Where Is the Choroid Plexus Located and What Does It Do?
The choroid plexus is an intricate network of ependymal cells and capillaries present prominently in the ventricles of the cerebrum in the human brain. It provides a safety barrier to the brain and the central nervous system. It also produces cerebrospinal fluid and saves the CNS from any kind of toxicity. In this article, we will study its location, structure, and important functions.
What is Choroid Plexus?
Our brain is an intricate system of nervous tissues and ganglions leading to the finest structure that enables us to do all our functions. This complex organ is well protected from the toxins, pathogens, and byproducts of metabolism by the cerebrospinal fluid and blood circulation. One such important part of the brain that aids in maintaining the health and functioning of the human brain is the choroid plexus.
By definition, it is the formation of specific tissues and cerebrospinal fluid inside the ventricular system of our brain. It means that a series of hollow spaces that are interconnected with each other and filled with cerebrospinal fluid is termed as plica choroidea or choroid plexus. It consists of modified and transformed ependymal cells that surround a network of connective tissues and capillaries.
Location of Choroid Plexus
Now that we know what choroid plexus is, let us proceed to find its location. It is present in the lateral, 3rd, and 4th ventricles of the human brain. They always remain within the meninges of the brain producing a major part of the cerebrospinal fluid.
Meninges are the membranous lining that covers and protects the central nervous system from shock, pathogens, and injuries. These meninges have three different layers, pia mater, arachnoid mater, and dura mater. The innermost layer of the meninges is the pia mater. Choroid tissues can also be found in this innermost layer as it shelters the spinal cord and cerebral cortex.
Structure of Choroid Plexus
As mentioned earlier, the choroid plexus is made of specialized ependymal cells or epithelial cells surrounding the cells of loose connective tissues and a network of blood capillaries. The special feature of this epithelial tissue is the presence of cilia or hair-like projections. These projections create a case enclosing the choroid plexus. The same type of epithelial cells also creates a covering over the cerebral ventricles and central canal of the spinal cord.
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If you recall, you will remember that the spinal cord is also filled with cerebrospinal fluid. It means that these cells are also creating this fluid inside the spinal cord in the same way they are doing it inside the ventricles of the brain. From this, we can easily confirm the choroid plexus location.
These altered or transformed epithelial cells can also be considered a genre of nervous tissues termed neuroglia. They help in producing a major part of the cerebrospinal fluid circulating in the brain ventricles and the central canal of the spinal cord.
Functions of Choroid Plexus
Brain Development
This organization of specialized epithelial cells promotes brain development. As it covers the empty spaces and central canals of the central nervous system, it provides nutrition and a medium to connect the neighbouring sections.
Barrier
As mentioned earlier, the capillary network present in this tissue organization secretes cerebrospinal fluid filling the cavities and giving a proper shape to the central nervous system. The ependyma tissue is responsible for the separation of the blood capillaries from the ventricles for regulating what is entering the cerebrospinal fluid.
This fluid, on the other hand, keeps the entire brain safe and supplies nutrition for its growth. In fact, the waste products are also filtered by the choroid plexus resulting in a safe environment for the brain cells by blocking the toxic byproducts of metabolism present in the blood.
Protection
These empty spaces are filled with this fluid giving the brain and the spinal cord proper strength and support. It also provides defensive measures extracting them from the blood capillaries to protect the brain and spinal cord from toxic substances and pathogens in the blood. Lymphocytes, dendritic cells, and macrophages enter the fluid through the choroid plexus and form a defence system inside the brain and spinal cord. This is the prime choroid plexus function that forms the blood-brain barrier.
Diseases Related to Choroid Plexus
Choroid Plexus Cyst
This is a disease where a cyst forms in the choroid plexus layer of an unborn baby inside a mother’s womb. It can be a small buildup in the brain region occurring in almost 2% of the pregnancies during the 2nd trimester. It can be detected using specific choroid plexus cyst radiology techniques. In most cases, this cyst clears up before a baby’s birth and does not need any medical intervention.
If it persists, a choroid plexus cyst causes intellectual disabilities and problems in kidneys, heart, brain, etc. If it persists after birth, it can also result in a stillborn baby during birth. The size of this cyst should be watched using detailed imaging techniques.
