ANSWERS

1. State the function of the endocrine system.
   The co-ordinating system responsible for communication within the body by chemical messengers called hormones.
2. What is the difference between an endocrine and an exocrine gland?
   An endocrine gland secretes hormones directly into the blood stream, whilst an exocrine gland secretes hormones via a duct.
3. Define hormone.
   A chemical substance which is generated in one organ and carried by the blood to another, in which it excites activity.
4. Although most hormones are produced by the endocrine glands, there are several exceptions. List 3, giving their source of production and function.
   • Chorionic gonadotrophin - ectodermal layer of chorion during pregnancy - helps maintain corpus luteum throughout gestation.
   • Gastrin - stomach wall - stimulates secretion of hydrochloric acid from the oxyntic cells.
   • Secretin - small intestine wall - stimulates secretion of pancreatic and intestinal juices.
5. What is meant by a "mixed gland"? Give an example.
   A gland with both endocrine and exocrine functions. An example is the pancreas.
6. What is the name of the endocrine part of the pancreas?
   The islets of Langerhans.
7. Name the 2 hormones secreted by the islets of Langerhans.
   • Insulin - secreted by the beta cells in response to a rise in blood glucose.
   • Glucagon - secreted by the alpha cells in response to a fall in blood glucose.
8. What is the name of the disease which is caused by a disturbance in the oxidisation and utilisation of glucose, which is secondary to a malfunction of the beta cells of the pancreas?
   Diabetes mellitus.
9. What is secreted by the exocrine part of the pancreas?
   Digestive enzymes.
10. Where are the thyroid glands situated?
    Either side of the midline on the ventral aspect of the first few tracheal rings.
11. List the 3 hormones secreted by the thyroid glands and give their functions.
    • Thyroxin - regulation of the body's metabolic rate.
    • Tri-iodothyronine - regulation of the body's metabolic rate.
    • Thyrocalcitonin - decreases the level of plasma calcium by slowing the resorption of the mineral from bone.
12. What is another name for hypothyroidism (a condition where an insufficiency of thyroxin and tri-iodothyronine secretion may result in obesity, lethargy and poor condition of the skin and coat)?
    Myxoedema.
13. What is the name of the hormone produced by the parathyroid glands, and what is its function?
    Parathormone. This hormone is responsible for the regulation of metabolism and distribution of calcium in the body.
14. Hyperparathyroidism is a condition in which excessive activity of the parathyroid glands cause drainage of calcium from the bones. Name the 3 ways in which hyperparathyroidism may occur.
    • Neoplasia (cancer) of the parathyroid glands - this may result in the overproduction of parathormone, which may lead to the demineralisation of bone.
    • Chronic renal failure - this may result in secondary indirect hyperparathyroidism; calcium is lost in the urine and the body compensates by absorbing more from the bone.
    • Feeding a diet that is too low in calcium - the daily calcium requirements are not met and the body compensates by absorbing more from the bone.
15. Hyperparathyroidism as a result of chronic renal failure is also known as renal rickets, but it has another name too. What is it?
    Rubber jaw (this is because there is often preferential resorption of calcium from the maxillae and mandibles).
16. Can you name the 3 hormones produced by the ovary? In addition, state the part of the ovary from which each originates. What are the functions of these hormones?
    • Progesterone - corpus luteum - maintenance of pregnancy (acts on the lining of the uterus and on the mammary tissue).
    • Oestradiol - ovarian follicle cell wall - preparation of the external genitalia and genital tract for coitus and the reception of fertilised eggs.
    • Relaxin - corpus luteum (late pregnancy) - relaxation of the ligaments of the birth canal in order to ease the passage of the foetus.
17. Can you name the 2 hormones produced by the testes? In addition state the name of the cells from which each originates. What are the functions of these hormones?
    • Testosterone - the cells of Leydig (interstitial cells) - sperm production, development and maintenance of male secondary sexual characteristics.
    • Oestrogen - the Sertoli cells - control of sexual development (overproduction feminise the dog resulting in large nipples and the development of a soft, pendulous prepuce).
18. Where are the adrenal glands located?
    Close to the anterior pole of each kidney.
19. There are 2 regions within the adrenal glands, each secreting different hormones. Name these regions.
    • Cortex.
    • Medulla.
20. Name the 2 hormones secreted by the adrenal medulla.
    • Adrenaline (epinephrine).
    • Noradrenaline (norepinephrine).
21. Adrenaline and noradrenaline are controlled by the fibres of the sympathetic nervous system and act to prepare the body for emergencies. List 3 clinical signs that occur as a result of the secretion of these hormones.
    • Increased rate and depth of respiration as a result of dilation of the bronchioles.
    • Raised blood pressure as a result of constriction of surface vessels and stimulation of cardiac output.
    • Increased blood glucose level as a result of increased glycogen breakdown.
22. Name the 3 groups of hormones produced by the adrenal cortex.
    • Glucocorticoids (cortisol & corticosterone).
    • Mineralocorticoids (aldosterone).
    • Adrenal sex steroids.
23. What do the hormones produced by the adrenal cortex have in common?
    • They are all naturally occurring steroids (a group of hormones chemically related to cholesterol).
    • Steroids may also be synthetically produced (e.g. Prednisolone - a steroid drug used in the treatment of inflammatory conditions).
24. What is the most likely cause of an increased secretion of glucocorticoids?
    Stress.
25. State the 2 main functions of the glucocorticoids.
    • Promotion of an increase in blood sugar levels.
    • Depression of inflammation.
26. What is the name of the hormone that plays an important role in the maintenance of the electrolyte balance of the body?
    Aldosterone. This aids the retention of sodium and the excretion of sodium.
27. Name the 2 components of the pituitary gland.
    • Anterior pituitary (adenohypophysis).
    • Posterior pituitary (neurohypophysis).
28. The anterior pituitary produces 7 hormones. Name them and state the function of each.
    • Thyroid stimulating hormone (also known as thyrotropic hormone or TSH) - regulation of the uptake of iodine by the thyroid gland, thyroid hormone production & the release of the thyroid hormones into the circulation.
    • Growth hormone (somatotrophin) - control of the growth rate of the epiphyses in the bones of young animals; also involved in protein synthesis, glucose conservation, fat metabolism and energy regulation.
    • Adrenocorticotrophic hormone (ACTH) - regulation of the secretion of the adreno-cortical hormones.
    • Prolactin - stimulation of milk production during late pregnancy & lactation.
    • Follicle stimulating hormone (FSH) - stimulation of the maturation of ovarian follicles.
    • Lutenising hormone (LH) - stimulation of the development of the corpus luteum in females, and control of testosterone secretion in males.
    • Interstitial cell stimulating hormone (ICSH) - stimulation of sperm production.
29. Name the 2 hormones produced by the posterior pituitary and state the function of each.
    • Antidiuretic hormone (ADH) - stimulates an increase in water absorption by the renal tubules, thus reducing the quantity of urine excreted and increasing water retention within the body.
    • Oxytocin - promotes contraction of the smooth muscle of the uterus and of the ducts in the mammary glands during pregnancy and parturition (birth).
30. By what other name is antidiuretic hormone known?
    Vasopressin.