Feedback and Thermoregulation PDF 12/12/2019

12/12/2019 HOMEOSTASIS: FEEDBACK MECHANISMS AND THERMOREGULATION 1 Homeostasis  Process by which the internal physical and chemical conditions are maintained within a tolerable range, despite changes in the external environment  Tolerable ranges d...

12/12/2019 HOMEOSTASIS: FEEDBACK MECHANISMS AND THERMOREGULATION 1 Homeostasis  Process by which the internal physical and chemical conditions are maintained within a tolerable range, despite changes in the external environment  Tolerable ranges differ (Discovered in 1932 by a physiology professor, Walter Cannon, who found that when animals were frightened their digestive processes stopped) 2 1  12/12/2019 Internal Conditions  Internal environment – extracellular fluid (“interstitial fluid”) surrounding cells and tissues and blood plasma  15 L in an adult (20% of body mass)  Transfers energy, transports chemicals, eliminates waste 3 Organ Systems Involved 4 2  12/12/2019 How Homeostasis is Regulated  Excretory system rids of waste, maintains water balance  Endocrine system regulates hormone levels 5 How Homeostasis is Regulated  Circulatory system delivers hormones and chemicals, distributes thermal energy  Immune system protects against infection 6 3  12/12/2019 How Homeostasis is Regulated  Digestive system detoxifies (liver)  Integumentary system maintains body temperature 7 Dynamic equilibrium  Our bodies fight to maintain stable conditions within a changing environment 8 4  12/12/2019 Examples: 9 Homeostatic Mechanisms  Maintain homeostasis by monitoring internal and external conditions and adjusts bodily functions accordingly 10 5  12/12/2019 Methods of Regulation  Negative feedback – the process by which a mechanism is activated to restore conditions to their original state  Likea thermostat: when a room falls below a set temperature the furnace switches on  Most homeostatic mechanisms in animals operate using negative feedback (preferred method) 11 Negative Feedback Mechanisms Consists of: 1. Stimulus – environmental change (ex. Cold outside) 2. Sensor – detects changes 3. Integrator – compares existing conditions with ideal conditions (control centre – brain) 4. Effector – system that returns the system to optimal state 5. Response – action of the effector returning the system to the desired point 12 6  12/12/2019 13 Thermostat example – pg. 432 14 7  12/12/2019 Example 15  Positive feedback – process by which a small effect is amplified, less common in the body Example: birth process in humans  A small amount of progesterone is released which causes oxytocin to be released which causes even more oxytocin to be released until the baby is expelled 16 8  12/12/2019 17 More positive feedback examples…  Platelets – when platelets clump to form blood clots that signals more platelets are activated  Lactation – when breastfeeding, the more the baby suckles the more milk is produced  Estrogen – during follicular phase it causes the thickening of the uterine lining 18 9  12/12/2019 Thermoregulation  Regulation of internal temperature by negative feedback mechanisms. 19 Poikilotherm & Homeotherm  Poikilotherm – body temperature varies  Homeotherm – body temperature is stable  How body temperature changes or is maintained varies, depending on the source of heat 20 10  12/12/2019 Ectotherms  Maintain their body temperature by absorbing heat from surroundings (metabolic heat production is too small)  Most are thermoconforms (can’t regulate their body temperature)  ex. Fish, amphibians, reptiles 21 Endotherms  Maintain a constant body temperature by internal mechanisms (metabolic heat production is high)  Are thermoregulators (actively regulate their body temperature)  ex. Humans, birds 22 11  12/12/2019 Example  An endotherm’s metabolism increases at low temperatures to generate heat  An ectotherm’s metabolism decreases at low temperatures to conserve heat 23 Not Black and White 24 12  12/12/2019  Some endotherms have special behavioural and physiological adaptations to help thermoregulation  Torpor – sleep-like state in which metabolic rate and body temperature drops (night or day time)  Ex. Hummingbird  Day: active, Night: HR drops from 1260 bpm - 50 bpm and energy is 1/50 25  Hibernation – greatly reduced metabolic rate and body temperature (short intervals or long)  Triggered by length of day (winter vs. summer)  Ex. Arctic ground squirrel  8-10 months, body temp. drops to – 3 ◦C 26 13  12/12/2019  Estivation – state of torpor that enables animals to survive warm summer months and scarce water.  Reduces demand for energy  Ex. Ground squirrel (burrows), ectotherms such as lungfish, frogs and desert lizards (dig into soil) 27 Lungfish 28 14  12/12/2019 Other Thermoregulatory Structures and Behaviours  Body structures – large structures increase surface area to allow heat to dissipate; uneven fur distribution (dogs)  Ex. Jackrabbits have large ears – lots of blood vessels to dissipate heat  Ex. Dogs curl up in a ball in the cold, fur areas exposed  Behaviours – exercise to increase body temperature (insects), panting (dogs) 29 Hypothalamus (Body’s Thermostat)  Part of a vertebrate’s brain responsible for coordinating nerve and hormone function  Contains central thermoreceptors  Sends info out to organs/glands that need to be adjusted 30 15  12/12/2019 31 Human body temp control Body temp rises to 38oC (exercise) Sensors trigger message to brain Co-ordinator (hypothalamus) turns on cooling system Regulators – skin blood vessels dilate, increase sweating, redirection of blood to skin Body temp lowers to 37oC (Response turned off) 32 16  12/12/2019 Human body temp control Body temp drops to 36.5oC Sensors trigger message to brain Coordinator (hypothalamus) – turns on heating system Regulators – skin blood vessels constrict, decrease blood flow to skin, shiver, hair standing up Body temp increases to 37oC (response turned off) 33 Homework…  Human Homeostasis Gizmo  Pg. 435 # 3, 13, 14  Pg. 441 # 6 – 8 34 17  12/12/2019 Examples 1. Evaporation of sweat regulates body temperature 35 5. Pancreas regulates blood sugar 36 18  12/12/2019 37 19