Cell Physiology PDF

# Cell ## Tachycardia & Bradycardia * **Tachycardia:** When the heart rate increases above 100 bpm. * **Bradycardia:** When the heart rate decreases below 60 bpm. ## Definition of a Cell It is the structural and functional unit of the living body. ## General Characteristics of the Cell 1. Each...

# Cell ## Tachycardia & Bradycardia * **Tachycardia:** When the heart rate increases above 100 bpm. * **Bradycardia:** When the heart rate decreases below 60 bpm. ## Definition of a Cell It is the structural and functional unit of the living body. ## General Characteristics of the Cell 1. Each cell in the body needs nutrition & oxygen. 2. Each cell in the body produces its own necessary for its growth, repair & other activities. 3. It eliminates CO₂ and other metabolic waste products. 4. It maintains the medium. 5. It shows immediate response to the entry of invaders such as bacteria or other toxic substances into the body. ## Structure of the Cell Each cell is formed by a cell body & a membrane covering the cell called the cell membrane. The structure of the cell is divided into cell membrane, cytoplasm, and nucleus. ### Composition of Cell Membrane The cell membrane is composed of three types of substances: 1. **Protein** (55%) 2. **Lipid** (40%) 3. **Carbohydrate** (5%) ### Function of the Lipid Layer of the Cell Membrane It is a semipermeable membrane and allows only the fat-soluble substances to pass through it. Examples of the fat-soluble substances are O₂, CO₂, and alcohol. Water-soluble substances like glucose, electrolytes, and urea are not passed through it. ### Function of Protein in the Cell Membrane 1. It provides the structural integrity of the cell membrane. 2. Channel protein helps in the diffusion of water-soluble substances like glucose and electrolytes. 3. Receptor proteins serve as a receptor sites for hormone and neurotransmitters. 4. Some proteins act as antigens and induce the process of antibody formation. ### Function of Carbohydrates in the Cell Membrane Carbohydrate molecules are negatively charged and do not permit the negatively charged substances to move in and out of the cell. Glycocalyx from the neighboring cell helps in the tight fixation of cells with one another. ### Function of the Cell Membrane 1. **Protective function:** Cell membrane protects the cytoplasm and the organelles present in the cytoplasm. 2. **Absorptive function:** Nutrients are absorbed into the cell through the cell membrane. 3. **Excretory function:** Metabolites and the other waste product from the cell are excreted out through the cell membrane. 4. **Exchange of gases:** O₂ enters the cell from the blood and CO₂ leaves the cell and enters the blood through the cell membrane. 5. **Maintenance of shape and size:** It is responsible for the maintenance of the shape of the cell. ## Cytoplasm The cytoplasm of the cell is the jelly-like material formed by the 80% of water. It contains a liquid portion called cytosol. The cytoplasm is made up of two zones: 1. **Ectoplasm:** Peripheral part of the cytoplasm situate just beneath the cell membrane. 2. **Endoplasm:** It is the inner part of the cytoplasm, interported between the ectoplasm and the nucleus. ## Organelles in the Cytoplasm 1. **Rough Endoplasmic Reticulum** 2. **Smooth Endoplasmic Reticulum** 3. **Golgi Apparatus** 4. **Lysosomes** 5. **Peroxisomes** 6. **Centrosomes** 7. **Mitochondria** 8. **Ribosomes** 9. **Cytoskeleton** 10. **Nucleus** ### Endoplasmic Reticulum Endoplasmic reticulum is a network of tubular and microsomal vesicular structures which are interconnected with one another. It is covered by a limiting membrane which is formed by protein and bilayered lipids. #### Types of Endoplasmic Reticulum **Rough Endoplasmic Reticulum:** * Synthesis of proteins * Degradation of worm-out organelles. **Smooth Endoplasmic Reticulum:** * Synthesis of non-protein substance. * Role in cellular metabolism. * Storage for and metabolism of calcium. * Catabolism and detoxification. * It is known as agranular reticulum. ### Golgi Apparatus Golgi apparatus is a membrane-bound organelle involved in the processing of proteins. It is present in all cells, except RBC. #### Function of Golgi Apparatus 1. Processing of materials 2. Packaging of materials 3. Labeling and delivery of materials. The Golgi apparatus is called the shipping department of the cell. It also known as the post office of the cell. ### Lysosomes The lysosomes are formed by the Golgi apparatus. #### Types of Lysosomes * **Primary lysosomes:** It is pinched off from the Golgi apparatus. * **Secondary lysosomes:** Secondary lysosome is the active lysosome formed by the fusion of a primary lysosome with phagosomes. #### Function of the Lysosome Lysosomes are often called garbage systems of the cell because of their degradation activity. #### Specific Function of Lysosomes 1. Degradation of macromolecules. 2. Degradation of worn-out organelles. 3. Removal of excess secretory produces in the cell. 4. Secretory function: take part in the secretory function. #### Important Lysosomal Enzymes * Protease * Lipase * Amylase * Nuclease #### Mechanism of Lysosomal Functions It is two mechanisms of function: 1. **Heterophagy:** Digestion of extracellular material engulfed by the cell via endocytosis. 