Human endocrine system — AQA GCSE Combined Science
Test yourself on Human endocrine system with AQA GCSE practice questions.
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Human endocrine system explained
Hormonal coordination uses endocrine glands as effectors that release hormones directly into the blood.
Read the full explanation
Each hormone travels in the blood plasma to specific target organs, where it binds to receptors and triggers a response. This produces widespread, relatively slow and long-lasting control of processes such as blood glucose concentration and growth. For example, the pancreas detects a rise in blood glucose and secretes insulin; insulin reaches the liver and muscle cells, causing them to take up more glucose, thereby lowering blood glucose levels. Students must describe this system of glands, blood-borne chemical messengers and target organs, and compare it with the faster, short-lived, electrical signalling of the nervous system.
The endocrine system is composed of glands which secrete chemicals called hormones directly into the bloodstream. The blood carries the hormone to a target organ where it produces an effect. Compared to the nervous system the effects are slower but act for longer.
The endocrine system is a set of ductless glands that secrete hormones straight into the blood. Blood plasma carries each hormone throughout the body, but an effect occurs only at a target organ whose cells have receptors that bind that hormone. For example, the adrenal glands secrete adrenaline into the blood; adrenaline reaches the heart, where it increases heart rate, and the liver, where it stimulates glycogen breakdown to release glucose. Because transport is by mass flow of blood and cells must be reached and respond, hormonal effects begin more slowly than nerve impulses. However, hormones persist in the blood and are removed gradually, so their effects act for longer and can be widespread. This contrasts with the nervous system, where electrical impulses travel along neurones and produce rapid, short-lived, precisely targeted responses.
The pituitary gland in the brain is a ‘master gland’ which secretes several hormones into the blood in response to body conditions. These hormones in turn act on other glands to stimulate other hormones to be released to bring about effects.
The pituitary gland sits at the base of the brain and is called the ‘master gland’ because it coordinates much of the endocrine system. It detects body conditions and secretes hormones into the blood. These hormones travel to other glands, such as the thyroid, adrenal glands and gonads, and stimulate them to release their own hormones, which then produce effects in target organs. For example, thyroid-stimulating hormone from the pituitary causes the thyroid to release thyroxine, which raises metabolic rate. Because the pituitary responds to changing conditions and controls other glands, it acts as a central coordinator for hormonal responses.
Students should be able to identify the position of the following on a diagram of the human body:
This practical skill requires you to locate endocrine glands on a diagram of the human body. You need to know where the pituitary gland, thyroid gland, adrenal glands, pancreas, ovaries and testes are positioned. The pituitary is at the base of the brain, the thyroid is in the neck, the adrenal glands sit on top of the kidneys, the pancreas is in the abdomen, the ovaries are in the female pelvis and the testes are in the male scrotum. Being able to identify these positions helps you link each gland to its hormones and their effects, and supports answers about hormonal coordination and negative feedback.
pituitary gland
The pituitary gland is a small endocrine gland located at the base of the brain. It is often called the master gland because it secretes several hormones into the blood in response to body conditions. These hormones in turn act on other endocrine glands, stimulating them to release different hormones that bring about specific effects. For example, the pituitary secretes thyroid-stimulating hormone (TSH), which travels in the blood to the thyroid gland and stimulates it to release thyroxine. Similarly, it releases FSH to stimulate the ovaries. In exams, students may be asked to name the pituitary gland, identify its position, or explain why it is referred to as the master gland using a valid example.
pancreas
The pancreas is an endocrine gland that secretes hormones directly into the blood to control blood glucose concentration. When blood glucose rises, it releases insulin, causing cells (like liver and muscle cells) to take up glucose and store it as glycogen. For Higher Tier (HT) students, the pancreas also releases glucagon when blood glucose falls. Glucagon causes glycogen to be converted back to glucose and released into the blood. HT students must also understand how insulin and glucagon interact in a negative feedback loop to keep blood glucose within a narrow range. In exams, you may be asked to identify the pancreas on a diagram or explain its role in restoring blood glucose.
thyroid
The thyroid is one of the glands in the human endocrine system. It lies at the front of the neck, just below the larynx, and is often drawn as two lobes joined across the trachea. For this specification statement, the examinable skill is recognising and locating the gland on a diagram alongside the pituitary, pancreas, adrenal glands, ovaries and testes. Use position rather than size or colour: find the neck, identify the trachea, then choose the gland wrapped around its upper part. The thyroid is an endocrine gland, so it releases hormones into the bloodstream; detailed thyroid-hormone control is outside this statement.
