PNB 2264 Unit 2 Tissues

what is a tissue

collection of cells that are serving a common function inside the body

give rise to organs

Tissues are defined by differences in:

cellular composition, extracellular makeup (or matrix) and function

extracellular matrix

contains proteins, salts, water and other macromolecules

four primary tissue types

epithelial, connective, nervous and muscle

functions of epithelia

epithelial tissue

physical protection: water, chemicals, physical injury

selective permeability

secretion and absorption

sensation

characteristics of epithelia

cellularity, polarity, attachment, avascularity, regenerative capacity

epithelia classification

based on function or structure:

exchange, transporting, ciliated, protective or secretory

exchange epithelia

permit the rapid exchange of materials between the two compartments

transporting epithelia

prevent free movement between adjacent cells

substances must instead pass through the epithelial cell, crossing the membrane as they do so

ciliated epithelia

promote movement of extracellular particles

ex. line the airways

pathology: Kartagener’s syndrome, a primary ciliary dyskinesia

protective epithelia

secretory epithelia

are usually organized into glands

endocrine glands: release their secretions into blood or interstitial fluid

exocrine glands: release their secretions into ducts

classification of glands: structure

based on number of ducts and architecture

unbranched duct: simple tubular, simple alveolar

branched duct: compound tubular, compound alveolar, compound tubuloalveolar

classification of glands: function

based on the mechanism of secretion

merocrine secretion (salivary glands): exocytosis

apocrine secretion (mammary glands): pinched off apex portion of the cell

holocrine secretion (sebaceous glands): ruptured cell

Intercellular junctions:

epithelial cells are strongly bound to each other on their lateral surface by membrane specialization called ___

types of intercellular junctions

tight junctions, adhering junctions, desmosomes, gap junctions

tight junctions

found along the membrane of interconnected epithelia

restrict movement of molecules between cells

ex. food poisoning

adhering junctions

found along the membrane of interconnected epithelia

attach to the cytoskeleton

often found on the basal membrane

desmosomes

found along the membranes of interconnected epithelia

physical connection between adjacent cells

flexibility and support

pathology: pemphigus vulgaris, an autoimmune disorder characterized by separation of epidermal layers and blistering

gap junction

found along the membrane of interconnected epithelia

electrochemical connection between adjacent cells

classification of epithelia: anatomical

based upon the shape of the cell and number of layers

simple squamous, simple cuboidal, simple columnar, stratified squamous, stratified cuboidal, pseudostratified columnar, transitional

pathology: cystic fibrosis

caused by a mutation in CFTR (cytic fibrosis transmembrane receptor)

connective tissue

most diverse and abundant tissue type

connects other tissues together

cells, protein fibers (collagen, elastin, etc), ground substance (water and ions)

these are often referred to collectively as the ECM (extracellular matrix)

connective tissue classification

connective tissue proper: loose ( 1. areolar, 2. adipose, 3. reticular) and dense (1.regular, 2.irregular, 3. elastic)

supporting connective tissue: cartilage (1. hyaline, 2. fibrocartilage, 3. elastic) and bone (1. compact, 2. spongy)

fluid connective tissue: blood and lymph

general function of connective tissue

physical protection, support and structure, storage, binding of structures, transport, immune protection

areolar tissue

loosely packed assembly of all fiber types, fibroblasts and immune cells; primary function is to cushion organs; contains key mediators of immunity to minimize invasion by infectious pathogens

location: supporting under epithelial layers and surrounding organs

adipose tissue

matrix is crowded by adipocytes which are tightly packed; serve to insulate and protect organs

location: around major organs and within the subcutaneous layer of the skin (under dermis)

reticular tissue

meshwork of reticular fibers loosely organized to form a flexible meshwork to support tissue and immune cells of few organs

location: lymph nodes, bone marrow and splenic pulp

regular tissue

fibroblasts embedded within a regularly ordered assembly of collagen fibers; functions to resist stress of being pulled in a given direction

location: attach muscle to bone (tendon) or bone to bone (ligament)

irregular tissue

irregularly arranged collagen fibers with fibroblasts embedded within; irregular organization provides tissue the ability to resist forces in many directions

