Tissues Introduction and Epithelium 1

Question 1

Tissues

Answer 1

An organized aggregation of cells that function in a collective manner is called a tissue

Question 2

What are the four basic types of tissues and how are they classified?

Answer 2

Tissues are classified accoridng to their function and structure.
There four basic types are:
1) Epithelial tissue: covers body surfaces and lines hollow organs, body cavities, and ducts with very little extracellular substance
2) Connective tissue: protects and upports the body and its organs. Various types of connective tissue bind organs together, store energy reserves as fat, and help provide immunity to disease causing organisms
3) Muscle tissue: generates the physical force needed to make body structures move and composed of elongated cells that have the specialized function of contradiction
4) Nervous Tissue: detects changes in a variety of conditions inside and outside the body and responds by generating nerve impulse that help to maintain homeostasis.

Question 3

What are the three primary germ layers that all of tissues of the body develop from?

Answer 3

Ectoderm, mesoderm, endoderm.

• All three primary germ layers contribute to epithelial tissues.
• Mesoderm gives rise to all connective tissues and most muscle tissues
• Ectoderm develops into nervous tissue.

Question 4

Main characteristics of Epithelial tissue

Answer 4

• Epithelia line and cover all body surfaces except the articular cartilage, the enamel of the tooth
• Most epithelial cells renew continuously by mitosis
• Epithelia lack a direct blood and lymph supply
• The cohesive nature of epithelia is maintained by cell adhesion molecules and junctional complexes
• Epithelia are anchored to a basal lamina
• Epithelia have structural and functional polarity

Question 5

What are the form and shapes of the epithelial cells?

Answer 5

Epithelial cells range from columnar to cuboidal to low squamous cells. The nuclei have distinctive shape varying from spherical to elongated to elliptical corresponding to the shape of the cell

Question 6

Functions of the Epithelial tissue

Answer 6

• Protection, covering, and lining of surfaces
• absorption
• secretion
• excretion
• gas exchange
• sensation
• contractility
• everything that enters or leaves the body must cross an epithelial sheet

Question 7

Epithelial polarity

Answer 7

• Apical surfaces may contain cilia or microvilli
• Lateral surfaces of an epithelial cell face the adjacent cells on either side
• The basal surface of an epithelial cell is opposite the apical surface and adheres to extracellular materials

Question 8

Basal lamina

Answer 8

this is the extracellular material that separates epithelial cells from the connective tissue

• may have an electron- lucent layer on one or bother sides of the lamina densa called lamina rara
• the main components of basal laminae are type 4 collagen, the glycoproteins laminin and entactin, fibronectin, and proteoglycans.
• basal laminae are attached to the underlying connective tissues by anchoring fibrils by type 7 collagen
• in some instances reticular functions are closely associated with the basal lamina, forming the reticular lamina

Question 9

Basement membrane

Answer 9

=basal lamina + reticular lamina

-Reticular lamina: a bunch of different types of collagen

Question 10

Laminin

Answer 10

• major component of the basal lamina and consists of three disulfide-linked polypeptide chains designated alpha, beta, and gamma chains
• have binding sites for cell surface receptors, type 4 collagen

Question 11

Fibronectin

Answer 11

glycoprotein formed by two identical chains joined by disulfie linkages close to C-terminal
- the two forms of fibronectin are: plasma fibronectin- produced by hepatocytes and secreted into the blood stream; cellular fibronectin- produced by fibroblasts, forms part of the extracellular matrix

Question 12

What are the functions of the basal lamina?

Answer 12

• provide support to the cells
• provide barrier that limits and regulate the exchange of macromolecules
• able to influence cell polarity, regulate cell proliferation, influence cell metabolism, and serve as pathways for cell migration

Question 13

Basal Infoldings

Answer 13

• cells that trnasport fluid have infoldings at the basal surface and they significantly increase the surface area of the basal cell domain
• prominent in cells that participate in active transport of molecules in proximal and distal tubules of the kidney and in certain ducts of the salivary glands

Question 14

Lateral membrane of epithelial cells

Answer 14

specialized intercellular junction that serve as site of adhesions and as a seal to prevent the passage of material through the intercellular membrane

Question 15

Zonula occludens

Answer 15

• tight junctions that form the primary intercellular diffusion barrier between adjacent cells
• three major groups of proteins found in teh zonula occludens which are occludin, claudins, and junctional adhension molecules (JAM)

Question 16

Zonula adherens (belt desmosome)

Answer 16

encircles the circle and provides the adhension of one cell to its neighbor
- composed of the transmembrane cell adhesion molecule E-cadherin

Question 17

Macula adherens or spot desmosomes

Answer 17

• desmosome is a complex disk-shaped structure at the surface of one cell that is matched with an identical structure at the surface of the adjacent cell
• since intermediate filaments of the cytoskeleton are very strong desomosomes provide a firm adhesion among the cells

Question 18

Pemphigus vulgaris

Answer 18

disease in which patients make autoantibodies to desmoglein proteins
- epithelial cells lossen casuing fluid accumulation and superficial blisters

