1
Q
what is the average transit time in the large intestine
A
men and kinds - 33h
women - 47h
average - 40h
2
Q
what is digestion
A
the breakdown of food molecules into their monomers by hydrolysis
3
Q
what is absorption
A
process of how monomers are transported across the wall of the small intestine into the blood and lymph
4
Q
what is metabolsim
A
the use of ingested food molecules in reactions of cell respiration to produce ATP
5
Q
what is the alimentary canal
A
- series of hollow organs joined in a long, twisting tube
- oral cavity to anus
- continuous with the environment on both ends
6
Q
what are the accessory organs in the digestive system
A
teeth, tongue, salivary glands, liver, gallbladder, pancreas
7
Q
what are the structures of the alimentary canal/digestive tract
A
- mouth, pharynx, esophagus, stomach, small intestine, large intestine, anus
8
Q
what are the layers (tunics) of the alimentary canal
A
mucosa
submucosa
muscularis
serosa
9
Q
mucosa layer
A
absorptive and secretory layer
10
Q
submucosa layer
A
highly vascular layer of connective tissue
11
Q
muscularis layer
A
responsible for contractions and peristaltic movements
(break and mix food with digestive enzymes)
12
Q
serosa layer
A
connective tissue continuous with the mesentery and visceral peritoneum (connects digestive tissues to abdomen walls)
13
Q
tongue structure
A
- the tongue is converted in backward facing projections called filiform papillae
- filiform papillae sense pressure
- have a scaly appearance
- papillae are constantly shedding this top layer of skin
14
Q
cat tounge
A
- hollow which allows them to secrete more saliva
- helps cats cool down
15
Q
what are the 3 pairs of salivary glands
A
- sublingual: under the tongue
- submandibular: under jaw
- parotid: posterior (close to ear) - largest pair
16
Q
functions of salivary glands
A
- lubrication of the mouth and throat
- solubilization of dry food (taste)
- oral hygiene - antimicrobial peptides attack pathogens in food
- alkaline buffering - prevents demineralization of enamel (from acidic foods)
- begins starch digestion (salivary amylase)
- evaporative cooling
17
Q
true or false: if you produce less saliva you have a greater chance of getting cavities
A
true
18
Q
how do the teeth contribute to digestion
A
teeth are responsible for mastication (chewing and mixing food with saliva)
19
Q
what are the jobs of the different types of teeth
A
incisors: rip and cut
canines: tear and pierce
premolars: grind and shear
molars: grind
20
Q
true or false: the teeth are the softest structure in the body
A
false - are the hardest
21
Q
tissues involved in deglutition (swallowing)
A
- involves 25 pairs of muscles in the mouth, pharynx, larynx and esophagus
striated muscles: mouth, pharynx and upper esophagus
smooth muscles: lower esophagus
22
Q
3 phases of deglutition (swallowing)
A
- oral phase: somatic - muscles of the tongue and mouth mix the food with saliva to create a bolus
- Pharyngeal phase: autonomic - nasal cavity and larynx are closed off
- Esophageal phase: autonomic - food bolus moved by peristaltic contractions
23
Q
what is the esophagus
A
- connects the pharynx to the stomach
- 25cm long muscular tube, located behind the trachea
- upper third = skeletal muscle
- middle third = mix of skeletal and smooth muscle
- lower third = smooth muscle
24
Q
what is esophageal peristalsis
A
moving food in a wave-like muscular contraction through the esophagus
25
how do peristaltic contractions move food
- move the bolus from the esophagus into the stomach
- contractions progress from the superior end of the esophagus to the gastroesophageal junction at a rate of 2-4 cm/second
26
what is the esophageal hiatus
- where the esophagus passes through the diaphragm
27
what is the lower esophageal sphincter
- the terminal portion of the esophagus where the lumen is slightly narrowed due to the thickening of muscle fibres
- sphincter relaxes = food enters the stomach
- sphincter constricts = prevents regurgitation of stomach contents
sphincter = misnomer
28
sphincter in rodants
- known as a true sphincter
- rodents cannot regurgitate because their sphincter prevents back flow
- mouth gaping = nausea (might have eaten something toxic)
29
the stomach of ruminants
1st chamber: rumen - allows to breakdown of cellulose
2nd chamber: reticulum - regurgitates food back to the ruminants mouth, cud is chewed and re-swallowed
3rd chamber: omasum
4th chamber: abomasum
30
3 main functions of the stomach
1. storage of swallowed food and liquids: muscles of the cardiac and fundus relax to accept large food volumes
