ANAPHY-MIDTERM-NOTES

Animal Tissues

Overview of Multicellular Functions

• In unicellular organisms, all functions are performed by a single cell.

• In multicellular organisms, similar basic functions are carried out by organized groups of cells.

• Example: The Hydra has different types of cells, each in the thousands.

• The human body contains billions of cells to perform various functions.

• Tissues are groups of similar cells along with intercellular substances that perform specific functions.

• The organization of cells, tissues, organs, and organ systems illustrates the division of labor necessary for survival.

Definition of Tissues

• A tissue is a group of cells, along with intercellular substances, performing one or more functions.

• Tissues vary in structure and are classified into four main types:

  • Epithelial

  • Connective

  • Muscular

  • Neural

Epithelial Tissue

• Commonly referred to as epithelium (plural: epithelia).

• Features:

  • Free surface facing body fluids or external environments; provides coverings or linings.

  • Compactly packed cells with minimal intercellular matrix.

Types of Epithelial Tissues

1. Simple Epithelium: Single layer of cells.

   • Squamous Epithelium: Thin, flat cells; found in blood vessel walls and lung air sacs; functions in diffusion.

   • Cuboidal Epithelium: Found in gland ducts and kidney nephrons; functions in secretion and absorption; may have microvilli for increased surface area.

   • Columnar Epithelium: Tall cells; nuclei at bases; may have microvilli; located in the stomach and intestine; aids in secretion and absorption.

   • Ciliated Epithelium: Contains cilia on surface; moves particles/mucus; found in bronchi and fallopian tubes.

   • Glandular Epithelium: Specialized for secretion; can be unicellular (Goblet cells) or multicellular (salivary glands).

2. Compound Epithelium: Multi-layered; provides protection against chemical and mechanical stresses; locations include skin and lining of ducts.

Cell Junctions

• Specialized connections between epithelial cells:

  • Tight Junctions: Prevent leakage between cells.

  • Adhering Junctions: Cement adjacent cells together.

  • Gap Junctions: Allow communication between cells.

Connective Tissues

• Most abundant and widespread tissues in complex animals; link and support organs.

• Include varieties from soft to specialized types such as cartilage, bone, adipose, and blood.

• Fibroblast cells in connective tissues secrete structural proteins like collagen and elastin for strength and flexibility.

• Matrix: A modified polysaccharide that accumulates between cells and fibers.

Types of Connective Tissue

1. Loose Connective Tissue:

   • Areolar Tissue: Loosely arranged cells and fibers; acts as a support framework below the skin; contains fibroblasts, macrophages, and mast cells.

2. Dense Connective Tissue: Compact fibers; categorized as:

   • Dense Regular: Tendons (muscle to bone) and ligaments (bone to bone); fibers oriented in line.

   • Dense Irregular: Fibers oriented in various directions, providing strength; found in skin.

3. Specialized Connective Tissue:

   • Cartilage: Flexible, resistant to compression; contains chondrocytes in cavities within a matrix.

   • Bone: Hard, non-pliable matrix rich in calcium; supports/protects organs and facilitates movement.

   • Blood: Fluid tissue containing plasma, RBCs, WBCs, platelets; regulates transport of substances.

Muscle Tissue

• Comprised of long cylindrical fibers capable of contraction in response to stimulation. Functions to enable movement and maintain posture.

• Types of Muscle Tissue:

  1. Skeletal Muscle: Voluntary, striated, attached to bones; consists of long, parallel bundles of striated fibers.

  2. Smooth Muscle: Involuntary, non-striated; tapered ends; found in internal organs; operates without conscious control.

  3. Cardiac Muscle: Striated, involuntary; exclusively in the heart, enables synchronized contractions through intercalated discs.

Nervous Tissue

• Controls and coordinates body responses to stimuli; composed of excitable neurons and supporting neuroglial cells.

• Neurons can generate electrical impulses; neuroglia provide support and protection.

• Functions include:

  1. Responsiveness to stimuli.

  2. Information transmission from body parts to the brain.

  3. Execution of commands from brain to body parts.