the heart

Question 1

what is the circulatory system and the two types

Answer 1

• link exchange surfaces (lungs) with cells throughout the body
• open: heart, gross blood vessels, released straight into tissues (small animals, not efficient)
• closed: more complex (mammals), muscular pump (heart), arteries, veins and capillaries

Question 2

what are the advantages of a closed circulatory system

Answer 2

• nutrient delivery and waste removal is more rapid (kidney, liver, lungs)
• resistant control selectively directs blood (maintain BP, vasoconstriction / dilation)
• cellular elements aid in transport (albumin)
• support higher levels of metabolic activities than open (mammals)

Question 3

describe the evolution of the heart

Answer 3

• from 2 to 4 chambers
• increase separation of blood flow to gas exchange organs and rest of body
• fish: 2 chambers, 1 atria and 1 ventricle, 2 capillary beds
• reptile: 3 chambers, mixed blood (low conc. oxygen)

Question 4

what does double circulation mean

Answer 4

• maintains BP in the organs
• oxygen rich and oxygen poor blood are pumped separately from right and left side of heart
• systemic: oxygen rich delivers oxygens to this circuit, HBP

Question 5

describe the actions of the heart (5)

Answer 5

• cardiac cycle: contracts and releases in a rhythmic code
• systole: pumping / contraction, ejects blood into circulation
• diastole: relaxation / filling
• beats per day: 100,000 times (does not fatigue)
• resting: muscles work hard, twice as hard as leg muscles of a sprinter, even at rest

Question 6

describe basic heart anatomy

Answer 6

• size of fist, 250-350g, 4 chambers
• middle of thoracic cavity, mediastinum between 2-5 intercostal rib space (12-14cm)
• oblique
• point of maximal intensity (5th intercostal space, feel vibration)
• left side of diaphragm (left lung = smaller)
• pericardium: sac like structure

Question 7

describe in detail the pericardium and its two layers (outer most)

Answer 7

• fibrous: superficial, external, tough, dense, connective, protects heart, prevents overfilling, anchors to surrounding structures
• serous: deep, thin, slippery, two layers, pericardial cavity in-between, parietal / visceral
• parietal: internal surface of fibrous pericardium
• pericardial cavity: film of serous fluid, mobility without friction (cardiac tamponade -excess fluid, blockage)
• visceral / epicardium: integral part of heart wall

Question 8

what are the walls of the heart made of

Answer 8

• epicardium: visceral layer of serous pericardium, contains fat deposits
• myocardium: thickness, circular / spiral bundles of cardiac muscle cells (allows squeezing / ejection), contracting layer, connective tissue (fibrous skeleton, stability, bones of heart)
• endocardium: flat, same tissue as BV, squamous endothelium, continuous with BV

Question 9

describe microscopic anatomy of cardiac muscle

Answer 9

• striated, short, fat, branched, interconnected, multi / uni nucleate
• t tubules: surround myofibrils, conduct impulses from surface of cell to sarcolemma and sarcoplasmic reticulum
• sarcoplasmic reticulum: similar to skeletal
• mitochondria: numerous, 25-35% of volume (no fatigue)
• intercalated discs: junctions, anchor adjacent cells (desmosomes - prevent separation during contraction)(gap - connection / pores, electrically couple)

Question 10

what BV supply the heart muscle

Answer 10

coronary arteries:
- left: branches into circumflex artery (LV) and anterior interventricular artery
- right: branches into right marginal artery (RV) and posterior interventricular artery
- posterior / anterior interventricular merge at apex - anastomoses
- coronary sinus: large vein in the centre of heart, empties blood from coronary arteries into RA
cardiac veins:
- great cardiac vein: left of heart
- small / middle / anterior cardiac veins

Question 11

what are examples of blockage of coronary circulation

Answer 11

• angina pectoris: not enough oxygen during exercise, thoracic pain, transient deficiency in blood delivery to myocardium, spasms of CA, cells weakened
• myocardial infarction: heart attack, complete / prolonged coronary blockage, myocardial cells die, cell death = replaced with scar tissue (weakened)

Question 12

what are the chambers of the heart

Answer 12

• two atria: right / left
• two ventricles: right (thinner) / left (thicker)
• interatrial septum
• interventricular septum
• internal wall (not smooth)

Question 13

what are the valves of the heart and their functions

Answer 13

• atrioventricular (AV): prevent back flow into atria when ventricles contract (mitral / tricuspid)
• semilunar (SL): prevent back flow into ventricles when pumping (aortic and pulmonary), three curses

Question 14

describe the pathway of blood flow through the heart

Answer 14

superior / inferior vana cava - right atrium - tricuspid valve - right ventricle - pulmonary SL. valve - pulmonary trunk - pulmonary artery - lungs - pulmonary veins - left atrium - bicuspid valve - left ventricle - aortic SL valve - aorta - body tissue / coronary arteries (heart tissue, cardiac veins, coronary sinus

Question 15

what differences are there in foetal circulation

Answer 15

• ductus arteriosus: connects pulmonary artery with descending aorta (doesn’t go to lungs), right V strengthens - becomes ligamentum arteriosum
• ductus venosus: connects umbilical vein to inferior vena cava (oxygenated blood by passes liver) - becomes ligamentum venosum
• foreman ovale: hold in interatrial septum, shunts highly oxygenated blood from RA to LA - closes to form fossa ovalis

Question 16

what are the sounds of the heart

Answer 16

• lub dub (closing of valves)
• first: AV valves close, beginning of systole
• second: SL valves close, beginning of diastole

