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Histology > Digestive system: Alimentary tract > Flashcards

Digestive system: Alimentary tract Flashcards

1
Q

what does the digestive system comprise of?

A

oral region and alimentry tract (oesophagus, stomach and small and large intestines) and several extrinsic glands

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2
Q

throughout the digestive system what is the general structure of the hollow tube of varying diameter?

A

from the lumen -

  1. mucosa: epithelia, lamina propria, muscularis
  2. mucosa
  3. submucosa
  4. muscularis externa
  5. serosa or adventitia
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3
Q

how is the alimentry canal innervated?

A

innervation of the alimentry canal is accomplished by the enteric nervous system, whose neurons are located in Meissner (submucosal) and Auerbach (myenteric) plexuses.

the function of the enteric nervous system is modified by the sympathetic and parasympathetic components of the ANS

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4
Q

what type of epithelium lines the oesophagus?

A

stratified squmous nonkeratinised epithelium

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5
Q

what glands are found in the lamina propria and submucosa of the oesophagus?

A

lamina propria - oesophageal cardiac glands

submucosa - oesophageal glands proper

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6
Q

what are oesophageal cardiac glands?

  • location
  • function
A

oesophageal cardiac glands

- similar to cardiac glands of the stomach 
- found in the lamina propria of the mucosa
- present in the terminal part of the oesophagus
- secretes neutral mucus
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7
Q

what are oesophageal glands proper?

- location
- function
A

oesophageal glands proper

- lie in the submuscosa
- scattered along the length of the oesophagus but more concentrated in the upper half
- small, compound, tubuloalveolar glands
- excretory duct is composed of stratified squamous epithelium
- secretes slightly acidic muscus to lubricate the luminal wall
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8
Q

what is the lamina propria of the oesophagus composed of?

A

the lamina propia is similar to that throughout the alimentary tract.

- diffuse lymphatic tissue is scattered throughout,
- lymophatic nodules are present (in proximity to ducts of the glands)
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9
Q

what is the muscularis mucosa of the oesophagus composed of?

A

the muscularis mucosa is composed of longitudinal smooth muscle. it begins near the cricoid cartilage.
it is unusually thich in the proximal part of the oesophagus (aids swallowing)

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10
Q

what is the composition of the muscularis externa of the oesophagus?

A

consistant to the general histological organisation of the alimentary tract, however differed by the type of muscle:

  1. upper third - skeletal
  2. middle third - combination of smooth and skeletal
  3. outer third - smooth
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11
Q

how does the oesopahgus convey a bolus of food from the pharynx into the stomach?
how does it ensure it travels in one direction?

A
  • peristaltic activity of the muscularis externa
  • two physiological sphincters in the muscularis externa
    1. pharyngoesophageal
    2. gastroesophageal
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12
Q

how is the muscle of the oesophageal wall innervated?

A

the muscle of the oesophageal wall is innervated by both the autonomic NS and somatic NS

the skeletal muscle in the upper third of the oesophagus is innervated by somatic motor neurons of the vagus nerve (cranial nerve X)

the smooth muscle of the lower part of the oesophagus is innervated by visceral motor neurons fo the vagus nerve

the motor neurons synapse with postsynaptic neurons whose cell bodies are located in the wall of the oesophagus

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13
Q

what does the stomach convert the bolus of food into?

A

the stomach acidifies the blous of food into a thick, viscous fluid known as chyme.

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14
Q

how is the stomach histologically divided?

- 3 regions

A

the stomach is divided into 3 regions based on the gland type that occur in the gastric mucosa that each contains.

 1. cardiac region - contains cardiac glands
 2. fundic region - largest part of the stomach contains gastric glands
 3. pyloric region - contains pyloric glands
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15
Q

what is the general structure of the stomach?

A
  • the stomach exhibits longitudinal folds of the mucosa and submucosa, called rugae, which disapear in distended stomach
  • the stomach has many gastric pits (foveolae), shallowest in the cardia deepest in the pylorus.
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16
Q

what type of epithelium is found in the gastric muscoa?

what is it composed of?

A

the gatric mucosa is simple columnar epithelium composed of mucinogenic-producing surface lining cells

NOT GOBLET CELLS

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17
Q

what is the compostion of the lamina propria of the stomach?

A

the lamina propria of the stomach is a loose connective tissue housing smooth muscle cells, lymphocytes, plasma cells, mast cells and fibroblasts.

the lamina propria of the stomach contains gastric glands

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18
Q

what is the composition of the muscularis mucosae of the stomach?

