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SOM 203 > WEEK 1: OVERVIEW OF THE GIT > Flashcards

WEEK 1: OVERVIEW OF THE GIT Flashcards

1
Q

State the structures of the GIT from the mouth ending at the anus.

A

*Long hollow tube

(Mouth, esophagus, stomach, duodenum, jejunum, ileum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum & anus).

NB! Sphincters and appendix!

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2
Q

State the accessory structures of the GIT.

A

Salivary glands, liver, gall bladder & exocrine pancreas
Teeth & tongue

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3
Q

State the structures that make up the upper and lower GIT.

A

Upper GIT
*(Mouth, esophagus, stomach).

Lower
*(Intestines aka ‘bowels’)

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4
Q

Describe the 4 continuous layers that make up the wall of the GIT from innermost to outermost.

A

Four (4) Continuous layers:
*Mucosa (innermost layer)

*Submucosa

*Muscularis externa (muscular layer)
-(Inner) Circular smooth muscle fibers
-(Outer) Longitudinal smooth muscle fibers

  • Serosa or visceral peritoneum (outer layer)
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5
Q

Describe the mucosa layer of the GIT.
*its sublayers
*3types of cells

A

(i) Mucosa (inner layer)

Lines the luminal surface of the GIT.

*Has 3 sub-layers

-Mucous membrane, lamina propria, muscularis mucosa

*Mucous membrane consists of 3 types of cells: exocrine gland cells (digestive juices), endocrine gland cells (GI-hormones) & epithelial cells (absorption)

Gut-associated lymphoid tissue (GALT) found in the lamina propria (a thin connective tissue).

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6
Q

What is the main function of the mucosa?

A

Main function of the mucosa is mucus production by epithelial cells for protection.

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7
Q

Describe the submucosa of the GIT.

A

Submucosa

*a thick connective tissue layer.
*Has blood vessels, nerves (submucosal plexus), lymphatics & secretory glands.

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8
Q

Describe the muscularis externa of the GIT.
Name the 2 types of smooth muscle fibers.
*Name the nerves found between the 2 layers.

A

Muscularis externa (muscular layer)

*The major smooth muscle layer of the GIT

-Inner circular smooth muscle fibers; contraction of the fibers reduces the lumen diameter

-Outer longitudinal smooth muscle fibers; contraction of the fibers shortens the tubular structure

A network of nerves (the myenteric plexus) lies between the 2 layers.

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9
Q

Describe the serosa or visceral peritoneum of the of the GIT.
*State its function.

A

Serosa or visceral peritoneum (outermost layer)

*Secretes serous fluid (watery & slippery)

*Helps lubricate and prevent friction between the digestive organs & the viscera.

*Serosa is continuous with a supportive structure (= mesentery); ensures the digestive organs in the abdominal cavity are held in place but with relative flexibility to move about.

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10
Q

GIT is part of the external environment.
State the characteristics that support this statement.

A

Stomach pH falls to 2; plasma pH compatible with life is 6.8 - 8.0.

*Digestives enzymes are secreted in their inactive forms (zymogens); become active only ‘outside’ the body.

*Harmless & beneficial bacteria found in the GIT particularly in the colon; however, they may become lethal if they found their way inside the “body” through an opening of surface of the mucus membrane.

*Complex food that we consume would initiate immune response if they were to be take inside the body undigested.

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11
Q

State the 4 factors that regulate the GIT function.

A

(i) Autonomous smooth muscle function
(ii) Intrinsic nerve plexuses
(iii) Extrinsic nerves
(iv) GI hormones

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12
Q

Describe the role of autonomous smooth muscle function in regulation of GIT function.

A

*Self-induced, spontaneous, rhythmic electrical activity, slow-wave potentials= basic electrical rhythm (BER)

*BER generated by pacemaker cells = interstitial cells of Cajal located in the muscularis externa

*BER propagated via gap junctions

*Functional syncytium= the whole smooth muscle layer

*Depolarization trigger for an AP is Ca2+
Repolarization trigger for an AP is K+

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13
Q

Describe the role of intrinsic nerves plexuses in the regulation of GIT function.

A

Nervous system of the GIT= enteric nervous system

*Consists of interneurons, sensory & motor neurons

*Found in the submucosa and smooth muscle layers.

*Permits self-regulation.

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14
Q

Describe the regulation of the GIT via the extrinsic nerves.

A

*Originate from the PNS & SNS of the autonomic nervous system.

*SNS slows down the digestive tract contraction and secretion.

*Action of the PNS (via the vagus nerve (CNX)) promotes GI tract contraction & secretion plus GI hormonal release.

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15
Q

State the main GI hormone in GI regulation.

A

GI hormones
As previously stated, mucous membrane consists of several cells including specialized endocrine cells.

