Chapter 4 - The Tissue Level of Organization

Question 1

define the term “tissue”

Answer 1

Tissue = a group of cells that usually have a common origin in an embryo and function together to carry out specialized activities.

Question 2

classify the tissues of the body into four major types and define each

Answer 2

1. Epithelial tissues cover body surfaces and line hollow organs, body cavities, and ducts; they also forms glands. This tissue allows the body to interact with both its internal and external environments.
2. Connective tissues protect and support the body and its organs. Various types of connective tissues bind organs together, store energy reserves as fat, and help provide the body with immunity to disease-causing organisms. 3. Muscular tissues are composed of cells specialized for con- traction and generation of force. In the process, muscular tis- sues generate heat that warms the body.
3. Nervous tissue detects changes in a variety of conditions in- side and outside the body and responds by generating APs

Question 3

What are cell junctions?

Answer 3

contact points between the plasma membranes of tissue cells.

Question 4

What are the five principal types of cell junctions.?

Answer 4

1. Tight junctions consist of weblike strands of transmembrane pro- teins that fuse together the outer surfaces of adjacent plasma mem- branes to seal off passageways between adjacent cells
2. Adherens junctions contain plaque (PLAK), a dense layer of proteins on the inside of the plasma membrane that attaches both to membrane proteins and to microfilaments of the cytoskeleton. Transmembrane glycoproteins called cadherins join the cells
3. desmosomes contain plaque and have transmembrane glycoproteins (cadherins) that extend into the intercellular space between adja- cent cell membranes and attach cells to one another
4. hemidesmosomes anchor cells not to each other but to the basement membrane
5. gap junctions, membrane proteins called connexins form tiny fluid-filled tunnels called connexons that connect neighboring cells

Question 5

What are 6 general features of epithelial tissue?

Answer 5

1. cells tightly packed together with little/no extracellular matrix
2. epithelial tissue has no blood vessels
3. form surface layers and are not covered by another tissue
4. consists of cells arranged in continuous sheets
5. form coverings and linings throughout the body
6. have their own nerve supply, but are avascular

Question 6

What 3 things does epithelial tissue serve as?

Answer 6

(1) selective barriers that limit or aid the transfer of substances into and out of the body;
(2) secretory surfaces that release products produced by the cells onto their free surfaces;
(3) protective surfaces that resist the abrasive influences of the environment.

Question 7

Epithelial tissues may be divided into what two types.

Answer 7

(1) Covering and lining epithelium forms the outer covering of the skin and some internal organs. It also forms the inner lining of blood ves- sels, ducts, and body cavities, and the interior of the respiratory, digestive, urinary, and reproductive systems.
(2) Glandular epithelium makes up the secreting portion of glands such as the thyroid gland, adrenal glands, and sweat glands.

Question 8

describe the structure, location and function of simple squamous epithelium

Answer 8

Structure

Single layer of flat cells ; central flat nucleus.

Location

lines the cardiovascular and lymphatic system (endothelium) and forms the epithelial layer of serous membranes (mesothelium)
Also found in air sacs of lungs, glomerular (Bowman’s) capsule of kidneys, inner surface of tympanic membrane (eardrum).

Function

Present at sites of filtration (such as blood filtration in kidneys) or diffusion (such as diffusion of oxygen into blood vessels of lungs) and at site of secretion in serous membranes. Not found in body areas subject to mechanical stress (wear and tear).

Question 9

describe the structure, location and function of simple cuboidal epithelium

Answer 9

structure

Single layer of cube-shaped cells; round, centrally located nucleus.

Location

Covers surface of ovary; lines lens of the eye; retina of the eye; lines kidney tubules and smaller ducts of many glands;

Function

Secretion and absorption.

Question 10

describe the structure, location and function of simple columnar epithelium (nonciliated)

Answer 10

Structure

Single layer of columnlike cells with oval nuclei near base of cells

Location

Lines gastrointestinal tract (from stomach to anus), ducts of many glands, and gallbladder.

Function

Secretion and absorption; larger columnar cells contain more organelles and thus are capable of higher level of secretion and absorption

Question 11

describe the structure, location and function of simple columnar epithelium (ciliated)

Answer 11

Structure

Single layer of ciliated columnlike cells with oval nuclei near base of cells. Goblet cells are usually interspersed among ciliated columnar epithelia.

Location

Lines some bronchioles (small tubes) of respiratory tract, uterine (fallopian) tubes, uterus, some paranasal sinuses, central canal of spinal cord, and ventricles of brain.

Function

Cilia beat in unison, moving mucus and foreign particles toward throat, where they can be coughed up and swallowed or spit out. Coughing and sneezing speed up movement of cilia and mucus. Cilia also help move oocytes expelled from ovaries through uterine (fallopian) tubes into uterus.

