The Endocrine System Class 10 ICSE Notes
ICSE Class 10 Biology Chapter 10 The Endocrine System Notes, Summary, Definition, Diagram. The Endocrine System Notes.
Endocrine glands- secrete certain chemicals known as hormones which regulate the body activities.
Hormones – secretions from specific cells or glands in the body and are carried to all parts through blood, but their effects is produced in one or more specific parts (target cells).
Hormones –
i.) Endocrine glands – secretion are poured directly into the blood and not through any special duct. Example – stomach and duodenum.
ii.) Endocrine glands – consists of several glands/glandular cells from which the hormones flows to organs. Example – pancreas and hypothalamus.
General properties of hormones –
i.) Hormones are secreted from their source directly into blood.
ii.) They regulate the physiological processes by chemical means.
iii.) They affect the enzymes systems of the body.
iv.) Act on target organs or cells
v.) Show similar influence in other species.
vi.) Some hormones are peptides, amides, steroids
vii.) Excess or deficiency may lead to serious consequences.
viii.) Hormones are not stored in body and are excreted from the system.
Endocrine glands
A.) Adrenal
i.) Central /adrenal medulla
– Secrete adrenaline (epinephrine and noradrenaline).
– Adrenaline prepares body to meet emergency situation (fight,fright,flight) – Function-
- Increase heart beat and increase in blood pressure
- Increase blood supply to muscles while decreasing it to skin and visceral organs.
- More glucose is released into blood by liver
ii.) Peripheral / adrenal cortex
– Secrete many hormone example cortisone (suppress inflammation)
– Cortical hormones –
a.) Mineralcorticoids – regulates mineral metabolism, specially Na+ and K+ ions.
b.) Glucocorticoids – regulates carbohydrate, protein and fat metabolism.
- Increase blood glucose concentration
- Influence fat and protein metabolism
- Regulate salt and water balance in body
- Adapt the body to “stresses” such as extreme heat or cold, burns, infections, etc.
c.) Sex corticoids- cotical hormones that behaves like sex hormones
→ Hyposecretion – from adrenal cortex causes Addison’s disease.
- Symptoms are loss of energy, skin pigmentation, loss of weight, nausea, hypoglycaemia (low blood sugar), sensitivity t cold and pain, increased susceptibility to infections, etc.
→ Hypersecretion – from adrenal cortex causes cushing’s syndrome .
- Symptoms are obesity, hypoglycemis (higher blood sugar), osteoporosis, weakness, salt and water retention
B.) Pancreas
→ Both a duct gland as well as ductless glands
→ Duct gland secrete – pancreatic juice into duodenum for digestion.
→ Ductless glands – hormone –secreting cells called Islets of Langerhans, which is scattered in the entire gland .
→ Islet cells –
i.) Insulin (secreted by beta cells) check rise of sugar in blood
→ Promote glucose utilisation by body cells, thereby reducing blood sugar level.
→ Stimulate deposition of extra glucose of blood as glycogen in liver and muscles.
→ Under-secretion of insulin =
– Insufficient secretion of insulin causes diabetes mellitus
– A diabetic person :
a.) Has high concentration of sugar in body
b.) Excretes a great deal of urine loaded with sugar.
c.) Feels thirsty because of loss of water through too much urination
d.) Loses weight and becomes weaker and weaker.
→ Over-secretion of insulin =
– Hypoglycaemia (Sugar level in the blood is lowered)
– Brain may enter a state of coma if the level becomes too low even for a few minutes.
ii.) Glucagon (secreted by alpha cells) stimulates the breakdown of glycogen in the liver to glucose, thus it raises sugar level in the blood
iii.) Somatostatin (from delta cells ) – inhibits secretion of insulin and glucagon.
C.) Thyroid-
→ Thyroid is bilobed (butterfly-shaped) structure situated in front of the neck just below the larynx.
→ Secretes thyroxine and calcitonin
→ Thyroxine regulates the basal metabolism. Also influences general growth of body, body temperature, mental development.
→ Undersecretion – (Hypothyroidism) – insufficient secretion of thyroxine may lead to
a.) Goitre (swelling of neck)- due to nsufficient quality of iodine in food.
b.) Cretinism (dwarfism and mental retardation) – affects children. This is due to defective develoment or early atrophy (degeneration) of thyroid.
c.) Myxoedema (sluggish with swelling of eyes and hands )-when thyroid doesnot work properly
→ Over-secretion (hyperthyroidism) – excess of thyroxine secretion may cause exophthalmic goitre.
– Shows-
– Increased metabolic rate
– Rapid heartbeat
– Shortness of breath
– Eyes are protruded
– Goitre in neck
D.) Pituitary-
→ Small projection present below hypothalamus.
→ Also known as master gland (as it controls all endocrine glands)
→ Weighs one-half grams
→ 2 lobes- anterior pituitary and posterior pituitary
I.) Hormones from anterior pituitary
a.) Growth hormone (GH)-
– Also called somatotropin
– Deficiency in childhood results in dwarfism
– Oversecretion in childhood results in gigantism
– Oversecretion suddenly in adults result excessive growth of bones in face,hand and feet , large nose and thick lips. This condition is called “ acromegaly”.
b.) Thyroid stimulation hormone (TSH)- activates thyroid to secrete thyroxin.
c.) Gonad stimulating (gonadotropic) hormone – regulate the activities of tesit and ovaries.
d.) Anrenocorticotropic hormone (ACTH)- regulates the activity of adrenal cortex.
II.) Hormone from posterior pituitary
a.) Antidiurectic hormone (ADH)
– Also called vasopressin
– Constricts blood vessels with rise in blood pressure.
– Acts of kidney increased reabsorption of water
– Deficiency causes diabetes insipidus (frequent urination resulting loss of water from body)
b.) Oxytocin
– Stimulates vigorous contractions of the uterus in a pregnant mother, leading to the birth of the baby.
– Stimulates milk ejection.
E.) Parathyroid
F.) Thymus
G.) Gonads
Control of Hormonal secretions (feedback mechanism)
→ If there is change in the body state, there are “messages” through wich they increase if fall below normal and decrease if rise above normal. This kind of ordering for the opposite is “negative feedback”, to restore normal state.
Most feedback mechanisms in our body are of this negative type.
Example : TSH level
When the level of thyroxine concentration exceeds the normal level in blood, then it inhibits the secretion of TRH by hypothalamus and the secetion of TSH from anterior pituitary gland.
→ Positive feedback – very few
Example- contraction of uterine during delivery
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