Major GI hormones: gastrin, secretin, CCK & glucose-dependent insulinotropic peptide (GIP)

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16
Q

Describe the role of gastrin in GI regulation.
Where is it released from?
Where does it work?

A

*It acts in multiple ways to increase the secretion of HCL, and pepsinogen involved in protein digestion.

*It enhances gastric motility, stimulates ileal motility, relaxes ileocecal sphincter and induces mass movement in the colon.

Thus, overall keep the contents moving through the tract on arrival of a new meal.

*It is a tropic not only to the stomach mucosa but also to the small intestine mucosa, helping maintain a well-developed, functionally viable digestive tract lining.

2.Gastrin is a hormone that is produced by ‘G’ cells in the lining of the stomach and upper small intestine.

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17
Q

What stimulates the release of secretin?

A

The presence of acid in the duodenum as the stomach empties into the duodenum.

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18
Q

Describe the role of secretin hormone.

A

*It prevents gastric emptying to prevent further acid from entering the duodenum until the acid already present is neutralized.

*It inhibits gastric secretion to reduce the amount of acid being produced.

*It stimulates pancreatic duct cells to release a large volume of aqueous Sodium Bicarbonate, which is emptied into the duodenum to neutralize the acid.

*It stimulates the release of sodium bicarbonate rich bile, which likewise is emptied into the duodenum and helps to prevent damage to the duodenal walls and provides a suitable environment for optimal functioning of pancreatic digestive enzymes, which are inhibited by acid.

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19
Q

What stimulates the release of CCK?

A

It is stimulated by fats and other nutrients when they enter the duodenum as chyme empties from the stomach.

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20
Q

State the role of CCK hormone in the GIT.
What is its broad function?
What does CCK stand for?
Where is it released from?

A

*Inhibits gastric motility and secretion, thereby allowing adequate time for the nutrients already in the duodenum to be digested and absorbed

*It stimulates the pancreatic acinar cells to increase the secretion of pancreatic enzymes, which continue the digestion of these nutrients in the duodenum, this is especially important for fat digestion by the pancreatic lipase.

*It also causes the contraction of the gall bladder and relaxation of the sphincter of Oddi so that bile is emptied into the duodenum to aid in fat digestion.

*It is also an important regulator of food intake. It plays an important role in satiety, the sensation of having had enough to eat.

2.It facilitates the digestion of ingested nutrients.

3.Cholecystokinin.

  1. CCK is synthesized and released by enteroendocrine cells in the mucosal lining of the small intestine (mostly in the duodenum and jejunum), called I cells
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21
Q

What does GIP stand for?
What stimulates its release?
What is its function?

A

*Glucose-dependent insulinotropic peptide
*It is stimulated by the presence of meal, especially glucose in the digestive tract.
*It initiates the release of insulin in anticipation of absorption, in feed forward fashion.

Insulin controls the absorptive phase.

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22
Q

Describe the different receptors of the GIT.

A

(i) Chemoreceptors
What kind of chemical is in the lumen?

(ii) Mechanoreceptors (pressure receptors)
How full is the gut?

(iii) Osmoreceptors
Responds to the change in the molar concentration of a chemical

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23
Q

State the 4 main digestive processes.
Ste the 3 other processes

A

1.
(i) Motility
(ii) Secretion
(iii) Digestion (chemical breakdown of food particles)
(iv) Absorption

2.
(v) Ingestion (food consumption)
(vi) Mechanical breakdown of food particles (=chewing)
(vii) Excretion

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24
Q

What is motility?
State and describe the 2 types of motility.
What controls gastric motility throughout the GIT?

A

1.*Motility refers to muscular contractions that mix food and move forward the contexts within the GIT.

2.*Propulsive movements: propel or push food forward through the digestive tract.

*Mixing movements:
-mixing food with the digestive juices
-facilitate absorption by exposing all parts of the intestinal contents to the absorbing surfaces of the digestive tract.

3.*Complex involuntary mechanisms

25
Q

Smooth muscle contraction within the walls of the digestive organs accomplishes movement through most of the digestive tract.

State the two exceptions in the GIT where motility involves skeletal muscle rather than smooth muscle.

State 3 processes in the GIT that are under voluntary control.

A

*Early part of the esophagus
*External anal sphincter.

*Chewing, swallowing, defecation.

26
Q

Describe secretion as one of the major processes of the GIT.

A

Produces both exocrine and endocrine secretions.

consists of water, electrolytes and other organic substances such as mucus and enzymes.

27
Q

What is digestion?
State the 3 main type of foods broken down and their absorbable units.

A

Digestion is the process of breaking down food into smaller components that can be absorbed into the bloodstream.

*Carbohydrates into monosaccharides (ie glucose, fructose, galactose).
*Proteins into dipeptides & amino acids
*Fats into monoglycerides (glycerol) & free fatty acids

28
Q

What is absorption?

