Digestive system Flashcards
(145 cards)
1
Q
6 essential activities of the digestive process
A
1) ingestion
2) Mechanical breakdown
- chewing (mouth)
- churning(stomach)
- segmentation (SI)
3) Chemical Digestion
4) Propulsion
- swallowing (oropharynx)
- peristalsis (esophagus, stomach, SI, LI)
5) absorption
- starts in stomach, most in SI
6) Defecation
2
Q
Digestive systems 2 groups of organs
A
1) alimentary canal
- oral cavity teeth tongue
- pharynx
- esophagus
- stomach
- SI
- LI (colon)
2) Accessory Organs
- salivary glands
- liver
- gallbladder
- pancreas
3
Q
See regions of abdominal digestive organs, slide 6
A
unga bunga
4
Q
4 basic layers (tunics) of alimentary canal
A
entire alimentary canal composed of 4 tunics
1) mucosa
2) submucosa
3) muscularis externa (SM)
4) serosa/adventitia
5
Q
tunics: Mucosa (3 parts of mucosa and list functions of mucosa as whole)
A
most internal tunic, touches foodstuff ingested
Epithelium
-stratified squamous (rss abrasion) or simple columnar (abs/secrete, sometimes goblet cells)
Lamina propria
-loose CT
-capillaries (nourishment and abs)
Lymphoid follicles (MALT - deals with ingested pathogens)
Muscularis mucosae
- SM (moves mucosa)
- NOT responsible for propelling foodstuff, just mucosa
Functions
- secretes mucus, digestive enzymes, hormones
- absorbs end products of digestion
- protects against infectious disease
6
Q
Tunics: Submucosa (6 parts and function as whole)
A
- loose CT
- Blood and lymphatic vessels, lymphoid follicles, glands, submucosal nerve plexus
Functions
- support mucosa
- binds layers together
7
Q
Tunics: Muscularis externa (3 parts, function as whole)
A
Circular layer
- SM
- “sphincter former”
Longitudinal layer
- SM
- runs length of tube and helps shorten it
Myenteric nerve plexus
- autonomic nerves
- helps coordinate above 2 layers
Functions
-segmentation and peristalsis
-sometimes forms sphincters to control passage/prevent backflow
+thickening of circular layer -> sphincter
8
Q
Peristalsis (4 steps, purpose)
A
1) Bolus of food arrives in digestive system
2) circular muscles contract behind bolus (pinch)
3) longitudinal muscles ahead of bolus contract (shorten)
4) contraction in circular muscle layer forces bolus forward
Purpose - propel food toward anus
9
Q
Segmentation
A
nonadjacent segments of alimentary tract organs alternatively contract and relax
- food moves forward then backward for food mixing
- SLOW food propulsion occurs
10
Q
Tunics: Serosa (AKA visceral peritoneum) [2 parts, overall function, retroperitoneal organs/adventitia]
A
PARTS:
1) Loose connective tissue
2) epithelium - mesothelium = simple squamous
FUNCTION
-permit mobility
Retroperitoneal organs have an adventitia:
- dense irregular CT to bind organs together
- organ either has serosa or adventitia NOT BOTH
11
Q
Peritoneum definition
A
serous membrane of abdominal cavity
12
Q
Parietal peritoneum
A
lines body wall
13
Q
visceral peritoneum
A
on external surface of most digestive organs
14
Q
peritoneal cavity (and role of fluid in cavity)
A
cavity between visceral and parietal peritoneum
-fluid lubricates mobile organs
15
Q
Intraperitoneal organs (and mesentery)
A
-surrounded by peritoneum
HAVE a mesentery
- double layer of peritoneum
- route for BVs, lymphatics, nerves
- holds organs in place and stores fat
16
Q
retroperitoneal organs
A
Located posterior to peritoneum
17
Q
The mesenteries (how do they connect)
A
The mesenteries are all cts with eachother
Anterior abdominal wall (falciform ligament) Liver (lesser omentum) stomach (greater omentum) Transverse colon (transverse mesocolon) Posterior abdominal wall
[ () indicates connecting mesenteries]
18
Q
Enteric NS
(type of nerve supply, fibre types and what link/synapse with)
(2 parts)
A
- intrinsic nerve supply of alimentary canal
- linked to CNS via afferent visceral fibres
- long ANS fibres synapse with enteric plexuses
more neurons than entire spinal cord (over 100 million)
Myenteric nerve plexus
