How does varying temperature affect the speed of woodlice? Sarah, Eliza and Lydia Temp (oC) Distance travelled (cm) Time taken (s) Speed (m/s) 10 16 20 5 40 23 Pip, Jack and Lewis Temp (oC) Distance travelled (cm) Time taken (s) Speed (m/s) 10 17 20 12 40 8 Calculate the speed for each set of results. (2) Describe and suggest reasons to the trends with each set of results (5)

Temperature Regulation By the end of the lesson you will be able to: (d) define the terms negative feedback, positive feedback and homeostasis; (e) explain the principles of homeostasis in terms of receptors, effectors and negative feedback; (f) 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.

Feedback Mechanisms

Feedback Mechanisms  examples negative feedback, (in physiology) a decrease in function in response to a stimulus. For example, the secretion of follicle-stimulating hormone decreases as the amount of circulating oestrogen increases. positive feedback, (in physiology) an increase in function in response to a stimulus. For example, micturition increases after the flow of urine has started, and the uterus contracts more frequently and with greater strength after it has begun to contract in labour.

Positive Feedback Mechanisms Homeostatic systems utilising positive feedback exhibit two primary characteristics: Time limitation – Processes in the body that must be completed within a constrained time frame are usually modified by positive feedback. Intensification of stress – During a positive feedback process, the initial imbalance or stress is intensified rather than reduced as it is in negative feedback. Typical Positive Feedback Process Stress Sensor Control Center Intensifies Effector

Homeostatic Regulation of Child Birth through Positive Feedback Nerve endings in the uterine wall carry afferent messages to the Hypothalamus Pressure of Fetus on the Uterine Wall Intensifies Production and Release of Oxytocin into the Blood Increasing strength of uterine contractions The birth of the child will bring this process to a close. Other examples of positive feedback regulation occur during milk letdown and blood clotting.

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

What is Homeostasis? Body cells work best if they have the correct Temperature Water levels Glucose concentration Your body has mechanisms to keep the cells in a constant environment.

What is Homeostasis? The maintenance of a constant environment in the body is called Homeostasis

Controlling body temperature All mammals maintain a constant body temperature. Human beings have a body temperature of about 37ºC. E.g. If your body is in a hot environment your body temperature is 37ºC If your body is in a cold environment your body temperature is still 37ºC

The Transfer of thermal energy

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 = ___________

Controlling body temperature Volume : Surface area ratio = 1:6 Volume : Surface area ratio = 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

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

Penguins huddling to keep warm

Why do we need to regulate: Internal body temperature To provide the optimum conditions for enzyme-catalysed reactions to be carried out.

Body Temperature Normal internal body temperature is 370C. Temperatures above this: denature enzymes and block metabolic pathways Temperatures below this: slow down metabolism and affect the brain.

Water Bath Temperature set on thermostat Too cool? Heater kicks on and temperature goes up Too warm? Heater stays off until bath cools down Constant checking and turning on and off

Control of homeostasis through feedback Feedback system- cycle of events in which the status of a body condition is continually monitored, evaluated, changed, re-monitored, re-evaluated, etc.

3 basic components of a feedback system 1) receptor sensor that responds to changes (stimuli) 2) control centre sets range of values, evaluates input and sends output 3) effector receives output from control centre and produces a response

Body Temperature Control The hypothalamus acts as a thermostat and receives nerve impulses from heat and cold thermoreceptors in the skin. There are also receptors in the hypothalamus- called central thermoreceptors. These detect changes in blood temperature.

Vasoconstriction and Vasodilatation

Correction of overheating Detected by thermoreceptors in the hypothalamus. Causes vasodilation. Sweating

Cooling down When it's hot and you need to cool down, muscles at each hair relax. Hairs lie close to the skin. Air does not act as an insulating layer.

Sweating How does it work? Heat energy in the body is used to convert the water in sweat to vapour cooling down the body.

What mechanisms are there to cool the body down? Sweating When your body is hot, sweat glands 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.

Sweating The skin

What mechanisms are there to cool the body down? Vasodilation Your blood carries most of the heat energy around your body. There are capillaries underneath your skin that can be filled with blood 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!

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

Correction of overcooling Detected by thermoreceptors in the hypothalamus. Causes vasoconstriction. Decreased sweating Shivering

Keeping warm When it's cold, the muscle contracts pulls the hair up. A layer of warm air accumulates around the hair and insulates the organism. Heat retained

Shivering How does it work?

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

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

What mechanisms are there to warm the body up? Piloerection This is when the hairs on your skin “stand up” . It is sometimes called “goose bumps” or “chicken skin” if you are a bit weird like Americans! 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.

Voluntary responses In humans the cerebrum “makes” people feel cold or hot. They can then e.g. put on more clothes, eat a hot meal, exercise etc as appropriate.