Communication: Homeostasis

Syllabus points Outline the need for communication systems within multicellular organisms, with reference to the need to respond to changes in the internal and external environment and to coordinate the activities of different organs. State that cells need to communicate with each other by a process called cell signalling. State that neuronal and hormonal systems are examples of cell signalling. Define the terms negative feedback, positive feedback and homeostasis. Explain the principles of homeostasis in terms of receptors, effectors and negative feedback. Describe the physiological and behavioural responses that maintain a constant core body temperature in ectotherms and endotherms, with reference to peripheral temperature receptors, the hypothalamus and effectors in skin and muscles.

Need for Communication Arctic fox – external environment

Need for Communication Internal environment

Major Systems of Communication Neuronal system Endocrine system

Homeostasis Ability to maintain a steady state within a constantly changing environment contributes towards the success of living organisms. “The constancy of the internal environment is the condition of a free life” Claude Bernard 1857 (French physiologist concerned with self regulation)

Homeostasis The maintenance of a constant internal environment: Temperature Concentration of dissolved substances Blood sugar level Water level pH Carbon dioxide concentration All rely on feedback in order to be kept constant

Alterations to the environment… Why is it important to control the following? Core body temperature Plasma water potential Plasma Glucose concentration Plasma CO2 concentration Blood pressure

Feedback All rely on feedback in order to be kept constant Negative Feedback reversal of a change in the internal environment to return to a steady state or optimum position

Pathway for Feedback System Stimulus Pathway for Feedback System Receptor Communication Pathway Effector Response

Regulation Negative Feedback Effectors bring about a return to resting level Detected by receptors Change from resting level Resting level Change from resting level Effectors bring about a return to resting level Detected by receptors

Positive Feedback Process that increases any change detected by the receptors and does not lead to homeostasis. Very rare in biological systems and leads to unstable and extreme states

Thermoregulation All animals derive heat from 2 sources: external environment and chemical energy within cells Ectothermic: (‘ecto’ = outside) rely more on heat derived from the environment. All animals excepts birds and mammals. Endothermic: rely on internal sources of heat

Adaptations to resist changes in temperature leads to thermoregulatory classification of animals: ecto- and endotherms Endotherms produce significant amounts of heat How do they do it? Inefficient metabolism -- leaky cells (uncoupling oxidative phosphorylation.) Production of waste heat -- shivering. Burning fuel without doing work -- brown fat.

Thermal Gradient Radiation: Heat transferred by electromagnetic waves. Bodies unable to absorb much radiated heat but transfer it to other bodies 50% of total heat loss in man Main route for controlled heat loss in animals Convection: heat transferred via air. In endotherms air is warmer than body, therefore a convection current is created bringing in more cool air to body. This can be deterred by fur, feathers, hair or clothing Conduction: Physical contact between two bodies. This is insignificant for most terrestrial animals Evaporation: heat lost by body surface as water converts to water vapour 1 cm3 requires the loss of 2.45 KJ from body Cannot be controlled

Heat Balance in Endotherms Endotherms (mammals and birds) maintain a constant body temperature through mechanisms aimed at balancing their heat gains and heat losses Radiation and conduction from the environment Radiation, conduction and convection to the environment Muscle contraction Evaporation of sweat General metabolism Expiration and excretion

Consider the ways in which this resting lioness is gaining and losing heat

Evaporation of water from lungs and body surface Radiation from the sun Radiation and conduction from warmer parts of the environment Radiation and conduction to cooler parts of the environment Convection of heat by air movements

Suggest why the red fox has an ear size that is intermediate between In terms of temperature control, provide an explanation for the relationship between ear size and habitat for the three different foxes Suggest why the red fox has an ear size that is intermediate between that of the Fennec and Arctic foxes

What is the significance of this behavioural and physiological response for thermoregulation in the mouse?

Endotherms Advantages: Constant body temperature regardless of environmental temperature Activity is possible when external temp is cool Disadvantages: Significant amount of energy intake is used to maintain body temperature in the cold More food required Less of energy from food is used for growth

Thermoregulation in Mammals Receptors Sensory cells detect changes in skin temperature and blood temperature flowing through hypothalamus Two different types of receptor (warm and cool) Coordinator Two areas in the hypothalamus: Heat gain centre – involved in limiting amount of heat loss from body and with heat generation from metabolism Heat loss centre – controls activities that will reduce body temperature Effectors Sweat glands, muscles, movement of hair, liver cells, blood flow in arterioles to capillaries Negative Feedback System