2. **Autophagy:** Digestion and degradation of intracellular material such as worn-out cytoplasmic organelles. ### Peroxisomes Peroxisomes or microbodies are the membrane-limited vesicle like the lysosome. Peroxisomes contain some oxidative enzymes such as: * catalase * urate oxidase * D-amino acid oxidase #### Function of Peroxisomes 1. It helps in breaking down the fatty acid by means of a process called beta-oxidation. 2. It helps in degradation of toxic substances such as hydrogen peroxide and other metabolic products by means of detoxification. 3. Peroxisomes form the major site of oxygen utilization in the cell. 4. Peroxisomes degrade purine to uric acid. 5. Peroxisomes play a role in the formation of bile acid. 6. Peroxisomes participate in the formation of myelin sheath. ### Centrosome & Centrioles The centrosomes are membrane bound cellular organelles situated almost in the center of the cell, close to the nucleus. It consists of two cylindrical structures called centrioles which are made up of proteins. Centrioles are responsible for the movement of chromosomes during the cell division. ### Secretory Vesicle Secretory vesicles are the organelles with limiting membrane and contain the secretory substances. These are processed and packed in the Golgi apparatus. These vesicles are formed in the endoplasmic reticulum. Secretory vesicles are present throughout the cytoplasm. When necessary, those vesicles are ruptured and secretory substances are released into the cytoplasm. ### Mitochondria Mitochondrion is a membrane-bound cytoplasmic organelle concerned with the production of energy. It is rod-shaped or oval shapes structure. The diameter is 0.521 μm. #### Function of Mitochondria 1. **Production of energy:** Mitochondria is called the power house of the cell and power plant of the cell because it produces the energy required for cellular function. 2. **Synthesis of ATP:** The components of the respiratory chain in mitochondria are responsible for the synthesis of ATP by utilizing the energy of oxidative phosphorylation. 3. **Apoptosis** 4. **Storage of calcium & detoxification of ammonia in liver.** ### Ribosomes Ribosomes are the organelles without limiting membrane. It is a granular and small dot-like structure. The diameter is 15 nm. Ribosomes are made up of 35% of proteins and 65% of RNA. #### Types of Ribosomes 1. **Ribosome that are attached to rough endoplasmic reticulum** 2. **Free ribosome that are distributed in the cytoplasm.** #### Function of Ribosomes Ribosomes are called protein factories because of their role in the protein synthesis. Messenger RNA carries the genetic code for protein synthesis from nucleus to ribosomes. Free ribosomes are responsible for the synthesis of proteins in the hemoglobin, peroxisome, and mitochondria. ### Cytoskeleton Cytoskeleton is the cellular organelles present throughout the cytoplasm. Cytoskeleton determines the shape of the cells, gives support to the cell. The cytoskeleton consists of three major components: 1. **Microtubles:** Microtubles are the straight, hollow and tubular structures of the cytoskeleton. Each tuble has a diameter of 20-30 nm. #### Function of Microtubles 1. Determine the shape of the cell. 2. Give structural strength to the cell. 3. Microtubles are responsible for the movement of centrioles and the complex cellular structures like cilia. 4. Microtubles act like conveyer belts which allow the movement of granules, vesicles, protein molecules and some organelles like mitochondria to different part of the cell. 2. **Intermediate filaments:** Intermediate filaments are the structures that form a network around the nucleus and extend to the periphery of the cell. The diameter of each filament is 10 nm. #### Subclasses of Intermediate Filaments **Intermediate filaments are divided into five substances** 1. Keratins 2. Glial filaments 3. Neuro filaments 4. Vimentin 5. Desmin #### Function of Intermediate Filaments 1. It maintains the shape of the cell. 3. **Microfilaments:** Microfilaments are long and thin thread like structures with a diameter of 3-6 nm. These filaments are made up of non-tubular contractile proteins called actin and myosin. Actin is more abundant than myosin. #### Function of Microfilaments 1. Microfilaments provide resistance to the cell against the pulling forces. 2. Microfilaments are responsible for cellular movements like traction/contraction, gliding and cytokinesis. ### Nucleus The nucleus is the most prominent and the largest cellular organelle. It has a diameter of 10 μm to 20 μm and occupies about 10% of the total volume of the cell. Nucleus is present in all cells except RBC. The cells with nucleus are called eukaryotes and those without nucleus are called prokaryotes. #### Structure of the Nucleus * Nucleus is covered by a membrane called nuclear membrane. * Major components are composed of nucleoplasm and nucleolus. #### Nuclear Membrane Nuclear membrane allows the nucleoplasm to communicate with the cytoplasm. #### Nucleoplasm Nucleoplasm is a highly viscous fluid that forms the ground substance of the cell nucleus. It is similar to cytoplasm, present outside the nucleus. #### Chromatin Chromatin is a thread-like material made up of large molecules of DNA. #### Function of Nucleus 1. Control of all activity of the cell. 2. Synthesis of RNA 3. Control of cell division 4. Sending genetic instruction to the cytoplasm for protein synthesis through messenger RNA. 5. Formation of sub units of ribosomes. 