A&P Chapter 4: Tissue: The Living Fabric

(4) Primary Tissue Types
Study of Tissues
Removal of tissues for diagnostic purposes
Function of Nervous Tissue
Internal Communication
Function of Muscle Tissue
Contracts to cause movement
Function of Epithelial Tissue
Forms boundaries between different environments, protects, secretes, absorbs, and filters
Function of Connective Tissue
Supports, protects, and binds other tissues together
(2) Main Forms of Epithelial Tissue
1. Covering and lining epithelia: On external and internal surfaces (ie. skin)
2. Glandular epithelia: Secretory tissue in glands (ie. salivary glands)
(5) Functions of Epithelial Tissue
1. Protecting underlying structures
2. Acting as barrier (prevent water loss, entry of toxins)
3. Permitting the passage of substances (oxygen, nutrients)
4. Secreting substances: enzymes, mucus
5. Absorbing substances: Lining the small intestine
(5) Distinguishing characteristics of Epithelial Tissues
1. Polarity
2. Specialized contacts
3. Supported by connective tissues
4. Avascular, but innervated
5. Regeneration (mitosis)
Apical Surface
Upper free side, exposed to surface or cavity
-Most are smooth, but some have cilia or microvilli
Basal Surface
Lower attached side, faces inwards towards body
-Attaches to basal lamina
Basal Lamina
Adhesive sheet that holds basal surface of epithelial cells to underlying cells
Specialized Contacts
-Bind adjacent epithelial cells together
-Include tight junctions and desmosomes
Basement Membrane
-Made up of basal and reticular lamina
-Reinforces epithelial sheet
-Resists stretching and tearing
-Defines epithelial boundary
Reticular Lamina
-Deep to basal lamina
-consists of network of collagen fibers
Avascular but Innervated
-No blood vessels are found in epithelial tissues
-nourishment comes from diffusion from underlying connective tissues
-Epithelia are supplied by nerve fibers
-Epithelial cells have high regenerative capacities
-Some cells are exposed to friction, some to hostile substances, resulting in damage, but are then replaced by mitosis
Simple Epithelia
-Single layer thick
Stratified Epithelia
-Two or more layers thick and involved in protection (ie. skin)
Flattened and scale-like
Box-like, cube shape
Tall, column-like shape
Simple Squamous Epithelium
Description: Single layer of flattened cells with disc-shaped central nuclei and sparse cytoplasm; the simplest of the epithelia
Function: Diffusion and Filtration
Location: Kidney, lungs (air sacs)
Simple Cuboidal Epithelium
Description: Single layer of cube-like cells with large, spherical central nuclei
Function: Secretion and absorption
Location: Secretory portion of small glands
Simple Columnar Epithelium
Description: Single layer of tall cell ; many cells microvilli, some bear cilia; layer may contain mucus-secreting unicellular glands (goblet cells)
Function: Absorption, secretion of mucus
Location: Digestive tract, bronchi, uterine/fallopian tubes
Pseudostratified Columnar Epithelium
Description: Single layer of cells of differing heights, some not reaching the free surface; nuclei seen at different levels; may contain mucus-secreting cells and bear cilia
Function: Propulsion by ciliary action, secretion of mucus
Location: Glands and upper respiratory tract
Stratified Squamous Epithelium
Description: Several layers, but named based on apical surface structure; Inner layers can be more cuboidal/columnar
Function: Protection
Location: Moist lining of esophagus, mouth, vagina, keratinized variety forms the epidermis of skin
Transitional Epithelium
Description: Surface cells can have dome-like shape or more squamous shape based on the amount of stretch in the organ
Function: Stretches readily, permits stored urine to distend urinary organ
Location: Lines the ureters, bladder, and part of the urethra
Endocrine gland
Internally secreting (hormones)
Ductless Glands
Secretions are not released into a duct; they are released into surrounding interstitial fluid and picked up by circulatory system
Exocrine Gland
-Secrete products into ducts
-Secretions are released onto body surfaces, such as skin, or into body cavities
-Examples: mucus, sweat, oil, saliva
Goblet Cells
-Produce mucin which dissolves in water to form mucus
-Found in intestinal tract and respiratory tract
Mucous Membranes
Epithelial tissues that secrete mucus
-Line many body cavities and tubular organs including gut and respiratory passages
Multicellular Exocrine Glands
-Composed of a duct and a secretory unit
-Usually surrounded by supportive connective tissue that supplies blood and nerve fibers to gland
Simple Duct Structure
Ducts with very few branches
Compound Duct Structure
Ducts with many branches
Tubular Ducts
Structure consists of small tubes (straight or coiled)
