physiology (Lec 1).pdf

Physiology Second stage The general and cellular basis of medical physiology. lecture :1 Physiology Physiology: It is the science Of body organs functions that explain the physical and chemical mechanisms that are responsible for the origin, development, and progression of life. Homeostasis...

Physiology Second stage The general and cellular basis of medical physiology. lecture :1 Physiology Physiology: It is the science Of body organs functions that explain the physical and chemical mechanisms that are responsible for the origin, development, and progression of life. Homeostasis : a condition in which the internal environment of the body remains relatively constant despite changes in the external environment. Examples would be the maintenance of body temperature and levels of glucose in the blood. Homeostasis is achieved through negative or positive feedback mechanism. Negative feedback: Includes most homeostatic control mechanisms. Turn off the original stimulus, or reduces its intensity Positive feedback: Increases the original stimulus to push the variable farther There are three components to a homeostatic system 1. The Sensor which detects the stress. 2. The Control Center which receives information from the sensor and sends a message to adjust the stress. 3. The Effector which receives the message from the control center and produces the response which reestablishes homeostasis Homeostatic Regulation of Body Temperature through Negative Feedback Hyperthermia Heat receptors Hypothalamus in the skin Stress Sensors Control Center Stress is reduced shutting down mechanism Increased activity of Perspiration(swea sweat glands t) evaporates cooling the skin Increased blood flow to the skin Effect Effectors  Level of Organization Cell :is defined as the structural and functional unit of the living body. Tissue : is defined as the group of cells having similar function. All the tissues are classified into four major types which are called the primary tissues: 1. Muscle tissue (skeletal muscle, smooth muscle and cardiac muscle) 2. Nervous tissue (neurons and supporting cells) 3. Epithelial tissue (squamous, columnar and cuboidal epithelial cells) 4. Connective tissue (connective tissue proper, cartilage, bone) Organ : is defined as the structure that is formed by two or more primary types of tissues, which execute the functions of the organ. Like: stomach, intestine, liver, gallbladder …. System: is defined as group of organs that work together to carry out specific functions of the body. Each system performs a specific function. Example: Digestive system is concerned with digestion of food particles.  Organization of the Cell -Water. The principal fluid medium of the cell is water, which is present in most cells, except for fat cells, in a concentration of 70 to 85 per cent. -Ions. The most important ions in the cell are potassium, magnesium, phosphate, sulfate, bicarbonate, and smaller quantities of sodium, chloride, and calcium. -Proteins. After water, the most abundant substances in most cells are proteins, which normally constitute 10 to 20 per cent of the cell mass. These can be divided into two types: structural proteins and functional proteins. -Lipids. Especially important lipids are phospholipids and cholesterol, which together constitute only about 2 per cent of the total cell mass. -Carbohydrates. Carbohydrates have little structural function in the cell except as parts of glycoprotein molecules, but they play a major role in nutrition of the cell. Cell Membrane The cell membrane is a protective sheath, enveloping the cell body. It is also known as plasma membrane or plasmalemma. This membrane separates the fluid outside the cell called extracellular fluid (ECF) and the fluid inside the cell called intracellular fluid (ICF). The cell membrane is a semipermeable membrane. So, there is free exchange of certain substances between ECF and ICF. Thickness of the cell membrane varies from 75 to 111Å Cell membrane is composed of three types of substances: 1. Proteins (55%) 2. Lipids (40%) 3. Carbohydrates (3-5%). Cell Membrane Structure cell membrane The membrane is a fluid with mosaic of proteins. “The fluid mosaic model” This model is accepted by the scientists till now. In this model, the proteins are found to float in the lipid layer instead of forming the layers of the sandwich-type model. PLASMA MEMBRANE- FLUID MOSAIC MODEL lipid bilayer is made of phospholipids and is fluid in nature. Phospholipids molecules make the ‘backbone’ of cell membrane and each molecule has two ends: ◦ Polar end: hydrophilic. ◦ Non-polar end: hydrophobic. Proteins are embedded in lipid bilayer. Cholesterol Molecules: ◦ Are between phospholipids. ◦ Contributes to fluidity and stability of cell membrane. Functions of Lipid Layer in Cell Membrane Lipid layer of the cell membrane is a semipermeable membrane and allows only the fat-soluble substances to pass through it. eg:oxygen, carbon dioxide and alcohol  Membrane Proteins 1. INTEGRAL PROTEINS These are the proteins which Penetrate completely or partially into the phospholipid bilayer. 