Cell Membrane Updated (2025) PDF

1st Year Histology (Plasma membrane - Plasma lemma -Limiting membrane)  Not seen? Very thin (But could be seen with special stains e.g. silver).  1. 7.5 to 10 nm in thickness. 2. Trilaminar appearance: 2 electron dense layers. 1 el...

1st Year Histology (Plasma membrane - Plasma lemma -Limiting membrane)  Not seen? Very thin (But could be seen with special stains e.g. silver).  1. 7.5 to 10 nm in thickness. 2. Trilaminar appearance: 2 electron dense layers. 1 electron lucent in-between (Unit membrane) 3. Stained by Osmium Tetroxide.  (1) Lipid : (bilayer) - It's formed mainly of phospholipid, glycolipid & cholesterol. - Phospholipid molecule consists of: 1. One Head: hydrophilic, directed inside & outside the cell (charged) ‫راس وا ﺪﻩ ﺮا و ﺟﻮا ﺑﺘﺤﺐ اﳌﯿﻪ و ﻠﳱﺎ ﴮﻨﺔ‬ 2. Two Tails: hydrophobic, directed to the center of the membrane (nonpolar) ‫ذﯾﻠﲔ ف اﻟﻨﺺ ﳛﺒﻮا ا!ﻫﻮن وﻣﻦ ﲑ ﴮﻨﺔ‬ So, Trilaminar appearance is due to deposition of stain in head in both side & not in tails ‫ﻋﻠﻝ ؟‬ DR. Ahmed Ammar 1  1st Year Histology (2) Protein :  It's the major molecular part of the membrane (in size).(1/2 of the mass)  Present in 2 forms: I. Peripheral protein: located on the inner & outer surfaces of cell membrane (mainly inner) ‫ﻫﺎﻡ‬. II. Integral proteins: embedded in lipid bilayer may arise from one surface but if arise from both surfaces it is called (Transmembrane protein). They form channels & carrier that help passage of molecules & ions across the membrane. (3) Carbohydrates:  Located on the outer surface of cell membrane attached to phospholipid (glycolipid) or protein (glycoprotein), called (Glycocalyx) ‫ﻏﻄﺎء اﻟﺴﻜﺮ‬.  They are polysaccharide. 1- Keep constant intracellular environment. 2- Keep the shape of the cell (e.g. Nerve cell). 3- Contain antigenic receptors: for recognition. 4- Contain signaling receptors: regulate the function of the cell. 5- Selective barrier: control the passage of substance in & out of the cell. DR. Ahmed Ammar 2  1st Year Histology : ‫ٔﻧﻮاع‬4 ‫ﻧﻮاع اﻟﻨﻘﻞ ﱪ ﻏﺸﺎء اﳋﻠﯿﻪ ﺛﻼﺛﺔ‬4ٔ 1). 2) : (vesicle ‫)ﺣﻭﻳﺻﻠﺔ‬ ♥ Changes at cell membrane at localized site followed by vesicle formation. ♥ There are 2 main types of Vesicular transport: 1. Endocytosis. 2. Exocytosis. 1. Endocytosis: (A)Pinocytosis: cell drinking. Occur by invagination of the cell membrane that entrap the fluid then pinch off of the vesicle. Not depend on clathrin. ‫ﻫﺗﻔﻬﻡ ﺍﻟﺻﻔﺣﻪ ﺍﻟﺟﺎﻳﻪ‬ Occur in endothelial cells of blood vessels :‫ﻣﺛﺎﻝ‬ (B)Phagocytosis: cell eating. Occur by cytoplasmic processes that surround the foreign substance, then the processes fuse together to form vesicle called phagosome. Occur in Macrophage & Neutrophils. May be Receptor-Mediated → phagocytosis of bacteria or Non-Receptor-Mediated → phagocytosis of dust & carbon. DR. Ahmed Ammar 3  1st Year Histology (C) Receptor mediated endocytosis: It's endocytosis of protein & hormone (ligand). Occur as following: 1- The ligand has 2 types of receptors → one present on the surface of the cell & others present on area called (coated pit). 2- The coat is formed of polypeptide (clathrin). 3- When the ligand bind to receptors on the surface→ They will invaginate to form coated pit → the invagination ↑↑ till it pinch off & form coated vesicle or early endosome.(ligand receptors complex) 4- Early endosome moves deep in the cytoplasm to form late endosome. 