B3.2 HL Transport in Animals [IB Biology HL]

Summary

This educational video delves into the intricacies of animal transport systems, focusing on the circulatory system's role in moving substances like oxygen, glucose, and carbon dioxide. It explains the high-pressure function of arteries and the low-pressure return through veins, highlighting the capillaries' crucial role in diffusion. The script covers passive diffusion of oxygen and glucose into tissues and the facilitated diffusion of glucose via sodium-glucose co-transporters. It also touches on the lymphatic system's role in fluid transport and provides an overview of the mammalian heart's structure and function, including the double circulation system, the heart's four chambers, and the coordination of atrial and ventricular contractions.

Takeaways

• 🚀 The circulatory system is organized with arteries carrying blood at high pressure away from the heart and veins returning it at low pressure, with capillaries facilitating the diffusion of substances like oxygen and glucose between blood and tissues.
• 🌀 Blood plasma is forced into the capillaries, creating tissue fluid that contains essential substances, which then diffuse into cells, while waste products like carbon dioxide diffuse out.
• 🔄 The reuptake of tissue fluid back into the capillaries is efficient due to the pressure differences in arteries and veins, maintaining a continuous flow of nutrients and waste products.
• 💧 Oxygen diffuses passively from the blood into tissues, moving along concentration gradients without the need for energy input.
• 🍬 Glucose often moves into tissues against its concentration gradient, facilitated by sodium-glucose co-transporters, which is an indirect form of passive transport.
• 🚫 Carbon dioxide, a product of cell respiration, diffuses passively out of cells and into the blood, moving from areas of high to low concentration.
• 🔄 The human circulatory system operates on a double pump mechanism, with separate loops for the lungs (low pressure) and the rest of the body (high pressure), ensuring efficient oxygen and carbon dioxide exchange.
• 🐟 Unlike mammals, fish have a single-loop circulatory system because the water provides enough pressure to balance the blood flow to and from the gills.
• ❤️ The heart has four chambers, with the right side receiving deoxygenated blood and the left side receiving oxygenated blood, separated by the septum.
• 💊 The SA node, also known as the pacemaker, initiates the heartbeat, and the AV node helps transmit the signal to the ventricles for coordinated contractions.
• 🏗️ Cardiac muscle tissue is distinct, featuring intercalated discs that facilitate electrical signal passage for coordinated contractions and is myogenic, meaning it can contract autonomously.

Q & A

What is the role of arteries in the circulatory system?

Arteries carry blood at high pressure away from the heart.

How do capillaries facilitate the exchange of materials between blood and tissues?

Capillaries allow the diffusion of oxygen, glucose, and waste products between the blood and tissues due to pressure differences.

What is tissue fluid, and how is it formed?

Tissue fluid is formed when blood plasma is forced out of capillaries due to high pressure, containing oxygen, glucose, and ions.

How do oxygen and glucose move into the cells from the blood?

Oxygen moves into the cells via passive diffusion, while glucose moves through sodium-glucose co-transporters.

What happens to carbon dioxide produced by cellular respiration?

Carbon dioxide diffuses out of the cells into the blood, where it is carried to the heart and then to the lungs for exhalation.

What percentage of fluid forced out of capillaries returns to the circulatory system, and where does the rest go?

About 85% of the fluid returns to the capillaries, while the remaining 15% drains into the lymphatic system.

Why do mammals have a double circulatory system?

Mammals have a double circulatory system to maintain high pressure for blood going to the body and low pressure for blood going to the lungs, ensuring efficient gas exchange.

How does the structure of the heart support its function in the circulatory system?

The heart has four chambers with thicker muscular walls in the ventricles, especially the left ventricle, to pump blood at high pressure throughout the body.

What is the role of the atrioventricular (AV) valves in the heart?

AV valves prevent the backflow of blood into the atria when the ventricles contract.

What is the significance of the SA and AV nodes in the heart?

The SA node initiates the heartbeat, acting as a pacemaker, while the AV node helps propagate the heartbeat signal to the ventricles.

How do the atria and ventricles work together during a cardiac cycle?

The atria contract to push blood into the ventricles, which then contract to pump blood into the arteries, maintaining continuous blood flow.

Why do arteries maintain higher pressure compared to other blood vessels?

Arteries have muscular walls that help maintain high pressure to ensure continuous blood flow even when the ventricles are relaxed.

