A&P - Cardiovascular System

Functions of the circulatory system

• Brings oxygen, nutrients, and hormones to cells

• Fights infections

• Regulates body temperature

Facts about the heart

• Made of cardiac muscle

• Average of 65-85 bpm (beats per min)

Chambers of the heart

• 4 chambers: Left and right atriums, left and right ventricles

• Right side (in anatomical position): Pumps deoxygenated blood to the lungs

• Left side (in anatomical position: Pumps oxygenated blood to the body

Valves of the heart

4 valves:

• Atrioventricular (AV):

  • Tricuspid

  • Bicuspid (mitral)

• Semilunar:

  • Pulmonary

  • Aortic

Tricuspid valve

The valve that separates the right atrium from the right ventricle

Bicuspid valve

The valve that separates the left atrium from the left ventricle

AKA “mitral valve”

Pulmonary valve

The valve that separates the right ventricle from the pulmonary artery leaving the heart

Aortic valve

The valve that separates the left ventricle from the aorta leaving the heart

Main blood vessels of the heart

• 2 veins:

  • Superior and inferior vena cavas

• 2 arteries:

  • Pulmonary artery

  • Aorta

Superior and inferior vena cavas

The veins of the heart that brings deoxygenated blood back to the heart through the right atrium

Pulmonary artery

The artery that takes deoxygenated blood away from the right ventricle in the heart and moves it to the lungs

Aorta

The artery that takes oxygenated blood away from the left ventricle in the heart and distributes it throughout the body

Interventricular septum

The muscular wall in the heart separating the left and right ventricles

Chordae tendineae

Thin, fibrous strands of connective tissue that anchor the AV valves’ leaflets to papillary muscles within the ventricles

AKA “heartstrings”

Papillary muscles

Specialized, pillar-like muscles in the ventricles that prevent AV valves prolapse and regurgitation during systole

Blood flow through the heart (deoxygenated)

1. Deoxygenated blood enters the right atrium via the superior and inferior vena cavas and coronary sinuses

2. The right atrium contracts, forcing blood through the tricuspid valve and into the right ventricle

3. The right ventricle contracts, forcing blood through the pulmonary valve and into the pulmonary trunk and arteries

4. The pulmonary arteries carry blood to the lungs, where it can ride itself of excess carbon dioxide and pick up a new supply for oxygen

Blood flow through the heart (oxygenated)

1. Freshly-oxygenated blood returns back to the heart in the left atrium through the pulmonary veins

2. The left atrium contracts, forcing blood through the bicuspid (mitral) valve into the left ventricle

3. The left ventricle contracts, forcing blood through the aortic valve and into the aorta for distribution throughout the body

Heartbeat/cardiac cycle

• Atria systole

• Atria diastole

• Ventricular systole

• Ventricular diastole

Actions of the heart

• Atria contracts (atria systole) while ventricle relaxes (ventricular diastole)

• Ventricle (ventricular systole) contracts while atria relaxes (atria diastole)

• Then, the atria and ventricles both relax for a brief period

Atria systole

Contraction of atria

Atria diastole

Relaxation of atria

Ventricular systole

Contraction of ventricle

Ventricular diastole

Relaxation of ventricle

Sounds of the heart

• Due to vibrations in heart tissues as the valves close

• Can be described as “lub-dub” sounds

  • “Lub” → Ventricular systole

  • “Dub” → Atrioventricular (tricuspid and bicuspid) valves closing

Heart murmur

An abnormal heart sound due to valve damage

Caused by valve stenosis or valve prolapse

Valve stenosis

A serious, progressive heart condition where the aortic valve narrows, restricting blood flow from the hear to the body

It causes the heart to work harder, leading to thickened heart muscle, potential heart failure, and death if untreated

Valve prolapse

A heart condition where the bicuspid (mitral) valve’s flaps (leaflets) are too stretchy, causing them to bulge or flop back into the left atrium during contraction, often resulting in leakage (regurgitation)

Blood supply to the heart

• The first branches off of the aorta (which carries freshly oxygenated blood) are the left and right coronary arteries that feed the heart muscle itself

• Branches of the coronary arteries feed many capillaries of the myocardium

• Blood flows best during the relaxation periods of the heart because contraction squeezes the blood vessels closed

Heart attack

The death of cardiac muscle cells, caused by plaque dislodges blocking a coronary artery

• Blocking of coronary artery results in cardiac muscle cells starved for oxygen, resulting in death

• After, scar tissue forms where cardiac muscle cells die, reducing function of the heart

• Severity of this disorder depends on the size and area supplied by the artery

• Risk factors: Smoking, high blood pressure (bp), high LDL cholesterol, diabetes

AKA “myocardial infarction (MI)”

Atherosclerosis

Plaque buildup that clogs arteries, reducing or even stopping bloodflow

• These plaques can break off, causing a heart attack or stroke

• Risk factors: Smoking, high blood pressure (bp), high LDL cholesterol, diabetes

AKA “coronary artery disease”

