Adrenal gland

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adrenal

[ah-dre´nal]

1. pertaining to one of the small glands just above each kidney. Called also suprarenal.

adrenal gland a small triangular endocrine gland situated in the retroperitoneal tissues at the cranial pole of each kidney; it is the result of fusion of two organs, one forming the inner core or medulla, and the other forming an outer shell, or cortex. These two structures are different in both their anatomy and the kinds of hormone they synthesize and secrete. Called also suprarenal gland.

Adrenal glands.

Adrenal Medulla. This is actually a glandular extension of sympathetic effector fibers or postganglionic neurons. It releases the hormones epinephrine and norepinephrine in response to stimulation of the sympathetic nervous system. These hormones enter the blood stream and are carried throughout the body where they indirectly act as stimulants to the various organs. Their production and distribution by the blood usually occur at the same time that the organs are being stimulated by the sympathetic nerves. In this way, the adrenal medulla and the sympathetic nerves support each other and can act as substitutes for each other. Epinephrine and norepinephrine both constrict blood vessels (except in muscle tissue) and are released in anticipatory states and other times of increased emotion, causing such changes as elevated blood pressure; release of glucagon, insulin, and fatty acids into the blood; and increases in heart rate, sweating, metabolic rate, and peristaltic activity. Epinephrine is important in initiating the physiological changes in the “fight or flight” response (see alarm reaction) and has a more prolonged effect than norepinephrine because of being removed more slowly from the blood.

Adrenal Cortex. The adrenal cortex synthesizes and secretes more than 30 different steroids and is responsible for the maintenance of several life-sustaining physiological activities. The steroids are divided into three major groups: glucocorticoids, mineralocorticoids, and androgens. The glucocorticoids get their name from the fact that they cause an increase in blood glucose levels (gluco-), are produced by the adrenal cortex (corti-), and are synthesized from cholesterol, which is a steroid (-oid). The mineralocorticoids, as their name implies, are chiefly concerned with the concentration of electrolytes (minerals) in the extracellular fluid. The adrenal cortex also secretes small amounts of androgens and is the major source of these hormones in females.

Glucocorticoids. The principal glucocorticoid is cortisol (also known as hydrocortisone), which is responsible for more than 95 per cent of all glucocorticoid activity. The remainder of the hormonal activity is provided by corticosterone and cortisone.

The physiologic effects of the glucocorticoids promote the metabolic breakdown or anabolism of carbohydrates, proteins, and fats. Cortisol increases the rate of gluconeogenesis by the liver, decreases the utilization of glucose by the cells, reduces cellular protein and enhances utilization of amino acids by the liver, and promotes mobilization of fatty acids from adipose tissue into the plasma. The net effect of these actions is to make these noncarbohydrate nutritive elements readily available for energy.

The regulation of cortisol secretion involves a complex closed-loop negative feedback system. Initially, the hypothalamus reacts to physical or psychogenic stress by secreting corticotropin-releasing hormone (CRH), which is carried to the anterior pituitary gland (adenohypophysis) via the hypothalamic-hypophyseal portal system. In response to the presence of CRH, the adenohypophysis secretes adrenocorticotropic hormone (ACTH), which stimulates the adrenal cortex to release cortisol. Cortisol then initiates a series of metabolic activities which help to relieve the physiologic effects of stress. Cortisol inhibits both release of CRH from the hypothalamus and of ACTH from the adenohypophysis. This exerts a negative feedback effect; high serum cortisol levels inhibit further production of cortisol. Thus, during times of relative calm when the body is not experiencing abnormal stress, the cortisol level returns to normal.

Another factor that influences the secretory rates of CRH, ACTH, and cortisol is a biologic clock mechanism that establishes a cyclic pattern of signals from the hypothalamus. This is a 24-hour cycle that has its peak right after completion of the major portion of a night's sleep, usually around 4 or 5 AM. About 12 hours later, the blood level of cortisol is at its lowest. This cycle is dependent on sleeping patterns; therefore, if a person changes the pattern and sleeps in the daytime, the cycle of hormonal levels changes accordingly. This information is significant in testing for cortisol levels as a means of diagnosing a disorder of the endocrine system. When blood is drawn for testing, the specimen should be clearly labeled as to the precise time it was taken.

Mineralocorticoids. The principal mineralocorticoid is aldosterone. This and other mineralocorticoids prevent excessive loss of sodium and chloride in the urine by enhancing their reabsorption from the distal ends of the renal tubules. They have the same effect to a lesser degree on the sweat and salivary glands and on the intestines. Additionally, aldosterone promotes excretion of potassium in the urine. The net result of these activities is the maintenance of fluid and electrolyte balance in the blood and extracellular fluid, which, in turn, affects cardiac output and blood pressure. A deficit of aldosterone secretion brings about a decrease in extracellular fluid and blood volumes, interference with the venous return to the heart, and a fall in cardiac output. If not corrected, the patient rapidly goes into profound shock.

