Dr. Mhawi 1 Digestive System 2 Flashcards

Question

Explain the characteristics of the stomach

Answer 1

Same organization as remaining gut _Mucosa, submucosa, muscularis, serosa_ Inner surface has **longitudinal folds called RUGAE** Poorly developed in upper stomach more elaborate in lower part _Disappear_ when stomach is distended Accommodate expansion 8.6.1

Answer 2

Cross section of one of the gastric folds (ruga). Note the four layers of the stomach wall namely, mucosa (M), submucosa (SM), muscularis externa, and serosa (Se). The mucosa and submucosa (asterisks) constitute the ruga. Thick arrows point to the three distinctive region of the mucosa. The most superficial region contains the gastric pits; the middle region contains the necks of the glands, and the deepest part of the mucosa contains the bottom of the gastric glands (stained heavily with hematoxylin).

Answer 3

cardia, fundus, pylorus

Answer 4

CARDIA (cardiac region) part near esophagus contains c_ardiac glands_ FUNDUS (fundic region) called the body largest part between cardia and pylorus Contains f_undic glands AKA gastric glands_ PYLORUS (pyloric region) part proximal to pyloric sphincter contains _pyloric glands_

Answer 5

Epithelium is **_simple columnar_** Called _SURFACE MUCOUS CELLS_ forms a continuous layer that lines the whole gastric lumen Cells have a large apical deposit (cup) of _mucin granules_ (see the TEM inset) Mucus forms a thick gel-like _coat_ on surface Epithelium _dips_ to form Gastric pits (black arrow) Light micrograph of the stomach mucosa. The lumen of the stomach is lined by simple columnar epithelium which is comprised of surface mucous cells that secrete thick mucus. The carbohydrate-rich mucus is stained well with PAS stain. Lower inset: Electron micrograph of the simple columnar epithelium lining the stomach. Electron-dense mucin granules (arrow) are deposited above the nucleus of the cell. 8.6.1

Answer 6

GASTRIC PITS or FOVEOLAE Easily seen in SEM Gastric pits lead into _GASTRIC GLANDS_ Long simple branch tubular a) Top view SEM of the stomach lining reveals gastric pits (P) surrounded by polygonal apical ends of surface mucous cells (smiley face). (b) Side view SEM of the gastric pits and glands. The large bulging cells on these glands (indicated by the asterisk) are the parietal cells. Note also that this particular gland branches at its base (white arrows). The opening of one of the pits is indicated by the black arrow.

Answer 7

Present throughout gastric mucosa Extend from bottom of the _GASTRIC PITS to MUSCULARIS MUCOSAE_ Produce gastric juice

Answer 8

MUCOUS NECK CELLS PARIETAL CELLS (AKA oxyntic cells) CHIEF CELLS ENTEROENDOCRINE CELLS Found in the gastric gland epithelium and scattered throughout the GIT UNDIFFERENTIATED (stem) CELLS located in upper neck region give rise to mature cells listed above

Answer 9

Fundic stomach. CC, chief cells; PC, parietal cells; L, lumen of the gland. 8.6.1

Answer 10

Fundic stomach. PAS stain for mucous. Note the large and round parietal cells (PC) and the dense granular chief cells (CC) at bases of glands. MM, muscularis mucosae.

Answer 11

Parietal (oxyntic) cells are large round to triangular cells with eosinophilic cytoplasm and centrally located nucleus (thin arrows). Chief cells are located towards the base of the gland. They are recognized by their basically located nuclei and basophilic granular cytoplasm (thick arrows). MM, muscularis mucosae.

Answer 12

Located in _neck region_ of the gastric glands Shorter than surface mucous cell Nucleus tends to be spherical rather than elongate as in surface mucous cells Secretes _soluble mucus_ compared to viscous surface mucus Fundic stomach mucosa. PAS stain. Both surface mucous cells (top) and mucous neck cells, which are interspersed among the parietal cells in the neck region of the gland, are stained magenta. MM, muscularis mucosae.

Answer 13

AKA OXYNTIC CELLS Secrete _HCl and intrinsic factor_ Most numerous in _upper and middle region_ of the gland Large cells Appear _round to triangular_ Under the influence of _gastrin hormone_ secreted by enteroendocrine cells (called _G-cells)_

Answer 14

Light micrograph of the fundus revealing many cell types of the gastric glands. The parietal cells (PC) appear, large in size and _eosinophilic (bc lots of mitochondria)_ and their shape is round to triangular. Their nuclei are prominent, round, and centrally located. Chief cells (CC) are noticeable at the base of the glands. Their cytoplasm are filled with pepsinogen granules. Green arrows point to the mucous neck cells. Note that the cytoplasm of these cells looks empty due to the washing of the mucus away from the cytoplasm during the preparation of the tissue for histologic examination. MM, muscularis mucosae.

