12th Zoology



The endocrine part of the pancreas consists of specialized groups of
cells known as Islets of Langerhans. These cells synthesize, store and
secrete two hormones namely insulin and glucagon. There are two kinds of
cells namely, alpha and beta cells. The alpha cells produce glucagon while the beta cells secrete insulin. In addition to alpha and beta cells another type
of cells called delta cells are present in human pancreas. According to some
investigators the delta cells represent the transitional forms of the two cell
types alpha and beta.

Insulin (Pancreas)

Insulin is a protein hormone or a polypeptide hormone with 51 amino
acid residues. Human insulin has a molecular weight of 5,734 daltons. It
consists of two chains A and B, which are linked together by disulphide bridges
formed between two cystine residues.

Physiological effects of Insulin

It decreases glucose level in the blood in three ways:
a. It increases conversion of glucose into glycogen and deposition of it in
liver and muscles.
b. It increases the rate of oxidation of glucose in the tissues.
c. It increases the rate of conversion of glucose into fat and facilitates its
storage in adipose tissue.
d. It also regulates the rate at which amino acids are catabolised into water
and CO2.
e. Moderately, it also regulates the gluconeogenesis in the liver.

Thus, insulin reduces the glucose level in the blood (Hypoglycemia).
If the insulin is not secreted sufficiently, the liver and the muscles are unable
to convert the glucose into glycogen. As a result more glucose enters into the
bloodstream raising the blood sugar level. This condition is called
Hyperglycemia. The excess of glucose is eliminated along with the urine
resulting in a disease called diabetes mellitus. A diabetic patient excretes
large amount of urine (polyurea) and consumes excessive fluid
(polydipsia). He always feels hungry and eats excessively (polyphagia).
When insulin levels are low, fat catabolism is increased and fats are
converted into glucose. This further increases blood glucose levels and
results in the accumulation of ketone bodies (Ketosis). (Pancreas)


The normal fasting blood glucose level is 70 to 110 mg/dl
(dl = deciliter). This range is maintained under varying conditions of food
intake, fasting or body exercise. After a carbohydrate meal the blood sugar
may reach a peak level of about 140mg/dl. If such a high level is maintained
for a prolonged time, the condition may be termed as hyperglycemia.
Hyperglycemia over a long period may cause degenerative changes in several
organs and systems leading to malfunctions and mortality. Elevated blood
sugar level of 400 mg/dl or more, in a few days causes dehydration leading
to coma and death. (Pancreas)


It means a low plasma glucose concentration. This concentration can
drop to very low values during fasting. It is termed as fasting hypoglycemia.
It may result due to excess of insulin or other physiological factors. There is
no fixed level of blood sugar at which hypoglycemia occurs.
Fasting hypoglycemia may show symptoms such as hunger, increased
heart rate, tremulousness, weakness, nervousness and sweating. These are
caused due to activities of the sympathetic nervous system. Other symptoms
such as headache, confusion, uncoordination and slurred speech are due to
availability of too little glucans to the brain. Serious brain defects such as
convulsions (epilepsy) and coma can occur if the plasma glucose
concentration goes low. (Pancreas)

Diabetes Mellitus

The name ‘diabetes’ in Greek means ‘syphon’ or ‘running through’.
This term describes the enormity of urinary volume excreted by people suffering
from this disease. A persistant hyperglycemia leads to
diabetes mellitus. This disease can be due to a deficiency of insulin or to a
hypo responsiveness to insulin.
In type I (insulin dependent) diabetes, the hormone is completely
or almost completely absent from the islets of Langerhans and the plasma. In
type II (insulin-independent) diabetes, the hormone is often present in plasma
at near normal or even above normal levels. (Pancreas)

The type I is less common. It is due to the total or near total destruction
of the pancreatic b cells.

The type II is due to insulin resistance. The insulin target cells do not
respond normally to the circulating insulin. This may result due to obesity,
over-eating and lack of exercise. The insulin hyporesponsiveness can be
corrected if the person reduces his or her caloric intake. Thus dietary control
without any other therapy is frequently sufficient to eliminate the elevated
blood glucose level of type II diabetics. An exercise programme is also
useful, since it will help to increase the number of insulin receptors.


Glucagon, secreted by the alpha cells of the pancreas is a polypeptide
hormone with 29 amino acids residues.