A

the muscularis mucosae of the stomach is composed of a poorly defined inner circular layer, an outer longitudinal layer and occassionally an outermost circular layer of smooth muscle.

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19
Q

what is the life span of surface mucous cells of the stomach?

A

the surface mucous cells of the stomach have a relatively short lifespan of 3-5 days. it is accomadated by mitotic activity in the isthmus, containing a reservoir of stem cells.

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20
Q

what is the composition of the gastric submucosa?

A

the gastric submucosa of dense, irregular collagenous connective tissue.
it contains fibroblasts, mast cells and lymphoid elements.

the gastric submucosa houses Meissner (submucosal) plexus

it also possesses arterial and venous plexuses that supply/drain the gastric mucosa.

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21
Q

what is the Meissner plexus?

A

the meissner (submucosal) plexus is found in the submucosa of the alimentary tract. it is composed of nerve fibres and ganglion cells that innervate the vessels of the submucosa and the smooth muscle of the muscularis mucosae.

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22
Q

what is the composition of the muscularis externa of the stomach?
what is it responsible for?

A

the gastric muscularis externa is composed of three layers of smooth muscle:

 - an incomplete inner oblique layer
 - a thick middle circular layer
 - an outer longitudinal layer

the middle layer forms the pyloric sphincter
the auerbach myenteric plexus is also present
it is responsible for mixing of gastric contents and emptying of the stomach

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23
Q

where is the Auerbach plexus found within the stomach?

A

the Auerbach myenteric plexus is located between the middle circular and outer longitudinal smooth muscle layers of the muscularis externa.
the Auerbach plexus are groups of ganglion cells and bundles of unmyelinated nerve fibres that provides innervation of the muscle layers.

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24
Q

what is the pyloric sphincter formed from?

A

the middle circular layer of the muscularis externa of the stomach

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25
Q

what is the general structure of gastric glands?

A

gastric glands are simple branched tubular glands in the lmaina propria of the cardia, fundus and pylorus.
each glands consists of an isthum (connects the gland to the base of a gastric pit), a neck and a base.

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26
Q

what are the cells of the fundic glands? (5)

A
  1. Parietal (oxyntic) cells
  2. Cheif (zymogenic) cells
  3. Mucous neck cells
  4. Diffuse neuroendocrine system (DNES) cells
  5. Regenerative cells
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27
Q

what are Parietal cells of fundic glands of the stomach?

  • location
  • secretes…
A
  • parietal cells are pyramidal cells concentrated in the upper half of the gland
  • they secrete HCl and gastric intrinsic factor
  • they possess a unique intracellular tubulovesicular system, many mitochondria, and secretory intracellular canaliculi (deep invaginations of the apical plasma membrane) lined by microvilli.
  • when parietal cells are stimulated to secrete HCl, the number and length of microvilli increase and the complexity of teh tubulovesicular system decreases.
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28
Q

what are chief cells of fundic glands of the stomach?

  • location
  • secretes…
A
  • chief cells are pyramidal cells residing in the lower half of the gland
  • chief cells secrete pepsinogen (pepsin precursor) as well as precursors to other enzymes, rennin and lipase.
  • chief cells display an abundance of basal RER, a supranuclear Golgi complex and many apical zymogen granules
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29
Q

what are mucous neck cells of fundic glands of the stomach?

  • location
  • secretes…
A
  • mucous neck cells are located in the neck of the gland interspersed with parietal cells
  • they are shorter than the surface mucous cell and contains considerable less mucinogen in the apical cytoplasm.
  • they produce a soluble mucus compared with the insouble, cloudy mucus produced by surface mucous cells.
  • release of mucinogen granules is induced by vagal stimulation (secretion do not occur in the resting stomach)
  • they possess short microvilli, apical mucous granules, a prominent golgi complex, numberous mitochondria and some basal RER.
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30
Q

what are DNES cells of fundic glands of the stomach?

A
  • DNES cells are also referred to as enteroendocrine cells (also APUD cells)
  • they include more than a dozen types of cells that house many small hormone-containing granules, usually concentrated in the basal cytoplasm. each secretes only one hormone.
  • they possess an abundant of mitochondria and RER and a well developed Golgi complex.
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31
Q

how are cardiac and pyloric glands different to fundic glands of the stomach?

A

cardiac and pyloric galnds are coiled tubular mucus-secreting glands and they lack cheif cells

32
Q

what is gastric intrinsin factor?

