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Homeostasis

Homeostasis. What is Homeostasis?. Body cells work best if they have the correct set points for: Temperature Water levels Waste levels Glucose concentration (blood glucose) Your body has feedback mechanisms to keep the cells in a constant environment. What is Homeostasis?.

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Homeostasis

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  1. Homeostasis

  2. What is Homeostasis? • Body cells work best if they have the correct set points for: • Temperature • Water levels • Waste levels • Glucose concentration (blood glucose) • Your body has feedback mechanisms to keep the cells in a constant environment.

  3. What is Homeostasis? • The maintenance of a constant internal environment in the body. • Negative feedback animation • The ability or tendency of an organism or cell to maintain internal equilibrium by adjusting its physiological processes. • Physiology: is the study of the mechanical, physical, and biochemical functions of living organisms

  4. Glossary • Maintain – keep up. • Constant – the same. • Internal – inside the body. • Environment – surroundings of the body.

  5. *Our bodies attempt to maintain an internal balance called HOMEOSTASIS. There are many conditions in which life processes are limited: • Eg. Most enzymes in our bodies work best at 37ºC. • pH of blood is maintained between 7.35 and 7.45. (recall – 7 is neutral, blood is slightly basic) • Too low, acidosis • Too high, alkalosis

  6. http://www.bellflower.org/home/index.asp?page=10&recordid=2006http://www.bellflower.org/home/index.asp?page=10&recordid=2006 http://timlinn.edublogs.org/2011/03/24/worlds-biggest-dog-tongue/

  7. http://tennis.topbuzz.com/tennis-pics/d/31693-1/Rafael+Nadal+shakes+off+sweat+from+his+hair.JPGhttp://tennis.topbuzz.com/tennis-pics/d/31693-1/Rafael+Nadal+shakes+off+sweat+from+his+hair.JPG http://www.fitsugar.com/What-Excessive-Sweating-23829676

  8. Negative Feedback • Body responds to change in such a way as to reverse the direction of a change in set point. • Because this tends to keep things constant (stabilizing effect), it allows us to maintain homeostasis. • Most common

  9. Positive Feedback • Body responds to change in such a way as to change even more in the same direction of set point change. • This has a de-stabilizing effect, so it does not result in homeostasis. • Positive feedback is used in certain situations where rapid change is desirable (adrenalin in fight or flight). • Not very common

  10. Feedback Loops (3 Major Components) • Sensor (receptor) • Detects variation in the set point • Sends message to coordinating center (CC) • Coordinating Center (Hypothalamus) • Receives message from receptor • Sends message to effector to rectify deviation in set point (nervous or hormonal mechanism) • Effector • Receives message from CC • Carries out instructions to rectify deviation in set point

  11. Negative Feedback Loop Control Center (Hypothalamus) Sensor/Receptor: Effector: Change: Change: Cause: Normal Condition:

  12. http://wps.aw.com/bc_martini_eap_5/105/27046/6923809.cw/index.htmlhttp://wps.aw.com/bc_martini_eap_5/105/27046/6923809.cw/index.html

  13. *MAJOR HOMEOSTATIC ORGAN • Hypothalamus (brain) = Homeostasis • The main function of the hypothalamus is homeostasis, or maintaining the body's status quo.

  14. *MAJOR HOMEOSTATIC ORGAN • The following factors are held to a precise value called the set-point: • blood pressure, • blood sugar • body temperature, • fluid and electrolyte balance, • and body weight • Although this set-point can migrate over time, from day to day it is remarkably fixed.

  15. Receptors and Effectors • *To achieve this task, the hypothalamus must: • receive inputs about the state of the body from nerve fibers/endings called receptors/sensors • Send a response to these changes to nerve endings called effectors i.e. if anything drifts out of whack.

  16. Intrinsic Receptors • *The hypothalamus has some intrinsic receptors, including: • thermoreceptors (sense degree of hotness and coldness) and • osmoreceptors(sense electrolyte balance). • The hypothalamus sends signals to effectors (nerve endings that respond) which can control heart rate, vasoconstriction, digestion, sweating, etc.

  17. *The Brain

  18. *We will concentrate on FOUR homeostatic processes: • thermoregulation • osmoregulation • blood glucose management • waste management • The first two and last two of these homeostatic processes are closely interrelated.

  19. *Thermoregulation: • The process of keeping the body at a constant temperature. • We are homiotherms (warm blooded). • Heat is constantly produced through metabolism (25% remains in the body) and lost (75%) • If your body is in a hot or cold environment your body temperature is 37ºC.

  20. *Thermoregulation: • Processes affected by temp. • enzyme function, disease control, metabolic rate • Body heat depends on metabolic rate (how the body uses nutrients, activity) • At rest muscles produce up to 30% of our body heat (brain) • During exercise, our muscles produce 40X more body heat than other tissues (only 25% efficient) • Normal body temp. 98.6ºF or 37ºC

  21. Controlling body temperature • Animals with a large surface area compared to their volume will lose heat faster than animals with a small surface area. Volume = _______ Surface area = ______ Volume : Surface area ratio = ___________ Volume = _______ Surface area = ______ Volume : Surface area ratio = ___________

  22. Controlling body temperature Volume : Surface area 1:6 Volume : Surface area 1:5 For every 1 unit of heat made, heat is lost out of 6 sides For every 1 unit of heat made, heat is lost out of 5 sides

  23. Controlling body temperature Volume : Surface area 1:6 Volume : Surface area 1:5 The bigger the Volume : Surface Area ratio is, the faster heat will be lost.

