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