CH4: Level of Organization of Tissues Flashcards
What is a tissue?
A tissue is a group cells with a common function and embryonic origin which carry out specialized activities
Name the 4 type of tissue and their functions
Epithelial: This tissue type covers body surfaces and lines hollow organs, body cavities, and ducts; it also forms glands. This tissue allows the body to interact with both its internal and external environments
Connective: Protects and supports the body and its organs. Various types of connective tissues bind organs together, store energy reserves as fat, and help provide the body with immunity to disease-causing organisms
Muscular: Is composed of cells specialized for contraction and generation of force. In the process, muscular tissue generates heat that warms the body
Nervous detects changes in a variety of conditions inside and outside the body and responds by generating electrical signals called nerve action potentials (nerve impulses) that activate muscular contractions and glandular secretions
Name the junction types and their functions
Tight junctions: Type of junction which contain a weblike transmembrane which seals of passageway between proteins by bringing plasma membranes of adjacent cells together. Inhibits contents from blood or other tissue leaking into the cell
Adhering junctions: resist separation during various contractile activities, such as when food moves through the intestines
Desmosomes: prevent epidermal cells from separating under tension and cardiac muscle cells from pulling apart during contraction
Hemidesmosomes: facilitate the stable adhesion of basal epithelial cells to the underlying basement membrane
Gap junctions: facilitate direct communication and the exchange of ions, molecules, and small metabolites between adjacent cells.
Differences between connective and epithelial
Epithelial tissue lack blood vessels and are more closely packed with less ecf between them, epithelial tissue almost always forms surface layers and is not covered by another tissue
General features of epithelial tissue
Cells are arranged in sheets and are densely packed due to the presence of cell junctions
Epithelial cells attach to a basement membrane
Epithelial tissue is avascular but does have a nerve supply
Mitosis occurs frequently because epithelial cells are often under stress resisting seperation
Name the two types of epithelial tissue and their functions
Surface epithelium is the covering and lining epithelium is responsible for covering and lining external and internal surfaces, like the skin, blood vessels, body cavitites etc
Glandular epithelium makes up the secreting portion of glands, such as the thyroid gland, suprarenal (adrenal) glands, sweat glands, and digestive glands.
Name the surfaces of epithelial tissue:
The apical surface, also known as the free surface, is the surface facing the body surface and often contains cilia or microvilli
The lateral surface of epithelium is the surface adjacent to other cells, which contains several tight junctions
The basal surface is the deepest surface which often binds to extracellular material like the basement membrane
Describe the two ways epithelial cells are categorized
The arrangment of cells into layers:
Simple epithelium: Single layer of cells that function for osmosis, diffusion, secretion, absorption
Pseudostratified: Appears to have multiple layers of cells because the cell nuclei lie at different levels and not all cells reach the apical surface; it is actually a simple epithelium because all its cells rest on the basement membrane
Stratified epithelium: Consists of two or more layers of cells that protect underlying tissues in locations where there is considerable wear and tear
Cell shapes:
Squamous: Flat and thin, allows the flow of substances through them quickly
Cuboidal cells are as tall as they are wide and are shaped like cubes or hexagons. They may have microvilli at their apical surface and function in either secretion or absorption
Columnar cells are much taller than they are wide, like columns, and protect underlying tissues. Their apical surfaces may have cilia or microvilli, and they often are specialized for secretion and absorption
Transitional cells change shape, from squamous to cuboidal and back, as organs of the urinary system such as the urinary bladder stretch (distend) to a larger size and then collapse to a smaller size
Name where the following epithelia are found and its structure/function
Simple Squamous:
Simple Cuboidal:
Simple columnar (ciliated and non-ciliated):
Pseudostratified columnar epithelium (nonciilated and ciliated)
Keratinized stratified squamous epithelium:
Non-keratinized stratified squamous epithelium
Stratified cuboidal epithelium:
Stratified columnar epithelium:
Urothelium or transitional epithelium (lines most of urinary tract):
Simple Squamous: Single layered flat cells that function for absorption and filtration. Lines lymphatic and cardiovascular system (endothelium) and serous membranes (mesothelium)
Simple cuboidal: Single layer of cuboidal shaped cells that function for secretion and absorption. Found in glandular (secreting) tissue and kidney tubules
Simple columnar (ciliated): Single layer of non ciliated column shaped cells. Lines GI tract and ducts of many glands, and gall blader. Functions for secretion and absorption.
