As mentioned in the previous chapter, aging takes place at the cellular level, but of course is apparent in the groups of cells we call tissues. In muscle tissue, for example, the proteins that bring about contraction deteriorate and are not repaired or replaced. The same is true of collagen and elastin, the proteins of connec- tive tissue such as the dermis of the skin. Other aspects of the aging of tissues will be more meaningful to you in the context of the functions of organs and systems, so we will save those for the following chapters.
SUMMARY
The tissues and membranes described in this chapter are more complex than the individual cells of which they are made. However, we have only reached an intermediate level with respect to the structural and functional complexity of the body as a whole. The fol- lowing chapters are concerned with the organ systems, the most complex level. In the descriptions of the organs of these systems, you will find mention of the tissues and their contributions to each organ and organ system.
84 Tissues and Membranes
Table 4–5 CONNECTIVE TISSUE MEMBRANES
Membrane Location and Function Superficial
fascia Periosteum
Perichondrium
Synovial
Deep fascia Meninges Fibrous
pericardium
• Between the skin and muscles;
adipose tissue stores fat
• Covers each bone; contains blood vessels that enter the bone
• Anchors tendons and ligaments
• Covers cartilage; contains capil- laries, the only blood supply for cartilage
• Lines joint cavities; secretes syn- ovial fluid to prevent friction when joints move
• Covers each skeletal muscle;
anchors tendons
• Cover the brain and spinal cord;
contain cerebrospinal fluid
• Forms a sac around the heart;
lined by the serous parietal peri- cardium
STUDY OUTLINE
A tissue is a group of cells with similar struc- ture and function. The four main groups of tissues are epithelial, connective, muscle, and nerve.
Epithelial Tissue—found on surfaces; have no capillaries; some are capable of secretion;
classified as to shape of cells and number of layers of cells (see Table 4–1 and Figs. 4–1, 4–2, and 4–3)
1. Simple squamous—one layer of flat cells; thin and smooth. Sites: alveoli (to permit diffusion of gases);
capillaries (to permit exchanges between blood and tissues).
2. Stratified squamous—many layers of mostly flat cells; mitosis takes place in lowest layer. Sites: epi- dermis, where surface cells are dead (a barrier to pathogens); lining of mouth; esophagus; and vagina (a barrier to pathogens).
3. Transitional—stratified, yet surface cells are
rounded and flatten when stretched. Site: urinary bladder (to permit expansion without tearing the lining).
4. Simple cuboidal—one layer of cube-shaped cells.
Sites: thyroid gland (to secrete thyroid hormones);
salivary glands (to secrete saliva); kidney tubules (to reabsorb useful materials back to the blood).
5. Simple columnar—one layer of column-shaped cells. Sites: stomach lining (to secrete gastric juice);
small intestinal lining (to secrete digestive enzymes and absorb nutrients—microvilli increase surface area for absorption).
6. Ciliated—columnar cells with cilia on free surfaces.
Sites: trachea (to sweep mucus and bacteria to the pharynx); fallopian tubes (to sweep ovum to uterus).
7. Glands—epithelial tissues that produce secretions.
• Unicellular—one-celled glands. Goblet cells secrete mucus in the respiratory and digestive tracts.
• Multicellular—many-celled glands.
• Exocrine glands have ducts; salivary glands secrete saliva into ducts that carry it to the oral cavity.
• Endocrine glands secrete hormones directly into capillaries (no ducts); thyroid gland se- cretes thyroxine.
Connective Tissue—all have a non-living intercellular matrix and specialized cells (see Table 4–2 and Figs. 4–4 and 4–5)
1. Blood—the matrix is plasma, mostly water; trans- ports materials in the blood. Red blood cells carry oxygen; white blood cells destroy pathogens and provide immunity; platelets prevent blood loss, as in clotting. Blood cells are made in red bone mar- row.
2. Areolar (loose)—cells are fibroblasts, which pro- duce protein fibers: collagen is strong, elastin is elastic; the matrix is collagen, elastin, and tissue fluid. White blood cells and mast cells are also present. Sites: below the dermis and below the epithelium of tracts that open to the environment (to destroy pathogens that enter the body).
3. Adipose—cells are adipocytes that store fat; little matrix. Sites: between the skin and muscles (to store energy); around the eyes and kidneys (to cushion). Also involved in appetite, use of insulin, and inflammation.
4. Fibrous—mostly matrix, strong collagen fibers;
cells are fibroblasts. Regular fibrous sites: tendons (to connect muscle to bone); ligaments (to connect bone to bone); poor blood supply, slow healing.
Irregular fibrous sites: dermis of the skin and the fascia around muscles.
5. Elastic—mostly matrix, elastin fibers. Sites: walls of large arteries (to maintain blood pressure); around alveoli (to promote normal exhalation).
6. Bone—cells are osteocytes; matrix is calcium salts and collagen, strong and not flexible; good blood supply, rapid healing. Sites: bones of the skeleton (to support the body and protect internal organs from mechanical injury).
7. Cartilage—cells are chondrocytes; protein matrix is firm yet flexible; no capillaries in matrix, very slow healing. Sites: joint surfaces of bones (to prevent friction); tip of nose and external ear (to support);
wall of trachea (to keep air passage open); discs between vertebrae (to absorb shock).
