Digestive system Flashcards
1
Q
What does the GI tract consist of in order?
A
Oral cavity > Pharynx > Larynx > Oesophagus > Stomach > Small intestine > Large intestine
Anus is considered a part of the large intestine babes
2
Q
What are the 3 parts of the small intestine called?
A
Duodenum
Jejunum
Ileum
3
Q
What are the parts of the large intestine called?
A
Ilio-caecal junction > Caecum > Ascending colon > Transverse colon > Descending colon > Sigmoid colon > Rectum > Anus
4
Q
How many pairs of major salivary glands are there?
A
3
5
Q
What words are used to describe the viscosity of the saliva produced?
A
- Serous: watery
- Mucous: thick
6
Q
What are the names of the 3 salivary glands?
A
- The parotid glands
- The submandibular glands
- The sublingual glands
7
Q
What kind of fluid do the parotid glands secrete? What length is the duct?
A
Serous fluid
Very long duct
Enters the mouth by the second upper molar
8
Q
Where do the parotid glands sit?
A
Back of cheek, next to ear
9
Q
What kind of fluid do the sub-mandibular glands secrete? What length is the duct
A
- Seromucous (in-between both) fluid
- Long duct
10
Q
Which is the longest kind of salivary gland?
A
Parotid
11
Q
What kind of fluid do the sublingual glands secrete? What length is the duct
A
- Mucous fluid
- Short duct
There are several short ducts
12
Q
What 2 salivary glands operate via long ducts?
A
Sub-mandibular and parotid
Parotid is longer
13
Q
What are the three regions of the oral cavity?
A
- Masticatory mucosa: gingivae and hard palatte - SSK
- Specialised mucosa: surface of tongue - incorporates taste buds
- Ordinary lining mucosa: everywhere else - SSNK
14
Q
What kind of epithelium is found in the oral cavity?
A
Stratified squamous, non-keratinised
15
Q
Describe the epithelium of the gingivae and hard palate
A
Stratified Squamous Keratinised
Epithelium
16
Q
Where is the specialised mucosa found in the mouth?
A
Surface of the tongue
17
Q
Where is the masticatory mucosa found?
A
Gingivae and hard palate
18
Q
What is the posterior 1/3 of the tongue called? what type of tissue does it contain?
A
Lingual tonsil - contains lymphatic tissue
19
Q
What is the anterior 2/3 of the tongue covered in?
A
Papillae and taste buds
20
Q
What are the four different types of taste bud?
A
- Filiform papilla - threadlike
- Fungiform papilla - mushroom like
- Circumvallate papilla - in a v
- Foliate papilla - leaf like
21
Q
What tastes is the tonue able to distinguish?
A
- Sweet
- Salty
- Bitter
- Umami
- Sour
22
Q
From top to bottom, name the three parts of the pharynx
A
Nasopharynx
Oropharynx
Laryngopharynx
the pharynx is like a shared hallway for breathing and eating - facilitates both the respiratory and digestive systems
23
Q
What type of muscle are the three parts of the pharynx?
A
Constrictor muscles, stacked on top of eachother
When they squeeze food is moved inferiorly towards the oesophagus - not peristalsis as it is reflexive
24
Q
What muscular transition occurs in the oesophagus?
A
Skeletal muscle (voluntary control) > smooth muscle (involuntary control)
Skeletal is superior, smooth is inferior
25
What 2 kinds of epithelium does the oesephagus transition between?
Stratified squamous non-keratinised (oesophagus) to simple columnar (stomach)
## Footnote
The junction of cell types is call the gastro-oesophageal junction - this is a common place for cancer to attack
26
What are the four key layers of the hollow tube GI tract?
1. Adventitia/serosa
2. Muscularis externa
3. Submucosa
4. Mucosa
## Footnote
From outside to inside
27
What are the layers that make up the mucosa?
- Epithelium (simple columnar)
- Lamina proporia
- Muscularis mucosa
28
What are the layers that make up the muscularis externa?
- Inner circular fibres
- Outer longitudinal fibres
29
What is the Meissner's Plexus?
It is associated with the muscularis mucosae of the mucosal layer and regulates fluid absorption as well as blood flow
30
What regulates motility in the GI tract? What part of the hollow tube is this associated with?
- Auerbach's Plexus
- It is associated with the muscularis externa
31
What are the fucntions of the stomach?
- **Break down** food into chyme
- Digest protein using **pepsin**
- Regulate the rate of passage into the duodenum
- Create **intrinsic factor**
32
What is the name of the folds in the stomach's lining that allow expansion?
