The Endocrine System

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The Endocrine System

• Chapter 15

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Introduction

• Nervous system and endocrine system share
  responsibility for control and coordination of
  entire body.
• Homeostasis- balance of the body.
• Systems have similarities and differences
• Both systems use chemicals to transmit their
  messages.
• Endocrine system produces hormones
• Nervous system produces neurotransmitters
• Endocrine system reacts more slowly to changes
  but can sustain response longer.
• Nervous system reacts more quickly to changes but
  cannot sustain prolonged responses.

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Basics

• Endocrine glands- basic units of the endocrine
  system.
• Secrete hormones directly into the bloodstream.
• Circulate throughout body and produce effects
  when attach to receptors in or outside of cells.
• Ductless glands.
• Exocrine glands- units that secrete their
  products onto epithelial surfaces through tiny
  tubes called ducts.

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Endocrine vs. Exocrine Glands
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Endocrine Glands
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Major Endocrine Glands

• Gland Hormone
  Target Effect
• Anterior pituitary Growth Hormone all body
  cells growth, metabolic
• (master endocrine gland) Prolactin mammary
  tissue (f) lactation
• Thyroid Stim Hor Thyroid gland Thy horm prod
• ACTH Adrenal cortex gluco-, mineralo-
• FSH follicles, semi tub egg, sperm prod
• LH follicles, inter cells CL, testosterone
• Posterior pituitary ADH kidney water
  reabsorption
• (Storage only) oxytocin uterus, mam
  gl contract, milk
• Thyroid Thyroid Hormone all body cells growth,
  metabolic
• Calcitonin bones Ca deposition
• Parathyroid PTH bones, kid, intest ? blood Ca
• Adrenal cortex glucocorticoids whole body ?glu,
  ?immunity
• mineralocorticoids kidneys Na retention
• sex hormones whole body minimal effects
• Adrenal medulla epi, NE whole
  body fight/flight resp
• Pancreas (islets) insulin all body cells ?
  blood glu
• glucagon whole body ? blood glu
• Testis androgens whole body masculinization

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Hormones

• Chemical messengers produced by endocrine glands
  and secreted directly into blood vessels.
• Produce effects when find their receptors in or
  on cells.
• Each body cell has specific receptors to certain
  hormones (target).
• If body does not have receptor, hormone will pass
  by.
• Only certain hormones can fit to receptors and
  when it occurs, then it changes the activity of
  the cell.

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Control of Hormone Secretion

• Negative Feedback System
• Endocrine glands will be stimulated to produce
  more hormone when it drops below a certain amount
  in the body.
• If hormone is of adequate levels, gland will
  either slow or stop production of the hormone.
• Direct Stimulation of Nervous System
• Secretion of some hormones is stimulated by
  sympathetic nerve impulses when an animal feels
  threatened.
• Fight or flight response from sympathetic nervous
  system

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Negative Feedback Loop
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Negative Feedback Loop
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Fight or Flight Response
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The Hypothalamus

• Part of diencephalon of brain.
• Has control of pituitary gland.
• Portal system of blood vessels links hypothalamus
  with anterior portion of pituitary gland

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Hypothalamus and anterior pituitary gland

• Portal system of blood vessels links hypothalamus
  with anterior portion of pituitary gland.
• Modified neurons in hypothalamus secrete
  releasing and inhibiting hormones into portal
  blood vessels
• Specific for a particular anterior pituitary
  hormone
• Either promote or inhibit the production of a
  specific hormone.

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Hypothalamus and Posterior Pituitary

• Hypothalamus produces antidiuretic hormone (ADH)
  and Oxytocin
• Are transported to posterior pituitary where they
  are stored.
• Released into bloodstream by nerve impulses from
  hypothalamus.

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The Pituitary Gland

• Also referred to as the hypophysis.
• Master endocrine gland.
• Many hormones direct activity of other endocrine
  glands.
• Very small
• Housed in pituitary fossa of skull.
• Actually two separate glands
• Anterior- adenohypophysis
• Produces seven known hormones
• Posterior-neurohypophysis.
• Does not produce any hormones but stores and
  releases ADH and Oxytocin.

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Anterior Pituitary Gland

• Hormones
• 1. Growth Hormone (GH)
• 2. Prolactin
• 3. Thyroid-stimulating Hormone (TSH)
• 4. Adrenocorticotropic Hormone (ACTH)
• 5. Follicle-stimulating Hormone (FSH)
• 6. Luteinizing Hormone (LH)
• 7. Melanocyte-stimulating Hormone (MSH).

