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Endocrine Exam 1 > 4 - Pancreas, Thyroid and Parathyroid Glands > Flashcards

4 - Pancreas, Thyroid and Parathyroid Glands Flashcards

1
Q

Describe the three parts of the thyroid gland

A

Right lobe, isthmus, left lobe

Pyramidal lobe at arrow is present in 40% of people

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2
Q

Where is the thyroid located?

A

located inferior to larynx

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3
Q

What is the pyramidal lobe?

A

Represents the inferior end of the thyroglossal duct that persists after the remainder of the thyroglossal duct has degenerated is present in about 40% of individuals

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4
Q

What is the thyroglossal duct?

A
  • As the thyroid gland develops and descends into the neck, a hollow duct, the thyroglossal duct forms which temporarily connects the developing thyroid gland to the foramen cecum of the tongue.
  • The thyroglossal duct eventually degenerates and normally disappears, however, in some individuals it may persist as a developmental remnant: a fibrous cord that extends from the fully-developed thyroid gland to the foramen cecum in the dorsum of the tongue.
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5
Q

What is the thyroid capsule?

A
  • The thyroid capsule is derived from the deep cervical fascia and consists of dense irregular collagenous connective tissue
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6
Q

What does the thyroid capsule give rise to?

A

Thyroid capsule gives rise to trabecula/septa that separate the gland into lobules
- septa carry blood vessels, lymphatic vessels, and nerve fibers deep into the gland.
- thyroid gland is
an endocrine gland and is VERY vascular

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7
Q

Where are the parathyroid glands located?

A

Parathyroid glands are located within the thyroid capsule covering the posterior surface of the thyroid gland

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8
Q

What is the function of the thyroid gland?

A

Synthesize hormones

  • T3 (triiodothyronine)
  • T4 (tetraiodothyronine) or thyroxine
  • Calcitonin
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9
Q

What processes are T3 and T4 involved in?

A

These hormones regulate cell and tissue metabolism

and heat production

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10
Q

What process is calcitonin involved in?

A

Is involved in the regulation of blood calcium levels

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11
Q

What are thyroid follicles?

A

The basic structural and functional unit of the thyroid gland

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12
Q

Describe thyroid follicles

A
  • spherical, cyst-like, variable diameter
  • surrounded by a basal lamina, reticular fibers, and then a fenestrated capillary plexus, and blind-ended lymphatic capillaries
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13
Q

What is the function of the thyroid follicles?

A

Store glandular secretory product in follicular lumen (extracellularly)

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14
Q

What surrounds the thyroid follicles?

A

Basal lamina

A capillary plexus also surrounds the follicles

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15
Q

Describe the epithelium of normal follicular cells

A

Simple cuboidal

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16
Q

Where are parafollicular cells founds?

A

Wedged between follicles, NOT exposed to colloid (within follicles)

Lie within basal lamina surrounding follicles, are near many capillaries and are light-staining

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17
Q

What do parafollicular cells secrete?

A

Calcitonin

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18
Q

What is the effect of calcitonin?

A

calcitonin lowers blood calcium levels to NORMAL as follows:
• It inhibits bone breakdown by osteoclasts
• It promotes calcium deposition in bones (osteoid calcification)

Lower blood calcium by putting it back into the bone***

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19
Q

What controls the synthesis of thyroid hormones?

A

Controlled by TSH and iodide levels

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20
Q

Give a basic overview of thyroid hormone synthesis

A
  • Follicular cells synthesize thyroglobulin (a glycoprotein) and release it into the follicular lumen. Each thyroglobulin molecule contains about 120 tyrosine residues.
  • Iodide from the bloodstream is pumped into the follicular cells. It is oxidized on the apical (microvillar) cell membrane facing the colloid into its active form (iodine) and it then remains in the follicular lumen.
  • The iodine iodinates the tyrosine residues of each thyroglobulin molecule to form monoiodotyrosine (MIT), and diiodotyrosine (DIT).
  • Neighboring MIT + DIT undergo a coupling reaction to form → triiodinated tyrosine (T3)
  • Neighboring DIT + DIT undergo a coupling reaction to form → tetraiodinated tyrosine (T4)
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21
Q

Describe the oxidation of iodide

A
  • oxidation of iodide takes place in the active sites of thyroid peroxidase (a membrane-bound enzyme) on the follicular APICAL cell membrane, facing the colloid
  • oxidation of iodide occurs in the colloid
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22
Q

What enzyme catalyzes the process of iodination of the tyrosine residues on thyroglobulin?

A

Thyroid peroxidase

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23
Q

Describe the release of thyroid hormones T3 and T4

A

Stimulated by TSH
• Follicular cells uptake colloid (thyroglobulin) from follicular lumen.
• Proteases cleave iodinated tyrosine residues from thyroglobulin, as uncoupled MITs and DITs
• triiodinated tyrosine (now free, called triiodothyronine = T3) and tetraiodinated tyrosine (now free, called tetraiodothyronine = T4)
are all released into the follicular cell cytoplasm
• Thyroid hormones are released from basal aspect of follicular cells into the extracellular space.
• Hormones then pass into the fenestrated capillary network which drains into the general circulation.
• Hormones are delivered to tissues and organs.

24
Q

Where is TSH released from?

A

Anterior pituitary gland basophils (thyrotropes) release TSH

25
Q

What are the physiological effects of T3 and T4 - What do they increase?

A
  • Cellular metabolism
  • Growth rate
  • Mental activity
26
Q

What are the physiological effects of T3 and T4 - What do they stimulate?

A
  • Endocrine gland functions

- Carbohydrate metabolism

27
Q

What are the physiological effects of T3 and T4 - Others?

