Chapter 12 – Cardiovascular System Lecture 1

Intro  Cardiovascular System has three types of blood vessels 1. Arteries 2. Capillaries 3. Veins

Arteries  Carry blood away from the heart to the capillaries  Largest in the body = Aorta  Small arteries are called arterioles

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

 The cardiac cycle Figure 42.7 Semilunar valves closed AV valves open AV valves closed Semilunar valves open Atrial and ventricular diastole 1 Atrial systole; ventricular diastole 2 Ventricular systole; atrial diastole sec 0.3 sec 0.4 sec

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 26  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

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) 28  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

Electrocardiogram (ECG or EKG) 29  P wave – begins when SA node fires (excitation of atria)  QRS waves – AV node excites ventricles  T wave – resetting of ventricles (to resting state)

The END!