Biology 55
Tissues
TISSUES – group of specialized cells with a common function
4 Basic Tissue Types: nervous tissue – detects changes and sends electrical signals to control muscle body functions
tissue – moves the body and the contents of organs connective epithelial
tissue – supports and connects other tissues of the body
tissue – covers and lines surfaces and forms glands
Cell Junctions – contact points between cells that join them into a functional unit tight junctions – web of membrane proteins on adjacent cells fuse together forming a watertight seal (eg. cells lining digestive tract) adhesion junction – plaques of dense membrane proteins held together by velcro-like protein filaments and linked to cytoskeleton of cells form strong connections between cells gap junctions – membrane proteins of adjacent cells bind together forming channels between cells allows communication between cells
NERVOUS TISSUE – detects changes in internal & external environment and responds by transmitting signals to other tissues to control body functions found in brain, spinal cord, nerves neurons – cells responsible for function of nervous system neuroglia – cells that support, nourish, and protect neurons
MUSCLE TISSUE – uses ATP to contract (shorten), causing movement of body parts
Skeletal muscle – usually attaches to bone striated (striped) appearance under microscope very long cells with multiple nuclei contractions are voluntary
Cardiac muscle – heart muscle branched, striated cells with 1 nucleus intercalated discs – gap junctions and adhesion junctions connecting cells contractions are involuntary
Smooth muscle – walls of hollow organs and vessels spindle-shaped with 1 central nucleus and no striations contractions are involuntary
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tightly packed layers of cells held together by cell junctions basement membrane – layer of proteins and carbohydrates that anchors epithelium tightly to underlying connective tissues
Functions of Epithelial Tissues cover surfaces and line cavities protect deeper tissues excrete or absorb substances form glands – produce secretions
Structure of Epithelial Tissue free surface – faces body surface, body cavity, or cavity in organ basal surface – adheres to basement membrane epithelium is avascular (no blood vessels) – cells are constantly damaged by their environment, are shed, and are replaced by division of stem cells
CLASSIFICATION OF EPITHELIUM by number of cell layers: simple epithelium – single layer of cells stratified epithelium – 2 or more layers of cells pseudostratified epithelium – 1 layer that appears multilayered classification by cell shapes: squamous – flat; nucleus in center cuboidal – cubes or hexagons; nucleus in center columnar – height greater than width; nucleus at base transitional – shape varies due to tissue stretching (flat to cuboidal) by cell modifications : cilia – hair-like microtubule structures on free surface sweep mucus and other materials on surface
(eg. upper respiratory tract, uterine tubes) microvilli – finger-like extensions of cell membrane on free surface increase surface area for absorption or secretion
(eg. small intestine, kidney tubules)
TYPES OF EPITHELIUM simple squamous – single, flat layer thin layer where molecules can cross by diffusion
(eg. lining of lungs, blood vessels, ventral body cavities) stratified squamous – many layers, layer on free surface is flat lines surfaces exposed to damaging environment (especially abrasion)
(eg. skin, mouth, esophagus, vagina)
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simple cuboidal – single cuboidal layer sites of secretion and absorption (may have microvilli)
(eg. most glands, kidney tubules) stratified cuboidal – 2 or more cuboidal layers (gives additional strength) lining large ducts of glands simple columnar – single columnar layer sites of much secretion and absorption (may have cilia or microvilli) thickness provides some protection
(eg. lining digestive tract, uterine tubes) stratified columnar – multiple layers, free surface layer is columnar pseudostratified columnar – lines most of respiratory airways thickness gives some protection, produces mucous secretions cilia – sweep mucus and trapped debris out of airways transitional – lines urinary bladder and ureters number of layers and shape of cells varies depending on fullness full – stretches out; appears flatter with fewer layers empty – not stretched; appears large and plump with more layers
GLANDS – clusters of epithelial cells that produce secretions (most by exocytosis) exocrine glands – secrete into ducts that empty onto epithelial surface
