Overview
This lecture explains the function and flow of blood in the circulatory system, focusing on the role of hemoglobin in red blood cells, and details the path of oxygenated and deoxygenated blood through the heart, lungs, and body.
Hemoglobin and Red Blood Cells
- Hemoglobin inside red blood cells binds oxygen, reducing plasma oxygen and encouraging diffusion from the lungs.
- Keeping hemoglobin inside red blood cells (not free in plasma) prevents blood from becoming too viscous (thick).
- Packaging hemoglobin in cells allows blood to flow efficiently.
Circulatory System Basics
- Blood travels from the body to the right atrium of the heart through the superior and inferior vena cava (veins).
- Blood then moves passively to the right ventricle.
- The right ventricle pumps deoxygenated blood to the lungs via the pulmonary artery.
- Blood is oxygenated in lung capillaries near alveoli.
- Oxygenated blood returns to the heart via the pulmonary veins into the left atrium.
- The left atrium moves blood to the left ventricle, which pumps it into the aorta and out to the body.
Arteries and Veins Distinctions
- Arteries always carry blood away from the heart; veins return blood to the heart.
- Pulmonary arteries carry deoxygenated blood to the lungs; pulmonary veins carry oxygenated blood to the heart.
- All other arteries carry oxygenated blood; all other veins carry deoxygenated blood.
Circulatory Loop and Branches
- The circulatory system is a complete loop; blood cycles through heart, lungs, and body continuously.
- Major arterial branches supply organs (e.g., hepatic artery supplies the liver, celiac trunk supplies abdomen).
- After delivering oxygen, blood returns to the right side of the heart via veins.
Key Terms & Definitions
- Hemoglobin — Oxygen-carrying protein inside red blood cells.
- Viscous — Thick and sticky; describes resistance to flow in liquids.
- Alveoli — Tiny air sacs in the lungs for gas exchange.
- Pulmonary artery — Vessel carrying deoxygenated blood from the heart to the lungs.
- Pulmonary vein — Vessel carrying oxygenated blood from lungs to the heart.
- Aorta — Main artery carrying oxygenated blood from the heart to the body.
- Inferior/Superior vena cava — Large veins bringing deoxygenated blood from the body to the right atrium.
- Atrium — Upper chamber of the heart where blood enters.
- Ventricle — Lower chamber of the heart that pumps blood out.
Action Items / Next Steps
- Review diagrams of the circulatory system, focusing on the flow between heart, lungs, and body.
- Watch the next video to learn how hemoglobin knows where to release oxygen.