Histology Chp1 Cytology

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cell membrane/ plasmalemma

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-8-10nm in width
-at E/M level, is trilaminar with outer and inner e- dense lamina and e- lucent intermediate lamina
- hydrophilic heads, hydrophob tails

-

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glycocalyx coat

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glycolipid and glycoprotein coat present in the external leaflet of the cell membrane
- protects cells from mechanical and chemical damage

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membrane proteins

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integral transmembrane proteins: span from one side of the cell membrane to the other
- also have peripheral membrane proteins

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functions of cell membrane

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-selectively permeable
- special receptor sites for antigen (foreign body) recognition and immunological mechanisms (phagocytosis)
-receptor sites for hormone-activated cellular events

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nucleus

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-contains chromatin, nucleolus or nucleoli and nuclear matrix
-skeletal muscle cells and osteoclasts are multinucleated
- absent in mammalian erythrocytes

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nucleus shapes

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-most spherical or ovoid
-spindle shaped in smooth muscle
- kidney shaped in monocytes
-multilobulated in neutrophil leukocytes

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euchromatin and heterochromatin

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-euchromatin: light, widely distributed, uniformly disbursed, indicates higher activity
-heterochromatin: basophilic, dark, clump, indicated lower activity

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nuclear envelope

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-two concentric membranes separated by 25nm wide space
-outer has ribosomes and is continuous with rough ER
-inner bound to the mem proteins and have specific sites of heterochromatin attached
-interrupted by pores which provide selective and active transport

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chromatin

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=DNA, basic proteins, histones and non-histone chromosomal proteins
- eu- and hetero- forms
- sex chromatin ( Barr body) is prominent in neutrophils (WBC) in females

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nucleolus

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-spherical and basophilic
-prominent in cells actively synthesizing protein
=loops of DNA which contain a group of rRNA genes
-involved in synthesis of rRNA and packaging into precursor of ribosomes

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Ribosomes

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-small, e- dense cytoplasmic particles (15-25 nm in diameter)
- singly or in groups called polysomes
-freely or in rough ER
- in all cells accept mature mammalian erythrocytes
-protein synthesis

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Endoplasmic reticulum

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-network of membrane bound tubules
- rough: basophilic, involved in protein synthesis

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smooth ER

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-abundant in cells involved in lipid metabolism
-enzymes for synthesis of steroid hormones located on membranes
-involved in drug detox
- release and recapture of Ca++ during contraction and relaxation of muscles

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golgi complex

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- appears as a black network of cisternae when stained with silver salt or osmium
-consists of parallel membranes bounded by flattened cisternae and associated tubules and vesicles on either side

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golgi complex functions

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-site for accumulation, concentration and packaging of secretory proteins into membrane bound vesicles
- biosynthesis of glycoproteins, glycolipids, phospholipids, and neutral lipids

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lysosomes

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- membrane-bounded vesicles that contain hydrolytic enzymes eg nucleases, proteases, lipases
-lysosomal enzymes are synthesized in the rER and subsequently transferred to the golgi complex where they enzymes are modified and packages as primary lysosomes

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how lysosomes function

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=primary lysosomes fuse with the phagocytosed material or obsolete cellular organelles (autophagy); the composite structure is termed a secondary lysosome
- after digestion the contents of the secondary lysosomes are retained as residual bodies or lipofuscin (age pigment)

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peroxisomes

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-membrane bound organelles containing oxidase and catalase enzymes which synthesize and destroy hydrogen peroxide
-energy derived from these processes
-in hepatocytes and cells of proximal convoluted tubules of the kidney
- peroxides detox (eg ethanol) and involved in gluoconeogenesis

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mitochondria

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-stained with janus green b in living
- abundant in cells with high metabolism eg muscles
- inner membrane thrown into folds (cristae) that contain respiratory enzymes that function in oxidative phosphorylation
- matrix contains DNA and ribosomes

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cytoskeleton

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composed of microfilaments, intermediate filaments, and microtubules imbedded in the cytoplasmic matrix or cytosol

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microfilaments

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-mainly composed of actin and myosin
- in most cells, form a thin sheath just beneath the plasmalemme and are associated with membrane activities such as endocytosis, exocytosis and cells migratory activity

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intermediate filaments

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-in almost all cells, but abundant in those subject to mechanical stress
- keratin tonofilaments= mechanical stability by forming desmosomes which are also present in keratinized epithelium
- desmin filaments support muscle
- neurofilaments support nerves
- glial filaments support astrocytes and neurolemmocytes (Schwann cells)

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microtubules

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- tubular structures that play significant role in maintenence of cell form and transport of organelles and vessels (eg. secretory granules)
- essential role in cell division and are major component of centriole

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centriole

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comprised of nine groups of three microtubules (triplets) in longitudinal and parallel arrangement
- triplets are interconnected through stabilizing linker proteins

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cytoplasmic inclusions

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-glycogen: by PAS reaction
- lipids: in adipose cells by osmic acid fixation
=melanin: skin and pigment epithelium of retina
- hemosiderin: result of hemoglobin degradation

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lipofucsin

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- is a cytoplasmic inclusion
-indigestible residue of phagocytosis
-commonly found in cardiac muscle, liver and nerve cells
- pigment increases with age

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tight intercellular junction

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-found in epithelial cells and consist of irregularly anastamosing ridges (transmembrane protein) that seal neigboring cells together in beltlike fashion
-constitutes a barrier that prevents the passage of water soluble molecules from the lumen to the intercellular space and vice versa
-may be selectively permeable to certain substances

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anchoring/adhering intercellular junctions

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three types: 1. zonula adherens
2. desmosomoes or macula adherens
3. hemidesmosomes

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zonula adherens

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-type of adhering/anchoring intercellular junction
- cells held together by a transmembrane protein linker
-a bundle of actin filaments run parallel to the junctional cell membrane
- prominent in lining of the intestine

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desmosomes or macula adherens

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-type of anchoring/adhering intercellular junction
- transmembrane linker plus an intercellular e- dense plaque
-intermediate filaments are attached to the plaque, forming a hairpin loop

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hemidesmosome

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- type of anchoring/adhering intercellular junction
-connect the cells from the extracellular matrix protein (similar to the half desmosome)

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communicating (gap) junction

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-permit direct passage of inorganic ions and other water-soluble molecules from cell to cell
- intercellular space is bridged by interlocking transmembrane proteins of the apposed membrane
- of considerable functional importance

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cilia

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-in respiratory, spermatozoa, oocytes
- surrounded by plasma membrane, it is composed of nine doublet microtubules around two central microtubules
- basal body is located at the base of the cilia, resembling centrioles
-flagellum= single long cilium as in spermatozoa

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microvilli

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cytoplasmic invaginations that increase the free surface for absorption
- in small intestine

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stereocilia

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long, rigid microvilli
- eg hair cells of the spiral organ (corti) of the inner ear