Question

What type of tissue is the adrenal medulla made of? What are its hormones and their actions? (page 338 )

Short answer

The adrenal medulla is composed of specialized neural tissue made up of chromaffin cells. It produces the hormones epinephrine and norepinephrine, which play key roles in the "fight or flight" response by increasing heart rate, blood pressure, energy production, focus, and other physiological changes essential for responding to stress or danger.

Step-by-step solution

Identify the adrenal gland and medulla

The adrenal gland is an endocrine gland located above each kidney, and it is divided into two main parts: the outer cortex and the inner medulla. In this exercise, we will be focusing on the inner part, the adrenal medulla.

Determine the type of tissue

The adrenal medulla is made up of specialized cells called chromaffin cells, derived from neural crest cells. These cells form a modified sympathetic ganglion, which is part of the autonomic nervous system and is responsible for producing and secreting hormones. Thus, the adrenal medulla is composed of a specialized type of neural tissue.

Identify the hormones produced by the adrenal medulla

The main hormones produced and released by the adrenal medulla are catecholamines, specifically epinephrine (also known as adrenaline) and norepinephrine (also known as noradrenaline).

Describe the actions of epinephrine and norepinephrine

Both epinephrine and norepinephrine function as hormones and neurotransmitters. Their main actions are related to the "fight or flight" response, which occurs in situations of stress or danger. They prepare the body to respond quickly and effectively by increasing heart rate, blood pressure, and blood flow to muscles, as well as mobilizing glucose and fatty acids for energy production. Additionally, they also increase awareness and focus, dilate airways, and slow down digestion. To summarize: - The adrenal medulla is made of specialized neural tissue composed of chromaffin cells. - The main hormones produced by the adrenal medulla are epinephrine and norepinephrine. - The actions of epinephrine and norepinephrine are related to the "fight or flight" response and involve increasing heart rate, blood pressure, energy production, focus, and other physiological changes essential for responding to stress or danger.

Key concepts

Chromaffin Cells

At the heart of the adrenal gland lies the adrenal medulla, an intricate network of specialized cells known as chromaffin cells. These cells are integral to our body's ability to react to stress and are so named because they stain a dark brown when exposed to chromium salts—a distinctive feature that aids in their identification under the microscope.

Originating from neural crest cells, which are multipotent stem cells during embryonic development, chromaffin cells are not ordinary neural tissue. They are a kind of modified postganglionic sympathetic neuron that, instead of forming synapses, release hormones directly into the blood. Thus, when the body signals a state of emergency—such as sudden stress or threat—these cells spring into action, secreting powerful hormones that enact swift physiological changes.

Catecholamines

Catecholamines encompass a group of biologically significant compounds, including the hormones epinephrine (adrenaline) and norepinephrine (noradrenaline), which are released into the bloodstream by the chromaffin cells of the adrenal medulla. They belong to a larger class of molecules known as monoamines, which all share a common structure: a catechol group (a benzene ring with two hydroxyl groups) attached to an amine group.

These potent chemicals serve dual roles as both hormones and neurotransmitters, communicating messages within the body. When released in response to stress, catecholamines bind to alpha and beta receptors scattered throughout various tissues, triggering a cascade of physiological effects. They spike glucose levels by promoting glycogen breakdown in the liver, boost oxygen supply to muscles and the brain by increasing heart rate and dilating blood vessels, and they also ramp up mental alertness and readiness for physical action.

Fight or Flight Response

The fight or flight response is the body's natural reaction to perceived threats or stressors. Its name aptly describes the two most primal reactions an organism can have when facing danger: stand and confront it or flee to safety. During this response, chromaffin cells release vast amounts of catecholamines, initiating a sequence of rapid physical changes.

These changes include acceleration of heart rate and breathing, dilation of pupils, and cessation of non-critical bodily functions, such as digestion—allowing the body to focus entirely on coping with the impending challenge. The response ensures that oxygen and energy reserves are directed where they are most needed: to the muscles and brain. Notably, this system is not just a relic of our ancient ancestors facing wild predators; it activates during modern stresses too—like taking an exam or giving a public speech—underpinning its relevance in contemporary life.