HOMEOSTASIS pH of 7.35 37C 0.1% blood sugar

Homeostasis and Control Systems Homeostasis – an equilibrium (steady state) between an organism’s various physiological functions, and between the organism and the environment. This is a balance in response to continually changing conditions in both the internal and external environments

Steady State achieved by self adjustment (see feedback) death results when then balance can no longer be maintained dynamic equilibrium – a condition that remains stable with fluctuation limits There are many factors that we, as organisms, must balance:  ex. blood glucose, water content (osmotic balance), temperature, hormones, etc.

Control Systems All homeostatic control systems have three components: a monitor  special sensors located in the organs of the body detect changes in homeostasis a coordinating centre,  receives message from sensors and relays information to appropriate regulator (organ/tissue that will act to restore steady state)  brain a regulator  restores normal balance  muscles and organs

FEEDBACK SYSTEMS MAINTAIN HOMEOSTASIS Components: 1. Receptors 2. Control Center 3. Effectors NEED TO KNOW THIS!!! Have receptors all over our body in every tissue; collect data constantly 5

Coordination of Body Functions The activity of various specialized parts of an animal are coordinated by the two major systems of internal communication: the nervous system – involved with high-speed messages the endocrine system – involved in the production, release, and movement of chemical messangers

All animals exhibit some coordination by chemical signals: hormones = produced by the endocrine system convey information between organs of the body pheromones = chemical signals used to communicate between different individuals neurotransmitters = chemical signals between cells on a localized scale (over short distances; between neurons)

The Endocrine System Has several key components: Hormones = secreted by endocrine or neurosecretory cells, travel into body fluids to target cells where it elicits a specific response Target Cell = cell equipped to respond to the given hormone Neurosecretory cells = neuron that receives signals from other nerve cells and responds by releasing hormones into body fluids or into a storage organ from which they are later released. Endocrine gland = ductless gland that secretes hormones into the body fluids for distribution through the body Note: Exocrine gland = glands that produce a variety of substances (e.g sweat, mucus, digestive enzymes) and deliver their produces via ducts, are NOT part of the endocrine system. More on the endocrine system in chapter 8…..

Excreting Waste Urinary System Formation of Urine Water Balance Kidney Disease Example: carbon dioxide levels  Levels increased during exercise Chemical receptors in brain are stimulated Nerve cells from the brain carry impulses to muscles that increase breathing rate. A group of arteries in the neck can detect low levels of oxygen in the blood and they send a message via a nerve to the brain, which then relays the message to the muscles that control breathing movements. Because we are constantly having to fix our levels so they stay within a range, we call it dynamic equilibrium. Mechanisms that make adjustments to bring the body back within its acceptable range are called negative feedback systems.

The body is self correcting by the use of negative feedback Most homeostatic control systems are negative feedback systems. These systems prevent small changes from becoming too large. A relationship in which the response is opposite to the stimulus (or impressed change) The body is self correcting by the use of negative feedback Example: glucose and insulin, thermostat (pg. 336) high glucose in blood ↑ insulin production

Response No heat produced Heater turned off Room temperature decreases Set point Too hot Set point Set point Too cold Control center: thermostat Study this on your own Room temperature increases Heater turned on Response Heat produced 11

NEGATIVE FEEDBACK ►decreases an action ►stops when return to normal ►most homeostatic control mechanisms are negative feedback 12

Positive Feedback systems: process by which a small effect is amplified A relationship in which the response is the same as the stimulus Leads to instability and possibly death Some rare limited examples: birthing process in humans: childbirth  hormone oxytocin

►must be turned off by outside event POSITIVE FEEDBACK (reinforces) ►increases an action ►must be turned off by outside event ►decreases ►could run away = death * blood loss - ↓ B.P. - ↓ heart beat * blood clotting 14

Decrease in progesterone ---->increase in uterine contraction ----> release of oxytocin ---> increase in stronger contractions---->baby is expelled----->contraction stop--->release of oxytocin stops ↓ progesterone contractions & oxytocin + Section 7.1 Questions, pp. 337, #1-5

Thermoregulation Thermoregulation: the maintenance of body temperature within a range that enables cells to function efficiently. Ectotherms: (reptiles etc.) rely on air temperature to regulate metabolic rates. Therefore activity is dependent on environment.  adaptations: seeking sun, shade Endotherms: (mammals etc.) maintain constant body temp (37°C) regardless of environment. Respond to changes in environmental temp. by using energy to produce heat Conduction: direct transfer of thermal motion(heat) between molecules of the environment and those of the body surface Convection: transfer of heat by the movement of air or liquid past the surface of a body Radiation: the emission of electromagnetic waves produced by all objects warmer than absolute zero  transfer heat between objects that are not in direct contact Evaporation: the loss of heat from the surface of a liquid that is losing some of its molecules as gas Endotherms generally consume much more food than ectotherms of equivalent size.