Negative Feedback in Temperature Control Heat energy lost from body as water evaporates. More heat lost by conduction and radiation. Insulating layer of air reduced. More heat lost by conduction. Less metabolic heat gained. Heat loss mechanisms Skin Blood flow (vasodilation) Body hairs Liver cells Skeletal movement Breathing via mouth, nose and lungs Detected by the hypothalamus Increase (usually due to exercise) Heat retention/gain mechanisms Skin Blood flow (vasoconstriction) Body hairs Liver cells Skeletal movement Breathing via mouth, nose and lungs Less heat lost by conduction and radiation. Insulating layer of air trapped. Less heat lost by convection. Generates metabolic heat. Energy released as heat rather than ATP Decrease (usually due to a fall in environmental temperature) Detected by the hypothalamus

Hypothermia video

Normal Body Temperature Skin Muscle Liver Liver Skin Detected by Thermoregulatory center Coordination Of response Temperature rises Temperature rises Less heat lost More heat produced message via hormone Impulse via Motor neurones 1. Hairs raised 2. Less/no sweat 3. Less blood flow to Skin (vasoconstriction) Skin Corrective action 1. Shivering Muscle Corrective action 1. Increase metabolic rate Liver Corrective action Normal Body Temperature 1. Reduce metabolic rate Liver Corrective action 1. Hairs lie flat 2. More sweat 3. More blood flow to Skin (vasodilation) Skin Corrective action Less heat produced More heat lost Impulse via Motor neurones message via hormone Temperature falls Temperature falls Coordination Of response Detected by Thermoregulatory center

Normal Body Temperature Coordination Receptor Stimulus Effectors Detected by Thermoregulatory center Coordination Of response Temperature rises Stimulus Effectors Temperature rises Less heat lost More heat produced message via hormone Impulse via Motor neurones Response Skin Corrective action 1. Hairs raised 2. Less/no sweat 3. Less blood flow to Skin (vasoconstriction) Muscle Corrective action 1. Shivering Liver Corrective action 1. Increase metabolic rate Normal Body Temperature Liver Corrective action 1. Reduce metabolic rate 1. Hairs lie flat 2. More sweat 3. More blood flow to Skin (vasodilation) Skin Corrective action Response Less heat produced More heat lost Impulse via Motor neurones message via hormone Effectors Temperature falls Temperature falls Stimulus Coordination Coordination Of response Detected by Thermoregulatory center Receptor

Ectotherms can use behavior to resist changes in temperature. But, endotherms also use behavior, and do so preferentially, and ectotherms have anatomical and physiological adaptations.

In “hot” fish, arterial blood flows under skin Anatomical adaptation in certain fast swimming fish make it possible to conserve metabolic heat in core and elevate muscle temp. In “hot” fish, arterial blood flows under skin And forms countercurrent heat exchangers With veins as it enters muscle. In most fish, cold arterial blood flows centrally to serve muscles.

Ectotherms also display various Physiological adaptations: Examples are heat production in flying insects, shivering in brooding pythons, and CV adaptations in marine iguanas. Water off Galapagos Is cold. Marine iguanas warm by basking. When they enter water to feed, heart rate and therefore blood flow to skin decreases conserving heat in the core. Reverse when they return to land.

Thermoregulation in an Ectothermic Reptile – The Desert Lizard Desert lizards, like many other reptiles, gain or lose heat by thermoregulatory mechanisms that involve: Burrowing behaviour when the ambient behaviour is low (25oC to 30oC) or high (above 38oC) Shifting between sun and shade Postural adjustments that maximise or minimise the exposure of the body surface to the sun Physiological adjustments: vasodilation of skin capillaries during basking behaviour and vasoconstriction during periods of low temperature; dispersion or contraction of black pigment cells in the skin with the lizards becoming lighter as the temperature increases

Postural adjustments and seeking out shade are behavioural mechanisms used by desert lizards to regulate their body temperature

3. Lizard maintains a relatively constant body temperature (38-40°C) by moving between the sun and shade as ambient temperatures rise towards mid-day 2. Lizard basks in the morning sun and body temperature rises to around 38°C 5. Lizard spends most of its time in the sun in the early evening and is very active before returning to its burrow for the night 4. Lizard spends much time in the shade during the heat of the afternoon 1. Early morning; lizard emerges from its cool burrow (body temperature around 20°C)

alternating between sun and shade sheltering alternating between sun and shade retreat to burrow for the night basking

Ectotherms Advantages: Body temperature fluctuates with external temperature. They are unable to increase respiration rates to generate heat internally and therefore rely on external sources of heat to keep warm. Behavioural and structural mechanisms important in limiting variation in body temperature Need less food than endotherms to supply their metabolic needs Disadvantages: Less active in cooler temperatures, warm up in morning before active Not capable of activity during winter so must have sufficient stores of energy to survive over winter Found in limited range of environments.

Temperature Regulation Behavioural changes: To warm up: Bask in sun or lie on warm surface To cool down: Stay underground or lie in the shade Physiological or anatomical adaptations: Horned lizard: can alter surface area by expanding or contracting its rib cage Frilled lizard uses its frill to help absorb heat Locusts increase their abdominal breathing movements to increase evaporation of water and aid cooling.