Simple columnar (nonciliated): : A single layer of ciliated column like cells with oval nuclei near base of cells. Lines digestive tract and female reproductive system
Pseudostratified columnar epithelium (nonciilated): Single deceptive layer of columnar cells. Lines epididymis, larger ducts of many glands and parts of male urethra, and functions for absorption and secretion
Pseudostratified columnar epithelium (Ciliated): Again, not really layered, it is pseudo-layered. Contains cells that extend to surface and secrete mucus (goblet cells) or bear cilia. Lines airways of most upper respiratory tract. Secretes mucus that traps foreign particles, and cilia sweep away mucus for elimination from body.
Keratinized stratified squamous epithelium: Most superficial layer of skin.
Non-keratinized stratified squamous epithelium: usually bears a mucous membrane, which serves as an additional protective and lubricating layer of the epithelium. It may be seen in the some parts of the oral cavity, pharynx, esophagus, distal ureters, vagina and external female genitalia.
Stratified cuboidal epithelium: Has two or more layers of cells; cells in apical layer are cube-shaped; fairly rate type. Found in ducts of adult sweat glands and esophageal glands, part of male urethra. Functions for limited secretion and protection
Stratified columnar epithelium: Basal layers consist of shortened, irregularly shaped cells; only apical layer has columnar cells; uncommon. Lines part of urethra; large excretory ducts of some glands, such as esophageal glands; small areas in anal mucous membrane; part of conjunctiva of eye. Functions to protect and secrete
Urothelium or transitional epithelium (lines most of urinary tract): Has a variable appearance (transitional). In relaxed or unstretched state, looks like stratified cuboidal epithelium, except apical layer cells tend to be large and rounded. As tissue is stretched, cells become flatter, giving the appearance of stratified squamous epithelium.
Difference between endocrine and exocrine glands
Endocrine glands secrete hormones into the bloodstream for widespread effects rather than into ducts.
Exocrine glands secrete hormones into ducts which reach an epithelial surface
Unicellular vs multicellular exocrine glands
Unicellular exocrine glands mainly are goblet cells, which are cells that secrete mucus directly onto the apical surface of an epithelial lining
Multicellular exocrine glands are more numerous and contain many cells that form a macroscopic or microscopic structure, such as sudoriferous glands or sebaceous glands.
How are exocrine cells functionally classified, and name these classes, giving a description and example
Exocrine glands are functionally classified by how their secretions are released
Merocrine glands: In merocrine glands, the ribosomes of the rough endoplasmic reticulum synthesize a secretion which the golgi apparatus, processes, sorts and packages into vesicles. They are then removed from the cell via exocytosis. Examples include sweat glands and pancreas.
Apocrine glands: In apocrine glands, the secretory product accumulates on the apical surface of the epithelium. That portion of the cell then pinches off via exocytosis, and the process repeats. Examples of this include the mammary gland.
Holocrine: The secretory product in holocrine glands is made inside the cell, and as the cell matures, it ruptures, releasing the secretion. Because the cell ruptures in this mode of secretion, the secretion is high in lipids of the plasma membrane and intracellular membranes.
Functions of connective tissue
Variety of functions:
Storing fat,
Supporting organs,
Protects and insulates internal organs
Blood is connective tissue, which has its obvious functions, Compartmentalizes organs
Features of connective tissue
Lots of space in extracellular fluid
Highly vascularized (except tendons and cartilage)
Lacks free surfaces
Consists of two components: cells ad extracellular matrix
What is the extracellular matrix
The extracellular matrix is the part of connective tissue that fills the space between cells. It consists of ground substance and protein fibers
