epithelia & connective tissue Flashcards
what is histology?
science that deals with the study of tissues
what is a tissue?
group of cells with a common embryonic origin and function together to carry out specialised activities
give examples of tissues
-hard tissue (bone)
-semisolid (fat)
-liquid (blood)
what are the four basic tissue types?
-epithelial
-connective
-muscular
-nervous
what does the epithelial tissue type do?
covers body surfaces and lines hollow organs, body cavities, duct and forms glands
what does the connective tissue type do?
Protects,supports and binds organs,also stores energy as fat,provides immunity
what does the muscular tissue type do?
Generates the physical force needed to make body structures move and generate body heat
what does the nervous tissue type do?
detects changes in the body and responds by generating nerve impulses
what are cell junctions?
contact points between membranes of tissue cells
what are the 5 main types of cells junctions?
-tight junctions
-adherens
-desmosomes
-hemidesmosomes
-gap junctions
what is the structure of tight junctions?
-web-like strands of transmembrane proteins
-found in the stomach, intestines and bladder
what do tight junctions do?
-fuse together at outer surfaces of cells
-seal passageways between cells
-prevent leakage and stop substances from passing between cells
what do adherens junctions do?
-contain plaque protein which anchors membrane proteins to cytoskeletons
-cadherins- transmembrane glycoproteins join adjacent cells
-form adhesion belts round cells
-helps resist cell separating under mechanical stress i.e during peristalsis
what do desmosomes do?
-like adheres they contain plaque protein and cadherins
-plaque attaches to intermediate filaments in cells (keratin)
-intermediate span cells providing stability
what do hemidesmosomes do?
-do not link adjacent cells
-contain integral transmembrane glycoproteins (not cadherins) which attach to intermediate filaments inside of the cells
-they anchor to basement membranes by binding to laminin
what is the cytoskeleton?
-a network of protein filaments throughout the cytosol
-it provides structural support for the cell
-there are 3 types
what are the three types of cytoskeleton?
-microfilaments-actin/myosin
-intermediate filaments
-microtubules
what do microfilaments do?
generate movement and mechanical support
what do intermediate filaments do?
stabilise organelle position and attaches cells together
what do microtubules do?
determines cell shape and the movement of organelles and vesicles
what are gap junctions?
-cells connected by connexiins
-they have fluid filled transmembrane holes made from connexins
what do gap junctions do?
-allows diffusion of ions/small molecules
-provides electrical coupling between cells
-is important in muscle contraction
compare epithelia and connective tissues…
-epithelial tissue has no blood vessels
-epithelia form surface layers and are not covered (except lining blood vessels)
-because of these differences they are almost always found together exchanging nutrients and waste
what are the functions of the epithelia?
-forms selective barriers
-provides secretory surfaces
-provides protective surfaces
what are the different surfaces of epithelial cells?
-apical surfaces that may contain cilia or microvilli
-lateral surfaces that may contain junctions
-basal surfaces which bind to the basement membrane
what does the basement membrane consist of?
-two extracellular layers
what are the two extracellular layers the basement membrane contains?
-basal lamina-containing laminin and collagen
-reticular lamina-containing fibroblasts which secrete collagen
how are epithelial cells classified?
-by the shape of the surface cells
-by the arrangement of cells into layers
what are the different shapes of the surface cells of epithelial tissues?
-squamous
-cuboidal
-columnar
-transitional
squamous
-flat shape and allows rapid passage of substances
cuboidal
-cube shaped, the cells are tall as they are wide
columnar
-tall column, the cells are taller than they are wide which protects the underlying tissues
transitional
-the shape varies with the tissue stretching (changing shape)
what are the different arrangement of cells into layers for epithelial cells?
-simple
-pseudostratified
-stratified
simple
-one layer, all cells are in contact with the basement membrane, this is important for diffusion, osmosis,filtration,secretion and absorption
pseudostratified
-two or more layers
-only the basal layer is in contact with the basement membrane and this protects underlying tissues
what do simple squamous epithelium do?
-they line surfaces involved in passive transport (diffusion)
what are some of the lining surfaces involved in diffusion?
-gases (lungs)
-liquids (walls of blood capillaries called endothelium)
-epithelial layer of serous membranes or serous (mesothelium)
-lining of pleural, pericardial,peritoneal cavities (visceral/parietal layers)
what do simple cuboidal epithelium do?
-functions in secretion and absorption
-usually lines small ducts and tubules
-covers the surface of the ovary
-lines the kidney,salivary and pancreatic tubules
what do non-ciliated simple columnar epithelium do?
-exhibits elongated nuclei
-found on highly absorptive surfaces i.e lining the gastrointestinal tract
-microvilli increase surface area for absorption
-goblet cells-secrete mucus
what do ciliated simple columnar epithelium do?
-exhibits elongated nuclei
-found on highly absorptive surfaces i.e lining the gastrointestinal tract
-microvilli increase surface area for absorption
-goblet cells-secrete mucus
how are pseudostratified columnar epithelium?
-they have several layers (stratified) but all cell contact basement membrane
-the nuclei are all at different levels (not columnar)
-ciliated variety is almost exclusive to the lining of the upper respiratory tract
how are stratified squamous epithelium?
