Body Cavities

∞ generated and posted on 2018.08.27 ∞

Body organs of specific types make up organ systems, many of which are located within specific body cavities.

Organ systems are made up of organs which often consist of repeated functional units and, as found in body cavities, organs are covered with serous membranes, where serous membranes also line those body cavities as well.

This page contains the following terms: Tissue membrane, Serous membrane, Functional units, Organ, Organ system, Smooth muscle, Dorsal cavity, Ventral cavity, Thoracic cavity, Pleural cavity, Pericardial cavity, Abdominal cavity, Stem cells

Tissue membrane

Combination especially of epithelia, fibroblasts, and associated fibers.
Tissue membranes thus consist to two tissue types, epithelial tissue and connective tissue. The body has four different types of tissue membranes known as cutaneous membrane (as making up the skin), mucous membrane, serous membranes, and synovial membranes.

It is important to not confuse tissue membranes with membranes that consist instead of lipid bilayers, such as the plasma membrane of a cell.

It is also important to not confuse a tissue membrane with a basement membrane. Basement membranes do not consist of cells, and also do not consist of lipid bilayers.

Bodies thus have three distinct types of membranes, only one of which is a lipid bilayer (basically, cell membranes), only one of which is neither lipid bilayer nor tissue (basement membrane), and only one of which consists in part of cells (tissue membrane).

Links to terms of possible interest: Basement membrane, Cutaneous membrane, Membrane, Mucous membrane, Serous membrane, Synovial membrane, Tissue membrane

The above video provides a quick introduction to the concept of "body" membranes, i.e., tissue membranes. After the introduction, the lecture then concentrates on the anatomy of the skin, which also is a form of body or tissue membrane.

Nice overview of basement membranes and their functions. These functions include providing mechanical support for epithelium, providing selective permeability so that epithelial cells can be fed since epithelial tissue don't otherwise have a blood supply of their own, and blocks on cancer cell movement, should they form, from these epithelial tissue to the rest of the body.

Serous membrane

The tissue that lines animal body cavities.
Serous membranes, also known simply as serosa, are tissue membranes that, as noted, line body cavities, that is, they line the body walls that define the extent of cavities as well cover various organs found within these body cavities.

Body cavities can be viewed as volumes that are found within mesodermally derived tissues, particularly muscle tissue. We thus have an abdominal cavity as well as a thoracic cavity (as associated with our chest), and serous membranes line each.

Specific types of serous membranes include what are known as pericardium (lining that portion of the thoracic cavity that surrounds the heart, that is, lining the pericardial cavity), peritoneum (as lines the abdominal cavity), and pleura (as lines that portion of the thoracic cavity that surrounds the lungs, i.e., the pleural cavity).

Serous membranes provide lubrication (serous fluid) between the walls of body cavities and the walls of the organs that are found within those cavities. This lubrication is secreted by the epithelial tissue that in part makes up the tissue membrane.

Links to terms of possible interest: Body cavity, Organ, Parietal pericardium, Parietal peritoneum, Parietal pleura, Serous membrane, Visceral pericardium, Visceral peritoneum, Visceral pleura

Nice, short introduction to the names and locations of important serous membranes.

OK, this video is a bit long, but it's awesome, really!

Functional units

Aspect of a body consisting of one or more cells that together are able to give rise to one or more specific processes.
Functional units can range from individual cells to entire organ systems. The beating of the entire heart, for example, is required for the pumping of blood, though the contraction of heart tissue is performed by individual cells.

The kidneys, by contrast, consist of multiple functional units, each of which consists of multiple cells. These kidney functional units, or nephrons, are individually employed to remove water, salts, and metabolic waste products from blood.

Functional units are particularly important from a pedagogical perspective, that is, in terms of how human physiology typically is taught, where generally one considers the functioning of the smallest unit that is able to display the function in question, again whether that is single cell, multiple cells, a single organ, a series of organs, etc.


Multi-tissue, discrete structure within an organism's body that is responsible for specific processes.
Many body functions are handled at least in part by organs such as the heart, lungs, kidneys, the stomach, the small intestine, the brain, etc. Though many organs represent functional units (e.g., the heart for pumping blood), they also can consist of multiple functional units that play specific roles in the larger process that an organ is responsible for (e.g., nephrons making up the kidneys). These functional units can be present, within a single organ, in either multiple or individual copies.

Within the heart, for example, there are various chambers, valves, and systems of nerves that individually play unique roles, but there also are multiple individual cells (individually responsible for contraction) as well as multiple arteries, veins, and capillaries that are responsible for supplying (as well as removing) blood from these muscle cells.

In addition to being made up of various functional units, so too organs often are associated in various ways to form what are known as organ systems.

Links to terms of possible interest: Anatomy, Bladder, Brain, Heart, Kidneys, Large intestine, Liver, Lungs, Organs, Ovaries, Pancreas, Small intestine, Stomach

A bit cheesy, and stops too soon, but the above video does provide one with a basic, general sense of what body organs are "all" about.