-controls GI tract motility
Submucosal nerve plexus
-regulates glands and SM (including BVs) in mucosa
19
Q
What are the 3 mechanisms that regulate and control digestive activities
A
1) local factors
2) neural control
3) hormonal control
20
Q
Local factors
A
primary stimulus for digestive activities including:
- change in lumen pH
- physical distortion
- presence of chemicals (nutrients/chem messengers)
21
Q
neural control
A
GI movement and chemical secretion is primarily controlled by local factors
Short reflexes
- triggered by chemoreceptors/stretch receptors in GI tract walls
- control myenteric plexus
Long reflexes
-involve interneurons and motor neurons in CNS
+providing higher level of control over digestive and glandular activities - generally control large peristaltic waves
22
Q
Hormonal Control
A
GI tract produces many hormones that affect almost every aspect of digestive F(x)
-peptides produced by enteroendocrine cells)
+endocrine cells in digestive tract epithelium
23
Q
Boundaries of Oral cavity (4) and what makes them
A
anterior and lateral boundary
- labium (lip)
- Cheek
Superior Boundary
- hard palate
- soft palate
inferior boundary
-tongue muscles
posterior boundary
- uvula
- palatine tonsil
- root of tongue
- lingual tonsil
24
Q
Functions of saliva (6)
A
- cleanses mouth
- moistens and dissolves food chemicals
- aids in bolus formation
- contains enzymes to begin digestion (oral cavity begins chem digestions)
- buffers pH (HCO3-)
- Lubrication
25
Intrinsic (buccal) salivary glands
- location
- f(x)
- scattered in oral mucosa
| - keep mouth at baseline level of salivation
26
Extrinsic salivary glands
- names (3)
- location
- parotid, submandibular, and sublingual glands
| - outside oral cavity
27
Review slide 20 for locations
EEEEEEEEEEE
28
Salivary glands cell types (2) and f(x)
1) serous cells
- produce watery secretion containing enzymes ions and tiny bit of mucin
2) mucous cells
- produce mucus
- (high in lipid so dont stain well on slide)
29
Submandibular glands
- cellular makeup
- f(x)
- mostly serous, small amount of mucous
| - make 60-70% total saliva volume
30
Parotid gland cellular makeup
mostly serous
31
sublingual glands cellular makeup
mucous cells
32
intrinsic (buccal) glands cellular makeup
serous and mucous cells
33
Composition of Saliva
- water content/pH
- electrolytes
- enzymes
- proteins
- metabolic wastes
- microorganism protection
- 97-99.5% water, almost neutral
- Na+, K+, Cl-, PO43-, HCO3-
- salivary amylase (starch -> maltose) lingual lipase (begins fat breakdown)
- mucin, lysozyme, igA, albumin
- urea and uric acid
- lysozyme, IgA, defensins, a cyanide compound
34
how much saliva produced each day
1-1.5L
35
Control of salivation
Intrinsic glands
-continuously keep mouth moist
```
Extrinsic salivary glands
-produce secretions when
+smell, taste, sound, sight
+Pressure in mouth (chew on tongue)
+Sleep, fatigue, Fear
```
NOTE: slide 23 goes into pathways and cranial nerves
36
Tooth structure (3 parts)
Crown
- exposed part above gingiva
- covered by enamel: hardest substance in body (Ca2+ salts + hydroxyapetite crystals)
Neck
-connects crown and root
Root
-portion embedded in bone
37
Dentin
- bonelike material
- maintain by ondontoblasts of pulp cavity
- not as hard as enamel
38
pulp
- makeup
- 2 parts
-connective tissue, BVs, nerves
Pulp cavity
-crown cavity containing pulp
Root canal
-pulp in root
39
Cementum
- Calcified connective tissue
- covers root
- anchored by periodontal ligament to bone
40
Deciduous (milk) teeth
| 5 unique
- central incisor (6mo)
- lateral incisor (9mo) - biting
- canine/eyetooth (18mo) - ripping
- first molar (12 mo)
- second molar (24mo)
41
Permanent teeth
| -(8 unique)
```
central incisor (6yr)
lateral incisor (8yr)
canine/eyetooth (12yr)
1st premolar/bicuspid (12yr) - replaces 1st molar of milk
2nd premolar/bicuspid (12yr) - replaces 2nd molar of milk
First molar (6yr)
second molar (12yr)
third molar/wisdom tooth (24yr)
