Structure of the Mammalian Heart | A-level Biology | OCR, AQA, Edexcel

Summary

This video offers an in-depth exploration of the heart's structure and function. It explains the dual pumping system of the heart, distinguishing between the pulmonary and systemic circuits. The script details the heart's four chambers—right and left atria and ventricles—and their roles in blood circulation. It also discusses the importance of the atrioventricular and semilunar valves in ensuring one-way blood flow. Additionally, the video delves into the unique properties of cardiac muscle, highlighting its automatic contraction capabilities and the structure that enables efficient blood pumping. The educational content is designed to simplify complex cardiac functions, making it accessible for learners.

Takeaways

• 💓 The human heart functions as a pump, designed to circulate blood throughout the body to deliver essential nutrients and gases.
• 🔄 The circulatory system is described as 'closed' and 'double', with two circuits: the pulmonary circuit (to the lungs) and the systemic circuit (to the rest of the body).
• 📍 The heart is divided into a right and left side, each responsible for pumping blood through one of the two circuits.
• 🔴 The right side of the heart handles the pulmonary circuit, sending deoxygenated blood to the lungs to be re-oxygenated.
• 🔵 The left side of the heart is tasked with the systemic circuit, delivering oxygenated blood to the body's tissues.
• 🔁 Blood from the body returns to the right atrium via the vena cava, while oxygenated blood from the lungs enters the left atrium through the pulmonary veins.
• 🫀 The heart is composed of four chambers: two atria and two ventricles, each with distinct roles in blood circulation.
• 🚫 Atrioventricular valves and semilunar valves ensure one-way blood flow within the heart, preventing backflow.
• 💪 Cardiac muscle is unique, with automatic contraction capabilities independent of the brain, and is structured with branched fibers for synchronized contractions.
• 🔁 The cardiac muscle's structure allows for a sequential contraction that effectively moves blood from the atria to the ventricles and then out to the body or lungs.

Q & A

What is the primary function of the human heart?

The primary function of the human heart is to pump blood around the body to supply all of the tissues with the necessary dissolved gases and nutrients they need to carry out their functions.

How is the human circulatory system described in terms of its structure?

The human circulatory system is described as closed because the blood is contained either within the heart or the vessels that branch out from the heart. It is also described as double because there are two circuits going away from the heart, serving the functions of the lungs and the rest of the tissues.

What are the two circuits of the human circulatory system and their purposes?

The two circuits of the human circulatory system are the pulmonary circuit, which replenishes the blood with oxygen and drops off carbon dioxide, and the systemic circuit, which delivers oxygen and nutrients to all of the body's tissues.

Why does the heart have a right and left side, and what is the function of each?

The heart has a right and left side to serve the two separate circuits of the circulatory system. The right side pumps blood around the pulmonary circuit to the lungs for re-oxygenation, while the left side pumps blood around the systemic circuit to deliver oxygen and nutrients to the body's tissues.

What are the four main vessels related to the heart and their functions?

The four main vessels related to the heart are the vena cava, which brings deoxygenated blood from the body to the right side of the heart; the pulmonary artery, which carries deoxygenated blood from the right side of the heart to the lungs; the pulmonary vein, which brings oxygenated blood from the lungs to the left side of the heart; and the aorta, which distributes oxygenated blood from the left side of the heart to the rest of the body.

How does the heart supply itself with oxygen and nutrients, and what are the vessels involved?

The heart supplies itself with oxygen and nutrients through the coronary arteries, which are branches of the aorta that deliver oxygenated blood to the heart muscle. The cardiac veins remove the cellular wastes back to the system from the heart muscle.

What are the four chambers of the heart and their roles?

The four chambers of the heart are the right atrium, left atrium, right ventricle, and left ventricle. The atria receive blood from the veins and have thin, elastic walls to withstand rising pressure. The ventricles have thicker walls with more muscle to pump blood out of the heart through the arteries to greater distances.

What are the atrioventricular valves and their function?

The atrioventricular valves are located between the atria and ventricles and prevent blood from flowing backward from the ventricles to the atria, ensuring that blood flows in the correct direction through the heart.

What are the semilunar valves and where are they located?

