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Endocrine 2 - physiology > Phys - Thyroid and Parathyroid > Flashcards

Phys - Thyroid and Parathyroid Flashcards

1
Q

Thyroid gland anatomy

A
  • 2 lateral lobes
  • medial isthmus
  • follicle cells create spaces called follicles which are filled with colloid
  • parafollicular cells
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2
Q

Colloid

- describe

A
  • amber, sticky

- thyroglobulin and iodine (makeup of TH)

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3
Q

Follicle cells

- describe

A
  • squamous and cuboidal thyrocytes

- produce thyroglobulin and secrete it into the follicle/follicular space

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4
Q

Parafollicular cells

- describe

A
  • secrete calcitonin

- fewer in number compared to follicle cells

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5
Q

Two hormones produced and secreted by the thyroid gland

A
  1. thyroid hormone

2. calcitonin

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6
Q

Thyroid hormone

- functions

A
  • cellular metabolism
  • regulate lipid and CHO metabolism
  • influences body mass
  • influences mentation
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7
Q

Calcitonin

- functions

A
  • fast action for blood calcium regulation
  • lowers blood calcium levels
  • antagonizes parathyroid hormone
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8
Q

Two isoforms of thyroid hormone

A
  • T3 (triiodothyronine): most biologically active. High receptor affinity
  • T4 (thyroxine): majority of thyroid secretion. Converted to T3 in target tissue by deiodination of T4
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9
Q

What is the stimulus for TH production?

A

TSH: binds to follicular cell receptors

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10
Q

What is first step in TH formation

A
  • Production of thyroglobulin (protein without iodine)
  • via protein synthesis
  • Glycosylation in ER
  • Packed into vesicles by Golgi
  • Exocytosis from cellular apex
  • goes into colloid
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11
Q

Second step to formation of TH

A
  • Iodination of thyroglobulin
  • follicle cells absorb iodides from circulation
  • secreted to colloid
  • thyroid peroxidase (on apical membrane) oxidizes iodide into iodine
  • Iodine is added to thyroglobulin = monoiodotyrosin (MIT)
  • Add another iodine to MIT = diiodotyrosine (DIT)
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12
Q

Coupling of thyroglobulins

A
  • T3 = MIT + DIT

- T4 = DIT + DIT

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13
Q

What is the reservoir for TH?

A

colloid

- enough for 2 months without iodine in diet

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14
Q

Release of TH

A
  • T3 and T4 have to be cleaved from the colloid by lysosomal enzymes
  • endocytosis of colloid by follicle cell - released into circulation
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15
Q

Which TSH isotope is released in greater amount?

A

T4

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16
Q

How is TH metabolized?

A

liver, eliminated in bile (dt the iodine)

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17
Q

General overview of TH transport

A
  • very little free

- most bound to protein

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18
Q

True/false: TH easily crosses the cell membrane

A
  • FALSE
  • polar molecule = not able to diffuse
  • has to cross cell membrane via transporter
19
Q

What is the TH receptor

A

THR: thyroid hormone receptor

20
Q

What happens when TH binds THR

A
  • in absence of TH, THR binds DNA and (usually) suppresses gene transcription
  • TH binding = conformational change of THR which activates gene transcription
21
Q

Action of TH

A
  • increased BMR
  • Calorigenesis (increased O2 consumption)
  • Enhanced catecholamine activity by increasing adrenergic receptors
    Energy production:
  • Increased glucose catabolism
  • Lipolysis
22
Q

How does TH affect cardiac output

A

Increases it by:

  • increasing myosin
  • increasing ion channels
  • increasing beta adrenergic receptors
  • increasing isotropy, chronotropy, and dromotropy
23
Q

Table 16.2

A

has a lot of info on it i’m not putting on a NC :)

24
Q

Calcium

  • location of majority
  • important fns
A
  • 99% in bone

- Functions: blood clotting, neuromuscular activity, membrane permeability, cell secretory activity

25
Q

What two hormones balance serum calcium

A
  • parathyroid hormone

- calcitonin

26
Q

What is normal serum calcium

A

9-11 dL

27
Q

Where are the parathyroid glands? how many are there

A

4

embedded in posterior thyroid

28
Q

Two main types of parathyroid cells (list)

A
  • Chief cells

- Oxyphil Cells

29
Q

Chief cells

  • describe
  • what is their roll
A
  • abundant, small, granulated

- synthesize and secrete PTH

30
Q

Oxyphil Cells

  • describe
  • role
A
  • large, lots of mitochondria
  • appear at puberty, increase with age
  • fn unknown
31
Q

PTH

  • type of hormone
  • function
A
  • protein hormone

- single most important regulator of calcium balance (not calcitonin)

32
Q

PTH

  • release stimulus
  • receptors
A
  • stimulated by falling serum calcium levels

- GPCR, acts through cAMP

33
Q

What are the three target organs of PTH

A
  • bone
  • kidney
  • small intestine
34
Q

PTH action on bone

A

increase osteoclast degradation of bone to release Ca

35
Q

PTH action on small intestine

A
  • increase absorption of calcium

- indirectly through stimulating calcitriol release

36
Q

PTH action on kidney

A
  • reabsorb Ca in distal tubule
  • decrease phosphate reabsorption at PCT
  • produce calcitriol, active vitamin D
37
Q

PTH regulation

A
  • circulating calcium: acts direction on parathyroid glands to decrease secretion
  • calcitriol: acts directly on parathyroid glands to decrease PTH
38
Q

Calcitriol

- MoA

A
  • binds VD receptor in nucleus of bone and SI cells
39
Q

Calcitriol

- action

A
  • increase osteoclast activity
  • increase GI absorption of calcium
  • seems to increase proliferation and differentiation of immune cells
40
Q

Calcitonin

  • type of hormone
  • released from what
A
  • protein hormone

- released from thyroid gland perifollicular cells

41
Q

Calcitonin

- released in response to waht

A
  • increasing Ca levels
42
Q

Calcitonin action (2)

A
  • bone: inhibits osteoclast activity, bone degradation, helps mineralize bones
  • *Calcium INto bone**
  • Kidney: inhibits calcium reabsorption by tubule cells, increasing calcium secretion
43
Q

Overview of calcium balance

- PTH

A
  • increases plasma calcium by mobilizing from bone
  • increases calcium reabsorption in kidney
  • increases formation of calcitriol
  • increases calcium absorption from the intestine
44
Q

Overview of calcium balance

- calcitonin

A
  • inhibits bone resorption

- increases calcium in the urine

Endocrine 2 - physiology (3 decks)

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