2Introduction to The Human Endocrine System The purpose of the Endocrine system is to aid in maintaining homeostasis.The endocrine system produces hormones. Hormones are chemical regulators produced by cells in one part of the body that affect cells in another part of the body.The endocrine system consists of a series of glands having no direct connection to other parts of the body, i.e.. they are ductless.Note: Exocrine Glands have a duct to connect them directly to a specific site in the body, e.g.. the salivary glands.
4HormonesHormones are produced and secreted into the blood stream by the endocrine glands. The circulatory system carries hormones to other parts of the body via the blood.Hormones are chemical messengers responsible for co-ordinating certain body functions. In general they are stimulatory.The word hormone comes from the Greek hormon, meaning “to excite or set into motion”.
5...Hormones Function of Hormones Hormones exert their effects on specific locations in the body called target tissues (this could be a whole organ or just a few cells). Their effects are long term, controlling functions such as growth, metabolism, maturity and the balance of chemicals in the body.
6...Hormones The Mode of Action of Hormones Hormones act at the molecular level by causing changes in cell metabolism, for example:protein synthesisenzyme activitypermeability of cell membranesDNA translationthere are two basic ways in which hormones do this, based on the type of hormone:
7(What’s Metabolism?)The sum of the chemical reactions occurring within a cell or a whole organism; includes the energy-releasing breakdown of molecules (catabolism) and the synthesis of new molecules (anabolism).
9...Hormones Steroid Hormones mcgraw-hill animation steroid hormonessteroid_hormone animationSteroid HormonesThe hormone diffuses directly into the cell.Here it fuses with a receptor molecule.This receptor molecule is only present in the target cells for that particular hormone.The hormone/receptor combination effects the translation of DNA in the nucleus.
11...Hormones Protein Hormones: The hormone binds to a receptor molecule located on the surface of the cells of the target tissue.This causes the production of a secondary messenger molecule within the cell, e.g.. cyclic AMP.The secondary messenger molecule causes a change in cell metabolism, e.g.. activates an enzyme.
12Negative FeedbackIn a negative feedback system some factor, such as blood pressure, changes. The change is detected by a sensor. The sensor sends a message to an integrating center which in turn stimulates an effector. The effector will do something to alter the factor that changed.In the example to the right blood pressure has increased. Receptors in the carotid arteries detect the change in blood pressure and send a message to the brain. The brain will cause the heart to beat slower and thus decrease the blood pressure. Decreasing heart rate has a negative effect on blood pressure.
13The Pituitary Gland: The Master Gland An outgrowth from the base of the fore-brain and in direct nervous contact with it.This gland secretes a range of hormones;Some of these hormones have a direct effect on their target organs...while others have an indirect effect by causing other glands to secrete further hormones.It is for this reason that the pituitary gland is often called the master gland, as it regulates the secretions of a number of other endocrine glands.
14... The Pituitary Gland Structure The pituitary gland consists of two lobes, the anterior and the posterior lobes. Each releases specific hormones under the direction of the hypothalamus.
15The POSTERIOR Pituitary The posterior lobe of the pituitary stores and releases hormones which have been produced by the hypothalamus. The hormones travel by way of specialized nerve cells from the hypothalamus to the pituitary.
16The Hormones of the POSTERIOR Pituitary Antidiuretic Hormone (ADH)regulates water balance in the body by increasing water absorption by the kidneysOxytocin:stimulates uterine contractions during birthalso stimulates milk production
17The ANTERIOR Pituitary The anterior lobe of the pituitary, unlike the posterior lobe, produces its own hormones.Like the posterior lobe, the anterior lobe is richly supplied with nerves from the hypothalamus.The hypothalamus regulates the release of hormones from the anterior pituitary. Hormones are secreted from the nerve ends of the cells of the hypothalamus and transported in the blood to the pituitary gland. Most of these hormones activate specific cells in the pituitary, causing the release of pituitary hormones, which are then carried by the blood to target tissues.
18The Hormones of the ANTERIOR Pituitary Somatotropin (STH) or Growth Hormone (GH)has a direct effect on the growth of tissuesis produced in greater quantities during childhoodThyroid Stimulating Hormone (TSH)has an indirect effect on metabolic rate, by affecting the thyroid glandstimulates the thyroid gland, causing it to produce the hormone thyroxin
19...The Hormones of the ANTERIOR Pituitary Adrenocorticotropic Hormone (ACTH)stimulates the adrenal cortex to produce a range of hormones responsible for stress reliefGonadotropic Hormones:Follicle Stimulating Hormone (FSH)Females: stimulates the development andproduction of ova, causes the release of estrogensMales: stimulates the production of sperm cellsLutinizing Hormone (LH)Females: causes the development of the corpus luteum. (A structure that develops in the ovary and secretes progesterone )Males: (called interstitial cell stimulating hormone - ICSH) stimulates the production of testosterone from the interstitial cells of the testes
20...The Hormones of the ANTERIOR Pituitary Prolactinstimulates milk production after birthMelanocyte Stimulating Hormone (MSH)stimulates melanin (a brown pigment) production in the skinresponsible for changing the skin colour of certain reptiles and amphibians
24Control of Pituitary Hormone Secretions: Brought about by the hypothalamus, which monitors the levels of hormones and other chemicals in the blood and forms a connection between the nervous and endocrine systems.
