53) Overview of Endocrinology

Question 1

What are the major endocrine glands within the body?

Answer 1

• Pineal (Head)
• Hypothalamus (Head)
• Pituitary (Head)
• Thyroid (Neck)
• Parathyroid (Neck)
• Thymus (Neck)
• Adrenal cortex (Abdomen)
• Pancreas (Abdomen)
• Testes (male pelvis)
• Ovaries (female pelvis)

Question 2

What are the secretions of the hypothalamus?

Answer 2

• They secrete stimulating and inhibiting hormones
• The pituitary gland and the hypothalamus work with each other
• Therefore these hormones are sent to the pituitary gland

Question 3

What are the secretions of the pituitary gland?

Answer 3

• They are divided into two lobes (Anterior and Posterior)
• Anterior lobe: Trophic (growth) hormones
• Posterior lobe: Oxytocin and vasopressin (ADH)

Question 4

What are the secretions of the Thyroid gland?

Answer 4

• Thyroxine and tri-iodothyronine

Question 5

What are the secretions of the adrenal glands?

Answer 5

• They are divided into two parts (cortex and medulla)
• Cortex: Cortisol and aldosterone
• Medulla: Adrenaline/ noradrenaline

Question 6

What are the secretions of the gonads?

Answer 6

• Testes secrete androgen

- Ovaries secrete oestrogen and progestagens

Question 7

What are the secretions of the pancreas?

Answer 7

• Insulin and glucagon

Question 8

What are the secretions of the parathyroid gland?

Answer 8

• Parathyroid hormone

Question 9

What are the different signalling mechanisms in the endocrine system?

Answer 9

• Endocrine: Hormones are secreted by cell and enter general circulation. It targets distant cells that have a receptor for the hormone
• Paracrine: Hormones released from the cell act locally/on adjacent cells that contain the receptor for the hormone
• Autocrine: Hormone released acts on the same cell it was secreted from as this cell may contain receptors for the hormone
• Intracrine: Inactive hormones within cells may become active

Question 10

What are the general functions of hormones?

Answer 10

• Reproduction, growth and development (e.g. sex steroids, thyroid hormone, prolactin and growth hormone
• Maintenance of internal environment (e.g. aldosterone, parathyroid, vitamin D)
• Energy production, utilization and storage (e.g.: Insulin, glucagon, thyroid hormone, cortisol, growth hormone)

Question 11

What are the four main families of hormones?

Answer 11

• Protein/peptide: Hypothalamic hormones, Pituitary hormones, Insulin and Calcitonin
• Steroids (cholesterol): Cortisol, aldosterone, sex hormones and vitamin D
• Amino acids (normally tyrosine or tryptophan): Melatonin, adrenaline, noradrenaline and thyroid hormone
• Fatty acid derivatives: Prostaglandin, prostacyclin and thromboxane

Question 12

Why is knowledge of solubility and nature of hormone important?

Answer 12

• Gives us information on activity, how long lasting they are and how they are transported

Question 13

What is the half life and transport of each family of hormones?

Answer 13

• Protein/peptide: Very soluble in blood plasma and circulate as free unbound proteins in circulation. Their half life are in minutes so are fast acting and short lived
• Amino acids (normally tyrosine or tryptophan): Some are very fast acting and work in seconds or minutes. However thyroid hormones in the are bound to plasma proteins which increases their half life to minutes or hours
• Cholesterol derivatives (steroids): Very low solubility in blood plasma so are carried around in carrier proteins and so have a longer activity with half lives of hours or days

Question 14

Why are thyroid hormones found bound to plasma proteins?

Answer 14

• Their iodine group affects their solubility and as a result they are bound to plasma proteins

Question 15

What is the the hypothalamic-pituitary axis?

Answer 15

• It is the master regulator within the endocrine system as the hypothalamus and pituitary are fundamental regulatory system within the body
• This axis is the interface between the neurosecretory cells of the brain and the connecting chemical signalling coming from the endocrine glands
• The hypothalamus sit above the pituitary gland more centrally in the brain whereas the pituitary gland hangs just below.
• The pituitary gland is made of two lobes (anterior and posterior)
• The hypothalamus and posterior lobe are connected to each other via the magnocellular neurones (neurosecretory cells) as they start in the hypothalamus and end in the vessels supplying the posterior lobe
• There are also parvicellular neurones (neurosecretory cells) in the hypothalamus which end at the portal capillary system. They release their hormones here which are transported directly into the endocrine glands of the anterior lobe which cause it to release hormones

Question 16

What is the three tier system of the hypothalamus-pituitary axis?

Answer 16

• The hypothalamus releases stimulating or inhibitory hormones which act on the pituitary gland
• The pituitary gland then secretes its own trophic (growth) hormones which circulate in the blood where they act on glands within the body