A

*Ensures absorbable units move from the GIT lumen into the blood or lymph where they become available for use by tissues.

*Most takes place in the small intestine.

29
Q

Describe the events that happen in the oral cavity when digestion starts.

A

1.Ingestion of food into the mouth.
2.Mastication: the motility of slicing, tearing, grinding and mixing of ingested food by the teeth in the mouth.
3.Secretion of saliva from the salivary glands which starts the digestion of salivary amylase into MALTOSE.

30
Q

What is occlusion and malocclusion?

A

*Occlusion is when the upper and lower teeth fit together when the jaw is closed.

*Malocclusion is when the upper and lower teeth do not fit together when the jaw is closed.
It is usually due to abnormal positioning of teeth, being overcrowded or too big.

31
Q

State the functions of chewing or mastication.

A

*To grind and break food into smaller pieces to facilitate swallowing and to increase surface area of food on which the salivary enzymes can act on.

*To mix food with saliva
*To stimulate taste buds

32
Q

State the function of saliva.

A

*Contains salivary enzyme which is used in the initial digestion of carbohydrates.
*Facilitates speech
*Is important for oral hygiene.
*Solvent for molecules that can stimulate the taste buds.

33
Q

State the contents found in saliva and their roles.

A

Water: 99.5%
Electrolytes: 0.5%
*Amylase- break down carbohydrates into maltose
*Mucus-moistening food particles and making them stick together.
*Lysozyme: destroys bacteria by
-Breaking its cell wall
-Bind to glycoprotein that binds IgA antibody
-By lactoferrin which tightly binds to the iron needed for
the bacterial multiplication
-Rinsing away material that may be a source of food for
the bacteria.

34
Q

Describe the 2 reflexes that stimulate saliva secretion.

A

*Simple salivary reflex:

Stimulation of the chemoreceptors and pressor receptors in the oral cavity send impulses to the salivary center in the medulla where impulses are sent to salivary glands to release saliva.

*Conditioned or acquired salivary reflex:

Occurs without oral stimulation, one may see, think, smell or hear preparation of food initiates. The impulses that arise are sent to the cerebral cortex which will send then to the medullary salivary center.

35
Q

Describe the effect of parasympathetic and sympathetic effect on the saliva secretion.

A

PARASYMPATHETIC: Abundant, watery saliva rich in enzymes

SYMPATHETIC: Small volume, thick saliva rich in mucus.

36
Q

What is the process in the GIT through which all food components are digested?

A

Hydrolysis

37
Q

Describe what happens at the pharynx and esophagus.

A

SWALLOWING: The entire process of moving food from the mouth through the esophagus into the stomach.

38
Q

Describe the process of swallowing. (11 steps)

A

1.tongue Presses bolus against the hard palate
2.Tongue propels bolus to the pharynx
3.Swallowing center inhibits the respiratory center.
4.Elevation of the uvula prevents food from entering into the nasal pathways.
5.Position of the tongue prevents food from re-entering into the mouth.
6.Tight alignment of the vocal cords prevent food from entering into the trachea.
7.Epiglottis fold over the closed glottis.
8.Contraction of the pharyngeal muscles pushes the bolus through opened pharyngo-esophageal sphincter into the esophagus.
9.Pharyngo-esophageal sphincter closes, oropharyngeal structures return to resting position and breathing resumes.
10.Persistalsis propels the bolus down the length of the esophagus
11.Gastro-esophageal sphincter relaxes as peristalsis pushes bolus into the stomach.
Swallowing is complete. Sphincter again contracts.

39
Q

What is the function of the following sphincters?
*Pharyngoesophageal sphincter
*Gastroesophageal sphincter

A

*Prevents air entering the digestive tract during breathing.
*Prevents reflux of gastric contents.

40
Q

Describe the primary and secondary peristaltic waves.
How long does primary peristalsis last for?
What controls peristalsis?

A

First, there is a primary peristaltic wave, which occurs when the bolus enters the esophagus during swallowing. The primary peristaltic wave forces the bolus down the esophagus and into the stomach in a wave lasting about 8–9 seconds.

The wave travels down to the stomach even if the bolus of food descends at a greater rate than the wave itself and continues even if for some reason the bolus gets stuck further up the esophagus.

*If the bolus gets stuck or moves slower than the primary peristaltic wave (as can happen when it is poorly lubricated), then stretch receptors in the esophageal lining are stimulated and a local reflex response causes a secondary peristaltic wave around the bolus, forcing it further down the esophagus, and these secondary waves continue indefinitely until the bolus enters the stomach.

*The process of peristalsis is controlled by the medulla oblongata.

41
Q

Describe the role of the stomach in digestion.