Dysfunction of the Adrenal Glands. Either increased levels or deficits of the adrenal hormones can produce various disorders. cushing's syndrome, called also primary aldosteronism, is related to excessive secretion of aldosterone. In addison's disease there is an overall hypofunction of the adrenal cortex, resulting in insufficient production of all three groups of adrenocortical hormones. adrenogenital syndrome, which is usually caused by a tumor of the adrenal cortex, results from excessive secretion of androgens. Since androgens have a masculinizing effect, the symptoms are primarily those of changes in the secondary sex characteristics.

gland

[gland]

an aggregation of cells specialized to secrete or excrete materials not related to their ordinary metabolic needs. Glands are divided into two main groups, endocrine and exocrine. adj., adj glan´dular.

The endocrine glands, or ductless glands, discharge their secretions (hormones) directly into the blood; they include the adrenal, pituitary, thyroid, and parathyroid glands, the islands of Langerhans in the pancreas, the gonads, the thymus, and the pineal body. The exocrine glands discharge through ducts opening on an external or internal surface of the body; they include the salivary, sebaceous, and sweat glands, the liver, the gastric glands, the pancreas, the intestinal, mammary, and lacrimal glands, and the prostate. The lymph nodes are sometimes called lymph glands but are not glands in the usual sense.

Classification of glands according to mode of secretion. From Applegate, 2000.

acinous gland one made up of one or more acini (oval or spherical sacs).

adrenal gland see adrenal gland.

apocrine gland one whose discharged secretion contains part of the secreting cells.

areolar g's Montgomery's glands.

axillary g's lymph nodes in the axilla.

Bartholin g's two small mucus-secreting glands, one on each side in the lower pole of the labium majus and connected to the surface by a duct lined with transitional cells, which opens just external to the hymenal ring. Their exact function is not clear but they are believed to secrete mucus to moisten the vestibule during sexual excitement. Called also major vestibular glands.

Bowman's g's olfactory glands.

bronchial g's seromucous glands in the mucosa and submucosa of the bronchial walls.

Brunner's g's glands in the submucosa of the duodenum that secrete intestinal juice; called also duodenal glands.

buccal g's seromucous glands on the inner surface of the cheeks; called also genal glands.

bulbocavernous g's (bulbourethral g's) two glands embedded in the substance of the sphincter of the male urethra, posterior to the membranous part of the urethra; their secretion lubricates the urethra; called also Cowper's glands.

cardiac g's mucus-secreting glands of the cardiac part (cardia) of the stomach.

celiac g's lymph nodes anterior to the abdominal aorta.

ceruminous g's cerumin-secreting glands in the skin of the external auditory canal.

cervical g's

1. the lymph nodes of the neck.

2. compound clefts in the wall of the uterine cervix.

ciliary g's sweat glands that have become arrested in their development, situated at the edges of the eyelids; called also Moll's glands.

circumanal g's specialized sweat and sebaceous glands around the anus; called also Gay's glands.

Cobelli's g's mucous glands in the esophageal mucosa just above the cardia.

coccygeal gland glomus coccygeum.

compound gland one made up of a number of smaller units whose excretory ducts combine to form ducts of progressively higher order.

Cowper's g's bulbourethral glands.

ductless g's endocrine glands.

duodenal g's Brunner's glands.

Ebner's g's serous glands at the back of the tongue near the taste buds.

eccrine gland one of the ordinary or simple sweat glands, which are of the merocrine type.

endocrine g's see endocrine glands.

exocrine g's glands that discharge their secretions through ducts opening on internal or external surfaces of the body; see gland.

fundic g's (fundus g's) numerous tubular glands in the mucosa of the fundus and body of the stomach that contain the cells that produce acid and pepsin.

gastric g's the secreting glands of the stomach, including the fundic, cardiac, and pyloric glands.

Gay's g's circumanal glands.

genal g's buccal glands.

glossopalatine g's mucous glands at the posterior end of the smaller sublingual glands.

haversian g's synovial villi.

holocrine gland one whose discharged secretion contains the entire secreting cells.

intestinal g's straight tubular glands in the mucous membrane of the intestines, in the small intestine opening between the bases of the villi, and containing argentaffin cells. Called also crypts or glands of Lieberkühn.

jugular gland a lymph node behind the clavicular insertion of the sternocleidomastoid muscle.

