Biology: Cell Tissues and Organs

Cell Basic Unit of Life

• The basic unit of life is a cell.
• Groups of cells that are similar in structure and function form tissues.
• There are four basic types of animal tissues: Epithelial, Connective, Muscular, and Nervous.

Epithelial Tissue

• Epithelial tissue is all tissues that are in contact with the external world.
• It has all the basic functions:
  • Protects underlying tissues (e.g. skin, epithelial lining of internal organs)
  • Absorbs (e.g. digestive and renal systems)
  • Secretes (e.g. glands)
  • Filters (e.g. small blood vessels in kidneys)
  • Excretes (e.g. digestive system)
  • Receives stimuli (e.g. sensory glands in mouth)

Epithelial Tissue Features

• Found in a continuous surface that forms a lining or covering.
• Avascular, meaning it is not directly supplied by blood vessels.
• Supplied by underlying connective tissue.
• Very regenerative.
• Cells are often joined tightly together and form thin sheets.

Classification of Epithelial Tissue Based on Shape

• Squamous cells:
  • Flattened or scale-like.
  • Classified as either simple or stratified.
  • Found in sites where filtration or diffusion takes place (e.g. alveoli of lungs, lining of blood vessels, serous membranes, inner lining of heart).
• Cuboidal cells:
  • As tall as they are wide.
  • Form a barrier and can secrete or absorb.
  • Found in glands, ducts, kidney tubules, small ducts of many glands, and upper respiratory tract.
• Columnar cells:
  • Taller than they are wide.
  • Function to protect, secrete, and absorb.
  • Found in lining of stomach, intestines, gallbladder, uterus, and some ducts of glands.

Classification of Epithelial Tissue Based on Arrangement

• Simple epithelium:
  • Has just a single layer.
  • Easily damaged, but effective for absorption, secretion, and filtration.
  • Named for the shape of the cell and arranged in a single layer.
• Stratified epithelium:
  • Has two or more layers of cells.
  • For protection.
  • The cells at the surface of the stratified tissue are usually flattened.

Characteristics and Locations of Epithelial Cells

• Squamous epithelial cells:
  • Thin, irregularly shaped cells.
  • Protect underlying tissues.
  • Found in surfaces that are subject to large amounts of friction (e.g. lining of mouth, inner layer of blood vessels).
• Stratified squamous epithelial cells:
  • Composed of squamous cells that are protecting the body and some glands.
• Transitional epithelium:
  • Has an ability to stretch.
  • Found in urinary bladder, ureters, and proximal part of the urethra.
  • Allows these organs to expand and contract as needed.

Connective Tissue

• The support and type of tissue which protects other tissues.
• Has specialized cells, ground substance, and fibers.
• Functions:
  • Binds and supports organs.
  • Provides protection for delicate organs.
  • Insulates the body.
  • Transports substances.
  • Stores energy reserves.

Types of Connective Tissue

• Loose connective tissue:
  • Includes areolar tissue, adipose tissue, and reticular tissue.
• Dense connective tissue:
  • Includes dense regular and dense irregular connective tissue.
  • Strong and durable.
  • Found in tendons, ligaments, and dermis of skin.

Cartilage

• Provides a firm but flexible support for the body.
• Lacks blood vessels.
• Nutrition diffuses through the matrix from surrounding connective tissues.
• Types of cartilage:
  • Hyaline cartilage:
    • Weakest type of cartilage.
    • Found in articular surfaces of bones.
  • Elastic cartilage:
    • Matrix contains many elastic fibers.
    • Found in external ear and epiglottis.
  • Fibrocartilage:
    • Strongest type of cartilage.
    • Found in intervertebral discs, knee joints, and symphysis pubis.

Human Connective Tissue

• Most abundant and widely distributed of the four basic types of tissues.

• Connects, supports, and protects body organs.

• Cells of connective tissue are scattered in a nonliving matrix.

• Matrix consists of protein fibers and a ground substance.

• Specialized connective tissues include cartilage, bone, and blood.### Blood Components

• There are three types of formed elements in blood: red blood cells, white blood cells, and platelets.

• Blood cells are produced in red bone marrow.

• Blood has various functions, including transportation of oxygen, carbon dioxide, nutrients, wastes, and hormones.

Blood Circulation

• Blood circulates steadily through the body, supplying cells with nutrients and oxygen.
• Blood also transports wastes away from the body.

Lymph Tissue

• Lymph is a fluid composed of water, lymphocytes, and other cells.
• It is a vital part of the immune system and the lymphatic system.
• Lymph fluid flows through the vessels of the lymphatic system, draining interstitial fluid from tissues and carrying it to the blood.

Tissue Functions

• The tissue system provides nourishment to the body, supporting the life of other tissues.
• It provides protection to the body with its outermost layer.
• The tissue system transports nutrients throughout the body.
• It serves as a communication network, delivering messages via nerves and hormones.
• The tissue system provides a framework, such as bones and cartilage, supporting the rest of the body.
• It is also involved in reproduction, forming the structure of sex organs.