Organ system

The largest of the discrete functional units making up bodies.
Within the human body there are eleven organ systems, which we will consider subsequently in varying levels of detail. These include (in alphabetical order):

(1) the circulatory system (2) the digestive system, (3) the endocrine system, (4) the lymphatic system, (5) the muscles, (6) the nervous system (7) the reproductive system, (8) the respiratory system, (9) the skeletal system, (10) the skin (or integumentary system), and (11) the urinary system (itself an aspect of what can be described as the excretory system).

Keep in mind that numerous organs, tissues (many somewhat unique), and cells (also many somewhat unique) make up each of these systems. Keep in mind as well that each of these systems plays unique roles in the functioning and survival of bodies as well as in reproduction.

Links to terms of possible interest: Circulatory system, Endocrine system, Gastrointestinal system, Immune system, Integumentary system, Musculoskeletal system, Nervous system, Organ systems, Reproductive system, Respiratory system, Urinary system

Discussion of a list of organ systems found in the human body starts at 5:53.

Smooth muscle

Contractile tissue associated with organs and mostly not under voluntary control.
Smooth muscle as contractile tissue contrasts with skeletal muscle as well as with cardiac muscle. The two latter muscle types are more linearly organized than smooth muscle, giving rise to a striated appearance when viewed under a microscope, whereas in smooth muscle striations are lacking. Hence, smooth muscle is comparatively "smooth" in appearance when viewed under a microscope.

Smooth muscle also is "smooth" in terms of its rates of contraction, which are slow and steady rather than more rapid and abrupt. Smooth muscle additionally does not fatigue in the same manner as one sees with skeletal muscle. Here "slow and steady" does not exactly win the race, but does otherwise keep our body functioning such as in terms of digestion, lactation, and the "standing up" of individual hairs, the latter such as in response to cold. Smooth muscle also plays key roles in the birthing process.

Links to terms of possible interest: Actin, Arteries, Glands, GI tract, Involuntary control, Muscle contraction, Muscle relaxation, Myosin, Sarcomere, Smooth muscle, Smooth muscle cell, Veins

The above video is a nice, very short, introduction to smooth muscles and their functions, with nice graphics.

Dorsal cavity

Volume within animals containing the central nervous system.
That is, in vertebrates the dorsal cavity is a body cavity containing the brain and the spinal cord.

Dorsal refers to the top of an animal, as in the dorsal fin of sharks.

The dorsal cavity is lined by the meninges, which are a type of tissue membrane. The meninges, that is, surround the brain and spinal cord. Meningitis in turn is an inflammation of the meninges. In association with the meninges is found cerebrospinal fluid.

Links to terms of possible interest: Abdominal cavity, Abdominopelvic cavity, Anterior, Bladder, Cranial cavity, Diaphragm, Digestive viscera, Dorsal body cavity, Mediastinum, Pelvic cavity, Pericardial cavity, Pleural cavity, Rectum, Reproductive organs, Superior mediastinum, Thoracic cavity, Ventral cavity, Ventral body cavity, Vertebral cavity

Pretty hilarious introduction to body cavities, featuring the dorsal cavity and ventral cavity as "cubby holes".

Ventral cavity

Volume within animals containing the numerous internal organs other than the brain and spinal cord.
Ventral refers to the bottom of the body for most vertebrates, and the front of the body for humans.

The ventral cavity – a specific body cavity – can be divided into two major regions, the thoracic cavity versus the abdominopelvic cavity. The diaphragm muscle, used in breathing by mammals, serves to divide the ventral cavity into these two parts.

Contained within these body cavities are the heart, lungs, the digestive system, the urinary system and much of the reproductive system.

Links to terms of possible interest: Abdominal cavity, Bladder, Brain, Cranial cavity, Diaphragm, Digestive viscera, Dorsal body cavity, Heart, Lateral, Lungs, Pelvic cavity, Rectum, Reproductive organs, Spinal cord, Thoracic cavity, Ventral body cavity, Vertebral cavity

Nicely done introduction to body cavities, featuring the dorsal cavity and ventral cavity.

Thoracic cavity

Volume within animals containing the heart and lungs.
The thoracic cavity is a component of the ventral cavity. Contained with the thoracic cavity are the pleural cavity and the pericardial cavity, containing the lungs and the heart, respectively.

The thoracic cavity in mammals is separated from the rest of the ventral cavity by the breathing muscle known as the diaphragm, which fittingly is also known as the thoracic diaphragm.

Links to terms of possible interest: Abdominal cavity, Bladder, Brain, Cranial cavity, Diaphragm, Digestive viscera, Dorsal body cavity, Heart, Lateral, Lungs, Pelvic cavity, Rectum, Reproductive organs, Spinal cord, Thoracic cavity, Ventral body cavity, Vertebral cavity

The above video walks through the anatomy associated with the thoracic cavity, using plastic models of human anatomy.