Answer 15

TEM of an inactive parietal cell. Note that the cytoplasm revealed many mitochondria (M) scattered among areas that are filled with membranes. These membranes are in the form of tubules and vesicles (tubulovesicular system; TV). The membranes of the tubulovesicular system contribute to the microvilli projecting into the lumen of the intracellular canalicular system formed when the cell becomes active (see next slide). MV, microvilli; N, nucleus.

Answer 16

TEM of active parietal cell in gastric gland. The cytoplasm of the active cells reveals an intracellular canalicular system (C), which is a deep, trough-like invagination of the apical cell surface opening into the lumen (L). The luminal surface area of the intracellular canalicular system is further increased by numerous microvilli, which are contributed by the tubulovesicular system (see previous slide). Mitochondria are abundant.

Answer 17

Composite diagram of a parietal cell, showing the ultrastructural differences between a resting cell (left) and an active cell (right). Note that the tubulovesicles (TV) in the cytoplasm of the resting cell fuse to form microvilli (MV) that fill up the intracellular canaliculi (IC) of active cell. G, Golgi complex; M, mitochondria.

Answer 18

Typical protein-secreting cells Occupy the _basal portion_ of the gland Cells easily identified by _intense basophilia_ Due to well-developed rER Secrete: _pepsinogen_ as precursor of pepsin a weak lipase

Answer 19

Open type - Directly contacts the lumen, _Chemoreceptor,_ Samples the content of the GIT, When stimulated by the sample _hormones are released basally_ into the lamina propria Closed type No direct contact with lumen, indirectly stimulated by the luminal content via _neural and paracrine_ mechanism, secrete their hormones (basally) Electron micrograph of “closed and open” enteroendocrine cells. tope: electron micrograph shows an example of the “opened” enteroendocrine cell. Note the microvilli at the free (luminal) end and the sub-nuclear cytoplasmic granules. bottom: This electron micrograph shows an example of the “closed” enteroendocrine cell. Arrowheads mark the boundary between the enteroendocrine cell and the adjacent epithelial cells. At its base, the enteroendocrine cell rests on the basal lamina (BL). This cell does not extend to the luminal surface. Numerous secretory vesicle (G) in the base of the cell are secreted in the direction of the arrows across the basal lamina and into the connective tissue (CT). En, endothelium of capillary; M, mitochondria; rER, rough endoplasmic reticulum; sER, smooth endoplasmic reticulum.

Answer 20

The function is to regulate: The peristaltic movement of the intestine Secretion of digestive enzymes Absorption of water and electrolytes Light micrograph of enteroendocrine cells (arrows) stained with silver salts. The secretory granules has affinity to _silver and chromium salts_ and appear black. MSC, mucous surface cell appear at the bottom of the gastric pits.

Answer 21

Caused by excessive secretion of _gastrin_ Due to tumor of the gastrin-producing enteroendocrine _G-cells_ in the duodenum or pancreatic islets of Langerhans Results in continuous stimulation of the _parietal cells_ Causes overproduction of _HCl_ Excess acidity cannot be neutralized Causes _gastric or duodenal ulcers_ Treated by the application of **_proton pump inhibitors_**

Answer 22

Limited to the cardiac region of the stomach near esophageal orifice Tubular glands Tortuous Composed of mainly _mucous secreting cells_ Mucus protects the esophagus from gastric acid Photomicrograph of cardiac glands. This photomicrograph shows the esophagogastric junction. Note the presence of the stratified squamous epithelium of the esophagus in the upper right corner of the micrograph. The cardiac glands are tubular, somewhat tortuous. They are composed mainly of mucus-secreting cells similar in appearance to the cells of the esophageal glands. Mucous secretion reaches the lumen of the gastric pit via a short duct segment containing columnar cells.

Answer 23

Located between fundus and pylorus _Tubular_ glands Coiled Glands empty into d_eep and tortuous gastric pits_ n. hat occupy ½ the thickness of the mucosa Secrete _mucus_ Pyloric gland (PG). Note the deep and tortuous (coiled) gastric pit (GP).

