Endocrine physiology

Question 1

Name and locate the major organs of the endocrine system

One of two major control systems in the body
* Nervous system regulates organ function via electrochemical impulses (fast responses)
* Endocrine system regulates organ function via hormones (slower responses)

Answer 1

The major organs of the endocrine system are:

Hypothalamus
Located in the brain, this organ connects the endocrine system to the nervous system. It controls the endocrine system by sending signals to the pituitary gland.

Pituitary gland
Located at the base of the brain, this pea-sized gland is sometimes called the “master” gland of the endocrine system. It controls the functions of many other endocrine glands.

Pineal gland
Located between the two halves of the brain, this gland produces melatonin, which influences the body’s internal clock.

Thyroid gland
Located at the front of the neck, just above where your collarbones meet, this gland makes hormones that control metabolism.

Parathyroid glands
Located in your neck near the thyroid gland, these four small, pea-sized glands make parathyroid hormone, which regulates calcium and phosphorus levels in your blood.

Pancreas
Located in the abdomen, this long, narrow organ secretes the hormones insulin and glucagon, which regulate glucose levels in the blood.

Ovaries
Located in the pelvic cavity, these organs produce hormones and are part of the female reproductive system.

Testes
Located in the scrotum, these organs produce sperm cells and hormones and are part of the male reproductive system.

Question 2

Compare and contrast neural and hormonal controls of physiological functions.

Answer 2

Question 3

Classify hormones chemically and discuss how this classification affects their mechanism of action

Answer 3

Hormones are classified chemically into three main groups based on their structure:

Peptide/protein-based: linked amino acids - most hormones fall into this category. Water-soluble and cannot cross plasma membrane.

Amino acid derivative: modifications of single amino acids (tyrosine: thyroid hormones, catecholamines & tryptophan: melatonin). Water soluble (except thyroid hormone) and cannot cross plasma membrane.

steroid-based: Made from cholesterol; bound to protein carriers in plasma (androgens, corticosteroids, calcitriol). Lipid soluble and can cross the plasma membrane. Bind to intracellular receptors.

The chemical structure of hormones affects their distribution, the receptors they bind to, and other aspects of their function. For example, lipid-derived hormones can diffuse across plasma membranes, while amino acid-derived and peptide hormones cannot.

Question 4

Describe how individual hormones interact to produce a coordinated physiological response

Answer 4

• Multiple hormones may act on same target cell at same time
• Four types of interactions:
  1. Antagonism: opposing actions
  2. Synergism: two hormones exert the same effect, which is amplified when combined
  3. Permissiveness: a hormone needs another hormone to exert its full effects
  4. Integrative: two hormones exert different but complementary effects

Question 5

Describe the structural and functional relationships between the hypothalamus and the pituitary gland

Answer 5

Hypothalamus:
* Part of brain
* Link between autonomic nervous system & endocrine system
* Directly regulates internal environment

Pituitary or hypophysis; “to grow under”:
* Size of a pea, in bony cavity at base of brain
* Connected to hypothalamus by a ‘stalk’: infundibulum
* Two lobes:
1. Anterior: glandular tissue –> produces & releases hormones – ‘true’ endocrine gland (The hypothalamus controls secretion in the anterior lobe of the pituitary gland by secreting releasing and inhibiting hormones.)
2. Posterior: neural tissue –> releases “neurohormones” made in hypothalamus – ‘storage’ site