the endocrine system
OpenStaxCollege
Learning objectives
By the end of this section, you will be able to:
- Describe the location and structure of the adrenal glands.
- Identify the hormones produced by the adrenal cortex and adrenal medulla and summarize their target cells and effects.
oKidney glandsare wedges of glandular and neuroendocrine tissue that are attached to the top of the kidneys by a fibrous capsule ([Link]). The adrenal glands have an abundant blood supply and experience one of the highest blood flow rates in the body. They are served by several arteries that branch from the aorta, including the adrenal and renal arteries. Blood flows to each adrenal gland in the adrenal cortex and then drains into the adrenal medulla. The left and right adrenal veins release adrenal hormones into the circulation.
Kidney glands
Both adrenal glands sit on top of the kidneys and are composed of an outer cortex and an inner medulla, all surrounded by a connective tissue capsule. The cortex can be subdivided into additional zones, all of which produce different types of hormones. LM × 204. (Micrograph provided by Regents, University of Michigan Medical School © 2012)
Check out the University of Michigan WebScope athttp://141.214.65.171/Histology/Endocrine%20System/New%20Scans/230_HISTO_40x.svs/view.apmlto explore the fabric swatch in more detail.
The adrenal gland consists of an outer cortex of glandular tissue and an inner medulla of nervous tissue. The cortex itself is divided into three zones: thezona glomerulosa, abundled area, It is likezona reticular. Each region secretes its own set of hormones.
oadrenal cortex, as a component of the hypothalamic-pituitary-adrenal (HPA) axis, secretes steroid hormones important for regulating the long-term stress response, blood pressure and blood volume, nutrient absorption and storage, fluid and electrolyte balance and inflammation. The HPA axis involves stimulation of the release of adrenocorticotropic hormone (ACTH) from the pituitary by the hypothalamus. ACTH then stimulates the adrenal cortex to produce the hormone cortisol. This route will be discussed in more detail below.
oadrenal medullaIt is a neuroendocrine tissue composed of postganglionic neurons of the sympathetic nervous system (SNS). It is really an extension of the autonomic nervous system, which regulates the homeostasis of the body. The sympathetic-medullary (SAM) pathway involves stimulation of the cord by impulses from the hypothalamus via thoracic neurons of the spinal cord. The medulla is stimulated to secrete the amine hormones epinephrine and norepinephrine.
One of the main functions of the adrenal gland is to respond to stress. Stress can be physical, psychological, or both. Physical stress includes exposing the body to injury, walking outdoors in cold and wet conditions without a coat, or malnutrition. Psychological stress includes the perception of a physical threat, a fight with a loved one, or just a bad day at school.
The body responds differently to short-term and long-term stress, following a pattern known asgeneral adaptation syndrome (GAS). Stage one of GAS is calledalarm reaction. This is the short-term stress, fight-or-flight response, mediated by the hormones epinephrine and norepinephrine from the adrenal medulla via the SAM pathway. Its function is to prepare the body for extreme physical exertion. Once this stress is relieved, the body quickly returns to normal. The section on the adrenal medulla covers this response in more detail.
If the stress is not relieved soon, the body adapts to the stress in the second stage calledresistance stage. If a person is starving, for example, the body can send signals to the gastrointestinal tract to maximize the absorption of nutrients from food.
However, if the stress continues for a long time, the body responds with very different symptoms than the fight or flight response. During thedepletion stage, people can begin to suffer from depression, suppression of their immune response, severe fatigue, or even a fatal heart attack. These symptoms are mediated by hormones from the adrenal cortex, primarily cortisol, released as a result of signals from the HPA axis.
Adrenal hormones also have a number of non-stress-related functions, including increasing blood sodium and glucose levels, which will be described in detail below.
The adrenal cortex consists of multiple layers of lipid storage cells found in three structurally distinct regions. Each of these regions produces different hormones.
visit thisLinkto view an animation describing the location and function of the adrenal glands. Which hormone produced by the adrenal glands is responsible for mobilizing energy reserves?
