Human endocrine system — AQA GCSE Biology
Test yourself on Human endocrine system with AQA GCSE practice questions.
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Human endocrine system explained
Hormonal coordination uses glands that secrete hormones directly into the bloodstream.
Read the full explanation
Each hormone travels in the blood until it reaches target cells with complementary receptors, where it produces a specific effect. Compared with nervous coordination, hormonal responses are slower but often longer lasting and act throughout the body. A useful example is the control of blood glucose: the pancreas detects a change, secretes insulin or glucagon into the blood, and the liver responds by storing or releasing glucose. Describe the general principles: a stimulus is detected, a gland secretes a hormone, blood transports it, a target organ responds, and negative feedback restores the internal environment.
The endocrine system is composed of glands which secrete chemicals called hormones directly into the bloodstream.
The endocrine system is a set of ductless glands that release hormones straight into the blood. Because hormones enter the bloodstream directly, they can be carried to every part of the body, but only target cells with matching receptors respond. Named glands include the pituitary, thyroid, adrenal, pancreas, ovaries and testes. For example, the pancreas secretes insulin into the blood, and the thyroid secretes thyroxine. This differs from exocrine glands, which release substances through ducts, such as salivary glands. When describing the system, state that glands are the source, hormones are the chemical messengers, and the bloodstream is the transport route.
The blood carries the hormone to a target organ where it produces an effect.
Once a hormone is secreted into the blood, it is transported around the body. A hormone only affects target organs or cells that have receptors complementary to that hormone. When the hormone binds to its receptor, it triggers a specific response. For example, insulin secreted by the pancreas is carried in the blood to the liver, where it stimulates liver cells to take up glucose and store it as glycogen, lowering blood glucose concentration. Adrenaline from the adrenal glands is carried to the heart, where it increases heart rate. This explains why hormones can act on distant organs while leaving other tissues unaffected.
Compared to the nervous system the effects are slower but act for longer.
The nervous system and the endocrine system are the two main coordination systems in the body. Nervous coordination uses electrical impulses travelling along neurones, so responses are almost immediate but short-lived. Endocrine coordination uses hormones secreted into the blood, which must be transported to target organs before they act, so responses are slower but the effects persist for longer. For example, the hormone adrenaline is released from the adrenal glands during a stressful event; its effects on heart rate and breathing develop over seconds to minutes and last well beyond the initial stimulus, whereas a reflex withdrawal of the hand from a hot object is instantaneous but stops as soon as the impulse ceases.
The pituitary gland in the brain is a ‘master gland’ which secretes several hormones into the blood in response to body conditions.
The pituitary gland is a small endocrine gland located at the base of the brain, just below the hypothalamus. It is called the master gland because it secretes several hormones into the blood in response to changing body conditions, and some of those hormones control other endocrine glands. For example, when body water content falls, the pituitary releases antidiuretic hormone (ADH), which increases water reabsorption in the kidneys. The pituitary also releases thyroid-stimulating hormone (TSH), which acts on the thyroid gland, and follicle-stimulating hormone (FSH), which acts on the ovaries. Because its secretions influence so many other glands and processes, the pituitary coordinates much of the endocrine system.
These hormones in turn act on other glands to stimulate other hormones to be released to bring about effects.
The endocrine system works as a hierarchy of glands. The pituitary gland secretes hormones that travel in the blood to other endocrine glands and stimulate them to release their own hormones. For example, thyroid-stimulating hormone (TSH) from the pituitary stimulates the thyroid gland to release thyroxine, which increases metabolic rate. Similarly, follicle-stimulating hormone (FSH) from the pituitary acts on the ovaries to stimulate egg maturation and oestrogen release. This chain of stimulation means one signal can amplify and coordinate a widespread response, and the final hormone usually feeds back to inhibit further release from the pituitary, keeping levels stable.
Students should be able to identify the position of the following on a diagram of the human body: • pituitary gland • pancreas • thyroid • adrenal gland • ovary • testes.
You need to recognise the positions of the main endocrine glands on a diagram of the human body. The pituitary gland sits at the base of the brain. The thyroid is in the neck, in front of the trachea. The adrenal glands are two triangular glands sitting on top of the kidneys in the abdomen. The pancreas lies behind the stomach in the upper abdomen. The ovaries are in the lower abdomen of females, one on each side of the uterus. The testes are in the scrotum below the penis in males. When labelling, use the correct name for each gland and place the label line clearly on the gland, not on a nearby organ such as the kidney or stomach.
