About Dietary Reference Intake (DRI)


 

 

The Dietary Reference Intake can be defined  a system of nutrition recommendations that estimates the amounts of nutrients required to prevent deficiencies and maintain optimal Health.

 

The DRI includes some concepts that sometimes are used as equivalents, when they are not. In other cases, the same concept receive different names, depending of the source of the article you are reading.

DRIs consists of four dietary reference standards:

 

1.- Estimated Average Requirement (EAR): Average daily nutrient intake level estimated to meet the requirement of one half of the healthy individuals in a specific age and gender group.

 

 2.- Recommended Dietary Allowance (RDA): Average daily Dietary intake level that is sufficient to meet the nutrient requirements of nearly all (97-98%) individuals (EAR+2DS) on each life state and gender group. It is approximately 20 % higher than the EAR. RDA are printed in food labels in the United States and Canada.  (The definition of RDA is similar to the definition of  Recommended Nutrient Intake (RNI)  used by the World Health Organization and other international organizations).

 

 3.- Adequate Intake (AI): Estimation of nutrient intake in healthy people (used when EAR and RDA are not known)

 

 4.- Tolerable Upper Intake Level (UL): Highest average daily intake level from food, water and supplements that is likely to pose no risk of adverse health effect from excess in almost all apparently healthy individuals in an age and gender specific population group. (This concept is important mainly in relation to nutritional supplements, since the ingestion of natural foods is regulated in the body through mechanisms of absorption and excretion), In absence of observations of known adverse effects, it is used a default value of 10 times de Recommended Dietary Allowance.

 

More information about these reference standards can be found at:

 

Dietary Reference Intake

Reference dialy Intake 

 Interactive DRI for health care professionals

 Yates, A.A.: Dietary Reference Intakes –What is new and how to use them (Power point presentation)

Who Experts Committee:

Vitamin and Mineral requirements in human nutrition

World Health Organization, 2004

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About Tea and Toasts


 

A 70 year-old English lady that lives alone is admitted to the hospital for evaluation of a leg wound that is not healing properly. The patient also complains of pain in muscle and bones. On the examination, you find some hemorrhagic lesions in the skin, including ecchymosis in buttocks and both legs and petechiaes in other areas of the skin. The nails show splinter hemorrhages. When asked about her dietetic habits, the patient refers that she is too old to eat so much, so she has a very frugal lunch and dinners based mainly in tea and toasts.

Laboratory examinations show normal blood coagulation tests and Hemoglobin of 9.8 g/dL

 

The treatment for the condition described above should consist mainly in the administration of the following vitamin:

 

a)     Ascorbic Acid

b)     Biotin

c)      Folic Acid

d)     Pantothenic acid

e)     Niacin

f)       Vitamin B1

g)     Vitamin B2

h)    Vitamin B6

i)       Vitamin B12

j)       Vitamin D

k)     Vitamin E

l)       Vitamin K

Biochemistry of platelets (II): Platelet receptors.


 

Platelet aggregates

Platelet aggregates

 

Platelet membrane is rich in glycoproteins organized as receptors of very different types: tyrosine kinase receptors, integrin family receptors, receptors rich in Leucine (LRR), protein G linked transmembrane receptors, immunoglobulin super family proteins, lectins and others.

 

Many of these receptors play an important role in the haemostatic function of platelets, participating in the interaction among platelets, between platelets and vascular tissue, and among platelets and coagulation factors and other agonists (ADP, epinephrine, thromboxane A2, and others)

 

Other platelet membrane receptors are involved in the participation of platelets in processes such as inflammation, tumor growth, metastasis and immunologic type reactions.

 

From the medical point of view, GPIIb-IIIa and GPIb receptors are particularly important.

 

[GP] IIb-IIIa is the most abundant receptor in the platelet surface, representing almost 15 % of all the proteins in the cell surface. This receptor is a member of the Integrin receptors family and is also called Integrin αIIb-β3. This is an important receptor in platelet aggregation, since it binds Von Willebrand factor and fibrinogen.  The relevance of this kind of receptors for an appropriate hemostasis is obvious if we consider that genetic mutations which provoke the absence or formation of lesser quantities of these receptors give rise to platelets that are not able of binding to fibrinogen and aggregate (Glanzmann Thromboasthenia).

Another important medical issue related to these receptors is the fact that nowadays antagonists of these receptors have been developed for inhibiting platelet aggregation, so we can use anticoagulant drugs that inhibit platelet aggregation regardless of the agonist. Examples of these drugs are Abciximab: a human monoclonal antibody, Eptifibatide, a cyclic hexapeptide derived from the venom of a snake) and Tirofiban, a synthetic non-peptide molecule.

 

GPI-b (GPIb-GPIX-GPV) is a Leucine Rich Receptor (LRR) formed by a multiprotein complex of 4 different types of glycoproteins: GPIb alfa and GPIb beta, (linked through disulfide bonds) and GPIX and GPV (associated by non covalent forces).

 

This receptor is crucial for the platelets initial attachment to the extracellular matrix of the damaged vessel. This attachment is made through the Von Willebrand factor, which acts as a bridge between the sub endothelial collagen (exposed as a consequence of the vessel damage) and the GPI-b receptors in the platelet membrane.

 

The Bernard-Soulier syndrome is an autosomal recessive disorder which appears as a consequence of an absence or decrease of the glycoproteins that form the GPIb-GPIX-GPV receptors.

