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Question 1

restriction enzymes

Answer 1

restriction enzymes usually cleave along palindromic sequences.
A palindrome is a sequence is one that is the same forward and backwards.
Ex: GGCC, TTAA

Question 2

Sex disorders

Answer 2

Female teenager + normal Tanner stages + vagina ends in blind pouch + normal/coarse pubic/axillary
hair: answer = Müllerian agenesis.

Karyotype = 46XX (karyotypic female).
Female teenager + normal Tanner stages + vagina ends in blind pouch + scanty/absent pubic/axillary
hair: answer = androgen insensitivity syndrome. Karyotype = 46XY (karyotypic male).

Answer 3

USMLE wants you to know hepatocellular death in hepatitis is due to T-cell-mediated
apoptosis.

Question 4

Birbeck granules

Answer 4

tennis racket-shaped organelles seen on electron microscopy

Question 5

Bernard-Soulier syndrome

Answer 5

deficient platelet glycoprotein Ib (GpIb), which leads to defective platelet adhesion to von Willebrand factor (vWF) as well as defective platelet anchoring to the vessel wall (i.e., impaired primary hemostasis)

A ristocetin cofactor assay can be used to detect GpIb deficiency because ristocetin activates vWF to bind GpIb

Question 6

TSH

Answer 6

TSH acts through both the Gs protein (activating the adenylyl cyclase signaling cascade) and the Gq protein (activating the phospholipase C cascade).

Question 7

Crohn disease

Answer 7

manifests with chronic, watery, nonbloody diarrhea and abdominal pain, mainly in the right lower quadrant. Extraintestinal manifestations, such as the oral aphthae

Question 8

Spina bifida

Answer 8

incomplete fusion of vertebral arches (typically affecting the lower lumbar or sacral spine) that results from incomplete closure of the caudal neuropore during neurulation

Question 9

Anencephaly

Answer 9

Failed closure of the rostral neuropore during neurulation

Question 10

Myeloschisis

Answer 10

Failed fusion of the neural folds during neurulation

Question 11

Medulloblastoma

Answer 11

the most common primary malignant brain tumor of childhood and has a peak incidence between 3–5 years of age. This tumor typically develops in the cerebellum.

Destruction of the cerebellar vermis causes truncal ataxia, and compression of the fourth ventricle by the tumor causes noncommunicating hydrocephalus

The main histopathologic feature of medulloblastoma is the presence of small round blue cells (primitive neuroectoderm cells) that surround a central, fibril-rich neuropil (Homer Wright rosettes).

Question 12

Neuroblastoma

Answer 12

tested for homovanillic acid and vanillylmandelic acid, which are produced when neuroblastoma cells metabolize catecholamines

opsoclonus-myoclonus ataxia is a paraneoplastic syndrome associated with neuroblastoma

Question 13

cytochrome P450 monooxygenase system

Answer 13

The primary function of the microsomal cytochrome P450 monooxygenase system is the metabolization of xenobiotics (e.g., drugs, toxins) and hydrophobic endogenous compounds (e.g., steroids) to allow for their excretion

Chronic exposure to aflatoxin, which is produced by some species of Aspergillus, is a risk factor for hepatocellular carcinoma (HCC)

Question 14

Nephrolithiasis

Answer 14

Calcium oxalate stones are overall the most common stone seen in nephrolithiasis and idiopathic hypercalciuria is the most common risk factor for this type of stone formation

Question 15

Luteinizing hormone

Answer 15

secreted by the pituitary gland and stimulates testicular Leydig cells to synthesize testosterone.

Question 16

Complication of liver transplantation

Answer 16

Hepatic artery thrombosis

Question 17

Chronic organ rejection

Answer 17

Intimal smooth muscle proliferation mediated by CD4+ T cells is one of the histopathological hallmarks of chronic organ rejection.

The release of cytokines by host CD4+ T cells induces a type IV hypersensitivity reaction, which damages the donor organ.

Question 18

Allogenic transplant with different sex donor

Answer 18

Chromosomal analysis in this female patient shows a male genotype (46,XY karyotype) because she received stem cells from a male donor (e.g., sex-mismatched transplantation).

