why is the blood brain barrier not present in the hypothlamus, pitutary gland, pineal gland and choroid plexus
All these require the large amount of blood as all act as endocrine glands.
If in these the bbb are present it will hinder with the concentration of hormones etc.
The BBB is present to protect neurons from the components of blood. The different glands you mentioned are not composed of neurons they are composed epithelial cells that secret directly or indirectly into the blood. The choroid plexus are special types of capillaries that filter blood plasma into cerebral spinal fluid and the hypothalamus does have BBB in certain areas where neurons are present.
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