Chapter 17 - Digestive System Flashcards
(116 cards)
1
Q
What is the order in which a food molecule will encounter the digestive tract?
A
- Pharynx
- Esophagus
- stomach
- duodenum
- cecum
- transverse colon
2
Q
what are the main 4 tunics of the digestive tract?
A
- serosa
- muscularis externa
- submucosa
- mucosa
3
Q
Muscularis externa tunic
A
- muscle tissue
- outer smooth muscle for length
- inner layer controls radius
- enteric nervous system & myenteric plexus
4
Q
Submucosa tunic
A
- connective tissue
- submucosal plexus
- located within muscularis externa
- contains nerves, circulatory and lymphatics
5
Q
Mucosa Tunic
A
- forms lumen
- three sublayers:
1. muscularis mucosae (smooth muscle; thin)
2. lamina propria (loose connective)
3. epithelial tissue forming lumen
6
Q
Serosa tunic
A
- contiguous with mesenteries
- contains blood vessels, nerves, lymphatics
7
Q
Peristalsis
A
- ** wavelike movements** through coordinated contraction of circular smooth muscle (controls radius) behind a bolus, and relaxation of circular sooth muscle in front of it.
- bolus moves forward
- contraction of longitudinal smooth muscle (length) which sends bolus forward (inchworm)
-** short distance** waves
8
Q
segmentation
A
- simultaneous muscle contractions of circular smooth muscle in front of AND behind bolus
- back and forth movements
- bolus gets mixed with digestive secretions
9
Q
Mechanical digestion
A
- begins in oral cavity
- does NOT break chemical bonds
- goal is to increase surface area for chemical digestion
10
Q
Chemical digestion
A
- begins in oral cavity but peaks in stomach and small intestine
- carried out by enzymes
- breaks chemical bonds to generate small molecules from large molecules
11
Q
____________and ____________ are the last of the major digestive processes.
A
secretion; absorption
12
Q
Secretion
A
- movement of substance from cells into the lumen
- e.g. secretion of HCl into stomach to start digestion
- PRODUCES ACID IN STOMACH
- highly selective
13
Q
Absorption
A
- movement of a substance from the lumen to cells
- highly selective process by specific region
14
Q
Functions of the oral cavity
A
- protects mouth/digestive system against physical and chemical abrasions and food-borne pathogens
- Increasing surface area of food
- Coating food with saliva
- Initiation of swallowing to deliver food to the stomach
15
Q
Mastication
A
Chewing
16
Q
Features of mastication
A
- mechanical digestion
- increases surface area
- mixes food with saliva
- under control of medulla oblongata
- done w/ teeth
17
Q
What teeth are for cutting and tearing food?
A
incisors (8) and canines (4)
18
Q
What teeth are for crushing and grinding?
A
premolars (8) and molars (12)
19
Q
What are all the components of saliva?
A
- water
- electrolytes
- mucous
- leukocytes
- epithelial cells
- glycoproteins
- enzymes
- IgA
- lysozymes
20
Q
Main features/functions of saliva
A
- pH between 6.5-7.5
- moistens epithelia and liquefies food
- 5% of polysaccharide breakdown (salivary amylase)
- innate immunity due to antimicrobial lysozyme and IgA
- secretion is stimulated by facial and glossopharyngeal nerves(CN VII & CN IX) in response to varied stimuli
21
Q
Saliva is secreted into oral cavity by 3 glands:
A
- parotid gland
- submandibular gland
- sublingual gland
22
Q
What are the 3 phases of deglutition?
