adrenal gland the adrenal gland made up of two words...
TRANSCRIPT
C.N. Saxena B.sc. IVth Sem. Assistant Professor,
Unit - iii Department of Zoology Sri J.N.M. P.G. collage (KKC),
Luclnow
ADRENAL GLAND
The adrenal gland made up of two words, AD – means - upon , RENAL- means
– kidney. Thus meaning thereby - upon kidney. This gland is situated over the
kidney, hence called Adrenal or supra renal gland.
The weight of adrenal gland is about 4 to 6 gram. The adrenal glands have a
rich blood supply. They are served by several arteries branching off the aorta, including the
suprarenal and renal arteries. Blood flows to each adrenal gland at the adrenal cortex and then
drains into the adrenal medulla. Adrenal hormones are released into the circulation via the
left and right suprarenal veins.
The gland has three parts.
1. Capsule
2. Cortex
3. Medulla
Major division 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.
Adrenal cortex
1. Zona glomerulosa –
The outermost, zona glomerulosa, is a thin layer of cells, which makes up about 15%
of the total cortical mass. The cells in this zone are capable of producing the steroid
aldosterone. This characteristic is given by the presence of the enzyme aldosterone synthase,
an enzyme essential for the synthesis of this hormone. Aldosterone is mainly responsible for
regulation of electrolyte balance and its production is stimulated by the circulatory
concentration of angiotensin II and potassium.
Aldosterone is the major mineralocorticoid. It is important in the regulation of the
concentration of sodium and potassium ions in urine, sweat, and saliva. For example, it is
released in response to elevated blood K+, low blood Na+, low blood pressure, or low blood
volume. In response, aldosterone increases the excretion of K+ and the retention of Na+,
which in turn increases blood volume and blood pressure. Its secretion is prompted when
CRH from the hypothalamus triggers ACTH release from the anterior pituitary.
Aldosterone is a key component of the renin-angiotensin-aldosterone system (RAAS) in
which specialized cells of the kidneys 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, to the hormone angiotensin I. Angiotensin I is
converted in the lungs to angiotensin II by angiotensin-converting enzyme (ACE).
Angiotensin II has three major functions:
1. Initiating vasoconstriction of the arterioles, decreasing blood flow
2. Stimulating kidney tubules to reabsorb NaCl and water, increasing blood volume
3. Signaling the adrenal cortex to secrete aldosterone, the effects of which further
contribute to fluid retention, restoring blood pressure and blood volume
Once the corticosteroids are secreted, they are transported in circulation by
carrier proteins. This increases their water solubility, serves as a temporary storage,
and increases the half-life of the steroid. Glucocorticoids are carried mainly by a
corticosteroid binding globulin (CBG) that is produced in the liver and secreted into
circulation. A smaller proportion is carried by albumin and about 10% is circulating
freely. On the other hand, 40% of mineralocorticoids are circulating freely, 50% are
bound to albumin and only 10% use CBG.
2. Zona fasciculata –
The central and largest zone of the adrenal cortex is the zona fasciculata, making up
about 75% of the cortex mass. Its main role is the secretion of glucocorticoids, in particular
cortisol and corticosterone. It also has the capability of secreting small amounts of androgens
and estrogens. the zona fasciculata, named as such because the cells form small fascicles
(bundles) separated by tiny blood vessels. The cells of the zona fasciculata produce hormones
called glucocorticoids because of their role in glucose metabolism. The most important of
these is cortisol, 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 by the anterior pituitary. ACTH
triggers the release of the glucocorticoids. Their overall effect is to inhibit tissue building
while stimulating the breakdown of stored nutrients to maintain adequate fuel supplies. In
conditions of long-term stress, for example, cortisol promotes the catabolism of glycogen to
glucose, the catabolism of stored triglycerides into fatty acids and glycerol, and the
catabolism of muscle proteins into amino acids. These raw materials can then be used to
synthesize additional glucose and ketones for use as body fuels. The hippocampus, part of
the temporal lobe of the cerebral cortices and important in memory formation, is highly
sensitive to stress levels because of its many glucocorticoid receptors.
3. Zona reticularis - The deepest region of the adrenal cortex is the zona reticularis, which produces small
amounts of a class of steroid sex hormones called androgens. During puberty and most of
adulthood, androgens are produced in the gonads. The androgens produced in the zona
reticularis supplement the gonadal androgens. They are produced in response to ACTH from
the anterior pituitary and are converted in the tissues to testosterone or estrogens. In adult
women, they may contribute to the sex drive, but their function in adult men is not well
understood. In post-menopausal women, as the functions of the ovaries decline, the main
source of estrogens becomes the androgens produced by the zona reticularis.