A

gastric intrinsic factor is secreted by the parietal cells of the gastric glands of the stomach. it is a glycoprotein that bind to vitamin B12 and is essential for its absorption, which occurs in the distal part of the ileum.

33
Q

what are the the components of gastric juice?

A

in addition to water and electrolytes, there are 4 major components of gastric juice:

1. HCl - (secreted by parietal cells)
2. Pepsin - (secreted as pepsinogen by chief cells)
3. Mucus 
4. intrinsic factor - (secreted by parietal cells)
34
Q

how is HCl secretion stimulated by parietal cells?

A

parietal cells have 3 different types of membrane receptors for substances that activate HCl secretion:

- gastrin receptors
- histamine H2 recetors
- acetylcholine M3 receptor

activation of gastrin receptor by gastrin, secreted by pylorous and the duodenum.

35
Q

how is gastric secretion regulated?

A

gastric secretion is regulated by neural activity (vagus nerve) and by several hormones.
1. gastrin and histamine - released by enteroendocrine cells in the gastric and duodenal mucosa, together with acetylcholine released by parasympathetic nerve fibres of the vagus nerve, stimulate of HCl.

2. somatostatin - produced by enteroendocrine cells of the pylorus and duodenum, inhibits the release of gastrin and thus indirectly inhibits HCl secretion.
3. urogastrone (human epidermal growth factor) - produced by brunner glands of the duodenum, and gastric inhibitory peptide along with prostaglandins, produced by enteroendocrine cells in the small intestine, dirtectly inhibits HCl secretion
36
Q

how is HCl secretion directly inhibited?

A

HCl is directly inhibited by Urogastrone (produced by brunners glands of the duodenum), gastric inhibitory peptide along with prostaglandins (produced by enteroendocrine cells in the small intestine).

37
Q

how is HCl secretion of the stomach indirectly inhibited?

A

HCl secretion is indirectly inhibited by somatostatin (produced by enteroendocrine cells in the pyloric and duodenum) which inhibits the release of gastrin

38
Q

how is gastric HCl release stimulated?

A

gastrin and histamine (released by enteroendocrine cells in the pyloric and duodenal muscoa), with acetylcholine (released by parasympathetic nerve fibres of the vagus nerve) stimulate HCl secretion.

39
Q

how long is the small intestine?

how is the small intestine divided?

A

the small intestine is the longest component of the digestive tract, measuring over 6m
the small intestine is divided into three anatomic portions:
1. Duodenum (~25cm long): is the first shortest and widest part of the small intestine. begins at the pylorus of the stomach and ends at the duodenojejunal junction

  1. Jejunum (~2.5m long): begins at the duodenojejunal junction. gradually changes its morphologic characteristics to become the ileum
  2. Ileum (~3.5m long): continuation of the jejunum, ending at the ileocecal junction.
40
Q

how is the absorptive surface area of the small intestine increased?

A

the absorptive surface area of the small intestine is increased by a factor of 400-600 by a collection of luminal surface modifications, namely:

  1. Plicae circulares (circular folds): 3-fold
  2. Villi: 10-fold
  3. Microvilli: 20-fold
41
Q

what are Plicae circulares?

A

Plicae circulares (circulare folds), also known as the valves of Kerckring, are permanent transverse folds that contain a core of submucosa.

each fold is circularly arranged and extends about a half to two thirds the way around the circumference of the lumen.

the folds begin to appear about 5-6cm beyond the pylorus. most numerous in the distal part of the duodenum and the beginning of the jejunum and become reduced in size and frequency in the middle of the ileum.

the Plicae circulares increase the surface area by 2-3 fold

42
Q

what are intestinal villi?

A

intestinal villi are finger-like and leaf-like projections of the mucosa that extend 0.5-1.5mm into the lumen.
they completely cover the surface of the small intestine.

intestinal villi possess in there connective tissue tissue core (lamina propria), numerous plasma cells and lymphocytes, fibroblasts,mast cells, smooth muscle cells, capillary loops and a single lacteal

intestinal villi increase the surface area 10-fold

43
Q

what are microvilli of the small intestine?

A

microvilli are found on the apical surface of epithelial cells of each villus of the small intestine and provide a major amplification of the luminal surface.

they possess actin filaments that interact with myosin filaments in the terminal web

microvilli increase the surface area about 20-fold

44
Q

what type of epithelia is found in the mucosa of the small intestine?
what types of cells make up this epithelia?

