Comprehensive Guide to Body Cavities and Membranes Explained

welcome back to the channel where medical and science topics are made easy in this video we're going to simplify

the different body cavities and membranes and by the end of the video you'll know this entire flow chart as

well as everything in the table so make sure to watch until the end we're going to come back to the flow chart

throughout the video and then summarize everything at the end with the table remember to turn on those captions down

below and read along this will help you remember everything so let's get right into it

first we have to ask ourselves what is a body cavity a body cavity is a space or compartment in the body that houses

organs or structures in other words they're the spaces left over when internal organs are removed

we're going to make body cavities simple to understand by making a flow chart first there are two main cavities in the

body they include the dorsal cavity and the ventral cavity we've talked about the terms dorsal and ventral in past

videos you might recognize this image from our previous video on anatomical directional

terms it'll be linked down below in the description in that video we learned that anterior

means front or toward the front of the body and that posterior means back or toward the back of the body

we also learned that another name for anterior is ventral and another name for posterior is dorsal

you can think of a ventriloquist for ventral which literally translates to stomach talker

and if you point to your stomach then you're pointing to the front of your body and this can help you remember

ventral means front for dorsal you can think of a dorsal fin on the back of a fish to help you

remember dorsal means back you might also recognize this image and table from our medical prefix video that

link will be in the description as well we learned that the prefix ventri means stomach abdomen toward the front or the

anterior aspect of the body we also learn the prefix dorsal means back or posterior

now that we know dorsal means back or posterior and ventral means front or anterior we can apply those terms to the

dorsal cavity and ventral cavity starting with the dorsal cavity we know dorsal means back or posterior so the

dorsal cavity is the cavity located in the back of the body the dorsal cavity is the green cavity on

the image let's highlight the dorsal cavity in red to make it pop out

you can see how the dorsal cavity is situated behind or posterior to the ventral cavity

so that means the ventral cavity is the cavity located in the front of the body which makes sense because ventral means

front or anterior the ventral cavity is the tan beige cavity on the image

let's also highlight this cavity in red and you can see how the ventral cavity is situated in front of or anterior to

the dorsal cavity now that we have a good understanding of the dorsal and ventral cavities each

cavity can be broken down even more let's start with the dorsal cavity the dorsal cavity can be subdivided into

two main parts we have the cranial cavity and the spinal cavity let's look at the cranial cavity first

we're going to go through the high yield features of each cavity the cranial cavity is the superior portion of the

dorsal cavity as we can see highlighted in red and labeled by the star the cranial cavity is enclosed by the

cranium or skull and it houses the brain the cranial cavity also contains fluid called cerebrospinal fluid that helps

protect and cushion the brain each cavity is also lined with thin sheets of tissue called membranes

the cranial cavity is lined by a three-layer membrane called the meninges which protect and cover the brain

the three meningeal layers are the dura mater arachnoid and pia mater let's take a closer look at the cranial

cavity and all of its features we're looking at a side view of the brain and skull called a sagittal view

as we mentioned before the cranial cavity is enclosed by the cranium or skull which we have highlighted in green

you can see how the skull has formed an empty space or cavity this space created by the skull is called the cranial

cavity which is shown in yellow we know the cranial cavity contains the brain which we'll color in red

now as we said before the cranial cavity also contains fluid called the cerebrospinal fluid or csf

the csf helps protect and cushion the brain along with other functions and it's located in the subarachnoid space

between the meningeal layers remember we said the cranial cavity is lined by a three layer membrane called

the meninges the pia mater is the innermost layer and closely adheres to the brain

the pia mater on the image is the inner black line between the brain and csf the dura mater is the outermost layer

and the arachnoid is the middle layer they're represented by the outer black line on the image between the skull and

csf remember the csf is located in the subarachnoid space between the arachnoid

and pia mater let's look at the diagram in the bottom left showing the layers to help refresh your memory