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Growth Hormone (GH)

• Also known as somatotropin and somatotropic
  hormone.
• Promotes growth in young animals.
• Helps regulate metabolism of proteins,
  carbohydrates, and lipids in bodys cells.
• GH breaks down lipids for energy while
  discouraging use of carbs for energy.
• Can cause hyperglycemic effect.

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Dwarfism
Rare now since GH is commercially available
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Giantism
Body proportions normal
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Acromegaly
Excessive GH after epiphyseal plates close
Responsive tissues bones of hands, feet,
face thickened facial features/tongue
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Dairy Cows

• Synthetic GH may be used to increase milk
  production of dairy cows.
• Bovine Somatotropin (BST)
• Enhances milk production by mammary glands.
• Can elevate body temperature.
• Reduce conception rates
• Increases risk of mammary gland infections
• Increases risk of digestive disorders.

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Prolactin

• Helps to trigger and maintain lactation
• Continues as long stimulation of nipple
  continues.
• Mammary glands will shrink to normal size once
  stimulation stops.
• Has no known effect in male.

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Thyroid-Stimulating Hormone (TSH)

• Also referred to as thyrotropic hormone.
• Stimulates growth and development of thyroid
  gland and causes it to produce hormones.
• TSH production is regulated by feedback from
  Thyroid gland.

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Adrenocorticotropic Hormone (ACTH)

• Stimulates growth and development of the cortex
  of adrenal gland.
• Stimulates release of some of adrenal glands
  hormones
• Can be released in two ways
• First by feedback system from adrenal glands
• Second during stress, can be released by
  stimulation of hypothalamus by other parts of
  brain.
• This sends releasing factor to anterior pituitary
  through blood vessels.

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ACTH stimulation test

• Test used to check for hyperadrenocorticism or
  hypoadrenocorticism.
• What are these also called?
• ACTH stimulates production of cortisol.

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Follicle-Stimulating Hormone (FSH).

• Stimulates growth and development of follicles in
  ovaries to create ovum.
• Helps produce estrogens as well.
• Can be used to produce superovulation
• Can then be harvested for Artificial
  Insemination.

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Luteinizing (LH)

• Completes process of follicle development that
  was started by FSH.
• Surge in LH is what causes ovulation to occur.
• High LH is maintained to produce corpus luteum
  which produces its own hormones.
• In male, LH stimulates interstitial cells to
  produce testosterone.
• Sometimes LH and FSH are called gonadotropins.

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Melanocyte-Stimulating Hormone (MSH)

• Associated with color changes in the melanocytes
  (pigment cells) of reptiles, fish, and
  amphibians.
• Can cause pigment to darken when administered
  artificially.
• Other effects are unknown.

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Posterior Pituitary Gland

• Does not produce, but stores and releases ADH and
  Oxytocin when stimulated.
• ADH
• Where does it act?
• What does it do?
• Lack of can cause what disease?
• Oxytocin
• Two targets are uterus and mammary glands.
• What does it do in uterus?
• What does it do in mammary glands?

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The Thyroid Gland

• Consists of two parts called lobes located on
  either side of the larynx.
• Connected by narrow band called isthmus in some
  species.
• Composed of tiny follicles, where thyroid hormone
  is produced.
• Each follicle consists of globule surrounding
  thyroid precursor called a colloid.
• Only endocrine gland that stores large amounts of
  hormone precursor for use later.
• Produces two hormones
• Thyroid hormone
• Calcitonin

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Thyroid Hormone

• T3(Triiodothyronine)- contains three iodine atoms
  per molecule.
• T4(Tetriodothyronine, thyroxine)-contains four
  iodine atoms per molecule.
• Production can be inhibited by stress on animal.
• These hormones are produced when TSH from
  anterior pituitary gland reaches the thyroid
  gland.
• T4 produced in greater abundance than T3 but is
  mostly converted to T3 before producing effects
  on target cells
• T3 more potent
• Necessary for normal growth and development in
  young animals.
• Influences development and maturation of the
  central nervous system, muscles and bones.

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Calorigenic Effect

• Helps to heat the body and regulates the
  metabolic rate of all the bodys cells.
• Allows an animal to generate heat and maintain a
  constant internal body temperature, when outside
  temperature changes.
• Production of thyroid hormone increases with
  exposure to cold temperatures.
• Increases bodys metabolic rate, which generates
  more heat.

