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Tissues, Organs and Systems

Lion Tracks

Although you will learn this material in the lab course
(and again, bit by bit, in the lecture course),
 I will not test you specifically on this material now.

Tissues

	Review Levels of Organization
	Tissues are the "fabric" that make up organs
	Four main types of tissues: epithelial, connective, muscle, nervous

Epithelial tissues

	Function Cover and line (form membranes) Secrete (form glands) - "secretory tissue" Endocrine glands (ductless glands) secrete hormones into blood Exocrine glands (ducted glands) secrete fluids onto surface (incl. into tubes)
	Structure Cellular junctions Cohesion Junctional complexes Desmosomes - "tangled filaments" hold cells together as in Velcro fasteners Gap junctions - channels in adjacent plasma membranes form "tunnels" that hold cells together structurally and functionally Syncytium - group of cells held together by gap junctions and acting (in some ways) as a single, giant cell Tight junctions - rows of connecting proteins, like "snaps" on a jacket form a collar-like seal all the way around a cell (as the plastic yoke on a six-pack) Basal surface is anchored; apical surface is "free" Basal layer attached to underlying connective tissue by glue-like basement membrane  Epithelial types are named for: Number of layers Simple = one layer of cells Stratified = more than one layer of cells (from stratum = layer) Pseudostratified = looks like more than one layer, but because all cells touch the basement membrane it's really just one layer Shape of cells in outermost ("free surface") layer (as seen in cross-section) Squamous = flat, scale-like cells Cuboidal = about as tall as wide Columnar = taller than wide Transitional = shape depends on how stretched the membrane is
	Examples of epithelial tissue types Simple squamous Simple cuboidal Simple columnar Pseudostratified columnar Stratified squamous Keratinized (has outer layers of dead cells that have filled with tough, waterproof protein called keratin --as in skin) Nonkeratinized Transitional (stratified)

Connective tissues

	Function Connects body parts in any of several ways Many different functions, really
	Structure Dominated by extracellular material ("extracellular matrix" or ECM)--with few, scattered cells Matrix contains fibers (made by fibroblast cells) and other materials Collagen fibers are tough, flexible, white Elastin fibers are elastic, yellow
	Major types of connective tissues Fibrous connective tissues Areolar (loose, ordinary) has collagen and elastin fibers scattered loosely Adipose tissue forms when fat-storing cells in areolar tissue enlarge as they accumulate more [triglyceride] fat Dense fibrous connective tissue has a dense arrangement of collagen fiber bundles Cartilage Chrondrocytes make cartilage matrix found within spaces called lacunae (sing. lacuna = "lake") giving cartilage a "Swiss cheese" appearance Hyaline cartilage - some collagen in matrix Elastic cartilage - some collagen and some elastin in matrix Fibrocartilage - dense collagen in matrix Bone Osteocytes (within lacunae) surrounded by collagen fibers encrusted with calcium salts Spongy bone - irregular beams of bone surrounded by red bone marrow (soft, blood-forming tissue) Compact bone - denser type of bone made up of cylindrical units composed of concentric layers (lamellae) of bone matrix Blood Liquid matrix (blood plasma) and circulating blood cells Blood cells are also called "formed elements" because plasma is "unformed" taking the shape of its container RBCs = red blood cells, WBCs = white blood cells, platelets = thrombocytes

Muscle tissue

	Function Contraction May be "voluntary" or "involuntary"
	Structure Cylindrical cells or "muscle fibers" Muscle fibers have highly organized cytoskeleton that "slides together" like a split deck of cards to contract the fiber
	Three types: skeletal, smooth, cardiac
	Skeletal muscle Also called "striated" because of striped appearance of overlapping filaments of cytoskeleton Voluntary muscle Connected to skeleton
	Cardiac muscle Faintly striated Branched fibers held together end-to-end by gap junctions, forming intercalated disks Involuntary In heart wall
	Smooth muscle Not striated (cytoskeleton organized differently) Involuntary In walls of hollow organs (except heart)

Organs and systems

	Organs are made up of different tissues
	Organs are organized into different body systems Organs may belong to more than one system Different biologists organize them differently

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