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Organs Systems Anatomy > Digestive System Physiology > Flashcards

Digestive System Physiology Flashcards

1
Q

What are the 6 essential activities of the digestive system ?

A

Can be described as a disassembly line through 6 stages :

  • ingestion
  • mechanical digestion
  • propulsion
  • chemical digestion
  • absorption
  • defecation
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2
Q

What is implied by mechanical digestion ?

A

Chewing (mouth)
Churning (stomach)
Segmentation (small ingestion)

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3
Q

What is implied by propulsion ?

A

Swallowing (oropharynx)

Peristalstism (esophagus, stomach, small intestine, large intestine)

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4
Q

Where is the site of ingestion ?

A

Only the mouth

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5
Q

What is the role of mechanical digestion ?

A

Preparing the food for chemical digestion by enzymes

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6
Q

Which place is the major absorptive site ?

A

Small intestine

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7
Q

What is absorption

A

The passage of digestive end products + vitamins minerals and water

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8
Q

What is defecation ?

A

Elimination of indigestible substances

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9
Q

What are the receptors involved into digestion ?

A

Mechanoreceptors and chemoreceptors

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10
Q

Give example of stimuli provoking digestive activity

A
  • stretch of organs by food in the lumen
  • osmolarity and pH of the content
  • presence of substrates and end products of digestion
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11
Q

What the reflexes initiated by GI stimuli ?

A

Activation or inhibition of glands secreting digestive juice in the lumen or hormones into the blood
Stimulate the smooth muscles of the GI walls to mix lumen contents and moves them along the tract

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12
Q

What are the types of exercise controls over the digestive system ?

A

Extrinsic

Intrinsic

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13
Q

What kind of exercise control takes place in the intrinsic control ?

A

Short reflexes : mediated by the local enteric in response to stimuli arising in the GI tract
Long relfexes : initiated by stimuli arising inside or outside the GI tract and involves CNS centers and extrinsic autonomic nerves

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14
Q

Describe the path of short reflex ?

A
  • ingestion of food
  • mechanoreceptors/ chemoreceptors
  • intrinsic nerve of organ is activated
  • effector contracts or secretes
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15
Q

Describe the path of long reflexes

A
  • receptors
  • brain
  • CNS
  • autonomic nervous system (sympathetic/ parasympathetic)
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16
Q

List the accessory organs of the mouth

A
  • tongue
  • teeth
  • salivary glands
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17
Q

What is the role of the salivary glands ?

A

Moisturizing the food to help forming the bolus

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18
Q

What is the role of saliva ?

A
  • cleanse the mouth
  • dissolve food chemicals so they can be tasted
  • moistens food and helps compacting it into a bolus
  • contains enzymes that initiate the chemical breakdown of starchy food
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19
Q

Name the extrinsic salivary glands

A
  • parotid gland
  • submandibular gland
  • sublingual gland
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20
Q

What is the composition of saliva ?

A

Mostly water, hypoosmotic, slightly acidic.
Contains electrolytes, digestive enzymes (salivary amylase and lingual lipase), proteins (mucin, lysozyme and IgA) and metabolic wastes (urea and uric acid)

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21
Q

How does the control of salivation work ?

A

When food enters the mouth, extrinsic salivary glands are activated and this reaction is controlled by the parasympathetic division. The salivatory nuclei is located between the pons and the medulla oblongata (brain stem).
The facial and glossopharyngial cranial nerve trigger output of watery (serous) enzyme-rich saliva.

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22
Q

What is the role of the teeth ?

A
  • masticate or chew the food
  • tear and grind the food
  • breaking food into smaller fragments
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23
Q

What are the anatomical divisions of the pharynx ?

A
  • oropharynx

- laryngopharynx

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24
Q

Describe the digestive process taking place in the mouth

A
  • ingestion
  • teeth begin mechanical digestion by chewing
  • mouth initiates propulsion through swallowing
  • saliva starts the chemical breakdown of polysaccharides (salivary amylase will breakdown starch and glycogen and lingual lipase is a fat digesting enzyme which also acts in the acidic environnement of the stomach)
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25
Q

What is the role of pharynx and esophagus ?