Choroid Plexus Papilloma
It is a genre of brain tumour and is considered benign in nature. It is common in the young but rarely seen in adults. They grow quite slowly and do not spread to other parts of the body. A detailed imaging scan can detect its presence.
Choroid Plexus Calcification
The deposition of iron and calcium in this tissue inside the brain and spinal cord leads to calcification. It progresses with age and can be diagnosed using CT scans.
Conclusion
This is what you need to know about the choroid plexus, its location, structure, and functions. It is the prime protective barrier that saves our central nervous system from pathogens and toxic byproducts and provides nutrition.
FAQs on Choroid Plexus: Key Functions and Importance in Biology
1. What is the choroid plexus and what are its primary functions?
The choroid plexus is a specialised, highly vascular tissue found within the ventricles of the brain. It is essentially a network of capillaries and ependymal cells. Its main functions are:
- Production of Cerebrospinal Fluid (CSF): Its most critical role is to produce the majority of the CSF that circulates around the brain and spinal cord.
- Formation of the Blood-CSF Barrier: It acts as a selective barrier, regulating the passage of substances from the blood into the CSF, thereby protecting the central nervous system.
- Waste Removal: It helps in clearing metabolic waste products from the brain.
2. Where is the choroid plexus located in the human brain?
The choroid plexus is not a single structure but is found in specific locations within all four ventricles of the brain. It is present in the two lateral ventricles, the third ventricle, and the fourth ventricle. This strategic placement allows for the effective production and circulation of cerebrospinal fluid throughout the central nervous system.
3. What is the histological structure of the choroid plexus?
The choroid plexus has a distinct villous structure, which increases its surface area for CSF production. Histologically, it consists of three main layers:
- A central core of connective tissue (pia mater).
- A dense network of fenestrated capillaries, which are leaky to allow plasma to filter out.
- A continuous layer of specialised cuboidal ependymal cells that face the ventricle. These cells are joined by tight junctions, forming the blood-CSF barrier.
4. How does the choroid plexus form the blood-cerebrospinal fluid (CSF) barrier?
The choroid plexus forms the blood-CSF barrier through the specialised ependymal cells that line its surface. Unlike the fenestrated capillaries beneath them, these ependymal cells are connected by tight junctions. These junctions act like a seal, preventing the free or unregulated passage of molecules from the bloodstream into the CSF. This ensures that only specific, necessary substances like water, ions, and nutrients are actively transported into the CSF, while toxins and pathogens are kept out, maintaining a stable environment for the brain.
5. Is the choroid plexus in the brain related to the choroid layer in the eye?
No, the choroid plexus and the choroid of the eye are two completely different structures with distinct locations and functions. The similarity in name is a common point of confusion.
- The choroid plexus is located in the ventricles of the brain and is responsible for producing cerebrospinal fluid.
- The choroid is a vascular layer of the eyeball, situated between the retina and the sclera, responsible for nourishing the outer layers of the retina.
They are not anatomically or functionally related.
6. What is a choroid plexus cyst and should it be a cause for concern?
A choroid plexus cyst is a small, fluid-filled sac that can form within the choroid plexus of the brain. These are most commonly detected during routine prenatal ultrasounds. For the vast majority of cases, a choroid plexus cyst is a transient and benign finding. It is considered a normal variation in fetal development and typically resolves on its own before birth without causing any harm to the baby or affecting brain function.
7. Why is the continuous production of cerebrospinal fluid (CSF) by the choroid plexus so important for the brain?
The continuous production and circulation of CSF by the choroid plexus is vital for brain health for several reasons. It is not just a filler fluid; it serves critical protective and metabolic roles:
- Buoyancy: CSF allows the brain to float within the skull, reducing its effective weight and protecting it from mechanical injury and the force of gravity.
- Cushioning: It acts as a shock absorber, protecting the delicate brain and spinal cord from physical trauma.
- Waste Clearance: CSF is essential for the glymphatic system, which flushes metabolic waste products and soluble proteins away from the brain tissue, particularly during sleep.
- Environmental Stability: It helps maintain a constant, optimal chemical environment for neuronal signalling and function.