A
-
swallowing = deglutition
1. voluntary phase
2. pharyngeal phase
3. esophageal phase
23
Q
Voluntary phase of swallowing
A
- mouth, tongue, teeth, and secretions make bolus
- tongue pushes bolus against hard palate and toward back of oral cavity into oropharynx and detected by receptors in pharyngeal wall
24
Q
Pharyngeal phase of swallowing
A
- contact of food w/ sensory receptors in posterior wall of oropharynx —> afferent info through trigeminal (CN 5) and glossopharyngeal (CN IX) nerves to swallowing center in medulla
- motor info travels —> trigeminal (CN V), glossopharyngeal (CN IX), vagus, and accessory nerves to soft palate and pharynx
- upper esophageal sphincter relaxes (involuntary)
25
Esophageal phase of swallowing
- ends swallowing process
- lower esophagus = smooth muscle (unconsciously controlled)
- upper esophagus = skeletal muscle (conscious control to initiate swallowing)
- food travels through esophagus --> stim. stretch receptors --> signal enteric nerve plexus to smooth muscle --> stim. contraction and peristalsis waves
- activates **efferent neurons**
- food enters stomach
26
Stomach
- short-term storage reservoir
- mix and grind stomach contents w/ HCl and pepsin --> chyme
- cont. chemical and enzymatic digestion (proteins)
- move chyme into small intestine
- connects to esophagus in **cardiac region**
27
What are gastric pits?
openings for secretions into the stomach
- parietal cells
- chief cells
- G cells (gastrin)
- D cells (somatostatin)
- Enterochromaffin cells
28
chyme
an acidic fluid containing partially digested food
29
chief cells
secrete and synthesize pepsins (major proteases active in stomach)
- contain hormone receptors that stimulate pepsin release
- preproenzyme --> pepsinogen --> pepsin
30
what are the pepsins synthesized by chief cells?
- **endopeptidases** that recognize A.A. sequences embedded within proteins
| responsible for bulk of protein digestion
31
Exopeptidases
cleave peptides from the ends of proteins into single amino acids
| includes carboxypeptidase
32
Parietal cells
- secrete **HCl** to a concentration of ~160 mM (0.8 pH) using active transport
- regulated by paracrine signaling
- secrete **bicarbonate** on basolateral side
- secrete **intrinsic factor**
- use enzyme, **carbonic anhydrase** to combine CO2 and H2O into carbonic acid (H2CO3)
- secrete H+ via active transport w/ H+/K+ ATPase proton pump
33
Enterochromaffin (ECL) cells
- secrete **histamine** to stimulate acid secretion
- Binds H2 receptors on parietal cells to stimulate their HCl secretion
34
D cells
- secrete **somatostatin**
- inhibits **gastrin** and **histamine** secretion
35
G cells
- secrete **gastrin** in response to food in lumen and stomach distension
- binds receptors on basolateral side of parietal cells to stimulate HCl release
- also stimulates **pepsin** (chief cells) and **histamine** (ECL cells) secretion
36
Proton Pump
- parietal cells secrete H+ into stomach lumen via H+/K+ - ATPase
- Cl- ions are transported into lumen via conductance channels
- HCl is formed in the lumen
37
Gastric/duodenal ulcer
- break in normal tissue lining stomach or small intestine
- **benign ulcers** caused by **imbalance** between defenses of stomach mucosal lining and the secretion of acid and pepsin
- 90% of all cases are bc of the bacteria **H. pylori**
- stress/spicy foods do NOT cause/worsen ulcers
- most receptive inhibitors: **H2 receptor antagonists** and **proton pump inhibitors**
- can also be treated w/ antacids, antibiotics, and dietary changes
38
Interstitial cells of Cajal
within greater curvature of stomach; act as pacemaker cells
- stimulate **tonic** (w/o outside stimulation) contractions
39
Pacemaker potentials
reduce the threshold for contraction of smooth muscle and can lead to burst of action potential/smooth muscle contraction
40
Steps of stomach motility contractions
1. food mixes with stomach secretions to form chyme
2. **tonic** smooth muscle contractions
3. **phasic** (stim. by nervous system/hormones/food) smooth muscle contraction
4. upper stomach expands, keeps constant pressure
5. mixing waves push chyme towards pyloric sphincter
6. stomach distension stimulates gastrin release
7. pyloric sphincter relaxes, food is pushed into duodenum
41
Functions of small intestine
- **mix liver and pancreatic secretions** w/ chyme
- to continue digesting carbohydrates and proteins, and to **initiate fat digestion**
- **absorb** nutrients
- move chyme to large intestine
- produce **hormones** that regulate digestive system
- produce increased numbers of **immune cells** that protect against pathogens associated with food and microbiome
42
How much digestion occurs in small intestine?
