Transcript Regulation of Heart Rate Cardioaccelatory center

Histology
• Elongated branching cells containing 1-2 central
nuclei
• Contains actin and myosin
• Intercolated discs for specialized cell to cell
communication
• Desmosomes hold together cells and gap junctions
allow AP like propogation
• Electrically, cardiac muscle acts as single unit
Fig. 20.12
Functions
• Generate blood pressure
• Routing blood to keep separated systemic from
pulmonary blood
• Ensuring one way blood flow with valves
• Regulating blood supply to parts of the body
– Changes is rate and force of contraction matches the
changing metabolic needs of the body
Fig. 20.1
Anatomy
• Pericardial Sac - parietal pericardium
– Fibrous Layer – outer layer consisting of tough,
fibrous connective tissue
• prevents over distension of the heart
• provides a protective membrane
• anchors the heart in the mediastinum
– Serous Layer - 2 layers - (parietal and visceral layer)
continuous with the epicardium - adheres to the heart
• Pericardial Cavity - a space between the parietal
and the visceral layer of the heart filled with
pericardial fluid - helps to prevent friction
Fig. 20.3
Layers of the Heart
• Three Layers
– epicardium - external layer
– myocardium - middle layer - muscle tissue layer responsible for contraction
– endocardium - inner layer - covers valves of the
heart, the inside of the myocardium and the tendons of
the valves, continuous with the endothelial lining of
the large blood vessels
Fig. 20.4
Chambers of the Heart
• Right and Left ATRIUM - upper chambers - Thin
muscle walls - low pressure
– auricle - (dog's ear) appendage in the atrium that
increases atrium surface area
– interatrial septum - separates R and L atrium
– fossa ovalis - a depression on the septum which
corresponds with the foramen ovali - an opening in the
interatrial septum of the fetus
Chambers of the Heart
• Right and Left VENTRICLES - lower chambers much greater pressure
– interventricular septum - separates R and L
ventricles
– L walls are even thicker than the R walls because it
must pump blood through the 1000's miles of blood
vessels
Fig. 20.7
Great Vessels and Blood Movement
• Arteries carry blood away from the heart, veins
carry blood toward the heart
• Right Atrium
• superior vena cava
• inferior vena cava
• coronary sinus
Blood Flow
• Blood travels through the right Atrioventricular
valve (A-V , Tricuspid) into the R ventricle. The
R ventricle contracts and pumps the blood through
the pulmonary semilunar valve into the
pulmonary trunk, the pulmonary trunk divides
into the R and L pulmonary arteries, which lead
to the lungs
Blood Flow Cont’d
• In the lungs the blood releases CO2 and takes up
O2 - returns to the heart via 4 pulmonary veins
- L atrium - blood flows through the L A-V
valve (Bicuspid valve, mitral valve) into the L
ventricle - the left ventricle pumps the blood out
through the aortic semilunar valve - to the
ascending aorta - feeds into the coronary
arteries, aortic arch, and the systemic
circulation system
Fig. 20.10
Valves
•
•
•
•
•
Permit blood flow only in one direction
Tricuspid ( R A-V) - 3 flaps (cusps)
Bicuspid (L A-V, mitral) - 2 cusps
Semilunar – pulmonary, aortic 3 flaps (cusps)
Cordae tendineae (cords) - that attach the valve
cusps to the papillary muscles, which keep the
valves from bring forced back into the atria
Fig. 20.9
Blood Supply of the Heart
• Coronary circulation - 2 major vessels that
branch off the ascending aorta. First vessels above
the aortic semilunar valve – most important to
make sure the heart has blood
Fig. 20.6
Blood Supply of the Heart
• Very few anastomoses (outlets) between the large
branches of the arteries. If the artery is blocked little or no blood can reach cells - they become
ischemic (deprived of 02) and may die myocardial infarction - MI. Heart loses some
of its contractility, active tissue is replaced by scar
tissue
• Anastomoses – provide a secondary blood supply
for the capillary beds. Arterial anastomoses can
occur in the brain, coronary circulation, or
peripheral circulation (often due to increase
demand – exercise – “use it or lose it”)
Fig. 20.a
Blood Supply of the Heart
• Angina pectoris "chest pain"- occurs when
coronary circulation is reduced:
– vasoconstriction - stress, smoking
– blockage in vessel - thrombus, embolus, plaque
– reduced blood flow to heart - exercising after
consuming a large meal
• Remedy - take nitroglycerin which dilates
coronary blood vessels, will result in increase
blood flow
Conduction System
• Autonomic nervous system increases or decreases
the time it takes to complete a cardiac cycle but it
does not initiate the contraction. SA node initiates
AP @ 70-80 BPM
• The conduction system consists of specialized
cardiac muscle cells - its sole purpose is
conduction of cardiac impulses.
