Week 4 CTL
Biology:
Tissue Tissues
Epithelial Histology I.
(Epithelia, Connective, Muscle, Nervous)
#1. Epithelial Tissues (epithelium):
- One of the 4 basic tissue types (nerve/muscle/connective/epithelial)
- A sheet/sheets of cells that covers a body surface or lines a body cavity.
- Where? : a) Covering & lining epithelium
b) Glandular epithelium
- Epithelia are avascular, but all epithelia "grow" on an underlying layer of vascular connective tissue.
- Form boundaries between different environments. (interface tissue)
- *Nearly all substances received or given off by the body must pass through an epithelium.
- General Functions: - Protection
- Absorption
- Filtration
- Excretion
- Secretion
- Sensory reception
Characteristics of Epithelium:
- Epithelium differ from other types of cells in that they:
o Exhibit Polarity: (apical-basal polarity)
§ Have an apical surface
• Surface exposed to the inside of the lined cavity.
• Most have microvilli (finger-like extensions of the plasma membrane)
• Some have cilia (arms that propel substances in 1 direction – eg. trachea)
o Power & recovery strokes
§ Have a basal surface
• Surface facing connective tissue on the outside of the lined cavity.
• Supported by a Basement Membrane:
o Lining the basal surface is a thin supporting sheet called the basal lamina -determines which
molecules can diffuse through the basal membrane.
o Below the basal lamina is the reticular lamina – fine network of collagen fibres belonging to the
underlying connective tissue.
www.MedStudentNotes.com
, o Bound by specialised contacts:
§ Tight junctions – maintain polarity – protect basal side from apical environment.
§ Desmosomes – resist mechanical forces – holds cells together
§ Gap junctions – Allows intercellular transfers & communication.
o Supported by Connective Tissue:
§ Provide support
§ Reinforces the epithelial sheet
§ Resists stretching/tearing forces
§ Defines epithelial boundary.
www.MedStudentNotes.com
Biology:
Tissue Tissues
Epithelial Histology I.
(Epithelia, Connective, Muscle, Nervous)
#1. Epithelial Tissues (epithelium):
- One of the 4 basic tissue types (nerve/muscle/connective/epithelial)
- A sheet/sheets of cells that covers a body surface or lines a body cavity.
- Where? : a) Covering & lining epithelium
b) Glandular epithelium
- Epithelia are avascular, but all epithelia "grow" on an underlying layer of vascular connective tissue.
- Form boundaries between different environments. (interface tissue)
- *Nearly all substances received or given off by the body must pass through an epithelium.
- General Functions: - Protection
- Absorption
- Filtration
- Excretion
- Secretion
- Sensory reception
Characteristics of Epithelium:
- Epithelium differ from other types of cells in that they:
o Exhibit Polarity: (apical-basal polarity)
§ Have an apical surface
• Surface exposed to the inside of the lined cavity.
• Most have microvilli (finger-like extensions of the plasma membrane)
• Some have cilia (arms that propel substances in 1 direction – eg. trachea)
o Power & recovery strokes
§ Have a basal surface
• Surface facing connective tissue on the outside of the lined cavity.
• Supported by a Basement Membrane:
o Lining the basal surface is a thin supporting sheet called the basal lamina -determines which
molecules can diffuse through the basal membrane.
o Below the basal lamina is the reticular lamina – fine network of collagen fibres belonging to the
underlying connective tissue.
www.MedStudentNotes.com
, o Bound by specialised contacts:
§ Tight junctions – maintain polarity – protect basal side from apical environment.
§ Desmosomes – resist mechanical forces – holds cells together
§ Gap junctions – Allows intercellular transfers & communication.
o Supported by Connective Tissue:
§ Provide support
§ Reinforces the epithelial sheet
§ Resists stretching/tearing forces
§ Defines epithelial boundary.
www.MedStudentNotes.com
