Overview of Endocrinology

Question 1

List some of the major endocrine glands and their secretions.

Answer 1

• HYPOTHALAMUS: releasing and inhibiting hormones
• PITUITARY GLAND: trophic (growth) hormones from the anterior lobe, oxytocin and vasopressin (ADH) from the posterior lobe
• THYROID GLAND: thyroxine, tri-iodothyronine
• ADRENAL GLAND: cortisol and aldosterone from the cortex, adrenaline and noradrenaline from the medulla
• GONADS: oestrogens, androgens, progestagens
• PANCREAS: insulin, glucagon
• PARATHYROID GLAND: parathyroid hormone

- OTHERS:
Kidney: Vitamin D, Erythropoietin
CVS: ANP, endothelins
Pineal Gland: melatonin
Thymus Gland: thymic hormones
Bone: phosphate
Adipose Tissue: leptin

Question 2

List and describe the different signalling mechanisms in the endocrine system.

Answer 2

ENDOCRINE:
Hormones are released by an endocrine cell into the general circulation and act on distance target sites.

PARACRINE:
Hormones are released by an endocrine cell and act locally on adjacent cells.

AUTOCRINE:
Hormones are released by a cell and act back on the same cell.

INTRACRINE:
Conversion of an inactive hormone to an active hormone that acts within the cell.

Question 3

What are some general functions of hormones?

Answer 3

• reproduction, growth and development
• maintenance of the internal environment
• energy production, utilisation and storage

Question 4

List the four main chemical classifications of hormones (based on structure), and list some examples.

Answer 4

PROTEIN/ PEPTIDE HORMONES: hypothalamic hormones, pituitary hormones, insulin, PTH, calcitonin

STEROID HORMONES: cortisol, aldosterone, oestrogens, androgens, progestagens, Vitamin D

AMINO ACID DERIVATIVES (TYROSINE/TRYPTOPHAN):
adrenaline, noradrenaline (tyrosine), thyroid hormone (tyrosine), melatonin (tryptophan)

FATTY ACID DERIVATIVES:
prostaglandins, thromboxanes, prostacyclin

Question 5

Cholesterol is the precursor of all steroid hormones.

List some major steroids.

Answer 5

• cortisol
• aldosterone
• oestrogens
• progestagens
• androgens
• Vitamin D

Question 6

For proteins and peptides, tyrosine derivatives/thyroid hormones and cholesterol derivatives, list their half-life in the circulation and how they’re transported through it.

Answer 6

PROTEINS AND PEPTIDES: half-life is in minutes, and they’re transported mainly unbound

TYROSIN DERIVATIVES (CA’s)/ THYROID HORMONES: half-life is seconds for CA’s and hours for thyroid hormones, and thyroid hormones are transported bound to plasma proteins

CHOLESTEROL DERIVATIVES: half-life is from hours to days, and they’re transported bound to plasma proteins

Question 7

The hypothalamus controls anterior pituitary secretions. It does so by releasing hormones that affect the expression of hormones from the anterior pituitary gland.
List some of these hormones, what hormone they affect and whether they affect it positively or negatively.

Answer 7

• Corticotrophin Releasing Hormone (CRH) positively affects Adrenocorticotrophic Hormone (ACTH).
• Thyroid Releasing Hormone (TRH) positively affects Thyroid Stimulating Hormone (TSH).
• Growth Hormone Inhibiting Hormone (GHIH) negatively affects Thyroid Stimulating Hormone (TSH)
• Gonadotrophin Releasing Hormone (GnRH) positively affects Luteinizing Hormone (LH) and Follicle Stimulating Hormone (FSH)
• Dopamine (dominant control) negatively affects Prolactin (PRL)
• Growth Hormone Releasing Hormone (GHRH)
  positively affects Growth Hormone (GH)
• Growth Hormone Inhibiting Hormone (GHIH) negatively affects Growth Hormone (GH)

Question 8

What are different ways in which disorders of the endocrine system can come about?

Answer 8

• having an excess or deficiency in certain hormones
• having impaired synthesis of certain hormones
• disorders with the transport and metabolism of hormones
• resistance to hormone action

Question 9

Describe the rhythms in hormone secretions.

Answer 9

All hormones are secreted in a pulsatile pattern:

• DAILY: circadian, diurnal
• MONTHLY
• ANNUALLY