Medical Biology (1st Year) Lecture Notes PDF

University of Mosul College of Medicine Lecture: 4 Subject/year: Medical Biology /1st Year Lecturer: Inaam A. Abdulhameed Department : Anatomy Date: 27/11/2024  The AIM of this lecture is To learn about different forms of transport across the cell membrane.  Intended learning outcome...

University of Mosul College of Medicine Lecture: 4 Subject/year: Medical Biology /1st Year Lecturer: Inaam A. Abdulhameed Department : Anatomy Date: 27/11/2024  The AIM of this lecture is To learn about different forms of transport across the cell membrane.  Intended learning outcomes: By the end of this lecture the student will be able to: Describe the process of diffusion , osmosis, and facilitated diffusion. Describe the process of active transport and bulk transport. Understand how organisms use simple and active transport.  Movement Across Cell Membranes The movement of substances across the membrane can be either "passive", occurring without the input of cellular energy , or "active", requiring the cell to expend energy in transporting it. There are two ways in which substances can enter or leave a cell: 1-Passive ways a ) Diffusion b) Osmosis (water only) c) Facilitated Diffusion 2- Active ways a ) Active Transport b) Bulk Transport  (Passive ways) a. Diffusion: Diffusion is the movement of molecules from a region of higher to lower concentration; it requires no energy and stops when the distribution is equal. Some examples of substances that use this process are oxygen (O2), carbon dioxide (CO2), and lipids. b. Osmosis: Osmosis is the diffusion of water across a partially permeable membrane from a dilute solution (high concentration of water) to a concentrated solution (low concentration of water).  There are three different types of osmotic solutions: -Isotonic Solution Normally body fluids are isotonic to cells. There is the same concentration of solutes and water on both sides of the plasma membrane. -Hypotonic Solution A hypotonic solution has a lower concentration of solute and a higher concentration of water than the cells. -Hypertonic Solution A hypertonic solution has a higher concentration of solute and a lower concentration of water than do the cells.  Effects of Osmosis on Cells  If a cell is placed in an isotonic solution, there is no net water movement, so there is no change in the size of the cell.  When a cell is placed in a hypotonic solution, water will enter the cell, and the cell will swell.  If a cell is placed in a hypertonic solution, water will leave the cell, and the cell will shrink.  Intravenous solutions given in medical situations are usually isotonic. c. Facilitated Diffusion: It is a type of diffusion in which the molecules move from the region of higher concentration to the region of lower concentration assisted by a carrier protein. It is passive and requires no energy from the cell. Common molecules entering/ leaving cells this way include : glucose and amino-acids. Type 2 diabetes mellitus results when cells lack a sufficient number of glucose transporters.  (Active ways( a. Active Transport Active transport is the energy-demanding transfer of a substance across a cell membrane, from lower concentration to higher concentration. Special proteins within the cell membrane act as carrier proteins.  Proteins involved in active transport often are called pumps. One type of pump , called the sodium – potassium pump ,is active in all the cells of the body for the movement of sodium ions (Na+) outside, and potassium ions (K+) inside ,the cell. This type of pump is associated especially with nerve and muscle cells.  b. Bulk Transport Cells use bulk transport to move large molecules, such as polysaccharides or polypeptides, across the membrane. These processes use vesicles rather than channel or transport proteins. Cells use two active transport processes to move these macromolecules into or out of the cell: 1. Endocytosis 2. Exocytosis 1. Endocytosis is the process of capturing a substance or particle from outside the cell by engulfing it with the cell membrane. There are 3 main kinds of endocytosis: a- Phagocytosis b- Pinocytosis c- Receptor- mediated endocytosis  Phagocytosis (‘cell eating’) : It refers to intake of solid particles by a cell. Example, Some white blood cells are able to take up pathogens (disease causing agents) by Phagocytosis.  Pinocytosis (‘cell drinking’): is a process by which the cell takes in the fluids and dissolved small molecules.  Receptor- mediated endocytosis: is a form of endocytosis in which receptor proteins on the cell surface are used to capture a specific target molecule.  An inherited form of cardiovascular disease occurs when cells fail to take up a combined lipoprotein and cholesterol molecule from the blood by receptor mediated endocytosis. 2. Exocytosis describes the process of vesicles fusing with the plasma membrane and releasing their contents to the outside of the cell. - Exocytosis occurs when a cell produces substances for export, such as a protein, or when the cell is getting rid of a waste product or a toxin. To summarize: Passage of molecules into or out of cells can be passive or active. Passive mechanisms do not require energy. Examples are diffusion, facilitated transport , and osmosis. Active mechanisms require an input of energy.Examples are active transport , endocytosis, and exocytosis.  Lets check our knowlege It is the net movement of water across a selectively permeable membrane. A. Endocytosis B. Osmosis C. Vesicle Transport D. Facilitated Diffusion E. Diffusion The process of cell eating is called A. Osmosis B. Exocytosis C. Facilitated diffusion D. Phagocytosis E. Pinocytosis References and recommended further readings: 1. Madder, S., S., and Windelelspecht, M., Human biology, 17th ed. Mc Graw – hill, USA, 2023. 2. Sylvia S. Madder, Biology, 6th ed. Mc Graw-Hill Education, USA,1999.