1. By the end of this lecture you will:
Tissues Part I
By the end of this lecture you will:
Be able to define what a tissue is and the role tissues play in A&P
Be able to describe and distinguish between the main categories of epithelial tissue

2. Tissues
The study of tissues is known as __________?

3. The study of tissues is known as Histology.
Histologists describe cells by their appearance:
The size and shape of the cells
How the cells are arranged in tissues (layers, scatterd, etc.)
How the cells are connected to each other
The amount of extracellular (EC) material in the tissue

4. Groups of cells similar in structure and function
Tissues
Groups of cells similar in structure and function
Types of tissues- 4 types in the human body
Epithelial tissue
Connective tissue
Muscle tissue
Nerve tissue

5. Nervous tissue: Internal communication
• Brain, spinal cord, and nerves
Muscle tissue: Contracts to cause movement
• Muscles attached to bones (skeletal)
• Muscles of heart (cardiac)
• Muscles of walls of hollow organs (smooth)
Epithelial tissue: Forms boundaries between different
environments, protects, secretes, absorbs, filters
• Skin surface (epidermis)
• Lining of GI tract organs and other hollow organs
Connective tissue: Supports, protects, binds
other tissues together
• Bones
• Tendons
• Fat and other soft padding tissue
Figure 4.1

6. Epithelial Tissue (Epithelium)
Epi (upon) thele (nipple)
Protect and separate the internal and external environment of the organism
Regulate exchange of materials between the internal and external environment
What type of materials?

7. Epithelial Tissue (Epithelium)
Epi (upon) thele (nipple)
Protect and separate the internal and external environment of the organism
Regulate exchange of materials between the internal and external environment
What type of materials?
Any substance that enters or exits the body must cross an epithelium
Significance- (disease, nutrition, homeostasis?)

8. Epithelial Tissue (Epithelium)
Two main types (by location):
Sheets of tissue covering and lining epithelia
On external and internal surfaces and the lumen of hollow organs
Glandular (secretory) epithelia
Secretory tissue in glands
Synthesize and release substances into the EC space

9. Characteristics of Epithelial Tissue
Cells have polarity—apical (upper, free) and basal (lower, attached) surfaces
Apical surfaces may bear microvilli (e.g., brush border of intestinal lining) or cilia (e.g., lining of trachea)
Noncellular basal lamina (or basement membrane) made of glycoprotein and collagen lies adjacent to basal surface

10. Characteristics of Epithelial Tissue
Are composed of closely packed cells
Continuous sheets held together by tight junctions and desmosomes
Supported by a connective tissue reticular lamina (under the basal lamina)
Avascular but innervated (what does this mean?)
High rate of regeneration (why?)

11. Classification of Epithelia
When classifying Epithelia, you need to ask two questions:
How many layers?
What type of cell?

12. Classification of Epithelia
When classifying Epithelia, you need to ask two questions:
How many layers?
1 = Simple epithelium
>1 = Stratified epithelium

13. (a) Classification based on number of cell layers.
_______ surface ?
_____ surface
______ surface ?
_____ surface
(a) Classification based on number of cell layers.
Figure 4.2a

14. (a) Classification based on number of cell layers.
Apical surface
Basal surface
Simple
Apical surface
Basal surface
Stratified
(a) Classification based on number of cell layers.
Figure 4.2a

15. Classification of Epithelia
What type of cell?
Squamous
Cuboidal
Columnar
(If stratified, name according to apical layer of cells)

16. (b) Classification based on cell shape.? ? ?
(b) Classification based on cell shape.
Figure 4.2b

17. (b) Classification based on cell shape.
Squamous
Cuboidal
Columnar
(b) Classification based on cell shape.
Figure 4.2b

18. Overview of Epithelial Tissues
Additionally, there are 5 functional types of Epithelia:
Exchange
Transporting
Ciliated
Protective
Secretory

19. Exchange Epithelial Tissues
Composed of simple, squamous layer that allows gases to pass rapidly across the epithelium (what gases do you think?)
Found in the lungs, heart, blood vessels,
The lining of heart and blood vessels is also called the Endothelium

20. Transporting Epithelial Tissues
Composed of simple, cuboidal or columnar layer
Selectively and actively regulates the exchange of ions and nutrients between internal and external environments- shaped by needs and hormones
Found in the kidneys and digestive system
The lumen of each is exposed to the external environment

21. Transporting Epithelial Tissues
Transporting Epithelia Characteristics:
Cell Shape- thicker than exchange epithelia, though still one cell thick- columnar and cuboidal
Membrane Modifications- large surface area on apical side (what structures?)
Cell Junctions- Adjacent cells are tightly attached to each other (why?) –Materials must go through cells, rather than around
Organelles- most need numerous mitochondria for energy requirements (why?)

