Part 2 Terms

Cardiovascular system

Heart and blood vessels.

Base

Wide, superior portion of heart, large vessels attach here.

Apex

Tapered inferior end, tilts to the left.

Pulmonary circuit

Right side of heart, Carries blood to lungs for gas exchange and back to heart.

Systemic circuit

Left side of heart, Supplies oxygenated blood to all tissues of the body and returns it to the heart.

Pericardium

Double-walled sac that encloses the heart.

• Allows heart to beat without friction, provides room to expand, yet resists excessive expansion.

• Anchored to diaphragm inferiorly and sternum anteriorly.

Fibrous pericardium:

Outer wall, not attached to heart.

Serous pericardium:

Parietal layer: lines fibrous pericardium

Visceral layer (epicardium): covering heart surface.

Pericardial cavity: space between parietal and visceral layers of serous pericardium, filled with pericardial fluid.

Heart wall has three layers:

Epicardium: (visceral layer of serous pericardium): Serous membrane covering heart, contains coronary blood vessels.

Myocardium: Cardiac muscle, spirals around heart which produces wringing motion.

Endocardium: Smooth inner lining of heart and blood vessels, continuous with endothelium of blood vessels

Epicardium (visceral layer of serous pericardium)

Serous membrane covering heart, contains coronary blood vessels.

Myocardium:

Muscular, middle layer of the heart.

Cardiac muscle, spirals around heart which produces wringing motion.

Fibrous skeleton of the heart:

-Framework of collagenous and elastic fibers, provides structural support and attachment for cardiac muscle and anchor for valve tissue.

• Electrical insulation between atria and ventricles.

• Important in timing/coordination of contractile activity.

• Separates atria and ventricles

Endocardium:

Smooth inner lining of heart and blood vessels,

continuous with endothelium of blood vessels.

Right and left atria:

Two superior chambers, receive blood returning to heart.

Right and left ventricles:

Two inferior chambers, pump blood into arteries.

Interatrial septum

Wall that separates atria.

Pectinate muscles

Internal ridges of myocardium in right atrium.

Interventricular septum:

Muscular wall that separates ventricles.

Trabeculae carneae:

Internal ridges in both ventricles;may prevent ventricle walls from sticking together after contraction.

Valves

Ensure one-way flow of blood through heart.

Atrioventricular (AV) valves:

Control blood flow between atria and ventricles.

Right AV valve

Has three cusps (tricuspid valve).

Left AV valve

Has two cusps (mitral valve, formerly 'bicuspid').

Chordae tendineae:

Cords connect AV valves to papillary muscles on floor of ventricles, prevent AV valves from flipping or bulging into atria when ventricles contract.

Semilunar valves:

Control flow into great arteries; open and close because of blood flow and pressure.

Pulmonary semilunar valve:

An opening between the right ventricle and pulmonary trunk.

Aortic semilunar valve:

An opening between left ventricle and aorta.

Coronary circulation

Circulation of blood through the coronary blood vessels to deliver oxygen and nutrients to the heart muscle tissue.

- 1st part of aorta.

- Prone to getting clogged.

- Bringing blood to cardiac muscle (Cardiac).

Veins

Blood vessels that carry blood TO the heart. Thin walled & flaccid.

No pulse + low pressure vessels

Capacitance vessels.

Artery

Blood vessel carrying blood AWAYYYY from the heart.

Atria

Superior Chamber.

Receiving chamber of the heart.

There will always be Veins.

Blood coming INTO the heart.

Ventricles

Inferior Chamber.

Discharge chambers of the heart.

Blood leaving the heart, passing through arteries.

Length of absolute refractory period

Cardiac Muscle - 250 ms -> Allows Tetanus

Skeletal Muscle - 1-2 ms -> Prevents Tetanus

Myocardial Infarction (MI):

Heart Attack

Sudden death of a patch of myocardium resulting from long-term obstruction of coronary circulation.

• (MI) is responsible for ~27% of all deaths in the US.

• Atheroma (Blood clot or fatty deposit) often obstructs coronary arteries.

• Cardiac muscle downstream of the blockage dies.

• Heavy pressure or squeezing pain radiating into the left arm.

• Some painless heart attacks may disrupt electrical conduction pathways, leading to fibrillation and cardiac arrest.

Cardiomyocytes:

Muscle cells that make up the heart.

Striated, short, small, thick, branched cells.

