8.1.2 - Endocrine system

Question 1

What is the endocrine system

Answer 1

A network of glands and organs that produce and release hormones to regulate essential body functions, including growth, metabolism, reproduction and maintaining homestosis.

Hormones are chemical messengers that travel through the bloodstream to target organs and tissues.

Question 2

Functions of endocrine system

Answer 2

• Maintaining homestasis: blood sugar, blood pressure, electrolyte balance.
• Control growth and decelopment: Growth hormone, thyroid hormones and sex hormones influence growth and physical development.
• Regulate metabolism: Thyroid hormones
• Facilitate reproduction: Hormones like FSH, LH, oestrogen, progesterone, and testosterone are critical for reproduction and development.
• Manage stress responses: cortisol and adrenaline prepare the body for stress (fight and flight response).

Question 3

Thyroxin

Answer 3

• Receptors in the hypothalamus detect a drop in the body temperature to below the tolerance limit.
• Hypothalamus releases a regulatory hormone (thyrotropin-releasing hormone) into the pituitary gland.
• Anterior pituitary gland releases thyroid stimulating hormones.
• Thyroid glands are stimulating to secrete thyroxin.
• Thyroxin is the means by which the message is transferred to the cells to increase their metabokic rate. in this process, energy is released for a number of purposes, one of which is to provide heat to maintain body temperature.

Question 4

Parathyroid hormone

Answer 4

• Parathyroid gland: small glands embedded in the surface of the thyroid gland.
• Maintains the level of calcium in the blood - for nervous system (required for the successful transfer of nerve impulses) and muscle contraction.

Parathyroid gland monitors the blood flowing through it. If it is detected too low, it secretes parathyroid hormone. This hormones travles to the following effectors:

• Bones: release calcium into the blood
• Small intestines - absorb more calcium from digested food.
• Kidneys - reabsorb more calcum in the tubules

The net result of this is to increase calcium levels to an optimal level. If it is too high, parathyroid glands stop secreting PTH.

Question 5

Aldosterone

Answer 5

Controls the level of sodium in the body. It is classified as a mineralocorticoid because its function in regulating minerals like sodium and potassium.

It is released by the adrenal glands, specifically by the outer layer called the adrenal cortex. It maintains the electrolyte balance, blood pressure, blood volume by controlling the level of sodium and potassium ions in the body.

If there is a drop of sodium ions:

• Detected by receptor cells in the kidneys. Stimulating the adrenal cortex to produce more aldosterone.
• Greater reabsorption of sodium ions, decreased reabsorption of potassium ion. This helps maintain the proper electrolyte balance.
• By increasing sodium reabsorption, water is also reabsorbed due to osmosis (concentration of ions increase; water flows back in due to concentration gradient), helping to regulate blood volume and pressure.
• In the distal convoluted tubules and collecting ducts of the nephron in the kidneys → stimulates synthesis of proteins that enhance sodium channels and sodium-potassium pumps.

Question 6

Antidiueretic Hormone (ADH)

Answer 6

Role: regulate water balance by controlling water reabsorption in the kidneys ; AKA vasopressin

It works alongside aldosterone by increasing water reabsorption in the kidneys. While aldosterone retains sodium, ADH directly increases water permeability in the collecting ducts. This allows for increased water flow from the kidneys to the bloodstream, and ensures that the solute level is not too high (higher water level)

Secreted by: the posterior pituitary gland.

• Specialised cells in the hypothalamus called osmoreceptors detect an increase in plasma osmolarity (high concentration of solutes). This triggers the posterior pituitary gland to release ADH, increasing the water reabsorption and reducing osmolarity.

ADH acts on the collecting ducts of the nephron in the kidneys. It increases the permeability of the collecting ducts by stimulating the insertion of aquaporin-2 (AQP2) water channels into the membrane of kidney cells. This allows water to be reabsorbed back into the bloodsteam, concentrating the urine and reducing water loss.

Once optimal levels are reached (solute concentration) hypothalamus sends the message to the pituitary gland to stop the release of ADH. If the water level is too high, the hypothalamus inhibits the secretion of ADH.

Question 7

Compare ADH and Aldosterone

Answer 7

ADH
Produced by: posterior pituitary (hypothalamus origin)
Stimulus for release: high plasma osmolarity, low blood volume
Target: collecting ducts
Primary action: increasing water reabsorption

Aldostrerone
Produced by: adrenal cortex
Stimulus for release: low sodium, low blood pressure
Target: distal tubules and collecting ducts
Primary action: increases the sodium reabsorption and potassium excretion.