What are the internal surfaces of body cavities actually made of?

In Ross's book of histology it says that the mesothelium that includes all body cavities is made of simple squamous epithelium but in other places it says that in the gastrointestinal tract it is made of simple columnar epithelium. Is it that the trachea and the the gastrointestinal tract are not classed as cavities?

The peritoneum, the pleura, the pericardium, the tunica vaginalis testis and the tunica serosa uteri are made of mesothelium (simple squamous epithelium) [1].

The GI tube is made of a specialized tissue composed from four layers: mucosa, submucosa, muscularis externa and adventitia. The innermost layer (mucosa) has an epithelium that is stratified, squamous and non-keratinising, for protective purposes. The internal organs in the peritoneal cavity are covered with the visceral sheet of peritoneum which is the adventita layer [2].

Trachea is made of respiratory epithelium, which serves to moisten and protect the airways. It is lined with pseudostratified columnar epithelium with goblet cells that produce mucus [3].

Trachea, stomach and intestines are considered cavitary organs as opposed to parenchymatous organs (lung, kidney, liver).


  1. Wikipedia contributors, "Mesothelium," Wikipedia, The Free Encyclopedia, (accessed June 26, 2014).

  2. Wikipedia contributors, "Gastrointestinal wall," Wikipedia, The Free Encyclopedia, (accessed June 26, 2014).

  3. Wikipedia contributors, "Trachea," Wikipedia, The Free Encyclopedia, (accessed June 26, 2014).

Body Cavities and Membranes

In anatomy and physiology, you’ll learn about the body cavities and membranes, which not only help protect the organs, but they also keep them compartmentalized, much like a toolbox contains cavities to keep the different tools protected in the different compartments.

Two Major Body Cavities: Dorsal and Ventral

The body contains two major cavities: a larger cavity called the ventral cavity, and a smaller cavity called the dorsal cavity.

If you think back to the video I made over the directional terms, you’ll know that ventral (or anterior) means toward the front of the body, and dorsal (or posterior) means toward the back of the body. That’s exactly where these two cavities are located.

Dorsal Body Cavity

The dorsal body cavity is located toward the back of the body, and it houses our central nervous system. Remember that the dorsal fin is on the dolphin’s back, and you’ll remember that the dorsal cavity is toward the back of the body.

The dorsal cavity can be subdivided into two main parts:

  • The cranial cavity (superior), which houses the brain
  • The vertebral cavity (inferior), which houses the spinal cord

Ventral Body Cavity

The ventral body cavity is the larger cavity located toward the front of the body, and it contains our visceral organs (or guts!). Remember: ventral contains the viscera! The ventral cavity can also be divided into two main parts: the thoracic cavity and abdominopelvic cavity, which are separated by the diaphragm.

The thoracic cavity, also called the chest cavity, sits superior (higher) to the abdominopelvic cavity, and it contains organs such as the heart, lungs, trachea, and esophagus. It can be subdivided into three main portions:

  1. The left pleural cavity, which houses the left lung
  2. The mediastinum (comes from a Latin word meaning “midway”) houses organs such as the heart, esophagus, thymus gland, and trachea. The heart is surrounded by its own cavity called the pericardial cavity (peri = around cardi = heart).
  3. The right pleural cavity, which houses the right lung

The abdominopelvic cavity (inferior to diaphragm) contains various digestive and reproductive organs, and it can be divided into two sub-cavities: an upper (abdominal) portion and a lower (pelvic) portion, which is really easy to remember because the name abdominopelvic is a dead giveaway!

  1. The abdominal cavity (superior), which contains organs such as the liver, stomach, pancreas, spleen, gallbladder, intestines, and kidneys
  2. The pelvic cavity (inferior), which contains the bladder, reproductive organs, and the distal portions of the large intestine (sigmoid colon and rectum)

Do you remember how, in the thoracic cavity, the lungs had their own fancy cavities called the pleural cavities, and the heart had its own cavity called the pericardial cavity? In the abdominopelvic cavity, there’s a fancy name for the cavity that surrounds most of the organs: it’s called the peritoneal cavity.