Your focus
- Describe how endocrine glands, hormones, blood and target organs work together.
- Explain the role of receptors in making hormonal responses specific.
- Apply the principles of hormonal coordination to a named example such as blood glucose control.
Show all 21 objectives
- Identify the main endocrine glands and the hormones they secrete.
- Describe how endocrine glands release hormones directly into the bloodstream.
- Distinguish endocrine glands from exocrine glands.
- Describe how blood carries hormones to target organs.
- Explain why only target organs respond to a given hormone.
- Give a named example linking a hormone, its target organ and its effect.
- Describe how nervous and endocrine coordination differ in speed and duration of effect.
- Explain why hormone responses are slower but longer-lasting than nervous responses.
- Apply the comparison to a named example such as adrenaline release or a reflex action.
- State the location of the pituitary gland and describe its role as the master gland.
- Name hormones secreted by the pituitary and outline their effects.
- Explain how pituitary secretions respond to changes in body conditions.
- Describe how pituitary hormones stimulate other endocrine glands to release hormones.
- Explain a named example of a hormone cascade, such as TSH acting on the thyroid.
- Relate the cascade to negative feedback control of hormone levels.
- Identify the pituitary, thyroid, adrenal, pancreas, ovary and testes on a human body diagram.
- State the location of each gland relative to nearby organs.
- Use correct gland names when labelling endocrine structures.
Human endocrine system exam tips
Marking Points
- State that endocrine glands secrete hormones directly into the bloodstream, not through ducts.
- Explain that blood transports hormones around the body to target organs or cells.
- Describe that target cells have receptors complementary to the hormone, so only specific cells respond.
- Give a named example, such as insulin from the pancreas acting on the liver to reduce blood glucose.
- Explain that hormonal responses are usually slower and longer lasting than nervous responses.
- Link hormonal control to negative feedback, where the response reverses the original change.
- Identify the endocrine system as a collection of glands, including named examples such as the pituitary, thyroid, adrenal, pancreas, ovaries and testes.
- State that endocrine glands are ductless and secrete hormones directly into the bloodstream.
- Define hormones as chemical messengers carried by the blood.
- Contrast endocrine glands with exocrine glands, which secrete through ducts.
- Explain that because hormones enter the blood, they can reach many organs, but only target cells respond.
- State that blood transports hormones from the secreting gland to target organs.
- Explain that target cells have receptors complementary to the hormone, making the response specific.
- Give a named example, such as insulin travelling from the pancreas to the liver to reduce blood glucose.
- Describe the effect produced at the target organ, such as glycogen storage in the liver or increased heart rate from adrenaline.
- Link the hormone, its target organ and its effect in a complete cause-and-effect sequence.
- Hormones are chemical messengers secreted by endocrine glands directly into the bloodstream.
- Hormones are carried in the blood to target organs, which takes time, so endocrine responses are slower than nervous responses.
- Nervous responses use electrical impulses along neurones and are rapid but short-lived.
- Endocrine effects act for longer because hormones remain in the blood and continue to stimulate target cells.
- A valid comparison must refer to both speed and duration, not just one feature.
- A suitable example, such as adrenaline increasing heart rate for a sustained period, can support the comparison.
- The pituitary gland is located in the brain, below the hypothalamus.
- It is described as the master gland because it controls the activity of other endocrine glands.
- It secretes hormones such as ADH, TSH and FSH directly into the blood.
- Its secretions are triggered by changes in body conditions, for example a fall in blood water content.
- Hormones from the pituitary travel in the blood to target organs, where they bring about specific effects.
- The pituitary itself is controlled by releasing factors from the hypothalamus.
- Hormones from the pituitary travel in the blood to other endocrine glands.
- The pituitary hormones stimulate those glands to secrete their own hormones.
- The second hormone brings about the specific effect on the target organ or tissue.
- An example is TSH from the pituitary stimulating the thyroid to release thyroxine.
- Another example is FSH from the pituitary stimulating the ovaries to release oestrogen.
- The final hormone often inhibits further secretion from the pituitary by negative feedback.
- Pituitary gland: at the base of the brain, below the hypothalamus.
- Thyroid: in the neck, in front of the trachea.
- Adrenal glands: on top of the kidneys in the abdomen.
- Pancreas: behind the stomach in the upper abdomen.
- Ovaries: in the lower abdomen of females, one on each side of the uterus.
