1. Endocrine glands secrete certain chemicals known as hormones. Hormones are
extremely importantsecretions for the regulation of body activities. The full setof
endocrine glands in the body includes numerous glands,but thesyllabus specifies only a few ofthem as mentionedabove.
NEED FORTHE REGULATIONOF BODYACTIVITIES
The activities inour body arehighly complex and theyneed tobe so regulated that everyactivity takes place at a proper time and
in a correct sequence for example, the gastric juice,bileandpancreaticjuiceshouldbe poured intothefood canal only whenthereis food
in it. Though this kindofregulation is doneto someextentby thenervous systemit is also brought about by chemicalregulators called
hormones (horma: to stirup // to excite// to put intoaction).
Hormones are secretions fromspecific cells or glands in the body,andare carried toall parts throughblood,but their effectis producedin one
or more specific parts (targetorgan orcells) only. Most hormones are secreted byspecial glands, theendocrine glands (endo: inside,crine:
separate) meaning "secrete internally", also called ductless glands becausetheir secretions are poured directlyinto thebloodand notthrough
any special duct. Certain hormones arealso produced fromsomesuch glands or body parts which otherwise havea different primary function;
for example, the stomach and duodenum.
Endocrine system: Endocrine system consists of several glands/glandular cells which bring about
the overall commonfunction of chemical coordination in the body. Almost allendocrine
glands act in a coordinatedmanner. They activate each other and work as a system
of organs called endocrine system. A system is defined as a group of organs
performing an overall common function. Endocrineglands secretecertain chemicals calledhormones.
GENERAL PROPERTIES OF HORMONES
l. Hormones aresecreted fromtheir source(anendocrinegland) directly into the blood.
2. They regulate the physiologicalprocesses by chemical means. They affect the enzyme
systemsofthe body.
3. They act on targetorgans or cells usually awayfrom theirsource.
4. Hormonesproduced in onespecies usually show similar influencein other species.
5. They are produced invery small quantitiesand are biologically very active. For example,
adrenaline is activeevenin a concentration of I partin 300,000,000 parts.
6. Chemically, some hormones are peptides (proteins such as insulin) which are water soluble,
some are amines (derived fromamino acids such as adrenaline) again water-solubleand
some are steroids (derived fromcholesterolsuch as testosterone) which are lipid-soluble.
7. Their excess (hypersecretion/oversecretion) or deficiency (hyposecretion/undersecretion), both may leadto serious
consequences.
8. Hormones are not stored in the body and are excreted from the system.
ENDOCRINEGLANDS
The principal endocrine (hormone-producing) glands in the human body have
been shown in These are enumerated below (only the ones in bold face are
included in the syllabus):
1. Adrenal 2. Pancreas 5. Parathyroid 7. Gonads
3. Thyroid 4. Pituitary 6. Thymus
2. The adrenalglands arelike caps onthe top ofeach kidney (ad: near, renal:kidney). Each adrenal gland consists of 2 parts
(i) a central medulla and (ii) a peripheral cortex.
(i) secretes adrenaline (also called epinephrineand noradrenaline). Adrenalineis a
hormone, which prepares thebody to meet any emergency situation,for "fight" i.e. to facedanger or
for "flight", to run away from it. Extra energy and strength is provided to the body in that situation.Extra hormone
is released into the blood at the time of emotional stress.When excited or angry, our adrenals producea lot of
adrenaline.The gland itself is stimulated by the nerve endings of the Autonomic Nervous System.
FUNCTIONS OF —THEEMERGENCYHORMONE
• It increases heart beat accompanied by an increasein bloodpressure.
• It increases blood supply to the muscleswhiledecreasing it to skinand visceral
organs.
• More glucose is released into the blood by theliver(like putting morefuelinto the engine). (The finaldashto win a
race is under theinfluenceofadrenaline).
(ii) secretes many hormones but the best known hormone is cortisone (which
suppresses inflammation).
The cortical hormones arecategorised as :
a. regulates mineralmetabolism, especially Na+
and K+
ions.
b. :regulates carbohydrate, proteinandfat metabolism.