The semilunar valves are located between the ventricles and the arteries they send blood to, specifically the pulmonary artery and the aorta. They prevent blood from flowing backward from the arteries into the ventricles.

What is cardiac muscle, and how does it differ from skeletal muscle?

Cardiac muscle is a specialized type of muscle tissue found only in the heart. It can contract on its own without any signal from the brain, a property known as automatic contraction. Unlike skeletal muscle, cardiac muscle has branched fibers and myofibrils, connected by intercalated discs, allowing the contraction to run through the whole sheet of muscle for coordinated pumping.

Outlines

00:00

🫀 Overview of the Heart's Structure and Function

This paragraph introduces the video's focus on the heart's external and internal structures, as well as the cardiac muscle. It explains the heart's role in pumping blood throughout the body via two circuits: the pulmonary circuit, which oxygenates blood in the lungs, and the systemic circuit, which delivers oxygen and nutrients to the body's tissues. The heart is divided into right and left sides, each responsible for pumping blood through its respective circuit. The right side handles the pulmonary circuit, while the left side manages the systemic circuit. Key vessels associated with the heart, such as the vena cava, pulmonary artery, pulmonary vein, and aorta, are also discussed, highlighting their roles in blood circulation.

05:02

🔍 Internal Structure of the Heart and its Chambers

This paragraph delves into the heart's internal structure, detailing its four chambers: the right and left atria and ventricles. The atria are characterized by their thin, elastic walls, which allow them to expand and fill with blood from the veins. The ventricles, with their thicker walls and more muscular structure, are responsible for pumping blood out of the heart through the arteries. The right ventricle pumps deoxygenated blood to the lungs via the pulmonary artery, while the left ventricle sends oxygenated blood throughout the body via the aorta. The paragraph also discusses the importance of the atrioventricular and semilunar valves, which ensure blood flows in the correct direction within the heart and its circuits.

10:03

💓 The Unique Properties of Cardiac Muscle

The final paragraph discusses the distinctive nature of cardiac muscle, which is found only in the heart. Unlike skeletal muscle, cardiac muscle can contract autonomously, a feature known as automatic contraction. This muscle type is essential for the heart's ability to pump blood continuously without direct brain control. The paragraph describes the structure of cardiac muscle, including its branched fibers and intercalated discs, which allow for coordinated contraction across the entire muscle sheet. The video concludes with a call to action for viewers to explore more educational content on biology.

Keywords

💡Heart

The heart is a muscular organ responsible for pumping blood throughout the body. In the video, it is described as having two sides—right and left—which pump blood through two separate circuits (pulmonary and systemic). Its function is crucial for delivering oxygen and nutrients to body tissues and removing waste products.

💡Pulmonary Circuit

The pulmonary circuit is the path through which blood travels from the heart to the lungs. In the video, this circuit is explained as the process where deoxygenated blood is pumped from the right side of the heart to the lungs via the pulmonary artery to get oxygenated before returning to the heart. This is one of the two main circulatory pathways in the body.

💡Systemic Circuit

The systemic circuit refers to the circulation of oxygenated blood from the heart to the rest of the body. After oxygenation in the lungs, the blood is pumped from the left side of the heart through the aorta, delivering oxygen and nutrients to body tissues. This circuit is vital for supplying the body with essential nutrients.

💡Vena Cava

The vena cava is a large vein that carries deoxygenated blood from the body back to the heart. In the video, it is discussed as the vein that delivers blood to the right side of the heart, marking the beginning of the pulmonary circuit. It plays a crucial role in returning blood for reoxygenation.

💡Aorta

The aorta is the largest artery in the body, responsible for carrying oxygenated blood from the left side of the heart to the systemic circuit. In the video, it is explained as the major vessel that distributes oxygen-rich blood to various parts of the body. The strength and size of the aorta allow it to handle large volumes of blood.

💡Atrioventricular Valve

Atrioventricular valves are valves that separate the atria from the ventricles, preventing the backflow of blood into the atria. In the video, these valves are emphasized as crucial in ensuring the correct direction of blood flow, from atria to ventricles and not backward. They contribute to efficient heart function.

