CIRCULATION (ANP 101)

Overview of the Circulatory System

• The circulatory system includes blood vessels, arteries, veins, and the heart.

• The heart is the central pump that moves blood, nutrients, waste, and oxygen throughout the body.

Heart and Lungs

• The heart is centrally located, functioning as the main pump.

• Lungs are essential for oxygen exchange; they are technically part of the respiratory system but connect to the circulatory system by supplying oxygen to the blood.

Circulation Types

Systemic Circulation

• Oxygenated blood is pumped from the heart to the rest of the body, delivering oxygen to tissues.

• Deoxygenated blood, carrying carbon dioxide from tissues, returns to the heart.

Pulmonary Circulation

• Deoxygenated blood flows from the heart to the lungs to exchange carbon dioxide for oxygen.

• Oxygenated blood returns to the heart, completing the circuit.

Blood Flow Pathway

1. Breathing in oxygen allows for its absorption in the lung capillaries.

2. Oxygenated blood travels back to the heart.

3. The heart pumps oxygenated blood into systemic circulation to nourish tissues.

4. Tissues utilize oxygen and produce carbon dioxide, which is transferred back into the deoxygenated blood.

5. Deoxygenated blood returns to the heart and is sent to the lungs for reoxygenation.

Arteries vs. Veins

Arteries

• Definition: Blood vessels that carry blood away from the heart.

• Characteristics:

  • Typically round and springy in form.

  • Carries oxygenated blood, usually color-coded red (though this is a simplification).

  • Elasticity helps maintain blood pressure and facilitate blood flow.

Veins

• Definition: Blood vessels that carry blood toward the heart.

• Characteristics:

  • Typically flat and larger in lumen compared to arteries.

  • Carries deoxygenated blood, usually color-coded blue.

  • Have valves to prevent backflow and pooling of blood.

Mechanisms of Blood Flow

• Arterioles are small branches of arteries leading to capillaries where gas exchange occurs.

• Capillary beds facilitate the exchange of oxygen and waste between blood and tissues.

• Venous return relies on:

  • Muscle contractions that push blood back to the heart.

  • Valves within veins that prevent backflow, especially crucial during periods of inactivity.

Varicose Veins

• Occur when valves in veins fail, causing pooling of blood and visible swelling of veins.

• Associated with aging or prolonged periods of standing still.

Structural Differences

• Arteries have more smooth muscle and layers than veins.

• Veins expand as they approach the heart; they start small (venules) and become larger.

• Capillary Dynamics: As blood enters capillaries, pressure decreases, and flow slows to facilitate oxygen and nutrient exchange.

Summary of Blood Flow Patterns

1. Blood pumped from heart (high pressure) into large arteries.

2. As arteries branch out, they become smaller and reach peripheral tissues as arterioles.

3. Oxygen exchanged at capillaries; deoxygenated blood returns via venules.

4. Blood gradually returns to heart through increasingly larger veins, ultimately entering the superior and inferior vena cavae.

Gas Exchange

• Oxygen moves from capillaries into tissues, while carbon dioxide moves into the capillaries to be transported back to the lungs.