5- The clathrin coat is separated & return to the surface then receptors also separated by the help of lysosome & return to the surface. DR. Ahmed Ammar 4  1st Year Histology 2. Exocytosis:  It's the process by which a cytoplasmic vesicle release its content outside the cell.  Exocytosis is affected by Ca++ in the cytoplasm. (↑ Ca → ↑ exocytosis)  2 Pathway for exocytosis: 1. Constitutive pathway: the vesicle leave the cell after its formation & not stored. e.g. antibodies. 2. Regulated pathway: the vesicle stored in cytoplasm & released by nervous or hormonal stimuli e.g. pancreatic enzyme. 3) Definition: It's communication between cells → to control their growth & coordinate their functions. DR. Ahmed Ammar 5  1st Year Histology Shape: Spherical or rod organelle. Stain: Not visible with H & E but stained with Janus green B (supra-vital) stain (1 x 10 µm). Site: according to energy utilization e.g.: → Apical part of ciliated cell. → Basal part of ion transferring cell. → Middle part of spermatozoa. Number: according to energy utilization e.g.: → ↑ Number of mitochondria in active cells as cardiac ms. cells. → ↓ Number of mitochondria in inactive cells as osteocyte. Fate: Can divide by simple binary fission & Contain their own circular DNA & RNA ‫ﺑﺄﻧﻭﺍﻋﻪ‬. Life span → 10 days. DR. Ahmed Ammar 6  1st Year Histology 1- Outer membrane: Smooth & have receptors for proteins to enter intercellular space. 2- Inner membrane: Contain folds called cristae: Directed into the the interior. The Cristae Flat in shape. Contain enzymes of oxidative phosphorylation & electron transport chain → produce ATP. N.B: The cristae is tubular in shape in steroid secreting cell. N.B2: The cristae is ↑ in number in active cells. 3- Intermembrane space: between outer & inner membrane. 4- Matrix space: contain → Protein & ribosomes. → Enzymes for kerbs cycle. → Ca++ (electron dense granule). → Mitochondrial DNA & RNA. ‫ﺍﻟﺗﻔﺎﺻﻳﻝ ﻟﻠﻔﻬﻡ‬ 1- Energy production (power house of the cell) be oxidation of CHO, fat & protein to produce energy then use this energy to convert ADP→ ATP (phosphorylation). 2- Regulation of Ca++ level in the cell & other ions (keep cytoplasmic Ca++ low). DR. Ahmed Ammar 7  1st Year Histology  Definition: It's an anastomosing network of channel & sacs formed by continuous membrane & contain space called cisternae.  Types: - Rough (RER): contain ribosomes (‫)ﻣﺣﺑﺑﺔ‬ - Smooth (SER): no ribosomes. (‫)ﻧﺎﻋﻣﺔ‬ Appear as basophilic area in cytoplasm due to ribosomes Not seen e.g. fibroblast. + ‫ﺍﻟﺗﻌﺭﻳﻑ‬ + ‫ﺍﻟﺗﻌﺭﻳﻑ‬ Attached to nuclear It differ from RER in: membrane. 1- No ribosome →smooth. With many ribosomes on 2- The cisternae is tubular surface ‫ﺃﻛﻳﺩ ﻁﺑﻌﺎ‬ not flat like RER. 1- Synthesis of protein that 1- Synthesis of steroid hormone released or secreted outside in suprarenal gland. the cell. 2- Synthesis of phospholipid for 2—Modification of protein all membranes in the cell.. 3- Storage & release of Ca++ for muscle contraction. 4- Detoxification of drugs in liver cells. 5- SER contain G-6–P enzyme which important in glycogen metabolism. DR. Ahmed Ammar 8  1st Year Histology  - Stain: Not seen by H&E but may appear as empty space called (-ve Golgi image). It can be seen by silver impregnation. - Site: a) Supranuclear: between nucleus & apical cell membrane e.g. epididymis. b) Infranuclear: between nucleus & basal cell membrane e.g. endocrine cell. c) Perinuclear: around the nucleus e.g. neuron.  ‫ﺍﺭﺳﻡ‬ - It formed of several saccules arranged in stacks with dilated periphery. - The apparatus has 2 faces: 1- Entry, convex, cis or immature face. 2- Exit, concave, trans or mature face - The cis face is associated with small vesicle containing immature protein from RER. while → The trans face is associated with large secretary vesicles with mature protein.  1- Concentration & packaging of protein in secretary vesicle. 2- Modification of protein e.g. glycosylation. 3- Formation of Lysosome. 4- Recycling of cell membrane. 5- Synthesis of CHO DR. Ahmed Ammar 9  1st Year Histology - Lysosomes are sites of intracellular digestion. - They increase in phagocytic cells e.g. macrophage. - Lysosomal enzymes like acid phosphatase are synthesized in RER & packed in Golgi apparatus. - They have optimal activity in acidic PH.  Can be demonstrated by histochemical reactions for their enzymes.  Rounded, electron dense vesicle surrounded by 2 membrane,. 0.5 µm in diameter.  1- Primary lysosome: not share in digestive event (homogenous). 2- Secondary lysosome: (heterogeneous) 1ry lysosome + phagosome → heterophagic vacuole. 1ry lysosome + pinocytotic vesicle → multivesicular bodies. 1ry lysosome + autophagosome → Autophagic vacuole. Autophagosome: (membrane surround old organelle or part of cytoplasm).  1. Nutrients: diffuse to the cytoplasm. 2. Indigestible substance: execrated by the cell (exocytosis) 3. In long lived cells as neuron & cardiac muscle, Indigestible substance retain ‫ & ﺗﻔﺿﻝ‬called (residual bodies). When residual bodies ↑ in amount in long – lived cell, they called (lipofuscin pigment). N.B: ‫ ﻟﻠﻔﻬﻡ‬The cell protect itself from lysosome by: 1- Membrane of lysosome 2- PH of cytoplasm. DR. Ahmed Ammar 10  1st Year Histology  Can be demonstrated by cytochemical reactions for catalase enzyme.  Like lysosome but → surrounded by 1 membrane. → Contain oxidative enzymes. → Arise from RER directly not Golgi. → Self-replicating like mitochondria  1- Produce H2O2 → remove H2 from organic substance& transfer it to molecular O2 2- Destroy H2O2 → H2O + O2 by catalase enzyme. 3- Catalase can degrades also toxin & drugs in liver cells. 4- Peroxisome involved in lipid metabolism & formation of bile acids & cholesterol. Secretary vesicle → They are found in cells that store their product until its release such as pancreatic cells & cells of thyroid gland Coated vesicle → see receptor mediated endocytosis. DR. Ahmed Ammar 11  1st Year Histology 20 - 30nm in size. Composed of 4 types of rRNA + 80 proteins. 2 forms of ribosome - Free: in the cytoplasm. - Attached: RER. Formation: 1- rRNA is synthesized in the nucleolus. 2- Proteins are synthesized in the cytoplasm. 3- Proteins enter the nucleus, associate with rRNA, return to cytoplasm as mature ribosome.  Very small to be seen but when aggregate they cause basophilic area In cytoplasm due to rRNA. (May be Diffuse, localized or spotty)  ♥ Formed of 2 subunit → large & small that held together by mRNA. ♥ Polysomes→ several ribosomes on the same mRNA strand. ♥ Ribophorins→ is a specific receptor on RER bind to large subunit of ribosome.  1- Translate mRNA to amino acids (polypeptide chain). 2- Free ribosome produce proteins retain in cytoplasm for use within cell e.g. Hb in RBCs. 3- Attached ribosome produce protein secreted by the cell e.g. (enzymes & hormones), lysosomal enzymes & produce integral protein of cell membrane. DR. Ahmed Ammar 12  1st Year Histology Non membranous protein complex that responsible for proteolysis of mal-formed proteins ! ‫ﺑﺱ‬ DR. Ahmed Ammar 13  1st Year Histology Cytoskeleton is formed of microtubule & filaments.  Not seen ?.  ♥ 25 nm in diameter & 5 nm in wall thickness. ♥ Present in 2 forms: 1- Labile: free microtubule in cytoplasm that polymerizes or depolymerizes according to temperature. 2- Stable: they form centriole, cilia & Flagella.  1) 1 microtubule is formed of 13 protofilament. 2) Each protofilament is formed of polymer of tubulin protein. 3) Tubulin protein is α & β dimer. 4) Microtubules have protein called MAP (microtubule associated protein). 5) Each microtubule ↑ in length from one end( + end)& ↓ from other end (-end). 6) Change in length (polymerization) is affected by Both (Ca++ & MAPS)  1- Maintain the shape of the cell. 2- Movement of the cell. 3- Movement of the organelle. 4- Mitotic spindle formation. 5- Formation of centriole, cilia & Flagella. N.B: Anticancer drugs stop polymerization of microtubule → colchicine, taxol & vinblastine. DR. Ahmed Ammar 14  1st Year Histology  It’s cylindrical, short highly organized microtubules. ( 0.5 µm in length)  2 small rods at right angle to each other with material called (microtubule organizing center) (MTOC).  2 centriole at right angle to each other at each cell → centrosome. Each centriole is formed of 9 triplets of microtubule. Each triplets → 3 microtubule A, B & C. A is complete microtubule (13 protofilament) but B & C are incomplete microtubule (10 protofilament) as they share in 3 protofilaments.  1- Form mitotic spindle during cell division. 2- Form the basal of cilia & Flagella. DR. Ahmed Ammar 15  1st Year Histology  Hair like processes of highly organized microtubule.  Formation: The centriole migrate to apical cell membrane to form the base of cilia. From each triplets, 2 microtubule (A & B) grow upward to form the shaft of cilia. Unorganized microtubule → Rootlet of cilia.  1- Rootlet → unorganized microtubules. 2- Base → similar to centriole. 3- Shaft → LM: acidophilic striation. EM: - Formed of 9 doublet of microtubules & 2 central singlets in a protein sheath ( axoneme) ‫ ﻳﻌﻧﻲ ﻣﺣﻭﺭ‬. - Each doublet is 2 microtubule (A) complete & (B) incomplete. - From A microtubule 3 proteins arise → 1- Radial spoke → to the center. 2- Nexin → from A to B of another doublets. 3- Dynein → 2 arms contain ATPase enzyme. Function: Brush away things from the surface of the cells Flagella  The same structure as cilia ( 100 µm ).  In human, the only cell with one flagellum is spermatozoa. DR. Ahmed Ammar 16  1st Year Histology LM: Appear as bundles of fibril by silver stain. EM: Show 3 types: 1- Thin filament (actin): 5nm in diameter. Present in 2 forms: Stable in muscle cell. Unstable in the ❶cell under cell membrane (exo & endocytosis) ❷ associated with organelle (moving them) ❸ in mitotic cell (cleavage). 2- Intermediate filament: 10nm in diameter. By immunecytochemical stain Types: - Keratin in skin epithelium. - Vimentin in cells of mesenchymal origin. - Desmin in muscles. - Glial in nervous tissue. - Neurofilament in nerve cell. 3- Thick filament (myosin): 15nm in diameter. (2 heavy chain & 4 light chains like golf stick) Present in muscle. DR. Ahmed Ammar 17  1st Year Histology ♥ 3 types → (1) Stored food :- Glycogen → LM :- not seen by H&E but appear red with best's carmine & magenta with PAS. EM :- electron dense particle 2 forms → β rosette & large α particle. Lipid → LM :- not seen by H&E but seen by Sudan III → orange Sudan black → black EM :- Electron lucent vacules. Secretion granules → Include mucous droplets & certain hormones (2) Pigments:- Endogenous pigment Lipofuscin Melanin Hemoglobin  Yellow brown Black in color  Red in color present in skin present in RBC Present in & retina neuron & Cardiac  most important muscle.  