Thyroid Gland & Hormone Regulation

• The thyroid gland sits below the larynx on each side of the trachea
• It has a high blood flow rate, at approximately five times the gland's weight per minute
• The thyroid gland secretes thyroxine (T4), triiodothyronine (T3), reverse T3 (rT3), and calcitonin
• T4 is more abundant, while T3 is the more active thyroid hormone
• Thyroid hormones increase metabolic rate

Hypothalamus and Pituitary Gland Relationship

• The hypothalamus produces TRH, CRP, and GnRH
• The anterior pituitary is stimulated to release hormones by the hypothalamus
• Endocrine organs like the thyroid, adrenal cortex, and gonads are controlled along this axis

Thyroid Hormone Synthesis Regulation Loop

• Parafollicular cells (C cells) produce calcitonin
• Follicular cells (thyrocytes, or A cells) produce thyroid hormones (T3 and T4)
• Thyroid hormone production involves a negative feedback loop, regulating TRH and TSH secretion

Hormone Types

• Lipid-soluble hormones, which require transporters, include steroids, corticosteroids, sex hormones, and thyroxine
• Water-soluble hormones, which generally don't require transporters, include proteins, peptides, and catecholamines like those from the pituitary, pancreas, and parathyroid

Thyrosine Production

• The body makes thyrosine from phenylalanine, which is obtained from food sources like proteins, eggs, and meat

Thyroid Hormone Facts

• 93% of metabolically active thyroid hormone produced in the gland is T4, while 7% is T3
• The functions of T4 and T3 are qualitatively the same, but T3 is approximately four times stronger
• Peripheral tissues, particularly the liver and kidneys, convert T4 to T3
• Almost all T4 is converted to T3 in tissues, making T3 the main driver of thyroid hormone activity in target cells
• The thyroid gland consists of follicles filled with colloid, lined by epithelial cells that produce and secrete colloid
• The major component of the colloid is thyroglobulin

Key Synthesis Steps

• Iodide ions are water-soluble and enter the blood
• At sea level, iodide is uptaken into follicles
• Oxidation of iodide (I-) to iodine (I2) occurs
• Organification (iodination) occurs when iodine (I2) is introduced into thyrosine with the help of thyroperoxidase
• Thyroid hormones are made by coupling

Thyroid Hormone Synthesis Details

• TSH binds to its receptor to stimulate thyroid hormone production
• Thyroglobulin, containing about 16 tyrosine residues, is synthesized in the ribosomes and then transported into the colloid
• Thyroglobulin is found abundantly inside the colloid

Key Enzyme and Steps

• With the help of thyroperoxidase, iodine molecules bind to thyroglobulin, leading to the formation of monoiodotyrosine (MIT) and diiodotyrosine (DIT)
• High to low (carrier mediated diffusion)
• Enzymes cause thyroid to angulph thyroglobulin
• Lysosomal enzymes then set at thyroglobulin
• MIT and DIT combine within thyroglobulin to form T3 and T4

Hormone Circulation

• Specific plasma proteins, produced in the liver, transport thyroid hormones
• Examples include thyroxine-binding globulin, thyroxine-binding prealbumin, and albumin
• T3 is less tightly bound to plasma proteins than T4, making it more available
• Free forms of T3 and T4 are biologically active

Hormone Conversion

• Target tissues uptake T3 from circulation except the brain and pituitary take up T4 and converts it to T3
• Propylthiouracil, propanolol, amiodarone and glucocorticoids inhibit peripheral conversion of T4 to T3 , besides in the brain or pituitary

Thyroid Hormone Actions

• Common cellular effects of thyroid hormones include increased mitochondria size and number, leading to increased protein synthesis and overall metabolic rate
• T3 binds to receptors in the cell nucleus, and increases transcription of proteins and expression proteins
• Because ATP is used, there is the need to burn even more carbohydrate molecules with even more oxygen