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Effect on Protein, Carbohydrate and Lipid
Metabolism by Thyroid Hormone

• Proteins
• Encourages synthesis of proteins if diet is
  adequate in energy sources.
• If energy sources are not adequate in diet, then
  can actually catabolize proteins.
• Carbohydrates
• Hyperglycemic effect.
• Helps to maintain homeostasis of the blood
  glucose level by helping to prevent it from
  dropping too low.
• Lipids
• Encourages their catabolism.

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Thyroid DysfunctionHypothyroidism

• Too little thyroid hormone produced.
• Occurs commonly in dogs.
• Symptoms include
• Alopecia
• Dry skin
• Lethargy
• Reluctance to exercise
• Weight gain
• Seeking out sources of heat.
• Easily treated with thyroid supplementation
• Usually occur in middle age.

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Thyroid Dysfunction Hyperthryoidism

• Too much thyroid hormone production.
• Commonly seen in cats.
• Symptoms include
• Nervousness
• Excitability
• Weight loss
• Increased appetite, but no weight gain
• Tachycardia
• Vomiting
• Diarrhea
• Polyuria
• Polydipsia
• Treated surgically by removing the thyroid gland,
  radioactive treatment, or drugs to suppress
  thyroid production.

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Thyroid Dysfunction Goiter

• Non-cancerous, non-inflammatory enlargement of
  the thyroid gland.
• Results from iodine deficiency which is a
  component of thyroid hormone.
• Not enough iodine produced, less hormone that can
  be produced.
• Causes hyperplasia of the gland
• Can be treated and prevented with iodine
  supplements.
• Iodized salt.

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Calcitonin

• Produced by C cells located between the thyroid
  follicles.
• Involved with maintaining homeostasis of the
  blood calcium levels.
• Will prevent hypercalcemia by decreasing blood
  calcium levels if they go too high.
• Encourages excess calcium to deposit in bones

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Parathyroid Glands

• Small nodules located near, in or on thyroid
  glands.
• Produce
• Parathyroid Hormone (PTH)

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Parathyroid Hormone (PTH)

• Also called parathormone.
• Opposite effect of calcitonin.
• Prevents hypocalcemia by increasing blood calcium
  if gets too low.
• Causes kidneys to retain calcium and intestines
  to absorb calcium from food.
• Can take calcium out of storage from the bones.

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Calcitonin/Parathormone
Ca to bone
Ca from bone Ca from kidneys Ca from GI
tract
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Parathyroid Dysfunction Hypocalcemia

• Milk fever- when parathormone is overwhelmed in
  lactating animals.
• Can cause muscle weakness and tremors.
• Can progress to seizures and spasms if left
  untreated.
• Downer cows
• Called Eclampsia in dogs and cats
• Treated by supplementing calcium rapidly into
  system

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Adrenal Glands

• Located on cranial aspect of kidneys.
• Composed of two glands wrapped around one
  another.
• Outer Adrenal Cortex
• Classic endocrine gland tissue
• Produce under direction of ACTH
• Glucocorticoid hormones
• Mineralcorticoid hormones
• Sex hormones
• Inner Adrenal Medulla
• Resembles nervous tissue
• Controlled by sympathetic portion of nervous
  system
• Produces
• Epinephrine
• Norepinephrine

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Glucocorticoid Hormones

• Hormones produced are
• Cortisone
• Cortisol
• Corticosterone
• General hyperglycemic effect by causing blood
  glucose levels to rise.
• Cause catabolism of proteins and lipids
• Products are ultimately converted back to glucose
  through gluconeogenesis.
• Also may help to maintain blood pressure and help
  body to resist stress.

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Glucocorticoid-Related Diseases

• Too much of cortisol in system-Hyperadrenocorticis
  mCushings Disease. (Iatrogenic Cushings)
• Symptoms include
• Polyuria
• Polydipsia
• Polyphagia
• Hair loss
• Muscle wasting
• Slow wound healing
• Too little of cortison in the system-
  HypoadrenocorticismAddisons Disease.
• Symptoms include
• Weakness
• Lethargy
• Vomiting
• Diarrhea
• Can lead to circulatory and kidney failure.

