Homeostasis. homeo: same/steady stasis: state

Transcription

1 Homeostasis

2 Homeostasis homeo: same/steady stasis: state

3 Homeostasis

4 Homeostasis is about staying the same THE MAINTENANCE OF STATIC OR CONSTANT CONDITIONS IN THE INTERNAL ENVIRONMENT Conditions at external environment change constantly External Environment External Environment External Environment Internal Environment External Environment The Internal Environment should not change

5 Homeostasis It is similar to the idea of equilibrium. All of our body's systems work together to maintain homeostasis inside our body. Homeostasis is achieved by making sure the temperature, ph (acidity), and oxygen levels (and many other factors) are set just right for your cells to survive. Homeostasis levels are different for each species.

6 Homeostasis: Why? Our body and its individual cells need just the right conditions to perform at their best. A cell s delicately balanced chemical reactions work best within narrow limits of temperature, ph, solute concentration etc.

7 Homeostasis: Why? Homeostasis is continually being disrupted by: External stimuli heat, cold, lack of oxygen, pathogens, toxins Internal stimuli Body temperature Blood pressure Concentration of water, glucose, salts, oxygen, etc. Physical and psychological distresses

8 Disruption of homeostasis can be harmful Homeostasis can be disrupted for several reasons. 1. sensors fail (don t detect changes) 2. targets do not receive messages (nerve issues) 3. injury (overwhelm homeostatic controls) 4. illness (viruses or bacteria) Disruption of homeostasis can begin in one organ and cause a chain reaction in the others therefore causing a major body disturbance.

9 Hypothalamus

10 Activities such as exercise change the rate at which we breathe... Homeostasis: Example Which increases the amount of CO2 in our blood Which changes the ph of the blood... Which is dangerous Potentially fatal, unless... The body responds homeostatically by changing the volumes of air we breathe and adjusting blood ph with buffers (HCO 3, Hb and others)

11 Homeostasis: Example

12 Homeostasis: Example

13 Homeostasis: Example

14 Homeostasis: Example Human body temperature

15 Maintaining Homeostasis The various organ systems of the body act to maintain homeostasis through a combination of hormonal and nervous mechanisms. In everyday life, the body must regulate respiratory gases, protect itself against agents of disease (pathogens), maintain fluid and salt balance, regulate energy and nutrient supply, and maintain a constant body temperature. All these must be coordinated and appropriate responses made to incoming stimuli. In addition, the body must be able to repair itself when injured and be capable of reproducing (leaving offspring).

16 Some Homeostasis Examples in Humans 1. Maintaining steady body temperature (~37ºC) 2. Maintaining steady water balance 3. Steady state of blood alkalinity (ph ) 4. Steady sugar level in blood 5. Number of red blood cells

17 Feedback Control System: Level Control

18 Feedback Control System: Level Control Flow in Flow out The inlet flow comes from an upstream process, and may change with time. The level in the tank must be kept constant in spite of these changes.

19 Feedback Control System: Level Control Flow in SP The level controller (LC) looks at the level (monitoring) LT LC Flow out If the level starts to increase, the LC sends a signal to the output valve to vary the output flow (change) This is the essence of feedback control

20 Feedback Control System Feedback control is the most important and widely used control strategy. It is a closed-loop control strategy Block diagram: disturbance comparator manipulated ysp set-point + error controller variable process y controlled variable transmitter

21 Feedback Control System: Level Control Flow in disturbance transmitter desired value (set-point) LT LC SP controlled variable (measurement) controller process Flow out manipulated variable

22 Closed-loop Feedback Control System

23 Open-loop System

24 Process models State-space models can be derived directly from the general conservation equation: Accumulation = (Inlet Outlet) + (Generation Consumption) Time-domain model State-space model Laplace domain model Input-output model d x( t) = dt y = h( x) f ( x; u; d; t) states Y ( s) = G( s) U ( s) U (s) Y (s) G(s) output G (s) is called transfer function of the process

25 First-order systems K P is the process steady state gain τ P is the process time constant ) ( d d t u K y t y P P = + τ ) ( 1 ) ( s U s K s Y P P + τ = 1 ) ( + τ = s K s G P P Time-domain model Laplace-domain model Transfer function of a first-order system:

26 Response of a First-order System We only consider the response to a step forcing function of amplitude A The time-domain response is: output, y τ P AK P AK P y( t) AK P 1 e t = τ P input, u 0 0 A time It takes 4 to 5 time constants for the process to reach the new steady state

27 Why Feedback? Open-loop system: Closed-loop system:

28 Negative/Positive Feedback Negative Feedback Negative feedback is a process that happens when your systems need to slow down or completely stop a process that is happening. Positive Feedback Positive feedback is the opposite of negative feedback in that encourages a physiological process or amplifies the action of a system. Positive feedback is a cyclic process that can continue to amplify your body's response to a stimulus until a negative feedback response takes over. During positive feedback, the system responds to the perturbation in the same direction as the perturbation. This feedback mechanism results in the amplification or growth of the output signal.

