Tuesday, October 7, 2014

cohort studyA cohort study is a type of observational investigation in which subjects are classified on the basis of level of exposure to a risk factor and followed to determine subsequent disease outcome.

Cohort study characteristics

  1. Observational study: No manipulation of the study factors
rs
  2. Have control group.
  3. From ‘cause’ to ‘outcome’.
l  “Prospective” = forward looking in time
l  Can be historical perspective
l  Also called follow-up, incidence, panel, or longitudinal study
  4. Could examine the causal association between the exposure and the outcome.

Cohort study types

1. Prospective cohort study: The basic type of cohort study
2. Historical cohort study Or retrospective cohort study
3. Ambispective cohort study

Prospective cohort studies

Prospective cohort studies are conducted by making all observations on exposure and disease status after the onset of the investigation

Retrospective cohort studies

Retrospective cohort studies involve observations on exposure and disease status prior to the onset of the study

Cohort Study design and practice

·         Selection of Subjects
       The Exposed Group
       The Unexposed Group
       The Outcome Event
l    Follow up
l    Data Collection

Selection of exposed group

Exposure determining is based on descriptive study and case-control study.The degree of exposure may differ depending on the goals of the study.

The investigator should identify an accessible population that is motivated to participate in the study and unlikely to discontinue participation

When the purpose of a cohort study is to investigate a community, such as in the Framingham Heart Study that community is the source of the unexposed persons.

Data Collection

Possible sources of data an exposure status include records, Interviews or Questionnaires, or Direct Measurements Made on Cohort Members.
Records

The available records include that Occupational records, medical and pharmacy records, census records and so on

Direct Measurements

Many exposures of interest cannot be determined with any accuracy, or perhaps at all, for individual study subjects from either records or interviews, but can be determined by direct measurement.

Cumulative incidence rate

Number of new cases of disease occurring over a specified period of time in a population at risk at the beginning of the interval.

Cumulative Incidence

the probability (risk) of an individual developing the disease (outcome) during a specific period of time.

Incidence density

Number of new cases of disease occurring over a specified period of time in a population at risk throughout the interval. The probability (risk) of an individual developing the disease (outcome) during a specific period of time, using total person-time as the denominator.  One subject followed one year contributes one person-year (PY). 

Incidence density requires us to add up the period of time each individual was present in the population, and was at risk of becoming a new case of disease.
                                                                               
Incidence density characteristically uses as the denominator person-years at risk.  (Time period can be person-months, days, or even hours, depending on the disease process being studied.)




descriptive studyDescriptive study includes activities relates to characterizing the distribution of disease within a population. Descriptive studies can yield valuable information about a population's health
status, and they can be used to measure risks and generate hypotheses. It is also useful in health service evaluation and can be used periodically to determine whether a particular service is improving

The type of descriptive study

  • Case reports
  • Case series
  • Cross sectional studies
  • Ecologic studies

Case reports and series

Case report: describes an observation in a single patient.
ª  “I had a patient with a cold who drank lots of orange juice and got better.  Therefore, orange juice may cure colds.”
Case series: same thing as a case report, only with more people in it.
ª  “I had 10 patients with a cold who drank orange juice….”

Cross sectional studies

A cross-sectional study is a descriptive study in which disease and exposure status are measured simultaneously in a given population. Also called a “survey” or “prevalence” study Cross-sectional studies can be thought of as providing a "snapshot" of the frequency and characteristics of a disease in a population at a particular point in time. This type of data can be used to assess the prevalence of acute or chronic conditions in a population.

Research aim of prevalence survey

  • To describe distribution of disease
  • To discovery clue of pathogenesis
  • Be used in secondary prevention
  • To evaluate prevention and cure effect
  • Surveillance of disease
  • Health demand, health project and health policy decision

Describe the distribution of disease or health status by person, place and time, then analyze that which factors are relate to the disease or health status.

Secondary prevention seeks to minimize adverse outcomes of disease through early detection, even before symptoms develop and care is sought. Mammography for early detection of breast cancer in asymptomatic women is an example.

An occupational physician planning a coronary prevention program might wish to know the prevalence of different risk factors in the workforce under his care so that he could tailor his intervention accordingly.



Friday, September 12, 2014


The acute phase response is a quickly mobilized non-specific defensive response elicited in response of the host to  infection, tissue injury or inflammation.

Acute phase proteins 

Acute phase proteins have been defined as the proteins whose plasma concentration increases (positive acute phase proteins) or decreases (negative acute phase proteins) during the acute phase responses.

Acute phase proteins: Composition and Resource

APs are synthesized mainly by hepatic cells, the monocytes, and fibroblasts.

