Cell Physiology 1 (Lecture 1) PDF

Lecture (1) Dr. Nardien Ekram Haliem Saleh Lecturer of medical physiology Faculty of Medicine – Minia University  Definition of physiology Physiology is the science which deals with the functions of human body under different external and internal environmental conditi...

Lecture (1) Dr. Nardien Ekram Haliem Saleh Lecturer of medical physiology Faculty of Medicine – Minia University  Definition of physiology Physiology is the science which deals with the functions of human body under different external and internal environmental conditions to maintain life. The goal of physiology is to explain the physical and chemical factors that are responsible for proper function of all body systems. N.B. The changes in environmental conditions are called stimuli (stimulus).  Organization of the Human Body The structural unit of the human body is the cell. Cells of the same shape and function arrange side by side are called tissue. The organ is formed of more than one tissue performing a special function. e.g. the stomach digests and the kidney excretes…… etc. A system is formed of more than one organ performing complementary functions. The sum of these functions produce the characteristic role of the system. The human body consists of group of systems (e.g. Cardiovascular system, Digestive system, Respiratory system, etc.)  Composition of the human body: The human body weight (average 70kg in adult) is divided into: - 60% water - 40% solids (organic, inorganic) >> * Proteins >> 18% of body weight. * Fats >> 15% of body weight. * Inorganic >> 7% of body weight. Body water (60% of body weight) Intracellular fluid (ICF) >>> 2/3 of body water (40% of body weight) Extracellular fluid (ECF) >>> 1/3 of body water (20% of body weight) ECF is divided into: * Intravascular >> ¼ of ECF (5% of weight). Example: Plasma & Lymph * Extravascular >> ¾ of ECF (15% of weight). It includes Interstitial fluid (= Tissue fluid) & transcellular fluid (e.g. cerebrospinal fluid, synovial fluid Intraoccular fluid).  Components of ICF & ECF Main cation (+) in ECF >>>> Sodium (Na+) Main cation (+) in ICF >>>> Potassium (K+) Main anion (-) in ECF >>>> Chloride (Cl-) & bicarbonate (HCO3-) Main anion (-) in ICF >>>> Phosphate& Sulfate & Proteinate {{{Non-diffusible}}}  Water (42L) (60% of BW) ECF (14L) ICF (28L) (1/3 of water) (2/3 of water) (20% of BW) (40% of BW) Intravascular (3.5L) Extravascular (10.5L) (25% of ECF) (75% of ECF) (5% of BW) (15% of BW)  Extracellular ions Intracellular ions 1- Na+ (142 mEq) K+ (140 mEq) Cations mainly. mainly. Small amount of K+ (4 Na+ (14 mEq) less mEq). Less Ca++ and more More Ca++ and less Mg++. Mg++. 2- Anions Chloride (cl-) & Phosphates & Bicarbonates (more). Proteinates (more). Phosphates & Chloride (cl-) & Proteinates (less). Bicarbonates (less).  Water balance Normally, water gain = Water loss. When water gain > water loss, this leads to Edema. When water loss > water gain, this leads to Dehydration. Dehydration is common in children more than adults.  Why dehydration is common in children more than adults? 1. Children are more vulnerable to gastroenteritis (vomiting & diarrhea). 2. ECF/ICF ratio in children more than in adults. ECF/ICF in adults = ½ ECF/ICF in children = 1/1 (lose water easily) 1. Kidney is not well developed (N.B. Anti-diuretic hormone act on kidney and leads to water retention).  Homeostasis It means maintenance of nearly constant conditions of the internal environment. It is such as maintaining constant temperature, blood pressure, pH, and constant ion concentrations. Endocrine and nervous systems (control systems) for homeostasis. Two mechanisms of homeostasis: Negative and positive feedback mechanisms. The majority of the control systems work by a negative feedback mechanisms. The Human Cell  The Human Cell The cell is the smallest structural and functional units of a living organism that is able to perform essential vital functions. All cells are surrounded by cell membrane enclosing the protoplasm which is formed of cytoplasm, nucleus, and other organelles. Cell membrane (plasma membrane) is a very elastic structure separating and keeps intracellular fluid completely different from extracellular fluid.  The Human Cell Nucleus It is the brain of the cell, surrounded by nuclear membrane. All cells contain at least one nucleus except mature red blood cells (RBCs) and blood platelets (no nucleus). - Function of nucleus: Contains the genetic material (chromosomes). The cytoplasm contains numerous membrane-bound subcellular structures known as cell organelles.  cell organelles 1- Mitochondria (power house of the cell): food oxidation to provide energy. It has its own DNA so it is capable of self- replication. 2- Ribosomes: Protein synthesis. 3- Smooth endoplasmic reticulum: synthesizes lipids and cholesterol. 4- Rough endoplasmic reticulum: synthesizes proteins by attached ribosomes. 5- Golgi apparatus: Packages protein molecules for transport and secretion. 