NURS 1750 Lecture Notes - Lecture 3: Perichondrium, Merocrine, Proteoglycan
28 Jun 2018
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Week Three (Sept. 25-29, 2017)
Anatomy and Physiology I
Chapter Four: The Tissue Level of Organization (Pgs. 106-140)
4.1 Types of Tissues
A tissue is a group of cells that usually have a common origin and function together to carry out
specialized activities.
1. Epithelial Tissue: Allows the body to interact with both its external and internal
environment. Covers body surfaces.
2. Connective Tissue: Protects and supports the body and its organs.
3. Muscular Tissue: Composed of cells specialized for contraction and
generation of force. In the proces, muscular tissue generates heat to warm
body.
4. Nervous Tissue: detects changes in a variety of conditions inside and outside
the body and responds by generating electrical signals called action
potentials (nerve impulses) that activate muscular contractions and glandular
secretions.
4.2 Cell Junctions
Cell junctions are contact points between the plasma membranes of tissue cells. They hold cells
together to form tissues. There are five main types of cell junctions.
1. Tight Junctions - Consist of web-like strands of transmembrane proteins that
fuse together the outer surfaces of adjacent plasma membranes to seal off
passageways between adjacent cells. They inhibit the passage of substances
between cells and prevent the contents of these organs from leaking into the
blood or surrounding tissues. → Stomach, intestines and urinary bladder.
2. Adherens Junctions: contain plaque (dense layer of proteins) on the inside of the
plasma membrane. Transmembrane glycoproteins called (cadherins) join the
cells. Each cadherin inserts into the plaque from the opposite side of the
membrane and connects to cadherins of an adjacent cell. → found in intestines.
→ In epithelial cells, adherens form adhesion belts because they encircle the cell
similar to a belt; helps resists separation during contractile activities (ie.
digestion).
3. Desmosomes: also contain plaque and have transmembrane glycoproteins that
extend into the intercellular space between adjacent cell membranes and attach
cells to one another. But, unlike adheren junctions, the plaque attaches to
intermediate filaments, which consist of keratin. Desmosomes prevent
epidermal cells from separating under tension and cardiac muscles from
pulling apart during contraction. → Make up outermost layer of skin
(epidermis).
4. Hemidesmosomes: Dense plaque proteins and transmembrane nous
glycoprotein(integrins) attach at intermediate filament keratin. Hemidesmosomes
anchor cells to protein laminin in the basement membrane (not to each other).
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5. Gap Junctions: Connexins allow ions and electrical impulses to pass through
(diffuse), but large molecules cannot pass. Gap junctions allow cells to
communicate with one another. The transfer of nutrients and wastes takes
place through gap junctions in the lense and cornea of eye. Gap junctions
enable nerve or muscle impulses to spread rapidly among cells; important for
the contraction of heart muscle, the gastrointestinal tract and the uterus.
4.3 Comparison between Epithelial and Connective Tissues
Epithelial Tissues Connective Tissues
- Many cells tightly packed together
with little or no extracellular matrix.
- No blood vessels.
- Forms surface layers not covered by
another tissue.
- Large about of extracellular material
separates cells (which are scattered).
- Significant networks of blood vessels.
-
→ Epithelial and connective tissues are always found adjacent to each other because
the blood vessels from the connective tissues enables epithelial tissues to make
exchanges with blood for the delivery of O2 and removal of wastes.
4.4 Epithelial Tissue
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Week Three (Sept. 25-29, 2017)
Recall: The epidermis is the protective layer of skin, whereas epithelial tissue is cells that are
arranged in layers or sheets that covers most internal/external surfaces
Epithelial Tissue consists of densely packed cells arranged in continuous sheets (in single or
multiple layers). Meaning there is little intercellular space between adjacent plasma membranes.
They have a nerve and a blood supply, are attached to the basement membrane via
hemidesmosomes junctions and they are the site of frequent mitosis.
→ The serve to secrete (mucus, hormones and enzymes), absorb
(nutrients in digestive tract) and excrete (substances in urinary
tract).
Arranged in two patterns:
- Covering and lining various surfaces. (Surface epithelium)
- Forming the secreting portions of glands. (Glandular
epithelium)
Structure/Surfaces
- Epithelial cells have two different sides.
- The exposed surface layer is called the apical surface. It faces body cavity or
space of organ and may contain cilia or microvilli.
- The base surface layer is called the basal surface.
- The basal layer of cells are attached to the basement membrane; which
consists of two layers:
- Basal Lamina: closer to and secreted by epithelial cells. Contains
proteins and collagens, glycoproteins and proteoglycans. Adhere
integrins in hemidesmosomes to basement membranes.
- Reticular Lamina: closer to underlying connective tissues and contains
collagen produced by connective tissue cells called fibroblasts.
-The basement membranes provide a surface which epithelial cells migrate
during growth or wound healing, restrict passage of larger molecules between
connective and epithelial tissues and participate in filtration of blood in kidneys.
→ Has own nerve supply but not own blood supply; thus you don’t bleed
when something penetrates skin lightly.
Classification of Epithelial Tissue
1. Arrangement of cells in layers.
a. Simple Epithelium - a single layer of cells that
functions in diffusion, osmosis, filtration, secretion
or absorption.
b. Pseudostratified Epithelium - appears to have multiple layers of cells
since nuclei lie at different levels and not all cells reach apical surface.
c. Stratified Epithelium: consists of two or more layers of cells that protect
underlying tissues in locations where there is considerable wear and tear.
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Document Summary
Chapter four: the tissue level of organization (pgs. A tissue is a group of cells that usually have a common origin and function together to carry out specialized activities: epithelial tissue: allows the body to interact with both its external and internal environment. Covers body surfaces: connective tissue: protects and supports the body and its organs, muscular tissue: composed of cells specialized for contraction and generation of force. Cell junctions are contact points between the plasma membranes of tissue cells. There are five main types of cell junctions: tight junctions - consist of web-like strands of transmembrane proteins that fuse together the outer surfaces of adjacent plasma membranes to seal off passageways between adjacent cells. They inhibit the passage of substances between cells and prevent the contents of these organs from leaking into the blood or surrounding tissues. Stomach, intestines and urinary bladder: adherens junctions: contain plaque (dense layer of proteins) on the inside of the plasma membrane.
