The Cell Part 1 PDF

The cell part 1 By Dr. Christina Samir; Lecturer of Histology, FOMSCU MD, PhD  Objectives Cell definition and main components Cytoplasmic membranous organelles Cytoplasmic non-membranous organelles Cell inclusions  D...

The cell part 1 By Dr. Christina Samir; Lecturer of Histology, FOMSCU MD, PhD  Objectives Cell definition and main components Cytoplasmic membranous organelles Cytoplasmic non-membranous organelles Cell inclusions  Definition The structural and functional unit of the body Cells → Tissue → Organ → System → Body The cell is divided into two major compartments: the cytoplasm and the nucleus. The cell Cytoplasm Nucleus Composed of fluid Nuclear Nuclear Nucleolus component (cytosol) Chromatin membrane sap Contains: organells inclusions membranous Non- membranous Protoplasm= cytoplasm+karyoplasm  A) Cytoplasm Colloidal solution where cytoplasmic matrix consists of inorganic ions and organic molecules such as carbohydrates, lipids, proteins. They all have the unit Membranous Cell membrane structure membrane Endoplasmic reticulum Mitochondria Golgi apparatus Lysosomes Peroxisomes Organelles Coated vesicles highly organized, living, essential to vitality of the Endosomes cell Inclusions Non-membranous non-organized, non-living, not essential to vitality of Ribosomes Cytoplasm contains the cell Stored food (glycogen- lipid) Cytoskeleton Centrioles Pigments (melanin, lipofuscin, dust, tattoo) proteasomes Cytosol: Protein solutions, Enzymes, Products of enzyme  Membranous organelles 1) Cell membrane (plasmalemma) LM: not visible, what is really seen is the cell coat (glycocalyx) by special stain (PAS) EM: 7.5 nm thick, trilaminar (inner electron dense, middle electron lucent, outer electron dense)  Membranous organelles 1) Cell membrane Molecular structure: (lipid bilayer, cholesterol, proteins, carbohyrates) a) Lipid bilayer: A double layer of phospholipids with the hydrophobic fatty acid chains (tails) located in a middle region away from water and the hydrophilic polar Extracellular head groups contacting the water towards intra and extracellular compartments b) Cholesterol: more in the inner half of the membrane Both constitute 40% of cell membrane Intracellular mass  Membranous organelles 1) Cell membrane molecular structure c) Proteins: Constitute approximately 50% of the total membrane mass Two types: Integral membrane proteins embedded within the lipid bilayer (partially) Span the lipid bilayer (transmembrane or multipass) peripheral membrane proteins not embedded within the lipid bilayer but Integral protein Peripheral bound to one of the two membrane surfaces, protein particularly on the cytoplasmic side  Membranous organelles 1) Cell membrane d) Carbohydrates: molecular structure 10% of the cell membrane mass in the form of glycolipids and glycoproteins forming cell coat Cell coat contains receptors as for hormones Cell coat  Membranous organelles 1) Cell membrane functions a) General: b) Cell membrane specializations: cell-cell recognition Free cell borders form microvilli (increase surface area as in intestine, flagella (motility exocytosis of sperm tail), cilia (lining trachea and Endocytosis (pinocytosis & fallopian tube with rhythmic, one direction phagocytosis) movement), stereocilia (in epididymis) receptor site for signaling Lateral cell border: cell junctions molecules Basal cell surface: share in basement Selective permeability membrane and hemidesmosomes formation Transport (passive, active)  Membranous organelles 2) Endoplasmic reticulum rough (RER) and smooth (SER) The endoplasmic reticulum is an anastomosing network of intercommunicating cisternae or tubules formed by a continuous membrane, with some regions that bear polysomes appearing rough and other regions appearing smooth  Membranous organelles 2) Endoplasmic reticulum rough (RER) and smooth (SER) A. Rough (granular) Endoplasmic Reticulum (RER) LM: localized or patchy basophilia prominent in cells specialized for protein secretion, such as pancreatic acinar cell, nerve cell Nissl granules EM: parallel stacks of flattened cisternae limited by membranes that are continuous with the outer membrane of the nuclear envelope and ribosomes attached to their cytosolic surface. The major function of RER is production of membrane associated proteins, proteins of many membranous organelles, and proteins to be secreted by exocytosis, it modifies proteins delivered to Golgi.  Membranous organelles 2) Endoplasmic reticulum rough (RER) and smooth (SER) A. Smooth (agranular) Endoplasmic Reticulum (SER) LM: responsible for relative acidophilia of cells they are abundant in lipid producing cells such as liver cell EM: consists of anastomosing tubules and occasional vesicles, their lumen is continuous with that of the RER and lack ribosomes. Functions: drug detoxification, glycogen metabolism, lipid and steroid hormones synthesis, HCl formation in stomach, release Ca for muscle contraction.  