6- Lysosomes: Contain hydrolytic enzymes capable of digesting damaged cellular parts (and phagocytosis). If it is overworked, it leads to inflammation, tissue destruction. It can be stabilized by cortisol (anti-inflammatory). 7- Centrosome: important at cell division.  Cell membrane (Plasma membrane)  Cell membrane (Plasma membrane) Functions of Cell Membranes: 1. It act as a boundary for cellular components. 2. Regulate the passage of substances into and out of cells → Selective permeability. All membranes in the human body are semipermeable. 3. Detect chemical messengers arriving at the cell surface through receptors. 4. Link adjacent cells together by membrane junctions.  Structure of cell Membrane Chemically, it is composed of: 1- lipids (phospholipid bilayer). 2- carbohydrates (Glycocalyx). 3- Proteins. 1) Lipid bilayer (Phospholipid): They form thin film composed of 2 lipid layers: A. Each phospholipid layer has a head and two tails: 1. Hydrophilic head (phosphate end that directed outwards) attracted to water on the intra and extra cellular sides. 2. Hydrophobic tails (fatty acids that directed inwards) attracted to each other in the interior of membrane.  Structure of cell Membrane B. Glycolipids: some carbohydrates attached to the outer lipids. C. Cholesterol: rigid structure represents 10- 15% of total lipids so it regulates the fluidity of the membrane. Proper cholesterol can hold phospholipid layer in place and membrane fluidity has the ability to regulate membrane protein arrangement, and the membrane semipermeability.  Structure of cell Membrane 2) Glycoproteins and glycolipids (glycocalyx): - Function: 1- Cell adhesion. 2- Cell recognition. 3- Act as receptor… self-receptor for immune recognition to protect against auto-immune disease. N.B. The cell membrane is dynamic; molecules are continuously degraded and resynthesized.  Structure of cell Membrane 3. Proteins: throughout the membrane. Types of membrane proteins: Surface proteins (peripheral) on outer or inner surfaces >>>> Receptor or enzyme Trans-membrane or integral proteins (through and through proteins) >>>> channel, carrier, or pump.  Structure of cell Membrane Functions of membrane proteins: 1. Structural part of cell membrane. 2. Protein acts as channels and carriers. 3. Pumps as Na+-K+ pump. 4. Receptors for hormones and neurotransmitters. 5. Enzymes: catalyze specific chemical reactions (Adenyl-cyclase converts ATP into cAMP) 6. Identify proteins mainly glycoproteins (Glycocalyx). 7. Forming intercellular connections.  Types of channels: integral protein molecule specific for one ion that pass in one direction either in or out): 1- Open (leak or Non-gatted) channels: They are smaller in diameter and less in number than other channels. 2- Gated channels: they are closed during rest by protein act as a gate. There are two types: A- Voltage gated channels that open or closed in response to membrane potential changes as voltage gated Na+, K+ and Ca++. B- Ligands gated channels that open or close by binding to chemical substance (ligands) like the neurotransmitters e.g. Ligand- gated Na+ channels in motor end plate or in the postsynaptic neurons. C- Mechanical gated channels that respond to stretch. Voltage-gated ion channel  Types of carriers: Uniport carrier that transmit only one substance in one direction e.g. glucose carrier, Ca+2 pump. Symport carrier that co-transport more than one substance at a time in only one direction (two substances in the same direction) e.g. Na+ and glucose carrier. Antiport carrier that counter-transport one substance in one direction in exchange for another in the opposite direction (two substances in the opposite direction) e.g. Na+-K+ pump, Na+- Ca+2 exchanger. Types of carriers Na K Pump  Intercellular connections Type Function Location 1. Tight junctions Close space between cells by fusing Intestinal lining cell membranes. 2. Desmosomes Bind cells by forming intermediate Cells of the outer skin filament network among cell layer membranes 3. Gap junctions Form tubular channels between Muscle cells of the cells that allow substances to be heart and digestive exchanged tract Intercellular connections  Explain why: 1. Children are more liable than adults to develop dehydration. What happen if: 1. Lysosomal membrane becomes unstable. 2. Water loss become more than water gain. 3. Self-receptor on cells is impaired. Mention: 1. Types of membrane proteins & example for each. 2. Types of protein carriers. 3. Types of channels through the cell membrane.  MCQ Extravascular fluid represents …… that of intravascular. (1/3 --- 3 times --- 1/4 --- 4 times) ECF represents ….. That of ICF. (2/3 -- ½ --- 2 --- 1/5) Tails of lipid bilayer are placed towards: (inside of the cell – outside the cell – interior of the membrane) Trans-membrane integral protein that responds to potential change is: (ligand gated channel–voltage gated channel–mechanical gated channel) Glucose may be transported by: (Uniport – symport – both of them)