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Semester 3 - Gastrointestinal > Session 8 - Some very intestine stuff > Flashcards

Session 8 - Some very intestine stuff Flashcards

1
Q

Give the properties of chyme in the small intestine?

A
  • Acidic
    • Hypertonic
    • Partly digested
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2
Q

How is the acidity of chyme corrected?

A

• HCO3- secretion from pancreas, liver and dudodenal mucosa

HCO3- produced during the production of gastric acid

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3
Q

How is hypertonic chyme corrected?

A

• The osmotic movement of water into the duodenum

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4
Q

How is chyme digested further in the small intestines?

A

• Completed by enzymes from the pancreas and duodenal mucosa with bile acids from the liver

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5
Q

How is the small intestine adapted for absorption?

A
  • Very long

* Surface area for absorption is increased by millions of vili projecting into the lumen

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6
Q

Where do epithelial cell arise from in the small intestine?

A

• Rapid division in the crypts between the villi, and then rapidly migrate towards the tips where they are shed

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7
Q

What is found on the villi which improves absorption?

A

• Many microvilli

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8
Q

What does the brush border form?

A

• An unstirred layer where nutrients meet and reach with enzymes secreted by enterocytes, completing digestion prior to absorption

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9
Q

What is the role of the large intestine?

A

• Äbsorbs water from the indigestible residue of chyme and converts it into semi-solid stool or faeces that is stored temporarily and allowed to accumulate until defecation occurs

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10
Q

What are the two main features of the large intestine?

A
  • Teniae coli

* Haustra

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11
Q

What are teniae coli?

A
  • Thickened bands of smooth muscle representing most of the longitudinal coat
    • Run the length of the large intestine
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12
Q

What are haustra, and how are they formed?

A

• Colon becomes baggy between contracted teniae, forming haustra

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13
Q

Give two overarching function of two sections of the small intestine

A 
• Secrete proteases/carbohydrase enzymes to complete digestion 
	• Secrete hormones
				○ Gastrin 
		○ Secretin
		○ Cholecystokinin
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14
Q

Give three functions specific to the duodenum]

A
  • Bile and pancreatic secretions added
    • Secretes HCO3- to neutralise chyme
    • Osmotic movement of water into the duodenum, making chyme more hypotonic
    • Absorption of iron
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15
Q

Give the two main functions of the jejunum

A 
• Absorption
		○ Carbohydrates 
		○ Amino acids
		○ Fatty acids
		○ Vitamins
		○ Minerals 
		○ Electrolytes
		○ Water
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16
Q

Give main functions of ileum

A

• Absorption
○ Vitamin B12
○ Bile
○ Anything not absorbed by the jejunum

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17
Q

How long does the large intestine take to finish absorption of food?

A

• 16 hours

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18
Q

What are the two functions of the large intestine?

A

• Absorption
○ Water
○ Any remaining absorbable nutrients
○ Vitamins created by colonic bacteria

Sends indigestable matter to the rectum

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19
Q

What vitamins are created and absorbed in the large intestine?

A
  • Vitamin K
    • B12
    • Thiamine

Riboflavin

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20
Q

What occurs in the rectum?

A

• Faeces stored and compacted

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21
Q

Outline the structure of starch

A
  • Amylose

* Amylopectin

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22
Q

What are the bonds in amylose?

A

Straight chain a-1,4 bonds

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23
Q

What are the bonds in amylopectin?

A

• Branched with a-1,6 bonds at branches

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24
Q

What does amylase act on, andwhere is it secreted?

A
  • A-1,4 bonds

* Secreted in saliva and by the pancreas

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25
Q

What do a amylases produce?

A

Glucose, maltose and a-limit dextrins from amylopectins

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26
Q

Give four sugar related enzymes found attached to the brush border of the small intestine

A
  • Isomaltase
    • Maltase
    • Sucrase

Lactase

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27
Q

What does isomaltase do?

A

• Breaks down branched molecules at a-1,6 bonds

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28
Q

What does maltase do?

A

Converts maltose -> Glucose

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29
Q

What does sucrase do?

A

Sucrose -> Glucose/Fructose diamer

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30
Q

What does lactase do?

A

• Lactose -> Glucose/galactose diamer

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31
Q

How is glucose absorbed across brush border of the small intestine?

A
  • Actively
    • Uses energy set up by Na+/K+/ATPase
    • Enters epithelial cell across its apical membrane via a Na+/Glucose symporter, SGLT1
32
Q

What two things, other than Na+, can SGLT1 transport?

A
  • Glucose

* Galactose

33
Q

How does glucose leave epithelial cell of brush border and move into blood stream?

A

• Moves across basolateral membrane through facillitated diffusion through the GLUT2 transporter

34
Q

What happens to proteins in stomach?

A

• Digested to short oligopeptides in the stomach by pepsin secreted from chief cells

35
Q

How big is an oligopeptide?

A

• 10-20 Aas long

36
Q

Where are peptidases found in the duodenum secreted from?

A

• The pancreas

37
Q

Name four types of peptidase

A
  • Pepsin
    • Trypsin
    • Chymotrypsin

Carboxypeptidase

38
Q

What does pepsin breakd own?

A

• Bonds near aromatic AA side chains

39
Q

What does trypsin break down?

A

Bonds near basic AA side chains

40
Q

What does chymotrypsin break down?

A

• Bonds near armoatic AA side chains

41
Q

What does carboxypeptidase breakdown?

