The Cardiovascular System: An Overview

Summary

Dr. Eric Strong introduces a series on the cardiovascular system, focusing on the heart and blood vessels. He outlines the system's function, including oxygen delivery and waste removal, and discusses the heart's anatomy, valves, and conduction system. The video also covers the cardiac cycle, types of blood vessels, and the heart's histological structure, providing foundational knowledge for deeper exploration of cardiovascular topics.

Takeaways

• 🧠 The primary function of the cardiovascular system is to circulate blood throughout the body to deliver oxygen and nutrients, and to remove waste products like carbon dioxide.
• ❤️ The heart consists of four chambers, with the right side handling deoxygenated blood and the left side oxygenated blood. It also includes four valves ensuring one-way blood flow.
• 🔬 The cardiac cycle is divided into systole, where the heart contracts, and diastole, where it relaxes, with the left ventricle having thicker walls due to higher pressure requirements.
• 🌐 Blood vessels are categorized into arteries, arterioles, capillaries, venules, and veins, each with specific roles in blood circulation and gas exchange.
• 🛡️ The heart's conduction system, starting with the sinoatrial (SA) node, regulates the heartbeat and ensures synchronized contractions of the heart chambers.
• 🔍 The coronary arteries supply blood to the heart muscle itself, with variations in their anatomy impacting the distribution of blood to different parts of the heart.
• 🩺 The heart's structure includes the endocardium, myocardium, and pericardium, with the myocardium being the muscular layer responsible for contractions.
• 🔬 Cardiomyocytes, the cells of the heart muscle, contain sarcomeres that enable contraction, and are interconnected through intercalated discs for efficient electrical signaling.
• 🌐 The lymphatic system complements the cardiovascular system by returning excess fluid from tissues back into the bloodstream.
• 🏥 Pathologies of the cardiovascular system can be categorized based on the affected component, such as valves, myocardium, pericardium, conduction system, or blood vessels.

Q & A

What is the primary function of the cardiovascular system?

The primary function of the cardiovascular system is to pump blood around the body, delivering oxygen and nutrients to cells and tissues, and removing waste products such as carbon dioxide.

What are the major anatomic structures of the heart?

The major anatomic structures of the heart include the four chambers (right atrium, left atrium, right ventricle, left ventricle), four valves (tricuspid, mitral, pulmonary, aortic), the coronary arteries, and the conduction system.

What is the difference between systole and diastole?

Systole is the period of the cardiac cycle during which the ventricles contract and pump blood out of the heart. Diastole is the period when the ventricles relax and fill with blood.

How does blood flow through the heart?

Blood flows through the heart in a specific sequence: from the right atrium through the tricuspid valve into the right ventricle, then into the pulmonary artery to the lungs. Oxygenated blood returns to the left atrium, through the mitral valve into the left ventricle, and then is pumped out through the aortic valve into the aorta and the rest of the body.

What is the role of the coronary arteries in the cardiovascular system?

The coronary arteries supply blood, oxygen, and nutrients to the heart muscle itself. They include the right coronary artery, the left main coronary artery which bifurcates into the left anterior descending artery and the left circumflex artery.

What are the different types of blood vessels in the body?

The different types of blood vessels include arteries, arterioles, capillaries, venules, and veins. Arteries carry blood away from the heart, arterioles are small vessels that regulate blood flow, capillaries facilitate exchange of substances, venules collect blood from capillaries, and veins return blood to the heart.

What is the conduction system of the heart and why is it important?

The conduction system of the heart is a network of specialized tissues that generate and coordinate electrical impulses to regulate the heartbeat. It includes the sinoatrial (SA) node, atrioventricular (AV) node, bundle of His, and Purkinje fibers. This system is crucial for the proper timing and synchronization of heart contractions.

How does the structure of the heart's valves contribute to its function?

The heart's valves, including the atrioventricular and semilunar valves, have a structure that allows blood to flow in one direction only. This prevents backflow of blood and ensures efficient circulation through the heart and body.