Physiological actions of glucagon

The major function of glucagon in the body is to elevate the blood
glucose level by glycogenolysis in the liver. As it raises the blood sugar level
it is also called as Hyperglycemic hormone. A second important function of
glucagon is the gluconeogenesis in the liver in which amino acids are used as
substrates. It promotes lipolysis and the release of fatty acids in the adipose
tissues. The increased fatty acid oxidation leads to ketogenesis. Glucagon
also stimulates the myocardial contractility. Glucagon exerts a direct effect
upon the kidneys and accelerates the renal plasma flow and glomerular
filtration rate. A proper balance between insulin and glucagon production is
necessary to maintain proper blood glucose level. (Pancreas)

Related Topics in Zoology:

Bio Zoology All Important Topics

  1. Human Physiology Introduction

  2. Nutrition

  3. Carbohydrates Poly hydroxyaldehydes (or) ketones

  4. Proteins (Polypeptides)

  5. Lipids

  6. Vitamins – Functions Of Vitamins

  7. Deficiency of Vitamin

  8. Minerals – Water – Role of water

  9. Balanced diet

  10. Obesity

  11. Digestive System

  12. Dental Caries (Tooth decay)

  13. Root Canal Treatment

  14. Peptic ulcer

  15. Hernia and Types

  16. Appendicitis (Appendix)

  17. Gall Stones

  18. Hepatitis

  19. Fractures – Types of fractures

  20. Mechanism of fracture

  21. Dislocation of joints

  22. Arthiritis

  23. Rickets and Osteomalacia – Orthopedics

  24. Muscles

  25. Mechanism of muscle contraction

  26. Types of muscle contraction

  27. Myasthenia Gravis

  28. Respiration – Process of pulmonary respiration

  29. Mechanism of Breathing

  30. Regulation of Respiration

  31. Pneumonia Tuberculosis Symptoms Treatment

  32. Bronchitis – Acute bronchitis, Chronic Bronchitis Causes

  33. Circulatory System – Functioning of Human heart

  34. Cardiac Cycle

  35. Coronary blood vessel and its significance

  36. Myocardial infarction

  37. Angina pectoris

  38. Angiogram – Angioplasty

  39. Atherosclerosis

  40. Heart block Echo cardiography Heart Valves

  41. Rheumatic Heart Disease (RHD), ICCU – (Intensive Coronary Care Unit)

  42. Blood Pressure

  43. Heart transplantation

  44. Pulse rate

  45. Cardio Pulmonary Resuscitation (CPR)

  46. Blood – Composition of plasma – Blood cells

  47. Clotting of Blood or Haemostasis

  48. Thrombosis

  49. Nervous system Co-ordination systems

  50. The Brain – Fore Brain, Midbrain, Hindbrain

  51. Memory

  52. Sleep – Types of sleep

  53. Stroke – Brain haemorrhage

  54. Alzheimer – Meningitis (Brain fever)

  55. Conditioned reflex

  56. Electroencephalography EEG

  57. Right and Left brain concept

  58. Spinal cord functioning

  59. Chemical co-ordination – Functions of Endocrine glands

  60. Hypothalamus

  61. Pituitary gland – hormone

  62. Hormones of Neurohypophysis – vasopressin

  63. Thyroid gland

  64. Parathyroid Gland

  65. Pancreas

  66. Adrenal gland

  67. Gonads

  68. Receptor Organs – Eye

  69. Photochemistry of Retinal visual Pigments

  70. Errors of refraction

  71. Optometry – Retinopathy

  72. Cataract – Lens Replacement – Glaucoma – Nyctalopia

  73. Eye Infections and Eye Care

  74. Ear

  75. Mechanism of hearing

  76. Defects of the ear

  77. Hearing Aid – Noise pollution

  78. Skin and functions of skin

  79. Melanin functions

  80. Effects of solar radiation / UV radiation – Skin grafting

  81. Dermatitis

  82. Tongue – Mechanism of Stimulation

  83. Excretion Ureotelism Nephron

  84. Mechanism of urine formation

  85. Renal Failure, Dialysis, Kidney Machines

  86. Kidney stone – Kidney transplantation

  87. Diabetes mellitus

  88. Functioning of male reproductive system

  89. Functioning of female reproductive system

  90. Ovulation and fate of the ovum – Menstrual cycle

  91. Fertilization

  92. Birth control

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