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Semester 4 (NME) > Intestines > Flashcards

Intestines Flashcards

1
Q

What is the name for the cells that line the SI, what type of cell are they?

A

Enterocytes

Simple columnar epithelium

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2
Q

How long is the duodenum? What parts is it split up into?

A

20-25cm

Superior/ descending/ inferior/ ascending (Terminates at duodenal flexure)

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3
Q

Where is the sphincter of Oddi found?

A

Surrounding the major duodenal papillae

ampulla of vater

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4
Q

What are vasa recta?

A

Straight arteries (which run longitudinally along jejunum and ileum)

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5
Q

What are plicae circulares?

A

Prominent folds which circle the lumen (mainly of jejunum and ileum)

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6
Q

What are some differences between the jejunum and ileum?

A

Jejunum is shorter and has a larger diameter
Jejunum has thicker walls and more plicae circulares
Jejunum has longer and less prominant vasa recta

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7
Q

How long is the SI and how does it change along it’s length?

A

6-7m

Gets thinner walls and smaller diameter the further along it you traverse

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8
Q

What is trypsinogen?

A

A pro-enzyme secreted by the pancreas (Pro-enzyme so that it doesn’t break down cells in the pancreas)
- It’s converted to trypsin by enteokinase which is an enzyme on the brush border of SI lumen wall

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9
Q

What is the function of trypsin?

A

Causes hydrolysis of:
Chymotrypsinogen > chymotrypsin
Procarboxypeptidase > carboxypeptidase
Proelastase > elastase

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10
Q

What happens once trypsin has finished it’s actions?

A

Once trypsin has converted all the other pro enzymes and they have acted you are left with a mix of AA’s/ dipeptides and tripeptides

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11
Q

How is the resulting mix of AA’s/ dipeptides and tripeptides broken down after trypsin and it’s pro-enzymes have acted?

A

More brush border enzymes (dipeptidase and aminopeptidase) in the lumen wall of SI break all into amino acids

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12
Q

How are dipeptides and tripeptides absorbed in the SI?

A

Absorbed through co transport with H+ (Broken down into AA’s by enteocytes and sent via blood to liver)
This is facilitated diffusion (primary active transport requiring ATP)

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13
Q

How are amino acids absorbed in the SI?

A

Absorbed through co transport with Na+ (Sent via blood to liver)
This is facilitated diffusion (primary active transport requiring ATP)

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14
Q

How do the enterocytes balance the amount of H+ being brought in with di/tripeptides?

A

H+ (out) / Na+ (in) antiporter balances this out

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15
Q

What is the overall effect of peptide/ AA absorption in the gut and how does this affect osmosis?

A

Net movement of Na+ into enterocytes

This draws in water by osmosis

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16
Q

Name three monosaccharide carbohydrates?

A

Glucose/ fructose/ galactose

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17
Q

Name three disaccharide carbohydrates?

A

Sucrose/ lactose/ maltose

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18
Q

Name a polysaccharide carbohydrate?

A

Starch (amylose and amylopectin)
Amylose= String of 1-4 linked glucose molecules
Amylopectin= String of 1-6 linked glucose molecules which also has branches

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19
Q

What is an oligosaccharide?

A

Not as big as poly but bigger than mono/di

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20
Q

How is starch broken down before the stomach?

A

Chewing and salivary alpha amylase (aka pytalin)

low pH of stomach inactivates pytalin

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21
Q

How is starch broken down once it reaches the duodenum?

A

Pancreatic alpha amylase
Brush border enzymes (maltase/ lactase/ sucrase)
80% broken down into glucose

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22
Q

How is glucose absorbed?

A

SGLT (Sodium glucose linked transporter) absorbs two Na+’s and 1 glucose into the enterocyte

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23
Q

What is the difference between primary and secondary active transport?

A

Primary: ATP used to move substance against conc gradient (has binding site for ATP)
Secondary: Energy comes from electrochemical gradient of pumping other ions out of the cell

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24
Q

How does glucose move from inside the enterocyte into the bloodstream?

