The Endocrine System

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The Endocrine System
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Endocrine system characteristics

• Endocrine system is mostly controlled by the
  nervous system
• Endocrine system controls most of the processes
  occurring in the body
• Divided into cranial extracranial endocrine
  glands
• Cranial hypothalamus, pituitary pineal glands
• Extracranial thyroid, parathyroid, thymus,
  pancreas, adrenals, gonads, GI tract placenta

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Cranial endocrine glands

• Hypothalamus
• Many nuclei within this region to control
  various aspects of homeostasis
• Exhibits control over pituitary gland
• Blood supply / blood flow pattern is important
  for control
• portal system capillaries in hypothalamus
  drain into portal venules (veins) that connect
  to capillaries in the pituitary gland
  (capillary-vein-capillary)
• Hypothalamic neurons will release releasing
  hormones or inhibiting hormones into these
  capillaries/portal veins to eventually target the
  pituitary gland

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Pituitary gland - Hypophysis

• Known as the conductor or master gland but is
  itself under control of the hypothalamus
• Inferior region of the brain, nestled within the
  sella turnica of the spenoid bone
• 2 regions (visibly different)
• Adenohypophysis (anterior lobe)
• Most of the hormones are produced here
• Neurohypophysis (posterior lobe)
• More neural area, 2 hormones

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Pituitary gland (hypophysis)

• Anterior lobe (adenohypophysis)
• Derived from ectodermal glandular tissue
• Linked to hypothalamus via the infundibulum
  which has the hypophysial portal vascular system
  (vascular communication)
• Body anterior pituitary proper secretes 5
  different hormones, prolactin (PL), growth
  hormone (GH), thyroid stimulating hormone (TSH),
  adrenocorticotropic hormone (ACTH), Follicle
  stimulating hormone (FSH) and luteinizing hormone
  (LH)
• Posterior lobe (neurohypophysis)
• Derived from nervous tissue
• extension of the brain
• Releases 2 hormones (which are synthesized in the
  brain but stored in the posterior pituitary),
  oxytocin and vasopressin (or antiduiretic hormone
  (ADH))
• Intermediate lobe
• Thin, sandwiched between the 2 above layers
• secretes a minor hormone (melanin-stimulating
  hormoneMSH)

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Pineal gland

• roof of the 3rd ventricle)
• Larger in children than adults
• Secretes melatonin involved in circadian rhythm

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Extracranial endocrine glandsThyroid gland

• Thyroid gland
• Below larynx, bi-lobed lateral to the trachea
• Largest endocrine gland
• Bloodflow via external carotid subclavian
  arteries
• Simple cuboidal epithelia (heavily reliant on
  iodine)
• Follicular cells secrete thyroxine (T4),
  Tri-iodo-thyronine (T3) , parafollicular cell or
  C cells secrete calcitonin

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Parathyroid glands

• Posterior to the thyroid gland (para around)
• 4 distinct glandular formations
• Secretes parathyroid hormone ( parathormone
  PTH)

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Pancreas

• Has BOTH endocrine exocrine functions
• Endocrine Endocrine cells grouped into the
  Islets (Islets of Langerhans).
• 3 types of cells
• Alpha cells secrete glucagon
• Beta cells secrete insulin
• Delta cells secrete somatostatin

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Minor gastrointestinal endocrine glands

• GI tract (gastrointestinal tract)
• Numerous endocrine cells distributed throughout
  GI tract (often single cells)
• Additional endocrine glands
• Salivary glands
• Brunners glands (duodenum)

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Adrenal glands

• Located on the top of the kidneys
• Composed of 2 major parts
• Adrenal cortex 3 layers
• Zona glomerulosa secretes mineralocorticoids
• Zona fasciculata secretes glucocorticoids
• Zona reticularis secretes sex hormones
• Adrenal medulla is an extension of the
  sympathetic autonomic nervous system (specialized
  2nd motor neurons which secrete adrenaline)

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Gonads

• Testicles Contains the seminiferous tubules
  where sperm is made. In between the tubules, the
  Leydig cells secretes testosterone
• Ovaries The developing follicle secretes
  estrogen and progesterone

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Placenta

• Transfers waste from fetus to mother and
  nutrients from mother to fetus
• Secretes estrogen progesterone
• Also secretes human chorionic gonadotrophin
  (hCG)whats used to change color of pregnancy
  test sticks

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Pituitary pathophysiology

• Panhypopituitarism reduced pituitary activity or
  total loss of pituitary function
• Abnormal growth hormone
• Inadequate during childhood pituitary dwarfism
• Inadequate during adulthood Simmonds disease
• Premature aging
• Oversecretion during childhood gigantism
• Oversecretion during adulthood acromegaly
• Bones thicken, soft tissues grow inappropriately

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Acromegaly
Gigantism
Occurs during adulthood
Begins during childhood
WHY are patients who suffer gigantism taller than
those who suffer acromegaly?
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Thyroid parathyroid pathophysiology

• Hypothyroidism
• During childhood cretinism (cretins)
• During adulthood myxedema
• Goiter (abnormal thyroid growth)
• Endemic inadequate iodine intake
• Graves disease

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Pancreatic pathophysiology

• Diabetes mellitus
• Type I diabetes insulin dependent due to
  autoimmune destruction of pancreatic beta cells
  (loss of insulin production)
• Type II diabetes insulin insensitive due to
  reduced responsiveness to insulin (metabolic
  obesity)

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Adrenal pathophysiology

• Pheochromatocytomas chromaffin cell tumor
• Excessive norepinephrine secretion resembles
  ANS overstimulation
• Addisons disease decreased mineralcorticoid
  glucocorticoid secretion
• Constant hypoglycemia, electrolyte imbalances
• Cushings syndrome increased glucocorticoid
  secretion (Zona fasciculata)
• Altered metabolism and physical changes
  indicative of edema

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Pediatric Cushings syndrome