💡Semilunar Valve

Semilunar valves are found between the ventricles and the arteries leading out of the heart, preventing blood from flowing backward into the ventricles. In the video, they are discussed in the context of maintaining the proper flow of blood from the right ventricle to the pulmonary artery and from the left ventricle to the aorta.

💡Cardiac Muscle

Cardiac muscle is a specialized type of muscle found only in the heart, responsible for its rhythmic contractions. The video explains that cardiac muscle can contract automatically, without input from the brain, allowing the heart to continuously pump blood throughout a person's life. It also highlights the muscle's unique structure with branched fibers and intercalated discs.

💡Coronary Arteries

Coronary arteries are the blood vessels that supply oxygen and nutrients directly to the heart muscle itself. In the video, these arteries are described as critical for maintaining the heart's function since the heart requires a constant supply of oxygen to continue pumping effectively. These arteries branch off from the aorta.

💡Atria

Atria are the upper chambers of the heart that receive blood from the veins. In the video, the atria are described as having thin, elastic walls that allow them to expand and receive blood. The right atrium receives deoxygenated blood from the body, while the left atrium receives oxygenated blood from the lungs, playing a key role in the heart's pumping process.

Highlights

The human heart is designed for pumping blood around the body to supply tissues with necessary dissolved gases and nutrients.

The heart acts as a pump with two closely associated pumps that force blood around the circulatory system.

The circulatory system is described as closed and double due to the presence of two circuits away from the heart.

The pulmonary circuit replenishes blood with oxygen and drops off carbon dioxide from body tissues.

The systemic circuit delivers oxygen and nutrients to all body tissues.

The heart is divided into a right side that pumps blood around the pulmonary circuit and a left side for the systemic circuit.

Blood from the body returns to the right side of the heart via the vena cava, which is low in oxygen and high in carbon dioxide.

The left side of the heart pumps oxygenated blood to the body through the aorta, the largest artery.

There are four main vessels related to the heart: vena cava, pulmonary artery, pulmonary vein, and aorta.

The heart is a muscular pump that requires its own supply of oxygen and nutrients, supplied by the coronary arteries.

Cardiac veins remove cellular wastes from the heart muscle back to the systemic circulation.

The heart has four chambers: two atria and two ventricles, with atria being thin-walled and elastic.

Ventricles have thicker walls with more muscle to pump blood through arteries to greater distances.

Atrioventricular valves separate atria from ventricles, preventing backflow of blood.

Semilunar valves are located between the ventricles and the arteries, ensuring one-way flow of blood out of the heart.

Cardiac muscle is a specialized muscle tissue found only in the heart, capable of automatic contraction without brain signals.

Cardiac muscle has branched fibers and intercalated discs, allowing the contraction to run through the whole sheet.

The structure of cardiac muscle ensures a pumping effect in a specific direction, from atria to ventricles and out to the body.

