9. Endocrine system

ICSE 10> HUMAN ANATOMY AND PHYSIOLOGY> 9.ENDOCRINE SYSTEM

Scope of syllabus

Endocrine System: General study of the following glands: Adrenal, Pancreas, Thyroid and Pituitary. Difference in Endocrine and Exocrine glands.
Correct location and shape of the gland in the human body should be discussed along with the hormones they secrete (Pancreas: insulin
and glucagon to be taught; Thyroid: only thyroxin to be taught).
Effects of hypo secretion and hyper secretion of hormones must be discussed.
The term tropic hormones should be explained in the study of pituitary.
Brief idea of feedback mechanism must be given.

Class Presentation

Types of glands

Human body has two types of glands based on the presence of ducts-

Exocrine glands-
These are glands with ducts Release their secretions through these ducts, like salivary gland and sweat gland.
Present near site of action.
Secretions are normally enzymes.

Endocrine glands-
These are glands without ducts Release their secretions directly into blood vessels, like thyroid and adrenal.
Present far away form site of action
Secretions are hormones.

Endocrine glands release hormones in the blood stream, that travels throughout the body and reach the target cell.
Hormones-

chemical messengers secreted by the endocrine glands.
they are released directly into the blood stream.
they act at a site away from where they are secreted.
they act on specific target tissue or organ.
they modify and regulate the activity of target tissue/organ.
they are secreted in small quantities.
deficiency of hormone can lead to disorders.

http://resource.rockyview.ab.ca/t4t/bio30/images/m2/b30_m2_021_l.jpg

list of endocrine glands-

Pituitary gland

Location- in the brain attached to hypothalamus
Pear shaped
Divided into three lobes –

Anterior pituitary –pars anterior
Intermediate lobe or pars intermedia
Posterior pituitary-neurohypophysis or pars nervosa

Pituitary is connected to the hypothalamus by a stalk called INFUNDIBULUM.
It is connected by the hypothalamo-hypophysial portal system and axons of hypothalamic neurons.

Anterior pituitary

Tropic hormones- These are hormones that activate other endocrine glands to release their hormones or act on target organs.

Thyroid stimulating Hormone (TSH) or Thyrotropin
Adrenocorticotropic Hormone (ACTH)
Follicle stimulating hormone (FSH)
Lutenizing hormone (LH) –In Females,
Interstitial Cell Stimulating Hormone (ICSH)- In Males.
Somatotrophic Hormone or Somatotrophin or Growth Hormone

Non tropic hormone-

Prolactin or Lactogenic or Luteotropic hormone.

Posterior pituitary

Posterior pituitary is an extension of the hypothalamus connected by nerve fibers.
It does not secrete any hormone, it stores and releases the hormones secreted by the hypothalamus.
The hormones released by posterior pituitary are-
1. Anti-diuretic hormone or vasopressin.
It stimulates re-absorption of water from the kidneys and increases blood pressure by acting as a vasoconstrictor.
2. Oxytocin or pitocin.
It stimulates contraction of uterine muscles during child birth and milk ejection from mammary glands.

How are the hormone levels regulated?

Feedback mechanism
The endocrine hormones are regulated by feedback mechanism.
The hormones released by the target gland regulates its further production. This effect may be positive or negative.
In positive feedback the endproduct stimulates the secretion of the releasing factor.
In negative feedback the endproduct inhibits the secretion of the releasing factors.
The feedback mechanism can be-
By hormones- when the increase or decrease in the target gland hormone acts as inhibitor or stimulator respectively.
By metabolites- the blood metabolite level control the hormone release.
By nervous control- Adrenal medulla hormones are controlled by the sympathetic nervous sytem.

Somatotrophic hormone or Somatotrophin or growth hormone
It is secreted by the anterior pituitary.

Stimulates body growth by stimulating mitosis.
Stimulates retention of proteins and calcium in the body.
Helps in growth of long bones.

Hyposecretion of STH (hGH)
Decrease in secretion during childhood.
Causes dwarfism- stunted growth of bones and other body organs.

Hypersecretion of STH (hGH)
Oversecretion from childhood
Causes gigantism - abnormal elongation of all bones, produces giant size persons called pituitary giants.
Over secretion of GH after adolescence, causes acromegaly. They are called disproportionate giants, elongation of certain body parts like hands, feet and jaws.

