Circulatory System

What were the initial evolutionary reasons for circulatory systems?

Initially, circulatory systems evolved to transport nutrients.

What was a later evolutionary reason for circulatory systems?

Later, circulatory systems evolved to help with gas exchange (O2 / CO2).

What are the three essential parts of all circulatory systems?

All circulatory systems have:

1. Pump → the heart
2. Pipes → blood vessels (Arteries, veins, capillaries)
3. Fluid (Blood in closed systems; Hemolymph in open systems)

Describe an open circulatory system.

Found in insects and most invertebrates, characterized by:

• Fluid = hemolymph
• Low blood pressure
• Slower flow
• Low efficiency
• Good for smaller or less active animals

Describe a closed circulatory system.

Found in vertebrates and active animals, characterized by:

• Fluid = blood, kept inside vessels
• High blood pressure
• Faster flow
• Much more efficient
• Supports larger and more active animals

What are the main functions and characteristics of Atria in the heart?

Atria:

• RECEIVE blood into the heart
• Send blood → ventricles
• Have thinner walls

What are the main functions and characteristics of Ventricles in the heart?

Ventricles:

• PUMP blood away from the heart
• Have much thicker muscular walls
• The left ventricle is the strongest pump

What is the function of AV (Atrioventricular) valves?

AV valves separate atria from ventricles and prevent backflow into the atria.

Name the two AV (Atrioventricular) valves.

The Right AV valve is the tricuspid valve.
The Left AV valve is the bicuspid / mitral valve.

What is the function of Semilunar valves?

Semilunar valves are located between ventricles and arteries, preventing backflow into the ventricles (e.g., Aortic semilunar, Pulmonary semilunar).

What does a heart "murmur" indicate?

A heart "murmur" indicates that a heart valve is not closing properly, leading to turbulence in blood flow.

Describe Serial Circulation as seen in fishes.

Fishes have:

• 1 atrium
• 1 ventricle
• ONE loop of circulation (heart → gills → body → heart)

This is called serial circulation.

What is a major drawback of serial circulation in fishes?

The major drawback is that blood loses pressure as it passes through the gills, reaching the body at low pressure. This results in a low metabolic rate, suitable for ectotherms with lower O_2 needs.

Describe Parallel Circulation as seen in birds and mammals.

Parallel circulation involves two separate circuits working together. The heart has 4 chambers, acting as two distinct pumps:

1. Right side: Sends low O2, high CO2 blood to the lungs (Pulmonary circuit).
2. Left side: Sends oxygen-rich blood to the body (Systemic circuit).

Why is it called "parallel" circulation?

It's called "parallel" because the two pumps (right and left sides of the heart) run separately side-by-side but work collaboratively as a team.

What are the benefits of parallel circulation?

Benefits of parallel circulation include:

• HIGH blood pressure to the body
• Efficient O_2 delivery
• Supports warm-blooded animals (birds & mammals)

What are the characteristics of Arteries?

Arteries:

• Carry blood AWAY from the heart
• Have thick, muscular, and elastic walls
• Experience high pressure
• Possess a small lumen
• Are elastic to absorb pressure surges

What are the characteristics of Capillaries?

Capillaries:

• Have the THINNEST walls (1 cell thick)
• Are the site of all gas/nutrient exchange
• Have the slowest blood flow for diffusion
• Each organ has capillary density based on its needs (e.g., high density in brain, muscles; low in cartilage, tendons)

What are the characteristics of Veins?

Veins:

• Carry blood BACK to the heart
• Have thinner walls
• Experience low pressure
• Possess a bigger lumen
• Are less muscular and less elastic

How does blood move through veins when vein pressure is low?

Blood moves through veins by:

1. Skeletal muscles contracting → squeezing veins and pushing blood upward.
2. Valves preventing backflow → ensuring one-way movement toward the heart.

What is Atherosclerosis?

Atherosclerosis is an artery disease caused by plaque buildup that makes the artery walls thicker, stiffer, and narrows the lumen.

How does atherosclerosis develop?

Atherosclerosis develops through:

1. Damage to the artery wall attracting leukocytes (WBCs).
2. Cholesterol & fats creating fatty plaques.
3. The artery wall becoming thicker, stiffer, and its lumen (opening) becoming smaller, forcing the heart to work harder.

What are the consequences of atherosclerosis?

Consequences of atherosclerosis include:

• High blood pressure
• Heart attack (if plaque blocks a coronary artery)
• Stroke (if plaque breaks off & blocks a brain artery)

How does Aspirin help in relation to atherosclerosis?

Aspirin blocks inflammation and prevents platelet aggregation, which reduces clotting.

What is the composition and function of Plasma in blood?

Plasma is the liquid part of blood (55%) that carries dissolved gases, nutrients, hormones, and wastes.

What are Erythrocytes (RBCs) and what is their function?

Erythrocytes (RBCs) contain hemoglobin (an iron-containing protein) and carry O2 to tissues and CO2 away from tissues. They have no nucleus, allowing more room for hemoglobin.

What are Leukocytes (WBCs) and what is their function?

Leukocytes (WBCs) fight infection and use immune responses. They have a nucleus and can multiply when there is an infection.