beta cells

(noun)

Beta cells (beta-cells, β-cells) are a type of cell in the pancreas located in the islets of Langerhans. They make up 65-80% of the cells in the islets, and store and release insulin, a hormone that controls the level of glucose in the blood.

Related Terms

Examples of beta cells in the following topics:

  • Overview of Pancreatic Islets

    • Alpha cells- the alpha cells produce glucagon, and make up 15–20% of total islet cells.
    • Beta cells- the beta cells produce insulin and amylin, and make up 65–80% of the total islet cells.
    • Insulin activates beta cells and inhibits alpha cells, while glucagon activates alpha cells, which activates beta cells and delta cells.
    • Somatostatin inhibits the activity of alpha cells and beta cells.
    • The small cells in the middle are beta cells, and the surrounding larger cells are alpha, delta, gamma and epsilon cells.

  • Types of Cells in the Pancreas

    • Beta cells- the beta cells produce insulin and amylin, and make up 65–80% of the total islet cells.
    • The paracrine feedback system is based on the following correlations: the insulin hormone activates beta cells and inhibits alpha cells.
    • The hormone glucagon activates alpha cells which, in turn, activates beta cells and delta cells.
    • Somatostatin hormone inhibits alpha cells and beta cells.
    • The right image is the same section stained by immunofluorescence against insulin, indicating beta cells.

  • Type 1 Diabetes Mellitus

    • Diabetes mellitus type 1 results from autoimmune destruction of insulin-producing beta cells of the pancreas and is potentially fatal.
    • The pathophysiology in diabetes type 1 is basically a destruction of beta cells in the pancreas, regardless of which risk factors or causative entities have been present.
    • Still, a process that appears to be common to most risk factors is an autoimmune response towards beta cells, involving an expansion of autoreactive CD4+ and CD8+ T helper cells, autoantibody-producing B cells, and activation of the innate immune system.
    • Some researchers believe it might be prevented at the latent autoimmune stage, before it starts destroying beta cells.
    • Experimental replacement of beta cells (by transplant or from stem cells) is being investigated in several research programs.

  • Interactions of Hormones at Target Cells

    • Bundles of cells in the pancreas, called the islets of Langerhans, contain two kinds of cells, alpha cells and beta cells.
    • Beta cells secrete insulin.
    • When the concentration of blood glucose rises, such as after eating, beta cells secrete insulin into the blood.
    • Liver and muscle cells convert glucose to glycogen, for short term storage, and adipose cells convert glucose to fat.
    • Alpha cells secrete glucagon.

  • Insulin Secretion and Regulation of Glucagon

    • Blood glucose level is carefully monitored by cells within the pancreas which respond by secreting key hormones.
    • Glucagon is produced by alpha cells in the pancreas and elevates the concentration of glucose in the blood by promoting gluconeogenesis and glycogenolysis.
    • Liver cells have glucagon receptors and when glucagon binds the liver cells convert glycogen into individual glucose molecules and release them into the bloodstream, in a process known as glycogenolysis.
    • Insulin is produced by beta cells in the pancreas and acts to oppose the functions of glucagon.
    • It's main role is to promote conversion of circulating glucose into glycogen via glycogenesis in the liver and muscle cells.

  • Adherens Junctions

    • This type of cell junction is located right below tight junctions and provides a strong bond between the sides of adjacent epithelial cell membranes. 
    • Anchor proteins, found inside each cell. 
    • These are called alpha-catenin, beta-catenin, gamma-catenin (aka plakoglobin), vinculin, and alpha-actinin. 
    • The extracellular part of one cell’s cadherin binds to the extracellular part of the adjacent cell’s cadherin in the space between the two cells. 
    • Each cell’s cadherin molecule also contains a tail that inserts itself inside its respective cell. 

  • Platelets

    • Platelets, also called thrombocytes, are membrane-bound cell fragments derived from the fragmentation of larger precursor cells called megakaryocytes, which are derived from stem cells in the bone marrow.
    • Platelets are not true cells, but are instead classified as cell fragments produced by megakaryocytes.
    • They are about 1/10th to 1/20th as abundant as white blood cells.
    • They also release wound healing-associated growth factors including platelet-derived growth factor (PDGF), which directs cell movement; TGF beta, which stimulates the deposition of extracellular matrix tissue into a wound during healing; and vascular endothelial growth factor (VEGF), which stimulates angiogenesis, or the regrowth of blood vessels.
    • Image from a light microscope (40×) from a peripheral blood smear surrounded by red blood cells.

  • Bone Remodeling

    • The cells also use paracrine signalling to control the activity of each other.
    • These factors include insulin-like growth factors I and II, transforming growth factor-beta, fibroblast growth factor, platelet-derived growth factor, and bone morphogenetic proteins.
    • The transforming growth factor-beta superfamily includes bone morphogenic proteins involved in osteogenesis.
    • Fibroblast growth factor activates various cells of the bone marrow including osteoclasts and osteoblasts.
    • Evidence suggests that bone cells produce growth factors for extracellular storage in the bone matrix.

  • Direct Gene Activation and the Second-Messenger System

    • Hormones can alter cell activity by binding with a receptor.
    • Receptors can either directly influence gene expression and thus cell activity, or induce a secondary signalling cascade which will in turn influence cell activity.
    • For lipophobic hormones which cannot pass the cellular membrane activity is mediated and amplified within a cell by the action of second messenger mechanisms (molecules which relay signals from receptors on the cell surface to target molecules inside the cell in the cytoplasm or nucleus).
    • The G-protein is bound to the inner membrane of the cell and consists of three subunits: alpha, beta and gamma.
    • The primary effector then has an action, which creates a signal that can diffuse within the cell.

  • Agonists, Antagonists, and Drugs

    • ACh binds to muscarinic receptors (M2) that are found principally on cells comprising the sinoatrial (SA) and atrioventricular (AV) nodes.
    • Gi-protein activation also leads to the activation of KACh channels that increase potassium efflux and hyperpolarizes the cells.
    • By hyperpolarizing the cells, vagal activation increases the cell's threshold for firing, which contributes to the reduction the firing rate.
    • Beta blockers (sometimes written as β-blockers) or beta-adrenergic blocking agents, beta-adrenergic antagonists, beta-adrenoreceptor antagonists or beta antagonists, are a class of drugs used for various indications.
    • As beta adrenergic receptor antagonists, they diminish the effects of epinephrine (adrenaline) and other stress hormones.