Download Notes 13 - Dr. Dorena Rode

Human Physiology
Lecture Notes for Chapter 13
Circulatory System Overview
1. cardiovascular system: blood, heart, blood vessels
2. lymphatic system: lymph, lymph vessels, associated lymphoid tissue (nodes, spleen)
Functions
cardiovascular system
lymphatic system
Transport
O2 and CO2
nutrients
waste
hormones and regulatory chemicals
immune cells
fat from villi
immune cells
return fluid to blood (vascular system)
Protection
clotting factors
immune cells
lymphoid tissue with associated
immune cells
Regulation
cardiovascular system is an important effector
for temperature regulation
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Vascular System
The vascular system performs its transport function by using series of vessels that are the conduit for blood.
(FOX Fig 13.25 gives anatomical differences.) In order for there to be adequate blood flow the body
maintains a constant blood pressure (one of the essential parameters).
arteries:
Thick muscular walls with a elastic layer. During systole (heart contraction) the arteries expand
from the pressure. Then when the heart is relaxing (diastole) the arteries “push” due to elastic
recoil. Although they don't actually contract the elastic recoil acts as a “pump” and maintains
blood pressure (BP). For this reason they are sometimes referred to as a pressure reservoir.
Mean arterial pressure (MAP)is 100mmHg
arterioles: less elastic, relatively thicker smooth muscle layer, smaller diameter
offer resistance to blood flow, greatest area of regulation
vasoconstriction/dilation (or precapillary sphincters) controls flow to capillary bed
capillaries:
single layer of endothelium
no cell is further than 3 to 4 cells from a capillary
5% of blood volume is here
only 30-50% of the capillary beds are open at one time (not enough blood)
different gaps between endothelium cells allows differences in movement
venous vessels:
veins and venules
thin walled, distensible (stretch easily), one way valve
average pressure 2 mmHg
64% of blood volume is here: volume reservoir
lymph vessels:
one way valves
pacemaker cells: smooth muscle contracts spontaneously
The following support the blood return to the heart: 1.
2.
3.
4.
pressure differential
one way valves
skeletal muscle pumps
decrease in thoracic pressure caused by inhalation
Heart Anatomy
Fox pages 394-406
(8th edition: pgs 378-390)
Chambers of the heart:
atria (singular = atrium)
receive venous blood.
ventricles pump blood to
either the lungs (pulmonary
circulation) or the body
(systemic circulation). The
blood flow to the body equals
the blood flow to the lungs.
The left ventricle is more
developed because the average
back pressure is 100mmHg,
while the pulmonary back
pressure averages about
15mmHg.
The valves between the atria and the ventricles are the AV valves (atrioventricular valves ).
The valves leaving the ventricles are semilunar valves (pulmonary semilunar valve and aortic semilunar
valve).
myocardial cells - short, branched, striated. Connected with gap junctions. The two atria contract as one
unit and are referred to as a myocardium. The two ventricle also contract as one unit and are a myocardium.
pacemaker cells - spontaneously depolarize and
fire A.P. The pacemaker cells in the sinoatrial
node (SA node) drive the rest of the heart to
depolarize. These are innervated (as mentioned in
chapter 9) by parasympathetic and sympathetic
neurons. (More on regulation in chapter 14)
Spread of depolarization:
Conduction through atria is fast (1m/sec), slows
through the atrioventricular node (AV node)
(0.03 to 0.05m/sec) and then speeds up again
through the bundle of His and Purkinje fibers
(5m/sec) to ensure even contraction of ventricles.
Ventricular contraction is delayed by 0.1 to 0.2
seconds from atrial contraction.
Review of action potentials (A.P.)
Action potentials in the SA node (pacemaker cells):
Calcium slowly “leaks” into the pacemaker cells
resulting in spontaneous depolarization to the
threshold of voltage gated calcium channels.
Opening of voltage gated calcium channels begins
the action potential. Repolarization is fostered by
opening of potassium channels.
SA nodes spontaneously fire A.P. at a rate of
70 to 80 per minute. Other cells in the conducting
tissue of the heart also spontaneously depolarize,
but at rate slower than the SA node, so they are
“driven” to fire A.P. at a rate that is set by the SA
node. (They are never given a chance to
spontaneously depolarize, except in pathological
conditions. When cells other than the SA node are
setting the heart beat it is referred to as an ectopic
focus.)
Action potential in the heart muscle cells
Notice long plateau phase. This extends the time of the
action potential. Action potentials in cardiac cells last
from 200 to 300 msec!
This long plateau prevents summation and tetanus. It
allows the muscle to relax between beats and ensures that
the chambers fill with blood before the next beat.
Action potential compared to contraction:
The Cardiac Cycle
Repeating pattern of contraction and relaxation of the heart.
systole - contraction (ventricular)
diastole - relaxation (ventricular)
Numbers refer to diagram on the next page.
1.
Atria and ventricles are relaxed (AV valves are open)
Chambers fill with blood (ventricles fill to about 80%)
2.
Atria contract and add the last 20% of blood to the ventricles
Ventricles 100% full (about 120ml) this is the end diastolic volume.
3.
Ventricles begin to contract
increase pressure causes AV valves to close
(pressure not high enough yet to open the semilunar valves)
isometric (or isovolumetric) contraction
4.
Pressure increases over arterial pressure (about 80 mmHg in the aorta)
semilunar valves open, blood is ejected
pressure continues to rise as ventricles contract (to about 120 mmHg for aorta and 25 mmHg in the
pulmonary artery)
isotonic contraction
two thirds of the end diastolic volume is ejected - this is called the stroke volume (about 80ml)
5.
Pressure drops below arterial pressure and semilunar valves shut from the back pressure
isometric (isovolumetric) relaxation of ventricles
this is the beginning of diastole (relaxation of ventricles)
6.
When pressure of ventricles is below atria the AV valves open and filling begins again (back to step 1)
Electocardiogram (ECG)
P wave: atria depolarize (and contract)
QRS wave: ventricles depolarize (beginning of systole)
ST segment: plateau phase of cardiac action potential
T wave: ventricles repolarize (beginning os diastole)
First heart sound immediately after this.
Second heart sound shortly after T wave begins