 

Excellent reviews on these issues can be found at the following links:

 

Platelet function defects.

 

Platelet function disorders 

 

Platelet receptors and signaling in the dynamics of thrombus formation

 

 Inherited Disorders of Platelets 

 

 Blood coagulation 

 

 Thromboasthenia of Glanzmann and Naegeli 

 

 Giant Platelet Syndrome

Q: About a patient with a glucagonoma.


 

Mouse Islet of Langerhans immunostained for Glucagon

 

Assume that you find a patient with a glucagon-secreting pancreatic tumor (glucagonoma). Which one of the following is most likely to result from hyperglucagonemia?

 

a)     Decreased lipolysis

 

b)     Hyperglycemia

 

c)      Increased muscle protein synthesis.

 

d)     Increased liver glycolytic rate

 

e)     Increased glycogenesis

Biochemistry of Platelets: Overview


Platelets or thrombocytes are blood cells which participate in the coagulation of blood.

 

Source of platelets.

 

Platelets are formed from their precursors in the hematopoietic tissue. 

 

Platelets, like other blood cells, are formed from Hemocytoblast that under certain conditions, and mainly under the effects of thrombopoietin, may be converted in a megacarioblast. Megacaryoblast is transformed into Promegacariocyte, and this cell in Megakaryocyte.

 

During Megakaryocyte maturation process,   DNA replication continues, and the nucleus suffers many divisions, but the cell continue undivided. While this process is going on, a large amount of cytoplasm accumulates.

 

Platelets are formed by the development of demarcation membranes in the cytoplasm, with subsequent release of the formed fragments to the venous sinusoids of the marrow bone.

 

A Megakaryocyte can release thousands of platelets, leaving the parenchyma cell with virtually only the nucleus and residual cytoplasma.

 

 

General structure:

 

Platelets are very small (1 to 4 microns in diameter) and circulate between 4 and 10 days, as flattened disks without nucleus. Platelet membrane is very rich in phospholipids and contains various glycoproteins that perform a fundamental role in the reception and transduction of intracellular signals. The cytoplasm of platelets contains a microphylament system and an actin/myosin contractile structure, called thrombosthenin, which, when activated, modify the conformation of the membrane. The cytoplasm also contains microtubules, which together with the microfilaments form an internal cytoskeleton responsible for the platelets conformation, but at the same time flexible enough to allow the conformational changes that occur during the platelet activation.

 

Platelet cytoplasm contains also residual endoplasmic reticulum(forming the so-called dense tubular system), mitochondria, glycogen and three different types of granules: Alpha granules, dense granules and lysosomal granules, containing biologically active substances that are released during the coagulation process The energy for platelet processes (aggregation, secretion and others) derive from the aerobic metabolism  in the mitochondria and anaerobic glycolysis (recall that the cytoplasm contains glycogen granules)

 

Platelet receptors and granules are particularly interesting from the physiological and medical point of view, so they will be discussed in more detail in future posts.

 

Recommended articles:

 

Flaumenhaft, R. et al:

The actin cytoskeleton differentially regulates platelet (alpha)granule and dense granule secretions.

 

The Online Metabolic and Molecular Bases of Inhereted Diseases.

The inhereted disorders of platelets

 

Wikipedia:

Platelet.

Question (B-15): Flavoproteins in Krebs Cycle


 

In this representation of Krebs Cycle, each reaction, is marked with a number.

Select the two reactions that require the participation of Flavoproteins.

 

a)     1 and 3

 

b)     2 and 4

 

c)      3 and 5

 

d)     4 and 6

 

e)     5 and 7

 

f)       6 and 8

AMEE Releases Agenda for the Next General Assembly


The International Association for Medical Education in Europe (AMEE) has released  a provisional Agenda for its General Assembly that will be held in Malaga, Spain, on September 1st.

 

Palacio de los Congresos, Malaga

Palacio de los Congresos, Malaga

 

General Assembly 2009

Palacio de Ferias y Congresos de Málaga, Málaga, Spain

Tuesday 1 September: 1300-1400 hrs

 

Draft Agenda

 

1.   Welcome and apologies   
2.   Minutes of the General Assembly of AMEE held on 2 September in Prague, Czech Republic   GA1/09 
3.   President’s Report   
4.   Financial Statement  GA2/09 
  4.1 Proposed increase in the AMEE Individual Membership Fee GA3/09
       
5.   Elections to the Executive Committee GA4/09
       
6   Conferences GA5/09
  6.1 AMEE 2009 Malaga, Spain  
  6.2 AMEE 2010 Glasgow, UK  
  6.3 AMEE 2011 Vienna Option  
  6.4 AMEE 2012 Marseille Option  
  6.5 Other potential venues for AMEE Conferences  
  6.6 Ottawa Conference 2010  
       
7   Update on AMEE’s activities GA6/09
  7.1 MedEdWorld and AMEE member benefits  
  7.2 Medical Teacher  
  7.3 Best Evidence Medical Education (BEME)  
  7.4 AMEE Position Paper on Bologna Process  
  7.5 A Medical Teachers Charter  
  7.6 Accreditation of Teaching  
  7.7 Orpheus  
  7.8 AMEE courses  
  7.9 Other activities  
       
8   Report from WFME and Regional Associations  
       
9   Have your say: an opportunity for suggestions from members   
10   Any other business   
11   Date of next meeting