  24. Penguins huddling to keep warm

  25. THERMAL RANGESProfessor Alan Hedge, Cornell University, January 2007 SKIN (Shell) • >45°C (>113°F) Burns • 42°C (108°F) Pain • 40°C (104°F) Uncomfortably hot • 25°C (77°F) Uncomfortably cold • 5°C (41°F) Numbness • 0°C (<32°F) Frostbite • -0.6°C (<31°F) Skin freezes

  26. BODY (Core) • >42°C (108°F) Fatal • 41°C (106°F) Coma, convulsions • 39.5°C (103°F) Upper acceptable limit - drowsiness • 37°C (98.6°F) normal • 35.5°C (96°F) Lower acceptable limit - mental dullness • 34.5°C (94°F) Shivering diminishes - extreme mental slowness • 33°C (91°F) Coma • <33°C (91°F) Deep Coma. Death • 27°C (81°F) Heart stops. Death

  27. What mechanisms are there to cool the body down? • Sweating • When your body is hot, sweat glands under the skin are stimulated to release sweat. • The liquid sweat turns into a gas (it evaporates) • To do this, it needs heat. • It gets that heat from your skin. • As your skin loses heat, it cools down. • animation

  28. Sweating The skin

  29. What mechanisms are there to cool the body down? • Vasodilation/Vasoconstriction • Your blood carries most of the heat energy around your body. • There are capillaries underneath your skin that can swell/dilate if you get too hot. • This brings the blood closer to the surface of the skin so more heat can be lost. • This is why you look red when you are hot!

  30. This means more heat is lost from the surface of the skin If the temperature rises, the blood vessel dilates (gets bigger).

  31. What mechanisms are there to warm the body up? • Vasoconstriction • This is the opposite of vasodilation • The capillaries underneath your skin get constricted/shrink (shut off). • This takes the blood away from the surface of the skin so less heat can be lost.

  32. This means less heat is lost from the surface of the skin If the temperature falls, the blood vessel constricts (gets shut off).

  33. What mechanisms are there to warm the body up? • Piloerection • This is when tiny muscles in the skin contract, causing the hairs on your skin “stand up” . • It is sometimes called “goose bumps” or “chicken skin”! • The hairs trap a layer of air next to the skin which is then warmed by the body heat • The air becomes an insulating layer.

  34. What mechanisms are there to warm the body up? • Shivering • Muscles contract and expand in speedy bursts producing heat http://4.bp.blogspot.com/-3z6pBxOV9IU/Tmq_kYEy2ZI/AAAAAAAACcY/HEUUgk_0x_E/s1600/shivering_new11.gif

  35. OSMOREGULATION:Water Regulation • Water makes up ~60% of total body composition, of this. • Water is constantly required and removed. • 73% of lean body mass (LBM) is composed of water • essential for survival • required for all cell functions • used for thermoregulation* • major component of blood volume

  36. OSMOREGULATION • Not enough water in the body – dehydration. • In dehydrated states, water is lost from the blood, electrolyte imbalance • Too much water in the body – edema(water retention swelling), electrolyte imbalance

  37. Homeostasis of Heat and Water • Body temp. monitored by the hypothalamus. • Skin surface: • 32 000 heat receptors/sq. inch • concentrated in fingertips, nose, elbows, upper lip, & chest. • Brain and blood vessels contain the thermal receptors for sensing core body temperature

  38. Heat Loss Mechanisms at Rest • Radiation – at rest 60% of heat loss from a nude body • Convection: air movement past body. Two ways, natural (air molecules) and forced (eg. Fan) (up to 30% lost through head and neck) • Evaporation: water loss through skin 15% of heat loss

  39. Heat Loss Mechanisms at Rest • Inhalation/Exhalation: 10% loss of heat and water loss (exhalation) • Conduction: skin contact with objects such as chairs, floors, etc. about 3% • Excretion of urine and feces, both water (major component, 400 – 800 mL/event) and heat loss (3%) • Winter survival

  40. SWEAT BASICS: • Each sq. inch of skin has 32 000 nerve fibers, 98 sebaceous glands & ~650 sweat glands • Heat and emotions affect sweating • Emotional tears are more toxic - healing • Men sweat 50% more than women. Older people (esp males) and children sweat ineffectively

  41. Sweat Composition • Eccrine glands produce sweat • 99% water • NaCl • Other electrolytes • traces of urea, lactic acid, fatty acids and proteins • Colorless and odorless http://www.sweathelp.org/English/PFF_Hyperhidrosis_Overview.asp

  42. SWEAT BASICS: • Eccrine glands produce • between 200 ml – 10 L per day depending on activity level and climate • 200 ml/hr at room temperature, and up to 1.5 L/h in extreme heat climates • The greatest number of sweat glands are on the forehead, neck, back of hand, forearm, back and front trunk; lowest on thighs, soles of feet, & palms of the hands.

  43. Sweat Glands E – Epidermal Layer D - Dermis H – Hair Follicles G – Sweat/Eccrine Glands S – Sebaceous Glands http://www.nature.com/milestones/skinbio/images/subject_index_02.gif

  44. http://vrc.belfastinstitute.ac.uk/resources/skin/skin.htm

  45. Hair Follicle

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