Equine biological systems

Transcription

1 Equine biological systems Pack 21 The endocrine system Pack Code: EBS21 This pack will help you to: List the functions of the endocrine system. Describe the glands and hormones of the endocrine system

2 About this pack Objectives When you have completed this pack you should be able to describe how the horse s endocrine system works. The pack will help you to: List the functions of the endocrine system. Describe the glands and hormones of the endocrine system. The pack is also relevant to the level 3 unit Understand Animal Anatomy and Physiology, and in particular: Outcome 1: Know the structure and functions of biological systems in animals. Outcome 3: Understand the biological control mechanisms in animals. Links to other packs This is one of a series of learning packs, each tackling an aspect of horse biological systems. They are: Pack 1: The skeleton Pack 2: Joints Pack 3: Circulation Pack 4: Respiration Pack 5: The digestive system of the horse Pack 20: The lymphatic system Pack 21: The endocrine system Pack 22: The nervous system There are also packs on: Reproduction Cells, tissues and sensory organs Breeding and genetics Equine biological systems 2

3 Introduction The endocrine system forms part of the horse s regulatory or control system. It contains a number of glands that produce hormones. These are vital to homeostasis keeping the horse s body in a stable condition. For example, hormones help regulate the balance of salt and water in the blood, and levels of blood glucose. Hormones are chemical messages which act on one or more of the body s organs by binding to receptors on the surface of cells in the target organ. Circulating hormones enter the bloodstream and act on distant organs, while local hormones act either on the cell producing them (autocrines) or a nearby cell (paracrines). Functions of the endocrine system Hormones regulate a number of vital body functions: Growth. The growth hormone stimulates growth of bone and tissue. Metabolism. A number of hormones help to regulate heart rate, blood pressure, digestion and other aspects of an animal s metabolism. Reproduction. Hormones such as testosterone (in males), and oestrogen and progesterone (in females) are vital to sexual function. The hypothalamus and the pituitary gland in the brain are the starting point for most of these functions. They produce hormones themselves, and also send messages to other glands to instruct them to produce hormones. This diagram shows the position in the horse of the hypothalamus and endocrine glands that we shall examine in this pack. Hypothalamus and pituitary gland Adrenal glands Kidneys Ovary Testes Thyroid and parathyroid glands Pancreas Equine biological systems 3

4 The hypothalamus and pituitary gland The main control centre of the endocrine system is a part of the brain called the hypothalamus and the pituitary gland, shown in the following diagram: Hypothalamus Pituitary gland The hypothalamus can respond to internal and external factors. For example: It responds to changes in the seasons and length of days to synchronise behaviour between mare and stallion so that both are ready to breed at the same time, and so that foals are born at a favourable time of the year. It responds to changes in the level of calcium in the blood to instruct glands to produce hormones which increase or reduce calcium absorption by the bones. It does this by secreting releasing hormones and responding to feedback. Osmoregulation part of homeostasis As an example, the hypothalamus regulates levels of water in the blood (osmoregulation). Here is how one hormone contributes to the process: 1 The hypothalamus detects that there is too little water in the blood. 2 The pituitary gland releases anitdiuretic hormone (ADH) into the bloodstream 3 ADH encourages the kidneys to reabsorb water from urine. 4 The blood water level returns to normal. 5 The hypothalamus detects this (feedback) and less ADH is produced. Too little water in blood Hypothalamus Detects and instructs Feedback Pituitary Blood water level returns to normal Kidneys reabsorb water ADH Equine biological systems 4

