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Flashcards in the heart Deck (31):
1

what is the circulatory system and the two types

- 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

2

what are the advantages of a closed circulatory system

- 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)

3

describe the evolution of the heart

- 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)

4

what does double circulation mean

- 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

5

describe the actions of the heart (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

6

describe basic heart anatomy

- 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

7

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

- 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

8

what are the walls of the heart made of

- 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

9

describe microscopic anatomy of cardiac muscle

- 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)

10

what BV supply the heart muscle

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

11

what are examples of blockage of coronary circulation

- 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)

12

what are the chambers of the heart

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

13

what are the valves of the heart and their functions

- 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

14

describe the pathway of blood flow through the heart

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

15

what differences are there in foetal circulation

- 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

16

what are the sounds of the heart

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

17

what is a pulse and where are they found

- 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)

18

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

- 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)

19

how does cardiac muscle contraction occur

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

20

what are the intrinsic and extrinsic features of the heart

- 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)

21

what are auto rhythmic cells and how does action potential occur

- 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

22

describe the sequence of excitation in the heart

- 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

23

what is the extrinsic innervation of the heart

- 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

24

what is the cardioaccelatory centre

- 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

25

what is the cardioinhibitory centre

- 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)

26

what is electrocardiography

- 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)

27

what are homeostatic imbalances

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

28

what is ventricular fibrillation

- 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

29

what is the role of chemicals in regulation of heart rate

- 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)

30

what effects does cocaine have on the heart

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

31

how is an ECG measured and what is deflection

- 12 leads / electrodes: placed at various sites of the body
- deflection: vector of depolarisation produces biggest deflection on lead that is parallel to vector