6. Storage of hereditary information in the gene. ## Cell Death Cell death occurs by three processes: 1. **Autophagy: ** Autophagy is a normal physiological process by which cells are destroyed in the body by protein degradation to maintain the normal function. It is also involved in the recycling of the destroyed organelles for new cell formation. It is considered as non-apoptotic programmed cell death. 2. **Apoptosis:** Apoptosis is a natural or programmed death of the cell under genetic control. Apoptosis is referred to as cell suicide because of the cell activates and an intracellular death program and killed themselves in a controlled way. 3. **Necrosis:** Necrosis is the uncontrolled and unprogrammed death of the cells due to unexpected and accidental damages. It is also called cell murder because the cell is killed by extracellular or external events. After necrosis, the harmful chemical substances released from the death cell caused damage of neighboring tissues. ### Causes for Necrosis: Common causes of necrosis are injury, inflamation, infection, infarction and cancer. ### Necrosis is induced by both physical and chemical events such as: * heat, radiation, trauma, hypoxia due to lack of blood flow, and exposure to toxins. #### Necrotic Process: 1. Cell swells causing damage of the cell membrane and appearance of many holes in the membrane. 2. Intracellular contents leak out into the surrounding environment. 3. Simultaneously, a large amount of calcium ions are released by the damaged mitochondria and other organelles. #### Calcium ions affect the organization & activities of proteins in the intracellular components. Calcium ions also induce release of toxic materials that activate the lysosomal enzyme. #### The lysosomal enzyme caused degradation of cellular organs components. Products broken down from the disassembled resulting in death cells are ingested by neighboring cells. #### Classification of Genetic Disorder It is of four types: 1. Single gene disorders: It occurs because of a variation on mutation in a single gene. Example: Sickle cell anemia. 2. Multifactorial genetic disorders: It is caused by a combination of environmental factors and mutations in multiple genes. Examples are coronary heart disease. 3. Chromosomal disorders: It is a genetic disorder caused by abnormalities in a chromosome. Chromosomal disorder is classified into two types: 1. Structural abnormality of chromosome which leads to disorders like chromosome instability syndrome. 2. Numerical abnormality of chromosome: * Monosomy * Trisomy 4. Mitochondrial DNA disorder: It is caused by the mutation of the DNA of mitochondria. ### Gene A gene is a portion of DNA molecules that contain the message or code for the synthesis of specific proteins from amino acids. A gene is considered as the basic hereditary unit of the cell. ### Apoptosis Apoptosis is defined as the natural or programmed death of the cell under genetic control. Apoptosis is referred to as cell suicide because of the cell activates and an intracellular death program and killed themselves in a controlled way. #### Functional Significance of Apoptosis Apoptosis plays a vital role in the cellular homeostasis. It is useful for the removal of cells that are damaged beyond repair by viruses or a toxin. It is also essential during the development and in the adult stage. #### Activation of Apoptosis Apoptosis is activated by either withdrawal of positive signals or arrival of negative signals. ### Necrosis Necrosis is the uncontrolled and unprogrammed death of the cells due to unexpected and accidental damages. It is also called cell murder because the cell is killed by extracellular or external events. After necrosis, the harmful chemical substances released from the death cell cause damage to neighboring tissues. #### Causes for Necrosis: The common causes of necrosis are injury, inflammation, infection, infarction, and cancer. ### Necrosis is induced by both physical and chemical even such as: * Heat, radiation, trauma, hypoxia due to lack of blood flow, and exposure to toxins. #### Necrotic Process: 1. Cell swells causing damage of the cell membrane and appearance of many holes in the membrane. 2. Intracellular contents leak out into the surrounding environment. 3. Simultaneously, a large amount of calcium ions are released by the damaged mitochondria and other organelles. ### Calcium ions affect the organization & activities of proteins in the intracellular components. Calcium ions also induce the release of toxic materials that activate the lysosomal enzyme. ### Lysomal enzyme caused degradation of cellular organs components. Products broken down from the disassembled resulting in death cells are ingested by neighboring cells.