Ch. 20 - The Heart Flashcards
Where is the heart located?
mediastinum; mostly left of midline
Pericardium: fibrous and serous pericardium
F - Dense irregular connective tissue. protects and anchors heart; prevents overstretching. Near the apex, anchored to the diaphragm. The diaphragm facilitates movement of blood by the heart
S - parietal layer fuses with F____ percardium; visceral layer in direct contact with the heart.
Layers are separated by the pericardial cavity. this contain serous fluid that reduces friction btwn layers of the serous pericardium as the heart moves
What are the layers of the heart wall?
Epicardium: outside (contains visceral layer of the serous pericardium and mesothelium)
Myocardium: thickest and has the most muscle, responsible for the pumping action of the heart
endocardium: smooth lining for the chambers of the heart, covers heart valves, minimizes friction as blood passes
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 action potentials that trigger heart contractions
- act as pacemaker, setting baseline rhythm of electrical excitation that causes contraction
- form conduction system; propagates AP through heart muscle
- allows heart to continue beating even when disconnected from the brain since they are self-excitable
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
-Hearts natural pace maker
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 ( ATRIA contraction!)
- QRS complex - rapid ventricular depol (contraction!)
- T wave - ventricular repol (relaxes)`
Explain the graph
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
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
-th lower the after load, the higher the stroke volume
Pericarditis
inflamation of the pericardium
myocarditis
inflamation of the myocardium
endocarditis
inflamation of the endocardium
Fibrous Skeleton of the Heart
-Dense connective tissue
-4 rings surround the valves of the heart and fuses w one another. merge w the interventricular septum
-prevent overstretching as blood flows
-acts as an electrical insulator : This allows for the atri to contract first
coronary circulation
Coronary arteries and veins that transports blood to and away the myocardium
myocardial ischemia
reduced blood flow to the myocardium
- can cause hypoxia (reduced oxygen supply)
-angina pectoris (pain)M
Myocardial infarction
Heart attack
-interrupted blood supply
The Conduction System
- SA Node sends an action potential to the atria. They contract
- Then the action potential goes through the AV node
- then into the AV bundle
- Purkinje fibres conduct the action potential to the remainder of the ventricular myocardium. Ventricles contract
Artificial Pacemaker
Sends out small electrical current to stimulate the SA node for the heart to contract
The Cardiac Cycle
Regulation of Heart Rate
-Autonomic nervous system
-Hormones
-ions
-gender
-age
-physical fitness
-temo
-Autonomic nervous system
Involuntary contractions
Hormones
Epinephrine and norepinephrine inhance the hearts pumping effectiveness. Both increase the heart rate and contractility
Cations
three cations—K+, Ca2+, and Na+—have a large effect on cardiac function. Elevated blood levels of K+ or Na+ decrease heart rate and contractility. Excess Na+ blocks Ca2+ inflow during cardiac action potentials, thereby decreasing the force of contraction, whereas excess K+ blocks generation of action potentials. A moderate increase in interstitial (and thus intracellular) Ca2+ level speeds heart rate and strengthens the heartbeat.
Gender
male and female slighty diff heart rate
physical fitness
a lot - higher stroke volume, contracts harder
temp
high temp increases heart rate
Factors that increase cardiac output
Excercise and the heart
-increase cardiac output
-increase high density proteins, good cholesterol
-decrease fat
-improve lung function
-assist in weight control
.
Explain the Cardiac Cycle
Help for Failing Hearts: Intra-aortic balloon pump (IABP)
Help weak heart to pump blood more affectively. Inserted into the aorta. When heart relaxes, the balloon inflates to push more blood towards the body. The balloon is inflated btwn heartbeats, this pushes blood both backwards and towards the heart.
During ventrical contraction, the balloon shrinks to allow the left ventricle to eject blood easier
VAD
Helps the ventricles to contract to send blood to the body. This can be used more longterm, usually used as a person waits for a heart transplant
Cardiomyoplasty
Heart wrapped in back muscle. An implanted pacemaker stimulates the muscle motor neurons to help the heart beat
Skeletal Muscle assist device
A piece of the patient’s own skeletal muscle is surgically removed
This muscle is shaped into a pouch
The pouch is placed between the heart and aorta
A pacemaker is connected to the muscle’s motor neurons
The pacemaker triggers the muscle to contract, creating a “booster” effect for the heart’s pumping action
Disorders: Homeostatic Imbalances
- Coronary artery disease. -reduced blood flow to the heart
- Atherosclerotic plaques. -cellular debris that accumulates in arterial walls reducing blood flow
- Congenital heart defects. - structural abnormalities present at birth
- Arrhythmia. - irregular heart rhythm
- Congestive heart failure. -heart unable to pump blood effectively
