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GI > Week 8 - Intestines and absorption > Flashcards

Week 8 - Intestines and absorption Flashcards

1
Q

How is the small intestine specialised for absorption?

A
  • Large SA -> the mucosa is folded into villi which have microvilli
  • Plicae Circulares Slow movement of contents
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2
Q

What are plicae circulares?

A

-Permanent folds in the jejunum which slow down gut contents to increase time for absorption

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3
Q

What is the name for intestinal epithelia?

A

-Enterocytes

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4
Q

Why does the intestine contain goblet cells?

A

-To produce mucus for protection

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5
Q

What is the benefit of epithelial shedding and renewal? How does it do this?

A
  • Shedding mucosa ensures that the mucosal barrier is always intact with healthy cells for protection
  • Intestinal glands contain stem cells at the base which migrate to the surface whilst maturing
  • When they reach the apex of the villi they undergo anoikis
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6
Q

What is anoikis?

A

-Programmed cell death as the intestinal cell detaches from surroundings and is sloughed into lumen

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7
Q

What cells can stem cells of the intestinal crypts mature into?

A

-Paneth cells, goblet cells, enteroendocrine cells, enterocytes

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8
Q

What are paneth cells?

A

-Cells involved in innate defence via production of antimicrobials

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9
Q

What do intestinal epithelia secrete?

A

-Enzymes into brush border to breakdown carbs and proteins

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10
Q

Which type of carbohydrate are absorbed by the gut?

A

-Monosaccharides

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11
Q

Name some monosaccharides

A

-Glucose, galactose, fructose

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12
Q

Where does final enzyme digestion of carbs take place?

A

-Brush border

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13
Q

Describe starch and its digestion

A

-Contains amylose (linear chains of glucose) and amylopectin (branched chains of glucose) which are broken down by amylase (salivary and pancreatic) and isomaltase (brush border) respectively

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14
Q

When amylose is broken down by salivary and pancreatic amylase, what is produced?

A

-glucose and maltose

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15
Q

Where is maltose broken down and by what?

A

-Brushborder by maltase

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16
Q

When amylopectin is digested by amylose what is produced? Where are these further digested?

A
  • a-dextrans

- Brushborder by isomaltase

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17
Q

What is sucrase?

A

-Glucose and fructose

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18
Q

What is lactase?

A

-Glucose and galactose

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19
Q

Describe monosaccharide absorption into enterocytes

A
  • NaKATPase on basolat provides the driving energy for SGLUT1 transporter to allow Na to diffuse down its conc gradient bringing glucose with it into the cell (secondary active transport)
  • Uses Glut2 to be transported from the enterocyte into blood
20
Q

Which monosaccharide uses GLUT5 as facillitated diffusion?

A

-fructose

21
Q

Explain the principle of oral rehydration

A
  • Uptake of Na generates an osmotic gradient and allows water to follow
  • Glucose uptake stimulates Na uptake
  • Therefore a mixture of glucose and salt will stimulate maximal water uptake
22
Q

What types of proteins are absorbed?

A

-a’a, dipeptides and tripeptides

23
Q

How is protein digestion started in the stomach?

A
  • Pepsinogen is secreted by chief cells and converted to pepsin by HCL
  • Pepsin acts on proteins and digests them to a’a and oligopeptides which are released into the small intestine
24
Q

How is protein digestion continued in the small intestine?

A
  • Pancrease secretes proteases as zymogens into the small intestine
  • Trypsinogen is converted to trypsin by enteropeptidase
  • Trypsin then activates all the other zymogen proteases to allow protein digestion to continue
25
Q

What are the major proteases released from the pancreas?

A
  • Endopeptodases -> trypsin, chymotrypsin, elastase

- Exopeptidases -> Carboxypeptidase A and B

26
Q

How are amino acids absorbed into enterocytes?

A

-Via active and passive processes using Na:amino acid transporters

27
Q

How are dipeptides and tripeptides absorbed into enterocytes?

A

-H+co-transporter and then converted to amino acids by cytosolic peptidases

28
Q

How is water absorbed into enterocytes?

A
  • NaKATPase on basolat
  • Creates Na gradient
  • Na and other nutrients diffuse into epithelia
  • Water follows by osmosis
29
Q

What is the differnce between water uptake in small and large intestine?

A
  • Small intestint absorbs more volume of water but large intestine’s function is water absorption as it absorbs residual water
  • Small intestine Na is cotransported
  • Large intestine Na channels which are induced by aldosterone
30
Q

Describe calcium uptake in the intestines

A

1) Active transcellular uptake where Ca enters via facillitated diffusion -> CaATPase pumps Ca out on basolateral membrane (requires vit D)creating low intracellular Ca
2) Passive paracellular

31
Q

What is calbindin?

A

-Molecule in enterocytes acivated by vit D allowinf Ca transfer through cell

32
Q

Describe the uptake of iron in the intestines

A
  • Gastric acid important in uptake
  • Iron absorbed across apical membrane and then binds to appoferritin which moves it across basolateral membrane and enters circulation bound to transferrin
33
Q

How are water soluble vitamins taken up in the intestines?

A

-Using Na:cotransport

34
Q

Describe how vit B12 is absorbed and its role in pernicious anaemia

A
  • Absorbed in terminal ileum bound to intrinsic factor which is secreted by parietal cells
  • Pernicious anaemia is autoimmune destruction of parietal cells causing b12 deficiency and aneamia as b12 is necessary for erythropiesis
35
Q

Name the types of intestinal mobility in the small intestines?

A
  • Intestinal gradient
  • Segmentation
  • Peristalsis
36
Q

Explain Intestinal gradient

A

-Occurs between meals-> intestinal pacemakers in the smooth muscle have a higher frequency proximally which drives slow caudal progression of contents

37
Q

Explain segmentation

A
  • Occurs following meals
  • Different sections of gut contract at different times causing food to move back and forth to promote mixing and slowing of progression
38
Q

What is the function of peristalsis in small intestine?

A

-To move contents along

39
Q

Name the types of intestinal mobility in the large intestine

A
  • Segmentation (haustra shuttling)

- Mass movement

40
Q

What is segmentation in the large intestine?

A

-Occurs in proximal colon to agitata food and allow remaining water to be absorbed forming faeces

41
Q

Explain mass movement

A
  • Co-ordinated contraction which occurs 1-3 times per day
  • Contents move rapidly from transverse colon into rectum
  • Often triggered by eating (gastro-colic reflex)
42
Q

Explain defaecation

A
  • Rectum normally empty but when fills to 25% there is an urge to defaecate and the internal sphincter relaxes due to pressure via parasympathetic control and external sphincter relaxes under voluntary control
  • Intra-abdominal pressure rises and faeces expelled
43
Q

What is the difference between internal and external sphincter?

A

-Internal is smooth muscle external is striated

44
Q

What is the ‘unstirred’ layer?

A

-Formed by the brush border

45
Q

What are tinea coli?

A

-Longitudinal muscle of large intestine

46
Q

What is the classical triad of pernicious anaemia?

A

-Weakness, glossitis and parasthesia

47
Q

What is the role of the intestines?

A

-To absorb nutrient, water and electrolytes from the gut lumen into the blood

GI (16 decks)

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