Communication and Homeostasis

Stimulus = A change in the internal or external environment

Response = The way in which an organism changes its behvaiour or physiology

All living organisms have an external environment which, when changed places stress on the organism. Changes in the environment must be monitored and the organism will change its behaviour to minimise the change.

Communication systems are needed within multicellular organisms so that the body can monitor and respond to changes in the internal and external environment and to coordinate the activities of different organs.

Homeostasis is the maintenance of a constant internal environment despite external changes.

Body temp, blood glucose levels, blood solute conc, water potential of blood, blood pressure, Co2 conc and removal of urea are examples of things that need to be controlled in our bodies.

Negative feedback is any process that brings about a reversal of any change in conditions. it ensures that optimum conditions are maintained and is essential for homeostasis. EG - A too low body temperature will be reversed by an increase in metabolic activity.

Positive feedback is where the body's response increases the change in the external environment, this destabilises the system and is usually harmful. EG - Below a certain temp, enzymes become less active so less exergonic reactions occur and less heat is released which cools the body further.

Useful positive feedback occurs at the end of pregnancy as when the cervix begins to stretch and dilate the change is signalled to the anterior pituitary gland. this secretes oxytocin which causes the cervix to stretch more which releases more oxytocin etc....

A change (known as a stimulus) is detected by receptors in your body. Stimuli travel as impulses around the body to the brain. From there they travel to an effector which causes the response. The effector can be a muscle or gland.

An ectotherm is an organism that is dependent on external sources of body heat.

Advantages = energy can be used for growth, less food required, energy is not required for maintaining body temp

Disadvantages = cannot maintain a constant body temp, activity not possible in cooler temperatures, not able to live in colder parts of the planet.

An endotherm is an organism that can use internal sources of heat, such as heat generated from metabolism in the liver to maintain its body temperature.

Advantages = Constant body temp despite external temp, activity possible despite cool external temp, ability to inhabit colder parts of the planet.

Disadvantages = significant part of energy must be used to maintain body temp, more food required, less energy is used for growth.

Endotherms can increase the rate of respiration in the liver to release heat and keep them warm. Many reactions are exergonic which means they release heat.

They can use behavioural mechanisms such as moving into the shade or sitting in sunlight, spreading limbs or rolling into a ball etc. They can also decrease activity levels.

They can also use physiological mechanisms such as sweat glands on the skin-sweat cools the skin down,

vasodilation of arterioles-heat can be released through the skin via radiation,

skeletal muscles-more contractions generate heat,

hairs on skin-trap a layer of air around the body which is insulating.

When an ectotherm is cold, it will change its behaviour or physiology to increase heat absorption from the environment. When it is hot it does the opposite.

Expose body to the sun-enables more heat to be absorbed

orientate body away from the sun-exposes larger surface area for more heat absorption

hide in burrow-reduces heat absorption by keeping out of the sun

alter body shape-exposes more or less surface area to the sun

increase breathing movements-evaporates more water