Heart Structure and Function review

• Endocardium
• Myocardium
• Epicardium

*The heart is enclosed in a fibroserous sac called the pericardium

The endocardium

*It is continuous with the endothelial lining of blood vessels entering and leaving the heart

The myocardium

The epicardium

The pericardium

60mL/min or 5L/min

The atria are receiving chambers

The right atrium receives deoxygenated blood from the upper part of the body by way of the superior vena cava, and from the lower part of the body by way of the inferior vena cava

*The right atrium also receives blood from the heart muscle through the coronary sinus

The ventricles are distributing chambers

pulmonary veins

After blood is reoxygenated in the lungs, it flows freely from the four pulmonary veins into the left atrium.

Blood then flows through an opened mitral valve into the left ventricle during ventricular diastole

With systolic contraction, the left ventricle generates enough pressure to close the mitral valve and open the aortic valve. Blood is then propelled into the aorta and into the systemic arterial circulation.

pulmonary circulation

*The right ventricle is small and thin walled because it contracts against minimal pressure

the systemic circuit

*The left ventricle is more muscular and thick walled because it contracts against relatively high pressure

• *Atrioventricular (AV) Valves
• -tricuspid valve
• -mitral (bicuspid) valve

• *Semilunar Valves
• -pulmonic valve
• -aortic valve

• 
• The superior and inferior vena cava, and veins and sinuses within the heart itself dump deoxygenated blood into the right atrium.

It goes from the right atrium to the right ventricle to the lungs.

Oxygenated blood returns to the left atrium to the left ventricle then out to the body

• *How does it get from atrium to venticle on both sides? Toliet Paper My Ass
• Tricuspid, Pulmonic, Mitral (bicuspid), Aortic

The Pathway of Blood to and from the Heart

• 1. Blood that has circulated through the body, which has lost its oxygen
• and collected carbon dioxide, enters through the vena cava into the
• right atrium of the heart.

2. The right atrium contracts (atrial systole) and pumps the blood through the tricuspid valve and into the right ventricle.

• 3. The right ventricle then pumps blood through the pulmonary artery
• into the lungs.

• 4. In the lungs, tiny blood vessels called capillaries absorb carbon dioxide
• from the blood and replace it with oxygen.

• 5. Oxygenated blood then flows through the pulmonary vein and into
• the left atrium.

• 6. Oxygenated blood then pumps through the mitral valve and into the
• left ventricle.

• 7. The left side of the heart contracts the strongest to send blood out the
• left ventricle and through the aortic arch on its way to all parts of the
• body. At this point, there are a few options for the blood flow...blood
• can be pumped
• • through the carotid artery and into the brain.
• • through the auxiliary arteries and into the arms.
• • through the aorta and into the torso and legs.

• 8. Blood will then move through the arteries, then through capillaries,
• and then return through the veins.

9. Deoxygenated blood will then return to the heart, and the cycle repeats.

• The Mitral (bicuspid) Valve separates the LA and LV
• 

The Tricuspid valve separates the the RA and RV (Tri Right)

The pulmonic valve separates the right ventricle and pulmonary artery

• Intima: the inner lining composed of a layer of endothelial cells next to the blood and an elastic layer that joins the media
• Media: the middle layer of muscle and elastic tissue
• Adventitia: the outer layer of connective tissue

• Smooth muscle cells: maintain blood pressure and blood flow. It contracts and relaxes in response to numerous stimuli, including local and circulating mediators.
• *Overall, regulation of tone in vascular smooth muscle depends on the intracellular concentration of calcium ions. Increased intracellular calcium leads to increased vascular tone.

• Endothelial cells: one function is structural, in which the cells act as a permeability barrier and regulate passage of molecules and cells acoss the blood vessel wall
• The second function is metabolic, in which the cells secrete opposing mediators that maintain a balance between bleeding and clotting of blood, constriction and dilation of blood vessels, and promotion and inhibition of vascular cell growth and inflammation

Peripheral vascular resistance

Arteries contain a layer of smooth muscle (the media) and are sometimes called resistance vessels. Their efficiency depends on their patency and ability to constrict or dilate in response to various stimuli.

The degree of constriction or dilation (vasomotor tone) determines peripheral vascular resistance, which is a major determinant of blood pressure.

