Chapter 20: Herat Part 2

Gibrous skeleton of heart, heart valve, cardiac conduction system, cardiac cycle, heart sounds

Fibrous skeleton of the Heart

• dense CT 4 rings sorround valves

• structural foundations for valves (anchor valve with dense CT), insertion for myocardia, electrically insulates atria and ventricles separately

  • pump 2 step process

Av valves

• in arota

• When open, cusps project into ventricles

  • blood flow from atrium into ventricle

• Blood moves from atria to ventricles

• valve open when Atrial pressure > ventricular pressure

• When closed, edges of cusps meet and create a barrier

  • so blood doesnt flow backwards

• Chordae tendineae prevent cusps from opening backwards into atria

• valves closes: Atrial pressure < ventricular pressure

Semilunar Valves

• in pulmonary vlave

• 3 crescent moon cusps

  • made og thicker CT

• Open for blood to pass from ventricles into arteries

• valve open when Ventricular pressure > arterial pressure

  • force cusps apart allowing blood to be ejected from ventricle to artery

• close when arterial pressure > Ventricular pressure

Autorhythmic cells

• repeatedly and rhythmically generate action potentials

  • doesnt need a stimulus

Pacemaker

sets rhythm of the heart

What are the cardiac muscle cells connected by in cardiac conjunction?

Gap junction

cardiac conjection order and what they do

1. SINOATRIAL (SA) NODE - in charge of generating AP is a pacemaker cell

2. ATRIOVENTRICULAR (AV) NODE - helps transmit impulse to contract from atrium to ventricles

3. ATRIOVENTRICULAR (AV) BUNDLE (BUNDLE OF HIS) - only place electrical actviity can cross atrium to ventricle

4. RIGHT AND LEFT BUNDLE BRANCHES

5. PURKINJE FIBERS - activate cardiac muscle of ventricles to initiate ventricular contraction

why is it important that there is a delay between the contraction of the atria and contraction of ventricles?

If no dely dont expect blood to nove if all 4 chambers contract at the same time. delay is necessary to give blood somehwere to go when chambers contract. The ventricles have to be relaxed to recieve blood when atria is contracting.

What initiates the contraction of the heart?

SA node

What transmits AP across the fibrous skeleton after short delay?

AV node

What carries AP to the apex of the heart?

His/ AV bundle and bundle branches

What delivers action potetnial to ventricular cardiac muscle cells

Purkenjie fibers

Membrane potential 

• difference in electrical potential (mV) on either side of the membrane

  • every cell has it but cant maniupulate it

  • muscle and neurons can alter MP in response to stimulus what makes them excitable

Resting membrane potential

• difference of inside and outside of an unstimulated cell

• Negative charges in cytosol, positive charges in ECM = polarized

  • inside of cell more negative than outside (polarized)

  • neg pole = inside

  • pos pole = outside

Depolarization

• decrease in difference between outside and inside cell (let sodium in)

  • in excitable cells if stimulated can respond to that by depolarizing which is a decrease in polarization between inside and outside of a cell

  • example is letting more positive enter the cell which will reduce the difference less polarized

  • have to go to Resting can't stay depolarized forever

  • let positive into depolarize to repolarize take positive out of the cel

Repolarization

• returning membrane to resting membrane potential after a disturbance

  • let potassium out

Action potential

• rapid depolarization and repolarization

  • Happens in one discrete part of membrane

  • influx of + ion charge (sodium) causes adjacent mebrane to depoloarize

  • depolarize happens in 1 part of membrane depolarizing and AP then cause next part of membrane to have it

ECG

tells us the pattern of electrical activity of the heart

3 waves of ECG

1. P wave – depolarization of atria

2. QRS wave – depolarization of ventricles

• stringer signal because lots of cardiac muscle in ventricles

1. T wave – repolarization of ventricles

Cardiac Cycle steps

1. relaxation period

2. atrial systole

3. ventricular systole

Relaxation period

• All 4 chambers in diastole – relaxation

• Atrial pressure > ventricular pressure < arterial pressure

Atrial systole

• Atria contract

• Atrial pressure > ventricular pressure < arterial pressure

Ventricular systole

• Ventricles contract

• 1st part of ventricular systole:

  • Atrial pressure < ventricular pressure < arterial pressure – all valves closed

• 2nd part of ventricular systole:

  • Atrial pressure < ventricular pressure > arterial pressure – semilunar valves open, blood is ejected

How many heart sounds

• 4 sounds caused by turbulence of blood

Sounds

S1 – AV valves closing (lub)

S2 – Semilunar valves closing (dub)

S3 – ventricular filling in relaxation (not heard)

S4 – atrial systole (not heard)