What is the role of the myocardium in the heart?

The myocardium is the muscular layer of the heart composed mainly of cardiomyocytes. It is responsible for the heart's contractile function, pumping blood through the heart chambers and into the circulatory system.

What is the significance of the cardiac cycle in the context of the cardiovascular system?

The cardiac cycle is the series of events that occur within the heart from one heartbeat to the next, including atrial and ventricular contractions and relaxations. It is significant as it describes the mechanical activity of the heart, which is essential for maintaining blood circulation.

Outlines

00:00

💓 Introduction to the Cardiovascular System

Dr. Eric Strong introduces the cardiovascular system, focusing on the heart and blood vessels. He aims to establish a foundational understanding before delving into specific topics. The video will cover the heart's function, major structures, cardiac cycle, blood vessels, and heart's histological structure. The heart's primary function is to pump blood for oxygen delivery and waste removal. It also transports various substances like hormones and immune components.

05:01

🔍 Detailed Anatomy of the Heart

The heart's anatomy is complex and challenging to represent in two dimensions. It consists of four chambers, four valves, and associated vessels. Blood follows a path from the vena cava to the aorta, with the lungs acting as an intermediary for oxygenation. The heart has two atria and two ventricles, separated by septa. The right and left sides of the heart handle deoxygenated and oxygenated blood, respectively. The video also discusses the heart's valves, their structures, and functions in preventing backflow.

10:03

🛠️ The Conduction System and Coronary Arteries

The heart's conduction system regulates the timing of contractions and relaxations. It starts with the sinoatrial (SA) node, which sends electrical signals through the atria and the atrioventricular (AV) node to the ventricles via the His-Purkinje system. The coronary arteries, which supply blood to the heart muscle, are also detailed, including their branching and variations in anatomy.

15:04

🩺 Inside Look at the Heart's Structure

The video provides a three-dimensional view of the heart's exterior and interior. It highlights the proximity of the great vessels and the coronary arteries. The interior view focuses on the valves, ventricles, and the coronary sinus. The cardiac cycle, including atrial and ventricular systole and diastole, is explained, detailing the sequence of events from one heartbeat to the next.

20:06

🌐 Blood Vessels and Lymphatics

This section discusses the blood vessels, starting with the aorta and moving through arteries, arterioles, capillaries, venules, and veins. The function of each type of vessel and their structural differences are highlighted. Lymphatic vessels, responsible for returning interstitial fluid to the bloodstream, are also mentioned, along with their role in health and disease.

25:07

🔬 Histology of the Heart

The heart's histological structure is explored, including the endocardium, myocardium, and pericardium. The myocardium, composed of cardiomyocytes, is responsible for contraction. The video explains the excitation-contraction coupling process and the role of the intercalated discs. The pericardium's function in protecting the heart is also discussed.

🏁 Summary of the Cardiovascular System

The video concludes with a summary of the cardiovascular system's functional components and how pathologies can affect them. It outlines the impact of diseases on the heart's valves, myocardium, pericardium, conduction system, and coronary arteries, as well as on blood vessels and lymphatics. The framework helps in categorizing diagnostic possibilities within the cardiovascular system.

Keywords

💡Cardiovascular System

The cardiovascular system is the body's circulatory system, which includes the heart, blood vessels, and blood. It is responsible for supplying oxygen and nutrients to the tissues, as well as removing carbon dioxide and other waste products. In the video, the cardiovascular system is the central theme, with an emphasis on its function to pump blood throughout the body, highlighting its critical role in maintaining life.

💡Systole

Systole refers to the phase of the cardiac cycle during which the heart muscle contracts, pumping blood out of the ventricles into the circulatory system. The video explains systole as part of the cardiac cycle, where it is contrasted with diastole, the phase of relaxation, to illustrate the heart's pumping mechanism.

