Heart

The Heart Chapter 19

Heart Anatomy

Size and Location
About the size of the fist and weighs less than a pound
Enclosed within the mediastinum, medial cavity of the thorax
Rests on superior surface of diaphragm
Anterior to vertebral column and posterior to sternum
Lungs flank laterally and partially obscure it
~ 2/3 of it lies to left
Broad, flat base or posterior surface

Coverings
Heart enclosed in double-wall sac called the pericardium
Loosely fitting superficial part of sac is the fibrous pericardium
The pericardium:
Protects heart
Anchors it to surrounding surfaces
Prevents overfilling of the heart with blood

Coverings (con’t)
Deep to fibrous pericardium is the serous pericardium, which is thin and slippery and composed of 2 layers.
The two layers have a film of serous fluid between them
Allows the hear to work in a relatively friction-free environment

Coverings (con’t)
Inflammation of the pericardium, pericarditis, hinders production of serous fluid and roughens the surfaces.
Creates a creaking sound that can be hear with a stethoscope and pain deep to the chest.
If persists, can cause adhesions and impede heart activity

Layers of Heart
Epicardium
- visceral layer of the serous pericardium
- often infiltrated with fat
2. Myocardium
- composed mainly of cardiac muscle
- forms bulk of heart
- layer that contracts
3. Endocardium
- glistening white sheet of endothelium
- lines heart chambers and covers valves

Heart Chambers The heart has 4 chambers: 2 superior atria and 2 inferior ventricles

The internal partition that divides the heart is the interatrial septum when it separates the atria and the interventricular septum when it separates the ventricles.

Atria: The Receiving Chambers
The atrium has two basic parts:
A smooth-walled posterior part
An anterior part with ridged walls
The interatrial septum has a shallow depression called the fossa ovalis. This marks the spot where the foramen ovale existed in the fetal heart.

Atria (con’t)
Receiving chambers for blood returning to the heart from the circulation.
Contract minimally to push blood into the ventricles; therefore, they are relatively small and thin.

Atria (con’t)
Blood enters the right atrium through 3 veins:
Superior vena cava – returns blood from body regions superior to the diaphragm
Inferior vena cava – returns blood from body areas below the diaphragm, and
Coronary sinus – collects blood from the myocardium

Atria (con’t)
Four pulmonary veins enter the left atrium, which make up most of the heart’s base.
The pulmonary veins transport blood from the lungs back to the heart.
These vessels are best seen in a posterior view of the heart.

Ventricles: The Discharging Chambers
Make up most of the heart
Right ventricle forms heart anterior surface
Left ventricle forms inferior surface
When contracted, blood is propelled out of the heart into circulation.
Right ventricle pumps blood into pulmonary trunk  to the lungs for gas exchange
Left ventricle pumps blood into the aorta  to the body’s systems

Pathway of Blood

Heart is two side-by-side pumps
Each side serves two different circuits:
Pulmonary Circuit
Systemic Circuit

Pulmonary Circuit Pump
Right side
Blood returns from body, which is oxygen-poor and carbon dioxide-rich and enters the right atrium.
Then, it passes into the right ventricle, which pumps it to the lungs via the pulmonary trunk.
In the lungs, blood unloads the carbon dioxide and pucks up oxygen.
Freshly oxygenated blood is carried to the left side of heart.

Systemic Circuit Pump
Left side of heart
Freshly oxygenated blood leaves lungs to return to left atrium and passes into left ventricle, which pumps into the aorta.
Blood is transported via smaller arteries to body tissues, where gases and nutrients are exchanged.
Blood loaded with carbon dioxide and oxygen depleted, returns through the systemic veins to right side of heart, where enters venae cavae.

Pathway (con’t)
Although equal volumes are pumped, 2 ventricles have unequal workloads.
Pulmonary circuit is short and low-pressure.
Systemic circuit is very long and high-pressure.
Encounters 5x’s as much friction
Walls are 3x’s as thick
Cavity is nearly circular

Coronary Circulation
Feeds the heart and is the shortest circulation of body
Actively delivers blood when heart is relaxed, but are ineffective when ventricles are contracting because:
They’re compressed by contracting myocardium, and
The entrances are partly blocked by flaps of valves.

Coronary Circulation (con’t)
Myocardial cells are weakened by temporary lack of oxygen, but don’t die.
Complete blockage of a coronary artery leads to tissue death and a myocardial infarction, or heart attack or coronary.
Cardiac muscle is amitotic, which is replaced by noncontractile scar tissue.

Heart Valves Blood flows through the heart in one direction: from atria to ventricles. One way traffic is enforced by heart valves. Valves open and close in response to changes in blood pressure.

Atrioventricular (AV) Valves
Located at each atrial-ventricular junction, preventing backflow into the atria when the ventricles are contracting.
Right AV valve, the tricuspid valve, has 3 flaps. Left AV valve, the bicuspid valve, has 2 flaps.
Attached to the valve flaps are tiny white collagen cords called chordae tendineae, or “heart strings,” anchor flaps to heart walls.

AV Valves
When heart is relaxed, AV flaps hang limply into ventricular chambers below; blood flows into atria and through open AV valves into ventricles.
When ventricles contract, blood is compressed into chambers, intraventricular pressure rises, forcing blood upwards against valve flaps.
Valve flap edges meet, closing valves.
Chordae tendineae serve as guidewires to anchor flaps in place.

Semilunar (SL) Valves
Aortic and pulmonary SL valves guard bases of large arteries that exit the ventricles.
When ventricles are contracting and intraventricular pressure rises, the SL valves are forced open and flaps flatten against the arterial walls and blood rushes by.
When ventricles relax, blood flows back toward the heart and closes the valves.

Cardiac Cycle
Heart writhes in the chest when it contracts
Forces blood out of chambers when it contracts and fills with blood when it relaxes.
Two terms are used to refer to heart contraction/relaxation:
Systole  contraction
Diastole  relaxation

Cardiac Cycle (con’t)
Includes all events associated with the flow of blood through the heart during one heartbeat.
Marked by a succession of pressure and blood volume change in heart.
Lasts about 0.8 seconds
Atrial systole  0.1 s
Ventricular systole  0.3 s
Total heart relaxation  0.4 s (quiescent period)

Cardiac Cycle (con’t)
Two important points:
Blood flow through the hear tis controlled by pressure changes, and
Blood flow along a pressure gradient is always from higher pressure to lower pressure through any available opening.

Heart Sounds
Two distinguishable sound during cardiac cycle can be heard.
Often described as “lub-dup”, which is associated with the closing of the heart valves.
Pause between lub-dup is the quiescent period.

Murmurs
An abnormal or unusual heart sound
Caused by obstruction along blood pathway
Fairly common in young children
Indicate valve problems (or possible hole in heart)
If a valve is incomplete, a swishing sound can be heard.

Cardiac Output (CO)
Amount of blood pumped out be each ventricle in 1 min.
Highly variable and increases in response to demands
Difference in resting and maximal CO is called the cardiac reserve.
Nonathletes’ reserve is 4-5x’s normal CO
Athletes’ reserve can be 7x’s the normal CO

Regulation of Heart Rate
With a healthy cardiovascular system the amount of blood pumped (stroke volume) is relatively constant.
When blood volume drops sharply or the heart is weakened, stroke volume declines and the heart maintains the CO by beating faster.
Also, the nervous system can affect heart rate. Fear, anxiety, stress, etc. causes an increase in norepinephrine, which causes the pacemaker to fire more rapidly and the heart beats faster.

Heart

by North PIke High School

Accessibility

Categories

Upload Details

Usage Rights

Statistics

Heart Presentation Transcript