In general, the cortical hormones
• Increase blood glucose concentration.
• Influence fatand protein metabolism.
• Regulate salt andwater balance in the body.
• Adapt the body to Stresses"
such as extreme heat or cold,
burns, infections, etc.
• Certain cortical hormones
behave like sex hormones.
They are both male as well as female
hormones in both sexes. An overgrowth
of cortex in young children leads to a
premature sexual maturity.
Hyposecretion fromadrenal
cortex causes Addison's
disease. Symptoms areloss
of energy, skinpigmentation, loss of weight, nausea, hypoglycemia (low blood
sugar), sensitivity to cold and pain, increased susceptibility to infections, etc.
Hypersecretion of adrenalcortex causes Cushing's syndrome. Symptoms are
obesity, hyperglycemia(higher bloodsugar), osteoporosis, weakness, salt and
water retention.
3. Pancreas is both a ductgland as wellas a ductlessgland. As a duct gland, its secretion (pancreatic
juice) is poured into the duodenum for digestion. As a ductless gland, ithas special groups of
hormone-secreting cells called Islets of Langerhans, which are scattered in the entire
gland (islets : little islands) Theislet cells produce3 hormones
—
from three different kinds of cells called beta,alpha and delta cells respectively. (Note : Somatostatin from delta
cells is excluded from syllabus).
(1) secreted by beta cells checks rise of sugar level inblood. This it does in
two principal ways:
(i) Itpromotes glucose utilisation by thebody
(ii) It stimulates deposition of extraglucose of the blood as glycogeninliver andmuscles.
Under-secretionof insulin
Insufficientsecretionofinsulin causes diabetes (morecorrectly diabetes mellitusor
hyperglycemia). Theword "mellitus"means honey, referring to the passageOf sugar (glucose) in urine.
A diabetic person :
• has high concentration of sugar in blood (hyperglycemia — hyper : excess, glyce: sugar(glucose), emia : blood).
• excretes a great deal of urine loaded withsugar. feels thirsty becauseof the loss of water through
too much urination.
• loses weight and becomes weaker and weaker. In
certain cases,the person loses eye sight or Vision.
The usual treatmentby administering insulin
is not a cure, but only a method of supplying the
hormonewhich is notbeing produced by the pancreas.
Over-secretion of insulin
• Sugar level in the blood is lowered
(hypoglycemia,hypo : below).
• Brainmay enter a state of coma ifthe level
becomes tooloweven for a few minutes.Asimilarthing may happen to a
diabetic patient ifan overdoseof insulin is given
— the patient may become unconscious. This is called
insulin shock or hypoglycemia and a prompt biteof
sweet biscuits or sugar candy is helpful.
Remember
It is wrong to say "insulin converts glucoseto glycogen." Instead, "insulinenables the cells toabsorb
glucose and use itor convert it into glycogen."
(2) is secreted from alpha cells. Itstimulates the breakdown of
glycogen in the liver to glucose, thus it raises sugar level inthe blood.
4. The thyroid is a bilobed(butterfly-shaped)
structure situated in front of the neck just below
the larynx. The twolobes are joined by a
narrow isthmus (interconnection).Itsecretes two
hormones and . (Note
Calcitonin isnotincluded in the syllabus).
regulates the basal metabolism,
i.e., the rate of cellular oxidation resulting
in heat productionat rest. An increase in
the secretion increases metabolismand a decrease in secretion lowers it. Italso
influences thegeneral growthof the body, ossificationof bones, body
temperature, mental development, etc.
A. Undersecretion (Hypothyroidism) Insufficientsecretion of thyroxine may lead to 3 conditions
simplegoitre, cretinismand myxoedema.
(i) Simple goitre is the enlargement of thethyroid and is visibleas a swelling in the neck
This is dueto insufficient quantity of iodine in food. This condition is common in the people livingin
hilly regions where iodineis deficientin soil and hencein the food grown there.
(ii) Cretinismis a conditionwhich affectsthe growthof children showing dwarfismand mental
retardation. This is due to defective development, or early atrophy (degeneration) Of the thyroid.
