H.A. 101: Membranes

Membranes are a vital component in protecting the body from its surrounding environment. In the human body, membranes are composed of Epithelial and Connective tissue. Each one of these membranes will consist of a sheet of epithelial cells and an underlying connective tissue layer. Membranes can be divided into four main categories:

  1. Mucous Membranes
  2. Serous Membranes
  3. Cutaneous Membranes
  4. Synovial Membranes
Mucous Membranes

Mucous membranes can be found in the digestive, urinary, respiratory, and reproductive tracts due to their ability to secrete a barrier of protection. This barrier of protection is responsible for resisting pathogen entry into the body and deeper tissues. The layer of secretion is created by mucous glands and it also helps maintain the moisture of epithelial cell surfaces.

In mucous membranes, the tissue that connects the epithelium to the underlying tissue is called the lamina propria. This is an areolar tissue that allows the epithelium to move free when compared to the deeper tissue.

Serous Membranes

Serous membranes are located in the lining of body cavities. Within these membranes, there are two major layers, the visceral and parietal layers. The visceral layer is responsible for covering the organ of the cavity. The parietal layer can be found lining the walls of the cavity the organ is located in. It is also important to know that within serous membranes there is a fluid called transudate. This serous fluid is responsible for reducing friction between layers. There are three types of serous membranes:

  1. Pleura
  2. Peritoneum
  3. Pericardium

Pleura serous membranes are responsible for lining the lungs. The parietal layer of this membrane is attached to the chest wall while the visceral layer is attached to the lungs. The fluid between these two layers is called the pleural fluid.

Peritoneum serous membranes can be found lining the peritoneal cavity (abdominal cavity). In this membrane, the visceral layer attaches itself to the organs of the peritoneal cavity such as the intestines, and helps hold it in place. This membrane helps reduce friction and maintain the organization of the organs during bodily processes and mechanical movements.

The pericardium serous membranes are found lining the heart. The main function of this membrane is to hold the heart in place and help it function properly.

Cutaneous Membranes

The cutaneous membrane is one of the largest membranes in your body and the most recognizable. This layer of epithelial cells and connective tissue in your skin consists of keratinized stratified squamous epithelium. The keratinization of the epithelium results in a waterproof and thick characteristic. The deeper cells are connected to areolar tissue and dense irregular tissue that helps maintain and secure the epithelial cells.

Synovial Membranes

Synovial membranes can be found lining the joint cavities of bones. These membranes are different from the other ones because it has no basal lamina or reticular lamina, the cells are created from fibroblasts and macrophages, and there are gaps between the cells.

Within this membrane, there is a fluid produced called synovial fluid. This functions to reduce friction between the joints to reduce damage to the bones and cartilage.

How Do Our Lungs Work?

The lungs are one of the most vital components of the human body. They are used every second of the day and without them, we would die in 4-6 minutes. The lungs are located in the thoracic cavity behind your pectoral muscles and behind your ribs. Within the Thoracic cavity, there are two pleural cavities. Each pleural cavity contains one lung. The pleural cavity is created by two membranes and a fluid called pleural fluid. Combined, these structures make it easier for the lungs to expand and contract during inhalation and exhalation.

Within the lungs, there is a combination of many structures that carry air from your oral and nasal airways. These include the bronchi, bronchioles, and alveoli (the major ones). The bronchi is one major airway that brings air to both lungs. The bronchioles are tree-like structures that branch from the bronchi. Finally, the alveoli are the tiny ball-like structures at the end of the bronchioles that oxygen and carbon dioxide transfer through its membrane.

So, we all know how to breathe but, do you know what is actually going on in your body? Breathing is a combination of multiple muscles contracting and relaxing. When breathing in your diaphragm will contract. This increases the volume of the thoracic cavity and thus decreases the pressure of the lungs. When this occurs, the pressure outside of your mouth is higher than in your body. The difference in pressures causes a rush of air through your nasal and oral cavities and into your lungs to try and make the pressures the same. Other muscles that aid in this decrease of pressure include the ribs and intercostal muscles.

When exhaling, the same muscles relaxed and the muscles between the ribs contract, making the volume of the thoracic cavity decrease. This decreased volume causes an increase in pressure and for the same reason air enters your lungs, it will now leave your lungs.