Copyright EMAP Publishing 2021 This article is not for distribution except for journal club use Clinical Practice Keywords Endocrine system/ Hormones/Adrenal glands Systems of life This article has been Endocrine system double-blind peer reviewed In this article... ● Endocrine functions of the adrenal glands ● Hormones of the adrenal glands ● The role of adrenal gland hormones in mediating essential physiological processes Endocrine system 4: adrenal glands Key points Authors Maria Andrade is honorary associate professor in biomedical science; There are two Zubeyde-Bayram Weston is senior lecturer in biomedical science; John Knight is adrenal glands: one associate professor in biomedical science; all at College of Human and Health located above each Sciences, Swansea University. kidney NT SELF- Abstract The endocrine system consists of glands and tissues that produce and ASSESSMENT Adrenal glands secrete hormones to regulate and coordinate vital bodily functions. This article, the Test your consist of two parts, fourth in an eight-part series on the endocrine system, explores the anatomy and knowledge. the cortex and the physiology of the adrenal glands, and describes how they regulate and coordinate After reading this medulla, which each vital physiological processes in the body through hormonal action. article go to produce different nursingtimes.net/ NTSAAdrenal hormones Citation Andrade M et al (2021) Endocrine system 4: adrenal glands. Nursing Times If you score 80% [online]; 117: 8, 54-58. or more, you will The adrenal cortex receive a certificate produces a diverse that you can use range of steroid as revalidation his eight-part series on the endo- colour and are positioned retroperito- evidence. hormones, using crine system opened with an neally (behind the peritoneal membrane cholesterol as a overview of endocrine glands and lining the abdominal cavity). The right substrate Tthe role of hormones as chemical adrenal gland is at, approximately, the signals that help maintain the homeostatic level of the 12th rib, while the left is located The main hormones balance that is essential to good health. slightly higher between the 11th and 12th produced by the This fourth article examines the anatomy ribs (Perrier and Boger, 2005). medulla are the and physiology of the adrenal glands. Normal, healthy adult adrenal glands ‘flight or fight’ are relatively small – they each weigh 4-6g, hormones Anatomy and are around 3cm wide, 5cm high and adrenaline and There are two adrenal (suprarenal) glands: 1cm thick; changes in size are often indica- noradrenaline one located immediately above each tive of underlying pathology (Lack and kidney (Fig 1). They are yellow to orange in Paal, 2019; Westphalen and Bonnie, 2006). The right adrenal gland is usually dis- Fig 1. Position and structure of the adrenal gland tinctly triangular in appearance, resem- bling a witch’s hat, while the left is more flattened and typically crescent shaped. The adrenals are highly vascularised, Adrenal Gland and each gland is supplied with oxygen- ated blood through superior, middle and Medulla inferior suprarenal arteries; deoxygenated blood is carried away from each gland via Cortex an adrenal vein (Perrier and Boger, 2005). Internal structure Left Kidney Capsule Each adrenal gland is protected by a thick collagen-rich outer capsule, with glan- dular tissues located beneath. The largest portion is the outer region, called the adrenal cortex, accounting for around 90% JENNIFER N.R. SMITH of total adrenal volume (Gorman, 2013). Nursing Times [online] August 2021 / Vol 117 Issue 8 54 www.nursingtimes.net Copyright EMAP Publishing 2021 This article is not for distribution except for journal club use Clinical Practice Systems of life The adrenal cortex produces a diverse range of steroid hormones, using choles- Table 1. Major physiological effects of adrenaline terol as a substrate. These include the long- Target organ/tissue Physiological effects term stress hormone cortisol, aldosterone Heart Interacts with beta-adrenergic receptors to accelerate heart (regulating levels of sodium and potas- rate and increase force of myocardial contraction sium in the blood) and a group of testos- terone-like hormones called androgens. Blood vessels Vasoconstriction in skin and gastrointestinal tract, vasodilation The adrenal medulla is the inner region in the musculature, coronary and hepatic circulation of the adrenal gland, accounting for Respiratory tract Increased respiratory rate and bronchodilation around 10% of adrenal volume (Gorman, 2013), and produces adrenaline (epineph- Gastrointestinal tract Reduced gut motility, reduced blood flow to gastrointestinal rine) and noradrenaline (norepinephrine). and liver tract, reduced digestion, increased breakdown