Cell Basic Unit of Life

• The basic unit of life is a cell.
• Groups of cells that are similar in structure and function form tissues.
• There are four basic types of animal tissues: Epithelial, Connective, Muscular, and Nervous.

Epithelial Tissue

• Epithelial tissue is all tissues that are in contact with the external world.
• It has all the basic functions:
  • Protects underlying tissues (e.g. skin, epithelial lining of internal organs)
  • Absorbs (e.g. digestive and renal systems)
  • Secretes (e.g. glands)
  • Filters (e.g. small blood vessels in kidneys)
  • Excretes (e.g. digestive system)
  • Receives stimuli (e.g. sensory glands in mouth)

Epithelial Tissue Features

• Found in a continuous surface that forms a lining or covering.
• Avascular, meaning it is not directly supplied by blood vessels.
• Supplied by underlying connective tissue.
• Very regenerative.
• Cells are often joined tightly together and form thin sheets.

Classification of Epithelial Tissue Based on Shape

• Squamous cells:
  • Flattened or scale-like.
  • Classified as either simple or stratified.
  • Found in sites where filtration or diffusion takes place (e.g. alveoli of lungs, lining of blood vessels, serous membranes, inner lining of heart).
• Cuboidal cells:
  • As tall as they are wide.
  • Form a barrier and can secrete or absorb.
  • Found in glands, ducts, kidney tubules, small ducts of many glands, and upper respiratory tract.
• Columnar cells:
  • Taller than they are wide.
  • Function to protect, secrete, and absorb.
  • Found in lining of stomach, intestines, gallbladder, uterus, and some ducts of glands.

Classification of Epithelial Tissue Based on Arrangement

• Simple epithelium:
  • Has just a single layer.
  • Easily damaged, but effective for absorption, secretion, and filtration.
  • Named for the shape of the cell and arranged in a single layer.
• Stratified epithelium:
  • Has two or more layers of cells.
  • For protection.
  • The cells at the surface of the stratified tissue are usually flattened.

Characteristics and Locations of Epithelial Cells

• Squamous epithelial cells:
  • Thin, irregularly shaped cells.
  • Protect underlying tissues.
  • Found in surfaces that are subject to large amounts of friction (e.g. lining of mouth, inner layer of blood vessels).
• Stratified squamous epithelial cells:
  • Composed of squamous cells that are protecting the body and some glands.
• Transitional epithelium:
  • Has an ability to stretch.
  • Found in urinary bladder, ureters, and proximal part of the urethra.
  • Allows these organs to expand and contract as needed.

Connective Tissue

• The support and type of tissue which protects other tissues.
• Has specialized cells, ground substance, and fibers.
• Functions:
  • Binds and supports organs.
  • Provides protection for delicate organs.
  • Insulates the body.
  • Transports substances.
  • Stores energy reserves.

Types of Connective Tissue

• Loose connective tissue:
  • Includes areolar tissue, adipose tissue, and reticular tissue.
• Dense connective tissue:
  • Includes dense regular and dense irregular connective tissue.
  • Strong and durable.
  • Found in tendons, ligaments, and dermis of skin.

Cartilage

• Provides a firm but flexible support for the body.
• Lacks blood vessels.
• Nutrition diffuses through the matrix from surrounding connective tissues.
• Types of cartilage:
  • Hyaline cartilage:
    • Weakest type of cartilage.
    • Found in articular surfaces of bones.
  • Elastic cartilage:
    • Matrix contains many elastic fibers.
    • Found in external ear and epiglottis.
  • Fibrocartilage:
    • Strongest type of cartilage.
    • Found in intervertebral discs, knee joints, and symphysis pubis.

Human Connective Tissue

• Most abundant and widely distributed of the four basic types of tissues.

• Connects, supports, and protects body organs.

• Cells of connective tissue are scattered in a nonliving matrix.

• Matrix consists of protein fibers and a ground substance.

• Specialized connective tissues include cartilage, bone, and blood.### Blood Components

• There are three types of formed elements in blood: red blood cells, white blood cells, and platelets.

• Blood cells are produced in red bone marrow.

• Blood has various functions, including transportation of oxygen, carbon dioxide, nutrients, wastes, and hormones.

Blood Circulation

• Blood circulates steadily through the body, supplying cells with nutrients and oxygen.
• Blood also transports wastes away from the body.

Lymph Tissue

• Lymph is a fluid composed of water, lymphocytes, and other cells.
• It is a vital part of the immune system and the lymphatic system.
• Lymph fluid flows through the vessels of the lymphatic system, draining interstitial fluid from tissues and carrying it to the blood.

Tissue Functions

• The tissue system provides nourishment to the body, supporting the life of other tissues.
• It provides protection to the body with its outermost layer.
• The tissue system transports nutrients throughout the body.
• It serves as a communication network, delivering messages via nerves and hormones.
• The tissue system provides a framework, such as bones and cartilage, supporting the rest of the body.
• It is also involved in reproduction, forming the structure of sex organs.