PANCREATIC ISLETS

Pancreas are both, exocrine as well as endocrine. the exocrine pancreas secrete pancreatic juice, while the endocrine pancreas consist of clusters of cells; known  as pancreatic islets present throughout the gland. the pancreatic hormones are secreted directly into the blood stream and circulated in the body; in the other hand, the exocrine pancreas follows a procedure.

There are main 3 types of cell available in pancreatic islets

• Alpha cells– they secrete glucagon
• Beta cells- they are present in large quantity and they secrete insulin.
• Delta cells– they secrete sematostatin.

The normal blood glucose level range is 3.5-8 mol/liter. To maintain this level of glucose in the body, insulin and glucagon works together but their action differs.

• insulin decreases the blood glucose level
• glucagon increases the blood glucose level.

INSULIN:- It is a polypeptide and consist of 50 amino acids. It function is to reduce the raised level of nutrients present in form of glucose, amino acids and fatty acids. These effects are known as anabolic, that is that they work for the storage purpose. when the glucose is present in excess, insulin is secreted which facilitates its storage. Insulin works by-

1.  Acting on the cell membrane and stimulate the uptake and use of glucose by  muscle and connective tissue.
2. Promotes the conversion of glucose to glycogen(glycogenesis)
3. Increases the use of amino acids and also promote protein synthesis
4. Promotes synthesis of fatty acids and its storage in adipose tissue
5. Decreases glycogenolysis (conversion of glycogen to glucose)

Secretion of insulin is stimulated by increased blood glucose level and parasympathetic stimulation. Secretion is decreased by sympathetic stimulation, glucagon, adrenalin, cortisol and somatostatin

GLUCAGON:- glucagon increases blood glucose level by-

•  promoting conversion of glycogen to glucose
• gluconeogenesis( formation of new glucose from protein)

Secretion is increased by reduced blood glucose level and sympathetic stimulation. secretion is inhibited by insulin and somatostatin

SOMATOSTATIN:- This hormone is also produced by hypothalamus. It inhibits the secretion of insulin, glucagon and growth hormone which is secreted in anterior pituitary.

PINEAL GLAND

The pineal gland is a small body attached to the roof of third ventricle of brain. It is connected to third ventricle by a short stalk of nerves, many of these nerves terminate in the hypothalamus. It is about 10mm long and is reddish brown in color and is surrounded by a capsule. It tend to atrophy(breakdown and reabsorption of tissue) after puberty.

Melatonin:- this is the main hormone secreted by pineal gland. Its secretion is controlled by daylight and darkness. The level of melatonin varies in each 24-hours; it is highest at night and lowest at the midday. its functions or association is with-

• inhibits the growth and development of sex organs before puberty, by preventing the synthesis or release of gonadotrophins.
• coordination of day and night rhythms of many tissue by influencing hypothalamus.

LOCAL HORMONES

a number of body tissues which are not described as endocrine gland but secrete substances which acts in tissue nearby, these are-

Histamine:- This is synthesized and stored by mast cells of tissues and also the basophils of WBCs in blood. It is released during the inflammatory response, during allergy and causes vasodilation. It also acts a neurotransmitter and causes contraction of smooth muscle of bronchi and alimentary tract which stimulates the secretion of gastric juice.

Serotonin:- this is present in the platelets, brain and intestinal wall. It causes intestinal secretion, contraction of smooth muscle and its role in hemostasis is to cause vasoconstriction. It is also a neurotransmitter in CNS and is also known to influence mood.

Prostaglandins:- These are lipid substances found in tissue. since they are quickly metabolized, they are short lived and act on near by cells. They have many physiological effects like-

1. inflammatory response
2.  fever
3. regulating BP
4.  blood clotting
5.  uterine contraction during labour

Multiple choice questions(MCQs)

1. Where are the pancreatic islets found?
A. exocrine pancreas B. adrenal gland
C. thyroid gland           D. endocrine pancreas

2. Which hormone is not secreted by the cells of pancreatic islets?
A. insulin B. glucagon
C. somatostatin D. none of the above

3. Where is the pineal gland situated?
A. roof of third ventricle B. roof of lateral ventricle
C. floor of third ventricle D. roof of fourth ventricle

4. Histamine is synthesized by?
A. mast cells B. platelets
C. goblet cells B. melanocytes

5. Match the following-
a. insulin              1. Causes vasodilation
b. melatonin        2. Increases blood glucose level
c. histamine        3. Decreases blood glucose level
d. glucagon         4. Inhibits the growth of sex hormone before puberty

6. What inhibits the secretion of insulin?
A. Sympathetic stimulation B. parasympathetic system
C. cortisol D. both A and C

7. What is the function of prostaglandins?
A. inflammatory response B. blood clotting

C. regulating BP D. all of the above

8. Which of the following statement is true?
A. insulin is a polypeptide consisting of 80 amino acids
B. histamine is synthesized by eosinophils
C. Prostaglandins are lipid substance
D. melatonin works for uterine contraction

9. Which of the following is not counted as a function of serotonin?
A. promotes intestinal secretion B. contraction of smooth muscle
C. vasoconstriction D. vasodilation

10. Which hormone other than insulin and glucagon is inhibited by somatostatin?
A. melatonin B. growth hormone
C. erythropoietin D. adrenaline

ANSWERS

1. endocrine pancreas
2. none of the above
3. roof of third ventricle
4. mast cells
5. a – 3 b – 4 c – 1 d – 2
6. both A and C
7. all of the above
8. prostaglandins are lipid substance
9. vasodilation
10. growth hormone

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REFERENCE: 1. Ross and Wilson-Anatomy and physiology in health and illness; 12th edition; page no.-: 226-229.