THE HUMAN ENDOCRINE SYSTEM

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• THE HUMAN ENDOCRINE SYSTEM
• Biology 12
• E. McIntyre

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Introduction 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.

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Endocrine Glands
Cross section of a brain!
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Hormones

• Hormones 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.

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...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.

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...Hormones

• The Mode of Action of Hormones
• Hormones act at the molecular level by causing
  changes in cell metabolism, for example
• protein synthesis
• enzyme activity
• permeability of cell membranes
• DNA translation
• there are two basic ways in which hormones do
  this, based on the type of hormone

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(Whats 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).

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...Hormones
mcgraw-hill animation steroid hormones
steroid_hormone animation

• Steroid Hormones
• The 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.

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...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.

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Negative Feedback

• In 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.

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The 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.

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... 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.

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The 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.

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The Hormones of the POSTERIOR Pituitary

• Antidiuretic Hormone (ADH)
• regulates water balance in the body by increasing
  water absorption by the kidneys
• Oxytocin
• stimulates uterine contractions during birth
• also stimulates milk production

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The 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.

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The Hormones of the ANTERIOR Pituitary

• Somatotropin (STH) or Growth Hormone (GH)
• has a direct effect on the growth of tissues
• is produced in greater quantities during
  childhood
• Thyroid Stimulating Hormone (TSH)
• has an indirect effect on metabolic rate, by
  affecting the thyroid gland
• stimulates the thyroid gland, causing it to
  produce the hormone thyroxin

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...The Hormones of the ANTERIOR Pituitary

• Adrenocorticotropic Hormone (ACTH)
• stimulates the adrenal cortex to produce a range
  of hormones responsible for stress relief
• Gonadotropic Hormones
• Follicle Stimulating Hormone (FSH)
• Females stimulates the development and
• production of ova, causes the release of
  estrogens
• Males stimulates the production of sperm cells
• Lutinizing 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

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...The Hormones of the ANTERIOR Pituitary

• Prolactin
• stimulates milk production after birth
• Melanocyte Stimulating Hormone (MSH)
• stimulates melanin (a brown pigment) production
  in the skin
• responsible for changing the skin colour of
  certain reptiles and amphibians

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Control 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.

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Control 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 pituitary
• these 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

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Control 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.

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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)

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Thyroid 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.

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Over 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.

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Under secretion of thyroxine

• Referred to as hypothyroidism
• In 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.

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Control of Thyroxine Production

• This provides an example of negative feedback
  control of the endocrine system

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The Parathyroid Glands

• These are located as two pairs of small glands on
  either side of the thyroid gland
• They 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.

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Over secretion of parathormone

• Hyperparathyroidism causes the bones to soften
  due to excess calcium released from the bone.

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Under secretion of parathormone

• Hypoparathyroidism causes muscle cramps due to
  lack of calcium for muscle contraction, it is all
  absorbed into bone.

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The 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 cortex clip
Adrenal gland clip
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Secretions 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.

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• Cortisol 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)

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• 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.

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• HORMONES THAT AFFECT BLOOD SUGAR

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Abnormalities Associated with the Pituitary

• Abnormalities Related to the Secretion of Growth
  Hormone
• Dwarfism
• Caused by under secretion of GH during childhood
  resulting in reduced over all growth.
• Under secretion in adults has been linked to
  early senility.

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• Gigantism
• caused by over secretion of GH during childhood.

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• Acromegaly
• caused 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
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• Gonadocorticoids (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.

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Control 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

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Secretions 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.

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• In 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.

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• 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 increases
• breathing rate increases
• pupils dilate
• blood is diverted from non-essential tasks, such
  as digestion, to the muscles for activity
• anal and bladder sphincters relax.
• face becomes pale (blood diverted from here)
• hair stands on end, sweating increases.

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The Pancreas

• The pancreas has both endocrine and exocrine
  functions
• Glucose control
• Digestive enzyme production
• It 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

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• The 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.

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Insulin

• Released 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.

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Glucagon

• Has 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.

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Glucose Control
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Diabetes 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.

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Symptoms

• 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.

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• 4. The smell of propanone (acetone) on the
  breath. Propanoneis a by product of fat
  metabolism.

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Treatment of diabetes

• There are two forms of diabetes mellitus,
  juvenile, or early-onset diabetes and adult, or
  late-onset diabetes.

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Adult 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.

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Juvenile diabetes

• Occurs 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.

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The 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.

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Males

• 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 hair
• increased muscle development
• deepening voice (due to lengthening of the vocal
  cords)
• sperm production

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Females

• 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.

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• Estrogen 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 development
• production of a fatty layer under the skin
• widening if the hips
• growth of pubic hair
• ovulation (as part of the menstrual cycle)

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• Progesterone 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.

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Thymus Gland

• Is 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.

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Homeostasis

• The 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.

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Review of Hormones and Glands (Take the Quiz)
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Endocrine Nervous System
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Bibliography

• Nelson Biology 12

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