Homeostasis, Cell Membrane, Physiology Lecture Notes

Dr. Asmaa Tarek Lecturer of physiology 1 What is physiology? Physiology is the dynamic study of life. It describes the vital functions of living organisms and their organs, cells & molecules. Physiology deals with how the human body functions, which depends on h...

Dr. Asmaa Tarek Lecturer of physiology 1 What is physiology? Physiology is the dynamic study of life. It describes the vital functions of living organisms and their organs, cells & molecules. Physiology deals with how the human body functions, which depends on how the individual organ systems function, how the component cell function &the interactions between subcellular organelles & countless molecules. So, it is the mother for many biological sciences.  Intended Learning Outcomes By the end of this lecture, you should be able to: 1.Structure of the cell membrane. 2. Define Homeostasis. 3. List the factors that must be homeostatically maintained in the internal environment of the body. 4. Outline how the body systems contribute to homeostasis. 5. Differentiate between negative and positive feedback mechanisms. 3 Chapter 1 The cell  The cell is the basic structural and functional unit of all forms of life. Every cell consists of cytoplasm enclosed within a membrane. Cells contain many organelles, each with a specific function. (such as the nucleus, endoplasmic reticulum and Golgi apparatus) are typically solitary, while others(suchas mitochondria, chloroplasts, peroxisomes, and lysosm es) can be numerous (hundreds to thousands). The cytosol is the gelatinous fluid that fills the cell and surrounds the organelles. Organelles are parts of the cell that are adapted and/or specialized for carrying out one or more vital functions, analogous to the organs of the human body (such as the heart, lung, and kidney, with each organ performing a different function) Structure of cell membrane o All cells are enveloped by a plasma membrane. o The cell membrane is semi-permeable, allowing some substances to pass through it, and excluding others. o Its permeability is greatly varied because it contains many regulated ion channels and transport proteins. o Plasma membrane maintains a unique composition to the intracellular fluid different from that of the extracellular fluid. A) Membrane Lipids  Types of membrane lipids 1-The major membrane lipids are phospholipid molecules. 2-There are few cholesterol molecules present in between the phospholipid bilayer.  Functions of lipid bilayer: 1) Forms a fence (barrier) around the cell. 2) Serves as a selective barrier to passage of substances between the ICF & ECF. 3) The continuous movement of phospholipids & cholesterol is responsible for the membrane fluidity (flexibility). This fluidity enables the cell to change its shape (muscle cells change shape as they contract). B) Membrane protein  Functions of Membrane Proteins: 1- Ion channels: allow passage of ions in & out of the cell. ( downhill transport). 2- Carriers: (= downhill transport). 3- Pumps: (= uphill transport) with use of energy (ATP). 4- Receptors (signal transduction):bind neurotransmitters or hormones & alter cell functions. 5-Enzymes:catalyze specific chemical reactions. 6- Cell adhesion molecules (CAM): hold cells together (intercellular junction).  C) Membrane Carbohydrates on the outer-membrane 1. glycoprotien. 2. Glycolipid. Functions of Membrane Carbohydrates: 1- Receptors for certain hormones. 2- Self-identity markers that enable cells to identify and interact with each other (Cell recognition molecules), so involved in the immune reactions. 3-Antigen-like e.g. blood group markers.  Chapter 2 Homeostasis  Homeostasis (Homeo = same - Stasis = staying) It is the maintenance of relatively stable (dynamic steady state) internal environment (ECF). Homeostasis is essential for survival and function of all cells. It is important because the cells and tissues of the body will survive and function efficiently only when these internal conditions are properly maintained. Homeostasis is not unlimited: The body can resist changes in the internal environment but to a variable range and time (Almost all diseases are failure of homeostasis). Body cells are bathed in a fluid medium (watery internal environment) Factors in the Internal Environment that must be homeostatically maintained Must Say within Normal o pH: 7.4. o Blood volume: 5 L. o Blood pressure: 120/80 mmHg. o Temperature: 37 ◦C. o Partial pressure of O2 = 100 mmHg, and CO2 = 40 mmHg, in arterial blood. o Concentration of water, salt, and other electrolytes. o Concentration of nutrients & waste products. The body Systems that share in homeostasis: 1- The circulatory system: Continuous movement of blood in the circulatory system. Transports nutrients, O2, CO2, wastes,electrolytes from one part of the body to another. 