Table 7 The absorption of monosaccharides

Lumen of intestine	Wall of intestine	Portal vein
I. Galactose II. Glucose III. Fructose IV. Pentoses	Na-Glucose transporter (act. tr.) Galactose Glucose GLUT (facilitated diffusion) Fructose ----------àsimple diffusionà	GLUT (Facilitated diffusion) Galactose Glucose Fructose Pentoses All monosaccharides ↓ liver ↓ glucose ↓ blood circulation

The conversion of glucose in tissues. Glucostatic function of liver

The following tissues and organs use glucose particularly intensive:

1) nervous tissue because glucose is only source of energy

2) muscles (for production of energy fro contraction)

3) wall of intestine (absorption demands the energy)

4) kidneys (formation of urine is energy dependent process)

5) adrenal glands (energy is necessary for synthesis of hormones)

6) erythrocytes

7) adipose tissue (glucose is necessary as source of glycerol)

8) mammary glands, particularly in lactation (glucose is necessary for lactose formation)

65% of glucose is oxidized; 30% of glucose is used for liponeogenesis; 5% of glucose is used on glycogen formation.

Glucostatic function of liver: is provided by 3 processes:

1) glycogenogenesis (formation of glycogen)

2) glycogenolysis (cleavage of glycogen)

3) gluconeogenesis (formation of glucose from intermediates).

Increase of glucose in blood causes increase of glycogenogenesis. Decrease of glucose in blood causes glycogenolysis and gluconeogenesis.

The normal level of glucose in blood is 3.4-6.1mM/L and liver regulates concentration of glucose in blood

Glycogenogenesis 2/5 of glycogen is stored in liver. 1/5 of glycogen is formed in muscles and other organs and tissues. Glycogen is a reserve of glucose. It is a high molecular compound and therefore doesn’t increase osmotic pressure in cells. This process is complex and consists of following stages:

ATP ADP UTP PP UDP

Glucose------------à Glucose-6-ph---------àUDP-glucose --------à (C6H10O5)n+1

Glycogenolysis 1) Phosphorolysis; 2) hydrolysis

Phosphorolysis occurs in different tissues:

Phosphorylase

(C6H10O5)n ----------------------à (C6H10O5)n-1 + Gl-1-Ph

+H3PO4 ↓ Gl-6-ph-ase

oxidation←Gl-6-Ph----------àglucose (in liver)

Hydrolysis of glycogen occurs in liver only:

γ-amylase

(C6H10O5)n -----------------------à (C6H10O5)n-1 + Glucose

+HOH

<== попередня сторінка	\|	наступна сторінка ==>
The role of carbohydrates	\|	Anaerobic glycolysis and its energetic value

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