Digestive systems Flashcards
(165 cards)
1
Q
What are the key components of the GI tract?
A
Oral cavity, pharynx, oesophagus, stomach, small intestine, large intestine.
2
Q
What does the oral cavity include?
A
Teeth, tongue, palate.
3
Q
What does the small intestine include?
A
Duodenum, jejunum, ileum, secretions from liver and pancreas.
4
Q
What does the large intestine include?
A
Ilio-caecal junction, caecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, anus.
5
Q
How many pairs of major salivary glands are there?
A
Three pairs.
6
Q
What do the three pairs of major salivary glands do?
A
Secrete serous (watery) or mucous (thick) secretions into the oral cavity - these secretions are on demand.
7
Q
What are the parotid glands?
A
Secrete a serous fluid into the oral cavity via a very long duct.
8
Q
Where does the parotid duct enter?
A
The mouth by the second upper molar.
9
Q
What are the submandibular glands?
A
Secrete a seromucous fluid into the oral cavity via a long duct.
10
Q
What are the sublingual glands?
A
Secrete mucous fluid into the oral cavity via several short ducts.
11
Q
What are the components of the oral cavity?
A
Hard palate, soft palate, uvula, opening of submandibular duct, gingivae (gums), tongue, palatine tonsils.
12
Q
What does squamous mean?
A
Flat.
13
Q
What does stratified mean?
A
Many layers.
14
Q
What is the epithelium of the oral cavity?
A
Stratified, squamous epithelium, non-keratinised.
15
Q
What are the layers of the oral cavity tissue?
A
Oral epithelium, basement membrane, laminate propria, oral mucosa (underlying tissues).
16
Q
What are the three basic regions of the oral cavities oral mucosa?
A
Masticatory mucosa, specialised mucosa, ordinary lining mucosa.
17
Q
What is the masticatory mucosa and where is it found?
A
Stratified squamous keratinised epithelium (very strong), gingivae and hard palate.
18
Q
What is the specialised mucosa and where is it found?
A
Incorporates taste buds, surface of tongue.
19
Q
What is the ordinary lining mucosa and where is it found?
A
Stratified squamous non-keratinised epithelium (strong), everywhere else in mouth.
20
Q
What is the tongues important function?
A
In mashing food against the teeth and hard palate.
21
Q
What sections is the tongue divided into?
A
An anterior 2/3 and a posterior 1/3.
22
Q
What is the posterior 1/3 of the tongue also known as?
A
The lingual tonsil.
23
Q
What is the anterior 2/3 of the tongue covered in?
A
Many taste buds.
24
Q
What are the taste buds found in relation to?
A
Four different papillae on the dorsal surface of the tongue.
25
Where does the pharynx sit?
Posterior to oral cavity.
26
What three parts is the pharynx divided into?
Nasopharynx, oropharynx, laryngopharynx.
27
What does the oropharynx allow?
Food from the oral cavity to reach the oesophagus.
28
What three muscles does the pharynx comprise of and how are they arranged?
A set of three constrictor muscles stacked on top of each other.
29
How do the three constrictor muscles of the pharynx work?
When they squeeze, food moved inferiorly toward the oesophagus.
30
What is the oesophagus and what does it do?
A muscular tube which carries masticated food from the pharynx to the stomach, passing through the diaphragm to enter the abdomen.
31
What are the two important transitions in the oesophagus?
Muscular and histological.
32
What is the muscular transition in the oesophagus?
Skeletal voluntary muscle in the superior portion, smooth muscle in the inferior portion and mixed in the middle.
33
What is the histological transition in the oesophagus?
Epithelium transitions sharply from SSNK to simple columnar at the gastrointestinal-oesophageal junction.
34
What does the GI tract form aside from the oral cavity and pharynx?
A hollow tube structure with four key layers.
35
What are the four key layers of the hollow tube?
Mucosa, submucosa, muscularis externa, adventitia/serosa.
36
What are the three subdivisions of the mucosa?
Epithelium, lamina propria, muscularis mucosa.
37
What are the two subdivisions of the muscularis externa?
Inner circular fibres, outer longitudinal fibres.
38
What forms the enteric nervous system?
Two plexi networks of nervous system tissues.
39
What is the Meissner’s Plexus?
Associated with the muscularis mucosae of the mucosal layer and regulates fluid secretion and absorption as well as blood flow.
40
What is the Auerbach’s Plexus?
Associated with the muscularis externa and regulates motility in the GI tract.
41
What does the stomach function to do?
Break down solid food into semi-solid chyme, deliver chyme to duodenum, digest protein using pepsin, regulate rate of passage into duodenum, create intrinsic factors.
42
What are the two ways food can be broken down into chyme?
Mechanically and chemically.
