## Learning Outcomes

- Understand how the endocrine system uses hormones to control body functions
- Identify the major endocrine glands and where they are found
- Recall the key hormones released by each major gland
- Explain how hormones act on target cells and target organs
- Distinguish between paired hormones with opposite effects, such as insulin and glucagon
- Link major glands and hormones to homeostasis, growth, reproduction and stress responses
- Avoid common exam confusions, such as anterior versus posterior pituitary and endocrine versus exocrine pancreas

## T Level Health (Core) Syllabus

For the T Level Health (Core), you are expected to understand the major glands of the endocrine system and the key hormones they produce, with a focus on the following syllabus points:

- Know that endocrine glands secrete hormones directly into the bloodstream
- Identify the location and main function of the hypothalamus, pituitary, thyroid, parathyroids, adrenals, pancreas, ovaries and testes
- Understand that hormones act only on target cells or target organs with the correct receptors
- Explain the difference between the anterior pituitary and posterior pituitary
- Identify key hormones including thyroxine, cortisol, growth hormone, FSH, oestrogen, testosterone, insulin and glucagon
- Understand how major hormones contribute to homeostasis, especially blood glucose regulation, water balance, calcium balance and metabolic rate
- Explain examples of negative feedback in endocrine control
- Distinguish between endocrine and exocrine functions of the pancreas

## Test Your Knowledge

_Attempt these questions before reading this article. If you find some difficult or cannot remember the answers, look more closely at that area during your revision._

1. What is the difference between an endocrine gland and an exocrine gland?
2. Which gland is often called the “master gland”, and why is that description only partly true?
3. Name the hormones that lower and raise blood glucose concentration.
4. What is the difference between the adrenal cortex and adrenal medulla?
5. Why do hormones travel throughout the bloodstream but affect only certain cells?

## Introduction

The endocrine system is a control system made of glands that release hormones into the blood. These hormones act as chemical messengers. They help control growth, metabolism, reproduction, stress responses and homeostasis. For T Level Health, this topic is high value because exam questions often ask you to match a gland to its hormone, then link that hormone to its main effect in the body.

A common mistake is to revise the glands as a disconnected list. That is not enough. You need to understand the logic: a gland releases a hormone, the hormone travels in blood, only target cells with the correct receptors respond, and the response helps keep body conditions within normal limits.

> **Key Term: endocrine system**
> A collection of glands that secrete hormones directly into the bloodstream to regulate body functions.

## Introduction to major glands and how hormones work

The endocrine system does not work as a set of isolated organs. It works as a coordinated network. Some glands respond directly to changes in the body, while others are controlled by signals from the brain.

![Major endocrine glands, their anatomical locations, and principal hormones including insulin, glucagon, thyroxine, cortisol, oestrogen, and testosterone.](https://static.pastpaperhero.com/images/ncfe-tlevel-health-core-endocrine-system-major-glands-and-key-hormones_00.png)

_Endocrine glands are labelled by anatomical position with selected hormones released from the hypothalamus, pituitary, thyroid, adrenals, pancreas, ovaries and testes._

> **Key Term: hormone**
> A chemical messenger released into the blood by an endocrine gland that acts on target tissues elsewhere in the body.
>
> **Key Term: endocrine gland**
> A ductless gland that secretes hormones directly into the bloodstream.

The major glands you need to know are:

- hypothalamus
- pituitary gland
- thyroid gland
- parathyroid glands
- adrenal glands
- pancreas
- ovaries
- testes

A useful pattern for revision is:

- **gland**
- **hormone**
- **main target**
- **main effect**

For example:

- pancreas
- insulin
- liver and muscle cells
- lowers blood glucose concentration

Hormones are carried all around the body, but they do not affect every cell.

> **Key Term: target cell**
> A cell that has the correct receptor for a particular hormone and can respond to it.
>
> **Key Term: target organ**
> An organ whose cells have receptors for a particular hormone and respond to it.

This matters because students sometimes think hormones “choose” where to go. They do not. Blood carries them widely. Specificity comes from receptors. If a cell has no receptor, that hormone has no effect there.

The endocrine system is also strongly linked to **homeostasis**, which means keeping the internal environment stable.