Rugae
33
What is the top of the stomach called?
Fundus
34
What is the proximal end of the stomach guarded by?
Cardiac/lower oesphageal sphincter
35
What is the sphincter at the distal end of the stomach called?
Pyloric sphincter
36
What cells in the stomach secrete gastric acid?
Parietal cells
37
What else do the parietal cells secrete?
Intrinsic factor
38
What do the D endocrine cells of the gastric glands produce? What does this do?
Somatostatin - inhibits acid secretion
39
What do the G endocrine cells of the gastric glands produce? What does this do?
Gastrin - stimulates acid secretion
40
What do the parietal cells produce?
Intrinsic factor and gastric acid (HCl)
41
What do the chief cells produce?
Pepsinogen
42
Where in the stomach are the mucus neck cells, the parietal cells, and the chief cells found?
Gastric pits
43
Which part of the small intestine is the longest?
Ileum
44
What is the main role of the small intestine?
Absorption of food products of digestion into the blood and urine
45
What does the stomach create?
Chyme
46
How is the duodenum shaped? Where is it located?
- Has a characteristic C shape
- Wraps around the head of the pancreas
47
How is the duodenum protected from stomach acid?
Many mucus glands, and bicarbonate ions from the pancreas which neutralise it
48
Where is bile produced and stored?
Produced in the liver and stored in the gallbladder
49
What is the role of bile?
Acts as surfactant
Aids emulsification of fats within the chyme
50
Secretions from which organs enter the small intestine through the duodenum? What are these secretions?
Liver/gallbladder - bile
Pancreas - pancreatic juice and digestive enzymes, bicarbonate ions to neutralise stomach acid
51
Where do secretions enter the small intestines?
The hepatopancreatic duct (junction where they merge is called the hepatopancreatic ampulla of Vater) found in the duodenum
52
What two ducts join together to form the hepatopancreatic duct? What organ(s) do these ducts come from?
- Pancreatic duct - pancreas
- Common bile duct - liver and gallbladder
53
What 2 sections are the principal sites of nutrient absorption in the GI tract?
Jejunum
Ileum
54
What is the muscular contraction pulling food along the GI tract called?
Peristalsis
55
What coordinates peristalsis?
Aurbach's plexus
56
Name the circular folds found on the submucosa of the jejunum and ileum
Plicae circularis
57
What are the three adaptations in the jejunum and ileum to increase surface area? What cell layer are they in?
1. Plicae circularis - sub-mucosa
2. Villi - mucosa
3. Microvilli forming a brush border - apical plasma membrane
58
What do the Crypts of Leiberkuhn contain and why?
Pools of stem cells, as the small intestine is an extremely harsh environment and enterocytes only live a few days at a time
## Footnote
The crypts are invaginations between the villi
59
Describe the epithelium of the small intestine
Simple columnar
Comprises enterocytes
## Footnote
(Isaac's slides say cuboidal but its columnar)
60
Define enterocytes
intestinal absorptive cells specialised for breakdown and transport of
small molecules derived from lipids, proteins and carbohydrates, as
well as water, electrolytes and vitamins.
61
What does intrinsic factor do?
Allows for absorption of vitamin B12
62
What can an attack on parietal cells (as in pernicious anaemia) lead to?
Decreased production of IF, therefore less absorption of vitamin B12, and formation of defective erythrocytes, leading to anaemia
63
What is the transition between the small and large intestine called?
The ilio-caecal junction/valve
64
What lies just inferior to the ilio-ceacal junction?
The appendix
## Footnote
It is highly variable in position and length
65
What are the four parts of the large intestine called?
1. Ceaeum
2. Colon
3. Rectum
4. Anal canal
66
What are the four parts of the colon?
1. Ascending
2. Transverse
3. Descending
4. Sigmoid
67
What is the main function of the large intestine?
Most nutrient absorption is completed by the small intestine, so the major function of the large intestine is the absorption of water and electrolytes
68
What are the bulges of the colon called? How are they formed?
Haustra - The longitudinal muscle layer forms three ribbons of muscle; the contracted intestine then forms bulges
69
What specialised feature is present in the large intestine? Why isn't the epithelium as structurally adapted as the small intestine?
- Crypts of Lieberkuhn
- The large intestine's tissue isn't as structurally adapted as the small intestine as it has a much smaller role in absorption
70
What triggers defecation?
The distension of the rectal walls
## Footnote
The rectum is empty until faeces is recieved from the sigmoid colon
71
What are the three steps in the process of defecation?