A

the epithelia is simple columnar

it is composed of goblet cell, surface absorptive cells and some DNES cells

45
Q

what are goblet cells found in the small intestine?

A

goblet cells are unicellular cells that produce mucinogen, which accumulates in membrane-bounded granules, distending the apical region (theca) of the cell.
goblet cells have their nucleus and other organelled in the basal region (stem) of the cell
goblet cells increase in number from the duodenum to the ileum

46
Q

where is the small intestine is the number of goblet cells the greatest?

A

in the ileum

the number of goblet cells increases from the duodenum to the ileum

47
Q

what is mucinogen (related to the small intestine)?

A

mucinogen is prodcued by goblet cells in the small intestine and accumulates in membrane-bounded granules, distending the apical region of the cell.

after being released, mucinogen becomes hydrates and is thus converted to mucin, a thick, viscous substance that acts as a protective coating of the epithelial lining of the lumen

48
Q

what are surface absortive cells (enterocytes) as in the small intestine?

A

enterocytes are tall columnar cells with numberous mitochondria, SER, and RER and a golgi complex

they possess a layer of closely packed microvilli (striated border) on their free apical surface

enterocytes have a glycocalyx, which overlies the microvilli and binds various enzymes, including disaccharides and dipeptides

49
Q

what do DNES cells produce and secrete in the mucosa of the small intestine?

A

DNES cells produce and secrete gastrin, cholecystokinin and gastric inhibitory peptide

50
Q

of the mucosa of the small intestine, what does the lamina propria contain?

A

the lamina propria occupies the cores of the villi and the interstices between the numerous glands - crytps of Lieberkuhn.

it consists of loose connective tissue with lymphoid cells, fibroblasts, mast cells, smooth muscle cells, nerve endings and lymphoid nodules.

the lamina propria found in the villi houses lacteals and capillary loops

51
Q

what are crypts of Lieberkuhn?

  • location
  • cell composition
A

crypts of Lieberkuhn are simple tubular glands that extend from the intervillious spaces to the lamina propria and muscularis mucosae of the small intestine.

the glands are composed of goblet and oligomucous cells, columnar cells (similar to absorptive cells), DNES cells, regenerative cells and Paneth cells.

52
Q

what are Paneth cells?

A

Paneth cells are found at the base of the crypts of Lieberkuhn of the small intestine

they are pyramidal cells that secrete the antibacteria enzyme lysozyme stored in large, apical, membrane-bounded secretory granules. they display extensive RER (basally), a large supranuclear golgi complex and many mitochondria

they also release defensins and tumor necrosis factor alpha

53
Q

what is the composition of lymphoid nodules as found in the small intestine?

A

lymphoid nodules are usually small and solitary and are located in the lamina propria of the dupdenum and the jejunum.

in the ileum, they increase in size and number where they form large contiguous aggregates, known as peyers patches, which frequently extend through the muscularis mucosae into the submucosa.

54
Q

what are peyers patches?

- cell types found

A

peyers patches are large contiguous aggregates of lymphoid tissue found in the ileum and extend through the muscularis mucosae into the submucosa.

Peyers patches contain:

  • M (microfold) cells
  • activated B lymphocytes
  • plasma cells
55
Q

what are M (microfold) cells?

A

M cells are highly specialised, have an unusual shape, and lie in the epithelium over lymphoid nodules and peyers patches.

they are derived from undifferentiated cells of the crypts of Lieberkuhn.

they sample antogens as well as bacteria, viruses and parasitic microorganisms.

56
Q

what is the components of the submucosa of the small intestine?

A

the submucosa of the small intestine consists of fibroelastic connective tissue containing blood and lymphatic vessels, nerve fibres and Meissner plexus.

the submucosa also contain Brunners glands, present only in the duodenum.

57
Q

what are Brunners glands?

A

Brunners glands are found only in the submucosa of the duodenum.
they produce alkaline fluid and urogastrone

the alkaline fluid protects the duodenal epithelium from the acidic chyme of the stomach.
urogastrone is a polypeptide hormone (human epidermal growth factor) that enhances epithelial cell division and inhibits gastric HCl production.

58
Q

why is pepsinogen, and other enzymes secreted from the gastric pits, secreted in an inactive form?

A

enzymes secreted intot he stomach are secreted in the inactive form as to not digest the glands before the enzyme reaches the lumen of the stomach.

59
Q

what is the composition of the muscularis externa of the small intestine?

