Lecture Slides-Physiological Processes and Controls

Lecture - Theme Cell Tissue and Organ Theme Cell Tissue and Organ Functions are Regulated by Control Systems through Negative and Positive Systems

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Unformatted text preview: Theme: Cell, Tissue and Organ Theme: Cell, Tissue and Organ Functions are Regulated by Control Systems through Negative and Positive Systems through Negative and Positive Feedback Mechanisms • Concept A: Maintenance of a constant internal environment (homeostasis) is necessary for the optimal functioning of physiological processes and requires energy-dependent steady state conditions. • Concept B: Feedback mechanisms allow organisms to self to self-regulate and maintain homeostasis. and maintain homeostasis • Concept C: Negative feedback loops are stabilized when input response times are faster than output response times. The Internal Environment • The organ systems of the body operate in a coordinated fashion to maintain a stable INTERNAL ENVIRONMENT Body cells are bathed in an INTERNAL ENVIRONMENT self ENVIRONMENT, self-contained within the within the body and from which all cells are nourished The maintenance of the constancy of this internal environment is termed HOMEOSTASIS Body Fluid Compartments T I S S U E /O R G A N BO UND ARY BLO O D V E S SE L CELLS IN T E R S T IT IA L F L U ID • In complex animals (like humans), the body fluids are distributed In complex animals (like humans) the body fluids are distributed between three between three anatomically defined fluid compartments: • The INTRACELLULAR (inside of cells) FLUID (illustrated in blue) • The EXTRACELLULAR (outside of cells)FLUID (ECF), which is subdivided into: subdivided into: The INTERSTITIAL (or tissue) FLUID (illustrated in green) The INTERSTITIAL (or tissue) FLUID (illustrated in green) The The BLOOD PLASMA (illustrated in red) • The INTERNAL ENVIRONMENT is comprised of the EXTRACELLULAR FLUID (ECF, i.e., that portion of the total body ti th water [~33%] located outside of cells) % of TOTAL BODY WATER Definition of the Internal Environment Internal Environment 120 100 80 INTERSTITIAL FLUID INTERNAL ENVIRONMENT = EXTRACELLULAR FLUID (33%) INTRACELLULAR WATER INTRACELLULAR FLUID (66%) BLOOD PLASMA 60 40 20 0 •~80% of the ECF is trapped between cells in tissues and is located outside of the cardiovascular system - the INTERSTITIAL FLUID –It is from this fluid that cells receive nutrients and into which they excrete wastes •The remaining ~20% of the extracellular fluid is confined to the cardiovascular system and comprises the BLOOD PLASMA Constancy of the Internal Environment Internal Environment • In order to function optimally, cells cannot tolerate wide fluctuations in the state or composition (temperature fluctuations in the state or composition (temperature, osmolality, pH, nutrient concentration, etc.) of the internal environment • Yet, most of these parameters vary widely and unpredictably in the external environment Dietary intake is sporadic and varied in composition Ambient temperature fluctuates widely temperature fluctuates widely Constancy of the Internal Environment: A Steady State St St • Constancy of the internal environment is a regulated of the internal environment is regulated STEADY STATE (requiring the expenditure of energy), not an equilibrium situation (input=output, but not an equilibrium) The nutrients consumed by cellular activity must be replaced from the external environment environment The waste products delivered to the internal environment must be dumped into the external environment external environment • Constancy of the internal environment is dependent on an energy-dependent exchange of materials between the internal and external environments the internal and external environments The Circulatory System and the Internal Environment Internal Environment • The circulatory system provides a vital link between individual cells and the sites of external exchange th Not Not all cells are located in close proximity to sites of surface exchange (e.g., lungs, intestine and kidneys) While While it takes <1 sec for a solute to diffuse from the center of an average cell to the surface, the center of an average cell to the surface, diffusion diffusion over distances of a meter or more may require years • There is a necessity for the bulk movement of fluids (e.g., the blood) between the internal tissues and organs and the sites of surface exchange th PRACTICAL APPLICATION OF HOMEOSTASIS HOMEOSTASIS • The concept of homeostasis provides the theoretical The concept of homeostasis provides the theoretical framework framework for clinical medicine • Hypothesis: organ systems of the body function to maintain the constancy of the internal environment maintain the constancy of the internal environment • Prediction: physiological parameters (e.g., blood pressure, blood glucose, blood osmolality, and hemoglobin levels) will remain within some regulated (i.e., normal) range will remain within some regulated normal) range • Values that fall outside of the accepted range indicate a pathology (i.e., a defect in some regulatory mechanism) Physiological Exchange Processes • DIFFUSION • OSMOSIS • FACILITATED DIFFUSION • ACTIVE TRANSPORT Physiological Exchange Reactions Wastes EXTERNAL ENVIRONMENT O2 