LECTURE - The Endocrine System Flashcards
(46 cards)
hormones may be comprised of … (4)
proteins, peptide molecules, cholesterol derived steroids, or amino acid derivatives
endocrine cells have three possible anatomical distributions:
- endocrine cells gathered together = specialized endocrine gland organ (eg. thyroid, pituitary, parathyroids, and adrenals)
- endocrine cells form discrete clusters in another specialized organ (eg. pancreas, ovary, testis)
- endocrine cells dispersed amongst other cells in epithelial tissues = diffuse neuroendocrine system; occurs particularly in the GI tract and respiratory system; action of hormones occur locally
bean shaped gland situated in the sella turcica at the base of the brainq
pituitary gland
- secretion controlled by the hypothalamus
the pituitary gland is anatomically divided into two main parts:
- adenohypophysis (anterior)
- neurohypophysis (posterior)
pituitary portal system
superior arteries form the external plexus close to nerve endings of cells located in hypothalamus
=> parallel capillary network which runs down the pituitary stalk to form portal vessels
=> capillaries run forward into the anterior pituitary, providing a direct vascular link between hypothalamus and cells of the anterior pituitary
this is derived from an epithelial outgrowth of the foregut (oral cavity) called Rathke’s pouch
anterior pituitary
> cord + clumped; surrounded by a fine capillary network, which brings blood from the hypothalamus (brings either inhibitory or secretory factors that affect secretion of hormones from anterior pit)
> darker than posterior
three components of the adenohypophysis
- pars distalis: forms most of the anterior pituitary
- pars intermedia: tends t be less defined in humans
- pars tuberalis: layer or extension of the anterior pit that surrounds the neural stalk of the hypothalamus
where do the secretions from the anterior pituitary cell diffuse into?
the vascular network, which eventually drains into the systemic circulation
this part of the anterior pituitary is responsible for the synthesis and secretion of melanocyte-stimulating hormone (MSH)
pars intermedia
- generally considered rudimentary in humans
five cell types found in the anterior pituitary and what they secrete:
- somatotrophs - growth hormone; 50%
- mammotrophs - prolactin; 25%
- corticotrophs - corticotrophin - ACTH (adrenocorticotropic hormone); 15-20%
- gonadotrophs - FSH + LH; 5-10%
- thyrotrophs - thyrotrophin - TSH); 5%
posterior pituitary
- continuation of hypothalamus
- comprised of axons of neuronal cells (lies in the supraoptic and paraventricular nuclei of hypothalamus) + supporting glial cells = pituicytes
oxytocin
secreted from the paraventricular nucleus in hypothalamus
vasopressin
- ADH
- secreted from supraoptic nucleus in hypothalamus
Herring bodies
oxytocin and vasopressin travel to posterior pituitary in neurosecretory granules via axons
- hormones stored in terminal ends of axons which appear as bulb like projections called herring bodies
neurosecretion and Herring bodies
when hormones need to be released, hypothalamus sends nervous impulses through axons = neurosecretion
where is the thyroid located?
- anterior neck, just in front of the trachea
- H-shaped, lobulated
T or F. The thyroid is encapsulated
T.
septae = lobules; blood vessels, nerves, and lymphatic channels; within gland = capillaries also surround follicles
how did the thyroid gland develop?
- in part as a downgrowth from fetal tongue (follicular epithelium)
- and in part from the fourth branchial pouch = calcitonin cells
function of the thyroid
- T4 (thyroxine): influence basal metabolic rate
- T3 (triiodothyronine): influence growth + development; regulated by TSH/thyrotrophin from anterior pituitary
- calcitonin: decreases calcium levels by inhibiting bone resorption; PTH antagonist; levels dependent on blood Ca
structure of thyroid
- capsule = thin, collagenous with internal septae, forms irregular lobules
- stroma = composed of connective tissue, blood vessels, and nerves
functional unit of thyroid gland
thyroid follicles
- tightly packed
- irregular
- single layer of cells resting on basement membrane
- simple cuboidal epithelium
the thyroid __________ cells synthesize and secrete hormones. how is this achieved?
follicular cells
- achieved by concentrating iodide from bloodstream, converting it to idine then secreting it into the follicular lumen
- production of T3 and T4 = controlled by TRH and TSH
- iodine combines w tyrosine residues in thyroglobulin (colloid) to form T3/T4 in their inactive form
- thyroglobulin synthesized in Rough ER
where are inactive T3 and T4 hormones stored?
follicular colloid
- homogeneous proteinaceous material
- colloid is engulfed and hydrolyzed by follicular cells
- hormones can diffuse in bloodstream in their active forms
this is found among follicular cells or interfollicular spaces and these secrete calcitonin when Ca levels are increased
parafollicular cells (C or clear cells) - pale and hard to see in routine light microscopy; use IHC Abs or EM
