Transcript Chapter 12 * Cardiovascular System

Chapter 12 – Cardiovascular System
Lecture 1
Intro

Cardiovascular System has
three types of blood vessels
1.
2.
3.
Arteries
Capillaries
Veins
Arteries



Carry blood away from the heart to the capillaries
Largest in the body = Aorta
Small arteries are called arterioles
Arteries
Arteries

Most carry oxygen
rich blood

Made up of three
different layers of
tissue, the middle
layer consisting of
smooth muscle
that can contract
and regulate blood
flow and pressure
Capillaries



Capillaries join arterioles to venules
They are extremely narrow and thin walls (single layer
of epithelium)
We have about 6,000 square meters of these things!
Capillary Beds


Capillary beds (network of capillaries) are present in all
tissues of the body
They are the site for diffusion and exchange of material
within the body (oxygen, carbon dioxide, glucose etc)
Capillary Beds


Only certain capillary beds are open at any given time
Each capillary bed has an arteriovenous shunt that
allows blood to go directly from the arteriole to the
venule.
Veins



Veins and venules (small veins) take blood from the capillary beds to
the heart
Venules drain blood from the capillaries and then join to form the vein
Veins bring oxygen poor blood to the heart.
Veins are Different than Arteries


Veins are made up of the same three layers at arteries
however, have less smooth muscle.
Veins have valves which allow blood to flow only toward
the heart and prevent back flow.
Veins are Different than Arteries


Because the walls of veins are thinner, they can expand.
70% of our blood is in veins at any given time = veins are
blood reservoirs.
Blood Vessels
The Heart



Cone shaped organ located between the lungs.
Two sides (right and left) of the heart are separated by
the septum.
Has four chambers.


Upper two – Atrium
Lower two – Ventricles (pump blood)
The Heart




Myocardium – the major
portion of the heart which
consists of cardiac muscle tissue.
Pericardium – thick
membranous sac that surrounds
the heart.
Endocardium – inner surface of
the heart.
Septum- separates the heart into
a right side and a left side.
The Heart

Valves

The heart has 4 valves that direct blood flow and prevent backflow

Atrioventricular valves: between the atria and the ventricles

Semilunar valves: located between the ventricles and their
attached vessels
Atrioventricular valves

Valves are supported by strong fibrous strings called
chordae tendineae

These support the valves and prevent them from
inverting when the heart contracts

Atrioventricular valve on the right side of the heart is
called tricuspid valve, (it has three flaps).

Atrioventricular valve on the left side is called the
bicuspid or mitral valve, (it has two flaps).
Semilunar Valves

The pulmonary semilunar valve lies between the right
ventricle and pulmonary trunk.

The aortic semilunar valve lies between the left ventricle
and the aorta.
The Cardiac Cycle
 Our
heartbeat (the "lub-DUPP" sound) is caused by
vibrations of the heart when VALVES CLOSE
 can be divided into TWO PHASES:
 ATRIA CONTRACT while VENTRICLES
RELAX and semilunar valves are closed
"lub" = closing of atrioventricular valves
 Then VENTRICLES CONTRACT while
ATRIA RELAX and atrioventricular valves
are closed.
"DUPP" = closing of the semi-lunar valves
The Cardiac Cycle
 SYSTOLE
= CONTRACTION of heart muscle
 DIASTOLE = RELAXATION of heart muscle
 The CARDIAC CYCLE (=
“heartbeat”) occurs about 70
times per minute (100,000
times per day) in the average
adult

2 Atrial systole;
ventricular
diastole
Semilunar
valves
closed
The cardiac cycle
0.1 sec
Semilunar
valves
open
0.3 sec
0.4 sec
AV valves
open
1 Atrial and
ventricular
diastole
Figure 42.7
AV valves
closed
3 Ventricular systole;
atrial diastole
What Controls the Heartbeat?
 Heart
beats without the brain telling it to
 it is INTRINSIC
 Heart
has SPECIAL TISSUE, called NODAL TISSUE
that has characteristics of both nerve and muscle tissue,
which controls the heartbeat

There are TWO nodal regions in the heart:
SA NODE
AV NODE
SA (sinoatrial) NODE



modified cardiac muscle cells in upper back wall of right atrium
INITIATES HEARTBEAT by sending out automatic signal (nerve
impulse) about every 0.85 seconds to make the ATRIA
CONTRACT.
called the “PACEMAKER” because keeps the beat regular
 irregular heartbeats can be corrected by implanting an
ARTIFICIAL PACEMAKER to stabilize heart rate
AV (Atrioventricular) Node
 at
base of right atrium near septum
 SA node sends its signal along fibers to the atria as well as to
the AV node
 when the pulse reaches AV node, the AV node itself sends out
a signal along special conducting fibers called PURKINJE
FIBERS
 Purkinje fibers take message to VENTRICLES, causing them
to contract (beginning at base/apex of heart and moving up
like a wave)
Cardiac Cycle

Heartbeat controlled by:



SA Node
causes atria to contract as it sends nerve impulses to AV Node
(AV valves open, semilunar valves closed)
AV Node gets stimulated and sends impulse along Purkinje
fibres

causes ventricles to contract (semilunar valves open, AV valves
close)
Cardiac cycle
 Events
that produce a single heartbeat
 2 phases
Diastole – atria contract and ventricles fill (blood pressure
lowest)
 Systole – ventricles contract and blood is ejected from the
heart (blood pressure highest)

 Heart
valves open and shut in response to pressure
gradients
26
Extrinsic Control of Heartbeat

While the heart can keep a steady beat on its own, the heart
rate (how fast it goes) is under NERVOUS CONTROL
 there is a HEART-RATE CENTER in the MEDULLA
OBLONGATA of the brain
Sympathetic Nervous System = increases heart rate
“fight or flight” response
 Parasympathetic Nervous System = decreases heart
rate
“rest and digest” response

Electrocardiogram (ECG or EKG)


Electrical currents generated in heart can be
detected by electrodes placed on surface of body
An electrocardiogram is a graphic display of heart’s
electrical activity
28
Electrocardiogram (ECG or EKG)



P wave – begins when SA node fires (excitation of atria)
QRS waves – AV node excites ventricles
T wave – resetting of ventricles (to resting state)
29
The END!