Pancreas

ENDOCRINE GLANDS

COURSE OUTLINE

  • 16.5 The Endocrine Pancreas

  • 16.6 Other Endocrine Glands and Hormone-Secreting Tissues

  • 16.7 Three Examples of Endocrine Control of Physiological Variables

UPCOMING SCHEDULE

Next Lecture:

  • Chapter 19 Blood

Canvas Quizzes:

  1. Endocrine Quiz II: Thyroid and Parathyroid Glands - due February 1, 11:59 PM

  2. Endocrine Quiz III: Adrenal & Pancreas - due February 3, 11:59 PM

  3. Endocrine Quiz IV: All of Chapter 16 - due February 3, 11:59 PM

Mastering Assignments:

  1. Finish Chapter 16 - Dynamic Study Module – Sections 4 – 7 (due January 30)

  2. Finish Chapter 16 – Interactive Reading – The Endocrine System (due February 1, 11:59 PM)

ENDOCRINE ORGANS

  • Anterior Pituitary Gland

  • Thyroid Gland

  • Parathyroid Glands

  • Thymus Gland

  • Adrenal Cortex

  • Pancreas

  • Ovaries (female)

  • Testes (male)

Neuroendocrine Organs:

  • Hypothalamus

  • Pineal Gland

  • Posterior Pituitary Gland

  • Adrenal Medulla

KEY CONCEPTS TO KNOW

  • Gland

  • Hormone(s)

  • Target Tissue(s)

  • Physiological Effects

  • Hypo- & Hypersecretion

THE PANCREAS

STRUCTURE OF THE PANCREAS

  • The pancreas is a club-shaped organ located in the abdominal cavity, mostly posterior to the stomach. It has:

    • Head

    • Body

    • Tail

  • Contains two main types of cells:

    • Pancreatic Islets (endocrine)

    • Acinar Cells (exocrine) that secrete enzymes and other products into small ducts delivered to the digestive tract

CELL TYPES IN PANCREATIC ISLETS

  • Alpha Cells: Secrete Glucagon

  • Beta Cells: Secrete Insulin

  • Delta Cells: Secrete Somatostatin (same as produced by the hypothalamus)

GROWTH HORMONE (GH)

  • Growth Hormone (GH): Also known as Somatotropin.

  • Produced by Somatotrophs.

  • Peak secretion occurs during sleep.

  • Regulates growth; target tissues include:

    • Skeletal and cardiac muscle

    • Adipose

    • Liver

    • Cartilage

    • Bone

  • Growth Hormone-Releasing Hormone (GHRH) stimulates release of GH.

  • Growth Hormone-Inhibiting Hormone (Somatostatin) inhibits GH.

ASSOCIATED HORMONES

  • TRH (Thyrotropin-Releasing Hormone): Stimulates Prolactin release.

    • Prolactin promotes breast development and milk production; inhibited by Dopamine (Prolactin-Inhibiting Factor).

  • TSH (Thyroid-Stimulating Hormone): Stimulates thyroid hormone secretion.

  • CRH (Corticotropin-Releasing Hormone):

    • Stimulates Adrenocorticotropic Hormone (ACTH) production.

    • Promotes adrenal gland development and secretion of steroid hormones.

  • GnRH (Gonadotropin-Releasing Hormone): Stimulates release of FSH and LH.

    • FSH engages in testosterone binding and estrogen production.

    • LH stimulates testosterone and estrogen/progesterone production.

PANCREATIC HORMONES

GLUCAGON

  • Promotes reactions that raise glucose and metabolic fuel levels in the blood.

  • Targets liver, muscle, and adipose tissue, causing:

    • Glycogenolysis: Breakdown of glycogen into glucose.

    • Gluconeogenesis: New glucose formation in the liver.

    • Protein breakdown in muscle for glucose increase.

    • Fat release from adipose tissue for gluconeogenesis.

KETONE BODIES

  • Formation of Ketone Bodies from fatty acids in the liver.

  • Ketone bodies are fuels for muscle and brain under extreme calorie restriction or starvation.

  • High levels can lead to Ketoacidosis when acidity increases blood pH.

GLUCAGON SECRETION TRIGGER

  • Triggered by:

    • Decrease in blood glucose concentration

    • Sympathetic nervous system stimulation

    • Ingested proteins

  • Inhibited by:

    • Elevated blood glucose levels

    • Somatostatin

INSULIN

  • Promotes uptake of nutrients, lowering blood glucose levels.

  • Secreted primarily from Beta Cells and helps store nutrients.

  • Targets:

    • Liver

    • Cardiac & skeletal muscle

    • Parts of brain

  • Actions include:

    • Promotes feelings of satiety.

    • Maintains glucose concentrations within a narrow range.

  • Stimulated by rising blood glucose, inhibited by somatostatin.

DISORDERS OF INSULIN

HYPERGLYCEMIA

  • Defined by insufficient insulin secretion or decreased insulin sensitivity.