5 Hormones produced by the pituitary gland The pituitary gland has two parts: the anterior lobe and the posterior lobe. The main hormones produced by the anterior lobe are as follows: Growth hormone. This stimulates the rate of growth of bone and tissue in foals. Thyroid-stimulating hormone. This stimulates the thyroid gland to produce a range of hormones which regulate metabolism. Adrenocorticotropin hormone. This stimulates the adrenal gland to produce a range of hormones. Follicular stimulating hormone and luteinising hormone. These stimulate production of reproductive hormones in the mare. An equivalent hormone, interstitial cell stimulating hormone, stimulates production of testosterone in stallions. Prolactin. This hormone regulates milk production. The posterior lobe produces: Anitdiuretic hormone. This controls water loss from the kidneys and helps to maintain homeostasis. Oxytocin. This helps to stimulate foaling and milk production. Review quiz 1 The hypothalamus is located in:! a) the brain! b) the pancreas 2 The hypothalamus instructs the pituitary by producing:! a) growth hormones! b) releasing hormones 3 Match the following pituitary hormones with their functions: Growth hormone Thyroid-stimulating hormone Adrenocorticotropin hormone Luteinising hormone Prolactin stimulates production of the mare s reproductive hormones stimulates the adrenal gland regulates milk production stimulates the thyroid gland stimulates the rate of growth of bone and tissue in foals Check your answers with those at the end of this pack. Equine biological systems 5

6 The thyroid and parathyroid glands The adrenal glands The thyroid and parathyroid glands (small glands beside the thyroid gland) are located at the front of the neck. They produce a range of hormones which regulate metabolism. The thyroid itself produces: Thyroxin. This helps maintain the metabolic rate and regulates oxygen in the cells. Calcitonin. If levels of calcium in the blood are too high, this hormone stimulates absorption of calcium by the bones so that it can be stored for later use. The parathyroid glands produce: Parathyroid hormone. If levels of calcium in the blood fall too low, this hormone raises calcium levels to the right amount. The adrenal glands are located on top of each kidney. Each adrenal gland has two parts: the adrenal cortex and the adrenal medulla. The adrenal cortex produces corticosteroids such as: Cortisol, which is released in response to stress and low levels of blood glucose. It increases blood sugar levels, suppresses the immune system and has an impact on the metabolism. Aldosterone, which contributes to the process of osmoregulation introduced earlier. It helps regulate the balance of salt and water in the blood by encouraging the kidneys to reabsorb sodium, so increasing water retention. The adrenal medulla produces catecholamines such as: Adrenalin, which forms part of a horse s fight or flight response to danger. If the horse faces a threat the adrenal glands release adrenalin, which increases heart rate and blood pressure, and dilates air passages. These responses help the horse to flee, or to face the threat. Equine biological systems 6

7 The reproductive glands The main reproductive glands are the ovaries (in mares) and the testes (in stallions). The ovaries produce hormones that help regulate ovulation, pregnancy and the mare s sexual development, in particular: Oestrogen. This is produced by the follicles and is important in the oestrus cycle and in preparation for mating. Progesterone. This helps prepare for and maintain pregnancy. In particular it prevents the mare coming into heat while she is pregnant. The testes produce: Testosterone. This stimulates sperm production as well as the stallion s sexual development and behaviour eg aggression or territoriality. Small amounts of oestrogen. This assists reproduction and metabolism. The pancreas and glucoregulation The pancreas is located close to the stomach. It produces hormones that regulate the blood glucose levels a process called glucoregulation: Insulin: This lowers levels of glucose in the blood. Glucagon. This raises levels of glucose in the blood. Somatostatin. This avoids big fluctuations in blood glucose levels. The pancreas also produces enzymes which are used in digestion. Activity 1 Which gland secretes each of the following hormones? a) testosterone b) adrenalin c) oestrogen d) calcitonin 2 What is the main function of each of the following hormones? a) parathyroid hormone b) calcitonin c) oestrogen d) thyroxin Check your answers with those at the end of the pack. Equine biological systems 7

