Tissue Types for Anatomy and Physiology OER Chapter 4

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Types of Tissues. The four tissue types include epithelial tissue, connective tissue, muscle tissue, and nervous tissue.

The embryonic origin of tissues. 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 forming 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. Totipotent means that each of these cells 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 form a distinct germ layer from which all of the tissues and organs of the human body eventually form. Each germ layer is identified by its relative position. The ectoderm is the outer layer, the mesoderm is the middle layer, and the endoderm is the inner layer. Epithelial tissues originate in all three layers, whereas nervous tissue derives primarily from the ectoderm, and muscle tissue arises from mesoderm.

Tissue membranes. There are two basic types of membranes; connective tissue membranes. and epithelial membranes. Connective tissue membranes. 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 freely moving joints. For example, the synovial membranes surrounding the joints of the shoulder, the elbow, and the knee. Fibroblasts in the inner layer of the synovial membrane release hyaluronan into the joint cavity. Hyaluronan effectively traps available water to form synovial fluid. Synovial fluid is a natural lubricant that enables the bones of a joint to freely move against one another, without causing too much friction. This synovial fluid readily exchanges water and nutrients with the blood, as do all bodily fluids. Epithelial membranes. The epithelial membrane is composed of epithelium, attached to a layer of connective tissue. The mucous membrane is also a composite of connective and epithelial tissues, sometimes called the mucosa. These epithelial membranes line the body cavities and hollow passageways that open up to the external environment. This includes the digestive, respiratory, excretory, and reproductive tracts. Mucus produced by the epithelial exocrine glands covers the epithelial layer. The underlying connective tissue, called the lamina propria, helps to support the fragile epithelial layer. A serous membrane is an epithelial membrane composed of mesodermally-derived epithelium, called the mesothelium, that is supported by connective tissue. These membranes line the cholemic cavities of the body, and cover the organs located within those cavities. They are essentially membranous bags, with mesothelium lining the inside, and connective tissues lining the outside. Serous fluid is secreted by cells of the thin squamous mesothelium, which lubricates the membrane and reduces abrasion and friction between organs. Serous membranes are identified according to location. Three serous membranes line the thoracic cavity. There are two pleura cavities that cover the lungs, and the pericardium which covers the heart. A fourth, is the peritoneum. This is the serous membrane in the abdominal cavity that covers the abdominal organs and forms double sheets of mesenteries that suspend many of the digestive organs. The skin is an epithelial membrane, also called the cutaneous membrane. It is a stratified squamous epithelial membrane resting on top of connective tissue. The apical surface of this membrane is exposed to the external environment and is covered with dead keratin-containing cells that help protect the body from desiccation and pathogens.

Cilia are microscopic extensions of the apical cell membrane that are supported by microtubules. They beat in unison and move fluids as well as chopped particles. Ciliated epithelium lines the ventricles of the brain where it helps circulate the cerebrospinal fluid. The ciliated epithelium of your airways forms a muco-ciliary escalator that sweeps particles of dust and pathogens trapped in the secreted mucus, towards the throat. It is called an escalator, because it continuously pushes mucus with trapped particles upward. In contrast, nasal cilia sweep the mucous blanket down towards the throat. In both cases, the transported materials are usually swallowed and end up in the acidic environment of your stomach.
The cell shapes can be squamous, cuboidal, or columnar. Mesothelial cells Pseudostratified columnar epithelium. Stratified epithelium.

Glandular epithelium. Endocrine glands. Hormones receptors The endocrine system i Exocrine glands. Exocrine glands