Thyroid, Parathyroid and Adrenal Glands Flashcards
What is the shape of the thyroid gland?
Somewhat butterfly like
What is the location of the thyroid?
Just below the larynx wrapped around the anterior and lateral surfaces of the trachea
What are the hormones made and secreted by the thyroid gland?
Thyroid hormone and calcitonin
What is the thyroid hormone important for?
Optimal metabolic rate
What is calcitonin important for?
Calcium homeostasis
What is the thyroid gland composed of?
Small spherical sacs called follicles
What are follicles surrounded by?
Follicular cells (simple cuboid epithelial cells) which is the site of thyroid hormone synthesis
What is found between follicles?
Clear cells/c cells which lie in clusters and make the hormone calcitonin
What is made in the thyroid follicles?
Thyroglobin (TGB) protein
What reacts with TGB?
Iodine which enters the follicle cell from the blood
What do thyroid hormones detach from?
Iodised TGB as needed
What are the two forms of thyroid hormone?
T3 and T4
What is the active form of thyroid hormone?
T3
What is the predominant form of thyroid hormone?
T4 but this can be converted into T3
What do T3 and T4 do?
Travel bound to a carrier protein (thyroid binding globulin, TBG) to target cells
What is iodine needed for?
It must be a part of our diet as it is required for the production of thyroid hormone
What is the storage of thyroid hormone?
It is made in abundance and stored until required
How does thyroid hormone travel?
Bound to a carrier protein
What does the thyroid hormone do once it reaches the target cell?
Detaches from the carrier protein and enters the target cell
What happens once the thyroid hormone is in the cell?
T3 binds to the T3 receptor in the nucleus (receptor is already bound to a specific DNA site)
What happens once T3 binds to the T3 receptor in the nucleus?
Specific genes are activated to transcribe mRNA
What happens once specific genes are activated to transcribe mRNA?
mRNA translation occurs in the cytoplasm and specific proteins are synthesised (e.g. sodium -potassium pump)
What is the response time of the thyroid hormone?
45 minutes to days
What is the stimulus for thyroid hormone release?
External and internal stimuli lead to CNS input to hypothalamus
What does the input at the hypothalamus cause (thyroid hormone)?
Release of thyrotropin releasing hormone (TRH) into the blood
What does thyrotropin releasing hormone do?
Cause release of thyroid stimulating hormone (TSH) from the anterior pituitary into the blood
What does thyroid stimulating hormone do?
Cause release of thyroid hormones T3 and T4 from the thyroid gland into the blood
What is the effect of thyroid hormones T3 and T4 on the metabolism?
Increasing basal metabolic rate by increasing the synthesis and activity of sodium potassium pump
What are the other effects of thyroid hormones T3 and T4?
Stimulates growth (fetes and early childhood) and nervous system (alertness and reflexes)
What does the thyroid hormone negatively effect?
The production of TRH and TSH in the hypothalamus and anterior pituitary
What is basal metabolic rate?
The body’s rate of energy expenditure under basal conditions
What are basal conditions?
Person is awake, at physical and mental rest, lying down, no muscle movement, at a comfortable temperature and fasted (12-18hours)
What are the trends in metabolic rate related to age?
Basal metabolic rate decreases as age increases (require less energy)
What are the trends in metabolic rate related to puberty?
From puberty onwards males tend to have a higher metabolic rate than females
What is the thyroid hormone required for?
Normal growth, alertness and metabolism
How does the thyroid hormone effect metabolism?
Increases body heat production, stimulates fatty acid oxidation (usage of stored fat) in many tissues, Increases proteolysis and effects glucose
How does the thyroid hormone increase body heat production?
Increase oxygen consumption and ATP hydrolysis
What is proteolysis and where does it occur?
The breakdown of proteins which occurs predominantly in muscle
What effects does thyroid hormone have on glucose?
Stimulates carbohydrate metabolism (usage of stored glucose), enhances insulin-dependent entry of glucose into cells, increases gluconeogenesis and glycogenolysis
What is the overall effect of the thyroid hormone on blood glucose concentration?
Does not cause a significant increase in blood glucose as there is a balanced increase in production and uptake by cells
How much calcium comes from the diet?
1000 mg a day
What happens with the consumed calcium?
It goes into the digestive tract and some is absorbed into the blood but 350 mg a day is lost in faeces
What happens to the calcium in the blood?