Muscle Tissue—specialized to contract and bring about movement (see Table 4–3 and Fig. 4–6)
1. Skeletal—also called striated or voluntary muscle.
Cells are cylindrical, have several nuclei, and have striations. Each cell has a motor nerve ending;
nerve impulses are essential to cause contraction.
Site: skeletal muscles attached to bones (to move the skeleton and produce heat).
2. Smooth—also called visceral or involuntary mus- cle. Cells have tapered ends, one nucleus each, and no striations. Contraction is not under voluntary control. Sites: stomach and intestines (peristalsis);
walls of arteries and veins (to maintain blood pres- sure); iris (to constrict or dilate pupil).
3. Cardiac—cells are branched, have one nucleus each, and faint striations. Site: walls of the four chambers of the heart (to pump blood; nerve impulses regulate the rate of contraction).
Nerve Tissue—neurons are specialized to generate and transmit impulses (see Table 4–4 and Fig. 4–7)
1. Cell body contains the nucleus; axon carries impulses away from the cell body; dendrites carry impulses toward the cell body.
2. A synapse is the space between two neurons; a neu- rotransmitter carries the impulse across a synapse.
3. Specialized cells in nerve tissue are neuroglia in the CNS and Schwann cells in the PNS.
4. Sites: brain; spinal cord; and peripheral nerves (to provide sensation, movement, regulation of body functions, learning, and memory).
Membranes—sheets of tissue on surfaces, or separating organs or lobes
1. Epithelial membranes (see Fig. 4–8)
• Serous membranes—in closed body cavities; the serous fluid prevents friction between the two layers of the serous membrane.
• Thoracic cavity—partial pleura lines chest wall; visceral pleura covers the lungs.
• Pericardial sac—parietal pericardium lines fibrous pericardium; visceral pericardium (epi- cardium) covers the heart muscle.
• Abdominal cavity—peritoneum lines the abdominal cavity; mesentery covers the abdominal organs.
• Mucous membranes—line body tracts that open to the environment: respiratory, digestive, uri- nary, and reproductive. Mucus keeps the living epithelium wet; provides lubrication in the diges- tive tract; traps dust and bacteria in the respira- tory tract.
2. Connective tissue membranes—see Table 4–5.
86 Tissues and Membranes
REVIEW QUESTIONS
1. Explain the importance of each tissue in its loca- tion: (pp. 70, 73, 79)
a. Simple squamous epithelium in the alveoli of the lungs
b. Ciliated epithelium in the trachea c. Cartilage in the trachea
2. Explain the importance of each tissue in its loca- tion: (pp. 77, 79)
a. Bone tissue in bones
b. Cartilage on the joint surfaces of bones c. Fibrous connective tissue in ligaments
3. State the functions of red blood cells, white blood cells, and platelets. (p. 75)
4. Name two organs made primarily of nerve tissue, and state the general functions of nerve tissue.
(p. 81)
5. State the location and function of cardiac muscle.
(p. 81)
6. Explain the importance of each of these tissues in the small intestine: smooth muscle and columnar epithelium. (pp. 72, 79)
7. State the precise location of each of the following membranes: (p. 82)
a. Peritoneum
b. Visceral pericardium c. Parietal pleura
8. State the function of: (pp. 74, 82, 84) a. Serous fluid
b. Mucus c. Blood plasma
9. State two functions of skeletal muscles. (p. 79) 10. Name three body tracts lined with mucous mem-
branes. (p. 82)
11. Explain how endocrine glands differ from exocrine glands. (pp. 73–74)
12. State the function of adipose tissue: (p. 76) a. Around the eyes
b. Between the skin and muscles 13. State the location of: (p. 84)
a. Meninges
b. Synovial membranes
14. State the important physical characteristics of col- lagen and elastin, and name the cells that produce these protein fibers (p. 75)
1. A friend suffers a knee injury involving damage to bone, cartilage, and ligaments. What can you tell your friend about the healing of these tissues?
2. Stratified squamous keratinizing epithelium is an excellent barrier to pathogens in the epidermis of the skin. Despite the fact that it is such a good bar- rier, this tissue would not be suitable for the lining of the trachea or small intestine. Explain why.
3. Many tissues have protective functions, but it is important to be specific about the kind of protec- tion provided. Name at least three tissues with a protective function, and state what each protects the body (or parts of the body) against.
4. Why is blood classified as a connective tissue?
What does it connect? What kinds of connections does it make?
FOR FURTHER THOUGHT
88
CHAPTER 5
Chapter Outline The Skin
Epidermis
Stratum germinativum Stratum corneum Langerhans cells Melanocytes Dermis
Hair follicles Nail follicles Receptors Glands Blood vessels Subcutaneous Tissue
Aging and the Integumentary System
BOX5–1 BURNS
BOX5–2 PREVENTING SKIN CANCER:COMMON SENSE AND SUNSCREENS
BOX5–3 COMMON SKIN DISORDERS
BOX5–4 ADMINISTERING MEDICATIONS
Student Objectives