Lecture 7 - Cardio System - Heart

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What are the 3 major components of the cardiovascular system?

1. Heart: muscular pump that pumps blood throughout the body

2. Blood vessels: arteries, veins, and capillaries that move blood and allow gas exchange

3. Blood - a fluid that carries oxygen, nutrients, hormones, and waste products

Function of the heart?

A muscular heart that pumps blood throughout the body

Approximately how many times does the heart beat in a 77-year lifespan?

Over 3 billion beats.

What tissue contraction pumps blood throughout the body?

Contraction of cardiac muscle tissue.

Functions of the heart (just list, don’t describe)

1. Generating blood pressure

2. Routing blood

3. Ensuring one-way blood flow

4. Regulating blood supply

Describe this function of the heart: generating blood pressure

Contractions of the heart generate blood pressure, which is responsible for moving blood through the blood vessels

Describe this function of the heart: Routing blood

The heart separates the pulmonary and systemic circulations and ensures that the blood flowing to the tissues has adequate levels of O₂

Describe this function of the heart: Ensuring one way blood flow

The valves of the heart ensure a one-way flow of blood through the heart and blood vessels

Describe this function of the heart: Regulating blood supply

The rate and force of heart contractions change to meet the metabolic needs of the tissues, which vary depending on such conditions such as rest, exercise, and changes in body positions

What is the pericardium?

The pericardium (pericardial sac) surrounds the heart and consists of two layers

What analogy helps describe the pericardium?

The heart can be thought of as being “double bagged”

What are the two major layers of the pericardium?

• Fibrous pericardium (superficial)

• Serous pericardium (deep)

What is the fibrous pericardium?

Tough fibrous connective tissue that anchors the heart within the thoracic cage

What is the serous pericardium? What does it do?

A thin, two-layered lubricated membrane forming a closed sac around the heart that reduces friction during cardiac contractions

Layers of the serous pericardium?

Fibrous parietal layer - aka parietal pericardium

Epicardium (visceral layer) - aka visceral pericardium

What is the epicardium in relation to the serous pericardium?

Epicardium is the visceral layer of simple squamous epithelium, which is part of the heart itself and lines the surface of the heart.

Heart wall layers

1. Epicardium

2. Myocardium

3. Endocardium

What is the epicardium? What is it composed of?

A thin superficial cell layer forming a smooth external surface of simple squamous epithelium and containing superficial adipose tissue.

What is the myocardium?

The thick middle layer of cardiac muscle tissue responsible for the heart’s ability to contract.

What is the endocardium? What is it composed of and what does it form?

The deepest layer, composed of simple squamous epithelium and connective tissue, forming the smooth inner surface of heart chambers.

How does heart anatomy relate to its physiology?

The structure of the heart reflects its role as a pump directing blood flow.

What are the two main types of cardiovascular circulation?

1. Pulmonary circulation

2. Systemic circulation

What does pulmonary circulation do?

Carries blood from the right side of the heart to the lungs, where:

• CO₂ from blood diffuses into lungs

• O₂ diffuses from lungs to blood

Where does pulmonary circulation return blood?

Left side of the heart

What does systemic circulation do?

Left side pumps blood through systemic circulation, which delivers oxygen and nutrients to body tissues.

What happens to waste products in systemic circulation?

CO₂ and other wastes are carried back to the right side of the heart.

Why is the heart described as “two pumps in one”?

Because it pumps blood through pulmonary circulation and systemic circulation.

What is coronary circulation?

The circulation that supplies blood to the heart itself.

How is blood delivered to the heart in coronary circulation?

Through coronary arteries.

Where does blood from coronary circulation return?

To the right atrium via cardiac veins.

What cells initiate electrical activity in the heart?

Special cardiac pacemaker cells.

Where are these pacemaker cells located?

In the Sinoatrial (SA) node.

How are pacemaker cell action potentials similar to neurons?

They involve ion channel activity that generates electrical signals.

What ion channel causes rapid depolarization in pacemaker cells?

Voltage-gated Ca²⁺ channels.

What channel causes slow depolarization to threshold in pacemaker cells?

A “leak” or “funny” Na⁺ channel.

What does the “funny” Na⁺ channel do?

Allows Na⁺ to enter when the cell is polarized, causing slow depolarization to threshold.

What does an electrocardiogram measure?

The electrical activity of the heartbeat.

What causes the electrical waves seen on an ECG?

Electrical impulses that cause the heart muscle to contract and pump blood.

What does a normal ECG show?

The rate and rhythm of contractions in the upper and lower chambers of the heart.

What does the P wave represent?

Atrial depolarization

What does the QRS complex represent?

Ventricular depolarization.

What does the T wave represent?

Ventricular recovery/repolarization (Rest)

What is commotio cordis?

A sudden blunt impact to the chest that stops the heart, causing cardiac arrest.

What famous event was used as an example of commotio cordis?

Collapse of Damar Hamlin

What is the proposed mechanism of commotio cordis?

Physical disruption of the cardiac plasma membrane, leading to abnormal ion conductance.

How well understood is the mechanism of commotio cordis?

It is poorly understood.

Why must heart rate vary?

To maintain homeostasis and meet the body's needs.

What is the approximate range of heart rate mentioned in the slides?

50–140+ beats per minute.

What are the two major types of heart regulation?

1. Intrinsic regulation

2. Extrinsic regulation

What is intrinsic regulation of the heart?

Regulation that occurs within the cardiovascular system itself, without neural or hormonal control.

What causes intrinsic regulation?

Stretching of cardiac muscle cells, which leads to stronger contractions.

What is Starling’s Law?

The stroke volume increases when the volume of blood in the ventricle increases before contraction.

Why does increased ventricular volume increase contraction force?

Because cardiac muscle fibers stretch, and stretched fibers contract more forcefully.

What happens when muscle fibers stretch more? (3 things)

• Contraction force increases

• Stroke volume increases

• Blood pressure increases

What is extrinsic regulation of the heart?

Regulation by neurons and hormones that control heart rate and blood vessel size.

What are baroreceptors and chemoreceptors? Where do they relay information?

Specialized sensory neurons that detect changes in the cardiovascular system and relay the info to the CNS

What do baroreceptors detect?

Changes in blood pressure.

What role do baroreceptors play in homeostasis?

They detect changes in BP, increasing/decreasing parasymp/ symp and adrenal medulla activity and restore homeostasis

ECG abnormalities

an area other than the SA node can initiate an impulse followed by a contraction - this is called an ectopic focus/ectopic pacemaker, and could be the result of localized ischemia via caffeine, acetylcholine, elevated symp/parasymp stimulation, digitalis