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BISC 125 Endocrine System


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Where is the thyroid gland located?
In the neck, below the larynx, with the lobes resting on the sides of the trachea
What shape is the thyroid gland?
At what time in development is thyroid development most important?
From birth to the age of two (important in growth of the CNS)
What are the functions of the thyroid gland?
Stimulates growth of the CNS (up to age 2), regulates basal metabolic rate, secretes hormones that depress plasma calcium level and balances the action of parathyroid hormone
What is the gross structure of the thyroid gland?
Two lobes connected by a C.T. isthmus and surrounded by a double C.T. capsule
What is a thyroid follicle?
The functional unit of the thyroid gland; a layer of cuboidal follicular cells encircling colloid
How does the shape of follicular cells in the thyroid gland indicate activity?
Squamous follicular cells indicate a lack of thyroid hormone, columnar follicular cells indicate too much thyroid hormone
What is colloid?
A product stored in the thyroid follicles; it is rich in thyroglobin (an iodinated glycoprotein)
What occurs as a result of a diet insufficient in iodine?
Goiters (swelling of the cells of the thyroid gland)
Why are tight junctions between follicular cells so important?
Because colloid is not recognized by the body, and if it got into the surrounding C.T., it may cause an autoimmune response.
Why are fenestrated capillaries important in the thyroid gland?
The capillaries carry the hormones produced in the gland and allow the monitoring of the amount of hormone in the bloodstream.
What are C cells?
Parafollicular cells, also known as clear cells because their cytoplasm does not stain
What do parafollicular cells secrete (and what does the secretion do)?
Calcitonin; secretion of calcitonin lowers blood calcium levels by stopping the activity of osteoclasts and allowing increased mineralization of bone.
What is the difference between the way secretions are stored in the cortex of the thyroid gland versus how they are stored in the medulla?
In the cortex, secretions are stored in cytoplasmic granules; in the medulla, they are stored near the core (central or eccentric)
Where are the parathyroid glands located?
On the posterior surface of the thyroid gland, between or outside the double capsule
What does the parathyroid gland secrete?
Parathyroid hormone
What does parathyroid hormone do?
Elevates blood calcium levels by stimulating osteoclasts to resorb bone; also targets osteoblasts to secrete substances that cause macrophages to become osteoclasts
What are the two types of cells found in the parathyroid gland?
Chief cells and oxyphill cells
What is the result of surgical removal of the parathyroid gland?
Hypocalcemia, increased excitability of nerves (pins and needles sensation), and attacks of tetany or epilepsy
How can symptoms related to removal of the parathyroid gland be corrected?
Injections of parathyroid hormone
What do chief cells in the parathyroid gland do?
Secrete parathyroid hormone (contain secretory granules)
What is the function of oxyphill cells?
The function is unknown; they may represent transitional chief cells. It is only known that they appear at puberty, increase with age, and have abundant mitochondria
What hormone balances the action of calcitonin (and how does it do so)?
Parathyroid hormone; it elevates plasma calcium levels
What causes rickets (in children) and osteomalacia (in adults)?
Deficiency in vitamin D; causes low mineralization of bone
How can osteoporosis be prevented?
With a good interaction between C cells and parathyroid hormone (from chief cells)
Where are the adrenal glands located?
On top of the kidneys ("adrenal" = "near kidneys")
How many layers does the adrenal cortex have (and what are their names)?
Three layers: the zona glomerulosa, the zona fasciculata, and the zona reticularis
Are the hormones of the adrenal gland stored in secretory granules?
No, there are big, fluffy areas where the hormones pass through the cell membrane.
How much of the adrenal cortex is made up of the zona glomerulosa?
10 to 15%
What region of the adrenal cortex has the largest volume?
The zona fasciculata (makes up about 75% of the adrenal cortex)
What zone of the adrenal cortex is most sensitive to ACTH?
The zona fasciculata; ACTH stimulates cells in this zone to produce cortisol
What does the zona glomerulosa secrete?
Mineralocorticoids, like aldosterone
What does aldosterone do?
