Choroid plexus cells are specialized structures deep within the brain. These cells form a network called the choroid plexus, which actively maintains the brain’s internal environment. Understanding these cells reveals how the brain is protected and nourished.
What Are Choroid Plexus Cells?
Choroid plexus cells are specialized epithelial cells that form the choroid plexus, a vascularized tissue found within the brain’s ventricles. This tissue is present in all four ventricles: the two lateral ventricles, the third ventricle, and the fourth ventricle. The choroid plexus consists of a layer of cuboidal epithelial cells surrounding a core of capillaries and loose connective tissue.
Tight junctions between these cells, located on the side facing the ventricle, create a selective barrier that regulates substance movement. The epithelial cells also have a brush border with microvilli, which increases their surface area.
The Primary Role: Cerebrospinal Fluid Production
The primary function of choroid plexus cells is the production of cerebrospinal fluid (CSF), which surrounds the brain and spinal cord. The choroid plexus secretes approximately 80% of CSF, with the rest originating from brain interstitial fluid. An adult human choroid plexus can secrete up to 500 milliliters of CSF per day. The total CSF volume in the central nervous system is around 150 milliliters, meaning it is replaced three to four times daily.
CSF cushions the brain against injury, reduces its effective weight, and maintains a stable chemical environment. It also delivers nutrients like glucose and amino acids to brain tissue and removes waste products. CSF formation involves selective filtration of blood components from capillaries within the choroid plexus, followed by active transport of ions and water by epithelial cells into the ventricular lumen. This ion movement, particularly of sodium, chloride, and bicarbonate, creates an osmotic gradient that drives water secretion into the CSF.
Beyond CSF: Barrier and Immune Functions
Beyond CSF production, choroid plexus cells contribute to the “blood-CSF barrier,” which regulates the passage of substances from the blood into the brain’s fluid environment. This barrier prevents the free passage of molecules from systemic circulation into the CSF, maintaining the brain’s internal stability and protecting it from harmful substances.
The choroid plexus also acts as a site for immune surveillance within the central nervous system. It houses various peripheral immune cells within its stromal core, including dendritic cells, macrophages, and T cells. These cells, along with the epithelial cells, detect pathogens and changes in the local environment, such as cytokine levels. Their activation can lead to the release of signaling molecules that recruit circulating immune cells, initiating an immune response at the choroid plexus interface.
Choroid Plexus Cells and Neurological Health
Dysfunction of choroid plexus cells can impact various neurological conditions. Imbalances in CSF production or circulation, for example, can lead to hydrocephalus, a condition characterized by increased intracranial CSF and ventricular enlargement. Hydrocephalus can arise from excessive CSF secretion, obstructed flow, or impaired reabsorption.
The choroid plexus is also linked to neurodegenerative diseases like Alzheimer’s and Parkinson’s disease, as well as conditions such as stroke and multiple sclerosis. Its role in brain waste clearance via the CSF system and its involvement in inflammation suggest that choroid plexus dysfunction could contribute to the progression of these disorders. Infections, such as meningitis, can also affect the blood-CSF barrier, potentially altering its protective functions and contributing to disease pathology.