💡Diastole

Diastole is the phase of the cardiac cycle when the heart is at rest and filling with blood. The video script describes diastole as the period when the ventricles are relaxing, allowing blood to flow back into the heart from the atria, and it is an essential part of the cardiac cycle for proper heart function.

💡Blood Vessels

Blood vessels are the network of tubes that transport blood throughout the body. They include arteries, veins, and capillaries. The video script discusses the different types of blood vessels, their structures, and their roles in the circulation of blood, emphasizing their importance in the cardiovascular system.

💡Conduction System

The conduction system of the heart is a network of specialized cells that generate and coordinate the electrical impulses needed for the heart to contract. The video script explains how the conduction system, including the sinoatrial (SA) node and atrioventricular (AV) node, regulates the heart's rhythm and is crucial for the proper functioning of the cardiovascular system.

💡Coronary Arteries

Coronary arteries are the blood vessels that supply blood, oxygen, and nutrients to the heart muscle itself. The video script describes the coronary arteries, including the right coronary artery and the left main coronary artery, and their significance in providing the heart with the necessary resources to function.

💡Valves

Valves in the heart are structures that ensure the unidirectional flow of blood. The video script discusses the various heart valves, such as the tricuspid, mitral, pulmonary, and aortic valves, and their roles in preventing backflow of blood, which is vital for the efficient pumping of blood by the heart.

💡Atrial Septum

The atrial septum is the wall that separates the two atria of the heart. The video script mentions the interatrial septum, particularly noting its thinness compared to the interventricular septum, and its role in separating the oxygenated and deoxygenated blood before they enter their respective ventricles.

💡Ventricles

The ventricles are the lower chambers of the heart responsible for pumping blood out to the body. The video script describes the left and right ventricles, their muscular walls, and how the left ventricle, in particular, has a thicker wall due to the higher pressure it must pump against.

💡Histology

Histology is the study of the microscopic structure of tissues. The video script touches on the histological structure of the heart, including the endocardium, myocardium, and pericardium, and how these layers contribute to the heart's function, such as the myocardium's role in muscle contraction and the endocardium's role in lining the heart valves.

💡Cardiac Cycle

The cardiac cycle refers to the series of events that occur within the heart as it contracts and relaxes once, from one beat to the next. The video script explains the cardiac cycle, detailing the phases of atrial and ventricular systole and diastole, and how these phases contribute to the heart's pumping action.

Highlights

Introduction to the cardiovascular system with a focus on the heart and blood vessels.

The cardiovascular system's function is to pump blood for oxygen delivery and waste removal.

Description of the heart's major anatomic structures including the coronary arteries and conduction system.

Explanation of the cardiac cycle and the phases of systole and diastole.

Types of blood vessels and their roles in the circulatory system.

Histological structure of the heart, focusing on the layers and their functions.

The importance of oxygen in cellular respiration and energy production.

Blood's role in carrying waste products like carbon dioxide and metabolic wastes.

Transport of electrolytes, glucose, fatty acids, and hormones by the blood.

The immune system's components carried by the blood, such as white blood cells and antibodies.

Gross anatomy of the heart, including its four chambers, valves, and great vessels.

Details on the heart's valves and their function to prevent backflow of blood.

The conduction system of the heart and its role in regulating heartbeats.

The sinoatrial node as the heart's pacemaker and its regulation by the autonomic nervous system.

The structure and function of the coronary arteries that supply blood to the heart muscle.

Three-dimensional view of the heart for better understanding of cardiac structures.

The cardiac cycle's sequence of events from one heartbeat to the next.

Different types of blood vessels and their characteristics from arteries to veins.

Lymphatic vessels' role in returning interstitial fluid to the bloodstream.

Summary of the cardiovascular system's functional components and their related pathologies.

