Animal Histology
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| What is histology? | The study of the microscopic structures of tissues |
| What are tissues? | Tissues are a set of differentiated cells that are located in the same region and occupy the same role. |
| What are tissues made up from? | Cells and all elements filling the intercellular and extracellular medium. |
| What are the types of tissues? | Covering tissues (epithelial tissues and glandular epithelial tissues)/ Non-specialized connective tissues and specialized connective tissues (adipose tissue, cartilage tissues, bone tissues and blood tissues)/ Skeletal striated muscle tissue, striated cardiac muscle tissue and smooth muscle tissue/ Nervous tissues of CNS and PNS |
| What is histogenesis? | The differentiation of tissues initially from the embryo (three germ layers). |
| What are the three primitive embryonic germ layers? | Ectoblast, Mesoblast and endoblast. |
| What are the derivatives of the Ectoblast germ layer? | Part of the epithelial tissues (epidermis) and the nervous tissue. |
| What are the derivatives of the mesoblast germ layer? | Non-specialized connective tissues, cartilage and bone, wall of the heart and vessels, smooth and striated muscles. |
| What are the derivatives of the endoblast germ layer? | Covering epithelium lining the intestine, respiratory system and urogenital tract. |
| Do organs only have a certain type of tissues? | No, an organ may contain several varieties of tissues issued from different embryonic cell layers. |
| What are epithelial tissues composed from? | Cells that are tightly packed together with very narrow intercellular spaces, at the limit of visibility under the light microscope. |
| What kind of cells are the epithelial cells? | Polarized, closely juxtaposed, integral with each other through adhesion junctions, involved in one or more physiological functions |
| Where do epithelial cells rest? | On the basal membrane separating it from the connective tissues. |
| Where are the epithelial tissues derived from? | All germ cell layers (ecto, endo and mesoblast) |
| How do epithelial cells differentiate? | Morphologically and functionally into two types; covering (surface or lining) epithelia that covers other tissues./ Glandular (with secretory function) specifically involved in the elaboration of secretory product. |
| What are the covering epithelia composed from? | One or more layers of epithelial cells closely juxtaposed with sometimes the presence of non epithelial cells. |
| Where do the covering epithelial cells rest ? | On basal lamina separating them from underlying connective tissues |
| Give three info about the epithelial cells | Innervated, non vascularized and have a great capacity for regeneration. |
| What do epithelia cover?, | The surface of the body (the epithelium of the skin is called epidermis) and its natural internal cavities (---open cavities that extend the inside of the body with the outside (airways, digestive tract,, urinary tract, genital tract) covered by mucosal epithelium ---closed cavities (cardiovascular cavities (vessels are covered by endothelium) and serous cavities (pleural (lungs), peritoneal (abdomen) and pericardial (heart) are covered by mesothelium) |
| Give four characteristics of the epithelial cells | Cohesion (adhesion molecules and specialized junction system attaches epithelial cells and maintain cohesion between these cells and the basal lamina.)/ morphology (because of the juxtaposition of epithelial cells and basal lamina, they either adopt squamous, cuboidal or cylindrical (columnar) shape) /Presence of intermediate filaments of cytokeratin in their cytoplasm help in polarity/ polarity(Apical pole, Lateral pole and Basal pole) assymmetrical distribution of components of the cytoplasm and of plasma membrane |
| Talk about the Apical pole | It is the domain in contact with the outer environment or faces the lumen of the cavities of the organisms. it's the most specialized since it contains most of proteins neccessary for most organ functions. And has membrane specializations (microvilli, cilia) |
| Talk about the lateral pole | It designates the surfaces that are apposed to neighboring cells, contains proteins necessary for fundamental processes common to all cells. There are anchoring and adhering junctions, and tight junctions connecting them to the apical pole |
| Talk about the basement membrane | Resets on basal lamina, hemi-desmosomes and focal adhesion points are obsereved |
| What are the roles of the basement membrane? | Polarization of epithelium, mechanically cohesion between the lateral pole and the underlying connective tissue, exchange and filtration processes and control of cellular metabolism. They also exist around some cells (adipose and muscular) |
| What are the criteria of classifications of the epithelial cells? | Number of cell layers, shape of the cells, specialization at the apical pole level. |
