It is the Terminal Cisternae- Sac like regions of the sarcoplasmic reticulum that serve as specialized resevoirs of calcium ions
Smooth ER
calcitonin (thyroid) used to break down calcium stores in the bone. and parathormone (parathyroid) - stores the excess calcium in the bones
The right way
vacuoles
It is the Smooth Endoplasmic Reticulum. The Smooth ER is the "hallways" of the cell, that lead products to the Golgi appratus. It synthesis lipids, metabolizes carbohydrates, and detoxifies drugs and poisons. It also stores calcium ions, which are necessary for muscle movement.
sarcoplasmic reticulum
The Sarcoplasmic Reticulum stores calcium and releases it through the terminal cisternae into the tubule.
Smooth ER
sarcoplasmic reticulum, i think. either that are T tubules
Sarcoplasmic reticulum stores and releases calcium ions within striated skeletal muscles.
sarcoplasmic reticulum (SR)
some calcium enters the cell from the extracellular space and triggers the release of larger amounts of calcium from intracellular stores
Without "the following" I can't say what tha answer you're looking for is, but I would assume it is related to muscle cells as the sarcoplasmic reticulum is a cellular structure only found in the three types of muscle tissue.
The Sarcoplasmic Reticulum stores calcium and releases it through the terminal cisternae into the tubule.
There is some calcium outside the cell but the bulk of it comes from intracellular stores.
rER makes secretory proteins and also serves as a membrane factory that grows in place by adding proteins and phospholipids.
calcium can typicaly be stored in your fingernails.