Metabolic Effects

• Blood LDL levels decrease through increased LDL receptor activity
• Thyroid hormones increase glucose production from glycogen
• They increase gluconeogenesis
• They increase the uptake of LDL

Heart

• The heart contains B1 receptors for thyroid hormones
• Thyroid hormones augment epinephrine and norepinephrine effects
• Thyroid hormones increase heart rate, blood pressure, and cardiac output

Brain

• Thyroid hormones are essential for the central nervous system's well-being
• During hormone deficiency there is the likely chance of irreversible brain damage
• Myelination, synapse number and nervous system activity are effected

Growth and Development

• Thyroid hormones stimulate linear growth, tooth development, and maturation of bones
• They contribute to reproductive function regulation

Other Physiological Effects

• In fat tissue, thyroid hormones increase lypolitic enzymes
• In hyperthyroidism, patients are thin and therefore they burn lots of calories
• Glucaneo genesis happens in adispose tissue

Muscle effects

• Thyroid hormones can break down or build muscle, depends on if the body is in balance with these hormones

Thyroid Hormone Effect on Other Systems

• Thyroid hormones increases O2 consumption, and therefore increases depth and respiration rate
• Thyroid hormones stimulates gastro intestinal mobility

Hormone Secretion Regulation

• The hypothalamus releases TRH
• This stimulates the anterior pituitary gland to release TSH
• TSH then stimulates the thyroid gland to secrete T3 and T4
• T3 and T4 stimulate metabolism throughout the body
• T3 and T4 can inhibit release of TSH by the pituitary, as well as TRH release by the hypothalamus

Factors Regulating TRH Release

• Cold temperatures, depression, norepinephrine, CART, msh enhance TRH
• High temperature, physical activity, starvation, somatostatin, dopamine, neuropeptide and glucocorticoids decrease TRH

TRH and TSH Actions

• TRH is a tripeptide and its stored in the median eminence
• It reaches the anterior pituitary gland by pituitary portal veins
• TRH and the receptors activate IP3 messengers
• TSH increases and releases hormones in the blood
• it also increases the iodide pump
• It effects the size and activity of thyroid cells

Hyperthyroidism

• Primary hyperthyrodism is from something wrong in the thyroid gland
• Secondary hyperthyroidism is something that stimulates the thyroid gland to cause hyper functioning

Primary Hyperthyroidism

• Graves Disease is the most common
• It is a autoimmune disease that causes plasma cells to produce AB's aganist the thyroid gland
• Tshi-AB cells stimulates the recepters
• High of T3, T4 and low of Thyrotropin is due to this
• Toxic Adenomas is a larage nodule
• Toxic mutlinodilar gaither is more than 1 and cause tosh -r Mutation

Secondary Hyperthyroidism

• Pituitary Adenomas is must common with tosh
• molar pragnancu = egg that contains no genetic and fertilzeity by a sperm
• High B- Hcg Acts links tsh

Conditions that Mimic Hyperthyroidism

• Hashimoto thyroiditis releases antibodies that attack the cells of thyroids
• Subacute and Drug induce is a virus
• iodine to much may cause hyperthyroditism

Conditions or Symptoms

• factitious cause due to to much thyroid
• Exogenous thyroid hormone

Hyperthyroidism signs

• Incerased metabolic rate, weight loss, increrased body temeprature
• Trechicardia, hypertension, increase bone resorbtion, anxiety, diarehha, hair growth

Hypothyroidism

• The auto immune system is not working right
• Subacture , drug introduce

Autoimmune Disease of Hypothyroidism

• Thyroiditis is known as Riedels thyditis

lodine and T3T4 relationship

• because of very little lodine there decreases production
• Becasue of excesssive Iodine there is deacreasedTPO

Central Hypothyroidism

• Thraumatic Brain injury
• Tumor

Congential hypothryodism is cause the most ab's attack and damages to fettal cells

Hypothyroidism manifestions

• GOITER
• Decreased body temperature
• DEcreased Heart rate
• Depresssion
• Delayed tendon refelexes
• Constipation