Outlines

00:00

🔬 Blood Transport and Capillary Exchange

This paragraph discusses the critical role of transport in animals, specifically focusing on the circulatory system. It explains how arteries carry blood at high pressure away from the heart and veins return it at low pressure. The capillaries are highlighted as the site of diffusion between blood and tissues, with blood plasma being forced out due to arterial pressure, forming tissue fluid rich in oxygen, glucose, and ions. This fluid facilitates the exchange of substances like oxygen and glucose into cells and waste products like carbon dioxide out of cells. The process relies on pressure differences between arteries and veins, making tissue reuptake highly efficient.

05:00

🌀 The Double Circulation System and Lymphatic Transport

The second paragraph delves into the double circulation system found in mammals, which involves separate loops for the body and the lungs due to pressure requirements. It contrasts this with the single loop system of fish, which do not require a double circulation due to the consistent pressure provided by water. The paragraph also introduces the lymphatic system as an alternative transport mechanism for the fluid that doesn't return to the cardiovascular system, highlighting its role in draining excess fluid known as lymph back into the circulatory system.

10:03

🫀 Anatomy of the Heart and Blood Flow

This paragraph provides an overview of the heart's anatomy, focusing on the right side where deoxygenated blood enters through the vena cava into the right atrium, then moves to the right ventricle before being pumped to the lungs via the pulmonary artery. It describes the heart's chambers, the atria and ventricles, and the valves that regulate blood flow, including the atrioventricular (AV) valves and the semilunar valves. The left ventricle's thicker muscular wall is noted for its role in pumping blood at high pressure throughout the body.

15:05

💓 Heart Function and the Cardiac Cycle

The fourth paragraph explains the functions of the heart, detailing the structures responsible for mixing and separating oxygenated and deoxygenated blood, such as the septum. It also discusses the coronary arteries that supply oxygen-rich blood to the heart tissue itself. The initiation of the heartbeat is attributed to the SA node, also known as the pacemaker, and the coordinated contractions of the cardiac muscle are highlighted as myogenic, meaning they can start without nerve impulses. The paragraph outlines the cardiac cycle, which includes systole (contraction) and diastole (relaxation), occurring about 70 times per minute.

20:07

🔄 The Coordination of Heart Chambers and Valves

This paragraph describes the coordination between the heart's chambers and the role of valves in preventing backflow of blood. It explains that the atria contract simultaneously to push blood into the ventricles through the open AV valves, and then the ventricles contract to push blood into the arteries through the semi-lunar valves. The importance of the timing between the contraction and relaxation of the atria and ventricles is emphasized to maintain efficient blood flow. The paragraph also mentions specialized cardiac tissue features like intercalated discs that facilitate coordinated contractions.

25:07

📈 Pressure Dynamics in the Cardiac Cycle

The final paragraph examines the pressure dynamics within the heart during the cardiac cycle, measured in mmHg. It illustrates how the atrium's pressure increases during contraction (systole) and decreases during relaxation (diastole), while the ventricle's pressure follows an inverse pattern. The paragraph emphasizes that the ventricles are always under higher pressure than the atria and that arteries maintain a consistently high pressure to ensure continuous blood flow. The importance of understanding these pressure changes for interpreting cardiac function is highlighted.

Keywords

💡Transport

Transport in this context refers to the movement of substances within and between cells, and throughout the body. It is central to the video's theme as it discusses how different components of the circulatory system facilitate the exchange of essential materials like oxygen, glucose, and waste products. For example, the script mentions how 'things are going to diffuse between the blood and the tissues' in capillaries, highlighting the importance of transport in maintaining life processes.

💡Circulatory System

The circulatory system is the body's network for transporting blood, nutrients, oxygen, and waste products. The video script delves into how this system is organized, with arteries, veins, and capillaries playing distinct roles. It is integral to the video's narrative as it explains the mechanics of blood flow and the exchange of substances at the capillary level, emphasizing the high-pressure environment in arteries and the low-pressure environment in veins.

💡Capillaries

Capillaries are the smallest blood vessels that connect arterioles to venules. They are crucial for the exchange of materials between the blood and body tissues. The script uses capillaries as a focal point to explain how 'blood plasma is going to make its way to the capillaries' and how this leads to the formation of tissue fluid, which is rich in oxygen, glucose, and other essential substances.

