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Physiology 214 > The digestive system-3 > Flashcards

The digestive system-3 Flashcards

1
Q

J-shaped chamber lying between oesophagus and small intestine

A

Stomach

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2
Q

Three parts of the stomach

A

-Fundus
(lies above gastroesophageal sphincter)
-Body (middle part of stomach)
-Antrum

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3
Q

______ muscle layer in the ______ is ______ than lower part of stomach.
Why is this difference important?

A

Smooth
fundus
thinner

Difference is important for gastric motility

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4
Q

Two mucosal linings:

A
  • Oxyntic mucosa

- Pyloric gland area

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5
Q

Difference between the two mucosal linings of the stomach is based on:

A

glandular secretion

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6
Q

terminal portion of stomach

A

Pyloric sphincter

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7
Q

Function of the pyloric sphincter

A

Serves as barrier between stomach and upper part of small intestine

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8
Q

Three main functions of stomach

A
  1. Stores ingested food until it can be emptied into small intestine.
  2. Secretes hydrochloric acid (HCl) and enzymes that begin protein digestion
  3. Mixing movements convert pulverized food (bolus) to chyme
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9
Q

The stomach stores ingested food until it can be emptied into small intestine

A
  • Rate optimal for digestion and absorption

- Release of food into duodenum must not exceed small intestine capacity

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10
Q

In the stomach, mixing movements convert pulverised food (bolus) to chyme

A
  • Thick liquid mixture of pulverized food mixed with gastric secretions
  • Pulverized food must be converted to chyme before being emptied into duodenum
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11
Q

Gastric (stomach) motility is complex and has four aspects:

A
  1. Filling
  2. Storage
  3. Mixing
  4. Emptying
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12
Q

involves receptive relaxation

A

Gastric filling

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13
Q

Explain gastric filling:

A

-involves receptive relaxation

-When empty, stomach has a volume of 50ml, after a meal, it can expand to 1L (1000ml).
> Accomplished through
numerous stomach folds

-During meal, folds become smaller and flatten as stomach fills (relaxes) with food (bolus)

>Response known as 
  receptive relaxation 
  mediated by vagus nerve 
>Enhances stomach’s ability to 
  accommodate the extra 
  volume of food with little rise 
  in stomach pressure 
>Triggered by act of eating
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14
Q

Explain gastric storage

A
  1. Pacemaker cells
    (interstitial cells of Cajal)
    in fundus generate slow-wave like potentials through length of stomach toward pyloric sphincter
  2. Rhythm of spontaneous depolarizations = basic electrical rhythm (BER) occur continuously and can be accompanied by stomach contractions
  3. Depending on level of excitability, peristaltic waves can be initiated
    > Weak in fundus and body,
    stronger in antrum
  4. Food mainly stored in body and mixing occurs in antrum
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15
Q

Pacemaker cells

A

interstitial cells of Cajal)

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16
Q

Takes place in the antrum

A

gastric mixing

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17
Q

Explain gastric mixing

A
  1. takes place in the antrum
  2. Strong, intense peristaltic contractions mix food (bolus) with gastric secretions into chyme
  3. Each peristaltic wave propels chyme towards pyloric sphincter
4. Pyloric sphincter is not entirely closed 
    > Opening large enough to 
       allow water and other fluids 
       to pass 
    > Particles larger than 2mm 
       in diameter cannot pass
  1. As peristaltic wave reaches pyloric sphincter, it closes
    - Larger particles are propelled
    back to body of stomach
    - When next wave arrives,
    larger particles propelled
    towards sphincter
    RETROPULSION –> shearing and grinding of particles to be small enough to be emptied into duodenum
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18
Q

shearing and grinding of particles to be small enough to be emptied into the duodenum

A

Retropulsion

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19
Q

controlled by duodenum

A

gastric emptying

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20
Q

driving force for gastric emptying

A

Antral peristatic contractions

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21
Q

Chyme that escapes during each contraction (during gastric emptying) depends on

A

strength of antral peristalsis

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22
Q

Intensity of antral peristalsis (rate of emptying) varies depending on

A

the signals received from stomach and duodenum

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23
Q

Signals (factors) influence stomach’s ________ by _______ or ________ of smooth muscle.

The greater excitability:
–>
The greater the strength of antral peristalsis
–>

A

excitability
depolarisation
hyperpolarization

–>the more frequent the BER will generate action potential

–> the faster the rate of emptying

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24
Q

Explain gastric emptying:

A
  1. A peristaltic contraction originates in the upper fundus and sweeps down towards the pyloric sphincter
  2. The contraction becomes 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 the antral contraction, the more chyme is emptied with each contractile wave.
  5. when the peristaltic contraction reaches the pyloric sphincter, the sphincter is tightly closed and no further emptying takes place.
  6. When chyme that was being propelled forward hits the closed sphincter, it is tossed back into the antrum.
    Mixing chyme is accomplished as chyme is propelled forward and tossed back into the antrum with each peristaltic contraction
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25
Q

