33.1 Epithelial Tissue
A. General Characteristics
1. Epithelial tissue is commonly called epithelium.
a. One surface is free (may have cilia or microvilli), and the other adheres to a noncellular basement membrane.
b. Simple epithelium consists of a single layer of cells (squamous, cuboidal, columnar); example: wall of capillaries.
c. Stratified epithelium consists of one or more layers of cells; example: skin.
2. In epithelial tissues, cells are linked tightly together, with little intervening material.
B. Cell-to-Cell Contacts
1. Epithelial cells adhere tightly to one another by means of special attachment sites; this prevents leakage (example: stomach acid).
2. The types of junctions include: tight junctions, adhering junctions ("spot welds"), and gap junctions (protein channels).
C. Glandular Epithelium and Glands
1. Gland cells secrete products, unrelated to their own metabolism, that are to used elsewhere.
2. Glands are multicelled secretory structures.
a. Exocrine glands often secrete through ducts to free surfaces; they secrete mucus, saliva, wax, milk, and so on.
b. Endocrine glands secrete hormones directly into intercellular fluid for distribution by the blood.
33.2 Connective Tissue
A. Most connective tissue contains cells and fibers (collagen and/or elastin) secreted by fibroblasts, all scattered in a ground substance.
B. Soft Connective Tissues
1. Loose connective tissue supports epithelia and organs and surrounds blood vessels and nerves; it contains fibroblast cells and fibers plus macrophages.
2. Dense, irregular connective tissue has thicker fibers and more of them, but fewer cells; it forms protective capsules around organs.
3. Dense, regular connective tissue has its fibers in parallel; this is the arrangement found in tendons (muscle to bone) and ligaments (bone to bone).
C. Specialized Connective Tissue
1. Cartilage contains a dense array of fibers in a jellylike ground substance.
a. It cushions and maintains the shape of body parts; it resists compression and is resilient.
b. Locations include the ends of bones, parts of the nose, external ear, and disks between vertebrae.
2. Bone tissue stores mineral salts, produces blood cells, and provides spaces for its own living osteocytes.
a. Organized as flat plates and cylinders, bones support and protect body tissues and organs; some have sites for blood cell production.
b. Bones work with muscles to perform movement.
3. Adipose tissue cells are specialized for the storage of fat, which can be used as an energy reserve and as cushions to pad organs.
4. Blood transports oxygen, wastes, hormones, and enzymes; it also contains clotting factors to protect against bleeding and components to protect against disease-causing agents.
33.3 Muscle Tissue
A. Muscle tissue contracts in response to stimulation, then passively lengthens.
B. There are three varieties of muscle:
1. Skeletal muscle tissue attaches to bones for voluntary movement; it contains striated, multinucleated, long cells.
2. Smooth muscle tissue contains spindle-shaped cells; it lines the gut, blood vessels, and glands; its operation is involuntary.
3. Cardiac (heart) muscle is composed of short, striated cells that can function in units.
33.4 Nervous Tissue
A. Nervous tissue exerts the greatest control over the body's responsiveness to changing conditions.
1. Neurons are excitable cells, organized as lines of communication throughout the body.
2. Neuroglia are diverse cells that protect and metabolically support the neurons.
B. Various neurons detect stimuli; others coordinate the body's responses; still others relay signals to muscles and glands for response.
33.5 Focus on Science: Frontiers in Tissue Research
33.6 Organ Systems
A. Overview of the Major Organ Systems
1. Eleven organ systems in vertebrates contribute to the survival of the living cells of the body: integumentary, muscular, skeletal, nervous, endocrine, circulatory, lymphatic, respiratory, digestive, urinary, and reproductive.
2. Each organ system contributes to the survival of all living cells of the animal body.
B. Tissue and Organ Formation
1. Germ cells in the parental gonads produce either sperm or eggs by meiosis; all other cells of the body are called somatic cells.
2. Fusion of gametes forms a zygote, which undergoes mitosis to form an embryo.
3. Cells in the embryo become arranged into three primary tissues:
a. Ectoderm gives rise to skin and nervous system.
b. Mesoderm gives rise to muscle, skeleton, and the organs of circulation, reproduction, and excretion.
c. Endoderm gives rise to the lining of the gut and its associated organs.