90%
43
Three parts of small intestine
1. duodenum
2. jejunum
3. ileum
44
Duodenum
- shortest segment (4%)
- **duodenal papillae**: common bile duct and pancreatic duct join w/ hepatopancreatic ampulla (allows small intestine to receive secretion from liver, pancreas, and gallbladder)
45
Duodenum
- shortest segment (4%)
- **duodenal papillae**: **common bile duct** and **pancreatic duct** join w/ hepatopancreatic ampulla (allows small intestine to receive secretion from liver, pancreas, and gallbladder)
46
Plicae
series of large projections formed by mucosa and submucosal layers
47
Villi
finger-like projections formed by mucosal layer; 0.5-1.5 mm in length (formation stim. by contraction of mucosal layer)
- **lacteal**: blood capillary network inferior to each villus
48
Brush border
major site of nutrient digestion and absorption; formed by microvilli
49
The intestinal epithelia lining the lumen of small intestine consists of:
- absorptive cells
- granular cells
- goblet cells
- enteroendocrine cells
- all continuously replaced as stem cells divide w/in tubular invaginations of mucosal layer aka **intestinal crypts** (at base of each villus)
50
absorptive cells
have increased microvilli and produce digestive enzymes
51
granular cells
participate in immune protection of small intestine
52
goblet cells
produce protective mucus
53
enteroendocrine cells
produce many different hormones
54
There is a (____) in number of (____) and (____) as the intestine progesses.
There is a **decrease** in number of **plicae** and **villi** as the intestine progesses
55
What are the major sites of nutrient reabsorption?
duodenum and jejunum
56
Peyer's patches
lymphoid nodules; numerous in ileum mucosal and submucosal layers
- play an important role in immune surveillance and part of gut-associated lymphoid tissue (GALT)
57
the ileum and large intestine join at the:
ileocecal junction (has a ring of smooth muscle, a sphincter, and the one-way ileocecal valve)
58
Describe motility in the small intestine
- both segmentation and peristalsis occur
- very few peristaltic contractions travel entire length
- slow chyme movement allows time for digestion
- ileocecal sphincter mildly contracted
59
describe the secretions from small intestine into the lumen
- do NOT contain HCl or pepsin
- contains mucus, electrolytes, and water (duodenal glands, intestinal glands, and goblet cells)
-intestinal mucosal enzymes attached to microvilli forming brush border (disaccharides, peptidases, and nucleases)
- hormones (**Enterogastrones**) released into bloodstream: **cholecystokinin** (CCK), **gastric inhibitory peptide** (GIP), **secretin**
60
describe the secretions into small intestine from accessory organs
- liver and pancreatic secretions --> duodenum
- pancreas supplies digestive enzymes and an alkaline broth to neutralize
- liver and gallbladder provide bile salts that aid in lipid digestion
61
Appendicitis
- inflammation of appendix
- **Symptoms**: lower abdominal pain, nausea, vomiting, decreased appetite
- **Causes**: appendix blockage by calcified fragments of feces, inflamed lymphoid tissue, parasites, gallstones or tumors
- **Treatment**: surgical removal of appendix
62
Functions of large intestine
- **absorption of water** from remaining chyme --> semi-solid feces
- secretion of **protective mucus** and facilitation of movement of undigested food
- provides a hospitable area for growth of extensive bacterial colonies that metabolize nutrients and steroids, produce vitamin K, and prevent growth of pathogenic bacteria
- production of large #s of **immune cells** organized into **Peyer's patches** and primary follicles --> protection
63
Large intestine extends from ________________ to the ____ and consists of:
ileocecal sphincter; anus; cecum, colon, and rectum
64
Cecum includes:
vermiform appendix (small, closed tube studded w/ lymph nodules providing immune surveillance)
65
What is the large intestine beyond the cecum called?
colon
66
Colon features
- 2 m in length
- made up of 4 parts: ascending, transverse, descending, and sigmoid
- does not form folds/villi
- does have tubular crypts
- circular smooth muscle layer --> complete
- longitudinal muscle layer --> incomplete
- 3 bands: **teniae coli**: run entire length of colon --> segmented appearance (each segment is called a **haustrum**)
67
How much chyme enters the cecum each day?
