Small And Large Intestine

Question 0

Outline the functions of different parts of the bowel

Answer 0

Small intestine - complete digestion, absorption

Large intestine - absorption of remaining water and salts, form faeces

Question 1

Describe the gross and microscopic anatomy of the large and small intestines and relate these to their function

Answer 1

Small - mucosa folded into villi, separated by crypts, micro villi forms brush border (increases SA, enzymes complete digestion)
Large - haustra allow for haustral shuttling (slow absorption)

Question 2

Describe the mechanisms of absorption of the following groups of nutrients in the small intestine: sugars, amino acids, vitamins

Answer 2

Carbohydrates:
Maltase (maltose –> glucose), isomaltase (a1,6 branches), sucrase, lactase
Absorbed by SGLUT1 and GLUT2
Amino acids –> oligopeptides:
Chymotrypsin (aromatic), trypsin (basic), carboxypeptidase (C terminal, basic)
5 Na+/aa co-transporters - neutral, basic, acidic etc
Calcium:
700mg/day, facilitated diffusion using Ca2+ATPase, require vit.D, PTH
Iron:
20mg/day, transferrin binds Fe2+, gastric acid/gastroferrin solubises
Vitamin B12:
Co-factor (intrinsic factor) in terminal ileum, deficiency = pernicious anaemia

Question 3

Describe the basis of oral rehydration therapy

Answer 3

Mixture of glucose and salt stimulates maximum water uptake

Question 4

Describe the patterns of motility in the small intestine

Answer 4

Segmenting
Intestinal pacemakers (more at stomach end) cause intermittent contraction
Gradual caudal progression

Question 5

Describe the functions of the large intestine

Answer 5

Slow absorption of remaining water and salts

Formation of faeces

Question 6

Describe the motility of the colon and rectum

Answer 6

Haustral shuttling:
Contraction of smooth muscle in haustra causes walls to shuttle contents back and forth
Slow absorption
Gentle progression towards sigmoid cold
Mass movement:
1/2x daily
Peristaltic, propulsive pattern from transverse –> descending colon
Forces faeces rapidly into rectum –> urge to defeacate
Stimulated by gastrocolic reflex

Question 7

Describe the mechanisms of defeacation

Answer 7

Filling of rectum stimulates pressure receptors
Internal anal sphincter - parasympathetic control
External anal sphincter - voluntary control
Control via sacral reflexes
Increase in intraabdominal pressure