Stroke

A blood vessel in the brain is blocked (by dislodged plaque, or bursts, starving the cells of oxygen)

• Symptoms: Numbness, vision changes, speech changes, confusion

• Risk factors: Smoking, high blood pressure (bp), high LDL cholesterol, diabetes

Cardiac conduction system

Specialized cardiac muscle tissue conducts impulses throughout the myocardium and compromises this system

1. Sinoatrial (SA) node fires

2. Excitation spreads through atrial myocardium

3. Atrioventricular (AV) node fires

4. Excitation spreads down AV bundle

5. Purkinje fibers distribute excitation through ventricular myocardium

Pacemaker physiology

• Each depolarization of the SA node sets off one heartbeat

  • At rest: Fires every 0.8 second or 75 bpm

• SA node is the system’s pacemaker

• SA node does not have a stable resting membrane potential

  • Starts at -60 mV and drifts upward from a slow inflow of Na⁺

  • When it reaches threshold of -40 mV, voltage-gated fast Ca²⁺ and Na⁺ channels open

    • Faster depolarization occurs peaking at 0 mV

    • K⁺ channels then open and K⁺ leaves the cell, causing repolarization

    • Once K⁺ channels close, pacemaker potential starts over

Electrocardiogram (ECG/EKG)

A recording of electrical changes that occur during a cardiac cycle

P wave

The first recorded wave of electrical changes in an ECG/EKG, which corresponds to the depolarization of the atria which leads to the contraction of the atria

QRS complex

In an ECG/EKG, this recorded complex corresponds to the depolarization of the ventricles, leading to the contraction of the ventricles and hides the repolarization of the atria

T wave

The last major recorded wave in an ECG/EKG that ends the pattern, which corresponds to ventricular repolarization and relaxation

What an ECG/EKG tells us

The intervals between the waves and the size of the waves give information about the heart’s ability to conduct impulses

Arrhythmia

An abnormal heart rhythm, with irregular or skipped heartbeats

• Cause: Normally, the heart uses electrical signals created in the SA node in the right atria to begin a heartbeat. However, irregular firing of the SA node causes abnormal rhythm. The atrial form of this condition are less dangerous than the ventricular form of this condition.

• Risk factors: Generally random, but factors are stimulants (ex. caffeine), fevers, stress, or genetic disorders

Tachycardia

A resting heart rate of 100+ bpm

Brachycardia

A resting heart rate of less than 60 bpm

Blood vessels

Carries blood to cells, lined with smooth muscle tissue and epithelium, simplest and most common route

Heart → arteries → arterioles → capillaries → venules → veins

Arteries

Carries oxygenated blood away from the heart to the rest of the body

• Has strong, thick, elastic walls adapted for high pressure that becomes smaller as they divide and give rise to arterioles

  • Walls of arterioles get thinner as they approach capillaries

• To regulate blood flow and pressure: Capable of vasoconstriction as directed by sympathetic impulses, and capable of vasodilation as directed by parasympathetic impulses

Aneurysm

A weak point in an artery or the heart wall

• Forms a thin-walled, bulging sac that pulsates with each heartbeat and may rupture

• Dissecting aneurysm: Blood accumulates between the tunics of the artery and separates them

• Most common sites: Abominal aorta, renal arteries, and arterial circle at the base of the brain

• Can cause pain by putting pressure on other structures

• Can rupture, causing a hemorrhage

• Results from congenital weakness of the blood vessels or result of trauma or bacterial infections (ex. syphilis)

  • Most common cause is atherosclerosis and hypertension (high blood pressure)

Capillaries

The smallest of the blood vessels (some have diameters as small as one red blood cell) that branch off arterioles, taking blood to cells where nutrients and gases are exchanged

• Their permeability varies from one tissue to another: Generally more permeability in the liver, intestines, and certain glands, while less permeability in muscle

• Areas with a great deal of metabolic activity have higher densities of these blood vessels

• Precapillary sphincters: Regulates the amount of blood entering a capillary bed, controlled by oxygen concentration in the area

  • If blood is needed elsewhere in the body, the capillary beds in less important areas are shut down

Hydrostatic pressure

Drives the passage of fluids and very small molecules out of the capillary at the arteriole end by diffusion

Osmotic pressure

At the venule end, osmosis causes much of the tissue fluid to return to the bloodstream

Venules

Leading from capillaries, merge to form veins that return deoxygenated blood to the heart

Veins

Carries deoxygenated blood towards the heart

• Have the same 3 layers as arteries have, except that the muscle layer is thinner, and have a flap-like valve inside to prevent backflow of blood

• The lumen of the vein is larger than an artery’s

• Don’t carry high-pressure blood

• Also functions as blood reservoirs

• Greater capacity for blood containment than arteries

• Thinner walls, flaccid, less muscular and elastic tissue

• Collapses when empty, expands easily

• Has steady blood flow

• Merges to form larger veins

• Subjected to relatively low blood pressure

  • Remains 10 mm Hg with little fluctuation

Varicose veins

Blood pools in the lower legs in people who stand for long periods of time, as it stretches the veins

