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Human Physiology 2 > Ch. Fourteen: Digestive System > Flashcards

Ch. Fourteen: Digestive System Flashcards

1
Q

2 Types of Digestive Motility

A
  1. Propulsive: push contents forward through digestive tract
  2. Mixing: serve two functions:
    - mixing food with digestive juices promotes digestion of foods
    - absorption
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2
Q

Digestive Secretions

A
  • consist of water, electrolytes, and specific organic constituents
  • secretions are released into digestive tract lumen on appropriate neural or hormonal stimulation
  • normally reabsorbed in one form or another back into blood after their participation in digestion
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3
Q

Digestion

A
  • biochemical breakdown of structurally complex foodstuffs into smaller, absorbable units
  • accomplished by enzymatic hydrolysis
  • complex foodstuffs and their absorbable units: carbohydrates to monosaccharides, proteins to amino acids, and fats to glycerol and fatty acids
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4
Q

Carbohydrates

A
  • consumed as disaccharides or polysaccharides
  • sucrose, lactose, maltose, starch, glycogen, and cellulose (not digested “fibre”)
  • only monosaccharides are absorbed by the intestinal cells for use in the body
  • disaccharides and polysaccharides must be digested to monosaccharides before they can be absorbed for use in the body
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5
Q

Protein

A
  • broken down to peptide fragments
  • peptide fragments are further digested to free amino acids
  • free amino acids then enter the epithelial cells
  • short chains of two or three amino acids are also absorbed
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6
Q

Fats

A
  • dietary fats as triglycerides

- digestion produces 2 free fatty acids and monoglyceride

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7
Q

Absorption

A
  • small units resulting from digestion, along the water
  • also: vitamins and electrolytes
  • transferred from digestive tract lumen into blood or lymph
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8
Q

Mucosa

A
  • innermost layer
  • lines luminal surface of digestive tract
  • highly folded surface greatly increases absorptive area
  • 3 layers: mucous membrane, lamina propria, muscularis mucosa
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9
Q

Mucous Membrane

A
  • serves as protective surface
  • modified for secretion and absorption
  • contains: exocrine (digestive juices), endocrine (secrete blood-borne gastrointestinal hormones), and epithealial cells (absorbing digestive nutrients)
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10
Q

Lamina Propria and Muscularis Mucosa

A
  • houses gut-associated lymphoid tissuse (GALT)
  • important in defense against disease causing intestinal bacteria
  • sparse layer of smooth muscle
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11
Q

Submucosa

A
  • thick layer of connective tissue
  • provides digestive tract with distensibility and elasticity
  • contains larger blood and lymph vessels
  • contains nerve network known as submucosal plexus
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12
Q

Muscularis Externa

A
  • major smooth muscle coat of digestive tube
  • 2 layers:
    circular (inner)- contraction decreases diameter of lumen
    longitudinal (outer)- contraction shortens the tube
  • contractile activity produces propulsive and mixing movements
  • myenteric plexus: lies between the two muscle layers and origin of rhythmic activity: Basic Electrical Rhythm
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13
Q

Serosa

A
  • secretes serous fluid: lubricates and prevents friction between digestive organs and surrounding viscera
  • continuous with mesentery throughout much of the tract:
  • attachment provides relative fixation
  • supports digestive organs in proper place while allowing them freedom for mixing and propulsive movements
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14
Q

Motility and Secretion Regulated By…

A
  • autonomous smooth muscle function: pace maker cells- interstitial cells of Cajal
  • intrinsic nerve plexuses:
  • ENS= myentric + submucosal plexuses
  • sensory and motor functions
  • extrinsic nerves: ANS
  • G.I. Hormones: Gastrin and Brain function
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15
Q

Palate

A
  • forms roof of oral cavity

- uvula (seals off nasal passages during swallowing)

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16
Q

Salivary Glands

A

3 pairs: parotid, sublingual, submandibular

  • secretion accomplished by large increase in blood flow
  • per gram, largest secretion of any exocrine gland
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17
Q

Saliva

A
  • produced largely by 3 major pairs of salivary glands

- composition: 99.5% water, 0.5% electrolytes and protein- amylase, mucus, lysozyme

