chp 18 Flashcards
The Pulmonary and Systemic Circuits
two side-by-side pumps
Pulmonary circuit (right side)
- receives oxygen-poor blood from tissues
Pumps blood to lungs to get rid of CO2, pick up O2
Systemic Circuit (left side)
- receives oxygenated blood from lungs
- Pumps blood to body tissues
Receiving chambers of heart
-Right atrium
Receives blood returning from systemic circuit
-Left atrium
Receives blood returning from pulmonary circuit
Pumping chambers of heart
-Right ventricle
Pumps blood through pulmonary circuit
-Left ventricle
Pumps blood through systemic circuit
Size, Location, and Orientation of Heart
Approximately the size of a fist
Weighs less than 1 pound
Location
-In mediastinum between second rib and fifth intercostal space
-Above diaphragm
-Two-thirds of heart to left of midsternal line
Anterior to vertebral column, posterior to sternum
base, apex, apical impulse
- Base (posterior surface) leans toward right shoulder
- Apex points toward left hip
- Apical impulse palpated between fifth and sixth ribs, just below left nipple
Coverings of the Heart
- Pericardium: double-walled sac that surrounds heart; made up of two layers
- Superficial fibrous pericardium: functions to protect, anchor heart to surrounding structures, and prevent overfilling
-Deep two-layered serous pericardium
–Parietal layer lines internal surface of fibrous pericardium
–Visceral layer (epicardium) on external surface of heart
Two layers separated by fluid-filled pericardial cavity
Why fluid?
Pericarditis
Cardiac tamponade
- Inflammation of pericardium
- Roughens membrane surfaces, causing pericardial friction rub (creaking sound) heard with stethoscope
- Cardiac tamponade
- -Excess fluid that leaks into pericardial space
- -Can compress heart’s pumping ability
- -Treatment: fluid is drawn out of cavity (usually with syringe)
Three layers of heart wall
-Epicardium: visceral layer of serous pericardium
-Myocardium: circular or spiral bundles of contractile cardiac muscle cells
-Endocardium: innermost layer; is continuous with endothelial lining of blood vessels
Lines heart chambers and covers cardiac skeleton of valves
Chambers and Associated Great Vessels
Internal features
Four chambers
Two superior atria
Two inferior ventricles
Interatrial septum:
Fossa ovalis
separates atria
remnant of foramen ovale of fetal heart
Interventricular septum:
separates ventricles
Surface features
- coronary sulcus
- Anterior interventricular sulcus
- Posterior interventricular sulcus
(atrioventricular groove)
Encircles junction of atria and ventricles
Anterior position of interventricular septum
Landmark on posteroinferior surface
Atria: the chambers
- auricles
- right atrium
- posterior portion contains
- posterier and anterior separated by
receiving
-Small, thin-walled chambers; contribute little to propulsion of blood
-Auricles: appendages that increase atrial volume
Right atrium: receives deoxygenated blood from body
Anterior portion is smooth-walled
Posterior portion contains ridges formed by pectinate muscles
Posterior and anterior regions are separated by crista terminalis
Three veins empty into right atrium:
- Superior vena cava: returns blood from body regions above the diaphragm
- Inferior vena cava: returns blood from body regions below the diaphragm
- Coronary sinus: returns blood from coronary veins
Left atrium
- pectinate muscles found
- ____ pulmonary viens
-pectinate muscles found only in auricles
receives oxygenated blood from lungs
-Four pulmonary veins return blood from lungs
Ventricles: right left where are they found -trabeculae carnea -paillary muscles
the discharging chambers
Make up most of the volume of heart
- Right ventricle: most of anterior surface
- Left ventricle: posteroinferior surface
- Trabeculae carneae: irregular ridges of muscle on ventricular walls
- Papillary muscles: project into ventricular cavity
- -Anchor chordae tendineae that are attached to heart valves
Ventricles: \_\_\_\_ walls than atria \_\_\_\_ pumps of heart right ventricle pumps blood into? left ventricle pumps blood into?
