Overview of Gastrointestinal Function Flashcards
1
Q
What do metabolic processes need?
A
A specific range of small molecule
2
Q
What does food have?
A
A wide range of mostly large molecules
3
Q
What is the problem with food?
A
The large molecules are locked into complex structures
It may be contaminated with pathogens
4
Q
What does digestion do to food?
A
Makes it into a sterile, neutral, and isotonic solution of small sugars, amino acids and small peptides, small particles of lipids, and other small molecules
5
Q
What can happen once food has been digested?
A
It is now ready for absorption and excretion
6
Q
Give the processes that occur in the GI tract, from eating food to excreting it
A
- Initial physical disruption
- Ingestion and transport to storage
- Initial chemic disruption and creation of suspension (Chyme)
- Disinfection
- Controlled release of Chyme
- Diluration and neutralisation
- Completion of chemical breakdown
- Absorption of nutrients and electrolytes
- Final absorption of water and electrolytes
- Producing faeces for controlled excretion
7
Q
What are the regions of the GI tract?
A
- Mouth and Oesophagus
- Stomach
- Duodenum
- Small intestine
- Large intestine
- Rectum
8
Q
What are the functions of the mouth and oesophagus?
A
- Mastication
- Saliva
- Swallowing
9
Q
What is the purpose of saliva?
A
- Protects mouth
- Lubricates food for mastication and swallowing
- Starts digestion
10
Q
How does saliva protect the mouth?
A
- Wets
- Bacteriostatic
- Alkaline
- High Ca2+
11
Q
How does saliva lubricate food?
A
- Wet
- Mucus
12
Q
What does the saliva digest?
A
Sugars
13
Q
What is the function of the mouth and oesophagus in swallowing?
A
- Formation of bolus
- Rapid oesophageal transport
14
Q
What is the function of the stomach?
A
- Storage
- Initial disruption
- Delivers Chyme slowly into duodenum
15
Q
How does the stomach acheive it’s storage function?
A
It relaxes to accommodate food
16
Q
How does the stomach acheive initial disruption?
A
- Contracts rhythmically to mix and disrupt
- Secretes acid and proteolytic enzymes to break down tissues and disinfect
17
Q
What happens once stomach has performed initial disruption of food?
A
The food is now called Chyme
18
Q
What is the function of the duodenum?
A
Dilation and neutralisation of Chyme
19
Q
How does the duodenum dilate and neutralise Chyme?
A
- Water drawn in from ECF. The stomach is impermeable, the duodenum is permeable
- Alkali (bile) added from liver and pancreas
- Enzymes added from pancreas and intestine
20
Q
What is the function of the small intestine?
A
- Absorption of nutrients and electrolytes
- Absorbs the majority of water
21
Q
How does the small intestine absorb nutrients and electrolytes?
A
- Fluid passes very slowly through the small intestine
- Large surface area
- Epithelial cells absorb molecules
- Pass into hepatic portal circulation
22
Q
How do epithelial cells absorb molecules?
A
Some actively, some passive
Often coupled to Na+ transport
23
Q
How much water does the small intestine absorbed?
Compare to large intestine
A
1.5L
Compared to 0.15L in large intestine
24
Q
What is the function of the large intestine?
A
- Final absorption of water
- Faeces form and accumulate
25
How fast is transit in the large intestine?
Very slow
26
Where does faeces form and accumulate in the large intestine?
In the descending and sigmoid colon
27
What happens to faeces after formation and accumulation in the large intestines?
It is propelled periodically into the rectum
28
What happens once the faeces has been propelled into the rectum?
You get the urge to defecate, and there is controlled relaxation of sphincters and expulsion of faeces
29
Label this diagram of the alimentary canal
* A - Salivary glands
* *ai - Parotid*
* *aii - Submandibular*
* *aiii - Sublingual*
* B - Oral cavity
* C- Pharynx
* D - Tounge
* E - Oesophagus
* F - Pancreas
* G - Stomach
* H - Pancreatic duct
* I - Ileum *(small intestine)*
* J - Anus
* K - Rectum
* L - Appendix
* N - Cecum
* N - Colon
* *ni- Transverse colon*
* *nii- Ascending colon*
* *niii- Descending colon*
* O - Common bile duct
* P - Duodenum
* Q- Gallbladder
* R - Liver
30
What does the alimentary canal consist of?
## Footnote
*From the oval cavity to the anus*
Four layers
31
What are the 4 layers of the alimentary canal?
1. Mucosa
2. Submucosa
3. Muscularis Externa
4. Serosa/Adventita
32
What does the alimentary mucosa consist of?
* Surface epithelia
* Lamina propria
* Muscle layer
33
What does the alimentary submucosa consist of?
Fibroelastic tissue with vessels, nerves, leucocytes, and fat cells
34
What does the alimentary Muscularis Externa consist of?
Inner circular and outer longitudinal layer of smooth muscle, with the myenteric plexus lying between the layers
35
What does the alimentary serosa/adventitia consist of?
A thin outer covering of connective tissue
36
What does the variation in cellular composition of alimentary layers do?
Provides adaptations for specific functions, whilst remaining a continuous hollow tube of variable diameter and shape
37
How much food do we ingest per day?
About 1kg
38
How much liquid do we ingest per day?
About a litre
39
What is food mixed with?
1.5L of saliva and about 2.5L of gastric secretions
40
What is formed when food is mixed with saliva and gastric secretions?
Chyme
41
What are the characteristics of Chyme?
* It is very hypertonic (*has a high osmotic strength*)
* Very acidic
42
What happens when Chyme is slowly released from the stomach?
Around 9L of water and alkali moves into it from the ECF via osmosis
43
How much of the fluid from Chyme is absorbed by the small intestine
~12.5L
44
How much of the fluid from Chyme is absorbed by the large intestine?