Minor Body Cavities

In addition to the major body cavities, the body also contains a few minor cavities such as the nasal cavity/sinuses, oral cavity, orbital cavities, middle ear cavities, and the synovial (joint) cavities, but those are beyond the scope of this lesson, which is only focusing on the major body cavities.

Body Membranes

The body cavities are lined with thin sheets of tissue called membranes, which cover and protect the various organs.

  • The dorsal body cavity is lined with three layers of protective membranes (the dura mater, arachnoid, and pia mater), which are called the “meninges.” In 2014, I remember reading a news story about a nursing student who began feeling ill. Her fever kept climbing, and she felt horrible. She logged into Twitter and posted a message that read, “I think I’m dying.” Soon after, she died from bacterial meningitis (inflammation of the meninges).
  • The ventral body cavity contains various serous membranes, which are filled with a watery substance that allows for lubrication and movement of organs:
    • Pleura: the membrane that lines the pleural cavity, which covers the lungs in the thoracic cavity
    • Pericardium: the membrane that lines the pericardial cavity, which covers the heart in the mediastinum (middle part of the thoracic cavity)
    • Peritoneum: the membrane that lines the peritoneal cavity abdominopelvic cavity and many of the organs found within it.

    In a previous video, I covered the directional terms of the body, such as superior/inferior, anterior/posterior, distal/proximal, etc.

    When it comes to these serous membranes, anatomists use additional directional terms to describe the location of the membrane’s lining:

    • The visceral layer of the membrane is the layer that touches the organs (viscera).
    • The parietal layer is the layer that forms the outer shell of the membrane and touches the surrounding structures and lines the wall of the cavity (parietal comes from a Latin word that means “wall”).
    • The name of the membrane is often preceded by the directional term, so if you’re talking about the pleura of the left lung, the visceral pleura will be the part of the membrane lining touching the lung, and the parietal pleura will be the part of the membrane touching the cavity’s wall.

    In addition, the peritoneal cavity doesn’t cover all of the abdominopelvic organs.

    • If the organ is behind the peritoneal space, it’s considered retroperitoneal (the prefix “retro” means “back” or “backwards”.
    • If the organ is within the peritoneal space, it’s considered intraperitoneal (the prefix “intra” means “within”)
    • If the organ is under the peritoneal space, it’s considered subperitoneal (sub means under)

    Quick Recap on Body Cavities and Membranes

    That wraps up the major body cavities and membranes. To recap, there are two major cavities in the body: the dorsal cavity and the ventral body cavity. The dorsal is divided into the cranial cavity, which contains the brain, and the vertebral cavity, which contains the spinal cord.

    The ventral body cavity can also be divided into two portions: thoracic (or chest) cavity, and the abdominopelvic cavity. The thoracic cavity contains the left pleural cavity, right pleural cavity, and the mediastinum, which contains the pericardial cavity that surrounds the heart, along with other organs.

    The abdominopelvic cavity can be subdivided into two additional cavities (let the name help you): abdominal and pelvic cavities, which not only contains various digestive and reproductive organs, but also contains the peritoneal cavity.

    Free Quiz and More Anatomy Videos

    Ready to test your knowledge? Take our free (and quick!) body cavities and membranes quiz. Also, you might want to watch more of our anatomy and physiology lectures on YouTube, or check our anatomy and physiology notes.

    Classification of Epithelia

    Epithelium has two names. The first name indicates the number of cell layers, the second describes the shape of its cell. Based on the number of cell layers, epithelia can either be simple or stratified.

    • Simple epithelia– consist of a single cell layer (found where absorption, secretion, and filtration occur).
    • Stratified epithelia– are composed of two or more cell layers stacked on top of each other (typically found in high abrasion areas where protection is needed).

