Body Tissues Ch.3 (Part II) The human body, complex as it is, starts out as a single cell, the fertilized egg, which divides almost endlessly. The millions of cells that result become specialized for particular functions. Some become muscle cells, otehrs the transparent lens of the eye, still others skin cells, and so on. Thus, there is a division of labor in the body, with certain groups of highly specialized cells performing functions that benefit the organism as a whole. Cell specialization carries with it certain hazards. When a small group of cells is indispensable, its loss can disable or even destroy the body. For example, the action of the heart depends on a very specialized cell group in the heart muscle that controls its contractions. If those particular cells are damaged or stop functioning, the heart will no longer work efficiently, and the whole body will suffer or die from lack of oxygen. Ch.3 (Part II)

Body Tissues Cells are specialized for particular functions Tissues Groups of cells with similar structure and function Four primary types Epithelium Connective tissue Nervous tissue Muscle

Body Tissues If we had to assign a single term to each primary tissue type that would best describe its overall role, the terms would most likely be: Covering (epithelium) Support (connective) Movement (muscle) Control (nervous) However, these terms only reflect only a tiny fraction of the functions that each of these tissues perform.

1. Epithelial Tissues Found in different areas Body coverings Body linings Glandular tissue (forms glands in body) Functions Protection Absorption Filtration Secretion

Special Characteristics of Epithelium: Cells fit closely together (except for glandular) to form connective sheets Tissue layer always has one free surface. This so called “apical surface” is exposed to the body’s exterior or to the cavity of an internal organ. The lower surface of epithelium is bound by a basement membrane (a structure less material secreted by cells) Avascular (have no blood supply) so they depend on diffusion from the capillaries in the underlying connective tissue for food and oxygen Regenerate easily if well nourished Pg. 86!!! Read to kids from here…extra info

Classification of Epithelium 1. Number of cell layers Simple – one layer Stratified – more than one layer Figure 3.17a

Classification of Epithelium 2. Shape of cells Squamous – flattened (like fish scales) Cuboidal – cube-shaped (like dice) Columnar – column-like (like columns…duh) Figure 3.17b

Simple or Stratified… Simple Stratified One layer of cells Most concerned with absorption, secretion, and filtration Because they are usually very thin, protection is not one of their specialties Consist of two or more cell layers More durable than the simple epithelia Function primarily to protect

Simple Epithelium 1. Simple squamous Single layer of flat cells Usually forms membranes where filtration or exchange of substances by rapid diffusion occurs. Lines body cavities Lines lungs and capillaries It is in the air sacs of the lungs, where oxygen and carbon dioxide are exchanged and it forms the walls of capillaries, where nutrients and gases pass between the tissue cells and the blood in the capillaries. Figure 3.18a

Simple Epithelium 2. Simple cuboidal Single layer of cube-like cells Common in glands and their ducts Forms walls of kidney tubules Covers the ovaries Figure 3.18b

Simple Epithelium 3. Simple columnar Single layer of tall cells Often includes goblet cells, which produce mucus Lines the entire digestive tract from the stomach to the anus Figure 3.18c

Simple Epithelium 4. Pseudostratified Single layer, but some cells are shorter than others Often looks like a double cell layer (false…hence the name pseudo) Sometimes ciliated, such as in the respiratory tract May function in absorption or secretion Rest on a basement membrane like the others, but because some of its cells are shorter than others, and their nuclei appear at different heights above the basement membrane…as a result, this epithelium give the false (pseudo) impression that it is stratified. Figure 3.18d

Stratified Epithelium 1. Stratified squamous Cells at the free edge are flattened but closer to the basement membrane, are cuboidal or columnar Found as a protective covering where friction/abuse is common Locations Skin Mouth Esophagus Figure 3.18e

Stratified Epithelium 2. Stratified cuboidal Two layers of cuboidal cells 3. Stratified columnar Surface cells are columnar, cells underneath vary in size and shape Stratified cuboidal and columnar Rare in human body Found mainly in ducts of large glands

