Endocrine System - Thyroid, Islets of Langerhans Flashcards
What is unique about the Thyroid gland that differentiates it from other endocrine glands?
It stores its own product (thyroglobulin)
What are the unique cells of the Thyroid gland? What are their roles?
Follicular Epithelial Cells: Production of Thyroglobulin (stored in lumen as colloid)
Parafollicular Cells: Production of Calcitonin (regulates blood calcium levels)
What are some unique features of the Thyroid?
It has fenestrated capillaries for movement of molecules across epithelia(?)
There are holes in the coloid just next to the follicular lining, which are responsible for reuptake (for production of T3 and T4)
Give a step-by-step analysis of how Thyroid hormones are synthesized/formed. What is this pathway called?
- rER produces thyroglobulin and sends it through the Golgi to be secreted into lumen.
- Iodide brought into cell through sodium-iodide symporter (NIS), and then turned into iodine by membrane-bound Thyroid Peroxidase as it passes through the iodide/chloride transporter (Pendrin)
- Iodine and thyroglobulin combine to make DIT (di-iodotyrosine) and MIT (mono-iodotyrosine). ALSO BY THYROID PEROXIDASE
- MIT + DIT = T3
- DIT + DIT = T4
- Thyroglobulins are reabsorbed and activated (into T3 and T4) before being secreted into lumen of the adjacent capillary.
THIS IS KNOWN AS THE LYSOSOMAL PATHWAY (5L).
What is a pathological version of the Lysosomal Pathway?
Megalin Pathway (5TE) - Instead of being activated, the whole thyroglobulin is incorporated and sent into bloodstream
What is the ratio of T3 to T4? Which is more active?
T3 is more active
T3:T4 is 20:1
What happens if the thyroid is over/underactive?
.Hypothyroidism: if present at birth, causes cretinism, mental retardation, and dwarfing (T3/T4 stimulate GH)
- if present in adulthood: myxedema - puffiness
Hyperthroidism: metabolic processes increase; body weight decreases.
What is the main function of the Parathyroid glands?
Regulates calcium and phosphate levels. PTH they produce is essential for life.
What are the two cell types of the Parathyroid gland? What are their functions?
Chief (Principal) Cells: produce PTH
Oxyphil Cells: also produce PTH, but are much more sensitive than Chief cells.
What does PTH do? How?
Increases blood calcium levels.
- Increases resorptive activity of osteoclasts in bone
- increase calcium reabsorption in kidney
- increase calcium absorption in the gut
What is the function of the endocrine Pancreas?
It’s a diffuse organ that secretes hormones to regulate blood glucose levels.
What are Islets of Langerhans? Where are they located most heavily in the pancreas?
They are the endocrine components of the pancreas. They are most numerous in the tail.
What typically surrounds the Islets of Langerhans?
Type III collagen (reticular fibers)
What are the three major cell types associated with the Islets of Langerhans, where are they, and what are their functions?
Alpha Cells: Secrete glucagon (antagonizes insulin) and resides in periphery of Islets of Langerhans.
Beta Cells: Secrete insuilin (promote uptake and utilization of glucose) and resides in the central region of Islets of Langerhans.
Delta Cells: Produce somatostatin (inhibits secretory activities of alpha and beta cells) and resides just outside the Islet.
Describe the effects of Insulin in more depth.
- decrease blood glucose
- stimulate storage of glucose
- stimulate glycerol synthesis
- promotes cellular glycolysis
- decreases gluconeogenesis and glycogenolysis
- stimulates FA synthesis
