Animal Tissues: Types and Organization

• Body tissue is an intermediate level of cellular organization where cells of similar origin and the extracellular matrix collaborate to perform specific bodily functions.
• Tissues are organized from cells, and further organize into organs, organ systems and ultimately an organism.

Levels of Organization

• Cells: Basic units of life (e.g., cardiomyocyte).
• Tissues: Cells of similar origin working together (e.g., muscle tissue).
• Organs: Collections of tissues performing specific jobs (e.g., heart).
• Organ System: Collection of cells, tissues, and organs working together (e.g., cardiovascular system).
• Organism: An entire multicellular living thing (e.g., human).

Types of Tissue

• There are epithelia, connective, muscle, and nervous tissues.

Epithelial Tissue

• Made of tightly connected cells arranged in sheets, forming barriers.
• Located in the skin, organ linings, and hollow organ cavities.
• Specialized for absorption, secretion, protection, separation, and sensation.
• Epithelial cells are polarized, having distinct apical (outer) and basal (inner) sides.
• The apical side faces the outside or the inside of a hollow organ and may be specialized for secretion or absorption.
• Lateral sides connect to adjacent epithelial cells via cell junctions, creating a strong barrier.
• The structure and shape of epithelial tissue vary based on its function.
• Cuboidal cells are cube-shaped, columnar cells are column-shaped, and squamous cells are flattened.
• Simple arrangement is a single layer, stratified is multiple layers, and pseudostratified appears multi-layered but is a single layer.

Epithelial Tissue Types

• Simple squamous: Found in alveoli and capillaries, facilitates diffusion.
• Simple cuboidal: Found in kidney tubules and glands, involved in secretion and absorption.
• Simple columnar: Found in ciliated tissues like bronchi, secretes mucus for protection.
• Pseudostratified columnar: Found in the upper respiratory tract, secretes mucus and protects.
• Stratified squamous: Found in the mouth and vagina, protects inner tissues.
• Stratified cuboidal: Found in sweat and mammary glands, secretes fluids and protects.
• Stratified columnar: Found in the male urethra and conjunctiva, protects and secretes.
• Transitional: Found in bladder, urethra, and ureters, allows for stretching and protects.
• Epithelial tissue originates from all three germ layers (ectoderm, mesoderm, and endoderm) during embryonic development.

Connective Tissue

• Binds organs and body parts together.
• The most abundant and widespread tissue type in the body.
• Has collagen, reticular, and loose fibers.
• Functions include supporting organs, transporting materials, storing energy, insulating, and protecting.
• Main classifications include connective proper, bone, blood, and cartilage.

Connective Tissue Subtypes

• Connective Proper:
  • Areolar: Found throughout the body, it is a packing material providing protection.
  • Adipose (fat): Found throughout the body, it insulates, protects, and regulates temperature.
  • Reticular: Found in lymph nodes, spleen, and bone marrow, it supports and protects.
  • Dense Regular: Found in tendons, ligaments, and fascia, it supports and binds.
  • Dense Irregular: Found in skin dermis and joint capsules, it handles multidirectional stress.
  • Elastic: Found in arterial blood vessels and bronchiole tubes, it regulates stretch.
• Bone:
  • Compact: Outer bone, protects and supports.
  • Trabecular: Inner bone, produces blood cells and reduces weight.
• Blood:
  • Found within blood vessels, it transports materials.
• Cartilage:
  • Elastic: Found in the external ear and epiglottis, it provides flexible support.
  • Hyaline: Found in the embryonic skeleton, ribs, nose, trachea, and larynx, it absorbs shock.
  • Fibrocartilage: Found in vertebral discs and knees, it cushions and withstands pressure.

Muscle Tissue

• Derived from the mesoderm, responsible for contraction.
• Exhibits excitability, allowing coordinated contraction.
• Functions include digestion, reproduction, movement, structure, and support.
• Three types: cardiac, skeletal, and smooth.

Muscle Tissue Types

• Cardiac:
  • Makes up the heart.
  • Striated and mononucleated.
  • Contains many mitochondria and myoglobin.
  • Intercalated discs enable wave-like contractions.
• Skeletal:
  • Striated and multinucleated.
  • Attached to the skeleton.
  • Controls voluntary movement.
• Smooth:
  • Non-striated and mononucleated.
  • Found in involuntary, hollow organs (e.g., digestive system, blood vessels).
  • Adjusts pupil size in the eyes.

Nervous Tissue

• Main tissue of the nervous system, responsible for communication, derived from the ectoderm.
• Functions include sensing, processing, responding to stimuli, and maintaining homeostasis.
• Two main types: neurons and glial cells.

Nervous Tissue Cells

• Neurons:
  • Electrochemical cells that send messages via electrical (action potential) and chemical (neurotransmitters) signals.
  • Have a cell body (soma), dendrites (receive signals), and an axon (sends signals to the axon terminal).
  • Sensory neurons: sense changes and send information to the brain.
  • Motor neurons: control actions and send information from the brain.
  • Interneurons: process information and connect other neurons.
• Glial cells:
  • Supporting cells that provide nutrients and support to neurons.
  • Types include Schwann cells, astrocytes, oligodendrocytes, and microglia.

Tissue Locations

• Epithelial Tissue: Skin, lining of hollow organs (uterus, stomach), lining of blood vessels, alveoli.
• Connective Tissue: Extracellular matrix, bone, cartilage, blood, adipose tissue.
• Muscle Tissue: Heart, skeletal muscles (biceps, triceps), inner layer of hollow organs (stomach, uterus).
• Nervous Tissue: Brain, spinal cord, nerves.

This lesson explores animal tissues, the level of cellular organization where cells collaborate. It discusses the organization from cells to organisms and describes the four main tissue types: epithelia, connective, muscle, and nervous.