25Control of Secretions from the Anterior Pituitary The hypothalamus contains neurosecretory cells which produce and release pituitary hormone releasing factors into the capillaries in the upper part of the anterior pituitarythese releasing factors stimulate specific cells in the anterior pituitary to produce and release the various tropins and other hormones of the anterior pituitary into the blood leaving the pituitary gland, to be carried to their target organs.Certain releasing factors inhibit the release of hormones from the anterior pituitary e.g.. dopamine inhibits the secretion of prolactin
26Control of the secretions from the posterior pituitary Unlike the anterior pituitary, the posterior pituitary does not actually produce its own hormones.The hormones released from the posterior pituitary are produced in the hypothalamus and pass down neurosecretory cells into the cells of the posterior pituitary. They are stored here and released into the blood leaving the pituitary gland when needed.
27Produces three hormones; The Thyroid Gland:Produces three hormones;Thyroxine which controls the basic metabolic rate and also influences growth rate by controlling the growth and differentiation of cells.Triiodothyroxine, which appears to have the same functions as thyroxine.Calcitonin which effects bone development and muscle contraction (both need calcium)
28Thyroid disorders Thyroid absorbs iodine from blood. Iodine is assimilated into thyroglobin.When stimulated, thyroglobin becomes thyroxine.Goiter is when there is no iodine, therefore the precursor to thyroglobin builds up in the thyroid gland.Iodine is added to table salt, i.e.. iodized salt, to overcome the problem of dietary deficiency of iodine.
29Over secretion of thyroxine: Referred to as hyperthyroidism.In adults this condition causes over-activity, decreased body weight, increased heart rate and blood pressure, which can lead to heart failure - called thyrotoxicosis.
30Under secretion of thyroxine: Referred to as hypothyroidismIn infants: results in retarded mental and physical development called cretinism. This can be easily treated by early administration of thyroid extract.In adults: causes sluggishness and over-weight. This condition is called myxoedema.
31Control of Thyroxine Production This provides an example of negative feedback control of the endocrine system:Clip 1
32The Parathyroid Glands: These are located as two pairs of small glands on either side of the thyroid glandThey secrete parathormone which increases plasma calcium concentrations (opposite effect to calcitonin)Parathormone stimulates the breakdown of calcium in the bones and causes it to be released into the blood.
33Over secretion of parathormone: Hyperparathyroidism causes the bones to soften due to excess calcium released from the bone.
34Under secretion of parathormone: Hypoparathyroidism causes muscle cramps due to lack of calcium for muscle contraction, it is all absorbed into bone.
35The Adrenal Glands: These are located just above each kidney They consist of two layers, an outer cortex and an inner medulla.Each layer secretes specific hormones.Adrenal gland clipAdrenal cortex clip
36Secretions from the adrenal cortex: Glucocorticoids - the most important being cortisol (a steroid hormone). This hormone stimulates the conversion of proteins and fats to glucose for use in cellular respiration and makes available amino acids for protein synthesis necessary for the repair of cells. This is important in the recovery of the body from stress.
38Cortisol also reduces the allergic and inflammatory responses caused in damaged tissues, by inhibiting the immune system. (Cortisone is a drug given in many instances to reduce inflammation or allergic response)
39Mineralocorticoids - the most important being aldosterone Mineralocorticoids - the most important being aldosterone. This hormone stimulates the absorption of sodium ions by the kidneys to maintain salt and water balance in the blood.
41Abnormalities Associated with the Pituitary Abnormalities Related to the Secretion of Growth Hormone:DwarfismCaused by under secretion of GH during childhood resulting in reduced over all growth.Under secretion in adults has been linked to early senility.
42Gigantismcaused by over secretion of GH during childhood.
43Acromegalycaused by over secretion of GH during adulthood, leading to excessive growth of facial bones and those of the hands and feet.Andre the Giant 7’ 4” 500 lbs
45Gonadocorticoids (Sex hormones) - in fact these are hormones very similar to the sex hormones and have similar effects, to maintain the viability of the gonads and cause the development of secondary sex characteristics.Clip 1
46Control of the secretions from the Adrenal Cortex: Secretions from the adrenal cortex are stimulated by ACTH from the anterior pituitary.The control of these secretions demonstrates the feedback mechanism:
47Secretions from the Adrenal Medulla: Unlike the adrenal cortex, which is under hormonal control, the release of hormones from the adrenal medulla is controlled by the nervous system, another illustration of the connections between the nervous and endocrine systems.