A

• C-terminal AA’s with basic side chains

42
Q

What is special about protein absorption in neonates?

A
  • Can absorb whole proteins through gut

* Enables breast milk to confer passive immunity on to babies via IgA absorption

43
Q

Give two ways in which AA are taken up by the gut?

A
  • Facilitated passive diffusion

* Scondary active transport

44
Q

Name five types of AA which are taken up via secondary active transport?

A
  • Small neutral AA’s
    • Neutral AA’s, Basic AA’s and Cysteine
    • Acidic AA’s
    • Immuno-AA’s
    • B AA’s
45
Q

How are dipeptides and tripeptides taken up?

A

• By active mechanisms associated with pumping H+ into the lumen which then returns by co-transport with the peptide

46
Q

Why are fats so hard to digest?

A
  • Insoluble in water

* Aggregate into large globules preventing effective action of digestive enzymes

47
Q

What enables fats to be digested?

A
  • Bile acids enable fats to be incorporated into small micelles with fats in the middle and polar components of bile acids on the outside
    • Micelles generate high surface area for the action of lipases
48
Q

What are micelles cleaved into?

A
  • Fatty acids

* Glycerol

49
Q

What happens to fatty acids and glycerol in the epithelial cells?

A

Converted into TAGs and re-expelled as chylomicrons

50
Q

Where do chylomicrons go after gut epithelial cells?

A

Transport of fat in the lymphatic system from the gut to the systemic veins

51
Q

How is sodium taken up into cells?

A
  • Taken up via diffusion into the cell and actively transported across the basolateral membrane by Na/K/ATPase
    • This provides the driving force for the majority of absorption
52
Q

How does chloride get into the epithelial cells?

A

• Follows movement of Na+ into cells.

53
Q

What does the movement of Na+ and Cl- provide?

A

• Osmotic gradient leading to the uptake of water

54
Q

How much calcium is absorbed per day? How does it enter cells?

A

• 700mg out of 6g consumed

Enters cells via facilitated diffusion

55
Q

How is Ca2+ pumped out of basolateral membrane?

A

• Ca2+ ATPase

56
Q

What does the absorption of Ca2_ require?

A
  • Vitamin D

* Stimulated by PTH

57
Q

How much iron is absored a day?

58
Q

• 120mg

How is iron absorbed?

A
  • Can only be absorbed in ferrous form
    • Gastric acid solubises iron complexes
    • Stomach also secretes gastroferrin (binds iron and keeps it ferrous)
59
Q

What do intestinal mucosal cells secrete to facilitate that absorption of Fe2+?

A

• Transferrin SEE MEMBRANES AND RECEPTORS

60
Q

How are water soluble vitamins absorbed?

A

• Via passive diffusion

○ Vitamin C, B vitamins

61
Q

How and where is vitamin B12 absorbed?

A

• Co-factor in the terminal ileum
○ Intrinsic factor - binds to b12 in the stomach to keep it soluble

Secreted by the stomach mucosa

62
Q

What is pernicous anaemia?

A
  • Occurs with vitamin B12 deficiency
    • Occurs when there is damage to stomach, preventing it from secreting intrinsic factor, or the terminal ileum has been damaged
63
Q

What is oral rehydration therapy?

A
  • The uptake of Na+ generates an osmotic gradient which water follows
    • Glucose uptake stimulates Na+ uptake, plus generates own osmotic gradient
64
Q

Outline how matter travels through small intestine?

A
  • Moved very slowly while being gentl mushed around

* Via segmenting

65
Q

What is segmenting?

A
  • Small intestine divided into sections, each with a pacemaker
    • Frequency of pacemaker gets less from the duodenum to the terminal ileum, a phenomen know as the intestinal gradient
    • Each contraction separacter the intestine into segments where muscle not contracted, whose contents are effectively mixed by movement from portions that do contract
66
Q

Does segmenting propel contents?

A
  • No, merely ensures that it is mixed

* Intestinal gradient responsible for movement

67
Q

What is haustral shuffling?

A
  • Circular muscle more complete than longitudinal
    • Taenia coli
    • Contraction of the smooth muscle in walls of Haustra shuffles contents back and forth, as slow absorption of remaining water and salts form faeces
    • Contents slowly progress towards the sigmoid colon, with control like segmenting
68
Q

What is a mass movement?

A

• Infrequent peristaltic movement propelling pattern from transverse to descending colon
Forces faeces rapidly into rectum, inducing urge to defecate

69
Q

What are mass movements triggered by?

A

• Eating, via the gastrocolic reflex

70
Q

What occurs once mass movement finished?

A
  • Urge to defecate arises due to pressure receptors in rectum.
    • Wave of contraction in the rectal muscle forces faeces towards anus
71
Q

What are the two anal sphincters?

A
  • Internal

* External

72
Q

Describe the internal anal sphincter? (Muscle type and control)

A

• Smooth muscle
• Parasympathetic control
○ Relaxes

73
Q

Describe the external sphincter (muscle type and control)

A

• Voluntary striated muscle
• Voluntary control
○ Relaxes

74
Q

What happens once both anal sphincters are relaxed?

A

• Intraabdominal pressure increases and expulsion of faeces

75
Q

When would one shit oneself?

A

• When voluntary control of external sphincter is overridden when rectal pressure becomes too high

Semester 3 - Gastrointestinal (28 decks)

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