Presented By
R.Ramya

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ISLETS OF LANGERHANS,PINEAL GLAND,THYMUS GLAND
ENDOCRINE PANCREAS
FUNCTIONAL ANATOMY:
 The endocrine part of the pancreas comprises numerous rounded collection of cells known as pancreatic islets or the islets of langherhans. These are embedded within the exocrine part.
 These are approximately 1 million islets in the pancreas, most numerous in the tail, and they constitute 1 to 5% of the human pancreatic mass.
ISLETS OF LANGERHANS :
The islets are very richly supplied with the blood through dense capillary plexus (as in all ductless glands) and inervated by vagal and sympathetic fibres.
HUMAN PANCREAS
CELLULAR STRUCTURE:
Each islets contains, an average 2500 cells which are of four types and arranged as:
 Beta(β) cells, make up to 60 to 70% of the total cells, and the constitute the central core of the islet. These cells secrete insulin.
 Alpha(α) cells, form about 20% of the total cells and constitute the outer rim of the islet. These cells secrete glucagon.
 Delta(δ) cells, form about 10% of total cells and are intermixed. These are the source of somatostatin.
• PP cells(F cells) : These are also pheripherlly placed scattered amongst the α cells. These are source of pancreatic polypeptide.
Gap junctions page link β cells to each other , α cells to each other, and β cells to α cells for rapid communication
FUNCTIONS OF INSULIN:
• Insulin secreted by the β cells is a polypeptide containing 51 amino acids with molecular weight of about 5807.
• Main functions is to lower the raised blood glucose levels.
• Proinsulin, is transported from the endoplasmic reticulum to the Golgi complex where it is packaged into granules and cleaved into insulin and residual connecting peptide, or c peptide.
Glucose is in excess of immediate needs insulin promotes their storage by:
• Acting on cell membrane and stimulating uptake and use of glucose by muscle and connective tissue cells.
• Increases the conversion of glucose to glycogen(glycogenesis) especially in liver and skeletal muscles.
• Promoting synthesis of fatty acid and storage of fat in adipose tissue (lipogenesis).
• Decreases glycogenolysis and prevents breakdown of protein and fat.
Major Stimulants:
• Increase blood glucose levels
• Parasympathetic stimulation
• Raised blood amino acid and fatty acid
• Gastrointestinal harmones (eg. Gastrin, secretin and cholecystokinnin-pancreozymin cck-pz )
• Sulfonylurea compounds and β-sympathetic fibres
Major inhibitors:
• Sympathetic stimulation
• Glucogon, adrenaline, cortisol and somatostatin(secreted by the pancreatic δ cells)
• Amylin,pancreastatin and α-sympathetic fibres
Insulin deficiency - diabetes mellitus
Diabetes mellitus is a disorder in which the following features are present : polyuria, polydipsia, polyphagia but weight loss, hyperglycemia and glycosuria.
Insulin excess – hypoglycemia
 affects cortical function, discharge of sympathetic nervous system.
 causes increase in the secretion of adrenaline, glucagon,glucocorticoids and growth harmone, all of which increase the blood sugar.
GLUCAGON:
 Glucagon is secreted by α cells of islets of langherans is a single chain polypeptide, composed of 29 amino acids of molecular weight 3500.
 Main function is to increase the blood glucose level.
ACTION OF GLUCAGON:
 Increases blood sugar levels by glycogenolysis.
 Promotes lipolysis.
 Stimulates the secretion of insulin, growth harmone, pancreatic somatostatin and hepatic bile secretion.
 Increases myocardial contractility.
Major stimulants:
 low blood glucose levels
 Amino acids,cholinergic fibres and β-sympathetic fibres
 Exercise
Major inhibitors:
 Somatostatin and insulin
 Glucose
 α- sympathetic fibres
SOMATOSTATIN
 Pancreatic somatostatin is a neuropeptide containing 14 amino acid, synthesized by δ cells and also by intestinal cells.
ACTIONS:
 Inhibits the secretion of glucagon and insulin.
 Increases the motility of stomach, deodenum and gall bladder.
 Decreases secretion of Hcl, pepsin, gastrin, secretin, intestinal juices and pancreatic juices.
