Ednofuckingcrine 3 Flashcards
Thyroid gland location
- just below larynx
- on the anterior and lateral surfaces of the trachea
Hormones secreted and made in the thyroid gland
- thyroid hormone - essential for optional metabolic activity
- calcitonin - hormone involved in calcium homeostasis
Structure of the thyroid gland
- composed of small spherical sacs called follicles
- each follicle is surrounded by follicular cells (simple cuboidal epithelial cells)
- clear (c) cells lie in clusters between follicles
The site of thyroud hormone synthesis
Follicular cells
What makes calcitonin
Clear cells
How we can store a lipid soluble hormone
They way it is made allows us to store it
First, thyroglobulin (TGB) protein is made in the thyroid follicle and contains tyrosine (Y)
- iodine (I) enters follicle cell from blood and reacts with tyrosine in TGB (iodises
- thyroid hormones detach from iodised TGB (once signal receives form the anterior putiutary to realisei hormone) - protein is too big to cross so they must detach.
- T3 is the active form - target cells and causes effects (3 iodines around a tyrosine)
- T4 is the more plentiful form - repository form, later gets turned to T3 to be active
(Two types of thyroid hormone)
T3 and T4 travel bound to a carrier protein (Thyroid binding globulin, TBG) and gets taken off round the body after diffusing through lipid bylayer
Thyroid hormone is a
Modified amino acid
Target cell activation by thyroid hormone
Thyroid hormone is made and stored until needed (unlike other lipid soluble hormones)
Travels bound to a carrier protein
Detached from carrier protein and enters target cell
T3 binds to T3 receptor in the nucleus (receptor is already bound to specific DNA site)
Specific genes are activated to transcribe mRNA
MRNA transcription occurs in the cytoplasm and synthesises new proteins such as (K+ and Na+ pump)
Duration: 45mins - days
Control of thyroid hormone secretion - RELEASE PLUS EFFECTS
External and internal stimuli lead to CNS input to hypothalamus
This causes hypothalamus to realise TRH (thyrotropin-releasing hormone) into Portal blood vessels where it travels to anterior pituitary gland where they cause the realise of TSH (thyroid-stimulating hormone)
This is released into systemic circulation and travels through body until reaching thyroid gland and then TSH causes cleavage of T3 and T4 from thyroglobulin in the thyroid gland
T3 and T4 moves all around body,
EFFECTS: increase it our basal metabolic rate (by increasing the synthesis of new NA+-K+ pumps and increasing the activity thus using more ATP)
OTHER EFFECTS: causes growth (foetus/early childhood), involved in normal levels of alertness and reflexes
Control of thyroid - INHIBITION - negative feedback control
Thyroid hormone inhibits the release of PRH and
TSH
What is basal metabolic rate?
BMR is the bodies rate of energy expenditure under basal conditions
Conditions to determine BMR
- person is awake
- at physical and mental rest
- lying down
- no muscle movement
- at a comfortable temperature
- fasted (12-18 hours)
Actions of thyroid hormone is required for normal:
- growth
- alertness
- metabolism
Effects of thyroid hormone on metabolism
- increases body heat production (increases oxygen consumption and ATP hydrolysis)
- stimulates fatty acid oxydation (usuage of stored fat) in many tissues
- increases proteolysis (breakdown into amino acids form proteins), predominantly from muscle
- stimulated carbohydrate metabolism (usage of stored glucose), enhances insulin-dependent entry of glucose into cells, increases gluconeogenesis and glycogonolysis
- thus doesn’t not cause a significant increase in blood glucose (balanced increases in production and uptake into/usage by cells)
Where does calcium come from?
- food (3/3) - usually maintain calcium homeostasis
- moves into digestive tract —- > most of it gets absorbed into the plasma (blood) ——> some is still lost through faecal loss (around 1/3)
Filtration by kidneys - to be lost by urine (around 2/3) or can be filtrated back into blood via reabsorbtion
If too much calcium is lost due to an unforeseen factor resorption by osteoblasts can occur (breakdown of the mineral part of bone by osteoclasts releasing calcium back into the blood)
If build up of calcium in blood you can deposit some into the bone via deposition by osteoblasts
- as growing will lose less then taking in
Calcium homeostasis
- calcium is essential for many physiological functions, e.g concentration of muscles and release of neurotransmitter
The concentration of extracellular (blood) calcium is tightly controlled
Bone is the bodies major store of calcium, immediate adjustments can be made by rapid chanced of calcium bertween bone and blood
- a balance exists between the constant build up and break down of bone
Three hormones are involves in calcium regulation: parathyroid hormone (PTH), calcitriol and calcitonin
Structure of parathyroid hormone and what it secretes
Low blood calcium response
Parathyroid gland is the receptor and the control centre
Stimulus: drop in blood glucose conc
Increase in parathyroid release from the parathyroid gland
Travels to bones and increases bone breakdown (resorbtion) - releasing calcium into blood, increasing calcium concentration
OR
Travels to kidney
- increases reabsortion - less calcium lost in urine, increasing concentration
- turns vitamin D into calcitriol (hormone- activated form of vitamin D) - acts on interntines to encourage more absorbtion (less lost through feaces) , increasing concentration
- this response removes the stimulus (negative feedback) therefore inhibits further lowering?
What systems dont involve hypothalamus
Parathyroid
Blood glucose
Calcitonin in humans can be ______ as a ______. Is it ______ produced _______.
Calcitonin in humans can be delivered as a medication. It is rarely produces naturally
Adrenal glands location
Superior to each kidney
Made of two separate glands - Adrenal cortex (outer region - has 3 layers) secretes steroid hormones
Addendal glands structure
Adrenal cortex what it does
- is the outer region and secretes steroid hormones
Adrenal cortex 3 layers
- Outer layer secretes: ALDOSTERONE
- Middle layer secretes: CORTISOL
- Inner layer secretes: ANDROGENS (minor reproductive role)
Adrenal medulla
- central reguion - part of the sympathetic nervous system
- secretes mainly adrenaline
Adrenaline is secreted by
- the adrenal medulla
What is released as a response to the sympathetic nervous systems response to stress
- adrenaline
- noradrenaline
Adrenaline and noradrenaline secretion form the adrenal medulla supplements…..
The actions of the sympathetic nervous system, particularly in times of stress
- flight, fright or fight response
Hypothalamus sympathic centre
Adrenaline - how it initiates a cellular response
- water soluble hormone (amino acid derivative)
- cell membrane receptor
- uses a second messenger system
- amplification of cellular response
- fast
Adrenaline secretion
Stimulus: stress
Hypothalamus decides upon the need of a stress response - action potentials, neural signals moving form the hypothalamus down the sympathetic preganglionic fibres.
This synapses(AcH binds to receptor) in adrenal medulla causing the secretion of adrenaline which travels in blood to target cells
Effects of Andrenaline secretion - metabolic and overall
Metabolic effects
Skeletal muscle and liver:
- increased breakdown of glycogen to glucose
Fat:
- increased breakdown of fat to fatty acids
Overalll effects: makes fuel (glucose and fatty acids) more readily available to cells
Calcitonin
- rarely produced naturally in humans
- can be used to bring Calcium levels down when too high - inhibits absorb ion reabsortion and bone breakdown
