● Releases chemical messengers (hormones) into the blood
● Hormones are long-distance chemical signals that control the metabolic activities
of cells.
● Organ response is often delayed but it’s prolonged
Features of the Endocrine System
● Ductless
● Releases hormones into surrounding tissue fluid
● Highly vascularized
2 types of glands! Exocrine glands produce non-hormonal molecules that travel through
ducts to a membrane surface. E.g. Goblet cells release MUCUS.
1. Sweat glands release sweat
2. Sebaceous glands release oils
Endocrine glands:
● Pituitary
● Pineal
● Parathyroid
● Thyroid
● Adrenal
Endocrine cells are also found scattered throughout the body:
● Adipose cells
● Thymus
● Small intestine
● Stomach
● Kidneys
● Heart
● Chemical substance released by cells to regulate cell metabolism
, ● Can be amino-acid-based or steroidal
● MOST are amino-acid-based
Functions of a Hormone
REGULATES THE ACTIVITY OF CELLS
1. They can change plasma membrane permeability
2. Can stimulate protein synthesis
3. Activate or deactivate enzymes
4. Induce secretion of molecules from cells
5. Stimulate mitosis
Amino-acid-based hormones → stay outside the cell, bind to a receptor, and activate a
transmembrane signaling system.
○ Hormone (1st messenger) binds to a receptor
○ The receptor then activates the G protein
○ The G protein activates adenylate cyclase
○ Adenylate cyclase converts ATP to cAMP (2nd messenger)
○ cAMP activates protein kinases
Steroid Hormones (& Thyroid Hormone)
Steroid hormones are also lipid-loving. Other steroid hormones are sex hormones,
including testosterone, progesterone, and estrogen.
● The steroid hormones diffuse across the plasma membrane and bind to an
intercellular receptor
● The receptor-hormone complex enters the nucleus
● The receptor-hormone complex binds to a specific DNA region
● Binding initiates transcription of the gene to mRNA.
● The mRNA directs protein synthesis
● Hormones are released in a direct response to levels of molecules or ions in the
blood.
, ● Parathyroid glands monitor blood Ca2+ levels.
● The pancreas monitors blood glucose levels
● The adrenal cortex monitors blood Na+ and K+ levels.
Stimulus: low concentration of Ca2+ in the capillary blood.
Response: The Parathyroid glands secrete PTH, which increases blood Ca2+ levels.
● When nerve activity stimulates hormone release
● The hormone release is caused by neural input
○ Example: the sympathetic nerve stimulation of the adrenal medulla to
release adrenalin.
● A hormone from one gland causes a hormone to be released from another
● Hormone release is caused by another hormone (a trophic hormone)
○ Example: you grow at night.
Stimulus: hormones from the hypothalamus
Response: The anterior pituitary gland secretes hormones that stimulate other endocrine
glands to secrete hormones.
● Hormones circulate throughout the body and the vascular system. It affects ONLY
certain tissue cells called .
● Target cells must have receptors specific to each hormone
○ Only cells of the adrenal cortex have ACTH receptors → lock & key
example.
● The response of target cells depends on:
○ Blood levels of the hormone
○ # of receptors on target cells
○ Affinity of binding between the hormone and the receptor.
● Hormones are long-distance chemical signals that control the metabolic activities
of cells.
● Organ response is often delayed but it’s prolonged
Features of the Endocrine System
● Ductless
● Releases hormones into surrounding tissue fluid
● Highly vascularized
2 types of glands! Exocrine glands produce non-hormonal molecules that travel through
ducts to a membrane surface. E.g. Goblet cells release MUCUS.
1. Sweat glands release sweat
2. Sebaceous glands release oils
Endocrine glands:
● Pituitary
● Pineal
● Parathyroid
● Thyroid
● Adrenal
Endocrine cells are also found scattered throughout the body:
● Adipose cells
● Thymus
● Small intestine
● Stomach
● Kidneys
● Heart
● Chemical substance released by cells to regulate cell metabolism
, ● Can be amino-acid-based or steroidal
● MOST are amino-acid-based
Functions of a Hormone
REGULATES THE ACTIVITY OF CELLS
1. They can change plasma membrane permeability
2. Can stimulate protein synthesis
3. Activate or deactivate enzymes
4. Induce secretion of molecules from cells
5. Stimulate mitosis
Amino-acid-based hormones → stay outside the cell, bind to a receptor, and activate a
transmembrane signaling system.
○ Hormone (1st messenger) binds to a receptor
○ The receptor then activates the G protein
○ The G protein activates adenylate cyclase
○ Adenylate cyclase converts ATP to cAMP (2nd messenger)
○ cAMP activates protein kinases
Steroid Hormones (& Thyroid Hormone)
Steroid hormones are also lipid-loving. Other steroid hormones are sex hormones,
including testosterone, progesterone, and estrogen.
● The steroid hormones diffuse across the plasma membrane and bind to an
intercellular receptor
● The receptor-hormone complex enters the nucleus
● The receptor-hormone complex binds to a specific DNA region
● Binding initiates transcription of the gene to mRNA.
● The mRNA directs protein synthesis
● Hormones are released in a direct response to levels of molecules or ions in the
blood.
, ● Parathyroid glands monitor blood Ca2+ levels.
● The pancreas monitors blood glucose levels
● The adrenal cortex monitors blood Na+ and K+ levels.
Stimulus: low concentration of Ca2+ in the capillary blood.
Response: The Parathyroid glands secrete PTH, which increases blood Ca2+ levels.
● When nerve activity stimulates hormone release
● The hormone release is caused by neural input
○ Example: the sympathetic nerve stimulation of the adrenal medulla to
release adrenalin.
● A hormone from one gland causes a hormone to be released from another
● Hormone release is caused by another hormone (a trophic hormone)
○ Example: you grow at night.
Stimulus: hormones from the hypothalamus
Response: The anterior pituitary gland secretes hormones that stimulate other endocrine
glands to secrete hormones.
● Hormones circulate throughout the body and the vascular system. It affects ONLY
certain tissue cells called .
● Target cells must have receptors specific to each hormone
○ Only cells of the adrenal cortex have ACTH receptors → lock & key
example.
● The response of target cells depends on:
○ Blood levels of the hormone
○ # of receptors on target cells
○ Affinity of binding between the hormone and the receptor.
