Heart

Heart

• muscular and functional device

• considered as a transport system

• it is surrounded by pericardium

Anatomy details of heart

• It is muscular pump which is located behind the chest bone in mediastinum cavity in the Thoracic cavity.

• Human heart weighs less then a pound, it is the size of your fist

• Our heart connected to Blood vessels which is (fuel line and transportation network)

• In mediastinum between second rib and fifth intercostal space

• On superior surface of diaphragm

• Two-thirds of heart to left of midsternal line

• Anterior to vertebral column and posterior to sternum

What are the deep two layered serous pericardium of the heart?

• two layers

  • parietal

  • visceral

what separates the pericardium layers?

• separated by pericardia cavity filled with fluid

Cardiovascular system

• means heart plus blood vessels

• delivers oxygen and nutrients to cells of body tissue through aorta(biggest artery in our body)

• it provides adequate perfusion

perfusion

delivery of blood per time per gram of tissue mL/min/g

Adequate perfusion

• sufficient delivery to maintain cells’ health

• Requires continual pumping of the heart and open, healthy

Blood vessels

• arteries

• veins

• capillaries

arteries

• carry blood away from the heart

• Most (not all) carry oxygenated blood

veins

• carry blood back to the heart

• Most (not all) carry deoxygenated blood

capillaries

• are sites of exchange of gases

• Between blood and air in lungs

• Between blood and body cells

Great vessels

• Transport blood to and from heart’s chambers

Which are the great vessels ?

• Pulmonary trunk

• aorta

• superior vena cava

• inferior vena cava

• pulmonary veins

Pulmonary trunk

• Transports blood from right ventricle

• Splits into pulmonary arteries

Aorta

Transports blood from left ventricle

Aorta

Transports blood from left ventricle

Pulmonary veins

Drain oxygenated blood into left atrium

Right side pump of the heart

• receives oxygen-poor blood from tissues

  • pumps to lungs to get rid of CO2,

  • pick up O2 via pulmonary circuit

Left side pump of the heart

• receives oxygenated blood from lungs

  • pumps to body tissues via systemic circuit

Two receiving chambers of heart

• right atrium

• left atrium

right atrium

• receives blood returning from systemic circuit

• Pectinate muscles

• Posterior and anterior regions separated by crista terminalis

left atrium

• receives blood returning from pulmonary circuit

• Pectinate muscles only in auricles

Pumping chamber of heart(departures)

• right ventricle

• left ventricle

Right ventricle

• pumps blood through pulmonary circuit

• most of anterior surface

left ventricle

• posteroinferior surface

• pumps blood through systemic circuit

• Pumps blood into Aorta (largest artery in body)

Congestive heart failure

• impaired ability of the heart to pump blood

• edema (swelling0 is a characteristic symptom

• Systemic edema

• pulmonary edema

Systemic edema

• May occur if right ventricle impaired

• More blood remaining in systemic circulation

• Additional fluid entering interstitial space

pulmonary edema

• May occur if left ventricle impaired

• More blood remaining in pulmonary circulation

• Swelling and fluid accumulation in the lungs

• Breathing difficulties and impaired gas exchange

Anatomy of heart

• Base (posterior surface) leans toward right shoulder

• Apex points toward left hip

• Apical impulse palpated between fifth and sixth ribs, just below left nipple

Pericardium

• Double-walled sac

• Superficial fibrous pericardium

• Protects, anchors to surrounding structures, and prevents overfilling

Parietal layer of pericardium

• lines internal surface of fibrous pericardium

Visceral layer (epicardium)

• on external surface of heart

• two layers separated by fluid-filled pericardial cavity (decreases friction)

Pericarditis

• Inflammation of pericardium

• Roughens membrane surfaces, as the beating heart rubs against its pericardial sac, its creates a cracking sounds called → pericardial friction rub (creaking sound) heard with stethoscope

• Cardiac tamponade or heart plug

• In some case a large amount of inflamed fluid seep into the pericardial cavity this Excess fluid sometimes compresses heart →limited blood  pumping ability