Transcripts

hi guys in this video we'll be looking

at the external structure of the heart

internal structure of the heart cardiac

muscle and then we'll finish with a

summary so the human heart is designed

for a purpose of pumping blood around

the body to supply all of the tissues

with the necessary dissolved gases and

nutrients that they need to carry out

their functions

and the heart is basically acting as a

pump to do this but it's made of two

closely associated pumps individually

that force blood around the circulatory

system

so when we talk about the human and a

lot of mammals circulatory systems we

call it closed because the blood is

contained either within the heart or the

vessels that branch out away from the

heart or to the heart

we also described the circuit as being

double because there are actually two

circuits that are going away from the

heart because of the functions of the

lungs and the rest of the tissues so

what we have is we have the heart in the

center here

and the heart is essentially sending

blood away around one circuit which

takes the blood to the lungs and this is

known as the pulmonary circuit

and the purpose of this circuit is to

replenish the blood with oxygen as we

breathe it in and also drop off carbon

dioxide that has been taken from the

body's tissues

after the blood has gone around the

pulmonary circuit it is sent around the

systemic circuit which takes it around

the rest of the body to all of the

tissues and this includes parts of the

body above the lungs as well

so this circuit is called the systemic

circuit so because of this we need two

pumps we need one pump to send blood

around the systemic circuit and one pump

to send it around the pulmonary circuit

and then every time the blood goes

through these two circuits it has to go

through the heart

twice heart can be divided into a right

and a left side the right side of the

heart is the one that pumps blood around

the pulmonary circuit or the lungs to

re-oxygenate the blood after it's

returned from the body tissues so

remember when we're looking at the heart

from the front of somebody's chest we

have to make sure that we are clear on

where the right and left is so imagine

this is looking at a human from head on

so face on and that means that their

right side is now on the left when you

look at them and their left side is now

on the right when we look at them

so in that respect we're going to call

this the right side and this the left

side so on the right side here we have

the pump which pumps blood around the

pulmonary system

so what we have is we have blood

returning from the body

into the vena cava

and the vena cava is a large vein that

basically collects blood that's come

from all of the tissues of the body

which is now low in oxygen and high in

carbon dioxide

this blood passes into the right side of

the heart and this then gets pumped to

the lungs or the pulmonary circuit so

you can see here that we've got the vena

cava represented by this part here

all of the veins draining to this vena

cava from all of the body tissues

and the right side of the heart is on

this side and it will start pumping

blood to the lungs to be replenished

with oxygen

the left side of the heart as you can

guess is the one that's going to pump

blood around the systemic circuit

delivering oxygen to all of the

respiring tissues of the body and the

nutrients that have been absorbed from

digestion as well so again here we have

our heart divided down the middle the

right side on this side and the left

side

so what you need to remember is that

veins always go to the heart

and arteries go away

if it helps you arteries begin with a

and sodas away so when we had the right

side of the heart the blood was sent to

the lungs via an artery which was

carrying that deoxygenated blood from

the body so this would have been the

pulmonary artery

this would have taken blood to the lungs

and the blood from the lungs come back

now to the pulmonary vein

and this then drains into the left side

of the heart so once the blood arrives

back into this side of the heart the

left side it's been oxygenated and now

it needs to be sent around the body so

the left side pumps it out

into a large artery called the aorta

which is the biggest artery in the body

and this then distributes it around

various parts of the body so there's

four main vessels related to the heart

there's the vena cava bringing

deoxygenated blood from the body to the

right side and then the right side sends

blood out to the lungs in the pulmonary

artery this blood comes back to the left

side through the pulmonary vein and the

left side sends blood out to the body

via the aorta

the heart is also a muscular pump so it

needs its own supply of oxygen and

nutrients to keep pumping as well and it

pumps throughout your whole life

so it needs its own supply and it

therefore it needs branches of this

oxygenated blood system to supply the

muscle and these are done with the

coronary arteries so they deliver oxygen

and nutrients to the heart tissue itself

and the cardiac veins are what remove

the cellular wastes back to the system

so as blood is pumped out of the left

side of the heart into the aorta

there's an immediate branch from the

aorta that sends blood into arteries

known as the coronary arteries

at various parts around the heart

this supplies all of the muscle and then

obviously that muscle is still producing

co2 and waste products

and so these drain into cardiac veins

which follow the course of the arteries

and they drain back eventually to the

right side of the heart like all other

veins do

so the whole system is about sending it

away and coming back

so now we've talked about the external

structure of the heart we need to look

inside the heart itself for the internal

structure

it's made up of four chambers which are

atria and ventricles so the atria are

two chambers there's one on the left

side and one on the right side

they're chambers that have a thin wall

and they're very elastic i.e they can

expand and withstand a lot of rising

pressure

and these receive the blood from the

veins

so remember veins are bringing blood

back to the heart so on this side we