2. mixes up food/liquid with digestive juices: in the lower pyloric region by muscles, begins protein digestion and acidity kills bacteria
3. slowly empties contents (chyme) into the duodenum
31
musculature of the stomach
- smooth muscle layers run longitudinal, circular and oblique
- provides complex motility to mix and mechanically break up food in the stomach
32
main regions of the stomach (top to bottom)
- cardiac region (fundus and body)
- pyloric region (antrum to pyloric sphincter)
33
food movement through the stomach
- food is delivered to the cardiac region of the stomach
- chyme is churned and enters the duodenum through the pyloric sphincter
34
what are gastric pits
- opening off of gastric glands, which are cells that line the folds into the stomach
35
What is the purpose of gastric glands
- contain many types of cells to produce a specific secretion in the stomach
- exocrine secretions of the gastric cells + large amount of water = gastric juice (highly acidic)
36
types of cells in the gastric glands of the stomach
mucous cells: secrete mucus
parietal cells: secrete HCl and intrinsic factor (bound to vit B12 - essential for life)
chief (zymogenic) cells: secrete pepsinogen
37
What do pepsinogen and HCl do in the stomach
- in the presence of HCl, the inactive enzyme pepsinogen becomes pepsin (active)
- pepsin can digest proteins into smaller polypeptides
- the high [HCl] makes gastric juice very acidic and denatures protein to make them more digestible
38
why doesn't the stomach digest itself
major barrier: adherent layer of gastric mucus on the epithelial surface
- epithelial surface has alkaline bicarbonate making pH at epithelial surface near neutral
- causes slow diffusion of pepsin to epithelial cells
- tight junctions between epithelial cells protect underlying tissues from acid/pepsin
- cell division replaces the entire gastric epithelium every 3 days
39
what are peptic ulcers
caused by erosion of the mucosa
- duodenal ulcers are caused by excessive gastric acid secretion
- peptic ulcers are caused by reduced barriers of self digestion
40
Helicobacter pylori
common bacteria that survives very acidic pH and cause digestion of protective barrier leading to peptic ulcers
41
regions of the small intestine
duodenum
- first 20-30cm, extends from pyloric sphincter
- mucous secretion, receives pancreatic secretions and bile from the liver
jejunum
- 1m in length, numerous folds and vili
Ileum
- last 2m, fewer folds and vili
- absorbs primarily bile salts, water and electrolytes
- contains Peter's patches
- empties into the large intestine via ileocecal valve
42
types of folds in the small intestine
- extensive folding increases surface area for absorption which increases rate of absorption
plicae circulares: big folds created from mucosa and submucosa
villi: microscopic folds of mucosa
microvilli: foldings on apical plasma membrane of epithelial cells
43
which regions of the SI are certain particles absorbed in
duodenum and jejunum: carbs, lipids, AAs, Ca2+, iron
ileum: bile salts, Vit B12, H2O, electrolytes
44
characteristics of Villi
- covered with columnar epithelial cells (enterocytes)
- goblet cells in villi secrete mucus
- epithelial cells at the tip of villi are continuously replaced
- invaginations of villi form pouches = intestinal crypts
- paneth cells at the base secrete antibacterial lysosomes and antimicrobial peptides (defensins) to protect against pathogenic bacteria while preserving commensal bacteria
45
characteristics of microvilli
- formed by foldings at the apical surface of each epithelial PM
- produce a brush border
- contain wide diversity of enzymes for absorption and digestion
46
Brush border enzymes
- remain attached to the PM other their active sites exposed to the chyme (in the lumen)
- examples of brush border enzymes are surcease, maltase, lactase, aminopeptidase, and enterokinase
47
how does food enter into the large intestine
- chyme enters through the ileum into the cecum (blind pouch)
48
structure of the large intestine
- covered by columnar epithelial cells and goblet cells, but no villi present
- external layer of smooth muscle (taenia coli)
- formation of haustra (pouches)
49
function of the large intestine
- little to no digestive function
- absorbs water, electrolytes and vitamins
50
microbiota of the large intestine
- has several thousand microorganisms
- composed of anaerobic bacteria
- commensal bacteria
- bacteria digest dietary fibre into monosaccharides and SCFA
51
what consequence for the large intestine might antibiotics pose
