BIOLOGY – CLASS X

THE ENDOCRINE SYSTEM

Q1. Define the following terms-

a. Endocrine glands- are the ductless glands which secrete chemicals called hormones

which are poured directly into the blood.

b. Hormones – are the secretions of the endocrine glands, which are transported by the

blood to the target cells.

c. Homeostasis – is a state of equilibrium produced by a balance of functions and of

chemical composition within the body of an organism.

Q2. Why are hormones often referred to as ‘chemical messengers’?

Hormones are produced in the body in response to changes in the environment within or

outside the body and thus help maintain homeostasis in the body of the individual.

Q3. List out the characteristics and functions of hormones

Hormones are secretions of the endocrine glands which are poured directly into the

blood.

They are produced in very small amounts.

Chemically, hormones may be proteins, polypeptides, amino acid derivatives or steroids.

Their action occurs in another part of the body far away from the source of production.

They are specific in their action –certain organs respond only to certain hormones.

Hormones help adjust and restore homeostatic balance.

They help the body cope with infections, stress, trauma, starvation and extreme

temperatures.

Q4. Differentiate between exocrine and endocrine glands.

Exocrine gland Endocrine gland

They are glands with ducts.

Their secretions maybe enzymes,

sweat, oil, or tears

The dutcs transport these secretions to a

region close to the source of

production.

Eg. Sweat gland, salivary gland

They are ductless glands

Their secrete chemicals called

hormones

They are transported by the blood to

target cells far away from the source of

production.

Eg. Adrenal gland, thyroid gland

Q5. Differentiate between hormones and enzymes.

Hormones Enzymes

Secretions of endocrine glands

Chemically maybe steroids, proteins or

amino acid derivatives

Transported by blood

Reaction occurs away from the site of

secretion in target cells or organs.

They may accelerate or inhibit specific

activity.

Their action may be slow or quick

Secretions of exocrine glands.

Chemically always proteins

Transported by ducts.

Reaction occurs close to the site of

secretion

Always accelerate chemical reactions

Their action is always quick.

Q6. Differentiate between nervous control and endocrine control

Nervous control Endocrine control

Works by the conduction of nerve

impulses.

Works rapidly.

Nerve impulse is conducted thorough

nerve fibres.

Effects of nerve impulses are shortlived

Does not influence chemical changes and

cannot regulate metabolism.

Does not affect growth.

THE ENDOCRINE SYSTEM

Works by release of hormones.

Works slowly.

Hormones travel via the blood.

It has a prlonged effect.

It brings about specific chemical

changes and regulates metabolism.

Affects growth

Question - Insulin is administered to individuals suffering from diabetes mellitus in the form of injection and not in the form of tablets. Answer- Insulin is proteinaceous in nature and hence undergoes digestion, if taken orally as a tablet. When injected, it is directly transported by the blood to the target cells.

PANCREATIC GLAND

EXOCRINE GLAND – these cells

produce pancreatic juice which

is transported by the

pancreatic duct to the

duodenum ( target organ)

ENDOCRINE GLAND- these cells

called the Islets of Langerhans

produce hormones which are

transported by the blood to the

target cells

LOCATION –below the

stomach, at the loop of

the duodenum

STRUCTURE – flattened leaf

like. Three types of cells are

differentiated in the Islets of

Langerhans. They are the

alpha, beta and the delta

cells.

FUNCTION

ALPHA CELLS secrete Glucagon. It converts the glycogen stored in the liver into glucose. It thus increases the glucose level in the blood. Secretion of glucagon is stimulated whenever there is a low level of glucose in the blood and while exercising.

BETA CELLS secrete Insulin. It converts the glucose in the blood into glycogen to be stored in the liver and muscles. It thus checks the level of glucose in the blood.

HYPOSECRETION- of insulin causes diabetes mellitus. In this disease the liver and muscle cells are unable to convert the glucose to glycogen, hence level of glucose in blood rises. This condition is also called Hyperglycemia. Symptoms- increased thirst , frequent urination, with presence of glucose in the urine (sweet or honey like).

HYPERSECRETION – increased secretion of insulin leads to hypoglycemia or decreased levels of glucose in the blood. If the glucose level falls too low, a person may enter into a coma state or may become unconscious. An excess intake can also cause this. Symptoms –weakness, tremor, sweating

ADRENAL GLAND Question: What is “Adrenal virilism”? Androgens are male sex hormones produced in the testes and in the adrenal cortex. It regulates secondary sexual characteristics in the male. Appearance of some male characters in the female is called virilism. Excess secretion of adrenal androgen in female produce male secondary sexual characteristics such as appearance of beard, low pitched voice and under developed breasts.