Alveolar Ducts
Structure consists of sac-like structures
Tubuloalveolar Ducts
Have both alveolar and tubular secretory units
Merocrine Glands
-Secrete their products by exocytosis
-Released into end of duct and moves out
-Examples: Sweat glands, salivary glands, pancreas
Holocrine Glands
-The entire secretory cell ruptures, releasing secretions and dead cell fragments
-Examples: Sebaceous oil glands
Apocrine Glands
-Present in other animals
-Apex of cell pinches off, releasing the secretory granules and a small amount of cytoplasm
-Cell repairs damage and process repeats
Ex. Mammary glands release lipid droplets (possibly)
Smooth Epithelium
-Reduces friction
-Example: Lining of blood vessels to reduce friction as the blood flows through the vessel
Microvilli on epithelial cells
-Increase surface area for absorption or secretion
-Example: Lining small intestine
-Elongated microvilli for sensation
-Example: Inner ear (for sound detection)
-Contain microtubules and move materials across surface of cell
-Example: Respiratory tract (mucociliary "escalator"), epithelial cells in uterus and uterine tubules to move mucus and oocytes along
Folds in Plasma Membrane
-Found in cells of transitional epithelium where organ must be able to change shape
-Example: urinary system (in bladder)
Basement Membrane
-Formed by secretions of both epithelium and connective tissue
-Lies between the two tissues
-Guides cell migration during tissue repair
Protein with sugar attached
Connective Tissue
-Most abundant of the primary tissues (found in every organ)
-consists of cells separated by ECM
(4) Main classes of Connective Tissue
1. Connective Tissue Proper (ex. fat, ligaments)
2. Cartilage
3. Bone
4. Blood
(7) Functions of Connective Tissue
1. Enclosing organs and separating them into layers
2. Connecting tissues to one another (tendons, ligaments)
3. Supporting and moving (bones)
4. Storage (fat, calcium in bone)
5. Cushioning and insulating (fat)
6. Transportation (blood transports nutrients and gases)
7. Protection (cells of immune system)
(3) Characteristics of Connective Tissue
1. Have common embryonic origin (all arise from mesenchyme)
2. Have varying degrees of vascularity (cartilage is avascular, bone is highly vascularized)
3. Cells are suspended in ECM (supports cells)
(3) Main Structural Elements of Connective Tissue
1. Ground Substance
2. Fibers
3. Cells
-ground substance and fibers make up the ECM
(3) Types of Protein Fibers
1. Collagen Fibers
2. Reticular fibers
3. Elastic Fibers
Ground Substance
-Found between cells and fibers
-Supports cells, binds them together, stores water, provides medium for exchange between blood and cells
(3) Major Components of Ground Substance
1. Interstitial Fluid (mostly water)
2. Adhesive Molecules (CAMs)
3. Proteoglycans (hyaluronic acid and chondroitin sulfate)
-Strongest and most abundant type
-Tough; provides high tensile strength
Elastic Fibers
-Networks of long, thin, elastin fibers that allow for stretch and recoil
Reticular Fibers
-Short, fine, highly branched collagenous fibers
-Form flexible "netting" that offers more "give"
Create the matrix (secrete ground substance and ECM fibers)
Become part of and help maintain health of the matrix
Break the matrix down for remodeling
Potential issue cause by osteoclasts
If blood calcium levels drop too low, osteoclasts will start to break down bone, releasing calcium. If this continues for too long, could lead to osteoporosis
(4) Other cell types in connective tissue
1. Adipose or fat cells (adipocytes)
2. White Blood cells (leukocytes): respond to injury and infection
3. Mast Cells: Initiate local inflammatory response against foreign microorganisms
4. Macrophages: Phagocytose or provide protection
Loose Connective Tissue, Areolar
Description: Gel-like with all three fiber types
Function: Support other tissues
Location: Under epithelium, surrounding organs
Loose connective Tissue, Adipose
Description: Matrix as in areolar, but very sparse; closely packed adipocytes, or fat cells, have nucleus pushed to the side by large fat droplet
Function: Shock absorption, insulation, energy storage
Location: Under skin, around kidneys
Loose Connective Tissue, Reticular
Description: Lots of thin reticular fibers
Function: Acts as a support for blood cells
Location: Lymph nodes, spleen, bone marrow
Dense Connective Tissue, Regular
Description: Very high tensile strength (LOTS of collagen fibers running parallel to direction of pull), great resistance to pulling. Waviness allows for a small amount of stretch as well. Very few cells and ground substances (mostly fibers)
Function: Attaches muscles to bones/muscles and bones to bones
Location: Tendons and ligaments
Dense Connective Tissue, Irregular