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18
Q

Saliva Functions

A
  • salivary amylase begins digestion of carbohydrates
  • moistens food
  • mucus provides lubrication
  • antibacterial action: lysozyme destroys bacteria, saliva rinses away material that could serve as food source for bacteria
  • solvent for molecules that stimulate taste buds
  • aids speech by facilitating movements of lips and tongue
  • helps keep mouth and teeth clean
  • rich in bicarbonate buffers
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19
Q

Digestion in Mouth

A
  • polysaccharides into disaccharides
  • mass of food contains amylase
  • digestion may continue in food bolus
  • amylase broken down in stomach
  • not essential
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20
Q

Digestion in Pharynx

A
  • swallowing:
  • motility associated with pharynx and esophagus
  • sequentially programmed all or none reflex
  • initiated when bolus is voluntarily forced by tongue to rear of mouth into pharynx
  • most complex reflex in body
  • can be initiated voluntarily but cannot be stopped once it has begun
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21
Q

Digestive in Esophagus

A
  • sphincters at each end:
  • pharyngoesphageal sphincter: prevents large volumes of air from entering esophagus and stomach during breathing
  • gastroesophageal sphincter: prevents reflux of gastric contents
  • peristaltic waves push food through esophagus
  • secretions are entirely protective
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22
Q

Digestion in Stomach

A
  • J-shaped sac chamber lying between esophagus and small intestine
  • fungus, body, antrum
    3 main functions;
  • store ingested food until it can be empties into small intestine
  • secretes HCl and enzymes that being protein digestion
  • mixing movements convert pulverized food to chyme
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23
Q

Gastric Mobility

A

4 aspects:

  • filing: 50mLs to 1L capacity; involves receptive relaxation
  • storage: takes place in body of stomach
  • mixing: takes places in antrum of stomach- thicker muscle
  • emptying: largely controlled by factors in duodenum
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24
Q

Factors Regulating Gastric Mobility and Emptying in stomach

A

Volume of Chyme: distension effects gastric smooth muscle excitability and acts through intrinsic plexuses (vagus nerve)- increased volume stimulates motility and emptying
- main factor that influences strength of contraction

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25
Q

Gastric Emptying Factors in duodenum

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
Acid: inhibits further emptying of acidic gastric contents
Hypertonicity: gastric emptying is reflexly inhibited when osmolarity of duodenal contents starts to rise
Distension: too much chyme in duodenum inhibits emptying of even more gastric contents

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26
Q

Factors Trigger Neural or Hormonal Response

A

Neural: mediated through both intrinsic nerve plexuses (short relfex) and autonomic nerves (long reflex)
Hormonal: involves release of hormones from duodenal mucosa collectively known as enterogastrones
- secretin and Cholecystokinin (CKK)

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27
Q

Additional Factors that Influence Mobility

A

Emotions:
- sadness and fear- tend to decrease motility
- anger and aggression- tends to increase motility
Intense pain:
- tends to inhibit motility
- SNS

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28
Q

Gastric Juice Secreted From…

A
  • oxyntic mucosa: lines body and fundus
  • pyloric gland area (PGA): lines the antrum
  • gastric pits at base of gastric glands
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29
Q

Oxyntic Mucosa

A

3 types of exocrine secretory cells:

  1. Mucous cells
    - lines gastric pits and entrance of glands
    - secrete thin, watery mucous- lubrication, protection from HCl and pepsin
  2. Chief cells
    - secrete enzyme precursor, pepsinogen
  3. Parietal (oxyntic) cells
    - secrete HCl and intrinsic factor (vit.B12 absorption- RBC)
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30
Q

Functions of HCl

A
  • activates pepsinogen to activate enzyme pepsin and provides acid medium for optimal pepsin activity
  • aids in breakdown of connective tissue and muscle fibres
  • denatures protein: allows digestion by pepsin
  • along with salivary lysozyme, kills most of the microorganisms ingested with food
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31
Q

Pepsinogen

A
  • major digestive constituent of gastric secretion which is converted to pepsin
  • pepsin splits certain amino acid linkages in proteins to yield small amino acid chains
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32
Q

HCl and Pepsinogen Secretion

A
  • gastrin +: stimulates histamine release from ECL cells
  • Histamine +
  • ACh+
  • Somatostatin -: low pH
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33
Q

