Chemical Coordination and Integration - Notes | Class 11 | Part 3: Thymus, Adrenals and Pancreas



It is located between lungs behind sternum on the ventral side of aorta. 

It secretes Thymosins (peptide hormones).

Functions of thymosins:
  • Differentiation of T-lymphocytes. It provides cell-mediated immunity.
  • Promote antibody production for humoral immunity.
Thymus is degenerated in old individuals. So, production of thymosins decreases. As a result, immune responses of old persons become weak.


It has 2 parts: Adrenal cortex & Adrenal medulla.

a. Adrenal cortex 

It has 3 layers: inner zona reticularis, middle zona fasciculata & outer zona glomerulosa.

It produces the following corticoid hormones:

o Glucocorticoids (mainly cortisol):
  • Involved in carbohydrate metabolism.
  • Stimulate gluconeogenesis, lipolysis and proteolysis.
  • Inhibit cellular uptake and utilization of amino acids.
  • Maintain cardiovascular system and kidney functions.
  • Cortisol stimulates RBC production.
  • Produces anti-inflammatory reactions and suppress immune response.
o Mineralocorticoids (mainly aldosterone):
  • Regulate the water (body fluid volume), electrolytic balance, osmotic pressure and blood pressure.
  • Aldosterone stimulates reabsorption of Na+ & water from renal tubules and excretion of K+ and PO43- ions.
o Androgenic corticoids: 
  • For growth of axial hair, pubic hair and facial hair during puberty.
Deficiency of corticoid hormones affects carbohydrate metabolism. It causes acute weakness and fatigue. This condition is called Addison’s disease.

b. Adrenal medulla 

Produces catecholamine hormones such as Adrenaline (epinephrine) & Noradrenaline (norepinephrine).

They are rapidly secreted in response to stress emergency situations so called emergency hormones (hormones of Fight or Flight).

These increase alertness, pupillary dilation, piloerection (rising of hairs), sweating, heartbeat, heart contraction and respiratory rate. Stimulate glycogenolysis to increase glucose in blood. Also stimulate lipolysis and proteolysis.


A composite (heterocrine) gland i.e. exocrine + endocrine.

Islets of Langerhans are the endocrine part. 

There are about 1-2 million Islets (1-2% of pancreatic tissue).

α cells and β cells in the islets secrete peptide hormones such as Glucagon and Insulin respectively. They maintain Glucose homeostasis in blood.


Hyperglycemic factor. It
  • Acts on hepatocytes and stimulates glycogenolysis resulting in an increased blood sugar (hyperglycemia).
  • Stimulates gluconeogenesis.
  • Reduces the cellular glucose uptake and utilization.

Hypoglycemic factor. It
  • Acts on hepatocytes and adipocytes to enhance cellular glucose uptake and utilization. So, glucose from blood rapidly moves to hepatocytes and adipocytes. Thus, blood glucose level decreases (hypoglycemia).
  • Stimulates glycogenesis (glucose converts to glycogen).
Prolonged hyperglycemia leads to Diabetes mellitus (loss of glucose through urine and formation of harmful compounds like ketone bodies). Treatment is insulin therapy.


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