Cardiovascular 2:Heart Anatomy and Histology

Summary

Dr. Deviant's lecture delves into the cardiovascular system, emphasizing the heart's unique blood supply and the perils of blockages leading to angina pectoris and myocardial infarction. He explains the heart's structure, highlighting the non-dividing nature of cardiac muscles and the formation of scar tissue post-damage. The lecture distinguishes between cardiac and skeletal muscles, focusing on the heart's synchronized contraction and the role of the cardiac conduction system in rhythm regulation. It also touches on the importance of heart valves, the phenomenon of heart murmurs, and the use of pacemakers and defibrillators in treating heart conditions.

Takeaways

• 😀 The heart needs its own blood supply through a capillary network, and any blockage can cause significant issues.
• 😟 Angina pectoris is a thoracic pain caused by temporary deficiency in blood flow, often related to stress or physical demand.
• 🚨 Myocardial infarction (heart attack) results from blocked blood flow leading to death of myocardial tissues, with scar tissue replacing the damaged heart muscle cells.
• 💔 Damage to the left ventricle, which pumps blood to the rest of the body, is particularly dangerous.
• 🔗 Cardiac muscles resemble skeletal muscles but are shorter and have intercalated discs that help cells connect and function as a unit.
• 🔋 Unlike skeletal muscles, cardiac muscles do not require neuron stimulation for contraction, thanks to gap junctions that allow heart cells to contract together as a functional syncytium.
• 🚫 Cardiac muscles do not exhibit sustained tetanic contractions like skeletal muscles, preventing prolonged contraction.
• 💡 The heart's contraction relies on oxygen, and low oxygen levels can lead to cell death, with high calcium and acidity causing gap junctions to close.
• 💓 The heart contracts and relaxes in a coordinated manner (systole and diastole), with the atria and ventricles working together to move blood through the body.
• ⚡ The cardiac conduction system controls heart rhythm through pacemakers like the SA node and AV node, with specialized fibers distributing the electrical signal across the heart.

Q & A

What is the importance of the blood supply to the heart?

The blood supply to the heart is crucial as it provides the necessary nutrients and oxygen to the heart muscle. Any blockage in this supply can lead to serious issues such as angina pectoris or myocardial infarction (heart attack).

What is angina pectoris and what causes it?

Angina pectoris is a type of chest pain caused by a temporary deficiency in blood flow to the heart. It is often related to stress, increased physical demand, or temporary weakening of the heart muscle.

How does a blockage in the blood supply to the heart lead to a myocardial infarction?

A blockage in the blood supply, often due to a cholesterol plaque, prevents blood flow to the heart muscle, leading to the death of myocardial tissues, which is known as a myocardial infarction or heart attack.

Why is damage to the left ventricle considered more serious than other parts of the heart?

Damage to the left ventricle is more serious because it is the thickest and most important chamber of the heart. It is responsible for pumping blood to the aorta and the rest of the body, so damage can significantly impair the heart's ability to circulate blood.

What is the difference between cardiac and skeletal muscles in terms of contraction?

Cardiac muscles contract autonomously without direct stimulation from neurons, whereas skeletal muscles require innervation from neurons to contract. Additionally, cardiac muscles contract as a unit due to gap junctions connecting each cell, unlike skeletal muscles which contract independently.

What are the three main differences between cardiac and skeletal muscles as mentioned in the script?

The three main differences are: 1) Cardiac muscles do not require stimulation by neurons to contract, unlike skeletal muscles. 2) Cardiac muscles exhibit functional syncytium, meaning the heart contracts as a whole unit, whereas skeletal muscles contract independently. 3) There is no sustained tetanic contraction in cardiac muscles, which is possible in skeletal muscles.

What is the role of the intercalated discs in cardiac muscle cells?

Intercalated discs in cardiac muscle cells are specialized structures that facilitate the connection between cells, allowing for the coordinated contraction of the heart muscle as a single unit.

Why are gap junctions important in the heart's function?

Gap junctions are crucial as they allow the electrical impulse to spread from one cardiac cell to another, enabling the heart to contract in a synchronized manner.

What is the significance of the cardiac conduction system in the heart's function?

