Transcript Fundamental Cells and Tissues

Chapter 3:
Fundamental Cells and
Tissues
Objectives – Lesson 1
• TSWBAT to define histology.
• TSWBAT to identify the four basic tissue types.
• TSWBAT to identify five important
characteristics of epithelial tissue.
• TSWBAT to identify four essential functions of
epithelial tissue.
Cells
In the late 1600’s British born Robert Hooke coined
the term "cell" to describe the basic unit of life.
Where did the term cell come
from?
•In 1665 Robert Hooke inspected
thin slices of cork and found that
they consisted of millions of
small, “irregular units”
•He used the term cell because
the small, bare spaces reminded
him of cells in a prison
Cell Basics
• Cells are the building blocks of all plants and
animals
• All cells come from the division of preexisting
cells
• Cells are the smallest units that perform all vital
physiological functions
• Each cell maintains homeostasis at the cellular
level
Cell Basics continued
Living cells are about 60 % H20
All body cells are constantly bathed in a dilute
saltwater solution called interstitial fluid (18
pints).
All exchanges between cells and blood are made
through this fluid
Cell Facts
• The human body contains trillions of cells (200
types of cells)
• The average cells is just 0.02mm across
• The largest cell in the body is an egg cell
(0.15mm)
• The longest cells are the nerve cells supplying
your legs (some measure as much as 4ft in
length)
• Five million of your body cells die every second
Tissues
Tissues - Groups of cells similar in structure and
function
The four types of tissues:
1.
2.
3.
4.
Epithelial
Connective
Muscle
Nerve (Neural)
Epithelial Tissue
Epithelium – A sheet of cells that covers a body surface or lines a
body cavity.
Occurs in the body in two ways:
1. Epithelia – layers of cells that cover internal or external surfaces
- Forms the outer layer of the skin
- Lines the open cavities of the reproductive, cardiovascular, nervous, digestive,
urinary and respiratory systems and covers the walls and organs (line all
passageways that communicate with the outside world)
2. Glandular Epithelium
- Forms the glands of the body (provide fluid secretions)
Epithelial Tissue Functions
A. Protection – protect exposed and internal
surfaces from abrasion, dehydration, and
destruction by foreign agents
B. Permeability – any substance that enters or
leaves your body must cross an epithelium
(provides selective absorption)
C. Sensation – provide information about the
external and internal environments (example sense smell)
D. Secretion – gland cells releases a substance
(example – mucus)
Special Characteristics of Epithelium
1. Cells fit closely together to form continuous sheets
(single/multiple layers)
2. Membranes always have one free surface or edge
(exposed to body cavity, exterior of the body or lining
an internal organ)
3. Lowest surface (basal surface) of epithelium rests on
a basement membrane
4. Epithelial tissues have no blood supply (avascular) of
their own (lack blood vessels); must obtain nutrients
by diffusion or absorption from nearby tissues
5. If well nourished, epithelial cells regenerate
themselves (high rate of mitosis)
Check point
• Define histology.
• Identify the four major
types of tissues in the
body.
Classification of Epithelia
• There are many different specialized types of
epithelia
• Organized into categories based on:
1. Cell shape
2. The number of cell layers between the
basement membrane and the exposed
surface of the epithelium
Classification of Epithelial Tissue
Cell Shape:
• Squamous = flat (attach like tiles)
• Cuboidal = thicker, cube shaped
• Columnar = tall, cylindrical
Classification of Epithelia
Squamous (skwa’mus) Flattened and
scalelike
Cubodial (ku-boi’dahl) Boxlike, as tall as
they are wide.
Columnar
column shaped.
Tall and
Figure 4.1b
Classification of Epithelial Tissue
Number of cell layers:
Simple = one layer of cells covers the basement
membrane
 Thin/Fragile
 Located in protected areas in the body (ventral body
cavities, heart chambers and blood vessels). Why?
 Regions in which secretion or absorption occurs (lining
of the intestines, lungs)
• Stratified = Multilayered (several layers cover basement
membrane)
 Located in areas that are exposed to stresses (mouth, skin)
Classification of Epithelial Tissue
Each epithelium is given two names.
1. The first name indicates the number of cell layers present
2. The second name describes the shape of its cells
3. Followed by epithelium or epithelial tissue
Example :
1. Simple (1 layer)
2. Squamous (Flat cell shape)
3. Epithelium
Epithelia: Simple Squamous
Figure 4.2a
Epithelia: Simple Cuboidal
• Single layer of cubelike cells with large,
spherical central nuclei
• Function in secretion and absorption
• Present in kidney tubules, ducts and secretory
portions of small glands, and ovary surface
Figure 4.2b
Epithelia: Simple Columnar
Figure 4.2c
Pseudostratified Columnar
• Includes several types of cells with varying shapes
and functions
• The distances between the cell nuclei and the
exposed surface vary, so the epithelium appears
to be layered (stratified)
• It is not truly stratified because every epithelial
cell contacts the basement membrane
• Typically possess cilia (slender organelle that
extends above the free surface of an epithelial
cell and undergoes movement)
Epithelia: Pseudostratified Columnar
• Single layer of cells with different heights;
some do not reach the free surface
• Nuclei are seen at different layers
• Function in secretion and propulsion of mucus
• Present in the male sperm-carrying ducts
(nonciliated) and trachea (ciliated)
Figure 4.2d
Epithelia: Stratified Squamous – Most
Common
• Thick membrane composed of several layers
of cells
• Function in protection of underlying areas
subjected to abrasion
• Forms the external part of the skin’s epidermis
(keratinized cells), and linings of the
esophagus, mouth, and vagina (nonkeratinized
cells)
Figure 4.2e
Epithelia: Stratified Cuboidal and
Columnar
Stratified cuboidal
– Quite rare in the body
– Found in some sweat and mammary glands
– Typically two cell layers thick
Stratified columnar
– Limited distribution in the body
– Found in the pharynx, male urethra, and lining of some
glandular ducts
– Also occurs at transition areas between two other types
of epithelia
Transitional Epithelium
• Unusual stratified epithelium because it
tolerates repeated cycles of stretching and
recoiling without damage
• It is called transitional because the appearance
of the epithelium changes as stretching occurs
Epithelia: Transitional
• Several cell layers, basal cells are cuboidal,
surface cells are dome shaped
• Stretches to permit the distension of the
urinary bladder
• Lines the urinary bladder, ureters, and part of
the urethra
Figure 4.2f
Epithelia: Glandular
Gland - One or more cells that makes and secretes
a particular product (secretion).
Classified by:
– Site of product release
endocrine (internally secreting)
exocrine (externally secreting)
– Relative number of cells forming the gland
unicellular (one-celled)
multicellular (many-celled)
Endocrine Glands
• Ductless glands that produce hormones
• Hormones are regulatory chemicals that enter
the blood or lymphatic fluid and travel to organs
• Each hormone prompts its target organ to
respond in some characteristic way
Exocrine Glands
• More numerous than endocrine glands
• Secrete their products onto body surfaces (skin)
or into body cavities
• Examples include mucus, sweat, oil, salivary
glands, the liver (secretes bile), the pancreas
(synthesizes digestive enzymes)
• Unicellular & Multicellular
Mitosis
• Equal division of material in the nucleus,
followed by division of the cell body (nuclear
cell division)
• Epithelial cells have a high rate of mitosis to
allow for frequent repair