• Treatment is inserting a syringe into the pericardial cavity and draining of excessive fluid.

layers of the heart wall

• epicardium

• myocardium

• endocardium

Epicardium

visceral layer of serous pericardium

Myocardium

• Spiral bundles of contractile cardiac muscle cells

• Cardiac skeleton:

• crisscrossing, interlacing layer of connective tissue

  • Anchors cardiac muscle fibers

  • Supports great vessels and valves

  • Limits spread of action potentials to specific paths

endocardium

• continuous with endothelial lining of blood vessels

• Lines heart chambers and covers cardiac skeleton of valves

Chambers

• four in total

• two superiors atria

• two inferior ventricles

Interatrial septum

• separates atria

• fossa ovalis - remnant of foremen ovule of fetal heart

• hole that shunted blood from right to left atrium in fetal life

Interventricular septum

separates ventricles

Associated great vessels to the chambers

• coronary sulcus

• anterior interventricular sulcus

• posterior interventricular sulcus

coronary sulcus

• antrioventricular groove

• encircles junction of atria and ventricles

anterior interventricular sulcus

anterior position of interventricular septum

posterior interventricular sulcus

• landmark on posteroinferior surface

Atria: the receiving chambers

• auricles

• right atrium

• left atrium

• Small, thin walled

• contribute little to propulsion of blood

• 3 veins empty into right atrium

• 4 pulmonary veins empty into left atrium

Auricles

Appendages that increase atrial volume

3 veins that empty into right atrium

1. superior vena cava

2. inferior vena cava

3. coronary sinus

Ventricles: the discharging chambers

• most of the volume of heart

• two ventricles

• trabeculae carneae

• papillary muscles

• have thicker walls than atria

• actual pumps of heart

Trabeculae carneae

irregular ridges of muscle on walls

papillary muscles

 anchor chordae tendineae

chordae tendineae attached to right wall

Heart valves

• ensure unidirectional blood flow through heart

• open and close in response to pressure changes

• Has 2 atrioventricular valves

• Has 2 semilunar valves

• chordae tendineae

2 atrioventricular valves

They prevent black flow intro atria when ventricles contract

1. tricuspid valve

2. mitral valve

Tricuspid valve

• right AV valve

• located between Right atria and right ventricle

Mitral valve

• left atria valve, bicuspid valve

• located between left atria and left ventricle

Chordae tendineae of heart valves

• anchor cusps to papillary muscles

• hold valve flaps in closed position

Two semilunar valves

2. aortic semilunar valve

3. pulmonary semilunar valve

What does the Aortic semilunar and pulmonary semilunar valve do?

1. Prevent backflow into ventricles when ventricles relax

2. Open and close in response to pressure changes

2 conditions that severely weaken heart

1. incompetent valve or insufficient valve

2. valvular stenosis

Incompetent valve or insufficient valve

Blood backflows so force the to heart repumps same blood over and over B/C the valve does not close properly and blood backflows

Valvular stenosis (narrowing):

• The valve Stiff flaps – constrict opening →heart must exert more force to pump blood,

• Mostly happened in Mitral valve.

• Due to calcium salt deposits or scar tissue that forms following endocarditis and constrict the opening. And heart contract more forcedly then normal

• In both conditions the heat’s workload  and may weaken the heart severely over time.

• Faulty Valve(often Miral valve) replaced with mechanical, animal, or cadaver valve

Teenage athletes and sudden cardiac death

• Sudden death caused by undetected cardiovascular disease

• Most due to congenital heart defects and coronary artery anomalies

• Result of cardiomegaly, increased thickness of heart

• Symptoms:swelling, dizziness, arrhythmia, and shortness of breath

• Revealed by standard x-ray

• Confirmed with echocardiogram

Pathway of through the heart

• pulmonary circuit

• systemic circuit

• Equal volumes of blood pumped to pulmonary and systemic circuits

• anatomy of ventricles reflects differences

  • left ventricle walls 3 times thicker than right

    • pumps with greater pressure

Pulmonary circuit

• It is short and low pressure circulation

• Right atrium → tricuspid valve →right ventricle

• Right ventricle →pulmonary semilunar valve →pulmonary trunk →pulmonary arteries → lungs