Transcripts

[Music]

hello i'm eric strong and i'm a clinical

associate professor of medicine at

stanford university

and this is the first video in this

series on the cardiovascular system

this will provide an overview of the

heart and blood vessels

starting from the basics in order to

provide a broad common

knowledge base for all viewers before

deep dives into individual topics

by the end of this video you will be

able to describe the overall function of

the cardiovascular system

identify the major anatomic structures

of the heart

including the coronary arteries and the

primary components of the conduction

system

you'll be able to describe the cardiac

cycle including the definitions of

systole and diastole

to list and describe the different types

of blood vessels

and to describe the histological

structure of the heart

in short the function or purpose of the

cardiovascular system

is to pump blood around the body

but why the simple answer is the

delivery of oxygen

deoxygenated blood that is blood that's

relatively lacking in oxygen

is pumped from the heart to the lungs

where oxygen is picked

up the now oxygenated blood returns to

the heart

from where it's pumped to the rest of

the body at which point the oxygen

is offloaded within other organs and

tissues

the oxygen is an essential part of

cellular respiration

this is the process by which cells

generate energy storing atp

from glucose and other molecules

containing chemical potential energy

but the movement of oxygen is just part

of the story

blood carries a lot more than that for

example waste products

most notably carbon dioxide which is a

byproduct of cellular respiration

and which the heart must pump back to

the lungs to be exhaled

blood carries other metabolic waste

products to the liver

such as bilirubin and lactate for

processing

and in some cases elimination from the

body for example in bile

it carries urea to the kidneys to be

excreted in the urine

blood transports electrolytes glucose

fatty acids

and it transports hormones like insulin

and cortisol

that allow one part of the body to send

signals to another

and it carries essential components of

our immune system

like white blood cells and proteins such

as antibodies and cytokines

so while it's true that the circulation

of oxygen

is the single most important function of

the heart

it is far from the only necessary one

to understand how the pumping mechanism

works let's first focus on the gross

anatomy of the heart

itself the heart is a surprisingly

difficult structure to represent with a

two-dimensional picture

no matter what angle or cross-section is

viewed at least one notable structure

will be hidden behind

others and kind of like a map of the

world there is no two-dimensional view

that accurately represents

both the relative size and location of

the chambers

i'll start with this view but i'll

switch around to other images as needed

on the most basic level the heart's

physical structure consists

of four chambers surrounded by muscular

walls

four valves a handful of so-called great

vessels

and a number of minor vessels to give a

lay of the land

i'll walk through the path that blood

takes as it returns from the body

in its deoxygenated state

first blood arrives in the chamber

called the right atrium

blood can reach the right atrium through

one of three paths

all blood returning from above the

diaphragm enters via the superior

vena cava all blood returning from below

the diaphragm

enters via the inferior vena cava

and most blood returning from the heart

muscle itself enters the right atrium

via this much smaller vessel called the

coronary sinus

from the right atrium blood travels

through a valved opening

called the tricuspid valve into the

right ventricle

from the right ventricle it travels

through another valve

called the pulmonary valve into the

pulmonary artery

which carries the still deoxygenated

blood to the right and left lungs

where carbon dioxide will be offloaded

and oxygen will be picked up

the oxygenated blood returns to the

heart via one of

four pulmonary veins bringing it to the

left atrium

from the left atrium it travels through

the mitral valve

into the left ventricle from the left

ventricle blood then exits the heart

through the aortic valve which is hidden

behind the pulmonary valve

in this particular view and then it

travels via the aorta

to the rest of the body this sequence of

steps from the vena cava to the aorta

