Pineal Body & Pancreas | Biology for JAMB PDF Download

Pineal Body

Position

• It is situated at the dorsal side of diencephalon of anterior part of brain i.e. prosencephalon. It is also known as Epiphysis cerebri. Pineal body is a part of brain. It is ectodermal in origin.
• There are pinealocyte cells (formed by the modification of nerve cells) and supporting interstitial cells or neuroglial cells in pineal body.
• Pineal body called as third eye in frog.

Hormone & Functions 

• Pineal body secretes a hormone melatonin, which is an amino acid.
• Melatonin is functional in lower vertebrates only.
• In amphibians and reptiles, this hormone is related with metachrosis (change in the colour of skin). It affects the Melanophores of skin, thus acts antagonistically to the MSH of pituitary i.e. it fairs the complexion of skin.
• Mid part of gland secretes antigonadial hormone.
• This hormone controls the sexual behaviour in mammals. It inhibits the sexual irritation, and also inhibits the development of genitalia and their functions.
• If pineal body is removed from rat, these will attain premature adolescence.
• The gland probably controls the sexual behaviour according to light differentiation, thus it acts as a biological clock.
• It is proved that the level of melatonin rises during periods of darkness and falls during periods of light.
• Children blind from birth attain puberty earlier than normal.
• Maximum development of pineal body upto 7 years & then it undergoes involution & at the age of 14 years interstitial tissue and crystals of CaCO3 or Ca3PO4 are deposited in it, these are called "Brain sand" or "Acervuli"

Pancreas

Position 

These are exocrine in nature. There are found numerous small endocrine glands scattered in between the acini, these small endocrine glands, are called Islets of Langerhans. They form only 1% part of the gland. These were discovered by Langerhans.

Each Islet of Langerhans has 4 types of cells. They are:

(A) Alpha cells (α - cells) : These are the largest cells present in peripheral region these are approximately 25% of the total cells. They secrete glucagon hormone.

(B) Beta cells (β- cells) : These are the small cells present in central region. These are about 60–65% part of total cells. They secrete Insulin hormone.

(C) Delta cells (d - cells) OR Gamma cells (g - cells) : These cells are found in middle region. These are about 10% part of total cells .They secrete somatostatin hormone which regulates the activities of α-cells and β - cells.

(D) F cell or PP– cells : Along with above mentioned cells, some other cells are also found in islet of Langerhans, these are called PP - cells which secrete pancreatic polypeptide hormone.

(1) Insulin 

• It was first prepared/found by Banting and Best.
• Molecular structure of insulin was given by A.F. Sanger (with the help of cow's insulin) The term insulin was also given by A.F. Sanger.
• Insulin is the first protein that is artificially synthesized in lab and is crystallized.
• Human insulin was synthesized by "Tsan"
• One molecule of Insulin is made up of 51 - amino acids that has 2 chains.
  (i) α - chain - It is made up of 21 aminoacids
  (ii) β - chain - It is made up of 30 amino acids. Both the branches or chains are bind together with cross bonds of disulphide bonds.
•  "A.F. Sanger"  was awarded by Noble Prize for it.

Functions of Insulin Hormone 

(I) Actions on cell membrane permeability.

(II) Actions on metabolism of : Carbohydrate, Protein, Fat, Nucleic acid, Mineral.

Hyposecretion of Insulin 

• Due to hyposecretion of insulin, body cells cannot use the sugar stored in blood. 
• So amount of sugar is increased in blood and this disease is called "Diabetes mellitus" or sugar disease. 
• In this disease, concentration of glucose in blood is increased from normal concentration.
• World diabetes day - 14 November

• Glucose is excreted through urine, if amount of glucose is in excess in the blood, this is known as "Glycosuria".
• In this stage. amount of glucose in blood increases upto > 180 mg./dl. of blood.
• The amount of water increased (in this stage) in the urine, so intervals of urination gets reduced, it is called polyuria.
• Polydipsia :- Due to excess excretion of urine (Urination at short intervals) probability of dehydration is enhanced.
• The patient feels thirsty, and there is a continuous loss of electrolytes from the body. 
• Polyphagia : excessive hunger.
• Due to active and incomplete decomposition of fats in fatty tissues, ketone bodies are formed. These ketone bodies are acetone, aceto acetic acid and beta hydroxy butyrate. Due to increased amount of these ketone bodies ketoacidosis starts in the body. These bodies are poisonous.
• The combined effect of ketoacidosis, dehydration and hyperglycemia may cause diabetic comma to the patient, patient becomes unconscious and even may die.
• Insulin hormone is given to the patient by injection in this disease, Insulin given orally is not effective, because it digests in the alimentary canal like protein.
• Now a days, oral insulin is used in following states :-
  (A) IZS - Insulin Zinc Suspension.
  (B) PZI - Protamine Zinc Insulin.

Hypersecretion of Insulin

• Due to hypersecretion of insulin, amount of glucose decreases in blood. It is called hypoglycemia.
• In hypoglycemia stage, body cells take more and more glucose from blood. So need of glucose for nervous system, retina of eye, genital epithelium is not fulfilled, as a result of that patient looses its reproductive power and sight. Due to excess irritation in brain cells, patient feels exhausted, unconsciousness, Cramps, and at last patient may die.
• "Insulin shock" - At the time of physical labour or fasting, if a diabetic patient takes an insulin injection, sugar level in blood reduces quickly up to 40 mg/100ml of blood. It is called insulin shock. The patient may be unconscious or even may die. 

(2) Glucagon

• This is secreted by α-cells.
• It was discovered by "Kimball and Murlin." 
• Glucagon is a hyperglycemia factor.
• It is made up of chain of polypeptide 29 amino acids.
• It is antagonistic to insulin. It is secreted by the gland, when sugar level of blood reduces.
• Glucagon hormone increase the amount of sugar (glucose) in blood.
• It stimulates gluconeogenesis in liver, as a result of that amount of glucose in the blood increases.
• It stimulates lipolysis of fats in fatty tissues.
• It decomposes the glycogen into glucose in liver i.e. it stimulates "glycogenolysis" in liver.
• The secretion of insulin and glucagon is controlled by a limit control feed back. When amount of sugar is increased in blood, then insulin is secreted by β-cells. As a result of it, when amount of glucose is reduced in blood, then glucagon is secreted by-cells. 

(3) Somatostatin

(4) Pancreatic Polypeptide (PP)