Ch. 20 - The Heart Flashcards
Where is the heart located?
mediastinum; mostly left of midline
C/C fibrous and serous pericardium
F - protects and anchors heart; prevents overstretching
S - parietal layer fuses with F percardium; visceral layer in direct contact with heart
*serous fluid found in between parietal and visceral pericardia
What are the layers of the heart wall?
epicardium, myocardium, endocardium
What are sulci?
grooves on outside of heart that separate chambers; contain BV and fat
What is an auricle?
pouch-like structure on anterior surface of each atrium; helps atria hold greater vol of blood
Which chambers receive?
atria
Which chambers pump?
ventricles
Where does the R atrium receive blood from? Where does it pump blood to?
superior/inferior vena cava, coronary sinus; right ventricle via tricuspid valve (right AV)
Where does the R ventricle receive blood from? Where does it pump blood to?
right atrium; into pulmonary trunk via right semilunar valve (pulmonary valve)
Where does the L atrium receive blood from? Where does it pump blood to?
oxygenated blood from lungs; left ventricle via bicuspid valve (left AV)
Where does the L ventricle receive blood from? Where does it pump blood to?
left atrium; aorta via left semilunar valve (aortic valve)
AV valves prevent back flow from…
…ventricles into atria
Semilunar valves prevent back flow from…
….arteries into ventricles
What triggers the opening and closing of heart valves?
pressure changes; not neurons/AP!
What are valves composed of?
dense irregular CT covered with endocardium
How do AV valves prevent back flow?
papillary muscles attached to valve cusps by chordae tendinae; chordae prevent valve cusps from opening into atrium
What are semilunar valves composed of?
3 moon-shaped cusps
When do semilunar valves open?
when pressure in ventricles exceed pressure in arteries
What is the function of coronary arteries?
supply myocardium cells with fresh nutrients and O2; branch off aorta
What is the function of coronary veins?
collect waste from cardiac muscle and drain into coronary sinus, which then empties into R atrium
What is systole and diastole?
S - contraction
D - relaxation
What does the cardiac cycle consist of?
systole + diastole of both atria followed by systole + diastole of both ventricles
What are characteristics of cardiac muscle?
branched, intercalated discs connected by gap junctions and desmosomes, involuntary, striated, single central nucleus
How do cardiac muscle sarcomeres differ form skeletal muscle?
- more mitochondria (25% of cell vol)
- T-tubules wider but less abundaent
- SR less prominent; need Ca2+ from outside cell
How do cardiac muscles produce ATP?
- aerobic cellular resp
a. at rest: use FA, glucose
b. during exercise; use lactic acid - creatine phosphate when something is wrong!
What are the role of autorhythmic fibers?
- generate spontaneous AP that trigger heart contractions
- act as pacemaker, setting baseline rhythm of electrical excitation that causes contraction
- form conduction system; propagates AP through heart muscle
What is the sinoatrial (SA) node?
- cluster of cells in wall of R atrium
- repeated spontaneous depolarization; no stable resting potential
- triggers contraction of both atria
What is the atrioventricular (AV) node?
- located in b/t 2 atria (atrial septum)
- signal is slightly delayed at AV node
Why is the delay of the signal at AV node important?
atria have to contract then relax; ventricles have to contract then relax
What is AV bundle?
- where signal can be transmitted from atria and ventricles
- send signal down ventricular septum to apex
- Purkinje fibers conduct signal up ventricle wall
- triggers contraction of ventricles
What are the 3 phases of an AP in a ventricular contractile fiber?
- rapid depolarization
- plateau
- repolarization: closure of Ca2+ channels and K+ outflow when additional K+ channels open
**prolonged refractory period
What occurs during depolarization phase?
Na+ inflow as Na+ channels open; resting membrane potential is -90mv
What occurs during plateau phase?
- Ca2+ inflow from outside cell/SR as Ca2+ channels open –> Ca2+ binds to troponin
- K+ outflow as K+ channels open
What occurs during repolarization phase?
- Ca2+ channels close
- K+ channels open to let K+ out of cell
- muscle contraction ceases –> relaxation!
Is tetanus possible in cardiac muscle cells?
no because potential is maintained
What occurs at atrial and ventricular diastole?
4 chambers are relaxed; passive filling of blood into heart
What occurs at atrial systole, ventricular diastole?
atria contract; blood pushes into ventricles
What occurs at atrial diastole, ventricular systole?
atria relaxes; ventricles contract; blood pushes out of heart
What does an electrocardiogram record?
spread of AP through heart
What are the recognizable waves in an EKG that appear with each heartbeat?
- P wave - atrial depol (contraction!)
- QRS complex - rapid ventricular depol (contraction!)
- T wave - ventricular repol (relaxes)`
Describe the AP propagation through the heart
- electrical impulse from SA node to walls of atria; atria contract=
- impulses reaches AV node; delay
- bundle branches carry signal from AV node to apex
- signal spreads through ventricle walls; ventricles contract
What causes the sound of a heartbeat?
turbulence of blood flow caused by closure of valves
What is the first heart sound?
- AV valves close soon after V systole begins
What is the second heart sound?
- SL valves close near beginning of V diastole
What does the R-R interval tell you?
length of time a heartbeat takes
What kinds of information can you get from an ECG?
how muscles are conducting AP; can detect valve malfunction
What is cardiac output? (CO)
vol of blood ejected from a ventricle each minute
What is stroke volume? (SV)
vol of blood ejected by the ventricle with each contraction
What is heart rate? (HR)
number of beats per minute
What is the formula for cardiac output?
CO = SV x HR
Depending on activity level, what are normal levels of cardiac output?
Resting - 5L/min
Mild exercise - 10L/min
Intense exercise - 19.5L/min
How many times can the average person increase their CO resting value? How about a top endurance athlete?
4-5 times; 7-8 times
What is a cardiac reserve?
difference between person’s max cardiac output & cardiac output at rest
What hormones influence heart rate?
epinephrine, norepinephrine
How are specific ion concentrations crucial to heart rate?
- increased K+ blocks AP generation
- increased Na+ blocks Ca2+
- increased Ca2+ speeds heart rate and force of contraction
What other factors influence heart rate?
age, gender, physical fitness (athletes have lower rate), body temp (increased temp leads to increased heart rate)
What are the 3 factors of regulation of stroke volume?
preload, contractility, afterload
What is preload?
degree of stretching
more blood filling chamber –> more stretching –> greater force of contraction
What is the amount of blood in chamber dependent on?
venous return and duration of diastole (relaxation)
What is contractility?
force of contraction of myocardium
C/C positive and negative inotropic agents
+ : increase contractility by increasing Ca2+ inflow
- : decrease contractility by decreasing Ca2+ inflow/increasing K+ outflow
What does inotropic mean?
drugs acting on contractility fibres
What is afterload?
amount of pressure required to open semilunar valves
What causes high afterload?
high BP
What leads to increased stroke volume?
increased preload + contractility, decreased afterload