Stratified Epithelium 4. Transitional epithelium Shape of cells depends upon the amount of stretching (near basement: typically columnar or cuboidal, at surface: varies) Lines organs of the urinary system like the bladder, ureters, and part of the urethra where considerable amounts of stretching occur. When the organ is not stretched, the membrane is many layered and the superficial cells are rounded and domelike. When the organ is distended with urine, the epithelium thins, and the surface cells flatten and become squamous-like. This ability of transitional cells to slide past one another and change their shape (undergo “transitions”) allows the ureter wall to stretch as a greater volume of urine flows through that tubelike organ. In the bladder, it allows more urine to be stored. Figure 3.18f

Glandular Epithelium Gland – one or more cells that secretes a particular product (secretion) Two major gland types develop from epithelial sheets: 1. Endocrine gland Ductless (hormones diffuse directly into the blood vessels that weave through the glands) Secretions are all hormones Examples of endocrine glands: thyroid, adrenals, and pituitary 2. Exocrine gland Empty through ducts to the epithelial surface Include sweat and oil glands, and liver and pancreas Are both internal and external

Connective Tissue Found everywhere in the body & connects body parts Includes the most abundant and widely distributed tissues Functions Binds body tissues together Supports the body Provides protection

Connective Tissue Characteristics: Variations in blood supply Some connective tissue types are well vascularized (good blood supply) Some have poor blood supply or are avascular like tendons and cartilages (these things heal slowly) Extracellular matrix Connective tissues are made up of many different types of cells plus varying amounts of non-living material that surrounds living cells (called the extracellular matrix)

Extracellular Matrix. Makes connective tissue different from Extracellular Matrix Makes connective tissue different from any other tissue. Two main elements Ground substance – mostly water along with adhesion proteins and polysaccharide molecules Fibers Produced by the cells Three types Collagen fibers Elastic fibers Reticular fibers

Extracellular Matrix Continued: Allows connective tissue to form a soft packaging tissue around other organs, to bear weight, and to withstand stretching and other abuses, such as abrasion that no other tissue could endure.

Connective Tissue Types: Bone (osseous tissue) Composed of: Bone cells in lacunae (cavities) Surrounded by a hard matrix of calcium salts Large numbers of collagen fibers Because of its rocklike hardness, bone is used to protect and support the body Figure 3.19a

Connective Tissue Types: Hyaline cartilage Most common cartilage (cartilage is found only in a few places in the body…is less hard and more flexible than bone.) Composed of: Abundant collagen fibers Rubbery matrix Blue-white appearance Entire fetal skeleton is hyaline cartilage (turns to bone by birth)! Also forms the supporting structure of the larynx (voicebox), attaches ribs to the breastbone, and covers the ends of bones where they form joints. Figure 3.19b

Connective Tissue Types: Elastic cartilage Provides elasticity Example: supports the external ear

Connective Tissue Types: Fibrocartilage Highly compressible Example: forms cushion-like discs between vertebrae Figure 3.19c

Connective Tissue Types: Dense connective tissue Main matrix element is collagen fibers Cells are fibroblasts (fiber forming cells) Forms strong ropelike structures (like the examples listed below) Examples Tendon – attach muscle to bone Ligaments – attach bone to bone Figure 3.19d

Connective Tissue Types: Areolar connective tissue Most widely distributed connective tissue Soft, pliable “cobwebby” tissue that cushions and protects the body organs Helps hold internal organs together and in their proper positions Contains all fiber types Can soak up excess fluid Can soak up excess fluid when a body region is inflamed like a sponge. Then the area swells and turns red (called edema). Many types of phagocytes wander through this tissue, scavenging for bacteria, dead cells, and other debris, which they destroy! Figure 3.19e