A

Pass food from mouth to stomach

26
Q

What are the 2 major phases of swallowing

A
  • buccale

- pharyngeal / esophageal

27
Q

Describe the 5 phases of swallowing

A

1- BUCCALE PHASE the upper pharyngeal sphincter is contracted. During the buccale phase the tongue presses against the hard palate, forcing the food bolus into the oropharynx where the involuntary phase begins.
2- the uvula and larynx rise to prevent food from entering respiratory passageways. The tongue blocks off the mouth, the upper esophageal sphincter relaxes allowing food to enter esophagus.
3- constrictor muscles of the pharynx contract forcing food into the esophagus, the upper esophageal sphincter closes.
4- food is moved through the esophagus to the stomach by peristalsis.
5- gastroesophageal sphincter opens and food enters the stomach

28
Q

Which part of the pharynx blocks the passage way while swallowing ?

A

The epiglottis

29
Q

Describe chemical digestive processes taking place in the stomach

A

Hydrochloride acid, pepsin (and rennin in infants) production for proteins digestion
Lingual lipase digests takes care of triglycerides digestion
Lipid soluble substances like alcohol and aspirin go into blood
Secretion of intrinsic factor responsible for the absorption of vitamin B12 (required to produce mature erythrocytes)

30
Q

What are the site of stimulii for gastric secretion

A

Head : cephlice phase
Stomach : gastric phase
Small Intestine : intestinal phase

31
Q

Describe the cephalic phase of gastric secretion

A

Happens before the food enters mouth / stomach. 2 pathways :

Sight or thought of food will reach cerebral cortex causing a conditioned reflex stimulating hypothalamus and medulla oblongata and finally the vague nerve.

Smell, taste will impact directly the hypothalamus and medulla oblongata.

32
Q

Describe the gastric phase 1 of digestion control

A
  • stomach distention activates stretch receptors
  • vagovagal reflexes are triggered, the stimuli reaches the medulla oblongata and the vagal nerve controlling the stomach secretory activity
  • local reflexes are triggered controlling directly stomach secretory activity
33
Q

Describe the gastric phase 2 of digestion control

A
  • food chemicals especially peptides and caffeine, as well as rising pH activate chemoreceptors
  • the chemical stimuli directly activates gastrin secreting enteroendocrine cells called G cells
  • G cells release gastrin in the blood which will stimulate the secretory activity of the stomach
34
Q

When the bolus reaches the stomach what happens to the pH in the stomach ?

A

PH in the stomach is higher than pH of the bolus, so when the bolus enters the stomach the overall pH diminishes.

35
Q

What are the inhibition factors of the cephalic phase ?

A
  • Loss of appetite

- depression

36
Q

What are the inhibition factors of the gastric phases ?

A
  • excessive acidity (pH < 2) : affecting G cells / gastrin secretion declines
  • emotional upset : affecting the sympathetic NS / overriding parasympathetic controls
37
Q

What are the two types of intestinal phase of digestion control ?

A
  • excitatory

- inhibitory

38
Q

Describe the intestinal phase 1 of digestion control

A
  • excitatory phase
  • in the presence of lowered pH, partially digested food, fats or hypertonic solution in the duodenum when the stomach starts to empty
  • intestinal gastrin release into blood
  • brief stimulatory effect on the secretory activity of the stomach
39
Q

Describe the intestinal phase 2 of digestion control

A
  • inhibitory
  • distention of the duodenum, presence of fatty, acidic, hypertonic chyme and / or irritants in the duodenum
  • this will inhibit local reflexes, vagal nuclei and activates sympathetic fiber that will cause the pyloric sphincter to tighten
  • this will activate antero gastric reflexes
  • trigger the release of enterogastrones : secretin, cholecystokinin and vasoactive intestinal peptide
40
Q

At what moment does the digestion start ?