The kidneys filter the blood, some is lost in urine (650mg/day) while some is reabsorbed into the blood
Where other than the diet can calcium also come from?
Bones and it can also be laid down by bones
What is the overall goal with regards to calcium?
Input be equal to output so that the blood calcium concentration is maintained between 8.5 and 11 mg/dL
What is calcium essential for?
Many physiological functions such as contraction of muscles and release of neurotransmitters
What is the major store of calcium?
Bone. Immediate adjustments can be made by rapid exchanges of calcium between bone and the blood
What does a balance exist between?
The constant build up and break down of bone
How many hormones are involved in calcium regulation?
3
What hormones are involved in calcium regulation?
Parathyroid hormone (PTH), calcitriol and calcitonin
How many parathyroid glands are there?
4
Where are the parathyroid glands found?
On the posterior aspect of the thyroid gland
What does the parathyroid gland secrete?
Parathyroid hormone which is essential for life
What is the stimulus for the parathyroid hormone?
Decrease blood calcium concentration
What happens when the blood calcium concentration decreases?
Parathyroid gland secretes parathyroid hormone
What does the parathyroid hormone effect?
Kidneys and bone
What does parathyroid hormone do to the kidneys?
Increase calcium reabsorption into the blood and conversion of vitamin D to calcitriol
What effect does increasing calcium reabsorption have?
Decreases urinary excretion of calcium
What effect does calcitriol have?
Increased calcium absorption from food in the intestine
What is the effect of the parathyroid hormone on bone?
Increase bone breakdown which increases release of calcium into the blood
What is the overall effect of the parathyroid hormone?
Increasing blood calcium concentration which restores blood calcium towards normal
How does the parathyroid hormone show negative feedback?
The response decreases the stimulus which means less parathyroid hormone will be secreted
What does calcitonin do?
Amplifies the effect of parathyroid hormone so it has a negative effect on the production of more calcitriol and makes sure the blood calcium concentration doesn’t get too high?
What doesn’t control the calcium regulation pathway?
The hypothalamus
How is calcitonin found?
It is rarely produced naturally but can be delivered a s medication in humans
What colour is the cortex of adrenal glands?
Yellow
What colour is the medulla of adrenal glands?
Red or grey
Where are the adrenal glands found?
Superior to each kidney
What is the adrenal gland made up of?
Two separate glands
What are the two glands the adrenal gland is made up of?
Adrenal cortex and adrenal medulla
What is the adrenal cortex?
The outer region of the adrenal gland which has 3 layers and secretes steroid hormones
What hormone does the outer layer of the adrenal cortex secrete?
Aldosterone
What hormone does the middle layer of the adrenal cortex secrete?
Cortisol
What hormone does the inner layer of the adrenal cortex secrete?
Androgens which have a minor reproductive role
What is the adrenal medulla?
The central region of the adrenal gland which is part of the sympathetic nervous system and secretes mainly adrenaline
What is noradrenaline secreted as part of?
The sympathetic nervous system response to stress
What does increases adrenaline and noradrenaline from adrenal glands do?
Supplements the actions of sympathetic nervous system, particularly in times of stress
What type of hormone is adrenaline?
A water soluble hormone (catecholamine)
What system does adrenaline use?
A second messenger system
Where is the receptor for adrenaline?
Cell membrane
What does adrenaline do as a result of the second messenger system?
Amplification of the cellular response
What is the speed of action of adrenaline?
Fast
What is the stimulus for adrenaline secretion?
Stress
What does the hypothalamus stimulate?
Sympathetic preganglionic fibres
What do sympathetic preganglionic fibres cause?
An action potential and acetylcholine binds to the receptor which stimulates the adrenal medulla to secrete adrenaline
What does adrenaline do?
Travels in the blood to target cells
What are the target cells of adrenaline?
Skeletal muscle, liver and fat
What effect does adrenaline have on the skeletal muscle and liver?
Increasing breakdown of glycogen to glucose
What effect does adrenaline have on fat cells?
Increasing the breakdown of fat to fatty acids
What is the overall effect of adrenaline?
Makes fuel (glucose and fatty acids) more readily available to cells which increases blood glucose concentration
What are some other sympathetic nervous system actions cause by adrenaline?
Some systems are activated for physical activity and some systems not crucial doe short term survival are shut down