-keratinised variety forms the superficial layer of skin (epidermis)
-non-keratinised variety lines the wet surfaces (mouth,oesophagus and vagina)
-they help protect against abrasion,water loss,UV,defence against microbes
how are stratified cuboidal epithelium?
-they are thin,usually only 2-3 cells thick
-found in ducts of sweat glands
-provides protection to other tissues
stratified columnar epithelium
very rare
how are transitional epithelium?
-they have a variable appearance
-exclusively lines the urinary system:bladder,ureters and urethra
-allows urinary organs to stretch and maintain the protective lining
what are the functions of the glandular epithelium-endocrine glands?
-secretion
-endocrine glands secretion enters the interstitial fluid and diffuse directly into the bloodstream without flowing through a duct
what is the secretion of endocrine glands called?
-hormones
what are examples of endocrine glands?
-pituitary glands
-ovaries
-thyroid
-adrenal
what does glandular epithelium involve?
-exocrine glands-secretions of exocrine glands released into ducts and onto a surface epithelium or lumen
what are examples of exocrine glands?
-sweat
-oil earwax glands of skin
-salivary glands
what are the functions of connective tissues?
-bind tissues together
-support and strengthen tissue
-protect and insulate internal organs
-compartmentalise and transport
-energy reserves and immune responses
what are connective tissues derived from?
-the mesenchyme:
immature cells have names that end in -blast e.g fibroblast
mature cells have names that end in -cyte e.g osteocyte
what are the features of connective tissues?
-all have:sparse cells and extracellular matrix
-it consists of protein fibres and grounds substance (may be fluid,semifluid,gelatinous or calcified)
-connective tissue is usually highly vascular and supplied with many nerves
what is the extracellular matrix?
- non-cellular material located between and around the cells
what connective tissues have exceptions to common features?
-cartilage and tendon-both have little or no blood supply and no nerves
what are the common CT cells?
-fibroblasts
-chondrocytes-make various cartilaginous CT
-adipocytes-store triglycerides
-osteocytes-make bone
-white blood cells-form part of blood
what do fibroblasts do?
-they are the most numerous cell of connective tissues
-they are large flat cells with branching processes
-they secrete protein (collagen,elastin & reticular fibres) and a ground substance
what are the different ways connective tissues can be classified?
-embryonic connective tissue
-mature connective tissue-there is loose connective tissue and dense connective tissue
-cartilage
what does embryonic connective tissue include?
-Mesenchyme-gives rise to all CTs
-mucous connective tissue (Wharton’s jelly)
what is mucous connective tissue?
-a gelatinous substance within the umbilical cord and it is a rich source of stem cells
what are the 3 types of loose connective tissue?
-areolar
-adipose
-reticular
what is areolar CT ?
-it is the most widely distributed in the body and contains several types of cells and all three fibre types
what does areolar CT do?
-it is used to attach skin and underlying tissues and as a packing between glands,muscles and nerves
where is adipose tissue located?
-in the subcutaneous layer deep to the skin and around organs and joints
what does adipose tissue do?
-reduces heat loss and serves as padding and as an energy source
what is reticular CT?
-a network of interlacing reticular fibres and cells
what does reticular CT do?
Forms a scaffolding used by cells of lymphoid tissues such as the spleen and lymph nodes
what are the three types of dense connective tissue?
-dense irregular CT
-dense regular CT
-elastic CT
what does dense irregular CT consist of?
-mainly of fibroblasts and collagen fibres randomly arranged
what does dense irregular CT do?
-provides strength when forces are pulling from many different directions
what is dense regular CT?
-it comprises of tendons, ligaments and other strong attachments where the need for strength along one axis is mandatory (a muscle pulling on a bone)
what does elastic CT consist of?
-mainly fibroblasts and freely branching fibres
what does elastic CT do?
-allows the stretching of certain tissues like the elastic arteries (aorta)
what is the cartilage?
-tissue with poor blood supply that goes slowly
-when injured or inflamed, repair is slow
what are the three types of cartilage?
-hyaline( glass like) cartilage
-fibrocartilage
-elastic cartilage
what is hyaline cartilage?
-the most abundant type of cartilage which covers the ends of long bones and parts of the ribs, nose,trachea,bronchi and larynx
what does hyaline cartilage do?
-provides a smooth surface for joint movement
what is fibrocartilage?
-a very strong tough cartilage that has thick bundles of collagen fibres
what does fibrocartilage do?
-fibrocartilage discs in the intervertebral spaces and the knee joints support the huge loads up and down the long axis of the body
what does elastic cartilage consist of?
-chondrocytes located in a threadlike network of elastic fibres
what does elastic cartilage do?
-makes up the malleable part of the external ear and epiglottis
what are epithelial membranes made up of?
-epithelium + connective tissue
what are the types of epithelial membranes?
-mucous membranes
-serous membranes
-cutaneous membranes (skin)
what does mucous membranes do?
-line the inferior body surfaces open to the outside (digestive, respiratory and reproductive tracts)
what do serous membranes do?
-line some internal surfaces (parietal layer next to the body wall, serous fluid between layers and visceral layer next to the organ)
