BSC2085 Anatomy-Physiology 1
Exam 2 Study Guide, Chapters 5 & 6
There are only four primary tissue types found in adult organs; epithelial, connective, nervous, and muscular tissue. Epithelial tissue lines body cavities, covers the body surface, and forms the lining of many organs. Connective tissue serves in most cases to bind organs to each other. Nervous tissue and muscular tissue are considered excitable tissues because they are very sensitive to outside stimuli. A simple epithelium consists of a single layer of cells with every cell touching the basement membrane. A stratified epithelium consists of 2 or more layers of cells with only the deepest layer of cells touching the basement membrane. The cells of an epithelium can be squamous (flat), columnar (tall and narrow), or cuboidal (round or cubed). Goblet cells are unicellular glands that produce the protective mucous coatings which cover the mucous membranes. They are usually found scattered throughout a simple columnar epithelium.
A keratinized epithelium has a surface layer of dead cells. The epidermis is a keratinized stratified squamous epithelium. A nonkeratinized epithelium lacks the surface layer of dead cells but provides a moist and slippery surface that is well suited to resist stress. The vagina, tongue, and esophagus consist of a nonkeratinized stratified epithelium. Cartilage is a supportive connective tissue with a flexible rubbery matrix. Differences in the fibers provide a basis for classifying cartilage into three types: hyaline cartilage, elastic cartilage, and fibrocartilage. Hyaline cartilage makes up the tip of our nose. Elastic cartilage is what gives the shape to our external ear. Fibrocartilage is found in the intervertebral discs. Dense regular connective tissue is named for two properties; the collagen fibers are closely packed and leave relatively little open space, and the fibers are parallel to each other. Collagenous fibers are very abundant in tendons and ligaments. Tendons and ligaments get their toughness, flexibility, and glistening white appearance from collagen fibers. Muscular and nervous tissues respond quickly to outside stimuli by means of changes in membrane potential, thus they are called excitable tissues.
Nervous tissue consists predominantly of two cell types, neurons and neuroglia (glial cells). Skeletal muscle is striated and voluntary. Cardiac muscle is striated and involuntary. Smooth muscle is nonstriated and involuntary. The three types of intercellular junctions are tight junctions, desmosomes, and gap (communicating) junctions. In the intestine, tight junctions ensure that most nutrients pass through the epithelial cells and not between them. The basal cells of an epithelium are linked to the underlying basement membrane by hemidesmosomes.
Endocrine glands secrete hormones into the blood. Exocrine glands secrete their product by way of a duct that either opens onto a body surface or into a body cavity.
Merocrine glands (such as tear glands) have vesicles that release their secretion by exocytosis. Holocrine glands accumulate a product and then the entire cell disintegrates, so the secretion is a mixture of cell fragments and the substance the cell had synthesized prior to its disintegration. The oil-producing glands of the scalp are holocrine glands. Simple glands have a single unbranched duct. Compound glands have branched ducts. If the duct and secretory portion are of uniform diameter the gland is called tubular. If the secretory cells form a dilated sac, the gland is called acinar and the sac is an acinus. A gland with secretory cells in both the tubular and acinar portions is called a tubuloacinar gland. Mucous membranes (mucosa) line passageways that open to the exterior environment. Serous membranes (serosa) line the inside of some body cavities and form a smooth outer surface on some of the viscera. The largest membrane of the body is the cutaneous membrane, or more simply, the skin. Tissue growth...
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