Question 19

Hemidesmosomes

Answer 19

• located in the contact zone between epithelial cells and the basal lamina, hemidesmosomes are observed
• take the form of hald of a desmosome and bind the epithelial cell to the subjacent basal lamina
• on jemidesmosomes the plaques are made of integrins

Question 20

Bullous pemphigoid

Answer 20

a blistering disease in which patients make autoantibodies in hemidesmosomes attachment plaques

Question 21

Gap junction or nexus

Answer 21

-Gap or communicating junctions can occur almost anywhere along the lateral membranes of epithelial cells
-not in skeletal muscle
-individual unit called connexon formed by six gap junctions proteins called connexins
-

Question 22

Microvilli

Answer 22

• fingerlike extensions that are found mainly on the free cell surface
• found in absorptive cells such as the lining of epithelium of the small intestine and the cells of the proximal renal tubule
• purpose is to increase surface area for the absorption or secretion
• have a central core of actin anchored to villin
• don’t wave back and forth
• Myosin 1 is associated with the actin filaments

Question 23

Stereocilia

Answer 23

• long, nonmotile extensions of cells of the epididymis and ductus deferens that are actually long and branched microvilli and should not be confused with true cilia
• increase the surface area of the cell
• also have a core of actin filaments and no villin

Question 24

Cilia

Answer 24

• motile structure capable of moving fluid and particles along epithelial surfaces
• surrounded by the cell membrane and contain a central pair of isolated microtubules surrounded by nine pair of microtubules

Question 25

Which two ways may epithelial tissue be classified?

Answer 25

1) Covering and lining epithelium forms
a. the outer covering of the skin and some internal organs
b. it also forms the inner lining of blood vessels, ducts, and body cavities
c. the interior of the respiratory, digestive, urinary, and reproductive systems
2) Glandular epithelium: constitutes the secreting portion of glands such as the thyroid gland, adrenal glands, and sweat glands

Question 26

Covering and lining epithelial tissue

Answer 26

• the types of covering and lining epithelial tissue are classified according to two characteristics:
  1) arrangement of cells into layer
  a. Simple epithelium
  b. stratified epithelium
  c. Pseudostratified epithelium
  2) shape of cells
  a. squamous- cells arranged like floor tiles and are thin
  b. cuboidal- are as tall as they are wide and shaped like cubes or hexagons
  c. columnar- much taller than they wide and protect underlying tissues and specialized for secretion and absorption
  d. transitional cells- change shape from cuboidal to flat and back as organs stretch to a larger size and then collapse to a smaller size

Question 27

Simple Squamous epithelium:

Answer 27

composed of a single layer of flattened cells
-diffusion takes place freely through this thin smooth lining of the following structures: alveoli of the lungs, heart, blood vessels, lymph vessels, bowman’s capsule

Question 28

Simple Cuboidal epithelium

Answer 28

• consists of cube-shaped cells fitting closely together lying on a basement membrane
• forms the kidney tubules and is found in some glands
• cuboidal epithelium is actively involved in secretion, absorption and excretion

Question 29

Simple columnar epithelium

Answer 29

• formed by a single layer of cells, rectangular in shape on a basement membrane
• found lining the organs of the alimentary tract and consists of a mixture of cells

Question 30

Pseudostratified columnar epithelium

Answer 30

All the cells are attached to the basement membrane in a single layer and this type is found in upper respiratory tract and in epididymis and vas deferens

Question 31

Stratified squamous epithelium

Answer 31

composed of layers of ells of different shapes representing newly formed and mature cells and have two types

• 1) non-keratinized stratified squamous epithelium
  2) keratinized stratified squamous epithelium

Question 32

Covering and lining epithelial tissue

Answer 32

• Stratified cuboidal epithelium: found in the lining of swear gland ducts
• Stratified columnar epithelium: present in the human body only in small areas such as the large ducts of salivary glands
• transitional epithelium: composed of several layers of pear-shaped cells and found in the lining of ureters, urinary bladder, urethra; exists in two states which are distented and relaxed or non distended

Question 33

Glandular Epithelium

Answer 33

The function of glandular epithelium is secretion and may consists of one or a group of cells. All glands are classified as endocrine or exocrine

• Exocrine glands discharge their secretion onto the epithelial surface and include mucus, saliva, digestive juices
• Endocrine glands discharge their secretion into blood and lymph

Question 34

Exocrine Glands Classification

Answer 34

1) By the number: unicellular or mutlicellular
2) By their ducts: simple( duct unbranched ) or compound ( duct branches)
3) By the shape of their secretory units: tubular, acinar ( flash-shaped), tubuloalveolar ( mixed type)
4) By their secretion: mucous, serous, or mixed
5) By the way they secrete : Merocrine- product is created and discharged by exocytosis without the loss of cytoplasm
; Holocrine- cell accumulates the product then dies and becomes part of the secretion; Apocrine- secretory product accumulates in apical cytoplasm and the region is lost with the secretion

Question 35

The Diffuse Neuroendocrine System

Answer 35

(DNES) are known as paracrine cells- they produce chemical signals that diffuse into the surrounding extracellular fluid to regulate the function of neighboring cells without passing through its vascular system