29 Negative/Positive Feedback Negative feedback loop Original stimulus reversed (shut off) Most feedback systems in the body are negative Positive feedback loop Original stimulus intensified Not very common in nature Some positive feedback systems are used by our body to its advantage

30 Positive Feedback

31 Negative Feedback

32 Negative/Positive Feedback: Examples

33 Negative/Positive Feedback: Examples This is a positive feedback loop. The input is increased carbon dioxide, which begins this positive feedback loop.

34 Positive Feedback Increases the changes away from set points Important when rapid changes needed Ex: Skin Cut Clotting proteins increased to seal the wound

35 Positive Feedback An example of positive feedback is the process of blood clotting. Hemostasis: 1. Vascular constriction limits blood flow 2. The loop is initiated when injured tissue releases signal chemicals (Thrombin) that activate platelets in the blood. 3. An activated platelet releases chemicals to activate more platelets, causing a rapid cascade and the formation of a blood clot. 4. To insure stability of the initially loose platelet plug, a fibrin mesh forms and entraps the plug. Excess thrombin splitting of more prothrombin to thrombin more thrombin more clotting! Fibrinolysis, antithrombin, fibrin adsorbs excess thrombin and makes it inactive

36 Positive Feedback Another example of positive feedback: Child birth

37 Positive Feedback of Fever Fever may be provoked by many stimuli. Most often, they are bacteria and their endotoxins, viruses, yeasts, spirochets, protozoa, immune reactions, several hormones, medications and synthetic polynucleotides. These are called exogenic pyrogens. Cells stimulated by exogenic pyrogens form and produce cytokines called endogenic pyrogens. These cytokines bind to their own specific receptors located in close proximity to the hypothalamus. This process leads to production of prostaglandin E2 (PGE2). PGE2 diffuses across the blood brain barrier, where it causes the set-point of the hypothalamic thermostat to rise.

38 Positive Feedback of Fever There are indications that the development of fever is of benefit as a normal body defense in combating some infections. Temperature elevation has been shown to enhance several parameters of immune function, including antibody production, T- cell activation, production of cytokines, and enhanced neutrophil and macrophage function. Fever increases the chemical reactions of the body by an average of about 12 per cent for every 1 C rise in temperature. It increases the metabolic rate, which increases heat production, which in turn raises body temperature even more. This is a positive feedback mechanism that will continue until an external event (such as antipyretic or death of the pathogens) acts as a brake. Aspirin and the non-steroidal anti-inflammatory drugs display antipyretic activity by inhibiting the cyclo-oxygenase, an enzyme responsible for the synthesis of PGE2.

39 Positive Feedback of Inflammation Inflammation is characterized by increased blood flow to the tissue causing increased temperature, redness, swelling, and pain. Inflammation is a beneficial process up to a point. Increased blood flow accelerates delivery of the white blood cells that combat invading foreign substances or organisms and clean up the debris of injured and dead cells. In addition, increased blood flow provides more oxygen and nutrients to cells at the site of damage and facilitates removal of toxins and wastes. It may, however, become a vicious cycle of damage, inflammation, more damage, more inflammation, and so on a positive feedback mechanism. Normal cortisol secretion seems to be the brake, to limit the inflammation process to what is useful for tissue repair, and to prevent excessive tissue destruction.

40 Homeostasis Needs Sensors to detect changes in the internal environment A comparator which fixes the set point of the system (e.g. body temperature). The set point will be the optimum condition under which the system operates Effectors which bring the system back to the set point Feedback control. Negative feedback stops the system over compensating (going too far) A communication system to link the different parts together

41 Homeostasis needs Perturbation in the internal environment Sensor Comparator Effector Return to normal internal environment Sensor Negative feedback

42 Homeostasis Components There are three main components involved when homeostasis is disrupted by a stimuli. The Receptor The Control Center The Effector

43 Homeostasis Components: Receptor The receptor is an organ or sensor that receives the chemical signal and communicates to the next Component ( the control center). In the case of blood sugar the liver is the main receptor.

44 Homeostasis Components: Control System The control system must be able to: Receive signal from the receptor. It also can sense deviations from the norm itself. Integrate this information with other relevant information. Send a signal to the appropriate organ or gland to make the necessary adjustment. Generally the Brain (hypothalamus) is the control center. However, the pancreas is its own control center for blood sugar.

45 Homeostasis Components: Effector The effector is the component that causes the change. It sends out the chemical to deal with the stimulus. In the case of blood sugar the pancreas would be the effector because it sends out the insulin.

46 Communication Systems in Homeostasis In animals there are two communication systems: The endocrine system based upon hormones The nervous system based upon nerve impulses

47 Organic substances Hormones Produced in small quantities Produced in one part of an organism (an endocrine gland) Transported by the blood system to a target organ or tissue where it has a profound effect

48 The Endocrine System The endocrine system produces chemical signals Each hormone is different and they travel relatively quickly through the blood stream all over the body Their effects may be very slow or very fast: - growth hormone acts over years - adrenaline acts in seconds

49 Nerve Impulses The nervous system sends signals along nerves to specific parts of the body The nerve impulses travel very quickly and affect their target tissues in milliseconds

50 The nervous system The nervous system is composed of excitable cells called neurons Neurons have long thin extensions which carry electrical nerve impulses This electrical signal of the nerve impulse needs to be converted into a chemical signal (a neurotransmitter) so that it can pass from one nerve cell to another nerve cell

51 Thermoregulation: Homeostasis of Body Temperature

52 Thermoregulation How much energy can be saved by staying in bed all day? Surprisingly, the answer is only about 30%. The other 70% keeps his body temperature at 37 C (98.6 F), and the solutions around his cells at just the right concentration.

