jimtrue.com : school : BSC2011 : CH 40: Introduction to Animal Tissue Structure and Function

Posted by Jim True on October 19, 2004 6:01 PM. Last Updated October 22, 2006 9:23 PM

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CH 40: Introduction to Animal Tissue Structure and Function

Tissue Groups

• In most groups of animals, germ layers give rise to tissues, and in some groups, tissues combine to form organs.
• Among all animal possessing tissues, there are only four main groups:
1. Epithelial
2. Connective
3. Muscle
4. Nervous

Epithelial Tissue

• Epithelial Tissue - all epithelial tissues have one surface in direct contact with the environment.
• These tissues form the "linings" of the inside and outside of the body, e.g., skin, linings of the digestive, respiratory, urinary and circulatory systems.
• These tissues arise from all three germ layes, depending on where in the body the tissue is located.
• Functions:
1. Protection - keeps underlying tissues from dehydration and physical damage.
2. Selectively permeable barrier - At some point, all substances entering or leaving cells and tissues cross an epithelial layer.
3. Sensory "platform" - most sensory structures are on or in epithelium.
4. Secretory - glands formed by epithelia cells release various substances, e.g., sweat, oil, mucus.
• Epithelial tissues are usually very thin (1-2 cell layers), and the cells regenerate easily via mitosis.
• Epithelial tissue types can be characterized by cell shape and the number of layers.
• Cell shape - Three basic shapes:
1. Cuboidal - roughly cube shaped. (Length = width = depth). ie Kidney tissues
2. Columnar - column or rectangular in shape. (Length > width or Depth). ie lining of the digestive tract.
3. Squamous - Flat cells with irregular outlines (Length < Width or Depth). ie Skin
• Number of Layers - Can vary anywhere from one to several cell layers.
1. Simple - One cell layer in thickness.
2. Stratified - several cell layers (strata) thick.
3. Pseudostratified - ("false" + "layers") - This tissue appears to have several layes but actually is a single layer thick.
• The cell type and number of layers can be used in combinatino to give a clear idea of the nature of the tissue. (ie simple columnar cilial epithelials.
• For example, human skin is stratified squamous epithelium.
• Stratified skin cells can produce and incorporate a fibrous protein keratin in response to age or skin stress - calluses.
• Glands - Special clusters of cells, usually stratified columnar epithelium, which secrete substances that produce a wide variety of respones.
• Exocrine glands - secrete their products via ducts, e.g., sweat, oil, salivary.
• Endocrine glands - ductless glands. Secretions diffuse into bloodstream, e.g. hormones from pituitary, thyroid, etc.

Connective Tissue

• Connective Tissue - All connective tissues (CT) have cells that are embedded or suspended in a solid, semi-solid or liquid acellular matrix.
• In some CT's the cells secrete the matrix directly.
• All CT's arise only from mesoderm.
• Functions:
• Depends on specific type, but all CT's directly or indirectly connect together parts or regions of the body. Three generalized functions:
1. Support - CT acts as framework for body, helps production definition and shape to body structures, regions. ie Bone, Cartilage
2. Protection - May protect underlying tissues from physical harm, immune defense against foreign cells. ie, adipose tissue, white blood cells
3. Transport - of nutrients and waste products (solid, liquid or gas). ie Blood
• Support - Most varied group of CT:
  1. Loose (Areolar) -- cells are in a semi-solid protein matrix.
  • Cells (fibroblasts) in matrix also secrete protein fibers (elastin - thin stretches easily; collagen - thick, resists stretching.
  • Lots of matrix many cells & many irregularly arranged fibers allow s ahigh degree of stretching in many regions.
  • Areolar tissue forms the layer to which skin attaches (sub-cutaneous layer).
  2. Dense CT - Very little matrix, few cells, and most of the fibers are collagen. Two types.
  • Dense regular - collagen fibers aligned parallel to each other, greatly resists stretching, found in tendons (muscle to bone) & ligaments (bone to bone).
  • Dense irregular - collagen fibers randomly aligned, found as the CT surrounding most organs, enclosing joints, and connecting muscles together within body.
  3. Elastic CT - Matrix filled with elastic fibers, allowing a great amount of flexibility. found in lungs and walls of blood vessels.
  4. Adipose - "Fat" cells, very thin cells surrounding lipid droplets inside them.
  • Cells often referred to as a "signet ring cells", with the nucleus being the "signet".
  • Important as energy reserve, also as insulation and for shock absorption.
  5. Cartilage - Cells (chondrocytes) are enclosed within "pits" (lacunae) and secrete a semi-rigid matrix which provides suport but has some flexibility. Several types of cartilage:
  • Hyaline - no fibers in the matrix, so matrix is essentially clear.
  • Hyaline cartilage is found at the ends of long bones, in the septum of the nose, makes up part of the lungs. also known as "gristle".
  • Elastic cartilage - Cartilage has large number of elastic fibers. This type is found in the ear.
  • Fibrocartilage - Cartilage has large number of collagen fibers. Found in the pubic symphysis, knees and spinal discs.
  • Provides flexible support in some areas (tip of nose and ears in humans) and can act as shock absorber (ends of bones).
  6. Bone - Cells (osteocytes) are enclosed within "pits" (lacunae) in a mineralized solid matrix secreted by another cell type.
  • Cells are interconnected by tiny channels within the bone matrix called canaliculi ("little channels"), which allow for nutrient and gas exchange.
  • While animal is alive, bone tissue is also a living tissue (has blood vessels & nerves).
  • Two types of bone, dense (compact) and spongy formed of a basic unit, the osteon.
  • The center of each osteon of compact bone is a tube, the Haversian canal, which contains blood vessels and nerves.
  • An osteon of compact bone is somtimes called a Haversian system. Form the shafts of long bones.
  • Spongy bone osteons are the same as compact except they do not have Haversian canals, and are at the ends of long bones.
  • Unlike cartilage, once fully formed, bone is rigid and inflexible.
• Transport - Blood. Cells of tissue are suspended in a liquid matrix (plasma).
• Plasma carries nutrients and wastes.
• Erythrocytes (red blood cells) transport respiratory gases. May or may not be nucleated cells. Animals without hemoglobin do not produce Erythrocytes; they have blue blood. Insects don't have any respiratory pigmented cells.
• Immune Defense - also from blood.
• Leukocytes (white blood cells) are larger and many fewer than erythrocytes. Some are typically phagocytic; some will release chemical compounds to destroy invading cells.
• they attack and destroy foreign invaders, such as bacteria.
• Use various means to destroy invaders, including phagocytosis and release of chemical compounds harmful to the bacteria.