ADRENAL GLAND

LOCATION- fits like a cap above each kidney. OR Is found superior

to each kidney.

STRUCTURE- is

divided into an

outer adrenal

cortex and an

inner adrenal

medulla.

FUNCTION

ADRENAL CORTEX-secretes 3 hormones 1. Mineralocorticoids 2. Glucocorticoids 3. Sex corticoids

ADRENAL MEDUL LA – Secretes a hormone called Adrenalin or Epinephrine

ROLE OF ADRENALIN 1. Stimulates the breakdown of glycogen in muscles and hence increases glucose level in the blood. 2. Increases the contractility of muscles. 3. Helps body to adapt to various situations such as stress, trauma, fasting, starvation, etc 4. Is often called the “emergency hormone” or the “flight and fight hormone”.

Eg. Cortisones Regulates carbohydrate and protein metabolism

Eg. Aldosterone Regulates metabolism of K+

and Na+ ions. Stimulates kidneys to retain Na+and excrete K + ions

Eg. Androgens Stimulates the development of external secondary sexual characteristics in males and females

HYPOSECRETION ADDISON’S DISEASE Skin pigmentation Hypoglycemia Low energy levels

HYPERSECRETION CUSHING’S SYNDROME Moon face Buffalo hump Spindly legs Hyperglycemia

Hypersecretion of adrenalin

puts an individual through a

prolonged version of “fight or

flight response” which in the

long run wears out the body.

Note- In ageing thyroid, body activities slow down and heat production reduced. So, old tend to feel cold faster.

THYROID GLAND

STRUCTURE-

Butterfly shaped , bi-

lobed structure. The

two lobes are joined

by a narrow piece of

tissue called isthmus.

LOCATION –

situated on the

lateral and ventral

sides of the trachea,

just below the larynx

FUNCTION- secretes an hormone called thyroxin. Iodine is an important constituent of thyroxin. 1. This regulates the basal metabolism,(BMR) which is the rate of cellular oxidation ,resulting in heat production and energy formation when the body is at rest. 2. It regulates general physical and mental growth and development esp. in children. 3. It controls body weight.

HYPOSECRETION HYPERSECRETION

CRETINISM- caused due to under

secretion of thyroxin in the growth

years. This is characterized by low

metabolic rate, retarded physical,

mental and sexual development.

MYXOEDEMA-caused due to the under

secretion of thyroxin in an adult.

Symptoms include puffiness and

swelling(edema) of facial muscles due to

fluid retention. Low metabolic rate, low

body temp. and general lethargy.

SIMPLE GOITRE- caused

due to iodine deficiency in

one’s diet. It leads to an

enlargement of the thyroid

gland to step up production

of thyroxin. Hence it

manifests as a swelling in

the neck.

EXOPHTHALMIC GOITRE- Its symptoms

include protrusion of the eyeballs due to

fluid retention behind the eyes.

Metabolic rate becomes high, high body

temp. sweating, high blood pressure.

PITUITARY

GLAND

LOCATION –ATTACHED TO THE

HYPOTHALAMUS OR BELOW

THE HYPOTHALAMUS.

STRUCTURE - pea sized gland. Divided into a

larger anterior lobe and a smaller posterior

lobe. In between is an intermediate lobe

which is more developed in animals.

FUNCTION

ANTERIOR LOBE POSTERIOR LOBE

Tropic hormones –

stimulate other

endocrine glands to

secrete their hormones

Hgh or the human

growth or

Somatotropin

regulates normal

body growth

Oxytocin –stimulates

the contraction of

the uterine muscles

at child birth

Vassopressin or

ADH-Anti Diuretic

Hormone-regulates

the reabsorption

of water in kidney

tubules

TSH- thyroid

stimulating

hormone-

stimulates thyroid

gland to produce

thyroxin

ACTH- Adreno

cortico tropic

hormone-

stimulates the

adrenal cortex to

produce its

hormones

FSH -follicle

stimulating

hormone –

stimulates testes

to produce

sperms and

ovaries to

produce ova.

LH- Luteinizing

hormone –

stimulates the

testes to produce

testosterone and

the ovaries to

produce

progesterone and

oestrogen

Prolactin –

stimulates the

breasts to

produce milk

at child birth.

Hyposecretion in

the growing years

results in

dwarfism .

Hypersecretion in

growing years causes

gigantism. In an adult, it

results in Acromegaly –

disproportionate growth

of bones.

Hyposecretion causes

Diabetes insipidus or

excessive urine

formation which leads

to dehydration and

extreme thirst.