have the vena cava

bringing deoxygenated blood from the

body

and this blood is going to enter the

right atrium because remember this is

the right side

so this is the right atrium

and as well as that on the left side of

the heart we have oxygenated blood

coming in to the pulmonary veins

because remember veins always bring

blood to the heart and this is entering

this chamber now which is the left

atrium so the atriums are the upper

chambers and there's one on the left and

there's one on the right the atria you

can see have thin walls and they're

elastic because they're going to be

filling up with blood coming back from

the body and they need to be able to

expand

the other types of chamber are known as

the ventricles and again there's a left

ventricle and a right ventricle just

below the atria

so these are much thicker walls because

they have more muscle around them and

these are thicker because they need to

pump blood out of the heart through the

arteries to greater distances

so on the right hand side of the heart

here we have this chamber

which is known as the right ventricle

and this is receiving that deoxygenated

blood from the right atrium which has

come from the body originally the vena

cava and this one is going to squeeze

and contract its cardiac muscle and send

it out to the lungs

via this vessel which is the pulmonary

artery because arteries go away from the

heart and this is going to the lungs to

pick up more oxygen so it's got thick

muscle because it needs to squeeze blood

all the way to the lungs which are

relatively nearby

but compared to the atria the wall is

much thicker because it needs to pump to

an actual organ rather than just to the

chamber next door so thicker walls

the left atrium has a different purpose

remember this has oxygenated blood

coming back through the pulmonary veins

from the lungs into the left atrium and

then into the left ventricle and the

ventricle now is going to squeeze blood

out to the rest of the body via the

aorta so this one has really thick full

walls

because it needs to squeeze it all the

way down to your feet up to your brain

down to your hands everywhere around the

body so it's got a lot of muscle here

the atria and ventricles obviously each

have their own function and so they need

to be separated by a particular valve

and the valve that separates an atrium

from a ventricle is called an

atrioventricular valve

it prevents blood flowing backwards in

the wrong direction so we have here the

right atrium and then down here we have

the right ventricle and then on the left

side we have the left atrium

and we have the left ventricle but

obviously we don't want blood to just be

squeezed randomly around the heart or it

wouldn't go anywhere we need it to go

from the atria into the ventricles

and then we need it to go out of the

ventricles into their respective vessels

so it always has to be atria to

ventricles

so the atria squeeze blood into the

ventricles and then from the ventricles

they need to go out to their various

vessels

so we can't have the blood going

backwards

from the ventricle to the atria and we

can't have blood going from vessels to

ventricles because this is backwards you

don't want deoxygenated blood going back

into the body and you don't want

oxygenated blood to not go forward

so the valves that separate them

are the atrioventricular valves

but there's also valves between the

ventricles and the vessels they're

sending blood out to

so the arteries leading from the heart

are separated

from the ventricles by valves called

semilunar valves so the previous ones

were named quite accordingly which were

atrioventricular

that's these two between the atrium and

the ventricles

but this time we have semilunar valves

which exist between the pulmonary artery

and the right ventricle

so that would be a semilunar valve there

and then on the left side we have a

similar setup where the valve would be

you can't quite see it here but it would

be going into the aorta

and this would also be a type of

semi-lunar valve as well

now we need to talk about what we mean

by cardiac muscle so we obviously have

muscle around the body related to our

skeleton to move certain limbs and

certain joints but we also have a type

of muscle called cardiac muscle and it's

very very special it's only found in the

heart

because it can contract on its own

without any signal from the brain so we

call this automatic contraction

and it's called cardiac muscle

so the heart actually can contract on

its own accord and do its sequence of

events without any input from the brain

all the brain does is modulate how fast

and how strongly it does this

but if you were to remove the brain from

the heart the heart would continue to

contract for a long time

so by definition cardiac muscle is a

specialized type of muscle cell or

muscle tissue found in the walls of the

heart so it's there in the walls to be

able to squeeze blood through those

chambers we were just talking about

the cardiac muscle unlike skeletal

muscle has branches so it's got branched

fibers and myofibrils

and they're separated by intercalated

discs

so you can see here we have one cardiac

myocyte

or muscle cell

and it's got different branches

throughout its structure

and this is important because this

connects the cardiac muscle all as one

single sheet

and because the cell is branched those

myofibrils inside the cell need to

branch as well

and the connections between the cells

are at these intercalated discs

and the discs allow the communication of

that muscle contraction to run through

the whole sheet rather than just ending

at the end of the cell

the cardiac muscle is structured in a

particular way so that the contraction

of the heart has a pumping effect

so obviously we don't want the whole

pump to just contract all in one go

because the blood wouldn't really end up

going anywhere

the blood has to be pumped in a

particular direction from atria to

ventricles and then out again

and therefore we need it to contract in

certain sequence of events and this is

controlled by the structure of the

cardiac muscle

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