PGA mucosa

A
  • plyoric gland area
  • secrete hormones/paracrine substances:
  • gastrin and somatostatin
34
Q

Phases of Gastric Secretion

A
  • cephalic phase: stimuli acting in the head before food reaches stomach
  • gastric phase: begins when food actually reaches the stomach, ex. peptides and amino acids; presence of protein increases gastric secretions (buffering of H+)
  • intestinal phase: inhibitory phase; helps shut off flow of gastric juices as chyme begins to empty into small intestine
35
Q

Gastric Mucosal Barrier

A
  • enables stomach to contain acid without injuring itself
36
Q

Mucus

A
  • surface of gastric mucosa covered by a layer of mucus
  • acts as a lubricant
  • prevents mechanical injury
  • protects against self-destruction
37
Q

Pancreas

A
  • mixture of exocrine and endocrine tissue
  • elongated gland located behind and below the stomach
  • endocrine function: islets of Langerhans (found in pancreas and secrete insulin and glucagon)
38
Q

Exocrine Pancreas

A
  • secretes pancreatic juice consisting of:
  • 3 different pancreatic enzymes actively secreted by acinar cells that form from the acini
  • aqueous alkaline solution actively secreted by duct cells that line pancreatic ducts
    function:
  • secretes pancreatic juice consisting of:
  • enzymes secreted by acinar cells called zymogen granules (inactive precursors)
  • duct cells secrete aqueous alkaline solution`
39
Q

Pancreatic Enzymes

A
  • proteolytic enzymes (digest protein)
  • Trypsinogen: converted to active trypsin
  • Chymotrypsinogen: converted to active form chymotrysin
  • Procarboxypeptidase: converted to active form carbpxypeptidase
  • pancreatic amylase: converts polysaccharides into disaccharide malstode
  • pancreatic lipase: only enzyme secreted throughout entire digestive system that can digest fat
40
Q

Liver

A
  • largest and most important metabolic organ in the body
  • body’s major biochemical factory
  • importance to digestive system- secretion og bile salts
  • via gallbladder and ducts
  • fat digestion and absorption
41
Q

Liver: Bile

A
  • actively secreted by liver and actievly diverted to gallbladder between meals (50mL capacity)
  • stored and concentrated in gallbladder
  • consists of:
  • bile salts, cholestrol, lecithin (phosopholipid), and bilirubin (yellow color)
  • after meal, bile enters duodenum
42
Q

Bile Salts

A
  • derivatives of cholesterol
  • convert large fat globules into liquid emulsion
  • after participation in fat digestion and absorption, most are reabsorbed into the blood
43
Q

Function of Bile Salt

A
  • vile salts break up large fat droplet with intestinal mixing
  • increase surface area for lipase
44
Q

Micelle

A
  • critical for fat absorption
  • water soluble structures
  • transport digested fats
  • monoglycerides and free fatty acids
  • also fat soluble vitamins (vit K)
45
Q

Gall Bladder

A
  • secreted bile is stored in gall bladder between meals
  • salt is actively transported out, with water following osmotically, concentrating bile
  • primary site precipitation of concentrated bile constituents into gallstones
46
Q

Small Intestine

A
  • site where most digestion and absorption take place
  • 3 segments: duodendum, jejunum, ileum
  • motility includes: segmentation, and migrating motility complex
47
Q

Segmentation

A
  • primary method of motility in small intestine during digestion of a meal
  • consists of ring-like contractions along length of small intestine
  • within seconds, contracted segments relax and previously relaxed areas contract
  • action mixes chyme throughout small intestine lumen
48
Q

Segmentation Frequency

A
  • initiated by pacemaker cells in small intestine
  • produced basic electrical rhythm (BER)
  • frequency varies with region
  • duodenum
  • ileum
49
Q

Segmentation Functions

A
  • mixing chyme with digestive juices secreted into small intestine lumen
  • exposing all chyme to absorptive surfaces of small intestine mucosa
  • slowly moves chyme through digestive tract
50
Q

Motility Segmentation

A
  • when most meal has been absorbed, segmentation contractions cease, replaced by migrating motility complex
  • migrating motility complex (MMC)
  • peristaltic wave sweeps intestines clean between meals
51
Q

