Categorias: Todos - homeostasis - receptors

por Jin Han 9 anos atrás

3524

Cell Communication - Thyroid Hormones

Researchers are delving into the impacts of long-term thyroid-stimulating hormone suppression on age-related macular degeneration (AMD). A potential connection has been found between elevated thyroxine levels and eyesight deterioration in the elderly, particularly in those with hyperthyroidism who exhibit a higher risk of AMD.

Cell Communication - Thyroid Hormones

Thyroid Hormone

Correct Mechanism

Negative Feedback
Diagram of Negative Feedback Loop

At the end, both TSH and TRH shut down and the loop starts over again.

TSH (Thyroid Stimulating Hormone) then receives the signal and stimulates Thyroid Hormones.

TRH (Thyroid Releasing Hormone) stimulates TSH

Produces and Releases -Triiodothyronine (T3) -Thyroxine (T4)
Thyroxine (T4)

the inactive form and most of it is converted to an active form called triiodothyronine by organs such as the liver and kidneys.

Triiodothyroine (T3)

affects almost every physiological process in the body, including growth and development, metabolism, body temperature, and heart rate.

Produces calcitonin
Regulating Calcium Levels in Animals
helps control blood calcium levels
Regulates metabolism

Faulty/Impaired Mechanism

Too little hormone secretion - hypothyroidism
Cannot keep pituitary gland from secreting TSH - leads to enlargement of thyroid gland and swelling of neck (goiter)
Mutations in the receptor beta gene abolish ligand binding

Is a dominant trait

Affected children show attention-deficit disorder

Individuals with this mutation show type of hypothyroidism characterized by goiter, elevated T3 and thyroxine, normal/elevated TSH

Too much hormone secretion - hyperthyroidism
Graves' disease - autoimmune disorder - immune system produces antibodies that activate thyroid hormone production
High body temperature, sweating, weight loss, high blood pressure, irritability

Cell Signaling Pathway

How the Thyroid Hormone Works
Ligand-bound State
Ligand-free State
Receptors: ~trans activation domain ~DNA binding domain ~ligand-binding and dimerization *BIND TO SEQUENCES OF DNA (T3 RESPONSE ELEMENTS [TREs]*
Mammalian thyroid hormone receptors consist of: ~alpha-1 gene ~beta-1 gene ~alpha-2 gene ~beta-2 gene

Thyroid Scan

Current Direction of Research

Future work - scientists research effects of long-term suppression of TSH (thyroid stimulating hormone) on AMD
Possible link between thyroxine and deterioration of eyesight in elderly people (AMD)
excess of thyroid hormones seem to accelerate deterioration of cones in the retinas
People with hyperthyroidism have highest risk of AMD
discovered that higher levels of free thyroxine mean increased risk of AMD
experimented on mice

lacking both alpha isoforms: died within first few weeks

beta-2 disruption: normal hearing, elevated TSH

mild disruption of entire beta gene: deafness, elevated TSH

no alpha-1 receptor: low body temperature, mild cardiac malfunctions

Basics

Thyroid function required iodine to synthesize T3 and T4 to send negative feedback to pituitary gland, which secrets TSH
Vertebrates need thyroid hormones for bone-forming cells and nerve cells during development
maintain normal blood pressure, heart rate, digestive function
Regulates homeostasis and development
Two very similar hormones from amino acid tyrosine
Thyroid mainly secretes T4 - cells convert most into T3
Thyroxine (T4) - four iodine atoms
Triiodothyronine (T3) - three iodine atoms

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