This video describes the function of the adrenal gland hormones and the stress response, including epinephrine, aldosterone, cortisol, and DHEA.
ADRENAL GLANDS AND THE STRESS RESPONSE
The adrenal glands are located above the kidneys. They consist of the outer adrenal cortex and the inner adrenal medulla (Figure 17.11). The adrenal cortex is divided into three zones. The outer zona glomerulosa secretes mineralocorticoids, mainly aldosterone; the middle zona fasciculata secretes glucocorticoids, mainly cortisol; and the inner zona reticularis secretes androgens, mainly dehydroepiandrosterone (DHEA) (Figure 17.12). The adrenal medulla is controlled by the autonomic nervous system, and stimulation from sympathetic preganglionic neurons causes the medulla to secrete epinephrine and a small amount of norepinephrine.
Aldosterone
Aldosterone is the main mineralocorticoid produced by the adrenal cortex. A steroid hormone made from cholesterol (Figure 17.4), aldosterone is produced when blood pressure is low and water needs to be reabsorbed. Its production is under the control of the renin-angiotensin system (see Chapter 21, Section 5). It causes the distal tubule and collecting duct of nephrons in the kidney to produce sodium ion channels; this causes more sodium to be reabsorbed into the bloodstream. When more sodium is reabsorbed, more water is also absorbed because of osmotic pressure gradients. And increase in water reabsorption brings blood volume, and therefore blood pressure, back to normal. Aldosterone also causes the nephrons to secrete potassium ions.
Cortisol
Cortisol is the main glucocorticoid produced in the adrenal cortex in response to the anterior pituitary hormone adrenocorticotropic hormone (ACTH). Cortisol is a steroid hormone produced from cholesterol (Figure 17.4). It is released during a 24-hour daily cycle, as well as during stress. The functions of cortisol include helping the body access stored nutrients so that cells can make energy (ATP). By stimulating glycogen and fat breakdown in the liver and in fat cells, cortisol increases blood sugar. It also inhibits the immune response in relation to the amount of cortisol secreted; that is, immune suppression is dose dependent. Normal cortisol secretions do not prevent the immune system from functioning, but they do act as a brake so the immune system doesn’t overreact.
In people who have a regular sleep schedule, their daily cortisol level begins to rise a couple hours before they wake up in the morning. This has a beneficial effect because it helps increase their blood sugar level—which lowered during the period of sleeping and not eating—so they have energy in the morning until they eat breakfast (Figure 17.13). Cortisol secretion increases during a stress response, along with epinephrine and norepinephrine.
Cushing’s Syndrome
Cushing’s syndrome results from an excess of cortisol secretion. An excess secretion can be caused by conditions that increase the production of corticotropin-releasing hormone (CRH) by the hypothalamus or that increase the release of adrenocorticotropic hormone (ACTH) by the anterior pituitary gland. It can also be caused by long-term glucocorticoid drug treatment, which is used to treat chronic inflammatory diseases because of its immune suppression abilities. People with Cushing’s syndrome have symptoms that result from excessive breakdown of fats, glycogen, and bone minerals; redistribution of stored body fat to the abdomen; and decreased production of new proteins. This condition leads to hyperglycemia, muscle weakness, osteoporosis, type-2 diabetes, immune suppression, poor wound healing, thin skin, bruising, depression, moodiness, fat redistribution from limbs to trunk and face, “moon face,” “buffalo hump,” hair loss, decreased fertility, fatigue, insomnia, menstrual irregularities, water retention, and high blood pressure. People who have chronic stress can experience these symptoms as well, although less extremely than Cushing’s Syndrome; this helps explain why chronic stress is a major risk factor for chronic diseases. (Figure 17.14).
Androgens
Androgens are secreted by the adrenal cortex in both males and females. In males, the testosterone produced by the testes during puberty plays a much more significant role in the development of secondary sex characteristics and sperm development than dehydroepiandrosterone (DHEA). In females, the adrenal cortex androgens contribute to libido and are converted into estrogens; after menopause, this is the only source of estrogen. Overstimulation of the adrenal glands can cause increased androgen production in some women, and, although rare, can lead to masculinization.
Adrenal Medulla and the Stress Response
The adrenal medulla secretes epinephrine and norepinephrine (NE)—also called adrenaline and noradrenaline, respectively—that are released due to stimulation of the preganglionic neurons of the sympathetic nervous system during a stress response (Chapter 15). Each adrenal medulla secretes primarily epinephrine, but also small amounts of norepinephrine; the neurons of the sympathetic system release primarily norepinephrine. Note that epinephrine and norepinephrine are hormones when released into the bloodstream by the adrenal medulla, and they are neurotransmitters when released by neurons of the autonomic nervous system. Recall from Chapter 15 that the sympathetic nervous system controls the fight-or-flight response that’s activated during physical or emotional stress. When stressed, epinephrine and norepinephrine help to break down stored fat to increase blood sugar that can be used to make ATP. These hormones also help cells utilize oxygen for the production of ATP during a fight-or-flight situation. Stressors that stimulate this response include fear, intense exercise, surgery, infection, illness, injury, pain, sleep deprivation, low blood sugar, cold temperatures, and any strong emotional response.
The effects of epinephrine—the main catecholamine that is secreted—include the following: increased heart rate; bronchiole dilation; pupil dilation; increased water retention and therefore increased blood pressure; vasodilation and increased blood flow in liver, skeletal muscles, cardiac muscle, and adipose tissue; vasoconstriction in the digestive tract; breakdown of glycogen and fat and therefore increased blood sugar, since epinephrine increases the effects of glucagon and thyroid hormones.
Cortisol is also secreted during a stress response and further increases blood sugar levels by breaking down fat and glycogen. This response is beneficial and adaptive for short-term physical stress: for example, at times when the blood sugar would be used, when the immune response wouldn’t overreact during infection, when healing could take place, or when muscles could contract during exercise or fleeing.
Long-term emotional stress, however, is very damaging to the body because the level of blood sugar remains high since it is not used by cells; protein synthesis cannot occur properly, so cells are not replaced; the immune system becomes overly suppressed, which leads to increased infections; it also causes an increase in the production of inflammatory cytokines, which increases chronic inflammatory conditions; and also causes muscle-wasting and weakness.
Did You Know?
Chronic cortisol secretion from emotional stress inhibits the production of proteins, including collagen and elastin in the connective tissue layers of the skin. This leads to premature aging of the skin, wrinkles, and loss of elasticity. Cortisol secretion also inhibits the immune response, so chronic emotional stress results in an increased risk of infection such as the common cold or influenza.
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I’m trying to find out which hormones the testes and ovaries produce that are similar, apart from testosterone and oestrogen. I know the ovaries also produce to smaller extend relaxin, inhibin, cortisol, vasopressin, oxytocin and DHEA. I’m wondering if the testes do so as well? Seeing they are very similar in function, form and aim. Any information would be greatly appreciated. I’ve research pubmed, sciencedirect etc. but nothing apart from inhibin, activin..
I’m writing a book about energy, emotions, hormones and self-development through Yoga, Ayurveda and Goddesses, giving women their emotional health back in a world designed for men 😉 Seeing emotions are the one subject every Logos ignores; philosophy, religion, science, medicine, I believe they’re also a nexus, along with physiology and hormones, to healing many aspects of self. Emotions can propel us into living well or wanton. Researching emotions I realise understanding hormone health and how to create it naturally, is vital to transform daily life.
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