L27 Flashcards by Nicole Menezes

Shape of thyroid

Butterfly

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Location of thyroid

Anterior and lateral surfaces of trachea, just below the larynx, wrapped around trachea

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hormone that thyroid produces

Thyroid hormone and calcitonin

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What is thyroid hormone useful for?

Essential for optimal metabolic activities

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Calcitonin uses

Maintains calcium homeostasis, not a lot of this hormone is produced

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Structure of the thyroid gland

*Has small spherical sacs called follicles
*Has simple cuboidal epithelial cells surrounding the follicle called folicular cells
- this is the site of thyroid hormone synthesis
*Entire thing called the thyroid follicle

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What makes Calcitonin

C cells

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What is thyroid

A modified amino acid

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Process of thyroid synthesis

Thyroglobulin (contain amino acid tyrosine [Y]) –> Iodine from our food travels to thyroid as only thyroid usues it as a substrate and binds to tyrosine –>. iodised tyrosine (3-4 iodines can be attatched) –> either T3/T4 produced

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What is T3

3 iodines
*The active form - targets cells and causes an effect

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What is T4

*Repository form
*More abundant
*Enzymes can just cut off an I to make the more active T3

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What gland causes release of thyroid hormone

signal from Anterior pituitary

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How is the hormone stored and released

On a protein Thyroglobulin (TGB), when signalled, it is cut from protein and as its lipid soluble, it diffuses into the blood

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How is T3 and T4 carried around the body

Through Thyroid binding globulin (TBG) which is a carrier protein

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Where does T3 bind to?

An intracelluluar receptor site on the DNA

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What is the response time of T3

45mins (as it can be stored) - days

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What does biding of T3 do?

Initiates transcription of mRNA and increases the production of proteins involved in E use

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production of proteins involved in E use?

eg Na+ K+ pump

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What initiates TRH release?

External and internal stimuli causes CNS input to hypothalamus

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What is TRH

Thyrotropin releasing hormone

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Where is TRH released?

Hypo secretes In the portal blood vessels of the AP

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What does AP secrete?

Thyroid stimulating hormone (TSH)

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What does TSH impact?

Travels to the thyroid gland and cleaves the T3 and T4 from the protein TGB

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What happens when the Thyroid hormones are released?

Causes an increase in the basal metabolic rate
-Making and using the Na+ K+ pump
-stimulates growth in foetus and early childhood
-Involved in normal levels of alertness

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What does the negative feedback of Thyroid hormones affect

TRH and TSH production

What is basal metabolic rate?

The rate of energy expenditure when the body is doing as little as possible eg no eating for 12-18 hours, at comfortable temp, no movement

When is BMR the highest?

In children

More muscle mass means....

A higher BMR, sexual diorphism as females have more body fat percentage

What is thyroid hormone required for?

Normal growth, alertness and metabolism

What does increase in activity and metabolism do?

The demand for E goes up *Increases body heat - O2 consumption and more ATP is made *Breakdown of fats (stored fat) and proteins (from muscle) *Liver breaks down glucose from glycogen i.e increase in gluconeogenesis and glycogenolysis

Why is Thyroid not considered to increase blood glucose levels?

As the glucose made is also used up

How is Ca2+ conc. regulated?

Similar to pancreatic control of blood glu conc., Ca2+ is controlled without the hypo and pit involved

How much Ca2+ usually taken through food?

1000mg everyday

How much Ca2+ is lost?

Most absorbed into the plasma but 1/3 (350mg) is lost through fecal matter as it wasnt absorbed

What organ modifies the Ca2+ levels in blood?

It is filtered through the kidneys and either reabsorbed into the blood or lost through urine

How is homeostasis of Ca2+ regulated?

What goes in, comes out. 2/3s lost through

As we are growing,...

We lose less Ca2+ and it is used in bone growth

What happens if Ca2+ is lost through digestive through events like diarhoea

The osteoclasts of bones breakdown matrix and release Ca2+ into the blood

What other functions is Ca2+ essential for?

Contraction of muscles and release of neurotrans, 2nd ory based messenger systems

3 main hormones involved in Ca2+ regulation

Parathyroid hormone (PTH), Calcitonin and Calcitriol

Main hormone involved in Ca2+ regulation

PTH

Where is PTH made?

In the parathyroid glands, 4 dots behind the thyroid

What happens if there was a genetic malformation that prevented PTH production

Foetus doesn't develop as Ca2+ is not regulated

Receptor and control centre in Ca2+ production

The parathyroid glands

What happens if there is a drop in blood Ca2+ conc.

Para secretes PTH, increases bone breakdown and release of store Ca2+ *increases Ca2+ absorbed in Kidneys *Turns Vit D into Calcitriol (activated form of vit D) --> encourages absorbtion from digestive system Negative feedback

Why don't our bodies usually make Calcitonin

Unless there's a v high conc of Ca2+

What does Calcitriol do?

Further increases Ca2+ absorption into blood from kidneys + resorption of Ca2+ from bones

As there is Calcitriol, what does it prevent

Conversion of vit D into more Calcitriol

What does Calcitonin do?

Negative feedback for bone resorption, kidney absorption and intestine absorption, given to patients as medication for high Ca2+ levels

What is the adrenal glands controlled by?

Hypo

Shape of adrenal

Triangular

Parts of adrenal

Red/greyish - is the medulla Yellow is the cortex

Where are the adrenal glands

on top of kidneys, posterior near ribs, near major arteries that go down abdominal cavity

Outer region of the adrenal glands

Adrenal cortex - has 3 layers

What does the outer layer secrete

Aldosterone (Na+ homeo)

What does the middle layer secrete (biggest layer)

Cortisol

What does the inner layer secrete

Androgens (minor repro role)

What does the medulla secrete (central region, middle)

Adrenaline

When is Adrenaline and Noradrenaline released

In response to the sym NS response to stress

What can noradrenaline act as

Both neurotrans (synapse) and hormone (blood)

What do these hormones in blood mean

Can have a prolonged response of flight or fight in addition to synapses

How is adrenaline and nor released from adrenal medullary secretion cells?

Pregan uses ACh --> synapses with adrenal medullary secretion cells --> secretes NE and A into blood, circulates until reaches target cells --> secondary messenger pathway --> amp of cellular response

Pathway of adrenaline secretion

Hypo integrates stress stimulus and initiates response --> pregan fibres --> stim adrenaline release into blood --> target cells --> breakdown of glycogen to glucose and fats to fatty acids (non glucose substrate) --> fuel increase