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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
Q

What happens to any starch not absorbed in the SI?

A

Undergoes bacterial fermentation in the colon then excreted

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26
Q

How are lipids digested before reaching the stomach?

A

Lingual lipase breaks down about 20% of the triglycerides (into monoglyceride + 2FA’s)
- Inactivated by low pH in the stomach

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27
Q

Once in the SI how are lipids broken down and absorbed?

A

FA’s and monoglycerides combine with bile salts to form complexes called micelles. These travel into the enterocyte by simple diffusion across the membrane

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28
Q

What happens to the micelles absorbed by enterocytes?

A

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
Q

What happens to chylomicrons in the enterocytes?

A

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
Q

How is water absorbed in the SI?

A

Via passive osmosis

Na+ is continually absorbed by enterocytes so Na+ conc in lumen falls resulting in water leaving

31
Q

How much water goes into the GI tract each day?

A

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
Q

How much water leaves the GI tract each day?

A
  1. 8L reabsorbed in SI
  2. 25L reabsorbed in colon
  3. 15L lost in faeces
33
Q

How is sodium absorbed into the body and how is this regulated?

A

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
Q

How is calcium absorbed into the body and how is this regulated?

A

Ca2+ absorbed by active transport.

Rate increased by calcitrol (active vitD)

35
Q

How are Mg2+ and Fe2+ absorbed into the body?

A

Active transport

36
Q

Which vitamins are fat soluble?

A

A, D, E, K

37
Q

How are fat solube vitamins absorbed?

A

Absorbed with lipids

38
Q

How often do you need to eat fat soluble vitamins?

A

Regularly but not daily as they can be stored in the liver or in fat

39
Q

Name 3 types of water soluble vitamins, how do they get absorbed?

A

Folinic acid, vit C, the B vitamins

Diffuse across epithelium through channels

40
Q

What is coeliac disease?

A

Allergy to gluten which causes villous atrophy

41
Q

What is pernicous anaemia?

A

Lack of intrinsic factor production (due to gastritis) resulting in an inability to absorb vitB12

42
Q

What is the main function of the duodenum and how is it adapted for this?

A

Digestion

Has villi and microvilli to increase surface area for brush border enzymes

43
Q

What is the main function of the jejunum?

A

Absorbtion

Sugars/ proteins/ lipids/ water/ ions

44
Q

What is the main function of the ileum?

A

Absorbtion of vitamins

B12/IF complex, ADEK + bile salts

45
Q

What are the two types of movement of the SI?

A

Propulsive- Peristaltic waves, caused by gastroenteric reflex (caused by stomach distension)
Mixing (aka segmental)- Local distension causes concentric contractions

46
Q

What are brunners glands in the duodenum and what do they do?

A

Release alkaline mucus in response to:

Touch, vagal stimulation, secretin

47
Q

What are crypts of lieberkuhn?

A

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
Q

What is the iliocecal valve?

A

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
Q

What is the gastroileal reflex?

A

After a meal cecum and ileocecal valves relax

50
Q

Where does the majority of iron absorbtion occur and what transporter facilitates this?

A

Duodenum
By DMT1

Basolateral: Ferroportin removes from cell into blood

51
Q

How does malabsorbption most commonly present?

A

Chronic diarrhoea, weight loss, muscle wasting

52
Q

What are the 4 types of diarrhoea?

A

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
Q

Pseudocysts are most commonly a complication of?

A

Pancreatitis

54
Q

What is the action of H2 receptor antagonists such as cimetidine?

A

Inhibit gastric acid secretion

55
Q

What are paneth cells and what is their function?

A

In the epithelium of SI

Secrete anti-microbial compounds when stimulated by bacterial presence

56
Q

What is the gastroenteric reflex?

A

Stretch in stomach wall stimulates movement of chyme into duodenum and causes peristalsis across whole of SI

57
Q

What is the gastroileal reflex?

A

Distension of stomach induces opening of ileocecal valve in order to move materials from SI to LI to create room

58
Q

How does material move along the SI?

A

Some weak peristalsis occurs periodically

Myenteric reflexes and PNS stimulation speed this up

59
Q

What is stomatitis?

A

Any inflammation of mucus membranes of mouth or lips with or without ulceration (many causes incl chemotherapy)

60
Q

Where is iron absorbed and how much of it do we need?

A

Absorbed in prox duodenum based on bodies need for it (1-2mg per day)

61
Q

Through which transporter does iron normally enter a cell, which other metals additionally enter through this transporter?

A

DMT-1

iron, zinc, copper, cobalt, manganese, lead

62
Q

What is transferrin?

A

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
Q

What type of anaemia is iron deficiency anaemia?

A

Microcytic (often cause by bleeding)

64
Q

What is haemochromotosis?

A

Iron overload

Causes deposits in tissues such as joints/ heart/ liver and induces free radical formation and cell damage

65
Q

What is the difference between short and long reflexes?

A

Long: Involves CNS and ENS
Short: Involves only ENS

66
Q

Where are enteroendocrine cells and what do they secrete?

A

In mucosa

Secrete gastrin/ secretin/ CCK etc

67
Q

What is the role of versatile enterochromaffin cells?

A

Make up 90% enteroendocrine cells

Detect luminal contents and then release 5-HT to 5-HT3 receptors on nerves to increase their firing

68
Q

How does PNS both excite and inhibit the ENS?

A

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
Q

Which enzyme converts trypsinogen to trypsin?

A

Enteokinase (on SI brush border)

Semester 4 (NME) (24 decks)

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