Digestive System Flashcards
1
Q
What are the digestive functions?
A
- ingestion
- mechanical processing
- digestion: chemical breakdown of food into small organic fragments
- secretion: water, acids, enzymes, buffers, and salts
- absorption: organic substrates, electrolytes, vitamins, and water
- excretion: waste products, defecation
2
Q
What is included in the gastrointestinal tract?
A
mouth
pharynx
esophagus
stomach
small intestine
large intestine
anus
3
Q
What are the accessory organs of the digestive system?
A
teeth
tongue
glandular organs: salivary glands, liver, pancreas
4
Q
What are monogastrics?
A
a single, true stomach
5
Q
What do ruminants have?
A
multiple compartment, including a large, fermentative compartment called the rumen
6
Q
What are the four major layers of the GI tract wall?
A
mucosa
submucosa
muscularis externa
serosa
7
Q
What is the digestive epithelium of the mucosa?
A
- a stratified squamous epithelium in the mouth, pharynx, and esophagus
- a simple columnar epithelium (containing goblet cells) in the stomach, small intestine and almost the entire length of the large intestine
8
Q
What is the lamina propria of the mucosa?
A
- a layer of areolar tissue
- contains blood vessels, sensory nerve endings, lymphatic vessels, smooth muscle cells (muscularis mucosae), mucosal glands, and lymphoid tissue
9
Q
Describe the longitudinal folds (rugae) of the mucosa
A
- disappear as the tract fills (circular folds or plicae)
- permanent transverse folds: villi, microvilli
these structures dramatically increase the surface area available for absorption
10
Q
What is the submucosa?
A
- a layer of dense irregular connective tissue that surrounds the muscularis mucosae
- contains large blood and lymphatic vessels, exocrine glands
- a network of nerve fibers and scattered neurons (submucosal plexus)
11
Q
What does the muscularis externa contain?
A
smooth muscle cells:
- an inner, circular layer
- an outer, longitudinal layer
12
Q
What does the muscularis externa do?
A
- an essential role in mechanical processing and in the movement of materials
- movements are coordinated primarily by neurons of the myenteric plexus
13
Q
What is the serosa?
A
a serous membrane
14
Q
What is the order of the lining of the GI tract?
A
mucosa
- epithelium
- lamina propria
- muscularis mucosa
submucosa
muscularis propria
- circular muscle
- longitudinal muscle
serosa or adventitia
15
Q
What is peristalsis in the movement of digestive materials?
A
- circular muscle contractions
- wavelike movement along the tract
- propel digestive tract contents along the tube ahead of them
16
Q
What is segmentation in the movement of digestive materials?
A
- periodic circular muscle contractions
- occur in different adjacent sites
- mixes digestive tract contents and slows their movement through the tract
17
Q
What are the neural mechanisms that control digestive function?
A
short reflexes
- the sensory neurons, interneurons, and motor neurons are all located in the myenteric plexus
- coordinating local peristalsis and triggering the secretion of digestive glands in one regions of the digestive tracts
long reflexes
- involve interneurons and motor neurons in the CNS (ANS)
- control large-scale peristaltic waves
18
Q
Describe the hormonal mechanisms that control digestive mechanisms
A
- the digestive tract produces at least 18 hormones
- affect evert aspect of digestive function and may affect the activities of the other systems
19
Q
What are the local mechanisms that control the digestive function?
A
local factors (pH, physical and chemical stimulations) affect adjacent cells within a small segment of the digestive tract
20
Q
What is included in the oral (buccal) cavity or mouth?
A
lips, tongue, teeth, salivary glands, hard plate, soft plate, and oropharynx
21
Q
What are the functions of the oral cavity?
A
- analysis of food
- mechanical processing
- lubrication by mixing with mucus and salivary secretions
- initiating the digestion of carbohydrates and lipid by the enzymes of salivary glands
22
Q
What are the salivary glands made of?
A
three pairs of compound tubuloalveolar glands
23
Q
What are the three glands of the salivary glands?
A
parotid glands
- largest
- produce watery saliva containing salivary amylase
submandibular glands
- secrete a mixture of buffers, glycoproteins and amylase
sublingual glands
- smallest
- produce a watery, mucous secretion that acts as a buffer and lubricant and lingual lipase
24
Q
What are the functions of the monogastric stomach?
A
- the bulk storage of ingested food
- the mechanical breakdown of ingested food
- the disruption of chemical bonds in food via acids and enzymes (mainly protein digestion by pepsin)
ingested food + secretions of stomach = highly acidic, partially digested chyme
25
What are the five regions of the monogastric stomach?
- the cardia: opening from the esophagus
- the fundus: distensible blind pouch
- the body: central portion of the stomach
- the pyloric antrum: lower part
- the pylorus: muscular sphincter guards the exit from the stomach
- in a relaxed state, the stomach lining contains numerous rugae
26
Describe the histology of the stomach
the epithelium produces mucus that covers the interior surfaces
gastric pits: mucous cells, mucus
in the fundus and body: gastric glands
- parietal cells: secrete hydrochloric acid
- chief cells: secret pepsinogen, which is converted by acids to the enzyme pepsin
in the pyloric antrum: endocrine cells
- G cells: secrete pepsin that stimulate the secretion of both parietal and chief cells and contraction of the gastric wall
27
What regulates gastric activity?