| Describe morpholigicaly unistratified epithelium cells | Consist of one layer of epithelial cells having same size and shape. Apical pole is facing the lumen of the covered cavity, and cells rest on basement membrane. |
| What is the roles of simple epithelial cells? | Selective diffusion, filtration, absorption or secretion |
| Where are monostratified epithelial cells mostly found? | Areas where risks of wear and injury are low |
| Describe the simple squamous epithelia | They are formed of a thin layer of flattened cells having the same size and shape. the nucleus is elongated, they are often permeable. |
| What are the main functions of the simple squamous epithelia? | Filtration, diffusion and osmosis. |
| Where are simple squamous epithelia mainly found? | In the alveolar sacs of the lungs |
| What are the two varieties of simple squamous ? | -endothelial ( cardiovascular system) -mesothelial (serous epithelium, covering pericardial, pleural and peritoneal closed cavities) |
| What is the main role of endothelium and mesothelium? | Phagocytic role |
| How is the basal lamina of the endothelium and the mesothelium? | Sometimes discontinuous with weak tight junctions. |
| What does Juxtaposed mean? | Side by side (juxta = next 'latin' and pose = placed 'french' |
| Describe the simple cuboidal epithelium | Consist of single layered cuboidal shaped epithelial cells with a spherical central nucleus. The cells are tightly attached to each other. |
| What are the main functions of cuboidal epithelium? | Secretion and absorption. |
| Where are simple cuboidal epithilia mainly localized? | At the surface of the ovaries (oviduct) and in the excretory ducts of certain exocrine glands (salivary and pancreas) |
| Describe the simple columnar epithelium | Cells are elongated and cylindrical, their nuclei are on the same level and located in the basal pole of the cell. |
| What are the functions of simple columnar epithelium? | Absorption and secretion. |
| Where are Simple columnar epithelium located | They line the stomach |
| How are simple cylindrical epithelium differentiated? | By the apical pole and what it is attached to (simple columnar- simple ciliated columnar epithelia) |
| What are the main differences between simple columnar and simple ciliated columnar epithelia? | Simple columnar with microvilli( apical pole is bordered by microvilli with striated plateau (small intestine) or with a bush boarder. simple ciliated (vibratile cilia line the fallopian tube) |
| Talk about the pseudo-stratified columnar epithelia | Simple epithelia having cells of different sizes but same shape (columnar) nuclei are located in various cites. However all cells rest on the basal lamina in a single layer, but some cells are short and don't reach the lumen, which suggests that tissue have several layers. Absorption and secretion. |
| Talk about pseudo-stratified columnar ciliated epithelium. | Cover most of the upper respiratory tract functioning in secretions and transports mucus (includes goblet cells) |
| Where are goblet cells mainly found? | Pseudo-stratified and simple columnar epithelium |
| What are stratified epithelial cells? | Epithelium consisting of several layers (at least 2) of superposed cells. Basal layer rests on basal lamina and superficial layer is facing the oitside or the lumen, the inner cells are called deep cells. |
| Where are most statified epithelial cells mainly found? | Regions subjected to friction, because they are resistant and able to protect underlying connective tissues. |
| How is the nomenclature of straified epithelial cells? | Based on the shape of the superficial cell. |
| What are the characteristics of regions that have stratified squamous epithelium? | Most abundant stratified one, observed in places that wear out alot of protection against abrasion |
| Talk about the keratinized stratified squamous epithelium. | They are the superficial layer of skin (epidermis) superficial cells are squamos and accumelate keratin but reject their nucleus and organelles, adapted for dessication (dehydration) forming a resistant and protective surface. |
| Talk about stratified cuboidal epithelium (presence, composition, role, site) | Less abundant than squamous, generally composed of two layers and play a better covering role than simple one, found in excertory ducts of sweat glands. |
| Talk about the stratified columnar epithelium | Rare, basal layers are made up from irreglar polyhedral cells, only superficial are cylindrical, role of protection and secretion found in urethra |
| Where are startified transitional epithelium mainly found? | (it is only found in the urinary system) . |
| Talk about the properties of covering epithelium? | --Renewal: they are exposed to wear and aging lowering their lifespan, they renew by proliferation of stem cells (replacement cells), stem cells divide and the rate of their renewal is different according to epithelium ---Permiability: they act as barriers however their permiability is selective because of the basal lamina (that separates it from chorion), serves as a selective filter. |