– Pacemaker cells
Conduction System
• Sinoatrial Node - SA node - pacemaker
– 100's of cells located in R atrium near the opening of
the superior vena cava
– Possess an intrinsic rhythm
– They initiate each cardiac cycle
– The impulse the SA node initiates spreads out over
both atria causing them to contract and also
depolarizing the AV node
Fig. pf 20.13
Conduction System
• Atrioventricular node - AV node - located
near the inferior portion of the interatrial septum one of the last parts of the R atrium to be
depolarized
• Atrioventricular Bundle - AV bundle (Bundle of His)
• Purkinje Fibers
ELECTROCARDIOGRAM
• ECG \ EKG
• Impulses through the heart's conduction system
can be recorded on the body's surface. Each
portion of the cardiac cycle produces a different
electrical impulse
• P wave - indicates artial depolarization (Contraction) SA node fires - impulse travels
through atria - atria contract after P wave begins
ELECTROCARDIOGRAM
• QRS complex - deflection wave - represents
ventricular depolarization - (Contraction)
– The spread of electrical impulse from AV node
→bundle of his → bundle branches →purkinje
fibers→ myocardial cells and papillary muscles.
QRS complex begins with a downward deflection,
continues as a large upright triangular wave and ends
as a downward wave at its base. The magnitude of the
QRS complex masks the deflection of atrial
repolarization.(Relaxation)
• T wave - indicates ventricular repolarization (Relaxation)
Fig. 20.16
Fig. 20.17b
Cardiac Cycle
• Heart is two pumps that work together, right
and left half
• Repetitive contraction (systole) and
relaxation (diastole) of heart chambers
• Blood moves through circulatory system
from areas of higher to lower pressure.
– Contraction of heart produces the pressure
Starling's Law of the Heart
• Increasing the length of the cardiac muscle fibers
intensifies the force of the ventricular contraction.
During exercise:
↑blood flow = ↑ fiber length = ↑ contraction strength
• “More in = more out”, Blood flow can increase
from 4-6 L/M to 18-30 L/M during exercise
Regulation of Heart Rate
• Cardioaccelatory center - located in medulla sympathetic fibers - release of norepinephrine
causes an increase in heart rate and contractility
(NE increases the force of contraction)
• Cardioinhibitory center - located in medulla parasympathetic fibers - release acetylcholine
which causes a decrease in HR and contractility.
– Bradycardia - HR less than 60 BPM
Fig. pf 20.22
Regulation of Heart Rate
• Pressoreceptors (baroreceptors) - responsible
for maintaining homeostasis between the systems.
– Carotid sinus maintains normal BP and O2 levels in
the brain. Contains baroreceptors and
chemoreceptors at the bifurcation of the carotid
arteries
Fig. pf 20.22
Cardiac Arrhythmias
• Tachycardia: Heart rate in excess of 100bpm
• Bradycardia: Heart rate less than 60 bpm
• Sinus arrhythmia: Heart rate varies 5% during
respiratory cycle and up to 30% during deep
respiration
• Premature atrial contractions: Occasional
shortened intervals between one contraction
and succeeding, frequently occurs in healthy
people
Effects of Aging on the Heart
• Gradual changes in heart function, minor
under resting condition, more significant
during exercise
• Hypertrophy of left ventricle
• Maximum heart rate decreases
• Increased tendency for valves to function
abnormally and arrhythmias to occur
• Increased oxygen consumption required to
pump same amount of blood
Fig. 20.11