Chapter 13: The Endocrine System Unit 1: Maintaining Dynamic Equilibrium II

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Nervous system vs. endocrine system The nervous system coordinates rapid and precise responses to stimuli using action potentials. The endocrine system maintains homeostasis and long-term control using chemical signals. The endocrine system works in parallel with the nervous system to control growth and maturation along with homeostasis. Endocrine messages are generally slower than nervous messages and the effects tend to last longer

Endocrine system The endocrine system is a collection of glands that secrete chemical messages we call hormones. These signals are passed through the blood to arrive at a target organ, which has cells possessing the appropriate receptor.

Endocrine system

There are two types of glands in the human body Endocrine glands Exocrine glands Endocrine glands are ductless glands that secrete hormones directly into the bloodstream Exocrine glands secrete products through ducts or tubes. Exocrine glands are not part of the endocrine system. Sweat glands, salivary glands, and digestive glands are examples of exocrine glands.

hormones Hormones are chemicals that circulate throughout the blood and control organs and tissues in the body. Hormones secreted into the blood come into contact with virtually all cells and tissues as they circulate through the body; however they trigger only a response in those cells which have specific receptor sites for the hormone There are two types of hormones: Non-steroid hormones Steroid hormones

Non-steroid hormones Made of proteins, peptides or amino acids Are water soluble, therefore they do not enter the cell but bind to plasma membrane receptors, generating a chemical signal, second messenger, inside the target cell. Second messengers activate other intracellular chemicals to produce the target cell response.

Steroid hormones Made of lipids (cholesterol) Pass through the plasma membrane and act in a two step process. Inside the cell they bind to the nuclear membrane receptors, producing an activated hormone-receptor complex. The activated hormone-receptor complex binds to DNA and activates specific genes, increasing production of proteins.

Factors in hormone production and function The level of hormone production in the body can increase or decrease in response to changing metabolic needs This can be affected by a number of factors: Fluid level Infection Physical injury Emotional stress

Factors in hormone production The impact of a hormone on a target depends on a number of things: Hormone production and secretion Hormone concentration in the blood The rate of blood flow to a target The half-life of the hormone Half-life is the length of time in which a hormone remains viable in the blood before it is degraded by the liver or other tissues. It can range from several hours to several days.

Endocrine System and Feedback The endocrine system uses cycles and feedback to regulate physiological functions There are two types of feedback: Negative Positive Negative feedback regulates the secretion of almost every hormone (one positive loop – oxytocin) These cycles can range from hours to months in duration

Endocrine System and Feedback Negative Feedback Positive feedback Reverses the changes Brings conditions back into balance, controls the rate of a process to avoid accumulation Example: body temperature Reinforces the changes continues to accelerate change until an outside event occurs to discontinue the feedback mechanism Example: childbirth