Tissues

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Tissues
-Whole body contains only 200 different cells
types that are organized into tissues

• Four primary tissue classes
• epithelial tissue
• connective tissue
• muscular tissue
• nervous tissue

• The extracellular fluid surrounding the cells
  within tissue is called interstitial fluid

• Histology (microscopic anatomy)
• study of tissues and how they form organs

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Epithelial Tissue
-Covers the entire surface of the body

• includes skin, lining of the lung, lining of the
  digestive tract, lining of the urinary tract,
  lining of the reproductive tract

-barrier between what is IN the body and
what is OUT of the body
-controls what substances enter/exit the
body and what substances stay in/out of the body

• Primary tissue type found in glands

• exocrine glands
• secrete substances outside of the body (sweat,
  salivary, digestive)

• endocrine glands
• secrete substances (hormones) into the blood
  (thyroid, adrenal, pituitary, pancreas

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Epithelial Tissue Basic Structure

• Made of epithelial cells that are connected to
  adjacent cells by proteins called tight junctions
  
• make the tissue leakproof
• create sheets of epithelial cells
• similar in structure to a six-pack of cans
• Epithelial cell surfaces face 2 different
  environments
• apical surface of the cell faces toward the
  OUTSIDE of the body
• basal surface of the cell faces toward the INSIDE
  of the body
• Anchored to the body by a structure called the
  basement membrane

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Classification of Epithelial Tissues

• Epithelial tissue is classified based on 2
  criteria
• Cell shape
• squamous (flattened cells)
• cell width is larger than cell height
• cuboidal (cube-like cells)
• cell width is equal to cell height
• columnar (column-like cells)
• cell height is larger than cell width

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Classification of Epithelial Tissues

• Number of layers of epithelial cells
• Simple
• one cell layer thick
• transports substances into or out of the body
• Stratified
• more than one cell layer thick
• protects body from mechanical damage (abrasion,
  puncture)
• Pseudostratified
• one cell layer thick made of different cell types

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Epithelia Simple Squamous

• single layer of squamous epithelial cells with
  flat nuclei

Small intestine and cheek
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Epithelia Simple Cuboidal

• single layer of cuboidal epithelial cells with
  spherical nuclei

Kidney
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Epithelia Simple Columnar

• single layer of columnar cells with oval nuclei

Interior of small intestine
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Epithelia Pseudostratified Columnar

• single layer of cells with different heights
  some do not reach the surface of the body
• the shape of the nuclei is similar to the shape
  of the cell

Trachea
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Epithelia Stratified Squamous

• thick epithelium composed of several layers of
  squamous cells with flat nuclei

Vagina
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Epithelia Stratified Cuboidal and Columnar

• Rare in the body
• Stratified cuboidal
• 2-3 layers of cuboidal cells with spherical
  nuclei

Sweat gland
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Epithelia Transitional

• The shape of the cells change based on the amount
  of stress (stretch) on the tissue
• can appear as cuboidal or columnar when not
  stretched or squamous when stretched

Umbilical cord and Urinary bladder
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Connective Tissue
-Most abundant and variable tissue type

• Consists of widely spaced cells separated by
  fibers and ground substance

-4 primary types

• Connective tissue proper
• characterized by histological appearance
• loose
• dense

• Cartilage
• Bone
• Blood

• Functions
• connects organs to each other
• gives support protection (physical immune)
• storage of energy heat production
• transport of materials

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Structural Elements of Connective Tissue
3 structural elements (components) of connective
tissue

• Ground substance
• unstructured (gel-like) material that fills the
  space between cells (interstitial space)

• Fibers
• very large proteins outside of the cell which
  make a web-like structure to hold the tissue
  together

-Ground substance fibers Extracellular Matrix

• Cells
• create the extracellular matrix by exocytosis

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Structural elements of connective tissue
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Fibers
3 primary types of extracellular protein fibers

• Collagen
• very thick and strong, do not stretch
• provides tough structure to tissue

• Elastic
• thin and strong, allow for stretch and then
  recoil (return to original length) when released
• made from the protein elastin

• Reticular
• thin collagen fibers
• provide delicate structure to tissue

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Cells
There are 4 different cell types which are
responsible for making the 4 different types of
connective tissue

• blast to build

• Fibroblasts
• connective tissue proper

• Chondroblasts
• cartilage

• Osteoblasts
• bone

• Hemocytoblast
• blood

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Loose Connective Tissue Proper Areolar
Walls of abdomen
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Loose Connective Tissue Proper Adipose

• stores lipids for use as fuel, insulates and
  protects

Under skin
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Loose Connective Tissue Proper Reticular
Kidney
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Dense Connective Tissue Proper Regular

• many parallel collagen fibers with a few elastic
  fibers
• attaches muscles to bone (tendons) and bone to
  bone (ligaments)

Tendons and ligaments
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Dense Connective Tissue Proper Irregular

• many non-parallel collagen fibers with a few
  elastic fibers

Skin - Dermis
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Connective Tissue Cartilage

• 3 types
• Hyaline
• Fibrocartilage
• Elastic
• made of chondrocytes found in a lacuna (pit)
  within the firm but flexible extracellular matrix
  comprised of a network of collagen fibers

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Ossification is the gradual replacement of
cartilage with bone
Occurs slowly so that by adulthood cartilage
remains in a limited number of places
- such as the ears, trachea, nose and between the
bones
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