The cardiac conduction system is responsible for generating and coordinating the electrical impulses that regulate the heartbeat. It includes the SA node, AV node, bundle of His, and Purkinje fibers, ensuring the heart contracts in a coordinated and efficient manner.

What happens if both the SA node and AV node fail in the heart?

If both the SA node and AV node fail, an implantable cardioverter-defibrillator may be used. This device monitors heart rhythms and delivers shocks to the heart to restore normal rhythm when necessary.

What is the difference between a heart murmur and a more serious heart condition?

A heart murmur is a sound caused by turbulent blood flow, often due to leaky valves, and is common in infants. However, in adults, a heart murmur can indicate valve damage or other serious heart conditions.

Outlines

00:00

💉 Understanding the Heart's Blood Supply and Blockages

In this section, Dr. Deviant discusses the importance of the heart's own blood supply, despite its role in pumping blood. The key issues that arise when there is a blockage in the heart's circulation include angina pectoris, a temporary thoracic pain, and myocardial infarction (heart attack), which is more serious as it leads to the death of myocardial tissues. The inability of cardiac muscle cells to divide results in scar tissue replacing dead cells, which cannot contract. Damage to the left ventricle is particularly dangerous as it impairs the heart's ability to pump blood to the rest of the body. The structure and function of cardiac muscles are compared to skeletal muscles, highlighting features such as intercalated discs and gap junctions that enable coordinated contraction.

05:02

💓 The Unique Contraction Mechanism of the Heart

This part emphasizes the unique functional syncytium of the heart, where all the cells contract as a unit due to the presence of gap junctions. Unlike skeletal muscles, which can sustain long tetanic contractions, the heart cannot, ensuring that the heart contracts and relaxes rhythmically without fatigue. The section also explains the critical role of oxygen in cardiac muscle function, the impact of high calcium levels and increased acidity, and how gap junctions close under stress, preventing the spread of action potentials.

10:03

🫀 Systole, Diastole, and Heart Valve Function

Dr. Deviant explains the pumping mechanism of the heart, detailing the phases of systole (contraction) and diastole (relaxation). He describes how atrial systole and ventricular diastole coordinate to fill the ventricles with blood, and how ventricular systole pushes blood out through the semilunar valves. The proper functioning of heart valves is crucial, and any issues, such as heart murmurs caused by leaky valves, can indicate serious problems. The importance of the correct timing of valve opening and closing during the heart's cycle is also highlighted.

⚡ Cardiac Conduction System and Pacemakers

This segment covers the heart's ability to generate action potentials and contract without neuronal stimulation, emphasizing the intrinsic nature of cardiac muscle contraction. The cardiac conduction system, including the SA node (the primary pacemaker), AV node, bundle of His, and Purkinje fibers, is detailed. The SA node initiates the heartbeat, and if it fails, the AV node takes over. Implantable defibrillators and pacemakers are mentioned as interventions for serious arrhythmias, such as ventricular fibrillation, with defibrillators resetting the heart's electrical activity.

Keywords

💡Cardiovascular System

The cardiovascular system, also known as the circulatory system, is responsible for the circulation of blood throughout the body. In the video, Dr. Deviant discusses the importance of this system, particularly focusing on the heart's blood supply and its implications for health.

💡Angina Pectoris

Angina pectoris is a type of chest pain that occurs due to insufficient blood flow to the heart muscle. It is often stress-related or due to increased physical demand. In the script, Dr. Deviant mentions it as a potential issue arising from a blockage in the heart's blood supply.

💡Myocardial Infarction

Myocardial infarction, commonly known as a heart attack, is a serious condition where blood flow to the heart muscle is blocked, leading to the death of heart tissue. Dr. Deviant explains that a cholesterol plaque can cause such a blockage, emphasizing its severity due to the irreversible damage it causes.

💡Cardiac Muscle

Cardiac muscle is the muscle tissue that makes up the heart. It is striated, similar to skeletal muscle, but has unique properties such as the ability to contract rhythmically without conscious control. The script describes how these muscles are interconnected through gap junctions, allowing for synchronized contractions.

