Blood Vessels Overview

Small lumen and thick walls, consisting of collagen, smooth muscle, and elastic fibers.
No valves; blood flows under high pressure away from the heart.
Primarily carry oxygenated blood, except the pulmonary artery.
Blood flow is rapid and pulsatile.

Tiny lumen, with walls just one cell thick (endothelium).
Facilitate exchange of materials (e.g., gases, nutrients) between blood and cells.
Blood can be either oxygenated or deoxygenated.

Arterioles are smaller branches of arteries; their muscle layer can constrict to reduce blood flow.
Venules are small veins formed from capillaries; contain low-pressure, deoxygenated blood rich in CO₂.

Deoxygenated blood exits the right ventricle via the pulmonary artery to the lungs; only artery carrying deoxygenated blood.
Blood loses CO₂ and gains oxygen in the lungs, then returns to the heart through the pulmonary veins (only veins carrying oxygenated blood).
Oxygenated blood enters the left atrium, moves to the left ventricle, then pumped into the aorta for systemic circulation.
Major arteries include the hepatic artery (to the liver), mesenteric artery (to intestines), and renal artery (to kidneys).
After passing through organs, blood returns to the heart through the inferior vena cava.

Portal veins connect two capillary beds; the hepatic portal vein carries nutrient-rich, deoxygenated blood from the intestines to the liver for processing.

Heart muscle is specialized, strong, and branched; a resting rate of approximately 75 beats per minute.
CO₂ levels are monitored by the medulla oblongata, which regulates the heartbeat.
Each heartbeat creates a pulse detectable at wrist or neck; represented by 'lub-dub' sound from closing heart valves.
'Lub' corresponds to the closure of bicuspid and tricuspid valves during ventricular contraction.