(iii) Myxoedemais a condition that affects an adult if his thyroid does not function properly;in this
condition,the person becomes sluggish with swelling of the face and hands.
B. Oversecretion (Hyperthyroidism) : Excess of thyroxinesecretion may also cause
a kind of goiter called exophthalmic goiter (exo outward, ophthalmos : eye).
A person having the problem of over secretion shows
• a marked increase in metabolic rate,
• rapid heartbeat,
• shortness of breath;
• are protruded, and
• forms a goiter in the neck.
The pituitarygland is a smallprojection (about the sizeof a pea) which
hangs from the base of the mid-brainbelowhypothalamus. It is popularly called the master
gland because it seems to control practically all other endocrine glands.
Pituitary gland has 2 distinctlobes, the anterior pituitary and posterior pituitary (the entire
pituitary gland weighs only aboutone-half gram). The front part oftheposteriorpituitary is differentfrom therest of
the lobe and is called the intermediatelobe. The intermediatelobeis almostabsentin humans but much
larger and morefunctional in some lower animals.
5. A. HORMONES FROMANTERIORPITUITARY
Some important hormones producedby theanteriorlobeareas follows:
1. (GH) is essential for normal growth. Itis also called
(somatic:body, tropic:stimulating).
• The deficiency of GH inchildhood results in dwarfism. (Adwarf, though fully developed, retains body
proportions of a child.)
• The oversecretion in childhood results in gigantism; the longbones lengthen beyond normal and
human giants upto 2.7 metres in height are produced
• If oversecretion of the growth hormone suddenly occurs in an adult, there is an extragrowth
of bones in the face (particularly the jaws) and in the hands and feet. The person
develops a large nose and thick lips. This condition is called acromegaly (acro.t height/ extremity, megaly: large).
2. hormone(TSH) activates thyroid to secrete thyroxin.
3. (Gonadotropic) hormones regulatethe activities of the
testes andovaries.
4. hormone(ACTH) regulates the activity of adrenal cortex.
The term tropic hormones refers to such hormones which stimulate other
endocrine glands to producetheir specific hormonesuch as gonadotropic
hormones secreted by anterior pituitary and also stimulate gonads to produce
certain hormones. "Tropic"means influencing the activity of the named organ
such as thyrotropic (for thyroid), adrenocorticotropic (for adrenalcortex), etc.
B. HORMONES FROM POSTERIORPITUITARY
The posterior lobe produces two hormones
named vasopressin and oxytocin.
l. hormone(ADH), also called , constrictsbloodvessels
with rise inblood pressure. Italso acts on the kidney increasing reabsorptionof
water from the kidney tubules.
• Deficiency of ADH causes diabetes insipidus (water diabetes) in which urination
is frequent andcopious, resulting in loss of water from the body and the person
becomes thirsty.
Remember "Diabetes" means passing outexcessive amounts of urine. The two types
Of "diabetes" : In diabetes mellitus,the urine contains sugar caused dueto insufficientinsulin,butin diabetes
insipidus,thereis no sugar in urine."Insipid"means tasteless (blank) referringto the absenceOf sugar in urineand
"melli"means honey/sweet.
2. (Gk. oxys : sharp/quick, tokos . childbirth) stimulates vigorous
contractions of the uterus in a pregnantmother, leading to the birth of the baby.
Italso stimulates milk ejection.
6. CONTROL OF HORMONAL SECRETIONS
(Feedback mechanism)
(Commands like saying "TOO much, slowdown" or "Too little, speedup" I — This
is the feedback mechanism.
The body has a mechanismto maintaina normal state. Whenever thereis a
change in this state there are "messages"throughthe body systems to "increase
if there is a fall below the normal, or to "decrease" if there is a riseabove the
normal. This kind of ordering for the opposite is "negative feedback",to restore
the normalstate. Most feed- back mechanisms in our body are of this negative
type. Example: TSH level.
Positive feed-backmechanisms areVery few. Oneexample is that of uterine
contractions during childbirth. Normalstate of uterus is uncontracted, one
contraction instead of commanding to come to normal gives a message to
continue to contractfurther (positive feed-back till delivery is completed).