Question 19

Acute rejection

Answer 19

The absence of C4d staining (a marker of antibody-mediated damage) and the presence of inflammatory infiltrate within the wall of tubules (tubulitis) indicate that the most likely mechanism for graft rejection in this patient is acute cellular rejection

Question 20

Cyclosporine

Answer 20

is the only calcineurin inhibitor to cause gingival hyperplasia,

Question 21

Mycophenolate mofetil

Answer 21

Side effects of this drug include hypertension and hyperlipidemia, as seen in this patient. However, it is not known to cause gingival hyperplasia. Further important adverse effects of mycophenolate mofetil include first-trimester pregnancy loss and congenital malformations, infection, malignancy, neutropenia, and hyperglycemia.

Question 22

Hyperacute graft rejection

Answer 22

mediated by preformed cytotoxic antibodies against donor class I HLA molecules or donor blood group antigens (type 2 hypersensitivity reactions).

Question 23

GFR

Answer 23

Serum creatinine levels do not start rising until the GFR is reduced by approx. 50%

Question 24

Serum cystatin C

Answer 24

A more precise indicator of the GFR than serum creatinine

Question 25

Blood urea nitrogen (BUN)

Answer 25

10:1–20:1 can be normal or may indicate a postrenal cause. ≥ 20:1 indicates prerenal cause ≤ 15:1 indicates intrarenal cause

Question 26

Fractional excretion of sodium (FeNa)

Answer 26

Definition: percentage of the glomerular filtered sodium (NaFiltered) that is eventually excreted in the urine (NaExcreted) FeNa = (NaUrine x CreaPlasma) / (NaPlasmax CreaUrine) Interpretation In acute kidney injury Low FeNa (< 1%): indicates a prerenal cause (renal hypoperfusion) High FeNa (> 2%): indicates an intrarenal etiology (e.g., acute tubular necrosis)

Question 27

Additional renal blood tests

Answer 27

Autoantibodies: antinuclear antibodies (ANCA) as an indication of glomerulonephritis Uric acid: a metabolite of purine bases Uric acid crystals can form in the joints, where they can trigger inflammatory reactions and pain (i.e., gout attack). Hyperuricosuria can lead to uric acid nephropathy

Question 28

Uric acid elevation

Answer 28

- Renal disorders .Uric acid nephrolithiasis .Acute uric acid nephropathy .Acute renal failure - Increased cell death (e.g., tumor lysis syndrome) - Lesch-Nyhan syndrome - Fanconi Syndrome - Antiuricosuric drugs (e.g., all diuretics, ethambutol, niacin, aspirin, diclofenac)

Question 29

Creatinine and inulin

Answer 29

In addition to being freely filtered from the glomerular capillaries into the Bowman capsule, small amounts of creatinine are actively secreted into the proximal tubules. This leads to an overestimation of the creatinine clearance by 10–20% and a resulting overestimation of the GFR. Inulin, on the other hand, is also freely filtered but is neither secreted nor reabsorbed.

Question 30

WBC casts

Answer 30

. WBC casts are most commonly found in patients with pyelonephritis but can also form in patients with acute interstitial nephritis or in renal transplant recipients experiencing graft rejection.

Question 31

Chagas disease

Answer 31

Romana sign: unilateral painless edema of the eyelids and periocular tissue Chagas disease is caused by the kissing bug and treated with nifurtimox or Benznidazole

Question 32

Onchocerciasis

Answer 32

Everything turns black in onchocerciasis: black flies, black skin nodules, black vision (blindness). Treat rIVER blindness with IVERmectin.

