Cardiovascular System Test

Friday

A closed system of the heart and blood vessels

• The heart pumps blood

• Blood vessels allow blood to circulate to all parts of the body

Functions of the cardiovascular system

Transport oxygen, nutrients, cell wastes, hormones to and from cells

Heart size and location

• Size of a human fist, weighing less than a pound

• Located in the thoracic cavity, between the lungs in the inferior mediastinum

Orientation

• Apex is directed toward left hip and rests on the diaphragm

• Base points toward right shoulder

Pericardium

a double-walled sac

Fibrous pericardium

is loose and superficial

Serous membrane

is deep to the fibrous pericardium and composed of two layers

Parietal pericardium:

1. outside layer that lines the inner surface of the fibrous pericardium

Visceral pericardium:

1. next to heart; also known as the *epicardium*

Serous fluid fills

the space between the layers of pericardium, called the *pericardial cavity*

Epicardium

* Outside layer; the visceral pericardium

Myocardium

• Middle layer

• Mostly cardiac muscle

Endocardium

* Inner layer known as *endothelium*

Atria (right and left)

• Receiving chambers

• Assist with filling the ventricles

• Blood enters under low pressure

Ventricles (right and left)

• Discharging chambers

• Thick-walled pumps of the heart

• During contraction, blood is propelled into circulation

Interatrial septum

* Separates the two atria longitudinally

Interventricular septum

Separates the two ventricles longitudinally

Heart functions as a double pump

• Arteries carry blood away from the heart

• Veins carry blood toward the heart

Double pump

• Right side works as the pulmonary circuit pump

• Left side works as the systemic circuit pump

Pulmonary circulation

* Blood flows from the right side of the heart to the lungs and back to the left side of the heart

Blood is pumped…

 out of right side through the pulmonary trunk, which splits into pulmonary arteries and takes oxygen-poor blood to lungs

Oxygen-rich blood returns…

* to the heart from the lungs via pulmonary veins

Systemic circulation

Oxygen-rich blood returned to the left side of the heart is pumped out into the aorta

Blood circulates to

* systemic arteries and to all body tissues

Left ventricle has thicker walls because…

* it pumps blood to the body through the systemic circuit

Oxygen-poor blood returns to…

* the right atrium via systemic veins, which empty blood into the superior or inferior vena cava

**Heart Valves**

* Allow blood to flow in only one direction, to prevent backflow

Atrioventricular (AV) valves

* —between atria and ventricles

Left AV valve:

bicuspid (mitral) valve

Right AV valve:

tricuspid valve

Semilunar valves

* —between ventricle and artery
* Pulmonary semilunar valve
* Aortic semilunar valve

AV valves

• Anchored the cusps in place by chordae tendineae to the walls of the ventricles

• Open during heart relaxation, when blood passively fills the chambers

• Closed during ventricular contraction

Semilunar valves

• Closed during heart relaxation

• Open during ventricular contraction

Valves open and close in response…

* to pressure changes in the heart

Blood in the heart chambers…

* does not nourish the myocardium

The heart has its own nourishing circulatory system consisting of:

• coronary arteries

• cardiac veins

• coronary veins

Coronary arteries

* —branch from the aorta to supply the heart muscle with oxygenated blood

Cardiac veins

* drain the myocardium of blood

Coronary sinus

a large vein on the posterior of the heart; receives blood from cardiac veins

Blood empties into…

* the right atrium via the coronary sinus

Two systems regulate heart activity

• Autonomic nervous system

• Intrinsic conduction system, or the nodal system

Atrioventricular (AV) node is…

* at the junction of the atria and ventricles

Tachycardia

rapid heart rate, over 100 beats per minute

Tunica intima forms a friction-reducing lining

Endothelium

Tunica externa forms protective outermost covering

• Mostly fibrous connective tissue

• Supports and protects the vessel

Intrinsic conduction system, or the nodal system does

• Sets the heart rhythm

• Composed of special nervous tissue

• Ensures heart muscle depolarization in one direction only (atria to ventricles)

• Enforces a heart rate of 75 beats per minute

Sinoatrial( SA) node

• Located in the right atrium

• Serves as the heart’s pacemaker

Atrioventricular (AV) bundle (bundle of His) and bundle branches

\

* are in the interventricular septum

Purkinje fibers spread

* within the ventricle wall muscles

The sinoatrial node (SA node)

* starts each heartbeat

Impulse spreads

through the atria to the AV node

Atria

\

* contract

At the AV node,

the impulse is delayed briefly

Impulse travels

* through the AV bundle, bundle branches, and Purkinje fibers

Ventricles contract

* blood is ejected from the heart

Bradycardia

* low heart rate, less than 60 beats per minutes

The *cardiac cycle* refers to

\

* one complete heartbeat, in which both atria and ventricles contract and then relax
* Systole = contraction
* Diastole = relaxation

Average heart rate

* approximately 75 beats per minute

Cardiac cycle length

* normally 0.8 second

Blood vessels form

* a closed vascular system that transports blood to the tissues and back to the heart

Vessels that carry blood away from the heart

* Arteries and arterioles

Vessels that play a role in exchanges between tissues and blood

* Capillary beds

Vessels that return blood toward the heart

* Venules and veins

Three layers (tunics)

* in blood vessels (except the capillaries)

Tunica media

• Smooth muscle and elastic tissue

• Controlled by sympathetic nervous system

Arteries have

a heavier, stronger, stretchier tunica media than veins to withstand changes in pressure

Veins have

* a thinner tunica media than arteries and operate under low pressure
* Veins also have valves to prevent backflow of blood
* Lumen of veins is larger than that of arteries
* Skeletal muscle “milks” blood in veins toward the heart

Capillaries

• Only one cell layer thick (tunica intima)

• Allow for exchanges between blood and tissue

Form networks called *capillary* *beds* that consist of:

• A vascular shunt

• True capillaries

Blood flow through a capillary bed is known as

*microcirculation*