CH.4 : THE TISSUE LEVEL OF ORGANIZATION Flashcards
What is tissue made up of?
-a group of cells that usually have a common origin in an embryo and function together to carry out specialized activities.
What is histology?
study of tissues
Body tissues can be classified into four basic types according to their structure and function, name and explain them.
1) Epithelial tissues cover body surfaces and line hollow organs, body cavities, and ducts; they also forms glands.
- allows body to interact with internal and external environments.
2) Connective tissues protect and support the body and its organs.
- bind organs together, store energy reserves as fat, and help provide the body with immunity to disease-causing organisms
3) Muscular tissues are specialized for contraction and generation of force.
- generate heat
4) Nervous tissue detects changes in conditions inside and outside the body and responds by generating nerve action potentials that activate muscular contractions and glandular secretions
What are cell junctions?
-contact points between the plasma membranes of tissue cells.
What are the 5 most important cell junctions?
- tight junctions, adherens junctions, desmosomes, hemidesmosomes, and gap junctions
Explain tight junctions. What type of tissue are they found in?
- consist of weblike strands of transmembrane proteins that fuse together the outer surfaces of adjacent plasma membranes to seal off passageways between adjacent cells
- epithelial tissues that line the stomach, intestines, and urinary bladder have many
Explain adherens junctions. What type of cell are they found in?
- contain plaque, 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.
- in epithelial cells, adherens junctions often form extensive zones called adhesion belts because they encircle the cell similar to the way a belt encircles your waist.
Explain desmosomes. Where are they found?
- contain plaque and have transmembrane glycoproteins (cadherins)
- plaque attaches to intermediate filaments, which consist of the protein keratin.
- common among cells that make up epidermis and among cardiac muscle cells in heart.
Explain hemidesmosomes.
- transmembrane glycoproteins are integrins
- on inside of plasma membrane, integrins attach to intermediate filaments made of protein keratin.
- On the outside of plasma membrane, the integrins attach to protein laminin, which is present in the basement membrane
- anchor cells not to each other but to the basement membrane
Explain gap junctions.
- membrane proteins called connexins form tiny fluid-filled tunnels called connexons that connect neighboring cells
- plasma membrane is separated by a very narrow intercellular gap (space).
- through connexons, small molecules can diffuse from cytosol of one cell to another, but passage of large molecules is prevented
- allow cells in tissue to communicate with one another
What are the major differences between epithelial tissue and connective tissue?
Epithelial tissue :
- cells are tightly packed together with little or no extracellular matrix
- has no blood vessels (avascular meaning that they rely on blood vessels of the adjacent connective tissue to bring nutrients and remove wastes)
- almost always form surface layers and are not covered by another tissue
Connective tissue:
- a large amount of extracellular material separates cells that are usually widely scattered.
- have significant networks of blood vessels
What are the 3 main functions of epithelial tissue?
(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
The various surfaces of epithelial cells often differ in structure and have specialized functions. Name all 3 surface types and explain them.
- apical (free) surface (most superficial layer) faces the body surface, a body cavity, the lumen (interior space) of an internal organ, or a tubular duct that receives cell secretions
- lateral surfaces, which face the adjacent cells on either side, may contain tight junctions, adherens junctions, desmosomes, and/or gap junctions.
- basal surface is opposite the apical surface
- basal surfaces of deepest layer adhere to extracellular materials such as the basement membrane
What is the basement membrane?
- a thin extracellular layer that commonly consists of two layers, the basal lamina and reticular lamina.
- form a surface along which epithelial cells migrate during growth or wound healing, restrict passage of larger molecules between epithelium and connective tissue, and participate in filtration of blood in the kidneys
What is the basal lamina? (one part of basement membrane)
- is closer to—and secreted by—the epithelial cells
- contains proteins such as laminin and collagen, as well as glycoproteins and proteoglycans.
- laminin molecules in the basal lamina adhere to integrins in hemidesmosomes and thus attach epithelial cells to the basement membrane
What is the reticular lamina? (second part of basement membrane)
-closer to the underlying connective tissue and contains proteins such as collagen produced by connective tissue cells called fibroblasts
Epithelial tissues may be divided into two types. Explain them.
(1) Covering and lining epithelium forms the outer covering of the skin and some internal organs.
- forms inner lining of blood vessels, ducts, and body cavities, and interior of respiratory, digestive, urinary, and reproductive systems
(2) Glandular epithelium makes up secreting portion of glands such as the thyroid gland
Types of covering and lining epithelial tissues are classified according to two characteristics: the arrangement of cells into layers and the shapes of the cells. Explain the 3 types of arrangement of cells in layers.
- Simple epithelium is a single layer of cells that functions in diffusion, osmosis, filtration, secretion, or absorption.
- Pseudostratified epithelium has multiple layers of cells because the cell nuclei lie at different levels and not all cells reach the apical surface, but it is actually a simple epithelium because all its cells rest on the basement membrane
- Stratified epithelium consists of two or more layers of cells that protect underlying tissues in locations where there is considerable wear and tear.