first we have the skull on the outside which is what the cranial cavity is enclosed by

below the skull is three layers of membrane called the meninges the three meningeal layers are represented by the

stars the outermost layer of the meninges is the dura mater which is located beneath

the skull below the dura mater we have the arachnoid which is the middle meningeal

layer there is a space below the arachnoid called the subarachnoid space and this

is where the csf is located the innermost meningeal layer is the pia mater which adheres closely to the brain

so hopefully this helps to visualize the cranial cavity better if we go back to the flow chart we now

have a good understanding of the cranial cavity and how it contains the brain now let's look at the features of the spinal

cavity the spinal cavity is also known as the vertebral cavity and it's the inferior

portion of the dorsal cavity the spinal cavity is continuous with the cranial cavity as we can see highlighted

in red and labeled by the stars the spinal cavity is enclosed by the vertebral column or spine and it houses

the spinal cord the spinal cavity also contains cerebrospinal fluid that helps protect

the spinal cord remember the cranial cavity and spinal cavity are continuous with one another

so it makes sense they both contain csf likewise the meninges line the spinal cavity just like the cranial cavity

let's take a closer look at the spinal cavity and its features we're looking at the same side view of

the brain and spinal cord as we mentioned before the spinal cavity is enclosed by the vertebral column which

we have highlighted in green you can see how the vertebral column has formed an empty space or cavity this

space created by the vertebral column is called the spinal cavity which is shown in yellow

you can see how the spinal cavity is continuous with the cranial cavity above it

we know the spinal cavity contains the spinal cord which we'll color in red now as we said before the spinal cavity

contains csf just like the cranial cavity because the two cavities are continuous with one another

the csf is again located in the subarachnoid space between the meningeal layers

remember we said the spinal cavity is lined by the meninges as well the spinal meninges are similar to what

we saw with the brain we can use the circular cross section as a reference it's like we're looking down

at the spinal cord we have the spinal cord in the center which is housed in the spinal cavity and the spinal cavity

is enclosed by the vertebral column represented in green the three meningeal layers line the

spinal cavity and are shown by the stars the pia mater is again the innermost layer and closely adheres to the spinal

cord the dura mater is the outermost layer and the arachnoid is the middle layer

remember the csf is located in the subarachnoid space between the arachnoid and pia mater

if we fill in our cranial cavity again you can really appreciate how the two cavities are continuous with one another

the cavities are enclosed by the skull and vertebral column in green which house the brain and spinal cord in red

and the cerebrospinal fluid in yellow is in the subarachnoid space around the brain and spinal cord so hopefully this

helps to visualize the spinal cavity better let's go back to our flow chart we now

know the cranial cavity and spinal cavity make up the dorsal cavity the cranial cavity contains the brain and

the spinal cavity contains the spinal cord in other words the dorsal cavity houses

the central nervous system because we know the central nervous system is made up of the brain and spinal cord

now let's move on to the ventral cavity the ventral cavity can also be subdivided into two main parts

we have the thoracic cavity and the abdominal pelvic cavity which are separated by the diaphragm

let's look at the thoracic cavity first the thoracic cavity is the cavity in the chest it's the superior portion of the

ventral cavity and it's above the diaphragm as we can see highlighted in red

the thoracic cavity is enclosed by the rib cage vertebral column and sternum the main contents of the thoracic cavity

include the heart lungs trachea esophagus and the great vessels the thoracic cavity is also lined by

membranes and in order to better understand these membranes let's first go back to our flow chart

the thoracic cavity can be subdivided even further into the pleural cavities and the mediastinum let's look at each

of these starting with the pleural cavities the thoracic cavity has two pleural

cavities a right and a left the pleural cavities surround the lungs the right pleural cavity surrounds the right lung

and the left pleural cavity surrounds the left lung you can see the right lung highlighted

in red with the right pleural cavity surrounding it shown in yellow the left lung is uncolored as a reference