```
42
what teeth appear first (typically)
lower before upper
43
Pharynx
Oropharynx and laryngopharynx
| -allow passage of food, fluids, and air
44
Esophagus
- 4 tunics and their makeup
- tube length/desc (3)
- f(x) of glands in submucosa
```
TUNICS
Mucosa -stratified squamous epithelium
submucosa -areolar CT
muscularis externa -circular layer and longitudinal layer
Adventitia - fibrous CT
```
TUBE
- flat muscular tube ~25cm long
- pierces diaphragm at esophageal hiatus (T10)
- collapsed when not involved in food propulsion
GLANDS
-glands in submucosa secrete mucous for lubrication
45
2 phases of degulation
| -how many total steps
1) buccal phase (steps 1)
2) pharyngeal-esophageal phase (steps 2-5)
5 total steps
46
Buccal phase (step 1 of deglutition)
- upper esophageal sphincter contracted
- tongue presses against hard palate (voluntary)
- Bolus forced into oropharynx (involuntary phase begins)
47
pharyngeal-esopphageal phase (step 2 of deglutition)
- uvula and larynx rise
- epiglottis closes larynx
- tongue blocks off anterior mouth
- upper esophageal sphincter relaxes
48
pharyngeal-esopphageal phase (step 3 of deglutition)
- constrictor muscles of pharynx contract (food forced into esophagus)
- upper esophageal sphincter contracts
49
pharyngeal-esopphageal phase (step 4 of deglutition)
food moved through esophagus by peristalsis
50
pharyngeal-esopphageal phase (step 5 of deglutition)
gastroesophageal sphincter opens (food enters stomach)
51
anatomy of infant (5) and adult oral cavity (3)
infant
-Oral cavity is small
-tongue and palate flatter
-epiglottis almost attached to soft palate
-airway and foodway separated except when swallowing
+can eat and drink at same time
Adult
-larynx is lower in neck
-food way and airway cross in pharynx
+cannot eat and drink at same time
52
Emetic Reflex (6 steps)
VOMITING
1) salivation and sensation of nausea
2) reverse peristalsis from upper SI and stomach
3) glottis closes (prevents aspiration), breath held mid inspiration
4) diaphragm and abdominal wall muscles contract to increase intra-abdominal P
5) Esophagus and sphincters relax
6) gastric contents ejected
53
Digestive Processes in stomach (6)
1) mechanical breakdown
2) denaturation of proteins
3) enzymatic digestion of proteins by pepsin (+rennin in infants)
4) secretes intrinsic factor
5) absorption of lipid soluble substances
6) delivers chyme to SI
54
Response to stomach filling
- how much hold
- stomach pressure held constant until
- how P relatively unchanging ? (2)
- Holds 50mL to 4L (vomit before hit 4L)
- stomach P remains constant until ~1.5L food injested
Relative unchanging P from:
-Receptive relaxation
+as food travels in esophagus, stomach muscles relax
-Gastric accommodation
+intrinsic ability of SM to exhibit stress relaxation response (when stretch it relax)
55
what makes up most of the stomach
the body
56
rugae (stomach)
folds seen by naked eye
-reason able to go from 50mL-4L
+lose folds as expand
57
Muscularis externa of stomach
longitudinal layer
circular layer
oblique layer - unique
Oblique layer
-facilitates mixing and churning of stomach contents
58
What branches into a gastric gland in the stomach
gastric pit
59
how much gastric jice produced daily
gastric mucosa produces 3L of gastric juice daily
60
mucosa epithelial cell distribution
cell types vary in different regions
61
Mucous surface cell (stomach)
-secretes mucus (alkaline)
62
mucous neck cell (stomach)
secretes mucus (acidic)
63
parietal cell (stomach) secretions and roles
-secretes HCL and intrinsic factor
intrinsic factor
-glycoprotein required for absorption of vitamin B12 in SI
```
HCl
-stomach pH 1.5-3.5
+denatures protein in food
+activates pepsin
+kills many bacteria
```
SEE ~slide 43 for how parietal cells produce HCl
64
```
mucosal protection (3 parts)
-surface cell lifespan
```
1) layer of HCO3- rich mucus protects the epithelial cells
2) tight junctions between epithelial cells - protects deeper layers from leakage