Question 33

Necator americanus

Answer 33

Necator americanus, Ancylostoma duodenale) larvae migrate to the intestines and cause chronic blood loss leading to iron deficiency anemia

Question 34

Praziquantel

Answer 34

causes contracted muscle paralysis in parasites by increasing calcium influx into the sarcoplasm of the parasite

Question 35

Adrenal gland

Answer 35

a bilateral endocrine gland with: outer cortex: steroid hormones inner medulla:catecholamines (e.g., epinephrine). Embryology Adrenal cortex: derived from mesothelial cells Adrenal medulla: derived from chromaffin cells, which originate in the neural crest

Question 36

Renal venous drainage

Answer 36

The right suprarenal vein drains into the inferior vena cava. The left suprarenal vein drains into the left renal vein

Question 37

Adrenal cortex zones

Answer 37

Zona glomerulosa Outermost layer Main site of aldosterone production Zona fasciculata Located between the zona glomerulosa and zona reticularis Main site of glucocorticoid production Zona reticularis Inner cortical layer Main site of androgen production

Question 38

Cholesterol

Answer 38

converted into pregnenolone via cholesterol desmolase. Cholesterol desmolase can be inhibited by azole antifungals.

Question 39

RAAS

Answer 39

RAAS regulates the release of mineralocorticoids

Question 40

Biosynthesis of aldosterone

Answer 40

Precursor Enzyme Product 1. Pregnenolone 3β-hydroxysteroid dehydrogenase Progesterone 2. Progesterone 21-hydroxylase 11-deoxycorticosterone 3. 11-deoxycorticosterone 11β-hydroxylase and aldosterone synthase Corticosterone 4. Corticosterone Aldosterone synthase Aldosterone

Question 41

Aldosterone

Answer 41

Aldosterone stimulates potassium excretion in the collecting duct of the kidney as well as sodium and water retention.

Question 42

Mineralocorticoid function

Answer 42

Mechanism of action: aldosterone binds to intracellular mineralocorticoid receptors in the distal tubule and collecting duct of the kidney, inducing protein synthesis and following changes: ↑ Na+/K+-ATPase in the basolateral membrane → transportation of Na+ out and K+ into the tubule cells ↑ Apical H+-ATPase → H+ excretion ↑ Na+ channels (ENaC; epithelial sodium channel) → ↑ Na+ reabsorption ↑ K+ channels (ROMK; renal outer medullary potassium channel) in the luminal membrane → ↑ K+ excretion

Question 43

Mineralocorticoid effects

Answer 43

These aldosterone-induced changes produce a concentration gradient → Na+ reabsorption → water reabsorption; and K+ secretion into the urine. ↑ blood pressure, hypokalemia, and ↑ pH level.

Question 44

Renin-angiotensin-aldosterone system (RAAS)

Answer 44

angiotensin II via angiotensin-converting enzyme (highest concentration in the lungs where it is produced by vascular endothelial cells). Regulation of secretion Positive feedback ↓ Renal perfusion (e.g., due to hypotension, stimulation of β1 receptors in the kidney) triggers renin release. ↑ Serum potassium concentration → stimulation of zona glomerulosa cells → ↑ secretion of aldosterone ↑ systemic arterial blood pressure → ANP release from atrial myocytes → inhibition of renin release → vasodilation, natriuresis, and ↑ diuresis

Question 45

Primary adrenal insufficiency Addison disease, Bronze disease

Answer 45

A state of decreased adrenal production of adrenocortical hormones (glucocorticoids, mineralocorticoids, and adrenal androgens) caused by a disorder of the adrenal glands. The most frequent cause of primary adrenal insufficiency is autoimmune adrenalitis. Less commonly, it is due to infection (tuberculosis, CMV) or adrenal hemorrhage.

Question 46

Congenital adrenal hyperplasia

Answer 46

A group of autosomal recessive defects in enzymes that are responsible for cortisol, aldosterone, and androgen synthesis. Characterized by low levels of cortisol, high levels of ACTH, and adrenal hyperplasia. The most common form (caused by a deficiency of 21β-hydroxylase) presents with hypotension, hyponatremia, hyperkalemia, metabolic acidosis, ambiguous genitalia and virilization (in females), and/or precocious puberty (in both males and females).

Question 47

Primary hyperaldosteronism Conn syndrome

Answer 47

An excess of aldosterone caused by autonomous overproduction. Typically due to adrenal hyperplasia or adrenal adenoma.

