2. ADRENAL GLANDS
Two adrenal glands
Each weighs 4 grams
Lie at the superior poles of the two kidneys
Two distinct parts, adrenal medulla and adrenal cortex
Adrenal medulla, central 20 % of the gland, is functionally
related to the SNS
It secretes epinephrine and norepinephrine in response to
sympathetic stimulation
Adrenal cortex secretes corticosteroids.
5. CORTICOSTEROIDS
Adrenocortical hormones:
Mineralocorticoids
Glucocorticoids
Androgens (small amounts)
Mineralocorticoids: affect electrolytes (“minerals”) of
extracellular fluids -sodium and potassium, in particular
Glucocorticoids : important effects that increase blood
glucose concentration + additional effects on protein and fat
metabolism
More than 30 steroids have been isolated from the adrenal
cortex
Aldosterone principal mineralocorticoid
Cortisol principal glucocorticoid.
6.
7. ADRENAL CORTEX
Three Distinct Layers
1. Zona glomerulosa, 15% of the adrenal cortex
A thin layer of cells that lies just underneath the capsule
Secrete aldosterone
Secretion is controlled by ECF concentrations of
angiotensin II and potassium, which stimulate aldosterone
secretion.
2. Zona fasciculata, 75% of the adrenal cortex
Middle and widest layer
Secretes glucocorticoids cortisol, corticosterone, and
small amounts of adrenal androgens and estrogens.
Secretion is controlled by the hypothalamic-pituitary axis
via adrenocorticotropic hormone (ACTH).
8. Zona reticularis, deep layer of cortex
Secretes adrenal androgens, dehydroepiandrosterone
(DHEA) and androstenedione, small amounts of estrogens
and glucocorticoids.
ACTH regulates secretion of these cells
Cortical androgen-stimulating hormone, released from the
pituitary, may also be involved.
10. ADRENOCORTICAL HORMONES ARE STEROIDS
Derived from Cholesterol
Cholesterol is provided by LDL in the circulating plasma.
Transport of cholesterol is regulated by feedback mechanisms
For example, ACTH increases the number of adrenocortical
cell receptors for LDL, as well as the activity of enzymes that
liberate cholesterol from LDL.
Cholesterol enters cell, delivered to mitochondria, cleaved by
enzyme cholesterol desmolase to form pregnenolone
This initial step in steroid synthesis is stimulated by the
different factors that control secretion of the major hormone
11. SYNTHESIS OF ADRENAL STEROIDS
Synthesis occur in two of the organelles of
the cell, mitochondria and endoplasmic
reticulum
Each step is catalyzed by a specific enzyme
system.
12.
13. MINERALOCORTICOIDS
1. Aldosterone (very potent, accounts for about 90 per
cent of all mineralocorticoid activity)
2. Desoxycorticosterone
3. Corticosterone
4. 9a-Fluorocortisol (synthetic)
5. Cortisol (very slight mineralocorticoid activity)
6. Cortisone (synthetic)
14. GLUCOCORTICOIDS
1. Cortisol (very potent, accounts for about 95
percent of all glucocorticoid activity)
2. Corticosterone
3. Cortisone (synthetic)
4. Prednisone (synthetic)
5. Methylprednisone (synthetic)
6. Dexamethasone (synthetic)
16. MINERALOCORTICOID DEFICIENCY
Causes Severe Renal Sodium Chloride Wasting and
Hyperkalemia.
Total loss of adrenocortical secretion death within 3
days to 2 weeks unless the person receives extensive salt
therapy or injection of mineralocorticoids.
Without mineralocorticoids:
Potassium ion concentration of ECF rises
Sodium and chloride are rapidly lost from the body
Total ECF volume and blood volume greatly reduced
Develops diminished cardiac output
Progresses to a shock like state
Followed by death
Mineralocorticoids are said to be the acute “lifesaving” portion
of the adrenocortical hormones.
17. RENAL AND CIRCULATORY EFFECTS
Increases Renal Tubular Reabsorption of Sodium and
Secretion of Potassium
From renal tubular epithelial cells especially in the principal
cells of the collecting tubules and, to a lesser extent, in the
distal tubules and collecting ducts.
Aldosterone causes sodium to be conserved in the ECF while
increasing potassium excretion in the urine.
