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Science of Obesity - Adipose Tissue as The Fat Reservoir (Pt I)

hello everybody and welcome to another

edition of physiology made easy with me

dr. Amir Sandow now in upcoming episodes

we're going to talk about the biological

mechanisms of obesity and we'll talk

about how we actually store fat from the

diet that we consume in specialized

cells within the body and we'll look at

some lifestyle factors which are the

most effective to reduce obesity and

body fat as well so we'll look at that

with the underpinning science and

hopefully the videos will enable you to

have more appreciation about some of the

the key theories and the key knowledge

that we have available about how we gain

fat so in terms of the learning outcomes

what I want you to get out of these

episodes is to try and understand the

importance of adipose tissues so adipose

tissue is the primary site where fat is

actually stored in the body so it's very

important before we think about you know

weight loss strategies we can understand

where the fat is actually stored and how

its regulated from a physiological

perspective we'll look at the changes

that the adipose tissue undergoes in

people who are obese as you start to

increase your weight and as I said

before we'll look at the lifestyle

factors especially focus on exercise

because there's some interesting stuff

about whether exercise is beneficial for

weight loss or not so we'll have a look

at that as well and all of the things

that we'll talk about in the the videos

in this video and the future upcoming

videos will be underpinned by scientific

research so there'll be hopefully not

only misconception it would just be a

summary of the available scientific

research so before we go forward in

terms of understanding what adiposity is

it's very important for us to to know

what body composition is okay now the

simple definition of body composition

which I've stated down here is the

relative amounts of fat mass that we

have in our body and the fat free mass

okay now fat mass can consist of a

number of different types okay now you

may have heard of these terms before and

some of them might be new terms or some

of them you may have heard the terms but

the definition has is incorrect so it's

very important that we're able to define

what these terms are now visceral fat is

commonly found around the organ so this

is fat that's stored around our

abdominal organs it's the worst type of

fat to actually have because as we shall

see in the remove the rest of the the

presentation fat can release harmful

chemicals into the circulation which can

attack the blood vessels and this is why

obesity is a major risk factor for

cardiovascular disease so visceral fat

deposited around the organs we also have

fat which is known as ectopic fat now

this is fat that's contained within an

organ okay so it's not around an organ

it might be you might visceral fat would

be fat that's deposited around the

outside structure of the organ ectopic

fat actually resides within the organ

itself and can manifest in various

pathological disorders then we have the

subcutaneous fat this is the fat that's

stored underneath our skin hence why

it's called subcutaneous and this is the

fat that helps to keep us warm you know

it provides an insulating layer and

throughout our whole body and helps to

keep us warm and we also have

intramuscular fat this is fat which is

interspersed between the muscles it can

be used to provide energy particularly

when you're doing low intensity long

duration exercise so this is an example

of the various types of fats fat mass

that make up our body now fat free mass

is quite easy to understand anything

that isn't fat in the body is going to

be fat free mass so it's all non fatty

tissue so we're looking we're looking at

our muscles which make up you know a

large majority of our fat free mass but

you've also got to consider things like

bones teeth nails hair the weight of our

internal organs all of the connective

tissue so your tendons or ligaments your

cartilage blood and other fluids within

and around the cells of the organs

that's all of those things constitute

the fat free mass and quite often when

you go to a sports facility or a health

clinic you'll see those scales which

give you an indication of your

fat mass and fat free mass the

relatively accurate so they're a good

way to to kind of understand whether you

you have a greater amount of fat or or

or fat free mass relative to each other

now

the key part in that beta so basically

where fat is stored in our body is the

adipose tissue okay so this is basically

an energy storage organ everything that

we eat that doesn't get used up in terms

of energy expenditure so even if we eat

something can go out and do you know a

long bout of exercise go for a cycle

ride or for a walk we're likely to use

up some of those calories but any excess

calories they're going to get stored in

the adipose tissue and it's actually 65%

approximately 65% of our excess calories

which are consumed with that we consume

sorry that basically gets stored in

adipocytes so anything that doesn't is

not needed for your normal metabolic

processes so your resting metabolic rate

you have energy actually needed to

digest food as well

and physical activity once that's all

done then the remaining energy that's in

your body gets stored in the adipose

tissue and what we can see here is that

the adipose tissue is deposited in

different sites of off the body okay now

if I bring up this last point here and

I'll explain to it and just I'll explain

in just a moment but before we actually

try and think about adipose tissue we've

got to think about these as individual

cells which hold the fat that we consume

in our diet okay and that fat can have

protective function as well so if we

look at the heart here we see that

there's epicardial adipose tissue around

the surface of the heart now that's not

necessarily a bad thing because when you