A. the cephalic phase
B. the gastric phase
C. the intestinal phase
28
What is the function of the cephalic phase?
prepare stomach for the arrival of food
29
What is the duration of the cephalic phase?
short (minutes)
30
What is the mechanism of the cephalic phase?
neural, via preganglionic fibers in vagus nerve and synapses in submucosal plexus
31
What are the actions of the cephalic phase
primary: increased volume of gastric juice by stimulation mucus, enzyme, and acid production
secondary: stimulation of gastrin release by G cells
32
Whens fo the gastric pahse begin?
begins with the arrival of food in the stomach
33
What are the functions of the gastric phase?
enhance secretion started in cephalic stage: homogenize and acidify chyme: initiate digestion of proteins by pepsin
34
What is the duration of the gastric phase?
long (3-4 hours)
35
What are mechanisms of the gastric phase?
neural: short reflexes triggered by
1. stimulation of stretch receptors as stomach fills
2. stimulation of chemoreceptors as pH increases
hormonal: stimulation of gastrin release from G cells by parasympathetic activity and presence of peptides and amino acids in chyme
local: release of histamine by mast cells as stomach fills
36
What are the actions of the gastric phase?
increased acid and pepsinogen production; increased motility and initiation of mixing waves
37
What is the function of the intestinal phase?
control rate of chyme entry into duodenum
38
What is the duration of the intestinal phase?
long (hours)
39
What are the mechanisms of the intestinal phase?
neural: short reflexes (enterogastric reflux) triggered by distention of duodenum
primary: stimulation of cholecystokinin (CCK), gastric inhibitory peptide (GIP), ans secretin release by presence of acid, carbohydrate, and lipids
secondary: release of gastrin stimulated by presence of undigested proteins and peptides (not shown)
40
What are the actions of the intestinal phase?
feedback inhibition of gastric acid and pepsinogen production; reduction of gastric motility
41
Describe digestion and absorption in the monogastric stomach
- preliminary digestion of proteins by pepsins
- limited digestion of carbohydrates and lipids by salivary amylase and lingual lipase for a variable period
- very little nutrient absorption
- some drugs can be absorbed in the stomach, such as alcohol and aspirin
42
What are some kinds of ruminants?
cattle, sheep, goats
43
What is rumination?
ruminants swallow their food and bring it back up the esophagus to their mouth (regurgitation) to chew on some more (remastication and reinsalivation) before swallowing it again (redeglutition)
44
What are the three pre-stomach compartments of a ruminant stomach?
rumen
reticulum
omasum
45
What is the one true stomach of a ruminant?
abomasum
46
What is the rumen?
a series of muscular sacs partially separated from one another by long muscular folds of rumen wall called pillars
47
What do reticulorumen contractions allow?
1. coordinated mixing of rumen contents
2. regurgitation for rumination
3. eructation: expelling the built-up carbon dioxide or methane gas
48
What is rumen motility controlled by?
the vagus nerve of the parasympathetic nervous system
49
What is the relevance of vagal indigestion?
- functional or mechanical disturbances of the ruminant stomach that impair gastrointestinal transit
- clinical signs include abdominal and ruminal distension as well as poor appetite, weight loss, dehydration, reduced fecal output, and bradycardia
- treatment depends on the underlying cause
50
What are the rumen microbes?
- the rumen is a large, fermentative vat
- an excellent anaerobic environment for growth of bacteria, protozoa and other microbes
51
How does the rumen digest carbohydrates?
- bacterial cellulase digest cellulose into monosaccharides
- no mammal is able to digest cellulose directly
- monosaccharides (glucose) are converted to volatile fatty acids (VFAs mainly acetic, propionic, butyric acids)
- ruminants absorbs VFAs
- acetic and butyric acids: main energy source
- propionic acid: gluconeogenesis in liver
52
How does the rumen digest proteins?
- rumen microbes break down rumen degradable protein (RDP) to amino acids (AAs), then ammonia (NH3)
- AAs and ammonia are used for microbial protein synthesis and growth
- the microbes also convert non-protein nitrogen (NPN, eg. urea) to ammonia
- some NH3 are absorbed into bloodstream and converted into urea in the liver (ureagenesis) which is recycled back to the rumen
53
How does the rumen digest lipids?
lipolysis: release of constituent fatty acids
biohydrogenation: fatty acids are more saturated with
54
Describe the reticulum
- the smallest
- honeycomb like lining
- coordinated contractions with rumen: reticulorumen contraction
55
Describe the omasum
1. break down food particles further
2. convery ingesta into the abomasum
3. absorb any VFAs
4. remove bicarbonate ions
5. abrob water
56
What does the abomasum do?
functions much the same as monogastric stomach
57
Describe the young ruminant digestive tract
primarily as a monogastric digestive system
reticular groove:
- conveys swallowed liquid from the esophageal opening directly to the omasum
- essentially bypass the rumen and reticulum
rate of development of rumen and reticulum is rapidly increased when calf is fed grain and roughage
with age and development of the rumen and reticulum, the reticular groove formation reflex almost completely disappears
58
What is rumen lactic acidosis (grain overload)
- a decrease in pH in the rumen of cattle
- develops when ingesting large amounts of unaccustomed foods rich in ruminally fermentable carbohydrate -> large quantities of VFAs
- cause ruminities, metabolic acidosis, lameness, hepatic abscessation, pneumonia and death
59
What is the relevance of bloat?