CO2 Nutrients Digestive System ORGANISM Respiratory System Circulatory System Excretory System Storage or Buffer Tissues Muscle Adipose INTERNAL ENVIRONMENT ⎨ Salt & Water Cells Interstitial fluid Blood plasma Net Diffusional Fluxes Exchange Surface Ci Co Unidirectional Efflux Unidirectional Influx NET FLUX = Influx - Efflux Ci > Co • A NET FLUX (the actual transfer of mass from one side of the membrane or epithelium to another) occurs whenever one whenever one unidirectional flux exceeds the other What Does Fick’s Law Say? Jnet = Influx - Efflux = DA([Co - Ci] /x) • A NET FLUX occurs only under nonequilibrium conditions NET FLUX occurs only under nonequilibrium At equilibrium, Ci = Co and Jnet = 0, however, the unidirectional fluxes are not zero, they are simply equal in magnitude and opposite in direction it di • What Are the Predictions of Fick’s Law? A linear relationship between the magnitude of the concentration difference ([Co - Ci] ) and the net flux Net flux is directly proportional to the surface area across which diffusion is occurring Net fl is in Net flux is inversely proportional to the distance across which to the distance ac diffusion is occurring Significance of Fick Law of Diffusion Fick’s Law of Diffusion • Fick’s law constrains certain features of plant and animal design animal design • For those physiological processes driven by diffusion, the efficiency of the process (as assessed by higher the efficiency of the process (as assessed by a higher flux rate) may be increased by: Maintenance of diffusion gradients (which normally tend to run down) tend to run down) Elaboration of surface area Minimizing the diffusion distance • All of these predictions are evident in the morphology of physiological exchange surfaces Osmosis Osmosis • • • • Osmosis is the diffusion of water across a semi-permeable semimembrane from a less concentrated solution of solute to to a more concentrated solution of solute SemiSemi-permeable membrane allows movement of water but allows movement of water but not not sucrose (solute) Water moves from right to left until sucrose concentrations are the same are the same Driving force for osmosis: the solute (sucrose) has the effect of lowering the effective concentration of water molecules, or more properly lowering the chemical activity of water Osmotic Pressure Osmotic Pressure • • • • • Hydrostatic (water) pressure in A needed to just prevent water entry is called the osmotic pressure of the solution in A. Depends on total number of osmotically active ions or osmotically active ions or molecules molecules in solution (not dependent on chemical properties) Effective osmotic concentration is directly proportional to osmotic pressure (1 osmolar solution pressure (1 osmolar solution contains contains 1 mole of osmotically active molecules or ions per liter) 2 M glucose solution has same osmotic pressure as 1 M NaCl; mixed solution of 2 M glucose and 1 M NaCl solution equivalent to 4 NaCl M glucose solution (colligative property) Important in many physiological processes including blood filtering processes by by kidney Facilitated Diffusion Facilitated Diffusion • Passive movement Passive movement through through a membrane involving a specific carrier protein carrier protein • Aids diffusion of polar substances • Carrier protein causes channel molecule to open • Insulin - glucose Active Transport Active Transport • Energy-dependent (ATP) Energytransport of a substance across membrane against conc. Gradient • Uniports-move single solute move single solute in in one direction • Symports- move two solutes in one direction • Antiports-move two solutes in opposite directions (Na-K (Napump) • Renal tubule External Physiological Exchange: Summary Summary • Constancy of the internal environment is made possible by processes of physiological exchange between the internal and external environments - major organ systems of the body carry out these exchange processes: The respiratory system acquires the oxygen required for cellular metabolism and eliminates carbon dioxide (a waste product of aerobic metabolism)-DIFFUSION The digestive system procures nutrients from the external environment and eliminates some waste products The excretory system regulates the amount of salt and water that appears in the urine, and thereby adjusts their concentration in the internal environment their concentration in the internal environment-OSMOSIS Internal Physiological Exchange: Summary Summary • Some organs serve as storage reservoirs to buffer the composition of the internal environment For example, the liver stores carbohydrates that are ingested in excess of immediate needs These stores can be drawn on at a later time, as needed (while fasting or during starvation) (while fasting or during starvation) The inability of some tissues (e.g., the CNS) to store nutrients makes them absolutely dependent on the function nutrients makes them absolutely dependent on the function of nutrient storage tissues and organs • Adipose tissue, and to a lesser extent muscle, also perform tissue and to lesser extent muscle also perform storage and buffer functions Biological Control Systems • Biological control systems involved in the maintenance of homeostasis operate on the principle of NEGATIVE FEEDBACK and involve the following components: A receptor that