Tissues General. each group of cells becomes specialized to do one or a few tasks very well ( much more efficiently):

Transcription

1 Tissues General in multicellular organisms such as humans the huge size and complexity dictates that individual cells specialize there are over 200 different kinds of cells in human body each group of cells becomes specialized to do one or a few tasks very well ( much more efficiently): eg. muscle cells contraction & movement eg. bone cells support eg. blood circulation but they lose their independence are dependent on each other for survival However, by becoming more specialized they lost their independence; sacrificed independence for efficiency groups of similar cells performing similar functions = tissues tissue = cells and any secretions ( =matrix) they produce matrix = fibrous proteins + ground substance histology = the study of tissues these tissues differ in the shape and structure of the cells the kinds of matrix or secretions the nature of any fibers that might be in the secretions all cells in human body can be classified into 4 general (=primary) tissue types 1. epithelial layers of closely packed cells cover surfaces functions: protection, secretion, absorption 2. connective cells loosely disbursed within a noncellular matrix usually more matrix than cells Microscopy, Cells, Tissues: Human Tissues; Ziser Lecture Notes,

2 functions: support, binding, protection, storage 3. muscular consists of elongated excitable cells specialized for contraction functions: voluntary & involuntary movement 4. nervous elongated, often branching cells; excitable functions: transmit signals throughout the body each of these primary tissue types can be further subdivided into specific subtypes of tissues 1. Epithelial Tissues line all body and organ surfaces both outer and internal: eg. outer portion of skin eg. outside and inside of stomach and intestine eg. inner lining of blood vessels and heart may also form secretory tissue and ducts of glands attached to tissues below by basement membrane tend to be arranged in thin sheets little or no matrix or fibers avascular = no blood vessels directly supply its cells receive nutrients and oxygen and get rid of wastes by diffusion from blood vessels in nearby tissues typically the basement membrane and underlying connective tissues are richly supplied with blood vessels Functions of Epithelial Tissues: 1. protection often thickened by being layered or stratified from microbes, physical injury, water loss, etc 2. absorption Microscopy, Cells, Tissues: Human Tissues; Ziser Lecture Notes,

3 of food, water etc (intestine) cells may have minute projections = microvilli which enhance absorption 3. transport sometimes have cilia (tiny hairlike processes) that move things along eg. oviducts move egg toward uterus eg. respiratory tract move dust and bacteria away from lungs 4. filtration in kidneys 5. gas exchange lungs 6. secretion eg. form glands that secrete various substances eg. mucous, sweat, digestive juices 2. Connective Tissues the most widespread and abundant type of tissue in the body the most diverse in structure and function most connective tissues are heavily vascularized connective tissues have an abundance of matrix the noncellular matrix often comprise the majority of the tissue volume the nature of the matrix and the fibers it contains identifies the specific kind of connective tissue (the kinds of cells is not as important) the matrix can be: fibrous loaded with protein fibers eg. collagen = dense connective tissues gellike soft and flexible, sometimes almost liquid; fewer fibers = loose connective tissues eg. areolar, adipose hard, rigid bone liquid blood Microscopy, Cells, Tissues: Human Tissues; Ziser Lecture Notes,

4 connective tissues consist of: 1. matrix 2. fibers 3. cells Fibers matrix may contain one or more kinds of protein fibers: collagen fibers: most abundant protein in body (to 25% of body protein) tough, flexible, resistant to stretching white fibers, tough, strong, often in bundles used for support or strength eg. bone, cartilage, tendons, ligaments, dermis reticular fibers: delicate spongelike networks that are used to support capillaries and nerve cells elastic fibers: contain elastin protein coiled protein extensible fibers that spring back eg some kinds of cartilage General Functions of Connective Tissue: 1. Glue areolar tissue 2. Support & movement eg. bones & cartilage 3. Nutrient Storage bones, adipose 4. Temperature Homeostasis fat for heat production and cold insulation 5. Transport blood, lymph Some Specific Kinds of Connective Tissues Microscopy, Cells, Tissues: Human Tissues; Ziser Lecture Notes,

5 a. Areolar (loose) acts as a sort of elastic glue that holds other tissues and organs together its matrix is semiliquid (semifluid) ~11% of body fluid is in areolar tissues contains a loose arrangement of various fibers WBC s move through matrix removing bacteria and debris functions: protection, glue, supplies nutrients and O 2 to epithelial cells eg. tissue secretions from every part of body; surrounds muscles and nerves; nearly every epithelium rests on areolar tissue; many serous and mucus membranes b. Adipose also a very loose or fluidy type of tissue stores fats as emergency food reserve fat pads also used as shock absorbers around critical organs also layer of fat under skin protects against cold not much matrix, mostly cells surrounded by reticular fibers each cell contains a large oil droplet (looks empty) functions: energy storage, thermal insulation, heat production by brown fat, protective cushion eg. subcutaneous fat, breasts, mesenteries, around heart, kidneys, eyes c. Dense Regular (white fibrous) matrix is packed with bundles of parallel collagen fibers hardly any cells: main cells are fibroblasts Microscopy, Cells, Tissues: Human Tissues; Ziser Lecture Notes,