Question 48

Type 4 renal tubular acidosis

Answer 48

A condition caused by impaired sodium reabsorption in the distal tubule, usually due to hypoaldosteronism. Manifests with a normal anion gap, hyperchloremic metabolic acidosis as well as hyperkalemia and low urine pH.

Question 49

Glucocorticoid function

Answer 49

Metabolism: Cortisol plays an important role in the mobilization of energy reserves. ↑ Gluconeogenesis to maintain blood glucose levels ↑ Glycogen synthesis to maintain glucose storage ↑ Protein catabolism ↑ Lipolysis ↑ Appetite ↑ Insulin resistance Immune system: antiinflammatory and immunosuppressive effects Wound healing: fibroblast inhibition → ↓ collagen synthesis → ↓ wound healing Blood pressure: mild mineralocorticoid effect (stimulation of aldosterone receptors in high concentrations) and ↑ potassium excretion → ↑ blood pressure To remember the effects of cortisol, think “A BIG FIB”: increased Appetite, Blood pressure, Insulin resistance, Glucose production, and decreased Fibroblasts, Immunity, and Bone formation.

Question 50

Hypothalamic pituitary gland adrenal cortex

Answer 50

a stimulus causes increased secretion of corticotropin-releasing hormone (CRH) → ↑ secretion of adrenocorticotropic hormone (ACTH) in the pituitary gland → ↑ secretion of glucocorticoids in the adrenal cortex. Negative feedback: Glucocorticoids themselves trigger a negative feedback loop that inhibits the secretion of CRH and ACTH. Circadian rhythm [6] Endogenous biological rhythm influences CRH secretion. Cortisol levels are highest early in the morning

Question 51

Adrenal insufficiency

Answer 51

A state of decreased production of adrenocortical hormones (glucocorticoids, mineralocorticoids, and adrenal androgens). Categorized as primary (adrenal dysfunction), secondary (pituitary dysfunction), or from chronic exogenous steroid use. Symptoms may include postural hypotension, nausea, vomiting, weight loss, anorexia, lethargy, depression, and/or hyponatremia.

Question 52

17α-hydroxylase defect

Answer 52

17α-hydroxylase defect causes a rare form of CAH involving pseudohermaphroditism in males and delayed puberty in females AnDRostenedione comes from the ADRenal glands and TESTostetone from the TESTes. In both men and women, DHEA and androstenedione are produced in the adrenal cortex, which are precursors for testosterone and estrogen. Testosterone is produced by Leydig cells in the testes in men and, to a lesser degree, ovarian stroma in women.

Question 53

Androgen

Answer 53

Adrenal androgens DHEA and androstenedione serve as precursors of: Androgens Androstenedione is converted into testosterone, which is then transformed into dihydrotestosterone (DHT) via 5α-reductase (defect leads to 5α-reductase deficiency). 5α-reductase inhibitors (e.g., finasteride) inhibit the conversion and are used in the treatment of BPH. Estrogen Aromatase converts testosterone into estradiol and androstenedione, which is then transformed into estrone Synthesized in men and postmenopausal women

Question 54

Effects of androgens

Answer 54

Testosterone stimulates the differentiation of the following structures: Epididymis Vas deferens Seminal vesicles DHT stimulates the differentiation of: Prostate Penis Scrotum

Question 55

***Biosynthesis of catecholamines***

Answer 55

Step Precursor Enzyme Cofactor Product First hydroxylation Phenylalanine Phenylalanine hydroxylase Tetrahydrobiopterin (THB) "Tyrosine" Second hydroxylation Tyrosine Tyrosine hydroxylase Tetrahydrobiopterin (THB) "DOPA (3,4-dihydroxyphenylalanine)" Decarboxylation DOPA DOPA decarboxylase Pyridoxal phosphate (Vitamin B6) Dopamine Hydroxylation of the β-C-Atom "Dopamine" Dopamine β-monooxygenase Vitamin C Norepinephrine Methylation "Norepinephrine" Phenylethanolamine-N-Methyltransferase (PNMT) (cortisol induces expression of PNMT) S-Adenosylmethionine (SAM) "Epinephrine" Epinephrine has the shortest half-life of the catecholamines.