Digestive System Flashcards
1
Q
What are two types of digestion?
A
- mechanical
- grinding, churning, mixing - chemical
- breakdown of large nutrient molecules (proteins, lipids, carbohydrates) into smaller
ones
- facilitated by enzymes
2
Q
what is absorption?
A
absorption is the movement of end-products of digestion from the lumen of the alimentary canal to the blood or lymphatic system
3
Q
what layers make up the GI tract?
A
order from superficial to deep:
- mucosa
- submucosa
- muscularis
- serosa
4
Q
what is the peritoneum?
A
it consists of:
- visceral peritoneum (covers many abdominal organs)
- parietal peritoneum (lines walls of the cavity)
- peritoneal cavity (space between layers, contains a small amount of serous fluid)
5
Q
what are peritoneal folds?
A
- two fused layers of serous membrane
- extend from posterior abdominal wall to the liver, stomach, spleen, most of small
intestine, and transverse colon - support organs nerves, blood vessels, and lymphatic vessels
6
Q
what are the major divisions of the digestive system?
A
- alimentary canal (digestive tract) - all structures on path from oral to anal openings
- accessory organs - all other components of the digestive system
7
Q
what makes up the alimentary canal?
A
- oral cavity
- pharynx
- stomach
- small intestine
- large intestine
8
Q
what makes up accessory organs?
A
- teeth
- tongue
- salivary glands
- liver
- gallbladder
- pancreas
9
Q
what are the contents of the mouth?
A
- formed by cheeks, hard and soft palate and tongue
- buccinator mm. in cheeks, orbicularis oris in lips
- lined with stratified squamous epithelium (mucous membrane)
10
Q
what are the contents of the oral cavity?
A
- hard palate
- soft palate
- uvula
- fauces (opening to pharynx)
- tongue
- lingual frenulum
- labial frenulum
- lip
11
Q
what makes up the salivary glands?
A
- parotid (inferior, anterior to the ear, between masseter muscle, and skin)
- submandibular (beneath base of tongue)
- sublingual (superior to submandibular)
12
Q
what is saliva?
A
- constantly secreted from many small glands in oral mucosa
- slightly acidic (pH 6.35-6.85)
- 1000-1500ml secreted/day (most from parotid, submandibular, sublingual glands)
- cleanses, moistens mouth and pharynx
13
Q
composition of saliva?
A
- 99.5% water
- 0.5% solutes
- ions, dissolved gases, wasted, mucus, antibodies, enzymes
14
Q
contents of saliva?
A
- water - dissolves food, facilitates taste and digestion
- mucus - lubricates food
- urea, uric acid - metabolic wastes
- antibodies - inhibits bacterial growth
- lysozyme - kills bacteria
- salivary amylase - acts on starch
- lingual lipase - acts on triglycerides
15
Q
what causes salivation?
A
- stimulated by:
- sights, smell, sounds, memory of food
- mechanical stimulation of oral mucosa
- inhibited by the sympathetic nervous system (SNS) (fear, anxiety)
16
Q
what is the tongue?
A
- skeletal muscle covered with mucous membrane
- taste buds on the surface
- papillae
17
Q
tongue continued
A
- extrinsic tongue muscles attach the tongue to the hyoid, mandible, hard palate and styloid process
- move tongue in-out, side-to-side
- facilitate chewing, swallowing
- intrinsic tongue muscle originate and insert into CT within the tongue
- change the shape and size of the tongue for speech, swallowing
18
Q
digestion in mouth?
A
- mechanical digestion (mastication or chewing) breaks food into pieces, mixed with saliva to form a bolus
- chemical digestion
- salivary amylase begins starch digestion
- lingual lipase begins the breakdown of triglycerides
19
Q
what are the phases of deglutition (swallowing)?
A
three phases:
- voluntary
- pharyngeal (involuntary)
- soft palate blocks nasopharynx
- epiglottis blocks larynx
- esophageal
20
Q
what happens during deglutition voluntary phase?
A
- tongue pushes bolus to back of oral cavity
21
Q
what happens during the deglutition pharyngeal phase?
A
- bolus stimulates receptors in the oropharynx
- impulses sent to the deglutition center in the brainstem
- uvula and soft palate block nasopharynx
- vocal cords close, epiglottis blocks glottis
22
Q
what happens during the deglutition esophageal phase?
