1. Chapter 35
The Endocrine System

2. Objectives – What you will need to know from this section
Define the term: hormone.
Outline the Endocrine System.
Compare action, distinguishing between exocrine & endocrine glands.
State the location of the principal glands in the human.
Outline for each gland, one hormone & its function.
Explain 1 Hormone giving a description of its deficiency symptoms, excess symptoms & corrective measures
Name 2 examples of hormone supplements & their use.

3. The ability to detect change and to respond is called sensitivity.
Response is a form of defence that allows organisms to survive.
The endocrine glands interact with the nervous system to provide the
communication,
co-ordination and
control within the body.
Thyroid
Pancreas
Adrenal
Pituitary O

4. The endocrine system is a group of glands that produce chemicals called hormones.
Most hormones are proteins, except for reproductive hormones e.g. Testosterone which are steroid based (a steroid is a form of lipid).
Hormones are chemical ‘messengers’, produced in specialised glands – 2 types, and are transported in the blood or via a duct to a particular area (the target organ), where they have their effect.

5. The endocrine glands (10) are often called ductless glands
The endocrine glands (10) are often called ductless glands. They do not have a duct / tubes and they produce hormones that are released directly into the blood e.g. insulin.
Exocrine glands have ducts to carry their secretions e.g. salivary glands, tear glands & sweat glands.

6. The action of hormones is slower and more general than nerve action.
They control mainly long-term changes such as growth, metabolism and sexual maturity.
On passing through the liver, the hormones are broken down and excreted by the kidneys.
The nervous system relies on electrical signals, carried by specialised cells, and is involved in fast responses.

7. LEARNING CHECK What is sensitivity? What are Hormones? Types?
What are endocrine glands?
What are exocrine glands?
How would you describe the action of Hormones?
What role does the liver play in relation to hormones?

8. ENDOCRINE GLANDS

10. The brain region keeps a check on internal organs and activities, such as the level of carbon dioxide or water in the blood.
Most hormone activity is controlled directly or indirectly by the hypothalamus and pituitary gland.

11. The pituitary is often called the ‘master gland’, as many of its hormones trigger other glands to release theirs. It produces
ADH to stimulate water reabsorption in the kidneys,
TSH which stimulates the thyroid gland to release thyroxine, and
FSH which controls the functions of the reproductive organs.

13. LEARNING CHECK
Which gland is often called the “master gland”?
Why? 

14. The thyroid gland, on the trachea in the neck, produces thyroxine, which controls the rate of all the body’s reactions -metabolism.
The parathyroid gland behind the thyroid gland produces parathyroid hormone, which controls calcium levels in the blood.
parathyroid hormone, which stimulates the release of calcium from the bones into the blood.

15. The adrenal glands located on top of the kidneys produces adrenaline, which helps the body cope with emergencies —the ‘flight/fright/fight’ hormone.

16. The pancreas is both an endocrine and exocrine gland.
Most of the pancreas produces enzymes e.g. amylase for digestion, which flow through ducts to the duodenum - exocrine gland.
The Islets of Langerhans produce insulin which is carried away by the blood.
Insulin stimulates cells e.g. Muscle cells to absorb glucose from the blood, and store it as glycogen.

17. The ovary produces oestrogen and progesterone to prepare the female for pregnancy.
The testes produce testosterone which triggers sperm production and growth in the male.

18. LEARNING CHECK Name the main endocrine glands in the body.
Name one hormone produced by each gland.
Give one function for each hormone.
Where would you find the Islets of Langerhans?
What hormone do they produce?
What is glucose stored in the human body as?
Name 3 hormones involved in the development of secondary sexual characteristics.

19. DISORDERS of the Endocrine System
Endocrine glands can sometimes malfunction

20. THYROID gland: thyroxine deficiency
Under production of thyroxine can cause reduced physical development in young children– cretinism.
In adults low levels of thyroxine can reduce the rate of metabolism – seen as tiredness, lack of energy.
It can cause the thyroid gland to swell – goitre.
Taking the hormone in tablet form once a day can solve the problem – hormone supplement

21. THYROID gland: thyroxine excess
Excess thyroxine can greatly increase metabolic rate. Symptoms included bulging eyes, hunger – known as Graves’s disease.
Treatment is often by removal of part of the gland.

22. Levothyroxine is a synthetic (man-made) version of the principle thyroid hormone, thyroxine (T4) that is made and released by the thyroid gland.
Thyroid hormone increases the metabolic rate of cells of all tissues in the body.
In the fetus and newborn, thyroid hormone is important for the growth and development of all tissues including bones and the brain.
In adults, thyroid hormone helps to maintain brain function, food metabolism, and body temperature, among other effects.

23. PANCREAS gland
In some people, the pancreas cannot produce or properly use insulin, which results in a disease - diabetes.
Insulin is a hormone that is needed to convert sugar, starches and other food into energy needed for daily life. Glucose cannot get into cells, which disrupts metabolism causing high concentrations of glucose in the urine or blood, severe thirst, tiredness.
It is thought that both genetics and environmental factors such as obesity and lack of exercise appear to play roles.

25. Type 1 diabetes is usually diagnosed in children and young adults, and was previously known as juvenile diabetes. In type 1 diabetes, the body does not produce insulin. It is controlled by regular insulin injections.
Type 2 diabetes is the most common form of diabetes. In type 2 diabetes, either the body does not produce enough insulin or the cells ignore the insulin.

26. Regular daily injections of insulin are required – hormone supplement.
When glucose builds up in the blood instead of going into cells, it can cause two problems:
Right away, your cells may be starved for energy.
2. Over time, high blood glucose levels may hurt organs - eyes, kidneys, nerves or heart.

27. OVARIES gland:
In oral contraceptives, oestrogen and progesterone are taken to prevent pregnancy – hormone supplement

29. LEARNING CHECK Name some disorders of the endocrine system.
For each one, give the symptoms and a possible treatment for the disorder.
What are hormone supplements?

30. Comparison of the endocrine and nervous systems - 1
Target organ
Received by
Blood
Carried by
Gland
Cells involved
Cells throughout the body
Message sent to
Chemical (Hormone)
Message
Endocrine

31. Comparison of the endocrine and nervous systems - 1
Cells involved
Gland
Sense receptor
Message
Chemical (Hormone)
Electrical(Impulse)
Carried by
Blood
Nerve cell
Message sent to
Cells throughout the body
A specific cell or tissue
Received by
Target organ
Effector (muscle or gland)

32. Comparison of the endocrine and nervous systems 2
long-lasting (hours)
Duration
Can be widespread
Effects
Usually slow
Speed of transmission
Endocrine

33. Comparison of the endocrine and nervous systems -2
Speed of transmission
Usually slow
Rapid
Effects
Can be widespread
Localised usually
Duration
long-lasting (hours)
Usually brief (seconds)

35. Feedback Mechanism of Hormone Control
The function of the thyroid gland is to take iodine, found in many foods, and convert it into thyroid hormones.
Every cell in the body depends upon thyroid hormones for regulation of their metabolism.
When the level of thyroxine drops too low,
the hypothalamus produces Thyroid Releasing Hormone (TRH) which
causes the pituitary gland to produce Thyroid Stimulating Hormone (TSH)
which stimulates the thyroid gland to produce thyroxine.

36. When thyroxine levels increase the pituitary senses this and responds by decreasing its TSH production.
Thyroxine levels
decrease
Thyroxine levels increase

37. THYROXINE control – Feedback