detects changes in the internal environment (i.e., stimuli) An integrating component (generally either the brain or an endocrine gland) that compares the sensory information (from the receptor) to the ideal or “set point” value An effector or responding system (i.e., some means of changing the state of the internal environment) A FEEDBACK LOOP, which in the case of negative feedback systems counteracts the original change in the variable being controlled Physiological Regulation and Physiological Regulation and Homeostasis • regulatory systems have set points and respond to feedback information • negative feedback corrects deviations from the set point • positive feedback amplifies responses • Feed forward information changes the set point Fig. 1-13 Negative feedback − A Enzyme 1 B D Excess D blocks a step D Enzyme 2 D C Enzyme 3 D (a) Negative feedback W Enzyme 4 Positive feedback + X Enzyme 5 Excess Z stimulates a step Z Y Z Z Enzyme 6 Z (b) Positive feedback Negative Feedback Negative Feedback •Reduces deviations in a regulatory system •Negative feedback may turn off or slow down a physiological process •Negative feedback may also turn on or accelerate a feedback may also turn on or accelerate physiological process Characteristics of Negative Feedback • Negative feedback systems do not maintain absolute constancy MINIMIZE CHANGES Deviation from set point is required to initiate a response • Set points around which regulation occurs vary with physiological status Sliding “set point” concept - the point of regulation may vary with the physiological status of the organism For example, body temperature varies: With time of the reproductive cycle in females – 0.5oC higher following ovulation Diurnally (36.2oC at night, 37.4oC daytime) (36 at night 37 daytime) With infection (i.e., pyrogen-induced fever) Control of Blood Sugar [Blood Glucose] - mg% 160 • NEGATIVE FEEDBACK is defined by the relationship of th the response to the stimulus, th not by the direction of deviation from the “set point” • Stimulus and response must be in opposite directions CARBOHYDRATE MEAL 140 120 STIMULUS RESPONSE 100 "SETPOINT" SET POINT Pancreatic Secretion of Insulin: Stimulates Glucose Uptake and Storage 80 60 0 10 20 30 40 Minutes •For example, a rise in the blood glucose level (the stimulus) detected by the endocrine pancreas results in insulin secretion (the effector response) by the endocrine pancreas •Insulin stimulates glucose uptake and storage, and a drop in blood glucose (the effector response) •Consequently, the effector response counteracts the stimulus Control of Blood Sugar BLOOD GLUCOSE REGULATION [Blood Glucose] - mg% 140 FASTING 120 "SET POINT" 100 STIMULUS RESPONSE 80 60 Pancreatic Secretion of Glucagon: Stimulates Glycogen Breakdown in Liver 40 20 0 0 10 20 30 40 • A drop in blood glucose stimulates glucagon secretion by the pancreas, secretion by the pancreas which in turn results in glucose mobilization from the liver and a rise in blood glucose • Both of these examples fit the definition of negative feedback even though the initial fluctuations in blood glucose levels are in opposite glucose levels are in opposite directions Minutes •Because negative feedback systems resist change, they promote stability and are thus homeostatic –Each control system (activated in response to either a rise or drop in blood glucose levels) operates to reduce the deviation bl from “set point” Examples of Negative Feedback Systems • Negative feedback systems resist change from some set point and thus promote stability (i.e., homeostasis) - common examples include: Thermostat Thermostat Cruise control Toilet Tank Float (regulates water level in Fl tank) Positive Feedback Positive Feedback • Response is in same direction as stimulus • Serves to amplify weak stimuli • Not as common as negative feedback control • Examples: uterine contractions by oxytocin; drug addiction Reliability of Reliability of Physiological Systems • Vital organ systems and tissues are reliability and can sustain homoeostasis and function under severe conditions. • Even if a part of the tissue is destroyed or fails to function homoeostasis can be fails to function homoeostasis can be maintained. Some Examples of Reserve Capacity Physiologic Parameter Normal Level Level Threshold Level Safety Factor Blood glucose 100 mg/dL 50 mg/dL 2 Blood calcium 10 mg/dL 6 mg/dL 1.6 Renal function (GFR) 85-125 ml/min 60 ml/min 2 Lung function 2 lungs 1 lung 2 Blood pressure (systolic) 110-120 mm Hg 70-80 mm Hg 1.6 Blood Flow (Cardiac Output) During Blood Flow (Cardiac Output) During Rest and Heavy Exercise Energy (Blood) Flow Adjustments During Adjustments During Exercise The brain and kidney each extract about 20% of available energy to about support functions Energy utilization by the brain and kid kidney do not change significantly i during exercise (cardiac demand) Energy utilization by the heart increases in proportion to cardiac increases in proportion to cardiac demand demand Energy flow to skeletal muscle increases significantly during increases significantly during exercise exercise ...
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This note was uploaded on 10/25/2010 for the course BIO 188 taught by Professor Capco during the Fall '08 term at ASU.

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