(eg. mucus, sweat, saliva, milk) endocrine glands – ductless glands which secrete hormones into interstitial fluid, from which it diffuses into bloodstream goblet cells – single-celled glands found in columnar epithelium
(eg. respiratory airways, digestive tract)
connects, supports, and protects tissues and organs stores energy, insulates and cushions, transports materials between tissues most have a rich vascular supply
2 Basic Components of All Connective Tissues
1) Specialized Cells – cell type varies depending on type of tissue
2) Matrix – material that the cells secrete around themselves matrix determines the tissue’s physical characteristics protein fibers – strengthen and provide a framework collagen fibers – composed to collagen protein very strong yet flexible fibers give strength to resist tearing elastic fibers – contain the protein elastin can be stretched, but it returns to itsoriginal shape reticular fibers – thin, branching network of collagen protein form a framework to support soft organs ground substance – water plus various proteins, carbohydrates, and/or minerals that surround and connect cells and protein fibers; the type and amount of ground substance determines whether the tissue is liquid, gel-like, or solid
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TYPES OF CONNECTIVE TISSUES
Fibrous Connective Tissues fibroblasts – main cell of most fibrous connective tissues matrix
– gel-like ground substance plus variable amounts of protein fibers
Loose Connective Tissue – many cells with loosely arranged fibers areolar connective tissue – soft “packing material” found between most other tissues and organs collagen and elastic fibers for strength and elasticity immune cells and inflammatory cells give protection adipose tissue – fatty tissue; stores energy, insulates, and cushions adipocytes – fat, round fibroblasts, filled with fat droplets little matrix seen reticular connective tissue – framework supporting cells of soft organs (e. liver, spleen, lymph nodes) reticular fibers and a few fibroblasts (called reticular cells)
Dense Connective Tissue – many collagen fibers, less cells and matrix connect body structures and resist tearing dense regular connective tissue – parallel collagen fibers fibers run in one direction, strong connection resists tearing
(eg. tendons and ligaments) dense irregular connective tissue
(eg. joint capsules, skin)
– network of collagen fibers resists tearing forces in multiple directions
Specialized Connective Tissues – specialized cell types and ground substance form tissues with specialized structures and functions
Cartilage – thick gel ground substance and many protein fibers form a solid, yet flexible matrix cartilage is avascular, so it heals slowly chondrocytes – cartilage cells found in small cavities in solid matrix lacunae – fluid-filled holes within matrix where cells live
3 types– based on type and amount of protein fibers in matrix hyaline cartilage – fine collagen fibers (not visible)
most common type in body
(eg. joint surfaces, nose, trachea, fetal skeleton) fibrocartilage – dense bundles of collagen fibers very tough to absorb shock
(eg. intervertebral discs, menisci [pads] of knee) elastic cartilage – elastic
(eg. ear, epiglottis) and collagen fibers strong but flexible
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Bone (Osseous) Tissue – mineral salt ground substance plus collagen fibers form an extremely hard matrix that supports the skeleton osteocytes – bone cells found within lacunae
2 types of bone – compact bone and spongy bone
Blood – fluid ground substance and soluble protein fibers form a liquid connective tissue that transports materials between cells blood plasma – fluid matrix red blood cells – transport oxygen white blood cells – provide protection platelets – cell fragments involved in blood clotting
– sheets of tissue
Epithelial membranes – epithelium plus underlying connective tissue mucous membranes (mucosa) – line body cavities open to the exterior
(eg. digestive, respiratory, reproductive tracts) protective barrier against microbes, chemicals, and physical injury secrete mucus – protects, lubricates, traps foreign material serous membranes (serosa) – line body cavities not open to the exterior
2 layers – parietal layer covers wall & visceral layer covers organs
(eg. pleura, peritoneum, pericardium) serous fluid (watery fluid) lubricates surfaces reduces friction and prevents adhesions cutaneous membrane – skin (next lecture)
Synovial membranes – line joint spaces connective tissue membranes (no epithelium) synovial fluid – thick,slippery secretion, lubricates joint surfaces
Meninges – cover brain and spinal cord connective tissue membranes that protect nervous tissues cerebrospinal fluid – cushioning fluid found within meninges
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