18. Excess Aldosterone Increases ECF Volume and
Arterial Pressure but Has Only a Small Effect on
Plasma Sodium Concentration
Concentration of sodium in the ECF rises only a few
milliequivalents, when sodium is reabsorbed by the
tubules, there is simultaneous osmotic absorption of almost
equivalent amounts of water.
ECF volume increases almost as much as the retained
sodium, but without much change in sodium concentration.
Aldosterone-mediated increase in ECF volume lasting
more than 1 to 2 days also leads to an increase in arterial
pressure
The rise in arterial pressure then increases kidney
excretion of both salt and water, called pressure natriuresis
and pressure diuresis
This return to normal of salt and water excretion by the
kidneys is called aldosterone escape
19. When aldosterone secretion becomes zero, large amounts
of salt are lost in the urine, not only diminishing the amount
of sodium chloride in the extracellular fluid but also
decreasing the ECF volume.
The result is severe ECF dehydration and low blood
volume, leading to circulatory shock.
Without therapy, this usually causes death within a few days
after the adrenal glands suddenly stop secreting
aldosterone.
20. EXCESS ALDOSTERONE CAUSES HYPOKALEMIA AND
MUSCLE WEAKNESS
Excess aldosterone causes loss of potassium ions from the
ECF into the urine and also stimulates transport of potassium
from ECF into most cells of the body.
Excessive secretion of aldosterone, may cause a serious
decrease in the plasma potassium concentration, This
condition is called hypokalemia.
When the potassium ion concentration falls below about one-
half normal, severe muscle weakness often develops.
21. TOO LITTLE ALDOSTERONE CAUSES HYPERKALEMIA
AND CARDIAC TOXICITY
When aldosterone is deficient, ECF potassium ion
concentration can rise far above normal.
When it rises to 60 to 100 per cent above normal,
serious cardiac toxicity, including weakness of heart
contraction and development of arrhythmia becomes
evident
Progressively higher concentrations of potassium lead
inevitably to heart failure.
22. EXCESS ALDOSTERONE INCREASES TUBULAR HYDROGEN
ION SECRETION, CAUSES MILD ALKALOSIS
Also causes secretion of hydrogen ions in exchange for
sodium in the intercalated cells of the cortical collecting
tubules.
This decreases the hydrogen ion concentration in the
extracellular fluid, causing a mild degree of alkalosis.
23. SWEAT GLANDS, SALIVARY GLANDS, AND
INTESTINAL EPITHELIAL CELLS
Aldosterone Stimulates Sodium and Potassium Transport
These glands form a primary secretion that contains large
quantities of sodium chloride, but most of it is reabsorbed,
whereas potassium and bicarbonate ions are secreted.
Aldosterone greatly increases the reabsorption of sodium
chloride and the secretion of potassium by the ducts.
This effect is used to conserve body salt in hot environments
The effect on the salivary glands is necessary to conserve
salt when excessive quantities of saliva are lost.
Aldosterone also greatly enhances sodium absorption by the
intestines, especially in the colon, which prevents loss of
sodium in the stools.
24. REGULATION OF ALDOSTERONE SECRETION
1. Increased potassium ion concentration in the
extracellular fluid greatly increases aldosterone
secretion.
2. Increased activity of the renin-angiotensin system
(increased levels of angiotensin II) also greatly
increases aldosterone secretion.
3. Increased sodium ion concentration in the extracellular
fluid very slightly decreases aldosterone secretion.
4. ACTH from the anterior pituitary gland is necessary for
aldosterone secretion but has little effect in controlling
the rate of secretion.
26. Cortisol Is the Primary Glucocorticoid Secreted by the
Adrenal Cortex
More than 95% of glucocorticoid activity exerted by the
adrenocortical hormones can be attributed to cortisol
known also as hydrocortisone
Most of the remaining glucocorticoid activity is due to
corticosterone.
Cortisol mediates most of its effects by binding with
intracellular receptors in target tissues and inducing or
repressing gene transcription
This results in alterations in the synthesis of enzymes
that alter cell function.
27. EFFECTS OF CORTISOL ON CARBOHYDRATE METABOLISM
Stimulation of Gluconeogenesis.
Formation of carbohydrate from proteins and some other
substances by the liver
Decreased Glucose Utilization by Cells
Elevated Blood Glucose Concentration and “Adrenal
Diabetes.”
