Zoology Reviewer

TISSUES

Zygote – somatic cell; forms from process of fertilization

• It undergoes mitosis

Cellular differentiation – development process that results in the formation of different (specialized) cell type

THREE GERM LAYERS

• ECTODERM 

• gives rise to the central nervous system (the brain and spinal cord
• Ectodermal development is called neurulation in regard to nervous tissue

• MESODERM 

• gives rise to connective tissue, cartilage, and bone

• ENTODERM

• gives rise to the epithelial lining of the gastrointestinal and respiratory tracts

Tissues

• Group of cells that have similar structures and functions.
• Histology – study of tissues

Four Categories of Tissues

EPITHELIAL TISSUES

General Characteristics

1. Embryonic Origin: develop from all three germinal layers (ectoderm, mesoderm, endoderm)
2. cells adhere closely with each other
3. non-vascular
4. found on the body surface or lining body cavities

Classification of Epithelial Tissues

• Based on arrangement (layering) of cells

1. Simple – single layer of cells
2. Stratified – multiple layer of cells

• Based on the shape of the cells

1. Squamous (flat) - polygonal
2. Cuboidal – cubelike; shorter but wider
3. Columnar – taller and thinner

Simple Squamous Epithelium

• SHAPE: Flat, thin, tile –like or hexagonal
• LOCATION: Air sacs of the lungs, linings of the blood vessels, lining of the heart
• FUNCTION: Allows passage of materials by diffusion and filtration

Simple Cuboidal Epithelium

• SHAPE: Dice-like appearance
• LOCATION: Urinary tubules of the kidney, liver, pancreas, glands of the body
• FUNCTION: Secretion and absorption

Simple Columnar Epithelium with Goblet cells

• SHAPE: Longer, taller than wide
• LOCATION: Linings of the stomach & intestine
• FUNCTION: Absorption, enzyme secretion

*Goblet cells – secretes mucus (act as protective covering and coat the lining of the stomach)

Pseudostratified ciliated columnar Epithelium

• LOCATION: Linings of the trachea
• FUNCTION: Propels mucus, or reproductive cells by ciliary action

*Cilia – push out dust or any other foreign material that you inhale

Transitional Epithelium

• Cells change its shape.
• Cells are rounded when organ is empty and flattened when organ is stretched
• LOCATION: Found in the linings of the urinary bladder

Stratified Squamous Epithelium

TWO TYPES

1. Stratified Squamous Non-Keratinized

• No dead layers of cells
• Makes up the lining of the oral cavity, anal canal, vaginal canal.

1. Stratified Squamous Keratinized

• Composed of dead layers of cells
• Makes up the epidermis of our skin

*Melanin- secreted by the melanocytes; dark brownish protein pigment; protects the skin from UV rays

CONNECTIVE TISSUES

General Characteristics

1. Develop only from mesoderm
2. Consist of cells and intercellular matter secreted by the cells
3. Highly vascularized
4. To connect and support other tissues of the body

Classification of Connective tissue

• Type of cell present
• Type of intercellular matter secreted by the cell

Loose Connective Tissues

• LOCATION: Widely distributed under epithelial of human body
• FUNCTION: Wraps and cushion organs
• CELLS PRESENT:

• Fibroblasts – principal cell type; secrete proteins into the spaces between the cells

1. Collagen protein fibers – confer strength to tissues
2. Elastin protein fibers – confer elasticity to tissues

• Macrophages – engulf foreign agents
• Mast cells – secrete histamine (chemical mediator of inflammation)

Adipose Tissue

• LOCATION: Around kidneys, eyeballs and heart, skin, buttocks and breast
• FUNCTION: Provides reserve food for energy (fuel); Insulator of heat
• CELL PRESENT: adipocytes

Dense Fibrous Connective Tissues

• CELLS PRESENT: fibroblast (secretes collagen)
• INTERCELLULAR MATTER: Collagen protein fibers

TWO TYPES OF DENSE FIBROUS (based on the arrangement of protein fibers)

1. Dense Fibrous Regular Connective Tissues – protein fibers are arranged in parallel bundles, strong in one direction

• LOCATION:

Tendon – connects muscle to bone

Ligaments – connects bone to bone