~2 L of chyme enters each day and >90% of volume is reabsorbed leaving ~200mL to be eliminated
68
Rectum
straight, muscular tube that extends from **sigmoid colon** to the **anal canal**
- thick smooth muscle layer forming **internal anal sphincter** (involuntary motor control)
- skeletal muscle forms the **external anal sphincter**(voluntary motor control)
69
Describe motility in large intestine
- **peristalsis** moves chyme through ascending colon
- **mass movements** occur 3-4 times a day in transverse and descending colon; lead to defecation reflex
- **enterocolic reflex** (stomach) and the **duodenocolic reflex** (small intestine) are changes in volume
70
Describe the secretions of large intestine
- colon's mucosal layer is lined w/ **goblet cells** and crypts
- large mass of gut flora produces **acid** in colon
- increased NaCl in colon pulls water through the colon wall by **osmosis**
- **diarrhea:** caused by increased colon secretion leading to distention of the colon and abnormal frequent discharge of fluid feces
71
What is the largest solid internal organ?
liver
72
Functions of liver
- detoxify a wide range of chemicals brought into body
- metabolizes and interconverts nutrients into a wide range of forms for storage/use by other tissues
73
Function of gallbladder
stores bile until it's needed for fat digestion
74
Bile consists of:
water, ions, and bile salts
75
Pathway bile salts take to enter small intestine:
1. bile salts produced by liver and moves through right and left hepatic ducts to fuse w/ the common hepatic duct
2. bile salts move through the ducts bc of peristalsis
3. bile salts also stored w/in gallbladder and move through the cystic duct to fuse w/ the common hepatic duct --> becomes common bile duct as it passes through pancreas
4. common bile duct and pancreatic duct fuse into single pancreatic duct, which takes bile salts and all pancreatic secretions into duodenum through sphincter of Oddi.
76
Cholelithiasis
gallstones
77
Lobes of liver
major lobes: left and right
minor lobes: caudate and quadrate
78
Septa
branching walls made of connective tissue that makeup the 3D structure of liver (blood, lymphatic vessels, and ducts)
79
Lobules of liver
each lobule is hexagonal w/ portal triads at vertices and a central vein in middle
- formed by hepatic portal vein, a hepatic artery, and a bile duct
80
Hepatocytes
- produce bile, metabolize nutrients, detoxify harmful substances, and synthesize blood components
- adjoined polyganol-shaped cells
- **space of Disse:** space between endothelium and hepatocytes; collects lymph for delivery to lymphatic capillaries
81
Hepatic Portal System
- majority of liver's blood is venous blood
- ~75% of blood is from portal vein ---> empties into hepatic sinusoids
- remove O2 and nutrients from blood to support metabolic needs
- plasma is filtered into space between endothelium and hepatocytes
- blood drains from sinusoids into central vein of each lobule --> C.V. drain into larger hepatic vein --> exits liver --> inferior vena cava
82
Order of ingested food molecule:
1. duodenal mucosa
2. hepatic portal vein
3. sinusoid
4. hepatocytes
5. central vein
6. hepatic vein
7. vena cava
8. right atrium of heart
9. systemic artery
83
Bile
- complex fluid containing water, electrolytes, and organic molecules (bile acids, cholesterol, lecithin, and bilirubin)
- **emulsifies** fat products --> micelles
- aids in absorption of fat-soluble vitamins
- neutralizes acidic chyme
- flows through biliary tract --> small intestine
- flow is lowest during fasting
84
Whenever chyme enters small intestine, acid and partially digested fats and proteins stimulate the secretion of ____________ and ___________.
cholecystokinin (CCK) and secretin
85
Cholecystokinin is released in response to what?
presence of fat in duodenum
- after, CCK stimulates contractions of gallbladder and common bile duct --> bile to small intestine
86
Secretin is released in response to what?
acid in duodenum
- after, it stimulates biliary duct cells to secrete bicarbonate and water --> expands volume of bile and increases flow into intestine
87
Functions of pancreas
- produces a watery secretion that is rich in HCO3-
- produces enzymes that aid in chemical digestion
88
Islets of Langerhans
small clusters of cells that secrete insulin, glucagon, etc.