💡Diffusion

Diffusion is the passive movement of molecules from an area of higher concentration to an area of lower concentration. It is a key concept in the video as it describes how oxygen and carbon dioxide move across the capillary walls. The script explains that 'oxygen... is going to diffuse from the blood into our tissues' and 'carbon dioxide... is going to diffuse out of the cells,' illustrating the passive nature of this transport mechanism.

💡Passive Transport

Passive transport refers to the movement of substances across cell membranes without the use of cellular energy. The video script mentions passive transport in the context of diffusion, stating that 'this is just simple diffusion' and 'movement of molecules from areas of high concentration to areas of low concentration without the input of energy.' It is a fundamental process that allows for the exchange of gases and nutrients in the body.

💡Concentration Gradient

A concentration gradient is the difference in concentration of a substance between two regions. It is essential for understanding how substances move passively, as they naturally move from areas of higher concentration to areas of lower concentration. The script uses the concept to explain the movement of glucose and oxygen into cells and carbon dioxide out of cells, stating that 'we need to understand the importance of concentration gradients in maintaining that movement.'

💡Tissue Fluid

Tissue fluid, also known as interstitial fluid, is the fluid that surrounds and bathes the cells of the body. It is formed when blood plasma is forced out of capillaries due to high pressure. The video script describes how 'the fluid is forced out due to the high pressure that is in this... arterial section of our blood network,' and this fluid contains 'oxygen and glucose and ions,' which are vital for cellular function.

💡Lymphatic System

The lymphatic system is a network of vessels and organs that transport lymph, a fluid containing white blood cells and proteins, around the body. In the video script, it is mentioned as an alternative transport mechanism that carries excess fluid, or lymph, which does not return to the cardiovascular system but is eventually drained back into it. This highlights the lymphatic system's role in maintaining fluid balance and immune function.

💡Double Circulation

Double circulation refers to the two separate loops of blood flow in the mammalian heart: one loop between the heart and lungs, and the other between the heart and the rest of the body. The script explains the necessity of this system due to pressure requirements, stating that 'we need separate loops... a low pressure loop that involves the lungs and a high pressure loop that involves the rest of the body.' This system allows for efficient oxygenation and nutrient delivery throughout the body.

💡Valves

Valves in the heart and blood vessels regulate the direction of blood flow, preventing backflow. The video script describes various valves such as the atrioventricular (AV) valves and the semilunar valves (also known as pulmonary or aortic valves), explaining their function in the cardiac cycle. For instance, 'these valves open this way, they can also shut... and these are something called the atrioventricular valves,' which ensures that blood flows in one direction through the heart.

Highlights

The circulatory system is organized with arteries carrying blood at high pressure away from the heart and veins returning blood back to the heart at low pressure.

Capillaries are where diffusion occurs between blood and tissues, driven by pressure differences.

Tissue fluid, formed from blood plasma, surrounds cells and facilitates the diffusion of oxygen and glucose into cells and waste products out of cells.

Oxygen and glucose move into cells from the blood using passive diffusion and sodium-glucose co-transporters, respectively.

Carbon dioxide, a waste product of cellular respiration, diffuses out of cells into the blood to be transported to the lungs for exhalation.

Approximately 85% of fluid forced out of capillaries returns to the cardiovascular system, while about 15% drains into the lymphatic system.

Mammalian circulatory systems have a double circulation loop: one involving the heart and lungs and the other involving the heart and the rest of the body.

The high-pressure loop involves the heart pumping blood to the rest of the body, while the low-pressure loop involves blood being sent to the lungs.

Fish have a single circulatory loop due to the balanced pressure provided by water around their gills.

The heart has four chambers: the right atrium, right ventricle, left atrium, and left ventricle, with valves ensuring one-way blood flow.

The right atrium receives deoxygenated blood from the body, which flows into the right ventricle and then to the lungs via the pulmonary artery.

Oxygenated blood returns from the lungs to the left atrium, flows into the left ventricle, and is then pumped to the rest of the body through the aorta.

The left ventricle has a much thicker muscular wall than the right ventricle to pump blood at high pressure throughout the body.

The septum separates the right and left sides of the heart, preventing the mixing of oxygenated and deoxygenated blood.

The SA node, also known as the pacemaker, initiates the heartbeat, and the AV node helps coordinate the contraction of the ventricles.

Cardiac muscle tissue is unique with features like intercalated discs that help coordinate contractions through electrical signals.

The cardiac cycle involves systole (contraction) and diastole (relaxation) phases, occurring about 70 times per minute.

