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Renin Angiotensin Mechanism.

HMP Shunt.

 

Definition:

It is an alternative minor pathway for glucose oxidation.

  • Does not produce ATP nor utilize it. 

  • Producing NADPH+H+, (Biosyn Lipids) and Ribose (Synthesis of NA).

  • Also called,

    • PPP (Pentose Phosphate Pathway)

    • HMP Shunt (Hexose Monophosphate Shunt)

Intracellular site and tissue distribution:

  • Cytosolic in tissues namely: liver, Adipose tissues, Lactating mammary gland, RBCs, Suprarenal cortex, Thyroid and testis. 

  • Not active in non-lactating mammary gland, and in skeletal muscles. 

Steps of HMP Shunt:

  • The pathway are divided into two phases:

    • 1. Phase I : Oxidative irreversible phase 

    • 2. Phase II : Non-oxidative reversible phase.

Regulation of HMP shunt: -

  • The key regulatory enzymes are G-6-PD and 6-phospho-gluconate dehydrogenase.

  • They are activated by fed state, glucose, insulin, thyroxine and NADP. 

  • But….

    • They are inhibited during starvation, diabetes mellitus and with high NADPH.H+/NADP ratio.

Significance of HMP Shunt:

  • I- Production of pentoses:

  • Tissues must satisfy their own requirement of pentoses since dietary pentoses are not utilizable and ribose is not a significant constituent of systemic blood. 

  • Pentoses are used for:

    • 1. Nucleic acids, Ribose for RNA and Deoxyribose for DNA.

    • 2. Coenzymes synthesis, e.g., NAD+, FAD, CoASH.

    • 3. Free nucleotide Coenzymes, e.g., ATP, GTP, 

    • 4. Synthesis of certain vitamins, e.g., B2 and B12.

  • II-HMP pathway is the major human source for production of NADPH.H+ required for:

    • 1. Fatty acid synthesis (lipogenesis) and fatty acid 

    • desaturation.

    • 2. Cholesterol and other steroid synthesis.

    • 3. Synthesis of sphingosine and cerebrosides. 

    • 4. Synthesis of non-essential amino acids, e.g., 

    • glutamate and tyrosine from phenylalanine.

    • 5. Regeneration of reduced glutathione (G-S-H).

    • 6. Metabolic hydroxylation with cyp450.

Commonly Asked Questions.

  1. Write in detail about HMP Shunt and its significance..

  2. Write significance of HMP Shunt.
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