- arranged in grape-like clusters (**acini**)
- pancreatic exocrine glands w/ ducts
89
Secretions of pancreas
- pancreatic juice (stim. as food enters stomach)
- made of: digestive enzymes and HCO3-
90
Majority of proteins are digested by:
pancreatic proteases
91
2 major pancreatic proteases are:
trypsin and chymotrypsin (inactive forms are trypsinogen and chymotrypsinogen)
- **CANNOT** digest proteins/peptides into single amino acids
92
Trypsinogen
- embedded in intestinal mucosa
- activated by the enzyme **enterokinase** by cleavage of a specific peptide sequence therefore changing its structure and function
- once trypsin is made, it activates chymotrypsinogen by cleavage of another specific peptide sequence
93
Carboxypeptidase
can break peptides into single A.A.s
94
Cholecystokinin (CCK)
- hormone secreted and synthesized by duodenal endocrince cells
- presence of partially digested proteins and fats in small intestine stimulates CCK secretion into blood
- CCK binds to receptors on pancreatic acinar cells, stimulating them to secrete large quantities of digestive enzymes
95
Secretin
- produced by duodenal exocrine cells in response to acid in the duodenum when chyme enters from stomach
- stimulates pancreatic duct cells to secrete water and HCO3- (digestive enzymes secreted by acinar cells are flushed out of pancreas to duodenum)
96
Gastrin
- secreted in large amounts by stomach in repsonse to gastric distention and irritation of stomach wall
- stimulates pancreatic acinar cells --> secrete digestive enzymes
97
Local control of digestive system from enteric nervous sytem in ________ and ________ plexuses.
submucosal; myenteric
98
Higher level control of digestive system comes from both ________ and ________ branch of ANS.
sympathetic; parasympathetic
99
2 neural-reflex arcs
short and long reflexes
100
short reflex arc
all reflex components are present w/in GI tract itself
101
Long reflex arc
begin w/ receptors in GI tract that send afferent signals to CNS which sends back an efferent signal to enteric plexi and GI effector cells
102
3 major types of enteric neurons
1. sensory neurons
2. motor neurons
3. interneurons
103
Sensory neurons
detect chemical changes in the composition of the digestive tract contents, and mechanical changes in digestive tract wall (Stretch)
104
Motor neurons
stimulate/inhibit smooth muscle contraction or glandular secretion
105
Interneurons
integrate signals between afferent and efferent neurons
106
(T/F): the enteric nervous system is capable of controlling the digestive tract independently of the CNS
True
ex. basal electrical rhythm
107
Pancreatic amylase
hydrolyzes starch into maltose
108
Lecithin
helps break down fats into mecelles
109
Septa of liver
branching network of connective tissue forming walls
110
Hepatic cords
radiate out from each central vein; filled with hepatocytes
111
Bile Cannaliculus
cleft-like lumen lying between each hepatic cord
112
Carbohydrate Digestion
**Oral cavity**
- polysaccharides and disaccharides are converted into smaller polysaccharides and maltose by salivary amylase
Small intestine
- pancreatic amylase converts into disaccharides
- disaccharides into monosaccharides
113
Protein digestion
begins in **stomach**
- pepsin converts proteins into small polypeptides
**Small intestine**
- uses pancreatic trypsin and chymotrypsin into smaller polypeptides
- pancreatic carboxypeptidases convert to small peptides
- Dipeptidases, carboxypeptidase, and aminopeptidase convert to amino acids
114
Nucleic acid digestion
**Small intestine**
- DNA and RNA converted to nucleotides by pancreatic nucleases
- Nucleotidases convert nucleotides into nucleosides
- Nucleosidases and phosphatases convert into nitrogenous bases, sugars, and phosphates
115
Fat digestion
**Small intestine**
- fat (triglycerides) converted into glycerol, fatty acids, and monoglycerides by pancreatic lipase
116
Tissue layers of digestive tract in order you would encounter moving from the **lumen** to the **abdominal cavity**
- mucosal epithelium
- lamina propria
- muscularis mucosa
- submucosa
- circular layer of smooth muscle
- myenteric plexus
- longitudinal layer of smooth muscle
- serosa