Answer 24

Consist of three layers instead of two Innermost: oblique Middle: circular Outermost: longitudinal

Answer 25

## Footnote Immature cells at the bottom of the gastric pit (encircled) are responsible for the renewal of the lining of the gastric mucosa.

Answer 26

plicae circulares, villi, and microvilli

Answer 27

_-valves of Kerckring_ _-permanent_ transverse folds that contain a _core of submucosa_ - Prominent in the _jejunum_ - Each fold circularly arranged - extends around half to 2/3 of circumference of lumen - Covered by _villi_ The internal surface of the small intestine is amplified to increase the effective surface area required for absorption. Upper panel: gross anatomical view of the plicae circularis (arrows). Lower panel: the plicae circularis are cut transversely for histological inspection. Each plica circularis has a core of dense connective tissue that extends from the submucosa. Note also that the plicae are covered by villi.

Answer 28

## Footnote 8.6.1

Answer 29

_Gross anatomical structures_ finger-like and leaf-like projections of _mucosa_ into lumen Covered by _columnar cells_ Core filled with l_amina propria_ Contain _lacteal_, smooth muscles, fenestrated blood vessels

Answer 30

_Microscopic_ structures Cover the apical surface of the absorptive cells are _major amplification_ of luminal surface each cell has _several thousands_

Answer 31

(a) SEM of the intestinal villi. Arrows indicate openings between bases of villi leading to the intestinal glands. (b) This three-dimensional diagram of the intestinal villi shows the continuity of the epithelium covering the villi with the epithelium lining the intestinal glands. Blood vessels and blind-ending lymphatic capillary (lacteal) are found in the core of the villi. Arrows point to the openings of the intestinal glands (crypts of Lieberkühn).

Answer 32

Intestinal glands AKA _Crypts of Lieberkϋhn_ Simple tubular, Extend from muscular mucosae, Open into the intestinal lumen at base of villi Glands composed of s_imple columnar epithelium_ continuous with the simple columnar epithelium covering the villi

Answer 33

Lamina propria - Surrounds intestinal glands - Fills the core of villi - Contains gut-associated lymphatic tissue (GALT): GALT includes: **_- Lymphocytes_** **_- Plasma cells_** **_- Macrophages_** **_- Dendritic cells_** **_- Eosinophils_** Small intestine. The lamina propria fills the core of the intestinal villi and surrounds the intestinal glands (arrows). MM, muscularis mucosae.

Answer 34

_Diffuse_ lymphatic tissue Cells are scattered throughout the lamina propria Lymphatic _nodules_ Cells are aggregated into discrete nodules e.g., _Peyer’s patches in the ileum_ Named after the 17th- century Swiss anatomist Hans Conrad Peyer

Answer 35

Stars are place at the lamina propria where cells of _diffuse lymphatic tissue_ are found. Deepest part of the mucosa, muscularis mucosae (MM), is made of two ill-defined layers. 8.6.1

Answer 36

Ileum; Peyer’s patches (pp) are good example of the lymphatic nodules. 8.6.1

Answer 37

Ileum, monkey. The lymphatic nodules (LN) are partly within the mucosa of the ileum and extend into the submucosa (SM). ME, muscularis externa; V, villi.

Answer 38

**ENTEROCYTES** absorption **GOBLET CELLS** **PANETH CELLS** **ENTEROENDOCRINE CELLS** **M CELLS (microfold cells)** nmodified enterocytes which cover enlarged lymphatic nodules in lamina propria of the ileum **STEM CELLS**

Answer 39

Section through the intestinal glands. 1, enterocyte; 2, goblet cell; 3, enteroendocrine cell (close type); 4, enteroendocrine cell (open type); 5, Paneth cells. M cells are not represented in the micrograph.

Answer 40

_Tall columnar_ cell basal nucleus Have well-developed _microvilli_ on luminal surface _Absorptive_ Upper panel: LM of the epithelium covering a villus of the small intestine. Enterocytes and goblet cells are visible. Lower panel: TEM of a part of the intestinal epithelium similar to the boxed area in the LM micrograph.

Answer 41

Electron micrograph of epithelium of the small intestine. Abundant microvilli at the cell apex of the enterocytes can be seen to form the brush border. At the left are 2 lymphocytes (L) migrating in the epithelium. In the center is an enteroendocrine cell (E) with its basal secretory granules

Answer 42

Increase in _number_ - from proximal to distal small intestine Most numerous in terminal _ileum_ Mucus is _water-soluble_ Ileum. Note the increase in the number of goblet cells (stained with PAS).

