Cells and Tissues 1 Flashcards
What are tissues and what are the 4 basic tissue types?
Cells are arranged into tissues and there are 4 basic tissue types which include: the epithelium, connective tissue, muscle and nerve.
Explain what the epithelium is.
The epithelium is comprised of tissues of closely related cells which are tightly bound together. They cover and line membranes, including any free surfaces. There are different types of epithelia and are specialized based on their function. They are separated from the other tissue through the basement membrane.
List the functions of the epithelia.
- Protect the underlying tissue
- Protects and separates areas of the body
- Helps hold tissues together
- Thermoregulation
- Helps release hormones
- Aids in absorption
List and explain the different types of epithelia.
They can either be simple (made up of 1 layer) or stratified (made up of several layers).
This can be further divided into different categorizations, as they can be squamous (flat), cuboidal (cubed), columnar (long) or transitional (varies in shape).
Describe how the structure of the different types of epithelia helps with the function of each.
Stratified squamous: This type of epithelia is generally used as protective tissue, due to the abundance of layers.
Simple squamous: Used in diffusion processes, due to the short passageways.
Transitional: Found within tissues which stretch a lot due to the variability of the structure.
Simple columnar: Seen in secretory and absorptive tissue, due to its ability to accommodate lots of organelles.
Simple cuboidal: Found in narrow passageways.
Explain what the basement membrane is.
Sheets of matrix at the interface of the functional tissue (epithelia) and the supportive tissue (connective tissue). Made up of type 4 collagen, glycoproteins (made from laminin secreted by the epithelial cells and fibronectin from fibroblasts), and glycosaminoglycans (GAG’s).
List and explain the functions of the basement membrane.
- Adhesion: helps connect the tissues together
- Permeability: Serves as barrier for the selective passing of molecules
- Controls growth and differentiation: helps organize the cells
- Protection: tumours must first go through the epithelia and breach the basement membranes, before reaching the other tissue and growing larger, as well as metastasizing.
Name the 2 different forms of cancers which can occur at the tissues.
Carcinomas: Cancer of the epithelia
Adenocarcinomas: Cancer of the glands
Explain what glands are and how they work with the epithelia.
Glands are epithelia which has been folded over and over again. They can vary in shape, and can either be tubular (long), acinar (short and wide) or a combination of both. They can be further classified as simple or branched. Within the gland itself the secretory portion of the gland is columnar, while the ducts are cuboidal epithelial.
List and describe the 2 different types of glands.
- Exocrine glands: secrete their products onto the epithelial surface directly or through the use of a duct for local action (i.e. sweat glands or the liver).
- Endocrine glands: Secrete directly into the blood to act on different tissues (i.e. pituitary and thyroid glands).
List and describe the 3 different types of exocrine glands.
- Merocrine: The Golgi apparatus creates vesicles which moves and merges with the cell membrane, in which the secretion is then released.
- Apocrine: A part of the gland which buds off with the secretion inside.
- Holocrine: The cell membrane dies and the secretion is released. A stem cell then regenerates in the place of the dead cell.
Explain what the connective tissue is as well as its function.
The supportive tissue of the body, which originates from the mesoderm. It is primarily composed of 5% cells and 95% extracellular matrix (made up of collagen and elastin fibres, as well as ground substance: glycoproteins and GAG’s). The cells within the tissues are fibroblasts (contain golgi and ER for packaging and exportation), which create ECM. Variation in the fibres and ground substance can lead to variations in the connective tissue.
Describe what collagen is and explain its function.
Collagen is a structural protein, which provides both tensile strength and structural support. There are approximately 16 types, however only 4 are primary types.
Explain the process of collagen biosynthesis.
Collagen is created inside the cell through a complex multistep process. The end product results in parts of a collagen fibre, with high tensile strength.
- Procollagen polypeptide chains are synthesized through the ribosomes on the rER, which are then secreted into the lumen.
- The chains are hydroxylated by proline and lysine residues, and twisted into a triple helix, which is then exported as procollagen (secreted by the extracellular space).
- The N and C terminals of the procollagen strands are cleaved off, and reassembled into fibrils, which is stabilized through the formation of covalent crosslinks.
Explain why the structure of collagen is important.
If the collagen is formed incorrectly, it can lead to reduced tensile strength as a result of collagen disorders. Examples of these collagen disorders include tissue laxity, joint hyper mobility and susceptibility to injury.