antibiotics may cause diarrhea by reducing the commensal bacteria population and thus SCFA production for water reabsorption
52
body fat % and intestinal microbiota
- obese subjects have less diversity and different relative abundance of particular microbes
- microbiota of obese subjects is more populated with bacteria that promote adipose storage and deficient in those that metabolize fiber
53
what is the appendix
- a small component of the colon
- contains numerous lymphoid nodules and may house a population of commensal bacteria that helps to replenish a normal microbiota
54
what is appendicitis
- inflammation of the appendix
- causes pain in the lower right quadrant of the abdomen and nausea
- a ruptured appendix can cause inflammation in the surrounding peritoneal membranes - peritonitis
- can cause circulatory shock and death
55
why do wombats poop cubes
- the wombats intestine is 10x the length of their body
- the digestive process is 4x longer than humans so they can extract all possible nutritional conent
- they extract all water, so their faces is extremely dry
- cubes formed within the last 17% of the colon
56
how muscles in wombat colons give their poop a cube shape
- azimuthal contractions of an elastic ring composed of stiff and soft regions
- increased stiffness ratio and higher Reynolds number yield shapes that are more square
- the corners arise from faster contraction in the stiff regions and relatively slower movement in the centre of the soft regions
57
what are sinusoids
- large capillary spaces that separate hepatic plates
- much more permeable than other capillaries
- contain Kupffer cells (liver-specific macrophages)
58
how is the liver able to regenerate itself
- if 2/3 of a rodents liver is removed the remaining tissue can regenerate to its original mass in one week
- hepatocytes in damaged liver convert to stem-like "progenitor" cells
- then proliferate and differentiate back to hepatocytes
59
what is the hepatic portal system
- system of blood vessels that delivers digestion products to and from the liver
- capillary to vein to capillary to vein
60
Path of the hepatic portal system
- digestion products absorbed into blood capillaries of the intestine first get delivered to the liver via the hepatic portal vein
- blood then passes through downstream liver capillaries and enters general circulation via the hepatic vein
61
what does the hepatic artery do
delivers blood from the heart to the liver
62
what does the hepatic portal vein do
- delivers blood to the liver from blood capillaries in the intestine
- also drains capillaries of the pancreas, gallbladder and spleen
63
what are portal lobules of the liver
- hepatic plates arranged into functional units, gets blood from the hepatic portal vein to the inferior vena cava
- the central vein is present in the middle of each lobule
- blood branches from the hepatic portal vein and hepatic artery open into sinusoids
- blood mixes and then enters the central vein
- central veins converge to form the hepatic vein and go to the inferior vena cava
64
functions of the liver
- detoxication of blood
- carbohydrate metabolism
- lipid metabolism
- protein synthesis
- secretion of bile*
- storage of molecules
65
how does bile from the liver get to the gallbladder for storage and then released to the small intestine
- Bile is produced by hepatocytes and secreted into bile canaliculi within each hepatic plate
- Bile canaliculi drain into bile ductules present in each portal lobule
- bile then drains into hepatic ducts
- the right and left hepatic ducts meet up with the cystic duct from the gallbladder and together form a common bile duct which then goes to the intestines
66
what is a trigger for bile release
a fatty meal reaching the duodenum
- bile salts in the intestines will form micelles around big pieces of fat to help break them down
67
what are the major constituents of bile
- bile acids/salts*
- bilirubin
- phospholipids
- cholesterol
- inorganic ions
68
formation of primary and secondary bile acids and salts
- cholesterol in the liver is used to produce primary bile acids
- primary bile acids get conjugated = bile salts
- bile salts are stored in the gallbladder or go to the small intestine
- intestinal microbiota convert primary bile acids to secondary bile acids
- small portions of secondary bile acids are excreted into feces and most get reabsorbed through the portal system
69
what are bile salts
- primary bile acids that get conjugated to AAs in the liver OR secondary acids that get re-conjugated
- they are amphipathic - the AA portion is hydrophilic
70
true or false: 95% of bile acids are recycled?