• Lungs →pulmonary veins → left atrium

Systemic circuit

• Long and high friction circulation

• Left atrium →mitral valve → left ventricle

• Left ventricle →aortic semilunar valve → aorta

• Aorta → systemic circulation

Coronary circulation

• functional blood supply to heart muscle itself

  • delivered when heart relaxed

  • left ventricle received most blood supply

• are terminal supply varies a month individuals

• contains many anastomoses (junctions)

  • provide additional routes for blood delivery

  • cannot compensate for coronary artery occlusion

Coronary circulation: arteries

• Arteries arise from base of aorta

• 1- Left coronary artery branches → anterior interventricular artery and circumflex artery

  • Supplies interventricular septum, anterior ventricular walls, left atrium, and posterior wall of left ventricle

• 2- Right coronary artery branches → right marginal artery and posterior interventricular artery

  • Supplies right atrium and most of right ventricle

Coronary circulation: veins

• Cardiac veins collect blood from capillary beds

• Coronary sinus empties into right atrium; formed by merging cardiac veins

  • Great cardiac vein of anterior interventricular sulcus

  • Middle cardiac vein in posterior interventricular sulcus

  • Small cardiac vein from inferior margin

  • Several anterior cardiac veins empty directly into right atrium anteriorly

Atherosclerosis

plaques narrow coronary arteries

• can lead to angina or myocardial infarction

Coronary spasm

sudden narrowing of vessels

• can lead to angina or myocardial infarction

Angina pectoris : pain

• Usually on left side of chest, left arm, or jaw

• Usually referred pain when performing a strenuous activity

• Treatments induce vascular dilation

Myocardial infarction: heart attack

• Sudden and complete occlusion of coronary artery

• Myocardium deprived of oxygen, possible tissue death

• Excruciating chest pain radiating down left arm

• Weakness, shortness of breath, nausea, anxiety, and sweating

Microscopic anatomy of cardio muscle

• Cardiac muscle cells striated, short, branched, fat, interconnected disc,

1 (perhaps 2) central nuclei

• Connective tissue matrix (endomysium) connects to cardiac skeleton

  • Contains numerous capillaries

• T tubules wide, less numerous and SR simpler than in skeletal muscle

• Numerous large mitochondria (25–35% of cell volume)

• Intercalated discs - junctions between cells - anchor cardiac cells

Desmosomes

prevent cells from separating during contraction

Gap junctions

• allows ions to pass from cell to cell and electrically coupled adjacent cells

  • allows heart to be functional syncytium

  • behaves as single coordinated unit

Metabolism of cardiac muscle

• high demand of energy

• able to use different types of fuel molecules

• relies mostly on aerobic metabolism

High demand for energy in metabolism of cardiac muscle

•Extensive blood supply

•Numerous mitochondria

Myoglobin and creatine kinase

Able to use different types of fuel molecules in metabolism of cardiac muscle

Fatty acids, glucose, lactic acid, amino acids, and ketone bodies

Aerobic metabolism in cardiac muscle metabolism

•Makes it susceptible to failure when ischemic (oxygen is low)

Interference with blood flow to heart muscle can cause cell death

What are the three differences from skeletal muscle in cardiac muscle contraction?

1.  1% of cells have automaticity (auto rhythmicity) B/C

2. All cardiomyocytes contract as unit means

3. absolute refractory period length (250 ms) is longer than skeletal muscle

• Cardiac muscle has 6 protein pores(gap junctions) that allow it to act as a functional Syncytium(work as a unit)

• The middle layer of the heart which is called myocardium that actually contract   

• Cardiac muscle unlike skeletal muscle cells Have A and I bands

• During contraction some Ca enter the cell from ECS to ICS to trigger the release of Ca  in inside the cell.

