Chapter 45-Hormones and the Endocrine System Simple Hormone Pathways Pathway Example Stimulus Low pH in duodenum S cells of duodenum secrete secretin ( ) Endocrine cell Blood vessel Pancreas Target cells Response Bicarbonate release – •Hormones are released from an endocrine cell, travel through the bloodstream, and interact with the receptor or a target cell to cause a physiological response Insulin and Glucagon: Control of Blood Glucose Homeostasis: Blood glucose level (about 90 mg/100 mL) Glucagon STIMULUS: Blood glucose level falls. Alpha cells of pancreas release glucagon. Liver breaks down glycogen and releases glucose. Blood glucose level rises. STIMULUS: Blood glucose level rises. Beta cells of pancreas release insulin into the blood. Liver takes up glucose and stores it as glycogen. Blood glucose level declines. Body cells take up more glucose. Insulin •Insulin and glucagon are antagonistic hormones that help maintain glucose homeostasis Target Tissues for Insulin and Glucagon Insulin reduces blood glucose levels by: Glucagon increases blood glucose levels by: Promoting the cellular uptake of glucose Slowing glycogen breakdown in the liver Promoting fat storage Stimulating conversion of glycogen to glucose in the liver Stimulating breakdown of fat and protein into glucose A negative feedback loop The pancreas has clusters of endocrine cells called islets of Langerhans
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Chapter 45-Hormones and the Endocrine System · Chapter 45-Hormones and the Endocrine System Simple Hormone Pathways Pathway Example Stimulus Low pH in duodenum S cells of duodenum•
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Chapter 45-Hormones and the Endocrine System
Simple Hormone Pathways
Pathway Example
Stimulus Low pH in
duodenum
S cells of duodenum secrete secretin ( )
Endocrine cell
Blood vessel
Pancreas Target cells
Response Bicarbonate release
–
•Hormones are released from an endocrine cell,
travel through the bloodstream, and interact with
the receptor or a target cell to cause a physiological
response
Insulin and Glucagon: Control of Blood Glucose
Homeostasis: Blood glucose level
(about 90 mg/100 mL)
Glucagon
STIMULUS: Blood glucose level
falls.
Alpha cells of pancreas release glucagon.
Liver breaks down glycogen and releases glucose.
Blood glucose level rises.
STIMULUS: Blood glucose level
rises.
Beta cells of pancreas release insulin into the blood.
Liver takes up glucose and stores it as glycogen.
Blood glucose level declines.
Body cells take up more glucose.
Insulin •Insulin and glucagon are
antagonistic hormones that help
maintain glucose homeostasis
Target Tissues for Insulin and Glucagon
Insulin reduces blood glucose levels by:
Glucagon increases blood glucose levels by:
Promoting the cellular uptake of glucose
Slowing glycogen breakdown in the liver
Promoting fat storage
Stimulating conversion of glycogen to glucose in
the liver
Stimulating breakdown of fat and protein into
glucose
A negative feedback loop
The pancreas has clusters of endocrine cells called
islets of Langerhans
Diabetes Mellitus
Type I diabetes mellitus (insulin-dependent) is an autoimmune disorder in which the immune system
destroys pancreatic beta cells
Type II diabetes mellitus (non-insulin-dependent) involves insulin deficiency or reduced response of target cells
due to change in insulin receptors
The endocrine and nervous systems act individually and together in regulating animal physiology
•Signals from the nervous system initiate and regulate endocrine signals
Spinal cord
Posterior pituitary
Cerebellum
Pineal gland
Anterior pituitary
Hypothalamus
Pituitary gland
Hypothalamus
Thalamus
Cerebrum
Attached to the hypothalamus is the pituitary gland