| What are malpighian epithelial cells composed from? | Stratified squamous, Composed of several layers of cells thick and well adapted to their protective role, cuboidal or columnar with circular nucleus, they reproduce via mitosis and as we go to the superficial layer they become flat with elongated nucleus, with capacity of regeneration (only upper part) , |
| Where are non-keratinized squamous stratified epithelium found? | They line the inner mouth,vagina and esophaguas (open cavities.) |
| What are urothelium mainly subjected to? | Subjected to significant variations in internal pressure and stretching |
| How is the structure of transitional epithelium? | , its thickness is variable according to the distention of the organ; bluky and rounded (empty bladder) squamous and flattened (full bladder ) -they dilate. |
| What are serous glands? | Their secretory products are fluid consistency (acinar cells of pancreas, stomach..) |
| How are endocrine glands classified according to mode of action of receptors? | Steroid and thyroid act on an intracytoplasmic or even intranuclear receptors, while peptides and aa bind to membrane receptors that will act on metabolism via a second messenger. |
| How can we classify endocrine glands according to their hormone type? | Steroid secreting: (androgens, estrogen) abundant with SER and mitochondria and lipid vacuoles. their lipid type makes them diffuse freely through plasma membrane without exocytosis. THYROID: synthesize thyroglobulins liposoluble hormones (T3 and T4) diffuse freely through plasma membrane Peptides : water soluble hormones (insulin) are released via exocytosis characterized by abundant RER Amino acid derivatives: (serotonin, melatonin) water soluble hormones rejected by exocytosis |
| What are hormones? | Any substance that are secreted via blood and will act on the receptors of target cells. |
| What are endocrine glands? | Cells capable of synthesizing storing and secreting into internal medium, via the bloodstream without a duct. |
| How do we classify exocrine glands according to the mode of secretion? | Merocrine : most common, cells produce and eject secretions by exocytosis cell integrity is respected (parotids) Apocrine: Secretory products are gradually accumelated at the apical pole detaching a small part of the cell in the form of a large vacuole ,released respecting integrity of cell membrane (mammary glands) Holocrine: secretory product completely fills cell cyroplasm for the cell undergoes degenration which then ruptures and releases its accumelated secretory substances (sebacceous glands) |
| Describe mucous cells? | Cytoplasm filled with mucigenic grains, flattened nucleus pushed to the lower part of the cell, wide lumen visiblilty |
| What are musous glands? | Secretory products are viscous liquids rich in GAG. |
| Describe serous cells? | Rounded nuclues localized at junctions of middle and lower third of the cell, apical pole has granulation, limits barely the visibility of its lumen, basal pole rich in RAR and mitochondrion, golgi apparatues developed, secretory apparatues occupy the top of the cell, densely, containing active or inactive enzymes (zymogen) merging with apical pole plasma membrane before going out |
| How can we classify exocrine glands according to their nature of secretory products? | Serous/Mucousal/ Sero-Mucosal (Submaxillary)/neither (sweat/sebous/salivary) |
| How do we classify exocrine glands based on secretory portions? | Acinous glands: acinus is a spherical or viral like structure, the wall is made of glandular cells in the form of a pyramide; the lumen of the secretory protion and the execretory duct are reduced (simple or compound) Tubular glands: elongated tube appearance with a wall made of cuboidal or columnar cells (striaght simple tubular, branched coiled compound...) Alveolar glands: in the form of a bag with a wide lumen relative to the acinous lumen of secretory portion are greater in size than acinous. |
| Can all kinds of secretory portions be avialabe at a specific gland? | Yes (submaxillary glands) |
| What are secretory cells? | Any cells thatexport out of their cytoplasm molecules they synthesized. |
| What are glandular cells? | Epithelial cells specialized in secretion; products are stored in secretory vesicles and are released on demand. |
| Talk about the histogenesis of glandular cells | They result from the differentaition of some covering epithelia that bud to form a cellular mass. that enters an underlying mesechyme they are either exocrine glands, maintain contact with covering epithelium and lumen of an organ through a duct endocrine glands; detach from covering epithelium, isolating in vascularized mesenchymal tissue. |
| How are glands classified? | Exocrine-endocrine-amphicrine |