The rise in blood glucose in turn stimulates secretion of
insulin.
High levels of glucocorticoid reduce the sensitivity of many
tissues to the stimulatory effects of insulin on glucose
uptake and utilization.
28. EFFECTS ON PROTEIN METABOLISM
Reduction in Cellular Protein.
Reduction of the protein stores in essentially all body cells
except those of the liver.
protein synthesis catabolism of protein in the cells.
amino acid transport into extra hepatic tissues
Enhance amino acid in plasma and increased transport
into liver cells
Cortisol Increases Liver and Plasma Proteins.
Increased conversion of amino acids to glucose-that is,
enhanced gluconeogenesis
29. EFFECTS ON FAT METABOLISM
Mobilization of Fatty Acids from adipose tissue
Increases concentration of free fatty acids in the plasma,
increases their utilization for energy.
Cortisol also enhance the oxidation of fatty acids in cells.
Obesity Caused by Excess Cortisol
A peculiar type of obesity, with excess deposition of fat in
the chest and head regions of the body, giving a buffalo-
like torso and a rounded “moon face.”
Results from excess stimulation of food intake, with fat
being generated in some tissues of the body more rapidly
than it is mobilized and oxidized.
30. Any type of physical or mental stress causes an immediate
and marked increase in ACTH secretion by the pituitary
gland, followed by greatly increased adrenocortical
secretion of cortisol
CORTISOL IN RESISTING STRESS AND INflAMMATION
31. ANTI-INflAMMATORY EFFECTS OF CORTISOL
Large amounts of cortisol have two basic antiinflammatory
effects:
1. It can block early stages of inflammation process before it
even begins
2. If inflammation has already begun, it causes rapid
resolution of the inflammation and increased rapidity of
healing
32. OTHER EFFECTS OF CORTISOL
Blocks Inflammatory Response to Allergic Reactions
Cortisol effectively prevents shock or death in anaphylaxis,
which otherwise kills many people
Effect on Blood Cells and on Immunity in Infectious
Diseases
Large amount of Cortisol decreases the number of
eosinophils and lymphocytes in the blood
Large doses also causes atrophy of lymphoid tissue, which
decreases the output of T cells and antibodies
The level of immunity for foreign invaders is decreased
Leads to increased infection and death from diseases
Useful drugs in preventing immunological rejection of
transplanted hearts, kidneys, and other tissues.
Cortisol increases the production of red blood cells
35. ADRENAL ANDROGENS
The adrenal androgens DHEA and androstenedione are
secreted in appreciable amounts, but they have only weak
androgenic effects.
Consequently, the normal plasma concentrations of these
hormones exert little effect on secondary sex
characteristics
In females, adrenal androgens are responsible for pubic
and axillary hair.
In males Most of the androgenic activity of adrenal
hormones may be due to the conversion of adrenal
androgens to testosterone in peripheral tissues
The secretion of adrenal androgens is stimulated by ACTH.
37. HYPOADRENALISM-ADDISON’S DISEASE
Failure of the adrenal cortices to produce adrenocortical
hormones
Most frequently caused by primary atrophy of the adrenal
cortices, caused by autoimmunity against the cortices.
Also caused by tuberculous destruction of the adrenal
glands or invasion of the adrenal cortices by cancer.
These processes usually are gradual, leading to a
progressive reduction in glucocorticoid and
mineralocorticoid function.
As a result of the decreased cortisol secretion, there is a
compensatory increase in ACTH secretion, which produces
hyperpigmentation.
38. Mineralocorticoid Deficiency
Excessive loss of sodium, hypovolemia, hypotension, and
increased plasma renin activity
Excessive potassium retention and hyperkalemia
Mild acidosis
Glucocorticoid Deficiency
Abnormal carbohydrate, fat, and protein metabolism
resulting in muscle weakness, fasting hypoglycemia, and
impaired utilization of fats for energy
Loss of appetite and weight loss
Poor tolerance to stress.
The inability to secrete increased amounts of cortisol
during stress leads to an Addisonian crisis that may
culminate in death if supplemental doses of adrenocortical
hormones are not administered.
39. Treatment
An untreated person with total adrenal destruction dies
within a few days to a few weeks because of weakness
and usually circulatory shock.
