0 Stratified cuboidal epithelium

The ducts of all the following glands consist of stratified cuboidal epithelium except ?
A) Sweat glands
B) Sebaceous glands
C) Salivary glands
D) Pancreas

ans:B Stratified cuboidal epithelia is a rare type of epithelial tissue composed of cuboidally shaped cells arranged in multiple layers.... They protect areas such as ducts of sweat glands, mammary glands, and salivary glands... Stratified columnar epithelia is a rare type of epithelial tissue composed of column shaped cells arranged in multiple layers.... Stratified columnar epithelia are found in the ocular conjunctiva of the eye, in parts of the pharynx and anus, the female's uterus, the male urethra and vas deferens.... The cells function in secretion and protection.

2 Coarctation of Aorta - 1st two ribs spared from Notching

Rib notching with coarctation:

  • Inferior rib notching is seen mostly in adults (post-ductal coarctation) over age 20 and is not seen in infants who usually have pre-ductal coarctation.
  • Location: ribs 3-9 (most pronounced in 3rd +4th ribs, less pronounced in lower ribs); 1st+ 2nd ribs do not participate because the posterior intercostal arteries originate from the costocervical trunk (not post stenotic Aorta).
  • Site: central + lateral thirds of posterior rib.

Almost always Bilateral with exceptions:
  1. Unilateral on left side: left aortic arch with aberrant right subclavian artery below coarctation.
  2. Unilateral on right side:
    -- normal aortic arch with coarctation proximal to origin of left subclavian artery
    -- right aortic arch with anomalous left subclavian artery below coarctation.

Thorax - Blood Supply:

First two posterior intercostal arteries <--- from superior intercostal artery <--- from costocervical trunk <--- from subclavian artery.
Posterior intercostal arteries - 3rd and below are branches from thoracic aorta.

Anterior intercostal arteries receive their supply:

  • upper 6: from internal thoracic artery 
  • lower 5: from its branch (muscolophrenic artery).

Internal thoracic artery comes off subclavian artery also.

What happens in Coarctation ?

Coarctation of thoracic aorta results in absent flow in posterior intercostal arteries (3rd and below).

However, Internal thoracic artery & musclophrenic artery sends blood to anterior intercostal arteries which continues into posterior intercostal arteries (3rd and below).

The 1st and 2nd posterior intercostal arteries receive blood from subclavian (unlike rest of posterior intercostal arteries).

Why are 1st two ribs spared ?

The high pressure first two posterior intercostals anastomose with the first two anterior intercostals which are also high pressured, so the anastomosis does not enlarge. (Hence no notching)

But 3rd posterior intercostals and those below it, are from descending aorta beyond the coarctation, so they have low pressure. The blood from anterior intercostals which are high pressured rushes into the low pressured posterior intercostals thus enlarging the anastamosis forming collaterals.

2 Coarctation with anomalous post-coarctation origin of the right subclavian artery.

Q. A 16 year old with headache and hypertension has a chest radiograph which demonstrates plain radiographic signs of coarctation of the aorta. Further investigations reveal anomalous post-coarctation origin of the right subclavian artery. The ribs most likely to demonstrate inferior rib notching would be:

a. Left third to ninth ribs

b. Bilateral third to ninth ribs

c. Right third to ninth ribs

d. Bilateral first and second ribs

Ans : a. Left third to ninth ribs
Due to anomalous origin of right SubClavian artery from the post coarctation segment , there is no collateral flow to the intercostal arteries on the right. Subsequently , there is no right sided rib notching.

Question source : http://www.cambridge.org/aus/catalogue/catalogue.asp?isbn=9780511671395&ss=exc

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