    All epithelial cells have six sides but they vary in height. For this reason, there are three ways to describe the shape and height of epithelial cells.

    1. Squamous cells– are flat and scale-like.
    2. Cuboidal cells– are box-like (same height and width).
    3. Columnar cells– are tall (column shaped).

    Simple squamous epithelium

    Simple squamous epithelium– are close fitting and flattened laterally. They’re found where filtration occurs (kidneys, lungs) and they resemble the look of a fried egg. Two simple squamous epithelia in the body have special names reflecting their location.

    1. Endothelium– provides a friction-reducing ling in lymphatic vessels and all hollow organs of the cardiovascular system (heart, blood vessels, capillaries).
    2. Mesothelium– is the epithelium found in serous membranes (membranes lining the ventral body cavity and covering the organs within it).

    Simple cuboidal epithelium– consists of a single layer of cells with the same height and width. Functions include secretion and absorption (located in small ducts of glands and kidney tubules).

    Simple columnar epithelium– is a single layer of tall, closely packed cells that line the digestive tract from the stomach to the rectum. Functions include absorption and secretion. They contain dense microvilli on their apical surface . Additionally, some simple columnar epithelia may display cilia on their free surface also.

    Pseudostratified columnar epithelium– vary in height. All of their cells rest on the basement membrane and only the tallest reach the apical surface. When viewing pseudostratified epithelium it may look like there are several layers of cells, but this is not the case. (because the cells have different heights, it gives the illusion of multiple cell layers). Most pseudostratified epithelia contain cilia on their apical surface and line the respiratory tract.

    Stratified squamous epithelium– is the most widespread stratified epithelia. It’s composed of several layers and is perfect for its protective role. Its apical surface cells are squamous and cells of the deeper layer are either cuboidal or columnar. Stratified squamous forms the external part of the skin and extends into every body opening that’s continuous with the skin. The outer layer of the skin (epidermis) is keratinized (contains keratin, a protective protein). Other stratified squamous in the body is nonkeratinized.

    Stratified cuboidal epithelium

    Stratified cuboidal epithelium– is somewhat rare in the human body. It’s mainly found in the ducts of glands (sweat glands, mammary glands) and is typically has two layers of cuboidal cells.

    Stratified columnar epithelium

    Stratified columnar epithelium– is also rare in the human body. Small amounts are found in the pharynx, male urethra, and lining of some glandular ducts. Stratified columnar epithelium occurs in transition areas (junctions) between other epithial types.

    The dorsal body cavity protects organs of the nervous system and has two subdivisions. The cranial cavity is the area within the skull and encloses the brain. The spinal (vertebral) cavity encases the vertebral column and spinal cord.

    Like the dorsal cavity, the ventral cavity has two subdivisions. The superior division is called the thoracic cavity. The thoracic cavity is surrounded by the ribs and muscles in the chest. It’s further sudivided into lateral pleural cavities (each pleural cavity envelopes a lung) and the mediastinum. Within The pericardial cavity lies within the mediastinum. It encloses the heart and remaining thoracic organs (trachea, esophagus, ect.).

    The inferior division of the ventral body cavity is called the “abdominopelvic cavity” and is separated from the thoracic cavity by the diaphragm. The abdominopelvic cavity is also separated into two subdivisions, the “abdominal cavity” and “pelvic cavity“. The abdominal cavity contains the stomach, spleen, liver, intestines, and a few other organs. The pelvic cavity (inferior) contains the urinary bladder, rectum, and some reproductive organs.

    Membranes in the Ventral body cavity

    The walls of the ventral body cavity and outer covering of its organs contain a thin covering called the serosa (also called serous membrane). It is a double-layered membrane made up of two parts called the “parietal serosa” (lines the cavity walls) and “visceral serosa” (covers organs in the cavity). The serous membranes are separated by a thin layer of fluid called “serous fluid“. Serous fluid is secreted by both membranes and acts as a lubricant, allowing organs to slide in the cavity without causing friction.

