Mediastinum (Middle Thorax)

Rests on the Diaphragm

• Apex: Bottom point of heart
           Points to left hip.
• Base: Top of heart
           Points to right shoulder. 

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Parietal Pericardium continues on to cover the heart itself and is then called the Visceral Pericardium.

• Epicardium Aka Visceral pericardium (Inner layer of pericardium): Outer heart wall
• Myocardium: heart muscle
• Endocardium: Innermost layer
• Simple squamous epithelium called endothelium which is continuous with blood vessel endothelium.
• Creates a seamless path for blood

Atria: Receiving chambers

Ventricles: Discharging chambers

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• Interatrial septum
• Interventricular septum
• Externally you can see the anterior and posterior Interventricular sulci

• Internally they have pectinate muscles
• Externally they have Auricles
• In the Interatrial septum they have the fossa ovalis
• Atrial walls are relatively thin because they don't have to pump blood far and blood is assisted by gravity.

The Fossa Ovalis is a depression which is a remnant of the foramen ovale.

The foramen ovale is present in the fetal heart. It directs the blood from going into the non-functional fetal lungs.

Immediately at birth the foramen ovale closes leaving a small depression in the interatrial septum called the Fossa Ovalis.

• Superior Vena Cava: Blood returning to heart from above the Diaphragm
• Inferior Vena Cava: Blood returning to heart from below the Diaphragm
• Coronary Sinus: Blood returning to heart from the heart wall

• 4 Pulmonary veins: 2R & 2L
• Blood high in O₂ because it's coming directly from the lungs.

• Discharge chambers
• Thicker walls- especially the left ventricle which send blood through the body.
• Trabeculae carnae: Muscle bundles
• Papillary Muscles: Anchor the heart valves by collagen strings.

What is the pathway of blood through the heart?

Pulmonary Circuit & Systemic Circuit

Pulmonary Circuit:

R atrium-->R ventricle-->pulmonary trunk-->

R & L pulmonary arteries-->lungs for oxygenation-->

Systemic Circuit:

L atrium-->L ventricle-->Aorta-->Body tissues

-->Veins-->Superior & Inferior Vena Cava

-->back to R atrium

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Circulation of the coronary arteries: 

-R & L Coronary arteries are the first 2 branches off the aorta.

-L coronary splits off into the Anterior ventricular artery and the circumflex artery

-R coronary artery continues over to the posterior side and becomes the posterior interventricular sulcus. posterior branch of the coronary is called the marginal artery

Anastomosis: Joining of blood vessels

Anterior interventricular artery joins the posterior interventricular artery at the heart apex.

Interventricular sulcus

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Coronary sulcus

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Heart Attack:

Due to lack of blood causing cell death

The Coronary Sinus in the Right Atrium. (Posteriorly)

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Atrioventricular Valves- passage way from atria to ventricles

Right AV Valve:

Tricuspid valve- has 3 cusps

** Remember: tri rhymes with right

left AV Valve:

bicuspid valve: has 2 cusps

usually called mitral valve

** 2 cusps look like bishops hat: miter

Pressure differences cause the valves to open and close with the flow of blood.

Chordae tendinae, which are attached to the papillary muscles, keep valves from opening the wrong way under pressure.

SL valves: Semilunar valves

Guard the exit of each ventricle

Valves that do not close all the way.

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Valves that do not open all the way due to calcification.

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• Striations
• One nucleus
• Intercalated discs
• the fibers branch
• Gap junctions
• Desmosomes

• Located in Intercalated discs
• Have opening in the middle to allow ions to pass freely
• Allows depolarization to spread rapidly throughout the heart so the heart contracts as one unit

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"one giant cell"

Means that the heart behaves as a single coordinated unit.

Protein patches that anchor 2 cells together to prevent pulling apart during contraction

• AP comes from the heart itself, not a neuron.
• called Automaticity or Autorythmicity
• Plateau phase of the AP- extends the period of depolarization so that the heart can contract long enough to eject all the blood from the ventricles
• The heart is a Functional Syncytium and all cells contract together as a whole unit.

1. Depolarization: Na⁺ enters cell
2. Plateau Phase: Ca²⁺ enters through slow Ca²⁺ gates.
• This phase extends the period of depolarization
• Ca²⁺ that entered the cell causes the SR to release more Ca²⁺ 
3. Repolarization: Ca²⁺ channels close and K⁺ channels to gates to open. K⁺ exits the cell and the cell repolarizes

What is the pacemaker potential?

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• the slow, positive increase in voltage across the cell's membrane that occurs between the end of one action potential and the beginning of the next action potential
• Takes place in the autorythmic cells to initiate contraction:
• Opening of Na⁺ channels by previous APs hyperpolarization
• Membrance potential never has a flat line.

What is the Intrinsic Conduction System of the Heart?

(5 parts)

• Pacemaker of the heart
• Located in Right atrium near the entrance of the superior vena cava
• Depolarizes at 75 bpm- faster than other components of intrinsic conduction system, therefore it causes them to depolarize at its rate
• Produces sinus rythm--Normal rythm
• Depolarization spreads rapidly through the atria and causes atrial contraction

• Located in lower interatrial septum of right atrium.
• Produces AV delay (.01 sec) to allow the atria to contract before the ventricles
• AV delay is produced by narrowing of cells in AV node and fewer gap junctions
• Depolarizes at 50 bpm therefore, if SA node is not functioning as pacemaker, the AV node sets the pace of the heart at 50 bpm.

What is the AV Bundle?

(Bundle of His)

• In upper interventricular septum
• Is the only electrical pathway into the ventricles
• Shortly divides into R & L Bundle branches that travel in the interventricular septum

• Start at the apex (from the AV bundle branches) and go up the walls and spread throughout the myocardium.
• If SA node and AV node fail as pacemakers then the Purkinje fibers set pace of heart at 30 bpm
• At this rate life is not sustainable and person will need to have artificial pacemaker put in.

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**Atrial repolarization is hidden in QRS complex

What are the heart sounds and their meanings?

heart sound: LUB DUP

First sound (LUB): caused by the closing of the AV valves

Second sound (DUP): caused by the closing of the SL valves

** Sound is produced by the vibration of the heart wall when the valves close.**

Incompetent valves produce a "whish" sound when the ventricle contracts and the blood regurgitates back the wrong way

Cardiac Output (CO): the amount of blood pumped by a ventricle in one minute

CO is determined by heart rate and stroke volume

HRxSV=CO

HR=beats per minute

SV=amount of blood in one beat

resting HR(heart rate): 75 bpm

SV(stroke volume): 70mL

75bpm x 70mL=5250mL/min

every minute the heart pump ~5L of blood: the entire blood volume.

bradycardia: <60 bpm

tachycardia: >100 bpm

How is SV calculated?

(stroke volume)

Calculated as the difference between what the ventricle has before contraction and what is left after contraction.

SV= EDV-ESV

EDV:End diastolic volume- the amount of blood at end of diastole(relaxation)

ESV:End systolic volume- the amount of blood at end of systole (contraction)

Preload: The amount of stretch of a ventricle by blood.

**Frank Starling Law

Afterload: The pressure of arterial blood

High blood pressure will make it harder to pump blood into the arteries and will decrease stroke volume

Working against pressure can damage the heart.

Sympathetic System: Increase heart rate by Norepinephrine and Epinephrine(adrenal medulla)

Parasympathetic System: Decrease heart rate by ACh