A tissue membrane is a thin layer or sheet of cells that either covers the outside of the body e. Two basic types of tissue membranes are recognized based on the primary tissue type composing each: connective tissue membranes and epithelial membranes Figure 4.
A connective tissue membrane is built entirely of connective tissue. This type of membrane may be found encapsulating an organ, such as the kidney, or lining the cavity of a freely movable joint e.
When lining a joint, this membrane is referred to as a synovial membrane. Cells in the inner layer of the synovial membrane release synovial fluid, a natural lubricant that enables the bones of a joint to move freely against one another with reduced friction.
An epithelial membrane is composed of an epithelial layer attached to a layer of connective tissue. A mucous membrane, sometimes called a mucosa, lines a body cavity or hollow passageway that is open to the external environment. This type of membrane can be found lining portions of the digestive, respiratory, excretory, and reproductive tracts.
Mucus, produced by uniglandular cells and glandular tissue, coats the epithelial layer. A serous membrane lines the cavities of the body that do not open to the external environment.
Serous fluid secreted by the cells of the epithelium lubricates the membrane and reduces abrasion and friction between organs. Serous membranes are identified according to location. Three serous membranes are found lining the thoracic cavity; two membranes that cover the lungs pleura and one membrane that covers the heart pericardium.
A fourth serous membrane, the peritoneum, lines the peritoneal cavity, covering the abdominal organs and forming double sheets of mesenteries that suspend many of the digestive organs. A cutaneous membrane is a multi-layered membrane composed of epithelial and connective tissues. The apical surface of this membrane exposed to the external environment and is covered with dead, keratinized cells that help protect the body from desiccation and pathogens.
The skin is an example of a cutaneous membrane. Aggregations of cells in the human body be classified into four types of tissues: epithelial, connective, muscle, and nervous. Epithelial tissues act as coverings, controlling the movement of materials across their surface.
Connective tissue binds the various parts of the body together, providing support and protection. Muscle tissue allows the body to move and nervous tissues functions in communication.
All cells and tissues in the body derive from three germ layers: the ectoderm, mesoderm, and endoderm. Membranes are layers of connective and epithelial tissues that line the external environment and internal body cavities of the body. Synovial membranes are connective tissue membranes that protect and line the freely-movable joints.
The next level of organization is the organ, where several types of tissues come together to form a working unit. Just as knowing the structure and function of cells helps you in your study of tissues, knowledge of tissues will help you understand how organs function.
The epithelial and connective tissues are discussed in detail in this chapter. Muscle and nervous tissues will be discussed only briefly in this chapter. The zygote, or fertilized egg, is a single cell formed by the fusion of an egg and sperm. After fertilization the zygote gives rise to rapid mitotic cycles, generating many cells to form the embryo.
The first embryonic cells generated have the ability to differentiate into any type of cell in the body and, as such, are called totipotent , meaning each has the capacity to divide, differentiate, and develop into a new organism. As cell proliferation progresses, three major cell lineages are established within the embryo.
Each of these lineages of embryonic cells forms the distinct germ layers from which all the tissues and organs of the human body eventually form. Figure 2 shows the types of tissues and organs associated with the each of the three germ layers.
Note that epithelial tissue originates in all three layers, whereas nervous tissue derives primarily from the ectoderm and muscle tissue from mesoderm. A tissue membrane is a thin layer or sheet of cells that covers the outside of the body for example, skin , the organs for example, pericardium , internal passageways that lead to the exterior of the body for example, abdominal mesenteries , and the lining of the moveable joint cavities. There are two basic types of tissue membranes: connective tissue and epithelial membranes Figure 3.
Figure 3. Tissue Membranes. The two broad categories of tissue membranes in the body are 1 connective tissue membranes, which include synovial membranes, and 2 epithelial membranes, which include mucous membranes, serous membranes, and the cutaneous membrane, in other words, the skin.
The connective tissue membrane is formed solely from connective tissue. These membranes encapsulate organs, such as the kidneys, and line our movable joints. A synovial membrane is a type of connective tissue membrane that lines the cavity of a freely movable joint. For example, synovial membranes surround the joints of the shoulder, elbow, and knee. The matrix is produced by cells called chondroblasts.
When these cells slow down, they reside is small spaces called lacunae. These mature cells in the lacunae are called chondrocytes. There are three types of cartilage: hyaline cartilage, elastic cartilage, and fibrocartilage.
Bone is a hard, mineralized tissue found in the skeleton. The bone matrix contains many collagen fibers as well as inorganic mineral salts, calcium carbonate, and calcium phosphate, all features that make it a very rigid structure. Bone cells, called osteoblasts , secrete the osteoid substance that eventually hardens around the cells to form an ossified matrix. The osteon forms the basic unit of compact bone. Within the osteon, the osteocytes mature bone cells are located in lacunae.
