13) The Intestines

Question 1

Describe the features of chyme when it reaches the intestines:

Answer 1

Isotonic
Neutral
Digestion nearly complete

Question 2

What is the intestines role?

Answer 2

Absorb nutrients

Absorb water/electrolytes

Question 3

How can these substances being absorbed move from gut lumen into blood (generally)?

Answer 3

Transcellular - apical and basolateral

Paracellular

Question 4

How is the small intestine adapted for absorption?

Answer 4

Large surface area by villi and microvilli

Slow transit time by plicae circularis

Question 5

Which cells make up the epithelium of the small intestine?

Answer 5

Enterocytes and goblet cells

Question 6

How does the intestine ensure it’s function of absorption across the epithelium in this harsh environment?

Answer 6

Mucosa constantly shed (3-6 days) and replaced by stem cells at base of crypt

Question 7

What cells are located in the crypt (intestinal gland)?

Answer 7

Stem cells
Enteroendocrine gland - hormones
Paneth cells - antibacterial

Question 8

What is involved in the final breakdown of carbohydrates?

Answer 8

Brush border hydrolases

Question 9

How are carbohydrates absorbed?

Answer 9

As monosaccharides

Question 10

What does starch consist of?

Answer 10

Amylose (alpha 1-4 bonds)

Amylopectin (alpha 1-4 and 1-6 bonds)

Question 11

What enzyme breaks alpha 1-4 bonds and what is the product?

Answer 11

Amylase forming glucose or maltose

Question 12

What enzyme breaks alpha 1-6 bonds and what is the product?

Answer 12

Isomaltase forming glucose or alpha dextrins

Question 13

What enzymes break down disaccharides?

Answer 13

Maltase, sucrase and lactase

Question 14

How does glucose move into enterocytes?

Answer 14

Through SGLT-1, sodium symporter

Question 15

What other sugar can move through SGLT-1?

Answer 15

Galactose

Question 16

How does fructose enter the cell?

Answer 16

Through GLUT-5 by facilitated diffusion

Question 17

How does monosaccharides move into blood?

Answer 17

Through GLUT-2 by facilitated diffusion

Question 18

What does oral rehydration fluid contain and what is its goal?

Answer 18

Mixture of glucose and salt to stimulate maximum water uptake in diarrhoea

Question 19

How are proteins absorbed?

Answer 19

As AAs, dipeptides and tripeptides

Question 20

How does the stomach contribute to protein digestion?

Answer 20

Acid unravels proteins

Pepsin starts break down on proteins into smaller peptides

Question 21

How is trypsinogen converted into its active form?

Answer 21

By enteropeptidase

Question 22

What is the function of exopeptidases?

Give an example

Answer 22

Break bonds at end of polypeptide to produce dipeptides and AAs
Carboxypeptidase (A+B)

Question 23

What is the function of endopeptidases?

Give an example

Answer 23

Break bonds within a polypeptide to produce shorter peptides

Trypsin, chymotrypsin, elastase

Question 24

How are amino acids transported into the cell?

Answer 24

Co-transport with sodium

Question 25

How are di/tripeptides transported into the cell?

Answer 25

H+ co-transporter (PepT1)

Question 26

What happens to di/tripeptides inside enterocytes?

Answer 26

Cytostolic peptidases convert them to amino acids

Question 27

Why is it more difficult for large intestine to absorb water?

Answer 27

Less water so smaller osmotic gradient

Question 28

What hormone can help large intestine to absorb water?

Answer 28

Aldosterone - induces insertion of Na+ channels

Question 29

How is calcium absorbed is intake is low?

Answer 29

Active transcellular absorption by facilitated diffusion (apical) and Ca2+ ATPase (basolateral)

Question 30

What substances are required for active transcellular absorption of Ca2+?

Answer 30

Vit D, calbindin

Stimulated by PTH

Question 31

How is calcium absorbed is intake is normal/high?

Answer 31

Passive paracellular absorption

Question 32

How is iron transported across apical membrane?

Answer 32

Co-transported with H+

Question 33

What happens to iron inside cells when levels are low?

Answer 33

Binds to transferrin and transported to stores in Hb, BM, liver and spleen

Question 34

What happens to iron inside cells when levels are high?

Answer 34

Iron contained in ferritin complexes (trapped in cell) and lost when enterocyte is replaced

Question 35

How are water soluble vitamins absorbed?

Answer 35

Na+ co-transport

Question 36

How is Vit B12 absorbed?

Answer 36

In terminal ileum bound to intrinsic factor

Question 37

What can cause Vit B12 deficiency and what can this lead to?

Answer 37

Gastritis or terminal ileal removal (Crohn’s)

Leading to pernicious anaemia (type of megaloblastic anaemia)

Question 38

What is segmentation?

Answer 38

Mixing of contents in small intestine

Question 39

How are contents moved along the small intestine?

Answer 39

Small intestine divided into sections, each with a pacemaker. Frequency of pacemaker higher proximally

Question 40

What is haustra and why do they form?

Answer 40

Sacs of circular muscle which from as taenia coli (longitudinal muscle running length of LI) is shorter than intestine

Question 41

What does haustral shuttling do?

Answer 41

Agitates and mixes food allowing remaining water to be absorbed

Question 42

What is mass movement?

Answer 42

1-3 times a day, contents move rapidly from transverse colon to rectum

Question 43

What triggers mass movement?

Answer 43

Often eating (gastro-colic reflex)

Question 44

How much does rectum fill before we get the urge to defecate?

Answer 44

25%

Question 45

How is faeces expelled? (think sphincters)

Answer 45

Internal sphincter relaxes (PSNS)
External sphincter relaxes (voluntary)
Intra-abdominal pressure rises

Question 46

What is tenesmos?

Answer 46

Urge to defecate due to something stretching rectum