think about the heart as its contracting

as a ventricles are contracting it's

exerting torsion or twisting forces on

the very delicate culinary vessels which

are on the surface of the vessel we

can't see them in this diagram but our

heart has these very delicate coronary

vessels now some of that fat actually

acts as a padding and protection from

those

twisting forces okay so some of the fat

actually has a beneficial effect of

being around the organ equally if the

heart has to work very hard then it's

able to actually get extract energy from

the the adipose tissue from the fat to

supply the the mitochondria which are in

the ventricles contracting so as the

heart works harder the the fat around

the heart can actually be used for

energy consumption okay now the reason

why and this actually links to this

point here now the reason when lipids

are more readily stored as fat as

compared to say for example

carbohydrates is because they actually

have a much greater energy yield than

other nutrients now what do we mean by

greater energy yield it means that when

you break down fat to produce energy you

get much more ATP adenosine triphosphate

this is like the usable form of energy

okay that our cells used to carry out a

particular function if I was to contract

my arm

the reason I'm able to do that is

because I'm using energy in the form of

adenosine triphosphate ATP and that is

more readily available when you have fat

being broken down as compared to some of

the other substrates that are available

now this figure here has actually been

taken from an excellent review article

which I'm going to put a link at to the

bottom of this video I would suggest

that you go and have a read through that

review article it's very well written

and it summarizes this whole concept

really really well and it's got some

excellent figures there so I don't take

credit for making this figure myself

it's adapted from a very fantastic

review referenced in the in the section

below in the video so now we need to

think about what makes what makes up the

components of the adipose tissue okay so

we've got to think about what adipose

tissue actually is when we break it down

essentially adipose tissue is basically

a cluster of cells which are housed

together in different parts of the body

and it's within here within each of

these cells that the fat actually gets

stored in okay then we need in each of

these cells where the fact

she get stored and we'll talk about that

process of storage a little bit later

but first of all we've got to think

we've got to treat adipose tissue as a

reservoir for storing energy so energy

that we consume in our in our diet fat

that we consume in our diet being stored

to be ready to use later on and this is

why you know you can you can actually

fast for quite a number of days and you

wouldn't actually you know you wouldn't

die from not eating food for five days

for example because we've got plenty of

reserve in these reservoirs here okay

plenty of reserve energy in the form of

the fat contained the adipose cells now

when we look at this diagram here we can

actually see that the adipose tissue is

very well nourished with blood vessels

okay now those blood vessels are

obviously taking they're transporting

those liquid particles the fact that we

consume in our diet from areas of the

body where the digestion has occurred to

be stored in the adipose site and

likewise the circulation is obviously as

a loop so if we need to use the energy

that's stored in here then a process

called lipolysis which we'll talk about

later on takes place and that energy can

be broken down transported to the blood

vessels to the target organ to be used

as energy we've also got these

supporting structures here we've got

fiber oblasts which help to kind of

support and provide structure to the

adipose tissue clumping together we've

got a pre a Depot site which is

basically a baby a Depot site which is

going to mature into one of these bigger

adipocytes with time now what's

extremely important that we can see here

is these cells called macrophages now

these are immune cells okay they're

involved in inflammatory response within

the body and they can be activated in

adipose tissue and this is why obesity

when you have too much adipose tissue is

said to be a low-grade inflammatory

condition because the adipose tissue the

adipose cells are constantly signaling

with each other let's crosstalk going on

between macrophages T cells as well

which we can see embedded within the

adipose tissue there's a crosstalk

gone between the cells and they can

actually activate become activated and

start causing an inflammatory response

within the body okay now some of that

inflammatory response can cause you know

direct injury to that particular organ

or tissue so if this adipose tissue was

around the liver for example it could

cause direct damage to the liver or it

can some of those inflammatory cells can

get into the circulation of let's say

for example the liver and then be

transported elsewhere to the rest of the

body and cause injury injury there so

the fact that the blood vessels and the

capillaries and adipose tissues are

highly vascularized suggests that if we

gain weight then any harmful effects

that we have from a gain and adipose

tissue will quite quickly start

affecting the rest of our organs and

tissues elsewhere in the body as well so

that's the most important thing to think

about in terms of the structure of the

adipose tissue these are some of the key

this is kind of like a key schematic in

terms of how to visualize how a clump of

actually looks like so you grab a little

bit of fat from from your belly and you

can imagine that that fact that you're

holding is consisting of you know these

cells clustered together with

inflammatory cells embedded in between

and it's highly vascularized as well so

this is the introductory parts of this

topic stay tuned for the next video

where we'll talk a little bit more in

detail about what happens to adipose

tissue during obesity