Lecture 4: Homeostasis Signalling Feedback Loops

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Questions and Answers

What is the primary function of the endocrine system in maintaining homeostasis?

Controlling the body's external environment

Sensing changes in the body's internal environment

Regulating the release of hormones into the bloodstream (correct)

Sending fast electric messages to the body

What type of feedback loop is responsible for counteracting changes from the set-point in homeostasis?

Positive feedback loop

Negative feedback loop (correct)

Only positive feedback loops occur in the body

Both positive and negative feedback loops

What is the primary function of a hormone receptor in signal transduction?

To transduce the signal from the hormone (correct)

To degrade the hormone

To synthesize the hormone

To amplify the signal through phosphorylation cascades

What is the role of hormones in the endocrine system?

Acting as chemical messengers to control cellular behavior Signup and view all the answers

What is the purpose of second messengers in hormone signaling?

To amplify the signal from the hormone receptor Signup and view all the answers

Which system works in conjunction with the nervous system to maintain homeostasis?

Endocrine system Signup and view all the answers

What is the primary mechanism of action for peptide hormones?

They bind to transmembrane receptors, which activates a signaling cascade Signup and view all the answers

What is an analogy for a positive feedback loop?

Toilet paper stocks Signup and view all the answers

What is the role of adenylate cyclase in hormone signaling?

It synthesizes cAMP from ATP Signup and view all the answers

What is the term for the maintenance of internal consistency, counteracting changes from the set-point?

Homeostasis Signup and view all the answers

What is a characteristic of second messengers, such as cAMP?

They act through other proteins to amplify the signal Signup and view all the answers

What is the role of kinases in hormone signaling?

They phosphorylate and activate target proteins Signup and view all the answers

What is the primary function of G proteins in GPCR signaling?

To mobilize and activate effector enzymes Signup and view all the answers

What is the effect of a dramatic increase in calcium ions in the cell?

It acts as a 'call to action' for various cellular responses Signup and view all the answers

What is the primary mechanism of hormone signaling for hormones that can readily enter cells?

Steroid receptor-mediated mechanism Signup and view all the answers

What is the role of calcium in neurotransmitter release?

It triggers synaptic vesicle exocytosis and neurotransmitter release Signup and view all the answers

What is the primary function of adenylate cyclase in GPCR signaling?

To amplify the signal through cAMP production Signup and view all the answers

What is the effect of glucagon on the liver?

It induces the enzymic conversion of glycogen to glucose Signup and view all the answers

Study Notes

Homeostasis and Feedback Loops

Homeostasis is the maintenance of internal consistency, counteracting changes to maintain a stable environment.
Feedback loops are used to maintain homeostasis, with two types: negative and positive.
Negative feedback loops counteract changes to move back to equilibrium, whereas positive feedback loops amplify initial stimuli to move further away from the starting point.

Negative Feedback Loops

Negative feedback loops have an upper limit set point and a lower limit.
Examples include regulating body temperature and blood glucose levels.

The Endocrine System

The endocrine system is a slower-acting, chemical-based messaging system that helps maintain homeostasis.
It consists of organs throughout the body that release chemical messengers (hormones) into the bloodstream.
Hormones are chemical/organic molecules made by endocrine cells that target specific organs or cells with receptors.

Hormone Signalling

Hormone signalling is a process of cellular decision making in response to an external stimulus.
The signal leads to a cell response, such as secreting, contracting, or dividing.
"Water-soluble" hormones, such as peptide hormones, require transmembrane receptors and signal amplification through phosphorylation cascades.

Second Messengers

Second messengers are molecules that act as intermediates, amplifying signals and regulating cellular responses.
Examples include cyclic AMP (cAMP) and calcium.
cAMP is synthesized from ATP by adenylyl cyclase and activates kinases, while calcium is released from storage and acts as a "call to action" due to its low resting state concentration.

Regulation of Second Messengers

cAMP is regulated by adenylyl cyclase, which is activated by G protein-coupled receptor (GPCR) signalling.
Calcium release is regulated by G protein-coupled receptor activation and mobilization of G proteins.
Calcium has profound effects on protein activity, interactions, and conformation.

Examples of Hormone Signalling

Glucagon is an example of a hormone that triggers enzymic conversion of glycogen to glucose in the liver.
Calcium plays a major role in triggering synaptic vesicle exocytosis and the release of neurotransmitters in neurons.

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Description

Learn about the concept of homeostasis, negative and positive feedback loops, and how cells, tissues, and organs communicate with each other and the outside world to maintain internal stability. Understand how the body counteracts change and maintains homeostasis.