Cell histology presentation by Dr.Rumaisa PT

THIS SLIDE CONTAINS ALL THE MICROSCOPIC structures of cells their organelles functions cell division etc and cover all the basic aspects regarding histology of cell.

1. The Cell General Histology – By Laiq Hussain Siddiqui Presented by: Dr.Rumaisa PT

2. Introduction Cell is the structural and functional unit of life Robert Hooke (1665): first described cells Prokaryotes: no nucleus; Eukaryotes: true nucleus + organelles Cell is basis for histology, physiology & pathology

3. Cell Theory All living organisms are composed of cells Cell is the basic unit of structure and function New cells arise from pre-existing cells Modern: DNA stores info; Organelles regulate activities

4. General Structure of Cell Plasma membrane – outer boundary Cytoplasm – cytosol + organelles + inclusions Nucleus – control center with DNA

5. Plasma Membrane Phospholipid bilayer with proteins – Fluid Mosaic Model Cholesterol provides fluidity & stability Selective permeability; transport; cell recognition & signaling The cell membrane performs multiple essential functions, including: Acting as a protective barrier. Regulating selective transport of substances. Facilitating cell communication via receptors. Supporting cell adhesion. Maintaining ion gradients with ATP-powered pumps. Enabling endocytosis and exocytosis.

6. Cytoplasm Cytosol: semi-fluid with ions, enzymes, proteins Contains organelles & inclusions Medium for metabolic activities

7. Cytoplasm functions 1. Structural Support and Shape: The cytoplasm, particularly the cytoskeleton within it, provides a framework that helps maintain the cell's shape and rigidity.  2. Transport: The cytoplasm acts as a medium for transporting various molecules, including proteins, nutrients, and waste products, throughout the cell.  3. Metabolic Processes: Many crucial biochemical reactions, such as glycolysis and protein synthesis, take place within the cytoplasm, often facilitated by enzymes.  4. Protection: The semi-fluid nature of the cytoplasm acts as a cushion, protecting the cell's organelles from physical damage.  5. Storage :. The cytoplasm can store various substances, including ions, nutrients, and waste products, until they are needed or removed from the cell.

8. Mitochondria Double membrane, inner folds = cristae Own DNA & ribosomes Clinical : mitochondrial myopathies

9. Mitochondria functions Energy Production: Their main role is to convert nutrients (like glucose and fatty acids) into ATP, the energy currency of the cell, via oxidative phosphorylation .   Metabolic Regulation: They are central to many metabolic pathways, including the Krebs cycle  beta-oxidation of fatty acids  and the synthesis of iron- sulfur clusters and  urea   Apoptosis (Programmed Cell Death): Mitochondria store proteins and factors that, when released, trigger the cellular death cascade, making them gatekeepers of cell death.  Calcium Homeostasis: They help regulate calcium levels within the cell, which is crucial for various cellular signaling processes.  Cell Growth and Differentiation: Mitochondria are involved in processes that control cell proliferation, differentiation, and overall cell cycle regulation.  Heat Production: In certain tissues, like brown adipose tissue, mitochondria produce heat through an alternative pathway involving the electron transport chain.  Mitochondrial DNA ( mtDNA ): Mitochondria possess their own DNA that encodes some proteins essential for their function, and they are responsible for replicating and transcribing this DNA.  Network Remodeling : Mitochondria are dynamic organelles that constantly fuse and divide to form and maintain interconnected networks within the cell, adjusting their shape to meet energy demands. 

10. Rough Endoplasmic Reticulum (ER) Rough Endoplasmic Reticulum (RER) Appearance:  Appears "rough" due to the numerous ribosomes attached to its outer surface.  Structure:  Typically a series of interconnected, flattened sacs called  cisternae . Functions: Protein Synthesis and Modification:  Assembles proteins and glycoproteins that are destined for secretion, insertion into membranes, or transport to other organelles.  Protein Folding:  Plays a role in the proper folding and quality control of these proteins.  Despatch:  Packages and sends proteins to the Golgi apparatus for further processing. 