is separated into two segments by the

lung with the right side of the heart

containing

deoxygenated blood and the left side of

the heart containing

oxygen in the blood the right and left

atria are separated by a relatively thin

inter atrial septum hidden here behind

the right ventricular outflow tract

while the left and right ventricles are

separated by the relatively thick

and muscular interventricular septum

as a side note while almost all diagrams

of the heart

show the right heart in blue and the

left heart in red

the oxygenated blood is not literally

blue

but rather more of a maroon color

also going back to my previous comment

about how no

single view of the heart is perfect this

view makes it appear that the right

heart is larger than the left

when in reality the left is larger than

the right

it's just that the left heart sits

somewhat posterior to the right

when viewed from this angle if we look

at a cross section of the heart taken

along this plane

we get a better idea of the relative

volume and shape

of the ventricular chambers the large

round

thick walled one is the left ventricle

and the smaller crescent-shaped one

is the right ventricle the left

ventricular wall needs to be much

thicker because it pumps against

much higher pressures than the right one

does

back to this view let's discuss the

valves a little more

the valves consist of leaflets or cusps

that allow movement of blood in

only one direction all of the valves

normally have

three cusps except the mitral valve

which normally has

two each valve belongs to one of the two

sides of the heart

right versus left and each has one of

two structures

atrial ventricular versus semilunar

the cusps of the two atroventricular

valves are attached to fibrous threads

called chordae tendineae or tendonous

cords

these are in turn attached at the other

end to the papillary muscles

which are conical projections from the

walls of their respective ventricles

the purpose of the chordae tendineae and

the papillary muscles are to prevent

backwards movement of the valve cusps

during the high pressures generated when

the ventricles contract

which otherwise could result in the

retrograde movement of blood from the

ventricles

backwards into the atria the semilunar

valves

named because their cusps are

reminiscent of half moons

are concave when viewed from above they

both normally have

three cusps and no chordae in this

classic cross-sectional view of the

heart known as the parasternal

long axis view we can see the

significant difference in structure

between the mitral valve with some of

its chordae and one of the papillary

muscles

and the adjacent smaller semilunar

aortic valve

one final point to make about the valves

is that although it can be hard to

appreciate

in most two-dimensional views the four

valves

sit in close proximity in roughly

similar plane to one another this plane

is composed of fibrous

tissue that includes fibrous rings

around the valve openings

these rings are stiff and they help to

maintain the valve shape

and provide structure to which the valve

cusps can attach

more generally this fibrous tissue

functionally acts as the skeleton of the

heart

it also is non-conductive of electricity

which is critical for proper regulation

of the heart rhythm

as it funnels electrical signals between

the atra and ventricles

to a relatively small location called

the av node

where it can be more easily regulated

although i've already mentioned them

individually to review

let me list the eight great vessels

these are the superior

and inferior vena cava which bring blood

from the body to the right atrium

the main pulmonary artery which

bifurcates into the right and left

pulmonary arteries

which travel to the right and left lungs

respectively

the aorta which is the main artery of

the body from which all other arteries

branch

except the pulmonary artery it's often

divided into four parts

the ascending aorta which then loops up

and posteriorly

into the aortic arch which continues

downward and becomes the descending

thoracic aorta coursing posterior to the

heart

and once the aorta crosses below the

diaphragm it's known as the

abdominal aorta and last the four

pulmonary veins

which bring blood from the lungs to the

left atrium

and this brings us to the conduction

system while we often think of the heart

as primarily a mechanical pump

there needs to be some mechanism that

tells

each chamber when to contract and when

to relax