    Typically, the serous membranes are named according to the cavity and organ they associate with. For instance, the parietal pericardium lines the pericardial cavity.

    Abdominopelvic regions and quadrants”

    Because it’s so large, the abdominopelvic cavity is separated into regions and quadrants. The quadrants are self-explanatory and can be figured out fairly easily by looking at the abdominopelvic cavity. They consist of the:

    • Right upper quadrant (RUQ)
    • Left upper quadrant (LUQ)
    • Right lower quadrant (RLQ)
    • Left lower quadrant (LLQ)

    Simply draw a cross over the cavity seperating it into four boxes, then use the directional terms accordingly.

    Abdominopelvic Regions: Image by Mary Weis

    The 9 regions of the abdominopelvic cavity are listed below (see image above also).


    In the human body there are more than 200 types of cells that are organized to form tissues that can be of four basic types:

    1. Epithelial tissue : covers organs and body cavities, both external and internal, and controls the passage of substances between surfaces.
    2. Connective tissue : forms various parts of the body that give mechanical and metabolic support, from the transport and storage of nutrients, to the protection and damping of organs.
    3. Muscle tissue: it is contractile tissue that allows the movement of the body.
    4. Nervous tissue : is responsible for the transmission of information.

    The simplest combination of tissues are the tissue membranes, formed by connective tissue or by a combination of epithelial tissue and connective tissue.


    The kidneys are part of the urogenital tract, and are involved in the manufacture and transport of urine as well as in the regulation of plasma urea concentrations. In skates and rays, they are either semi-lunar shaped or ribbon-like, dorsoventrally flattened, dark red organs that are highly lobed and lie dorsally on either side of the spinal column outside of the body cavity. A tough membrane, called the peritoneum, separates the kidneys from the rest of the body cavity. The kidneys are drained into the cloaca by the ureters.

    2. Connective Tissue

    -Most abundant tissue in your body, found throughout
    -Binds structures together
    -Provides support, protection, framework, fills space, stores fat, produces blood cells, fights infection
    -Composed of more scattered _________________ with intercellular _____________
    -Made up of a ground substance (fluid, semi-solid) and fibers
    -Most has a good ________________________
    -Cells can reproduce

    Three common types of cells:

    -collagenous fibers Strong, flexible Found: ____________________
    - elastic fibers Found ______________________________


    A. LOOSE C.T. or AREOLAR TISSUE - binds skin to underlying organs and organs to organs, forms delicate, thin ____________________ throughout the body

    B. ADIPOSE TISSUE - aka FAT ' Function: Protective cushion, insulation to preserve body heat, stores ______________________________, cells are called adipocytes

    C. FIBROUS C.T. - dense tissue, closely packed, thick collagenous fibers and fine network of elastic fibers. Few cells, poor blood supply, thus slow healing.

    D. CARTILAGE (all cartilage cells are called ______________________)




    E. BONE TISSUE - _____________________________ tissue. Rigid due to mineral salts.

    F. BLOOD TISSUE - circulates throughout the body

    Connective Tissues

    Connective tissues are composed of fibers forming a network and a semi fluid intracellular matrix. It is where blood vessels and nerves are embedded. It is responsible for distributing nutrients and oxygen throughout the tissues. It forms the skeleton, the nerves, fat, blood and the muscles. It functions not only to support and protect but it binds other tissues to promote a way for communication and transport. In addition the adipose, one type of connective tissue is responsible for providing heat in the body. The connective tissues are vital and significant component of almost all organs in the body.


    The teeth are a group of hard organs found in the oral cavity. We use teeth to masticate (or chew) food into tiny pieces. They also provide shape to the mouth and face and are important components in producing speech.