22. Ciliated Epithelial Tissues
Composed of simple, cuboidal or columnar layer
Apical side contains cilia to move fluid across cell and tissue surface
Found in the respiratory system and parts of female reproductive system

23. Protective Epithelial Tissues
Composed of stratified layers- squamous in top layers, thicker in bottom layers
Toughened by protein keratin (same protein found in hair and nails)
Found in the epidermis (system?), and linings of mouth, pharynx (location?), esophagus, urethra, and vagina

24. Protective Epithelial Tissues
Cells have short life span and are replaced by newer cells from deeper layers
Why? Functionally, is this important?

25. Secretory Epithelial Tissues
Secrete a substance outside the cell
Scattered throughout epithelia, or grouped to form glands
Two main types:
Exocrine
Endocrine

26. Secretory Epithelial Tissues
Exocrine:
Release secretions to external environment through ducts
Skin surface, lumen, etc.
Can be harmful to life- stomach acid, digestive enzymes,
Or beneficial- breast milk
Sweat, salivary, and mammary glands, liver, pancreas, goblet cells

27. Secretory Epithelial Tissues
Endocrine:
Ductless glands
Release secretions (hormones) to internal environment through blood and lymph
Which type of glandular tissue is more common, Exocrine or Endocrine?

28. Overview of Epithelial Tissues
For each of the following types of epithelia, note:
Description
Function
Location

29. (a) Simple squamous epithelium
Description: Single layer of flattened
cells with disc-shaped central nuclei
and sparse cytoplasm; the simplest
of the epithelia.
Air sacs of
lung tissue
Function: Allows passage of
materials by diffusion and filtration
in sites where protection is not
important; secretes lubricating
substances in serosae.
Nuclei of
squamous
epithelial
cells
Location: Kidney glomeruli; air sacs
of lungs; lining of heart, blood
vessels, and lymphatic vessels; lining
of ventral body cavity (serosae).
Photomicrograph: Simple squamous epithelium
forming part of the alveolar (air sac) walls (125x).
Figure 4.3a

30. Epithelia: Simple Squamous
Two other locations
Endothelium
The lining of lymphatic vessels, blood vessels, and heart
Mesothelium
The epithelium of serous membranes in the ventral body cavity

31. (b) Simple cuboidal epithelium
Description: Single layer of
cubelike cells with large,
spherical central nuclei.
Simple
cuboidal
epithelial
cells
Function: Secretion and
absorption.
Basement
membrane
Location: Kidney tubules;
ducts and secretory portions
of small glands; ovary surface.
Connective
tissue
Photomicrograph: Simple cuboidal
epithelium in kidney tubules (430x).
Figure 4.3b

32. (c) Simple columnar epithelium
Description: Single layer of tall cells
with round to oval nuclei; some cells
bear cilia; layer may contain mucus-
secreting unicellular glands (goblet cells).
Simple
columnar
epithelial
cell
Function: Absorption; secretion of
mucus, enzymes, and other substances;
ciliated type propels mucus (or
reproductive cells) by ciliary action.
Location: Nonciliated type lines most of
the digestive tract (stomach to anal canal),
gallbladder, and excretory ducts of some
glands; ciliated variety lines small
bronchi, uterine tubes, and some regions
of the uterus.
Basement
membrane
Photomicrograph: Simple columnar epithelium
of the stomach mucosa (860X).
Figure 4.3c

