Physiology Lec 1 (Reference) PDF

1 Physiology General Physiology ( Cell ) Dr.Mohammed Khan, BDS Designed by: Zainab Akeel | Team Dentity  Introduction CELL TISSUE ORGANS SYSTEMS The structural and...

1 Physiology General Physiology ( Cell ) Dr.Mohammed Khan, BDS Designed by: Zainab Akeel | Team Dentity  Introduction CELL TISSUE ORGANS SYSTEMS The structural and The group of The structure Group of organs functional unit of cells having that is formed functioning together the living body similar function. by two or more to perform a specific primary tissues. function of the body.  CELL The basic living unit of the body is the cell Each cell is formed by a cell body and a cell membrane or plasma membrane that covers the cell body. The Important parts of the cell are The Important parts of the cell are 5  Cell Membrane Is a protective sheath that envelops the cell body. It separates the fluid outside the cell called extracellular fluid (ECF) and the fluid inside the cell called intracellular fluid (ICF). It is a semipermeable membrane and allows free exchange of certain substances between ECF and ICF The cell membrane is composed of three types of substances: 1. Proteins (55%) 2. Lipids (40%) 3. Carbohydrates (5%)  Cell Membrane Lipid Layer of Cell Membrane It is a bilayered structure formed by a thin film of lipids. It is fluid in nature and the portions of the membrane along with the dissolved substances move to all areas of the cell membrane. The major lipids are: a. Phospholipids b. Cholesterol  Cell Membrane Functions of lipid layer The lipid layer is semi permeable in nature and allows only the fat-soluble substances like oxygen, carbon dioxide and alcohol to pass through it. It does not allow the water-soluble materials like glucose, urea and electrolytes to pass through it.  Cell Membrane Protein Layers of the Cell Membrane The protein layers of the cell membrane are the electron dense layers situated on either side of the central lipid layer. The protein substances present in these layers are mostly glycoproteins. These protein molecules are classified into two categories: a. Integral proteins b. Peripheral proteins  Cell Membrane Functions of Protein layers 1. Integral proteins: provide structural integrity of the cell membrane 2. Channel proteins: provide route for diffusion of water-soluble substances like glucose and electrolytes 3. Carrier proteins: help in transport of substances across the cell membrane 4. Receptor proteins: serve as receptor sites for hormones and neurotransmitters 5. Enzymes: some of the protein molecules form the enzymes which control chemical reactions within the cell membrane 6. Antigens: Some proteins act as antigens and induce the process of antibody formation.  Cell Membrane Carbohydrates of the Cell Membrane Carbohydrate molecules form a thin loose covering over the entire surface of the cell membrane called glycocalyx (pericellular matrix). Some carbohydrate molecules are attached with proteins and form glycoproteins, and some are attached with lipids and form glycolipids.  Cell Membrane Functions of Carbohydrates 1. The carbohydrate molecules are negatively charged and do not permit the negatively charged substances to move in and out of the cell. 2. The glycocalyx from the neighboring cells helps in the tight fixation of cells with one another. 3. Some of the carbohydrate molecules form the receptors for some hormones. 13  Cytoplasm Is the fluid present inside the cell. It contains a clear liquid portion called cytosol which contains various substances like proteins, carbohydrates, lipids and electrolytes. Cytoplasm  Cytoplasm Organelles in Cytoplasm All the cells in the body contain some common structures called organelles in the cytoplasm. Some organelles are bound by limiting membrane and others do not have limiting membrane  Cytoplasm - Organelles With Limiting Membrane 1. Endoplasmic Reticulum 2. Golgi Apparatus 3. Lysosomes 4. Peroxisomes 5. Centrosome & Centriole 6. Secretory Vesicles 7. Mitochondrion - Organelles Without Limiting Membrane 1. Ribosomes 2. Cytoskeleton  Cytoplasm 1. Endoplasmic Reticulum Endoplasmic reticulum is made up of tubules and microsomal vesicles. These structures form an interconnected network which acts as the link between the organelles and cell membrane Types of Endoplasmic Reticulum - Rough Endoplasmic Reticulum - Smooth Endoplasmic Reticulum  Cytoplasm Golgi Apparatus Golgi apparatus (Golgi body or Golgi complex) is present in all the cells except red blood cells The Golgi apparatus is situated near the nucleus. It has two ends or faces namely, cis face & trans face. The cis face is positioned near the endoplasmic reticulum. The trans face is situated near the cell membrane.  Cytoplasm Functions of Golgi Apparatus 1- It is concerned with the processing and delivery of substances like proteins and lipids to different parts of the cell. 2- It functions like a post office because, it packs the processed materials into the secretory granules, secretory vesicles, and lysosomes and dispatch them either out of the cell or to another part of the cell. 3- It also functions like a shipping department of the cell because it sorts out and labels the materials for distribution to their proper destinations.  Cytoplasm Lysosome These are small globular structures filled with enzymes. These enzymes are synthesized in rough endoplasmic reticulum and transported to the Golgi apparatus. These are processed and packed in the form of small vesicles. Lysosome Then, these vesicles are pinched off from Golgi apparatus and become the lysosomes.  Cytoplasm Types of Lysosomes Lysosomes are two types: - Primary lysosome Which is pinched off from Golgi apparatus. It is inactive in spite of having the hydrolytic enzymes. - Secondary lysosome Which is active lysosome formed by the fusion of a primary lysosome with phagosome or endosome.  Cytoplasm Functions of Lysosomes 1- Digestion of unwanted substances With the help of hydrolytic enzymes like proteases, lipases, amylases and nucleases, lysosome digests and removes the unwanted substances. 2- Removal of excess secretory products in the cells Lysosomes in the cells of the secretory glands play an important role in the removal of excess secretory products by degrading the secretory granules. 