A

When food enters into the pylorus

41
Q

What is the response of stomach to filling ?

A

Gastric motility and emptying

42
Q

What is the capacity of the stomach under constant pressure ?

A

1,5L of food

43
Q

How does the stomach manages to keep a constant pressure within its structure ?

A
  • reflex mediated receptive relaxation

- gastric accommodation

44
Q

Explain the reflex mediated relaxation of the stomach

A

Anticipation of and in response of food movement

Swallowing center of the brain stem and mediated by the vagus nerve acting on serotonin and no-releasing enteric neuron

45
Q

Explain the gastric accommodation

A

Ability of the visceral muscle to stretch without greatly increasing its tension and contracting expulsively

46
Q

Describe the gastric contractile activity

A

1) propulsion : peristaltic waves move from the fundus toward the pylorus / pyloric valve is closed
2) grinding : the most vigorous peristalsis and mixing action occur close to the pylorus / pyloric valve is closed
3) retropulsion : the pyloric end of the stomach acts as a pump that delivers small amounts of chyme in the duodenum, simultaneously forcing most of its contained material backward into the stomach

47
Q

What is the pace of gastric emptying ?

A

Within 4 hours after a meal but : the bigger the meal the faster the stomach empties
Fatty meals makes you angry faster because the stomach doesn’t digest the fats
So gastric emptying depends on the contents of the duodenum and on what happened in the stomach

48
Q

With which structures is associated the small intestine ?

A

Liver and pancreas

49
Q

What is the function of the small intestine ?

A
  • absorption

- intestinal juice production (1 to 2 L per day)

50
Q

What is bile ?

A

Yellow green alkaline solution containing bile slats, bile pigment, cholesterol, triglycerides, phospholipids and electrolytes but only bile salts and phospholipids interfere in the digestion

51
Q

What is pancreatic juice ?

A

Composed mainly of water, bicarbonate ions and enzymes

52
Q

Describe the hormonal regulation of bile and pancreatic secretions

A

1) chyme entering the duodenum causes the release of cholecystokinin and secretin from duodenal enteroendocrine cells
2) cholecystokinin and secretin enter the blood stream
3) cholecystokinin will induce the production of enzyme-rich pancreatic juice and secretin causes the secretion of HCO3- rich pancreatic juice
4) bile salts stimulate liver to produce bile more rapidly
5) cholecystokinin causes gallbladder to contract and hepatopancreatic sphincter to relax so bile can enter the duodenum —> start of fats digestion
6) during cephalic and gastric phases vagal nerve stimulation causes weak contractions of the gallbladder

53
Q

What are the primary functions of intestinal digestive activity

A

1) digestion with help of bile, digestive enzymes and bicarbonate ions imported from liver and pancreas
2) absorption accomplished by absorptive cells

54
Q

What is the most common motion of the small intestine ?

A

Segmentation

55
Q

Which factors can affect the segmentation rhythm ?

A
  • long and short reflexes which parasympathetic enhances and sympathetic activity decreases and hormones
56
Q

When does «true peristalsis occur ?

A

Later in the intestinal phase : motilin

57
Q

What are the digestive functions of the big intestin ?

A
  • absorb most of the remaining water from indigestible food residues
  • store the residues temporarily
  • eliminate them out of the body under the form of semi solid feces
58
Q

What stimulates the motility of the colon ?

A

Presence of food in the stomach activates the Gastrocolic reflex

59
Q

Describe the motility of the colon

A

It’s a mass peristalsis, where movements are long and slow but the contractile waves are powerful and called haustral contractions

60
Q

Describe the nervous control of defecation

A

1) distension or stretch of rectal walls due to movement of feces into the rectum stimulates stretch receptors present there.
2) stretch receptors transmit signal along afferent fibers of the spinal cord neurons
3) if it is convenient to defecate voluntary motor neurons are inhibited allowing the external anal sphincter to relax so that feces may pass.

Organs Systems Anatomy (13 decks)

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