true - in the intestines microbiota can unconjugate bile salts to make bile acids that enter enterohepatic circulation
71
What is the gallbladder
- Sac-like organ attached to the interior surface of the liver
- stores and concentrates bile from the liver
72
how does the gallbladder release stored bile
- contraction of the muscularis layer ejects bile through the cystic duct into the common bile duct which guest to the duodenum
73
how does bile enter the gallbladder for storage
- when the small intestine is empty the sphincter of the ampulla at the end of the common bile duct closes - this forces bile to move up the cystic duct and enter the gallbladder
74
what are gallstones
- form when bile stored in the gallbladder hardens into mineral deposit
- may be due to too much cholesterol, bile salts or bilirubin
- may block hepatic, cystic or common bile ducts
- may use shock waves to break up stones or perform a cholecystectomy
75
what is the exocrine function of the pancreas
- secretes pancreatic juice through the pancreatic duct into the duodenum for digestion
76
what are pancreatic acini
exocrine secretory units within the pancreatic lowest
- each one consists of a single layer of epithelial cells surrounding a lumen which secretes juice
77
difference between the endocrine and exocrine portions of the pancreas
endocrine: includes pancreatic islets
exocrine: includes pancreatic acini
78
what is pancreatic juice
a mixture od bicarbonate and many other digestive enzymes including...
amylase: digests starch
trypsin: digests proteins
lipase: digests triglycerides
79
example of how digestion requires pancreatic enzymes PLUS brush border enzymes
- the inactive form of trypsin (pancreatic enzyme) is activated at the brush border by the enzyme enterokinase
- trypsin is a protease that can then activate other pancreatic enzymes
80
time-restricted eating: mice experiment
- mice were given a high-fat diet - one group had access 8hr/day and one 24hr/day
- 24hr mice weighed 38% more than the 8hr mice after 4 months
- 24hr mice had 4x body fat
- TRF also protected them against diabetes, liver diseases and inflammation
81
benefits of time-restricted eating
- reduced total cholesterol and LDL levels, increased HDL
- increased insulin sensitivity
- reduced inflammation
82
current hypothesis about TRE
eating for 12-15 hr a day may disrupt circadian rhythm and can increase risk of CV disease, cancer and diabetes
- known as chrononutrition
83
negative impacts of time restricted eating
- irritability
- increase feeling of hunger and thought of food
- bingeing during eating windows
- difficulty concentrating
- fatigue
84
what determines the caloric value of food
- carbs (50%)
- protein (16%)
- fat (makes up the rest)
85
what is required of macromolecules for absorption
- requires for food molecules to be hydrolyzed into their free monomers (except for cholesterol)
86
common carbohydrates
- most carbs are ingested as starch which are long polysaccharide chains of glucose
- most commonly ingested sugars are sucrose and lactose
87
steps in chemical digestion of carbohydrates
- starch (polysaccharides) are digested by salivary and pancreatic amylases
- disaccharides are digested by brush border enzymes
88
carbohydrate brush border enzymes
Lactase: cleaves lactose --> glucose and galactose
Sucrase: cleaves sucrose --> fructose and glucose
Maltase: cleaves maltose --> multiple glucose
a-dexrrinase (glucoamylase): cleaves small glucose polymers
89
digestion of carbs by a-amylase (ptyalin)
- digestion begins in the mouth with salivary amylase
- ptyalin hydrolyzes starch into maltose and other short glucose polymers
- ptyalin is inactivated by stomach pH and the rest of complex carbs get digested by pancreatic amylase
90
digestion of carbs by pancreatic amylase
- digestion of carbs mainly occurs in the duodenum by pancreatic amylase
- pancreatic amylase is more potent that the salivary source
- it cleaves straight chains of starch to produce maltose, maltose, and short, branched oligosaccharides
91
how long does it take to hydrolyze all carbs into small glucose polymers
30 minutes
92
digestion pathway of carbs
mouth: salivary amylase
duodenum: pancreatic amylase
rest of the SI: dextrinase and glucoamylase
brush border: lactase, maltase, sucrase
93
Carbohydrate absorption at the small intestine
- disaccharides are hydrolyzed to their monosaccharides by brush border enzymes on microvilli