A

GLUT2 transporter on basal surface

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25
What happens to any starch not absorbed in the SI?
Undergoes bacterial fermentation in the colon then excreted
26
How are lipids digested before reaching the stomach?
Lingual lipase breaks down about 20% of the triglycerides (into monoglyceride + 2FA's) - Inactivated by low pH in the stomach
27
Once in the SI how are lipids broken down and absorbed?
FA's and monoglycerides combine with bile salts to form complexes called micelles. These travel into the enterocyte by simple diffusion across the membrane
28
What happens to the micelles absorbed by enterocytes?
Enterocyte uses FA's and monoglycerides to form new triglycerides. They combine with steroids/ phosholipids/ fat soluble vitamins and protein to form complexes called CHYLOMICRONS
29
What happens to chylomicrons in the enterocytes?
Leave enterocyte via exocytosis Stay in interstial spaces as too big for capillaries and travel via lymphatic capillaries (called LACTEALS) and enter blood stream via the L subclavian vein
30
How is water absorbed in the SI?
Via passive osmosis | Na+ is continually absorbed by enterocytes so Na+ conc in lumen falls resulting in water leaving
31
How much water goes into the GI tract each day?
2L food and drink 1.5L from saliva 1.5L from stomach 1L from liver bile 1L from pancreatic juice 2.2L from SI and colon TOTAL OF 9.2L/ day
32
How much water leaves the GI tract each day?
7. 8L reabsorbed in SI 1. 25L reabsorbed in colon 0. 15L lost in faeces
33
How is sodium absorbed into the body and how is this regulated?
Uptake mainly with other substances but also by active transport . Uptake is increased by Na content in food and increased by raised aldosterone levels
34
How is calcium absorbed into the body and how is this regulated?
Ca2+ absorbed by active transport. | Rate increased by calcitrol (active vitD)
35
How are Mg2+ and Fe2+ absorbed into the body?
Active transport
36
Which vitamins are fat soluble?
A, D, E, K
37
How are fat solube vitamins absorbed?
Absorbed with lipids
38
How often do you need to eat fat soluble vitamins?
Regularly but not daily as they can be stored in the liver or in fat
39
Name 3 types of water soluble vitamins, how do they get absorbed?
Folinic acid, vit C, the B vitamins | Diffuse across epithelium through channels
40
What is coeliac disease?
Allergy to gluten which causes villous atrophy
41
What is pernicous anaemia?
Lack of intrinsic factor production (due to gastritis) resulting in an inability to absorb vitB12
42
What is the main function of the duodenum and how is it adapted for this?
Digestion | Has villi and microvilli to increase surface area for brush border enzymes
43
What is the main function of the jejunum?
Absorbtion | Sugars/ proteins/ lipids/ water/ ions
44
What is the main function of the ileum?
Absorbtion of vitamins | B12/IF complex, ADEK + bile salts
45
What are the two types of movement of the SI?
Propulsive- Peristaltic waves, caused by gastroenteric reflex (caused by stomach distension) Mixing (aka segmental)- Local distension causes concentric contractions
46
What are brunners glands in the duodenum and what do they do?
Release alkaline mucus in response to: | Touch, vagal stimulation, secretin
47
What are crypts of lieberkuhn?
In SI they lie between villi. They have an epithelum of goblet cells and enterocytes which secrete water and electrolytes (along with reabsorbing some)
48
What is the iliocecal valve?
Protrudes into lumen of cecum so is forcefully closed when pressure in cecum tried to push contents back into SI. It's normally mildly constricted but relaxes after a meal
49
What is the gastroileal reflex?
After a meal cecum and ileocecal valves relax
50
Where does the majority of iron absorbtion occur and what transporter facilitates this?
Duodenum By DMT1 Basolateral: Ferroportin removes from cell into blood
51
How does malabsorbption most commonly present?
Chronic diarrhoea, weight loss, muscle wasting
52
What are the 4 types of diarrhoea?
Secretory- Isotonic stool, persists in fasting Osmotic- (Due to absorbed solutes) Malabsorptive- Failed nutrient absorption (steatorrheoa and relieved in fasting) Exudative- Due to inflam disease (bloody/ continues in fasting)
53
Pseudocysts are most commonly a complication of?
Pancreatitis
54
What is the action of H2 receptor antagonists such as cimetidine?
Inhibit gastric acid secretion
55
What are paneth cells and what is their function?
In the epithelium of SI | Secrete anti-microbial compounds when stimulated by bacterial presence
56
What is the gastroenteric reflex?
Stretch in stomach wall stimulates movement of chyme into duodenum and causes peristalsis across whole of SI
57
What is the gastroileal reflex?
Distension of stomach induces opening of ileocecal valve in order to move materials from SI to LI to create room
58
How does material move along the SI?
Some weak peristalsis occurs periodically | Myenteric reflexes and PNS stimulation speed this up
59
What is stomatitis?
Any inflammation of mucus membranes of mouth or lips with or without ulceration (many causes incl chemotherapy)
60
Where is iron absorbed and how much of it do we need?
Absorbed in prox duodenum based on bodies need for it (1-2mg per day)
61
Through which transporter does iron normally enter a cell, which other metals additionally enter through this transporter?
DMT-1 | iron, zinc, copper, cobalt, manganese, lead
62
What is transferrin?
Carrier iron in blodd, saturation is normally 20-45% (anything over is iron overload) RBC's take up iron from transferrin by receptor mediated endocytosis)
63
What type of anaemia is iron deficiency anaemia?
Microcytic (often cause by bleeding)
64
What is haemochromotosis?
Iron overload | Causes deposits in tissues such as joints/ heart/ liver and induces free radical formation and cell damage
65
What is the difference between short and long reflexes?
Long: Involves CNS and ENS Short: Involves only ENS
66
Where are enteroendocrine cells and what do they secrete?
In mucosa | Secrete gastrin/ secretin/ CCK etc
67
What is the role of versatile enterochromaffin cells?
Make up 90% enteroendocrine cells | Detect luminal contents and then release 5-HT to 5-HT3 receptors on nerves to increase their firing
68
How does PNS both excite and inhibit the ENS?
Excites (ACh and substance P) = Increased motility Inhibits (NO and VIP) = Decreased motility Remember acts with ENS first!!! Allows PNS to do two different things at once (gall bladder contract/ duodenal sphincter relax)
69
Which enzyme converts trypsinogen to trypsin?
Enteokinase (on SI brush border)

Semester 4 (NME) (24 decks)

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