adrenal gland
The adrenal glands are key components of the human endocrine system, situated directly above the kidneys. All students must be able to identify their precise position on a diagram of the human body. The endocrine system is composed of various glands that secrete chemicals called hormones directly into the bloodstream. The blood then carries these hormones to target organs where they produce an effect. Compared to the nervous system, the effects of the endocrine system are slower but act for longer. Students should be able to locate the adrenal glands accurately on a diagram and distinguish them from other glands such as the pancreas or thyroid. Remember that 'renal' relates to the kidneys.
ovary
The ovaries are paired endocrine glands in the female reproductive system. As endocrine organs they secrete the hormones oestrogen and progesterone directly into the bloodstream, so they act on distant target tissues rather than through ducts. Oestrogen drives development of female secondary sexual characteristics at puberty and helps regulate the menstrual cycle; progesterone maintains the uterus lining and supports early pregnancy. The ovaries also contain the follicles that release eggs, so they have both an endocrine role and a reproductive role. In exam questions, identify the ovary as the source of oestrogen and progesterone, and link each hormone to its effect, for example oestrogen causing breast development or progesterone maintaining the lining of the uterus.
testes.
The testes are the paired male reproductive glands and also act as endocrine glands. They secrete testosterone directly into the bloodstream, so testosterone travels around the body and acts on target tissues. Testosterone is the main male sex hormone: it stimulates sperm production in the testes and brings about male secondary sexual characteristics at puberty, such as deepening of the voice, growth of facial and body hair, and increased muscle development. Because the testes have both an endocrine role and a reproductive role, exam answers should distinguish hormone secretion from sperm production. When a question asks for the gland that produces testosterone, name the testes; when it asks for an effect, link testosterone to sperm production or to a named male secondary sexual characteristic.
Your focus
- Identify endocrine glands and state that they secrete hormones directly into the bloodstream.
- Explain how a hormone reaches and affects only its target organ.
- Compare the characteristics of hormonal coordination with nervous coordination.
Show all 30 objectives
- Describe how endocrine glands secrete hormones directly into the bloodstream and how blood carries them to target organs.
- Explain why hormonal effects are slower to begin but longer lasting than nervous effects.
- Apply the gland-hormone-target organ model to a named example such as adrenaline acting on the heart and liver.
- Identify the pituitary gland as the master gland located in the brain.
- Describe how the pituitary secretes hormones into the blood in response to body conditions.
- Explain how pituitary hormones stimulate other glands to release hormones that produce effects.
- Identify the position of the pituitary, thyroid, adrenal glands, pancreas, ovaries and testes on a diagram of the human body.
- Relate the position of each gland to its role in the endocrine system.
- Use correct anatomical terms to describe gland locations.
- Identify the pituitary gland and state its location in the brain.
- Describe how pituitary hormones are transported and act on target organs.
- Explain the pituitary's role as the master gland in controlling other endocrine glands.
- Identify the pancreas on a diagram and state that it secretes insulin into the blood.
- Describe the effects of insulin on blood glucose concentration and glycogen storage.
- (HT only) Explain how negative feedback involving insulin and glucagon controls blood glucose concentration.
- Identify the thyroid on a diagram of the human endocrine system.
- Describe the thyroid’s position at the front of the neck around the upper trachea.
- Distinguish the thyroid from the pituitary, adrenal glands, pancreas, ovaries and testes by location.
- Identify the adrenal glands as endocrine glands above the kidneys on a diagram of the human body.
- Describe the endocrine system as a system of glands that secrete hormones into the bloodstream.
- Locate the adrenal glands in relation to other major endocrine glands on a diagram.
- Identify the ovaries as endocrine glands that secrete oestrogen and progesterone.
- Describe the roles of oestrogen and progesterone in the female body.
- Explain how ovarian hormones travel in the blood to reach target organs.
- Identify the testes as endocrine glands that secrete testosterone.
- Describe the roles of testosterone in sperm production and male secondary sexual characteristics.
- Explain how testosterone travels in the blood to reach target organs.
Human endocrine system exam tips
Marking Points
- Endocrine glands are effectors that secrete hormones directly into the bloodstream.
- Hormones are chemical messengers carried in the blood plasma to target organs.
- A target organ responds to a specific hormone because it has complementary receptors.
- Hormonal responses are usually slower to begin than nervous responses but often last longer and affect more widespread areas.
- Named examples include insulin from the pancreas lowering blood glucose, adrenaline from the adrenal glands, and thyroxine from the thyroid.
- Endocrine glands are ductless and secrete hormones directly into the bloodstream.
- Blood plasma transports hormones around the body to target organs.
- A target organ has cells with receptors that the hormone binds to, producing a specific effect.
- Hormonal effects are slower in onset than nervous effects because hormones must travel in the blood and reach target cells.
- Hormonal effects act for longer than nervous effects because hormones persist in the blood and are broken down gradually.
- A valid example is adrenaline from the adrenal glands increasing heart rate and blood glucose concentration.