3) Damaged epithelial cells quickly replaced by division of stem cells
-surface cell lifespan 3-6 days
65
Regulation of HCl secretion (stomach)
-3 chemicals
+their F(x)
ACh, Histamine, Gastrin
- stimulate parietal cells through second messenger systems
- all 3 are necessary for maximum HCl secretion
66
Chief cell secretions (stomach)
-Pepsinogen (inactive enzyme) released at base of gastric gland
+activated to pepsin by HCl and by pepsin (pepsinogen not activated until reach stomach lumen)
- small amounts of lipases
- rennin in infants (helps with breast milk digestion)
67
Gastric enteroendocrine cells
| -
-Hormone producing G cell
secrete chemical messengers into lamina propria
-go into BVs so can go elsewhere
68
Gastric enteroendocrine cells: Gastrin from G cells
Gastrin released from G cells
- increase HCl secretion
- stimulates gastric emptying (minor effect)
- stimulates parietal cell maturation
- stimulates chief cells to secrete pepsinogen
- increases intestine muscle contraction
- relaxes ileocecal valve
- stimulates mass movements
69
Gastric enteroendocrine cells: histamine from enterochromaffin-like cells
increase parietal cells HCl release
70
Gastric enteroendocrine cells: seretonin from enterochromaffin-like cells
- increases contraction of stomach muscle
| - makes 90% of total body serotonin
71
Gastric enteroendocrine cells: somatostatin from Delta (D) Cells
- inhibits secretion from stomach and pancreas
- inhibits small intestine absorption
- inhibits gallbladder and liver release of bile
ONLY INHIBITOR DISCUSSED
Table of cell types and what released/do ~49
72
Regulation of Gastric Secretion
- what mechanisms (2)
- what phases (3) what events occur in phases
- neural and hormonal mechanisms
- stimulatory and inhibitory events occur in phases
1) cephalic (reflex) phase: few minutes prior to food entry
2) gastric phase: food entering stomach to 3-4 hours later
3) internal phase: brief stimulatory effect as partially digested food enters duodenum, followed by inhibitory effects
73
Cephalic Phase of Gastric secretion
ALL STIMULATORY
-sight, smell, taste, thought of food ->CNS -> (vagus nerve CN X) -> submucosal plexuses - > mucous cells (mucus), chief cells (pepsinogen), parietal cells (HCl), G cells (gastrin)
+myenteric and submucosal plexuses stimulate mixing waves
+elevated pH stimulates chemoreceptors activating myenteric and submucosal plexus (-> all cells and mixing waves... cyclic)
+distention stimulates stretch receptors activating myenteric and submucosal plexus (-> all cells and mixing waves... cyclic)
GASTRIN (still stimulatory) from G cells
- stimulates chief cells
- stimulates mixing waves
74
G cell inhibition
| -what stim?
inhibited at pH below 2
| -partly digested proteins, caffeine, high pH
75
Names and what release (SI secretions)
CCK
GIP
secretin
```
CCK = cholecystokinin,
GIP = Gastric inhibitory peptide (glucose-dependent insulinotropic peptide
```
RELEASE
CCK and GIP = presence of lipids and carbs
Secretin = decreased pH
76
Intestinal phase of gastric secretion
CCK, GIP, secretin
-inhibit Chief cells, parietal cells, peristalsis
Duodenal stretch and chemoreceptors
- inhibit myenteric plexus
- ENTEROGASTRIC REFLEX
77
Small intestine Gross anatomy
- F(x)
- diameter
- L of parts
- length of SI in life
- major organ of digestion and absorption
+most things absorbed by time leave SI
-Diameter - 2.5-4cm
Duodemun - 25cm (c-shaped)
Jejunum - 2.5m (upper left)
ileum - 3.6m (lower right)
In life only 2-4m long due to muscle tone
78
Structural modifications that increase surface area (SI)
-more SA, more nutrient absorption
- circular folds (plicae circulares) ~1cm deep
-villi ~1mm hgih
microvilli ~100-2000nm high
total surface area = 200m^2
79
Intestinal mucosa
- 7 parts
- interval for villus epithelium replacement
Absorptive cells - simple columnar epithelium
Lacteal - all lipids and fats that go to lymphatics enter lacteal
