Site of Antidiuretic hormone (ADH) action is:

 # Site of Antidiuretic hormone (ADH) action is:

A. Proximal tubule

B. Loop of Henle

C. Vasa recta

D. Collecting tubule

The correct answer is D. Collecting tubule.

Human vasopressin, also called antidiuretic hormone (ADH), arginine vasopressin (AVP) or argipressin, is a hormone synthesized from the AVP gene as a peptide prohormone in neurons in the hypothalamus, and is converted to AVP. It then travels down the axon terminating in the posterior pituitary, and is released from vesicles into the circulation in response to extracellular fluid hypertonicity (hyperosmolality). AVP has two primary functions. First, it increases the amount of solute-free water reabsorbed back into the circulation from the filtrate in the kidney tubules of the nephrons. Second, AVP constricts arterioles, which increases peripheral vascular resistance and raises arterial blood pressure.

Acute increase of sodium absorption across the ascending loop of Henle. This adds to the countercurrent multiplication which aids in proper water reabsorption later in the distal tubule and collecting duct.

Pyruvate dehydrogenase complex contains all EXCEPT:

 # Pyruvate dehydrogenase complex contains all EXCEPT:

A. Biotin

B. NAD

C. FAD

D. Co-A

The correct answer is A. Biotin.

Pyruvate dehydrogenase complex (PDC) is a complex of three enzymes that converts pyruvate into acetyl-CoA by a process called pyruvate decarboxylation. Acetyl-CoA may then be used in the citric acid cycle to carry out cellular respiration, and this complex links the glycolysis metabolic pathway to the citric acid cycle. Pyruvate decarboxylation is also known as the "pyruvate dehydrogenase reaction" because it also involves the oxidation of pyruvate.

The enzymes involved in PDC are Pyruvate dehydrogenase (E1), Dihydrolipoyl transacetylase (E2), and Dihydrolipoyl dehydrogenase (E3). The cofactors involved are: TPP (thiamine pyrophosphate), magnesium, lipoate, coenzyme A, FAD and NAD+. 

Reference: https://en.wikipedia.org/wiki/Pyruvate_dehydrogenase_complex

The benign neoplasm of ‘brown fat’ noted in oral/pharyngeal region is:

 # The benign neoplasm of ‘brown fat’ noted in oral/pharyngeal region is:

A. Lipoma

B. Hibernoma

C. Teratoma

D. Brown tumor

The correct answer is B. Hibernoma. 

Hibernomas are uncommon neoplasms of brown adipose tissue. The most frequent sites of occurrence include the thigh, shoulder, and back. Less common myxoid and spindle cell hibernoma variants are likely to be located in the posterior neck and shoulder. Hibernomas are benign lipomatous neoplasms and have no potential for malignant transformation.  Hibernomas contain brown fat, and the name was coined about the presence of brown fat in hibernating animals. First described by Merkel 1906, these tumors are similar to lipomas in clinical behavior but have unique imaging and histopathologic features. Hibernomas generally present in young adults with a mean age of 38. In summary, these tumors are:

• Composed of brown fat
• Represent benign neoplasms
• Generally well-circumscribed masses
• Generally are small in size
• Exhibit slow growth
• Histopathologically composed of brown fat cells
• Chief differential diagnosis include well-differentiated liposarcomas (WDLS)
• Most often involve the thigh, trunk, and chest.
• Rare locations seen in less than 10% of cases include retroperitoneal, thorax, and intraabdominal regions.
• Fewer than 20% are intramuscular in location.

Reference: Tafti D, Cecava ND. Hibernoma. [Updated 2023 May 22]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK570579/

SNA angle describes the relationship of the:

 # SNA angle describes the relationship of the:

A. Maxilla to the cranial base

B. Mandible to the cranial base

C. Maxilla to mandible

D. Maxilla to the upper incisors

The correct answer is A. Maxilla to the cranial base. 

SNA: the angle between the sella/nasion plane and the nasion/A plane (normal value at the end of growth 82 ± 2°). This angle assesses the antero-posterior position of the maxilla relative to the upper cranial structures.