Cell Structure (Cytology) 1446 - 2024 Lecture Notes PDF

KINGDOM OF SAUDI ARABIA Ministry of Education Najran University College of Medicine Anatomy Department CELL...

KINGDOM OF SAUDI ARABIA Ministry of Education Najran University College of Medicine Anatomy Department CELL STRUCTURE (CYTOLOGY) 1446 - 2024 ‫العام‬ Dr. Abdel Hafeez Yagoub Mohamed The learning objectives of this lecture is to enable students to. 1- Know about cell structure including cell membrane, cytoplasm and nucleus 2- Corelate between cell organelles structure and their main functions.  Cytology ❖ Cytology is study of cell structure. ❖ There are about 200 types of cells in human body. ❖Each type of cell specializes in a specific function within the body ❖ Electron microscope is used for the study of cell fine structure.  Cell theory Cell is the smallest independent living thing that can live independently (unicellular organism e. g., flagellates, amebas) All living things are made of cells Cells arise only from pre-existing cells.  Cell basic properties 1- Metabolism and the Generation of Energy 2- Reproduction by cell division ❑ Mitosis: cells simply divide to form new cells. This is termed asexual reproduction ❑ Meiosis : is a part of sexual reproduction occurs in testis and ovary. 3- Sensitivity to Stimulation and Response to Stimulation  Cell Number and Size ❖ The human body is composed of roughly 75000 billion cells and about 200 types of cell. ❖ The sizeof each cell varies in the human body between 5 μm (e. g., small lyphocytes) and 150 μm (the ovum of the female). ❑ Cell number is affected by body size ❑ Cell size is affected by function  Cell Shape ❖The shapes of human cells vary considerably, Ova are round, neuron form processes, muscle cell form fibril.(shape affected by function) (WBCs shape changeable) ❖Animal cells are mostly round and irregular in shape while plant cells have fixed, rectangular shapes (cell wall)  Types of cells There are two main 1- Eukaryotic Cells Have define nucleus bound by nuclear membrane. Possess organelles bound by membrane e.g Golgi, Mitochondria RER, SER This type of cells include human, animals and plants cells Eukaryotic Cells  2- Prokaryotic Cells Have no define nucleus (no nuclear membrane) Have Nucleoid (region of DNA concentration) Have no membrane-bound organelles e.g., RER, Golgi This type of cells include bacteria (bacterium)  Animal cells vs Plant cells ❑ Plant cells have ▪ cell wall, ▪ chloroplasts ▪Plastids ▪ large central vacuole, whereas animal cells do not have the above structures 1. Cell membrane (Plasma membrane or Plasmalemma) ❖ It forms the outer boundary of all cells ❖ Cell membrane is a lipid bilayer Cell membrane is composed of Lipid form about 35% (phospholipids and Cholesterol) Proteins 60% Carbohydrate 5%  Molecular structure of cell membrane 1- Phospholipids: Consist of A- Hydrophilic heads point outwards B - Hydrophobic fatty acid tails in the middle. 2- Proteins are A- Intrinsic proteins (integral) (Trans membrane protein) lie in the cell membrane. B- Extrinsic proteins (peripheral) present on the outer and inner surfaces. Extrinsic proteins serve in transport of molecules and as receptors Carbohydrates: form glycocalyx coat on the outer surface of the cell membrane Cell membrane specializations (Projectons) 1- Microvilli (microvillus) Are finger-like projections that increase cell free surface area for absorption as in intestines. 2 – Cilia (cilium): are motile processes that extend from the free surface of cells as in respiratory system & oviduct in female. 3- Stereoclia: are not true cilia; but are very long microvilli as in the epididymis (have absorption function). 4 – Flagella (flagellum) : are cilia-like structure e.g., form tail of mature sperms (help in sperms movement)  Types of cell junctions Cell junctions attach cells to adjacent cells Some epithelial cells, smooth muscle cells and cardiac muscle cells are attached at their margins by specializations of the cell membrane called cell junctions like: 1- Tight junction 2- Adherens junction 3- Desmosome 4- Gap junction 5- Hemidesmosomes.  Main functions of cell membrane A- Transfer of nutrients and metabolites e.g., by 1- Active transport (require energy) 2- Passive transport (no energy is required) (Osmosis: hypertonic, isotonic and hypotonic) 3- Phagocytosis: intake of solid material. 4- Pinocytosis: intake of liquid material. 5- Exocytosis: discharge of materials outside the cell. 6- Endocytosis: intake of materials inside the cell. B- Communication with the external environment. C - Attachment of the cell to adjacent cells and to extracellular matrix (by cell junctions) Endocytosis and Exocytosis  Movement Across the Plasma Membrane ❑ A few molecules move freely across cell membrane e.g Water, Carbon dioxide, Ammonia, Oxygen ❑ Carrier proteins transport some Insulin molecules (Insulin for entrance of glucose into body cells)  MEDICAL APPLICATION Defects or mutation in protein of cilia or flagella can lead to 1- Male infertility: cause by spermatozoa immobility 2- chronic respiratory infection cause by the lack of the cleansing action of cilia in the respiratory tract. (immotile cilia syndrome)