Thyroid, Endocrine pancreas and Parathyroid glands Flashcards
(29 cards)
What are the endocrine cells of the pancreas?
Islets of langerhans, which include: Alpha cells, beta cells, delta cells and PP cells
What do the endocrine cells of the pancreas do?
Alpha cells: produce glucagon
Beta cells: produce insulin
Delta cells: produce somatostatin
PP cells: produce pancreatic peptide
What regulates blood glucose?
Insulin and glucagon help keep blood glucose within a set range (4-7.8 mmol/L)
What is the tyrosine kinase second messenger?
An enzyme located within the cytosol, when activated phosphorylates intracellular proteins to produce anabolic reactions
What are GLUT 4 transporters?
- When there is no insulin present, glucose cannot enter the cell
- When insulin is present it signals the cell to insert GLUT 4 transports into the membrane for glucose to pass through
What are the effects of insulin on carbohydrates?
- (+) Cellular uptake of glucose
- (+) Glycolysis (ATP production)
- Liver: (+) Storage of glucose as glycogen
What are the effects of insulin on proteins?
- (-) Gluconeogenesis
- Glucose used over AAs as a source of ATP
- (+) Cellular uptake of AAs
- (+) Protein synthesis
- Lack of insulin: AAs used as fuel source
What are the effects of insulin on proteins?
- (-) Gluconeogenesis
- Glucose used over fat as a source of ATP
- Adipose tissue: (+) Conversion of glucose to fat (storage)
- Lack of insulin: fatty acids used as fuel source
What are the effects of glucagon primarily on the liver?
- Glycogenolysis: Breakdown of glycogen to glucose
- Gluconeogenesis: Synthesis of glucose from non-carbohydrate molecules e.g. fatty acids, AAs
- Release of glucose by hepatocytes
What are the effects of glucagon secondarily on the liver?
- Lowers blood levels of AAs (glucagon release is stimulated by a protein-rich meal)
- Sequestration of AAs triggers gluconeogenesis
How does glucagon act?
Via the cyclic AMP second messenger system
Vascular supply of the thyroid?
It is very vascular:
- Superior & inferior thyroid arteries
- Superior, middle & inferior thyroid veins
External structure of the thyroid?
-Two lobes and an isthmus on the anterior neck
Internal structure of the thyroid?
- Composed of hollow spherical follicles
- A ring of follicular ells form the walls of each follicle supported by a basement membrane
What do thyroid follicular cells secrete?
Thyroglobulin
What is thyroglobulin?
A glycoprotein that is the precursor of the thyroid hormones (T4 & T3) (Essential role in regulating metabolism)
Where is thyroglobulin stored?
In the follicular lumen, suspended in a viscous gel called colloid
What do parafollicular (C cells) cells secrete?
Calcitonin
What is calcitonin?
Has minor effects of storing calcium in the bone
What are the thyroid hormones?
T3- Triiodothyronine
T4- Thyroxin or Tetraoidothyronine
How are the thyroid hormones synthesised?
- Thyroglobulin acts as a precursor
- Iodide is actively transported into follicular lumen
- It is oxidised to iodine and attached to tyrosine molecule (requiring thyroid peroxidase enzyme)
- Monoiodothyronine (T1) and diiodothyronine (T2) are linked together to form T3 and T4
How are thyroid hormones released?
- Hypothalamus (TRH)
- Anterior pituitary (TSH)
- TSH binds to receptors on follicular cells (Which release stored thyroid hormone and synthesis of more thyroglobulin to restock colloid)
- T4 and T3 circulate bound to thyroxine-binding globulins and albumin (small circulate in free form)
Which thyroid hormone is released more and which is more biologically active?
T4 and T3
What do thyroid hormones perform for gene transcription associated with glucose oxidation?
- Basal metabolic rate
* (+) Body heat production
