Endocrine System (Troyer) Flashcards
Location of the Pituitary Gland?
IN the sphenoid bone of the skull
Origin of the Pituitary Gland?
2 Parts
- ectoderm from roof of oral cavity that grows upward as Rathke’s pouch =becomes anterior pituitary
- neuroectoderm from diencephalon that grows downward = becomes posterior pituitary
What is a portal system?
series of veins that are interposed between two sets of capillaries
How does the hypothalamus “control” the adenohypophysis?
- Releasing and Inhibiting factors (hormones) are synthesized by special secretory neurons in hypothalamus
- Hormones are transported to and stored in axon terminals ending in the median eminence
- After receiving appropriate stimulus, hormones are discharged into capillaries and travel into hypophyseal portal system to capillaries in pars distalis
What is the median eminence?
hypothalamic tissue extending into the pituitary (infundibular) stalk
Pars distalis
parenchyma of cords or clusters of cells associated with sinusoids
part of adenohypophysis
Where is the pars tuberalis?
forms collar around neural stalk of pituitary gland
What is secreted by the pars intermedia?
- MSH - melanocyte stimulating hormone
- ACTH
What does CRH release?
ACTH or corticotropin
What does TRH release?
TSH or thyroid stimulating hormone
What does GnRH release?
gonadotropins
What does somatostatin do?
inhibits somatotropic hormone release
Origin of the Thyroid?
outgrowth from the floor of the buccal cavity
How many lobes are in the thymus?
two lobes that are usually connected by an isthmus
T/F: Dogs have an isthmus
False
Follicular Cells in the Thymus
- cuboidal epithelium
- microvilli on apical edge
- held together by tight junctions
Parafollicular Cells in the Thymus
- found in isolated clusters beside the follicle
- larger, paler cells than follicular cells
- produce calcitonin which lowers serum calcium levels
What does calcitonin do?
lowers serum calcium levels
Function of the Thymus?
- endocrine
- ‘storage’ phases of production (unusual among endocrine glands)
Follicular Cells and storage phases
synthesize and secrete thyroglobulin
Where is thyroglobulin stored?
extracellularly in lumen of follicle, where it is partially iodinated
Follicular Cells and endocrine phase
- stored thyroglobulin = taken up by follicular cells
- broken down by lysosomal enzymes to active thyroid hormone
- TH then released into blood
What is T4?
- thyroxine or tetraiodothyronine
- prohormone = one iodine is removed to make T3
- most abundant form
What is T3?
- triiodothyronine
- active hormone
- less abundant than T4
Where can T4 become T3?
- liver, kidney, and muscles
- deiodinase removes one iodine
What does T3 do?
- increases metabolic rate of target cells
- increases numer of mitochondria = hence mitochondrial respiration
Colloid
- made up of thyroglobulin, a glycoprotein
- tyrosine amino acyl residues of thyroglobulin are iodinated
- represents storage phase of secretion
Location of Parathyroid Glands
In or around thyroid gland
external parathyroids = vary from cranial to thyroids to level of thoracic inlet
internal parathyroids = embedded in, on, or near thyroid
Structure of Parathyroid Glands
- capsule of internal parathyroids is areolar CT of thyroid
- parenchyma: cords, clusters w/ numerous capillaries
What is the predominant cell type of the parathyroid glands? Are they subdivided in any way?
Chief cells
Yes = dark and light chief cells
Dark cells produce parathyroid hormone
In what species are oxyphil cells found? What is the function?
Found in humans, ox, and horses
Exact function unknown
What is the function of parathyroid hormone (PTH)? How is this function carried out?
raise blood calcium levels
increases osteoclast activity to tear down bone to release calcium
Origin and location of adrenal gland
cortex = from mesoderm medulla = from neural crest
Location: cranial pole of kidney
Structure of the Adrenal Glands
capsule around adrenal sends trabeculae into the parenchyma
also fine reticular fibers within the parenchyma
Three regions of adrenal gland cortex
- zona glomerulosa
- zona fasciculata
- zona reticularis
What is produced in the zona glomerulosa of the adrenal cortex?
What’s the function?
How is it stimulated?
Mineralocorticoids
act on kidney to retain Na+ and water
Mostly stimulated by angiotensin
What is produced in the zona fasciculata of the adrenal cortex?
How is it stimulated?
glucocorticoids
stimulated by ACTH
What is produced in the zona reticularis?
weak androgens
Secretions of the Pineal Gland?
- melatonin
- serotonin
