Homeostasis and Chemical Messengers Lecture Review

Flashcards covering key concepts from Chapters 1 and 5 on Homeostasis and Chemical Messengers, including definitions, processes, and examples of feedback systems and types of intercellular communication.

What is the primary function of physiology?

The study of function.

What percentage of total body weight does total body water (TBW) account for?

About 60% of total body weight.

What are the two major compartments of extracellular fluid (ECF), and what percentage of ECF does each account for?

Blood plasma (20% of ECF) and Interstitial fluid (80% of ECF).

What percentage of total body water (TBW) is contained within intracellular fluid (ICF)?

About 2/3 of TBW.

Why does the body primarily monitor and maintain the composition of extracellular fluid (ECF)?

If the composition of ECF changes significantly, the composition of ICF also changes, affecting cell function, and potentially leading to disease or death.

What is the purpose of negative feedback in homeostatic regulation?

To restore a regulated variable to homeostasis if it is disturbed, resisting or negating the deviation from the normal value.

What are the components of a typical reflex arc?

Stimulus, sensory receptor, afferent pathway, integration center, efferent pathway, effector organ(s), response, and negative feedback inhibition.

What is the purpose of feedforward mechanisms?

To increase the speed of the body's homeostatic responses and minimize fluctuations in the variable being measured by anticipating a needed change.

Describe extrinsic regulation as a type of negative feedback.

Nervous or endocrine systems adjust activities of cells, tissues, organs, or organ systems through long-distance communication to maintain homeostasis.

Give an example of extrinsic regulation involving abnormal blood glucose levels.

High glucose in blood plasma triggers insulin release from the pancreas, which allows glucose to enter cells and restores normal blood glucose levels.

Describe intrinsic regulation (autoregulation or local regulation) as a type of negative feedback.

Activities of cells, tissues, organs, or organ systems change locally and automatically to maintain homeostasis when faced with an environmental change, typically through short-distance communication.

What are the three main functional classes of intercellular chemical messengers released into the ECF?

Hormones, Neurotransmitters, and Paracrine agents.

How do hormones travel in the body, and what is the characteristic duration of their effects?

Hormones travel in the blood and their effects may take a while to begin but can last for hours or days.

What are neurohormones?

A category of hormones secreted by neurons into the interstitial fluid, which are then picked up by the blood plasma to circulate to target cells.

By what mechanism do neurotransmitters communicate, and what is their characteristic speed and duration compared to hormones?

Neurotransmitters allow for synaptic communication, which is faster but shorter-lived than endocrine communication.

What are paracrine agents?

Chemicals released by cells that act on neighboring cells within the same tissue, facilitating local communication (intrinsic control).

Which major category of paracrine agents is derived from arachidonic acid, a constituent of plasma membrane phospholipids?

Eicosanoids.

What are autocrine agents?

Chemicals released by cells that act on the very same cell that secreted them, often also acting as paracrine agents.

What type of direct communication between cells does not involve chemical messengers released into the ECF, and what are their channels called?

Direct communication through gap junctions, which are fused membrane channels between two cells, also known as connexons.

What determines whether a chemical messenger is considered a hormone, neurotransmitter, or paracrine/autocrine factor?

The context of its action: if it travels through the blood to distant tissues (hormone), communicates between nerve cells (neurotransmitter), acts on neighboring cells (paracrine), or acts on the secreting cell itself (autocrine).

Give three examples of 'normal' positive feedback mechanisms in the human body.

Birth, blood clotting, and generating action potentials.

What is the unifying theme of physiology?

Homeostasis, the maintenance of a relatively constant internal environment.

What does 'steady-state' mean in the context of a regulated variable?

Maintenance of a regulated variable within a healthy range, which requires energy.

Which part of the brain is probably the 'pacemaker' for biological rhythms, such as circadian rhythms?

The hypothalamus.

Which gland is regulated by the hypothalamus and secretes melatonin during darkness?

The pineal gland.