Download Cardiovascular System

Lecture 10: Cardiovascular System
Silverthorn Chapter 14
Cardiovascular system consists of a pump (the heart) which is made of cardiac muscle tissue, and a network of pipes (vessels) that
allow blood to be moved throughout the body. In our exploration of the cardiovascular system, we will look at the anatomy and
physiology of the heart (how does it function as an efficient and effective pump?). Then we’ll take a closer look at the vessels, where
blood pressure is a critical measurement. Finally, we’ll examine blood and its role in capillary exchange and blood clotting.
mm Anatomy of the CV system
The heart consists of 4 chambers (2 atria and 2 ventricles), which are separated by one way valves.
Pulmonary circulation moves blood between the heart and the lungs, while systemic circulation moves blood
between the heart and the body.
Your Task:
Draw a picture of the circulatory system, including the following anatomical
structures:
a. Right/left ventricles
b. Right/left atria
c. Pulmonary veins
d. Pulmonary arteries
e. Aorta
f. Vena cava
g. Body
h. Lungs
i. Capillaries
j. Other veins (and venules)
k. Other arteries (and arterioles)
Cardiac muscle cells (aka “myocardium”)
Begin by comparing cardiac muscle cells to skeletal muscle cells…(see table 12.3 pg 440 in 5th ed...pg 434 in 6th ed)
1. Single nucleus in each cell
2. Branching cells connected by intercalated discs
A. Intercalated discs include desmosomes (structures that strongly connect cells together) and gap junctions (which allow
depolarizations to spread from cell to cell)
3. Many mitochondria (1/3 of the cell volume is filled by mitochondria)
A. Heart beats 100,000x in 1 day!
B. Heart begins beating after 22 days in the womb! Source: http://www.meddean.luc.edu/lumen/MedEd/GrossAnatomy/
thorax0/heartdev/main_fra.html
4. Smaller SR…what does this mean?
5. Do not require nervous input to contract! (However, nerve input can control heart rate…) See http://www.youtube.com/
watch?v=lmhBEeEMqYo&feature=related for evidence!
6. 2 types of cells
A. Autorhythmic cells
B. Contractile cells
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Contractile cells
Autorhythmic cells generate the AP, but contractile cells enable the heart to contract. They also have a unique AP graph...
1. Resting membrane potential: -90 mV
2. Action Potential enters contractile cell from adjacent cell through intercalated disks causing voltage gated Na+ (and K+)
channels to open so the cell depolarizes, 20 mV
3. Na+ gates snap shut, fast K+ gates open.
4. Voltage gated Ca2+ gates suddenly open (10% of needed Ca2+ enters this way), fast K+ gates close
A. Ryanodine receptors (RyR) found on the SR bind with the Ca2+ and open, letting more Ca2+ out into the sarcoplasm (90%
of the Ca2+ enters this way)
i. Malfunctioning RyR is correlated with arrhythmias and heart failure!
ii. Ryanodine is also a drug/insecticide that binds with these receptors
B. This surge of Ca2+ is considered a spark, that initiates contraction in thin and thick filaments
C. Ca2+ is removed from the sarcoplasm by the Sodium-Calcium Exchanger
5. Ca2+ gates shut and very slow K+ channels finally open so the cell repolarizes
Note: Cardiac muscle contractions can be “graded” by varying Ca2+ permeability. More Ca2+ causes increased force…less makes
less force. This is different from skeletal muscle...which contracts in an “all or none” manner. Because of this, modifying calcium
permeability can affect the force of contraction in the heart. Applications?
Autorhythmic cells
AR cells generate periodic action potentials, completely without input from the nervous system! The action potential graph of an AR
cell is pretty unique.
1. AR cells do not have a resting potential…they have the “Pacemaker Potential” that starts at -60 mV and slowly becomes more
positive…
A. Funny Na/K channels (If channels) are leaky and open…Na comes in faster…
B. As the membrane becomes more positive, Ca2+ channels open too!
C. All of this causes the cell to slowly depolarize
2. Threshold is reached at -40mV
A. Ca2+ channels open, and the steep depolarization begins
3. At the peak, Ca2+ gates close, and K+ gates open…leads to repolarization…
4. K+ gates close…
5. Ca+ is pumped back into the ECF by Na/Ca exchanger
A. 1 Ca+ pumped out (against the gradient)
B. 3 Na+ pumped IN (with its gradient)
C. Then the 3 Na+ are used in the Na/K pump
Placement of autorhythmic cells (Electrical conduction system)
AR cells are found in specific areas in the heart. The AP begins in the SA node...and follows this path:
1.
2.
3.
4.
5.
6.
SA node (in the top of right atrium), act as the pacemaker of the heart.
Internodal pathways
AV node (near the base of the right atrium)...the AP slows down slightly here.