and that mechanism is the conduction

system which delivers

electrical signals to different chambers

at different times

electrical impulses normally originate

within a specialized tissue called the

sinoatrial node

sa node or sometimes just sinus node

it's located in the superior posterior

aspect of the right atrium

the frequency of these impulses is

governed by a balance between the

sympathetic and parasympathetic

divisions

of the autonomic nervous system the

sympathetic nervous system

tells the sa node to fire more

frequently while the parasympathetic

nervous system

tells it to fire less frequently in

normal

healthy adults the balance between these

two results

in a resting heart rate between 50 and

90 beats per minute

electrical impulses fired from the sa

node travel throughout the two atria

triggering their contraction and the

ejection of blood through the av

valves into their respective ventricles

the electrical signal will next reach

the atrioventricular or

av node within the inferior part of the

interatrial septum

while the sa node can be thought of as

the pacemaker of the heart

the a b node is more of a gatekeeper as

mentioned it's the sole

location in which electricity can

normally pass from the atria to the

ventricles

and it conducts relatively slowly

providing time for blood to move

from the contracted atria into the

relaxed ventricles

after holding up the signal by a hundred

or so milliseconds

or a tenth of a second the a b node lets

it continue through a band of conducting

fibers called the hiss bundle

that divides into right and left bundle

branches which travel to the right and

left ventricles respectively

the right and left bundles terminate in

a network called the purkinje fibers

which rapidly deliver the signal to the

ventricles

the overall consequence of this system

is the rapid

and nearly simultaneous contraction of

the right and left ventricles

in a wavefront that begins inferiorly at

the cardiac apex

and travels upwards towards the valves

which helps to increase the efficiency

with which the heart ejects blood

to see the coronary arteries that is the

arteries that supply the heart muscle

itself

we need an exterior view and again the

limitations of two dimensions

make it impossible to see all of them at

once

coming off the aorta immediately above

the aortic valve

are two coronary arteries one is the

right coronary artery or rca

which predominantly supplies blood to

the right ventricle

and usually to the sa and av nodes of

the conduction system

the other is the left coronary artery

more commonly known as the left

main coronary artery which quickly

bifurcates into the left anterior

descending artery or lad

which supplies the anterior

interventricular septum

and anterior wall of the left ventricle

and the left

circumflex artery which wraps around

behind

to supply the lateral wall of the left

ventricle

the coronary circulation contains a

number of anastomoses or distal

connections

between these three arterial territories

that allow for some redundancy of blood

supply in the event that one artery

becomes

obstructed also there are many normal

and pathologic anatomic variations to

the coronary circulation

most notably the normal variations in

how blood is supplied to the posterior

interventricular septum and the inferior

wall of the left ventricle

as i mentioned the heart is a difficult

organ to accurately represent

anatomically

in two dimensions so therefore i'm going

to show you what it looks like

in three dimensions so you can get a

better idea of how different

cardiac structures relate to one another

here is the exterior of the heart we can

start with the great vessels and we can

immediately see that several are in

very close proximity to one another here

is the svc or superior vena cava

here is the aorta which loops upwards

and posterior into the aortic arch

and here's the main pulmonary artery

which bifurcates into the

left and right pulmonary arteries

we can also see the four pulmonary veins

as they enter the left

atrium on the posterior side

another structure apparent from the

outside one which i have not discussed

yet

are these funny shaped things which

extend a little over the surface

anonymists call these the oracles of the

right and left atrium

but most clinicians refer to these as

the right and left atrial appendages

these are important particularly the

left atrial appendage because

these out pouchings are a region of

relative stasis for blood