  • Commonly causes:

    • Type 1 and Type 2 Diabetes Mellitus.

    • Damages blood vessels and increases risks of heart attacks and wounds.

    • Leads to complications like Peripheral Neuropathy and blindness.

HYPOGLYCEMIA

  • Occurs due to high insulin levels, reducing blood glucose.

  • Symptoms include:

    • Weakness, dizziness, rapid breathing, nausea, sweating.

  • Severe cases can cause confusion, hallucinations, seizures, coma, and even death.

TYPE 1 DIABETES MELLITUS

  • Affects 5-10% of diabetes cases in the U.S.

  • Caused by immune system destruction of Beta Cells leading to:

    • Inability of target cells to absorb glucose.

    • Increased ketone production from glucagon action.

SYMPTOMS

  • Glucosuria: Loss of glucose in urine.

  • Ketonuria: Loss of ketones in urine.

  • Leads to: Frequent urination, excessive thirst, and potential for diabetic ketoacidosis.

TYPE 2 DIABETES MELLITUS

  • Affects up to 95% of adult diabetes cases.

  • Involves insulin resistance due to:

    • Beta cells' decreased responsiveness to glucose.

    • Target cells’ reduced response to insulin.

  • Often manageable with lifestyle changes; may require oral hypoglycemics or insulin therapy.

BLOOD GLUCOSE REGULATION

INCREASING BLOOD GLUCOSE LEVELS

  1. Stimulus: Blood glucose increases (normal range is 70−99 mg/dl).

    • Can occur from feeding or cortisol response.

  2. Receptor: Beta cells detect increased glucose concentration.

  3. Control Center: Beta cells increase insulin secretion.

  4. Effector/Response: Insulin increases glucose uptake by cells and storage of glucose.

  5. Return to Normal: Upon normalization, beta cells decrease insulin production.

DECREASING BLOOD GLUCOSE LEVELS

  1. Stimulus: Blood glucose decreases below normal range (70−99 mg/dl).

  2. Receptor: Alpha cells detect decreased glucose.

  3. Control Center: Alpha cells increase glucagon secretion, insulin secretion decreases.

  4. Effector/Response: Glucagon raises blood glucose through glycogen breakdown and gluconeogenesis.

  5. Return to Normal: Alpha cells adjust glucagon levels once normal range is restored.

GONADS AND HORMONES

TESTES: TESTOSTERONE

  • Sex steroid hormone produced primarily in the testes.

  • Influenced by GnRH from the hypothalamus leading to secretion of LH and FSH from the anterior pituitary.

  • Effects:

    • Anabolic: Stimulates bone growth and increases muscle mass.

    • Androgenic: Development of male secondary sex characteristics (e.g., deeper voice, facial hair).

OVARIES: ESTROGENS AND PROGESTERONE

  • Estrogens and Progesterone are vital for female reproductive health.

  • Regulated through feedback loops involving GnRH, LH, FSH.

  • Effects include development of female secondary sex characteristics and regulation of menstrual cycle.

  • Progesterone supports preparation for pregnancy and fetal development.

THYMUS

  • Irregularly shaped organ in the mediastinum.

  • Site for T lymphocyte maturation, secretes Thymosin and Thymopoietin.

  • Larger and more active in infants; atrophy occurs in adults, replaced mainly with fat.

PINEAL GLAND - MELATONIN

  • Part of the epithalamus in the diencephalon.

  • Secretes melatonin, regulating sleep-wake cycles based on ambient light.

  • Effectiveness of melatonin supplements for sleep enhancement is debated.

ADIPOSE TISSUE: LEPTIN

  • Leptin: Protein hormone released by adipocytes.

  • crosses the blood-brain barrier, interacts with the hypothalamus to induce satiety and prevent overeating.

  • Amount of leptin relates to adipose tissue quantity, complex feeding regulation mechanisms are at play.

HEART: ATRIAL NATRIURETIC PEPTIDE (ANP)

  • Produced by cardiac muscle in response to stretch.

  • Causes vasodilation to lower blood pressure and blood volume.

KIDNEYS AND ENDOCONCRINE ROLES

  • Erythropoietin (EPO) production in response to low blood oxygen, stimulates red bone marrow.

  • Renin: Converts angiotensinogen to angiotensin-1, part of the renin-angiotensin-aldosterone system that controls blood pressure.

  • Activation of Vitamin D, converting it to Calcitriol, stimulated by parathyroid hormone.

HORMONE-SECRETING TISSUES

  • Pineal Gland: Melatonin - Regulates sleep-wake cycle.

  • Adipose Tissue: Leptin - Induces satiety.

  • Heart: Atrial Natriuretic Peptide (ANP) - causes vasodilation, decreases blood pressure, and promotes natriuresis.

  • Kidneys: Erythropoietin, Renin, Vitamin D.