Goblet cell
microvilli - brush border
enteroendocrine cells - produce hormones
intestinal crypt
Paneth cells - (deep in crypts) release antimicrobial agents
(pic slide ~56)
villus epithelium replaced every 2-4 days
80
Where are villi found in GI tract
only in SI
81
Duodenum modifications
duodenal glands
-secrete HCO3-
+help neutralize acidity from stomach
82
Ileum modifications
Aggregated lymphoid nodules
| -lot of Immune cells
83
Jejunum modifications
lots folds, great for absorption
84
SI secretions
| -4pts
- secreted in response to distension or irritation of mucosa by HYPERTONIC or ACIDIC chyme
- slightly alkaline (pH 7.4-7.8) and isotonic with blood plasma
- largely water, enzyme-poor, contains mucus
- facilitates transport and absorption of nutrients
85
Digestions in SI
- chars of chyme
- duration and f(x) of SI
CHYME from stomach contains:
- partially digested carbs and proteins
- Undigested fats
3-6 hours in SI
- most water absorbed
- Nearly all nutrients absorbed
86
How does chyme enter duodenum from stomach
- 3 steps
- what vol chyme enters
1) propulsion
- peristaltic waves move from fundus to pylorus
2) Grinding
- most vigorous peristalsis and mixing occurs close to pylorus
3) retropulsion
-pyloric end acts as pump
+delivers ~3mL of chyme into duodenum
+simultaneously forces most material backward into stomach
87
requirements for digestion and absorption in SI (3)
1) slow delivery of acidic hypertonic chyme
2) delivery of bile, enzymes, and HCO3- ions from LIVER and PANCREAS
3) mixing
88
Ileocecal sphincter/valve
closed when chyme exerts backward pressure
- prevents regurgitation into ileum
Relaxes to admit chyme into LI when:
- Gastroileal reflex enhances force of segmentation in ileum
- gastrin increases motility of ileum
89
liver
- largest gland in body (~3 LBS)
| - 4 lobes based on surface fts (8 based on vascular and biliary supply)
90
Falciform ligament (3)
- suspends liver from diaphragm and anterior abdominal wall (a mesentery)
- separates right and left lobes
- round ligament (ligamentum teres): remnant of fetal umbilical vein
- actually is a mesentary (ventral mesentary
91
Liver: blood supply
blood enters liver at porta hepatis via:
1) hepatic arteries
2) hepatic portal veins
blood exits liver through hepatic veins into IVC
THINGS ABSORBED IN GI CAPILLARIES GO TO LIVER FIRST
+first pass metabolism
92
Liver blood supply
| 5 BVs
hepatic veins
hepatic portal vein
inferior vena cava
R. hepatic artery
L. hepatic artery
93
Liver microscopy
Liver lobules
-hexagonal structures
-filter and process nutrient rich blood
-composed of plates of hepatocytes radiating from longitudinal central vein
+ventral veins all go to hepatic vein -> IVC
Connective tissue septum separates the hexagonal lobules
+CT septum differs in thickness btwn diff species
- liver sinusoids (leaky capillaries btwn hepatic plates) [btwn hepatocytes froming series of irregular plates)
- portal triads
94
Portal triad
```
portal triad
-at ea corner of lobule
-composed of :
+bile duct
+branch of HPV
+branch of hepatic artery
```
portal triad found in middle of portal lobule
-sends blood to 3 sep central veins
95
Kupffer cells (stellate macrophage)
in liver sinusoids
self sustaining population of macrophages within liver
remove debris (bacteria, worn out blood cells)
act as a gate-keeper for immune responses
96
```
Hepatocyte functions
(6)
```
1) process blood borne nutrients
2) synthesize and secrete hormones
3) storage
4) perform detoxification
5) immune surveillance
6) produce bile
97
hepatocyte function: process blood borne nutrients (6)
metabolism
-carb, protein, and fat metabolism
metabolism and detoxification of xenobiotics (CYP450)
Use AAs to make plasma proteins
- albumins (oncotic P)
- lipoproteins (VLDL, LDL, HDL, for cholesterol homeostasis)
- alpha/beta globins for transport: Ceruloplamsin (copper), transferrin (iron), Haptoglobin (hemoglobin), retinol binding protein (retinol), etc.
