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usmle u world step 1- immunology and histology question bank
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1. Histological evaluation of a portion of the gastrointestinal tractshows ramified, tubular glands located in the submucosal layer.
The glands contain secretions with pH close to 9.0. Which of the
following portions of the gastrointestinal tract is most likely
inspected?
A. Stomach
B. Duodenum
C. Jejunum
D. Ileum
E. Ascending colon
Answer: B
Explanation:
Superficially, the duodenal lamina propria contains villi, which are finger-
like outpouches that project into the lumen. The villi are covered by a
simple columnar epithelium with a brush border (surface absorptive
cells) interspersed with goblet cells and APUD (amine precursor uptake
and decarboxylation) cells. Deeper within the lamina propria are crypts
of LieberkUhn, which are simple tubular glands that rest immediately
stop the muscularis mucosae and deliver secretions into the intervillar
spaces. Deep to the muscularis mucosae is the submucosa, which is
occupied by compound tubular Brunner's glands. Unique to the
duodenum, these glands secrete alkaline mucus into ducts that track
upward through the muscularis mucosae and into the crypts of
LieberkUhn for release into the lumen.
(Choice A) The fundic stomach is superficially characterised by
numerous gastric pits lined by simple columnar epithelium. At the base
of each pit are two to four fundic glands that primarily contain parietal
cells and chief cells. Below these glands is the muscularis mucosae.
(ChoiceC)The villi of the jejunum contain more goblet cells than the villi
of the duodenum. The crypts of LieberkUhn persist in the jejunum,
opening into the intervillar spaces. Heavy lymphocytic infiltration of the
lamina propria is common.
,(Choice D) The ileum is similar in appearance to the jejunum, though
lymphatic nodules termed Peyer's patches are commonly found
immediately adjacent to the villi and crypts.
(Choice E) In the colon, the crypts of LieberkUhn persist and are heavily
populated by mucus-producing goblet cells. However, no pits or villi are
present, distinguishing this region from the stomach and small intestine.
2. A population of cells are exposed to radiation and then examined by
electron microscopy. Ribosomes are found to be detached from the
endoplasmic reticulum. This structural change will cause loss of which of
the following functions?
A. Synthesis of steroid hormones
B. Synthesis of cytosolic proteins
C. Drug detoxification
D. Synthesis of secretory proteins
E. Endocytosis
F. ATP production
Answer: D
Explanation:
Ribosomes are cellular organelles that synthesise proteins. Each
ribosome consists of two subunits. The small ribosomal subunit is
responsible for binding m RNA (the template for protein synthesis) and
tRNA (carry amino acids). The larger subunit contains peptidyl
transferase, the enzyme that catalyses peptide bond formation between
amino acids.
Ribosomes can exist free in the cytoplasm or bound to the rough
endoplasmic reticulum (RER). Free ribosomes synthesise proteins that
are used in the cytosol and cellular organelles. Ribosomes attached to
the RER synthesise secretory, membrane-bound, and lysosomal
,proteins. The RER is responsible for subsequent protein modification,
folding, and transfer. The RER is \'Veil-developed in protein-secreting
cells (e.g. enzyme-secreting pancreatic cells).
Ribosomes attach to the RER via ribophorin, receptors for the large
subunit.
(Choices And C) Synthesis of steroid hormones and drug
detoxification occur in the smooth endoplasmic reticulum (SER).
(Choice B) Cytosolic proteins are synthesised by free ribosomes.
(Choice E) Endocytosis occurs via cell membrane invagination.
3. The adrenal gland is the site of synthesis for a number of hormones. A
section of a normal adrenal gland is shown on the slide below.
The structure indicated by the arrow is most likely to contain cells that
will be activated by which of the following substances?
A. Acetylcholine
, B. ACTH
C. Angiotensin II
D. Epinephrine
E. Norepinephrine
Answer: A
Explanation:
The adrenal gland is made up of an outer cortex and an inner medulla.
The outer cortex is divided into 3 zones. The outermost zone is the zona
glomerulosa (1), which contains cells arranged in rounded or arched
clusters that secrete mineralocorticoid hormones(primarily aldosterone).
The Middle Zone Is The Zona fasciculata (2), which contains foamy-
appearing cells in columns that secrete glucocorticoid hormones
(primarily cortisol). The inner zone is the zona reticularis (3), containing
basophilic cells in anastomosing cords that secrete small amounts of
androgens. There is a sharp interface between the cortex and the
medulla (4), which is composed of chromaffin cells with a deeply
basophilic cytoplasm. Chromaffin cells are modified postganglionic
sympathetic neurons derived from the neural crest that receive
sympathetic input (neuroendocrine cells).
All sympathetic preganglionic neurons release acetylcholine, which
activates nicotinic acetylcholine receptors on postganglionic neurons.
Typically, these postganglionic neurons release norepinephrine to
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