Thicker walls than atria
Actual pumps of heart
-Right ventricle
Pumps blood into pulmonary trunk
Left ventricle
Pumps blood into aorta (largest artery in body)
Heart Valves
- ensure
- two major types
- open and close when
- location of valves
-Ensure unidirectional blood flow through heart
-Open and close in response to pressure changes
-Two major types of valves
Atrioventricular valves located between atria and ventricles
Semilunar valves located between ventricles and major arteries
No valves are found between
major veins and atria; not a problem because:
Inertia of incoming blood prevents backflow
Heart contractions compress venous openings
Two atrioventricular (AV) valves prevent backflow into atria when ventricles contract
Chordae tendineae: anchor
- Tricuspid valve (right AV valve): made up of three cusps and lies between right atria and ventricle
- Mitral valve (left AV valve, bicuspid valve): made up of two cusps and lies between left atria and ventricle
cusps of AV valves to papillary muscles that function to:
Hold valve flaps in closed position
Prevent flaps from everting back into atria
Two conditions severely weaken heart:
Incompetant valve
Valvular stenosis
-Incompetent valve
Blood backflows so heart repumps same blood over and over
-Valvular stenosis
Stiff flaps that constrict opening
Heart needs to exert more force to pump blood
Defective valve can be replaced with mechanical, animal, or cadaver valve
volumes of blood are pumped to pulmonary and systemic circuits
Pulmonary circuit is___, ____-pressure circulation
Systemic circuit is___,
___-friction circulation
Anatomy of ventricles reflects differences
Equal volumes of blood are pumped to pulmonary and systemic circuits
Pulmonary circuit is short, low-pressure circulation
Systemic circuit is long, high-friction circulation
Left ventricle walls are 3× thicker than right
Pumps with greater pressure
Coronary circulation
delivered when
___ circulation in body
____ventricle receives ___
-Functional blood supply to heart muscle itself
-Shortest circulation in body
-Delivered when heart is relaxed
Left ventricle receives most of coronary blood supply
WHY?-biggest
Coronary arteries
heart receives ___ of blood supply
Both left and right coronary arteries arise from
Both _____ heart in coronary sulcus
Arteries contain many
- Both left and right coronary arteries arise from base of aorta and supply arterial blood to heart
- Both encircle heart in coronary sulcus
- Branching of coronary arteries varies among individuals
- Arteries contain many anastomoses (junctions)
- -Provide additional routes for blood delivery
- -Cannot compensate for coronary artery occlusion
- Heart receives 1/20th of body’s blood supply
Left coronary artery
supplies interventricular septum, anterior ventricular walls, left atrium, and posterior wall of left ventricle; has two branches:
- Anterior interventricular artery
- Circumflex artery
Right coronary artery
supplies right atrium and most of right ventricle; has two branches:
Right marginal artery
Posterior interventricular artery
Coronary veins
Cardiac veins collect blood from
Coronary sinus empties into
formed by merging
- 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
Angina pectoris
Thoracic pain caused by fleeting deficiency in blood delivery to myocardium
Cells are weakened
Myocardial infarction
Prolonged
Areas of cell death repaired with
(heart attack)
- Prolonged coronary blockage
- Areas of cell death are repaired with noncontractile scar tissue
Microscopic Anatomy
Cardiac muscle cells
- striated, short, branched, fat, interconnected
- One central nucleus (at most, 2 nuclei)
- Contain numerous large mitochondria (25–35% of cell volume)
- Sarcomeres
- Z discs, A bands, and I bands all present
- T tubules are wider, but less numerous
- -Enter cell only once at Z disc
-SR simpler than in skeletal muscle; no triads
Microscopic Anatomy
Intercalated discs
are connecting junctions between cardiac cells that contain:
- Desmosomes: hold cells together; prevent cells from separating during contraction
- Gap junctions: allow ions to pass from cell to cell; electrically couple adjacent cells
- -Allows heart to be a functional syncytium, a single coordinated unit
How Does the Physiology of Skeletal and Cardiac Muscle Differ? Similarities with skeletal muscle
- Muscle contraction is preceded by depolarizing action potential
- Depolarization wave travels down T tubules; causes sarcoplasmic reticulum (SR) to release
- Excitation-contraction coupling occurs
- – binds troponin causing filaments to slide
Differences between cardiac and skeletal muscle
- Some cardiac muscle cells are self-excitable
- -Two kinds of myocytes
- Contractile cells: responsible for contraction
- Pacemaker cells: noncontractile cells that spontaneously depolarize
- —Initiate depolarization of entire heart
- —-Do not need nervous system stimulation, in contrast to skeletal muscle fibers
functional syncytium
Heart contracts as a unit
Contraction of all cardiac myocytes ensures effective pumping action
–Skeletal muscles contract independently
Influx of calcium from extracellular fluids triggers CA release from SR
-Depolarization opens slow CA channels in sarcolemma, allowing CA to enter cell