1. Contraction of the colon
2. Relaxation of the **involuntary** anal sphincter
3. relaxation of the **voluntary** anal sphincter
72
What epithelium type is found in the anal canal?
Stratified squamous non-keratinised (SSNK) epithelium
## Footnote
Simple columnar epithelium (intestines) -> SSNK epithelium
73
What are the 3 phases of secretion?
1. Cephalic
2. Gastric
3. Intestinal
74
What initiates the cephalic phase? Where does this effect? What control is it under?
- Thoughts and sensations
- Effects the cerebral cortex / hypothalamus
- Under parasympathetic control
## Footnote
Travels via the vagus nerve
75
Where is stomach acid secreted from?
Parietal cells
76
What are the three types of control over the gastric phase of digestion?
- Neural control
- Hormonal control
- Control over HCl secreting parietal cells
77
How does neural control over the gastric phase work?
- Stretch receptors and chemoreceptors in the stomach wall detect distension
- Signals are sent to the submucosal plexus
- This stimulates peristalsis to mix and move stomach contents
78
How does hormonal control over the gastric phase work?
- Distension of the stomach, along with the digestion of proteins and caffiene stimulates the **G cells in the stomach lining**
- It is **regulated by pH**
- These cells release **gastrin** into the blood stream
## Footnote
High pH = more gastrin produced, low pH = gastrin production inhibited
79
What 3 chemicals is parietal cell HCl release stimulated by?
Gastrin
Acetylcholine
Histamine
## Footnote
All 3 are needed for strong acid secretion
80
What is gastrin secretion regulated by? Why?
When pH rises, it is released to stimulate gastric acid production to break down food
## Footnote
if the pH is already low, then no more acid needs to be produced to break down food
81
What does gastrin stimulate?
- Release of gastric acid and enzymes
- Increases motility
- Relaxes pyloric sphincter
- Contracts the lower oesophageal (cardiac) sphincter
82
How does the intestinal phase of digestion begin?
- when chyme enters the duodenum
- This triggers a neural and hormonal response
## Footnote
This slows down stomach activity to allow digestion to proceed in the intestine
83
What is the enterogastric reflex? What is it triggered by?
- stops the stomach emptying, secretions, and contractions
- It is triggered by the distension of the duodenum
## Footnote
This is a neural reflex
84
What cells secrete the hormones that inhibit gastric activity? Where are they?
**Enteroendocrine** cells in the **small intestine**
85
What do enteroendocrine cells in the small intestine release?
Cholesystokinin - CCK
Gastric inhibitory peptide - GIP
Secretin
86
What 3 things inhibit gastric secretion?
Cholesystokinin CCK
Gastric inhibitory peptide GIP
Secretin
87
What does cholecystokinin (CCK) do?
- Stimulates the **pancreas** to release digestive enzymes
- Stimulates the **gallbladder** to secrete bile
- Slows gastric emptying
88
What does gastric inhibitory peptide (GIP) do?
- Inhibits **gastric** **secretions**
- Stimulates **insulin** release from the pancreas
89
What does secretin do?
- Stimulates the pancreas to release **bicarbonate**
- Reduces gastric **secretions** and **motility**
- Stimulates **bile production** in the liver
## Footnote
The bicarbonate neutralises the acid
90
What are the hormones that accelerate/decelerate stomach activity?
Acceleration: Gastrin
Deceleration:
- CCK
- GIP
- Secretin
## Footnote
CCK, GIP, and secretin can be considered part of the 'breaking system' of digestion
91
What kind of impulses along the vagus nerve stimulate pancreatic enzyme release?
Parasympathetic
92
Name the 6 hormones involved in satiety signals
CCK
Oestrogen
Leptin
Insulin
Peptide YY
Glucagon-like peptide-1
93
What two hormones are peripheral hunger signals mediated by? What do they act on?
- Ghrelin and leptin
- They act on the **hypothalamus**
94
What does ghrelin do?
- Only GI tract hormone to increase **food intake**
- Secreted by the **endocrine cells** of the **gastric mucosa**
- Increases **hunger**, growth hormone secretion, and fat stores
## Footnote
Gas pedal for hunger sensations
95
What does leptin do? What is it produced by?
- Increases energy expenditure
- Supresses appetite
- produced by the adipose tissue
## Footnote
Helps you regulate weight over time based on your fat stores - leptin resistance is a key issue in weight gain
96
What are signals that reduce appetite called?
Anorexigenic
97
What are signals that increase appetite called?
Orexigenic
98
What is the melanocortin system? Where is it?