💡Mitotic

Mitotic refers to the ability of cells to divide and reproduce. Dr. Deviant points out that cardiac muscle cells are non-mitotic, meaning they cannot divide. This is significant because when these cells die, they are replaced by scar tissue, which cannot contract, leading to potential heart dysfunction.

💡Left Ventricle

The left ventricle is the chamber of the heart that pumps oxygen-rich blood to the rest of the body via the aorta. It is the thickest and most muscular part of the heart. In the script, Dr. Deviant highlights that damage to the left ventricle is particularly dangerous because it can impair the heart's ability to circulate blood effectively.

💡Intercalated Discs

Intercalated discs are specialized structures that connect cardiac muscle cells, allowing for the rapid transmission of electrical signals between cells. They are likened to corrugated cardboard in appearance and are essential for the coordinated contraction of the heart. Dr. Deviant mentions them as a feature that distinguishes cardiac from skeletal muscle.

💡Functional Synchrony

Functional synchrony refers to the coordinated contraction of the heart muscle as a single unit. This is made possible by the interconnected nature of cardiac muscle cells through gap junctions. Dr. Deviant explains that unlike skeletal muscles, which contract independently, the heart contracts as a whole due to functional synchrony.

💡Cardiac Conduction System

The cardiac conduction system is a network of specialized cells that generate and coordinate the electrical impulses controlling the heartbeat. Dr. Deviant outlines the components of this system, including the SA node, AV node, and Purkinje fibers, which are crucial for the heart's rhythmic contractions.

💡Ventricular Fibrillation

Ventricular fibrillation is a life-threatening condition where the heart's ventricles quiver chaotically, preventing effective blood circulation. Dr. Deviant discusses the use of defibrillators to reset the heart's electrical activity in such cases, emphasizing the importance of timely intervention.

💡Heart Murmur

A heart murmur is an abnormal sound heard during a heartbeat, often caused by turbulent blood flow through the heart's valves. While common in infants, persistent murmurs in adults can indicate valve damage, as mentioned by Dr. Deviant. This can be a sign of an underlying heart condition requiring medical attention.

Highlights

The heart requires its own blood supply through a capillary network.

Blockages in the heart's blood supply can lead to angina pectoris, a thoracic pain due to temporary blood flow deficiency.

Myocardial infarction, or heart attack, is dangerous as it can lead to the death of myocardial tissues due to blocked blood flow.

Cardiac muscles are non-mitotic, meaning they cannot divide, and scar tissue replaces dead cells, which cannot contract.

Damage to the left ventricle is particularly serious as it is the thickest and most important chamber for pumping blood to the body.

Cardiac muscles are striated and resemble skeletal muscles but are shorter and interconnected through intercalated discs.

Cardiac muscle cells are connected by gap junctions, allowing the heart to contract as a unit, a concept known as functional syncytium.

Skeletal muscles contract due to nerve stimulation, unlike cardiac muscles which contract intrinsically.

Cardiac muscles do not exhibit sustained tetanic contractions, unlike skeletal muscles.

Cardiac muscles are dependent on oxygen, and low oxygen levels can lead to cell death.

High calcium levels and increased acidity can cause the gap junctions to close, blocking the action potential from traveling between cells.

The heart's pumping involves systole (contraction) and diastole (relaxation), with atria and ventricles working in coordinated phases.

Valves such as tricuspid, bicuspid, and semilunar play crucial roles in ensuring one-way blood flow during the heart's pumping cycle.

Heart murmurs are common in infants but can indicate valve damage in adults.

The cardiac conduction system, including the SA node, AV node, and Purkinje fibers, is responsible for generating and distributing electrical impulses for contraction.

Implantable cardioverter-defibrillators are used to monitor heart rhythms and can shock the heart to regain normal rhythm in case of fibrillation.

Defibrillators are used to depolarize the entire myocardium in cases of ventricular fibrillation, resetting the heart's electrical activity.

