Anatomy: Cardiovascular System

Cardiovascular system function

Transport (via the blood)
nutrients and metabolic waste
CO2 and O2
Hormones
Heat
Etc

Circulatory routes

Pulmonary circuit= delivers blood to and from the lungs= for external respiration
Systemic circuit= delivers blood to and from the rest of the body= For internal respiration

General circulatory principles

Capillary beds- where exchange takes place
Artery- delivers blood from the heart to capillary beds (oxygenated blood- most arteries not all)
Vein- delivers blood from capillary beds
Back to the heart (most veins)
Or to another capillary bed (these veins are portal veins)
Deoxygenated blood- most veins (not all)

Hepatic portal system

The heart

A muscular pump that circulates the blood
Surrounded by pericardial cavity in mediastinum

Coverings of heart (superficial to deep)

The heart is enclosed in pericardium
Fibrous pericardium (outer)- not serosa
Parietal layer of serous pericardium
Pericardial cavity- contains serous fluid
visceral layer of serous pericardium

Cardiac tamponade

Compression of the heart due to excess fluid in pericardial cavity

The wall of the heart (from outer to inner)

Epicardium= visceral layer of serous pericardium
Myocardium- cardiac muscle layer
Endocardium- has simple squamous epithelium (endothelium) lines inner heart (including valves)

Chambers and vessels overview

Chambers and vessels

Atria (receive blood from veins)
Right atrium: receives deoxygenated blood from: inferior and superior vena cava; coronary sinus- returns blood from heart tissue
Left atrium: receives oxygenated blood from: pulmonary veins
Ventricles (eject blood from heart)
Right ventricle: pumps deoxygenated blood to: pulmonary trunk -> pulmonary arteries
Left ventricle: pumps oxygenated blood to:
aorta- coronary arteries (supplying blood to heart tissues) are branches of aorta

Heart valves

Prevent backflow of blood
Atrioventricular valves
Semilunar valves
Mnemonic: tri before you bi

Atrioventricular valves (AV valves)

Between atrium and ventricle
Tricuspid (R AV) valve- between the right atrium and ventricle
Bicuspid (mitral, L AV) valve- between left atrium and ventricle
These valves held in place by chordae tendinae, which are anchored to papillary muscles- prevents eversion (prolapse)

Semilunar valves (SL valves)

Between great arteries and ventricles
Aortic SL valve- between left ventricle and aorta
Pulmonary SL valve- between right ventricle and pulmonary trunk

Heart sounds in each heartbeat

First heart sound (“lub”)= closing of both AV valves when L and R ventricles begin contracting
Second heart sound (“dup”)= closing of both SL valves when L and R ventricles begin relaxing

Conducting system

Heart muscle has intrinsic rhythm
Conducting system= specialized cardiac muscle cells
Initiates electrical signal (“firing”)
Signals heart chambers to contract in proper sequence
gap junctions spread signal from one cardiac muscle cell to another

Sequence of conduction

Sinoarterial node (SA node)= pacemaker
Note: all cardiac muscle cells can spontaneously fire, but SA node cells have fastest rate
Atrioventricular node (AV node)
Bundle of His (AV bundle)
Bundle branches
Purkinje fibers

Disorders of conducting system

Heart block= damage to AV node or bundle of His (the only path from atria to ventricles)
Signal doesn’t reach ventricles
Ventricles still beat but at a slower pace
Artificial pacemaker restores normal function

Blood

A type of connective tissue
Components of blood:
Plasma= fluid with dissolved nutrients, etc.
Erythrocytes (red blood cells)- carry oxygen
Leukocytes (white blood cells)= immune cells
Platelets= cell fragments for clot formation

Function of blood vessels

Capillary- allows diffusion between blood and other tissues
Artery= carries blood away from heart
Vein= carries blood away from capillary beds
-eventually back to heart

General structure of blood vessel wall

1. Tunica intima (has endothelium= a simple squamous epithelium)
2. Tunica media (smooth muscle, collagen, elastin- all circularly arranged)
3. Tunica externa (collagen, elastin- all longitudinally arranged)

Arteries structure

(Compared to veins and capillaries)
Subject to highest pressure
Thicker walls- mainly due to thicker tunica media
More elastic

Types of arteries

Elastic arteries= conducting arteries
largest artery is 1 cm to 1 in wide
Thick wall, highest elastin content
Very elastic- smooths out pressure fluctuations
Muscular arteries- most of the named arteries
0.3 mm to 1 cm wide
thickest tunica media relative to vessel diameter
Regulate blood pressure and distribution
Arterisles
Smallest arteries, 0.01 to 0.3mm
Regulate blood pressure and distribution

Capillaries structure

Facilitates diffusion
Wall only has tunica intima (mostly endothelium)- very thin wall
Tiny: capillary diameter

Capillary beds

Precapillary sphincters open when tissue is active- lets blood in the capillaries
Precapillary sphincters close with tissue in active- shuts off exchange
Blood still travels though metarteriole and thoroughfare channel

Types of capillaries

Continuous capillaries
Fenestrated capillaries
Sinusoid capillaries

Continuous capillaries

Many tight junction between endothelial cells
In brain:
Completely sealed by tight junctions
all molecules must go across membrane of endothelial cell
least leaky of all
Blood-brain barrier
In most organs (muscles, lungs, skin, etc.):
Not completely sealed by tight junctions
Small molecules can pass through intracellular clefts (where tight junctions are absent)

Fenestrated capillaries

Have fenestrations= holes through endothelial cells (in other aspects, similar to continuous capillaries)
Allows more rapid exchange of small molecules
Kidney, endocrine glands, intestines, synovial membranes

Sinusoid capillaries

have fenestrations
Intercellular clefts are large (very few tight junctions)
Allows exchange of proteins and cells, lots of fluid
Liver, lymphoid organs (spleen, red bone marrow)

Vein structure

Very low pressure system
thinner walls than arteries- less smooth muscle and elastin- collapsible
Larger lumen then arteries- blood reservoir, ≈65% of total body blood
Have valves to prevent backflow of blood

Types of veins

Venules (small veins)- receive blood from capillary beds
veins (other than venules) receive blood from venules
Portal veins- deliver blood from capillary bed to capillary bed (ex: hepatic portal vein)

Mechanisms of enhancing venous return

Return of blood to heart is slow because of low pressure
Need ways to enhance blood return to heart
E.g., skeletal muscular pump: pressure changes (and valves) drive blood back to heart