each pleural cavity has a small amount of fluid called pleural fluid this helps lubricate the lungs as well as the

membrane lining the cavity when breathing in and out the pleural fluid is located in the

pleural cavity also known as the pleural space which is the potential space and yellow between the lungs and chest wall

each pleural cavity is lined by a serous membrane called the pleura the pleura folds on itself to create a double

layered membrane shown in green and purple the inner green membrane that lines the

lung is called the visceral pleura and the outer purple membrane that lines the chest wall or thoracic cavity is called

the parietal pleura the potential space between the visceral and parietal pleura is the pleural

cavity or space shown in yellow here is another picture of the lung to show the inner visceral pleura which

lines the lung and the outer parietal pleura which lines the chest wall or thoracic cavity

you can also see the pleural cavity or space between the visceral pleura of the lung and the parietal pleural of the

chest wall the pleural cavity contains a small amount of pleural fluid so now we know the right and left

pleural cavities and lungs make up part of the thoracic cavity as we can see highlighted in blue but now we have this

middle area of the thoracic cavity highlighted in yellow that we need to talk about

this is called the mediastinum and it makes up the middle portion of the thoracic cavity you can remember the m

in middle and mediastinum to help you remember this the main contents of the mediastinum

include the heart trachea esophagus great vessels and thymus gland we can see how the outer parietal pleura

we discussed before lines the mediastinum there is one more cavity to talk about

within the mediastinum and that's the pericardial cavity the pericardial cavity surrounds the heart within the

mediastinum let's talk about the features of the pericardial cavity and then we'll look

at an image the pericardial cavity is located within the mediastinum in the thoracic cavity

and it surrounds the heart just like how the pleural cavity contain pleural fluid the pericardial cavity

contains a small amount of fluid called pericardial fluid and just like how the pleural cavity was

lined by a double layered serous membrane called the pleura the pericardial cavity is lined by a double

layered serous membrane called the pericardium similar to the lungs there is an inner

visceral layer called the visceral pericardium and an outer parietal layer called the parietal pericardium

the potential space between those layers is the pericardial cavity there is also a fibrous pericardium that

surrounds the cirrus pericardial layers let's look at an image to better understand this

if we zoom in on the outside of the heart we can see the heart is surrounded by the layers of the pericardium the

pericardium can be divided into a double layered serous membrane represented by the stars and an outer fibrous membrane

represented by the circle the inner layer of the serous pericardium is the visceral pericardium

and it surrounds the heart this is similar to the visceral pleura that surrounded the lungs

the parietal pericardium is the outer layer of the serous membrane and it lines the inside of the fibrous

pericardium the potential space between the visceral and parietal layers is the pericardial

cavity or space and it contains a small amount of serous fluid called pericardial fluid that helps lubricate

and protect the heart as it beats the outermost layer of the pericardium is the fibrous pericardium

so we can see how the pericardial cavity in yellow surrounds the heart and the cavity is lined by the visceral and

parietal layers of the pericardium let's go back to our flow chart we now have a good understanding of the

thoracic cavity the thoracic cavity can be subdivided into the right and left pleural cavities which surround the

lungs and the mediastinum which contains the heart trachea esophagus great vessels and thymus gland

within the mediastinum there is another cavity called the pericardial cavity which surrounds the heart and the roots

of the great vessels now let's move on to the abdominal pelvic cavity

the abdominal pelvic cavity is the inferior portion of the ventral cavity and it's below the diaphragm as we can

see highlighted in red as the name suggests the abdominal pelvic cavity consists of both the

abdominal and pelvic cavities so if we go back to our flow chart we can divide the abdominal pelvic cavity

into the abdominal cavity and pelvic cavity let's look at the abdominal cavity first

the abdominal cavity makes up the middle part of the ventral cavity or the superior part of the abdominal pelvic

cavity as we can see highlighted in red the abdominal cavity is enclosed mainly by the rib cage abdominal muscles and