2- The respiratory system: While blood passes through the lungs, It picks up oxygen and releases carbon dioxide into the alveoli. So, Keep the level of oxygen and carbon dioxide in the blood 3- Digestive system: Digest and absorb nutrients. 4- The nervous system (rapid): Controls and coordinates bodily activities that require rapid responses. Detects and initiates reactions to changes in external environment. 5- The endocrine system (slow): Secreting glands of endocrine system regulate activities that require duration rather than speed. Carries out its effects by secreting hormones. Controls concentration of nutrients and, by adjusting kidney function, controls internal environment’s volume and electrolyte composition. N.B: Nervous & endocrine systems are the 2 major regulatory systems 6- The musculoskeletal system: Coordinating the movements Stabilizing the human body. 7- The immune system: Defense mechanism against Infection. 8- The Skin: Biological Barrier Prevent entrance of any foreign body or particle Plays a role in Vitamin D activation. 9- The urinary system: Excrete wastes, excess water, electrolytes and hydrogen.  What are the Components of Homeostatic Control Systems? Feedback : refers to responses made after change has been detected. Consists of: Receptor=sensor=detector: structures that monitor a controlled condition and detect changes (detect stimuli). Afferent pathway: neural or hormonal. Control center= integrator: Compare to set point and determines the suitable effector Efferent pathway: neural or hormonal. Effector: Receives orders from the control center. Produces a response that restores the controlled condition (muscles or glands).  Generally , when a physiological variable becomes away from its normal whether exceeding or below normal……. a control system elicits a feedback response consisting of one or a series of changes that returns the variable to within its normal physiological range.  Types of feedback (control) systems: Negative : ▪ This is a response that opposes the initial change. ▪ Most of the body’s compensatory homeostatic mechanisms function by negative feedback. Positive: Change is driven further away from original set- point (exaggerate the change) e.g: during normal childbirth. Examples 1- Negative feedback (90%): (Opposes an initial change & promotes stability, has importance in physiological regulastion) 1. Blood pressure changes. 2. Body temperature changes. 3. Blood glucose changes. 4. Blood gases changes. A- Body temperature changes B-Blood glucose changes 2- Positive feedback mechanism (Amplifies an initial change, its temporary, has some physiological importance, may cause vicious death cycles) 1. During the birth of a baby. ( later in blood ) 2. Blood Clotting. 3. Stress.  Birth Of a Baby ( Positive feedback mechanism) Stretch receptors in walls of uterus send signals to the brain. Brain induces release of hormone (oxytocin) into bloodstream. Uterine smooth muscle contracts more forcefully. More stretch, more hormone, more contraction etc. Cycle ends with birth of the baby. Birth Of a Baby ( Positive feedback mechanism)  Feedforward It responds in anticipation of a change in a regulated variable. Less frequently used. Examples: 1. Increase saliva because of sight, smell or thought of food. 2. Rise in respiration before exercise. 3. Shivering before diving into the cold water. 4. Increased secretion of insulin because of presence of food in digestive tract, which avoids excessive rise of glucose in blood after meal.  Homework Define homeostasis. Draw a diagram showing the way the body regulates the lowering of blood glucose level. Compare between positive and negative feedback with examples. References: 1. Ganong’s Review of Medical Physiology. Kim E. Barrett (editor), 26th edition, 2019. Lange Basic Science 2. BRS physiology 6Th edition. 3. Guyton and Hall Physiology Review, 2nd edition, freely downloaded https://www.medicinebau.com/uploads/7 /9/0/4/79048958/physiology_review.pdf