blood-brain barrier

Examples of blood-brain barrier in the following topics:

• Blood-Brain Barrier

  • Tight junctions present in the blood-brain barrier separate circulating blood from cerebrospinal fluid, regulating diffusion into the brain.
  • The blood-brain barrier (BBB) is a separation of circulating blood from the brain extracellular fluid in the central nervous system (CNS).
  • The concept of the BBB (then termed hematoencephalic barrier) was proposed by Lewandowsky in 1900.
  • Also, BBB cells actively transport metabolic products such as glucose across the barrier.
  • The BBB effectively protects the brain from many common bacterial infections, so brain infections are very rare.

• Transcytosis

  • Transcytosis has been shown to be critical to the entry of Cronobacter sakazakii across the intestinal epithelium and the blood-brain barrier.
  • Pharmaceutical companies are currently exploring the use of transcytosis as a mechanism for transporting therapeutic drugs across the human blood-brain barrier.
  • Exploiting the body's own transport mechanism can help to overcome the high selectivity of the blood-brain barrier, which typically blocks the uptake of most therapeutic antibodies into the brain and central nervous system.

• Circumventricular Organs

  • Circumventricular organs are situated adjacent to the brain ventricles and sense concentrations of various compounds in the blood.
  • They are among the few sites in the brain that have an incomplete blood-brain barrier.
  • As a result, neurons located in circumventricular organs can directly sense the concentrations of various compounds, particularly peptide hormones, in the bloodstream without the need for specialized transport systems that move those compounds across the blood-brain barrier.
  • A useful mnemonic device for remembering this aspect of their function, though not the source of the name, is that they allow factors to circumvent' the blood-brain barrier.
  • Median eminence: Allows for the transport of neurohormones between the CSF and the peripheral blood supply.

• Physical and Chemical Barriers

  • The innate immune response has physical and chemical barriers that exist as the first line of defense against infectious pathogens.
  • The skin is considered the first defense of the innate immune system; it is the first of the nonspecific barrier defenses.
  • Some pathogens have evolved specific mechanisms that allow them to overcome physical and chemical barriers.
  • Once inside, the body still has many other defenses, including chemical barriers.
  • The blood-brain barrier also protects the nervous system from pathogens that have already entered the blood stream, but would do significantly more damage if they entered the central nervous system.

• Listeriosis

  • If the infection spreads to the nervous system it can cause meningitis, an infection of the covering of the brain and spinal cord.
  • This involves a bacterial protein "internalin" which attaches to a protein on the intestinal cell membrane "cadherin. " These adhesion molecules are also to be found in two other unusually tough barriers in humans - the blood-brain barrier and the feto-placental barrier, and this may explain the apparent affinity that Listeria has for causing meningitis and affecting babies in-utero.
  • In the advent of listeriosis, bacteremia should be treated for two weeks, meningitis for three weeks, and brain abscess for at least six weeks.
  • A bacterial infection caused by a Gram-positive, motile bacterium, Listeria monocytogenes which is shown here on a blood agar plate.

• The Brain

  • The human brain is the center of the human nervous system.
  • Despite being protected by the thick bones of the skull, suspended in cerebrospinal fluid, and isolated from the bloodstream by the blood-brain barrier, the human brain is susceptible to many types of damage and disease.
  • A number of psychiatric conditions, such as schizophrenia and depression, are thought to be associated with brain dysfunction, although the nature of such brain anomalies is not well understood.
  • The cerebral hemispheres form the largest part of the human brain and are situated above most other brain structures.
  • Distinguish between the cerebellum, cerebral cortex, and brain stem regions of the brain

• Brain Tumors

  • A brain tumor is a pathological abnormal growth of cells in the brain.
  • A brain tumor is an intracranial solid neoplasm—a tumor (defined as an abnormal growth of cells)—within the brain or the central spinal canal.
  • They are created by an abnormal and uncontrolled cell division, usually in the brain itself, but also in lymphatic tissue, in blood vessels, in the cranial nerves, in the brain envelopes (meninges), skull, pituitary gland, or pineal gland.
  • Symptoms of solid neoplasms of the brain (primary brain tumors and secondary tumors alike) can be divided into three main categories:
  • Chemotherapy: is a treatment option for cancer, however it is seldom used to treat brain tumors as the blood and brain barrier prevents the drugs from reaching the cancerous cells

• Cerebrospinal Fluid and Its Circulation

  • Between 50 to 70% of CSF is produced in the brain by modified ependymal cells in the choroid plexus, and the remainder is formed around blood vessels and along ventricular walls.
  • CSF is reabsorbed into venous sinus blood via arachnoid granulations.
  • Since the subarachnoid space around the brain and spinal cord can contain only 135 to 150 ml, large amounts are drained into the blood through arachnoid granulations in the superior sagittal sinus.
  • Chemical stability: CSF flows throughout the inner ventricular system in the brain and is absorbed back into the bloodstream, rinsing the metabolic waste from the central nervous system (CNS) through the blood-brain barrier.
  • Prevention of brain ischemia: Decreasing the amount of CSF in the limited space inside the skull decreases total intracranial pressure and facilitates blood perfusion.

• Blood Flow in the Brain

  • Cerebral circulation is the movement of blood through the network of blood vessels supplying the brain, providing oxygen and nutrients.
  • Cerebral circulation refers to the movement of blood through the network of blood vessels supplying the brain.
  • The arteries deliver oxygenated blood, glucose and other nutrients to the brain and the veins carry deoxygenated blood back to the heart, removing carbon dioxide, lactic acid, and other metabolic products.
  • Since the brain is very vulnerable to compromises in its blood supply, the cerebral circulatory system has many safeguards.
  • Too much blood can raise intracranial pressure (ICP), which can compress and damage delicate brain tissue.

• The Nervous System

  • The brain contains structurally- and functionally-defined regions.
  • The dura mater also contains vein-like structures that carry blood from the brain back to the heart.
  • The brain floats in CSF, which acts as a cushion and shock absorber, making the brain neutrally buoyant.
  • Nor does it have a barrier between itself and the blood, leaving it exposed to toxins and mechanical injuries.
  • It dilates the blood vessels that carry blood to the muscles, releases glucose from the liver, and makes other adjustments to provide for the sudden increase in activity.