• Depolarization wave also opens slow Ca2+ channels in sarcolemma → SR to release its Ca2+

• Ca2+ surge prolongs the depolarization phase (plateau)

• Action potential and contractile phase last much longer:

  • This allow blood ejection from heart

• Repolarization result of inactivation of Ca2+ channels and opening of voltage-gated K+ channels

  • Ca2+ pumped back to SR and extracellularly

1% of cells have automaticity (auto rhythmicity) B/C in cardiac muscle contraction

•Do not need nervous system stimulation

Can depolarize entire heart

All cardiomyocytes contract as unit means in cardia muscle contraction

• Myocardial cells:

• They all- or- none Law as applied to cardiac muscle  means:

• that the entire heart contracts as a unit

• it does not contract at all.

absolute refractory period length (250 ms) is longer than skeletal muscle which in cardiac muscle contraction

• Prevents tetanic contractions

• If this length was as the same length of Refractory period in Skeletal muscle?:

• It would cause also as titanic contraction, which would stop the heart’s pumping action.

Three similarities of cardiac muscle contraction with skeletal muscle

1. Depolarization opens few voltage-gated fast Na+ channels in sarcolemma

2. Depolarization wave down T tubules →SR to release Ca2+ →

3. Excitation-contraction coupling occurs

Similarities of cardiac muscle with skeletal muscle: Depolarization opens few voltage-gated fast Na+ channels in sarcolemma →

•Reversal of membrane potential from –90 mV to +30 mV

Brief and Na channels close rapidly

cardiac muscle similarities with skeletal muscle Excitation-contraction coupling occurs

Ca2+ binds troponin → filaments slid

Membrane potential steps

1. depolarization

2. plateau phase

3. repolarization

Depolarization

due to Na+ influx through fast voltage-gated Na+ channels. A positive feedback cycle rapidly opens many Na+ channels, reversing the membrane potential. Channel inactivation ends this phase.

Plateau phase

due to Ca2+ influx through slow Ca2+ channels.

This keeps the cell depolarized because few K+ channels are open

Repolarization

due to Ca2+ channels inactivating and K+

channels opening. This allows K+ efflux, which brings the membrane potential back to its resting voltage.

Cardiac muscle energy requirements

• Has many mitochondria

  • Great dependence on aerobic respiration

  • little anaerobic respiration ability

• Readily switches fuel source for respiration

  • Even uses lactic acid from skeletal muscles

Homoestatic imbalance: Ischemic cells cause → anaerobic respiration → lactic acid → causes:

High H+ concentration → high Ca2+ concentration

Homeostatic balance: High H+ concentration → high Ca2+ concentration causes:

→ Mitochondrial damage → decreased ATP production

→ Gap junctions close and causes→ fatal arrhythmias

Heart electrical events

• heart depolarizes and contracts without nervous system stimulation

• rhythm can be altered by autonomic nervous system

Coordinated heartbeats is a function of:

1. Presence of gap junctions

2. Intrinsic cardiac conduction system

Setting the basic Rhythm: Intrinsic cardiac conduction system

• Network of noncontractile (autorhythmic) cells

• Initiate and distribute impulses → coordinated depolarization and contraction of heart

Pacemaker cells

• autorhythmic cell

• A pacemaker is a small device that helps your heartbeat more regularly. It does this with a small electric stimulation that helps control your heartbeat.

• 1- Heart cells have unstable resting membrane potentials (pacemaker potentials or prepotentials) due to opening of slow Na+ channels and causes continuously depolarization

•  At threshold, Ca2+ channels open.

Happens when at threshold, Ca2+ channels open

• Explosive Ca2+ influx produces the rising phase of the action potential

• If we were able to artificially change the membrane permeability of pacemaker cells, so that Na influx is more rapid:

• Heart rate would increase due to decrease time of depolarization of the pacemaker cells.

Action potential initiation by pacemaker cells

1. pacemaker potential

2. depolarization

3. repolarization

pacemaker potential

Repolarization closes K+ channels and opens slow Na+ channels → ion imbalance →

depolarization

Ca2+ channels open → huge influx → rising phase of action potential