Such a person can live for years if small quantities of
mineralocorticoids and glucocorticoids are administered
daily.
40. HYPERADRENALISM-CUSHING’S SYNDROME
Hypersecretion by the adrenal cortex causes a complex
cascade of hormone effects called Cushing’s syndrome.
Hypercortisolism can occur from multiple causes:
1) adenomas of the anterior pituitary ACTH
adrenal hyperplasia cortisol secretion
2) abnormal function of the hypothalamus CRH
ACTH release
3) “ectopic secretion” of ACTH by a tumor in the body
4) adenomas of the adrenal cortex
5) by administration of large amounts of exogenous
glucocorticoids.
When Cushing’s syndrome is secondary to excess
secretion of ACTH by the anterior pituitary, this is referred
to as Cushing’s disease.
41. Symptoms:
Mobilization of fat from the extremities to the abdomen, face,
and supraclavicular areas
Protein depletion resulting in muscle weakness, loss of
connective tissue and thinning of the skin (leading to purple
striae), and impaired growth in children
Osteoporosis and vertebral fractures
Impaired response to infections resulting from a suppressed
immune system
Impaired carbohydrate metabolism, hyperglycemia, and
even insulin-resistant diabetes mellitus
Masculinizing effects when adrenal androgens are secreted
in excess
42. Treatment
Remove an adrenal tumor
Hypertrophied pituitary glands can be surgically removed or
destroyed by radiation.
Drugs that block steroidogenesis, such as metyrapone,
ketoconazole, and aminoglutethimide, or that inhibit ACTH
secretion can also be used.
If ACTH secretion cannot easily be decreased, the only
satisfactory treatment is usually bilateral partial (or even
total) adrenalectomy, followed by administration of adrenal
steroids to make up for any insufficiency that develops.
44. FUNCTION OF THE ADRENAL MEDULLAE
Stimulation of the sympathetic nerves to the adrenal
medulla causes large quantities of epinephrine and
norepinephrine to be released into the circulating blood.
About 80% of the secretion from the adrenal medulla is
epinephrine, and about 20% is norepinephrine.
The effect of the epinephrine and norepinephrine released
from the adrenal medulla lasts 5 to 10 times longer than
when they are released by sympathetic neurons because
these hormones are slowly removed from the blood.
45. ADRENERGIC RECEPTORS
Alpha and Beta Receptors
Norepinephrine excites mainly alpha receptors but
excites the beta receptors to a lesser extent as well.
Conversely, epinephrine excites both types of
receptors approximately equally.
Therefore, the relative effects of norepinephrine
and epinephrine on different effector organs are
determined by the types of receptors in the organs.
46. ALPHA AND BETA RECEPTORS
The stimulation of α-receptors results in vasoconstriction,
dilation of the iris, contraction of the intestinal and bladder
sphincters, and contraction of the pilomotor muscles.
The β-receptor is subdivided into β1-, β2-, and β3
receptor subtypes.
Stimulation of β1-receptors causes an increase in heart
rate and strength of contraction.
Stimulation of β2-receptors causes skeletal muscle
vasodilation, bronchodilation, uterine relaxation,
calorigenesis, and glycogenolysis.
Stimulation of β3-receptors induces lipolysis in adipose
tissue and the conversion of energy in lipids into heat
(thermogenesis).
47. NOREPINEPHRINE
The circulating Norepinephrine causes:
Vasoconstriction
Increased heart rate and contractility
Inhibition of the gastrointestinal tract
Dilated pupils.
48. EPINEPHRINE
Epinephrine causes almost the same effects as those
caused by norepinephrine, except
The circulating epinephrine has a greater effect on
cardiac performance
Epinephrine causes only weak constriction of the blood
vessels in muscles
Slight increase in arterial pressure
A dramatic increase in cardiac output.
The metabolic rate of every cell of the body is increased
by these hormones, especially by epinephrine, as much
as 100 per cent above normal
49. Epinephrine and norepinephrine are almost always
released by the adrenal medullae at the same time that
the different organs are stimulated directly by
generalized sympathetic activation.
Therefore, the organs are actually stimulated in two
ways: directly by the sympathetic nerves and indirectly
by the adrenal medullary hormones.
The two means of stimulation support each other, and
either can, in most instances, substitute for the other.
