Lecture 28 Flashcards
Where is the thyroid gland?
Its in the throat below the larynx on the anterior and lateral surfaces of the trachea
What hormones are made at the thyroid gland?
Thyroid hormone and calcitonin
What is the thyroid gland made up of?
Composed of small spherical sacs called follicles
What is each follicle surrounded by?
Follicular cells
Follicular cells are the site of synthesis for what hormone?
Thyroid hormone
What lies in the clusters between the follicles?
Clear cells or C cells
What hormone does C cells or clear cells make?
Calcitonin
How is thyroid hormones synthesised?
Iodine enters follicle cell from blood and travels into the follicle cavity, follicle cells release protein, thyroglobulin into follicle. Iodised TGB moves into the follicular cells and then thyroid hormones detach from TGB as needed, T3 and T4
What form is T3?
The active form
What form is T4?
The more plentiful form
How do T3 and T4 get to target cells?
They travel bound to a carrier protein
Why is iodine a necessary part of our diet?
It is required for the production of the thyroid hormone
Is the thyroid hormone lipid soluble?
Yes
Can thyroid hormones be stored?
Yes they are made and then released when required
How does the thyroid hormone activate the cell?
They detach from the carrier protein and enter the target cell. T3 binds to the T3 receptors in the nucleus and specific genes are activated to transcribe messenger RNA (mRNA), mRNA translation occurs in the cytoplasm and specific proteins are synthesised
What is the response time when the thyroid hormone has activated the target cell?
45 minutes to days
How the thyroid hormone controlled?
Negative feedback loop
What causes the hypothalamus to secrete hormones?
External and internal stimuli lead to CNS input to the hypothalamus.
What is the hormone released from the hypothalamus?
It secretes thyrotropin-releasing hormone
What occurs when the hypothalamus releases the thyrotropin releasing hormone?
Stimulates the anterior pituitary gland to secrete thyroid-stimulating hormone, which then stimulates the thyroid gland to secrete the thyroid hormones (T3, T4).
What are the effects from the release of thyroid hormones?
The metabolism basal metabolic rate increases, it also stimulates growth and the nervous system responses so normal alertness and normal reflexes.
How does the thyroid hormone stop the release of more hormones?
It inhibits the anterior pituitary gland and the hypothalamus
What is basal metabolic rate?
BMR is the body’s rate expenditure under basal conditions: Person is awake, at physical and mental rest, lying down, no muscle movement, at a comfortable temperature and is fasted.
The thyroid hormone is required for what?
Growth, alertness and metabolism
What are the effects on the metabolism?
Increases body heat production (increases oxygen consumption and ATP hydrolysis), stimulates fatty acid oxidation in many tissues, increases proteolysis predominantly from muscle and stimulates carbohydrate metabolism enhances insulin-dependent entry of glucose into cells, increases gluconeogenesis and glcygenolysis.
What is infantile hypothyroidism?
Not enough thyroid hormone (hypo-secretion) in newborns to:
- Low metabolic rate
- Cold intolerant
- Brain development is inhibited
- Growth is retarded
What causes hypothyroidism?
Lack of iodine in mother’s diet.
What is graves’ disease?
Too much thyroid hormone.
What are the symptoms of graves’ disease?
- High metabolic rate
- weight loss
- Heat intolerant
- Increased heart rate
- Nervousness
- Hair loss
- Exophthalmos (BULGING EYEBALLS)
- Thyroid swelling
What is the cause of graves’ disease?
Autoimmune disorder
Where does our calcium come from?
Dietary requirement
Where does our calcium go that is from our diet?
some is absorbed from the digestive tract into the plasma, some lost in faecal matter, the gut absorbs the food with calcium and the kidneys reabsorbs a lot of the calcium, we can also get it from our bones.
How do you get rid of calcium?
Deposition by osteoblasts
Calcium is essential for what functions?
Physiological functions
What is the major store of calcium?
Bones
What adjustments can be made?
By rapid exchanges of calcium between bone and the blood
What thee hormones are involved in calcium regulation?
Parathyroid hormones (PTH), calcitriol and calcitonin
Where are parathyroid hormones made?
Parathyroid glands
What happens when you have low blood calcium?
The parathyroid gland secretes PTH, which has two main target organs, there is an increase in bone breakdown with increase release of calcium into the blood to hopefully bring blood calcium back up. In the kidneys there is more calcium reabsorption, it converts vitamin D to calcitriol. Therefore decreases urinary excretion of calcium and an increase in absorption of calcium from food.
What prevents further release of PTH?
The out come, so response decreases the stimulus= negative feedback
What is the calcitonin secretion pathway?
The stimulus is an increase in calcium concentration which stimulates the thyroid gland to secrete calcitonin, calcitonin decrease bone breakdown so more calcium is deposited into the bones and out of the blood thus bringing blood calcium down.
How do you stop calcitonin from being released?
When the blood calcium decreases it uses negative feedback to get the calcitonin to stop.
What happens when there is a decrease in plasma [Ca2+]?
leads to increase in PTH release
What happens when there is an increase in plasma [Ca2+]
Leads to decrease in PTH release
Is calcium regulation controlled by the hypothalamus?
NO
What happens when blood Ca2+ is too low?
Hypocalcemia-
- Increased excitability of the nervous system
- Leads to muscle tremors, spasms, or cramps.
What happens when blood Ca2+ is really really low?
You get paraesthesia (burning/tingling sensation) in hands and face, muscle cramps and in some cases the muscles of the larynx may contract tightly which can shut off air flow and cause suffocation
What is hypocalcemia caused by?
- Vitamin D deficiency
- Diarrhoea
- Thyroid tumors
- Under-active parathyroid glands or removal of the thyroid glands
- Pregnancy and lactation
What happens when blood Ca2+ is too high?
Hypercalcaemia
What are the symptoms with hypercalcaemia?
Nerve and muscle cells less responsive and excitable
Can lead to depression fo the nervous system, emotions disturbances, muscle weakness, sluggish reflexes.
What happens is blood Ca2+ is extremely high?
Can lead to cardiac arrest
Hypercalcemia causes an increase of calcium in the membrane therefore?…
Increasing the membrane potential outside the cell to 20mV therefore increasing the inside of the cell to -90mV
Hypocalcemia causes a decrease of calcium in the membrane there?..
Decreasing the membrane to -40mV and therefore changing the inside of the cell to -60mV