Transcripts

hello this is dr deviant and we are

continuing

with cardiovascular system

all right so we talked about the blood

supply to the heart and we noticed

that the blood supply to the heart which

itself

may be a little confusing because you're

thinking it's pumping blood

so it doesn't need to have its own

circulation but it

absolutely absolutely has to have

this kind of capillary network and

if there is any blockage then that will

create

lots of issues okay so here

what are the issues if there's a

blockage so first is

angina pectoris so this is a thoracic

pain

caused by temporary deficiency in the

blood flow

often it is stress related often it is

increased physical demand

or temporary weakening this is not that

serious okay

now myocardial infarction which is a

heart attack

is dangerous why because here what

happens is

that it leads to the death of myocardial

tissues you are noticing that

there is a cholesterol plaque which is

not allowing the flow of blood

all right which leads to heart attack

now what is the issue the main issue the

cardiac muscles are

a mitotic that means they cannot divide

and what happens is that the scar tissue

the fibrous scar tissues

replaces the dead myocardial cells but

these scar tissues will not have the

ability

to contract so what happens is that

there is

there is an issue now it says damage to

the left ventricle which is more serious

why

because notice what we are saying is

that the

the left ventricle which is the thickest

of all and the most

important chamber because remember it

pumps the blood

to the aorta to the rest of the body all

right so

here what happens is if there is this if

this is damaged

will you supply will you be able to

supply the blood to the rest of the body

the answer is what no yes so here it is

going to be most dangerous

now the cardiac muscles should remind

you

exactly of the skeletal muscles except

that the cardiac muscles are going to be

shorter so they are striated striated

means

they have actin and myosin once again

good time to look

up go back and look at your 201 uh

skeletal muscle fiber nose okay so here

they look very much like the skeletal

muscle fibers

except that they are what that they are

intercalated so here

they look like the ends have

intercalated discs

that means they look like corrugated

cardboard look out here interpolated

disc

right here this is much more obvious and

these cells

are connected to each other by desperate

zones which look like cell snaps

i'm sure you have this i know uh seen

the snap

button on your um shirts oh and how do

they connect with each other

through gap junctions these are pores

through which a cytoplasm is continuous

from one cell into the other

and uh here they have

the cardiac muscles uh muscle cells

they will pull and push against the

skeletal like muscle there's no skeleton

but skeletal like

muscles all right so here

not going into too much of detail but

there are myofibrils

just like the sarcomere they have the t

tbus just like the these skeletal

muscles

and sarcoplasmic reticulum very much

like the

skeletal muscle okay so uh without going

into too much of detail

i definitely want to see what are the

differences

so here what happens the skeletal

muscles contract

because they're stimulated by nerve

ending do you remember

that or if i can show you here so here

is the here is my neuron and my neuron

has endings

and then the neuron ending will fire an

action potential

and this muscle will contract yes now

here

this is a neuron so this is how a

skeletal muscle

um acts now here there is none in a

cardiac muscle

there is no innervation from a neuron

so uh so cardiac muscles they do not

require stimulation by not

important number one in skeletal muscle

there is no spread

of cell impulse from one cell to another

like

so a contraction of your uh biceps

is independent of cons a contraction say

for example

of your pectoralis major they're not

connected are they

absolutely not right so here but what

i'm saying

is that in a heart because of the gap

junctions

each cell is connected to each other so

the heart contracts as a unit this is

important you have to know this

what is it called functional singtion so

what i'm saying is when this contracts

this also contracts this also contracts

this also contracts

the heart will contract as a whole so

this

is difference number two got to know it

number three what's the difference there

is no sustained

technique contraction in the cardiac

muscle so the skeletal muscle

what happens if this is one contraction

let me draw this

and there's another contraction what

happens is

that this contraction and this

contraction can merge and you can have a

sustained

long technique contraction now that does

not happen

in a heart all right so these three

differences just keep in mind i'm not

going to go into

great detail out here all right so

here um the uh uh

t let's go let's go to tissue damage so

tissue damage

is that the cardiac muscles are

dependent on oxygen

and if there is low oxygen

then what happens is that we talked

about there is death right

now there are some defense mechanisms

and what is that

is when there's too much of high calcium

level we'll see why

why high calcium level will cause

a high a surge in the

rate and a rate and

force of contraction so you don't want a

huge

high surge in calcium level but if

there's excessive high calcium level

and increase acidity why increase