11. Smooth endoplasmic reticulum Appearance:  Lacks ribosomes, resulting in a smooth, tubular appearance.  Structure:  A network of fine, tubular vesicles.  Functions: Lipid and Steroid Synthesis:  Manufactures lipids, phospholipids, cholesterol, and steroid hormones.  Detoxification ;  Detoxifies harmful substances, particularly in liver cells.  Metabolism:  Involved in the metabolism of some sugars and the storage of calcium ions

12. Golgi Apparatus Stacked cisternae: cis → medial → trans Protein modification, packaging, secretion Forms lysosomes

13. Golgi apparatus functions Processing and Modification: Receives proteins and lipids from the endoplasmic reticulum (ER) and modifies them through enzymes, such as adding sugar chains (glycosylation) or phosphate groups (phosphorylation).  Sorting and Packaging: Sorts these modified molecules and packages them into membrane-bound  vesicles for transport to their correct destinations.  Transport: Directs vesicles to various cellular destinations, including lysosomes, the  plasma membrane, or for secretion outside the cell.  Synthesis of Complex Carbohydrates: Synthesizes complex polysaccharides, which are components of the plant cell wall and other extracellular matrices.  Lysosome Formation: Participates in the creation of lysosomes, which contain digestive enzymes for cellular waste.  Secretion: Involved in the formation of secretory vesicles and the subsequent secretion of hormones, enzymes, and other proteins from the cell. 

14. Lysosomes Contain hydrolytic enzymes Intracellular digestion, autophagy, waste removal Defects → lysosomal storage diseases

15. Lysosomes functions Waste Digestion: They break down macromolecules, worn-out organelles, and foreign invaders like bacteria and viruses.  Autophagy: Lysosomes degrade and recycle internal cellular components, such as damaged organelles and proteins, through the formation of autophagosomes .  Phagocytosis: They fuse with phagosomes to digest engulfed foreign particles and pathogens, such as when immune cells engulf invaders.  Apoptosis: Lysosomes can trigger programmed cell death by releasing digestive enzymes that break down the cell's own components.  Cellular Signalling: Lysosomes act as a platform for signaling pathways, such as the mTORC1 pathway, which integrates signals related to growth, metabolism, and cell stress.  Plasma Membrane Repair: Lysosomes contribute to the repair and restoration of the cell's plasma membrane.  Immune Response: They play a critical role in the immune system by destroying pathogens.  Endocytosis: They fuse with endosomes to digest macromolecules taken up from outside the cell. 

16. Peroxisomes Contain oxidases & catalases Oxidize fatty acids, detoxify H2O2 Disorders: Zellweger syndrome

17. Peroxisomes functions Fatty Acid Breakdown: Peroxisomes are involved in the process of beta-oxidation, which breaks down fatty acids into smaller molecules.  Lipid Metabolism: They synthesize lipids, including cholesterol and plasmalogens , which are a crucial type of phospholipid found in the brain and lungs.  Detoxification: Liver and kidney cells use peroxisomes to detoxify toxic substances and harmful molecules, such as hydrogen peroxide (H₂O₂).  Other Catabolism: Peroxisomes also catabolize (break down) other substances like D-amino acids, purines, and polyamines.  Oxidative & Biosynthetic Functions Reactive Oxygen Species (ROS) Detoxification: A primary function is neutralizing toxic hydrogen peroxide, a byproduct of many oxidative reactions, by converting it to water and oxygen.  Synthesis of other lipids: They are involved in synthesizing bile acids in the liver, which are derived from cholesterol. 

18. Ribosomes Made of rRNA + proteins Free ribosomes: cytoplasmic proteins RER ribosomes: secretory & membrane proteins

19. Ribosomes functions Protein synthesis (translation):  This is the main function of all ribosomes. Ribosomes read the genetic code from an mRNA molecule and use it as a template to link specific amino acids together. Polypeptide chain formation:  Ribosomes link amino acids together by catalyzing the formation of peptide bonds, creating a long polypeptide chain. Decoding genetic information:  Ribosomes bind to the mRNA, deciphering the sequence of codons (three-nucleotide units) to determine the correct order of amino acids. Post-translation protein folding : While a protein is being synthesized, the ribosome actively participates in and facilitates the proper folding of the new polypeptide chain. 