This is not quite the most informative video about the thoracic cavity, but it does provide at least some context of where it is located, as actual tissue in the rat, and the numerous blood vessels emanating from it or converging into it.

Pleural cavity

Volume within animals containing the lungs.
The pleural cavity is found within the thoracic cavity, which in turn is found within the ventral cavity.

The pleural cavity is demarcated by the serous membrane known as the pleura. The pleura in turn provide lubrication to the exterior of the lungs, allowing lung expansion without friction against the thoracic cavity wall (i.e., the chest wall).

Though a single tissue membrane, the pleura is folded upon itself forming and outer layer in contact with the chest wall (known as the parietal pleura) and an inner layer that is in contact with the lungs (the visceral pleura).

BTW, as a mnemonic, consider that there are two lungs, therefore they are pleural [sic].

Links to terms of possible interest: Lungs, Parietal pleura, Pleural cavity, Serous membrane, Visceral pleura

The above video provides a fairly detailed introduction to the pleural cavity and what can go wrong with pleura and the pleural cavity in terms injury and disease.

Pericardial cavity

Volume within animals containing the heart.
The pericardial cavity is found within the thoracic cavity, which in turn is found within the ventral cavity.

The pericardial cavity is demarcated by the serous membrane known as the pericardium. The pericardium in turn provides lubrication to the exterior of the heart, allowing beating without friction against the thoracic cavity wall (i.e., the chest wall), and also provides a cushioning against sudden movement. Sudden deceleration of your body, e.g., such as following a fall, thus is much less likely to result in damage to your heart.

Like the pleura, the pericardium consists of multiple layers together forming the pericardial sac.

Links to terms of possible interest: Pericardial cavity, Parietal pericardium, Serous membrane, Visceral pericardium

Abdominal cavity

Volume within animals containing the bulk of internal organs as well as the bulk of the digestive system.
The abdominal cavity is a component of the abdominopelvic cavity which, in turn, is a component of the ventral cavity. It is separated from the thoracic cavity via the thoracic diaphragm, which is found superior to the abdominal cavity in humans (that is, our thoracic cavity is found above our abdominal cavity).

Below the abdominal cavity in humans (i.e., inferior to it) is found the pelvic cavity. Contained within the abdominal cavity are the liver, stomach, gallbladder, pancreas, small intestine, large intestine, spleen, and kidneys (as well as the adrenal glands).

The serous membrane lining the abdominal cavity is called the peritoneum, which provides protection against damage caused by motion.

Links to terms of possible interest: Abdominal cavity, Epigastric, Hypochondriac, Hypogastric, Iliac, Lumbar, Umbilical

The above video is a laparoscopic tour of the human abdominal cavity. It is pretty amazing if only because this is living tissue with living tissue color. Just fantastic stuff, though a little gory especially towards the end. Note the following features/terms, in order of apperance: liver, stomach, spleen, gallbladder, small intestine, colon, large intestine, sigmoid colon, appendix, pancreas, ureter, uterus, fibroid, fallopian tubes, ovaries, splenule, adhesion, and ovarian cyst.

Stem cells

Cells that supply the body with new cells by dividing and then differentiating into more specialized cells.
Stem cells are basically body cells that are specialized for dividing rather than for having additional, physiologically crucial functions. What they do is to divide and then undergo cellular differentiation towards becoming what otherwise are normal body cells. When those normal body cells need to be replaced, often there will be stem cells that can then undergo replication (cell division) to effect that replacement, or when the body is growing it is the stem cells that are dividing to produce new body cells, which then mature into specialized, differentiated components of the body.

Note that stem cells can be differentiated into embryonic stem cells versus adult stem cells, where the former have the potential to divide and then differentiate into a broader variety of cells than the latter (because, essentially, the former are less specialized than the latter). The degree of cell types that a stem cell can give rise to is referred to in terms of its potency, with the terms totipotent and pluripotent implying a (very) broad range of such cell types and multipotent or unipotent referring to a narrower range of cell types.

Note that an additional as well as crucial property of stem cells is their ability to self-renew, that is, to divide towards giving rise to new stem cells.

Links to terms of possible interest: Blood cell, Blood stem cells, Blood vessel, Bone marrow, Bone marrow stromal cells, Bone stem cells, Brain, Cardiac muscle, Cellular differentiation, CNS stem cells, Epithelial cells, Fat cell, Glial cell, Liver, Multipotent, Muscle stem cells, Nerve stem cells, Neuron, Pluripotent, Potent, Red blood cells, Skeletal muscle Stem cells, Totipotent, Unipotent, White blood cells

This video provides an overview of both the diversity of stem cells and what exactly they are.

The above video discusses the potential of stem cells towards regenerative medicine.

This video provides a longer overview of stem cells, starting with an overview of very early embryology, with pretty computer generated graphics.

More on stem cells and regenerative medicine.