6 provides strength but retains flexibility eg. esp tendons and ligaments g. Cartilage h. Bone both bone and cartilage begin as the same gel-like matrix with embedded collagen fibers in both bone and cartilage the cells are confined to small spaces or cavities within the matrix = lacunae in cartilage the matrix is soft and fluid enough that oxygen and nutrients can diffuse into and out of cells there is no direct blood supply to cells = avascular cartilage cells (=chondrocytes) lie in lacunae three types of cartilage differ in abundance and kinds of fibers in matrix: a. hyaline most common most of fetal skeleton covers articular surface of joints forms rings around tracheae and bronchi cartilages of larynx b. fibrous matrix is packed with collagen fibers the strongest form of cartilage eg. intervertebral discs, menisci of knee joint, pubic symphysis c. elastic lots of elastic fibers as well as collagen fibers eg. external ear, nose, eustacean tube, epiglottis both bone and cartilage begin as the same gel-like matrix with embedded collagen fibers in bone calcium deposits harden the matrix into a dense solid material Microscopy, Cells, Tissues: Human Tissues; Ziser Lecture Notes,

7 i. Blood 3. Muscle Tissues in bone the hardened matrix prevents easy diffusion of materials cells in bone tissue have a direct connection to blood vessels via intricate series of canals and passageways = Haversian canal system haversian canal lamellae lacunae canaliculi spongy bone vs compact bone spongy (=cancellous) bone has numerous spaces between haversian systems resulting in scaffolding = trabeculae these trabeculae are arranged along lines of strain compact bone matrix is a fluid = plasma rather than a solid cells float in fluid; RBC s, WBC s platelets unlike other tissue the blood is in constant motion in vessels in lymphatic vessels its called lymph different chemical composition close to half of body consists of muscle tissue elongated cells, spindle shaped, up to 1 ft long = muscle fibers very little matrix, instead embedded in framework of fibrous connective tissue highly contractile and elastic all cells contract to some degree, but muscle cells are much stronger and contract much more efficiently Microscopy, Cells, Tissues: Human Tissues; Ziser Lecture Notes,

8 eg. calf muscles can support 1 ton muscle cells generally stop dividing at birth (# fixed at birth) but each cell can expand greatly in volume Major Functions of Muscle Tissue: 1. movement voluntary skeletal muscles involuntary internal muscles 2. posture 3. heat generation three types of muscle tissue (more later): a. striated: most abundant, voluntary b. smooth: internal organs c. cardiac: heart 4. Nervous Tissues our perceptions of the world around us and our responses to it are mediated by nervous tissue nervous tissues are specialized for coordination and control cells are characterized by their: irritability very sensitive to stimuli conductivity can conduct an impulse along its length two major kinds of nervous tissues a. neurons impulse conduction generally no mitosis after birth b. neuroglia support, protection, insulation, etc [need specialized cells because of unique sensitivity of neurons to their environment] some mitosis tissue cells can grow because: Tissue Growth and Development Microscopy, Cells, Tissues: Human Tissues; Ziser Lecture Notes,

9 a. the number of cells increases hyperplasia eg. most childhood growth b. or the size of the cells increase hypertrophy eg. skeletal muscle cells, adipose cells neoplasia = development of a tumor Tissue shrinkage = atrophy results from aging or disuse Necrosis premature, pathological death of tissue due to trauma, toxins, infections, etc Gangrene any tissue necrosis resulting from an insufficient blood supply Infarction sudden death of tissue, eg heart muscle, that occurs when blood supply is cut off Apoptosis = programmed cell death normal death of cells that have completed their function billions of cells die every hour by apoptosis don t trigger inflammation since cell contents never escape; cell is engulfed by macrophages Tissue Repair eg. embryo produces ~ twice as many neurons as we need those that make connections survive, those that don t die eg. embryo has webbing between digits this normally goes away as cells between digits die eg. causes free earlobes in those with trait eg. causes shrinkage of uterus after pregnancy ends eg. immune cells can trigger cancer cells to commit suicide by apoptosis Microscopy, Cells, Tissues: Human Tissues; Ziser Lecture Notes,

10 damaged tissue can be repaired by regeneration or fibrosis Fibrosis = replacement of damaged tissue by scar tissue does not restore normal function Marfan Syndrome Some Diseases of Tissues a hereditary defect in elastin fibers; 1 in 20,000 live births some think Abe Lincoln had it symptoms: hyperextension of joints, hernias of groin, vision problems; typically tall stature, long imbs, spidery fingers, spinal curvature some have weakened heart valves and arterial walls; aorta sometimes enormously dilated Brittle Bone Disease =osteogenesis imperfecta hereditary defect of collagen deposition in bones bone fractures often present at birth may have hearing impairment due to malformed ear bones children sometimes mistaken for battered children require very careful handling, braces and prompt treatment of fractures Ehlers-Danlos Syndrome mutation in collagen gene abnormally long, loose collagen fibers results in stretchy skin, loose joints, slow wound healing, abnormalities in blood vessels, intestines and urinary bladder Microscopy, Cells, Tissues: Human Tissues; Ziser Lecture Notes,