Question 17

what is a pulse and where are they found

Answer 17

• not heart beat
• direct measure of heart beat caused by movement of waves of pressure through vascular system due to contraction of muscles
• higher in newborns
• carotid (neck), femoral (gluteus maximus), brachial (anterior elbow), radial (wrist)

Question 18

what is heart muscle called the differences in electrical activation of the heart in comparison to skeletal cells

Answer 18

• myocyte: activation is similar to that of nerve cell
• self-excitable: all connected to neural cells, , some can cause depolarisation of other cells (activating themselveS), only muscle that can contract without nervous connection
• motor unit: contract at the same time, single unit
• length of refractory period: longer (250ms) than in skeletal (2ms), prevent tachycardia (too many beats per minute)

Question 19

how does cardiac muscle contraction occur

Answer 19

1. depolarisation opens the voltage-gated fast Na+ channels in sarcolemma
2. reversal of membrane potential from -90 mV to +30 mV
3. depolarisation wave in t-tubules causes the SR to release Ca2+
4. SR releases more Ca2+ (calcium sparks)
5. Ca2+ surge prolongs the depolarisation phase (plateau = the cells continue to contract)
6. Ca2+ channels inactivate and K+ channels open
7. K+ efflux, which brings the membrane potential back to its resting voltage
8. Ca2+ pumped back into SR and extracellular space

Question 20

what are the intrinsic and extrinsic features of the heart

Answer 20

• intrinsic: cardiac conduction system, auto rhythmic cells, initiate / distribute impulses to coordinate depolarisation / contraction, without nerve connections
• extrinsic: nervous connections, ANS, ability to modify activity of heart (increase / decrease HR)

Question 21

what are auto rhythmic cells and how does action potential occur

Answer 21

• pacemaker cells
• unstable resting potential, slow opening of Na channels (into cell), reduction of negative charge (gradual), never a flat line
• threshold: depolarisation, Ca channels open (into cell), influx of Ca, rising phase, Na close
• repolarisation: inactivation of Ca channels, opening of voltage gated K channels (out of cell), negative charge restored

Question 22

describe the sequence of excitation in the heart

Answer 22

• spread of electric current
  1. SA node: pacemaker, right atrial wall, generates impulses about 75x per min (damage = slow HB)
  2. AV node: inferior portion of interA septum, pauses impulses for 0.1 seconds
  3. AV bundle: bundle of His, superior part of interV septum, electrical connection between A and V (problem = contract independently)
  4. right / left bundle branches: pathways, interV septum, carry impulses to apex of heart
  5. purkinje fibres: sub-endocardial conducting network, depolarises contractile cells of both V

Question 23

what is the extrinsic innervation of the heart

Answer 23

• HB modified by ANS (two cardiac centres in medulla)
• ganglia: parallel to spinal cord in chest and neck (PNS)
• vagus: 10th cranial nerve, runs to heart, decreases HR and force
• sympathetic cardiac nerves: increase HR and force of contraction

Question 24

what is the cardioaccelatory centre

Answer 24

• innervates SA and AV nodes, heart muscles and coronary arteries
• projects to sympathetic neurons in T1-T5
• pre-ganglionic neurons: synapse with post ganglionic neurons in cervical and upper thoracic sympathetic trunk
• post-ganglionic fibres: run through cardiac plexus to heart, innervate structures above

Question 25

what is the cardioinhibitory centre

Answer 25

• inhibits SA and AV nodes
• send impulses to parasympathetic dorsal vagus nucleus in medulla, inhibit impulses to heart via branches of vagus nerves
• located in most parasympathetic post-ganglionic motor neurons (ganglia of heart and their fibres project heavily to SA and AV nodes)

Question 26

what is electrocardiography

Answer 26

• ECG / EKG
• recording of electric currents produced by the heart
• composite of all action potentials generated by nodal and contractile cells at given time
• P wave: A depolarisation / contraction, initiation = SA node
• QRS complex: ventricular depolarisation / contraction (after R), begins at apex (complex pathway / bigger muscles hence bigger wave), atrial repolarisation (occurs at same time, not shown)
• T wave: ventricular repolarisation, begins at apex
• PR: A depolarisation / contraction (contraction)
• QT: ventricular depolarisation / repolarisation (contraction)
• ST: plateau phases of ventricular myocyte’s, ventricular myocardium is depolarised
• RR: time between heartbeats (0.8-1 sec)

Question 27

what are homeostatic imbalances

Answer 27

• tachycardia: fast HR (>100BPM), may lead to fibrillation, sport activity / fever
• brachycardia: slow HR (<60BPM), inadequate circulation, endurance training

Question 28

what is ventricular fibrillation

Answer 28

• synchronous ventricular depolarisation is interrupted
• ventricular cells fire and propagate action potentials randomly
• destroys pumping action of heart, not a unit
• death within 3 minutes without defibrillation or CPR

Question 29

what is the role of chemicals in regulation of heart rate

Answer 29

• hormones: epinephrine (enhances HR / contractility), thyroxine (increases HR, enhances effects of norepinephrine and epinephrine)
• ion conc. (Ca /K), maintained for normal HB, increase Ca = increase HR, increase K = block activity of heart
• toxins: fever / fighting infection, digitoxin / fox glove (inhibits NaK pump, brachycardia, atrial fibrillation), oleandrin (plant, inhibits NaK pump)

Question 30

what effects does cocaine have on the heart

Answer 30

• stimulates sympathetic nervous system (inhibits catecholamine reuptake)
• increase HR, BP, block NaK channels, inflammation of heart (myocarditis), cardiomyopathy (disease of heart)

Question 31

how is an ECG measured and what is deflection

Answer 31

• 12 leads / electrodes: placed at various sites of the body

- deflection: vector of depolarisation produces biggest deflection on lead that is parallel to vector