Ch. Fourteen: Digestive System Flashcards
1
Q
2 Types of Digestive Motility
A
- Propulsive: push contents forward through digestive tract
- Mixing: serve two functions:
- mixing food with digestive juices promotes digestion of foods
- absorption
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
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
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
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
6
Q
Fats
A
- dietary fats as triglycerides
- digestion produces 2 free fatty acids and monoglyceride
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
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
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)
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
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
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
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
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
15
Q
Palate
A
- forms roof of oral cavity
- uvula (seals off nasal passages during swallowing)
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
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
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
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
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
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
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
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
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
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
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)
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
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
29
Q
Oxyntic Mucosa
A
3 types of exocrine secretory cells:
- Mucous cells
- lines gastric pits and entrance of glands
- secrete thin, watery mucous- lubrication, protection from HCl and pepsin - Chief cells
- secrete enzyme precursor, pepsinogen - Parietal (oxyntic) cells
- secrete HCl and intrinsic factor (vit.B12 absorption- RBC)
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
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
32
Q
HCl and Pepsinogen Secretion
A
- gastrin +: stimulates histamine release from ECL cells
- Histamine +
- ACh+
- Somatostatin -: low pH
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
