Animal Tissues: Epithelial, Muscle, Nervous, Connective

Epithelial Tissue

Lining Epithelia

• Simple Epithelia: Flattened cells (endothelium) lining capillaries and blood vessels.
• Polyhedral Cells: Lining the inside of the intestine (villi).

Stratified Epithelia

Formed by several layers of cells. Lining the mouth, esophagus, and vagina.

Glandular Epithelia

• Endocrine Glands: Ductless; empty secretions into the blood.
• Exocrine Glands: Secretion to the exterior (e.g., sweat glands, shedding skin).

Muscle Tissue

Responsible for movements.

Striated Muscle Fiber

Contractile element involves myofibrils (actin and myosin).

• Skeletal Muscle: Voluntary reaction, responsible for skeletal movement.
• Heart Muscle: Involuntary reaction.

Smooth Muscle

Cells are uninucleate and fusiform (found in invertebrates).

Nervous Tissue

Responsible for reception of stimuli and transporting them.

• Neuron (Basic Unit):
  • Soma: Neuron's body.
  • Dendrites: Extensions receiving stimuli.
• The neuron transforms stimuli transported through a long extension called the axon.
• Synapses: The functional connection between two or more neurons or an organ and neurons.
• Neuroglia: A variety of non-nerve cells providing metabolic functions and support (e.g., Schwann cell, which surrounds the axon of many neurons).

Connective Tissue

Cells are scattered and show little variety.

Components

• Intercellular Substance (Space between cells):
  • Fiber Protein: Contains much collagen and elastin.
  • Gelatinous Fundamental Substances: Contain polysaccharides.

Tissue Types

Loose Connective Tissue

Fills space between organs and other tissues.

• Fibrocytes: Manufacture intermolecular chemicals (e.g., make elastin).
• Macrophages: Eliminate invaders and remains (useful in tissue vessels).
• Adipocytes: Store fat.

Dense Connective Tissue

Tissue poor in cells but rich in collagen fibers (found in tendons and ligaments).

Cartilaginous Tissue

Soft and flexible.

Chondrocytes: Involved in intercellular substance, protein fibers, and tissue consistency.

Bone Tissue

The most resistant substance due to the deposition of mineral salts (mineralization).

• Compact Bone: Laminated structure featuring the Haversian system (a set of cylindrical lamellae structure).
• Spongy Bone Tissue: Found in the epiphysis of long bones and in the marrow cavities.