• Cusps of the valves pull apart in enlarged superficial veins further weakening vessels

• Blood backflows and further distends the vessels, causing their walls to become weak and develop into these type of veins

• Hereditary weakness, obesity, and pregnancy also promote problems

• Hemorrhoids: Varicose veins of the anal canal

Treatment for varicose veins

• Sclerotherapy

• Laser surgery

Sclerotherapy for varicose veins

Procedure where the doctor injects the veins with a solution that scars and closes the veins, causing the blood to reroute through healthier veins

• Vein ligation/striping

Laser surgery for varicose veins

Procedure that sends strong bursts of light into the vein that make the vein slowly fade and disappear, often less effective than sclerotherapy, but no incisions or needles are used

Blood pressure

A measure of the force exerted by the blood on the wall of the arteries using a sphygmomanometer

• Pressure decreases as distance from the left ventricle increases

• Rise with age: Arteries are less distensible and absorb less systolic force

• Determined by cardiac output, blood volume, peripheral resistance, and blood viscosity

Systolic pressure/diastolic pressure (ex. 120/80)

Systolic pressure

The result of the contraction of the ventricles (normal is 110-140)

Diastolic pressure

The relaxation of the ventricles (normal is 70-90)

Hypertension

High blood pressure with diastolic pressure over 90

• Chronic if resting blood pressure is greater than 140/90

• Consequences: Atherosclerosis, and can weaken small arteries and cause aneurysms

• Why it’s dangerous: Excessive pressure can cause arteries to thicken, blood vessels to weaken and rupture, leading to heart failure, stroke, kidney failure, and loss of sight when vessels in eye burst

• Risk factors: Genetics, obesity, limited physical activity, smoking, alcohol consumption, certain medications

Hypotension

Chronic low resting blood pressure caused by blood loss, dehydration, and/or anemia

Cardiac output

Stroke volume x heart rate

• Stroke volume: The amount of blood discharged from the ventricles with a contraction (about 70 mL)

• Heart rate: Bpm (average is 72 bpm)

Blood volume

The sum of the formed elements and plasma volume in vascular system

• Varies with age, body size, gender, and dehydration

• Normally, blood pressure is directly proportional to the volume of blood within the cardiovascular system

Peripheral resistance

The opposition to flow that blood encounters in vessels away from the heart

• Vessel radius: The most powerful influence over flow

  • Vasoconstriction: Increases resistance, increases blood pressure

  • Vasodilation: By relaxation of smooth muscle, decreases resistance, decreases blood pressure

Blood viscosity

Greater the viscosity, greater the resistance to flow

• Increase in blood cells and plasma

• Dehydration also increases viscosity

Control of blood pressure

• Blood pressure is determined by cardiac output times peripheral resistance; BP = CO (heart rate X stroke volume) x PR

• The body maintains normal BP by adjusting cardiac output and peripheral resistance

• Frank-Starling law of the heart: The relationship between fiber length and force of contraction

  • As blood enters the heart, the walls are stretched, giving a stronger contraction

  • Stronger contraction increases stroke volume and therefore increase cardiac output as well

• Baroreceptors sense change in BP

  • The volume of blood that enters the right atrium is normally equal to the volume leaving the left ventricle

  • If arterial pressure increases, the cardiac center of the medulla oblongata sends parasympathetic impulses to slow the heart rate (cardioinhibitory reflex)

  • If arterial pressure drops, the medulla oblongata sends sympathetic impulses to increase heart rate to adjust blood pressure (cardioaccelerator reflex)

• Other factors (ex. emotional upset, exercise, rise in temperature) can result in increased cardiac output and BP

• Peripheral resistance also controls BP

  • Sympathetic nerves change the diameter of arterioles in response to BP changes

  • Vasodilation decreases PR and BP, while vasoconstriction increases PR and BP

• The vasomotor center of the medulla oblongata can adjust the sympathetic impulses to smooth muscles in arteriole walls, adjusting BP

• Certain chemicals can also affect PR by affecting precapillary sphincters and smooth muscle of arteriole walls

  • Increased CO², decreased O², and decreased pH causes vasodilation into tissues with high metabolic needs

  • Epinephrine and norepinephrine cause vasoconstriction

Hormonal control of blood pressure

• Hormones influence blood pressure through vasoactive effects and regulating water balance

• Angiotensin II: Potent vasoconstrictor that raises BP, promotes Na⁺ and water retention by kidneys, and increases blood volume and pressure

• Atrial natriuretic peptide: Increases urinary sodium excretion, reducing blood volume and promotes vasodilation, lowering BP

• Antidiuretic (ADH) hormone: Pathologically high concentrations that are also vasoconstrictors that promotes water retention and raises BP

• Epinephrine and norepinephrine: Most blood vessels bind to α-adrenergic receptors causing vasoconstriction, while skeletal and cardiac muscles bind to β-adrenergic receptors causing vasodilation