Krause's gland an accessory lacrimal gland deep in the conjunctival connective tissue, mainly near the upper fornix.

lacrimal g's the glands that secrete tears; see also lacrimal apparatus.

g's of Lieberkühn intestinal glands.

lingual g's the seromucous glands on the surface of the tongue.

lingual g's, anterior seromucous glands near the apex of the tongue.

Littre's g's

1. preputial glands.

2. the male urethral glands.

lymph gland lymph node.

major vestibular g's Bartholin glands.

mammary gland a specialized gland of the skin of female mammals, which secretes milk for the nourishment of their young; it exists in a rudimentary state in the male. See also breast.

meibomian g's sebaceous follicles between the cartilage and conjunctiva of the eyelids. Called also tarsal glands.

merocrine gland one whose discharged secretion contains no part of the secreting cells.

mixed g's

1. seromucous glands.

2. glands that have both exocrine and endocrine portions.

Moll's g's ciliary glands.

Montgomery's g's sebaceous glands in the mammary areola; called also areolar glands.

mucous g's glands that secrete mucus.

olfactory g's small mucous glands in the olfactory mucosa; called also Bowman's glands.

parathyroid g's see parathyroid glands.

parotid g's see parotid glands.

peptic g's gastric glands that secrete pepsin.

pineal gland pineal body.

pituitary gland see pituitary gland.

preputial g's small sebaceous glands of the corona of the penis and the inner surface of the prepuce, which secrete smegma; called also Littre's glands and Tyson's glands.

prostate gland prostate.

pyloric g's the mucin-secreting glands of the pyloric part of the stomach.

salivary g's see salivary glands.

sebaceous gland a type of holocrine gland of the corium that secretes an oily material (sebum) into the hair follicles.

Glands: The relationship of the hair follicle, eccrine and apocrine sweat glands and sebaceous glands. From Copstead, 1995.

sentinel gland an enlarged lymph node, considered to be pathognomonic of some pathologic condition elsewhere.

seromucous g's glands that are both serous and mucous.

serous gland a gland that secretes a watery albuminous material, commonly but not always containing enzymes.

sex gland (sexual gland) gonad.

simple gland one with a nonbranching duct.

Skene's g's the largest of the female urethral glands, which open into the urethral orifice; they are regarded as homologous with the prostate. Called also paraurethral ducts.

solitary g's solitary follicles.

sublingual gland a salivary gland on either side under the tongue.

submandibular gland (submaxillary gland) a salivary gland on the inner side of each ramus of the mandible.

sudoriferous gland (sudoriparous gland) sweat gland.

suprarenal gland adrenal gland.

sweat gland see sweat gland.

target gland any gland affected by a secretion or other stimulus from another gland, such as those affected by the secretions of the pituitary gland.

tarsal g's meibomian glands.

thymus gland thymus.

thyroid gland see thyroid gland.

tubular gland any gland made up of or containing a tubule or tubules.

Tyson's g's preputial glands.

unicellular gland a single cell that functions as a gland, e.g., a goblet cell.

urethral g's mucous glands in the wall of the urethra; in the male, called also Littre's glands.

uterine g's simple tubular glands found throughout the thickness and extent of the endometrium; they become enlarged during the premenstrual period.

vesical g's mucous glands sometimes found in the wall of the urinary bladder, especially in the area of the trigone.

vulvovaginal g's Bartholin's glands.

Waldeyer's g's glands in the attached edge of the eyelid.

Weber's g's the tubular mucous glands of the tongue.

su·pra·re·nal gland

[TA]

a flattened, roughly triangular body positioned in relation to the superior end of each kidney but attached primarily to the diaphragmatic crura; it is one of the endocrine (ductless) glands furnishing internal secretions (epinephrine and norepinephrine from the medulla and steroid hormones from the cortex).

Synonym(s): glandula suprarenalis [TA], adrenal body, adrenal gland, atrabiliary capsule, epinephros, glandula atrabiliaris, paranephros, suprarenal body

adrenal gland

Either of two small, dissimilarly shaped endocrine glands, one located above each kidney, consisting of the cortex, which secretes several steroid hormones, and the medulla, which secretes epinephrine. Also called suprarenal gland.

Adrenal Gland

Either of a pair of small flat triangular glands which lie atop or adjacent to each kidney and which are composed of
(1) The outer adrenal cortex, an endocrine gland composed of three layers, from the outermost zona glomerulosa, which produces mineralocorticoids, primarily aldosterone that regulates blood pressure, the middle zona fasciculata, which produces glucocorticoids, primarily cortisol, and the inner zona reticularis, which produces androgens, primarily DHEA and DHEA-S, and
(2) The central adrenal medulla, a neuroendocrine "organ" which produces catecholmines (epinephrine/adrenaline & norepinephrine/noradrenaline) in response to stress signals from the peripheral nervous system.
Blood supply
Arterial
• Superior suprarenal artery from the inferior phrenic artery
• Middle suprarenal artery from the abdominal aorta
• Inferior suprarenal artery from the renal artery
Venous
• Right suprarenal vein to the inferior vena cava
• Left suprarenal vein to the left renal vein or the left inferior phrenic vein

su·pra·re·nal gland

(sū'pră-rē'năl gland) [TA]

A flattened, roughly triangular body resting on the upper end of each kidney; an endocrine gland the medulla of which producesepinephrine and norepinephrine and cortex produces cortisol and aldosterone.
Synonym(s): adrenal gland, epinephros, paranephros.

