Tissues: The Living Fabric Epithelial Tissues

1
Mariebs Human Anatomy and Physiology Marieb w
Hoehn

• Chapter 4
• Tissues The Living FabricEpithelial Tissues
• Lecture 9

2
Lecture Overview

• Introduction to Tissues
• Epithelial Tissues
• Location
• General characteristics
• Functions
• Classification
• Glandular Epithelium

3
Where are Tissues in Our Organizational Scheme?
Figure from Holes Human AP, 12th edition, 2010
4
Introduction to Tissues
Tissue - a group of cells working together to
perform one or more specific functions Histology
the microscopic study of tissues
Four primary types of tissues found in the adult

1. Epithelial (covering/lining, protection, glands)
   pl. epithelia
2. Connective (binding together, support,
   transport, energy)
3. Muscle (movement, heat production)
4. Nervous (information and short-term control)

5
Major Types of Epithelial Tissues

• Covering and Lining Epithelium
• External Surfaces, e.g., skin
• Internal surfaces 2 major types
• 1. Those that communicate with outside, e.g.,
  digestive, respiratory, reproductive and urinary
  tracts
• 2. Those that dont communicate with outside,
  e.g., chest cavity, abdominal cavity, endothelium
  of blood vessels and heart
• Glandular Epithelium
• Often lie in clusters deep to covering and lining
  epithelium
• Specialized for secretion into ducts, on to a
  surface, or into the blood

6
Functions of Epithelial Tissue

• Physical protection
• Protect from abrasion, dehydration, and
  destruction by chemical or biological agents
• Control of permeability
• Secretion
• Absorption
• Filtration
• Provide sensation
• Extensively innervated by sensory nerves
• May function in senses (smell, taste, etc.)
• Provide specialized secretions (glands)

7
Characteristics of Epithelial Tissue

• Specialized contacts with other cells
• Polarity (different ends of cell do different
  things)
• Avascularity (no blood supply)
• Regeneration (can divide to make new cells)
• Cellularity (lots of cells in close contact)

Remember Epithelial tissues always have a free
surface and a basement membrane
8
Characteristics of Epithelial TissueSpecialized
Contacts
Figure from Martini, Anatomy Physiology,
Prentice Hall, 2001
9
Characteristics of Epithelial TissuePolarity
Outside surface note modifications
Inner surface attached to underlying tissue by
a basement membrane
Figures from Martini Visual AP, 1st edition,
2011
Notice the polarity and differential distribution
of the cellular organelles
10
Characteristics of Epithelial TissueAvascularity
and Regeneration

• Does not contain blood vessels (avascular)
• Nutrients must be obtained by
• Diffusion from underlying tissue (125 µm limit)
• Absorption from free surface
• High rate of cell division and replacement
• Lost cells are continually replaced by dividing
  epithelial stem cells
• Rate of cell division (mitotic rate) is much
  higher than other tissues

11
Characteristics of Epithelial TissueCellularity
Figure from Holes Human AP, 12th edition, 2010

• Cells are bound closely together
• Little intercellular material
• - May form sheets cells usually slough off in
  sheets

12
Modifications of Epithelial Cells
Cilia movement of substances
Microvilli greatly increase absorptive
(surface) area
Figures from Martini, Anatomy Physiology,
Prentice Hall, 2001
13
Basal Lamina
Formerly called Basement membrane
Two components Lamina Lucida - glycoproteins
and fine protein filaments - Barrier for passage
of substances from underlying tissue
into epithelium Lamina Densa - bundles of
coarse protein fibers - gives basal lamina its
strength
Lamina thin layer
Figure from Martini, Fundamentals of Anatomy
Physiology, Benjamin Cummings, 2004
14
Classification of Epithelial Tissues
Epithelial tissues are classified according to
both their

• Shape
• Squamous (Thin, flat, irregular in shape)
• Cuboidal (Square or cuboidal)
• Columnar (Rectangular, tall)
• Type of layering (stratification)
• Simple (one layer)
• Stratified (two or more layers)
• Note that classification of stratified epithelium
  is based on the shape of the superficial, not
  deep, layers

15
Epithelial Tissues
Figure from Holes Human AP, 12th edition, 2010
Mesothelium lines ventral body cavities (serous
membranes) Endothelium lines blood vessels

• Simple squamous
• single layer of flat cells
• substances pass easily through
• line air sacs of lung, blood vessels, lymphatic
  vessels
• reduce friction, absorption/secretion

16
Epithelial Tissues
Figure from Mariebs Human AP, 9th edition, 2013
17
Epithelial Tissues
Figure from Mariebs Human AP, 9th edition, 2013
18
Epithelial Tissues

• Pseudostratified columnar
• single layer of elongated cells
• appear stratified, but they ARE NOT
• all cells attach to basement membrane some do
  not reach surface
• often have cilia and goblet cells
• line respiratory passageways
• function protection, secretion