A
- upper esophageal sphincter relaxes, bolus enters the esophagus
- lower esophageal sphincter relaxes as bolus approaches bolus enters the stomach
23
Q
what is the function of the esophagus?
A
- moves ingested substances through peristalsis from pharynx, through thoracic cavity, to
stomach (passes through the diaphragm at the esophageal hiatus)
24
Q
histology of esophagus
A
- mucosa, submucosa,
- muscularis
- superior 1/3 skeletal muscle
- middle 1/3 mixed (skeletal and smooth muscle)
- inferior 1/3 smooth muscle
- adventitia
25
what is the stomach?
- j-shaped sac
- about 1.5 L capacity
- in left upper quadrant of the abdominal cavity
- inferior to diaphragm
- anterior to pancreas
26
what are the contents of the stomach?
- esophagus
- lower esophageal sphincter
- cardia
- fundus
- body
- pyloric region
- pyloric sphincter
- duodenum
- greater and lesser curvature
27
histology of stomach
- mucosa (simple columnar epithelium)
- submucosa
- muscularis
- serosa (visceral peritoneum)
28
what are the gastric secretions?
- mucus
- protects underlying tissue
- pepsinogen
- inactive
- hydrochloric acid
- activates pepsinogen (converts it to pepsin)
- intrinsic factor
- needed for vitamin B12 absorption
29
muscularis of stomach
- 3 layers of muscle
- outer longitudinal
- middle circular
- inner oblique
- churns, mixes food with gastric juice
30
gastric physiology (mechanical digestion)
- bolus enters stomach > gentle mixing waves occur every 15-25 seconds
- bolus + gastric juice forms watery, acidic chyme
- more vigorous waves being in body, intensify near pylorus (few waves in fundus)
- each contraction squirts 1-2 ml chyme to duodenum
31
gastric physiology (chemical digestion)
- fat digestion
| - gastric lipase splits triglycerides in milk fat (limited role in adults)
32
regulation of gastric function
- three phases of gastric stimulation:
- cephalic phase
- gastric phase
- intestinal phase
33
what is the cephalic phase?
- before food reaches the stomach
- triggered by sight, smell, taste, thought of food
- impulses from olfactory and taste centers > stomach via vagus nerve > increase gastric
motility, secretion
34
what is the gastric phase?
- activated by bolus in stomach
- nervous control keeps stomach active
- stretch receptors, chemoreceptors stimulated by distension, food chemistry
- > continued vigorous peristalsis secretion
- chyme released to the duodenum
- distension, chemicals in bolus (especially proteins) > gastrin secreted to blood
- gastrin stimulates
- gastric juice secretion
- gastric churning
- relaxation of pyloric sphincter
35
what is the intestinal phase?
- begins when chyme enters
- stretch receptors in the duodenum activate sympathetic nerves > decrease stomach activity
- fatty acids, sugar in chyme > release of secretin, CCK to blood > less secretion, motility
36
regulation of gastric emptying
two mechanisms:
- neural
- enterogastric reflex
- hormonal
- enterogastrones
37
enterogastric reflex
- initiated by:
- distension of the duodenum
- partially digested food in the duodenum
- low pH in the duodenum
- effects:
- inhibits gastric motility
- constricts pyloric sphincter (inhibits movement of gastric contents to duodenum)
38
enterogastrones
- a group of hormones secreted from the wall of the duodenum
39
gastrin
- distension of the stomach partially digested proteins and caffeine in the stomach, and high pH of stomach chyme stimulates gastrin secretion by enteroendocrine G cells, located mainly in the mucosa of the pyloric antrum of the stomach.
- major effects:
- promotes secretion of gastric juice, increases gastric motility, promotes the growth of gastric mucosa
- minor effects:
- constricts lower esophageal sphincter, relaxes pyloric sphincter
40
secretin
- acidic (high H+ level) chyme that enters small intestine stimulates secretion of secretin by enteroendocrine S cells in the mucosa of duodenum
- major effects:
- stimulates secretion of pancreatic juice and bile that are rich in HCO3- (bicarbonate ions)
- minor effects:
- inhibits secretion of gastric juice, promotes normal growth and maintenance of pancreas, enhances effects of CCK.