    A tooth can be divided into two main parts: the crown and root. Found above the gum line, the crown is the enlarged region of the tooth involved in chewing. Like an actual crown, the crown of a tooth has many ridges on its top surface to aid in the chewing of food. Below the gum line is the region of the tooth called the root, which anchors the tooth into a bony socket known as an alveolus. Continue Scrolling To Read More Below.

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    Each tooth is an organ consisting of three layers: the pulp, dentin, and enamel.

    • The pulp of the tooth is a vascular region of soft connective tissues in the middle of the tooth. Tiny blood vessels and nerve fibers enter the pulp through small holes in the tip of the roots to support the hard outer structures. Stem cells known as odontoblasts form the dentin of the tooth at the edge of the pulp.
    • Surrounding the pulp is the dentin, a tough, mineralized layer of tissue. Dentin is much harder than the pulp due to the presence of collagen fibers and hydroxylapatite, a calcium phosphate mineral that is one of the strongest materials found in nature. The structure of the dentin layer is very porous, allowing nutrients and materials produced in the pulp to spread through the tooth.
    • The enamel — the white, outer layer of the crown — forms an extremely hard, nonporous cap over the dentin. Enamel is the hardest substance in the body and is made almost exclusively of hydroxylapatite.

    Teeth are classified into four major groups: incisors, canines, premolars, and molars.

    • Incisors are chisel-shaped teeth found in the front of the mouth and have a flat apical surface for cutting food into smaller bits.
    • Canine teeth, also known as cuspids, are sharply pointed, cone-shaped teeth that are used for ripping tough material like meat. They flank the incisors on both sides.
    • Premolars (bicuspids) and molars are large, flat-surfaced teeth found in the back of the mouth. Peaks and valleys on the flat apical surface of premolars and molars are used for chewing and grinding food into tiny pieces.

    Babies are born without teeth, but grow a temporary set of twenty deciduous teeth (eight incisors, four canines, and eight molars) between the ages of six months and three years. Baby teeth fill the child’s tiny jaws and allow the child to chew food while larger, stronger adult teeth develop inside the mandible and maxilla bones. At about six years of age the deciduous teeth are slowly shed one at a time and replaced by permanent adult teeth.

    Adult teeth develop while hidden within the maxilla and mandible after the deciduous teeth have erupted. When an adult tooth erupts, it triggers the roots of the deciduous tooth above it to atrophy. This causes the baby tooth to become loose and eventually fall out. The new permanent tooth slowly pushes up through the gums to replace the baby tooth. Eventually, a total of thirty-two permanent adult teeth form and erupt. The adult teeth are arranged in both the upper and lower jaws from the midline of the mouth as follows: central incisor, lateral incisor, canine (cuspid), first premolar (bicuspid), second premolar, first molar, second molar, and third molar.

    The first twenty-eight adult teeth are fully erupted by the age of eleven to thirteen with the third molars, known as wisdom teeth, erupting in the back of the jaw several years later in early adulthood. Sometimes the wisdom teeth become impacted when they grow and become wedged at an abnormal position in the jaws and fail to erupt. In some cases there is not enough room in the jaw to accommodate a third set of molars. In both cases the wisdom teeth are surgically removed, as they are not needed to properly chew food.

    Mastication, or chewing, is the main function of the teeth. The teeth are aligned in the jaws so that the peaks of one tooth align with the valleys of its counterpart on the other jaw. Every bite forces food into the interface of the teeth to be chopped, while lateral motion of the jaw is used to grind food in the premolars and molars.

    Tooth decay and cavities are important health concerns related to the teeth. The enamel that covers the crown in each tooth can be broken down by acids produced by bacteria that live in the mouth and assist in digestion of small bits of food. This process of enamel erosion by acids is called decay. To prevent decay, good oral hygiene, consisting of daily brushing and flossing, is necessary. Decay can eventually lead to cavities, also known as dental caries, where holes appear in the enamel and expose the dentin. Cavities require medical intervention to prevent their growth, usually resulting in the removal of the affected tissue and the filling of the cavity with a hard material to restore the strength and function of the tooth.

