THE ENDOCRINE SYSTEM PART 1.5: PANCREATIC ISLETS AND PINEAL GLAND

Pancreatic Islets

contains three main types of hormone-secreting cells: α (alpha) cells, β (beta) cells, and δ (delta) cells

α (alpha) cells

glucagon is secreted by:

Glucagon

• increases blood glucose levels by glucogenolysis and gluconeogenesis

• increased secretion by low blood sugar and exercise

Glycogenolysis

Breakdown of stored glycogen into glucose for energy during fasting or stress

Gluconeogenesis

Creation of glucose from non-carbohydrate sources (e.g., amino acids, lactate) to maintain blood sugar levels

β (beta) cells

insulin is secreted by:

Insulin

• Polypeptide hormone consisting of 51 amino acids

• Cannot cross the cell membrane so receptors are present on plasma membrane of all body cells

• reduces blood glucose levels

• increased secretion after meals, during parasympathetic stimulation, raised amino acids, and fatty acid levels

glucose transport mechanisms

FUNCTIONS OF INSULIN:
a. Activating _______________________________ (↑ uptake by tissues)

b. Increasing ________________ (glucose → glycogen)

c. Accelerating uptake of _____________

d. Decreasing _______________ (glycogen → glucose)

e. Preventing ____________________

a = ?

glycogenesis

FUNCTIONS OF INSULIN:
a. Activating _______________________________ (↑ uptake by tissues)

b. Increasing ________________ (glucose → glycogen)

c. Accelerating uptake of _____________

d. Decreasing _______________ (glycogen → glucose)

e. Preventing ____________________

b = ?

amino acids

FUNCTIONS OF INSULIN:
a. Activating _______________________________ (↑ uptake by tissues)

b. Increasing ________________ (glucose → glycogen)

c. Accelerating uptake of _____________

d. Decreasing _______________ (glycogen → glucose)

e. Preventing ____________________

c = ?

glycogenolysis

FUNCTIONS OF INSULIN:
a. Activating _______________________________ (↑ uptake by tissues)

b. Increasing ________________ (glucose → glycogen)

c. Accelerating uptake of _____________

d. Decreasing _______________ (glycogen → glucose)

e. Preventing ____________________

d = ?

gluconeogenesis

FUNCTIONS OF INSULIN:
a. Activating _______________________________ (↑ uptake by tissues)

b. Increasing ________________ (glucose → glycogen)

c. Accelerating uptake of _____________

d. Decreasing _______________ (glycogen → glucose)

e. Preventing ____________________

e = ?

δ (delta) cells

Somatostatin is secreted by:

Somatostatin

• Produced by the hypothalamus

• Inhibits secretion of insulin and glucagon: serves as the brake or pedal: If there is too much production of glucagon/insulin, somatostatin stops it

Pineal Gland

• tiny endocrine gland in the middle of your brain that helps regulate your body's circadian rhythm by secreting the hormone melatonin

• Responsible for the sleep/wake cycle.

Melatonin

• Daylight and darkness help dictate the circadian rhythm. Light exposure stops the release of melatonin, which helps control circadian rhythms.

• Functions may be associated with:

  • Coordination of circadian rhythm

  • Mood, implicated in seasonal affective disorder (SAD)

  • Sleepiness during darkness

  • Maturation of sex organs at puberty