Endocrine System 1

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Hormones of the Endocrine System

Pineal Gland

The pineal gland secretes melatonin.
  • Sets diurnal rhythm (circadian rhythm)
  • Contributes to Seasonal Affective Disorder
  • Inhibits reproductive functions until puberty
  • Antioxidant: protects CNS neurons from free radical injury

Anterior Pituitary Gland

The anterior pituitary gland secretes:

Growth Hormone
  • Stimulates cellular growth
  • Regulates metabolism
  • Increases protein synthesis, protein catabolism and uptake of amino acids
Thyroid Stimulating Hormone
  • Controls secretions and activities of thyroid gland
Follicle Stimulating Hormone
  • In males: stimulates sperm maturation
  • In females: stimulates follicle development and oestrogen secretion
Lutenizing Hormone
  • In males: stimulates leydig cells to synthesise androgens
  • In females: stimulates ovulation and oestrogen and progesterone secretion
Prolactin
  • Stimulates mammary gland development
  • Initiates and maintains milk production by mammary glands
Melanocyte Stimulating Hormone
  • Stimulates melanocytes to secrete melanin, which darken the skin
  • Is in circulation during foetal development, childhood and pregnancy
ACTH (Adrenocorticotrophic hormone)
  • Stimulates the adrenal cortex to release glucocorticoids

Posterior Pituitary Gland

The posterior pituitary gland secretes two hormones.

Anti-Diuretic Hormone (ADH)
  • Decreases water lost at kidneys
  • Increases blood pressure and volume
Oxytocin
  • Stimulates the smooth muscle in the uterus
  • Stimulates contractile cells in mammary glands
  • Secretion and milk ejection

Thyroid Gland

The thyroid gland secretes thyroid hormone (T3 and T4). Thyroid hormone functions to:
  • Consume energy
  • Produce heat
  • Degrade liver glycogen stores, fat stores and muscle protein
  • Increase cardiac output and workload
  • Increase sensitivity to sympathetic stimulation
  • Maintain sensitivity to O2 and CO2 levels at respiratory centres
  • Stimulate RBC production
  • Accelerates bone mineral turnover
The thyroid gland contains follicles, which secrete thyroid hormone, but also C cells which are parafollicular cells and secrete calcitonin.
  • Functions in calcium homeostasis
  • Decreases calcium in the blood
  • Inhibits osteoclasts
  • Increases calcium excretion by the kidneys

Parathyroid Gland

The parathyroid gland produces and secretes parathyroid hormone.
  • Functions in calcium homeostasis
  • Opposes calcitonin
  • Increases free calcium in blood
  • Increases reabsorption of calcium (and phosphate) in kidneys
  • Increases resorption of calcium from bone
  • Activates vitamin D3 (calcitriol)

Adrenal Cortex

The adrenal cortex produces steroid hormones. It is divided into three regions:

Zona Glomerulosa (outermost)
  • Mineralocorticoids, e.g. aldosterone
  • Regulates electrolyte composition of the extracellular fluid
  • Targets the kidneys to increase blood volume and pressure
  • Stimulates Na+ reabsorption - water moves out of filtrate, following Na+
  • Stimulates H+ and H+ secretion
Zona Fasiculata (middle)
  • Glucocorticoids, e.g. cortisol, corticosterone and cortisone
  • Maintains blood sugar levels
  • Increases glucose synthesis in the liver
  • Stimulates glycogen formation
  • Anti-inflammatory and immunosuppressive
    • Decrease of phagocyte migration
    • Decrease of histamine released from mast cells
    • Decrease in swelling and inflammation
Zona Reticularis (innermost)
  • Gonadocorticoids, e.g. androgens
  • Sexual differentiation during puberty
  • e.g. DHEA, which becomes oestrogen in females

Adrenal Medulla

The adrenal medulla releases catecholamines, released in response to sympathetic stimulation. These are the 'flight or fight' hormones, i.e. epinephrine (adrenaline) and norepinephrine (noradrenaline).
  • Stimulate glycogen mobilisation in skeletal muscles to produce ATP
  • Release stored fats for energy
  • Increase cardiac output
  • Increase blood glucose through the breakdown of liver glycogen stores

Pancreas

The pancreas is both an endocrine and exocrine organ.

Insulin
  • Decreases blood glucose
  • Increases glucose take up by cells
  • Accelerates glucose utilisation and enhanced ATP production
  • Stimulates glycogen formation
  • Stimulates amino acid absorption and protein synthesis
  • Stimulates triglyceride formation in adipose tissue
Glucagon
  • Increases blood glucose
  • Stimulates breakdown of glycogen and release of glucose by liver
  • Stimulates breakdown of triglycerides in adipose tissue 

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