Circulatory System

Consists of ?

Heart and blood vessels (Arteries/Veins/Cappillaries)

Functions (CVS)

•Pumps oxygenated blood and nutrients to the tissues of the body

•Pumps deoxygenated blood to the lungs

•Returns waste metabolic substances from the peripheral tissues to the heart so that it pumps them to the kidneys for excretion

Heart

pump propelling blood through the system

situated in the middle mediastinum

Greek name - cardia

Latin name - cor

Arteries

Carry blood to tissues

End as arterioles

Capillaries

Smallest blood vessels.

Are the exchange vessels.

Sites of O2 , CO2 , nutrient, and metabolic waste product exchange between blood and tissues.

Veins

Result from venules.

Carry blood to the heart.

Macrovasculature

> 0.1 mm in diameter

Elastic arteries.

Muscular arteries.(brachial, radial, femoral arteries)

Muscular veins.

Microvasculature

visible only with a microscope.

- Arterioles

- Capillaries

- Postcapillary venules

particularly important as the site of interchanges between blood and surrounding tissues in normal conditions and in inflammation.

Vascular wall Structural constituents(Blood vessels)

Endothelium

Smooth muscular tissue

Connective tissue

Components of Capillaries and postcapillary venules

endothelium

basal lamina

pericytes

Endothelium

Is a simple squamous epithelium that lines the internal surface of all components of blood and lymphatic systems

Endothelium Functions

Semipermeable barrier

Anti-thrombogenic

Regulate local vascular tone and blood flow

Several roles in inflammation and local immune responses

Secrete various growth factors

Weibel-Palade bodies

are storage granules within endothelial cells which contain a number of chemicals(P selectin and vwf)

von Willebrand disease (VWD)

Deficiency of vWF

which is characterized by bleeding diathesis of the skin and mucous membranes

endothelin 1 and angiotensin converting enzyme [ACE]

stimulate smooth muscle Contraction

nitric oxide [NO] and prostacyclin

stimulate smooth muscle Relaxation

What process do P selectins and interlukins help in?

transendothelial migration at sites of injury or infection

Vascular Smooth Muscle (6 )

Smooth muscle cells are frequent

arranged in helical layers in the tunica media of the blood vessels

Each muscle cell is enclosed by a basal lamina

Absent in capillaries and pericytic venules

connected by communicating (gap) junctions

Permit vasoconstriction and vasodilation

Vascular connective tissue components

Collagen fibers

Elastic fibers

Ground substance

Collagen Fibers

Are ubiquitous

Found between muscle cells/adventitia/ Sub endo layers

Collagen types

IV-basement membranes

III-tunica media

I-adventitia

Elastic fibers

resilient shrinkage of the expanded vascular wall

Predominate in large arteries where they are organized in parallel lamellae

Ground substance

Forms a heterogeneous gel in the extracellular spaces of the vessel wall

affects the diffusion and permeability across the wall

Concentration of glycosaminoglycans is higher in arterial than in venous tissue

Layers of the Heart Wall

Epicardium – visceral layer of the serous

pericardium

Myocardium – cardiac muscle layer forming the bulk of the heart

Endocardium – innermost layer

What are the 3 components of the endocardium?

Endothelium

Subendothelial layer

Subendocardial layer

Describe the subendothelial layer of the endocardium

Thin layer of loose connective tissue

Contains elastic fibers, collagen fibers, and smooth muscle cells

Describe the subendocardial layer of the endocardium.

Connects myocardium to the subendothelial layer

Deeper layer of connective tissue within the endocardium

Lacks smooth muscle cells

Contains veins, nerves, and in the ventricles, branches of Purkinje cells

Which layer is the thickest layer of the heart?

Myocardium

What is the myocardium mainly composed of, and how are its fibers arranged?

Mainly cardiac muscle with its fibers arranged spirally around each heart chamber.

Why is the myocardium much thicker in the walls of the ventricles, particularly the left ventricle, compared to the atrial walls?

Because strong force is required to pump blood through the systemic and pulmonary circulations.

What percentage of the heart mass do myocardial cells constitute?

Approximately 75%

What are the two fundamental functions of myocardial cells?

Initiation and conduction of electrical impulses.

Contraction.

What are the predominant type of myocardial cells, and what is their main function?

myocytes,

responsible for contraction.

What is the function of the small number of myocardial cells specifically designed as electrical cells?

Initiation and conduction of electrical impulses.

What is the conducting system of the heart composed of? Are they nervous tissue?

Modified myocytes lacking adequate myofibril components. They are not nervous tissue.

What is the function of the conducting system cells?

To generate electrical impulses which are then conducted to the myocytes, leading to contraction by excitation-contraction coupling.

What factors can modify the rate of electrical impulse generation and the force of myocardial contraction?

Numerous factors including autonomic input and stretch (Frank-Starling law).

Describe the structure of the epicardium.

Is a simple squamous mesothelium

Supported by a layer of loose connective tissue containing blood vessels and nerves

What layer of the pericardium does the epicardium correspond to?

The visceral layer of the pericardium, the membrane surrounding the heart.

Where do the large vessels enter and leave the heart in relation to the pericardium?

Where the large vessels enter and leave the heart, the epicardium is reflected back as the parietal layer lining the pericardium.

How are underlying structures cushioned during heart movements?

Underlying structures are cushioned by deposits of adipose tissue in the epicardium.

How is friction within the pericardium prevented?

Friction within the pericardium is prevented by lubricant fluid produced by both layers of serous mesothelial cells

What is pericardial effusion?

An abnormal accumulation of fluid in the pericardial cavity.

What condition commonly accompanies an episode of acute pericarditis?

Pericardial effusion.

What is cardiac tamponade?

When a large volume (> 500mL) collects in the pericardial cavity.

What does cardiac tamponade lead to?

Compromise of ventricular filling and embarrassment of the circulation.

What is Beck's triad, and what condition is it associated with?

Beck's triad is a collection of three medical signs associated with cardiac tamponade:

Raised JVP (Jugular Venous Pressure)

Hypotension

Muffled heart sounds