A&P Exam 2: The Heart

Where is the heart located?

Located in the mediastinum in the pericardial sac

Directional term of base of the heart

Superior

Directional term of apex of the heart

Inferior/lateral

Layers of the Heart

Epicardium, myocardium, and endocardium

Epicardium

Outer later of the heart (visceral pericardium)

Myocardium

Thick cardiac muscle layer

Endocardium

Inner layer that is continuous with blood vessels

Types of Blood Flow

Systemic and pulmonary

Systemic Blood Flow

Blood flow to the body

Pulmonary Blood Flow

Blood flow to the lungs

Veins carry blood ___ the heart

Towards

Arteries carry blood ___ the heart

Away from

What are the upper chambers of the heart called?

Atria

What are the lower chambers of the heart called?

Ventricles

The right ventricle sends blood to the ___

Lungs

Oxygenated blood from the lungs returns to the heart through the ___

Left atrium

What is the function of valves have in the heart?

Act as a one-way entry to prevent blood from flowing backwards

Where does the inferior vena cava get its blood from?

Trunk, visceral organs, and lower body

Where does the superior vena cava get its blood from?

Head and upper body

What do the superior and inferior vena cava do?

Bring deoxygenated blood from the body back to the heart through the right atrium

Pulmonary artery

Carries deoxygenated blood away from the heart and to the lungs to be oxygenated

Pulmonary veins

Carry oxygenated blood back to the heart and empty blood into the left atrium

Aorta

Carries oxygenated blood to the rest of the body

Where do the coronary arteries branch off/arise from?

The aorta/aortic valves

What connects cardiac muscle cells to each other?

Intercalated discs

What are the components of intercalated discs?

Desmosomes and gap junctions

What do desmosomes in intercalated discs do?

Physically link adjacent cells together and allow them to contract as one unit

What do gap junctions in intercalated discs do?

Link cell cytoplasms

What is a functional syncytium?

A fused mass of cells that function as one; Linked mechanically, electrically, and chemically

Sarcomeres

Basic functional unit of cardiac muscles; Bundles of protein filaments that contract together

Sarcoplasmic Reticulum

Stores Ca++ when muscle fibers are at rest and release Ca++ when contraction is going to happen

Transverse Tubules (T-Tubules)

Allow the transmission of action potentials across the cell

T-Tubule Structure

Filled with interstitial fluid and walls are continuous with plasma membrane of cells

Action Potential

Short lived wave of depolarization on the plasma membrane of an excitable cell

What is the net charge of the inside of a cell?

Negative

What do action potentials do in muscle fibers?

Trigger contraction

Depolarization

Plasma membrane becomes more positive due to ion movement across the membrane (action potential)

What ion/molecule must be present for contraction to occur?

Calcium ions/Ca++

What type of metabolism does cardiac muscle rely on?

Aerobic

Why is the elastic recoil of the aorta useful?

Helps push blood forward in the aorta and back into the coronary arteries

Resting potential

-90 mV

Threshold for action potential

-75 mV

Voltage gated ____ channels open and cause depolarization at threshold

Na+ channels

Voltage gated Na+ channels close and Ca++ channels open at ____ mV

+30 mV

What happens in the plateau phase of action potential?

Na+ is being pumped out via active transport and Ca++ is flowing in

What channels open when Ca++ channels close?

K+ channels

What happens during the rapid repolarization stage?

K+ is flowing out of the cell and Ca++ is being pumped out and taken up by the sarcoplasmic reticulum

Sinoatrial (SA) Node

Group of cells that depolarize the fastest (leakiest cells); Called pacemaker cells

Atrioventricular (AV) Node

Group of cells that are slow at action potential conduction (delay AP)

SA node and AV node are connected by _____

Internodal pathways

Where does the electrical signal for contraction begin?

SA node

Systole

Contraction

Diastole

Relaxation

P-Wave

Depolarization of the atria

QRS Complex

Depolarization of the ventricles

T-Wave

Repolarization of the ventricles

Arrythmia

Abnormal heart rhythm

Cardiac Cycle definition

Period between the start of one heartbeat to the beginning of the next heartbeat

Absolute Refractory Period

Another action potential cannot occur; Na+ channels are already open or inactive

Relative Refractory Period

Another action potential is possible, but Na+ channels will only respond to a larger stimulus

What is the purpose of the long action potential and long refractory period of cardiac muscle cells?

Prevent tetanus (sustained max. contraction) and limit the heart rate

Cardiac muscle cells do/do not require a nerve/neuron impulse to cause contraction

Do not

Why do cardiac muscles repolarize on their own?

They are leaky to Na+ and Ca++

Heart Beat Steps

1. SA node depolarizes

2. Conducting cells take action potential to AV node while the atria depolarizes (delay at the AV node)

3. Atrial contraction begins

4. Stimulus travels through AV node, AV bundle, AV branches, and Purkinje fibers

5. Atrial contraction ends, ventricles depolarize, and contract from apex to base

Electrocardiogram (ECG/EKG)

Graph of the heart’s electrical activity

Step 1 Cardiac Cycle

Atrial systole: Ventricles fill and the end quantity of blood = diastolic volume

Step 2 Cardiac Cycle

Atrial diastole

Step 3 Cardiac Cycle

Ventricular systole - Phase 1: AV valves close and pressure increases/no blood movement

Step 4 Cardiac Cycle

Ventricular systole - Phase 2: As ventricular pressure becomes greater than arterial pressure, ventricular ejection occurs. Amount ejected = Stroke volume

Step 5 Cardiac Cycle

Ventricular diastole: Ventricular pressure falls and semilunar valves close. When ventricular pressure falls below atrial pressure, AV valves open and ventricles fill passively. Both atria and ventricles are in diastole.

Cardiac Output

Amount of blood pumped out of the left ventricle in one minute

Controls of Cardiac Output

Nervous innervation (autonomic nervous system), blood volume reflexes, and hormones

Nervous Innervation

Both sympathetic and parasympathetic divisions of the ANS innervate the SA and AV node and atrial fibers

Mechanisms of Nervous Innervation

• Neurons monitor blood pressure, O2, and CO2

• Release of neurotransmitters which open K+ channels to slow depolarization

• Release of neurotransmitters which open Na+ or Ca++ channels to increase depolarization

Blood Volume Reflexes

1. Atrial Reflex (Bainbridge): When venous return increases, stretching of the right atrium stimulates sympathetic activity and increases heart rate

2. Frank-Starling Principle: When more blood flows into the ventricles (higher end diastolic vol.) ventricles contract more forcefully and pump more blood out (SV) because sarcomeres are in a more optimal position

Hormones

Epinephrine, norepinephrine, thyroid hormone, and glucagon increase contractility

Length Tension Relationship

Tension generated depends on the length of muscle sarcomeres

Heart Sound “Lub Dub”

Lub = Slamming of AV valves

Dub = Slamming of semilunar valves

Murmur

Abnormal heart sounds (i.e. “Lub dush” or “lush dub”)

What is happening at 1?

Leaking of Na+ and Ca++ ions

What is happening at 2?

Threshold is reached (-75 mV) and voltage gated Na+ channels open

What is happening at 3?

Rapid depolarization; Na+ is flowing in

What is happening at 4?

Voltage gated Na+ channels close and Na+ is being pumped out. Voltage gated Ca++ channels open around 0 mV

What is happening at 5?

Plateau phase; Na+ is pumped out and Ca++ flows in

What is happening at 6?

Ca++ channels close and K+ channels open. K+ flows out

What is happening at 7?

Rapid repolarization