One central nucleus.

- Repair of damage of cardiac muscle is almost entirely by fibrosis (scarring).

• Cardiac muscle is not good regenerators.

Intercalated discs:

Join cardiomyocytes end to end.

Mechanical junctions (desmosomes):

Tight mechanical linkages that prevent contracting cardiomyocytes from being pulled apart from each other.

• Act like zippers that hold the heart together

Electrical junctions (gap junctions):

Allow ions to flow between cells

• can stimulate neighbors, entire myocardium of either two atria or two ventricles acts like single, unified cell.

Interdigitating folds:

Folds interlock with each other.

Increase surface area of contact.

The Conduction System

Coordinates the heartbeat: Composed of internal pacemaker and conduction pathways through myocardium

Generates and conduction rhythmic electrical signals in the following order.

• Sinuatrial (SA) node:

• Atrioventricular (AV) node:

• Fibrous skeleton:

• Atrioventricular (AV) bundle (Bundle of His):

• Subendothelial conducting networks (Purkinje fibers):

Sinuatrial (SA) node:

Modified (Cardiac muscle cells) cardiomyocytes.

Located in right atrium near base of superior vena cava.

Pacemaker of the heart. Sets / Initates heart rate.

Pacemaker will initiate the heart rate, which then starts the signal that will spread to the Atria to structure #2 → Atrioventricular (AV) node:

Atrioventricular (AV) node:

Located near the right AV valve at the bottom of the interatrial septum.

• Electrical gateway to the ventricles.

• Due to the fibrous skeleton, The only way for the signal to go from the atria to the ventricle is through the AV Node. (This slows things down, traffic like)

Fibrous skeleton:

Insulator prevents currents from getting to ventricle by any other route.

Atrioventricular (AV) bundle (Bundle of His):

• Branches pass through the interventricular septum toward apex, forks into right and left bundle branches.

Subendothelial conducting networks (Purkinje fibers)

Nerve-like process spread throughout ventricular myocardium.

• Cardiomyocytes then pass signal from cell to cell through gap junctions.

  • takes electrical signal from the apex up through walls of the ventricles.

Systole

Contraction

Diastole

Relaxation

Sinus rhythm

Normal heartbeat triggered by the SA node, adult at rest is typically 70 to 80 beats per minute (bpm) Cranial nerve: (Vagal tone) - “Brake pedal”

Three phases to cardiomyocyte action potential:

Depolarization Phase (Very Breif):

Plateau Phase (200 to 250 ms):

Repolarization phase:

Depolarization Phase ( VERY BREIF):

Stimulus opens voltage-
regulated Na+ gates (Na+ rushes in), membrane depolarizes rapidly, action potential peaks at +30 mV, Na+ gates close quickly.

Plateau Phase (200 to 250 ms):

• Gives long absolute refractory period, so you have contraction and relaxation + coordinated pumping action from the heart.

• Sustains contraction for expulsion of blood from heart, voltage-gated slow Ca2+ channels open admitting Ca2+ which triggers opening of Ca2+ channels on sarcoplasmic reticulum (SR), Ca2+ (mostly from SR) binds to troponin triggering contraction.

Repolarization phase:

Ca2+ channels close, K+ channels open, rapid diffusion of K+ out of cell returns it to resting potential, has a long absolute refractory period of 250 ms (compared to 1 to 2 ms in skeletal muscle) that prevents wave summation and tetanus which would stop the pumping action of the hear.

Electrocardiogram (ECG or EKG):

- Measuring electrical activity as it sweeps through the heart.

• Composite of all action potentials of nodal and myocardial cells detected, amplified and recorded by electrodes on arms, legs, and chest.

Normal Electrocardiogram:

1: P Wave

2: QRS Complex

3: T Wave

P wave:

Atrial depolarization

SA node fires, atria depolarize and contract; atria systole (contraction) begins immediately after SA Signal.

QRS complex:

Ventricular depolarization

Complex shape of spike due to different thickness and shape of the two ventricles.

Ventricular systole (Contraction).

T Wave:

Ventricular repolarization + relaxation.

Ventricular fibrillation:

When there is no circulation, no coordinated pumping of the heart.

Serious arrhythmia caused by electrical signals traveling randomly.

- Heart cannot pump blood; no coronary perfusion.

- Hallmark of heart attack (MI).

- Kills quickly if not stopped.