- clotting proteins (fibrinogen and prothrombin)
- anti-clotting proteins (plasminogen, antithrombin III)
make immune proteins (complement and C-reactive peptide)
make apoproteins (lipoprotein metabolism)
converts unconjugated bilirubin (indirect) to conjugated bilirubin (direct)
98
hepatocyte function: synthesize and secrete hormones (4)
- insulin-like growth factor 1 (growth hormone mediator)
- angiotensinogen (BP and fluid balance)
- Thrombopoietin( platelet production)
- hepcidin (iron homeostasis)
99
hepatocyte function: Storage (4)
-Fat soluble vitamins (A,D,K,E) and vit B12
-iron and copper
-store glucose as glycogen (glycogenesis); makes glucose from noncarbohydrate sources (glugoneogenesis)
+releases when needed (glyconeolysis)
-fat
100
hepatocyte function: Perform detoxification (1)
```
Ammonia (NH3) -> Urea
-ammonia is toxic to CNS (Crosses BBB)
-sources of ammonia:
+colon
+kidneys
+erythrocyte breakdown
+muscle metabolism
```
101
hepatocyte function: Immune surveillance (1)
Kupffer cells (AKA stellate macrophages) destroy bac, worn out erythrocytes, and other foreign substances in food
102
hepatocyte function: Produce Bile
- how much produce
- colour
- content (7)
- hepatocytes produce ~900mL bile/day (~500mg bile acids)
- yellow-green, alkaline solution
CONTENTS:
1) water (95-97%)
2) bile salts [bile acid (hydrophobic) conjugated with taurine or glycine (hydrophillic)]
+primary acids synthesized by liver from cholesterol (cholic and chenodeoxycholic acids)
+secondary bile acids synthesized from primary bile acids by colonic bacterial enzymes (deoxycholic and lithocholic acids)
3) bilirubin (conjucated/direct) -> metabolism by small intestines bacteria produces stercobilin
4) phospholipids
5)electrolytes (Na+, Ca2+, HCO3-)
6) Xenobiotics (things body trying get rid of)
7) IgA
103
Biliary Tree
R/L hepatic duct ->common hepatic duct +input from cystic duct from gall bladder -> bile duct
104
Gall Bladder
- thin walled muscular sac on inferior/anterior surface of liver
- Stores and concentrates bile by absorbing its water and ions
105
Functional relationship in storage and ejection of bile (4 steps)
-relative movement of blood and bile
1) Liver continuously secretes bile
2) bile is stored and concentrated in gallbladder
3) duodenum releases CCK which triggers dilation of hepatopancreatic sphincter and contraction of gallbladder
+ejects bile into duodenum through duodenal ampulla
4) Bile salt emulsifying lipid droplet in digestive tract lumen
-Blood and bile move in opposite directions
+bile go CV -> portal triads
+ blood go portal triad -> CV
106
enterohepatic circulation (4 steps)
1) bile salts (cholic and chenodeoxycholic acids) are secreted into duodenum
2) as bile salts travel through SI, allow lipid digestion and absorption to occur
3) 95% bile salts reabsorbed by ileum
4) reabsorbed bile salts travel via hepatic portal vein back to liver where recycled. Only 5% bile salts newly synthesized ea time
107
Digestion in SI
Chyme slowly released into duodenum
- released in small amount so acidity dosent dmg duodenum, needs be buffered
- hypertonic and low pH, requires constant mixing for proper digesions
- no fat digestion
- carbs and proteins are partially digested
- virtually all nut abs occurs in SI
108
Motility in SI
- what is most common
- what initiates
- where move contents
most common motion in SI is segmentation
- initiated by pacemaker cells (cajal cells)
- moces contents steadily twd ileocecal valve
- constant back and forth mixing in SI
109
Control of motility - segmentation
Frequency of cajal cell pacemaker activity differs:
+3 /min in stomach
+12-14 /min in duodenum
- 8-9 /min in ileum
+3 /min in colon
110
what controls intensity of segmentation
Intensity of segmentation altered by long and short reflexes
Long reflex
- PNS activity enhances
- SNS activity decreases
More intense contractions greater mixing effect
basic contractile rhythms of various intestinal regions remain unchanged
111
purpose of segmentation
absorption along GI tract
- only stuff touching lumenal walls can be abs'd
- segmentation allows constant mixing so more likely abs more nuts
slide 7 has list of what abs in diff regions GI tract
112
Control of peristalsis
- when occur
- what occur at this point (3)
Peristalsis occurs after most nuts have been absorbed
-at this point segmenting movements wane and the duodenal mucosa begins release of motilin
-peristaltic waves begin in duodenum, sweep slowly along intestine
+move 50-70cm before dying out
-each wave initiated more distally MIGRATING MOTILITY COMPLEX (MMC)
+takes ~2hrs
process sweeps last remnants of meal, bac, and other debris into LI
113
control peristalsis - ACh
- proximal vs distal impulses
- mvmnt of chyme/SI segments
ACh-releasing (cholinergic) sensory neuron in SI send messages to sev diff interneurons in myenteric plexus, regulates:
- impulses sent proximally by cholinergic effector neurons cuase contraction and shortening of circular muscle layer
- impulses sent distally to certain interneurons cause shortening of longitudinal muscle layer and distension of intestine
As result proximal area constricts and forces chyme along tract
-lumen of distal part of intestine enlarges to receive
114
Regulation of pancreatic secretion
- 4 steps
- neural input
- CCK/secretin act on anything else?
