Chapter 20: The Cardiovascular System

1
Chapter 20 The Cardiovascular System

• THE HEART

2
(No Transcript)
3
Heart Anatomy

• Location
• diaphragm, mediastinum, 2/3 left of midline
• Orientation
• Apex- points anterior, inferior, left
• Base- directed posterior, superior, right
• Vessels
• Superior and Inferior Vena Cava
• Pulmonary trunk? pulmonary arteries(?lungs)
• Pulmonary veins
• Aorta

4
(No Transcript)
5
(No Transcript)
6
Pericardium- figure 20.2

• Membrane that surrounds protects
• Confines to position in mediastinum
• 2 main parts
• Fibrous pericardium- superficial, anchor
• Tough, inelastic, dense irregular CT
• Baglike, open end attached to vessels
• Prevents overstretching of heart
• Serous pericardium- thinner, delicate
• Forms double layer (pericardial fluid in
  pericardial cavity - reduces friction, allows
  movement)
• Parietal layer- fused to fibrous
• Visceral layer- inner EPICARDIUM- adheres
  tightly to heart surface

7
(No Transcript)
8
(No Transcript)
9
(No Transcript)
10
Layers of the heart wall

• Epicardium- thin, transparent, outer
• Visceral layer of serous pericardium
• Smooth slippery outside of heart
• Myocardium- middle
• Cardiac muscle- striated but involuntary
• Bulk of heart
• Pumping action
• Endocardium- inner
• Thin endothelium over CT
• Smooth lining of chambers and valves
• Continuous with b.v.

11
(No Transcript)
12
(No Transcript)
13
Heart Anatomy fig 20.3-6

• Heart chambers 4
• 2 Atria
• Right- receives blood from vena cavae
• Left- receives blood from pulmonary veins
• 2 Ventricles
• Right- pumps deoxygenated blood to lungs
• Left- pumps oxygenated blood to systemic circ
• Myocardium much thicker than right ventricle
• Heart valves 4
• Atrioventricular valves tricuspid bicuspid
• Semilunar valves aortic and pulmonary

14
(No Transcript)
15
(No Transcript)
16
(No Transcript)
17
(No Transcript)
18
(No Transcript)
19
Valve function

• When AV valve open
• Cusps project into ventricle
• Ventricle relaxed ? papillary muscle relaxed ?
  chordae tendineae slack
• Blood ? pressure atria ? ? pressure ventricle
• Ventricle contracts, pressure ? cusps up, ? close
• Papillary muscles contract ? chordae tendineae
  tighten
• SL valves open when pressure in ventricles
  exceeds pressure in arteries
• As ventricles relax blood moves back toward heart
  ? SL valves close

20
(No Transcript)
21
(No Transcript)
22
(No Transcript)
23
Terms

• Auricles on anterior surface of atria
• Increases capacity of each atrium so each can
  hold a greater volume of blood
• Coronary sulcus separation between atria and
  ventricles
• Systole contraction
• Diastole relaxation
• Tachycardia high heart rate, gt 100bpm
• Bradycardia low heart rate, 50 bpm

24
Pulmonary and systemic circuits
25
(No Transcript)
26
Coronary circulation (1)
27
Coronary circulation (2)

• Coronary crown, encircles heart
• ? contracts, little blood flows ? coronary artery
  but as ? relaxes, aorta pushes blood thru
  coronary arteries
• Anastomoses area where 2 or more arteries
  supply the same region
• Provide alternate routes for blood to reach a
  particular organ or tissue
• Myocardium contains
• Provides detours if main route is obstructed

28
Problems

• Myocardial ischemia partial obstruction of
  blood flow in coronary arteries
• ? blood flow to myocardium
• hypoxia may weaken cells w/out killing them
• Silent episodes without pain, dangerous in that
  no forewarning to ? attack
• Angina pectoris strangled chest
• Severe pain usually accompanies myocardial
  ischemia
• Tightness or squeezing sensation
• Can occur during exertion when ? requires more O2
• Pain referred to neck, chin, left arm

29
Myocardial infarction (MI)

• Heart attack
• Complete obstruction of blood flow to coronary
  artery
• Infarction death of tissue area due to
  interrupted blood supply
• Tissue distal to obstruction dies, replaced by
  non-contractile scar tissue ? loses strength
• May also disrupt conduction system and cause
  sudden death ventricular fibrillation rapid
  uncoordinated twitching that disrupts regular
  rhythm
• treatment injection of clot dissolver, plus
  heparin, coronary angioplasty or coronary artery
  bypass

30
Properties of cardiac muscle cells

• Shorter than skeletal
• Branching
• Central nucleus, sometimes binucleate
• Intercalated discs- thickenings of sarcolemma,
  contain
• Desmosomes- hold fibers together
• Gap junctions- for AP conduction
• Mitochondria large numerous
• Like skeletal- arrangement of proteins
• SR smaller ? less intracellular Ca2
• T-tubules wider but less abundant

31
(No Transcript)
32
(No Transcript)
33
Functional syncytium

• stimulation of individual muscle cell results in
  contraction of all muscle cells due to gap
  junctions in intercalated discs
• an application of the all-or-none principle
• If stimulus in cardiac muscle is great enough to
  initiate contraction of a single cell, the entire
  muscular syncytium will undergo contraction