ADRENAL GLANDS

adrenal gland

Either of two triangular glands covering the superior surface of each kidney. Synonym: suprarenal gland See: illustration

Embryology

Each adrenal gland is a two-part organ composed of an outer cortex and an inner medulla. The cortex arises in the embryo from a region of the mesoderm that also gives rise to the gonads. The medulla arises from ectoderm, which also gives rise to the sympathetic nervous system.

Anatomy

The entire gland is enclosed in a tough connective tissue capsule from which trabeculae extend into the cortex. The cortex consists of cells arranged into three zones: the outer zona glomerulosa, the middle zona fasciculata, and the inner zona reticularis. The cells are arranged in cords. The medulla consists of chromaffin cells arranged in groups or in anastomosing cords. The two adrenal glands are retroperitoneal, each embedded in perirenal fat above its respective kidney. In an adult, the average weight of an adrenal gland is 5 g (range: 4 to 14 g).

Physiology

The adrenal medulla synthesizes and stores three catecholamines: dopamine, norepinephrine, and epinephrine. The chief effects of dopamine are the dilation of systemic arteries, increased cardiac output, and increased flow of blood to the kidneys. The primary action of norepinephrine is constriction of the arterioles and venules, resulting in increased resistance to blood flow, elevated blood pressure, and slowing of the heart. Epinephrine constricts vessels in the skin and viscera, dilates vessels in skeletal muscle, increases heart rate, dilates the bronchi by relaxing bronchial smooth muscle, increases the conversion of glycogen to glucose in the liver to increase the blood glucose level, and diminishes activity of the gastrointestinal system. The three catecholamines are also produced in other parts of the body.

The adrenal medulla is controlled by the sympathetic nervous system and functions in conjunction with it. It is intimately related to adjustments of the body in response to stress and emotional changes. Anticipatory states tend to bring about the release of norepinephrine. More intense emotional reactions, esp. those in response to extreme stress, tend to increase the secretion of both norepinephrine and epinephrine; epinephrine is important in mobilizing the physiological changes that occur in the “fight or flight” response to emergency situations.

The cortex synthesizes three groups of steroid hormones from cholesterol. These are 1) glucocorticoids (cortisol, corticosterone), which regulate the metabolism of organic nutrients and have an anti-inflammatory effect; 2) mineralocorticoids (aldosterone, dehydroepiandrosterone), which affect metabolism of the electrolytes sodium and potassium; and 3) androgens and estrogens (estradiol), which contribute to body changes at puberty. See: aldosterone; cortisol; steroid

Pathology

Hypersecretion of adrenal cortical hormones results in Cushing syndrome. Hypersecretion of aldosterone results in a surgically correctable form of hypertension (aldosteronism). Adrenocortical insufficiency may be acute or chronic; acute insufficiency of adrenal hormones produces circulatory shock, while chronic insufficiency results in Addison disease. See: Addison disease; aldosteronism; Cushing syndrome; pheochromocytoma

adrenal gland

an endocrine organ consisting of a medulla (central part) secreting ADRENALINE and NORADRENALINE, and a cortex (outer zone) secreting ADRENAL CORTICAL HORMONES. The two parts are closely associated in mammals, but are sometimes separated into distinct organs in other vertebrates, e.g. fish. The activity of the medulla is controlled by the sympathetic nervous system, and that of the cortex by ADRENOCORTICOTROPIC HORMONE secreted by the pituitary gland. In mammals there is a pair of adrenal glands situated anteriorly to the kidneys; other vertebrates have more than two adrenals.

Adrenal gland

Gland located above each kidney consisting of an outer wall (cortex) that produces steroid hormones and an inner section (medulla) that produces other important hormones, such as adrenaline and noradrenaline.

Mentioned in: Anabolic Steroid Use, Cryptococcosis, Histoplasmosis, Neuroblastoma, Stress Reduction, Vasodilators

su·pra·re·nal gland

(sū'pră-rē'năl gland) [TA]

A flattened, roughly triangular body positioned in relation to the superior end of each kidney but attached primarily to the diaphragmatic crura.
Synonym(s): adrenal body, adrenal gland.