Small Intestine

A
  • secretion:
  • juice secreted by small intestine does not contain any digestive enzymes
  • lubrication and salt solution
  • synthesized enzymes act within brush-border membrane of epithelial cells:
  • enterokinase, disaccharidases, aminopeptidases
52
Q

Brush-border Enzymes

A
  • enterokinase: trypsinogen to trypsin
  • disaccharidases: disaccharides to monosaccarides (maltase, sucrase, lactase)
  • aminopeptidases: peptides to amino acids
53
Q

Small Intestine- Digestion

A
  • pancreatic enzymes continue carbohydrate and protein digestion
  • brush-border enzymes complete digestion of carbohydrates and protein
  • fat is digested entirely within small intestine lumen by pancreatic lipase
54
Q

Small Intestine- Absoprtion

A
  • absorbs almost everything presented to it
  • ingested liquids and solids
  • most occurs in duodenum and jejunum
  • spare capacity in ileum
  • Vit B12 and bile salts absorption
  • several adaptations to increase surface area
55
Q

Small Intestine Absorptive Surface

A
  • large surface area: x600 of flat surface
  • inner surface has permanent circular folds
  • microscopic projections called villi
  • brush-border microvilli arise from luminal surface of epitherlial cells
  • lining is replaced about every 3 days
  • NA+ and water reabsorption similar to nephron
  • products of fat digestion undergo transformations that enable them to be passively absorbed; eventually enter lymph
  • crypt secrete watery solution and new epithelial cells
56
Q

Large Intestine

A
  • primarily a drying and storage organ
  • consists of: colon, cecum, appendix, rectum

contents received from small intestine:
- indigestible food residues, unabsorbed biliary components, and remaining fluid
colon:
- extracts more water and salt from contents
- feces- what remains to be eliminated
taeniae coli: longitundinal bands of muscle
Haustra: pouches or sacs
- actively change location as result of contraction of circular smooth muscle layer

57
Q

Haustraul Contractions

A
  • main motility- slow (1 per 30mins)
  • initiated by autonomous rhythmicity of colonic smooth muscle cells
  • mass movements: massive contractions
  • moves colonic contents into distal part of large intestine
58
Q

Mass Movements

A
  • gastrocolic reflex
  • from stomach to colon by gastrin and by autonomic nerves
  • most evident after first meal of the day
  • often followed by urge to defecate
59
Q

Defecation Reflex

A
  • stretch receptors in rectal wall stimulated by distension

- causes internal anal (smooth muscle) sphincter to relax and rectum and sigmoid to contract more vigorously (PNS)

60
Q

Function of Bile Salt

A
  • vile salts break up large fat droplet with intestinal mixing
  • increase surface area for lipase
61
Q

Micelle

A
  • critical for fat absorption
  • water soluble structures
  • transport digested fats
  • monoglycerides and free fatty acids
  • also fat soluble vitamins (vit K)
62
Q

Gall Bladder

A
  • secreted bile is stored in gall bladder between meals
  • salt is actively transported out, with water following osmotically, concentrating bile
  • primary site precipitation of concentrated bile constituents into gallstones
63
Q

Small Intestine

A
  • site where most digestion and absorption take place
  • 3 segments: duodendum, jejunum, ileum
  • motility includes: segmentation, and migrating motility complex
64
Q

Segmentation

A
  • primary method of motility in small intestine during digestion of a meal
  • consists of ring-like contractions along length of small intestine
  • within seconds, contracted segments relax and previously relaxed areas contract
  • action mixes chyme throughout small intestine lumen
65
Q

Segmentation Frequency

A
  • initiated by pacemaker cells in small intestine
  • produced basic electrical rhythm (BER)
  • frequency varies with region
  • duodenum
  • ileum
66
Q

Segmentation Functions

A
  • mixing chyme with digestive juices secreted into small intestine lumen
  • exposing all chyme to absorptive surfaces of small intestine mucosa
  • slowly moves chyme through digestive tract
67
Q

Motility Segmentation

A
  • when most meal has been absorbed, segmentation contractions cease, replaced by migrating motility complex
  • migrating motility complex (MMC)
  • peristaltic wave sweeps intestines clean between meals
68
Q