A
  • Decrease the formation of phospholipids and triglycerides
  • Enhance the synthesis of cholesterol
  • Increase the formation of fatty acids
28
Q

An increase in thyroid hormone synthesis results in…

A
  • A decrease in body weight

- An increase in HR, metabolsim, RR, muscle function, appetite

29
Q

Very high levels of thyroid hormone results in…

A
  • Muscle tremor
  • Fatigue
  • Impotence in men
  • Abnormal menstrual bleeding in women
30
Q

What will you see in Grave’s disease?

A

Hyperthyroidism
- Exophthalmos – eyes sticking out
- Enlarged thyroid
Autoantibodies (IgG) which bind to TSH receptors (they are imposters)
This stimulates colloid uptake, leading to excessive amounts of T3 and T4 will be in the circulation

31
Q

What accounts for the exopthalmos seen in hyperthyroidism?

A
  • Fibrosis of the rectus muscles
  • LCT will also accumulate behind the eye
  • While no widespread fibrosis of skeletal muscles will occur, mild fibrosis of cardiac muscle interstitium can occur
32
Q

Describe the anatomy of the parathyroid glands

A
  • 4 small ovoid glands, located posterior to thyroid gland
  • collagenous connective tissue capsule with septa that carry blood vessels, lymphatic vessels, and nerve fibers into glands
  • Becomes adult-sized by age 20
33
Q

What cell types will be present in parathyroid glands?

A
  • Chief cells
  • Oxyphil cells
  • Intermediate cells
34
Q

What is the function of the chief cells in the parathyroid glands?

A

Secrete granules which contain parathyroid hormone (PTH)

35
Q

What is the function of oxyphil cells?

A

function unknown, may be dormant, inactive chief cells

Intensely eosinophilic (due to mitochondria)

36
Q

What is the function of intermediate cells?

A

Unknown

37
Q

What are the physiological effects of parathyroid hormone (PTH)?

A
  • PTH is essential for life

- Regulates calcium and phosphate levels in the blood ***

38
Q

What is the effect of PTH in the bone?

A
  • PTH attaches to osteoblast receptors
  • This causes osteoblasts to release osteoclast-stimulating factor, which triggers osteoclast activity (bone breakdown / erosion), freeing Ca++ and phosphate from bone to enter the bloodstream
39
Q

What is the effect of PTH in the kidney?

A
  • Conserves Ca++

- Excretes phosphate

40
Q

What is the effect of PTH in the GI tract?

A
  • PTH regulates the formation of vitamin D in the kidneys

- Vitamin D facilitates Ca++ absorption in the GI

41
Q

What has the opposite effect as PTH?

A

Calcitonin

42
Q

Describe the difference between PTH and calcitonin

A
  • PTH increases low blood Ca++ levels to normal
  • Calcitonin decreases elevated blood Ca++ levels to normal

KNOW THIS

43
Q

What happens in the case of a thyroidectomy?

A

Parathyroid glands often get taken accidentally

  • Parathyroid glands need to be left behind
  • Complete removal of the parathyroid glands will drop blood calcium level.
  • This will cause tetanic contraction of muscles, including the laryngeal and respiratory muscles that will result in death.
44
Q

Describe the tetany that would develop from hypocalcemia

A

Is characterized by Neuromuscular irritability(ranges from numbness / tingling in distal extremities to laryngospasm and generalized seizures)

45
Q

What would happen if you had hyperparathyroidism?

A
  • Osteoclasts would erode excess bone
  • Hypercalcemia would result
  • This would lead to urinary tract stones, calcification of lungs, myocardium, stomach and blood vessels
46
Q

Describe the anatomy of the pancreas

A
  • Located in the retroperitoneal space
  • Divided into head, body, tail and uncinate process
  • Enclosed in a connective tissue capsule
  • Consists of exocrine and endocrine portions which produce digestive
    juices and hormones, respectively
47
Q

Describe the connective tissue capsule of the pancreas

A

Septa partition gland into lobules, carry blood vessels, lymphatic vessels, nerves and gland ducts

48
Q

What structures are found in the endocrine pancreas?

A

Islets of Langerhans, which produce hormones

49
Q

What cells are found in Islets of the endocrine pancreas?

A
  • Alpha cells
  • Beta cells
  • Delta cells
  • PP cells (F cells)
  • G cells
50
Q

What do alpha cells of islets secrete?

A

Glucagon

This increases blood glucose levels

51
Q

What do beta cells of islets secrete?

A

Insulin

This decreases blood glucose levels

52
Q

What do delta cells of islets secrete?

A

Somatostatin

This reduces smooth muscle contraction of the digestive tract and gallbladder

53
Q

What do PP cells of islets secrete?

A

Pancreatic polypeptide

This inhibits pancreatic exocrine secretions

54
Q

What do G cells of islets secrete?

A

Gastrin

This stimulates synthesis of HCl by parietal cells in the stomach mucosa

55
Q

Describe insulin production

A
  • preproinsulin (a polypeptide chain) is synthesized on the RER of the beta cells
  • preproinsulin is converted to proinsulin within the RER
  • proinsulin is packaged into vesicles within the trans GA
  • a segment of the proinsulin is cleaved to form insulin
  • elevated blood glucose levels stimulate the release of
    insulin in the intercellular space
56
Q

Describe the exocrine pancreas

A

The exocrine pancreas is a compound tubuloacinar gland which produces a fluid rich in bicarbonate with proenzymes.

Centroacinar cells and intercalated ducts synthesize a serous, bicarbonate-rich alkaline fluid which neutralizes the acidic chyme released into the duodenum by the stomach

Endocrine Exam 1 (18 decks)

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