- States that the pituitary gland is located in the brain and is known as the ‘master gland’.
- Explains that the pituitary secretes hormones into the blood in response to body conditions.
- Describes how pituitary hormones act on other glands, such as the thyroid, adrenal glands or gonads.
- Explains that stimulation of other glands causes them to release their own hormones, which bring about effects.
- Uses a named example, such as thyroid-stimulating hormone acting on the thyroid to release thyroxine.
- Labels the pituitary gland at the base of the brain.
- Labels the thyroid gland in the neck.
- Labels the adrenal glands on top of the kidneys.
- Labels the pancreas in the abdomen.
- Labels the ovaries in the female pelvis and the testes in the male scrotum.
- Names the pituitary gland as a gland located in the brain that secretes hormones directly into the bloodstream.
- States that pituitary hormones travel in the blood plasma to specific target organs.
- Explains that the pituitary is called the master gland because its hormones control the activity of other endocrine glands.
- Uses a named example, such as TSH stimulating the thyroid gland to release thyroxine, or FSH acting on the ovaries.
- Describes the difference between nervous and hormonal coordination, noting that hormonal responses are carried by blood and are generally slower but longer lasting.
- Identifies the pancreas as the endocrine gland that secretes insulin into the blood.
- Explains that insulin lowers blood glucose by causing cells to take up glucose and store it as glycogen.
- (HT only) States that glucagon is released when blood glucose falls, raising it by converting glycogen to glucose.
- (HT only) Describes the negative feedback loop involving insulin and glucagon that regulates blood glucose.
- Distinguishes the endocrine role of the pancreas from its exocrine role in producing digestive enzymes.
- Identifies the thyroid as a gland in the human endocrine system.
- Locates the thyroid at the front of the neck, below the larynx and around the upper trachea.
- Uses anatomical position to distinguish it from the pituitary in the brain and adrenal glands above the kidneys.
- States that, as an endocrine gland, it releases hormones directly into the bloodstream.
- Identifies the adrenal glands as endocrine glands located above the kidneys on a body diagram.
- Recognises that the adrenal glands are part of the endocrine system.
- States that endocrine glands secrete hormones directly into the bloodstream.
- Identifies that hormones from glands like the adrenal gland travel in the blood to target organs.
- States that the ovaries are endocrine glands that secrete hormones directly into the blood.
- Names oestrogen and progesterone as the main hormones produced by the ovaries.
- Links oestrogen to female secondary sexual characteristics and to regulation of the menstrual cycle.
- Links progesterone to maintenance of the uterus lining and support of early pregnancy.
- Recognises that the ovaries also release eggs, so they have a reproductive role as well as an endocrine role.
- Uses the idea of a target organ or target tissue when explaining how ovarian hormones produce their effects.
- States that the testes are endocrine glands that secrete testosterone directly into the blood.
- Names testosterone as the main hormone produced by the testes.
- Links testosterone to sperm production in the testes.
- Links testosterone to male secondary sexual characteristics such as voice deepening, facial hair growth or muscle development.
- Recognises that the testes also produce sperm, so they have a reproductive role as well as an endocrine role.
- Uses the idea of a target organ or target tissue when explaining how testosterone produces its effects.
Examiner Tips
- 💡Use the terms gland, hormone, bloodstream, and target organ in every full description of the endocrine system.
- 💡When comparing with the nervous system, give one similarity and at least two differences, such as speed of onset and duration of effect.
- 💡Use a three-part chain: gland secretes hormone, blood carries it, target organ responds.
- 💡For comparison questions, pair each difference with a reason, such as slower because transport is by blood rather than along neurones.
- 💡Name one gland, its hormone and its target organ effect to make the description concrete.
- 💡Link the pituitary to a specific example, such as thyroid-stimulating hormone and thyroxine, to show understanding of the chain of control.
- 💡Use the phrase ‘in response to body conditions’ to explain why the pituitary is described as a master gland.
- 💡When describing hormonal control, always state the gland that releases the hormone, the target gland or organ, and the effect produced.
- 💡Practise labelling a blank diagram of the human body until you can place each gland accurately without prompts.
- 💡Use body landmarks such as ‘base of the brain’, ‘neck’, ‘on top of the kidneys’ and ‘abdomen’ to remember positions.
- 💡If a question asks for the position of a gland, give both the named gland and its location in the body.
- 💡Use the phrase master gland only with a reason, specifically that its hormones stimulate other endocrine glands to release their own hormones.
- 💡When describing pituitary action, clearly distinguish between the hormone released by the pituitary (e.g. TSH) and the hormone released by the target gland (e.g. thyroxine).
- 💡Name the target cells for insulin as liver and muscle cells and state the storage product as glycogen.
- 💡(HT only) Use the phrase negative feedback when explaining how blood glucose returns to normal.