| Why do we call the exocrine glandular cells polarized? | Since they show a morpho-functional polarization by having an apical pole which is bordering the lumen, poor in cell organelles and elaborated products are stored in it until secretion. Basal pole, rests on basement membrane that separates epi from CT |
| What is the contractile myoepithelial cells? | Cells located between glands and basal lamina help in secretion via contaction. |
| How do we classify exocrine glands by number of cells? | Uni cellular (goblet cells in intestine digestive and respiratory system producing mucus to protect them multicellular (secretory part and excretory part envelped by CT) |
| How do we classify exocrine glands by excretory canal (duct) | Simple (having a unique excretory duct associated either with one or more secretory portions compound having branched excretory duct and branched secretory portions. |
| What are exocrine glands? | Glands that discharge their secretory products in the external enivroment or in a natural cavity towards the outside. |
| How are connective tissues characterized? | Presence of cells and great intermolecular spaces between them filled with extracellular matrix |
| Where do connective tissues originate from? | Mesenchyme (non differentiated germ layer) |
| What are the two main characteristics of connective tissues? | Highly vascularized (except cartilage) and extremely abundant. |
| What are the main functions of CT | Protection/ exchange/ defense/ support/ nutrition/ energy storage/ transport and communication. |
| How are the first two layers of basement membrane synthesized? | By cells that they rest on, from type IV collagen, proteoglycans, and glycoproteins. (laminin, fibronectin) |
| What are the layers of basement membrane? | Lamina rara or lucida (clear, electron lucent) Lamina densa (middle, wide and electron dense, main layer of basal lamina) Lamina reticularis (AKA par fibroreticularis very clear represents junction between lamina densa and underlying CT secreted by cells of CT type III collagen) |
| Talk about non-specialized connective tissus. | AKA proper, common or classic, characterized by presence of cells (fixed or wandering) and a very abundant ECM (ground substances, fibers, structural glycoproteins) originate from mesenchyme. |
| How are non-specialized cells? | Non polar divided into two categories wandering and fixed cells. |
| How are fixed non-specialized cells? | Non-motile consist mainly of fibroblast (and adipocytes) |
| What are fibroblasts? | Principal and least specialized connective cell, compared to others, originate from the mesenchyme. |
| Describe the fibroblast? | Spindle shaped cells with long cytoplasmic processes (extensions) and lack a basement membrane. their size varies according to the activity level. significant mitotic activity. basophilic cytoplasm nucleus is central ovoid large and elongated with one or two nuecleoles, active fibroblasts contain abundant organelles involved in protein synthesis cytoskeleton is well developed and formed of actin filaments. |
| What roles do fibroblast have? | Control and maintain ECM (synthesis and secretion of macromolecules of ECM/ produce enzymes for catabolism of these macromolecules.) Tissue repair |
| What happens when fibroblasts deactivate? | Nucleus condenses, cytoplasm loses basophilic characteristics absence of any genetic activity, it becomes a fibrocyte. |
| Talk about wandering non-specialized cells. | Move actively, presence is variable and occasional, cells of the immune system, reach CT through bloodstream by crossing capillary barriers through diapedesis. (lymphocytes, granulocytes, monocytes..) |
| What is the ECM of non-specialized connective tissues? | Composed of amorphous ground substance, fibrous proteins and glycoproteins, very abundant. |
| What are ground substances? | Highly hydrated gel-like material, implicated in the diffusion of molecules between cells and blood, primarily made of GAG and proteoglycans |
| What are GAG? | Glycosaminoglycans, polysaccharide chains mainly made up of disaccharides hydrophilic and form a gel-like matrix sucks alot of water (hyaluronic acid, chondrition sulphate, dermatan sulphate heparan sulpahte. |
| What are proteoglycans? | Molecules that consist of core protein covalently attached to several sulphated GAGs Hyaluronic acid can form non covalent bonds with it, form the framework of the ECM and play an essential role in serving molecular exchanges through connective tissues. they form gels fix growth and control activity of enzymes and cell migration. |
| What are the two types of fibers? | Collagen and elastin |
| What are collagen fibers? | Collagen is the most abundant proteins in the human body, very resistant glycoproteins, insoluble in water but soluble in highly salted boiling water, can be denatured by collagenase.. alpha polypeptide chain organized in triple helix (called procollagen) aa chain differs according to the type of synthesized collagen. |