Adrenal medulla
The medullary tissue is composed of unique postganglionic SNS neurons
called chromaffin cells, which are large and irregularly shaped, and produce the
neurotransmitters epinephrine (also called adrenaline) and norepinephrine (or noradrenaline). Epinephrine is produced in greater quantities—approximately a 4 to 1 ratio
with norepinephrine—and is the more powerful hormone. Because the 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.
Catecholamines are neurotransmitters, as well as hormones. In their role as
neurotransmitters they are synthesized all through the organism. In their role as hormones
they are produced by the adrenal medulla in response to sympathetic stimulation. The most
common are epinephrine and norepinephrine.
Catecholamines may bind at least 4 types of receptors. Alpha receptors are more
potently stimulated by norepinephrine (α1 and α2), although norepinephrine can weakly
stimulate beta (β1 and β2) receptors. The final response of a tissue depends on the types of its
available receptors. For example, heart tissue has mainly β1 while smooth muscle has mainly
β2 receptors. Therefore, these tissues respond more to epinephrine.
Function of adrenaline hormone
1) Pupillary dilation
2) It constricts erecter pilli muscle of hair known as(piloerection)
3) Increase sweating
4) Increase heartbeat
5) Stimulate trachea and bronchi muscle to relax (due to this
adrenaline also used in the cure of asthma)
6) Constrict blood vessels of the skin
7) Increase the concentration of glucose in blood break down
glycogen
8) Produce contraction of spleen so that it releases its stored blood
9) Clotting period of blood reduced.
Endocrine
Gland
Hormone Exercise
effect
Target organ Major function
HYPO AND HYPER FUNCTION OF ADRENAL GLAND;
Addison's disease:-
Addison's disease, also called adrenal insufficiency, is an uncommon disorder that occurs
when body doesn't produce enough of certain hormones. In Addison's disease, adrenal
glands, located just above kidneys, produce too little cortisol and, often, too little
aldosterone.
Addison's disease occurs in all age groups and both sexes, and can be life-threatening.
Treatment involves taking hormones to replace those that are missing.
Symptoms
Addison's disease symptoms usually develop slowly, often over several months. Often, the
disease progresses so slowly that symptoms are ignored until a stress, such as illness or
injury, occurs and makes symptoms worse. Signs and symptoms may include:
Extreme fatigue
Weight loss and decreased appetite
Darkening of your skin (hyperpigmentation)
Low blood pressure, even fainting
Salt craving
Low blood sugar (hypoglycemia)
Nausea, diarrhea or vomiting (gastrointestinal symptoms)
Abdominal pain
Muscle or joint pains
Irritability
Depression or other behavioral symptoms
Body hair loss or sexual dysfunction in women
Acute adrenal failure (addisonian crisis)
Sometimes the signs and symptoms of Addison's disease may appear suddenly. Acute adrenal
failure (addisonian crisis) can lead to life-threatening shock. Seek emergency medical
treatment if you experience the following signs and symptoms:
Severe weakness
Confusion
Pain in your lower back or legs
Severe abdominal pain, vomiting and diarrhea, leading to dehydration
Reduced consciousness or delirium
In an addisonian crisis you will also have:
Low blood pressure
High potassium (hyperkalemia) and low sodium (hyponatremia)
Cushing syndrome:-
Cushing syndrome occurs when body is exposed to high levels of the hormone
cortisol for a long time. Cushing syndrome, sometimes called hypercortisolism, may
be caused by the use of oral corticosteroid medication. The condition can also occur
when body makes too much cortisol on its own.
Too much cortisol can produce some of the hallmark signs of Cushing syndrome —
a fatty hump between your shoulders, a rounded face, and pink or purple stretch
marks on your skin. Cushing syndrome can also result in high blood pressure, bone
loss and, on occasion, type 2 diabetes.
Treatments for Cushing syndrome can return body's cortisol production to normal
and noticeably improve your symptoms. The earlier treatment begins, the better your
chances for recovery.
Symptoms
The signs and symptoms of Cushing syndrome can vary depending on the levels of
excess cortisol.
Common signs and symptoms of Cushing syndrome
Weight gain and fatty tissue deposits, particularly around the midsection and
upper back, in the face (moon face), and between the shoulders (buffalo hump)
Pink or purple stretch marks (striae) on the skin of the abdomen, thighs, breasts
and arms
Thinning, fragile skin that bruises easily
Slow healing of cuts, insect bites and infections
Acne
Signs and symptoms women with Cushing syndrome may experience
Thicker or more visible body and facial hair (hirsutism)
Irregular or absent menstrual periods
Signs and symptoms men with Cushing syndrome may experience
Decreased libido
Decreased fertility
Erectile dysfunction
Other signs and symptoms that may occur with Cushing syndrome
Severe fatigue
Muscle weakness
Depression, anxiety and irritability
Loss of emotional control
Cognitive difficulties
New or worsened high blood pressure
Headache
Increased pigmentation of the skin
Bone loss, leading to fractures over time
In children, impaired growth
Cushing syndrome
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