The aortic valve separates the left ventricle and aorta

• A (arteries) – Away Blood is moving away from the heart.
• V (veins) – Toward Blood is moving toward the heart.
• Capillaries are small blood vessels that connect the arteries and veins.

• The left anterior descending (LAD)
• The left circumflex (LCX)

Through the coronary arterial system

*The coronary arteries originate at the base of the aorta in the aortic cusps just beyond the aortic valve

*The left main coronary artery divides into two branches: the left anterior descending (LAD) and the left circumflex coronary artery (LCX)

Diastole, when coronary vascular resistance is minimized

*To maintain adequate blood flow through the coronary arteries, mean arterial pressure (MAP) must be at least 60-70mm Hg to maintain perfusion of major body organs

• automaticity
• excitability
• conductivity
• contractility
• refractoriness

The phases of the cardiac cycle are related to changes in pressure and volume in the left ventricle during filling (diastole) and ventricular contraction (systole).

Myocardial contraction results from the release of large numbers of calcium ions from the sarcoplasmic reticulum and from the blood. These calcium ions then diffuse into the myofibril sarcomere (the contractile unit of the myocardial cell) which produces myocardial contraction

Cardiac muscle relaxes when calcium ions are pumped back into the sarcoplasmic reticulum, causing a decrease in the number of calcium ions around the myofibrils.

Diastole

Systole

• cardiac output (CO)
• This is the amount of blood pumped from the left ventricle each minute
• *Cardiac output depends on the relationship between heart rate and stroke volume CO=HR x SV

Cardiac Output (CO)

• Cardiac output is the amount of blood pumped from the left ventricle each minute
• It depends on the relationship between the heart rate and stroke volume

Between 60 and 100 beats/min

Autonomic nervous system (ANS)

The ANS adjusts rapidly when necessary to regulate cardiac output

The parasympathetic (vagus nerve)

The parasympathetic (vagus nerve) system slows the HR, whereas sympathetic stimulation increases the HR

Beta Blockers

Stroke volume

HR, preload, afterload, and contractility influence stroke volume and, ultimately, affecting cardiac output

Preload

The stretch imposed on the muscle fibers results from the volume contained within the ventricle at the end of diastole.

Preload is determined by the amount of blood returning to the heart from both the venous system (right heart) and the pulmonary system (left heart) (known as the left ventricular end-diastolic volume)

Starling's law of the heart: The more the heart is filled during diastole, the more forcefully it contracts.

Afterload

The amount of resistance is directly related to arterial blood pressure and the diameter of the blood vessels

Myocardial contractility

• Contractility is increased by factors such as sympathetic stimulation, calcium release, and positive inotropic drugs.
• It is decreased by factors such as hypoxia and acidemia

• Provides a route for blood to travel from the heart to nourish various body tissues
• Carries cellular wastes to the excretory organs
• Allows lymphatic flow to drain tissue fluid back into circulation
• Returns blood to the heart for recirculation

*The vascular system is divided into the: arterial system and the venous system

The arterial system

• At the tissue level, nutrients, chemicals, and body defense substances are distributed and exchanged for cellular waste products
• The arteries then transport the waste to excretory organs like the kidneys and lungs

These vessels also contribute to temperature regulation in the tissues because blood can be either directed toward the skin to promote heat loss or diverted away from the skin to conserve heat.

• Blood Pressure
• Volume, adequate contracting ventricles, and vascular tone are necessary to maintain blood pressure

• BP is determined primarily by the cardiac output and by the resistance in the arterioles
• Blood pressure=Cardiac output X Peripheral vascular resistance

Any factor that increases cardiac output or total peripheral vascular resistance increases the blood pressure

The autonomic nervous system (ANS), which excites or inhibits sympathetic nervous system activity in response to impulses from chemoreceptors and baroreceptors

The kidneys, which sense a change in blood flow and activate the renin-angiotensin-aldosterone mechanism

The endocrine system, which releases various hormones (e.g., catecholamine, kinins, serotonin, histamine) to stimulate the sympathetic nervous system at the tissue level

Systolic Blood Pressure

It is a measure of how effectively the heart pumps and is an indicator of vascular tone

