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What is the embryological origin of the thyroid gland?
It originates from an outgrowth during the fourth week of pregnancy.
Which part of the thyroglossal duct is normally lost during development?
The part that is lost can be identified as the foramen caecum.
What is the main characteristic structure of thyroid tissue?
These structures consist of single-cell layers of follicular cells surrounding a central region filled with colloid.
What is the primary function of parafollicular cells in the thyroid gland?
These cells produce a hormone involved in blood calcium regulation.
Which type of innervation of the thyroid gland is most prominent?
This type of innervation comes mainly from the superior cervical ganglion.
What is the main blood supply to the upper parts of each thyroid lobe?
These arteries branch off the external carotid arteries.
In which vein does the blood from the inferior thyroid vein drain?
This vein also receives blood from the left subclavian vein and left internal jugular vein.
What type of cells are found in the thyroid gland that produce iodothyronines?
These cells are also occasionally called thyrocytes.
How does the activity of thyroid follicles affect the appearance of follicular cells?
The appearance of these cells changes depending on their degree of stimulation.
What are the two main physiologically active thyroid hormones?
These hormones are iodinated molecules.
How does iodide enter the follicular cells against an electrochemical gradient?
This symporter transports two sodium and one iodide ions into the cell.
Which hormone stimulates the synthesis of thyroglobulin and controls the sodium–iodide symporter?
This hormone is produced by the anterior pituitary gland.
Which transporter is involved in transporting iodide out of the follicular cell at the apical membrane and into the follicular lumen?
This transporter's process is also stimulated by thyrotrophin.
What is the function of thyroglobulin in thyroid hormone synthesis?
Which enzyme provides the energy necessary to drive the sodium–iodide symporter (NIS)?
This enzyme pumps three sodium ions out of the cell in exchange for two potassium ions.
Which membrane glycoprotein is found on the basolateral membranes of salivary glands, gastric mucosa, and mammary glands during lactation, allowing them to take up iodide?
This glycoprotein is also found in thyroid follicular cells.
What is the role of deiodinases in the synthesis and function of iodothyronines?
Deiodinases are involved in the conversion of thyroid hormones in peripheral cells.
What is the primary function of the parafollicular cells found interspersed between the follicles in the thyroid gland?
These cells operate independently of the main thyroidal tissue.
A 30-year-old woman presents with fatigue and weight gain during pregnancy. Laboratory tests reveal an increase in total thyroid hormone levels. What is the primary cause of this increase in circulating iodothyronine concentrations during pregnancy?
The change in circulating hormone levels is related to a pregnancy-induced increase in a specific plasma protein.
A patient is found to have elevated levels of reverse T3 (rT3). Which deiodinase is responsible for the conversion of T4 to rT3?
This deiodinase removes the iodine atom at the 5' position of T4.
Which enzyme is responsible for oxidizing inorganic iodide to reactive iodine in the apical membrane–colloid border?
This enzyme is involved in the iodination and organification reactions.
In the thyroid follicle, what is the main reservoir of iodothyronines?
This substance is located in the follicle
Which transporter mechanism is responsible for secreting T3 and T4 through the basolateral membranes of follicular cells into the general circulation?
This transporter is located on the basolateral membrane of follicular cells.
Which thyroid hormone has a shorter biological half-life?
Compare the half-life of the more potent thyroid hormone with the less potent one.
What is the result of linkage between two tyrosyls in the coupling reaction in the thyroid follicle?
This product is formed by linking specific di-iodotyrosyls with mono- or di-iodotyrosyls.
What type of thyroid hormone is primarily stored in the thyroid gland's follicular colloid?
This hormone is stored in larger quantities than the more potent thyroid hormone.
Which specific transporters are involved in the transport of free, unbound iodothyronines across peripheral cell membranes?
These transporters are responsible for the movement of iodothyronines into their target cells.
Which TR is restricted to the hypothalamus and pituitary and is associated with the negative feedback actions of the iodothyronines?
This specific TR is involved in the feedback mechanism of thyroid hormones.
Which enzyme primarily converts T4 to the more active T3 molecule within target cells?
This enzyme plays a crucial role in the intracellular activation of thyroid hormones.
What is the suggested action of iodothyronines on mitochondrial metabolism once they are bound to high-affinity binding sites in mitochondrial membranes?
This action is related to energy production and heat synthesis in the mitochondria.
What type of action can account for the effects of iodothyronines that have a much shorter latency than those normally associated with T3 and T4?
These actions do not involve the activation or inhibition of specific gene transcription processes.
What is the main action of deiodinase D3 in peripheral tissues?
This enzyme is involved in the inactivation of thyroid hormones.
What is the primary role of iodothyronines in the regulation of basal metabolic rate?
This action involves the utilization of energy in the form of ATP.
What are the two other potential mechanisms of action for iodothyronines, in addition to the nuclear genomic mechanism?
These actions involve either mitochondrial DNA or direct effects on mitochondrial metabolism.
What is the primary effect of T3 on energy provision in the cell?
T3 plays a crucial role in regulating the metabolism and energy utilization within cells.
Which type of receptors do iodothyronines bind to after crossing the nuclear membrane in target cells?
These receptors are also known as thyroid hormone receptors.
Which receptor has a far greater affinity for T3 than for T4?
These receptors are involved in the cellular response to thyroid hormones.
Which process is influenced by iodothyronines when they act on mitochondrial DNA?
This action occurs when iodothyronines bind to high-affinity binding sites in mitochondrial membranes.
A 30-year-old woman presents with increased sensitivity to cold, a decrease in her body temperature, and weight gain. What could be the possible underlying cause of her symptoms?
Hypothyroidism is characterized by decreased heat production and the patient feels the cold.
A 45-year-old man presents with weight loss, muscle weakness, and intolerance to heat. What condition could be causing these symptoms?
Hyperthyroidism is associated with increased heat production, and the patient becomes heat intolerant.
In a child with hyperthyroidism, what effect does the condition have on their linear growth and bone development?
T3 affects specific TRs in bone end-plate chondrocytes, bone marrow stromal cells, and osteoblasts, resulting in overall stimulation of bone synthesis.
A patient with hyperthyroidism exhibits symptoms of moderate hyperglycemia. What is the likely cause of this condition?
The balance between glycogenesis and glycogenolysis depends on the overall thyroid hormone level in the circulation.
Which of the following effects can hyperthyroidism have on children's growth and bone development?
Hyperthyroidism affects bone age and growth in children.
Which hormones primarily control thyroid iodothyronine synthesis, storage, and release?
These hormones come from the anterior pituitary and hypothalamus.
How do high concentrations of glucocorticoids affect biologically active thyroid hormone levels?
Glucocorticoids affect the conversion of T4 to T3 in target tissues.
What is the main cause of primary hypothyroidism?
Primary hypothyroidism is often due to the body attacking its own thyroid gland.
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