34
Contraction physiology

• 1 of cardiac fibers become autorhythmic during
  embryonic development
• Pacemaker function- set rhythm of electrical
  excitation
• Conduction system- network of specialized fibers
  provide path for excitation to progress thru
  heart
• Ensuring coordinated contraction of chambers
• Both atria contract at same time
• Both ventricles contract at same time
• Cardiac AP goes thru following sequence

35
Contraction physiology (2)

• Pathway of stimulation
• 1. Sinoatrial (SA) node- cells do not have a
  stable resting membrane potential
• depolarized spontaneously pacemaker potential
• 2. Atrioventricular (AV) node
• 3. Bundle of His
• 4. Bundle branches
• 5. Purkinje fibers
• 6. Ventricular cells- contraction pushes blood up
  to SL valves

36
(No Transcript)
37
(No Transcript)
38
Cardiac Action Potentials, 20.11

• Depolarization Na gates open fast channels
• Rapid depolarization because they open fast
• Plateau opening of slow Ca2 channels in the
  sarcolemma
• More Ca2 outside cell ? ? cytosol also causing
  Ca2 to pour out of SR
• ? Ca2 ? contraction
• K channels opening but Ca2 balances it ?
  remains depolarized for about 0.25 sec
• (in skeletal muscle 0.001 sec, no plateau phase)
• Repolarization K outflow restores resting m.p.
• Ca2 channels also are closing

39
(No Transcript)
40
Cardiac Action Potentials (2)

• Positive inotropic agents ? contractility
  (substances promote inflow of Ca2 channels ?
  strength ? contractions
• NE and Epinephrine modify
• Timing
• strength of contraction
• Do NOT establish a rhythm
• Digitalis
• ? interstitial Ca2
• Negative inotropic agents ? contractility
• Ach released by Parasymp NS slows SA node pacing
  from 100 to about 75 AP/minute
• Also anoxia, acidosis, some anesthetics, ? K,
  Ca2 channel blockers

41
(No Transcript)
42
Long refractory pd- cardiac muscle

• Refractory pd- time interval during which second
  contraction cannot be triggered
• In cardiac- longer than contraction pd
• Another contraction cannot happen until
  relaxation is happening
• Tetanus cannot occur
• If tetanus occurred blood flow would cease

43
(No Transcript)
44
(No Transcript)
45
(No Transcript)
46
(No Transcript)
47
Arrhythmias

• Irregular rhythm due to conduction defect
• Causes
• Caffeine, nicotine, alcohol, other drugs,
  anxiety, hyperthyroidism, K deficiency, some
  heart disease
• Examples
• Heart block AP slowed or blocked (3 types)
• 1st AP slow thru AV, 2nd some AP not thru
  AV node, 3rd no AP thru AV node
• Atrial flutter rapid atrial contractions
• Atrial fibrillation asynchronous cont- atrial
  fibers
• Ventricular fibrillation async cont ventricular
  fibers
• Premature ventricular contraction ectopic area
  of high excitation ? abnormal AP (before SA node
  intends)

48
(No Transcript)
49
Cardiac excitation and the ECG
50
Electrocardiogram (ECG)

• P wave atrial depolarization ? atrial
  contraction ? ventricular filling
• QRS complex ventricular depolarization ?
  ventricular contraction ? SL valves open ? blood
  ejection
• Rt ventricle?pulmonary trunk? pul arteries? lungs
• Left ventricle ? aorta ? systemic circulation
• T wave ventricular repolarization

51
Heart sounds

• A. Normal
• First sound lubb closure of AV valves
• Second sound dupp closure of SL valves
• B. Abnormal sounds (murmurs)
• 1. stenosis failure of valve to open
• 2. insufficiency failure of valve to close

52
The Cardiac Cycle

• Ventricular filling
• AV open, SL closed
• Isovolumetric contraction
• AV closed, SL closed
• Ventricular ejection
• AV closed, SL open
• Isovolumetric relaxation
• AV closed, SL closed
• Ventricular filling

53
(No Transcript)
54
Regulation of Cardiac Output

• Cardiac output stroke volume x heart rate
• CO SV x HR
• Stroke volume ml/ beat
• EDV - ESV
• Heart rate beats/ min
• Cardiac output L/ min
• rest 5.25 L/min (70 mL/beat x 75 bpm)
• exercise 19.5 L/min (130mL/beat x 150bpm)

55
Regulation of stroke volume

• 1. Effect of preload Frank-Starling Law of the
  Heart
• gt preload ? gt force of contraction
• rubberband
• 2. Effect of afterload
• Pressure rqrd for ejection of blood
• 3. Effect of contractility-each individual fiber
• Positive inotropic agents- eg. norepinephrine
• Negative inotropic agents - eg. propranolol

56
(No Transcript)
57
Regulation of Heart Rate

• 1. Normal rate vagal tone
• 2. Regulation
• 1. Autonomic Nervous system
• 2. Chemical
• a. Hormones
• b. Ions

58
(No Transcript)