of glycogen to These have diverse physiological effects, glucose in liver but function primarily to activate the sym- Central nervous Activation of the sympathetic branch of the autonomic pathetic branch of the autonomic nervous system nervous system system (ANS) and prepare the body for immediate action (VanPutte et al, 2017). activated in acutely stressful situations. The effects of adrenaline and noradren- Adrenal medulla The adrenal medulla itself is innervated aline are rapid and usually observed within The major cells of the adrenal medulla are with sympathetic nerve endings that, a few seconds of release; the primary effect called chromaffin cells because they take when activated, initiate the release of more of adrenaline in accelerating heart rate up stains containing chromium salts adrenaline, further amplifying the fight- ensures its rapid distribution throughout (Mubarik and Aeddula, 2021). Chromaffin or-flight response (Verberne et al, 2016). the body. Adrenaline is a short-acting hor- cells produce amino acid-derived hor- Adrenaline and noradrenaline have mul- mone with a half life of around 2-3 min- mones called catecholamines. tiple and diverse physiological effects that utes; it is rapidly metabolised by the liver prepare the body for immediate action. The and excreted in the urine (Electronic Medi- Adrenaline and noradrenaline most-obvious effects of the sudden release cines Compendium, 2020). The two major catecholamines are adrena- of catecholamines (adrenaline rush) pri- line (epinephrine) and noradrenaline (nor- marily centre on the cardiovascular system. Adrenal cortex epinephrine), which are enzymatically Adrenaline binds to beta-adrenergic recep- The adrenal cortex lies immediately below derived from the amino acid tyrosine. tors associated with the sinoatrial node the protective collagenous adrenal capsule These are commonly referred to as the (SAN) of the heart (Macdonald et al, 2020). and continually takes up cholesterol as the ‘fight-or-flight' hormones, and will be The SAN functions as the heart’s natural substrate to generate a diverse range of explored later in this article. pacemaker and adrenaline dramatically steroid hormones. Histologically, the Tyrosine is a non-essential amino acid accelerates the heart rate, often way beyond cortex consists of three distinct layers of that can be obtained through diet or the upper limit for normal resting heart rate tissue, each producing its own class of derived from the essential amino acid phe- of 100 beats per minute (bpm). This is often steroid hormones: nylalanine. Chromaffin cells continually perceived as a notable thumping in the ● Zona glomerulosa (outer layer) – synthe- take up tyrosine and, through the sequen- chest and, as cardiac output and blood pres- sises mineralocorticoids that help tial actions of several enzymes, convert it sure increase, the pulse may be perceived regulate electrolyte concentrations; into the active catecholamines L-dopa, (without palpation) in other areas of the ● Zona fasciculata (middle layer) dopamine, noradrenaline and adrenaline. body, such as the neck and temples. – synthesises glucocorticoids that Tyrosine is also taken up by the neurons in Adrenaline also further increases blood primarily function as long-term stress the ANS to generate noradrenaline, which pressure by promoting vasoconstriction in hormones; functions as a key neurotransmitter in the the skin and gastrointestinal tract, hence ● Zona reticularis (inner layer) – marks sympathetic branch of the ANS. the expression of skin turning ‘ashen with the boundary between the cortex and In the adrenal medulla, adrenaline is fear’ and the common sensation of ‘butter- the medulla, producing a class of the major product of catecholamine bio- flies in the stomach’. Simultaneously, testosterone-like hormones called synthesis, accounting for around 95% of adrenaline promotes vasodilation of the androgens. the medullary hormones released into the arteries in the skeletal muscles and coro- blood (Berends et al, 2019). nary circulation, diverting oxygenated Aldosterone blood to the major muscle groups and As their name suggests, the mineralocorti- Fight-or-flight response myocardium of the heart. Adrenaline coid hormones produced by the zona glo- When we perceive a threat (for example, by improves oxygen uptake by dilating the merulosa regulate plasma concentrations a predator) or are in a potentially dan- airways and increasing the breathing rate, of minerals/salts (electrolytes). The most gerous or exciting situation (for example, increasing blood glucose, and improving important mineralocorticoid in humans is at the top of a bungee jump), adrenaline sensory perception and response times aldosterone, which regulates blood con- and smaller amounts