Endocrine System

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Endocrine System
A. Introduction 1. endocrine organs -
hypophysis, thyroid gland, adrenal gland,
parathyroid gland, pineal gland
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3. Typical secretions hormones which affect
distant targets and/or many tissues a.
peptide hormones - proteins, glycoproteins, or
peptides which bind to receptors on cell
surfaces work via second messengers, water
soluble e.g. insulin, glucagon, follicle
stimulating hormone b. steroid hormones -
lipid soluble and bind to intracellular targets,
e.g. to DNA or hormone receptors derived from
cholesterol, e.g. progesterone, estradiol,
testosterone c. amino acid derived hormones
- water soluble, catecholamines, thyroxin and
epinephrine
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• B. Hypophysis, aka pituitary gland
• 1. Basic structure and origin
• direct connection between nervous system and the
  other endocrine organs
• lies in the sella turcica, a depression in the
  sphenoid bone (hypophyseal fossa), with two
  ridges cranial and caudal to it (supposed to look
  like a Turkish saddle....)

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Canine, dorsal view, calvarium removed.
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Ventral view, canine brain
Hypophysis
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• B. Hypophysis, aka pituitary gland
• 1. Basic structure and origin
• divided into two main regions, neurohypophysis
  and adenohypophysis

Sagittal section
Brain, diencephalon
Cranial
Caudal
Adeno-hypophysis
Neuro-hypophysis
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Arcuate n
Mammillary Body
Superior Hypophyseal a
Median eminence with primary capillary bed
Adeno- hypophysis
Neurohypophysis
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These factors are transported to the
adenohypophysis by small portal veins where they
leave the capillaries to act on the secretory
cells there.
Portal v
Adenohypophysis
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Releasing or inhibiting factors bind to receptors
in or on the secretory cells in the
adenohypophysis to affect their secretion rates
of a DIFFERENT hormone. E.g. Corticotropin
releasing hormone stimulates the release of
corticotropin (ACTH)
Releasing hormone
Secondary hormone
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• C. Adrenal Glands
• 1. General morphology
• Embedded in the adipose tissue on top of
  kidneys.
• Triangular shape
• (sometimes)

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Capsule
Cortex
Medulla
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3. Cortex Divided into 3 visibly different
zones, all of which are steroid-secreting and all
of which synthesize hormones from cholesterol,
but in different regions different types of
hormones are produced.
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3. Cortex a. zona glomerulosa outermost
layer, cells look clustered
Secretes mineralocorticoids (e.g. aldosterone,
which is involved in salt balance via the
kidney), and deoxycorticosterone. Secretion is
stimulated by angiotensin II from juxtaglomerular
apparatus and ACTH from hypophysis.
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• 3. Cortex
• b. zona fasciculata
• middle layer, longitudinal cords of cells
• secretes glucocorticoids (e.g. cortisol,
  corticosterone) and adrenal androgens
• secretion stimulated by ACTH

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• 3. Cortex
• c. zona reticularis
• innermost layer, much thinner than other layers,
  network of cell cords
• cells secrete androgens and small amounts of
  glucocorticoids
• secretion stimulated by ACTH

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• 4. Medulla
• Secretion is triggered separately by
  preganglionic axons (norepinephrine release is
  associated with fear, epinephrine with pain), the
  fight or flight responses.
• Portal system glucocorticoids stimulate
  conversion/synthesis of norepinephrine to
  epinephrine. The cell distribution is related to
  capillary distribution, so that the epinephrine
  secreting cells are nearest to capillaries from
  cortex.

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Adrenal gland, medulla
Chromaffin cells (virtually every
cell) Ganglion cell