    Parts of the Alimentary Canal [back to top]

    1. Mouth (Buccal cavity) [back to top]

    The teeth and tongue physically break up the food into small pieces with a larger surface area, and form it into a ball or bolus. The salivary glands secrete saliva, which contains water to dissolve soluble substances, mucus for lubrication, lysozymes to kill bacteria and amylase to digest starch. The food bolus is swallowed by an involuntary reflex action through the pharynx (the back of the mouth). During swallowing the trachea is blocked off by the epiglottis to stop food entering the lungs.

    2. Oesophagus (gullet) [back to top]

    This is a simple tube through the thorax, which connects the mouth to the rest of the gut. No digestion takes place. There is a thin epithelium, no villi, a few glands secreting mucus, and a thick muscle layer, which propels the food by peristalsis. This is a wave of circular muscle contraction, which passes down the oesophagus and is completely involuntary. The oesophagus is a soft tube that can be closed, unlike the trachea, which is a hard tube, held open by rings of cartilage.

    3. Stomach [back to top]

    This is an expandable bag where the food is stored for up to a few hours. There are three layers of muscle to churn the food into a liquid called chyme. This is gradually released in to the small intestine by a sphincter, a region of thick circular muscle that acts as a valve. The mucosa of the stomach wall has no villi, but numerous gastric pits (10 4 cm 𔂬 ) leading to gastric glands in the mucosa layer. These secrete gastric juice, which contains: hydrochloric acid (pH 1) to kill bacteria (the acid does not help digestion, in fact it hinders it by denaturing most enzymes) mucus to lubricate the food and to line the epithelium to protect it from the acid and the enzymes pepsin and rennin to digest proteins.

    4. Small Intestine [back to top]

    This is about 6.5 m long, and can be divided into three sections:

    (a) The duodenum (30 cm long). Although this is short, almost all the digestion takes place here, due to two secretions: Pancreatic juice, secreted by the pancreas through the pancreatic duct. This contains numerous carbohydrase, protease and lipase enzymes. Bile, secreted by the liver, stored in the gall bladder, and released through the bile duct into the duodenum. Bile contains bile salts to aid lipid digestion, and the alkali sodium hydrogen carbonate to neutralise the stomach acid. Without this, the pancreatic enzymes would not work. The bile duct and the pancreatic duct join just before they enter the duodenum. The mucosa of the duodenum has few villi, since there is no absorption, but the submucosa contains glands secreting mucus and sodium hydrogen carbonate.

    (c) The ileum (4 m long). These two are similar in humans, and are the site of final digestion and all absorption. There are numerous glands in the mucosa and submucosa secreting enzymes, mucus and sodium hydrogen carbonate.

    The internal surface area is increased enormously by three levels of folding: large folds of the mucosa, villi, and microvilli. Don't confuse these: villi are large structures composed of many cells that can clearly be seen with a light microscope, while microvilli are small sub-cellular structures formed by the folding of the plasma membrane of individual cells. Microvilli can only be seen clearly with an electron microscope, and appear as a fuzzy brush border under the light microscope.

    Circular and longitudinal muscles propel the liquid food by peristalsis, and mix the contents by pendular movements - bi-directional peristalsis. This also improves absorption.

    5. Large Intestine [back to top]

    This comprises the caecum, appendix, ascending colon, transverse colon, descending colon and rectum. Food can spend 36 hours in the large intestine, while water is absorbed to form semi-solid faeces. The mucosa contains villi but no microvilli, and there are numerous glands secreting mucus. Faeces is made up of plant fibre (cellulose mainly), cholesterol, bile, mucus, mucosa cells (250g of cells are lost each day), bacteria and water, and is released by the anal sphincter. This is a rare example of an involuntary muscle that we can learn to control (during potty training).

    Watch the video: Body Cavities - Body Cavity Anatomy - Major Body Cavities (January 2022).