Notes on Type 1 Diabetes and Insulin Therapy

Intended Learning Outcomes

  • Describe the regulation of blood glucose levels in a healthy individual
  • Describe diabetes mellitus and the underlying reasons for its occurrence
  • Describe the treatment of type 1 diabetes and the various regimens for insulin replacement therapy

The Pancreas

  • Function as an organ:
    • Glandular organ serving both digestive and endocrine systems.
    • Exocrine function: secretes digestive enzymes to aid nutrient absorption.
    • Endocrine function: synthesizes metabolic hormones (insulin, glucagon, somatostatin).
    • Highly vascularized for effective hormone distribution.

Structure of the Pancreas

  • Divided into parts: Head, Body, Tail, each connected to ducts that transport secretions.

Pancreatic Secretions

Exocrine Secretions
  • Enzymes digest proteins, carbohydrates, and lipids:
    • High bicarbonate content neutralizes stomach acid
    • Key Enzymes:
    • Proteases (trypsinogen, chymotrypsinogen)
    • Pancreatic lipase
    • Amylase
    • Secretion regulated by hormones (e.g., gastrin) and mechanical distension.
Endocrine Secretions
  • Islets of Langerhans:
    • Composed of multiple cell types:
    • Alpha cells: produce glucagon (raises blood glucose).
    • Beta cells: produce insulin (lowers blood glucose).
    • Delta cells: produce somatostatin (inhibits alpha and beta cells).
    • Gamma cells (PP cells): produce pancreatic polypeptide.

Regulation of Blood Glucose

  • Importance of glucose:
    • Primary energy source for cells; stored as glycogen or fat for later use.
    • Insulin: main hormone regulating glucose uptake and storage.
  • Blood glucose control mechanisms:
    • High blood sugar promotes insulin release (lowers blood sugar).
    • Low blood sugar prompts glucagon release (raises blood sugar).

Discovery of Insulin

  • Insulin discovery by Banting and Best in 1921, critical for diabetes treatment.
    • Initial animal studies led to human trials (purified extract in 1922).
    • Resulted in Nobel prize recognition for impactful medical advancement.

Insulin Structure and Function

  • Insulin:
    • Peptide hormone consisting of two chains of amino acids connected by disulfide bonds.
    • First protein to be sequenced (Frederick Sanger, 1952).
    • Advances included synthetic and recombinant insulin production.

Insulin Release Mechanism

  • Glucose-Stimulated Insulin Release:
    • Glucose uptake into beta cells stimulates insulin release via a cascade involving ATP and calcium ions.

Insulin Receptor and Actions

  • Insulin Receptor:
    • Binds insulin, initiating signaling pathways (MAPK and PI-3K) affecting cell growth and metabolism.
  • Metabolic Effects of Insulin:
    • In liver: decreases glucose production, increases utilization, promotes synthesis of fatty acids, proteins, and glycogen.
    • In fat tissue: increases glucose uptake and triglyceride synthesis, decreases lipolysis.
    • In muscles: increases glucose uptake and protein synthesis, encourages muscle mass.
    • Additional effects on blood vessels and immune cells.

Diabetes Mellitus Overview

  • Definition:
    • Condition characterized by high blood glucose levels (hyperglycemia).
  • Symptoms:
    • Glycosuria, polyuria, polydipsia.
  • Subtypes:
    • Type 1 (autoimmune, beta-cell destruction) vs. Type 2 (insulin resistance).

Type 1 Diabetes (T1D)

  • Characteristics of T1D:
    • Autoimmune attack on beta cells, leading to insulin deficiency.
    • Symptoms include thirst, weight loss, and fatigue.
    • Without treatment, can lead to severe conditions: ketoacidosis, cardiovascular issues, kidney disease, neuropathy.
  • Treatment Requirements:
    • Insulin replacement therapy is essential for blood glucose control.

Comparison of T1D and T2D

  • Prevalence (UK):
    • T1D: 0.3 million, T2D: 2.9 million.
  • Age of onset:
    • T1D: typically under 40; T2D: usually over 40.
  • Insulin issues:
    • T1D: deficiency; T2D: resistance and possible deficiency.

Treatment Approaches for T1D

Insulin Replacement Therapy:
  • Forms of Insulin:
    • Short-acting and long-acting insulins to mimic physiological release.
  • Administration Routes:
    • Subcutaneous injections, pumps producing continuous infusion.
  • Flexible Treatment Regimens:
    • Fixed dose vs. flexible doses allowing personalization.
Novel Therapeutic Approaches
  • Insulin pumps provide continuous infusion; inhaled, transdermal, buccal routes under investigation.
  • Advanced Treatments:
    • Immunotherapy (e.g., Teplizumab) approved to delay T1D onset.
    • Stem cell therapies show promise in restoring insulin independence.

Conclusion

  • Understanding insulin regulation pivotal for managing diabetes mellitus effectively.
  • Current and future therapies focus on mimicking normal physiology and improving patient quality of life.