Because the bone matrix is very dense, the osteocytes get their nutrition from the central canal via tiny canals called canaliculi. Blood is c onsidered a type of fluid connective tissue because the matrix of blood is not solid.
The fluid matrix is called plasma, and formed elements of this tissue include white blood cells, red blood cells, and platelets. Read more about the composition and function of blood in the cardiovascular system chapter.
Epithelial tissue is made up of cells that line inner and outer body surfaces, such as the skin and the inner surface of the digestive tract.
Epithelial tissue that lines inner body surfaces and body openings is called mucous membrane. This type of epithelial tissue produces mucus , a slimy substance that coats mucous membranes and traps pathogens, particles, and debris. Epithelial tissue protects the body and its internal organs, secretes substances such as hormones in addition to mucus, and absorbs substances such as nutrients.
Most epithelial tissue is described with two names. The first name describes the number of cell layers present and the second describes the shape of the cells. One layer of epithelial cells is called simple and more than one layer of epithelial cells is called stratified. There are three basic shapes of epithelial cells, squamous, cuboidal, and columnar. Squamous cells are thin and flat; cuboidal cells have a shape of a cube; columnar cells have a shape of a pillar.
For example, simple squamous epithelial tissue describes a single layer of cells that are flat and scale-like in shape. These tissues are found at various locations in our body and they have many functions. Some locations and functions are listed below:.
Muscle tissue is made up of cells that have the unique ability to contract or become shorter. Neurons are composed of cell body and extensions.
The cell body contains the nucleus and the extensions make connections with the other tissues and neurons. Neurons transmit electrical messages and the glial cells play supporting roles. Nervous tissue makes up the central nervous system mainly the brain and spinal cord and peripheral nervous system the network of nerves that runs throughout the rest of the body.
If you are a blood donor, then you have donated tissue. Blood is a tissue that you can donate when you are alive. Deceased people can donate many different tissues, including skin, bone, heart valves, and the corneas of the eyes. If you are not already registered as a tissue donor, the information below may help you decide if you would like to register.
Each year, approximately 30, people donate tissues, which supply tissues for up to 1 million tissue transplants. One tissue donor can enhance or save the life of more than 50 people! Unlike organs, which generally must be transplanted immediately after the donor dies, donated tissues can be processed and stored for a long time for later use.
Donated tissues can be used to replace burned skin and damaged bone and to repair ligaments. Corneal tissues can be used for corneal transplants that restore sight in blind people. In fact, each year 48, patients have their sight restored with corneal transplants.
Unfortunately, there are not enough tissues to go around, and the need for donated tissues keeps rising. There are both ciliated and on-ciliated cells in this epithelium.
Note the difference in size between the cilia and the microvilli on the non-ciliated cell surface. Human Cells Like the ciliated bronchial cells in the micrograph above, many other cells in the human body are very distinctive and well suited for special functions.
Variation in Human Cells Some cells act as individual cells and are not attached to one another. Different but Identical All the different cell types within an individual human organism are genetically identical, so no matter how different the cells are, they all have the same genes. Examples of Human Cell Types Many common types of human cells — such as bone cells and white blood cells — actually consist of several subtypes of cells.
Each type has a different form and function: Osteocytes are star-shaped bone cells that make up the majority of bone tissue. They are the most common cells in mature bone and can live as long as the organism itself. They also control the function of bone cells called osteoblasts and osteoclasts.
Osteoblasts are cells with single nuclei that synthesize new bone. They function in organized groups of connected cells called osteons to form the organic and mineral matrix of bone. Osteogenic cells are undifferentiated stem cells that differentiate to form osteoblasts in the tissue that covers the outside of the bone.
Osteoclasts are very large, multinucleated cells that are responsible for the breakdown of bones through resorption. The breakdown of bone is very important in bone health because it allows for bone remodeling.
White Blood Cells White blood cells also called leukocytes are even more variable than bone cells. Monocytes make up about 5 percent of leukocytes. They are the biggest cells with extensions and a kidney-shaped nucleus.
They engulf and destroy phagocytize pathogens in tissues. Eosinophils make up about 2 percent of leukocytes. They have and a bilobed nucleus. They attack larger parasites and set off allergic responses. Basophils make up less than 1 percent of leukocytes. Like eosinophils, these cells also have granules and a bilobed nucleus.
They release proteins called histamines that are involved in inflammation. Lymphocytes make up about 30 percent of leukocytes. These are small cells with a large circular nucleus. They include B cells and T cells.
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