Question 12

describe the structure, location and function of each of pseudostratified columnar epithelium

Answer 12

Description

Appears to have several layers because cell nuclei are at various levels. All cells are attached to basement membrane in a single layer, but some cells do not extend to apical surface. When viewed from side, these features give false impression of a multilayered tissue (thus the name pseudostratified; pseudo 􏰆 false).

Pseudostratified ciliated columnar epithelium contains cells that extend to surface and secrete mucus (goblet cells) or bear cilia. Pseudostratified nonciliated columnar epithelium contains cells without cilia and lacks goblet cells.

Location

Ciliated variety lines airways of most of upper respiratory tract; nonciliated variety lines larger ducts of many glands, epididymis, and part of male urethra.

Function

Ciliated variety secretes mucus that traps foreign particles, and cilia sweep away mucus for elimination from body; nonciliated variety functions in absorption and protection.

Question 13

describe the structure, location and function of each of stratified squamous epithelium

Answer 13

Description

Two or more layers of cells; cells in apical layer and several layers deep to it are squamous; cells in deeper layers vary from cuboidal to columnar. As basal cells divide, daughter cells arising from cell divisions push upward toward apical layer. As they move toward surface and away from blood supply in underlying connective tissue, they become dehydrated and less metabolically active. Tough proteins predominate as cytoplasm is reduced, and cells become tough, hard structures that eventually die. At apical layer, after dead cells lose cell junctions they are sloughed off, but they are replaced continuously as new cells emerge from basal cells.
Keratinized stratified squamous epithelium develops tough layer of keratin in apical layer of cells and several layers deep to it (see Figure 5.3). (Keratin is a tough, fibrous intracellular protein that helps protect skin and underlying tissues from heat, microbes, and chemicals.) Relative amount of keratin increases in cells as they move away from nutritive blood supply and organelles die.
Nonkeratinized stratified squamous epithelium does not contain large amounts of keratin in apical layer and several layers deep and is constantly moistened by mucus from salivary and mucous glands; organelles are not replaced.

Location

Keratinized variety forms superficial layer of skin; nonkeratinized variety lines wet surfaces (lining of mouth, esophagus, part of epiglottis, part of pharynx, and vagina) and covers tongue.

Function

Protection against abrasion, water loss, ultraviolet radiation, and foreign invasion. Both types form first line of defense against microbes.

Question 14

describe the structure, location and function of stratified cuboidal epithelium

Answer 14

Description

Two or more layers of cells; cells in apical layer are cube-shaped; fairly rare type.

Location

Ducts of adult sweat glands and esophageal glands, part of male urethra.

Function

Protection; limited secretion and absorption

Question 15

describe the structure, location and function of stratified columnar epithelium

Answer 15

Description

Basal layers usually consist of shortened, irregularly shaped cells; only apical layer has columnar cells; uncommon.

Location

Lines part of urethra; large excretory ducts of some glands, such as esophageal glands; small areas in anal mucous membrane; part of conjunctiva of eye.

Function

Protection and secretion.

Question 16

describe the structure, location and function of transitional epithelium

Answer 16

Description

Variable appearance (transitional). In relaxed or unstretched state, looks like stratified cuboidal epithelium, except apical layer cells tend to be large and rounded. As tissue is stretched, cells become flatter, giving the appearance of stratified squamous epithelium. Multiple layers and elasticity make it ideal for lining hollow structures (urinary bladder) subject to expansion from within.

Location

Lines urinary bladder and portions of ureters and urethra.

Function

Allows urinary organs to stretch and maintain protective lining while holding variable amounts of fluid without rupturing.

Question 17

define the term “gland”

Answer 17

A gland may consist of a single cell or a group of cells that secrete substances into ducts (tubes), onto a surface, or into the blood.
All glands of the body are classified as either endocrine or exocrine.

Question 18

give the Description, location, and function of endocrine glands.

Answer 18

Endocrine

Description = Secretions (hormones) enter interstitial fluid and diffuse directly into bloodstream without flowing through a duct. Endocrine glands will be described in detail in Chapter 18.
Location = Examples include pituitary gland at base of brain, pineal gland in brain, thyroid and parathyroid glands near larynx (voice box), adrenal glands superior to kidneys, pancreas near stomach, ovaries in pelvic cavity, testes in scrotum, thymus in thoracic cavity.
Function = Hormones regulate many metabolic and physiological activities to maintain homeostasis.

Question 20

Give the description location and function of exocrine glands

Answer 20

Exocrine

Description = Secretory products released into ducts that empty onto surface of a covering and lining epithelium, such as skin surface or lumen of hollow organ.
Location = Sweat, oil, and earwax glands of skin; digestive glands such as salivary glands (secrete into mouth cavity) and pancreas (secretes into small intestine).
Function = Produce substances such as sweat to help lower body temperature, oil, earwax, saliva, or digestive enzymes.