Endocrine Glands - Revision
In the pancreas:
Organisation of the pancreas:
• The bulk of the pancreas by volume consists of exocrine cells that release pancreatic juices via a duct.
• Only about 5% of the volume of the pancreas consists of endocrine cells
• These cells secrete hormones that play a role in controlling glucose metabolism. The endocrine cells
are closely associated with large numbers of blood capillaries into which they secrete either insulin
or glucagon directly into the blood stream.
ATP closes it
1 (usually open)
3
4
2
5
(usually closed)
6
, Hormones - Revision
Hormone - chemicals that act like messengers, secreted by endocrine glands into the blood stream without
ducts and carried to the target organ.
The pancreas is an endocrine gland because it does not have a duct (ductless) and releases insulin and gluca-
gon. It is also an exocrine gland because it secretes enzymes such as amylase.
Types of hormones:
• Protein and peptide hormones
Not soluble in the membrane so do not enter the cell. These therefore require complimentary
receptors on the cell surface membrane e.g. insulin, glucagon, and adrenaline
• Steroid hormones
Can pass through the membrane and enter the cell. They act upon DNA in the nucleus.
Key words & definitions
Glycogenesis - conversion of glucose to glycogen under the influence of insulin in response to a rise
in blood glucose
Gluconeogenesis - production of glucose from sources other than glycogen (e.g. amino acids)
Glycogenolysis - breakdown of glycogen to glucose under the influence of glucagon in response to a
fall in blood glucose.
Glycogen phosphorylase - converts glycogen to glucose.
Glycogenesis produces glycogen
Insulin (from beta cells)
(high blood sugar)
Glucose Glycogen
(low blood sugar)
Glucagon (from alpha cells)
Gluconeogenesis and glycogenolysis produce glucose
In the pancreas:
Organisation of the pancreas:
• The bulk of the pancreas by volume consists of exocrine cells that release pancreatic juices via a duct.
• Only about 5% of the volume of the pancreas consists of endocrine cells
• These cells secrete hormones that play a role in controlling glucose metabolism. The endocrine cells
are closely associated with large numbers of blood capillaries into which they secrete either insulin
or glucagon directly into the blood stream.
ATP closes it
1 (usually open)
3
4
2
5
(usually closed)
6
, Hormones - Revision
Hormone - chemicals that act like messengers, secreted by endocrine glands into the blood stream without
ducts and carried to the target organ.
The pancreas is an endocrine gland because it does not have a duct (ductless) and releases insulin and gluca-
gon. It is also an exocrine gland because it secretes enzymes such as amylase.
Types of hormones:
• Protein and peptide hormones
Not soluble in the membrane so do not enter the cell. These therefore require complimentary
receptors on the cell surface membrane e.g. insulin, glucagon, and adrenaline
• Steroid hormones
Can pass through the membrane and enter the cell. They act upon DNA in the nucleus.
Key words & definitions
Glycogenesis - conversion of glucose to glycogen under the influence of insulin in response to a rise
in blood glucose
Gluconeogenesis - production of glucose from sources other than glycogen (e.g. amino acids)
Glycogenolysis - breakdown of glycogen to glucose under the influence of glucagon in response to a
fall in blood glucose.
Glycogen phosphorylase - converts glycogen to glucose.
Glycogenesis produces glycogen
Insulin (from beta cells)
(high blood sugar)
Glucose Glycogen
(low blood sugar)
Glucagon (from alpha cells)
Gluconeogenesis and glycogenolysis produce glucose