43
What are intrinsic factors required for?
Absorption of vitamin B12 in intestine.
44
Where is the stomach located?
Inferior to the diaphragm.
45
What are key anatomical features of the stomach?
Oesophagus, cardiac, lesser curvature, pylorus, rugae, fundus, muscularis externa, body, greater curvature.
46
What is the proximal end of the stomach guarded by?
The lower oesophageal sphincter.
47
What does the pyloric sphincter do?
Regulates at the distal end the continuation to the duodenum.
48
What forms the stomach tissue?
Secretory sheet, gastric pits, gastric glands and muscularis mucosae.
49
What is the gastric pit made up of?
Mucus Layer, surface mucus cells.
50
What is the gastric gland made up of?
Mucus neck cells, parietal cells, endocrine cell and chief cells.
51
What is the importance of the mucus layer?
Large amounts of mucus needed to protect gastric epithelium from low pH.
52
What are the surface mucus cells called?
The secretory sheets.
53
What do the parietal cells produce?
HCl and intrinsic factor.
54
What cells are included within the endocrine cell and what do they produce?
G cells that produce gastric and D cells that produce somatostatin.
55
What do chief cells produce?
Pepsin.
56
How many components does the small intestine have?
Three components.
57
What is the order of small intestine components from proximal to distal?
Duodenum, jejunum, ileum.
58
What are the average sizes of each components of the small intestine?
D = ~25cm, J = ~1m, I = ~2m.
59
What are principal characteristics of the small intestines?
Tightly folded in abdomen and three components quite similar.
60
What are the small intestines principally responsible for?
The absorption of products of digestion into the blood and lymph.
61
What are the characteristics and functions of the duodenum?
Receives chyme from stomach, forms C-shape wrapping around head of pancreas, protected from acid by mucus glands.
62
What are the key components of the duodenum?
Pyloric sphincter, superior part, descending part, horizontal part, ascending part.
63
What enters the GI tract at the duodenum?
Secretions from the liver and pancreas.
64
What is bile?
Produced by the liver and stored in gall bladder, acts as surfactant and aids emulsification of fats within chyme, secreted continuously.
65
Where are pancreatic juice and digestive enzymes produced?
By the pancreas.
66
What do the intermittent secretions of the pancreas include?
Digestive enzymes, trypsin, chymotrypsin, amylase, plus bicarbonate ions to neutralise acid.
67
What key structures surround the duodenum?
Gall bladder, panreas, main pancreatic duct, hepatopancreatic ampulla of vater.
68
Where do both pancreatic juice and bile reach the duodenum?
Through a shared duct emerging from the second part of the duodenum.
69
What happens when chyme enters the duodenum?
Sphincter guarding ampulla relaxes, gall bladder contracts, bile and pancreatic juice exit to duodenum and mix with chyme.
70
What are the jejunum and ileum?
The principal site of nutrient absorption in the GI tract.
71
What does the peristalsis do?
Propels digested food along the track with movements.
72
What controls the movements used by peristalsis?
Auerbach’s plexus.
73
What is the most important function of the jejunum and ileum part of the GI tract?
Absorption.
74
What does the jejunum and ileum have to enable maximum absorption?
Several specialisations to the epithelium - that work collectively to increase surface area.
75
What are pilicae circularis?
Circular folds that are a feature of the submucosa that increase surface area for absorption.
76
What are villi?
A feature of the mucosal layer that aid in increasing surface area.
76
What are microvilli?
Plasma membrane projections that form a brush border, a feature of the apical plasma membrane to increase surface area.
77
What is the environment of the lining of the small intestine like?
Very harsh and hostile - enterocytes only live a few days.
78
What are enterocytes?
Intestinal absorptive cells specialised for breakdown and transport of small molecules derived from proteins lipids and carbs, as well as water electrolytes and vitamins.
79
What is required to replace the cells being sloughed off in the small intestine?
A pool of stem cells.
80
Where are the pools of stem cells needed for the small intestine found?
In the Crypts of Lieberkuhn - invaginations between villi.
81
What is the epithelium of the small intestine made of?
Simple cuboidal and comprises of enterocytes.
82
What is the process that causes anaemia?
Parietal cells in stomach produce reduced IF, B12 binds to IF in small intestine, complex absorbed by enterocytes in terminal ileum, B12 for erythrocyte proliferation and differentiation so lack of forms defective erythrocytes.
83
What are erythrocytes?
Red blood cells.
84
What is the transition from the small intestine to the large intestine?
The junction between the ileum and caecum.
85
What is the caecum?
First part of the large intestine, food arrives 3-4hrs after swallowing.
86
What is the entrance to the caecum guarded by?
The ilio-caecal valve.