1) -Acidic chyme enter duodenum causing enteroendocrine cells of duodenal wall release secretin.
- fatty protein-rich chyme induces release of CCK
2)CCK and secretin enter BS
3) CCK induces secretion of enzyme-rich pancreatic juices
- secretin causes copious secretion of bicarbonate rich pancreatic juice
During cephalic and gastric phases
-stimulation by vagal nerve fibres cause release of pancreatic juice and weak contractions of gallbladder
secretin and Cholecystokinin (CCK)
-also stimulates secretion of bile from liver
115
Acinus of pancreas
acinar cells (acinus associated) and centroacinar (ducts) are exocrine ducts
- centroacinar cells makeup small ducts that secrete HCO3-
- zymogen granules = enzymes stored in acinar cells
116
Pancreas - sphincter of Oddi
Sphincter of oddi = hepatopancreatic sphincter
- muscular valve controlling flow of digestive juices (bile and pancreatic juice)
- relaxed by hormone CCK
117
Composition of pancreatic juice (2)
contains enzymes and electrolytes (mostly HCO3-)
+neutralize acid chyme and provide optimal env
-some enzs are released in inactive (zymogen) form and activated
118
GIP
targets pancreas causing release of insulin improving nutrient absorption
119
VIP
improves nutrient absorption
120
Absorption of nutrients (5) strucs
Villi, microvilli, and large circular folds massively inc SA of SI
- lacteal
- blood capillaries
121
Absorption of carbohydrates
Salivary amylase
- begins starch digestion
- in mouth, destroyed once reach stomach
Pancreatic amylase
-digest starch to oligosaccharides
+oligosaccharides hydrolized by brush border enzymes
122
amylase
| -what breaks into single C mols?
work on storage forms of carbs (glycogen and starch)
starch brocken by amlase -> short oligosaccharides, maltriose (3C mol), Maltose (2C mol)
Brush border enzs break down into single C mols
123
Absorption of Carbs
| -what disach->monosach + exception
Dissacharides -> monosaccharides
- catalysis by Brush border enzymes
- EXCEPTION = beta-1,4 bonds in cellulose
124
Sucrase
sucrose -> glucose + fructose
125
Maltase
Maltose -> glucose + glucose
126
Lactase
Lactose -> glucose + Galactose
127
Digestion of proteins
Pepsin
- released by chief cells
- in stomach
- cleaves proteins into smaller polypeptides
IN SMALL INTESTINE
pancreatic enzymes
+trypsin, chymotrypsin, carboxypeptidase
Brush border enzymes
+ aminopeptidases, carboxypeptidases, dipeptidases
128
Activation of enzymes in SI
-tripsinogen --> trypsin
+activated by trypsin and membrane bound enteropeptidase
-chymotrypsinogen --> chymotrypsin
-procarboxypeptidase --> carboxypeptidase
+both activated by trypsin
129
Protein absorption
- AA abs
- di/tripeptide abs
AA by cotransport with Na+
Dipeptides and tripeptides transported by secondary AT using H+ gradient
130
Chemical digestion of fats
| -bile salts
-without bile salts SA would be too low to effectively degrade droplet with enzs
+bile salts inc SA by degrading fat droplet
- lipases and other fat degrading enzs digest fats
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Bile salts
-modified cholesterol molecules
-polar and nonpolar regions
-form micelles, inc SA of fat droplets
+polar head face exterior, non-polar tail face inward to droplet
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Triglycerides from degredation enter epithelial cell layer and become chylomicrons, becoming secretory vesicles shipped into lacteal
131
bunch of shit on slide 25, idk if important
132
Chemical Digestion of nucleaic acids
(DNA and RNA)
Absorption: AT via membrane carriers
+absorbed in villi and transported to liver by hepatic portal vein
Enzymes used:
-pancreatic ribonucleases and deoxyribonucleases in SI
after above, brush boarder enzymes:
+ nucleosidases and phosphatases
Final degradation products:
pentose sugars, N-containing bases, phasphate ions
+these are what get abs into capillary blood in billi etc
133
Electrolyte absorption
Na+ coupled with abs of glucose and AA
Iron transported into cell where it binds to ferritin
Anions passively follow electrical potential established by Na+
K+ diffuses across teh intestinal mucosa in response to osmotic gradients
Ca2+ absorption regulated by vitamin D and Parathyroid hormone (PTH)
134
Vitamins transport out of lumen
- water sol (exception?)
