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Endocrine (F&F) > Thyroid hormone, glucocorticoids, catecholamines > Flashcards

Thyroid hormone, glucocorticoids, catecholamines Flashcards

1
Q

Thyroid hormone production

A
  1. Iodide ions are absorbed form the diet and delivered to thyroid gland by blood. Carrier proteins in basal membrane of follicle cells transport them into the cytoplasm
    - TSH required for the ion pump
  2. Iodide ions diffuse to apical surface of the follicle cell where they are enzymatically converted to activated iodine form (T3 and T4) by binding to thyroglobulin. Released into follicle cavity
    - T3= 3 iodide molecules, T4= 4 iodide molecules
  3. Follicle cells remove thyroglobulin from follicle cavity by endocytosis
  4. Lysosomal enzymes breakdown the thyroglobulin and the released amino acids and thyroid hormones enter the cytoplasm. Amino acids are recycled to make more thyroglobulin
  5. T3 and T4 molecules diffuse across the basement membrane and enter the bloodstream
  6. A lot of the thyroid molecules bind to transport proteins called thyroid-binding globulins (TBGs). These bound molecules act as the thyroid hormone reserve and are only released gradually
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2
Q

What is the most abundant form of thyroid hormone in circulation?

A
  • T4 most abundant circulating form
  • T3 most metabolic effects (more biologically active) but not as much released into blood
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3
Q

Tests for serum thyroid hormone levels

A

Measured using techniques called radioimmunoassay (RIA) OR Enzyme linked immunosorbent assay (ELISA)

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4
Q

Units for circulating levels of thyroid hormones

A

nmol/L

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5
Q

Tissue specific actions of thyroid hormone

A

has multiple functions in regulating energy homeostasis
- Brown adipose tissue: increases thermogenesis and decreased body weight
- White adipose tissue: increases lipolysis, decreases body weight
- Effect in liver, muscle, pancrease, and parts of the brain

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6
Q

Metabolic actions of thyroid hormone

A
  • Stimulates oxygen utilization
  • Promotes heat production
  • Increases utilization of carbohydrates
  • Increases protein catabolism
  • Promotes excretion of nitrogen
  • Enhances oxidation of fat
  • Causes loss of body weight
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7
Q

Thyroxine

A

T4

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8
Q

Triiodothyronine

A

T3

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9
Q

Transporter protein of thyroid hormone in circulation

A

Thyroglobulin

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10
Q

Cell membrane transporter of thyroid hormone

A

TH-transporters

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11
Q

Mechanism of thyroid hormone action

A
  1. Transported in blood bound to thyroglobulin
  2. Released from thyroglobulin and transported into the cell by TH-transporters
  3. T4 changes to T3, and then all T3 move into the nucleus and undergoes Nuclear T3 signaling (transcription of DNA –> translation of mRNA –> synthesis of new proteins)
  4. Conduct physiological roles in other systems (focus on metabolic effects)
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12
Q

Metabolic effects of thyroid hormones

A
  1. Basal metabolic rate
    - Increase Na/K pump
    - Increases O2 consumption
    - Increase heat production
    - Increase BMR
  2. Metabolism
    - Increase glucose absorption
    - Increase glycogenolysis
    - Increase gluconeogenesis
    - Increase lipolysis
    - Increase protein synthesis and degradation (net catabolic)
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13
Q

Hypothalamo-pituitary-thyroid feedback loop

A
  1. Hypothalamus released thyroid releasing hormone (TRH)
  2. TRH stimulates anterior pituitary glands to produce thyroid stimulating hormone (TSH)
  3. TSH moves into the blood and will stimulate the secretion of certain thyroid hormones by the thyroid gland
  4. Thyroid hormones will move into the blood and reach target cells. The presence of thyroid hormones in circulation will inhibit the production of TSH and TRH
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14
Q

Hormones released by adrenal cortex

A
  • Cortisol
  • Corticosterone
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15
Q

Main glucocorticoids in different animals

A
  • Horses, pigs, sheep, dogs, cats, humans: cortisol
  • Rabbit, mouse, rats: corticosterone

**however both are present in all species, but the relative abundance/ration varies

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16
Q

Measuring serum cortisol levels

A
  1. Radioimmunoassay (RIA)
  2. Enzyme linked immunosorbent assay (ELISA)
17
Q

Unit of serum cortisol levels

A

ng/ml

18
Q

Cortisols effect on liver

A
  • stimulates gluconeogenesis, glycogenolysis, ketogenesis
  • increases plasma glucose and ketone bodies
19
Q

Cortisols effect on skeletal muscle

A
  • stimulates glycogenolysis
  • anti-insulin effect
  • proteolysis
  • release of amino acids and glucose
20
Q

Cortisols effect on adipose tissue

A
  • stimulates lipolysis
  • release of fatty acid and glycerol
  • increases plasma free fatty acids and glucose
21
Q

Cortisols effect on endocrine glands

A

release of glucagon and epinephrine which stimulates glycogenolysis and increases plasma glucose

22
Q

Cortisols effect on hypothalamus

A
  • increases NPY release and therefore increases food intake
  • leads to obesity and insulin resistance
23
Q

Overall effect of cortisol

A
  • anti-insulin
  • prodiabetogenic
  • ketogenic
24
Q

Hypothalamo-pituitary-adrenal feedback loop

A
  1. PVN of hypothalamus releases Cortocotropin releasing hormone and AVP which sitmulates pituitary
  2. Pituitary releases ACTH which stimulates adrenal cortex to release circulating cortisol
  3. Cortisol has a negative effect on glucocortical receptors at the pituitary, PVN region of hypothalamus and the hippocampus
25
Q

Adrenal medullary hormones

A

Catecholamines

26
Q

Epinephrine and norepinephrine reaction

A
  • Made from tyrosine
  • Reversible reaction between the two
27
Q

Why is it hard to measure catecholamines constantly?

A

They have a very short half life

28
Q

Metabolic function of catecholamines

A

Lungs
-Increases surfactant release and decreases lung water

Heart
- Increases cardiac output, blood pressure, peripheral resistance

Liver (alpha1 and beta2 receptors)
- Increases glycogenolysis, glyconeogenesis

Pancreas
- Increases glucagon (alpha2; insulin increased will be beta2), decreases insulin

Brown adipose tissue
- Increase thermogenesis

Muscle (beta2 receptor)
- Increases glycogenolysis and decreases glucose untilization

29
Q

Receptors of catecholamines

A

Both alpha and beta adrenoreceptors
- There are different versions of alpha and betas

Endocrine (F&F) (13 decks)

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