- the monosaccharides formed are lactose, glucose and fructose
94
absorption of specific monosaccharides
- glucose is co-transported with 2 Na+ into the epithelial cell cytoplasm (secondary active transport)
- glucose moves through the GLUT transporter (facilitated diffusion) across the basolateral membrane into the capillary
- fructose can be directly absorbed - doesn't need a transporter
95
post-absorptive events of glucose: after a meal
- blood leaving the villi of the SI drain into blood vessels that lead directly to the liver via the hepatic portal vein
- a rise in blood glucose causes insulin release from the endocrine pancreas
- results in an increased uptake of glucose by the liker and skeletal muscle
96
what is glycogenesis
- the formation of glycogen from glucose for storage
-
97
post-absorptive events of glucose: in between meals
- in between meals blood glucose levels decrease
- causes the release of glucagon from the endocrine pancreas which stimulates glycogen breakdown in the liver = GLYCOGENOLYSIS
98
what is glycogenolysis
generates free glucose from glycogen that can be released into the blood
99
what is glycemic index
- the rate at which food makes your blood sugar rose
- high = blood sugar rises quickly after a meal
- can be seen as the area under the 2h blood glucose response curve after ingestion
100
which food have high medium and low GL
high = rice and donut
medium = whole wheat bread and mango
low = banana and soy protein shake
101
what is the AUC test food/AUC standard (glucose
GI =100
- average GI calculated from multiple subjects
102
high glycemic index
- blood sugar rises quickly after a meal
- carbohydrates break down quickly and are rapidly released into blood stream
103
what is cholesterol
- cholesterol is essential for the functioning of all animal cells - a component of cell membranes
- it is a precursor for the synthesis of steroid hormones
- it is the base substrate for the synthesis of bile acids and vitamins D3
104
post-absorptive events of cholesterol
- a small molecule that is absorbed from food without being digested
- most blood cholesterol is produced in the liver, only 20% comes from diet
- can directly pass through microvilli into intestinal epithelial cells where it is incorporated into chylomicrons which enter lymphatic vessels
- will drain into the venous circulation and go to the liver
105
how is cholesterol transported in the blood
- in the blood cholesterol is associated with lipoproteins
- cholesterol produced in the liver is transported to organs and blood vessels via LDLs
- elevated LDL-cholesterol levels mean lipids can't deposit in arterial vessel walls = atherosclerosis
- excess cholesterol is returned to the liver attached ti HDLs
- HDLs bind to receptors in blood vessels and take up free cholesterol (protection against atherosclerosis
106
what are the 3 major lipid groups in out diet
- triglycerides, phospholipids and sterols (such as cholesterol)
107
digestion of lipids
- up to 30% of fat digestion occurs in the mouth and stomach by lingual and gastric lipase
- majority of fat is digested in the small intestine by pancreatic lipase
- the arrival of lipids in the duodenum stimulates the secretion of bile to help with emulsification
108
emulsification of lipids
- emulsification is when bile salt micelles are secreted into the duodenum from the gallbladder and liver
- bile salts act as detergents to break up fat droplets into smaller emulsification droplets
- NOT chemical digestion
- the smaller emulsification droplets presents a greater surface area for enzymatic action
109
how does Colipase work I lipid digestion
- colipase is secreted by the pancreas and coats emulsification droplets and anchors pancreatic lipase to them
-
110
hydrolysis of tryglycerides
lipase cleaves triglycerides into 2 FFAs and a monoglyceride
111
phospholipase A
- digests phospholipids
112
how do lipids get to the BBM
- free fatty acids and monoglycerides are incorporated into micelles of bile salts
- they move to the brush border where they will be absorbed
113
3 steps in lipid digestion in the SI
- emulsification of fat droplets by bile salts
- hydrolysis of triglycerides in emulsified fat droplets into fatty acid and monoglycerides
- dissolving of fatty acids and monoglycerides into micelles to produce mixed micelles
114
absorption of lipids
once we get to the brush border...
