backflow of blood, carrying blood to the heart.

Capillary Structure and Function

Capillaries form a network connecting arteries and veins throughout the body. Their walls are only one cell thick, facilitating the diffusion of nutrients and oxygen into tissues. This process occurs via a fluid called tissue fluid.

The Coronary Artery

The coronary artery supplies the heart muscle with oxygen and nutrients. It is crucial because blockages or damage can lead to heart muscle damage due to insufficient supply. Severe damage may necessitate a heart transplant.

Excretory System Components

The excretory system manages waste removal:

• Ureter: Tubes that carry urine from the kidneys to the bladder.
• Renal Vein: Carries blood away from the kidney after it has been balanced.
• Renal Artery: Carries blood to the kidney for cleaning and balancing.
• Cortex: The outer part of the kidney where blood is filtered and substances are selectively reabsorbed.
• Medulla: Contains tubes that transport urine to the renal pelvis. Water is reabsorbed here to balance blood concentration.
• Pelvis: Collects urine from the medulla before it passes down the ureter to the bladder.

Nephrons: Kidney's Functional Units

Nephrons are the microscopic structural and functional units of the kidneys, with millions present in each kidney.

Kidney Filtration and Reabsorption

In the nephron:

• Filtered substances: Water, urea, and small molecules like salts and glucose are filtered.
• Reabsorbed substances: Water and NaCl (salt) are reabsorbed back into the blood.
• Excreted substances: Urea, salts, and excess water are passed into the urine and out of the body.

Excretory System Functions

• Kidney: Prepares urine for removal from the body.
• Ureter: Transports urine from the kidneys to the urinary bladder.
• Urinary Bladder: Stores urine.
• Urethra: Drains the bladder.
• Renal Artery: Supplies oxygenated blood to the kidney, carrying 'dirty' blood for filtration.