Defibrillation:

Strong electrical shock with intent to depolarize the entire myocardium and reset heart to sinus rhythm.

(Not a cure for artery disease, but may allow time for other corrective action)

Papillary Muscle*

Finger like muscle

Cardiac cycle:

Two main variables govern which fluid of movement?

One complete contraction and relaxation of all four chambers of the heart.

Pressure causes flow and resistance opposes it.

Phases of cardiac cycle

1. Ventricular filling

2. sovolumetric contraction

3. Ventricular ejection

4. Isovolumetric relaxation

All completed in less than half a second.

Ventricular Filling

Ventricles expand and their pressure drops below the pressure within the atria.

AV Valves open and blood flows into ventricles.

Filling occurs in 3 phases

Rapid ventricular fillings: First one third. 1a

Diastasis: Second one third; slower filling, P wave occurs at the end of diastasis. 1b

Atrial systole: Final one tihrd; Atria contract, end diastolic volume (EDV) achieved in each ventricle. (~130 mL of blood) 1c

Congestive heart failure (CHF)

Results from the failure of either ventricle to eject blood effectively.

One side of heart cannot keep up with other side.

Usually due to a heart weakened by myocardial
infarction, chronic hypertension, valvular insufficiency, or congenital defects in heart structure.

Isovolumetric contraction

• Atria repolarize, relax and remain in diastole for rest of cardiac cycle.

• Ventricles depolarize, causing QRS complex, and
begin to contract.

• AV valves close as ventricular blood surges back
against the cusps.

• Heart sound S1 occurs at the beginning of this phase.

• “Isovolumetric” because although ventricles contract, they do not eject blood.

• Pressures in aorta and pulmonary trunk are still
greater than those in the ventricles.

• Cardiomyocytes exert force, but with all four valves closed, the blood cannot go anywhere.

Isovolumetric relaxation

During Ventricular Diastole.

• T wave ends and ventricles begin to expand.

• Blood from aorta and pulmonary trunk briefly flow
backward filling cusps and closing semilunar valves.

• Creates pressure rebound that appears as dicrotic notch in graph of artery pressure.

• Heart sound S2 occurs.

• “Isovolumetric” because semilunar valves are closed and AV valves have not yet opened.

• Ventricles are therefore taking in no blood

When AV valves open, ventricular filling begins again

Ventricular ejection

Begins when ventricular pressure exceeds arterial pressure and semilunar valves open.

• First: rapid ejection: blood spurts out of ventricles quickly.

• Then: reduced ejection: slower flow with lower pressure.

• Ejection lasts about 200 to 250 ms - corresponds to plateau phase of cardiac action potential.

• T wave of ECG occurs late in this phase.

• Stroke volume (SV) is ~70 mL.

• Ejection fraction is about 54% of EDV (130 mL)

• Remaining blood (~60mL) is end-systolic volume.
(ESV) = EDV − SV

Left Ventricular Failure

Blood backs up into the lungs causing pulmonary edema.

Unable to push out blood, causing backup in pressure.

• Shortness of breath or sense of suffocation.

Right Ventricular Failure

Blood backs up in the vena cava causing systemic edema.

- Either abdominal or extremities affected.

• Enlargement of the liver, ascites (pooling of fluid in abdominal cavity), distension of jugular veins,
swelling of the fingers, ankles, and feet.

• Eventually leads to total heart failure.

Blood Pressure is determined by 3 variables:

Cardiac Output:

Heart Rate X Stroke Volume

Blood Volume:

Regulated mainly by kidneys, except for beating o the heart, kidneys have the largest influence on blood pressure of any organ.

Peripheral resistance:

Any opposition that blood encounters as it passes through the vessels. Resistance hinges on three variables: blood viscosity, vessel length, vessel radius.

Resistance Vessels: Arterioles

Cardiac Output

Amount ejected out by each ventricle in 1 minute.

Red Blood Cell leaving the left ventricle will arrive back in the left ventricle in about 1 minute.

~ 4 to 6 L/min at rest (Resting Cardiac output: 5 L/min at rest)

Pulse

Surge of pressure produced by heartbeat that can be felt by palpating a superficial artery.

Trachycardia

Resting adult heart rate above 100 bpm

Fast Heart Rate

Stress, Anxiety, Drugs Fever

Bradycardia

Resting adult heart rate less than 60 bpm

Slow heart rate

In sleep, low body temperature, and endurance trained athletes.