the vertebral column the diaphragm forms the superior boundary of the abdominal cavity and an

imaginary line at the pelvic inlet forms the boundary between the abdominal and pelvic cavities

some of the main contents of the abdominal cavity include the liver stomach pancreas spleen kidneys and

intestines the abdominal cavity is lined with a serous membrane called the peritoneum

similar to the pleura and pericardium the peritoneum has two layers the inner visceral peritoneum that covers the

internal organs or viscera and the outer parietal peritoneum that lines the wall of the abdominal cavity

the peritoneal cavity is the space between the visceral and parietal peritoneal layers and it contains fluid

called peritoneal fluid the peritoneal fluid helps lubricate most of the abdominal organs

the terms peritoneal cavity and abdominal cavity are different so let's take a closer look at these features

let's look at a side view of the small intestine in the abdominal cavity the small intestine is attached to the

posterior abdominal wall by the mesentery the peritoneum is a continuous serous

membrane that folds on itself to create two layers the inner layer is called the visceral

peritoneum and it covers most of the internal visceral organs of the abdominal cavity

the outer layer is called the parietal peritoneum and it lines the walls of the abdominal cavity

there is a potential space between the visceral and parietal layers called the peritoneal cavity or space

and it contains serous fluid called peritoneal fluid that helps lubricate the organs

the peritoneal cavity is exaggerated in this image since the other internal organs are removed

the organs that are completely wrapped by the visceral peritoneum are known as intraperitoneal organs and they include

the liver stomach spleen jejunum and ilium to name a few there are also structures that are in

the abdominal cavity but they are extra peritoneal meaning they are not covered by visceral peritoneum

for example abdominal organs can be located behind the peritoneum or peritoneal cavity as indicated by the

star these structures are called retroperitoneal structures because they

are behind the peritoneum and the retroperitoneal space remember in our medical prefix video we

said retro means back or behind if you look at the star you can see these structures are covered by the

parietal peritoneum anteriorly and attached to the posterior abdominal wall posteriorly

some example organs located in the retroperitoneal space include the kidneys adrenal glands and part of the

pancreas organs can also be below or inferior to the peritoneum or peritoneal cavity as

indicated by the circle these structures are known as subperitoneal structures because they're

below or inferior to the peritoneum an example is the bladder so make sure you know the difference

between the abdominal cavity and peritoneal cavity the abdominal cavity is the entire cavity whereas the

peritoneal cavity is the potential space between the visceral and parietal peritoneum

finally we have the pelvic cavity the pelvic cavity is the inferior portion of the ventral cavity it is enclosed by the

pelvis and pelvic floor muscles the pelvic cavity is continuous with the abdominal cavity superiorly at the

pelvic inlet the pelvic cavity mainly houses the urinary bladder reproductive organs

pelvic portion of the colon and rectum since the pelvic cavity is continuous with the abdominal cavity the fluid and

membranes will be the same the pelvic cavity is lined by the peritoneum which includes both the inner

visceral peritoneum and outer parietal peritoneum just like we saw with the abdominal cavity

the peritoneal cavity is the potential space between the visceral and parietal peritoneum and it contains a small

amount of peritoneal fluid remember some of the structures in the pelvic cavity such as the bladder are

going to be subperitoneal below the peritoneum as shown by the blue circle so the pelvic cavity is the entire

cavity enclosed by the pelvis as shown in green whereas the peritoneal cavity is the potential space between the

visceral and parietal peritoneum if we go back to our flow chart we can now see we have a good understanding of

all the different body cavities by organizing them and breaking them down here is a table that summarizes

everything we learned to make it easier for you the flow chart and table can all be found on the website linked down

below in the description hopefully this helped you better understand the different body cavities

and membranes if you found the video useful please show your support and hit that subscribe button don't forget to

like and comment as well as always you can find all of the notes and pictures for this video on the

website linked down below in the description thanks for watching and hope you check out future videos