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Cushings Disease
Excessive amount of glucocorticoids
pot belly long hair laminitis
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Addisons Disease
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Glucocorticoid-Related Drugs

• Drugs include
• Hydrocortisone
• Prednisone
• Dexamethasone
• Triamcinolone
• How they act
• Suppress immune system
• Affect WBC count
• Slow wound healing
• Catabolic effect of proteins
• Premature parturition
• Hyperglycemia
• Suppress adrenal cortex stimulation

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Mineralcorticoid Hormones

• Regulate levels of electrolytes in body.
• Principle hormone
• Aldosterone
• Affects Sodium, Potassium, and Hydrogen Ions in
  the body.
• Targets kidney (why?)

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Sex Hormones

• Adrenal cortex produces small amounts of sex
  hormones and effects are generally minimal.
• Male sex hormones- androgens
• What is main male hormone?
• Where is it produced?
• Female sex hormones-estrogens.

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Adrenal Medulla

• Inner gland of adrenal glands and resembles
  nervous tissue.
• Concerned with sympathetic nervous system.
• Direct stimulation on target tissues.
• Produces
• Epinephrine
• Norepinephrine

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The Pancreas

• Long and flat, located near the duodenum.
• Has both endocrine and exocrine functions
• What is the difference between these two?
• What exocrine functions does pancreas have?
• Pancreatic islets (islets of langerhans) are tiny
  clumps of cells that produce hormones
• Produces
• Insulin- by beta cells
• Glucagon- by alpha cells
• Somatostatin- by delta cells

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Insulin

• Controls metabolism and use of glucose.
• Is essential for life
• Causes glucose, amino acids, and fatty acids to
  be absorbed from bloodstream into bodys cells.
• Lowers level of glucose in the blood.

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Glucagon

• Opposite effect of insulin
• Raises glucose level in the blood.
• Stimulates liver to convert glycogen to glucose
• Stimulates gluconeogenesis
• Other hormones do similar things so deficiency is
  not as devastating.

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Somatostatin

• Inhibits the secretion of insulin and glucagon
  and GH and diminishes activity of the GI tract.

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Diabetes Mellitus

• Caused by deficiency of insulin.
• Results from build up of glucose in the system.
• Symptoms include
• Polyuria
• Polydipsia
• Polyphagia
• Weight loss
• Weakness
• Not curable but treatable through injections of
  insulin.

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The Gonads

• Reproductive organs
• Testes (when LH stimulates testes)
• Testosterone
• What all does this do?
• Where is it produced within the testes?
• Ovaries (when FSH and LH stimulate)
• Estrogens
• Estradiol
• Estrone
• What all do these do?
• Progestins
• Progesterone
• Produced by corpus luteum after ovulation
• Drugs can be used to delay estrus and synchronize
  estrous periods in a group.

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The Kidneys

• Produce Erythropoietin
• Stimulates red bone marrow to increase production
  of red blood cells.
• Production is stimulated by decrease of oxygen in
  the blood.
• Lack of production may result in anemia.
• Synthetic forms are used in cases of cancer.
• Procrit

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The Stomach

• Produce Gastrin
• Where is gastrin produced?
• By what cells?
• What does gastrin do?

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The Small Intestine

• Produces
• Secretin
• Stimulates pancreas and helps with intestinal
  motility.
• Cholecystokinin
• Stimulates release of digestive enzymes from
  pancreas to duodenum.
• Used in fat digestion.

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The Placenta

• Produces small amounts of estrogen and
  progesterone
• Produces chorionic gonadotropin
• What is tested for in pregnancy tests.

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The Thymus

• Very important during early development, will
  shrink as animal approaches adulthood.
• Important in immune system development
• Produces
• Thymosin
• Thymopoietin
• Seem to transform into t-lymphocytes (T-cells)
  which help to attack foreign invaders in the
  body.

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Pineal Body

• Influences bodys biological clock
• Produces
• Melatonin
• hormone-like substance that affects moods and
  wake-sleep cycles
• Also plays a role in timing of seasonal estrous
  cycles in some species

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Melatonin
Production varies with daylight -sets bodys
biological clock
Production varies with age -associated with
sleep patterns
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Prostaglandins

• Derived from unsaturated fatty acids
• Sometimes called tissue hormones due to the fact
  they travel short distances.
• Organized in groups A-I
• Remember PGE and PGI?
• Produced in a variety of body tissues including
• Skin
• Intestine
• Brain
• Kidney
• Lungs
• Reproductive organs
• Eye

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Prostaglandin effects

• Influence blood pressure
• GI function
• Respiratory function
• Kidney function
• Blood clotting
• Inflammation
• Reproductive functions
• PGEs initiate inflammation so NSAIDs inhibit PGE
  production.