 Inhibits absorption of glucose, xylose and triglycerides across the mucosal membrane.
 Inhibits the release of growth harmones and almost all peptides.
 Inhibits gastric,pancreatic and biliary secretions.
 Used to treat both endocrine and exocrine functions.
PANCREATIC POLYPEPTIDE:
Pancreatic polypeptide has 36 amino acids synthesized by PP cells of islets.
ACTIONS:
 Inhibit exocrine pancreatic secretion.
 Increases the plasma levels of PP serve as markers for the presence of islet cell tumuors and response to treatment.
 A failure of plasma pancreatic polypeptide to increase when plasma glucose is sharply reduced suggest the loss of cholinergic pancreatic islets innervations.
PINEAL GLAND
 Pineal gland is also known as epiphysis.
 It is a small structure (5mm*7mm)
 It shaped like a pine cone.
 It is situated in the groove between the superior colliculi in diencephalic area of the brain above the hypothalamus
 It forms the posterior boundary of third ventricle and lies the posterior end of corpus callosum.
 It has a stalk which divides anteriorly into two laminae.
 The superior lamina contains the habenular commissure while the inferior lamina has the posterior commisure.
The pineal stroma has two types of cells:
Neuroglial
Parenchymal
• Parenchymal cells of the pineal synthesize and secrete an indole called melatonin from serotonin, which is derived from the essential amino acid tryptophan.
MELATONIN RECEPTORS:
It has two types of receptors:
 ML-1 : high affinity melatonin binding site.
 ML-2 : low affinity melatonin binding site.
FUNCTIONS OF MELATONIN:
 It has a important role in circardian rhythm of the body.
 Both inhibitory and facilitatory effects of melatonin on the gonads are described depending upon the species.
 An inhibitory effect of melatonin, on MSH(melanocyte stimulating harmone) and ACTH( cortico trophic harmone) secretion has reported.
 Other actions of melatonin include the induction of sleep, and inhibition of puberty.
ABNORMALITIES:
 Pineal gland tumours (pinealomas) are rare.
 Increase melatonin secretion causing delay in puberty.
 Decrease melatonin secretion causing precocious puberty.
 Because of the location, large pineal tumours cause accumulation of cerebrospinofluid and increase in intracranial pressure, and neurological symptoms.
THYMUS GLAND
FUNCTIONAL ANATOMY:
 Thymus is a small lymphoid structure located in the lower part of the neck in front of the trachea, below the thyroid gland.
 At birth, it is small (weighing 10-12gm), gradually increases till the puberty when it weight 20-30gm, and then it starts decreasing in size and in the old age weighs about 3-6 gm.
 The sex glands exerts a depressed effect on the thymus, therefore, castration(removal of gonads) prolongs the period of persistance of the thymus.
Thymus consists of inner medulla and outer cortex.
(i)Medulla : It comprises reticular epithelial cells, a few lymphocytes and
concentric corpuscles of Hassall.
(ii)Cortex : it includes actively multiplying, closely packed lymphocytes and contains no Hassall’s corpuscles
Thymus has two functions:
 Immunological functions
 Endocrinal functions
IMMUNOLOGICAL FUNCTIONS:
 Formation of blood cells.
 Development of immunologically competant T-lymphocytes is the essential function of thymus.
ENDOCRINAL FUNCTIONS:
Thymus tissue secretes two harmones, thymosin and thymin.
 THYMOSIN : It is a peptide, promotes proliferation of T-lymphocytes in the thymus and pheripheral lymphoid tissue.
 THYMIN : It is also called thymopoietin, inhibits acetylcholine release at motor nerve ending and thus suppresses neuromuscular activity.
ABNORMALITIES:
Hyperactivity of Thymus occurs myasthenia gravis.
 Effect of removal of Thymus:
Thymectomy in new born mice causes:
 Reduction in number of lymphocytes in blood and lymphoid tissues.
 loss of cell-mediated immune response (due to deficiency of T cells).
 Decrease ability to produce antibodies. The animals succumb to infection.
 Failure to grow at normal rates, and development of a wasting diseases.