Arteries maintain high pressure even when ventricles relax, ensuring continuous blood flow through muscular walls.

Transcripts

in this video we'll talk about transport

in animals and this is particular for

the higher level content in b3.2 on

transport so when thinking about how our

uh circulatory system is organized again

we have arteries carrying blood at high

pressure away from the heart and then

veins returning blood back to the heart

at low pressure but it's actually these

capillaries where things are going to

diffuse between the blood and the

tissues or between our tissues and the

blood and all of that works on this

concept of pressure so blood plasma um

is going to make its way to the

capillaries and it's going to be forced

out okay so we call this the tissue

fluid and that fluid is um full of

things like oxygen and glucose and ions

and stuff like that well that is forced

out due to the high pressure that is in

this um you know arterial section of our

blood uh Network okay so once that fluid

is forced out it starts surrounding the

cells and our tissues and things like

oxygen and glucose are going to diffuse

into the cells waste products like

carbon dioxide are going to diffuse out

of the cells and then that fluid will

return back to the capillaries here okay

and that blood um or I should say that

fluid will return back to those

capillaries because this is in an area

of low pressure so our veins are taking

blood um back to the heart under low

pressure and so this tissue reuptake is

very efficient due to the differences in

pressure in Our arteries and our veins

so let's take a look at the different

transport mechanisms to get all these

important things exch changed between

the blood that's in our capillaries so

this is a capillary and the nearby cells

that make up our

tissues okay now oxygen which I have

here in these little blue circles is

going to diffuse from the blood into our

tissues using passive diffusion okay so

this is just simple diffusion that's the

movement of molecules from areas of high

concentration to areas of low concent

rtion without the input of energy so as

long as we have a high concentration of

oxygen in our blood then that oxygen

will passively diffuse into this um area

where our tissues are um just using

simple diffusion we also need glucose to

move into our tissues like out of our

blood into our tissues now sometimes

that's going to be against the

concentration gradient like we're moving

it from a low concentration um to a

relatively High concentration but it's

still going to be passive because most

often what we're going to find is that

it's this sodium glucose

co-transporters that are helping to move

that so you may recall that is um an

indirect form of passive transport so

energy is used to actively pump um

sodium ions and create an area of high

concentration and then glucose and

sodium move together into an area where

there's a low concentration of sod iium

that's in another topic you can go back

and review that on your own but that's

going to be the main mechanism of

movement the important part here to

understand is that glucose needs to move

into the cells so from the blood into

the cells Just Like Oxygen and that

should make sense glucose and oxygen

should be moving together because we

need them both for cell respiration so

as long as you can remember that you're

in a good spot so if oxygen and glucose

are are moving into the cells and they

are the substrates necessary for cell

respiration then the product of cell

respiration carbon dioxide needs to be

moving out of the cells and that's going

to be carried by the blood to the heart

will to be pumped to the lungs and

exhaled well that is going to move via

passive diffusion so from the cells into

our blood and that moves on

concentration gradients so from high to

low so as long as the concentration of

carbon dioxide is relatively low in our

blood that will help the movement of

carbon dioxide out of our tissues and

into our blood so what we're going to

notice here are two important themes one

is that we need to understand which

materials are moving into our cells and

which are moving out and we need to

understand the importance of

concentration gradients in maintaining

that

movement now out of all of the fluid

that's forced out of the capillaries and

into the surrounding tissues about 85%

of that then returns to the capillary

Network and then through the veins Etc

but not all of it about 15% of that

fluid is going to drain not into our

cardiovascular system but our lymphatic

system and that fluid is then called

lymph So eventually that will drain back

into our heart and blood and circulatory

system but I just want to let you know

we do have an alternative transport

mechanism it isn't just the

cardiovascular um arteries veins

capillaries it's also the lymphatic

system that can carry some of that

excess fluid as well so let's do a very

rough overview of how um the circulatory

systems in mammals work I know the human

heart has four chambers and we'll get to

that later but for now I'm just going to

draw two sides of the heart this side

and this side because they they kind of

have different jobs right so what we're

going to find is that blood is going to

leave this side of the heart and it's

going to travel to the rest of the body

and that has to be under very high

pressure so if we think about my little

heart has to be able to pump blood all

the way down to my toes we're going to

need a lot of pressure in that part of

our circulatory Loop okay so of course