blood contains:

platelets, erythrocytes (red blood cells), lymphocytes (white blood cells) and neutrophils (white blood cells)

bone

heterogenous structure

two kinds: compact/ cortical bone and trabecular/ cancellous/ spongy/ diploe bone

compact/ cortical bone

absorbs a great deal of mechanical energy before fracture

organized in an osteon haversion system: bones is a system of tubes within tubes — key vocab: periosteum, lamellae, osteon, osteocyte, lacunae, central canal, canaliculi

trabecular/ cancellous/ spongy/ diploe bone

can be deformed without fracture

bone matrix is a ___ material.

at any one time, most of the calcium in the body exists as ____

bones are a ___ and ____ reservoir

composite

hydroxyapatite (Ca10(PO4)6(OH)2)

calcium; phosphate

bone cell types:

stem cells (osteoprogenitors), osteoblasts, osteocytes, and osteoclasts

osteoprogenitor cells develop into osteoblasts; some osteoblasts (form the bone matrix) differentiate into osteocytes (maintains bone matrix)

resorption

breakdown of bone

Cartilage

many similarities with bone

found throughout the entire body

semi-rigid connective tissue, not as strong as bone but more flexible

chondroblasts

begin to produce extracellular matrix

chondrocytes

cells that continue to produce matrix and become surrounded by the matrixh

chondroclasts

breakdown cartilage

hyaline

flexible, firm gel matrix secreted by chondroblasts which become embedded in lacunae (chondrocytes); cushions, supports and reinforces other tissue and organs

location: nose, trachea, ribs, ends of long bones, and embryonic skeleton

fibrocartilage

firm hyaline matrix but with more organized collagen fibers; capable of resisting compressive force

location: components of joints with limited flexibility such as intervertebral discs, menisci and pubic symphysis

elastic cartilage

organization is same as hyaline cartilage enriched with elastin fibers to promote greater degree of flexibility and stretch and allowing tissue to return to original shape

location: outer ear and epiglottis

Models of cartilage growth

interstitial and appositional growth

interstitial growth

1. chondrocytes housed in lacunae undergo mitotic division, 2 chondrocytes occupy one lacuna

2. the cells begin to synthesize and secrete their own extracellular matrix and are now separated from each other by a matrix border

3. the result is two chondrocytes, two lacunae and more extracellular matrix secretion

appositional growth

1. stem cells along the internal edge of the perichondrium begin to divide into chondroblasts

2. chondroblasts begin to produce extracellular matrix and differentiate into chondrocytes and from new lacunae and add to the already existing matrix

cartilage is ____

avascular

this gives it only limited repair capacity

Four tissue types:

epithelial, connective, muscle, and nerve

epithelial tissue characteristics

minimal matrix, basal lamina matrix, no direct blood supply, microvilli and cilia

location: covers body surface; lines cavities and hollow organs and tubes; secretory glands

cell arrangements and shapes: variable number of layers from one to many; cells= flattened, cuboidal or columnar

connective tissue characteristics

extensive matrix, varied matrix (protein gibers in ground substance that ranges from liquid to gelatinous to firm to calcified), cartilage has no blood supply

location: supports skin and other organs; cartilage, bone and blood

cell shape and arrangement: cells not in layers; usually randomly scattered in matrix; cell shape irregular to round

muscle tissue characteristics

minimal matrix, external lamina matrix, able to generate electrical signals, force and movement

location: makes up skeletal muscles, hallow organs and tubes

cell arrangement and shape: cells linked in sheets or elongated bundles; cells shaped in elongated, this cylinders; heart muscle cells may be branched

nerve tissue characteristics

minimal matrix, external lamina matrix, able to generate electrical signals

location: throughout body; concentrated in brain and spinal cord

cell arrangement and shape: cells isolated or networked; cell appendages highly branched and / or elongated

Metaplasia

one tissue type is replaced by another

hypertrophy

cell growth in the absence of cell division

hyperplasia

tissue growth due to “normal” cell growth

neoplasia

tissue growth due to “abnormal” cell growth

apoptosis

programmed cell death

necrosis

uncoordinated cell division