3- Secretory function – Secretory lysosomes lysosomes having secretory function called secretory lysosomes are found in some of the cells, particularly in the cells of immune system.  Cytoplasm Peroxisomes They are pinched off from endoplasmic reticulum Peroxisomes contain some oxidative enzymes such as catalase, urate oxidase and D-amino acid oxidase. Peroxisomes are called as micro bodies. Peroxisomes  Cytoplasm Functions of Peroxisomes 1- Degrade the toxic substances like hydrogen peroxide and other metabolic products by means of detoxification 2- Form the major site of oxygen utilization in the cells 3- Break down the excess fatty acids 4- Accelerate gluconeogenesis from fats 5- Degrade purine to uric acid 6- Participate in the formation of myelin and bile acids.  Cytoplasm Centrosome & Centriole The centrosome is situated near the center of the cell close to the nucleus Centrosome It consists of two cylindrical structures called centrioles which are responsible for the movement of chromosomes during cell division. Centriole  Cytoplasm Secretory Vesicles Are globular structures, formed in the endoplasmic reticulum, and processed and packed in Golgi apparatus. When necessary, the secretory vesicles rupture and release the secretory substances into the cytoplasm.  Cytoplasm Mitochondrion The mitochondrion is a rod or oval shaped structure with a diameter of 0.5 to 1 μ. It is covered by a double layered membrane The outer membrane is smooth and encloses the contents of mitochondrion. The inner membrane forms many folds called cristae The cristae also contain many enzymes and other protein molecules which are involved in respiration and ATP synthesis So, cristae are collectively known as respiratory chain or electron transport system. The mitochondria contain their own DNA which is responsible for many enzymatic actions.  Cytoplasm Functions of Mitochondrion 1- Production of energy The mitochondrion is called the ‘Power house of the cell’ because it produces the energy required for the cellular functions. The energy is produced by oxidation of the food substances like proteins, carbohydrates and lipids by the oxidative enzymes in cristae. 2- Synthesis of ATP The components of respiratory chain in the mitochondrion are responsible for the synthesis of ATP by utilizing the energy through oxidative phosphorylation. 3- Apoptosis Mitochondria are involved in apoptosis  Cytoplasm Ribosomes Are small granular structures with a diameter of 15 nm. Some ribosomes are attached to rough endoplasmic reticulum while others are present as free ribosomes in the cytoplasm. The ribosomes are made up of - Proteins (35%) - RNA (65%)  Cytoplasm Functions of Ribosomes Synthesis of Proteins Ribosomes are called protein factories - Messenger RNA (mRNA) passes the genetic code for protein synthesis from nucleus to the ribosomes. The ribosomes, in turn arrange the amino acids into small units of proteins. The ribosomes attached with endoplasmic reticulum are involved in the synthesis of proteins like the enzymatic proteins, hormonal proteins, lysosomal proteins and the proteins of the cell membrane. - The free ribosomes are responsible for the synthesis of proteins in hemoglobin, peroxisome and mitochondria.  Cytoplasm Cytoskeleton Is a complex network that gives shape, support and stability to the cell. It is also essential for the cellular movements and the response of the cell to external stimuli. The cytoskeleton consists of three major protein components a. Microtubules: Mechanical support, Organization of the cytoplasm, Transport, motility and chromosome segregation. c. Microfilaments: actin filaments b. Intermediate filaments: withstand the mechanical stress that occurs when cells are stretched. 32  Nucleus Spherical shape Structure located near the center of the cell. Some Cells have nucleus and Known as eukaryotes And those cell can divide and produce enzymes Other cells without nucleus are known as prokaryotes ( ex. red blood cell) And cannot divide or synthesize the enzymes  Nucleus Structure of Nucleus 1- Nuclear Membrane The nucleus is covered by a double layered membrane called nuclear membrane. It encloses the fluid called nucleoplasm. Nuclear membrane is porous and permeable in nature, and it allows nucleoplasm to communicate with the cytoplasm.  Nucleus 2- Nucleoplasm It is a gel like ground substance and contains large quantities of the genetic material in the form of DNA. The DNA is made up of chromatin threads. These chromatin threads become the rod shaped chromosomes just before the cell division. 3- Nucleoli One or more nucleoli are present in each nucleus. The nucleolus contains RNA and some proteins, which are similar to those found in ribosomes. The RNA is synthesized by chromosomes and stored in the nucleolus.  Nucleus Functions of Nucleus 1. Controls all the activities of the cell 2. Synthesizes RNA 3. Forms subunits of ribosomes 4. Sends genetic instruction to the cytoplasm for protein synthesis through mRNA 5. Controls the cell division through genes 6. Stores the hereditary information (in genes) and transforms this information from one generation of the species to the next. Cell Death  Cell Death The cell death occurs by two distinct processes: Apoptosis Necrosis  Cell Death Apoptosis Is the programmed cell death under genetic control. Apoptosis (means ‘falling leaves’ in Greek) refers to the process by which the leaves fall from trees in autumn. It is also called ‘cell suicide’ since the genes of the cell play a major role in the death. This type of programmed cell death is a normal phenomenon, and it is essential for normal development of the body.  Cell Death Necrosis Is the uncontrolled and Unprogrammed death of cells due to unexpected and accidental damage. Necrosis (means ‘Dead’ in Greek) It is also called ‘cell murder’ because the cell is killed by extracellular or external events. Common causes of necrosis are injury, infection, inflammation, 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. After necrosis, the harmful chemical substances released from the dead cells cause damage and inflammation of neighboring tissues. Thank You Designed by Zainab Akeel | Team Dentity 41