A key appetite-regulating pathway in the arcuate nucleus of the hypothalamus
99
What peptides are involved in the melanocortin system? What effect do these hormones have on the appetite?
- Adrenocorticotropic hormone (ACTH)
- Melanocyte-stimulating hormone (MSH)
- These peptides are anorexigenic
100
What is the melanocortin system activated by?
- POMC neurons
- CART neurons
101
What is the melanocortin system inhibited by?
- NPY
- AgRP
## Footnote
These are both types of neuron!!
102
What effect do AgRP and NPY have on appetite?
They oppose the melanocortin system and therefore have an orexigenic effect
103
What are the NPY/AgRP neurons suppressed by?
Leptin and ghrelin
104
What do the NPY/AgRP neurons do when activated?
- NPY: binds to Y receptors, stimulating feeding behaviour
- AgRP: blocks the appetite suppressing effects of α-MSH
105
What are the four parts of the ruminant stomach?
1. Rumen
2. Reticulum
3. Omasum
4. Abomasum
106
What happens in the rumen?
- Absorption occurs here
- Liquid is rapidly re-swallowed, coarse materila is chewed again before swallowing
107
What is the epithelium of the rumen? What specialisations does it have?
- SSK (stratified squamous keratinised) epithelium
- specialisation: ruminal pipillae
108
What important thing is within the rumen / reticulum?
The rumen and reticulum provide a culture system for **micoorganisms**
109
What type of organisms are the reticulo-rumen microorganisms? What is their relationship with the host?
- Mostly anaerobic bacteria and fungi
- Heterotophic and autotrophic
- Synbiotic relationship with host
## Footnote
Synbiotic = pre + probiotics
110
What do the microorganisms produce when they break down food?
Volatile Fatty Acids (VFAs)
111
What is the epithelium in the reticulum?
SSK epithelium
112
What is the function of the muscularis mucosa in the reticulum?
Muscularis mucosa surrounds the top of the stomach, separating bigger chunks, and allowing liquid through
113
What is the fucntion of the omasum?
- Water and VFA absorption
- Regulates the entry of food into the abomasum
- May return food to the reticulo-rumen
114
What is the function of the abomasum?
- Functions very similarly to the human stomach
- has gastric pits and parietal and chief cells like the human stomach
115
What type of epithelium is present in the abomasum?
Simple columnar epithelium
## Footnote
like the human stomach
116
What is cellulose? What are its properties?
- Chain of glucose units bound by beta-1,4-linkages
- High tensile strngth, rigid, insoluble in water or dilute acids
## Footnote
Held together by intermolecular H bonds, allowing the development of a crystalline lattice
117
Where does cellulose digestion occur?
Reticulorumen
## Footnote
about 10% of cellulose digestion occurs elsewhere
118
What is a cellulosome?
- large muti-enzyme complex used by some bacteria to break down cullulose into usable sugars
119
What is hemicellulose?
- Polysaccharide (mixture)
- Forms cross-links between cellulose fibres and lignin
120
What is lignin?
- A polymer that only binds to hemicellulose
- Forms a matrix around cellulose
- High strength under compression
## Footnote
Lignin is not very digestible
121
What is the main way in which glucose is stored in the body? What are the subunits that make up this polymer?
Stored as starch
Subunits:
- Amylose
- Amylopectin
122
What bonds are present in amylose and amylopectin?
- Amylose: α-1,4-linkages
- Amylopectin: α-1,4-linkages with α-1,6-branch points
123
Where does the majority of starch digestion occur? what enzyme breaks it down?
Rumen by alpha-amylase
124
What is starch broken down into? What do these turn into
Oligosaccharides
These degrade into glucose
## Footnote
The microorgs feed on this
125
What are the 3 main VFAs?
- Propionate
- Acetate
- Butyrate
126
How does protein digestion work in ruminants?
- Microorganisms mainly digest protein in the rumen
- Broken down into peptides, AAs, and ammonia
- Most of the protein that reaches the abomasum is microbial in origin
## Footnote
If urea is added to the diet, the animal can synthesise more AAs
127
What are the advantages of ruminant digestion?
- Utilise feeds too fibrous for non-ruminants
- Uses the most abundant carbohydrate (cellulose)
- Produces high-quality microbial protein from non-protein nitrogen
- Produces vitamin B complexes
128
What are the disadvantaes of ruminant digestion?
- Large quantities of alkaline saliva needed
- Large amounts of gas produced
- Needs powerful mechanical breakdown
- Metabolic adaptations for VFA use
## Footnote
Basically, its a very complex mechanism
