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Chapter 4

Anatomy and Physiology HAP101 Chapter Notes - Chapter 4: Stratified Squamous Epithelium, Adherens Junction, Goblet Cell


Department
Anatomy and Physiology
Course Code
Anatomy and Physiology HAP101
Professor
Tania Killian
Chapter
4

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HAP101 Chapter 4: Tissues (Part One)
LO 4.1: Summarize the four basic types of tissue
(1) Epithelial Tissue: covers body surfaces and lines hollow organs, body cavities, and ducts. It also forms glands
and allows the body to interact with both its internal and external environments
(2) Connective Tissue: protects and supports the body and its organs. Various types of connective tissues bind
organs together, store energy reserves as fat, and help provide the body with immunity to disease-causing
organisms
(3) Muscular Tissue: composed of cells specialized for contraction and generation of force. In the process, muscular
tissue generates heat that warms the body.
(4) Nervous Tissue: detects changes in a variety of conditions inside and outside the body and responds by
generating electricity signals, i.e. nerve impulses that activate muscular contraction and glandular secretions
How are cells held together to form tissues?
Most epithelial cells, some muscle, and nerve cells are held together by cell junctions
Cell Junctions: contact points between the plasma membranes of tissue cells. There are five types:
Junction Description
Tight Junction Strands of membrane that fuse the outer surfaces of adjacent plasma together to seal off
passageways between adjacent cells. These are present in the stomach, intestines, and
urinary bladder because they inhibit the passage of substances between cells and prevent
anything from leaking into the blood or surrounding tissues
Adherens Junction Contain plaque (layers of protein) on the inside of plasma membrane that attaches both to
membrane proteins and to microfilaments of the cytoskeleton. Cadherins join the cells and
each cadherin inserts into the plaque from the opposite side of the plasma membrane,
crosses the intercellular space and connects to cadherins of an adjacent cell. They often
form adhesion belts to encircle the cell and resist separation during contractile activities.
Desmosomes Contain plaque and have cadherins that extend into the intercellular space between adjacent
cell membranes and attach cells to on another. Desmosomes plaque attaches to cytoskeleton
elements, i.e. intermediate filaments consisting of keratin. These filaments extend across the
cytosol from one desmosome to the opposite, allowing stability of the cells and tissues. This
junction makes up the epidermis and cardiac muscles of the cell, also preventing them from
separating under tension and heart contraction.
Hemidesmosmes Hemi = half; resemble desmosomes but do not link adjacent cells. The transmembrane
glycoproteins are integrins and on the inside of the plasma membrane hey attach to
intermediate filaments made of protein. On the outside, they attach to laminin, in the
basement membrane.
Gap Junctions Membranes called connexions form fluid-filled tunnels called connexions. These connect
neighbouring cells. The plasma membranes are separated by a very narrow intercellular
space.+++++++++
LO 4.2: Describe the structure, location and function of the various types of epithelial tissue
Cells are arranged in continuous sheets, in either single or multiple layers. There is little intracellular space between
adjacent cell membranes due to many cell junctions. These tissues form coverings and linings throughout the body.
The epithelial has three main functions: (1) a selective barrier that limits or aids in the transfer of substances in and
out of body; (2) a secretory surface the releases products produced by the cells onto its free surface; and (3) a
protective surface that resists the abrasive influences of the environment.
The surfaces differ in structure and specialized functions:
oApical (free) surface: faces the body surface, a body cavity, the lumen of an internal organ, or a tubular duct
that receives cell secretions. This surface may contain cilia or microvilli.
oLateral surface: face the adjacent side of an epithelial cell and may contain tight junctions, adherens junction,
desmosomes, and/or gap junctions.
oBasal surface: opposite to apical surface. The surfaces of the deepest layer of epithelial cells adhere to
extracellular materials, such as the basement membrane. The basement membrane is a thick extracellular layer
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that consists of two layers, the basal lamina – a thin layer that is closer to and secreted by the epithelial cells;
contains proteins and glycoproteins and proteoglycans, and the reticular lamina – closer to the underlying
connective tissue and contains proteins, such as collagen.
Epithelial tissue has its own nerve supply, but it is avascular, i.e. it relays on blood vessels of adjacent connective
tissue to bring nutrients and remove waste through diffusion
It is subjected to physical stress and injury but is able to quickly repair through high rates of cell division
Epithelial has many important roles in the body: protection, filtration, secretion, absorption and excretion. It also
combines with nerve tissue to form organs for smell, hearing, vision and touch.
This tissue may be divided into two types:
o(1) Covering and lining epithelium: forms the outer covering of the skin and some internal organs. Forms the
inner ling of blood vessels, ducts, and body cavities; the interior of the respiratory, digestive, urinary, and
reproductive systems.
o(2) Glandular epithelium: makes up the secreting portion of glands such as the thyroid gland, adrenal glands,
and sweat glands.
The type of covering and lining epithelial tissues are classified according to two characteristics: arrangement of
cells into layers and shapes of the cells
Arrangement of Cells in
Layers
Description
Simple Epithelium A single layer of cells that functions in diffusions, osmosis, filtration, secretion
(production and release of substances, such as mucus, sweat, enzymes), or absorption
(intake of fluids or other substances)
Pseudostratified
Epithelium
Appears to have multiple layers of cells, as the cell nuclei lie at different levels and not
all cells reach the apical surface; it is actually a simple epithelium because all the cells
are at the basement membrane. Cell that extend to the apical surface contain cilia; others
(goblet cells) secret mucus
Stratified Epithelium Consists of two or more layers of cells that protect underlying tissues in locations where
there is wear/tear
Cell Shapes Description
Squamous Cells Flat, think, allowing rapid passage of substances through
Cuboidal Cells Tall, wide, shaped like cubes/hexagons. May have microvilli at apical surface and either secrete
or absorb
Columnar Cells Taller than they are wide, protect underlying tissue; apical surface may have cilia/microvilli;
absorb and secrete
Transitional Cells Change shape from squamous to cuboidal and back when organs stretch and relax (e.g. bladder)
When the above arrangement and shapes are combined together, the following is formed
Type Analysis
Simple
Squamous
Epithelium
Single layer (look like tiled floors) that has a centrally located nucleus that is flat and oval. Lines
the cardiovascular/lymphatic system and forms the epithelial layer of serous membranes. Present
at sites of filtration, diffusion or secretion in serous membranes
Simple Cuboidal
Epithelium
Single layer of cube-shapes cells; round centrally located nucleus. Covers surface of ovary, lines
part of the eye and forms pigment, makes up secreting portion of gland. Main job is to secrete and
absorb
Non-ciliated
Simple
Non-ciliated column-like cells with oval nuclei near base; contains columnar epithelial cells with
microvilli at apical and goblet cells. Microvilli increase surface area of plasma membrane, thus
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