> **Key Term: homeostasis**
> The maintenance of a stable internal environment in the body.
>
> **Key Term: negative feedback**
> A control mechanism in which a change from normal triggers responses that oppose the change and move conditions back towards normal.
>
> **Test Tip:** If an exam question asks how a hormone system helps maintain stability, the answer often needs the phrase **negative feedback** and a clear direction of change, such as “high blood glucose stimulates insulin release, which lowers blood glucose.”

### The hypothalamus and pituitary gland

The hypothalamus and pituitary are best revised together because they form the main control link between the nervous system and the endocrine system.

The **hypothalamus** is in the brain. It monitors internal conditions such as water balance and temperature, and it controls the pituitary gland. It is especially important because it helps coordinate many homeostatic responses.

The **pituitary gland** sits just below the hypothalamus. It is often called the **master gland** because it controls other endocrine glands. That is useful exam language, but it is incomplete. The hypothalamus regulates the pituitary, so the pituitary is not acting alone.

The pituitary has two parts:

- **anterior pituitary**
- **posterior pituitary**

This distinction is often tested.

The **anterior pituitary** secretes hormones including:

- growth hormone (**GH**) — supports normal growth in infancy and childhood
- follicle-stimulating hormone (**FSH**) — stimulates development of egg follicles in the ovaries
- luteinising hormone (**LH**) — involved in ovulation and stimulates testosterone production in males

It also produces other important hormones such as TSH and ACTH, which stimulate other glands, though questions at this level often focus more on GH, FSH and LH.

The **posterior pituitary** is different. It does not make its main hormones itself. Hormones such as **ADH** are produced in the hypothalamus and then stored and released from the posterior pituitary.

This is a classic confusion point.

> **Key Term: pituitary gland**
> An endocrine gland below the hypothalamus that releases hormones controlling growth, reproduction and other endocrine glands.
>
> **Key Term: hypothalamus**
> A region of the brain that links the nervous system and endocrine system and controls pituitary hormone release.
>
> **Key Term: ADH**
> Antidiuretic hormone, a hormone that increases water reabsorption by the kidneys and helps regulate water balance.

Why this matters: if the body is becoming dehydrated, more ADH is released. The kidneys reabsorb more water, less water is lost in urine, and the body moves back towards normal water balance. That is negative feedback in action.

> **Test Tip:** Learn this exact distinction: **ADH is produced by the hypothalamus and stored/released by the posterior pituitary.** This is a frequent short-answer question.

### Thyroid, parathyroids and adrenal glands

The **thyroid gland** is in the neck, in front of the trachea. Its main role is regulation of metabolic rate.

> **Key Term: metabolic rate**
> The rate at which energy is transferred by the body’s chemical reactions.

The key thyroid hormone for this course is **thyroxine**. Thyroxine acts on most body cells and increases metabolic activity. That means it affects how quickly the body uses energy.

If thyroxine levels are too low, body processes slow down. If too high, they speed up too much. This is why thyroid control is important for normal functioning rather than just “energy” in a vague sense.

The thyroid also produces **calcitonin**, which lowers blood calcium concentration.

The **parathyroid glands** work closely with the thyroid but have the opposite effect on calcium balance. They produce **parathyroid hormone (PTH)**, which raises blood calcium concentration.

These two hormones are a useful comparison pair:

- **calcitonin** lowers blood calcium
- **PTH** raises blood calcium

Students often reverse them.

The **adrenal glands** sit above the kidneys. Each adrenal gland has two parts with different functions.

The **adrenal medulla** produces **adrenaline** and is involved in the immediate fight-or-flight response. Adrenaline increases heart rate and prepares the body for rapid action.

The **adrenal cortex** produces **cortisol**. Cortisol has a longer-term role in stress response and also helps increase blood glucose concentration.

So the key contrast is:

- adrenal medulla = rapid stress response
- adrenal cortex = longer-lasting hormonal response
  > **Key Term: thyroxine**
  > A hormone secreted by the thyroid gland that regulates metabolic rate.
  >
  > **Key Term: calcitonin**
  > A hormone secreted by the thyroid gland that lowers blood calcium concentration.
  >
  > **Key Term: parathyroid hormone (PTH)**
  > A hormone secreted by the parathyroid glands that raises blood calcium concentration.
  >
  > **Key Term: adrenal glands**
  > Endocrine glands above the kidneys made of an outer cortex and inner medulla.
  >
  > **Key Term: cortisol**
  > A hormone produced by the adrenal cortex that helps the body respond to stress and can increase blood glucose concentration.