- Testes: in the scrotum of males, below the penis.
Examiner Tips
- 💡Use the sequence stimulus, gland, hormone, blood, target organ, response, feedback when describing hormonal control.
- 💡Name specific glands and hormones, such as pancreas and insulin, to support general principles.
- 💡Compare hormonal and nervous coordination explicitly if the question asks for principles rather than a single example.
- 💡Use the phrase 'ductless glands secrete hormones directly into the bloodstream' when defining the endocrine system.
- 💡Name at least two glands and their hormones to show breadth of knowledge.
- 💡Distinguish endocrine from exocrine secretion if the question asks for a comparison.
- 💡Write the route as gland, hormone, blood, target organ, effect to make the sequence clear.
- 💡Name the target organ and the specific effect rather than saying 'it causes a change'.
- 💡Use examples such as insulin acting on the liver or adrenaline acting on the heart to show understanding.
- 💡Use comparative language such as slower and longer, because the question asks you to compare the two systems.
- 💡Link each statement to a named example, such as a reflex action for the nervous system and adrenaline for the endocrine system.
- 💡Check that your answer covers both speed and duration, as marks are often awarded for each distinct comparison.
- 💡Name at least one pituitary hormone and its effect, such as ADH increasing water reabsorption in the kidneys.
- 💡Explain the term master gland by linking it to control of other glands, not just to hormone release.
- 💡Use the phrase in response to body conditions to show that secretion is regulated by internal change.
- 💡Use the sequence pituitary hormone, target gland, second hormone, effect to structure your answer.
- 💡Give a named example with both hormones, such as TSH and thyroxine, to show the chain clearly.
- 💡Mention negative feedback where the question asks how hormone levels are controlled.
- 💡Draw label lines that end clearly on the gland, not in the space around it.
- 💡Use the exact names given in the specification, such as adrenal gland rather than adrenal.
- 💡Check whether the diagram shows a male or female body before labelling the testes or ovaries.
Common Mistakes
- Saying hormones travel along nerves; the correction is that hormones are carried in the bloodstream.
- Claiming every cell responds to every hormone; the correction is that only target cells with complementary receptors respond.
- Describing hormonal responses as faster than nervous responses; the correction is that hormonal responses are generally slower but longer lasting.
- Saying hormones are released into ducts; the correction is that endocrine glands are ductless and secrete hormones directly into the blood.
- Confusing hormones with enzymes; the correction is that hormones are chemical messengers carried in the blood, while enzymes are biological catalysts.
- Naming only one gland as the endocrine system; the correction is that the system includes several glands, such as the pituitary, thyroid, adrenal, pancreas, ovaries and testes.
- Saying the blood carries the hormone to every organ and every organ responds; the correction is that only target organs with complementary receptors respond.
- Confusing the gland that secretes a hormone with the organ it acts on; the correction is to name both, for example the pancreas secretes insulin and the liver responds.
- Stating that hormones are carried by nerves; the correction is that hormones are transported in the bloodstream.
- Stating that hormones travel along nerves; correction: hormones travel in the blood plasma to target organs.
- Claiming that nervous responses last longer than endocrine responses; correction: nervous responses are rapid and short-lived, while endocrine effects are slower to start but last longer.
- Writing that hormones act on any cell they contact; correction: hormones act only on target cells that have the complementary receptors.
- Saying the pituitary gland is in the abdomen; correction: it is in the brain, at the base of the brain below the hypothalamus.
- Writing that the pituitary secretes all the body's hormones; correction: it secretes several hormones, some of which stimulate other glands to release their own hormones.
- Confusing the pituitary with the pancreas; correction: the pancreas secretes insulin and glucagon to control blood glucose, while the pituitary secretes hormones such as ADH and TSH.
- Stating that the pituitary hormone itself produces the final effect; correction: the pituitary hormone stimulates another gland, and that gland's hormone produces the effect.
- Confusing which gland secretes which hormone, for example saying the thyroid secretes TSH; correction: the pituitary secretes TSH and the thyroid secretes thyroxine.
- Omitting the blood as the transport route; correction: hormones are carried in the blood plasma from the gland that secretes them to the target gland or organ.
- Labelling the adrenal gland on the kidney itself; correction: the adrenal glands sit on top of the kidneys.
- Placing the thyroid in the abdomen; correction: the thyroid is in the neck, in front of the trachea.
- Confusing the pancreas with the stomach; correction: the pancreas lies behind the stomach in the upper abdomen.