Positive chronotropic agents

Factors that raise heart rate.

Negative chronotropic agents

Factors that slow down the heart rate.

Stroke Volume

Blood ejected from ventricle per beat.

End diastolic volume - End systolic volume = Stroke Volume

3 Variables govern stroke volume:

Preload, Contractility, Afterload.

Preload

The amount of tension in ventricular myocardium immediately before it begins to contract.

• Increased preload causes increased force of contraction

• Cardiomyocytes generates more tension during contraction

  As blood fills up the heart, as it gets stretched it will contract with more force to move extra blood out.

Frank Starling Law

Stroke Volume is proportional to End Diastolic Volume.

• Ventricles eject as much blood as they receive .

• The more they are stretched, the harder the force of contraction

Contractility

How hard the myocardium contracts for a given preload.

Force of contraction, not directly related to stretch

Positive inotropic agents

Increase contractility

Negative inotropic agents

Decrease contractility

Afterload

Blood pressure. Force that opposes ejection of blood from the ventricle.

High blood pressure = Increased after load

• largest part of afterload is is blood pressure in the aorta and pulmonary trunk

• Opposes opening of semilunar valves.

  Anything that impedes arterial circulation can also increase afterload.

  - Emphysema, chronic bronchitis, and black lung disease

Cor pulmonale

Right ventricular failure due to obstructed pulmonary circulation.

Capillaries

Connect smallest arteries to smallest veins to create a circuit.

Exchange Vessels: Gases, nutrients, wastes, and hormones pass between the blood and tissue fluid.

3 Capillary types are distinguished by permeability:

Continuous capillaries: Least permeable

Fenestrated capillaries: More permeable

Sinusoids: Leakiest

Arteries

Resistance Vessels

• Can slow down circulation because of their strong/resilient tissue structure.

Conducting (elastic or large arteries)

Biggest arteries, expand during systole, recoil during diastole to keep pressure on the blood.

Expansion takes pressure of smaller downstream vessels and recoil maintains pressure during relaxation, keeps blood flowing.

Distributing (Muscular or medium) arteries

Distribute blood to specific organs.

Resistance (small) arteries: Arterioles

smallest of the resistance arteries, control amount of blood to various organs.

Metarteriole

Shortcut allowing blood to get to capillary bed.

Continuous capillaaries

Least permeable

Occurs in most tissues, endothelial cells have tight junctions and form a continuous tube with intercellular clefs, allow passage of solutes such as glucose.

Fenestrated capillaries

More permeable

Occur in organs that require rapid absorption and filtration, endothelial cells riddled with holes called filtratiojn pores (fenestrations), allows passage of only small molecules, protein and larger particles stay in bloodstream

Sinusoids

Leakiest

Found. in liver, bone marrow, spleen , irregular blood- filled spaces with large fenestrations, allows proteins and new blood cells to enter the circulation. Large openings in between endothelium cells.

Capillary beds

Networks of 10 - 100 capillaries.

• Most control involves constriction of upstream arterioles.

• Precapillary sphincters control flow in capillary beds.

• When sphincters are relaxed, capillaries are well perfused with blood.

• When sphincters contract, they constrict the entry to the capillary and blood bypasses the capillary.

Blood Flow

Amount of blood flowing through an organ, tissue, or blood vessel in a given time (mL/min)

• At rest, total flow is constant & equal to cardiac output (5.25 L/min)

Important for delivery of nutrients, oxygen, & removal of metabolic wastes.

• Hemodynamics

Hemodynamics:

Physical properties of blow flow based on pressure & resistance.

• The greater the pressure difference between two points, the greater the flow; the greater the resistance, the less the flow.

Blood Pressure (BP):

Force blood exerts against a vessel wall.

BP tends to rise with age

• Measured at brachial artery using sphygmomanometer.

• Two pressures are recorded.

  • Systolic pressure

  • Diastolic pressure

Systolic Pressure:

Peak arterial BP (Blood pressure) taken during ventricular systole. (contraction)

• Contraction

Diastolic pressure:

Minimum arterial BP (Blood pressure) taken during ventricular diastole. (relaxation)

• Relaxation

Pulse pressure:

Difference between systolic and diastolic pressure.

Arteriosclerosis:

Stiffing of the arteries due to deterioration of elastic tissues of the artery walls.

• Increase resistance