CIRCULATORY SYSTEM

Mr. Jeremy Schriner

The Heart

4 chambers Located between the

lungs 2/3 of heart left of

midline Apex points downward

& contacts the diaphragm

It lies in the pericardial cavity

The Heart

It is separated from the other organs by a double-layered membrane = Pericardium

The Pericardium is composed of a Fibrous Pericardium & a Serous Pericardium. The serous pericardium has 2 parts: 1.    Parietal layer - attached to the back of the fibrous

pericardium 2.    Visceral layer (epicardium) - attached to the heart

muscle These two are separated by a fluid filled space = pericardial

cavity.

The Heart Wall

A. Epicardium - outermost, = Visceral layer of the serous pericardium  

Heart Wall

 B. Myocardium - middle, = Cardiac muscle cells (very thick)

   

The Heart Wall

 C. Endocardium - innermost, forms valves, & is continuous with the endothelium of the blood vessels that enter & leave the heart

Chambers

4 chambers 2 upper: Lt. & Rt. Atrium 2 lower: Lt. & Rt.

Ventricle

Valves

4 valves 2 Atrioventricular (AV)

Valves Rt. AV valve = tricuspid Lt. AV valve = bicuspid,

mitral

2 semilunar valves: found at the base of 2 large vessels leaving the heart = Pulmonary & Aortic valves

Blood Flow

1. Rt. Atrium: receives deoxygenated (venous) blood from 3 vessels;

A. Superior vena cava - blood from above the heart

B. Inferior vena cava - blood from below the heart

C. Coronary sinus - blood from the heart muscle    

Blood Flow

2. Blood flows through Rt. AV valve into Rt. Ventricle (the flaps of AV valves are held in place by Chordae Tendineae & Papillary Muscles to prevent back flow)  

Blood Flow

3. Rt. Ventricle contracts & blood exits through the Pulmonary Semilunar valve. It enters the Pulmonary trunk which divides into Lt. & Rt. Pulmonary arteries. Blood goes to lungs (carbon dioxide out, oxygen in)  

Blood Flow cont.

4. Oxygenated blood returns from the lungs through the Pulmonary veins to the Lt. Atrium  

  

Blood Flow

 5. Blood flows through the Lt. AV valve (bicuspid, mitral) to the Lt. Ventricle  

Blood Flow

6. Lt. Ventricle contracts & blood exits through the Aortic Semilunar valve & enters Ascending Aorta.

Coronary circulation (Blood flow to Heart Muscle) First vessels off of the

Ascending Aorta = Lt. & Rt. Coronary Arteries

Coronary Circulation cont.

The blood returns from the heart muscle via 2 major veins  1. Great Cardiac vein: brings

deoxygenated blood back from the anterior heart wall 

2. Middle Cardiac vein: brings deoxygenated blood back from the posterior heart wall.

Both vessels empty into the Coronary Sinus (a large vein on back of heart). It empties into Rt. Atrium

Conduction system

An electrical system. It determines the rate & rhythm of the heartbeat

1. Sinoatrial node (SA node,

pacemaker) - Neurons fire at 70/80 beats per minute, causes atria to contract  

2. Atrioventricular node (AV node) - neurons fire at 40-50 beats per minute; typically the SA node overrides it, but if SA node is not functioning it will ultimately cause ventricles to contract at a slower rate.  

Conduction System

3. Atrioventricular Bundle (Bundle of His) - conducts impulses between ventricles   

4. The AV Bundle divides into lt & rt Bundle Branches which go to the ventricles.  

5. Purkinje fibers - deliver impulses directly to the

myocardium of the ventricles.  

Blood – connective tissue with fluid matrix A. Fluid = plasma B. Blood cells = formed

elements 1. Red blood cells (RBC's)

= ERYTHROCYTES a. Flattened, biconcave,

anucleated discs b. Life span - 120 days c. Function: transport

oxygen & carbon dioxide bound pigmented protein = hemoglobin

Blood cont.

2. White blood cells (WBC's) = LEUKOCYTES a.granulocytes

i. eosinophils ii. Basophils iii. Neutrophils 

Blood cont.

2. White blood cells (WBC's) = LEUKOCYTES b. Agranulocytes

i. Monocytes ii. Lymphocytes

Blood cont.

3. Thrombocytes = PLATELETS; not cells. Cytoplasmic fragments of megakaryocytes. Assists in blood clot formation.

Hemopoiesis = Blood Cell formation. Occurs in red bone marrow. A. Erythropoiesis =

RBC formation B. Leukopoiesis = WBC

formation C. Thrombopoiesis =

platelet formation

Blood vessels: blood flow

Blood flows from the heart through progressively narrowing vessels;             artery ->arteriole -> capillary

And returns through progressively enlarging vessels;

venules -> vein-> heart  

Blood vessels Structure: arteries and veins

have 3 tunics 1. Tunica Externa (adventitia)

- Outermost, loose connective tissue, this is the thickest layer in veins  

2. Tunica Media - middle, smooth muscle layer, this is the thickest layer in arteries  

3. Tunica Intima - innermost a. Endothelium - simple

squamous + c.t. b. Subendothelial layer - c.t.

Arteries (carry blood away from heart) Elastic - large amount

of elastin expandable Muscular - tunica media

is predominantly smooth muscle.

There is an elastic lamina on each face of the tunica media

Arterioles -

Smallest, tunica media very thin (<10 layers)

Capillaries

"Functional units" of circulatory system, very thin-walled, allows for exchange of gases, nutrients, & waste products.

Composed of the Tunica Intima only

Venules  

Usually lack a tunica media. They have the other two tunics

Veins

Carry blood to the heart) All 3 tunics present. Veins have a very

Low pressure, The blood flow through them is dependent on: A. Contraction of

surrounding musculature = Skeletal muscle "pump"

B. One-way valves