L1 Ogq PDF - Homeostasis and Cell Biology

What is meant by homeostasis? Homeostasis means keeping the internal environment conditions constant of the body. Some limited changes may occur internally or externally affect the chemical and physical properties of the internal environment Homeostasis means physiologic mechanisms to...

What is meant by homeostasis? Homeostasis means keeping the internal environment conditions constant of the body. Some limited changes may occur internally or externally affect the chemical and physical properties of the internal environment Homeostasis means physiologic mechanisms to return or keep internally constant.  Control Nervous system Endocrine system Feed back controlling system: A) negative B) positive Feed forward controlling Cell organelles and cell membrane Cell organelles: Nucleus --division and control ( DNA & RNA) Mitochondria – cell respiration Golgi apparatus– storage Endoplasmic reticulum– smooth & rough Smooth –synthesis of lipids Rough---synthesis of proteins Ribosomes--- synthesized proteins Lyzosomes --- destruction of large particles Cell membrane  The cell membrane This is a very thin elastic semipermeable membrane that surrounds the cell. Chemically, the cell membrane is composed primarily of proteins (55 %), lipids (42 %), together with a small amount of carbohydrates (3 %) combined almost entirely to proteins forming glycoproteins. The basic structure of the cell membrane is a lipid bilayer, embedded in which in a random way large globular protein molecules.  The major lipids are phospholipid molecules, the shape of which is similar to a clothespin. The head of the molecule contains the phosphate portion and is quite soluble in water (= hydrophilic), while its tail is insoluble in water (= hydrophobic. The proteins in cell membranes are 2 kinds (a) Integral proteins (which extend all the way through the cell membrane) (b) Peripheral proteins (which are only attached to the outer and inner surfaces of the cell membrane, but they do not penetrate it Functionally, these proteins are classified into the following 7 types : (1) Structural proteins : Some of these contain lipids (lipoproteins) while others contain carbohydrates (glycoproteins). (2) Pumps: These actively transport ions across the cell membranes. (3)Receptors: These bind neurotransmitters and hormones, which initiates physiological changes inside the cell (4)Carriers: These transport various Transport across cell membrane (1)DIFFUSION This is a passive process (i.e. requiring no energy) by means of which a substance in solution (or in a gas) expands to occupy all of the available volume. It is produced by the kinetic motion of the molecules (which makes them in a continuous random movement), and it occurs in the direction of their concentration (= chemical) or electrical gradients ie. from areas of high concentration to areas of lower  Simple diffusion This occurs through the lipid bilayer as well as through channels present in the cell membrane called the channel proteins. (A)Simple diffusion through the lipid bilayer The following substances can cross through the lipid bilayer (I) Lipid-soluble substances (e.g. O2, N and alcohol) : These substances dissolve in the lipid bilayer, so they cross the cell membranes easily.  (B) Simple diffusion through protein channels This is important for diffusion of ions and the large water-soluble molecules. Protein channels are highly selective e.g. there are specific channels for transport of Na, K and Ca (called Na*, K* & Ca2* channels). Some channels are continuously open (= leak channels) while most of them are gated i.e. they have gates that open or close. These are either : Voltage-gated i.e. open or close by alterations  Facilitated diffusion This mechanism of diffusion also moves substances passively in the direction of their chemical or electrical gradients, but it requires transport proteins called carrier proteins (so it is also called carrier-mediated diffusion). The molecules of substances that diffuse by this mechanism (e.g. glucose and amino acids) bind to one of the carrier proteins. This caused conformational change in the protein which leads to movement of the bound molecule from one side of the cell to the other i.e. the carrier protein facilitates diffusion of the substance to the other side. In many sites, facilitated diffusion is regulated by hormones eg. insulin can increase the rate of glucose diffusion into the cells 10-20 Permeability of the membrane: The greater the permeability of the membrane. the more rate of diffusion, and vice versa  permeability is influenced by the following factors: 1) Thickness of the membrane: The greater the thickness, the  Active transport This is the transport of substances against their electrical or concentration gradients (i.e. from a lesser to a greater concentration). It requires specific carrier proteins as well as energy. The latter is provided mainly by hydrolysis of ATP (therefore, the carrier molecules are mostly ATPase enzymes that catalyze the hydrolysis of ATP). A typical example of active transport is the transport of Na and K across the membranes of muscle and nerve fibers by the Na - K* pump (refer to  ** Both facilitated diffusion and active transport are carrier-mediated transport mechanisms. However, active transport requires energy and occurs against concentration and electrical gradients. while facilitated diffusion does not require energy and occurs only along concentration and electrical gradients There are 3 types of carrier proteins which are the following : Uniports: These transport only one substance.  Pinocytosis (A) and exocytosis (B). - Pinocytosis (= cell drinking) This is a transport mechanism by means of which large particles (e.g. proteins) cross cell membranes and enter the cells (when simple diffusion, facilitated diffusion and active transport cannot occur). The particle first contacts the cell membrane. Then, the latter is depressed (making an invagination into the cell) and on each side it rises and folds over the particle (which will become a vacuole inside the cytoplasm the  FORCES THAT AFFECT MOVEMENT OF SUBSTANCES BETWEEN COMPARTMENTS (1) OSMOSIS This is the movement of water through a semipermeable membrane from an area containing pure water or a diluted solution of a solute (e.g. NaCI or glucose) to an area in which there is a higher concentration of this solute. The pressure required to apply on the concentrated solution so as to prevent water movement from the diluted solution is called the osmotic pressure. The amount of osmotic pressure is directly proportional to the number of particles per unit volume of solution. So, ionizing solutes (e.g. NaCI) are more osmotically active (because each ion is active by itself) than non-ionizable solutes (e.g. glucose). The osmotic pressure is expressed in osmoles or milliosmoles (which can be converted to mmHg (one milliosmole =1 / 1000 osmole = 19.3 mmHg). All body fluids have the same osmolality (about 290 milliosmoles per litre = about 5500 mmHg = about 73 atmospheric pressure). Solutions that have an osmolality equal to that of the plasma are called isotonic solutions, while those having a higher osmolality are hypertonic, and those having a lower osmolality are hypotonic. ** A 0.9 % NaCl solution and a 5 % glucose solution are both isotonic. However, in the latter condition glucose is metabolized in the body, and the net effect will be that of a hypotonic solution.  (2) FILTRATION AND ULTRA- FILTRATION Filtration is a process by means of which a fluid (with its dissolved molecules) is forced through a porous membrane due to a difference in hydrostatic pressure on the 2 sides of the membrane. The amount of the filtered fluid per unit time is directly proportional to the difference in pressure, the surface area of the membrane and its permeability. An example of filtration is the formation of the interstitial (= tissue) fluid Body fluids  THE BODY FLUIDS THE TOTAL BODY WATER (TBW) AND ITS DISTRIBUTION TB W is normally about 60 % of body weight in young adult males, 51 % in young adult females, and 5 % in obese persons Therefore. in a young adult male 70 Kg. the TBW is normally 42 lit res, and is divided into (1) Intracellular fluid (ICF) : constitutes about 2/3 or the TBW i.e. about281itres  control Control of its osmolality ( tonicity) Control of its volume Regulation of local blood flow to tissues This includes : short and long term mechanisms mechanisms mechanisms  Short term mechanism Depend on regulation of arteriolar diameter  Long term mechanisms Angiogenesis Development of collateral circulation  Long term mechanisms Angiogenesis Development of collateral circulation