Endocrine System
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Endocrine System. A. Introduction 1. endocrine organs - hypophysis, thyroid gland, adrenal gland, parathyroid gland, pineal gland. 3. Typical secretions: hormones which affect distant targets and/or many tissues

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Endocrine System

A. Introduction

1. endocrine organs -

hypophysis, thyroid gland, adrenal gland,

parathyroid gland, pineal gland


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


  • B. Hypophysis, aka pituitary gland targets and/or many tissues

  • 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....)


Canine, dorsal view, calvarium removed. targets and/or many tissues


Ventral view, canine brain targets and/or many tissues

Hypophysis


Sagittal section

Brain, diencephalon

Cranial

Caudal

Adeno-hypophysis

Neuro-hypophysis


Arcuate n targets and/or many tissues

Mammillary

Body

Superior

Hypophyseal a

Median eminence

with primary capillary

bed

Adeno-

hypophysis

Neurohypophysis


These factors are transported to the targets and/or many tissuesadenohypophysis by small portal veins where they leave the capillaries to act on the secretory cells there.

Portal v

Adenohypophysis


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


  • C. Adrenal Glands the secretory cells in the adenohypophysis to affect their secretion rates of a DIFFERENT hormone. E.g.

  • 1. General morphology

    • Embedded in the adipose tissue on top of kidneys.

    • Triangular shape

    • (sometimes)


Capsule the secretory cells in the adenohypophysis to affect their secretion rates of a DIFFERENT hormone. E.g.

Cortex

Medulla


3. Cortex the secretory cells in the adenohypophysis to affect their secretion rates of a DIFFERENT hormone. E.g.

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.


3. Cortex: the secretory cells in the adenohypophysis to affect their secretion rates of a DIFFERENT hormone. E.g.

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.


  • 3. Cortex the secretory cells in the adenohypophysis to affect their secretion rates of a DIFFERENT hormone. E.g.

  • b. zona fasciculata

    • middle layer, longitudinal cords of cells

    • secretes glucocorticoids (e.g. cortisol, corticosterone) and adrenal androgens

    • secretion stimulated by ACTH


  • 3. Cortex the secretory cells in the adenohypophysis to affect their secretion rates of a DIFFERENT hormone. E.g.

  • 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


  • 4. Medulla the secretory cells in the adenohypophysis to affect their secretion rates of a DIFFERENT hormone. E.g.

    • 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.


Adrenal gland, medulla the secretory cells in the adenohypophysis to affect their secretion rates of a DIFFERENT hormone. E.g.

Chromaffin

cells (virtually every cell)

Ganglion cell


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