- exracellular CA then causes SR to release its intracellular CA
- skeletal muscles do not use extracellular CA
Tetanic contractions
cannot occur in cardiac muscles
- Cardiac muscle fibers have longer absolute refractory period than skeletal muscle fibers
- –Absolute refractory period is almost as long as contraction itself
- —Prevents tetanic contractions
- —Allows heart to relax and fill as needed to be an efficient pump
The heart relies almost exclusively on _____ respiration
aerobic respiration
- Cardiac muscle has more mitochondria than skeletal muscle so has greater dependence on oxygen
- —Cannot function without oxygen
-Skeletal muscle can go through fermentation when oxygen not present
-Both types of tissues can use other fuel sources
Cardiac is more adaptable to other fuels, including lactic acid, but must have oxygen
18.5 Electrical Events of the Heart
Heart depolarizes and contracts without nervous system stimulation, although rhythm can be altered by autonomic nervous system
—Sympathetic and parasympathetic
Coordinated heartbeat is a function of:
- Presence of gap junctions
- Intrinsic cardiac conduction system
- Network of noncontractile (autorhythmic) cells
- Initiate and distribute impulses to coordinate depolarization and contraction of heart
Action potential initiation by pacemaker cells
- Cardiac pacemaker cells have unstable resting membrane potentials called pacemaker potentials or prepotentials
- Three parts of action potential
1.Pacemaker potential:
K+ channels are close, but slow na+ channels are open, curing interior to become more positive
2.Depolarization Ca channels open allowing huge influx of Ca leading to rising phase of action potential
3. Depolarization K+ channels open, allowing efflux of K+ and cell becomes more negative
Sequence of excitation
Cardiac pacemaker cells pass impulses, in following order, across heart in ~0.22 seconds
Sinoatrial node →
Atrioventricular node →
Atrioventricular bundle →
Right and left bundle branches →
Subendocardial conducting network (Purkinje fibers)
- Sinoatrial (SA) node
- Pacemaker of heart in right atrial wall
- -Depolarizes faster than rest of myocardium
- Generates impulses about 75×/minute (sinus rhythm)
- -Inherent rate of 100×/minute tempered by extrinsic factors
- Impulse spreads across atria, and to AV node
2.Atrioventricular (AV) node
- In inferior interatrial septum
- Delays impulses approximately 0.1 second
- –Because fibers are smaller in diameter, have fewer gap junctions
- –Allows atrial contraction prior to ventricular contraction
- Inherent rate of 50×/minute in absence of SAnode input
3.Atrioventricular (AV) bundle (bundle of His)
- In superior interventricular septum
- Only electrical connection between atria and ventricles
- -Atria and ventricles not connected via gap junctions
4.Right and left bundle branches
Two pathways in interventricular septum
Carry impulses toward apex of heart
Defects in intrinsic conduction system may cause:
- arrhythmias
- fibrillation
-Arrhythmias: irregular heart rhythms
Uncoordinated atrial and ventricular contractions
-Fibrillation: rapid, irregular contractions
Heart becomes useless for pumping blood, causing circulation to cease; may result in brain death
Treatment: defibrillation interrupts chaotic twitching, giving heart “clean slate” to start regular, normal depolarizations
To reach ventricles, impulse must pass through AV node
If AV node is defective, may cause a
heart block
-Few impulses (partial block) or no impulses (total block) reach ventricles
-Ventricles beat at their own intrinsic rate
Too slow to maintain adequate circulation
-Treatment: artificial pacemaker, which recouples atria and ventricles
Heartbeat modified by ANS via cardiac centers in medulla oblongata
Cardioacceleratory center
Cardioinhibitory center:
-Cardioacceleratory center: sends signals through sympathetic trunk to increase both rate and force
Stimulates SA and AV nodes, heart muscle, and coronary arteries
-Cardioinhibitory center: parasympathetic signals via vagus nerve to decrease rate
Inhibits SA and AV nodes via vagus nerves
Electrocardiograph
can detect electrical currents generated by heart
Electrocardiogram
ECG or EKG) is a graphic recording of electrical activity
-Composite of all action potentials at given time; not a tracing of a single AP
-Electrodes are placed at various points on body to measure voltage differences
12 lead ECG is most typical
main features p wave qrs complex t wave p-r wave s-t segment q-t interval
Main features:
P wave: depolarization of SA node and atria
QRS complex: ventricular depolarization and atrial repolarization
T wave: ventricular repolarization
P-R interval: beginning of atrial excitation to beginning of ventricular excitation
S-T segment: entire ventricular myocardium depolarized
Q-T interval: beginning of ventricular depolarization through ventricular repolarization
enlarged r waves
elevated or depressed S-T waves
prolonged q-t interval
Enlarged R waves may indicate enlarged ventricles
Elevated or depressed S-T segment indicates cardiac ischemia
Prolonged Q-T interval reveals a repolarization abnormality that increases risk of ventricular arrhythmias
Junctional blocks, blocks, flutters, and fibrillations are also detected on ECG
