BIOL 2420 Lecture Notes - Lecture 6: Paul Langerhans, Pancreatic Polypeptide, Amylin
26 Apr 2018
School
Department
Course
Professor
Unit 10 – Lecture 6
Homeostatic Control of Metabolism
- endocrine system has primary responsibility for metabolic regulation
o the nervous system plays a role particularly in terms of governing food intake
- many hormones are involved in long-term regulation of metabolism but hour-to-hour regulation
depends primarily on the ratio of insulin to glucagon
o two hormones secreted by endocrine cells of the pancreas
o both hormones have short half-lives and must be continuously secreted if they are to
have sustained effect
The Pancreas Secretes Insulin and Glucagon
- Paul Langerhans
o German anatomist
o Described small clusters of cells known as islets of Langerhans
▪ Scattered throughout the body of the pancreas
- Most pancreatic tissue is devoted to the production and exocrine secretion of digestive enzymes
and bicarbonate
o Lagerhas foud the pacreas’s edocrie cells which ake up less tha 2% of the
total mass
o Islets of Langerhans contain 4 distinct cell types, each associated with secretion of one
or more peptide hormones
- ~1/3 of islet cells are ß-cells
o ß-cells produce insulin and a peptide called amylin
- 20% are alpha-cells
o secrete glucagon
- the remaining cells are somatostatin
o secrete D-cells
- a few are rare PP cells (or F cells)
o produce pancreatic polypeptide
- islets are closely associated with capillaries into which the hormones are released
o both sympathetic and parasympathetic neurons terminate on the islets
▪ provide a means by which the nervous system can influence metabolism
The Insulin-to-Glucagon Ratio Regulates Metabolism
- insulin and glucagon act in antagonistic fashion to keep plasma glucose concentrations within an
acceptable range
o both hormones are present in the blood most of the time
o the ratio of the 2 hormones determines which hormone dominates
- in fed-state
o body is absorbing nutrients
o insulin dominates
o body undergoes net anabolism
o ingested glucose is used for energy production
▪ any excess is stored as glycogen or fat
o amino acids go primarily to protein synthesis
find more resources at oneclass.com
find more resources at oneclass.com
