6.1

Circulatory System

• The circulatory system is a complex network of vessels and organs transporting blood throughout the body.
• Its goal is to deliver oxygen and nutrients to all cells, while removing carbon dioxide and waste products.
• It's also known as the cardiovascular system. "Cardio" refers to the heart, and "vascular" refers to the blood vessels.

Arteries

• Structure: Thick, muscular, elastic tissues with an inner layer of epithelium, surrounded by a thick layer of smooth muscle encased in connective tissue. The inner space (lumen) has a small diameter.
• Function: Arteries stretch when the ventricles eject blood from the heart, then recoil, pushing blood through. Large arteries branch into smaller arterioles, carrying blood away from the heart.
• Location: Found deep within the body, alongside bones.

Veins

• Structure: Thin walls with an inner layer of epithelium, surrounded by a thin layer of smooth muscle and connective tissue. The lumen (inner space) is large, and veins contain valves that allow blood to flow only in one direction.
• Function: Veins stretch to accommodate incoming blood, then recoil to push blood forward. Valves prevent backflow as vein recoil isn't strong enough to overcome gravity.
• Location: Located near the surface, surrounded by skeletal muscle. Veins carry blood back to the heart.

Capillaries

• Structure: Single-cell-thick, simple squamous epithelium, surrounded by smooth muscle sphincters to control blood flow into a capillary bed.
• Function: Connect arteries to veins, facilitating gas exchange between blood and tissues.
• Location: Found everywhere in the body, close to all cells.

Arterioles and Venules

• Arterioles: Smaller versions of arteries enabling regulation of blood flow to specific capillary beds.
• Venules: Smaller versions of veins, collecting blood from capillaries.

Major Blood Vessels

• A major blood vessel is a large vessel that moves large amounts of blood to/from the heart. Damage can cause significant blood loss and potentially be fatal.

Aorta

• Structure: Largest artery in the body, similar in diameter to a garden hose, curving over the heart and descending along the spine.
• Function: Transports blood away from the heart to the rest of the body.

Coronary Arteries and Veins

• Structure: First branches off the aorta, located on the surface and inner parts of the heart.
• Function: Supply the heart muscle (myocardium) with oxygen and nutrients; carry deoxygenated blood away from the heart tissue to be replenished.

Carotid Arteries

• Structure: Two arteries branching off the aortic arch, supplying the head and brain.
• Function: Detect oxygen and blood pressure levels.

Jugular Veins

• Structure: Counterparts to carotid arteries, lacking valves for gravity-assisted drainage of blood.
• Function: Conduct blood out of the head to the superior vena cava.

Subclavian Arteries and Veins

• Structure: Branch off the aortic arch, travelling under the collarbone, carrying blood to/from the arms to the superior vena cava.
• Function: Conduct blood to and from the arms, taking lymph fluid from the arms to the superior vena cava.

Renal Arteries and Veins

• Structure: Branch off the descending aorta, carrying blood to/from kidneys, located in the lumbar region.
• Function: Transports blood to the kidneys for filtering, with the filtered blood returning via the inferior vena cava.

Iliac Arteries and Veins

• Structure: Branch off the aorta in the pelvic region, then branching again to one artery for each leg. The two common iliac veins merge to form the posterior vena cava below the abdomen.
• Function: Convey blood to and from the legs, merging into the posterior/inferior vena cava.

Superior/Inferior Vena Cava

• Structure: Largest veins in the body, branching to receive blood from the upper/lower body.
• Function: Collect blood from the body and empty it into the right atrium of the heart.