Stimulates the retention of water and Na+ in the kidney and encourages the renal secretion of K+ and H+; important in regulating BP and sodium levels
What zone of the adrenal cortex has a "tangled" arrangement of microtubules and cells?
The zona glomerulosa
What are the target organs of aldosterone, secreted by the adrenal cortex?
Kidneys, sweat glands, and salivary glands
What zone of the adrenal cortex has cords of cells arranged in relatively straight lines?
The zona fasciculata
What do the cells of the zona fasciculata secrete?
Glucocorticoids, principally cortisol
What is the function of cortisol?
It is an antiinflammatory (is involved in suppression of the immune response) and stimulates an increase of glucose concentration in the blood (acts opposite of insulin)
Where are spongiocytes found?
In the zona fasciculata of the adrenal cortex
Why do people under a lot of stress tend to have poor immune responses?
Stress causes an increase in ACTH output, which stimulates the zona fasciculata of the adrenal cortex to produce cortisol, which is an antiinflammatory that supresses the immune system.
About how much of the adrenal cortex is made up by the zona reticularis?
About 5-10% of the cortex
Are the cells of the zona reticularis acidophobic or acidophilic?
What do the cells of the zona reticularis secrete?
Sex steroids
What is unique about the blood supply in the adrenal gland?
Three arteries enter, supplying the capsule, cortex and medulla with blood. However, veins are only present in the medulla, so all blood has to travel through the medulla to exit the gland.
What are catecholamines?
Norepinephrine or epinephrine, secreted by the adrenal gland
What type of cells are found in the adrenal medulla?
Chromaffin cells
What are chromaffin cells?
Cells found in the adrenal medulla; they are modified sympathetic (postganglionic) neurons that secrete one of two catecholamines
Where are the islets of Langerhan's located?
In the endocrine portion of the pancreas
What is the structure (general) of the islets of Langerhan's?
Anastomosing cords of endocrine cells surrounded by fenestrated capillaries.
What is the insuloacinar portal system?
Found in the pancreas; special portal system in which venules leave the islets of Langerhan's and supply blood to the exocrine acini of the pancreas. It allows the islet cells to exert some influence over the exocrine acini.
What are the four types of cells found in the islets of Langerhan's (endocrine pancreas)?
Alpha cells, beta cells, delta cells, and F cells
How many of the cells of the adrenal medulla secrete epinephrine? How many secrete norepinephrine?
About 80% of the cells secrete epinephrine, and about 20% secrete norepinephrine.
What does the insuloacinar portal system allow the endocrine pancreas cells to do?
Exert some influence over the exocrine acini and control their activity in enzyme production and release.
Where are alpha cells found and what do they secrete?
They are found in the islets of Langerhan's in the pancreas, and they secrete glucagon.
What does glucagon do?
Glucagon causes an elevation in blood glucose level by stimulating increased hepatic glycogenolysis.
Where are beta cells found and what do they secrete?
Beta cells are found in the islets of Langerhan's in the endocrine pancreas; they secrete insulin.
What does insulin do?
Insulin lowers blood glucose levels; together with glucagon from alpha cells, it maintains blood sugar levels.
In a person with diabetes melitus, what cells aren't functioning properly?
Beta cells in the endocrine pancreas are not producing enough insulin.
What is an insulinoma?
A tumor in the beta cells that causes too much insulin to be produced and secreted.
Where are delta cells found and what do they secrete?
Delta cells are found in the islets of Langerhan's in the endocrine pancreas; they secrete gastrin and somatostatin.
What does somatostatin do?
Somatostatin inhibits the release of insulin and glucagon in the pancreas
What does gastrin do?
Activates receptors that stimulate gallbladder contraction.
Where are F cells found and what do they secrete?
F cells are found in the islets of Langerhan's in the endocrine pancreas; they secrete pancreatic polypeptide.
What does pancreatic polypeptide do?
Pancreatic polypeptide inhibits the release of somatostatin; it also blocks secretion of bile by inhibiting contraction of the gallbladder (conserves bile and digestive enzymes between meals)

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