~1.35L
45
What is the enteric nervous system?
A subdivision of the autonomic nervous system
46
What does the enteric nervous system do?
Directly controls the GI system
47
What is the enteric nervous system made up of?
Two nerve plexuses
48
Where are the nerve plexuses that make up the enteric nervous system located?
In the wall of the gut
49
Can the nerve plexuses that make up the enteric nervous system act independantly of the CNS?
Yes, *in the short reflex pathway*
50
How can the activity of the enteric nervous system be modified?
By both branches of the ANS *(long reflex pathway)*
## Footnote
*_Parasympathetic control is most significant_*
51
What is the role of the enteric nervous system?
Coordinates secretion and motility
52
How does the enteric nervous system perform its coordination role?
Using a range of neurotransmitters, *not just ACh as you may expect*
53
Where are the endocrine cells of the alimentary canal found?
In the walls of the gut
54
What do the endocrine cells in the wall of the gut do?
A dozen or more peptide hormones
55
What kind of signalling do the hormones secreted by the wall of the gut use?
Both endocrine and paracrine
56
What do the hormones secreted by the wall of gut comprise?
Two structurally related groups- the **gastrin** group and the **secretin** group
57
What is the function of the hormones of the gut?
Released from one part of the gut to affect the secretions or the motility of other parts
58
Give 18 common disease processes affecting the gut
1. Dysphagia
2. Acid reflux
3. Barrett's Oesophagus
4. Oesophageal Varices
5. Peptic Ulceration
6. Pancreatitis
7. Jaundice
8. Gallstones
9. Malabsorption
10. Appendicitis
11. Peritonitis
12. Inflammatory Bowel Disease
13. Acute blockage of small intestines
14. Haemorrhoids
15. Prolapse
16. Diverticula
17. Meckels' Diverticulum
18. Colorectal cancer
59
What is dysphagia?
Difficulty swallowing
60
What may cause dysphagia?
* Problems with the oesophagus
* Neurological
61
What problems of the oesophagus can cause dysphagia?
* Musculutare
* Obstruction by tumour
62
What neurological problems can cause difficulty swallowing?
Stroke
63
What are the tumours of the oesophagus called?
* High up are **squamous cell carcinoma**
* Lower down are **adenocarcinomas**
64
What are the symptoms of acid reflux?
* Irritation
* Pain *(heartburn)*
65
What causes acid reflux?
Sphincter between oesophagus and stomach is weak, and so acid refluxes into the oesophagus
66
What is Barrett's Oesophagus?
Metaplasia of the lower oesophageal squamous epithelium to gastric columnar
67
What causes Barrett's Oesophagus?
It is a protective mechanism against acid reflux
68
What is Oesophageal Varices?
Dilation of sub-mucosal veins in the lower part of the oesophagus
69
What causes Oesophageal Varices?
The portal venous system is overloaded due to cirrhosis, and so blood is diverted to the oesophagus through connecting vessels
70
What is peptic ulceration?
An area of damage to the inner mucosa of the stomach or duodenum
71
What is peptic ulceration due to?
Irritation from gastric acid
72
What is pancreatitis?
Inflamed pancreas
73
What are the symptoms of pancreatitis?
Considerable pain
74
What is pancreatitis characterised by?
The release of amylases into the blood stream
75
What causes jaundice?
Liver cannot excrete bilirubin, which accumulates in the blood.
76
What are the types of jaundice?
* Pre-hepatic jaundice
* Post-hepatic/obstructive jaundice
77
What is pre-hepatic jaundice?
If the build up of bilirubin is due to excess haemoglobin breakdown
78
What is post-hepatic/obstructive jaundice?
If build up of bilirubin is due to bile duct obstruction, and the back up of bile causes liver damage
79
What forms gallstones?
Precipitatin of bile acids and cholesterol in the bladder
80
What are the consequences of gallstones?
Often asymptomatic, but may move within the gall bladder causing painful **biliary colic**, or move to obstruct biliary outflow
81
What may mimic the effects of gallstones?
**Tumours of the pancreas** may also obstruct outflow
82
What is malabsorption?
Several conditions that affect how well the intestines can absorb things
83
What is appendicitis?
Inflammation of the appendix
84
How does appendicitis present?
As a sharp pain in the side at the same level as T10, which then localises to the right lower quadrant
85
What is peritonitis?
Inflammation of the peritoneum
86
Give two types of inflammatory bowel disease
1. Ulcerative colitis
2. Crohn's disease
87
How does acute blockage of the small intestines present?
* Pain *(in the back)*
* Vomiting
* Bloating
88
What are haemorrhoids?
Vascular structures in the anal canal that aid with stool control
89
What is the clinical significance of haemorrhoids?
They may become swollen and inflamed
90
What happens when haemorrhoids become swollen and inflamed?
They are painful, itchy, and blood may be present in the stool
91
What is a prolapse?
A condition where the organs fall or slip down out of place
92
Give an example of a location that can prolapse
The rectum
93
What is a diverticula?
An abnormal 'outpouching' in the colon to form a hollow
94
What causes a diverticula?
Pressure being too high in the colon
95
What portion of the colon is most prone to a diverticula?
The sigmoid colon
96
Why is the sigmoid colon most prone to a diverticula?
As the blood supply causes an area of weakness
97
What is Meckels' Diverticulum?
A pouch in the lower part of the small intestine, a vestigal remnant of the yolk sac
98
What is the clinical significance of Meckels' Diverticulum?
It can produce ectopic gastric mucosa, that may then produce gastric acid, causing irritation
99
What is the clinical significance of colo-rectal cancer?
The large intestine is a common site of malignancies, and colo-rectal cancer is a major cause of mortality