- vitamin B12
- Fat soluble vitamins
Water soluble (except b12)
- diffusion
- folows [ ] gradient
vitamin b12
- AT
- must be bound to intrinsic factor b4 abs
Fat soluble vitamins
- diffusion
- absorbed from micelles tgthr with dietary lipids
135
Water absorption
- 95% water abs in SI by osmosis
- Water moves in both directions across intestinal mucosa
- net osmosis occurs whenever [ ] gradient established by AT of solutes into mucosal cells
136
Large intestine
- 3 unique fts
- cecum and appendix
Unique geatures
1) Teniae coli
- 3 bands of longitudinal SM in its muscularis
2) Haustra
- pocketlike sacs caused by the tone of the teniae coli
3) Epiploic appendages
- fat-filled pouches of visceral peritoneum
saclike cecum lies below ileocecal valve and contains a wormlike veriform appendix
137
veriform appendix f(x)
thought to store good bacteria
138
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Large intestine (colon) mucosa
-anal canal
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- simple columnar epithelium except in anal canal
| - anal canal has stratified squamous epithelium that merges with true skin surrounding anus
139
Colon modifications
- what lack
- what has and f(x)
-No circular folds, villi, almost no cells that secrete digestive enzymes
-mucous produced by goblet cells
+eases passage of feces
+protects intestinal wall from irritating acids and gases
140
Motility in LI: haustral contractions
Haustral contractions
-slow segmenting movements lasting ~1min that occur every 30min
-occur mainly in Transverse and descending colon (rare in DC)
+reflect local controls of SM within walls of individual haustra
-as haustrum fills with food residue, distension stimulates its muscle to contract
+propels luminal contents into next haustrum
141
Motility of LI: mass movements and reflexes
| -bulk
Mass movements
-contractile waves that move over large areas of colon 3-4x/day and force contents twd rectum
Presence of food in stomach activates
- gastroileal reflex in SI
- Gastrocolic reflex in colon
Bulk (fiber)
-in diet inc str of colon contractions and softens the stool
+pulls H2O into LI and softens stool
142
LI (fx)
- digestion
- reclamation
- major f(x)
- essential for life?
Other than digestion of enteric bacteria, no further digestion takes place
vitamins, H2O and electrolytes (K+, HCO3-, H+, Cl-, Na+ )reclaimed
MAJOR FUNCTION
-propulsion of fecal material twd anus
Not essential for life, but convenient able control when defecate
143
Colon bacteria
- where from and f(x)
- what release
- how much gas/day
- what synthesize
remaining bac from SI colonize colon
- metabolize some host derived proteins (mucin, heparin, hyaluronic acid)
- ferment some indigestible carbs (cellulose, xylan, others)
release irritating acids and mix of gases (dimethyl sulfide, H2, N2, CH4, CO2)
~500mL gas (flatus) produced each day
+more when certain carb rich foods (sa beans) eaten
Synthesize B complex vitamins and most of vitamin K Liver requires to synthesize some of clotting proteins
144
Anus
- pectinate line (2)
- superficial venous plexuses (hemroidal veins)
- inflammation of SVP
- sphincters (which is voluntary/involuntary)
pectinate line - line in anus structure
+superior (above line) - mucosa innervated by visceral sensory fibres and relatively insensitive to pain
+inferior (below line) - very sensitive to pain (somatic fibers)
Two superficial venous plexuses associated with anal canal
1) part of anal columns
2) anus
-if these hemorrhoidal veins are inflamed, itchy varicosities called hemorrhoids form
+prolapsing (fall out anus)
+internal hemorrhoids - not painful
+external hemorrhoids - very painful
External anal sphincter = conscious control
internal anal sphincter = involuntary control
145
Defecation
- how occur
- voluntary signals control what sphincter
How occur
-distension of rectal walls by feces
+stimulates contraction of rectal walls
+relaxes internal anal sphincter (involuntary)
Voluntary signals
-stimulate relaxation of external anal sphincter and defecation occurs