A

*Provides a temporary storage for food until it can be emptied into the small intestine at a rate optimal for digestion and adsorption.
*The stomach secretes hydrochloric acid and enzymes that begin protein digestion.
*The stomach mixing movements mixes the food ingested with gastric secretions to produce a thick liquid mixture called CHYME.

42
Q

Describe the role of the stomach in digestion.

A

*Provides a temporary storage for food until it can be emptied into the small intestine at a rate optimal for digestion and adsorption.
*The stomach secretes hydrochloric acid and enzymes that begin protein digestion.
*The stomach mixing movements mixes the food ingested with gastric secretions to produce a thick liquid mixture called CHYME.

43
Q

Describe the digestive processes that take place in the stomach.

A

*Gastric filling: via RECEPTIVE RELAXATION, the rugae provide more surface area as they flatten when the stomach fills.

*Gastric storage: in the antrum of the stomach
*Gastric mixing: takes place in the antrum of the stomach via vigorous contraction of the muscles due to the AP conducted from the FUNDUS which was initiated by the INTERSTITIAL CEELS OF CAJAL. The antrum has thick muscular layer.
CHYME is then produced.

GASTRIC EMPTYING:

44
Q

Describe the process of gastric emptying.

A

1.A peristaltic contraction originates in the upper fundus and sweeps down toward the pyloric sphincter.
2. The contraction become more vigorous as it reaches the thick-muscled antrum.
3.The strong antral peristaltic contraction propels the CHYME FORWARD.
4. A small portion of chyme is pushed through the partially open sphincter into the duodenum.

-The stronger ANTRAL CONTRACTION, the more chyme is emptied with each contractile wave.

45
Q

List the factors that influence gastric emptying in the stomach.

A

1.The amount of CHYME in the stomach, gastric distention
2.Degree of fluidity
3.Gastrin hormone
4.The PNS and SNS

46
Q

List factors of the duodenum that influence gastric emptying.

What cells release CCK AND Secretin?

A

*Prescence of fat, acid, hypertonicity or distention.

*THEY INDUCE THE RELEASE OF: CCK, Secretin

CCK: I cells.
SECRETIN: S cells
NOTE: Both these cells are enteroendocrine cells.

47
Q

State factors outside the GIT that can influence gastric emptying.

A

*Emotions
*Intense pain: sympathetic activity stimulated, inhibits gastric motility and emptying.

48
Q

What is vomiting?
What is the term used to refer to vomiting?

A

*It is forceful expulsion of gastric contents out through the mouth.
*Emesis

49
Q

State factors that can cause vomiting.

A

*Tactile stimulation of the throat.
*Irritation or distension of the stomach.
*Elevated intracranial pressure caused by cerebral hemorrhage.
*Rotation of the head causing dizziness
*Chemical agents
*

50
Q

State the effect of vomiting in the body.

A

*Can result in loss of large secreted fluids and acids that are normally reabsorbed.
*There will be low plasma volume resulting in dehydration which can affect circulation.
*Loss of acid lead to metabolic alkalosis.

51
Q

Describe the process of vomiting.

A
52
Q

State the effect of vomiting in the body.

A

*Can result in loss of large, secreted fluids and acids that are normally reabsorbed.
*There will be low plasma volume resulting in dehydration which can affect circulation.
*Loss of acid lead to metabolic alkalosis.

53
Q

Where is gastric juice produced?
State the 4 components of gastric juice.

State the cells in the gastric pits and glands that produce these components.

A

1.*It is secreted by the gastric glands located at the base of the gastric pits.

2.*HCL- Parietal cells
*Pepsinogen-Chief cells
*Mucus-Mucous cells
*Intrinsic Factor-Parietal cells

54
Q

State the secretions of the following entero-endocrine cells.

A

G cells- Gastrin: stimulate parietal cells
I cells-Secretin
D cells-: Somatostatin: Inhibit parietal cells, G cells and ECL cells
Endo-chromaffin cells: Histamine

55
Q

Describe the secretion of HCL process.

A
56
Q

State the functions of HCL.

A

*Provides optimal pH for the activation of Pepsinogen into pepsin
*It denatures proteins
*HCL kills most of micro-organisms ingested with food, although some grow and multiply in the large intestine

57
Q

Describe the 4 ways how the gastric mucosal barrier prevents the stomach lining from gastric secretions.

A

*The gastric mucosal cells are impermeable to hydrogen ion so that HCL cannot penetrate into the cells.

*The cells are joined by tight junctions that prevent HCL from penetrating between them.

*A mucus coating over the gastric mucosa serves as a physical barrier to acid penetration between them.

*The bicarbonate ion rich mucus also serves as a chemical barrier that neutralizes acid in the vicinity of the mucosa.
-Even when the luminal pH is 2, the mucosa pH is 7.

58
Q

State 2 substances with can be absorbed by the stomach mucosa.

A

*Alcohol
*Aspirin

SOM 203 (13 decks)

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