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1. Anatomy
1.1 Immune system, blood and lymphoreticular system
1.2 Nervous system and special senses
1.3 Skin and subcutaneous tissue
1.4 Musculoskeletal system
1.5 Anatomy of the cardiovascular system
1.6 Respiratory system
1.7 Respiratory system additional information
1.8 Renal and urinary system
1.9 Renal system additional information
1.10 Gastrointestinal system
1.11 Gastrointestinal system additional information
1.12 Duodenum
1.13 Liver
1.14 Female reproductive system and breast
1.15 Female reproductive system additional information
1.16 Fallopian tubes
1.17 Male reproductive system
1.18 Male reproductive system additional information
1.19 Prostate
1.20 Endocrine system
1.21 Embryology
1.22 Additional information
2. Microbiology
3. Physiology
4. Pathology
5. Pharmacology
6. Immunology
7. Biochemistry
8. Cell and molecular biology
9. Biostatistics and epidemiology
10. Genetics
11. Behavioral science
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1.7 Respiratory system additional information
Achievable USMLE/1
1. Anatomy

Respiratory system additional information

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  1. Carina: The carina is the point or level at which the trachea divides into the right and left main bronchi. This is usually midline with the spinous process being behind it. The carina is also the location that is used by healthcare providers when assessing the proper position of an endotracheal tube (ET) after intubation. Typically, the tip of the ET tube should be 3-4 centimeters above the carina so that both lungs are properly oxygenated.

  2. Clavicle: The head of the clavicle is attached to the lateral surface of the sternum. The location of the clavicular heads in relation to the trachea can help determine proper positioning of the patient at the time the chest radiograph was taken. The two clavicular heads should be on either side of the trachea and with the spinous processes being in the middle.

  3. Hemidiaphragms: The right hemidiaphragm normally sits slightly higher than the left due to the presence of the liver under the diaphragm which prevents the right hemidiaphragm from going down further with inspiration. Important clinical pearls include:

    1. Each dome of the diaphragm is innervated by its own nerve supply from the phrenic nerve. Therefore, damage to the nerves for one side will not affect the other. On chest radiograph you would see the paralyzed hemidiaphragm as being higher than the other hemidiaphragm during inspiration (creating a paradoxical pattern of movement with respiration).
    2. You should also not see free air under the hemidiaphragm. If free air is found you will see a black line under the hemidiaphragm which would be concerning for a bowel perforation. This requires emergent evaluation with a CT scan and surgical consult. Do not confuse the normal gastric bubble seen on many chest radiographs with free air.

  4. Trachea: The trachea should sit midline and be in between the right and left clavicular heads. Any deviation from the midline could suggest that the patient was either rotated at the time of the chest radiograph, the presence of a mediastinal mass, or presence of a tension pneumothorax.

  5. Box for Clara cells: Clara cells or club cells are non-ciliated, cubical, secretory cells. They have prominent Golgi apparatus, endoplasmic reticulum and cytochrome P-450. They secrete club cell protein or CC16, also known as uteroglobin or secretoglobin which is stimulated by gamma interferon and TNF-α. Clara cells are one of the primary source of stem cells in the respiratory epithelium. They have an immunomodulatory role and also protect surfactant. Deficiency of CC16 is associated with an increased risk of viral infections and oxidative stress in the lungs. Apart from the lungs, they are also present in the prostate, kidneys and gravid uterus.

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