87
What is the appendix?
Blind-ended tube projecting from the caecum which has a highly variable position and length - function debated.
88
Where does the large intestine span and how long is it?
Spans from caecum to anal canal with a total length of ~1.6m.
89
What are the main components of the large intestine?
Transverse colon, ascending colon, illeo-caecal valve, caecum, appendix, descending colon, sigmoid colon.
90
What does the longitudinal muscle layer form in the large intestine?
Three ribbons of muscle.
91
What does the contracted intestine form?
Bulges known as haustra.
92
What is the main function of the large intestine?
Absorption of ions and water.
93
Where is most nutrient absorption completed?
Small intestine.
94
What does peristalsis continue to do in the large intestine?
Mixing and advancing contents, aided by strong waves 3-4 times per day.
95
How long post-eating does material reach the end of the large intestine?
Around 12hours.
96
How long after eating do contents move into the rectum to stimulate the need to defecate?
Around 24hours.
97
Why doesn’t the large intestinal epithelium need the three levels of structural adaptation seen in the small intestine?
Has far less role in absorption.
98
What are present in the large intestine epithelium?
Deep Crypts of Lieberkuhn.
99
When does the rectum remain empty til?
Until it receives faeces from the sigmoid colon.
100
When is the three process defecation triggered?
When rectal walls distend.
101
What are the three steps of defecation?
Contraction of colon, relaxation of involuntary anal sphincter, relaxation of voluntary anal sphincter.
102
What key histological transition is present in the anal canal?
Transition from the simple columnar epithelium of the intestines back to the stratified squamous non-keratinised epithelium.
103
What is the overview of the digestive systems function from start to end?
Ingestion of food, mechanical breakdown via mastication, mechanical and chemical breakdown into chyme, digestion through hepatic gastric pancreatic secretions, absorption of nutrients and ions, regulation of water balance, excretion of waste.
104
What is the primary role of the stomach?
Regulation of gastric secretion and motility.
105
What is the stomach regulated by?
Combination of nervous and hormonal factors.
106
What are the three stages of secretion within the stomach?
Cephalic, gastric, intestinal.
107
What are the causes and effects of the Cephalic phase?
Causes - sensations and thoughts, effects on cerebral cortex/hypothalamus, parasympathetic (vagus x cranial nerve).
108
What is the mechanisms that the gastric phase uses?
Neural negative feedback - stretch receptors and chemoreceptors routed via submucosal plexus (peristalsis stimulated).
109
What does the hormonal negative feedback mechanism control in the gastric phase?
Emptying of the stomach.
110
What stimulates the G enteroendocrine cells in the gastric phase?
Distension, partly digested proteins, caffeine.
111
When is gastrin secretion inhibited and stimulated in the gastric phase?
Inhibited at pH < 2, stimulated when pH rises.
112
How is gastrin transported in the gastric phase?
In blood to the gastric glands.
113
What does gastrin promote in the gastric phase?
Stimulates gastric secretions, contraction of lower esophageal sphincter, increased motility, relaxes pyloric sphincter.
114
What three signal chemicals stimulate the control of HCl secreting parietal cells in the gastric phase?
Gastrin, acetylcholine, histamine (all three needed for strong H+ secretion).
115
What is the intestinal phase in the stomach?
Enterogastric reflex and enterogastrone secretion.
116
What do endocrine cells in the small intestine release during the intestinal phase?
Cholecystokinin (CCK), gastric inhibitory peptide (GIP), secretin.
117
What do the hormones secreted by enteroendocrine cells in the small intestine during the intestinal phase do?
They inhibit gastric secretion.
118
What is the ileal brake?
Slow gastric emptying.
119
What does cholecystokinin do?
Secreted in response to food, reduces appetite and inhibits eating, hypothalamus neurotransmitters to inhibit eating.
120
When is the glucagon like peptide 1 and peptide YY released?
From intestine in response to food.
121
Where is Leptin released from?
White adipose tissue.
122
What are the five hormones for satiety signals?
Insulin, oestrogen, glucagon like peptide 1, peptide YY, leptin.
123
What are the characteristics of peripheral hunger signals?
Mediated by ghrelin, only GIT hormone to increase food intake, secreted by endocrine cells of gastric mucosa, increases hunger, growth hormone secretion and fat stores.
124
What are the components of gut hormone and appetite regulation?
Arcuate nucleus (ARC), lateral hypothalamus area (LHA), para ventricular nucleus (PVN), POMC (pro-opiomelanocortin), CART (cocaine-amphetamine regulated transcript), stimulated by leptin.
125
What are the characteristics of 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, inhibited by NPY and AgRP.
126
What are NPY/AgRP neurons?