then blood is going to return to the

heart okay back to the body this way but

it's going to be

deoxygenated so that blood then needs to

be sent to the lungs okay where it's

going to pick up oxygen and it's going

to return to the heart again so that it

can be pumped to the rest of the body

and we can kind of complete that Loop so

we started here it's pumped to the body

it returns to the heart it's pumped to

the lungs and it returns to the heart

and then we have this whole thing going

so what we can kind of see here are two

separate Loops all right so if I kind of

do if I kind of like split them in half

right I have a loop that involves the

heart and the lungs and then I have a

loop that involves the heart and the

rest of the body and so this is what we

call the double pump okay or the double

circulation in mammals and this is all

necessary because of pressure I need

again a lot of pressure okay to get that

blood from the heart to the rest of the

body but if I had that higher pressure

if this Blood right here was under very

high pressure going to the lungs we

wouldn't be able to get the diffusion of

oxygen from the Alvi into the

capillaries if the pressure in the

capillaries was too high then I would

never be able to get oxygen to move from

the capillary or from the Alvi into the

capillary it just would not happen we

need the pressure in the Alvi to be

higher than the pressure inside the

capillary in order to help get this gas

to diffuse um efficiently so we need

this Loop here the loop that involves

the lungs to be under a much lower

pressure right so that is is the reason

why in mammals we need separate

circulatory systems right we need

separate Loops we need a low pressure

Loop that involves the lungs and a high

press Loop that involves the rest of the

body now fish don't need this double

circulatory Loop they can send blood

from their heart to their gills at the

same high pressure that is required from

getting the blood from the gills to the

rest of the organ or an because instead

of air being outside of the gills what's

out here is water and that water is com

um creating enough pressure to where

that blood that's coming through the

gills um isn't going to overwhelm or pop

those gills or pop any blood vessels

okay we're getting this balanced uh area

of pressure and so fish don't need that

double Loop in their circulatory system

that the high pressure that they need to

get blood from their gills to their

organs is an okay amount of pressure

when it's coming to the gills now on my

paper I normally do this in pencil and

then I'll go back over it with pen and

the reason is because um I'm going to

start off with four chambers to my heart

but I'm going to end up drawing in some

holes or using my Eraser to draw some

holes and actually it's not an even four

chambers it's a little bit uh bigger

here on the bottom so blood is actually

going to enter this top chamber of the

heart okay and again one of the things

that I need to be able to understand is

what I'm looking at here that on my on

my paper this looks like the left side

but this is actually the right side I

got to think of it as like a patient is

lying down on my operating table so

blood is going to enter the right side

of the heart and it's entering through a

structure called the

vinaa all right so that's this blood

vessel right here and blood is then

going to flow into this um chamber of

the heart so this is my right atrium

okay so the right atrium is this chamber

right here and then from there it's

going to flow into this bottom chamber

and this bottom chamber is called the

right ventricle so the

ventricles um of the heart are here on

the bottom in order to get there it's

got to pass through a series of valves

okay and so these valves open this way

they can also shut they can swing this

way to where they're shut but right now

I have them shown in their open position

and these are something called the atrio

ventricular valves okay so here I have

this section of the heart okay now blood

is going to then be leaving the right

ventricle and I'm I see that here okay

so here's my right atrium here is the AV

valve here is the right ventricle and

it's going to go through this blood

vessel right here and it's going to be

going to the lungs so what I'm going to

do is I'm just going to make a space to

where I can kind of draw a blood vessel

that's leaving and so it's leaving from

the vent ventrical and it's going to go

to the lungs okay and it's got these

little valves in here that point this

way so they open this way okay they can

also shut okay but they open that way

and these are called the semi lunar

valves now some people may refer to them

as the pulmonary Valves and that's named

after this blood vessel that they are um

connected to and this is the

pulmonary artery okay so artery because

it's going away from the heart pulmonary

means it's going to the lungs okay so

blood is going to flow from the vnea

into the right atrium through these AV

valves when The ventricle squeezes it's

going to force the blood into the

pulmonary artery and it is going to go

to the lungs now blood is going to then

become oxygenized it's going to return

from the lungs through this blood vessel

here and this is the pulmonary

vein it's going to flow into the left

atrium and it's going to flow through a

set of Av or atrio ventricular valves so

just like what we talked about on this

side and then into the left ventricle

the left ventricle when it squeezes is

going to force blood through this big

blood vessel here to the rest of the