2. PERIPHERAL PROTEIN Are attached to inner and outer surface of membrane  MEMBRANE PROTEINS CAN ACT AS 1. Transport Proteins: 2. Membrane-bound enzymes. 3. Receptor sites. 4. Cell adhesion molecules (CAMs) which perform the function of intercellular joining.  Carbohydrates GLYCOCALYX: The loose carbohydrate coat on the outer surface of cell. It is made of Glycoproteins = Carbohydrate + protein Glycolipids = Carobhydrate + lipid. IMPORTANT FUNCTIONS OF GLYCOCALYX: (1) Many of them have a negative electrical charge, that repels other negative objects e.g. bacteria. (2) The glycocalyx of some cells attaches to the glycocalyx of other cells (3) Many of the carbohydrates act as part of the receptors for binding hormones, (4) Some carbohydrate moieties enter into immune reactions. FUNCTIONS OF CELL MEMBRANE 1.Protective function 2. Selective permeability 3. Absorptive function 4. Excretory function 5. Exchange of gases 6. Maintenance of shape and size of the cell Cytoplasm, Organelles, Nucleoli (continued)  Cytoplasm  The aqueous content of a cell (fluid, jellylike substance), that lies b/w cell membrane & nucleus in which organelles are suspended.  Serves as matrix substance in which chemical reactions occur.  ‘cytosol’ is the term used to describe fluid portion of the cytoplasm.  ORGANELLES IN CYTOPLASM Subcellular structures within the cytoplasm that perform specific functions. Some organelles are bound by limiting membrane and Others do not have limiting membrane  Cytoplasmic Organelles: Structure & Function Component Structure Function Endoplasmic System of interconnected Agranular (smooth) ER metabolizes nonpolar reticulum membrane- (network of compounds & stores Ca2+ in striated muscle cells; tubular structures). granular (rough) ER assists in protein sysnthesis Ribosomes Granular particles composed Synthesize proteins of protein & RNA Golgi complex Cluster of flattened Synthesizes carbohydrates & packages molecules for membranous sacs secretion. Secretes lipids & glycoproteins Mitochondria Membranous sacs w folded Release energy from food molecules & transform energy inner partitions into usable ATP Lysosomes Membranous sacs Digest foreign molecules & damaged organelles  Rough Endoplasmic Reticulum Rough appearance is due to the attachment of granular ribosomes to its outer surface-granular endoplasmic reticulum Functions of Rough Endoplasmic Reticulum 1. Synthesis of proteins 2. Degradation of worn-out organelles  Smooth Endoplasmic Reticulum formed by many interconnected tubules. So, it is also called tubular endoplasmic reticulum. Functions of Smooth Endoplasmic Reticulum 1. Synthesis of non-protein substance 2. Role in cellular metabolism 3. Storage and metabolism of calcium 4. Catabolism and detoxification An illustration of the processing of proteins by the granular endoplasmic reticulum & Golgi complex. Notice the formation of vesicles at the ends of some of the flattened sacs of the Golgi complex. The endoplasmic reticulum. Agranular ER lacks ribosomes attached to its surface, whereas granular ER has ribosomes.  ORGANELLES WITHOUT LIMITING MEMBRANE Ribosomes are the organelles without limiting membrane. These organelles are granular and small dot-like structures. 35% of proteins 65% of ribonucleic acid(RNA). RNA present in ribosomes is called ribosomal RNA (rRNA). Ribosomes are called ‘protein factories’ because of their role in the synthesis of proteins. Types of Ribosomes Ribosomes attached to rough endoplasmic reticulum -synthesis of proteins such as the enzymatic proteins, hormonal proteins, lysosomal proteins. Free ribosomes -synthesis of proteins in hemoglobin, peroxisome and mitochondria  A model structure of a ribosome. It is composed of two subunits: smaller (lighter) & larger (darker) subunits. The space between the two subunits accommodates a molecule of transfer RNA, needed to bring amino acids to the growing polypeptide chain. MITOCHONDRION  Concerned with production of energy. rod-shaped or oval-shaped structure It is covered by a bilayered membrane The outer membrane is smooth This membrane contains various enzymes such as acetyl-CoA synthetase and glycerolphosphate acetyltransferase.  The inner membrane is folded in the form of shelf-like inward projections called cristae synthesis of adenosine triphosphate (ATP). Functions of Mitochondrion 1. Production of energy 2. Synthesis of ATP 3. Apoptosis 4. Other functions- storage of calcium and detoxification of ammonia in liver. GOLGI APPARATUS  each cell has one Golgi apparatus. Some of the cells may have more than one Golgi apparatus. Each Golgi apparatus consists of 5 to 8 flattened membranous sacs called the cisternae. Functions of Golgi Apparatus Processing, packing, labeling and delivery of proteins and other molecules like lipids to different parts of the cell.  