Histology L1 PDF

Histology lecture (1) Cell structure (1) Histology Cell structure Cytoplasmic organelles Cytoskeleton Cell inclusions Membranous: Non-membranous: ▪ Mitochondria....

Histology lecture (1) Cell structure (1) Histology Cell structure Cytoplasmic organelles Cytoskeleton Cell inclusions Membranous: Non-membranous: ▪ Mitochondria. ▪ Ribosomes.. ▪ Endoplasmic reticulum. ▪ Golgi apparatus. ▪ Lysosomes. A Cell Membrane = Plasma Membrane = Plasmalemma Definition The outer limiting membrane that surrounds the cell Thickness 7.5 : 10 nm & thus visible only by electron microscopy (E.M). E/M Trilaminar appearance:  Two electron dense lines (black) separated by electron lucent one (white). Trilaminar appearance PM: Plasma membrane MV: microvilli Histology Molecular structure 1. Phospholipids :  Consist of : a) Head: Hydrophilic (water attracting). b) Tail: Hydrophobic (water-repelling).  Organized into a double layer (bilayer) : a) Heads → facing water & Charged hydrophilic part (head) outward. b) Tails → directed toward the middle, away from water. 2. Cholesterol :  Between the phospholipid molecules. Lipid :  They regulate the fluidity of the phospholipid bilayer & stabilise it. Protein :  Composed of two parts : Integral proteins Peripheral proteins  Firmly embedded in the lipid bilayer.  Loosely attached to the outer or  Not easily extracted. inner membrane surfaces.  Can be easily extracted. Trans-membrane proteins  Large, Completely span the lipid bilayer.  Usually attached to microfilaments in the cytoplasmic side (for fixation).  Act as channels. Histology  Glycolipids and glycoprotein. Carbohydrate :  They are projecting from the external surface of the membrane, forming the Cell Coat or Glycocalyx. Histology Functions Passive  For gases and ions. diffusion  According to concentration gradient. active  For amino acids, glucose & fatty acid. transPort  Needs enzymes & energy. selective  For hormones, drugs & bacteria. transPort  Needs receptors & energy.  For solid (Cell eating). Phagocytosis  Example: macrophages can engulf certain bacteria. Pinocytosis  For fluid (cell drinking). recePtor-  Needs receptors (integral proteins). mediated  For large molecules. endocytosis  Example: protein hormones & some drugs.  Opposite to phagocytosis & The cell expels any waste products.  Adhesive function: for adjacent cells.  Immunity (recognize the cell of its own type and the foreign cells).  Participates in the formation of basement membrane. Histology b Mitochondria Definition Membranous organelles containing enzymes specialized for production of energy(ATP) It is the power house of the cell. Size & shape Vary in size and shape. May be elongated, rod-shaped or spherical. Number Highly variable depending on the activity of the cell :  liver cells contain numerous mitochondria.  Lymphocytes contain very few. The number of mitochondria is modified by mitochondrial division. Sites Mitochondria are very mobile. They localise at sites of maximum energy requirement e.g. Between myofibrils in cardiac muscle cells. Histology Light microscopy (L/M) Hematoxylin (H) Eosin (E) Nature Basic (alkaline). Acidic. Colour Blue. Red.  Reacts with acidic structures  Reacts with basic structures inside the cell: inside the cell: usually E.M.  DNA: in nucleus. cytoplasm which is rich in  RNA: in ribosomes & RER. mitochondria. Cytoplasm rich in ribosomes & RER is Cytoplasm rich in mitochondria is basophilic e.g. plasma cell acidophilic e.g. renal tubules  It is an enzyme of Krebs citric acid cycle and is exclusive to mitochondria. H&E Succinic dehydrogenase enzyme activity Histology Electron microscopy (E/M) The mitochondria is a double membranous organelle. Each mitochondrion consists of 4 compartments: Outer membrane  Smooth, no folds.  Forms complex folds called cristae. Inner membrane  The number of cristae is increased in more active cells. Intermembranous  Between inner & outer membrane. space Mitochondrial  Mitochondrial DNA. matrix  Ribosomes. Histology Functions 1. Provide the cell with ATP: Aerobic respiration takes place within the matrix & on the inner membrane to produce energy. 2. The mitochondrial matrix contains :  DNA so can divide & ↑↑ their number according to energy need of the cell.  Ribosomes so the Mitochondria can synthesize most of its own proteins. Histology c Ribosomes  Non-membranous organelles. Definition  The ribosome is the protein factory of the cell. Size  Very small (20-30 nm in diameter).  The individual ribosome is too small to be seen by L.M.  Aggregation of ribosomes leads to basophilia of cytoplasm due to rRNA. L.M.  Ribosomes are small electron-dense particles.  Composed of two subunits: small & large subunits. E.M.  The two subunits are formed of rRNA and about 80 different protein molecules. Types Free ribosomes Attached ribosomes (polyribosomes or polysomes)  Many ribosomes bound to a  Single ribosome or polysomes single mRNA molecule. are attached to the surface of Def endoplasmic reticulum forming RER.  Synthesize proteins :  Synthesize proteins  For use of cell:  To be secreted outside cell Function Cytoplasmic & as secretory proteins OR cytoskeletal proteins.  Remain in cytoplasm as primary lysosomes. Histology Free ribosomes Attached ribosomes