It’s a layer located outside of the cell envelope
The answer is alveolates. The sac-like structures under their plasma membrane are called alveoli. The alveoli provide support to the plasma membrane. Examples of groups of alveolates are ciliates, such as Paramecium, dinoflagellates, apicomplexa, and foraminifera. They lie under the phylum, Ciliophora.
Generally, epithelial cells serve the function of protection of the inner layers of the structure they are on. The fact that these columbar epithelium and transitional epithelium cells have smooth walls and are dome shaped allows them to stretch. This stretching helps the bladder retain more urine than it would be able to if the epithelial cells were rigid.
For Hypothalamo-Pituitary-Adrenal Axis of endocrine gland secretion, follow the root "CORTI" (C). This will be a great memory tool. Also, nearly all hypothalamic hormones that stimulate anterior pituitary secretion have the word RELEASING (hence "R" in their acronyms). So if asked what secretes CRH, GnRH, TRH, or GHRH... the answer will be the Hypothalamus because of the R.
Now... back to CRH... we're following the "C" for CORTI. What other endocrine hormone has C for CORTI??
ACTH = Adreno[Corti]coTropic Hormone
Which will then stimulate secretion of [Corti]sol (a glucocorticoid), amongst others from the cortex of the adrenal gland. Notice the [Corti] follows the whole pathway from Hypothalamus to adrenal Cortex: Hypothal. (CRH) --> Ant. Pituit. (ACTH) --> Adrenal Cortex (Cortisol)
Sorry this was so long-winded, but I was hoping to help you grasp a portion of how the Endocrine System works!
Good luck and hmu should you have any further Anatomy/Physiology questions.