Golgi apparatus is situated near the nucleus. It has two ends or faces, namely cis face and trans face. The cis face is positioned near the endoplasmic reticulum. Reticular vesicles from endoplasmic reticulum enter the Golgi apparatus through cis face. The trans face is situated near the cell membrane. The processed substances make their exit from Golgi apparatus through trans face  Lysosomes The lysosomes are formed by Golgi apparatus. The enzymes synthesized in rough endoplasmic reticulum are processed and packed in the form of small vesicles in the Golgi apparatus. Then, these vesicles are pinched off from Golgi apparatus and become the lysosomes. lysosomes have the thickest covering membrane-bilayered lipid material. Types of Lysosomes Two types: 1. Primary lysosome, which is pinched off from Golgi apparatus. It is inactive in spite of having hydrolytic enzymes 2. Secondary lysosome, which is the active lysosome. It is formed by the fusion of a primary lysosome with phagosome or endosome.  Functions of Lysosomes Lysosomes are often called. ‘garbage system’ of the cell because of their degradation activity. Important lysosomal enzymes Proteases, which hydrolyze the proteins into amino acids Lipases, which hydrolyze the lipids into fatty acids and glycerides Amylases, which hydrolyze the polysaccharides into glucose Nucleases, which hydrolyze the nucleic acids into mononucleotides. Mechanism of lysosomal function Lysosomal functions involve two mechanisms: 1. Heterophagy: Digestion of extracellular materials 2. Autophagy: Digestion of intracellular materials (worn-out cytoplasmic organelles)  Cytoplasmic Organelles: Structure & Function (continued) Component Structure Function Peroxisomes Spherical membranous Contain enzymes that detoxify harmful vesicles molecules & break down hydrogen peroxide Centrosome Nonmembranous mass Helps to organize spindle fibers & distribute of 2 rodlike centrioles chromosomes during mitosis Vacuoles Membranous sacs Store & release various substances within the cytoplasm Microfilaments Thin, hollow tubes Support cytoplasm & function as cytoskeleton, & microtubules transport materials within the cytoplasm Cilia & flagella Minute cytoplasmic Move particles along cell surface, or move the projections that extend cell from the cell surface  PEROXISOMES Peroxisomes are pinched off from endoplasmic reticulum. Functions of Peroxisomes Breakdown the fatty acids Degrade the toxic substances such as hydrogen Peroxide (produced by alcohol) and other metabolic products by means of detoxification. Participate in the formation of myelin Play a role in the formation of bile acids. CENTROSOME AND CENTRIOLES Centrosome is the membrane-bound cellular organelle situated almost in the center of cell, close to nucleus. It consists of two cylindrical structures called centrioles which are made up of proteins. Centrioles are responsible for the movement of chromosomes during cell division.  SECRETORY VESICLES Contain the secretory substances. Formed in the endoplasmic reticulum and are processed and packed in Golgi apparatus. Present throughout the cytoplasm. When necessary, these vesicles are ruptured and secretory substances are released into the cytoplasm  CYTOSKELETON Cytoskeleton is the cellular organelle present throughout the cytoplasm. It determines the shape of the cell and gives support to the cell. It is also essential for the cellular movements and the response of the cell to external stimuli. The formation of the cytoskeleton by microtubules. Microtubules are also important in the motility (movement) of the cell, & movement of materials within the cell. Cytoskeleton consists of three major 1. Microtubule 2. Intermediate filaments 3. Microfilaments Cell Nucleus  Structure of the Nucleus -the nuclear envelope -nucleoplasm ] the two major types of materials The Nucleus -chromatin -the nucleolus  Features -The nucleus is the genetic control center of a cell. -In most cells, there is only one nucleus. It is spherical, making up 10% of the cell’s volume. -The nucleus is “command center,” as it controls all functions of the cell. -It regulates the actions of the cells. -It has message to synthesis the cell’s proteins.  Nuclear Envelope -The nuclear envelope is a double-layered membrane perforated with pores, which control the flow of material going in and out of the nucleus. -The outer layer is connected to the endoplasmic reticulum, communicating with the cytoplasm of the cell. The exchange of the large molecules (protein and RNA) between the nucleus and cytoplasm happens here.  Nucleoplasm -A jelly-like (made mostly of water) matrix within the nucleus -All the other materials “float” inside -Helps the nucleus keep its shape and serves as the median for the transportation of important molecules within the nucleus Nucleoli: ◦ Dark areas within the nucleus, not surrounded by membrane. ◦ Centers for production of ribosomes. Chromatin: ◦ Thread like material that makes up chromosomes.