1st Session Physiology PDF

Introduction GENERAL PHYSIOLOGY BMS11 4  Physiology Physiology is the study of the functions of living things. Specifically, it focuses on how the human body works. Levels of structural organization in the body: Cellular level: The cell is the basic structural and functional...

Introduction GENERAL PHYSIOLOGY BMS11 4  Physiology Physiology is the study of the functions of living things. Specifically, it focuses on how the human body works. Levels of structural organization in the body: Cellular level: The cell is the basic structural and functional unit of the body. Tissue level: The tissue is group of cells of similar structure and function. Organ level: An organ is a unit made up of different types of tissues carry out specific function. System level: Body system is a collection of related organ  Plays a role in cell division 1- Cellular respiration. 2- Formation of ATP (the source of energy in the body). 1- Processing and packaging of substances formed in RER into vesicles. 2- Storage of secretory vesicles till the time of release. Responsible for synthesis of protein Contain digestive enzymes (intracellular digestive system). Most cells have 3 subdivisions: 1- the plasma membrane 2- The nucleus 3- The cytoplasm. Many cells share some common features despite diverse structure and functional specialization.  Cell Structures & functions Cell membrane: It is very thin membrane structure that enclose each cell, separating the cell’s contents from the surrounding. The fluid contained inside the cell is called intracellular fluid (ICF), and the fluid outside the cell is extracellular fluid (ECF).  Cell Membrane It is formed of (1) phospholipid bilayer with globular proteins interspersed in the thin lipid film. The shape of phospholipids molecule is that of a clothes pin. It is formed of a polar head (phosphate charged group, polarized & hydrophilic= soluble in water) and two nonpolar tails (2 fatty acid chains, nonpolarized & hydrophobic=insoluble in water). The phospholipid bilayer is important for the flexibility and selective permeability of the cell membrane.  Cell Membrane There are 2 types of cell membrane (2) proteins: a. Integral proteins: passes all the way of the membrane. b. Peripheral proteins: attached only to one surface of the membrane and do not penetrate it. The cell membrane proteins form complexes with (3) Carbohydrates (glycoproteins) that are important as recognition sites and act as antigens for cell self-recognition immune system and differentiation. The (4) cholesterol molecules are completely hydrophobic and embedded in the phospholipid bilayer. They affect the permeability of the membrane. Cell Membrane Functions of cell membrane proteins 1) Structural proteins 2) Form passive channels Non-gated channels (open all time), Gated channels (Voltage gated & ligand gated) 3) Carriers in facilitated diffusion 4) Carriers in active transport (= Pumps):Carriers in facilitated diffusion 5) Receptors Body compartments The body of normal adult male is composed of: 1. 60% water (Total Body Water) (TBW). 2. 18% proteins. 3. 15% fat. 4. 7% minerals. More K+ less Na+ Less K+ More Na+ Movement of molecules across cell membrane  Transport of molecules 1-Passive transport 2-Active transport 3-Bulk transport Simple diffusion. Primary Endocytosis Osmosis. Secondary Exocytosis Facilitated diffusion. 1-Passive transport a- Simple Diffusion: it is a transport of small substance from high concentration to low concentration. It is passive process: no need for energy or carrier, but it needs gradient. Types of simple diffusion. (a) Nonpolar molecules can move by simple diffusion through the double phospholipid layers of the plasma membrane. e.g., CO2, O2. (b) Inorganic ions(Na+ , K + ) and water molecules can move by simple diffusion through protein channels in the plasma membrane. The rate of diffusion of a substance depends on: 1- Concentration gradient of the substance. 2- Electrical gradient: particularly affects the rate of diffusion of ions. 3- Surface area. 4- Permeability of the membrane: Increased permeability increase the diffusion rate. Membrane permeability is influenced by: a- Temperature: Increased temperature increase diffusion rate (because heat increases the motion of the molecules). b- Lipid solubility of the substance: Increased lipid solubility increase diffusion rate. c- Molecular weight of diffusing substances: Increased M.W decreases diffusion rate. d- Thickness of the membrane: Increase thickness decrease diffusion rate. e-Number of protein channels: Increased number of protein channels in the unit area increase rate of diffusion. b-  c- Facilitated diffusion It a passive transport down concentration gradient (from high to low concentration) for large molecules needs a carrier that facilitates the diffusion. No need for energy, but it needs for carrier and gradient. i.e., glucose. 2- Active transport The transport of substance across the cell membrane against an electrochemical gradient. From lower concentration to higher concentration Need specific carrier proteins, and need for energy (as ATP) A- Primary active transport: its energy is provided by ATP , Phosphorylation and dephosphorylation of transporter B-Secondary active transport: is a transport against gradient but its energy is not provided directly by ATP but by the gradient, supplied by other. Example of secondary active transport: absorption of amino acids or glucose with sodium in the intestine (symport). Or secretion of hydrogen in urine with reabsorption of Na (antiport) 3- Bulk Transport It Is the movement of macromolecules that are enclosed inside cell membrane bound vesicles. It is of two types: endocytosis and exocytosis. A- Endocytosis: the movement from outside the cell to the inside, molecules can enter the cells as small invaginating vesicles. a) Pinocytosis: cell drinking. b) Phagocytosis: cell eating. e.g., bacteria and dead tissue as WBCs. B- Exocytosis: The movement from inside the cell to the outside, as glands secretion.  What is Homeostasis? The maintenance of a constant internal environment (extracellular compartment) in the body is called Homeostasis. Your body has mechanisms to keep the cells in a constant environment. Body temperature regulation as an example of this homeostasis.  Components of a homeostatic system (mechanism) Receptors to detect changes in the internal environment. An integrating center which fixes the set point of the system (e.g., as hypothalamus in case of body temperature). The set point is the optimum condition under which the system operates ( 37c). Effectors which bring the system back to the set point.(e.g., muscle, blood vessel). A communication system to link the different parts together (nerves or hormones). There are two communication systems 1- The endocrine system: Communication is based upon hormones 2-The nervous system: Communication is based upon nerve impulses.  Regulation of body temperature is an example for negative feedback Homeostasis of body temperature Thermoreceptors receptors in the skin and deep structures sense the changes in body temperature and send these changes in the form of electric signals through nerves to the thermoregulatory center in the hypothalamus. The thermoregulatory center in the hypothalamus interprets the changes and send orders in the form of electric signals through nerves to many effectors in the body to antagonize the change in body temperature. As long as this homeostatic mechanism is operating, the body temperature is kept at the set point.i.e.~37°C.