Endocrine Flashcards
Which is the most active form of thyroid hormone
T3
Which is the predominant form of thyroid hormone in the plasma
T4
What cells make up the thyroid gland
Follicle cells
What is colloid
Colloid is an extracellular fluid space found in the follicle cells where it contains predominantly thyroglobulin which is required for thyroid hormone synthesis
What is hyperthyroidism, causes and symptoms
Overactive thyroid gland. producing too much thyroid hormones. Graves disease, hypersectreting thyroid tumour and secondary to excess of TSH and TRH. Sweating in normal temperatures, excessive weight loss, elevated metabolic rate, heart palpitations, muscle weakening, bulging of eyes commonly seen in graves disease.
What is hypothyroidism, causes and symptoms
Inactive thyroid gland secreting too little thyroid hormones. Hashimoto autoimmune thyroiditis, secondary to deficiency in TSH and TRH, inadequate supply of dietary iodine. Excessive weight gain due to decrease metabolic rate, sensitive to cold, easily fatigure due to lack of ATP, weak pulse, slow mentation and reflexes.
What is pinocytosis, name a cell that uses this method
Follicle cells, uses this method during the secretion process of TG structures in the colloid into the cell.
What enzyme is essential for the formation of MIT and DIT from iodide and thyroglobulin
Thyroid peroxidase
How does T3 and T4 leave the follicle cells
They are lipophilic in nature so they are able to leave the follicle cell and travel to other organs
Describe the formation of TG vesicles
Amino acids are used to synthesis TG and it travel through the golgi and forms TG vesicles and is released out of the atypical membrane into the colloid
How is iodide taken up from the blood stream and released into the colloid
Taken up from the blood stream via Na/I cotransporter through active transport into follicle cells and exits through another transporter, pendrin
what are the 2 important components to form thyroid hormones
phenyl rings-derived from tyrosine residues and iodine taken up from diet
What is the hypothalamus-pituitary-thyroid axis
The hypothalamus released Thyrotropin releasing hormones which stimulated anterior pituitary to release TSH which acts on the thyroid glands by binding to the TSH receptor of follicle cell which stimulates the production of thyroid hormones. The presence of these hormones in the circulation will cause a negative feedback to the TRH neurons of Hypothalamus and Tyrotrophs of the Anterior pituitary.
What are the key functions of TSH
- increases the follicle cell size, cell number
- increases follicle cell formation - thyroid gland bigger
- TIPP - trap iodide, iodination of tyrosine on thyroglobulin and stimulates thyroid peroxidase, pinocytosis of colloid and proteolysis of TG
How are most T3 synthesized
They are synthesized mainly through deionidation of T4 in the hepatocytes not throught TSH
How does T4 get converted to T3
T4 is deionised by iodinase into T3
How does T3 cause gene transcription
It binds to the Thyroid hormone receptor in the nucleus which is bind to cofactor retinoid X receptor which is bounded to the thyroid response element
How does T3 and T4 effect metabolic rates - give eg.
Increases metabolic rate through calorigenic effect - stimulates o2 consumption in most cells which increase metabolic rate and heat production. Also in skeletal muscles too much TH means muscle wasting, too little muscle weakening
How does T3 and T4 affect growth and development
essential for normal somatic cells growth and neural devleopment esp in myelination of nerves
What is the cardio response when Thyroid hormones is released?
Increases response to catecholamines via increases expression of adrenoreceptors and stimualtion of downstream cellular events which increases HR and force of contraction
Name the 4 sections of the adrenal glad starting from the outer most layer
Z. glomerulosa, Z. fasciulata, Z. reticularis and medulla
What hormones can be found in each section of the adrenal gland
Z.G - aldosterone released by angiotenisoogen for water retention. Z.F - cortisol released by ACTH in pituitary for stress. Z.R - sex steroid for reproduction also ACTH. Medulla - epinephrine and nor, for fight and flights, SNS
Name the types of steroid hormones and an example
Glucocortocoids - cortisol, Sex steroids - Testosterone and Mineralcorticoids -aldosterone
What is the precursor of steroid horomones
Cholesterol
How is cholesterol synthesized
Synthesized throught cells from acetate or LDL uptake via LRL-mediated endocytosis
What is the immediate precursor of cholesterol and enzyme responsible for the process
Preogenolone and cytochrome P-450scc
What is cytochrome p-450scc
It is a rate limiting enzyme, a side chain cleavage enzyme that can be found in the inner mitochondrial membrane
Where can the conversion system of cholesterol to steroid hormones be found?
It can be found in adrenal cortex, ovarian follicle -thecal cells and the testes - leydig cells
Does free cortisol or bounded cortisol affect negative feedback response
Free cortisol
what are the symptoms of cushing syndrome
thin extremities/ muscle wasting/ osteoporosis/ obesity / - abdominal straie/ easy bruising/ Hyperglycemia
Symptoms of Addisons disease
Hypoglycaemia/ dehydration/ shock and confusion
What are the endogenous causes of cushing syndrome
Tumour in pituitary - adenome benign or tumor in adrenal gland which causes abnormal z. fasciulata cell growth - increases ACTH production. Abnormal sources of ACTH - small cell lung tumor
What are the exogenous causes of Cushing syndrome
Steroids medication - have the same structure as cortisol and can mimic actions on various tissue resulting in negative feedback of cortisol resulting in insufficeint stimulation resulting in atrophy. despite decrease in endogenous cortisol does not make up for the huge increase in exogenous (meds) cortisol levels
What is addison’s disease
Adrenal insufficiency - failure in producing sufficient steroid hormones due to an autoimmune disease whcih destroys the adrenal cortex
