Application Questions 1 David has an ultrasound of his nearly 90 percent blocked

Question

Application Questions 1 David has an ultrasound of his nearly 90 percent blocked. He wonders how the right side of is so occluded. What do you tell him? common carotid arteries, which shows that his right common carotid artery is his brain is getting enough blood if this artery 2 Your patient presents with severe a lodged in the celiac trunk. Wh causing abdominal pain? bdominal pain. Your team orders a CT scan and discovers a large blood clot at organs could this blood clot potentially affect? Why do you think the clot is 18 Certain drugs cannot be taken by mouth because the entire dose of the drug is destroyed in the liver beforeit ever reaches the general circulation. Explain why these same drugs can be given by injection, either intravenously or intramuscularly. (Hint: Consider the hepatic portal system.) 3

Explanation / Answer

Brachiocephalic trunk is divided into right subclavian and right common carotid artery. The right common carotid artery divides into right internal and right external carotid arteries.

The external carotid arteries supply the structures which are external to the skull while the internal carotid artery supplies to the ear, eye and its structures.

Hence, blockage in the right common carotid artery will affect the blood supply to the above said organs but not the right side of the brain.

Right subclavian artery before its entry into the axilla gives a major branch called Right vertebral artery which passes through foramina of trnasverse porcessses of the sixth through first cervical vertebrae and enters the skull through foramen magnum to reach the inferior surface of the brain. Here it unites with the left vertebral artery to form the basilar artery. The vertebral artery supplies the posterior portions of the brain. The basilar artery gives off several branches which supply the cerebellum, pons and inner ear.

Hence, when blockage occurs in vertebral artery the blood supply to brain will be affected but not the common carotid arteries.

2. Celiac trunk is the first visceral branch from the aorta inferior to the diaphragm and divides into three branches namely Left gastric, splenic and common hepatic arteries.

Left gastric artery supplies blood to the stomach and oesophagus while splenic artery supplies pancreas, stomach, greater omentum, with its branches. CoMmon hepatic artery supplies the liver, gall bladder, stomach, duodenum, small intestine, pancreas, greater omentum through its branches.

Hence, the blood clot in celiac trunk would affect organs like Liver, gall bladder, stomach, duodenum, small intestine and abdominal pain is due to the poor blood supply that led to the oxygen deficiency and ischemia of the tissues of the above organs (especially Liver)

3. Hepatic portal circulation results in first pass metabolism of several drugs like propranolol, lidocaine, chlormethiazole.

Veins from stomach, pancreas and large intestine drain the blood to splenic vein while veins from small intestine, portions of large intestine, stomach and pancreas drain into Superior mesentric vein.

Both splenic vein, and superior mesentric vein drain into Hepatic portal vein. Hepatic portal circulation carries venous blood (which contains the nutrients and other substances like drugs absorbed from digestive organs) from gastrointestinal organs and spleen to the liver.

Thus, in order to avoid the first pass metabolism and increase the bioavailability, the drugs which are prone to first pass metabolism are given by injection or parenteral routes such that the drug bypasses the first pass metabolism via hepatic portal circulation and reaches the heart from which it is circulated to the entire body.

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