(16.10.11) The Pineal Gland and Pancreas

Describe Structure and Function of Pineal Gland

• STRUCTURE

  • Small gland hanging from roof of third ventricle

• FUNCTION

  • Pinealocytes secrete melatonin, derived from serotonin

Describe the importance of Melatonin

1. Timing of sexual maturation and puberty

2. Day/Night cycles

3. Physiological processes that show rhythmic variations

4. Production of antioxidant and detoxification molecules in cell

Describe Structure and Function of the Pancreas

• STRUCTURE

  • Triangular gland located partially behind stomach

• FUNCTION

  • Has both exocrine and endocrine cells

    1. Acinar cells (exocrine)

    2. Pancreatic islets (endocrine cells)

Role of Acinar cells

• Exocrine cells

• Produce enzyme-rich juice for digestion

Role of Pancreatic islets and list Hormones produced

• FUNCTION

  • Contain endocrine cells

• HORMONES

  1. Alpha cells → produce glucagon (hyperglycemic hormone)

  2. Beta cells → produce insulin (hypoglycemic hormone)

Explain Regulation of Release of Glucagon

• STIMULATED by

  1. Decreased BG levels

  2. Rising amino acid levels

  3. Sympathetic nervous system

• INHIBITED by

  1. Elevated BG levels

     • NEGATIVE FEEDBACK

Glucagon Target and Effect 

• Raises blood glucose levels by traveling from the pancreas into the bloodstream to targeting liver to: 

  • Glycogenolysis → Break down glycogen into glucose

  • Gluconeogensis → Synthesize glucose from lactic acid and other non-carbohydrates

  • Release glucose to the blood

Explain Regulation of Release of Insulin

• STIMULATED by

  • Increased BG

  • Synthesized as proinsulin that is then modified

• INHIBITED by

  1. Low BG levels

     • NEGATIVE FEEDBACK

Insulin Target and Effect 

• Lowers blood glucose levels by traveling from the pancreas into the bloodstream to target the liver, muscles, and adipose tissue

  • Inhibits breakdown of glycogen to glucose

  • Inhibits conversion of amino acids or fats to glucose

  • Enhances membrane transport of glucose into fat and muscle cells

Compare and contrast the effects of the two major pancreatic hormones

Glucagon

• STIMULATED by

  1. Decreased BG levels

  2. Rising amino acid levels

  3. Sympathetic nervous system

• INHIBITED by

  1. Elevated BG levels

     • NEGATIVE FEEDBACK

• Raises blood glucose levels by traveling from the pancreas into the bloodstream to targeting liver to: 

  • Glycogenolysis → Break down glycogen into glucose

  • Gluconeogensis → Synthesize glucose from lactic acid and other non-carbohydrates

  • Release glucose to the blood

Insulin

• STIMULATED by

  1. Increased BG

  2. Synthesized as proinsulin that is then modified

• INHIBITED by

  1. Low BG levels

     • NEGATIVE FEEDBACK

• Lowers blood glucose levels by traveling from the pancreas into the bloodstream to target the liver, muscles, and adipose tissue to:

  • Inhibits breakdown of glycogen to glucose

  • Inhibits conversion of amino acids or fats to glucose

  • Enhances membrane transport of glucose into fat and muscle cells

What are Factors that Influence Insulin Release 

1. Elevated BG levels → Primary stimulus 

2. Raising blood levels of amino acids and fatty acids 

3. Hormones glucagon, epinephrine, GH, thyroxine (T₄), glucocorticoids 

4. Somatostatin and sympathetic nervous system inhibit insulin release

Causes and Effect of Hyposecretion of Insulin

• Diabetes mellitus (DM)

  • A chronic metabolic disorder characterized by high blood sugar (glucose) levels due to an imbalance between insulin production and insulin resistance

• CAUSES

  • Hyposecretion of insulin: Type 1

  • Hypoactivity of insulin: Type 2

List the symptoms of Diabetes Mellitus

1. Polyiria: huge urine output

   • Glucose acts as osmotic diuretic

2. Polydipsia: excessive thirst

   • From water loss due to polyuria  

3. Polyphagia: excessive hunger and food consumption

   • Cells cannot take up glucose and are “starving”

Explain Ketoacidosis 

• When sugar cannot be used as fuel, as in Diabetes Mellitus, fats are used, causing lipidemia → high levels of fatty acids in blood 

• Fatty acid metabolism results in formation of ketones (ketone bodies) 

• Ketones are acidic, and their build-up in blood can cause ketoacidosis 

  • Also causes ketonuria: ketone bodies in urine

Causes and Effect and Treatment of Hypersecretion of Insulin

• Hyperinsulinism → Excessive insulin secretion

  • Anxiety

  • Nervousness

  • Disorientation

  • Unconsciousness

  • Even death

• CAUSES:

  • Hypoglycemia 

  • Rare → islet cell tumor

• TREATMENT:

  • Sugar ingestion

Explain the difference between Type 1 and Type 2 Diabetes

• Type 1

  • A form of diabetes mellitus in which the pancreas makes little or no insulin due to the destruction of pancreatic beta (β) cells by the immune system

  • Hyposecretion of insulin

• Type 2

  • A form of diabetes mellitus in which insulin receptors are resistant to or unable to respond to insulin

  • Hypoactivity of insulin

Explain the treatment strategies for Diabetes Mellitus

• Type 1

  • Continuous glucose monitors

  • Frequent insulin injections (up to four times daily, or better yet, by a continuous infusion pump)

  • Coupling glucose sensors to an insulin pump to make a true artificial pancreas

  • Pancreatic islet cell transplants

• Type 2

  • Weight loss

  • Regular exercise

  • Healthy diet

  • Medications