Sample Course Notes
THE ENDOCRINE SYSTEM
Throughout a mammal's body, there are groups of specialised cells which form large glands. These glands are unlike all other glands because they have no duct and so pour their secretions directly and by diffusion into the blood vessels. Because of this unique feature they are called ductless, or endocrine, glands. The secretions of endocrine glands are called hormones and these belong to two main chemical groups, the steroids and the amino acid derivatives.
The secretions of the endocrine glands play an important part in regulating the functions of the body and some of them act directly on muscles and other glands in a way that is very similar to the actions of nerve impulses. Other hormones are concerned with the regulation of the body's metabolism and growth. Some endocrine glands are themselves stimulated by hormones from other glands, but are under the control of the nervous system and thus are able to respond very rapidly to changes.
Examples of endocrine glands include: the pituitary body; the thyroid; the parathyroids; the testes and ovaries; the pancreas; the thymus and the mucous membranes of the stomach and small intestines. These are discussed in more detail below. Again, do not try to learn all the organs and hormones off by heart. The following is included to give you background knowledge so that when you come across the hormone in later courses you will be familiar with its name.
The Pituitary Body
This is a fairly large gland situated in the base of the skull just below the hypothalamus. The hormones produced by the pituitary that are of interest to the animal manager are:
Thyroid-stimulating hormone (T.S.H.) which influences the development of the thyroid gland. (The thyroid gland controls growth and performance).
Follicle stimulating hormone (F.S.H.) and the luteinising hormone (L.H.), both of which are involved in reproduction.
Adrenocorticotropic hormone (A.C.T.H.) which stimulates the activity of the adrenal body. (The adrenal body has an important role in regulating the heart beat, blood pressure and the level of glucose in the blood).
Lactogenic hormone (L.T.H.) which starts milk production in the pregnant female.
Somatrophic hormone (S.T.H.) which stimulates growth. In excess, it causes the formation of giants. It also stimulates the release of glucagon from the pancreas.
Oxytocin which is released when the mammary glands are stimulated by suckling and which causes the ejection of milk.
Antidiuretic hormone (A.D.H.) which increases the re-absorption of water and sodium back into the body and so decreases the amount of urine produced.
The Thyroid
This is a relatively large gland lying in the region of the throat. The main hormone produced is thyroxine whose main function is to promote growth in the young animal and to speed up most of the body functions in the adult. A deficiency of thyroxine causes a general slowing down and sluggishness in the animal while an excess has the opposite effect.
The Parathyroids
These are found next to the thyroid. Parathyroids produce a hormone which works with Vitamin D to maintain an adequate concentration of calcium in the blood. The effect of this hormone is thought to be one reason for "milk fever" in newly calved cows. Milk fever is caused when the demand for milk by the calf produces a lack of calcium in the mother's body.
The Thymus
This is found next to the heart. Its main function is to produce lymphocytes in the young animal. It also helps to develop immunological reactions which defend the animal against bacterial and viral infections. The thymus becomes less active as the animal grows.
The Adrenal Bodies
These are found near the kidneys. The important hormones produced are:
Adrenalin which increases the rate of the heart beat and output of the heart so that more blood is brought to the muscles. It increases the amount of glucose in the blood by increasing the rate of breakdown of glycogen in the liver. This is accompanied by increased oxygen consumption and an increase in the production of heat and energy. Adrenalin causes symptoms of anxiety in humans and animals.
Noradrenaline has very similar effects to adrenalin but increases the blood pressure by constricting the arteries through stimulation of the smooth muscle in their walls.
Corticosteroids which increase the level of glucose in the blood by increasing the rate of breakdown of protein and fats. They also induce male secondary sexual characteristics (such as more muscling, coarse hair etc).
These hormones are steroids and are often taken by athletes (especially weight-lifters) to increase their muscle and so their strength. Women who take these steroids are quite likely to develop male characteristics such as hair on the face and chest!
The Pancreas
This organ is situated beside the liver. It produces two protein hormones : insulin and glucagon. Insulin lowers the level of glucose in the blood by increasing the rate at which it is converted to glycogen. Glucagon acts to opposite way by increasing the rate at which glycogen in the liver is converted into glucose. Between them, these two hormones control the amount of glucose in the blood.
The Testes
The testes produce a series of steroid hormones called androgens, the chief one being testosterone. Their functions are to maintain the male ducts and glands in good condition; to develop male characteristics (horn, hair, deep voice etc.); to stimulate sperm production and to increase the rate of protein build-up when necessary.
The Ovaries
Ovarian hormones include oestrogen, progesterone and relaxin. The first two hormones are steroids and the last is a protein hormone.
Oestrogen prepare the reproductive tract for reproduction. They also produce many secondary sexual characteristics such as the enlargement of the mammary glands at puberty.
Progesterone also prepares the reproductive tract for pregnancy and activates the mammary glands to secrete milk. This hormone will suppress ovulation while the female is pregnant. Oestrogen and progesterone are released at different times in a cycle that is repeated until fertilisation takes place. After pregnancy and birth, the cycle sets up again.
Relaxin causes the cervix of the uterus to widen at birth and also stops uterine contractions.
The Pineal Body
This is found in the brain and produces a hormone called melatonin. This appears to be sensitive to light and is thought to control seasonal sexual activity in animals (e.g. coming into heat in spring because of the longer day light hours).
The Mucous Membrane of the Stomach
This membrane produces the hormone gastrin which affects the breakdown and digestion of foodstuffs.
The Mucous Membrane of the Small Intestine
This membrane produces the hormone secretin which travels to the pancreas via the bloodstream and stimulates the production of the pancreatic juices.
EXAMPLE ASSIGNMENT
1. Distinguish between the major animal types used in primary production, including birds, fish, ruminants, and non ruminants. Write no more than 150 words.
2. List different types of products commercially produced or derived from various farm or wild animals, such as:
- cattle
- sheep
- deer
- poultry
- pigs
- fish
- elephants
- kangaroos.
3. Explain the role of pastures for animal husbandry, in your locality. Write no more than 100 words.
4. Report on the scope of animal production in your locality. Write no more than 100 words.
5. Using the internet or other reference materials identify parts of an animal cell and make a diagram using the following:
- cell membrane
- nucleus
- cytoplasm
- flagellum
- cilium
- centriole
- ribosomes
- endoplasmic reticulatum
- nucleolus
- chromosomes
- golgi body
- mitochondrion
- lysosome
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Dr. Gareth Pearce BSc(Hons), BVSc, MA, MVetS, PhD, GradCertEd(HE), PGCertAqVetS, PGCertWLBio&Cons, DiplECPHM, MRCVS. Gareth has over 25 years of experience in teaching and research in agriculture, veterinary medicine, wildlife ecology and conservation in a variety of colleges and universities in the UK, Australia and New Zealand. He qualified as a veterinary surgeon at the Universities of Melbourne and Bristol, having previously graduated in Agricultural Science and gained a PhD in Livestock Behaviour and Production. He also has post-graduate qualifications in Education, Wildlife Conservation Medicine, Aquatic Veterinary Studies and Wildlife Biology & Conservation.
Anna Sylvester B.Sc.Hons.(Human Biology), M.Sc.Equine
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Marius Erasmus B.Sc.Agric., B.Sc.(Wildlife), M.Sc.Agric.
Subsequent to completing a BSc (agric) degree in animal science, he completed an honours degree in wildlife management, and a masters degree in production animal physiology. Following the Masters degree, he has worked for 9 years in the UK, and South Africa; in wildlife management, dairy, beef and poultry farming.
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