17.1 Introduction to the Endocrine System & General Functions of the Endocrine System

The endocrine system serves as one of the 2 major control systems that do what?

Regulates the human body.

What is the endocrine system composed of?

Endocrine glands, which are located throughout the body.

What do endocrine glands synthesize and secrete?

Molecules called hormones.

What are hormones?

Molecules that communicate with and control other body cells.

How do hormones communicate with body cells?

Body cells display various cellular receptors for specific types of hormones.

What are target cells?

Cells that have specific receptors for hormones

Each hormone differs in what?

In target cells, thus they also differ in cellular activities that they regulate.

How do the hormones synthesized and secreted by the endocrine glands travel to their targeted glands?

1. Endocrine glands lack ducts (unlike exocrine glands) which release their secretions into ducts. Hormone molecules are instead released from endocrine gland cells into the interstitial fluid (fluid surrounding the cells) and then enter the blood within capillaries, which are the smallest blood vessels

2. These hormone molecules are transported within the blood from the endocrine gland's associated capillaries by the cardiovascular system to all body tissues , a process that is relatively slow (in comparison to the nervous system).

3. The hormones randomly leave the blood from the capillaries and enter the interstitial fluid, which provides the hormone molecules access to potentially all body cells. Consequently, the response induced by each hormone can be widespread.

4. The hormone binds to its target cells' receptors, which may be either within the cell or in the plasma membrane. The binding of hormones to cellular receptors either activates or inhibits selective metabolic activities within these cells (e.g., activate enzymes, open ion channels, stimulate protein synthesis or cellular division).

   These altered metabolic activities can have long-lasting effects and may continue after removal of the hormone.

What do the nervous system and endocrine system have in common?

1. In response to stimuli, they both release chemical substances called ligands (hormones or neurotransmitters) to communicate with particular target cells.

2. The ligand binds to a cellular receptor of a target cell to initiate a cellular change.

What are ligands?

Molecules or ions that bind to biological macromolecules and induce a change in macromolecules’ chemical shape (ex. hormone, neurotransmitters)

What varies in the communication method in the endocrine system and the nervous system?

Endocrine System: Endocrine glands secrete hormones; hormones are transported within the blood to target cells throughout body.

Nervous system: Neurotransmitter is released from a neuron into a synaptic cleft/

What varies in the target of stimulation in the endocrine system and the nervous system?

Endocrine System: Any cell in the body with a receptor for the hormone.

Nervous System: Other neurons, muscle cells, and gland cells.

What varies in the response time in the endocrine system and the nervous system?

Endocrine System: Relatively slow: Seconds to minutes to hour.

Nervous System: Rapid: Typically milliseconds or seconds.

What varies in the range of effect in the endocrine system and the nervous system?

Endocrine System: Widespread effects (typically)

Nervous System: Localized, specific effects (typically)

What varies in the duration of response in the endocrine system and the nervous system?

Endocrine System: Long-lasting: Minutes to days to weeks; may continue after stimulus is removed.

Nervous System: Short- term: Milliseconds: terminates with removal of stimulus

What are the General Functions of the Endocrine System?

• Regulating development, growth, and metabolism.

• Maintaining blood composition and volume.

• Controlling digestive processes.

• Controlling reproductive activites?

How does the endocrine system regulate development, growth, and metabolism?

Hormones have regulatory roles in both cell division and cell differentiation, which occur during development and growth of the body.

They also control our metabolic activities-both anabolic (synthesis) and catabolic (degradation) processes. For example, growth hormone controls growth (see section 17.7d) and thyroid

hormone regulates cellular metabolism

How does the endocrine system maintain blood composition and volume?

Hormones regulate the amount of specific substances dissolved within blood plasma, such as glucose, amino acids, and ions (e.g., Nat, Calt). Additionally, hormones also regulate other characteristics of blood, including its volume, its cellular concentration (erythrocytes and leukocytes), and number of platelets. Insulin, for example, is a hormone that regulates blood glucose levels.

How does the endocrine system control digestive processes?

Several hormones influence both the secretory processes and the movement of materials through the gastrointestinal tract in our digestive system. An example is gastrin, which is released from the stomach and controls digestive processes by increasing stomach secretions and contractions

How does the endocrine system control reproductive activities?

Hormones affect both development and function of the reproductive system as well as expression of sexual behaviors. One example is prolactin.Prolactin stimulates formation of breast milk in the mammary glands