Mammalian Transport System

Ch. 8 Part 4 Heart Function

Structures to Know• Atria (Atrium) or auricle

• Upper chambers• Receive blood from veins

• Ventricles• Lower chambers• Blood flows into from the atria and out through

arteries• Aorta• Pulmonary artery• Venae cavae (vena cava)• Pulmonary veins• Coronary arteries

• Bring oxygenated blood back to the heart• Septum

• Wall of muscle that separates chambers on the right side of the heart from the chambers on the left side of the heart

• Blood cannot pass through

Valves and Nodes to know• Atrioventricular valves (between the atrium and the

ventricle)• Mitral/bicuspid valve (LEFT SIDE OF HEART)• Tricuspid valve (RIGHT SIDE OF HEART)

• Semilunar valves• Pulmonary Valve• Aortic Valve

• Sinoatrial node (SAN)• Patch of specialized muscle fibers in RIGHT ATRIUM• Pacemaker

• Atrioventricular node (AVN)• Patch of conducting muscle fiber located in upper septum

• Purkyne tissue• Conducting muscle fibers running down septum, along the

right and left ventricles

Valves• Atrioventricular valves

(between the atrium and the ventricle)• Mitral/bicuspid valve

(LEFT SIDE OF HEART)

• Tricuspid valve (RIGHT SIDE OF HEART)

• Semilunar valves• Pulmonary Valve• Aortic Valve

Important!!!!• Heart is myogenic does NOT need outside nerve

impulses to initiate heart beat• Valves in heart do NOT actively open and close• Valves open and close due to PRESSURE changes in

chambers

Closing of valves create thump-thump

of heartbeat

Structure of Heart• Atrium walls thin, muscular walls

• Low pressure exerted• Ventricle walls thick and muscular

• Right ventricle small force needed to push blood to lungs

• Left ventricle large force needed to push blood all over body• VERY MUSCULAR• Greater pressure developed in

left ventricle than left atria

The Cardiac Cycle• Sequence of events that

make up 1 heart beat• Heart beats about 70x a

minute• 3 stages of the cycle

1. Atrial systole2. Ventricular Systole3. Ventricular Diastole

Systole ContractionDiastole Relaxation

Atrial Systole• Heart filled with blood• Muscle in atrial walls (very

thin) contract• Not a lot of pressure from

this contraction• Enough pressure to force

blood in atria through ATRIOVENTRICULAR VALVES (AV) into ventricles

• No back flow of blood into pulmonary veins or vena cava b/c of semilunar valves

Ventricular Systole• Ventricles contract 0.1 s after atria

contracts• Thick, muscular ventricle walls

push blood out (exert high pressure)

• AV valve shut when pressure in ventricles exceeds pressure in atria

• Semilunar valves open• Blood rushes up into aorta &

pulmonary artery• Lasts for 0.3 seconds

Ventricular Diastole • After 0.3 seconds, ventricular muscle

relaxes• Ventricle pressure decreases• Semilunar valves shut, preventing

backflow of blood• Blood only fills in cusps of valves• Blood from veins flow into the 2 atria• Blood is at low pressure• Walls of atria expand to accommodate

blood (very little resistance)• Some blood trickles into ventricles

through AV valve• Atria contracts and cardiac cycle begins

again

Control of the Heart Beat• Myogenic muscles

• Naturally contracts and relaxes• No nerve impulses required

• Sinoatrial Node (SAN) • Set out rhythm for all other muscle

cells to contract• SAN contraction rhythm slightly

faster than the rest of the heart• SAN contracts wave of excitation

(depolarization) sent across all of the atria & muscles of atria contract

Things NOT to say when describing nodes:

• “Signal”• “Wave” alone • “Pulse”• “Message”• “Nerve impulse”You SHOULD describe the function of SAN using:• “Wave of excitation”• “depolarization”• “impulse”

Ventricle contraction• SAN causes contraction of all atria muscles• Ventricle muscles delayed due to band of

fibers between the atria and ventricles that does NOT conduct electric impulses

• Only path for impulses to reach ventricles is through path of conducting fibers in septum called ATRIOVENTRICULAR NODE (AVN)

• AVN receive excitation from atria, delays it 0.1s and then passes it to another bunch of conducting fibers called the PURKINJE FIBERS or PURKYNE TISSUE

• Wave of excitation is sent up ventricle walls—bottom-up

Fibrillation• When muscular walls of heart flutter

rather than contract and relax as a whole

• Rapid, irregular, unsynchronized contraction of muscle cells

• Atrial fibrillation (non fatal) Afib• Can lead to stroke

• Ventrical fibrillation (fatal) Vfib• Faint, cardiac arrest

• Caused by:• Electric shock or damage to large

areas of muscle in walls of heart• Miss firing of electric impulse from

atria• Instead of electrical impulse going

from atria to AVN to Purkinje tissue in the ventricle, all muscle cells in ventricle get excited in all directions

Electrocardiograms (ECGs)• Graph plotting voltage vs. time• Records electrical potentials of heart

over time• Place electrodes over opposite sides of

heart• P= wave of excitation over atrial walls

• Q, R, S= wave of excitation over ventricle walls

• T = recovery of ventricle walls• Contraction time = time b/t Q and T• Filling time = time b/t T and Q

How To Read an ECG• EKG paper is a grid where time is measured along the horizontal axis. • Each small square is 1 mm in length and represents 0.04 seconds. • Each larger square is 5 mm in length and represents 0.2 seconds.

• Voltage is measured along the vertical axis.• 10 mm is equal to 1mV in voltage.

Calculating Heart from ECG

1. Determine rate of strip• Time of strip is given; measure strip with

ruler and divide length by sec of strip or…• May be given 20mm * s-1

2. Measure distance of one cardiac cycle• Beginning of one P to the beginning of the

next P