#46 Study Biology Section!

For the last year, we have discussed the best way to share information and education through My Biology Experience. We have discussed using notes from classes and materials used in class. But, we found that those materials were hard to read and understand because each person takes notes differently. We have also discussed creating a discussion board where people can post questions and the community can answer. However, with the platform we have created, we decided to do something better!

The Study Biology section will be published in the coming days and be an ongoing work in progress for the coming years as My Biology Experience continues to grow. The home page will consist of a list of courses like Human Anatomy, Introduction to Biology, and many other courses than can be requested by YOU! Within these “classes” you will have the opportunity to select posts made about the topic. For example, we have already begun to post material for Human Anatomy. You can select lessons on Epithelial tissue and others! This information can be used as an extra piece of material in the classroom or as a self-taught lesson!

We would love to hear what the community has to say about this project. Please feel free to ask questions about the lessons and we will be sure to update you in the future on our plans!

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.

H.A. 101: Epithelial Tissue


The foundation of Human life can be categorized into numerous groups, each larger than the last. First, we identify atoms that make molecules. Things such as Oxygen, Carbon, and Nitrogen are critical atoms that create the foundation of molecules. Molecules are combinations of atoms that result in the creation and foundation of cells, the smallest life form. Groups of Cells can combine to create one of four primary tissues (Epithelial, Connective, Muscle, and Nervous). Together, a group of tissue will function to create an organ such as the stomach, brain, and kidney. Finally, organs work together to create organ systems that provide the functions of an organism.

Epithelial Characteristics

Epithelial tissue has characteristics that make it completely different from other tissues. These Characteristics include Cellularity, Polarity, Attachment, and Avascularity.

Cellularity is the characteristic that cells are bound closely together and there is no intercellular space.

Polarity means that the cells have structural and functional differences based on the area of the cell. The apical surface of an epithelial cell is exposed and has things such as cilia and microvilli for absorption.

The basal surface is attached to deeper tissue to stabilize the cell. This is also called Attachment and the epithelial cell’s basal layer is attached to the basal lamina.

Finally, avascularity is the characteristic that epithelial tissue does not contain blood vessels.

Epithelial Function

The functions of Epithelial tissue vary based on the shape, polarity, and many other factors. The main functions include:

  1. Physical protection from abrasion, dehydration, and destruction
  2. Controlling permeability
  3. Provides sensations (Neuroepithelia)
  4. Produces secretions with special gland cells

Within Epithelial cells, there are specializations when it comes to the apical surface. The major specializations are Microvilli, Stereocilia, and Ciliated Epithelium. Microvilli help increase surface area to increase absorption of nutrients and materials. They are often found in the urinary and digestive tracts. Stereocilia are long microvilli found in the inner ear and male reproductive tract. In the ear, they help with balance and hearing. Finally, Ciliated Epithelium helps transport material along the apical surface to another location. These are found in the lining of the respiratory tract and are used to push mucus out of your airways.

Maintaining Integrity of Epithelium

Epithelial cells are often small, fragile, and numerous. So, how do they keep their shapes and overall integrity to perform their functions? Three major factors are involved in this:

  1. Intercellular Connections
  2. Attachment to the basal lamina
  3. Self-perpetuated epithelial maintenance and renewal

Intercellular Connections are extensive connections present between epithelial cells that hold them together and prevent the passage of chemicals and pathogens. Some examples of Intercellular Connections include Cell junctions and CAMs (Cell adhesion molecules)

Attachment to the Basal Lamina is created between the cell membrane and the basement membrane. Within this connection, there are typically two layers called the Basal Lamina and Reticular Lamina. The Basal Lamina is the layer closest to the epithelial cell and connects to the Plasma membrane. The Reticular Lamina is the next layer and attaches to the underlying tissue. These two layers help create a boundary between the Connective Tissue and Epithelial cells.

Maintaining Epithelium is extremely important to assure all functions are operating properly. They are replaced frequently because of exposure to enzymes, toxic chemicals, abrasion, and pathogens. So, how are these cells replaced? Epithelial cells are replaced through stem cell division located near the basal lamina.