48In stressful situations the sympathetic nervous system stimulates the release of two hormones from the adrenal medulla: adrenaline and noradrenaline (also called epinephrine and norepinephrine)These two hormones essentially have the same functions, to prepare the body for stressful or exciting situations when vigorous activity may be required.Clip 1
49They cause the following effects: Epinephrine & Norepinephrine serve to prolong and maintain the body in a state of preparation for activity longer than could be maintained by the nervous system alone.They cause the following effects:heart rate increasesbreathing rate increasespupils dilateblood is diverted from non-essential tasks, such as digestion, to the muscles for activityanal and bladder sphincters relax.face becomes pale (blood diverted from here)hair stands on end, sweating increases.Clip 1
50The Pancreas: The pancreas has both endocrine and exocrine functions; Glucose controlDigestive enzyme productionIt also has patches of specialized cells which produce two hormones, insulin and glucagon, that are secreted into the blood stream.These patches of cells are referred to as the islets of Langerhans
51The islets have two types of secretory cells within them, alpha cells which secrete glucagon and beta cells which secrete insulin.These two hormones are responsible for the control of glucose metabolism by controlling the breakdown and synthesis of glycogen, the carbohydrate store in the body.Clip 1
52InsulinReleased into the bloodstream in response to increasing blood glucose concentration, for example after a meal. It has two effects:1. It increases the permeability of the cells of the liver and muscles to glucose so that glucose is readily absorbed by these cells.2. It promotes the conversion of glucose to glycogen in these cells.
53GlucagonHas an antagonistic effect to insulin, it promotes the break down of glycogen to glucose and its release into the blood stream, therefore increasing the blood glucose level in the blood.It is released when the blood glucose level falls during periods of exercise or fasting between meals.Clip 1
55Diabetes Mellitus:When the beta cells of the pancreas deteriorate and fail to produce adequate amounts of insulin and the blood sugar level rises above normal.This is known as hyperglycemia.Clip 1
56Symptoms:1. Glucose in the urine (glycosuria) caused by excretion of glucose by the kidneys as the blood glucose level rises above renal threshold (160mg/100mL of blood)2. Production of large volumes of urine (diuresis) in order to excrete the glucose results in dehydration and excessive thirst. (This symptom is usually the first noticed by new diabetics)3. Low energy levels due to the unavailability of glucose for cellular respiration. Despite the abundance of glucose in the blood, little moves into the cells and so the cells are starved of energy. This may cause unconsciousness.
574. The smell of propanone (acetone) on the breath 4. The smell of propanone (acetone) on the breath. Propanoneis a by product of fat metabolism.Clip 1
58Treatment of diabetes: There are two forms of diabetes mellitus, juvenile, or early-onset diabetes and adult, or late-onset diabetes.
59Adult or late-onset diabetes Around 90% of diabetics develop the condition as adults.It is due to reduced insulin output by the beta cells of the pancreas.Sulfonamide drugs are also prescribed to stimulate the beta cells to produce a little more insulin.Not necessary to give insulin and so this condition is also known as non insulin dependent diabetes.
60Juvenile diabetesOccurs usually before the person reaches about 20 years of age and is caused by the early degeneration of the beta cells in the pancreas.Daily injections of insulin are necessary to replace the missing insulin, for this reason this type of diabetes is also known as insulin dependent.Injections are administered by the patient subcutaneously, since insulin is a protein hormone and would be digested if given orally.
61The Gonads (reproductive organs) These produce the sex hormones which are responsible for the development of secondary sex characteristics in both males and females. They also maintain physiological, anatomical and behavioural factors leading to reproduction. Sex hormones in both males and females are steroids.
62Males:Male sex hormones are referred to as androgens, the principle one being testosterone.Testosterone production is under the control of the anterior pituitary gland, which cause the development of male secondary sex characteristics:increased facial and pubic hairincreased muscle developmentdeepening voice (due to lengthening of the vocal cords)sperm production
63Females:The two principle female sex hormones are estrogen and progesterone. Both are produced in the ovaries, which are located in the female pelvic cavity.The anterior pituitary also controls the release of these two hormones by producing FSH and LH during a cycle of events lasting approx. 28 days from the onset of puberty until menopause.
64Estrogen is produced by the follicle cells in the ovary and is responsible for the development of female secondary sex characteristics and the preparation of the uterus for the possible implantation of a fertilized ovum.breast developmentproduction of a fatty layer under the skinwidening if the hipsgrowth of pubic hairovulation (as part of the menstrual cycle)
65Progesterone is produced from the cells of the corpus luteum after ovulation. It is responsible for the maintenance of the uterine lining and prevents ovulation during pregnancy by a negative feedback effect on the pituitary gland.Clip 1
66Thymus GlandIs located in the thoratic cavity behind the sternum, close to the heart.It produces the hormone thymosin which is involved in the production and development of lymphocytes by the lymphatic tissue.
67HomeostasisThe term used to express the coordinating influence of the endocrine system through hormonal action producing rhythmic patterns of activity, controlling long term physiological processes and responding to stressful situations.The endocrine system also fulfils a homeostatic function by regulating the internal environment of the body by controlling processes such as blood glucose level, water and mineral balance, temperature and metabolic rate.The endocrine system operates on a series of feedback mechanisms where the hormone “feeds back” to switch off the cause of its own production.