41
cholecystokinin (CCK)
- partially digested proteins (amino acids), triglycerides, and fatty acids that enter small intestine stimulate secretion of CCK cells in mucosa of small intestine; CCK is also released in brain
- major effects:
- stimulates secretion of pancreatic juice rich in digestive enzymes, causes ejection of bile from gallbladder and opening of sphincter of the hepatopancreatic ampulla (sphincter of Oddi), includes satiety (feeling full to satisfaction)
minor effects:
- inhibits gastric emptying, promotes normal growth and maintenance of pancreas, enhances effects of secretin
42
what does the stomach absorb?
- limited
- water
- electrolytes
- some drugs (e.g., aspirin)
- alcohol
43
anatomy of pancreas
- soft, pinkish-grey gland 12-15 cm long
- posterior to the stomach
- head lies in the curve of the duodenum, tail reaches the spleen
- hepatopancreatic sphincter
- regulates entry to the duodenum
- common bile duct joins with the pancreatic duct to form hepatopancreatic ampulla
- attaches to the duodenum 10cm distal to the pyloric sphincter
44
histology of pancreas
- acini
- 99% of gland
- secrete pancreatic juice to duodenum via pancreatic duct
- pancreatic islets
- 1% of gland
- secrete hormones to blood
45
control of pancreatic juice
- secreted to duodenum
- regulated by:
- vagus nerve
- local hormones
• secretin
• CCK
46
what is the liver?
- triangular reddish-brown organ, four lobes
- about 1.4 kilograms
- located in the right hypochondriac and epigastric regions
47
histology of liver
- hepatocytes arranged in lobules
- sinusoids arranged between layers of hepatocytes
- stellate reticuloendothelial cells in walls of sinusoids phagocytize microbes and foreign matter
48
pathway of bile secretion
- hepatocytes secrete bile to bile capillaries (canaliculi)
- canaliculi drain to bile
- bile ducts drain to hepatic ducts
- order:
1. hepatic ducts
2. common hepatic duct
3. common bile duct
4. hepatopancreatic ampulla
5. duodenum
49
bile storage
- diverted via cystic duct to gallbladder when sphincter closed
50
what is the gallbladder?
- small pear-shaped sac attached to the posterior surface of the liver
- 3 layers of smooth muscle covered with serosa, lined with simple columnar epithelium
51
control of bile secretion
- secreted to duodenum
- regulated by:
- vagus n. and local hormones
- secretin
- CCK
52
what is bile
- yellow, brownish or olive-green alkaline liquid (pH 7.6 to 8.6) produced by the liver
- liver secretes 800 - 1000 ml/day
- stored, concentrated in the gallbladder
- contains:
- water
- cholesterol
- bile salts (cholesterol derivatives) emulsify fats
- bile pigments (breakdown products of Hb) give colour to bile and feces
53
function of the livers
- nutrient metabolism (carbohydrate, lipid, protein)
- detoxifies blood (removes or alters drugs, alcohol, hormones)
- stores vitamins (A, B12, D, E, K) and minerals (iron, copper)
- phagocytoses RBCs, WBCs, bacteria
54
anatomy of small intestine
- about 3 m long (6.5 m in cadaver), 2.5 cm in diameter
- extends from pyloric sphincter to ileocecal valve
- Large surface area for absorption
- 3 parts:
- duodenum (~25 cm long, retroperitoneal)
- jejunum (~1 m long)
- ileum (~2 m long, attached to large intestine at ileocecal valve)
55
histology of small intestine
- Circular folds
- permanent 10 mm. tall mucosal folds in duodenum, jejunum
- increase surface area, enhance absorption
- villi
- 1,, tall finger0like projections of mucosa, lamina propria
0 contain blood lymphatic capillaries
- intestinal glands
- secretes intestinal juice
- microvilli
- 1 micron long on free surface of absorptive cells
- 200 million/mm2
- increase surface area
- form brush border (contain digestive enzymes)
- function in digestion, absorption
- absoptive cell
- digest and absorbs nutrients
- goblet cell
- secretes mucous
- enteroendocrine cell
- secretes hotomones
- paneth cell
- phagocyte
- secretes lysozomes
56
mechanical digestion in the small intestine
- migrating motility complex (MMC)
- weak peristalis migrates slowly (1.5-2 hours) from lower portion of stomach to distal ileum
- 3-5 hours to move chyme through
- segmentation
- localized mixing contraction of portions of lumen distended by chyme
- sloshes chyme back and forth 8-12x/min
57
chemical digestion in the small intestine
- chyme entering small intestin contains partially digested carbohydrates, proteins, lipids
