Disorders of protein metabolism

Proteins

= complex organic substances that have amino acids in their structure

 Functions of proteins:

- energy role - by burning a gram of protein => 4.3 cal

- structural role

- enzymatic role

- role of hormone

- role in maintaining osmotic colloid pressure

- role in maintaining the acid-base balance

- role in defense

Proteins are:

- of animal origin

- of vegetable origin

 balanced diet contains: -60% protein of vegetable origin

-40% vegetable protein

Catabolism products

= substances that are released as a result of protein metabolism and which are normally released through the kidneys

 The normal protein intake is 1g / kg body weight.

 All proteins are made up of amino acids and have different functions => protein specificity is given by the sequencing of amino acids in the protein structure - the sequence of amino acids in the protein structure is responsible for the specificity of each protein.

 Normal value of total serum proteins - 6-8.5g%

Electrophoresis

= separation of protein fractions in the electric field; it is based on the different migration rate of proteins that depends on the number of electrical charges of the protein molecules.

o Separate the following fractions:

• albumin 45-60%

• globulins:

 α1-3-7%

 α2-8-12%

 β- 10-14%

 γ- 18-23%

a. By immunoelectrophoresis (coupling with antibodies after separation in the electric field) γ globulins are separated into the following immunoglobulins: IgA, IgM, IgD, IgE, IgG.

o Almost all proteins are synthesized in the liver except for globulins which are synthesized in the lymphoplasmacytic system.

Plasma protein systems

Renin-angiotensin-aldosterone system

- involved in homeostasis of blood pressure

- when we have an arterial hypoirrigation-> hemorrhage that leads to decreased blood levels or fluid loss => hemoconcentration- stasis occurs and renal hyperperfusion occurs- stimulates the production of renin that acts on the angiotensinogen in the liver; angiotensinogen leads to the formation of angiotensin1 which under the action of a conversion enzyme is transformed into angiotensin2 (it has 8 amino acids and is one of the most powerful vasoconstrictors in the body); angiotensin 2 increases adrenal production in the adrenal gland; Aldosterone promotes sodium reabsorption followed by water reabsorption

- activation of the renin-angiotensin-aldosterone system will result in increased sodium reabsorption followed by increased water reabsorption => increased blood volume => increased angiotensin production2

 There is a system of plasma quinines - bradykinin, lysyl bradykinin, methionylisyl bradykinin.

Disorders of protein metabolism

1. Hyperproteinemia - increase in proteinemia over 8.5g%

2. Hypoproteinemia - decrease in proteinemia below 6g%.

o Both hyperproteinemias and hypoproteinemias are of two types: - apparent and real.

a. Apparent hyperproteinemia - blood serum concentration

b. Real hyperproteinemia - by intensifying the synthesis - monoclonal gamopathies - during this condition there is an anarchic (malignant) tumor proliferation of an Ig clone - a single fraction of Ig (IgM and IgG) grows

Ex: multiple myeloma, plasmacytoma

Hypoproteinemia

 Causes:

 deficient protein intake-in terms of quantity (uncommon) -insufficient intake: prolonged fasting, pers. with mental and neurological disorders.

 In terms of quality

a. poor absorption:

- in inflammatory bowel disease

- glutemic enteropathy

- intestinal resections

- exacerbation of intestinal bacterial flora

b. synthesis deficiency - liver cirrhosis, liver cancer, acute hepatitis.

c. exaggerated losses

- renal (nephrotic syndrome - 3.5 grams of protein are lost)

- digestive (exudative enteropathy)

- plasmorrhea

- skin (burns)

 Proteins are filtered glomerularly, but all are reabsorbed at the level of the proximal convoluted tube => in the final urine there are fine traces of proteins (tubular proteins, IgA).

 In nephrotic syndrome, proteins appear in the final urine with low molecular weight - pure nephrotic syndrome; or high molecular weight - impure nephrotic syndrome

dysproteinaemias

= change in the concentration of serum protein fractions.

- can be: hereditary and secondary.

1. Inheritance:

 are based on the lack of a protein fraction.

 Example:

 Analbunimenia, atransferinemia, transcobalamin deficiency (manifested by megaloblastic anemia) etc.

2. Secondary

a. Reactive dysproteinemia from acute inflammation

 Alpha 1 and alpha 2 globulins increase, albumin decreases.

b. Dysproteinemia in liver disease

 In chronic hepatitis and liver cirrhosis, polyclonal hyperimmunoglobulinemia occurs as a result of the chronic inflammatory process.