Zona Glomerulosa Hormones
The most superficial region of the adrenal cortex is the zona glomerulosa, which produces a group of hormones collectively referred to asmineralocorticoidsdue to its effect on the body's minerals, especially sodium and potassium. These hormones are essential for fluid and electrolyte balance.
aldosteroneIt is the main mineralocorticoid. It is important in regulating the concentration of sodium and potassium ions in urine, sweat, and saliva. For example, it is released in response to elevated levels of K in the blood.+, blood goes down already+, low blood pressure or low blood volume. In response, aldosterone increases K excretion.+and Na retention+, which in turn increases blood volume and blood pressure. Its secretion is stimulated when CRH from the hypothalamus triggers the release of ACTH from the anterior pituitary.
Aldosterone is also a key component of the renin-angiotensin-aldosterone system (RAAS), in which specialized kidney cells secrete the enzyme renin in response to low blood volume or low blood pressure. Renin then catalyzes the conversion of the blood protein angiotensinogen, produced by the liver, into the hormone angiotensin I. Angiotensin I is converted in the lungs to angiotensin II byangiotensin converting enzyme(TOWARD). Angiotensin II has three main functions:
- Initiating vasoconstriction of the arterioles, decreasing blood flow.
- Stimulate the renal tubules to reabsorb NaCl and water, increasing blood volume.
- Signaling the adrenal cortex to secrete aldosterone, the effects of which further contribute to fluid retention, restoring blood pressure and blood volume.
For people with hypertension or high blood pressure, there are medications that block the production of angiotensin II. These drugs, known as ACE inhibitors, prevent the ACE enzyme from converting angiotensin I to angiotensin II, thus mitigating the latter's ability to raise blood pressure.
Zona Fasciculata Hormones
The middle region of the adrenal cortex is the zona fasciculata, so named because the cells form small fascicles (bundles) separated by tiny blood vessels. The cells of the zona fasciculata produce hormones calledglucocorticoidsdue to its role in glucose metabolism. The most important of them iscortisol, some of which the liver converts to cortisone. A glucocorticoid produced in much smaller amounts is corticosterone. In response to long-term stressors, the hypothalamus secretes CRH, which in turn triggers the release of ACTH from the anterior pituitary. ACTH triggers the release of glucocorticoids. Its overall effect is to inhibit tissue formation while stimulating the breakdown of stored nutrients to maintain an adequate supply of fuel. Under conditions of prolonged stress, for example, cortisol promotes the catabolism of glycogen to glucose, the catabolism of stored triglycerides to fatty acids and glycerol, and the catabolism of muscle protein to amino acids. These raw materials can then be used to synthesize additional glucose and ketones to use as fuel for the body. The hippocampus, which is part of the temporal lobe of the cerebral cortex and is important in memory formation, is highly sensitive to stress levels due to its numerous glucocorticoid receptors.
You are probably familiar with prescription and over-the-counter medications that contain glucocorticoids, such as cortisone injections into swollen joints, prednisone pills and steroid inhalers used to control severe asthma, and hydrocortisone creams that are applied to relieve itchy rashes. These drugs reflect another function of cortisol: downregulation of the immune system, which inhibits the inflammatory response.
Hormones of the Zona Reticularis
The deepest region of the adrenal cortex is the zona reticularis, which produces small amounts of a class of steroidal sex hormones called androgens. During puberty and most of adulthood, the gonads produce androgens. Androgens produced in the zona reticularis complement gonadal androgens. They are produced in response to ACTH from the anterior pituitary and are converted in the tissues to testosterone or estrogen. In adult women, they can contribute to sexual desire, but their role in adult men is not well understood. In postmenopausal women, as ovarian function declines, the main source of estrogen becomes androgens produced by the zona reticularis.