- digestion completed in small intestine by actions of pancreatic juice, bile, intestinal juice
58
carbohydrate digestion
- in mouth:
- salivary amylase
- in duodenum:
- pancreatic amylase act on starches
- intestinal brush border enzymes (maltase, sucrase, lactase) convert disaccharides to monosaccharides
59
protein digestion
- in stomach:
- hcl denatures proteins
- pepsin converts proteins to peptides
- in duodenum:
- pancreatic proteases split peptides into amino acids
- intestinal brush border enzymes split amino acids, dipeptides
60
lipid digestion
- in mouth and stomach:
- lingual lipase, gastric lipase (weak)
- in duodenum:
- bile emulsifiers fats
- pancreatic lipase converts tryglercides to fatty acids, monoglycerides
61
nutrient absorption
- carbohydrates enter absoptive epithelial cells by facilitated diffusion and active transport, move to blood capillaries by facilitated diffusion as monosaccharides
- amino acids, peptides enter absorptive cells by active transport, move to blood capillaries by diffusion as amino acids
- short chain fatty acids pass through absorptive cells to blood capillaries by diffusion
- long chain fatty acids, monoglycerides enter absorptive cells by diffusion, combine with phosoplipids and cholesterol > chylomicrons, enter lacteals
62
water absorption
- 9L secreted to GI tract/day
- most reabsorbed by osmosis to blood capillaries within villi
- 8L reabsorbed in small intestine
- 90% of remaining water reabsorbed in large intestine
63
anatomy of large intestine
- about 1.5 m long, 6.5 cm in diameter
- extends from ileocecal valve to anal opening
- attached to posterior abdominal wall by mesocolon
- cecum
- appendix
- extends from cecum
- contains large amount of lymphatic tissue
- ascending colon
- meets right colic flexture
- transverse colon
- meets left colic flexture
- descending colon
- sigmoid colon
- rectum
- last 20 cm of GI tract
- anterior to the sacrum, coccyx
- internal anal sphincter
- smooth muscle
- involuntary
- external anal sphincter
- skeletal muscle
- voluntary
- anal canal
64
histology of large intestine
- mucosa, submucosa contain lymphatic nodules
- muscularis
- inner layer circular fibers
- outer layer thickened in places (teniae coli), gathers colon haustra
65
mechanical digestion in the large intestine
mechanical activity
- inactive much time
- contractions sluggish and short lived
- kinds of contractions:
- haustral churning
- peristalsis (3-12 contractions/min)
- mass peristalsis
- haustral churning
- occurs every 30 minutes
- slow segmenting movements
- move food to adjacent haustra
- mass peristalsis
- 3-4x/day, during or just after eating (activated by gastrocolic reflex)
- begin near middle of transverse colon
- large section of colon contracts moves contents towards rectum
66
control of mechanical digestion in large intestine
- gastroilial reflex
- gastrin released when stomach is full relaxes ileocecal sphincter so small intestine will empty
- gastrocolic reflex
- when stomach fills, mass peristalsis moves contents of transverse colon into rectum
67
chemical digestion in large intestine
- no enzyme secreted (only mucus)
- bacteria (most abundant is E. coli)
- ferment indigested carbohydrates produce CO2, methane gas
- break down undigested proteins (lead to odour), bilirubin (lead to colour)
- produce vitamin K and B12
68
absorption in large intestine
- limited absorption
- water (most absorbed in small intestine)
- some electrolytes
- vitamins
69
how are feces formed?
- chyme enters from the small intestine
- becomes solid or semisolid after 3-10 hours in colon, now called feces
- consists of dead epithelial cells, undigested food (e.g., cellulose), live and dead bacteria
70
regulation of defecation
- defecation involves both:
- a reflex (the defecation reflex)
- somatic motor activity
71
defecation reflex
- sensory part of the reflex:
- feces forced into the rectum by mass peristalsis stimulate stretch receptors in the rectum wall
- impulses pass to the sacral area of the spinal cord
- motor part of the reflex:
- sensory stimulation causes the internal anal sphincters to relax; walls of the sigmoid colon and rectum contract
- feces in the anal canal lead to impulses to the brain (conscious awareness)
72
somatic motor activity for defecation
- involves voluntary relaxation of the external ana; sphincter