Acute phase proteins: Main Functions

1. To help the immune system adapt to various environmental stresses. removal of exogenous substance and necrotic tissue to promote the healing .for example:c-reactive protein c-reactive protein + combine with bacterial wall  activate complement classic pathway promote phagocytosis induce the expression of inflammatory cytokines and tissue factor in monocytes.
2. Inhibit the activity of protease: The protease inhibitors can protect tissues from over injuries by protease 
3. up-regulation of fibrinogen in the acute phase response is beneficial  to increasing the hemostatic power and the wound healing
4. ceruloplasmin,haptoglobin and hemopexin can bind copper and heme, and avoid the injuries of tissues by overmany copper and iron. Ceruloplasmin exhibit an antioxidant function against oxidative stress injuries.
5. serum amyloid protein A associated HDL3 seems to facilitate the uptake and removal of cholesterol from moncytes/macrophages at the inflammatory site



Monday, July 28, 2014

Material metabolism in liver

liver metabolism
  • carbohydrate metabolism
  • lipid metabolism
  • protein metabolism
  • vitamin metabolism
  • hormone metabolism 

Carbohydrate metabolism

Functions

Maintaining the constancy of the concentration of sugar in blood; supplying energy to peripheral tissues, especially to brain and erythrocytes.

Main pathways for carbohydrate metabolism

  • gluconeogenesis
  • glycogenesis and glycogenolysis
  • glycolysis 

Carbohydrate metabolism in varied nutrient conditions in liver

    --  glycogenesis↑
          --  excess carbohydrate is converted to fatty acids and exported in VLDL form
  • postabsorption state
     --  glycogenolysis↑→release glucose to replenish blood sugar
  • starvation state
     --  gluconeogenesis
     --  lipid mobilization↑→acetone body↑→saving glucose

Lipid metabolism


Functions: 

Play important role in digestion, absorption, synthesis, catabolism and transportation of lipids.  

 Main pathways lipid metabolism

  • oxidation of fatty acids
  • synthesis of fatty acids and esterification
  • formation of ketone bodies
  • synthesis of lipoproteins and apolipoproteins (VLDLHDLapoC II)
  • degradation of lipoproteins

Role of liver in varied processes of lipid metabolism

  • digestion and absorption
    --  biliation.  Bile acid is essential for lipid digestion and  absorption
     --  liver dysfunction→fatty diarrhea
  • synthesis
     --  fatty acid, triacylglycerol, ketone body, cholesterol,phospholipid
     --  liver dysfunction→fatty liver, Ch/ChE↑
  • catabolism
     --  β-oxidation of fatty acids, degradation and excretion of cholesterol, degradation of LDL
  • tranportation
     --  synthesis and secretion of VLDL, HDL, apoC II and LCAT

Protein metabolism


Functions: synthesis (γglobulin is excepted), secretion and elimination (albumin is excepted) of plasma proteins.

Liver dysfunction:

  • albumin↓→edema, A/G↓
  • plasma thromboplastin component ↓ →disturbance of blood coagulation
  • blood ammonia
  • amine↑→hepatic encephalopathy 

Vitamin metabolism

Functions

  • absorption of fat-soluble vitamins
  • storadge of vitamins (VA, VK,VE,VB12)
  • transpotation of vitamins synthesis of retinol-binding protein and VitD-binding protein
  • transformation of vitamins
  • β-carotene→VitA Vit D3 → 25-(OH)-Vit D3 water-soluble vitamins →cofactors

Liver dysfunction

  • biliary obstruction→VitK↓→hemorrhagic tendency
  • hepatic rickets

Hormone metabolism

Functions: inactivation of hormones
Manner: biotransformation

Liver dysfunction:

  • Spider angioma of skin
  • liver pulms
  • cutaneous pigmentation
  • hypoglycemia



Saturday, March 15, 2014

Magnesium function
Magnesium is the fourth most common cation in the human body and second most abundant intracellular cation in the human body. Human body contains approximately 24g (1000mmole) of magnesium and it is involved in many intracellular processes and is very essential for life. The metabolic irregularity or disturbance is associated with various abnormalities. The main sources of magnesium are vegetables, soybeans, nuts, whole grain cereals, eggs and seafood. The minimum daily dietary magnesium intake to maintain magnesium balance in normal person is about 240mg per day.

Magnesium functions – Co-factor and agitator of many enzymes

Magnesium plays an important in role in functions of more than 300 enzymes, Na+. K+ ATPase, hexokines, choline esterase. It actively participates in many metabolic activities in the body. Magnesium helps to metabolize proteins, lipids, carbohydrates and nucleic acid. Magnesium is also vital in regulating the cellular distribution of sodium and potassium through involvement in Na+, K+ ATPase.

