Endocrine System Notes in Physiology

Endocrine System

What are hormones?

Hormone Interactions

• Synergistic
• 2 or more hormones are additive/complementary in effect
• Example: Thyroid Hormone + Growth Hormone
• Antagonistic
• 1 hormone offsets another hormone
• Example: The regulation of plasma glucose involves insulin [for increased blood glucose] and glucagon [for decreased blood glucose] hormones
• Permissive
• 1 hormone will enhance the responsiveness of a target to another hormone
• Example: Increased thyroid hormone levels, tissues become more responsive to catecholamine

Hormone Concentrations

• Threshold- hormone will not have any physiological effect until hormone threshold is reached

• Concentration effect- differential physiology depending on concentration
• Example: Testosterone- surge of testosterone after puberty
• à Growth of auxiliary/pubic/facial hair, and muscle mass.
• Injection of large amount of testosterone can lead to even more effects such as acne and growth of breast tissue.

• Half-life- the time it takes for the concentration of a hormone to reduce 50%
• Liver filters the concentration of hormones via blood. Kidney can excrete a certain amount of hormones.
• Endocrine has the longest half-life because it has to enter the blood stream and travel to the target.
• Autocrine has the shortest half-life because it is the target.

• Receptor Saturation- hormone receptor are not a set number. Can down regulate if bombarded with hormones

Types of Hormones

Pancreas

• Endocrine function of Pancreas. Production of hormones (glucagon and insulin)
• A few cells made in Islets of Langerhanns.
• Alpha cells make glucagon
• Beta cells make insulin.
• Exocrine function (made digestive enzymes)
• Consisted of 97% cells of pancreas
• Stored glucose as glycogen stored in liver and skeletal muscle.
• Mainly in the hepatocyte.

Glucagon and Insulin

Growth Hormone

• From the anterior pituitary gland
• The anterior pituitary gland is signaled by the hypothalamus by hypothalamo-hypotheseal through portal system
• Remember that tract is for posterior pituitary.

Growth hormoneà binds to G-proteinà dissociation of subunitsà leads to activation of phospholipase C

Overproduce GH—gigantism
Under-produce GH—dwarfism

Phospholipase C leads to 2 second messengers

1. DAG

• Nonpolar part of the phospholipid (fatty acid and glycerol)
• DAG is hydrophobic, can directly diffuse through cell membrane
• Leads to activation of protein kinase C, which affects genes in nucleus
• Increase levels of DAG promote cell division

2. IP3
1. Goes to smooth ER (place where Ca2+ is sequestered/stored)
2. IP3 opens up Ca2+ channels (Calcium released into cytoplasm)
3. These Ca2+ binds to Calmodulin

• which promotes exocytosis of cell.
• Also activates phosphodiesterase
• Phosphodiesterase cause reaction of cAMP into AMP

Growth Hormones reduce level of cAMP, causing inhibitory effect of glucagon, that’s why GH works with Insulin in blood glucose regulation because GH inhibits glucagon.

Phospholipid—3-Carbon glycerol, 2 fatty acids attach to 2 carbons, and 1 phosphate binds to 1 the last carbon.

Exercise causes release of GH. Increase exercise, increase GH level… Therefore increase insulin levels.

(endocrine system)
(endocrine system notes)

Type I diabetes

• You don’t produce insulin or insufficient insulin levels because of some reasons like autoimmune disease attacking the beta cells.

• Prescription is supplemental insulin

Type II diabetes

• Eating so much sugar or food that the cells have became desensitized
• Prescription: careful diet, exercise, lose weight
• Glucose is a stimulus for taste bud. So is Fructose, but it takes twice as much.

End of Endocrine System Notes

Endocrine System--Back to Learn Physiology
Endocrine System - Back to SG Learn Online