Download Digestion and Absorption (8)

Digestion and Absorption
Dr. Mohammed Alzoghaibi
Digestion and Absorption




Carbohydrates, proteins and lipids are
digested and absorbed in the small
intestine
Absorption
The surface area for absorption in the small intestine is
greatly increased by the presence of the brush border
Pathways of Absorption
- cellular
- paracellular
Structure of intestinal wall


Longitudinal folds (finger-like villi)
- longest in duodenum & shortest in ileum
- increases surface area 600 fold
The significance of villi & microvilli
- increase the surface area
- maximizing the exposure of nutrients to
digestive enzymes
Digestion and absorption of
lipids
Abnormalities of lipids digestion
1.
Pancreatic insufficiency (chronic pancreatitis
and cystic fibrosis)
2.
Acidity of duodenal content (zollinger-Ellison
syndrome)
3.
4.
Deficiency of bile salts (ileal resection)
Bacterial over growth (deconjugation of bile
salts)
5.
6.
Decrease intestinal cells for absorption
Failure of synthesis of apoproteins
(abetalipoproteinemia)
Digestion and absorption of
carbohydrates
Carbohydrate malabsorption




Lactose malabsorption syndrome
Symptoms
- gurgling noises in the intestine
- flatulence
- diarrhea
Sucrase-isomaltase deficiency
- decrease level of sucrase
- suppression of transporter protein
Glucose-galactose malabsorption syndrom
- deficiency in transporter protein
Digestion and absorption of
proteins
Vitamins and Electrolytes
transport and Diarrhea
Dr. Alzoghaibi
Absorption of vitamins



In terms of absorption, vitamins are
classified to whether they are lipid-soluble
or water-soluble
The fat-soluble vitamins include A, D, E, &
K
The water-soluble vitamins are C, B1, B2,
B6, B12, and folic acid
Absorption of vitamins (cont)
A.
B.
C.

Fat-soluble vitamins are incorporated into
micelles and absorbed along with other lipids
Most water-soluble vitamins are absorbed by
Na-dependent cotransport mechanisms
Vitamin B12 is absorbed in the ileum and
requires intrinsic factor
Gastrectomy results in the loss of parietal cells and loss
of intrinsic factor
pernicious anemia
Absorption and secretion of
electrolytes and water


o
o
Electrolytes and H2O may cross intestinal
epithelial cells by either cellular or
paracellular
The permeability of the tight junctions
varies with the type of epithelium
A tight epithelium is the colon
Leaky epithelia are the small intestine and
gallbladder
Absorption and secretion of
electrolytes and water
Absorption of NaCl:
Na moves into the intestinal cells by the
following mechanisms
1) Passive diffusion
2) Na-glucose or Na-amino acid cotransport
3) Na-Cl exchange
4) Na-H exchange

Absorption and secretion of
electrolytes and water

Cl absorption accompanies Na absorption
by the following mechanisms:
3)
Passive diffusion
Na-Cl cotransport
Cl-HCO3 exchange

Absorption and secretion of K

K is absorbed in the small intestine by passive diffusion
K secretion in the colon is stimulated by aldosterone
Excessive loss of k in diarrheal fluids causes
hypokalemia
1)
2)


Heme transport
Ca Absorption by Enterocytes

plasma Ca
parathyroid hormone
25-hydroxy-vitamin D3
kidney
1,25 dihydroxy-vitamin D3
Stimulates synthesis of Ca-binding protein
and Ca-ATPase in enterocytes
Diarrhea





Diarrhea
To run through 
 ECF   arterial pressure
 HCO3 (relative to Cl)  Hyperchloremic metabolic
acidosis
 K  Hypokalemia
Causes of Diarrhea:
 Decreased surface area for absorption
 Osmotic diarrhea (lactase deficiency)
 Secretory diarrhea
Hormonal control of absorption &
secretion

Glucocorticoid = absorption of H2O & ions
(small & large intestine)
Catecholamines = intestinal secretion

Somatostatin =

Epinephrine =

Aldosterone = synthesis of Na channel (colon)

H2O & ions absorption
(ileum & colon)
NaCl absorption (ileum)