19
Epithelial Tissues
Figure from Holes Human AP, 12th edition, 2010

• Stratified squamous
• many cell layers
• top cells are flat
• can accumulate keratin
• outer layer of skin
• line oral cavity, throat, vagina, and anal canal

Main function is protection (abrasions,
pathogens, chemicals)
20
Epithelial Tissues
Figure from Holes Human AP, 12th edition, 2010

• Transitional
• many cell layers
• cube-shaped and elongated cells
• line urinary bladder, ureters, and part of
  urethra

Located in places where acute, short term
stretching occurs
21
Glandular Epithelium
Composed of cells that are specialized to produce
and secrete substances
Endocrine glands are ductless secrete directly
into the blood Exocrine glands have ducts
secrete into a duct or on to a surface

• Unicellular exocrine gland
• composed of one cell
• Example goblet cell
• Multicellular exocrine gland
• composed of many cells
• Examples sweat glands, sebaceous glands,
  salivary glands, etc.

22
Structural Types of Exocrine Glands

• Classified by
• Shape of secretory portion of gland
• Branching pattern of the duct

23
Exocrine Glands

• Classified by
• Shape of secretory portion of gland
• Branching pattern of the duct

24
Types of Glandular Secretions

• Merocrine glands
• fluid product
• exocytosis
• salivary glands
• pancreas
• sweat glands

• Holocrine glands
• secretory products
• whole cells
• sebaceous glands in hair follicles

25
Membranes
A membrane is a combination of epithelium and
connective tissue that covers and protects other
structures and tissues. Technically, then, a
membrane is an organ.

• Serous
• line body cavities that lack openings to outside
• reduce friction
• inner lining of thorax and abdomen
• cover organs of thorax and abdomen
• secrete serous fluid

• Mucous
• line tubes and organs that open to outside world
• lining of mouth, nose, throat, digestive tract,
  etc.
• secrete mucus

• Synovial
• surround joint cavities

• Cutaneous
• covers body
• skin

26
Epithelial Membranes
Notice that each type of membrane is composed of
TWO different types of tissues epithelial and
connective
Figure from Martini, Anatomy Physiology,
Prentice-Hall, 2001
27
Review of Epithelial Tissues

• Tissue - a group of cells working together to
  perform one or more specific functions
• Epithelial tissues are covering, lining, and
  glandular tissues that function in
• Physical protection
• Control of permeability
• Sensation
• Secretion
• Characteristics of epithelial tissue include
• Specialized contacts
• Polarity
• Avascularity
• Regeneration
• Cellularity

28
Review of Epithelial Tissues

• Covering and lining type tissue
• Characteristics S-P-A-R-C
• Attached to underlying tissue by a basal lamina
  (basement membrane)
• Epithelial tissue always has a free surface
• Classified according to shape and number of layers

29
Review of Epithelial Tissues

• Glands are specialized epithelium
• Exocrine
• Secrete on to a surface or into a duct
• Multicellular exocrine glands are classified by
• Shape of secretory portion of gland
• Branching pattern of the duct
• Endocrine - Secrete into the blood

30
Review of Epithelial Tissues

• Exocrine glands have several different mechanisms
  of secretion
• Merocrine
• Release of product from vesicles by exocytosis
• Most common mode of secretion
• Example watery sweat used to cool skin
• Holocrine
• Entire cell is packed with secretion and then
  bursts
• Destroys cell
• Example sebaceous glands associated with hair
  follicles
• Apocrine (may not be present in humans listed
  here only for informational purposes)
• Loss of apical cytoplasm containing secretion,
  not entire cell
• Example thick, sticky underarm perspiration

31
Review
NAME OF ET DESCRIPTION STRUCTURE LOCATION FUNCTION
SIMPLE SQUAMOUS a single layer of flattened cells linings of air sacs, capillaries, lymph vessels, body cavities covering ventral organs diffusion, reduction of friction
SIMPLE CUBOIDAL a single layer of cube-shaped cells with large centrally located nuclei linings of kidney tubules, ducts of glands absorption, secretion
SIMPLE COLUMNAR a single layer of tall cells with basally located nuclei, goblet cells, mucrovilli lining of intestine protection, absorption, secretion
PSEUDO- STRATIFIED COLUMNAR a single layer of tall cells with scattered nuclei, cilia, goblet cells lining of trachea, lining of fallopian tube protection, secretion
32
Review
NAME OF ET DESCRIPTION STRUCTURE LOCATION FUNCTION
STRATIFIED SQUAMOUS many layers of flattened cells keratinized epidermis non-keratinized lining of vagina, anus, throat, mouth protection
TRANSITIONAL several layers of cells that change shape under pressure lining of urinary bladder and ureters Distensibility (able to stretch)
GLANDULAR simple cuboidal lining the ducts of glands secretion