body so I need a way to draw that in so

I'm just going to make a little hole

here this is why I used pencil and this

hole is for this giant blood vessel

called the aorta okay

aorta and it has its own pair of semi

lunar valves here and here some people

call those the aortic valves okay um

aortic valves

because they um separate The ventricle

from the aorta so you can either call

them semilunar valves or aortic valves

and this is a very rudimentary picture

of the blood vessels and valves in the

heart but we're not quite done yet so

what you'll have noticed by now I'm sure

is that the muscular walls of the Atria

are much thinner than the muscular walls

of the ventricles I need to make sure

that my drawings are proportional so I'm

going to make sure that the muscular

walls of my ventricles are much thicker

than the muscular walls of my aorta and

I'm also going to make sure that the

muscular wall of my left ventricle is

much thicker than the right so there's a

good reason for that this left ventricle

has to be able to pump blood at an

extraordinarily High high pressure all

the way to the rest of the body this

right ventricle only has to create

enough pressure to get to the lungs so

they're going to be much different in

their thickness I'm also going to label

um a couple of other things here so I

have this thing called the septum and

the septum is this separation right here

in the middle of my heart so this is

going to separate the the right side of

my heart from the left side and then

let's see I'm also going to find some

specialized tissue and that will help to

initiate the heartbeat and for this I'm

actually going to draw this in a

different color just because my drawing

is getting a little bit confusing so

right here in the right atrium I have

something called the SA node okay the SA

node stands for Ceno atrial

node okay and that's going to help

initiate the heartbeat also in the right

atrium I'm going to have another node

and this one is called the

AV node okay so those are right here um

and we'll talk more about their features

in just a minute all right so we've got

the form part down now what about all of

the functions so if I think about which

structure pra mixing oxygenated and

deoxygenated blood well deoxygenated

blood is typically over here on the

right side of the heart and oxygenated

blood comes from the lungs and is pumped

out by the left side of the heart so

that structure that separates the two of

them that is of course the septum okay

bringing oxygenated blood to the heart

tissue itself okay well branching off of

the aorta and we didn't draw this in our

drawing drawings that would be crazy um

these are the coronary arteries okay so

the coronary arteries Branch off of the

aorta and they carry that oxygen rich

blood to the heart tissue itself the

heart's a muscle it needs stuff okay the

initiation of the heartbeat um is the SA

node and some people call this the

pacemaker okay um that's another name

for that node collecting blood

Contracting to squeeze blood into the

ventricles those are the Atria so the

two atria are going to both contract at

the same time and both of them squeeze

blood into the

ventricles the um parts of the heart the

chamers that contract to plump blood

into the arteries those are the

ventricles and those ventricles also

contract simultaneously so when these

both contract the right ventricle will

send blood to the lungs and the left

ventricle to the rest of the body

preventing the black flow of blood into

the Atria when The ventricle contracts

okay so I can imagine when this

ventricle contracts we want the blood

flowing through the arteries we don't

want it going back into the Atria and

that is exactly what these AV valves are

for okay and then preventing blood from

flowing back into the ventricle when The

ventricle is relaxed okay well all this

happens on opposite um timing um when

The ventricle is Contracting it's

pushing blood through the arteries when

The ventricle is relaxing that's because

the Atria is Contracting and pushing

blood in there so when this ventricle is

relaxed we're going to have the tendency

for blood to want to flow back into the

ventricle and we need this set of valves

to prevent that and that's the job of

those semi lunar valves

those semi lunar valves um you again

could call them either the pulmonary

valve or the aortic valves um can close

to prevent that back flow the one node

that we labeled but we didn't talk about

is the AV node the AV node has a

function in getting that heartbeat

signal to these

ventricles now if you've already taken a

look at the topic on muscles um then

this will be a quick review but the

cardiac muscle itself if I zoom in and I

look at how the cells are put together

we're going to notice that cardiac

muscle tissue is much different than

like skeletal muscle tissue so it's got

a couple of features that I think are

worth your time to go back and review if

you've already studied this um one of

which is called an intercalated dis okay

and these intercalated diss are going to

help um form connections and passages of

electrical signals since we have a lot

of contractions happening there there we

also need those contractions to be

coordinated throughout the heart tissue

and so that's where this cell branching

is really helpful okay so we can have

more coordinated contractions and we

also say that these cardiac contractions

are what we call myogenic and that means

um that they can contract without the

input of nerve uh impulses so myo