A

the muscularis externa is composed of two layers, an inner circular layer and and outer longitudinal layer.
Auerbach plexus is housed between the two layers

the inner layer participates in the formation of the ileocecal sphincter.

60
Q

is the small intestine covered in serosa?

A

most of the small intestine is covered in serosa. it covers all of the jejunum and ileum and the distal part of the duodenum.

the first 2cm of the duodenum is covered by adventita.

61
Q

what contributes the large intestine?

A

the large intestine is made up of the cecum, the colon (ascending, transverse, descending, sigmoid), the rectum, the anal canal and the appendix.

62
Q

what is the primary function of the large intestine?

A

the primary function of the large intestine is the absorption of electrolytes, fluids and gases.
dead bacteria and indigestible remnants of the ingested material are compacted into feces.

the large intestine produced abundant mucus, which lubricants its lining and facilitates the passage and elimination of feces.

63
Q

what is the composition of the mucosa of the cecum and colon?

  • epithelium
  • lamina propria
  • muscularis mucosae
A

the cecum and colon lacks villi and possesses no specialised folds, unlike the former part of the alimentary tract, the small intestine.

the epithelium of the cecum and colon is simple columnar with numerous goblet cells, surface absorptive cells and DNES cells

the lamina propria is similar to that of the small intestine, possessing lymphoid nodules and lymph vessels, and closely packed crypts of Lieberkuhn, which lack paneth cells

the muscularis mucosae consists of an inner circular and outer longitudinal layer of smooth muscle cells

64
Q

what cells are not present in the crypts of Lieberkuhn of the cecum and colon?

A

they lack paneth cells

65
Q

what are teniae coli?

A

teniae coli are three narrowed, thickened equally spaced bands of the outer longitudinal layer of the muscularis externa.

they are primarily visible in the cecum and colon and absent in the rectum, anal canal and the vermiform appendix.

66
Q

what are Haustra coli?

A

Haustra coli are sacculations between the teniae coli on the external surface of the cecum and the colon.

67
Q

what covers the cecum and the colon?

A

adventitia covers the ascending and descending portions of the colon

serosa covers the cecum and the remainder of the colon. fat-filled outpockets of the serosa are characteristic of the transverse and sigmoid colon

68
Q

what type of epithelium is found in the mucosa of the anal canal?

A
  1. simple columnar to simple cuboidal proximal to the anal valves
  2. stratified squamous nonkeratinised distal to the anal valves
  3. changes to stratified squamous keratinised (epidermis) at the anus.
69
Q

what is the structure of anal valves?

A

the anal mucosa displays longitudinal folds called anal columns (rectal columns of Morgagni), which join each other to form anal valves

the regions between adjacent valves are known as anal sinuses.

70
Q

what is the external anal sphincter composed of?

A

the external anal sphincter is composed of skeletal muscle whose superficial and deep layers invest the anal canal

it exhibits continuous tonus, thus maintaining a closed anal orifice. the degree of tonus is under voluntary control, so the retention or evacuation of feces normally can be controlled at will

71
Q

what is the internal anal sphincter composed of?

A

the anal muscularis externa is composed of an inner circular layer and an outer longitudinal layer of smooth muscle.

the inner circular layer forms the internal anal sphincter.

72
Q

what is the appendix?

A

the appendix is a short diverticulum arising from the blind terminus of the cecum.
it has a narrow, stellate, or irregularly shaped lumen that often contains debris
the wall is thickened by large aggregates of lymphoid nodules in the mucosa and even in the submucosa

73
Q

what is the type of epithelium found in the mucosa of the appendix?

A

simple columnar and contains surface columnar cells and goblet cells

74
Q

how are carbohydrates digested? (3 steps)

A
  1. salivary and pancreatic amylases hydrolyse carbohydrates to disaccharides
  2. disaccharides present in the glycocalyx of the brush border cleave disaccharides into monosaccharides
  3. monosaccharides are actively transported into surface absorptive cells and then discharged into the lamina propria, where they enter the circulation
75
Q

how are proteins digested? (3 steps)

A
  1. pepsin in the lumen of the stomach partially hydrolyses proteins, forming a mixture of high-molecular-weight polypeptides.
  2. pancreatic proteases within the lumen of the small intestine hydrolyse the polypeptides recieved from the stomach into dipeptides
  3. dipeptides are cleaved into amino acids by dipeptidases present in the glycocalyx of the brush border. amino acids are transported into surface absorptive cells, discharged into the lamina propria, where they enter the circulation

Histology (16 decks)

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