Endocrine System

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Endocrine System

• Biology 211 Anatomy Physiology 1
• Tony Serino, Ph.D.
• Biology Department
• Misericordia University

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Endocrine System

• Controls and modifies the internal environment by
  releasing chemicals (hormones) into the blood
• Slower response time but longer duration of
  action compared to nervous system

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Chemical Messengers (hormones)

• Hormone secreted by cell into blood and acts on
  another cell some distance away
• Neurohormone secreted by neuron into blood to
  affect a target cell some distance away
• Local hormones secreted by cell into
  interstitial fluid to affects cells nearby
• Paracrines affect neighboring cells
• Autocrines affect the secreting cell
• Pheromones secreted by cell onto body surface to
  affect cells of another individual

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Hormones

• Chemical Classification
• Amines single or few amino acids, most water
  soluble
• Epinephrine, Thyroxine (but water insoluble),
  Melatonin
• Proteins short to long chains of amino acids
  water soluble
• GH, FSH, LH, Insulin, Glucagon, ADH, etc.
• Steroids derivatives of cholesterol water
  insoluble
• Estrogen, Testosterone, Progesterone, Cortisol,
  Aldosterone

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Steroid Hormones
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Characteristics Common to all Hormones

• Must have target cell with appropriate receptor
  molecules
• Receptor-hormone complex must trigger events in
  target cell that changes its physiology
• Mechanisms for deactivating the hormone response
  must be present

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Controlling Hormone Response

• Half-life of the hormone
• Physiological range
• Modifying target cell response
• Up and down regulation
• Turning off secretion
• Negative feedback
• Control by other hormones, neurons and metabolites

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Control of Hormone Secretion
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Mechanisms of Hormone Action
2nd messengers
Water Soluble
Water Insoluble
Carrier protein
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2nd Messengers cAMP
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2nd Messengers IP3 and Ca-Calmodulin
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Steroid Hormone Transduction
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Different Styles of Secretion

• Prohormone a hormone that is made as a larger
  (inactive form) that must be changed prior to
  secretion (allows for storage of hormone in
  secreting cell)Ex. proinsulin,
  pro-opiomelanocortin
• Prehormone a hormone that is secreted in an
  inactive form that must be changed near or in the
  target cellEx. Thyroxine, Angiotensinogen

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Proinsulin
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Types of Endocrine Disorders

• Hypersecretion
• Too much secretion of the hormone
• Hyposecretion
• Too little secretion of hormone
• Hyporesponsiveness
• Normal secretion, but little to no response by
  target cells

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Endocrine Glands
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Hypothalamus Control of Pituitary
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Posterior Pituitary
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Anterior Pituitary
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Control of Growth

• Growth periods prenatal and postnatal (consists
  of pre-puberal (especially the first 2 years
  infancy) and puberty
• Several factors influence growth genetics, diet,
  health, and hormonal balance
• Prenatal growth dominated by insulin secretion,
  post-natal dominated by GH, thyroxine, and sex
  hormones

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GH secretion and effects
GH secretion stimulated by exercise, fasting,
sleep (diurnal rhythm), stress, decreased plasma
glucose, increased plasma AA (such as after a
high protein meal)
Increase differentiation
Increase protein synthesis
(increase mitosis)
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GH interactions with other Hormones

• Thyroxine essential and permissive for GH
• Needed to maintain energy levels for growth
• Increases sensitivity of target cells to GH
  effects
• Insulin essential for GH effects
• Dominant hormone for pre-natal growth
• Estrogen and Testosterone surge at puberty
  stimulates GH release, synergistic with GH
  anabolism also trigger epiphyseal closure
• Cortisol anti-growth effects decrease GH
  secretion, cell division, and increase catabolism

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GH pathologies

• Hypersecretion
• Gigantism in children with responsive epiphyseal
  plates
• Acromegaly in adults, with closed epiphyseal
  plates

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GH pathologies

• Hypofunction
• Dwarfism in children
• Pituitary decreased GH secretion
• Laron decreased responsiveness due to lack of GH
  receptors

28 yo woman withpituitary dwarfism 45 tall
Achondroplastic Dwarfism (genetic dwarf) due to
failure of cartilage to form in epiphyseal plate
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Thyroid Location
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Thyroid Follicle
(follicular cells ? thyroxine)
Parafollicular cells ? calcitonin
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T3 T4 Formation and Secretion
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T3 T4
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Control of Thyroxine Secretion
Short loop
Long loop
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Thyroid Malfunction

• Hypothyroidism
• Endemic goiters due to iodine deffeicency
• Cretinism i thyroxine in child results in
  igrowth (dwarf) and severe mental retardation
• Myxedema i thyroxine in adult, leads to swelling
  of tissues plus other symptoms

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Cretinism
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Thyroid Malfunction

• Hyperthyroidism
• Toxic goiters (Graves disease) Ab may stimulate
  thyroid without negative feedback control
• Exophthalmos symptom present in many
  hyperthyroid patients

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Parathyroid Location
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Parathyroid
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PTH Actions

• Stimulates resorption of bone ? hCa and PO4- in
  blood
• Stimulates Ca absorption in intestine (active
  Vit. D3 necessary for Ca absorption)
• Stimulates Ca reabsorption and PO4- excretion in
  kidney
• Stimulates Vit. D3 formation (skin) and
  activation (kidney)
• Vital for life

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Adrenal Location and Structure
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Adrenal Layers
(Epinephrine (adrenalin))
(Androgens)
(Glucocorticoids (cortisol))
(Mineralocorticoids,(Aldosterone))
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GAS (General Adaptation Syndrome)
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Adrenal Malfunction

• Hypersecretion
• Cushings syndrome increase in glucocorticoids
• Usually due to over secretion of ACTH by
  pituitary or from adrenal cortex tumors
  stimulating an increase in glucocorticoids.
  Characteristic obesity of trunk only and
  development of buffalo hump (a fat pad behind
  the shoulders). Will develop hypertension,
  atherosclerosis, muscular weakness and fatigue.
• Conns syndrome excess amount of aldosterone
• Salt imbalance, water retention, hBP, muscle
  weakness
• Adrenogenital syndrome too much androgen
• Premature sexual development in children or
  masculinization in women

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Cushings
Obesity of trunk
(buffalo hump)
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Adrenogenital syndrome
A 15 yo girl, note typical masculinebuild, under
developed breasts, andexcessive body hair
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Adrenal Cortex Malfunction

• Hyposecretion Addisons disease
• Due to decrease amounts of mineral and
  glucocorticoids
• Can be due to over use of steroids or an
  autoimmune mechanism resulting in destruction of
  the gland
• Dehydration, K loss, iBP, fatigue, pigmentation
  deepening (bronzing of skin) may be symptom of
  loss of negative feedback

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Pineal Gland

• Plays a major role in circadian rhythm control
  through its sympathetic connection to the
  hypothalamus
• Melatonin increases at night and decreases during
  daylight
• Implicated in the control of major life changes
  (such as the onset of puberty and adulthood

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Thymus Gland

• Bilobed organ that is largest in children, but
  begins to regress sharply at the onset of puberty
  (around age 11)
• It is the site of T-cell lymphocyte production
  and produces hormones (such as, thymosin) that
  modifies their physiology