Chapter 23- Endocrine system Flashcards
What are the two endocrine cell types of the thyroid gland?
C cells, secreting calcitonin
Follicular cells secreting thyroid hormones
What are thyroid hormones derived from and why are they unusual?
They are derived from tyrosine and are unusual because they contain iodine
What is the structure of the follicular cells of the thryoid like?
The follicular cells have a spherical shape with a single layered wall of epithelial cells. It has a hollow center filled with colloid
What does colloid of the follicular cells contain?
Colloid contains thyroglobulin and enzymes for thyroid hormone synthesis
What do the thyroid hormones influence?
They influence metabolic rate
protein, fat, and carbohydrate metabolism
T3 and T4, which one is the more active and how much more active?
T3 is more active, by 3-5 times
How does T3 get made?
T4 is converted in the target cell by deiodinases
What are the steps of thyroid hormone synthesis?
- A Na+/I- symporter brings I- into the cell and into the colloid
- The follicular cell synthesizes enzymes and thyroglobulin for the colloid
- Thyroid peroxidase adds iodine to tyrosine, making T3 and T4
- Thyroglobulin is taken back into the cell in vesicles
- Intracellular enzymes seperate T3 and T4 from the protein
- T3 and T4 enter into the circulation as free hormones
What does the hormonal pathway regulating thyroid hormones look like? Name the hormone and where it is synthesized/secreted from. Is there a feedback system in place? What is it?
TRH- Hypothalamus
TSH- anterior pituitary
T3, T4 - thyroid gland
T3 and T4 provide negative feedback for TSH and TRH
What is the main function of thyroid hormones?
To provide substrates for oxidative metabolism
What is goiter?
When there are elevated levels of TSH stimulating the thyroid gland. The thyroid enlarges
What is hyperthyroidism? What are symptoms?
Hyperthyroidism is when there is an excess of thyroid hormones.
Symptoms include
-increase oxygen consumption and metabolic rate, causing heat production (often warm and sweaty)
- increased muscle protein breakdown causing weightloss
- hyperexcitable reflexes, psychological disturbance
-Rapid heartbeat and increased force of contraction due to effect on B1 adrenergic receptors
What is Graves’ disease? Symptoms?
Graves’ disease is a disease in which Thyroid stimulating immunoglobulins (TSI antibodies) act as an agonist on TSH receptors on the thyroid. They experience hyperthyroidism and goiter, as well as bulging eyes
What is hypothyroidism? What are the symptoms?
Hypothyroidism is a deficiency of thyroid hormones.
Symptoms include:
- Slowed metabolic rate and oxygen consumption
- decreased protein synthesis
- Slowed heart rate
What is Hashimoto’s thyroiditis? What are symptoms?
Hypothyroidism in which the patient experiences weight gain, depression, mania, sensitivity to temperature, and chronic fatigue
Why can hypothyroidism cause clinical depression?
T3 is found in synaptic junctions and regulates activity and amounts of serotonin, norepinephrine and GABA in the brain. Insufficient regulation causes chemical imbalance
What is the most common cause of primary hypothyrodism?
A lack of iodine in the diet. Without iodine, thyroid hormones are not produced
What are causes of primary hyperthyroidism? and secondary?
- TSI or thyroid gland tumours
- pituitary tumours secreting TSH
How can hypothyroidism result in goiter?
In hypothyroidism, absence of negative feedback increases TSH secretion, which means there is more acting on the thyroid, enlarging it
What are four functions of Ca2+?
- Act as a signalling molecule (second messenger pathways, muscle contraction, exocytosis)
- As a part of the glue holding cells together at tight junctions
- As a cofactor in the coagulation cascade
- Plasma concentrations of Ca2+ affect neuroexcitability
Which three hormones regulate Ca2+ movement between bone, kidney, and intestine?
PTH, vitamin D3 (Calcitriol) and calcitonin
What are the three ways PTH raises plasma Ca2+?
- PTH mobilizes Ca2+ from the bone pool
- PTH stimulates retention of Ca2+ in the kidneys
- Encourages increased intestinal absorption of Ca2+ through acting on vitamin D3
What are the three functions of calictriol?
- enhances Ca2+ uptake in the small intestine
- facilitates renal absorption of Ca2+
- helps mobilize Ca2+ out of the bone
What are the three components of calcium homeostasis?
- Calcium intake through diet absorbed in small intestine
- Calcium loss through urine and feces
- Distribution of calcium among ECF (2.5 mM), intracellular (0.001 mM), and bone
How is calcitriol (D3) made?
D3 is made from vitamin D from diet or from sunlight, which is converted in the liver and the kidneys
A patient has low Ca2+, what do we expect to happen with regards to hormones?
An increased synthesis of PTH, an increase in D3 synthesis, Ca2+ being reabsorped from the bone, retention in the kidneys, increased uptake in the intestine
What does calcitonin do?
It is released when plasma Ca2+ is elevated. It decreases bone reabsorption and increases renal excretion of calcium. Plays only a minor role in calcium metabolism
What is osteoperosis?
A disorder in which bone resorption exceeds bone deposition
What is rickets?
A disorder of bone growth in children caused by vitamin D deficiency or low Ca2+ intake
What are osteoblasts, osteoclasts, and osteocytes?
Osteoblasts are the cells that synthesize bone. Osteoclasts reabsorb and break down the bone. Osteocytes are inactive osteoblasts that are highly branched in the bone interior
Why is calcitonin a treatment option for Paget’s disease?
In paget’s osteoclasts are overactive and bone is weakened by reabsorption. Giving calcitonin lowers the rate of reabsorption of bone
What are some roles of phosphate in the body?
To form hydroxyapatite together with calcium
Energy transfer and storage
Activiation/deactivation of enzymes, transporters, and ion channels
Part of the DNA and RNA backbone
Hydroxyapatite attaches to …………………… support. Calcium provides the bone with ………. while ……….. provides the bone with flexibility
Collagenous
Strength
collagen
What provides input for PTH stimulation/inhibition?
CaSR (Ca2+ sensing receptor) that monitors plasma Ca2+ levels
Which risk factors are there for osteoperosis?
Women after menopause (absence of estrogen)
Smoking
Low dietary calcium intake
Thin, small body type
Osteocytes are linked through their …………………… allowing Calcium and ……………………. exchange between the bone matrix and the blood
gap junctions
chemical signal
