(05) Endocrine System - Thyroid Gland

Question 1

(thyroid gland)

1. this shield shaped unpaired gland develops as what? forming how many lobes? with out without connecting isthmus?
2. capsule comprised of? continues into gland as what? In what animals in the connective tissue component thick?
3. Parenchymal functional unit =
4. final secretory product is what?

Answer 1

1. foregut endodermal out-growth; two; can be either
2. thin connective tissue; septa; pig and ox
3. follicles
4. thryoid hormone (T3 and T4) (a tyrosine derivative with either 3 or 4 iodine atoms)

Question 2

1. What is a cluster of cells surrounding a lumen called (sphere-like structure)?
2. What are the two types of follicular cells?

Answer 2

1. thyroid follicles
2. active (stimulated) cells and inactive cells

Question 3

(Thyroid Follicles)

(Follicular Cells)

(Active Cells)

1. what shape?
2. surface modifications?
3. long what which extend into lumen?
4. organelles?

Answer 3

1. cuboidal to columnar
2. apical (luminal surface) microvilli
3. pseudopodia
4. cytoplasmic organelles (lysosomes, RER, and golgi)

Question 4

(Thyroid Follicles)

(Follicular Cells)

(Inactive Cells)

1. cell shape?
2. follicular cells rest on what? surrounded by what?

Answer 4

1. low cuboidal or squamous
2. peripherally located basement membrane which is surrounded by sinusoidal capillaries and lymphatics

Question 5

(Thyroid Follicles)

(Follicle Lumen)

1. contains what?

Answer 5

1. stored colloid (gel-like mass of viscous, proteinaceous material comprised of thyroglobulin and other compounds)

Question 6

(Thyroid Follicles)

1. secretory process simple or complex?

2-3. involves many membrane bound vesicles containing substances that cell is doing what two things with?

Answer 6

1. complex
2. releasing into the follicle lumen (colloid)
3. luminal products cells is taking back into it’s cytoplasm for processing

Question 7

1. do all steps of thyroid hormone synthesis by follicular cells occur within a single cell?

Answer 7

1. yes

Question 8

(Thyroid hormone synthesis)

Put these 9 steps in order

(a) Thyroglobulin iodination (in colloid)
(b) Sugars added to thyroglobulin (golgi)

(c) T3 and T4 enter extracellular space and
diffuse into capillaries

(d) Lysosomes fuse with endosomes (enzymes formed in RER)

(e) Thyroglobulin protein core synthesized
(RER)

(f) Amino acids and iodide from capillaries
(g) Thyroglobulin taken up by endocytosis
(h) Thyroglobulin broken down
(i) Thyroglobulin & thyroperoxidase released by exocytosis (secretion)

Answer 8

(f), (e), (b), (i), (a), (g), (d), (h), (c)

Question 9

(Thyroid Hormone Synthesis by Follicular cells)

1. What is synthesized and released into the follicle lumen?
2. What happens to it in the lumen?
3. Product remains “stored” within the lumen until needed, at which time iodated thyroglobulin is taken into what by what?
4. What degrade the thyroglobulin? What does this release? What happens to the stuff that gets released?
5. release is stimulated by what?

Answer 9

1. thyroglobulin
2. it becomes iodinated
3. into follicular cells by endocytosis
4. lysosomal proteases; T3 and T4; diffuse from basolateral cell and are taken up into the circulation
5. thyroid stimulating hormone

Question 10

(thyroid hormone)

1. target?

(function)

2. binds to what? ligand/receptor complex then binds to what?
3. Activation of nuclear DNA leads to what (3 things)?
4. Thyroid hormone acts in concert with other hormones to cause some effects, e.g., GH, cortisol?

Answer 10

1. many, perhaps most, cells, and many metabolic processes
2. cytosolic receptors; thyroid hormone response elements in nuclear DNA
3. upregulation of general protein synthesis, increased metabolic rate, increased mitochondrial acitivity in target cells.
4. yes

Question 11

(Clinical Considerations)

1. What is general depression of metabolism and activity called?
2. Will occur if TSH is present but circulating what is low? What may cause this?
3. In humans what will result from continued stimulation of TSH (no negative feedback to limit TSH release)?

Answer 11

1. Hypothyroidism

2. T3/T4 levels; May be that T3/T4 is not being made (no iodine) or not released

3. Goiter (enlarged thyroid)

Question 12

(Clinical Considerations)

1. What is characterized by severe metabolic disturbances and weight loss?
2. In vet practice - commonly seen in what?
3. The hyperplastic thyroid (often palpably enlarged) secretes an excess of what?

Answer 12

1. hyperthyroidism (grave’s disease)
2. elderly cats
3. thyroid hormone

Question 13

(Thyroid Parafolicular Cell)

1. aka what?
2. of what origin? (via the what)?
3. Located throughout the thryoid both within what and what?
4. What is cytoplasm like? mitochondria? small membrane bound granules?

Answer 13

1. C-cells
2. neural crest origin (via the ultimobranchial body)
3. follicular basement membrane (singly) and between follicles (in clusters)
4. pale, acidophillic; many; yes

Question 14

(Thyroid Parafolicular Cell)

(cont)

1. synthesize and secrete what?
2. what is it? released in response to what?
3. calcitonin does what by inhibitng osteoclast activity? thus decreases what?
4. opposes activity of what hormone?

*Parafollicular cells also contain somatostatin and serotonin in varying amounts (in the same cells with calcitonin)

Answer 14

1. calcitonin (thyrocalcitonin)
2. polypeptide released in response to increased blood Ca
3. decreases blood calcium; bone break down
4. parathyroid hormone