Human Circulatory System: Heart, ECG, Vessels & Blood Pressure

What are the main functions of the circulatory system?

Transport of nutrients, waste, gases, metabolic products, thermoregulation, and communication between cells and organs.

What are the two main types of circulatory systems?

Open and closed circulatory systems.

Which animals typically have open circulatory systems?

Arthropods (insects, crustaceans, spiders) and mollusks (clams, oysters, squid, octopus).

What is hemolymph?

The fluid in an open circulatory system that is similar to interstitial fluid.

How does blood flow in a closed circulatory system?

Blood is pumped through vessels and is separated from interstitial fluid, with exchange occurring at capillaries.

What is the difference between single and double circulation?

Single circulation has blood flow through the heart once per cycle, while double circulation has separate circuits for gas exchange and systemic circulation.

What is the main function of the gills in fish?

To encourage the exchange of dissolved gases (like oxygen) between capillaries and water.

How many chambers does the human heart have?

Four chambers: two atria and two ventricles.

What is the role of the left ventricle?

To pump blood through the systemic circuit.

What prevents backflow of blood in the heart?

Heart valves, including atrioventricular (AV) valves and semilunar valves.

What are the phases of the cardiac cycle?

Diastole (relaxation) and systole (contraction).

What occurs during diastole?

The heart chambers relax and fill with blood; both AV valves are open.

What occurs during systole?

The atria contract first, followed by the ventricles, forcing blood out of the heart.

What is the significance of the cardiac action potential?

It leads to coordinated muscle contraction in the heart.

What is an electrocardiogram (ECG)?

A test that measures the electrical activity of the heart.

What is the role of gap junctions in cardiac muscle?

They allow the flow of current (Na+) between cardiac cells for coordinated contraction.

What is the structure that connects cardiac muscle cells?

Intercalated discs.

What is the primary difference in the structure of cardiac muscle cells compared to skeletal muscle cells?

Cardiac muscle cells are smaller, have one nucleus per cell, and branch.

What regulates heart contraction during the cardiac cycle?

Sequential contraction of chambers and coordinated contraction of muscle cells.

What is the function of the right ventricle?

To pump blood through the pulmonary circuit.

What is the thicker wall of the left ventricle necessary for?

To generate more force to move blood through the systemic system compared to the pulmonary system.

What are the types of heart valves?

Atrioventricular (AV) valves and semilunar valves.

What is the function of the pulmonary valve?

To prevent backflow when the ventricles relax.

What happens to the AV valves during ventricular contraction?

They close to prevent backflow into the atria.

What is the role of valves in the circulatory system?

To ensure directional flow of blood.

What is the significance of the thickness of the left ventricle wall?

It is thicker to generate the necessary force for systemic circulation.

What are cardiac muscle cells joined by?

Gap junctions

What is the junction between two cardiac muscle cells called?

Intercalated disc

What initiates the wave of depolarization in the heart?

The SA node

What does an electrocardiogram (ECG) measure?

The electrical potential difference between electrodes

What does the P wave in an ECG represent?

Depolarization and contraction of the atria

What do the Q, R, and S waves in an ECG indicate?

Depolarization of the ventricles

What does the T wave in an ECG signify?

Relaxation and repolarization of the ventricles

What condition is indicated by the absence of QRS waves following P waves?

Poor conduction between atria and ventricles

What is fibrillation?

Rapid, irregular, and unsynchronized contraction of muscle fibers

What is tachycardia?

An abnormally fast heart rate, usually over 100 beats per minute

What is the role of a defibrillator?

To deliver a large electrical current to depolarize heart cells simultaneously

What is the natural rate of depolarization for the SA node?

About 70 beats per minute

What influences the heart rate besides the SA node?

Inputs from the autonomic nervous system, hormones, and drugs

What are the two branches of the autonomic nervous system that regulate heart rate?

Sympathetic and parasympathetic

How do beta-blockers affect heart rate?

They slow down the heart rate by blocking sympathetic activity

What is the function of arteries?

To carry blood away from the heart

What are arterioles responsible for?

Controlling blood distribution to capillary beds

What is the primary function of capillaries?

Exchange between blood and interstitial fluid

What do veins do?

Return blood to the heart

What structural feature helps veins return blood to the heart?

One-way valves

What is the role of smooth muscle in arterioles?

To control blood flow to various tissues

What are precapillary sphincters?

Smooth muscle cuffs that regulate blood flow to specific capillary beds

What causes local dilation of arterioles?

High CO2, low O2, and byproducts of cellular metabolism

What is the structure of capillaries?

A single layer of endothelial cells

What is the function of endothelial cells in blood vessels?

To provide a smooth surface and prevent leakage

What materials are found in the walls of arteries?

Extracellular collagen and elastin fibers

What is the purpose of elastic recoil in arteries?

To push blood forward during diastole (heart relaxation)

What causes local dilation in blood vessels?

High CO2, low O2, byproducts of cellular metabolism, lactic acid, low pH, and locally produced factors like histamine and nitric oxide.

What substances can diffuse directly across endothelial cells in capillaries?

O2 and CO2.

What do the gaps between endothelial cells in capillaries allow?

They provide a pathway for water-soluble substances like glucose, amino acids, and salts.

What happens to blood pressure as blood moves through the circulatory system?

Blood pressure drops throughout the system, with the biggest drop observed in the arterioles.

What are the two forces that affect fluid movement between capillaries and interstitial fluid?

Blood pressure and osmotic pressure.

What is the role of the lymphatic system in fluid movement?

The lymphatic system takes up excess water from interstitial fluid and returns it to the circulatory system.

What is systolic pressure?

The pressure in the arteries during the contraction of the heart (when blood is ejected).

What is diastolic pressure?

The pressure in the arteries when the heart is at rest between beats.

What is considered normal blood pressure?

120-129 systolic over 80-84 diastolic.

What can happen if blood pressure is too low?

Tissues may not receive enough blood flow, potentially leading to various health issues.

What are the potential consequences of high blood pressure?

It can lead to coronary artery disease, stroke, heart failure, atrial fibrillation, and chronic kidney disease.

How does exercise affect blood pressure?

Exercise increases heart rate and blood flow to muscles, but vasoconstriction helps maintain overall blood pressure.

What is atherosclerosis?

A condition characterized by hardened plaque deposits in the arteries, leading to reduced blood flow.

What is ischemic heart disease?

A condition of recurring chest pain due to insufficient blood flow to the heart.

What is a thrombus?

A blood clot that forms and sticks to plaque in the arteries.

What can happen if a coronary artery becomes completely blocked?

It can lead to a heart attack, which may destroy part of the heart muscle.

What factors can disrupt blood pressure?

Drinking, standing up/sitting down, sweating, stress, and exercising.

What happens to blood flow to digestion and kidneys during exercise?

The percentage of blood flow to these areas decreases significantly.

What is the significance of the elastic recoil of arteries?

It helps maintain blood flow between heartbeats by preventing pressure from dropping to zero.

What is the function of precapillary sphincters?

They regulate blood flow into capillary beds.

What happens to endothelial cells as we age?

They become less elastic and can attract immune responders, leading to vascular disease.

What is the relationship between vasodilation and blood pressure?

Vasodilation lowers blood pressure by increasing the diameter of blood vessels.

What is the role of valves in the lymphatic system?

They ensure one-directional flow of lymph fluid back to the circulatory system.

What is the net movement of water between capillaries and interstitial fluid?

There is a net movement of water out of the capillaries due to blood pressure being higher than osmotic pressure.