8 Endocrine disorders Problems arise when the endocrine system produces too much, or not enough, of a hormone. Endocrine disorders are less common in horses than in other mammals but the two most common disorders for horses are: Pituitary Pars Intermedia Dysfunction Pituitary Pars Intermedia Dysfunction (PPID sometimes also known as equine Cushings disease) happens when the pituitary glad produces to many hormones (sometimes as the result of a tumour) and this leads to the adrenal glands producing too many corticosteroids. Symptoms include chronic infections, laminitis, a long coat and failure to shed, sweating and increased water intake and urination. The condition cannot be cured but can be managed and treated. Glossary Equine Metabolic Syndrome Equine Metabolic Syndrome is caused by too much cortisol in fat cells. Symptoms include laminitis, unusual fat deposits and insulin resistance (where the body reacts inappropriately to insulin). Again, the condition cannot be cured but can be managed, especially through the diet. Less common disorders include: Horses can occasionally suffer hypothyroidism a shortage of thyroxin which can cause stunted growth in foals, and sluggishness in older horses. In rare cases a horse may suffer hyperlipemia (or fatty liver disease), hyperthyroidism (too much thyroxin) or diabetes (where the pancreas does not produce enough insulin). Glucoregulation Homeostasis Hyperparathyroidism Hypothalamus Osmoregulation PPID Regulation of levels of blood sugar by the pancreas Processes that keep the body in a stable condition Too much parathyroid hormone Part of the brain which helps control the endocrine system Regulation of levels of water in the blood by the hypothalamus and kidneys Pituitary Pars Intermedia Dysfunction Equine biological systems 8

9 Further reading Answers to activities Reece, W. O., Functional Anatomy and Physiology of Domestic Animals (4 rd Ed) Wiley-Blackwell Lane, D. R. and Cooper, B., Veterinary Nursing (formerly Jones s Animal Nursing, 3 rd Revised Ed). Butterworth Heinemann Review quiz on page 5 1 The hypothalamus is located in (a) the brain 2 The hypothalamus instructs the pituitary by producing (b) releasing hormones 3 Match the following pituitary hormones with their functions: Growth hormone Thyroid-stimulating hormone Adrenocorticotropin hormone Luteinising hormone Prolactin stimulates the rate of growth of bone and tissue in foals. stimulates the thyroid gland stimulates the adrenal gland stimulates production of the mare s reproduction hormones regulates milk production. Activity on page 7 1 Which gland secretes each of the following hormones? a) testosterone the testes b) adrenalin the adenal glands c) oestrogen the ovaries d) calcitonin the thyroid 2 What is the main function of each of the following hormones? a) parathyroid hormone if levels of calcium in the blood fall too low, this hormone raises calcium levels to the right amount b) calcitonin if levels of calcium in the blood are too high, this hormone stimulates absorption of calcium by the bones so that it can be stored for later use c) oestrogen is important in the oestrus cycle and in preparation for mating d) thyroxin helps maintain the metabolic rate and regulates oxygen in the cells Equine biological systems 9

10 Knowledge quiz Check your knowledge with the following questions. 1 Give three functions of the endocrine system: a) b) c) 2 Which gland secretes each of the following hormones? a) prolactin b) adrenalin c) progesterone d) calcitonin 2 What is the main function of: a) prolactin? b) growth hormone? c) thyroxin? d) insulin? e) parathyroid hormone? 4 Give two disorders of the equine endocrine system: a) b) Equine biological systems 10

11 Acknowledgements This learning pack has been produced by the Land Based Colleges National Consortium Ltd. The LBCNC is a consortium of colleges working in the land-based sector which cooperate in the development and production of quality flexible learning materials which encourage independent learning. We would like to acknowledge the contributions made by the following individuals and colleges in the development of this learning pack. Critical review Claudine Sutton, Derby College Lorna Cameron, Sparsholt College Cover photograph: Steve Watson, Riseholme College Developed and produced for LBCNC by Learners First Revised in September The Land Based Colleges National Consortium Ltd. All rights reserved. Permission to photocopy or adapt the material in this learning pack is granted to members of the Land Based Colleges National Consortium Ltd. only. For further information please contact the LBCNC project management team at 7 Tyne Road, Bishopston, Bristol BS7 8EE. Tel Equine biological systems 11