- 💡On an unlabelled body diagram, find the neck and trachea before selecting the thyroid.
- 💡Use the gland’s position, not the colour or drawing size, because diagrams may use different styles.
- 💡Learn the positions of all major endocrine glands, including the adrenal glands, for diagram labelling questions.
- 💡Remember that 'renal' refers to kidneys, so 'ad-renal' helps you remember they are located on the kidneys.
- 💡Read the command word carefully: describe needs linked detail, whereas identify or name needs only the gland or hormone.
- 💡When asked for a hormone, give its name and one clear effect, such as progesterone maintaining the uterus lining.
- 💡Use precise terms such as endocrine gland, bloodstream and target organ rather than vague phrases like 'controls the body'.
- 💡If asked to name the gland that produces testosterone, answer 'testes' rather than 'testicle' or 'male gland'.
- 💡Support each hormone with one specific effect, such as testosterone stimulating sperm production or deepening the voice.
- 💡Use the terms endocrine gland, bloodstream and target organ to show understanding of hormone transport.
Common Mistakes
- Writing that hormones travel along nerve cells or through ducts: correct this by stating that glands secrete hormones directly into the bloodstream and the blood carries them.
- Claiming that any cell responds to any hormone: correct this by explaining that only specific target organs with complementary receptors respond.
- Saying hormonal effects are always faster than nervous effects: correct this by stating that hormonal effects are slower in onset but generally longer lasting.
- Stating that hormones are carried by nerves: correct this by saying hormones are secreted into the bloodstream and carried in the plasma.
- Writing that hormones affect every cell equally: correct this by explaining that only target organs with complementary receptors respond.
- Confusing slower onset with weaker effect: correct this by stating that hormonal effects are slower to start but often longer lasting and can be widespread.
- Thinking the pituitary gland directly produces all the body’s hormones; correction: it releases hormones that stimulate other glands to release theirs.
- Confusing the pituitary with the pancreas or thyroid; correction: the pituitary is in the brain and acts as a master gland, while the pancreas and thyroid are separate glands. The pancreas responds directly to blood glucose, not to pituitary hormones.
- Believing hormones travel along nerves; correction: hormones are secreted into the blood and carried in the bloodstream.
- Placing the adrenal glands inside the kidneys; correction: they sit on top of the kidneys.
- Confusing the thyroid gland with the pituitary gland; correction: the thyroid is in the neck, while the pituitary is in the brain.
- Putting the pancreas in the chest or near the stomach incorrectly; correction: the pancreas is in the abdomen, below the stomach.
- Thinking the pituitary gland is in the abdomen: correct this by locating it at the base of the brain.
- Saying pituitary hormones travel along nerves: correct this by stating that hormones are secreted into the blood and carried to target organs.
- Confusing the pituitary with the pancreas or thyroid: correct this by linking the pituitary to the control of other glands, rather than direct control of blood glucose or metabolic rate.
- Saying the pancreas secretes insulin into the digestive system: correct this by stating hormones enter the blood.
- (HT only) Reversing the actions of insulin and glucagon: remember insulin lowers blood glucose and glucagon raises it.
- Thinking the pancreas stops working in all diabetes: in Type 1 insulin secretion is reduced, while in Type 2 cells respond poorly.
- Placing the thyroid in the brain: correct this by locating it in the neck; the pituitary is the gland in the brain.
- Choosing the adrenal glands near the kidneys: correct this by finding the upper trachea at the front of the neck.
- Calling the thyroid an exocrine gland with a duct: correct this by remembering that endocrine glands release hormones into the blood.
- Placing the adrenal glands in the neck: correct this by locating them just above the kidneys.
- Confusing the adrenal glands with the pancreas: the pancreas is located centrally behind the stomach, whereas the adrenal glands sit on top of the kidneys.
- Drawing the adrenal glands attached to the digestive system: they are located on the superior pole of the kidneys in the excretory system area.
- Writing that the ovaries release hormones through ducts: correct this by stating that endocrine glands are ductless and secrete hormones into the bloodstream.
- Confusing oestrogen with testosterone: correct this by naming oestrogen and progesterone as ovarian hormones and testosterone as the main male sex hormone from the testes.
- Claiming the ovaries produce insulin or adrenaline: correct this by matching each gland to its hormones, for example pancreas to insulin and adrenal glands to adrenaline.
- Writing that the testes release testosterone through a duct: correct this by stating that endocrine glands are ductless and secrete hormones into the bloodstream.
- Confusing testosterone with oestrogen: correct this by naming testosterone as the main male sex hormone from the testes and oestrogen as an ovarian hormone.
- Saying the testes produce sperm and testosterone in the same way: correct this by separating sperm production, which is a reproductive function, from hormone secretion, which is an endocrine function.