Answer 43

Goblet Cell.

Answer 44

Found in _bases of intestinal glands_ May be seen in colon as well Contains large _supranuclear secretory granules_ very _eosinophilic_ _refractile_ granules permit _identification_ of these cells Lower panel: Light micrograph of the base of the intestinal glands (crypts of Lieberkuhn) in which Paneth cells (arrows) with their characteristic eosinophilic granules are visible.

Answer 45

Right panel: Photomicrograph of intestinal glands showing Paneth cells. This photomicrograph shows the base of intestinal glands in an H&E preparation. The gland on the right side of the micrograph is sectioned longitudinally; the circular cross-sectional profile of another gland is seen on the left side of the micrograph. Paneth cells are typically located in the base of the intestinal glands and are readily seen in the light microscope because of the intensive eosin staining of their vesicles. The lamina propria contains an abundance of plasma cells, lymphocytes, and other connective tissue cells. Note several lymphocytes in the epithelium of the gland (arrows). ×240. Inset. This high magnification of the area indicated by the rectangle shows the characteristic basophilic cytoplasm in the basal portion of the cell and large accumulations of intensely staining, eosinophilic, refractile secretory vesicles in the apical portion of the cell. An arginine-rich protein found in the vesicles is probably responsible for the intense eosinophilic reaction. ×680. Left panel: TEM image of a region similar to the boxed area in the inset of the right panel. Two Paneth cells surrounding a columnar cell at the base of the crypt of Lieberkuhn are indicated. Paneth cells are characterized by the presence in the cytoplasm of well-developed rough endoplasmic reticulum and apical large secretory granules.

Answer 46

Granules contain **LYSOZYME** LYSOZYME digests cell walls of certain bacteria **nα-DEFENSINS** Paneth cells probably Regulate normal **_bacterial flora_** of the small intestine

Answer 47

Closed Open Hormone-containing granules are _subnuclear_ nCompare with Paneth cells (granules occupy _supranuclear_ location) Like those in stomach _Secrete into lamina propria_

Answer 48

Electron micrograph of epithelium of the small intestine. Abundant microvilli at the cell apex can be seen to form the brush border. At the left are 2 lymphocytes migrating in the epithelium. In the center is an enteroendocrine cell (E) with its basal secretory granules.

Answer 49

M Cells (Microfold cells) Epithelial cells that _overlie Peyer’s patches_ and other lymphatic nodules Nearly squamous Have surface _MICROFOLDS_ instead of microvilli

Answer 50

take up sample from lumen of the intestine by _endocytosis_ vesicles transported basally Sample is released by _exocytosis_ to lymphocyte-rich underlying compartment Therefore, M cells are **_antigen-transporting cells_** They _should not be defined as antigen-presenting cells_ A, Electron micrograph of an M cell (M) located between two absorptive enterocytes and covering small nest of lymphocytes and macrophages. The thin cytoplasm of M cell facilitates a quick transportation of samples from the lumen of the intestine to the underlying lymphocytes and macrophages. B, interpretive schematic diagram.

Answer 51

Consists of _dense connective tissue_ Conspicuous feature of duodenum is _submucosal glands (BRUNNER’S GLANDS)_ Duodenum. M, mucosa; SM, submucosa; ME, muscularis externa. Note the presence of submucosal (_Brunner’s) glands._

Answer 52

Cells of Brunner’s glands have characteristics of both _mucous and serous secretions_ pH of secretions is _8.1-9.3_ protects _proximal_ small intestine neutralizes acid from the stomach creates _optimal pH for enzymes_ Duodenum. In this section the arrow points to one of Brunner’s glands piercing muscularis mucosae (MM) and opens into the intestinal gland (crypt of Lieberkühn).

Answer 53

Duodenum. In this field of view many Brunner’s glands (arrows) are penetrating mascularis mucosae to open into crypts of Lieberkühn.

Answer 54

Crosse section of the duodenum. Note that one of Brunner’s glands is piercing the muscularis mucosae by its duct (arrow) and opens into the intestinal (Lieberkühn) gland.

Answer 55

Cross section of the Duodenum. V, villi; Muc, mucosa; MM, muscularis mucosae; SubM, submucosa; ME, muscularis externa; BGl, Brunner’s glands; D, duct through which the glands open into the lumen of the duodenum; S, serosa.