53 Homeostasis Temperature Regulation Core body temperature Humans: 37º C (98.6º F) Hypothermia = decrease in body temperature Hyperthermia = increase in body temperature Above 41º C is dangerous Above 43º C is deadly

54 Homeostasis Temperature Regulation Mechanisms of heat transfer between body and external environment Radiation thermal energy as electromagnetic waves Conduction thermal energy through contact Evaporation heat loss through evaporation of water Insensible water loss Sweating Convection heat transfer by movement of fluid or air

55 Homeostasis Temperature Regulation

56 Thermoregulation

57 Thermoregulation: Penguins huddling to keep warm

58 Thermoregulation: Household Thermostat Let us consider that we want to maintain the room temperature is set to 25 C ( normal temperature ). When the temperature falls below 25 C, the thermostat recognizes change in normal temperature and switches on the furnace. When the thermometer detects a temperature above 25 C, the thermostat switches off the furnace. Negative feedback control system

59 Homeostasis Example: Body Temperature (Internal temperature) Effect of environmental temperature on different animals Effect of environmental temperature on human

60 Negative Feedback Control of Body Temperature

61 Thermoregulation: Negative Feedback

62 Homeostasis Temperature Regulation: Components Receptors = thermoreceptors Central: found in CNS (hypothalamus) Peripheral: found in PNS (mainly skin) Effectors Glands: sweat glands Muscles: skeletal muscles, and smooth muscle of cutaneous blood vessels Integrating center Thermoregulatory center in hypothalamus Signals Nerve impulses via neurons Chemicals via hormones

63 Homeostasis: Body Temperature The Skin

64 Mechanism of Homeostasis: Body Temperature

65 Mechanism of Homeostasis: Body Temperature

66 Mechanism of Thermoregulation: Body Temperature

67 Mechanism of Homeostasis: Body Temperature: Fever Rise in core body temperature Accompanies infection White blood cells secrete pyrogens Body temperature set point increases Fever enhances immune response

68 Glucose Homeostasis

69 Glucose Homeostasis

70 Glucose Homeostasis

71 Long Term: Diabetes Normal Cells Glucose circulates in blood; pancreas releases insulin If high glucose levels: insulin tells cells to intake glucose If low glucose levels: pancreas creates glucose Type 1 Diabetes Immune system destroys cells to produce insulin Pancreas fails Blood ph decreases (more acidic) Type 2 Diabetes Insulin production decreases Glucose level in blood rises Cells starve

72 Glucose and Insulin Level in a Healthy Person

73 Glucose Control by Pancreas β-cells produce Insulin α-cells produce Glucagon INSULIN Lowers blood glucose levels!!! Is released when blood glucose rises above 110 mg/dl Forces liver and muscles to take up glucose from blood stream Forces liver to make glycogen (animal starch) by linking glucose molecule together

74 Glucose Control by Pancreas β-cells produce Insulin α-cells produce Glucagon GLUCAGON Raises blood glucose Is released when blood glucose falls below 70 mg/dl forces liver break down glycogen into glucose and release it into the blood stream

75 Glucose Control

76 Glucose Control

77 Artificial Pancreas: Glucose Control

78 Artificial Pancreas: Glucose Control Open-loop control Closed-loop control

79 Glucose Control: Modeling

80 Minimal Model (Bergman, 1981): Glucose Control: Modeling

81

82 Glucose Control: Model Validation

83 Glucose Control: Closedloop Control

84 Glucose Control: Fuzzy Logic Control

85 Glucose Control: Fuzzy Logic Control

86 Negative Feedback Control of Blood Pressure

87 Negative Feedback Control of Blood Pressure The body has mechanisms to alter or maintain blood pressure and blood flow. There are sensors that sense blood pressure in the walls of the arteries and send signals to the heart, the arterioles, the veins, and the kidneys that cause them to make changes that lower or increase blood pressure.

88 Negative Feedback Control of Blood Pressure

89 Negative Feedback Control of Blood Pressure

90 Negative Feedback Control of Blood Pressure

91 Negative Feedback Control of Blood Pressure

92 Negative Feedback Control of Blood Pressure Blood volume is regulated by the hormone aldosterone Aldosterone affects the rate of sodium ion reabsorption, which in turn affects the rate of water reabsorption Increased aldosterone increased water reabsorption higher blood pressure Decreased aldosterone decreased water reabsorption lower blood pressure

93 Negative Feedback Control of Water Balance Hypothalamus directs the pituitary gland of the endocrine system to control levels of the hormone vasopressin or antidiuretic hormone (ADH) in the blood This hormone travels through the blood to the kidneys where it directs the rate of water reabsorption Increased vasopressin increased water reabsorption Decreased vasopressin decreased water reabsorption