The biological levels of organization atoms-biomolecules-cells-tissues(group of similar cells)-organs-organ systems. In this course we will consider tissues, organs and organ systems.
A tissue is composed of similar specialized cells that perform a common function in the body:
There are 4 main type of tissues found in the human body:
Epithelial tissue-covers bodysurfaces and lines body cavities
Connective tissue- binds and supports body parts
Muscular tissue- moves the body and its parts
Nervous tissue- receives stimuli and conducts nerve impulses
Consists of tightly packed cells that form a continuous layer
Covers surfaces and lines body cavities
Has many functions:
Protection- from injury , drying out ,invasion of pathogensSecretion- you led out a substance for a special purpose, oil secretion , oil is necessary, sweat
Absortion- of molecules from kidneys and intestines
Excretion- trash , waste product , let it out
Types of Epithelium
Single- one layerStratified- 2 or morelayers
Pseudostratified- looks like stratified but is not.
Basement membrane below epithelium
A basement membrane joins epithelium to underlying connective tissue.
It is composed of a glycoprotein secreted by the epithelium and collagen fibers secreted by the connective tissue
Classification of epithelial tissue
Epithelium is classified according to the shape of itscells and the number of layers in the tissue.
Columnar – rectangular
Number of layers
Simple- one layer
Stratified- two or more layers
Transitional- six or more layers
Epithelium that secretes a product is a gland.
A gland can be a single epithelial cell such as a goblet cell that secretes mucus , or various cells.
Exocrine glands- secretetheir products into ducts
Endocrine glands- secrete their products directly into the bloodstream
Mixed glands- are glands that are both endocrine and exocrine
Connective tissue : characteristics
Connective tissue consists of a matrix, cells, and fibers
The matrix is a noncelular material secreted by the cells,that varies in consistency from liquid to solid.
The matrix can have 1 of 3 typesof fibers which are also produced by the cells:
Collagen fibers- give flexibility and strength
Reticular fibers- support networks
Elastic fibers- give elasticity
Example of queratin : nails and hair
Collagen: in bones and below the skin is connective tissue
Connective tissue : functions
Connective tissue has the following functions:
-.Binds organs together
-.Provides support andprotection
-.Produces blood cells
Connective tissue : types
Loose fibrous connective tissue – covers muscle, supports epithelium and internal organs.
Dense fibrous connective tissue –has cells called fibroblasts , a jellylike matrix with collagen and elastic fiber , and is found in
Tendons- connect muscle to bone
Ligaments-connect bone to bone
Adipose tissue consists of fibroblasts that can enlarge and store fat.
It is found beneath skin, around kidneys and on the heart.
Its functions include energy storage, insulation, and organ protection.
Connective tissue: reticular
Reticular connective tissue forms the supporting meshwork of lymphoid tissue in lymph nodes, spleen, thymus and bone marrow.
All types of blood cells areproduced in the bone marrow.
Connective tissue :cartilage
Cartilage is a connective tissue consisting of cells called condrocytes which lie in chambers called lacunae separated by a matrix that is solid but flexible. Fibers found in the matrix determine the type of cartilage.
-.Hyaline cartilage- contains only very fine collagen fibers and is found in the nose, ends of long bone, and the fetal...
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