Answer 56

All mature cells in intestinal epithelium come from **A SINGLE STEM CELL POPULATION** Stem cells localized at _base of crypt_ Regeneration of the epithelial lining of the stomach and small intestine. Note differences in the location of stem cells.

Answer 57

Epithelial cells migrating from the base of the crypt onto the villus differentiate into: _Absorptive_ or _goblet cells_ Renewal time is **5-6 days** _Enteroendocrine_ or _Paneth cells_ Renewal time **4 weeks** unidirectional, compare with stomach Crypts of Lieberkuhn cut longitudinally (upper panel) and transversely (lower panel). In the upper panel dividing stem cells showing mitotic figures are shown just above Paneth cells. Note the supranuclear eosinophilic granules of Paneth cells and the presence of an enteroendocrine cell.

Answer 58

_Mucosa is smooth (no plicae circularis, no villi)_ Outer longitudinal layer of the muscularis externa (ME) Modified to 3 equally spaced _bands_ _Tenia coli_ Cross section of the colon. The four layers that make up the wall of the colon are mucosa (Muc), Submucosa (SubM), Muscularis externa (ME) and serosa (S). Although these layers are the same as those in the small intestine, several differences are noted; namely, the absence of the plicae circularis, mucosa has no villi, and the muscularis externa is arranged in a distinctive manner. The outer longitudinal layer of the muscularis externa [ME(l)] is substantially thinner than the inner circular layer [ME(c)] and modified to three equally spaced bands called tenia coli (TC). BV, blood vessel.

Answer 59

_Covered with simple columnar epithelium_ Similar to those of the small intestine Absorptive cells _absorb water and electrolytes_ Contains numerous _CRYPTS OF LIEBERKUHN_ straight tubular glands, extend through full thickness of mucosa, Composed mostly of goblet cells Photomicrograph of a section of large intestine with its various layers. Black arrows point to crypts of Lieberkuhn. Note the absence of villi. M, mucosa; SubM, submucosa; Me, muscularis externa; S, serosa (red arrow). Note that a lymphatic nodule (LN) extends from the lamina propria to the submucosa

Answer 60

Cross section of the human colon. Note crypts of Lieberkuhn (the arrows point to their openings) and the absence of the villi (smooth surface).

Answer 61

Secrete mucus Consists of _highly glycosylated glycoproteins called **mucins**_ Viscus Physically _imped_ microorganisms Mucin is negatively charged _Binds_ positively charged defensins Facilitates elimination of waste material Highly magnified section of a large intestinal gland showing its absorptive and mucous goblet cells. Observe that the goblet cells are secreting and beginning to fill the lumen of the gland with its secretions. The microvilli in the absorptive cells (not visible in this section) participate in the process of water absorption. PT stain.

Answer 62

_Absorptive cells outnumber goblet; 4:1_ Not apparent in histological sections _Absorptive cells_ are located more toward the lumen of the colon (arrows) _Goblet cells_ more toward the intestinal glands Near _rectum ratio is 1:1_

Answer 63

All mucosal epithelial cells arise from stem cells at _bottom of crypts_ Turnover times are _6 days_ for absorptive and goblet cells _4 weeks for enteroendocrine cells_

Answer 64

Diffuse _lymphatic tissue_ and large _lymphatic nodules_ lymphatic nodules distort regular spacing of crypts and _extend into submucosa_ Reflects large number of _microorganisms_ present in colon lumen Section of the colon showing lymphatic nodule (LN) in the lamina propria.

Answer 65

Cecum is a thin finger-like extension of the cecum Appendix (image) Appendix is different in that it has a _complete layer of the outer longitudinal muscle_ in the muscularis

Answer 66

true ## Footnote 8.6.1

Answer 67

## Footnote 8.6.1

Answer 68

Upper panel shows the histology of the transition of the epithelium from simple columnar that lines the rectum to stratified columnar epithelium to stratified squamous epithelium. Lower panel is endoscopic view of the anorectal junction. The transition of the epithelium from simple columnar epithelium (appears dark brown) to stratified squamous epithelium (appears light) is indicated by the arrows.

Answer 69

Simple columnar (the lining of the rectum) to stratified columnar to stratified squamous (lining of anus)

Answer 70

## Footnote 8.6.1

Dr. Mhawi 1 Digestive System 2 Flashcards

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