- animals are grazing young, lush pasture, particularly if the pasture has high legume content
- large volumes of gas cannot be escaped from the rumen
60
What is the important of the small intestine and associated glandular organs?
most of the important digestive and absorptive functions
61
What are the segments of the small intestine?
duodenum: short
jejunum
- longest
- the main site for digestion and nutrient absorption
ileum
- separated from colon by ileocecal sphincter
associated glandular organs
- digestive secretions and buffers
- the pancreas, liver, and gallbladder
62
What are the parts of the small intestine mucosa?
plicae
villi
microvilli (brush border)
crypts: invaginations of mucosa around villus
63
What do goblet cells do?
produce mucus
helps protect the intestinal mucosa
64
What doe the intestinal glands do?
- at the bases of the villi
- lined by enteroendocrine cells
-produce intestinal hormones: cholecystokinin (CCK), secretin, gastric inhibitory peptide (GIP)
65
What doe the submucosal glands do?
- in duodenum
- produce mucus, buffers: help elevate the pH of the chyme from 1-2 to 7-8
66
When does intestinal juice come in?
arrived by osmosis out of the mucosa and secreted by the glands
67
What is the pancreas composed of?
-composed of endocrine and exocrine glandular tissue
exocrine portion: 98-99%
- compound acinar gland
- pancreatic duct empties into the duodenum
- secretes water,ions, and digestive enzymes: alpha-amylase, lipases, nucleases, proteases, and peptidases
endocrine portion: 1-2%
- pancreatic islets
68
What regulated secretion in the pancreas?
secretin triggers secretion of a watery buffer solution
vagus nerves and CCk stimulate the production and secretion of enzymes
69
What is the liver?
- largest gland in the body
- hepatic lobes: 4 in humans, 7 in cattle
hepatic lobules:
- basic functional units of the liver
- hepatocytes form a series of irregular plates arranged as wheel spokes
- sinusoids between adjacent plates empty into the central vein
70
What is the order of the liver functions?
bile canaliculi -> bile ducts -> gallbladder -> common bile duct -> the duodenum
71
What are the functions of the liver?
- filter materials absorbed from the GI tracts; hepatic portal system (dual blood supply)
- removes toxins and old/damaged RBCs from the blood
- store nutrients and regulate metabolite levels in blood -- keep constant supply of sugars, fats, amino acids, nucleotides, cholesterol
- produce plasma proteins: eg. serum albumin
- secrete bile
72
What are the functions of the gallbladder?
- storage of bile
- concentration of bile fivefold to tenfold
- ejection of the concentrated bile into the duodenum
73
What are the functions of bile?
- bile is composed of water, ions, bile acids, organic molecules (including cholesterol, phospholipids, bilirubin)
- acids and salts emulsify fats for absorption across wall fo small intestines
- the water and ions assist in the dilution and buffering of acids in chyme
74
Describe carbohydrate digestion in the small intestine
- starch converted into disaccharides into lumen of the duodenum by pancreatic amylase
- disaccharides further digested by enzymes in microvilli cell membranes
- resulting monosaccharides transported across the microvilli cell membrane and absorbed into the blood
75
How is protein digested in the small intestine?
- gastric pepsin breaks some protein chains into smaller polypeptides
- five pancreatic proteases: trypsin, chymotrypsin, elastase, aminopeptidase, and carboxypeptidase --> partially digest peptides
- partially digested peptides further digested by peptidases in microvilli cell membranes
- amino acids, dipeptides, and some tripeptides are then absorbed across the cell membrane
76
How is fat digested in the small intestine?
- agitation of pyloric antrum in stomach breaks fat globules (triglycerides) into small droplets
- bile acids coat the fat droplets in duodenum
-pancreatic lipases penetrate bile acid coating
- digest fat molecules to produce glycerol, fatty acids, and monoglycerides
- droplets fragment into smaller particles (micelles)
- micelles - bile acid-lid component absorbed through microvilli
77
How is secretion and absorption coordinated in the small intestine?
- neural and hormonal mechanisms coordinated the activities of digestive glands
- gastrointestinal activity is stimulated by parasympathetic innervation and inhibited sympathetic innervation
- the enterogastric, gastroenteric, and gastroileal reflexes coordinate movement from the stomach to the large intestine
78
What are the major functions of the large intestine?
- reabsorption of water and compact materials into feces
- absorb vitamins produced by bacteria
- store fecal material prior to defecation
79
What does the large intestine consist of?
cecum
- blind sac
- collects and store material
colon
- some microbial action --> VFAs
rectum
- temporary storage
- vary greatly among species
- in horses and cattles the colon and cecum (hindgut) is tremendously developed