As noted above, the adrenal cortex releases glucocorticoids in response to long-term stress, such as severe illness. Rather, the adrenal medulla releases its hormones in response to short-term acute stress mediated by the sympathetic nervous system (SNS).
The medullary tissue is composed of single postganglionic neurons of the SNS calledcromafimcells, which are large and irregular in shape, and produce the neurotransmittersepinephrine(also called adrenaline) andnorepinephrine(or norepinephrine). Epinephrine is produced in the largest amounts, approximately 4 to 1 with norepinephrine, and is the most potent hormone. Because chromaffin cells release epinephrine and norepinephrine into the systemic circulation, where they travel widely and exert effects on distant cells, they are considered hormones. Derived from the amino acid tyrosine, they are chemically classified as catecholamines.
Medullary secretion of epinephrine and norepinephrine is controlled by a neural pathway that originates in the hypothalamus in response to danger or stress (the SAM pathway). Both epinephrine and norepinephrine signal the liver and skeletal muscle cells to convert glycogen to glucose, which increases blood glucose levels. These hormones increase heart rate, pulse, and blood pressure to prepare the body to fight or flee from a perceived threat. In addition, the airways dilate the airways, raising the levels of oxygen in the blood. It also stimulates vasodilation, further increasing oxygenation to important organs such as the lungs, brain, heart, and skeletal muscle. At the same time, it triggers vasoconstriction in blood vessels that serve less essential organs such as the gastrointestinal tract, kidneys, and skin, and regulates some components of the immune system. Other effects include dry mouth, loss of appetite, dilated pupils, and loss of peripheral vision. The main hormones of the adrenal glands are summarized in[Link].
| Hormones of the adrenal glands | |||
|---|---|---|---|
| adrenal gland | associated hormones | chemistry class | It's done |
| adrenal cortex | aldosterone | Steroid | Increases blood Na+levels |
| adrenal cortex | Cortisol, corticosterone, cortisone | Steroid | Increase blood glucose levels |
| adrenal medulla | epinephrine, norepinephrine | amina | Stimulate the fight or flight response |
Several disorders are caused by the dysregulation of the hormones produced by the adrenal glands. For example, Cushing's disease is a disorder characterized by elevated blood glucose levels and accumulation of lipid deposits on the face and neck. It is caused by hypersecretion of cortisol. The most common source of Cushing's disease is a pituitary tumor that secretes cortisol or ACTH in abnormally high amounts. Other common signs of Cushing's disease include the development of a moon-shaped face, a buffalo hump on the back of the neck, rapid weight gain, and hair loss. Chronically elevated glucose levels are also associated with an increased risk of developing type 2 diabetes. In addition to hyperglycemia, chronically elevated glucocorticoids impair immunity, resistance to infection, and memory, and can cause rapid weight gain and hair loss.
On the other hand, hyposecretion of corticosteroids can lead to Addison's disease, a rare disorder that causes low blood glucose and low blood sodium. The signs and symptoms of Addison's disease are vague and also typical of other diseases, making it difficult to diagnose. They can include general weakness, abdominal pain, weight loss, nausea, vomiting, sweating, and cravings for salty foods.
The adrenal glands, located above each kidney, consist of two regions: the adrenal cortex and the adrenal medulla. The adrenal cortex, the outer layer of the gland, produces mineralocorticoids, glucocorticoids, and androgens. The adrenal medulla in the center of the gland produces epinephrine and norepinephrine.
The adrenal glands mediate both a short-term stress response and a long-term stress response. A perceived threat results in the secretion of epinephrine and norepinephrine from the adrenal medulla, which mediate the fight-or-flight response. The long-term stress response is mediated by CRH secretion from the hypothalamus, which triggers ACTH, which in turn stimulates corticosteroid secretion from the adrenal cortex. Mineralocorticoids, primarily aldosterone, cause sodium and fluid retention, which increases blood volume and blood pressure.
visit thisLinkto view an animation describing the location and function of the adrenal glands. Which hormone produced by the adrenal glands is responsible for mobilizing energy reserves?
cortisol.