Diastolic Blood Pressure

• Baroreceptors: located in the arch of the aorta and internal carotid arteries. Baroreceptors are stimulated when the arterial walls are stretched by an increased blood pressure. Impulses from these baroreceptors inhibit the vasomotor center located in the pons and medulla.
• Inhibition of the vasomotor center drops blood pressure

• Peripheral chemoreceptors: are located in the carotid arteries and along the aortic arch
• These receptors are sensitive to hypoxemia (decreased O2). When stimulated, these chemoreceptors send impulses along the vagus nerves to activate a vasoconstrictor response and raise blood pressure

The central chemoreceptors in the respiratory center of the brain are stimulated by hypercapnia (increased CO2) and acidosis *CO2 has a stronger effect on the CNS than hypoxia

• Stretch receptors: located in the vena cava and right atrium are sensitive to pressure or volume changes.
• When a patient is hypovolemic, stretch receptors in the blood vessels sense a reduced volume or pressure and send fewer impulses to the CNS.
• This reaction stimulates the sympathetic nervous system to increase the heart rate and constrict the peripheral blood vessels which increases blood pressure

• When renal blood flow or pressure decreases, the kidneys retain sodium and water.
• Blood pressure rises because of fluid retention and activation of the renin-angiotensin-aldosterone mechanism which results in vasoconstriction and sodium retention (thus fluid retention).

Vascular volume is also regulated by the release of antidiuretic hormone (vasopressin) from the posterior pituitary gland

To complete the circulation of blood by returning blood from the capillaries to the right side of the heart

• Veins have the ability to accommodate large shifts in volume with minimal changes in venous pressure.
• This is what allows the administration of IV fluids and blood transfusions, as well as to maintain pressure during blood loss and dehydration.

Skeletal muscles in the extremities.

The superior and inferior vena cava do not have valves, which allows unimpeded blood flow return to the heart

Calcification and mucoid degeneration occur, especially in mitral and aortic valves

• Nursing Interventions:
• -Assess heart rate and rhythm and heart sounds for murmurs (murmurs may be detected before other symptoms. Valvular abnormalities may result in rhythm changes)
• -Ask patient about dyspnea

• Pacemaker cells decrease in number. Fibrous tissue and fat in the SA node increase
• Few muscle fibers remain in the atrial myocardium and bundle of His.
• Conduction time increases

• Nursing Interventions:
• Assess the ECG and heart rhythm for dysrhythmias or a heart rate less than 60 beats/min (The SA node may lose its inherent rhythm)
• (Atrial dysrhythmias occur in many older adults; 80% of older adults experience premature ventricular contractions or PVCs)

• The size of the left ventricle increases
• The left ventricle becomes stiff and less distensible
• Fibrotic changes in the left ventricle decrease the speed of early diastolic filling by about 50%

• Nursing Interventions
• -Assess the ECG for a widening QRS complex and a longer QT interval. (Ventricular changes result in decreased stroke volume, ejection fraction, and cardiac output during exercise; the heart is less able to meet increased oxygen demands)
• -Assess the heart rate at rest and with activity (Maximum heart rate with exercise is decreased)
• -Assess for activity intolerance (The heart is less able to meet increased oxygen demands)

The aorta and other large arteries thicken and become stiffer and less distensible. Systolic blood pressure increases to compensate for the stiff arteries

Systemic vascular resistance increases as a result of less distensible arteries; therefore the left ventricle pumps against greater resistance, contributing to left ventricular hypertrophy

• Nursing Interventions:
• -Assess blood pressure (Hypertension may occur and must be treated to avoid target organ damage)
• -Assess for activity intolerance and shortness of breath
• -Assess the peripheral pulses

Baroreceptors become less sensitive

• Nursing Interventions:
• -Assess blood pressure lying and then sitting or standing (Orthostatic postural and postprandial changes occur because of ineffective baroreceptors)
• -Assess for dizziness when patient changes from a lying to a sitting or standing position (Changes may include blood pressure decreases of 10mm Hg or more, dizziness, and fainting)
• -Teach patient to change positions slowly

• "Many Things Are Possible"
• Mitral, Tricuspid, Aortic, Pulmonic

• "All Prostitutes Take Money"
• Aortic (RUSB)
• Pulmonary (LUSB)
• Tricuspid (LLSB)
• Mitral (Apex)

Tricuspid heart valve and tri-lobed lung both on the right side

Bicuspid and bi-lobed lung both on the left side