Chapter 4 - Tissues Flashcards
Histology
study of tissues
4 types of Tissues:
- Epithelial - lining, covering, glands
- Connective - support (ie. bone, cartilage)
- Nervous - control
- Muscle - movement
Cell Junctions
membrane connections between neighboring cells; not all tissues have cell junctions but epithelial has a lot
3 Types of Cell Junctions:
- Tight junctions - prevents materials from crossing cell layers; important in epithelial tissues (ex. lining of stomach)
- Desmosomes - anchoring junctions; ex. skin cells (outer layer of skin), hair cells
- Gap junctions - communication junctions; ex. heart-cardiac muscle–cells in heart receive signals @ same time & muscles must contract at same time
Membrane Specialization; Microvilli
highly folded plasma membrane; increases surface area for absorption; ex. small intestines (absorption occurs rapidly)
Characteristics of Epithelial Tissue–most exposed tissue in body
- closely packed cells
- specialized contacts - tight junctions & desmosomes most common
- polarity-has top (apical) & bottom layer (basal)
- supported by connective tissue - always next to it
- avascular - no direct blood supply
- innervated - has nerves
- highly regenerative - replaces cells rapidly
Apical Surface
surface exposed; not attached; top
Basal surface
attached to underlying tissue; connective tissue is ALWAYS next to epithelial tissue
Avascular
no blood vessels; connective tissue is usually vascular–blood vessels in it that supplies epithelial
Glandular Epithelial Tissue
gland - one or more cells that secrete a particular product (usually by exocytosis); product released - secretion (water-based fluid that usually contains protein)
3 Ways to Describe Gland:
- # of cells
- What it secretes
- How it secretes
of Cells (Glands):
a. unicellular - 1 cell; ex. goblet cell–secretes mucous
b. multicellular - many cells; all glands are multicellular except one (goblet cell)
What it Secretes (glands):
a. Endocrine gland-secretes hormones; always secretes into interstitial fluid; ductless gland; blood system transports hormone around; ex. thyroid gland
b. Exocrine glands-secretes a non-hormone product; secretes into a tube; usually have ducts; secrete into a specific part of the body; ex. sweat glands
How It Secretes:
a. Merocrine - secretes by exocytosis; most common type of secretion; cell not harmed at all
b. Apocrine - pinches off the apical portion; only 1 example–fat secretion in mammary glands; loses a portion of itself
c. Holocrine - releases contents by cell rupture; cell self-destructs; ex. subaceous glands; releases oil & cell fragments
Sebum
combo of oil & cell fragments
Characteristics of Connective Tissue (CT)
most diverse & most abundant tissue;
- common origin - come from one type of CT–mesenchyme (embryonic CT)
- vary in vascularization
- composed mainly of extracellular matrix
Vascularization of CT
- cartilage - avascular
- dense CT - poorly vascularized
- loose CT, bone, blood - richly vascularized
Extracellular
outside of cell; non-living material; support tissue of body; has to hold up body; needs cells strong enough to hold up body; fibers & ground substance
Components of CT
- Fibers
- Ground substance
- Cells
Types of Fibers (CT)
extracellular; fibrous proteins;
a. Collagen - most abundant protein found in body; tough; built like a rope
b. Elastic - stretchy
c. Reticular - thin for lighter support; thin collagen
Types of Ground Substance (CT):
fills in spaces between fibers & cells;
a. fluid - mostly water
b adhesion proteins
c. proteoglycans - part protein & part carb; function–negatively charged (carb groups); attract water (hold the water)
Extracellular Matrix
bulk of connective tissue
Types of Cells (CT):
living units are what makes the fibers & ground substance
- loose & dense CT
- cartilage
- bone tissue
- blood
Loose & Dense CT (Cells)
CT proper;
FIBROBLASTS - immature young cells that are productive; responsible for making materials unique to loose dense CT;
FIBROCYTES - older cells; no longer able to make fibers
