6.2 The Function of the Endocrine System: AQA Psychology A level Revision

The Function of the Endocrine System

Composed of glands that secrete hormones directly into the bloodstream. The blood carries the hormone around the body, and when it reaches a target cell/organ, it produces an effect.

Compared to the nervous system, the effects of hormones are slower, but they act for longer.

Pituitary gland: a ‘master gland’ making hormones such as FSH and LH;

Pancreas: produces insulin, which regulates the blood glucose level;

Thyroid: produces thyroxine, which controls the metabolic rate and affects growth;

Adrenal glands: produces adrenaline;

Ovaries (females): produce estrogen;

Testes (males): produce testosterone.

Pituitary Gland

• Called the “master gland” → controls release of hormones from other endocrine glands.

• Controlled by the hypothalamus.

• Secretes hormones into blood → these stimulate other glands to release their hormones.

• Example: releases thyroid-stimulating hormone (TSH) → stimulates thyroid to release thyroxine (regulates metabolism).

Glands & Hormones

Endocrine glands synthesise substances such as hormones and release them into the bloodstream.

Hormones are chemical substances that circulate in the bloodstream and only affect target organs. They control ongoing internal functions and enable our bodies to react according to changes in the environment.

Pineal Gland

This releases melatonin which is responsible for important biological rhythms, including the sleep-wake cycle. It receives information from the environment about the light-dark cycle which influences the production and secretion of melatonin.

Thyroid Gland

plays a role in controlling heart, muscle and digestive function, brain development and bone maintenance. It releases thyroxine, which is responsible for regulating our metabolism through other organs like the liver and kidneys.

Pancreas Gland

This plays a signficant role in digestion by producing enzymes to break down food and hormones to help regulate blood-sugar levels and appetite.

The main hormone it produces is insulin. Insulin helps your body break down carbohydrates to produce glucose, which we use for energy.

Adrenal Gland

The adrenal gland is divided into two parts, the adrenal medulla and adrenal cortex. The adrenal medulla releases adrenaline and noradrenalin which plays a key role in ‘fight or flight’ response. The adrenal cortex releases cortisol which stimulates the release of glucose while suppressing the immune system.

Testes

The testes release the hormone testosterone. Testosterone is responsible for the development of male sex characteristics during puberty, including muscle growth, fat distribution and sperm production.

Ovaries

The ovaries release estrogen, which controls the regulation of the female reproductive system, including the menstrual cycle and pregnancy.

Jaren is visiting the doctor for their yearly check-up. The doctor mentions that they will conduct a full examination, including tests focused on key parts of their endocrine system.

Describe the function of the endocrine system, using at least two examples of glands and hormones.

To regulate organ activity within the body by secreting hormones into the bloodstream. When the hormone reaches its target organ, it produces the necessary effect.

Two examples of glands and the appropriate hormones for instance:

Adrenal glands > adrenaline

Pancreas > insulin

“For instance, within the adrenal glands, the adrenal medulla produces adrenaline, which is key in the ‘fight or flight response’.”

The Fight or Flight Response

During situations that create stress, fear or excitement, the neurons of the sympathetic nervous system will stimulate the adrenal medulla (of the adrenal gland) to secrete adrenaline.

Adrenaline is a hormone that will prepare your body for reacting to a stressful situation . The effects of adrenaline lead to the typical symptoms we experience during stressful situations, such as increased heart rate, dry mouth, increased sweating, etc.

Endocrine and ANS working together: fight or flight

• Immediate Response (SAM system):
  A stressor activates the hypothalamus, which triggers the sympathetic branch of the ANS.
  → This stimulates the adrenal medulla to release adrenaline and noradrenaline.
  → These hormones increase heart rate, breathing rate and blood pressure, dilate pupils, divert blood to muscles, and inhibit digestion — preparing the body for rapid action.

• Endocrine Pathway (HPA axis):
  At the same time, the hypothalamus signals the pituitary gland, which releases ACTH. (adrenocorticotrophic hormone)
  → ACTH stimulates the adrenal cortex to release cortisol, providing energy by releasing glucose and suppressing non-essential functions.

• Parasympathetic Response (Rest and Digest):
  Once the threat has passed, the parasympathetic branch of the ANS restores balance by slowing heart and breathing rate, re-starting digestion, and returning the body to its resting state.

Blood vessels

• Sympathetic activation: blood vessels to non-essential organs (digestion, skin) constrict.

• Blood vessels to vital organs + muscles dilate → ↑ oxygen + glucose supply for action.

• Brain blood supply stays constant (always needs oxygen).

• Controlled by autonomic nervous system + hormones (e.g. adrenaline).