meaning muscle Geno meaning to start

they literally start on their own so a

complete set of steps um is what we call

a cardiac cycle and this cardiac cycle

happens about 70 times per minute

although that can vary with a lot of

things and it involves two basic

concepts cysto which is contraction and

diaso which is relaxation so here's how

I remember that syy sounds like

squeezing and diast sounds like dilate

right to come open and relax so that's a

good way to remember those so in the

first part here um what we're going to

show is the Atria Contracting and it's

important to remember that both Atria

are going to contract at the same time

that the left and the right side of the

heart are coordinated so here's what

we're seeing I'll try to draw them in

over here so these Atria contract and

that's going to be right in this step

over here here okay so when both of

these Atria contract that is going to

force these AV vales to open and when

they open that blood is going to start

to flow into the ventricles okay so the

Atria contract the AV valves open blood

flows into the ventricles because if the

ventrical are relaxed and the Atria are

contracted okay that blood is going to

want to flow towards W the lower

pressure so in this section the Atria

are in syy and the ventricles are in

diast there's about a 1C Gap and that's

due to this SA node and AV node firing

at different times so the SA node fires

and it makes the Atria contract then

there's a small Gap and that AV node

will fire and then we're into this

second step here so now in this part of

the diagram we can see the ventricles

Contracting when the ventricles contract

what that's going to do is it's going to

slam these AV valves shut so they were

open when blood was flowing into the

ventricles when the ventricles are

squeezing it's going to force those AV

valves to shut and that prevents blood

from flowing back into those Atria

that's very important it also forces

these semi lunar valves here to open and

that that means that blood is able to go

from these ventricles into the arteries

okay and then we start this cycle all

over again so after the ventricles have

been in syy okay then we're going to

switch okay then they're going to go in

diast okay these Atria have meanwhile

filled with blood and we start this

cardiac cycle all

over so in this diagram we're going to

look at the length of one cardiac cycle

so it's it's a little bit less than a

single second and we're going to be

tracking the pressure now there's lots

of different ways that you can measure

pressure usually when we're talking

about our cardiovascular system we're

talking about mmhg or millimeters of

mercury so um an interesting unit for

pressure there and we're going to look

at the pressure in three different

places an Atrium a ventricle and an

artery so when we're first starting the

atrium it's going to be at relatively

low pressure and then when it under goes

cyly that pressure is going to increase

it doesn't increase for very long it's a

relatively short time and during that

time the pressure of The ventricle is

going to be going down so what we can

notice here is that in general The

ventricle is just under higher pressure

anyways think about this The Atrium only

has to push the blood into The ventricle

The ventricle got to be able to push

blood either to the all the way to the

lungs or to the rest of the body the

important part here is that we can

understand that as the atrium is

increasing in pressure it's under Cy and

then while that's happening The

ventricle needs to be in diast um so

that it can fill up with blood now that

Atrium is then going to relax okay and

what's going to happen when the atrium

is relaxing that ventricle is going to

contract okay and that ventricular

contraction is going to take take um a

little bit of a longer time all right so

that ventricular contraction will last a

little while and that atrial contraction

again the Atria needs to be relaxed

while The ventricle is Contracting so

the way that we can kind of connect

these two things when something is

Contracting the pressure is going to go

up think about it it's squeezing the

blood when something is relaxed that

pressure is going to go down okay so

when the Atria contract the ventricles

have to relax and when the ventricles

contract the Atria have to contract and

then we would see this happening over

again okay so I would get this cardiac

cycle happening multiple times what's

very interesting here is that these

arteries are always going to be at

relatively high pressure that they're

going to be at a higher pressure even at

The ventricle

now their pressure is going to increase

when the ventricles contract but it's

never going to go all the way back down

why is that well because we can't just

have blood stop flowing through our body

it's important to maintain the flow of

blood in Our arteries so remember Our

arteries have muscular walls so even

when the ventricles are relaxed the

arteries can contract and keep that

blood moving through there so arteries

are always at high pressure they uh the

pressure can increase when those

ventricles contract and that we feel as

our pulse right um but they're always

going to be at a much higher pressure

you do not need to know how to draw this

diagram but you do need to know how to

interpret it and again the main

takeaways here are ventricles are always

under higher pressure than Atria that

when one chamber is Contracting the

other one must relax and that arteries

are always under high pressure to

maintain the blood

flow