Relationship between body temperature & Environmental temperature 40 River otter (endotherm) 30 Body temperature (°C) 20 Largemouth bass (ectotherm) 10 10 20 30 40 Ambient (environmental) temperature (°C) 17

B. Modes of Heat Exchange Organisms exchange heat by four physical processes: conduction, convection, radiation, and evaporation Radiation: radiate heat between objects not in contact. Evaporation: removal heat from surface of liquid lost as gas Convection: transfer heat by mvt air Conduction: direct transfer heat between molecules in contact 18

B. Balancing Heat Loss and Gain In thermoregulation, physiological and behavioral adjustments balance heat loss and heat gain 5 general adaptations in animals’ thermoregulation: Insulation Circulatory adaptations Cooling by evaporative heat loss Behavioral responses Adjusting metabolic heat production 19

1. Insulation Insulation is a major thermoregulatory adaptation in mammals and birds It reduces heat flow between an animal and its environment Examples are skin, feathers, fur, and blubber In mammals, the integumentary system acts as insulating material This is how we regulate our heat 20

2. Circulatory Adaptations Many endotherms & some ectotherms alter amount of blood flowing between the body core & skin Vasodilatation = ↑ blood flow in skin = ↑ heat loss Vasoconstriction = ↓ blood flow in skin = ↓ heat loss Like when we work out and our faces get red; our blood is flowing faster and our vessels are expanding to let off more heat. 21

important for reducing heat loss Many marine mammals & birds have arrangement blood vessels called counter current heat exchanger which are important for reducing heat loss 22

3. Cooling by Evaporative Heat Loss Many types of animals lose heat through evaporation of water in sweat Panting augments the cooling effect in birds and many mammals Bathing moistens the skin, helping to cool animal 23

4. Behavioral Responses Both endotherms and ectotherms use behavioral responses to control body temp Some terrestrial invertebrates have postures that minimize or maximize absorb solar heat More extreme behavioral adaptations = hibernation or migration to more suitable climate Like when we shiver and tense our muscles when we are cold. 24

5. Adjusting Metabolic Heat Production Some animals can regulate body temperature by adjusting their rate of metabolic heat production Many species of flying insects use shivering to warm up before taking flight Preflight warmup in hawkmoth = shiver-like to help muscles produce enough power to take off 25

C. Feedback Mechanisms in Thermoregulation Mammals regulate body temperature by negative feedback involving several organ systems In humans, the hypothalamus (a part of the brain) contains nerve cells that function as a thermostat 26

Physiological Response Adjustment Decreased environmental temperature Stimulus Physiological Response Adjustment Decreased environmental temperature Constriction of blood vessels in skin-hairs on body erect shivering Heat is conserved more heat is generated by increased metabolism Increased environmental temperature Dilation of blood vessels of skin-sweating Heat is dissipated Vasodilation/Vasoconstriction/ Counter-current heat exchange

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Human thermostat = hypothalamus (control centre)

increase sweat (glands) vasodilatation (blood vessels) Responses to heat stress: (nerve messages from sensor via hypothalamus) increase sweat (glands) vasodilatation (blood vessels) Responses to cold stress: (nerve messages from sensor via hypothalamus) smooth muscles contract vasoconstriction (blood vessels) hair stands on end to trap warm air near skin (follicles) (goosebump = muscle contraction in area of hair follicle) rhythmic skeletal muscle contraction = shivering to generate heat Mammalian Diving Reflex Section 7.2 Questions, pp. 341, # 1-7 Torpor: alternative physiological state in which metabolism decreases and the heart and respiratory system slow down  conserve energy when food supplies are low and environmental temperatures are extreme Hibernation: long-term torpor during which the body temp. is lowered as an adaptation to winter cold and food scarcity Estivation: summer torpor  slow metabolism and inactivity that enables an animal to survive long periods of high temps. And scarce water supplies