Description: Irregularly arranged collagen. Forms sheets instead of bundles (bundles found in dense regular) so can resist tension in many directions
Function: Provide structural strength
Location: Skin, joint capsules
Dense Connective Tissue, Elastic
Description: Lots of elastic fibers. Allows a lot of recoil after stretching
Function: Allows for stretching
Location: Walls of large arteries (need to stretch when blood is forced through such as in the aorta), within ligaments of vertebral column
-composed of chondrocytes
-ground substance composed of proteoglycans and hyaluronic acid complexed together to trap water
-allows tissue to spring back after being compressed
-avascular and no nerve supply --> heals slowly
-cartilage cells
Hyaline Cartilage
Most abundant form of cartilage in the body
Description: Chondrocytes within lacunae. Collagen fibers form imperceptible network
Function: Support
Location: Costal cartilage of the ribs
Elastic Cartilage
Description: Similar to hyaline but more elastic
Function: Support with flexibility
Location: Pinna of outer ear
Fibrocartilage Cartilage
Description: Similar to hyaline but less firm
Function: Shock absorption
Location: Intervertebral disks, discs of knee joint
Description: Osteocytes within lacunae and a hard calcified matrix, highly vascularized
Function: Support, storage of calcium and fat, bone marrow is the site of blood cell formation
Location: Bones
Description: Red and white blood cells in a fluid matrix (plasma)
Function: Transport respiratory gases, nutrients, wastes, and other substances
Location: Within blood vessels
Muscle Tissue
-Possess contractile proteins (actin, myosin)
(3) Types of Muscle Tissue
Skeletal Muscle
Description: Long, cylindrical multinucleate cells with obvious striations
Functions: Voluntary movement, manipulation of the environment, facial expression
Location: Skeletal muscles attached to bone or occasionally to skin
Cardiac Muscle
Description: Branching, striated, generally anucleate cells that interdigitate at specialized junctions (intercalated disks)
Function: As it contracts, it propels blood into the circulation; involuntary control
Location: Walls of the heart
Smooth Muscle
Description: Spindle-shaped (elongated) cells with central nuclei; no striations; cells arranged closely to form sheets
Function: Propels substances or objects along internal passageways; involuntary control
Location: Walls of the gut, leading to peristalsis, or in walls of the bladder
Nervous Tissue
Description: Neurons are branching cells; cell processes that may be quite long extend from the nucleus-containing cell body; also includes non-excitable supporting cells
Function: Neurons transmit electrical signals from sensory receptors and to effectors; supporting cells support and protect neurons
Location: Brain, spinal cord, and nerves
Cutaneous Membrane
-Stratified squamous epithelium (epidermis) attached to a thick layer of connective tissue (dermis)
-Outer layer contains keratinized cells --> the skin is a dry membrane
Mucous Membrane
-Line the body cavities that are open to the exterior (nasal cavity, mouth, lung, etc.)
-Bathed by secretions
Serous Membrane
-Line body cavities that are closed to the exterior
-Parietal serosae line internal body cavity walls
-Visceral serosae cover internal organs
-Cavity between layers contains slippery serous fluid
Serous membrane of the lungs
Serous membrane of the heart
Serous membrane of the abdomen
Tissue Regeneration
-Same kind of tissue replaces destroyed tissue
-Original function is restored
-Connective tissue replaces destroyed tissue
-Original function lost to some degree
(3) Steps of Tissue Repair
1. Inflammation
2. Organization
3. Regeneration and Fibrosis
1. Inflammation
-Severed blood vessels bleed
-Inflammatory chemicals are released
-Vessels become more permeable; WBCs, fluid, clotting proteins, plasma proteins seep into area
-Clotting occurs, surface dries and scab forms
(4) Effects of inflammatory chemicals
-Dilation of blood vessels
-Increase blood vessel permeability
-Increased pain sensation
2. Organization
-Clot is replaced by granulation tissue which restores the vascular supply
-Fibroblasts produce collagen fibers that bridge the gap
-Macrophages phagocytize dead and dying cells and other debris
-Surface epithelial cells multiply and migrate over the granulation tissue
3. Regeneration and Fibrosis
-The fibrosed area matures and contracts; the epithelium thickens
-A fully regenerated epithelium with an underlying area of scar tissue results
(3) Ways scar tissue can affect function
-May cause organ to lose volume capacity
-may block substrates from moving through the organ
-may impair ability for muscles to contract ot may impair nerve transmission