The adrenal glands are superiorly connected to which organ?
- thyroid
- liver
- rinses
- hypothalamus
C
What type of secretory cell is found in the adrenal medulla?
- chromaffin cells
- neuroglial cells
- follicular cells
- oxyphil cells
AND
Cushing's disease is a disorder caused by ________.
- abnormally low cortisol levels
- abnormally high cortisol levels
- abnormally low aldosterone levels
- abnormally high aldosterone levels
B
Which of the following responses is not part of the fight or flight response?
- pupil dilation
- increased oxygen supply to the lungs
- suppressed digestion
- reduced mental activity
D
What are the three regions of the adrenal cortex and what hormones do they produce?
The outer region is the zona glomerulosa, which produces mineralocorticoids such as aldosterone; the next region is the zona fasciculata, which produces glucocorticoids such as cortisol; the inner region is the zona reticularis, which produces androgens.
If the innervation of the adrenal medulla were interrupted, what would be the physiological result?
Damage to the innervation of the adrenal medulla would prevent the adrenal glands from responding to the hypothalamus during the fight or flight response. Therefore, the answer would be reduced.
Compare and contrast the response to stress in the short and long term.
The short-term stress response involves the hormones epinephrine and norepinephrine, which work to increase oxygen delivery to organs important for extreme muscular action, such as the brain, lungs, and muscles. In the long-term stress response, the hormone cortisol is involved in catabolism of glycogen, protein, and triglyceride stores, glucose and ketone synthesis, and downregulation of the immune system.
Glossary
- adrenal cortex
- outer region of the adrenal glands consisting of multiple layers of epithelial cells and capillary networks that produce mineralocorticoids and glucocorticoids
- Kidney glands
- endocrine glands located on top of each kidney that are important in regulating the stress response, blood pressure and blood volume, water homeostasis, and electrolyte levels
- adrenal medulla
- inner layer of the adrenal glands that plays an important role in the stress response by producing epinephrine and norepinephrine
- angiotensin converting enzyme
- the enzyme that converts angiotensin I to angiotensin II
- alarm reaction
- the short-term stress, or fight-or-flight response, of the first stage of general adaptation syndrome mediated by the hormones epinephrine and norepinephrine
- aldosterone
- hormone produced and secreted by the adrenal cortex that stimulates sodium and fluid retention and increases blood volume and blood pressure
- cromafim
- Neuroendocrine cells of the adrenal medulla
- cortisol
- glucocorticoid important in gluconeogenesis, glycogen catabolism, and downregulation of the immune system
- epinephrine
- the primary and most potent catecholamine hormone secreted by the adrenal medulla in response to short-term stress; also called adrenaline
- general adaptation syndrome (GAS)
- the three-stage response pattern of the human body to short- and long-term stress
- glucocorticoids
- hormones produced by the zona fasciculata of the adrenal cortex that influence glucose metabolism
- mineralocorticoids
- hormones produced by cells in the zona glomerulosa of the adrenal cortex that influence fluid and electrolyte balance
- norepinephrine
- secondary catecholamine hormone secreted by the adrenal medulla in response to short-term stress; also called norepinephrine
- depletion stage
- stage three general adaptation syndrome; the body's long-term response to stress mediated by hormones from the adrenal cortex
- resistance stage
- stage two of the general adaptation syndrome; the body's ongoing response to stress after stage one slows
- bundled area
- middle region of the adrenal cortex that produces hormones called glucocorticoids
- zona glomerulosa
- most superficial region of the adrenal cortex, which produces hormones collectively called mineralocorticoids
- zona reticular
- deeper region of the adrenal cortex, which produces the sex steroid hormones called androgens
FAQs
What is the anatomy and physiology of the adrenal glands? ›
Adrenal glands, also known as suprarenal glands, are small, triangular-shaped glands located on top of both kidneys. Adrenal glands produce hormones that help regulate your metabolism, immune system, blood pressure, response to stress and other essential functions.
