Detailed notes – 2 – chapter 6 – class 9

6.3 Animal Tissues

1. Movement and Muscle Cells:

   • Specialized cells called muscle cells are responsible for movement in the body.
   • Contraction and relaxation of these muscle cells result in the movement of body parts, such as the chest during breathing.

2. Oxygen Absorption and Transport:

   • During breathing, oxygen is inhaled and absorbed in the lungs.
   • Oxygen is then transported to all body cells through the bloodstream.

3. Importance of Oxygen for Cells:

   • Cells require oxygen for various metabolic processes, including cellular respiration, which occurs in mitochondria.
   • Mitochondria utilize oxygen to generate energy in the form of ATP, which is essential for cell function and survival.

4. Functions of Blood:

   • Blood serves as a transport medium, carrying oxygen, nutrients, and other substances to all cells of the body.
   • It also collects metabolic wastes from cells and transports them to organs like the liver and kidneys for disposal.

5. Types of Animal Tissues:

   • Animal tissues can be classified into different types based on the functions they perform.
   • Examples include:
     • Epithelial tissue: Covers surfaces and lines body cavities, providing protection and secretion.
     • Connective tissue: Supports, connects, and protects various body structures, including blood.
     • Muscular tissue: Contracts and generates force to produce movement.
     • Nervous tissue: Coordinates and transmits signals within the body, facilitating communication and control.

6. Blood and Muscles as Examples of Tissues:

   • Blood is classified as a type of connective tissue, as it connects and transports various substances throughout the body.
   • Muscles form muscular tissue, which contracts and generates force to produce movement in the body.

6.3.1 EPITHELIAL TISSUE

1. Role of Epithelial Tissues:

   • Epithelial tissues serve as covering or protective layers in the animal body, covering most organs and cavities within.
   • They form barriers that keep different body systems separate and regulate the exchange of materials between the body and the external environment, as well as between different parts of the body.

2. Characteristics of Epithelial Tissues:

   • Epithelial tissue cells are tightly packed and form a continuous sheet, with only a small amount of cementing material between them and almost no intercellular spaces.
   • Regardless of the type, all epithelium is usually separated from the underlying tissue by an extracellular fibrous basement membrane.

3. Types of Epithelial Tissues and Their Functions:

   • Simple Squamous Epithelium: Found in areas where transportation of substances occurs through a selectively permeable surface, such as blood vessels, lung alveoli, esophagus, and the lining of the mouth. These cells are extremely thin and flat, facilitating exchange.
   • Stratified Squamous Epithelium: Found in the skin and areas requiring protection, consisting of multiple layers of squamous epithelial cells to prevent wear and tear.
   • Columnar Epithelium: Present in areas where absorption and secretion occur, such as the inner lining of the intestine. These cells are tall and facilitate movement across the epithelial barrier.
   • Ciliated Columnar Epithelium: Found in the respiratory tract, characterized by the presence of cilia on the outer surfaces of epithelial cells. Cilia movement helps clear mucus.
   • Cuboidal Epithelium: Forms the lining of kidney tubules and ducts of salivary glands, providing mechanical support.
   • Glandular Epithelium: Specialized epithelial cells that can secrete substances at the epithelial surface. Multicellular glands may form when a portion of the epithelial tissue folds inward.

6.3.2 CONNECTIVE TISSUE

1. Connective Role:

   • Connective tissue provides structural support and binds various tissues and organs together within the body.
   • It forms a network of fibers and cells that help hold organs in place and maintain their shape and integrity.

2. Supportive Function:

   • Connective tissue supports and cushions organs and structures, providing mechanical support and protection against external forces.
   • It forms the framework upon which other tissues and organs are built, providing structural integrity to the body.

3. Matrix Composition:

   • Connective tissue consists of cells that are loosely spaced within an intercellular matrix.
   • The matrix can vary in consistency, being jelly-like, fluid, dense, or rigid, depending on the specific function of the connective tissue.

4. Examples of Connective Tissues:

   • Connective tissues include a variety of types such as bone, cartilage, adipose tissue (fat), blood, and loose or dense connective tissue proper.
   • Each type of connective tissue has a distinct matrix composition and structure tailored to its specific function within the body.

5. Concordance with the Introduction:

   • The introduction likely refers to the concept that connective tissue helps “connect” various parts of the body together, thus supporting the body’s overall structure and function.
   • By providing support, binding, and connecting various tissues and organs, connective tissue plays a vital role in maintaining the body’s overall organization and function.

6.3.3 MUSCULAR TISSUE

1. Composition and Function:

   • Muscular tissue consists of elongated cells, also known as muscle fibers, responsible for movement in the body.
   • These muscle fibers contain contractile proteins that enable them to contract and relax, thus causing movement.

2. Skeletal Muscles:

   • Skeletal muscles, also known as voluntary muscles, are mostly attached to bones and facilitate body movement.
   • Under the microscope, skeletal muscles exhibit alternate light and dark bands or striations when appropriately stained, hence they are called striated muscles.
   • Skeletal muscle cells are long, cylindrical, unbranched, and multinucleate, containing many nuclei.

3. Smooth Muscles:

   • Smooth muscles, also known as involuntary muscles, control movements such as the movement of food in the alimentary canal or the contraction and relaxation of blood vessels.
   • These muscles are found in various organs such as the iris of the eye, ureters, and bronchi of the lungs.
   • Smooth muscle cells are long with pointed ends (spindle-shaped) and uninucleate, containing a single nucleus.
   • They are called unstriated muscles because they lack the striations or alternating light and dark bands seen in skeletal muscles.

4. Cardiac Muscles:

   • Cardiac muscles are involuntary muscles found in the heart, responsible for rhythmic contraction and relaxation throughout life.
   • These muscle cells are cylindrical, branched, and uninucleate, containing a single nucleus.

6.3.4 NERVOUS TISSUE

1. Specialization for Rapid Communication:

   • Nervous tissue is highly specialized for being stimulated and rapidly transmitting the stimulus from one place to another within the body.

2. Composition of Nervous Tissue:

   • The nervous tissue comprises cells called nerve cells or neurons, which are found in the brain, spinal cord, and nerves.
   • Neurons consist of a cell body with a nucleus and cytoplasm, from which long thin hair-like parts arise.
   • Each neuron typically has a single long part called the axon and many short, branched parts called dendrites.

3. Characteristics of Neurons:

   • Neurons are specialized for transmitting signals in the form of nerve impulses.
   • A single neuron may be up to a meter long, with its long axon transmitting signals over long distances within the body.

4. Nerve Impulse:

   • The signal that passes along the axon of a neuron is called a nerve impulse.
   • Nerve impulses allow us to move our muscles voluntarily by transmitting signals from the nervous system to muscles.

5. Functional Combination with Muscle Tissue:

   • The functional combination of nerve and muscle tissue is fundamental to most animals.
   • This combination enables animals to move rapidly in response to stimuli, allowing for coordinated movement and response to the environment.