and therefore they can be the site of

blood clot formation

particularly during abnormal heart

rhythms in which the atria do not

contract

such as one called atrial fibrillation

on the outside we also see the coronary

vessels this one here

is the right coronary artery which

supplies the right ventricle

the left main coronary artery is hidden

behind the pulmonary artery

as is its bifurcation but here is the

left anterior descending artery

supplying the anterior wall of the left

ventricle and around the back

is the left circumflex artery supplying

its lateral wall had mentioned that

there were a large number of variations

to coronary anatomy

including which artery supplies blood to

the inferior wall of the left ventricle

in this case if we follow this muscle

right here backwards

we'll see that it originates from

the right coronary artery so therefore

this is called

right dominant circulation

the last thing to note on the outside is

this blue vessel

right here which at its most distal end

is known as the coronary sinus

which drains blood from the heart itself

into the right atrium

now let's take a look inside few things

to note here

first are the valves specifically how

close together they are

particularly the aortic and the mitral

valves

these white extensions are the chordae

tendineae

we can also better appreciate the

difference in size and shape between the

two ventricles

the right ventricle which is down here

inferior to the tricuspid valve

is relatively small and moon shaped

while the left ventricle

is slightly larger and a little bit more

round

we also can see here just superior to

the tricuspid valve

is the entrance of the coronary sinus

where the coronary sinus drains into the

right atrium

on the inside surface of the ventricles

we can note this mesh of

muscular bundles here these are known as

trabeculations

and it's actually not known what

function they serve

the cardiac cycle is a sequence of all

events within the heart

that occur from one heartbeat to the

next

each cycle is triggered by the sa node

firing an electrical signal

this signal triggers the right and left

atria to contract

squeezing blood through the already open

tricuspid and mitral valves

into the right and left ventricles this

period of atrial contraction

is formally referred to as atrial

systole

but is more commonly referred to as the

atrial kick

after the electrical signal reaches the

av node and undergoes the brief av

delay allowing time for filling of the

ventricles during the atrial kick

the signal propagates through the

hispurkinji system

and triggers ventricular contraction as

we've already discussed

the rapid increase in pressure within

the ventricles causes the av

valves to quickly snap shut triggering

the first heart sound in the classic

lobe dub of the heartbeat this first

heart sound is known

as s1 and the intraventricular blood is

ejected through the now open

semilunar valves after a brief period of

time

the ventricles relax again at this point

there is

higher pressure in the pulmonary artery

and aorta than in the right and left

ventricles respectively

so the semilunar valves snap shut

resulting in the second heart sound

known predictably as s2

at this point the ventricles have

emptied much of their blood

and relaxed to the point that the

pressure in the atria

are now higher than in the ventricles

and so the av

valves open once again and this pressure

gradient

drives the passive filling of blood into

the ventricles

even before the next sa node impulse

triggers atrial contraction

and a repeat of the cycle the period of

the cycle during which the ventricles

are contracting

is called ventricular systole or usually

just systole

and the period of the cycle during which

the ventricles are relaxing

is called ventricular diastole or just

diastole confusingly

the timing of ventricular diastole

includes atrial systole

which is why atrial systole is usually

referred to as

the atrial kick or sometimes just atrial

contraction

and blood blood is moving from the atria

to the ventricles

throughout all diastole so both before

and during atrial contraction

the final point about the cardiac cycle

systole

is always shorter than diastole although

the relative fraction of the cardiac

cycle each takes up

is dependent on the heart rate as the

heart rate increases

diastole shortens much more so than

systole

such that at extremely fast rates they

can be

almost equal in duration

[Music]

