Receptor Density and Affinity Definition (Simplistic Explanation and Detailed Explanation Given Separately)

RECEPTOR DENSITY :: Meaning :: What does Receptor Density Mean???

A:  ➜ ➜    Density of a Receptor refers to the Concentration (amount) of a Receptor in a given tissue or portion of the Brain. 

• A DECREASE in Receptor density would mean (⇣)  (less receptors); a decrease in Numbers.
• An INCREASE in Densities would remark the opposite, a net increase (⇡) in the amount of Receptors in a given area of the body or brain.

**B_{max refers to a 'total number' of Receptors and thus refers to 'whole' density increases 
(so therefore in a study that states ; in the 'control' group no} Bmax changes were noted but in the 'drug-receiving group' or 'test group' the B_max 
was increased by 32% - this refers to a 32% increase in the total number of Receptors).**

PLACEBO GROUP : Refers to a 'sugar-pill' , empty pill, or useless pill that is used to determine the group of Test subjects differences between those in the active recipient or 'TEST GROUP'. 

In other words; 'Placebo' group is the 'normal' group which receives no drugs, no alteration in diet - basically just rats, guinea pigs, monkey's , humans etc that THINK they are taking something to determine if there are any REAL changes between them and the group being studied and receiving the Drug or parameter alteration.

ACTIVE RECIPIENT  / TEST GROUP : The Group or test subjects that are RECEIVING the Drug or alteration in diet; the Group being SCREENED for major differences so as to determine the EFFECTS AND/OR EFFICACY (efficiency, total usefulness) of a drug or diet alteration.

  AFFINITY / BINDING AFFINITY MEANING :: WHAT Does 'AFFINITY' :: Mean??? ::
 AFFINITY DEFINITION

A: ➜ ➜ Refers to the rate of binding to a given receptor (how much a chemical 'sticks' to a receptor and the rate of 'sticking'). Increase or Decrease in Affinity refers to something or some change *CAUSING* a drug or natural compound to not 'stick' as much to the Receptor in question.

• Affinity is not the same thing as "downregulation" but is often found in the same context; for example downregulation may manifest as 'decreased affinity' or perhaps other systemic changes that CO-OCCUR (happen at the same time) are leading to joint decreasing of receptor {densities} (decrease in number) as well as decreased ability for chemicals to Bind. 
• 'Displacement' of a Receptor (a chemical competing FOR domination/binding of a Receptor) also relies  , in Part, on AFFINITY.

**REFERENCES**

Receptors - A brief note ~ anaesthetist.com

~Bmax and KD~