What is adrenal gland short answer? ›A small gland that makes steroid hormones, adrenaline, and noradrenaline. These hormones help control heart rate, blood pressure, and other important body functions. There are two adrenal glands, one on top of each kidney.
What is adrenal glands quizlet? ›Adrenal glands (suprarenal glands) are paired, each located superior to a kidney. Each adrenal gland is structurally and functionally differentiated into two regions: the outer adrenal cortex making up the bulk of the gland (yellow in slide 1), and the inner adrenal medulla (the dark red area). Tap the card to flip 👆
Where are the adrenal glands quizlet? ›The two adrenal glands are triangular-shaped glands located on top of each kidney. The adrenal glands are made up of two parts. The outer part is called the adrenal cortex, and the inner part is called the adrenal medulla.
What are the 3 adrenal gland hormones? ›Your adrenal glands are endocrine glands located on top of your kidneys. They produce many important hormones, including cortisol, aldosterone and adrenaline. The adrenal hormones help regulate several bodily functions including metabolism, blood pressure and your body's response to stress.
Where are the adrenal glands? ›The adrenal glands are two small triangle-shaped glands in the upper abdomen. One gland is located on top of each kidney. Triangular-shaped glands located on top of the kidneys. They produce steroid hormones such as aldosterone, cortisol, and precursor sex steroids that can be converted into estrogen and testosterone.
What does the adrenal gland produce? ›The adrenal cortex produces several hormones. The most important are aldosterone (a mineralocorticoid), cortisol (a glucocorticoid), and androgens and estrogen (sex hormones). Aldosterone helps the kidneys control the amount of salt in the blood and tissues of the body.
What is the role of the adrenal gland in the body quizlet? ›An endocrine gland located above the kidney. The adrenal glands help control heart rate and blood pressure and regulate the fight-or-flight stress response.
What controls the adrenal glands quizlet? ›It is controlled by the sympathetic division of the autonomic nervous system. The adrenal medulla has two cell populations. What do they produce? One produces epinephrine (adrenaline) and the other produces norepinephrine (noradrenaline).
What are the 4 hormones produced by the adrenal glands? ›What hormones do the adrenal glands make? The adrenal glands mainly make the hormones adrenaline, noradrenaline, cortisol and aldosterone. Adrenaline and noradrenaline are involved in the body's stress (or 'fight or flight') response.
What are adrenal hormones quizlet? ›
Adrenal hormone functions. regulation of protein synthesis and carb metabolism. ACTH. A protein hormone produced by anterior pituitary. Induces or inhibits release of cortisol and aldosterone from adrenal gland.
What is the gross anatomy of the adrenal gland? ›The adrenal gland is composed of two distinct tissues: the outer cortex and the inner medulla. The adrenal cortex tends to be fattier and thus has a more yellow hue. The adrenal medulla is more of a reddish-brown color. A thick capsule consisting of connective tissue surrounds the entire adrenal gland.
What is the physiology of adrenal medulla? ›The adrenal medulla is mainly responsible for the synthesis of the catecholamines, adrenaline and noradrenaline, but also has other secretory functions such as the production of dopamine. Both adrenaline and noradrenaline are produced from the amino acid tyrosine, through multiple reactions.
What is histology and physiology of adrenal gland? ›The adrenal gland consists of an outer cortex of glandular tissue and an inner medulla of nervous tissue. The cortex itself is divided into three zones: the zona glomerulosa, the zona fasciculata, and the zona reticularis. Each region secretes its own set of hormones.
What is adrenaline in anatomy? ›Adrenaline (epinephrine) is a hormone your adrenal glands make to help you prepare for stressful or dangerous situations. Adrenaline rush is the name for the quick release of adrenaline into your bloodstream. This gets your body ready for a “fight or flight” response.