Heart, Blood, and Circulation: Key Functions and Components

Which Nerve Slows the Heart Down?

The Vagus Nerve

Function of Heart Valves

Heart valves ensure one-way blood flow.

Atrioventricular Valves

• Tricuspid valve (3 cusps): Located between the right atrium and right ventricle.
• Bicuspid (mitral) valve (2 cusps): Located between the left atrium and left ventricle.
• Chordae Tendineae: Also known as 'heart strings'.

Semilunar Valves

• Pulmonary semilunar valve: Directs blood from the right ventricle to the pulmonary trunk.
• Aortic semilunar valve: Directs blood from the left ventricle to the aorta.

Arteries vs. Veins

Arteries carry oxygenated blood away from the heart to the body, while veins carry oxygen-poor blood back from the body to the heart.

Three Functions of Blood

Blood has three main functions:

1. Transportation: Carries nutrients, hormones, heat, and waste products.
2. Regulation: Maintains pH and body fluid balance.
3. Protection/Defense: Contains white blood cells, blood clots, and antibodies.

Blood Plasma Composition

Blood plasma is composed of:

• 91.5% water
• 8.5% solutes, including:
  • Plasma proteins: Maintain osmotic pressure, transport hormones, iron, lipids, vitamins, and aid in blood clotting.
  • Other solutes: Electrolytes, nutrients, enzymes, and waste products like urea, ammonia, and CO2.

Agranulocyte Function

Agranulocytes are white blood cells with a one-lobed nucleus and no granules in their cytoplasm. They make up about 35% of all white blood cells.

Hemostasis and Erythrocyte Function

Hemostasis occurs in adults. Erythrocytes (red blood cells) have no nucleus and are continually replaced. They make up 45% of total blood volume. Their function is to deliver oxygen from the lungs to body tissues. They are anucleated biconcave disks with great carrying capacity, no mitochondria, and produce ATP anaerobically. There are approximately 4.6 million cells per mm³, and they contain hemoglobin.

How Blood Typing Works

Blood typing is based on cell surface antigens:

• Group O RBC: React with neither A nor B antibodies; universal donor, can only receive Type O blood.
• Group AB RBC: React with both A & B antibodies; universal recipient, can receive all 4 blood types.
• Group A RBC: React with anti-A antibodies; person's blood has anti-B antibodies; can receive Type A or Type O blood.
• Group B RBC: React with anti-B antibodies; person's blood has anti-A antibodies; can receive Type B or Type O blood.