Circulatory system
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The Circulatory System: Blood, Heart, and Blood Vessels
1. Blood Composition
Blood Components: Blood is composed of cells suspended in plasma, consisting of four components: red blood cells, white blood cells, platelets, and plasma.
Red Blood Cells: Approximately 242 to 270 million per drop, containing hemoglobin to carry oxygen.
White Blood Cells: Fewer in number, transparent, part of the immune system to fight infections.
Platelets: Cell fragments that assist in preventing blood loss and promote clotting.
Plasma: Straw-colored liquid, 91.5% water, 8.5% solutes (proteins, electrolytes, nutrients, gases, hormones, enzymes, vitamins, and waste products).
2. The Heart
Function: A muscular pump that circulates oxygen and nutrients throughout the body.
Structure: Divided into two halves (left and right), each with two chambers (atrium and ventricle).
Flow of Blood: Atria receive blood from veins, ventricles provide the force to push blood to various destinations.
Valves: Different valves perform specific tasks within the heart.
3. Blood Circulation
Venous Return: Deoxygenated blood returns from the body to the right atrium via the inferior and superior vena cava, then is sent to the lungs via the pulmonary artery.
Oxygenation: Blood in the lungs absorbs oxygen and becomes bright red, entering the left atrium via the pulmonary vein.
Systemic Circulation: Left ventricle ejects oxygenated blood into the systemic circulation via the aorta.
Direction of Blood Flow: Arteries carry blood away from the heart, while veins carry blood to the heart.
4. Cardiac Function
Pacemaker: The Sinoatrial node in the right atrium initiates cardiac muscle contraction.
Stimulation: The autonomic nervous system stimulates the myocardium to contract.
5. Blood Vessels
Vasoconstriction & Vasodilation: Blood vessels can narrow (vasoconstrict) or widen (vasodilate) due to smooth muscle in their walls.
Regulation: This ability directs blood flow to different tissues based on oxygen and nutrient requirements.
Blood Pressure: Blood vessel regulation also plays a role in blood pressure control.
Considerations: Eating close to exercise or during shock can impact blood flow distribution.
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