The Tissue Level of Organisation Flashcards
Tissues
Collections of specialised cells and cell products that carry out a limited number of functions
Histology
The study of tissues
4 types of tissue
- Epithelial tissue: covers exposed surfaces, lines internal passageways and chambers, and forms glands
- Connective tissue: fills internal spaces, provides structural support for other tissues, transports material within the body, and stores energy
- Muscle tissue: specialised for contraction and includes the skeletal muscles of the body, the muscle of the heart, and the muscular walls of hollow organs
- Nervous tissue: carries information from one part of the body to another in the form of electrical impulses
Types of epithelial tissue
Epithelia (layers of cells that cover external or line internal surfaces) and glands (structures that produce fluid secretions, attached to or derived from the epithelia)
Functions of epithelial tissue
- To provide physical protection
- To control permeability
- To provide sensation
- To produce specialised secretions
Neuroepithelium
An epithelium that is specialised to perform a particular sensory function
Gland cells
Epithelial cells that produce secretions
Characteristics of epithelial tissue
- Polarity (structural/function differences between the exposed, apical surface and the attached, basal surface)
- Cellularity (closely bound to other cells)
- Attachment (bound to basement membrane
- Avascularity (lacking blood vessels)
- Regeneration (continually replaced)
Cell junctions
Interconnections between cells
Specialisation of epithelial cells
- Movement of fluids over the epithelial surface, providing protection and lubrication
- Movement of fluids through the epithelium to control permeability
- The production of secretions that provide physical protection or act as chemical messengers
Ciliated epithelium
Motile cilia present
How is the physical integrity of the epithelium maintained?
- Intercellular connections
- Attachment to the basement membrane
- Epithelial maintenance and repair
Cell adhesion molecules (CAMs)
Transmembrane proteins that connect opposing plasma membranes
3 common types of cell junctions
- Gap junctions (cells held together by connexons)
- Tight junctions (lipid portion of two interlocking membrane proteins tightly bound together)
- Desosomes (CAMs and proteoglycans link opposing plasma membranes)
Lumen
Passageways lined by epithelial cells
Two types of desosomes
- Spot desmosomes (small discs connected to bands of intermediate filaments)
- Hemidesmosomes (attaches a cell to extracellular filaments in the basement membrane)
Basic shapes of epithelial cells
- Squamous (thin and flat)
- Cuboidal (boxes)
- Columnar (tall and slender rectangles)
Epithelial cell layers
- Simple epithelium (one layer covers the basement membrane)
- Stratified epithelium (several layers cover the basement membrane)
Where are simple epithelial cells found?
They line the internal compartments and passageways of the pleural, pericardial and peritoneal cavities; the heart chambers; and blood vessels
Additionally, they are found where secretion or absorption occurs e.g. the lining of the intestines and gas-exchange surfaces of the lungs
Where are stratified epithelial cells found?
In areas that are exposed to mechanical/chemical stresses e.g. the surface of the skin and the lining of the mouth
Functions of simple squamous epithelium
- Reduces friction
- Controls vessel permeability
- Performs absorption and secretion
e.g. alveoli, thoracic and abdominopelvic cavities
Mesothelium
The simple squamous epithelium that lines the body cavities enclosing the lungs, heart and abdominal organs
Endothelium
The simple squamous epithelium lining the inner surface of the heart and all blood vessels
Functions of stratified squamous epithelium
Provides physical protection against abrasion, pathogens and chemical attacks
e.g. surface of the skin, lining of the mouth
Functions of simple cuboidal epithelium
- Limited protection
- Secretion and absorption
e.g. glands, ducts
Functions of stratified cuboidal epithelium (rare)
- Protection
- Secretion and absorption
e.g. lining of some ducts (rare)
Transitional epithelium
Unusual stratified epithelium in which cells change between squamous and cuboidal shape
Functions of transitional epithelium
Permits repeated cycles of stretching without damage
e.g. urinary bladder, ureters
Functions of the columnar epithelium
- Protection
- Secretion and absorption
e.g. lining of the stomach, intestine
Pseudostratified ciliated columnar epithelium
A columnar epithelium that includes serval types of cells with varying shapes and functions
Not truly stratified because each epithelial cell contacts the basement membrane
Functions of the pseudostratified ciliated columnar epithelium
- Protection
- Secretion
- Moves mucous with cilia
e.g. lining of nasal cavity, trachea
Function of the sratified columnar epithelia
Protection
e.g. epiglottis, anus
Glands
Collections of epithelial cells that produce secretions
Glandular epithelia
Epithelia containing gland cells
Two types of glands
- Endocrine glands - release hormones into the blood
2. Exocrine glands - release secretions onto epithelial surfaces usually via ducts
Unicellular exocrine glands
Consist of single cells called goblet cells that secrete mucin (mucin + water = mucous)
What determines whether a cell is classified as a mucous cell or a goblet cell?
Their location:
Goblet - scattered among the absorptive cells in the columnar epithelium of the small and large intestines
Mucous - scattered among other epithelial tissue