Digestion Flashcards
(60 cards)
1
Q
What does the GI tract consist of?
A
- oral cavity
- pharynx
- oesophagus
- stomach
- small intestine –> duodenum, jejunum, ileum
- large intestine –> ilio-caecal junction, caecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, anus
2
Q
What is the function and location of the paratoid glands?
A
- secrete a serious fluid into the oral cavity via a very long duct
- positioned close to the ear
3
Q
What is the function and location of the submandibular glands?
A
- secrete a seromucous fluid into the oral cavity via a long duct
- positioned under the sublingual gland, near the base of the jaw
4
Q
What is the function and location of the sublingual glands?
A
- secrete a mucous fluid into the oral cavity via several short ducts
- positioned closest to the mouth
5
Q
What is masticatory mucosa?
A
- forms the gingivae and hard palate
- stratified squamous keratinised epithelium
- very strong
6
Q
What is specialised mucosa?
A
- forms the surface of the tongue
- incorporates taste buds
7
Q
What is ordinary lining musocsa?
A
- forms other structures in the mouth
- stratified squamous non-keratinised epithelium
- strong
8
Q
Describe the tongue, including the different papillae
A
- posterior 1/3 is the lingual tonsil
- anterior 2/3 is covered in many taste buds
- foliate papilla, fungiform papilla, circumvallate papilla, filiform papilla
9
Q
Describe the pharynx
A
- sits posterior to the oral cavity
- 3 parts –> nasopharynx, oropharynx, laryngopharynx
- oropharynx allows food from the oral cavity to reach the oesophagus
- comprises a set of 3 constrictor muscles stacked on top of each other
10
Q
Describe the oesophagus
A
- skeletal muscles in the superior portion
- smooth muscle in the inferior portion
- epithelium transition sharply from SSNK (in oesophagus) to simple columnar (in stomach) as the gastro-oesophageal junction
11
Q
Describe the structure of the hollow tube
A
- Mucosa
- epithelium
- lamina propria
- muscularis mucosa - Submucosa
- Muscularis externa
- inner circular fibres
- outer longitudinal fibres - Adventitia/serosa
12
Q
What is Meissner’s plexis?
A
-Associated with the muscularis mucosae of the mucosal layer and regulates fluid secretion and absorption, as well as blood flow
13
Q
What is Auerbach’s plexus?
A
associated with the muscularis externa and regulates motility in the GI tract
14
Q
What is the function of the stomach?
A
- break down solid food into semi-solid chyme –> mechanical, chemical
- deliver chyme to the duodenum
- digest protein using pepsin
- regulate rate of passage into the duodenum
- create intrinsic factor required for the absorption of vitamin B12 in the intestine
15
Q
Describe the proximal and distal ends of the stomach
A
- the proximal end is guarded by the lower oesophageal (cardiac) sphincter
- continuation to the duodenum is regulated at the distal end by the pyloric sphincter
16
Q
What is the function of the secretory sheet?
A
secretes mucus to protect the gastric epithelium from low pH
17
Q
What is the function of parietal cells?
A
produce HCl and intrinsic factor
18
Q
What is the difference between G cells and D cells?
A
G cells produce gastrin
D cells produce somatostatin
19
Q
What is the function of chief cells
A
produce pepsin
20
Q
Describe the duodenum
A
- receives chyme from the stomach
- forms a characteristic C-shape, wrapping around the head of the pancreas
- protected from acid by lots of mucus glands
21
Q
What is the function of bile?
A
Acts a surfactant and aids emulsification of lipids within the chyme
22
Q
What is the purpose of the pancreas secreting bicarbonate ions?
A
to neutralise stomach acid
23
Q
Describe the processes that occur when chyme enters the duodenum
A
- the sphincter guarding the ampulla relaxes
- the gall bladder contracts
- bile and pancreatic juice exit into the duodenum and mix with the chyme
24
Q
What is cholelithiasis?
A
gall stones
25
26
Describe the specialisations of the epithelium in the jejunum and ileum
1. pilcae circularis (circular folds) - a feature of the submucosa
2. villi - a feature of the mucosal layer
3. Microvilli - a feature of the apical plasma membrane
27
What are the crypts of Lieberkuhn?
- invaginations between the villi of the small intestine
- contain a pool of stem cells
28
Describe the epithelium of the jejunum and ileum
simple cuboidal and comprises enterocytes
29
What are enterocytes?
intestinal absorptive cells specialised for breakdown and transport of small molecules derived from lipids, protein and carbohydrates, as well as water, electrolytes and vitamins
30
Describe the process by which parietal cells govern erythrocyte proliferation and differentiation
- parietal cells in stomach produce intrinsic factor
- in the small intestine vitamin B112 binds to IF
- B12-IF complex absorbed by enterocytes in the terminal ileum
- B12 required for erythrocyte proliferation and differentiation
31
What are the bulges of the large intestine known as?
haustra
32
Describe the processes that occur during defecation
1. contraction of the colon
2. relaxation of the involuntary anal sphincter
3. relaxation of the voluntary anal sphincter
(aided by transition from simple columnar epithelium of the intestines back to SSNK epithelium)
33
List the 3 phases of secretion in the stomach
- cephalic
- gastric
- intestinal
34
What is the cause and effect of the cephalic phase?