Connective Tissue Types: Adipose tissue: Commonly called fat! Matrix is an areolar tissue in which fat cells predominate Many cells contain large lipid deposits Functions Insulates the body Protects some organs Serves as a site of fuel storage Adipose tissue is found right beneath the skin where it insulates the body and protects it from extremes of both heat and cold. Kidneys are surrounded by a capsule of fat, and adipose tissue cushions the eyeballs in their sockets. There are also fat “depots” in the body, such as the hips and breasts, where fat is stored and available for fuel if needed. Figure 3.19f

Connective Tissue Types: Reticular connective tissue Delicate network of interwoven fibers Forms stroma (internal supporting network) of lymphoid organs Lymph nodes Spleen Bone marrow Figure 3.19g

Connective Tissue Types: Blood (vascular tissue) Blood cells surrounded by fluid matrix (called plasma) Fibers are visible during clotting Functions as the transport vehicle for the cardiovascular system, carrying nutrients, wastes, respiratory gases, and many other substances throughout the body. Figure 3.19h

Muscle Tissue Skeletal muscle Cardiac muscle Smooth muscle Function is to produce movement Three types Skeletal muscle Cardiac muscle Smooth muscle

Muscle Tissue Types: 1. Skeletal muscle Can be controlled voluntarily Form the muscular system Cells attach to connective tissue Cells are striated (striped) Cells have more than one nucleus When the skeletal muscles contract, they pull on bones or skin. The result of their action is gross body movements or changes in our facial expressions. Figure 3.20a

Muscle Tissue Types 2. Cardiac muscle Found only in the heart Function is to pump blood (involuntary) Cells attached to other cardiac muscle cells at intercalated disks (have gap junctions …remember this mean info can pass freely from cell to cell….) Cells are striated One nucleus per cell Under involuntary control Figure 3.20b

Muscle Tissue Types 3. Smooth muscle AKA: visceral muscle Involuntary muscle Surrounds hollow organs Spindle-shaped (pointed at each end) Attached to other smooth muscle cells No visible striations (hence the name smooth) One nucleus per cell Smooth muscle is found in the wall so hollow organs such as the stomach, bladder, uterus, and blood vessels. As smooth muscle contracts, the cavity of an organ alternately becomes smaller (constricts on smoothe muscle contraction_ or enlarges (dilates on smooth muscle relaxation) so that substances are propelled through the organ along a specific pathway. Smooth muscle contracts much more slowly than the other two muscle types. Peristalsis, a wafelike motion that keeps food moving through the small intestine, is typical of its activity. Figure 3.20c

Nervous Tissue Neurons and nerve support cells Function is to send impulses to other areas of the body Irritability Conductivity All neurons receive and conduct electrochemical impulses from one part of the body to another; thus irritability and conductivity are their two major functional characteristics. The structure of neurons is unique….their cytoplasm is drawn out into long processes (extensions), as much as 3 feet or more in the leg, which allows a single neuron to conduct an impulse over long distances in the body. Neurons, along with a special group of supporting cells that insulate, support, and protect the delicate neurons, make up the structures of the nervous system-the brain, spinal cord, and nerves. Figure 3.21

Tissue Repair (Wound Healing) Tissue repair occurs in two major ways… 1. Regeneration Replacement of destroyed tissue by the same kind of cells 2. Fibrosis Repair by dense fibrous connective tissue (scar tissue is formed) Determination of method Type of tissue damaged Severity of the injury

Tissue injury sets a series of events into motion… Capillaries become very permeable Introduce clotting proteins Wall off injured area Formation of granulation tissue Regeneration of surface epithelium Be prepared to read pg. 98 while the kids write here!!!

Regeneration of Tissues Tissues that regenerate easily Epithelial tissue Fibrous connective tissue and bone Tissues that regenerate poorly Skeletal muscle Tissues that are replaced largely with scar tissue Cardiac muscle Nervous tissue within the brain and spinal cord Read about Homeostatic Imbalance on pg. 98 and make notes….