acidity because

oxygen is low and so because of lactic

acid production

the gap junctions are going to close so

those gap junctions which connect

one cell to another cell these are going

to to close

and therefore what happens is the the

action potential will be

blocked it will not travel all right so

um

now let's look at pumping of the heart

so pumping of the heart

involves what systole and dye stone

systole is when they contract diastole

is when they relax now both what we are

noticing is that both the atrium

are going to contract at the same time

which is called the

atrial systole and when the atrium

contract

the ventricles are going to relax

together

and that's called ventricle diastole so

when

these two contract these two relax

when these two contract these two relax

all right now let's see when the atrium

are contracting that means they are

going through systole

then what happens is that these valves

what are these valves the tricuspid and

the bicuspid will open

because they are squeezing the blood

from the atrium

into the ventricle you understand that

the ventricles are relaxed

but the blood the semilunar valve which

is going to push the blood from the

ventricles

out this into the lungs and this into

the rest of the body the aorta

will close i repeat when the

atrium contract the tricuspid and the

bicuspid valve open

so that the blood will fill into the

ventricles and the ventricles are nice

and relaxed

they're filling when the winter so

but at the same time these two valves

the semilunar valves are going to be

closed why because we are going to wait

to push the blood out

okay so they're going to be filled in

here

then when the ventricles go into

contraction that means when they're

going to systole

trims relax what's relaxation called

diastole

and when they're going to die a stone

these

two valves what are these two valves the

tricuspid and the bicuspid they will

what

they will close you don't you know and

the

atrium are relaxed ventricles are

contracting squeezing the blood

out so obviously the semilunar valves

will remain open

allowing the blood to be pushed out

through these semilunar valves into the

lungs

in this case and to the aorta in this

case

do we understand this all right

so here the heart sound is loved up

there's a very common heart sound called

the heart murmur

and this is because of the leaky valves

it uh

leaky valves are very common in small

infants

murmur heart murmur is very common but

adults having murmur is not

good and correct and it indicates valve

damage all right now there is the

cardiac conduction system what did we

say

in the last presentation we said that

the

heart muscles are able to

generate an action potential

as well as contract so here unlike

a skeletal muscle there is no neuron

and nerve endings innervating a muscle

all right so here the cardiac muscle

contraction is

intrinsic now there is of course

some control of heart rhythm but it is

generated the contraction

is uh the action potential is generated

within

all right so there are some

non-contractile cardiac muscles which

are specialized

for initiating and distributing all

right

so let's see them so before

uh let's see right here i think

this is good yes so there is the sa node

and from the sa node which is the

default pacemaker of the heart

from the from the sa node there's a

atrial syncium

that goes into the junctional fibers and

the junctional fibers

end up in the av node the av

node is the second fallback

a pacemaker so if sa node fails av node

kicks in

the av node leads into the av bundle

which is also called the bundle of haze

and separates out in the right and the

left branch

goes to the apex of the heart and

becomes

and turns around and goes into the

purkinje fibers you can see the spine

branches

per perkins fibers and these parking g

fibers go into the ventricular syncia

this is the cardiac conduction

system all right so

here is the labeling for you the sa node

here are the the junctional fibers the

av

node here is the the bundle of his

bundle of his going into the right and

left branch

going to the apex of the heart and

finally going into smaller branches

called the parking g fibers

and then going into the ventricular

allowing the ventricular sinks

okay all right

if by chance

both the essay and the av node

the pacemakers of the heart fail

then uh uh you know then uh implantable

cardio what uh uh water defibrillator

this is the one that is a pacemaker is

placed right

and what happens is that it is going to

monitor the heart rhythms

and detect fibrillation so anytime what

happens is it will shock the heart and

cause mycard

myocardium to depolarize we'll see all

that what it means

it will reset all the cell membranes so

it can sa node can regain control

all right now here what happens if there

is

a if there is a ventricular fibrillation

which is very

dangerous and we will see that in the

ekg

then you have to use a defibrillator

and what a defibrillator is i'm sure

you've seen a defibrillator

and you've seen that in all these uh

movies

and tv shows where basically they will

shock your heart

so here it depolarizes the entire

myocardium what is depolarizing

and repolarizing and polarizing again

look at your 201 notes for that okay

it will reset the heart so we'll stop

here we'll continue with our next

presentation

i thank you for listening to me for

questions or concerns

please contact me have a good day