LECTURE - The Endocrine System Flashcards
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
grossly, can appear as coffee coloured lands that are small and ovoid in shape
parathyroid glands
how did the PTH glands develop and where are they located
- developed from the third and fourth branchial pouches (surrounded by a thin, fibrous capsule; septae)
- located in the neck where thyroid is; posterior
the septae of the PTH gland carries…
lymphatics, nerves, and blood vessels
three cell types of PTH glands
- chief (principal) cells: PTH; increases Ca levels in blood by promoting bone resorption via osteoclasts; cells are spherical in shape with pale pink to clear cytoplasm + small dark nuclei
- oxyphil: rare before puberty; increase in # as we age; larger than chief cells; eosinophilic cytoplasm + small, dark nuclei; cytoplasm may be granular due to large #s of mitochondria
- adipocytes: appear at time of puberty and continue to increase till midlife = remain constant; help to form stroma (found in oxyphil and chief cells)
chief and oxyphil = cord and clump formations
two triangular shaped glands located in upper poles of kidneys
adrenal glands
two distinct endocrine systems found in the adrenal gland
- adrenal cortex (outer) = synthesizes + secrete hormones produced from cholesterol, controlled by the pituitary gland, the hypothalamus, as well as the RAAS
- adrenal medulla (inner) = vasoactive amines, adrenaline, noradrenaline, controlled by sympathetic nervous system
RAAS
renin angiotensin aldosterone system
layers of the adrenal cortex
fourth outermost layer involutes after birth
- Zona glomerulosa: mineralocorticoids (aldosterone)
- Zona fasciculata: thickest layer; glucocorticoids (cortisol)
- Zona reticularis: androgenic steroids (DHEA + DHEA-S) and some glucocorticoids
DHEA, DHEA-S
- dehydroepiandosterone
- dehydroepiandrosterone-sulfate
hyperadrenalism
excess secretion of glucocorticoids = Cushing’s syndrome +
excess secretion of mineralocorticoids = Conn’s syndrome
hypoadrenalism
hormones of adrenal cortex are not secreted (due to cellular destruction for example = Addison’s disease
MATCH: (layers of adrenal cortex)
a) thin layer; cells with eosinophilic cytoplasm (stains darkly); cells may contain lipofuscin pigment
b) thin subcapsular layer; small compact cells w scant lipids arranged in clumps and separated by stroma which is composed of largely thin-walled capillaries in trabeculae
c) occupies most of adrenal cortex; large reticular cells with clear cytoplasm; lots of smooth ER and mitochondria; intracytoplasmic accumulation of lipid droplets (lighter staining cells)
a) zona reticularis
b) zona glomerulosa
c) zona fasciculata
adrenal medulla
- the center of the gland
- control via sympathetic nervous system
- polyhedral cells are large with pale staining nuclei and finely granular, somewhat basophilic cytoplasm
- cells arranged in clumps + columns with a prominent capillary network
- cells contain neurosecretory granules where catecholamines (epi/norepi) are stored
intense brown colour of adrenal medulla when exposed to strong oxidizing agents (like potassium dichromate)
due to high catecholamine content in cells
chromaffin cells
type of cell that makes neurohormones (chemicals that are made by nerve cells and used to send signals to other cells) and releases them into the blood. Chromaffin cells make epinephrine (adrenaline) and norepinephrine (noradrenaline). They are found in the adrenal glands or in groups of nerve cells called ganglia.
major endocrine component of the pancreas
Islets of Langerhans
> more numerous in tail
> paler staining
> capillary networks are in close contact ith cells of the islets
enterochromaffin cells
in pancreas
- motilin
- ghrelin
- serotonin
VIP
vasoactive inhibitory peptide
four main cells in endocrine pancreas
- B = insulin; 70%; lowers blood glucose
- A = glucagon; 20%; increases blood glucose
- D = somatostatin; 5-10%; inhibit GI secretions
- PP = pancreatic polypeptide; 1-2%; increases motility in GI
these cells occur throughout the islet and have a well-developed rER, a prominent Golgi and numerous neurosecretory granules
insulin secreting cells
these cells are located mainly at the periphery of islet
glucagon secreting cells
disorder wherein cells normally responsive to insulin show resistance to insulin’s effects
type II DM
- B cells of islets are still able to produce insulin
- treatment = lifestyle modifications such as diet + exercise as well as drug treatment regimens