33. (d) Pseudostratified columnar epithelium
Description: Single layer of cells of
differing heights, some not reaching
the free surface; nuclei seen at
different levels; may contain mucus-
secreting cells and bear cilia.
Cilia
Mucus of
mucous cell
Pseudo-
stratified
epithelial
layer
Function: Secretion, particularly of
mucus; propulsion of mucus by
ciliary action.
Location: Nonciliated type in male’s
sperm-carrying ducts and ducts of
large glands; ciliated variety lines
the trachea, most of the upper
respiratory tract.
Basement
membrane
Photomicrograph: Pseudostratified ciliated
columnar epithelium lining the human trachea (570x).
Trachea
Figure 4.3d

34. (e) Stratified squamous epithelium
Description: Thick membrane
composed of several cell layers;
basal cells are cuboidal or columnar
and metabolically active; surface
cells are flattened (squamous); in the
keratinized type, the surface cells are
full of keratin and dead; basal cells
are active in mitosis and produce the
cells of the more superficial layers.
Stratified
squamous
epithelium
Function: Protects underlying
tissues in areas subjected to abrasion.
Nuclei
Location: Nonkeratinized type forms
the moist linings of the esophagus,
mouth, and vagina; keratinized variety
forms the epidermis of the skin, a dry
membrane.
Basement
membrane
Connective
tissue
Photomicrograph: Stratified squamous epithelium
lining the esophagus (285x).
Figure 4.3e

35. (f) Transitional epithelium
Description: Resembles both
stratified squamous and stratified
cuboidal; basal cells cuboidal or
columnar; surface cells dome
shaped or squamouslike, depending
on degree of organ stretch.
Transitional
epithelium
Function: Stretches readily and
permits distension of urinary organ
by contained urine.
Location: Lines the ureters, urinary
bladder, and part of the urethra.
Basement
membrane
Connective
tissue
Photomicrograph: Transitional epithelium lining the urinary
bladder, relaxed state (360X); note the bulbous, or rounded,
appearance of the cells at the surface; these cells flatten and
become elongated when the bladder is filled with urine.
Figure 4.3f

36. Epithelia: Stratified Cuboidal
Quite rare in body
Found in some sweat and mammary glands
Typically two cell layers thick

37. Epithelia: Stratified Columnar
Limited distribution in body
Small amounts in pharynx, male urethra, and lining some glandular ducts
Also occurs at transition areas between two other types of epithelia

38. Glandular (Secretory) Epithelia
A gland is one or more cells that makes and secretes an aqueous fluid
Classified by:
Site of product release—endocrine or exocrine
Relative number of cells forming the gland—unicellular (e.g., goblet cells) or multicellular

39. Unicellular Exocrine Glands
The only important unicellular gland is the goblet cell
Cell that produces and secretes mucous
Glycoproteins & Proteoglycans

40. Microvilli Secretory vesicles containing mucin Rough ER Golgi
apparatus
Nucleus
(a)
(b)
Figure 4.4

41. Multicellular Exocrine Glands
Multicellular exocrine glands are composed of a duct and a secretory unit
Classified according to:
Duct type (simple or compound)
Structure of their secretory units (tubular, alveolar, or tubuloalveolar)

42. Compound duct structure
Simple duct structure
(duct does not branch)
Compound duct structure
(duct branches)
Tubular
secretory
structure
Simple tubular
Simple branched
tubular
Compound tubular
Example
Intestinal glands
Example
Stomach (gastric)
glands
Example
Duodenal glands of small intestine
Alveolar
secretory
structure
Simple
alveolar
Simple branched
alveolar
Compound alveolar
Compound
tubuloalveolar
Example
No important
example in humans
Example
Sebaceous (oil)
glands
Example
Mammary glands
Example
Salivary glands
Surface epithelium
Duct
Secretory epithelium
Figure 4.5

43. Modes of Secretion Merocrine Holocrine Apocrine
Products are secreted by exocytosis (e.g., pancreas, sweat and salivary glands)
Holocrine
Products are secreted by rupture of gland cells (e.g., sebaceous glands)
Apocrine
Products are secreted by a partial rupture of the apical cell surface (active in armpits, groin areas after puberty

44. Review Questions
It is observed that the smoke from cigarettes and other tobacco products can paralyze cilia. From this observation, what tissue(s) will be most affected by the smoke, and what consequences could this have?
What characteristics might you find on or in cells whose main function is absorption?
What are Goblet cells and in what type of tissue will you most likely find them? Where is this tissue most common in the human body?