A common error is to say “the adrenal gland secretes adrenaline” without naming the medulla. That may get some credit, but precise terminology is stronger and safer.

### Pancreas, ovaries and testes

The **pancreas** is one of the most important glands for exam questions because it has both **endocrine** and **exocrine** roles.

Its exocrine role is to make digestive enzymes. Its endocrine role is carried out by the **islets of Langerhans**, which release hormones into the blood.

Inside the islets:

- **beta cells** secrete **insulin**
- **alpha cells** secrete **glucagon**

These two hormones act antagonistically.

- **insulin lowers blood glucose concentration**
- **glucagon raises blood glucose concentration**

This is one of the clearest examples of endocrine control in homeostasis.

When blood glucose rises, insulin promotes uptake and storage of glucose, especially in liver and muscle cells. When blood glucose falls, glucagon promotes release of glucose into the blood.

> **Key Term: pancreas**
> A gland with both endocrine and exocrine functions; its endocrine cells release insulin and glucagon.
>
> **Key Term: islets of Langerhans**
> Groups of endocrine cells in the pancreas that secrete hormones including insulin and glucagon.
>
> **Key Term: insulin**
> A hormone produced by pancreatic beta cells that lowers blood glucose concentration.
>
> **Key Term: glucagon**
> A hormone produced by pancreatic alpha cells that raises blood glucose concentration.

This gland is often used to test whether you understand endocrine versus exocrine.

- endocrine pancreas = hormones into blood
- exocrine pancreas = enzymes into ducts

The **ovaries** produce the female sex hormones **oestrogen** and **progesterone**. Oestrogen helps regulate the menstrual cycle and supports female secondary sexual characteristics. Progesterone helps maintain the lining of the uterus, especially after ovulation and in pregnancy.

The **testes** produce **testosterone**. Testosterone supports male secondary sexual characteristics and is required for sperm production.

A good exam answer does more than list the hormones. It links them to a function:

- ovaries → oestrogen, progesterone → menstrual cycle and reproduction
- testes → testosterone → sperm production and male reproductive development
  > **Key Term: oestrogen**
  > A hormone produced mainly by the ovaries that helps regulate the menstrual cycle.
  >
  > **Key Term: progesterone**
  > A hormone produced mainly by the ovaries that helps maintain the uterus lining.
  >
  > **Key Term: testosterone**
  > A hormone produced mainly by the testes that supports male reproductive development and sperm production.

A final pattern to remember is the use of hormone pairs with opposite effects:

- insulin vs glucagon
- calcitonin vs PTH

These are high-yield because they show how the endocrine system controls body conditions through balance, not through one hormone acting alone.

> **Test Tip:** In longer questions, organise your answer as **gland → hormone → target → effect → link to homeostasis**. This structure keeps your explanation accurate and stops you drifting into vague statements.

## Key Point Checklist

_This article has covered the following key knowledge points:_

- The endocrine system is made of glands that secrete hormones directly into the bloodstream
- Hormones are chemical messengers carried in the blood to target cells or target organs
- Only cells with the correct receptors respond to a hormone
- The hypothalamus links the nervous and endocrine systems and controls the pituitary gland
- The anterior pituitary secretes hormones such as GH, FSH and LH
- The posterior pituitary stores and releases hormones such as ADH that are produced by the hypothalamus
- The thyroid gland secretes thyroxine to regulate metabolic rate
- The thyroid secretes calcitonin, which lowers blood calcium concentration
- The parathyroid glands secrete PTH, which raises blood calcium concentration
- The adrenal medulla releases adrenaline, while the adrenal cortex releases cortisol
- The endocrine pancreas contains islets of Langerhans, where beta cells secrete insulin and alpha cells secrete glucagon
- Ovaries secrete oestrogen and progesterone, while testes secrete testosterone
- Insulin lowers blood glucose concentration and glucagon raises it
- Negative feedback is the main mechanism used to keep internal conditions close to normal

## Key Terms and Concepts

- endocrine system
- hormone
- endocrine gland
- target cell
- target organ
- homeostasis
- negative feedback
- pituitary gland
- hypothalamus
- ADH
- metabolic rate
- thyroxine
- calcitonin
- parathyroid hormone (PTH)
- adrenal glands
- cortisol
- pancreas
- islets of Langerhans
- insulin
- glucagon
- oestrogen
- progesterone
- testosterone


Endocrine system - Major glands and key hormones