L-27 Flashcards
Where is the thyroid gland located?
Just inferior to the larynx on the anterior and lateral surfaces of the trachea
What hormones does the thyroid gland secrete?
- thyroid hormone (T3+T4)
- calcitonin
What is calcitonin involved in?
Calcium homeostasis
What is the thyroid gland composed of?
Small sacs called follicles surrounded by follicular cells
How is thyroid hormone made, stored, and transported?
- Thyroglobulin (TGB) protein is made in thyroid follicles and contains tyrosine
- iodine enters follicle and reacted with tyrosine in TGB
- Thyroid hormone in either T3 of T4 form can detach from iodised TGB as needed
- Thyroid hormone travels bound to a carrier protein to target cells
Why is iodine important in our diets?
For the production of thyroid hormone
How does thyroid hormone interacts with the receptors?
- detatches from carrier and diffuses into cell
- binds to receptor in mitochondria
- specific genes are activated to transcribe mRNA
- mRNA translation occurs in cytoplasm and specific proteins are synthesised such as sodium potassium pumps
What is the response time for thyroid hormone receptors?
45 mins- days
Explain the process leading to thyroid hormone excretion: what are the effects of thyroid hormone
- external stimulus leads to CNS input t hypothalamus
- hypothalamus secretes thyrotropin releasing hormone into the blood
- anterior pituitary secretes thyroid stimulating hormone into the blood
- thyroid gland secretes T3+ T4 into the blood
- effects are increased basal metabolic rate
- other effects are stimulation of foetus and early child growth and maintained e of normal alertness and reflexes
What is the Basal metabolic rate?
The bodies rate of energy expenditure under basal conditions
What are basal conditions? (5)
- person is awake
- person is at physical and mental rest
- person is lying down with no muscle movement
- person is at comfortable temp
- person has fasted for 12-18 hrs
What is the thyroid hormone required for?
Normal:
- growth
- alertness
- metabolism
What are the thyroid hormones effect on metabolism? (4)
- increases body heat production which increases oxygen consumption and ATP hydrolysis
- stimulates fatty acid oxidation (usage of stored fat) in many tissues
- Increases proteolysis (protein breakdown) in muscle
- stimulates carbohydrate metabolism, enhances insulin-dependant entry of glucose into cells, increases gluconeogenisis + glycogenolysis
What is the bodies main store of calcium?
Bone
What 3 hormones are involved with calcium regulation?
- parathyroid hormone (PTH)
- calcitriol
- calcitonin
Where are the parathyroid glands?
Surround the thyroid gland laterally and posterially
What occurs when low blood calcium is detected?
- parathyroid gland secretes PTH
- PTH stimulates increased calcium reabsorption in kidneys and increased bone breakdown
- this causes decreased urinary excretion of calcium, increased calcium absorption from food and increased release of calcium into the blood
- this leads to increased blood calcium which decreases the stimulus and acts as negative feedback
What homeostatic hormone response pathway is not controlled by the hypothalamus
calcium homeostasis by release of PTH from parathyroid gland
Where are the adrenal glands?
Superior to each kidney
What are the 2 separate glands that make up the adrenal glands?
- adrenal cortex
- adrenal medulla
What does the adrenal cortex secrete?
- outer layer secretes aldosterone
- middle layer secretes cortisol
- inner layer secretes androgens
What does the adrenal medulla secrete
- adrenaline
What is adrenaline secreted as a response to?
Stress
What is adrenaline?
- water soluble hormone
What is the adrenaline secretion pathway?
- stimulus is stress
- this stimulates the hypothalamus
- stimulates the sympathetic nervous system pregangkionis neuron
- stimulates adrenal medulla secretion of adrenaline and noradrenaline
- this travels in blood to target cells
What are the metabolic effects of adrenaline?
- increased breakdown of glycogen to glucose in muscle and liver
- increased breakdown of fat to fatty acids
- overall affect is making fuel mor readily available in cells
