Synthesis & Transport of Thyroid Hormones

The thyroid secretes 2 iodine-containing hormones: thyroxine (T4 ) and triiodothyronine (T3). The iodine necessary for the synthesis of these molecules comes from food or iodide supplements. Iodide ion is actively taken up by and highly concentrated in the thyroid gland, where it is converted to elemental iodine by thyroidal peroxidase ( See the Figure ).
The protein thyroglobulin serves as a scaffold for thyroid hormone synthesis. Tyrosine residues in thyroglobulin are iodinated to form monoiodotyrosine (MIT) or diiodotyrosine (DIT) in a process known as iodineorganification.
Within thyroglobulin, 2 molecules of DIT combine to form T4, while 1 molecule each of MIT and DIT combine to form T3. Proteolysis of thyroglobulin liberates the T4 and T3, which are then released from the thyroid. After release from the gland, T4 and T3 are transported in the blood by thyroxine-binding globulin, a protein synthesized in the liver.

This figure also show Sites of action of some antithyroid drugs. I–, iodide ion; I°, elemental iodine. Not shown: radioactive iodine (131I), which destroys the gland through radiation.

Synthesis of eicosanoid autacoids

The eicosanoids are an important group of endogenous fatty acid derivatives that are produced from arachidonic acid, a 20-carbon fatty acid lipid in cell membranes. Major families of eicosanoids include the straight-chain derivatives (leukotrienes) and cyclic derivatives (prostacyclin, prostaglandins, and thromboxane). Inhibitors of the eicosanoids are shown in Figure below.

ABCD causes of BUN:creatinine elevation

BUN stands for blood urea nitrogen which measures the amount of urea nitrogen, a waste product of protein metabolism, in the blood. Urea is formed by the liver and carried by the blood to the kidneys for excretion. Because urea is cleared from the bloodstream by the kidneys, a test measuring how much urea nitrogen remains in the blood can be used as a test of renal function. However, there are many factors besides renal disease that can cause BUN alterations, including protein breakdown, hydration status, and liver failure.


values for BUN:
* Adult: 7-20 mg/100 ml; men may have slightly higher values than women
* Pregnancy: values decrease about 25%
* Newborn: values slightly lower than adult ranges
* Elderly: values may be slightly increased due to lack of renal concentration

##BUN:creatinine elevation: causes ABCD:

• Azotremia (pre-renal)


• Bleeding (GI)


• Catabolic status


• Diet (high protein parenteral nutrition)

establishment of The asymmetry of the cell membrane

The asymmetry of the cell membrane is established primarily by which of the following?

• a.Membrane synthesis in the endoplasmic reticulum
• b.Membrane modification in the Golgi apparatus
• c.Presence of carbohydrates on the cytoplasmic surface
• d.The distribution of cholesterol
• e.Flipping proteins between the leaflets of the lipid bilayer

The answer is:  ( a ).
 Asymmetry of the lipid bilayer is established during membrane synthesis in the endoplasmic reticulum (answer a) before reaching the Golgi apparatus (answer b). Carbohydrates are associated with the N terminals of transmembrane proteins that extend from the extracellular surface, not the cytoplasmic surface (answer c).
Cholesterol is different from proteins and phospholipids that are asymmetrically distributed within the bilayer (answer d). Cholesterol is found on both sides of the bilayer. The small polar head group structure of cholesterol allows it to flip-flop from leaflet to leaflet and respond to changes in shape. In contrast to cholesterol, most proteins and phospholipids are capable of only rare flip-flop (answer e). For example, transbilayer movement of phospholipid is limited mostly to the endoplasmic reticulum.

Names of B vitamins

"The Rhythm Nearly Proved Contagious":
· In increasing order:

• Thiamine (B1)
• Riboflavin (B2)
• Niacin (B3)
• Pyridoxine (B6)
• Cobalamin (B12)

Agents for Spinal anesthesia

"Little Boys Prefer Toys":

• Lidocaine
• Bupivicaine
• Procaine
• Tetracaine

NOTES :
1-Lidocaine provides a short duration of anesthesia and is primarily useful for surgical and obstetrical procedures lasting less than one hour.

2-Tetracaine Vs Bupivacaine:Tetracaine and bupivacaine are used for procedures lasting 2 to 5 hours. Tetracaine appears to provide a somewhat longer duration of anesthesia and a more profound degree of motor block than does bupivacaine. On the other hand, compared with tetracaine, bupivacaine has been demonstrated to be associated with a decreased incidence of hypotension.
In addition, bupivacaine may be better than tetracaine for use in orthopedic surgical procedures since it appears to be associated with a lower incidence of tourniquet pain.

3-Vasoconstrictors can prolong the duration of spinal anesthesia of all three agents. However, the greatest duration is seen when vasoconstrictors are added to tetracaine solutions.