Vassopressin or Antidiuretic hormone
It acts on the kidney and stimulates reabsorption of water, thereby reducing the loss of water through urine.
It also causes narrowing of arteries acting as a vasoconstrictor.Hyposecretion causes Diabetes insipidus.
Large amounts of urine excreted, dehydration and thirst.

THYROID GLAND

It is a butterfly shaped gland, consisting of two lobes connected by a strip of connective tissue - isthmus
Location- Either side of the trachea, in front of larynx.
The thyroid secretes two main hormones-
Thyroxine
Triiodothyronine

Functions of the hormone-
Regulate the basal metabolic rate (BMR).
Essential for normal development of brain and mental alertness.
They also promote normal skeletal growth.

Hypothyroidism

1. Cretinism in children
Retarded mental & physical growth
Immature sexuality &retarded sexual characters

2. Myxoedema or Gull’s disease in adults
Low BMR, body temperature & BP
Mental, physical dullness & loss of memory
Degenerated sex organs

3. Simple Goitre
Enlargement of thyroid due to deficiency of iodine in food.

Hyperthyroidism

Increased BMR, High body temperature, increased heart rate, damage to heart, muscles, leading to heart failure mental restlessness & increased irritability.
Osteoporosis
Exopthalmic Goiter or Graves disease

Adrenal glands

Adrenal glands are triangle-shaped glands located on top of the kidneys. Each adrenal gland is approximately 3 inches wide, and a half inch high.
Each gland is divided into an outer cortex and an inner medulla.
The cortex and medulla of the adrenal gland secrete different hormones.

Hormones of adrenal cortex:
1. Glucocorticoids
•Cortisol- metabolism of carbohydrates, fats &protein •Construction of blood vessels during excessive bleeding
2. Mineralocorticoids
•Metabolism of Na & K & water balance. •Aldosterone reduces removal of Na but increases K elimination •Retention of Na in blood increases absorption of water & increases blood vol.
3. Sex steroids
•Proper functioning of sex organs & development of sex character. •Androgens and estrogens

Hyposecretion of cortisol & aldosterone
•Causes Addison’s disease
•Bronze like pigmentation of skin
•Muscular weakness, low BP, low blood sugar, odema, nausea, insomnia, diarrhea etc.

Hypersecretion:
Excessive cortisol
•Cushing’s syndrome •Excessive deposition of fat on face (obesity) •In males –hirsutism-excessive body hair growth In female- masculinisation-growth of beard, moustache etc.
Excessive aldosterone
•Aldosteronism/Conn’s syndrome •High plasma Na, low K+ •Increase blood volume & BP, muscular weakness •polyuria (excessive urination)
Excessive adrenal androgens
•Adrenal virilism / adreno-gential syndrome •Reversal of sex characters in adults •Female tend change to males uterus & ovaries degenerate.

Hormones of the adrenal medulla
Two hormones:
1.Non Adrenaline- (Non Epinephrine)
•Regulates BP, transmits nerve impulse
2. Adrenalin (Epinephrine)
•Secreted during emergency like emotional stress, anger, fear & grief.
•Vasoconstrictor
•Carbohydrate metabolism
•Bronchodilating treatment of Asthma

The Pancreas

pancreas is an oblong flattened gland located deep in the abdomen sandwiched between the stomach and the spine The pancreas is made up of glandular tissue and a system of ducts
The endocrine (endo= within) cells of the pancreas produce and secrete hormones into the bloodstream. The pancreatic hormones, insulin and glucagon, work together to maintain the proper level of sugar in the blood. This part is called islets of Langerhans.
Secretes two hormones
1.Insulin (beta cells) –Lowers blood glucose –Induces protein synthesis –Induces synthesis of enzymes converting glucose – glycogen –
Deficiency •Diabetes mellitus •Hyperglycemia •Diuresis
2.Glucagon (alpha cells) –changes liver glycogen-glucose –forms glucose from amino acid –increases blood glucose level

Diabetes mellitus
Caused due to decrease in insulin levels.
Results in hyperglycemia

Diabetes insipidus
caused due to decrease in ADH levels
results in excess urination