BIO 265 – Human A&PBIO 265 – Human A&P

Chapter 18

The Heart

The Heart

Size Form Location – mediastinum

– Figure 18.1 and from other text

Heart Anatomy

Pericardium (pericardial sac)– Figures 18.1 and 18.2

Heart Anatomy

Heart Wall– Epicardium– Myocardium– Endocardium– Figure 18.2

Heart Structure and Function

What are the heart chambers? Overview of heart function Figure 18.5

Coronary Circulation

In order for the heart to function, it must have a constant supply of oxygen

The coronary arteries carry the blood to the heart

Figure 18.7

Heart Attack

What is a heart attack or myocardial infarction?

CD Animation

Heart Valves

What are the 4 valves in the heart?– Figure 18.8

Heart Valves

Heart valve function – Figures 18.9 and 18.10

Heart Valves

Heart sounds result from the closing of the heart valves

Heart murmurs occur when a valve does not open or close properly

CD Animation

Histology

What are the characteristics of cardiac muscle?– Branched fibers– Mitochondria– T-tubules– Intercalated disks with gap junctions– Figure 18.11

Conducting System

What are the components?– Figure 18.14

Conducting System

All cardiac muscle cells are autorhythmic– They can generate spontaneous AP– But the SA node is the pacemaker (it

depolarizes faster than other areas of the heart)

Figure 18.13

Conducting System

Once the AP is generated it spreads through the atria to the AV node

What role does the AV node play?– Delays the AP for a split second

The AP then passes very quickly through the bundle branches– The effect is contraction at the apex first– Figure 18.14

Electrical Properties

Cardiac muscle has an RMP similar to skeletal muscle

Differences between cardiac and skeletal AP – Figure from other text

Cardiac Action Potentials

Phases of AP in contractile cells:– Depolarization

• Na+ channels (fast channels) open • K+ channels are closed• Ca2+ channels (slow channels) begin to open

– Early repolarization and plateau• Na+ channels close • Some K+ channels open• Ca2+ channels stay open

– Figure from other text

Cardiac Action Potentials

– Final repolarization• Ca2+ channels close

• many K+ channels open

– Figure from other text

Cardiac Action Potentials

How would the AP in cardiac muscle stimulate a contraction?– Notice that Ca2+ comes from the extracellular

fluid as well as the SR

Cool CD Animations! (my CD)

Electrocardiogram

ECG wave patterns – Figures 18.16, 18.17, and 18.18

The Cardiac Cycle

The cardiac cycle refers to the repetitive pumping process that occurs in the heart– Systole – contraction of the heart– Diastole – relaxation of the heart– CD animation

The Cardiac Cycle Steps:

– Ventricular filling• Passive – during complete diastole

• Active – during atrial systole

– Ventricular Systole• Isovolumetric Contraction – closes AV valves and

opens semilunar valves

• Period of Ejection – blood leaves the ventricles

– Ventricular Diastole• Isovolumetric relaxation – semilunar valves close

– Figure 18.20

The Cardiac Cycle

Assuming an average 75 bpm:– Cardiac Cycle = 0.8 s– Atrial systole = 0.1 s– Ventricular systole = 0.3 s– Diastole = 0.4 s

Awesome CD animation (my CD)

Cardiac Output

Cardiac output (CO) =Heart rate (HR) x Stroke volume (SV) of one

ventricle

Calculations (p.698)– Resting 75 bpm x 70 ml/beat = 5250 ml/min– Or in other words your entire volume of blood

passes through each side of your heart each minute!!!

– Exercise 20 liters/min to 35 liters/min

Regulation of the Heart

Regulation of cardiac output is critical for homeostasis

Starlings law of the heart:– The greater the venous return to the heart,– The greater the stretch of the heart wall,– This results in a more forceful contraction and

therefore a greater stroke volume

Regulation of the Heart

Neural regulation:– The heart is innervated by both sympathetic

and parasympathetic fibers– Parasympathetic – decrease heart rate by

releasing acetylcholine• It opens ligand-gated K+ channels

• Effect?

• Figure 18.15

Regulation of the Heart

– Sympathetic – increases heart rate and force of contraction (stroke volume)

• Norepinephrine (a neurotransmitter) stimulates the opening of the slow Ca2+ channels

• It works through a G-protein system that synthesizes cAMP

• Figures 18.22 and 18.15

Regulation of the Heart

Hormonal Control– Epinephrine and norepinephrine – same effect

as above

Problems in Regulation:– Tachycardia – over 100 bpm– Bradycardia – under 60 bpm (can be normal in

athletes)

Regulation of the Heart

– Congestive Heart Failure – cardiac output is too low to meet body tissue needs

• Blood builds up in the veins (causing the “congestion”)

– Causes:• Coronary Atherosclerosis – decreases the hearts

pumping ability

• Hypertension (high blood pressure) – ventricles can’t push the blood out into the arteries

• Myocardial infarction

Heart and Homeostasis How does the heart help maintain

homeostasis?– Blood pressure example

• Baroreceptors, the cardioregulatory center, and nerves

– Figures from other text

The Fetal Heart There are some interesting differences

between the fetal and adult hearts Why?

– Foramen ovalis in the atrial septum– Ductus arteriosis between the pulmonary trunk

and the aorta– Figures 18.4b and e