Cause:
- sensations and thought
Effect:
- cerebral cortex/hypothalamus
- parasympathetic - vagus (x cranial nerve)
35
Describe the gastric phase
Neural negative feedback
- stretch receptors and chemoreceptors routed via the submucosal plexus --> peristalsis stimulated
Hormonal negative feedback - emptying
- distention, partly digested proteins, caffeine, stimulate the G (enteroendocrine) cells
Gastrin secretion
- inhibited at pH < 2
- stimulated when pH rises
- transported in the blood to the gastric glands
- stimulates gastric secretions
- contraction of lower esophageal sphincter
- increases motility
- relaxes pyloric sphincter
36
What stimulates parietal cells to secrete HCl?
- gastrin
- acetylcholine
- histamine
37
Describe the intestinal phase
Enterogastric reflex
- enteroendocrine cells in the small intestine release cholecystokinin (CGK), gastric inhibitory peptide (GIP) and secretin
- they inhibit gastric secretion
38
Describe the mechanisms that occur in the liver
1. parasympathetic impulses along vagus nerves stimulate bile production in liver
2. fatty acids and amino acids in chyme entering duodenum stimulate secretion of CCK and secretin
3. CCK causes contraction of the gallbladder
4. Secretin enhances flow of bile rich HCO3- from liver
39
What is the purpose of the ileal brake?
slows gastric emptying
40
What is cholecystokinin?
- secreted in response to food
- reduces appetite and inhibits eating
- in hypothalamus neurotransmitter to inhibit eating
41
What is ghrelin?
- only GIT hormone to increase food intake
- secreted by endocrine cells of gastric mucosa
- increases hunger, growth hormone secretion and fat stores
42
Describe the melanocortin system
- peptides adrenocorticotropin and melanocyte-stimulating (MSH) hormones
- anorexigenic
- occurs in arcuate nucleus of hypothalamus
- integrates long term and short term signals
- activated by POMC and CART (stimulated by leptin)
- inhibited by NPY and AgRP
43
What are NPY/AgRP neurons
- suppressed by insulin and leptin
- neurotransmitters in hypothalamus
- NPY --> activates its receptor which are GPCR, stimulates eating
- AgRP --> binds to and inhibits MC4R, inhibits anorexigenic effects of a-MSH
44
List the pathway of ruminant digestion
1. rumen
2. reticulum
3. omasum
4. abomasum
45
Describe the features of the rumen
- contents are mostly water
- ruminal papillae
- stratified squamous epithelium - keratinised
- absorption still occurs here
- material is drawn back into the oesophagus and muscle contractions return it to the mouth
- liquid rapidly re-swallowed, coarse material chewed again before swallowing
- each bolus chewed 40-50 times
46
Describe the reticulo-rumen microorganisms
- mostly anaerobic bacteria and fungi
- symbiotic relationships
- heterotrophic and autotrophic
- chemostat
47
What is the purpose of the reticulo-rumen microorganisms?
- different bacterial/fungi break down different food sources
- fermentation produces volatile fatty acids (VFAs), gas and more microorganisms
48
Describe the reticulum
- keratinised stratified squamous epithelium
- particle sorting
- muscularis mucosa --> around top of each compartment, aid separation, mixing , breakdown
49
Describe the Omasum
- regulates entry of food into the abomasum
- may return food to the reticulo-rumen
- water and VFA absorption
50
Describe the Abomasum
- true stomach - like the fundus
- oesophageal groove
- simple columnar
- glandular --> gastric pits
- parietal and chief
51
Describe the structure of cellulose
- a chain of glucose units bound by beta-1,4-linkages
- intramolecular H bonds decrease flexibility, increase tensile strength and decrease solubility in water
- intermolecular H bonds allows the development of a crystalline lattice
52
Describe the structure of hemicellulose
- mixture of pentose, hexose, uronic acids bound to a beta-1,4-linked core composed primarily of xylose
- closely bound to lignin than cellulose
53
What is lignin?
- a poorly defined polymer of phenylpropane
- binds to hemicellulose only
- forms a matrix around cellulose
- increases strength under compression
- lignification is a significant factor in reducing digestibility
54
Describe cellulose digestion
- transport of bacteria to fiber --> slow, dependent on number of bacteria
- nonspecific adhesion of bacteria to sites on substrate --> most commonly at cut or macerated areas
- specific adhesions of bacteria with digestible cellulose --> cellulosome: large, multienzyme complexes for adhesion and hydrolysis of cellulose
55
Describe starch
- chief storage polysaccharide in plants
- composed of amylose (a-1,4-linkages) and amylopectin (a-1,4-linkages with a-1,6-branch points)
56
Describe starch digestion
- majority digested in rumen
- digested by alpha-amylase to oligosaccharides
- oligosaccharides degraded to glucose --> protozoa uptake, bacterial uptake
57
What are volatile fatty acids?
- end products of microbial carbohydrate digestion
- propionate, acetate, butyrate
58
Describe protein digestion
- microorganisms in the reticulorumen
- Most of the protein that reaches the abomasum will
be of microbial origin
- There is an optimum level of ammonia in the
reticulorumen
– Can add urea to the diet from which they can make amino
acids
59
List the advantages of ruminant digestion
– Utilise feeds too fibrous for non-ruminants.
– Uses the most abundant carbohydrate
– Produces high-quality microbial protein from NPN
– Produces vitamin B complexes
60
