Lecture 10: Endocrine tissues and glands Flashcards
What is the structure of endocrine glands?
- Ductless
- Secrete hormones directly into circulatory system
- Contain clumps or cords of secretory cells which are surrounded by an extensive network of blood capillaries
What is the portal circulatory route?
- Blood passes through 2 sets of smaller vessels before returning to the heart
- Blood from the first set of capillaries collects in portal vessels which then begin to branch again to supply a capillary network to a second location before entering a series of veins which will lead to the heart
What is the structure of the thyroid gland?
- Thyroid gland consists of 2 almost spherical lobes joined together by small connecting piece called the isthmus
- Positioned low in the anterior surface of the neck
- Isthmus lies inferior to the cricoid cartilage in the neck
- Thyroid lobes lay on either side of the trachea and away from the midline
What is the structure of the parathyroid gland?
- Usually 4 parathyroid glands, each a small ovoid structure on the posterior wall of the thyroid
- Composed of masses and cords of epithelial cells supported by reticular fibers and in close association with rich network of capillaries
What is the function of thyroid gland?
- Parafollicular cells in thyroid produces calcitonin (peptide hormone)
- Role is to monitor plasma calcium concentration and decrease the level
- Major effect: inhibits osteoclasts activity in bone
- Minor effect: inhibits renal calcium and phosphate re-absorption in tubular cells, more calcium and phosphate excreted
What is the function of parathyroid gland?
- Constantly monitor plasma calcium concentrations
- Plasma calcium is low = make parathyroid hormone (PTH)
- PTH causes bones to release calcium into blood and absorb more from GI tract
- Calcium provides electrical system for our nerves and muscles, allowing the nerves to conduct electricity and the muscles to contract
What is the structure of the adrenal gland?
- Pair of small, flattened endocrine glands, one of them being closely applied to the upper pole of each kidney
- Consists of medulla and cortex
What is the function of the adrenal medulla?
- Cimposed if chromaffin cells (modified neurons)
- Pre-synaptic sympathetic nerve fibers are passed to chromaffin cells
- Chromaffin cells releases adrenaline and noradrenaline
- Considered as equivalent of post-synaptic neurons
- Example of neurocrine secretion
What is the structure and function of adrenal cortex?
Three layers:
Outer - zona glomerulosa (aldosterone regulates BP)
Middle - zona fasciculata (glucocorticoids mobilizes fats, proteins and carbohydrates)
Inner - zona reticularis (androgen precursors)
Main indication: stress response
What is the structure of the pancreas?
- Contains mixed endocrine / exocrine gland structure
- Approximately 15cm long
- Lies behind stomach
What is the function of the pancreas?
- Secretes digestive enzymes into the duodenum and hormones into the bloodstream
- Exocrine: closely packed secretory acini which drain into highly branched duct system
- Endocrine: clumps of secretory cells (Islets of Langerhans)
What is the exocrine function of the pancreas?
Produces:
- trypsinogen
- chymotrypsinogen
- lipase
- amylase
- ribonuclease
- deoxyribonuclease
- gelatinase
- elastase
What is the endocrine function of the pancreas?
Alpha cell - glucagon (catabolises glycogen to glucose)
Beta cell - insulin (uptake and storage of glucose)
Delta cell - somatostatin (inhibits insulin and glucagon secretion)
PP cell - pancreatic polypeptide