Factors in stomach influencing rate of gastric emptying

A
  1. Main gastric factor influencing
    strength of contraction =
    amount of chyme in stomach
  2. Stomach distention (enlargement) triggers gastric motility
  3. degree of fluidity of chyme
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26
Q

amount of chyme in stomach

A

Stomach empties at rate proportional to volume of chyme

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27
Q

Stomach empties at rate proportional to volume of chyme

A

Occurs via stretching of smooth muscle but ALSO through intrinsic nerve plexus, vagus nerve stimulation and secretion of gastrin (hormone)

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28
Q

degree of fluidity of chyme

A 
Stomach contents MUST be converted into finely divided into thick liquid form before being emptied 
> The sooner the appropriate 
  degree of fluidity is reached, 
  the more rapidly the contents 
  can be released
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29
Q

Factors in duodenum influencing rate of gastric emptying

A
  1. Duodenum must be ready to receive chyme
    > If not ready, strength of
    antral peristaltic waves is
    reduced
  2. Main factors in duodenum important for gastric emptying include:
    a. Fats
    b. acid
    c. hypertonicity
    d. distention
    > Presence of one or more in
    duodenum, triggers neural OR
    hormonal response, slowing
    down rate of emptying
  3. Blood carries hormones to stomach (released from small intestine) to reduce gastric emptying
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30
Q

Neural response mediated by

A

intrinsic (short) and autonomic (long) nerve plexus

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31
Q

nerves plexus for gastric emptying

A

ENTEROGASTRIC REFLEX

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32
Q

Hormonal response involves release of several hormones – collectively known as

A

ENTEROGASTRONES

33
Q

Blood carries hormones to the stomach (released from the small intestine) to reduce gastric emptying.
Two important hormones include:

A

secretin and cholecystokinin (CCK)

34
Q

released from S-cells

A

Secretin

35
Q

released from I-cells

A

cholecystokinin (CCK)

36
Q

S- and I-cells from

A

duodenum & jejum mucosa

37
Q

Fat (lipids)

A
  • Fat digestion and absorption takes place only within lumen of small intestine
  • When fat is already in duodenum, further gastric emptying of additional fatty stomach contents is prevented
38
Q

Acid

A

Unneutralized acid in duodenum inhibits further emptying of acidic gastric contents until neutralization can be accomplished

39
Q

Hypertonicity

A

Gastric emptying is reflexly inhibited when osmolarity of duodenal contents starts to rise

40
Q

Distention

A

Too much chyme in duodenum inhibits emptying of even more gastric contents

41
Q

Additional factors that influence gastric motility

A

Emotions:

  • Sadness and fear – tend to decrease motility
  • Anger and aggression – tend to increase motility

Intense pain
– tends to inhibit motility

41
Q

Additional factors that influence gastric motility

A

Emotions:

  • Sadness and fear – tend to decrease motility
  • Anger and aggression – tend to increase motility

Intense pain
– tends to inhibit motility

42
Q

______ of gastric juices secreted daily.
Cells responsible _____ the stomach:
______ lines the fundus and body.
______ line antrum

A

2L
line
oxyntic mucosa
pyloric gland area

43
Q 
\_\_\_\_\_\_ of the stomach contains \_\_\_\_\_\_ (pockets) formed by \_\_\_\_\_\_\_\_\_\_\_\_
The first part referred to as 
\_\_\_\_\_\_\_\_\_\_
The base is referred to as 
\_\_\_\_\_\_\_\_\_
Secretory cells in folds:
>
>
>
A 
Lumen
deep pits
numerous folds
gastric pits
gastric glands
Exocrine
Endocrine
Paracrine
44
Q

What secretes HCl

A

Parietal cells

45
Q

Functions of HCl

A

Activates pepsinogen to active enzyme pepsin and provides acid medium for optimal pepsin activity

  • Aids in breakdown of connective tissue and muscle fibers
  • Denatures protein
  • Along with salivary lysozyme, kills most of the microorganisms ingested with food
46
Q

kills most of the microorganisms ingested with food

A

HCl and salivary lysozyme

47
Q

Rate of gastric secretion is influenced by:

A

a. Factors arising before food (bolus) reaches stomach
b. Factors resulting from food (bolus/chyme) in the stomach
c. Factors in the duodenum after food (bolus/chyme) has left the stomach

48
Q

Control of gastric secretions involves three phases:

A

Cephalic
Gastric
Intestinal

49
Q

Cephalic phase

A

Refers to increased secretion of HCl and pepsinogen that occurs in response to stimuli acting in the head before food reaches stomach

50
Q

Gastric phase

A
  • Begins when food actually reaches the stomach

- Presence of protein increases gastric secretions

51
Q

Intestinal phase

A
  • Inhibitory phase

Helps shut off flow of gastric juices as chyme begins to empty into small intestine

52
Q

Gastric secretions gradually ______ as food empties from stomach into __________

A

decrease

small intestine

53
Q

protects the stomach lining from gastric secretions

A

Gastric mucosal barrier

54
Q

Carbohydrate digestion continues in the _____ of the stomach, protein digestion begins in _______ of the stomach