Protect body pigment. ↑ with age from UV ray of the sun. DR. Ahmed Ammar 18  1st Year Histology Exogenous pigment Carbon Carotene  black color  orange color  With smoking in lung or  present in Vitamin A rich Tatoo in skin. food as carrot. (3) Crystals:- Present in some cells as sertoli cell of testis.  Colloid substance in which (organelle, inclusion & cytoskeleton) are suspended.  Form 50% of cell volume.  Function → 1- Coordinate movement of Organelle. 2- Contain enzyme that share in metabolism. 3- Transport signals from cell membrane to sites inside the cell. 4- Provide viscosity of cytoplasm. DR. Ahmed Ammar 19  1st Year Histology  The most prominent structure in the cell.  - Shape → Rounded, Oval, flat, lobulaled & irreqular. - Size → Small, medium & large. - Site → central, peripheral, apical, Basal & eccentric. - Stain→deep basophilic(inactive cell)& vesicular basophlic(active cells) - Number → usually single nucleus - 2 nuclei in liver cell mullinucleated in muscle cell -No nuclei in RBC's  not true cell.  4 Companents: A- Nuclear envelope. B- Nucleolus. C- chromatin. D- Nuclear matrix. (A) Chromatin ♥ DNA + Histone protein → chromatin. ♥ Coiled chromatin → chromatid. ♥ 2 chromatid = chromosome. ♥ In non-dividing cell, DNA present in the form of chromatin. DR. Ahmed Ammar 20  1st Year Histology ♥ 2 types of chromatin: Eu chromatin Hetero chromatin - active DNA - Inactive DNA - Extended uncoiled - Highly coiled - LM: Light basophilic (vesicular) - Deep basophilic - EM: Electron lucent granule. - Electron dense granule. - 3 types: Peripheral Nucleolus associated Islets (B) Nuclear envelope:  It's 2 unit membrane (inner & outer), separated by a space called (perinuclear space) or (intermembranous space) 40-70 nm.  The 2 membrane fuse together at certain points to form (nuclear pore) that connect between nucleus & cytoplasm. 1- Outer membrane: Continuous with RER. 2- Inner membrane: Contain fibrous lamina that:- Stabilize the nuclear envelope. Provide a site for chromatin in non dividing cell. 3- Nuclear pore: Octagonal structure: ‫ﻟﻠﻔﻬﻡ‬ Annulus: 8 large protein granule arranged in inner & outer ring in each pore. Radial spoke: from 8 granules to the center of the pare. Plug: electron dense granule in the center. DR. Ahmed Ammar 21  1st Year Histology Function of nuclear pore → 1) Allow passage of mRNA. 2) Allow passage of Ions & molecules < 9 nm without energy. 3) Molecules > 9 nm can pass by active transport utilizing energy. (C) Nucleolus: - Spherical structure up to 1mm & contain rRNA + protein. - LM: intense basophilic. - EM: 3 component: 1- Nuclear organizing region: Pale area contain DNA that code for rRNA. Chromosome (13, 14, 15, 21, 22) 2- Fibrillar components: (10 nm) Maturing ribosome , ribosomal subunit that not mature yet & waiting to be exported to cytoplasm. 3- Granular components: (20 nm) Mature ribosome → rRNA + protein. Function: rRNA synthesized in nucleolus & protein synthesized in cytoplasm then bind together & migrate to cytoplasm as mature ribosome. (D) Nuclear Matrix: - It fill the space between chromatin & nucleolus. - Contain protein, enzyme, metabolites, ions & fibril called (nucleoskeleton). N.B: Function of nucleus: 1- Carries all genetic information. 2- Formation of RNA. 3- Play major role in cell cycle & cell division. DR. Ahmed Ammar 22  1st Year Histology DR. Ahmed Ammar 23