Welcome to this lesson on the adrenal glands. Today you will be looking at the structure and function of the adrenal glands and the role they play in the endocrine system. Specifically, you will learn about:
- Adrenal Glands Overview
- Adrenal Glands Structure
- Adrenal Cortex
- Adrenal Medulla
1. Adrenal Glands Overview
The adrenal glands are located just above the kidneys. You have two kidneys and, therefore, two adrenal glands. Adrenal glands produce hormones that help regulate various things, such as glucose levels of the blood, blood pressure, and blood circulation.
2. Adrenal Gland Structure
The image below is a cross-section of an adrenal gland. The adrenal cortex is the outer part of the adrenal gland, and the adrenal medulla is the inner part. It's important to understand the structure of adrenal glands because each of the parts of the adrenal gland possesses different functions.
2a. Adrenal Cortex
The adrenal cortex
and mineralocorticoids. These are two classes of hormones that are secreted by the adrenal cortex. Glucocorticoids help to increase blood glucose levels and also play a role in decreasing inflammation of tissues. Cortisol is a glucocorticoid that stimulates the liver to synthesize glucose, which is a process called gluconeogenesis
is a condition in which a person has chronic low blood sugar and sometimes occurs because too little cortisol (a glucocorticoid hormone) is produced.
Cortisol also plays a role in inflammation; Cortisone is an over-the-counter drug that you can buy at any drugstore acts like cortisol to reduce inflammation.
Mineralocorticoids are the other class of hormones that are produced by the adrenal cortex. Mineralocorticoids help to adjust the concentration of mineral salts, like potassium or sodium, in your extracellular fluids.
An example of a mineralocorticoid is aldosterone, which acts on the kidneys. Aldosterone stimulates sodium reabsorption and therefore, water reabsorption. Aldosterone secretion is triggered by a decrease in blood pressure or blood volume, or a decrease in sodium levels of the blood.
- Adrenal Cortex
- The outer covering of the adrenal gland that secretes hormones that regulate body mineral levels, metabolism, and aid in the production of sex hormones.
- Hormones that affect glucose metabolism of the body, the most abundant one being cortisol, a.k.a. the stress hormone.
- The process of converting amino acids and lipids into glucose; this process takes place in the liver.
- The clinical term for low blood sugar.
- Hormones that maintain mineral homeostasis; aldosterone is a hormone that stimulates the kidneys to retain sodium.
2b. Adrenal Medulla
The adrenal medulla
is the inner part of the adrenal gland. The adrenal medulla produces and secretes epinephrine
. Normally epinephrine and norepinephrine act as neurotransmitters elsewhere in the body, however when they're released by the adrenal medulla, they help to regulate blood circulation.
Epinephrine and norepinephrine help to increase heart rate. They also help to dilate and constrict arterioles, along with dilating bronchioles. This allows oxygen to flow to cells that demand more energy when the body is stressed or excited. They're often called stress hormones because they play a big role when the body is in the flight or fight response.
- Adrenal Medulla
- The adrenal medulla releases hormones called catecholamines (adrenaline) that elevate our metabolism in response to stress; the adrenal medulla is controlled by the sympathetic nervous system (SNS).
- Classified as a catecholamine (adrenaline) and is secreted from the adrenal medulla; epinephrine is found in higher amounts in the blood than its counterpart norepinephrine and has slightly more of an effect on the heart.
- Classified as a catecholamine (adrenaline) and is secreted from the adrenal medulla, norepinephrine is found in lower amounts in the blood than its counterpart epinephrine and has slightly more of an effect on the blood vessels.
This lesson has been an overview on the structure, function, and role of the adrenal glands in the endocrine system. Specifically, you learned about functions of the adrenal cortex and the adrenal medulla.
Keep up the learning and have a great day!