Histology Part 1 PDF

# General Summary ## 1. Cell membrane - Formed from 30% lipid - Consists of phospholipid molecules which are arranged into 2 layers: - **Polar Head:** - Hydrophilic - Directed outwards - Found on outer and inner surfaces - **Non-polar Tail:** - Hydrophobic...

# General Summary ## 1. Cell membrane - Formed from 30% lipid - Consists of phospholipid molecules which are arranged into 2 layers: - **Polar Head:** - Hydrophilic - Directed outwards - Found on outer and inner surfaces - **Non-polar Tail:** - Hydrophobic - Directed inwards - Tails interact forming a stable center - **Cholesterol:** - Present at hydrophobic regions ## 2. Protein Component (60%) - Consists of: - **Extrinsic (Peripheral) Protein:** Found on both surfaces - **Intrinsic (Integral) Protein:** - Large integral proteins cross the membrane (Trans-membrane) - Act as pathway for ions and molecules (channel proteins) - **Alpha Helix:** - Helps the cell membrane to move and enclose phagocytosed particles - Helps cells to migrate by making pseudopodia - Acts as pathway ## 3. Carbohydrates (10%) - Conjugated with proteins or lipids to form glycocalyx - **Functions of the cell membrane include:** ### Functions of the cell surface coat: - **Cell adhesion (attachment)** - **Immunity:** By recognition of own cells. Antigens on the surface of the cell bind to lymphocytes and antigen presenting cells to assist with the immune response. - **Cell membrane modification includes:** ## Functions of the Cell Membrane ### 1. Simple transport (diffusion) - **Passive diffusion:** For gases, water, urea, and non-organic ions. - **Facilitated diffusion (Carrier-mediated diffusion):** Large molecules like glucose need carrier molecules (proteins) to pass through integral proteins. ### 2. Active transport - It needs energy, as in the sodium pump, to go against the concentration gradient. ### 3. Bulk transport: - **Endocytosis:** The uptake of materials across the cell membrane into the cytoplasm of the cell. This process is divided into: - **Phagocytosis:** The power of the cell membrane to pass solid particles forming phagosomes (phagocytic vesicles). - **Pinocytosis:** The power of the cell membrane to enclose and pass droplets of fluid, forming pinocytic vesicles. - **Receptor-mediated endocytosis (Selective transport):** The surface coat has specific receptors which permit the passage of certain materials only. - **Exocytosis:** The power of the cell membrane to extrude waste products outside the cell. ### Cell membrane modification - **Microvilli:** Increase the surface area. - **Cilia:** Push particles in one direction. - **Flagella:** Allow sperm movements. - **Stereocilia:** Long microvilli. ## Cystic Fibrosis - **In the lungs:** A hereditary disease of mucus-secreting cells where lungs have thick, sticky mucus. This traps germs in the lungs which causes permanent lung damage. - **In the pancreas:** Mucus blocks the channels that carry enzymes. This prevents the body from absorbing food, especially fats. - **Children with cystic fibrosis have problems gaining weight.** ## Organelles vs Inclusions | **2. Organelles** | **3. Inclusions** | |---|---| | 1. Living structures. | 1. Non living structure. | | 2. Permanent components of the cytoplasm | 2. Temporary components of the cytoplasm | | 3. Essential for life of each cell. | 3. Not essential for life of cells. | | 4. Metabolically active because they contain enzymes. | 4. Metabolically inert as they do not contain enzymes. | | 5. Present in all nucleated cells. | 5. Not in all cells. | | 6. Have vital functions. | 6. Result from cell vital activity | ## Membranous Organelles vs Non-membranous Organelles | **Membranous Organelles** | **Non-membranous Organelles** | |---|---| | 1. Cell (plasma) membrane | 1. Ribosomes | | 2. Mitochondria | 2. Cytoskeleton: | | | a) Microtubules | | 3. Endoplasmic reticulum (rough and smooth) | b) Filaments| | 4. Golgi body (apparatus)| | | 5. Lysosomes | | ## Mitochondria - A membranous organelle present in all nucleated cells except red blood corpuscles. - Vary in number and location. - **Structure includes:** - **Functions:** - **Power house:** Stores and produces ATP. - **Regulates:** Calcium and magnesium. - **Forms:** Proteins (has ribosomes). - **Can divide:** Self-replication (has its own DNA). - **The electron microscopic structure (EM) of mitochondria:** - Each mitochondrion appears as a vesicle surrounded with two membranes. - The outer membrane is smooth, while the inner membrane is rough (because the inner membrane projects into the cavity of the mitochondrion, forming shelves called cristae). - Cristae increase the surface area for deposition of enzymes, enhancing the production of Adenosine triphosphate (ATP). - **Mitochondrial matrix contains:** - Enzymes of the Krebs cycle that synthesize ATP. - Matrix granules that bind calcium and magnesium. - Mitochondrial DNA and RNA. - Ribosomes. ## Endoplasmic Reticulum - **Rough Endoplasmic Reticulum:** - Located between the nuclear membrane and the plasma membrane. - Present in protein-forming cells such as fibroblasts, osteoblasts, plasma cells, and pancreatic cells. - Ribosomes are attached. - Functions: - Synthesizes secretory proteins and proteins destined for lysosomes (lysosomal enzymes). - **Smooth Endoplasmic Reticulum:** - Lack ribosomes. - Present in: - Cells that synthesize lipids and carbohydrates such as liver cells. - Steroid-forming cells such as endocrine glands. - **Functions of SER:** - Plays a role in detoxification of excess drugs in liver cells. - Glycogen synthesis and storage in both liver and skeletal muscle cells. - Lipid synthesis and storage. - Synthesis of steroid hormones, such as testosterone and cortisol. - Muscle contraction and relaxation in skeletal muscle cells, as SER is involved in the release and recapture of calcium ions (calcium pump). - Regulation of HCl formation in the stomach. ## Golgi Apparatus - **Functions:** - Well developed in protein secretory cells. - Considered as a secretory apparatus. - Found in nerve and liver cells (surrounding the nucleus). - Located between the nucleus and the free border(surface) of the cell. - Structure includes: - **Golgi Saccules:** Formed of small flat sacks forming stacks. - **Convex immature surface:** Cis face. - **Concave mature surface:** Trans face. - **Functions:** - **Transfer or Micro Vesicle:** Small sacs filled with proteins originating from RER and fusing with the cis face of the Golgi apparatus. They are transformed into secretory vesicles. - **Secretory or Macro Vesicle:** Entered proteins are collected, modified, concentrated, and transformed into secretory vesicles. - **Fate of secretory vesicle:** - Released outside by exocytosis. - Remain inside in the form of lysosomes. - **Functions of Golgi included:** - **Alzheimer's disease:** - The Golgi apparatus regulates the proteins that cause neurodegeneration. - By aging of the Golgi, the release of proteins (not controlled) leads to Alzheimer's disease and Parkinson's disease. - **Functions of Golgi apparatus:** - Responsible for collecting, concentrating, and packaging secretory proteins of the cells. - Modification of proteins delivered from rough endoplasmic reticulum by the addition of sulfates and carbohydrates. - Shares in the formation of lysosomes with the rough endoplasmic reticulum. - Plays an important role in keeping the cell membrane and cell coat in a good condition.