Human Endocrine System Quiz

Thyroid Gland

• Located on the lower portion of the neck, anterior to the trachea.
• Butterfly-shaped, with two lobes (5 cm long) connected by the isthmus.
• Attached to the trachea, allowing the gland to move upward when swallowing.
• Function: Releases calcitonin (regulates calcium homeostasis), T3 and T4 (regulate metabolism of most cells), and stores iodine and thyroglobin (used for thyroid hormone synthesis).
• Regulated by the anterior pituitary gland (TSH).
• Blood supply: Superior and inferior thyroid arteries (thyroid ima artery supplies the isthmus in some people), drained by the superior and middle thyroid veins into the internal jugular vein and the inferior thyroid veins into the brachiocephalic vein.

Pancreas

• Each pancreatic islet contains four types of hormone-secreting cells:
  • Alpha (α) cells (17%): Secrete glucagon, which raises blood glucose.
  • Beta (β) cells (70%): Secrete insulin, which lowers blood glucose.
  • Delta (δ) cells (7%): Secrete somatostatin, which inhibits both glucagon and insulin release.
  • F or pp cells (remaining cells): Secrete pancreatic polypeptide, which inhibits somatostatin and digestive enzymes.

Parathyroid

• Located on the posterior surface of each lobe of the thyroid gland (total of four) and can vary in number (2-6).
• Size: 5 mm in diameter.
• Contains chief cells, oxyphil cells, and adipocytes.
• Function: Regulates calcium and phosphate homeostasis.
• Regulated by negative feedback based on calcium levels.
• Blood supply: Inferior thyroid arteries.

Adrenal Glands

• Paired retroperitoneal glands situated over the superior pole of each kidney.
• Right gland: Pyramidal shape.
• Left gland: Semi-lunar shape.
• Divided into medulla and cortex.
• Function: Secrete steroid and catecholamine hormones directly into the blood.
• Regulation:
  • Adrenal cortex: Regulated by the pituitary gland (ACTH).
  • Adrenal medulla: Regulated by the sympathetic nervous system.

Adrenal Cortex Hormones

• Glucocorticoids (e.g., cortisol): Released in response to stress.
• Mineralocorticoids (e.g., aldosterone): Regulate blood volume.
• Androgens: Sex hormones.

Adrenal Medulla Hormones

• Catecholamines: Adrenaline and noradrenaline.

Adrenal Gland Blood Supply

• Superior adrenal artery: Arises from the inferior phrenic artery.
• Middle adrenal artery: Arises from the abdominal aorta.
• Inferior adrenal artery: Arises from the renal arteries.
• Right and left adrenal veins drain the glands.

Thyroid Disorders

• TSH high, T3 low, T4 low: Hypothyroidism (low T3 and T4 due to disease, cold, pregnancy, low t3 t4, or adrenaline).
• TSH low, T3 high, T4 high: Graves disease (autoimmune, raised T3 and T4).

Hypothalamus and Pituitary Gland

• Hypothalamus releases hormones that regulate the pituitary gland
• Anterior pituitary releases TSH, GH, ACTH, LH, FSH, PRL
• Posterior pituitary releases ADH and oxytocin

Thyroid Gland

• Located anterior to the trachea, butterfly-shaped, two lobes connected by isthmus
• Function: releases calcitonin (calcium homeostasis) and thyroid hormones T3 & T4 (regulate metabolism)
• Thyroid hormones require iodine and thyroglobulin for synthesis
• Regulated by anterior pituitary gland (TSH)
• Blood supply: superior and inferior thyroid arteries, drained by superior and middle thyroid veins into the internal jugular vein, inferior thyroid veins into the brachiocephalic vein

Pancreatic Islets

• Alpha (α) cells: secrete glucagon (raises blood glucose)
• Beta (β) cells: secrete insulin (lowers blood glucose)
• Delta (δ) cells: secrete somatostatin (inhibits glucagon and insulin release)
• F cells: secrete pancreatic polypeptide (inhibits somatostatin and digestive enzymes)

Endocrine Disorders

• Addison's disease: Adrenal insufficiency
• Hypothyroidism: Thyroid gland, low T3 and T4
• Cushing's disease: Adrenal gland, raised cortisol (or too much steroid medication)
• Diabetes: Pancreas
• Conn's disease: Adrenal gland, too much aldosterone
• Grave's disease: Thyroid gland, autoimmune, raised T3 and T4
• Acromegaly: Pituitary gland, too much growth hormone

Thyroid Hormone Functions

• Increase basal metabolic rate
• Increase body temperature (calorigenic effect)
• Increase use of glucose and fatty acids
• Stimulate lipolysis
• Regulate development and growth of nervous tissue and bones

Parathyroid Gland

• Located on the posterior surface of each lobe of the thyroid gland (total 4)
• Structure: 5mm in diameter, chief cells, oxyphil cells, and adipocytes
• Function: calcium and phosphate homeostasis
• Regulated by negative feedback, calcium levels
• Blood supply: inferior thyroid arteries

Adrenal Glands

• Paired retroperitoneal glands situated over the superior pole of each kidney
• Right gland is pyramidal, left gland is semi-lunar
• Separated into medulla and cortex
• Secrete steroid and catecholamine hormones directly into blood
• Adrenal cortex regulated by pituitary gland (ACTH), adrenal medulla regulated by sympathetic nervous system

Adrenal Cortex

• Glucocorticoids: in response to stress (cortisol)
• Mineralocorticoids: regulate blood volume (aldosterone)
• Androgens: sex hormone

Adrenal Medulla

• Catecholamines: adrenaline and noradrenaline

Adrenal Blood Supply

• Superior adrenal artery: arises from inferior phrenic artery
• Middle adrenal artery: arises from abdominal aorta
• Inferior adrenal artery: arises from renal arteries
• Right and left adrenal veins drain the glands

Test your knowledge on the thyroid gland and pancreas, key components of the human endocrine system. Learn about their structures, functions, and hormone regulation. Challenge yourself with questions that cover metabolism and glucose homeostasis.