A

body

the antrum

55
Q

Stomach absorbs:

A

alcohol and aspirin

BUT NOT food

56
Q

Accessory digestive organs

A
  • Accessory digestive organs

- Elongated gland located behind and below the stomach

57
Q

Islets of Langerhans

A

Endocrine function of accessory digestive organs

  • Found throughout the pancreas
  • Secrete insulin and glucagon
58
Q

Exocrine function of accessory digestive organs

A

Secretes pancreatic juice consisting of:

  • Pancreatic enzymes actively secreted by acinar cells that form the acini
  • Aqueous alkaline solution actively secreted by duct cells that line pancreatic ducts
59
Q

Exocrine secretion of the pancreas is regulated by:

A
  • secretin

- CCK

60
Q

Digest protein

A

Proteolytic enzymes

61
Q

Proteolytic enzymes: (pancreatic and biliary secretions)

A

Trypsinogen-converted to active form-trypsin

Chymotrypsinogen- converted to active form- chymotrysin

Procarboxypeptidase- converted to active form carboxypeptidase

62
Q

Converts polysaccharides into disaccharides

A

Pancreatic amylase

63
Q

Only enzyme secreted throughout entire digestive system that can digest fat

A

Pancreatic lipase

64
Q

explain the control of pancreatic aqueous NaHCO3-

A
  1. Acid in the duodenal lumen is detected.
  2. Increased release of secretin from duodenal mucosa
  3. Secretin carried by blood to pancreatic duct cells.
  4. Pancreatic duct cells then stimulated to secrete aqueous NaHCO3 solution into duodenal lumen
  5. Acid is now neutralized
65
Q

Explain the control of pancreatic digestive enzyme secreation

A
  1. Fat and protein products in the duodenal lumen
  2. Increased release of CCK from duodenal mucosa
  3. CCK is carried in blood to pancreatic acinar cells
  4. Which then stimulates the secretion of pancreatic digestive enzymes into duodenal lumen
  5. The fat and protein products are now digested
66
Q

Largest and most important metabolic organ,
Major biochemical factory
Secretes bile salts (NB for digestive system)

A

Liver

67
Q

Liver functions not related to digestion:

A
  1. Metabolic processing of the major categories of nutrients
  2. Detoxifying or degrading body wastes and hormones, drugs, and other foreign compounds,
  3. Synthesizes plasma proteins
  4. Stores glycogen, fats, Fe, Cu, and many vits
  5. Activates vit D
  6. Removes bacteria and worn-out red blood cells
  7. Excretes cholesterol and bilirubin
68
Q

Stored and concentrated in the gallbladder

A

Bile

69
Q

Bile is actively secreted by the _______ and it is actively _________to the __________ between meals. And after a meal, bile enters the ___________

A

liver
diverted
Gallbladder
duodenum

70
Q

Bile consists of:

A
  • Bile salts
  • Cholesterol
  • Lecithin
  • Bilirubin
71
Q

Bile salts:

  • Derivatives of ____________
  • Convert large ________ into ________
  • After participation in fat digestion and absorption, most are _________
A
  • Cholesterol
  • fat molecules; liquid emulsion
  • Reabsorbed into the blood
72
Q

GI hormones

A
  • Gastrin
  • Secretin
  • CCK
  • GIP
73
Q
  • Release is stimulated by presence of protein in stomach

- Secretion is inhibited by accumulation of acid in the stomach

A

Gastrin

74
Q

Gastrin function

A
  • Acts in several ways to increase secretion of HCL and pepsinogen.
  • Enhaces gastric motility
  • stimulates ileal motility
  • Relaxes ileocecal sphincter
  • Induces mass movements in colon
  • Helps maintain well-developed, funtionally viable, digestive tract lining
75
Q

Presence of acid in duodenum stimulates release

A

Secretin

76
Q

funtions of secretin

A
  • Inhibits gastric emptying in order to prevent further acid from entering duodenum until acid already present is neutralized.
  • Inhibits gastric secretion to reduce amount of acid being produced.
  • Stimulates pancreatic duct cells to produce large volume of aqueous NaHCO3 secretion
  • Stimulates liver to secrete NaCO3 rich bile which assists in neutralization process.
  • Along with CCK, is trophic to exocrine pancreas
77
Q

CCK funtions

A
  • Inhibits gastric motility and secretion
  • Stimulates pancreatic acinar cells to increase secretion of pancreatic enzymes
  • Causes contraction of gallbladder and relaxation of sphincter Oddi
  • Along with secretin, is trophic to exocrine pancreas
  • Implicated in long-term adaptive changes in proportion of pancreatic enzymes in response to prolonged diet changes
  • Important regulator of food intake.
78
Q
  • Glucose dependent insulinotrophic peptide

- Stimulates insulin release by pancreas

A

GIP

Physiology 214 (26 decks)

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