- fatty acids and monoglycerides can leave the micelles and enter the intestinal epithelial cells
- triglycerides are resynthesized by fatty acids and monoglycerides
- triglycerides combine with phospholipids, cholesterol and protein to form small particles = chylomicrons
- chylomicrons are secreted by exocytosis, enter lacteals (lymphocytes) and go into the venous circulation
115
transport of lipids in the blood
- chylomicrons acquire a protein called ApoE which allows binding to receptors on the PM of endothelial cells in muscles and adipose tissue
- triglycerides of chylomicrons are digested by lipoprotein lipase on the PM of these cells
- after the triglycerides are broken up the remnant particle containing cholesterol is released and travels back to the liver
116
what is the fate of digested triglycerides of chylomicrons
- releases free FAs that can enter tissues
- heart and skeletal muscles use for energy
- stored in adipose tissue
117
digestion of proteins in the stomach
- protein digestion begins in the stomach
- high [HCl] makes gastric juice very acidic, thereby denaturing digestible proteins to make them more digestible
- pepsin is a protease that digests proteins into short-chain polypeptides
- this helps produce a more homogenous chyme
118
digestion of proteins in the small intestine
- major protein digestion happens in the duodenum and jejunum
- trypsin, chymotrypsin and elastase are pancreatic juice enzymes that cleave peptide bonds in the interior of polypeptide chains = endopeptidases
- carboxypeptidase and amino peptidase cleave the ends of polypeptide chains
119
exopeptidases
carboxyl peptidase: pancreatic juice enzyme, removes AAs from the c-terminal end
aminopeptidase: brush border enzyme, removes AAs from the N-terminal end
120
absorption of proteins
- results in amino acids, dipeptides and tripeptides
- free AAs are absorbed across the BBM by different secondary active transport carriers
- di and tripeptides enter epithelial cells by a single membrane carrier and are hydrolyzed into free AAs in the cytoplasm
- free AAs enter interstitial fluid by facilitated diffusion, then travel through capillary blood and the hepatic portal vein to get to the liver
121
absorption of proteins: adults vs babies
- in adults only free AAs will enter the hepatic portal vein
- newborns can absorb a substantial amount of undigested protein - allows them to absorb antibodies from mom through breast milk (passive immunity)
122
absorption of minerats
calcium
- absorption by active, carrier-dependent process and passive, paracellular process in the small and large intestine
- active process is vitamin D-dependent (PTH)
Iron ions
- absorbed in the duodenum
- most easily absorbed when bound to heme
K+, Mg2+ and phosphate
- direct absorption through the intestinal mucosa
123
absorption of fat soluble vitamins
- occurs mainly be passive diffusion in the jejunum and ileum
- absorbed with dietary lipids (Vits A, E, D, K)
124
absorption of water soluble vitamins
- include Vit C and the B vitamins - diffuse into the blood, except for B12
- B12 combines with intrinsic factor produced by the stomach, which the intestine absorbs by endocytosis
- water-soluble vitamins pass into urine when their concentration in plasma exceeds the renal capacity for reabsorption
BIOM 3200
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