20. Cytoskeleton Microfilaments: actin, shape & movement Intermediate filaments: mechanical support Microtubules: intracellular transport, mitotic spindle

21. Cytoskeleton functions Structural Support : It provides a rigid framework that gives animal cells their shape and maintains the organization of the cytoplasm and organelles.  Cell Motility : The cytoskeleton enables cells to move and to contract, allowing for functions like cell migration.  Intracellular Transport : It acts as a "highway" system, transporting organelles and vesicles to different parts of the cell.  Cell Division : The cytoskeleton plays a crucial role in the proper segregation of chromosomes during cell division and cytokinesis.  Cell Adhesion : It helps link animal cells to each other and to the extracellular matrix, stabilizing tissues.  Cellular Communication : The cytoskeleton is involved in signalling pathways within the cell and contributes to the uptake of materials from outside the cell (endocytosis). 

22. C entrosomes and centrioles Centrosome: microtubule organizing center Centrioles: cylindrical, form spindle fibers Essential for mitosis & cilia formation

23. Centrosomes and centrioles functions Centrosome Functions   Acts as the primary microtubule-organizing center (MTOC). Organizes microtubules to provide structure to the cell. Replicates before cell division and forms the two poles of the mitotic spindle. Plays a role in cell division by helping to separate chromatids (a form of DNA) into two new cells. Regulates the cell cycle. Involved in cell polarity and migration. Centriole Functions Are the barrel-shaped components that make up the centrosome.  Serve as basal bodies, which are the structures from which cilia and flagella grow.  Help organize microtubules and contribute to the formation of the mitotic spindle during cell division. 

24. Nucleus Nuclear envelope with pores, nucleoplasm Chromatin (euchromatin & heterochromatin) Nucleolus: ribosome synthesis Controls cell activities

25. Nucleus functions Stores and protects DNA : The nucleus contains the cell's hereditary material (DNA), which carries the genetic instructions for the cell's functions.  Controls cellular activities : It coordinates essential processes like growth, metabolism, and protein synthesis.  Regulates gene expression : The nucleus controls which genes are turned on or off, dictating the cell's specific activities.  Facilitates DNA replication : During the cell cycle, the nucleus ensures that DNA is accurately copied before cell division.  Site of transcription : RNA molecules are synthesized from DNA within the nucleus.  Ribosome production : The nucleolus, found inside the nucleus, is responsible for making ribosomes, which are necessary for protein production.  Mediation of cell division : The nucleus plays a critical role in cell reproduction by ensuring the correct and accurate distribution of genetic material to new cells. 

26. Chromatin & Chromosomes Euchromatin: active transcription Heterochromatin: inactive, condensed Humans: 46 chromosomes (23 pairs)

27. Cell Inclusions Glycogen granules: carbohydrate storage Lipid droplets: energy reserves Pigments: melanin, lipofuscin

28. Cell Division Cell cycle: G1 → S → G2 → M Mitosis: 2 identical diploid cells Meiosis: 4 haploid gametes Errors → cancer, aneuploidy (Down syndrome)

29. Cell division importance and functions Growth and Development: Allows a single-celled organism to become a multicellular organism with trillions of cells.  Tissue Repair: Replaces damaged or dead cells to maintain the integrity of tissues and organs.  Reproduction: In single-celled organisms, cell division is the primary means of reproduction.  Genetic Continuity: Mitosis ensures that daughter cells receive an identical copy of the parent cell's genetic information.  Genetic Diversity: Meiosis introduces genetic variation through recombination and independent assortment, which is vital for the adaptation and evolution of species

30. Specialized Cells Muscle cells: contraction Neurons: impulse conduction RBCs: oxygen transport Epithelial cells: secretion & absorption

31. Clinical Correlations Cancer: uncontrolled cell division Mitochondrial diseases: muscle weakness, fatigue Lysosomal disorders: Tay-Sachs, Gaucher’s Cytoskeletal disorders: Alzheimer’s, immotile cilia

32. Summary Cell is the fundamental unit of life Organized into membrane, cytoplasm, organelles & nucleus Organelles perform vital specialized functions Cell pathology explains many diseases

33. References Laiq Hussain Siddiqui – General Histology Junqueira’s Basic Histology Gartner & Hiatt – Color Textbook of Histology