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.