Magnesium functions -Maintains irritability of the cells

Magnesium acts as an inhibitor to central nervous system, neuromuscular and cardiac muscles. For neuromuscular irritability magnesium and calcium are synergic and for cardiac muscles they are antagonist.

Magnesium functions – Maintains homeostasis of cells

Magnesium is an essential cofactor in correlative enzymes of DNA, cell cycle and apoptosis. In plasma, magnesium is important for maintaining DNA structure and veracity of DNA replication, and activating DNA repairing including nucleotide excision repair, base excision repair, miss match repair and microtubilin assembly. 



Tuesday, March 11, 2014

necosisCell death is the one of the most crucial event in pathology, affecting every cell type and being a major consequences of ischemia, infection, toxin,and immune reaction. There are two types of pattern of cell injury and deaths, necrosis and apoptosis. Necrosis refers to a spectrum
of morphologic changes that follow cell death in living organisms. Necrosis is characterized denaturation of cytoplasmic proteins, failure of membrane integrity , break down of cell organelles and swelling of lethally injured cells.

 

Types of necrosis 

Necrotic cells have different morphological types. It can be classified into total of five types

Coagulative Necrosis

Coagulative necrosis is the most common type of necrosis in which cells death happen after exogenous or endogenous stimuli, occurring after such stresses as ischemia, virus toxin, physical and chemical injury. It is manifested by severe cell rupture, denaturation and coagulation of cytoplasmic proteins.
In coagulative necrosis, the texture of the tissue will be normal or firm, but later it may become soft as a result of digestion by macrophages. The myocardial infarction is the typical example of coagulative necrosis. 




Caseous necrosis

Caseous necrosis is a distinctive form of coagulative necrosis in tuberculosis infection. The term caseous is derived from the gross appearance of area of the necrosis. On microscopic examination, the necrotic focus appear as amorphous coarsely granular eosinophillic debris, without any original out line of cells and tissues. This distinctive types of necrosis is generally attributed to the toxic affect of unusual cell wall of mycobacterium, which contain complete waxes. 



Liquefactive necrosis


Liquefective necrosis is a characteristics of focal bacterial or occasionally fungal infections, because these agents constitute powerful stimuli to the accumulation of inflammatory cells. The polymorphonuclear leukocytes in the acute inflammatory reactions are endowed with potent hydrolases, capable of completely digesting dead cells. For the reasons of the presence of more abundant lysosomal enzymes or different hydorlases and the lack of any substantial supporting stroma specific to the nervous cells, hypoxic death of cells within the central nervous system often evokes  liquefactive necrosis. 



Fibroid necrosis

Fibroid necrosis refers to an alteration of injured tissues which are homogenous, deeply eosinophilic in necrosis. For example, malignant hypertension, the wall of the arterioles is under such necrosis, because of the insudation and accumulation of immunoglobulins, plasma proteinsard especially the consequences deposition of fibrin.  

Gangrenous necrosis

Gangrenous necrosis is a necrosis putrefaction of the tissues as a results of the action of the saprophytic bacteria, mainly clostridium. There are three types of gangrenous necrosis:
1.       Dry gangrenous
2.       Wet gangrenous
3.       Gas gangrenous 

Tuesday, January 14, 2014

The primary functions of the thyroid hormone basically include:
Functions of Thyroid Hormone
Heat Production
Increases oxygen consumption and BMK of targeted tissues, especially in liver, cardiac muscles and kidney

Protein Metabolism
Promote the synthesis of proteins and enzymes

Carbohydrate Metabolism
Elevates the glucose level in the blood

Fat Metabolism
Promotes oxidization of fatty acids and strengthen the effects of catecholamine and glycogen of lypolysis.

Effects on growth and development
Essential for mental and physical development in human, especially for the development of brain and bone tissues

Effects on CNS
Increases the effectiveness of permissive antigen and increase the excitability of CNS

Effects of Cardiovascular System

Increases heart rate, cardiac contractility, cardiac output and vasodilatation  


Friday, January 10, 2014

structure of BCR complex
It’s a membrane Ig (IgM), associated glycoporotein, Ig α and Igβ , which has a moderately large cytoplasmic domain. These domains each include a short region important for transmitting a signal indicating antigen has bound. This region is called immune tyrosin based activation motif ( ITAM ).

Functions of BCR complex

On activation by antigen, B cells differentiate into plasma cells producing antibody molecules of the same antigen specificity as the receptors.


Saturday, January 4, 2014


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