Lab 6 Flashcards
Tissues
• are groups of similar cells which perform a common function. • four basic tissue types: - epithelial tissue - connective tissue - muscle tissue - nervous tissue
Types of Tissues
- epithelial tissue - a tissue which covers the body, lines body cavities and forms glands
- connective tissue - a tissue which binds and supports various organs
- muscle tissue - a contractile tissue
- nervous tissue - a tissue which initiates and conducts electrochemical impulse
The study of tissues is known as
histology
3 primary germ layers in the embryo
- ectoderm - outer layer that gives rise to the outermost layer of the skin and nervous system.
- mesoderm - (middle layer) gives rise to a gelatinous tissue called mesenchyme which in turn gives rise to muscle, blood vessels and all connective tissues.
- endoderm- gives rise to the mucous membranes of the digestive, respiratory, and urinary tracts as well as digestive glands
epithelium
• Consists of cells arranged in continuous sheets in single or multiple layers.
• Covers surfaces, lines body cavities, and forms glands.
• Closely packed with little space between them and are held together by specialized cell junctions - tight junctions and desmosomes.
• Has an apical (free) surface which faces the external body surface, a body cavity, the lumen (inside) of an internal organ, or a tubular duct that receives cell secretions.
• The basal surface is opposite the apical surface.
- If the cell is found in a single layer or is found in the deepest cell layer, the basal surface sits on the basal lamina.
- This sheet consists of glycoproteins secreted by epithelial cells plus some collagen fibers.
• Reticular Lamina:
- Below the basal lamina
- a fine network of collagen fibers produced by cells in the connective tissue
Basement membrane.
- sits between epithelial tissues including mesothelium and endothelium, and the underlying connective tissue.
- two laminae (basal lamina is the reticular lamina) form the basement membrane
Two criteria are used to classify epithelial tissue
(i. ) number of cell layers
(ii. ) shape of the cells at the apical surface
simple epithelium
consists of a single layer of cells, all of which are in contact with the basement membrane
stratified epithelium
consists of several cell layers, superimposed one upon the other, with only the basal cells in contact with the basement membrane
Common shapes of epithelial cells - 3
List
Describe
- Squamous - cells flat and plate like
- Cuboidal - cells resemble little squares
- Columnar -cells are tall and column shaped
Simple squamous epithelium
• consists of a single layer of flattened cells.
• thinest epithelium in humans
• The cells resemble fried eggs, with a bulging, round or oval nucleus (the “yolk”) and a flat, clear cytoplasm (the “white”).
• cell boundaries are usually indistinct
•FUNCTION: is present in organs where diffusion occurs.
-Kidneys: functions in diffusion (loop of Henle) and filtration (Bowman’s capsule).
-Lungs: alveoli (air sacs)
Simple Cuboidal Epithelium
• a single layer of box-shaped cells
• cell boundaries are often distinct and the round nucleus is near the center of the cell
• FUNCTION: in secretion and absorption
- thyroid gland, kidney tubules, and ducts of many glands
Simple Columnar Epithelium
• cells that are rectangular-shaped in cross section
• columnar cells being taller that they are wide
• very closely packed together, with an oval nucleus located at the base of each cell
• contain goblet cells
• FUNCTION: in absorption and secretion
- line the stomach, small and large intestines and ducts of various glands
goblet cells
- They produce mucus which acts as a lubricant and protective barrier.
- Goblet cells are very abundant in some regions of the digestive tract.
- enlarged, lightly stained cells
Pseudostratified Columnar Epithelium
• single layer of columnar cells of varying shapes and heights
• the nuclei are staggered at various levels (creates an impression of a stratified epithelium)
• As ALL the cells in this epithelium contact the basement membrane, the impression is a false one, hence the name “pseudo - stratified”.
• FUNCTION: protects the lungs against dust and other debris that can interfere with respiration.
• found in the upper respiratory tract - lines the nasal cavities, trachea and bronchi.
-ciliated and contains goblet cells and functions in secretion and protection
-The goblet cells produce mucus, which traps inhaled foreign particles.
-The cilia are organelles that extend from the exposed surface of the cells and are capable of “beating” rhythmically. When the cilia “beat”, the foreign particles trapped by the mucus are propelled away from the lungs towards the throat.
-This protects the lungs against dust and other debris that can interfere with respiration.