AV bundle (in the ventricular septum)...aka “bundle of his”
R + L bundle branches
Purkinje fibers (spread out into the ventricular myocardium from the bottom UP...)
Cardiac cycle
The cardiac cycle includes all the events that take place during one complete heartbeat, including:
•
•
•
•
1.
Atrial and ventricular contraction (systole) and relaxation (diastole)
Blood pressure
Heart sounds (valve actions)
ECG (EKG) events
The heart is relaxed
A. Atria are filling with blood from veins, they expand…
B. AV Valves open
C. Ventricles fill passively
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2. SA Node FIRES
A. Positive charge leaks through gap junctions, and spreads throughout the contractile cells
B. Fires the fastest…90 beats/min, so it is the leader
3. Internodal pathways
A. FAST transmission through atria, stimulating atrial contraction
B. Atria slowly contracts, blood is pushed into the ventricles
C. AP cannot pass to ventricles b/c of fibrous structure between atria and ventricles
4. Atrial contraction
A. Push blood into ventricles
B. (A little goes backwards into veins…apparently you can see this in the jugular vein if someone lies at a 30 degree angle??)
5. AV Node: Only way AP can reach the ventricles!
A. There must be a pause here, while the ventricles fill with blood!
B. The AV Node cells (autorhythmic) fire their AP at 1/20 the rate of other autorhythmic cells!
6. AV Bundle: Starting down the ventricular septum
7. Rt and Lft bundle branches
8. Purkinje Fibers
A. Super – fast conduction through ventricles, ensuring all ventricular fibers contract together
B. (Atria are beginning to REPOLARIZE…)
9. Early ventricular contraction
A. Increased pressure in ventricles slam AV valves closed (lub)
B. All valves are closed, creating increased pressure as the ventricles continue to contract (Isovolumetric contraction)
C. Atria start to relax…
10. Ventricular ejection
A. High pressure (from the squeezing muscle) opens the semilunar valves, and blood rushes out
11. Ventricular relaxation
A. Ventricles relax
B. Semilunar valves snap shut to prevent backflow (dup)
Heart Rate
The heart rate is initiated by autorhythmic cells in the SA node, which fire at 90 beats per minute if there is NO nervous input.
1. How could you SLOW DOWN this “default” heart rate?
A. Increase K+ permeability…
B. Decrease Ca2+ permeability…
2. How could you SPEED IT UP?
A. Increased Ca2+ permeability…
B. Increased Na+ permeability…
Your body regulates HR via NTs and hormones.
Parasympathetic input:
1. Slows HR (can get as low as 30 bpm)
2. Adds ACh!
3. ACh activates muscarinic receptors which increase K+¬ permeability.
Sympathetic input:
1. Speeds it up! (max: 250-300 bpm)
2. Adds catecholamines (Norep and Ep)
3. Increase permeability of Ca2+ and If channels…
How can the Average human heart rate be 70 bpm?
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External Brain 10: Cardiovascular System
Study Guide Questions
1. Compare and contrast cardiac muscle tissue and skeletal muscle tissue. (This includes comparing individual cells).
2. Compare and contrast the functions of autorhythmic cells and contractile cells in the heart.
3. Clearly describe the events during an action potential in an autorhythmic cell.
4. Clearly describe the events during an action potential in an contractile cell.
5. Be able to compare and contrast the action potentials in autorhythmic cells, contractile cells, and neurons.
6. Describe the events leading up to contraction in a cardiac contractile cell. (Where does the stimulus to “contract” come
from?)
7. What is the sodium-calcium exchanger? How does it work? What other pump is required in order for it to work? Why is this
other pump required?
8. Be able to clearly describe how heart rate is controlled. Address the roles of the parasympathetic and sympathetic branches
of the ANS and be able to suggest a MECHANISM by which each branch could exert its effect.
9. Be able to draw a graph of an action potential that would result in a fast heart rate and a slow heart rate.
10.Be able to describe the significance of ryanodine receptors found on the SR of cardiac contractile cells.
11. Know the path that blood follows around the body and know whether blood is oxygenated or NOT at various anatomical
locations (see big heart diagram at the beginning of lecture today).
12.What is the cardiac cycle?
13.Be able to describe the intrinsic conduction system of the heart. Know the basic anatomy of the heart, so you can give a clear
description.
14.Be able to suggest a possible mechanism for how different structures in the intrinsic conduction system can conduct action
potentials at different speeds.
15.What might be an evolutionary advantage of different structures in the intrinsic conduction system conducting action
potentials at different speeds?
16.Compare and contrast the SA node and the AV node.
17.Describe the stages of the cardiac cycle (to the degree discussed in lecture).
18.What causes the sounds heard during a heart beat?
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