Small Intestine

A
  • secretion:
  • juice secreted by small intestine does not contain any digestive enzymes
  • lubrication and salt solution
  • synthesized enzymes act within brush-border membrane of epithelial cells:
  • enterokinase, disaccharidases, aminopeptidases
69
Q

Brush-border Enzymes

A
  • enterokinase: trypsinogen to trypsin
  • disaccharidases: disaccharides to monosaccarides (maltase, sucrase, lactase)
  • aminopeptidases: peptides to amino acids
70
Q

Small Intestine- Digestion

A
  • pancreatic enzymes continue carbohydrate and protein digestion
  • brush-border enzymes complete digestion of carbohydrates and protein
  • fat is digested entirely within small intestine lumen by pancreatic lipase
71
Q

Small Intestine- Absoprtion

A
  • absorbs almost everything presented to it
  • ingested liquids and solids
  • most occurs in duodenum and jejunum
  • spare capacity in ileum
  • Vit B12 and bile salts absorption
  • several adaptations to increase surface area
72
Q

Small Intestine Absorptive Surface

A
  • large surface area: x600 of flat surface
  • inner surface has permanent circular folds
  • microscopic projections called villi
  • brush-border microvilli arise from luminal surface of epitherlial cells
  • lining is replaced about every 3 days
  • NA+ and water reabsorption similar to nephron
  • products of fat digestion undergo transformations that enable them to be passively absorbed; eventually enter lymph
  • crypt secrete watery solution and new epithelial cells
73
Q

Large Intestine

A
  • primarily a drying and storage organ
  • consists of: colon, cecum, appendix, rectum

contents received from small intestine:
- indigestible food residues, unabsorbed biliary components, and remaining fluid
colon:
- extracts more water and salt from contents
- feces- what remains to be eliminated
taeniae coli: longitundinal bands of muscle
Haustra: pouches or sacs
- actively change location as result of contraction of circular smooth muscle layer

74
Q

Haustraul Contractions

A
  • main motility- slow (1 per 30mins)
  • initiated by autonomous rhythmicity of colonic smooth muscle cells
  • mass movements: massive contractions
  • moves colonic contents into distal part of large intestine
75
Q

Mass Movements

A
  • gastrocolic reflex
  • from stomach to colon by gastrin and by autonomic nerves
  • most evident after first meal of the day
  • often followed by urge to defecate
76
Q

Defecation Reflex

A
  • stretch receptors in rectal wall stimulated by distension
  • causes internal anal (smooth muscle) sphincter to relax and rectum and sigmoid to contract more vigorously (PNS)
  • if external anal sphincter (skeletal muscle under voluntary control) is relaxed, defecation occurs
  • remember micturition (sounds familiar)
77
Q

Large Intestine Secretion

A
  • no digestive enzymes secreted
  • colonic secretions consist of an alkaline mucous solution
  • colon has plentiful bacteria and they provide beneficial functions
  • colon normally absorbs salt and water
78
Q

Constipation and Diarrhea

A
  • large amount of feces
  • blockages causing discomfort
  • decreased motility due to age, low-bulk diet
  • loss of watery material- colon cannot absorb it all
  • fluid bulk: not increased motility
  • increased secretion (cholera)
  • NaCl loss, therefore water, K+ and HCO3 (metabolic acidocis)
79
Q

Gastrointestinal Hormones: Gastrin

A
  • release is stimulated by presence of protein in stomach
  • secretion inhibited by accumulation of acid in stomach
  • functions:
  • acts in several ways to increase secretion of HCl and pepsinogen
  • enhances gastric motility, stimulates ileal motility, relaxes ileocecal sphincter, induces mass movements in colon
  • helps maintain well-developed, functionally viable digestive lining
80
Q

Gastrointestinal Hormones: Secretin

A
  • presene of acid in duodenum stimulates release
  • functions:
  • inhibits gastric emptying in order to prevent further 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
81
Q

Gastrointestinal Hormones: CCK

A
  • functions:
  • inhibits gastric motility and secretion
  • stimulates pancreatic acinar cells to increase secretion of pancreatic enzymes
  • causes contraction of gallbladder and relaxation of sphincter of Oddi
  • along with secretion, 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

Human Physiology 2 (10 decks)

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