Neurons suppressed by insulin and leptin, stimulation releases NPY and AgRP (removal of inhibition), neurotransmitters in hypothalamus.
127
What does NPY do?
Activates its receptor which are GPCR, stimulates eating.
128
What does AgRP do?
Binds to and inhibits MC4R, inhibits anorexigenic effects of alpha-MSH.
129
What are the key components of a cows digestive system?
Rumen, abomasum, omasum, reticulum.
130
What percentage of live weight is the rumen?
10-20%.
131
How much saliva do cows produce per day and how much is water?
~150L per day - contents 85-93% water.
132
What are the characteristics of the rumen?
Ruminal papillae, stratified squamous epithelium - keratinised, absorption occurs here.
133
How long a day do cows spend grazing and ruminating?
~8hrs a day grazing and ~8hrs a day ruminating.
134
What is the process of rumination?
Material drawn back into 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.
135
What do the rumen and reticulum provide for microorganisms?
Culture system.
136
What are characteristics of reticulo-rumen microorganisms?
Over 200 species identified so far, mostly anaerobic bacteria and fungi, synbiotic relationships, heterotrophic and autotrophic, chemostat, complex interrelationships.
137
What are the processes that take place in reticulo-rumen microorganisms?
Different bacterial/fungi break down different food sources, fermentation produced volatile fatty acids which are absorbed, gas, and more microorganisms - more than 30L/day.
138
What structural changes occur during development of the reticulo-rumen?
At birth the abomasum is the largest chamber, at 18months the reticulorumen occupies >90% of stomach.
139
What are structural characteristics of the reticulum?
Keratinised stratified squamous epithelium, particle sorting, muscularis mucosa, keratinised.
140
What does the muscularis mucosa of the reticulum do?
Around top of each compartment, aid separation, mixing, breakdown.
141
What does the Omasum do?
Regulates entry of food into abomasum, may return food to reticulo-rumen, water and VFA absorption.
142
What are characteristics of the abomasum?
True stomach like the fundus, broadly same digestive functions as humans, oesophageal groove, simple columnar, glandular, gastric pits, parietal and chief.
143
What are common carbohydrates in ruminant feedstuffs?
Soluble sugars, cellulose, hemicellulose, pectin, starch, lignin.
144
What is wrong with common carbs in ruminant feedstuffs?
Pose significant challenges to digestion due to structure.
145
What are the structural qualities of cellulose?
A chain of glucose units bound by beta-1,4-linkages, intramolecular H bonds, intermolecular H bonds.
146
What do the intramolecular H bonds in cellulose do?
Decreases flexibility, increased tensile strength, decreases solubility in water or dilute acid.
147
What do the intermolecular H bonds in cellulose do?
Allows the development of a crystalline lattice.
148
What is 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.
149
What is Lignin?
A poorly defined polymer of phenylpropane - binds to hemicellulose only, forms a matrix around cellulose, increased strength under compression.
150
What is lignification?
Significant factor in reducing digestibility.
151
Where is 90% of cellulose digestion?
In the reticulorumen.
152
What are characteristics of transport of bacteria to fiber in cellulose digestion?
Slow, dependent on number of bacteria.
153
What is nonspecific adhesion during cellulose digestion?
Adhesion of bacteria to sites on substrate, most commonly at cut or macerated areas.
154
What other kind of adhesion as well as nonspecific happens during cellulose digestion?
Specific adhesions of bacteria with digestible cellulose.
155
What is cellulosome?
Large, multienzyme complexes for adhesion and hydrolysis of cellulose.
156
What are the characteristics of starch?
Chief storage polysaccharide in plants, two components - amylose and amylopectin (branched).
157
How is starch digested?
47-95% digested in rumen, digested by alpha-amylase to oligosaccharides (70% associated with particulate bound microorganisms), oligosaccharides degraded to glucose - Protozoa and bacterial uptake.
158
What are the end products of microbial carbohydrate digestion?
VFA, heat, gas, microbial mass.
159
Where does the glucose required by cows come from?
~70% from VFAs, ~20% from protein.
160
What are the key volatile fatty acids produce from microbial carbohydrate digestion?
Propionate, acetate, butyrate.
161
What are key characteristics of 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 diet from which they make amino acids).
162
What are advantages of ruminant digestion?
Utilise feeds too fibrous for non-ruminants, uses most abundant carbohydrate, produces high quality microbial protein from NPN, produced vitamin B complexes.
163
What are disadvantages (complex mechanism) of ruminant digestion?
Large quantities of alkaline saliva needed, large amounts of gas produced, needs powerful mechanical breakdown, metabolic adaptations for VFA use.
164
What is utilised to overcome the problems of ruminant digestion?
Utilisation of microorganisms, compartmentalisation of the stomach.