Membranous organelles 3) Mitochondria Mitos=thread & chondros=granule Shapes: spheres, rods, elongated filaments, and even coiled structures rapidly changing shape, fusing with one another and dividing, and are moved through the cytoplasm along microtubules Number: more numerous in cells that use large amounts of energy such as Skeletal muscle striated muscle cells and liver cells but none in mature RBCs & terminal keratinocytes. Site: where the cell needs energy such as near the contractile elements of striated muscle cells (intermyofibrillar) LM: contribute to the acidophilia of the cytoplasm. vitally stained with Janus green B → blue green & iron hematoxylene→ black blue Liver cell  Membranous organelles 3) Mitochondria EM: membranous vesicles surrounded by two membranes (outer & inner with intermembrane space) enclosing mitochondrial sap. Outer membrane: smooth, sieve-like containing porins, trilaminar unit structure Inner membrane: folded into cristae (why?), trilaminar unit membrane Mitochondrial matrix: circular DNA, mRNA, tRNA, enzymes, granules (store calcium) Functions: Generation of ATP and cell respiration NB: mitochondria can divide by binary fission (why?)  Membranous organelles 4) Golgi apparatus Pancreatic acinar cell Site: between nucleus and secretory surface of secretory cells (eg. Pancreatic acinar cell), allover the cytoplasm near the nucleus(nerve cell) LM: not stained with H&E→ negative Golgi image, stained with Ag impregnation→ Darkly stained threads near the nucleus Golgi EM: appears as a series of stacked, flattened, smooth membranous saccules, and transport vesicles.  EM of Golgi Transfer vesicles Secretory vesicles Golgi saccules Micro Macro (thin center and thick Non modified protein Modified protein peiphery Origin from RER and fuse with cis face Origin from trans face to form (lysosomes or secretory vesicles) Cis Golgi network Medial Golgi Trans Golgi network convex network concave Entry face Between cis and trans exit face, Immature Mature closer to the toward the cell membrane. nucleus  Membranous organelles 4) Golgi apparatus Functions: 1) post-translational modifications of proteins produced in the RER 2) packaging, sorting and addressing these proteins to their proper destinations (secretory granules or lysosomes). 3) Add plasmalemma  Membranous organelles 5) lysosomes LM: can’t be seen by H&E EM: spherical, electron dense, from 0.05 to 0.5 μm in diameter Function: 1. sites of intracellular digestion and turnover of cellular components by hydrolytic enzymes 2. abundant in cells with great phagocytic activity (eg, macrophages,) and play a role against bacterial invasion  Membranous organelles 5) lysosomes Types: 1. 1ry: just coming out of Golgi 2. 2ry: 1ry fusing with a phagosome forming heterolysosome pinocytotic vesicles forming multivesicular body Dead organelles forming autophagosome 3. Residual body: undigested material  Non-membranous organelles Cytoskeleton Thin filaments Intermediate Centrosome Ribosomes Proteasomes filaments and centrioles Thick filaments Microtubules  Non-membranous organelles 1) Ribosomes LM: responsible for basophilia of cytoplasm (why?), 3 forms: 1. Diffuse basophilia: in rapidly dividing cells eg erythroblast (due to free ribosomes) 2. localized basally: eg. pancreatic acinar cell (due to ribosomes attached to RER) 3. Patchy basophilia: as Nissel granules in nerve cells (due to ribosomes attached to RER)  Non-membranous organelles 1) Ribosomes EM: 1. free or attached 2. Two subunits : large and small formed of proteins and rRNA Function: protein synthesis  Non-membranous organelles 2) Proteasomes Large, barrel-shaped protein complexes located in both the cytoplasm and nucleus, degrade and digest damaged or unneeded proteins  Non-membranous organelles 3) Cytoskeleton Microfilaments (actin filaments( Microtubules 6 to 8 nm Intermediate filaments 20 to 25 nm Actin protein monomers organized 8 to 10 nm Hollow cylinders composed of into two thin, intertwined protein Eg. Keratin and neurofilaments. tubulin protein filaments Maintain cell shape and Provide structural support; stabilize rigidity, organize and move Maintain cell shape; support junctions between cells organelle , separate microvilli; share in muscle chromosomes during the contraction process of cell divisions.  Non-membranous organelles 4) Centrosome Amorphous region adjacent to nucleus; contains a pair of centrioles Each centriole is composed of nine highly organized microtubule triplets Organizes microtubules; participates in mitotic spindle formation during cell Division  Cell inclusions Lipid droplet Glycogen Pigment granules