Types of covering and lining epithelial tissues are classified according to two characteristics: the arrangement of cells into layers and the shapes of the cells. Explain the 4 types of cell shapes.
1) Squamous cells are thin, which allows for the rapid passage of substances through them.
2) Cuboidal cells are as tall as they are wide and are shaped like cubes or hexagons. They function in either secretion or absorption
3) Columnar cells are much taller than they are wide, like columns, and protect underlying tissues. They often are used for secretion and absorption.
4) Transitional cells change shape, from squamous to cuboidal and back, as organs such stretch to a larger size and then collapse to a smaller size.
Simple squamous epithelium. Location and function?
(1) lines the cardiovascular and lymphatic system
(2) forms the epithelial layer of serous membranes
- filtration, diffusion and secretion
Simple cuboidal epithelium. Location and function?
- Covers surface of ovary; lines anterior surface of capsule of lens of the eye etc..
- Secretion and absorption
Nonciliated simple columnar epithelium. Location and function?
- Lines gastrointestinal tract (from stomach to anus), ducts of many glands, and gallbladder
- Secretion and absorption
Ciliated simple columnar epithelium. Location and function?
- Lines some bronchioles (small tubes) of respiratory tract, uterine (fallopian) tubes, uterus, and ventricles of brain.
- Cilia move mucus and foreign particles toward throat, where they can be coughed up and swallowed or spit out.
- also help move oocytes expelled from ovaries through uterine tubes into uterus.
Pseudostratified columnar epithelium, Location and function?
- Ciliated lines airways of most of upper respiratory tract
- nonciliated lines larger ducts of many glands, epididymis, and part of male urethra
- Ciliated secretes mucus that traps foreign particles, and cilia sweep away mucus for elimination from body;
- nonciliated functions in absorption and protection.
Stratified squamous epithelium, Location and function?
- 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.
- Protection against abrasion, water loss, ultraviolet radiation, and foreign invasion.
Stratified cuboidal epithelium, location and function?
- Ducts of adult sweat glands and esophageal glands, part of male urethra
- Protection; limited secretion and absorption.
Stratified columnar epithelium, 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.
- Protection and secretion.
Transitional epithelium, location?
- Lines urinary bladder and portions of ureters and urethra.
- Allows urinary organs to stretch and maintain protective lining while holding variable amounts of fluid without rupturing
What is 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.
What do endocrine glands (hormones) do? Location example?
- enter interstitial fluid and diffuse directly into bloodstream without flowing through a duct
- Examples include pituitary gland at base of brain
- regulate many metabolic and physiological activities to maintain homeostasis
What do exocrine glands (hormones) do? Location example?
- Secretory products released into ducts that empty onto surface of a covering and lining epithelium, such as skin surface
- Sweat for ex
- Produce substances such as sweat to help lower body temperature, oil, earwax, saliva, or digestive enzymes
Exocrine glands are classified as_____ or _______.
unicellular, multicellular
_____ cells are important unicellular exocrine glands that secrete mucus directly onto the apical surface of a lining epithelium.
Goblet
Multicellular glands are categorized according to two criteria:
(1) whether their ducts are branched or unbranched
(2) the shape of the secretory portions of the gland
What is a simple gland?
If the duct of the gland does not branch, it is a simple gland.
What is a compound gland?
If the duct branches, it is a compound gland.
What are tubular glands?
Glands with tubular secretory parts are tubular glands;
What are acinar glands?
those with rounded secretory portions are acinar glands (also called alveolar glands)
What are tubuloacinar glands?
Tubuloacinar glands have both tubular and more rounded secretory parts.
Multicellular exocrine glands: Simple glands: Explain simple tubular and give an example.
Tubular secretory part is straight and attaches to a single unbranched duct.
Example: glands in the large intestine
Multicellular exocrine glands: Simple glands: Explain simple branched tubular and give an example.
Tubular secretory part is branched and attaches to a single unbranched duct.
Example: gastric glands.
Multicellular exocrine glands: Simple glands: Explain simple coiled tubular and give an example.
Tubular secretory part is coiled and attaches to a single unbranched duct.
Example: sweat glands.
Multicellular exocrine glands: Simple glands: Explain simple acinar and give an example.
Secretory portion is rounded and attaches to a single unbranched duct.
Example: glands of the penile urethra.
Multicellular exocrine glands: Simple glands: Explain simple branched acinar and give an example.
Rounded secretory part is branched and attaches to a single unbranched duct.
Example: sebaceous glands
Multicellular exocrine glands: Compound glands: Explain compound tubular and give an example.
Compound tubular. Secretory portion is tubular and
attaches to a branched duct. Example: bulbourethral
(Cowper’s) glands
Multicellular exocrine glands: Compound glands: Explain compound acinar and give an example.
Compound acinar. Secretory portion is rounded and attaches to a branched duct.
Example: mammary glands