up until now i've just been discussing

the heart but the heart is only

one half of the cardiovascular system

the other half is the blood vessels

which are the conduits through which

blood is pumped around the body

moving from the heart to the peripheral

tissues and from the peripheral tissues

back to the heart

there are five basic types of vessels

starting from the heart

all blood leaves the left ventricle via

the aorta

from the aorta branch off large and

medium-sized arteries

which are thick-walled with significant

elastic tissue

and smooth muscle allowing them to

handle high pressure

arteries divide into smaller arterioles

which

are the site of greatest resistance to

blood flow through the circulation

and arterioles eventually divide and

divide again

into microscopic networks of extremely

small vessels

called capillaries which are so small as

to be lined by a single layer of

endothelial cells sometimes

the capillaries are where gas exchange

between blood

and peripheral tissues actually occurs

although the capillaries are tiny

there are billions of them in the body

such that their net cross-sectional area

is many times that of the aorta or of

any other level of blood vessel

as a consequence the capillaries are

where blood travels the most

slowly through the circulation which is

of course helpful for the exchange of

gas

nutrients and waste after the

capillaries

blood next moves to the venules which

are analogous to the arterials

and from there to the veins in contrast

to arteries

veins are relatively thin walled and

lack much elastic tissue

resulting in significant distensibility

this dissensibility allows veins to act

as a reservoir for blood volume

arteries and veins are typically named

for either the part of the body they

travel through

or which organ they bring blood to or

away from

and they often exist as matching pairs

for example

the left renal artery and left renal

vein or the right femoral artery and

right femoral vein

there are of course numerous exceptions

in addition to the blood vessels there

are also conduits called

lymphatics lymphatic vessels are

responsible for returning

interstitial fluid that is extra

vascular fluid that surrounds the cells

and sits in the connective tissue back

to the bloodstream

lymphatic capillaries merge into ever

larger vessels

until eventually most feed into a

conduit called the thoracic duct

which empties into large veins of the

thorax

the last topic i'll discuss is histology

and the microscopic structure of the

heart

from a histological perspective the

heart is composed of three layers

first is the thin inner endocardium

partly composed of endothelial cells

similar to those that line the blood

vessels the endocardium also forms the

lining of the heart valves

immediately beneath the endothelium is

the sub endocardium

composed of loose connective tissue and

is also the location of the purkinje

fibers

the next major layer is the thick

myocardium which is the heart muscle

and which is composed predominantly of

cardiomyocytes

cardiomyocytes or cardiac muscle cells

each contain long myofibrils that

contain a repeating microstructure

called

sarcomeres which are the fundamental

contractile units of the cell

within the sarcomeres are filaments of

two proteins called actin and myosin

whose atp and calcium-dependent

interaction

is responsible for myocyte contraction

cardiomyocytes contain a high density of

mitochondria

necessary for the continuous production

of energy containing atp

the cells are connected to one another

via porous bridges called intercalated

discs

which allow for the free movement of

electrolytes which is necessary for

rapid transmission of electrical signals

from one cell to the next through the

muscle tissue

this rapid transmission of signal is

necessary for coordinated contraction

the overall process by which an

electrical signal results in myocyte

contraction

is called excitation contraction

coupling

external to the myocardium is the

pericardium

the pericardium is a fibrosyrus

structure that encases the heart and the

roots of the great vessels

it consists of a tough outer fibrous

pericardium

which is tethered to the diaphragm in

the sternum and which keeps the heart in

place

and there is a inner smooth serous

pericardium that's folded over on itself

to make two separate layers containing a

potential space between them

the outer of these serous layers is the

parietal pericardium

which is fused to the fibrous

pericardium

the inner of the serous layers is the

visceral pericardium

which lies on the myocardium and is

sometimes referred to as the epicardium

yes the terminology is frustrating to

keep straight

the potential space between the two

serous layers is called the pericardial

space

and is normally much thinner than it is

in this image

it contains a thin film of fluid that

allows the heart to beat in a near

frictionless environment

however in certain pathologic states

this space can significantly enlarge

due to the pathologic excessive

accumulation of fluid

negatively impacting cardiac function

to summarize what i've discussed so far

the cardiovascular system

can be very broadly considered a

collection of

nine functional components five in the

heart

and four in the periphery and pathologic

conditions of the system

can usually be mapped to just one of

these components

for example the heart is made up of the

valves

which are affected by valvular heart

disease and an infection called

endocarditis

the myocardium which is affected by

heart failure and

myocarditis the pericardium which is

affected by pericardial effusions

and pericarditis the conduction system

which is affected by a very diverse

collection of arrhythmias or abnormal

heart rhythms

and the coronary arteries which are

involved in coronary artery disease

colloquially known as heart disease and

which is responsible for

the conventional types of heart attacks

the blood vessels can be subdivided into

arteries

including arterioles which are impacted

by peripheral artery disease

the veins including venials which are

impacted by

a condition called venous insufficiency

the capillaries which are rarely the

primary site of pathology

but which can be the site of

manifestations of sepsis

and lymphatics which cause a condition

called lymphedema

when obstructed when approaching a

patient with an undiagnosed disease

i find this framework to be helpful in

considering and categorizing

different diagnostic possibilities

within the cardiovascular system

keeping in mind that the framework

somewhat excludes congenital heart

disease

which can involve just one component

like a bicuspid aortic valve

but which usually spans multiple

functional components

or which transcends this framework

altogether

that concludes this introductory

overview of the cardiovascular system

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