Muscle Tissue

• Muscle - Muscles do all the work of the body. ALL movement is the result of muscle activity.
• All muscle tissues are produced by mesoderm.
• Muscles are given special terms for their cell (muscle fiber), cell membrance (sarcolemma) and cytoplasm (sarcoplasm).
• Functions::
• the most basic function of ANY muscle is to contract (shorten) along its lengths when stimulated, and to relax lengthen) when not stimulated.
• Protection - of underlying tissues and organs.
• Body heat - most comes from waste heat from muscle contractions.
• There are three basic muscle types.
• Differences are based on the structure of the cell and number of nuclei, the speed and control of contractions.
1. Smooth -Muscle fibers are short cells, tapered at each end, uninucleate, slow contracting and involuntarily controlled.
• Found lining blood vessels, digestive tract, urinary system.
2. (Striated) Skeletal - Fibers are very long and appear striped (striations).
• Fibers are multinucleate, fast contracting and under voluntary control.
• All physical movement of body produced by skeletal muscles.
3. Cardiac - has elements of both smooth and skeletal.
• Cells are short, usually uninucleate (at most 2 nuclei) and involuntary.
• Fibers are striated and fast contracting.
• Unique to cardiac muscle is branching of the fibers.
• Fibers interconnect in a "weave" fashion, allowing lateral expansion/contraction of the muscles.
• Found only in the heart.

Nervous Tissue

• nervous - Involved in the reception, generation and transmission of electrochemical signals (nerve impulses).
• nerve tissue is derived from ectoderm.
• Functions:
• Awareness of, and response to, environment (external and internal).
• Processing and storage of information.
• Control of body functions.
• Two groups of cell types work together to form nervous tissue, neuroglia and neurons.
1. Neuroglia (Glial cells) - the more numerous of the two groups.
• Small cells that perform a variety of physical and metabolic support functions for the neuron. Six different types in humans.
2. Neuron - cells which carry the electric current.
• Highly variable in length, but an individual cell can be up to several meters long!
• The neuron consists of an enlarged, nucleated cell body.
• Extending off the cell body may be numerous filaments of two types.
• Dendrites - May be numerous and are usually highly branched. These receive the nervous impulses.
• Axon - Usually single and may be extremely long.
• Produce and transmit electrical impules.
• Some axons are insulated by a special protein sheat which increases transmission speed (~300 mph).
• Insulated axon type neurons are found where fast response to stimuli is needed, e.g., sensory and motor neurons that deal with touch, pressure, temperature.
• Uninsulated axons found in regions where slower response is acceptable, e.g., connections with internal organs.
• A nerve fiber is any axon or dendrite, a nerveis a bundle of fibers (usually axons).

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