MANUEL ARBOLEDAFELIPE MEJÍA

The endocrine system is the system of glands, each of which secretes a type of hormone directly into the bloodstream to regulate the body.

The endocrine system is made of a series of glands that produce chemicals called hormones. A number of glands that signal each other in sequence is usually referred to as an axis, for example, the hypothalamic-pituitary-adrenal axis.

Hormones are substances (chemical mediators) released from endocrine tissue into the bloodstream where they travel to target tissue and generate a response. Hormones regulate various human functions, including metabolism, growth and development, tissue function, and mood.

It involves maintaining the internal environment between safe limits, including blood pH, carbon dioxide concentration, blood glucose concentration, body temperature and water balance.

Is the ability to maintain a constant internal environment in response to environmental changes. It is a unifying principle of biology. In other words is when an organism keeps stable its bodily conditions. It does so by regulating its inner equilibrium.

When homeostasis works: There is a water balance (around 90% of

blood volume) CO2 concentracion (10-13kPa) Body temperature (36°C-38°C) Blood glucose concentration (80-110mg

dl-1) Blood pH (7.35-7.45)

The nervous and endocrine systems control homeostasis in the body through feedback mechanisms involving various organs and organ systems. Examples of homeostatic processes in the body include temperature control, pH balance, water and electrolyte balance, blood pressure, and respiration.

Negative feedback occurs when the output of a system acts to oppose changes to the input of the system, with the result that the changes are attenuated. If the overall feedback of the system is negative, then the system will tend to be stable.

This is best explained by giving an example:

-Cortisol is a hormone that is important for carbohydrate and protein metabolism. Too much cortisol can be harmful as it suppresses the immune system and prevents growth and repair of damaged tissue.

-Cortisol is manufactured in the adrenal glands and production is stimulated by ACTH, a hormone made in the pituitary gland. ACTH is produced in response to CRF, another hormone made in the hypothalamus.

-If cortisol levels become too high in the blood then the production of CRF is reduced, which in turn reduces ACTH production and leads to less cortisol being made in the adrenal glands.

-A negative feedback in the body is where a change the level of one chemical leads directly to a reduction in it's formation, reduction in it's absorption or increase in its excretion. Negative feedbacks are important in maintaining homeostasis in the body.

Sweating, shivering, skin capillaries and hairs are involved in the control of the tempetature.

Too hot• Sweat glands in the skin release more sweat. This

evaporates, removing heat energy from the skin.• Blood vessels leading to the skin capillaries

become wider - they dilate - allowing more blood to flow through the skin, and more heat to be lost.

Too cold• Muscles contract rapidly - we shiver. These

contractions need energy from respiration, and some of this is released as heat.

• Blood vessels leading to the skin capillaries become narrower - they constrict- letting less blood flow through the skin and conserving heat in the body.

A. Hair muscles pull hairs on end. D. Hair muscles relax. Hairs lie flat so heat can escape.

B. Erect hairs trap air. E. Sweat secreted by sweat glands. Cools skin by evaporation.

C. Blood flow in capillaries decreases.

F. Blood flow in capillaries increases.

Too cold Too hot

When there´s a high glucose concentration, the beta cells in the pancreas release insulin, that turns glucose into glycogen that is stored in the liver and muscles.

When there´s a low glucose concentration, the alpha cells in the pancreas release glucagon, that turns glycogen stored in the liver and muscles into glucose.

Is a disease where the concentration of glucose in the blood is not fully controlled by he body.

Type I: the body does not produce any insulin.

Type II: ocurrs when the pancreas does not produce enough insulin for the proper function or when the cells do not react to insulin (insulin resistance).