Lecture 2 Control of the Internal Environment

Steady state

physiological variable is unchanging, but not necessarily “normal” resting value

ex: HR during submaximal exercise

ex: body core temp during prolonged submax exercise

Homeostasis

during resting conditions

Biological control systems

series of interconnected components that maintain a physical or chemical parameter at a near constant value

Components of biological control system

Sensor/receptor

Control center

Effector

Negative feedback

Response reverses the initial disturbance in homeostasis

exs:

• increase in extracellular CO2 triggers a receptor

• sends info to respiratory control center

• respiratory muscles are activated to increase breathing

• CO2 concentration back to normal

Blood glucose negative feedback

Elevated blood glucose signals the pancreas to release insulin

Insulin causes cellular uptake of glucose to restore homeostasis

failure of effector (beta cells) is type 1 diabetes

failure of biological control system

results in disturbance of homeostasis and disease

Positive feedback

response increases original stimulus. childbirth.

Gain of a control system

degree to which a control system maintains homeostasis

a system with large gain is more capable of maintaining homeostasis that system with low gain

pulmonary and cardiovascular systems have large gain

Exercise and homeostasis

Exercise disrupts homeostasis by producing changes in pH and temp in cells.

submaximal exercise + cool environment = body can maintain

intense or prolonged exercise + hot/humid = exceeding ability to maintain a steady state + fatigue

Adaptation

Change in structure and function of cell or organ system. Result is improved ability to maintain homeostasis.

Acclimation

Adaptation to environmental stresses (ex: heat). Results in improved function of homeostatic system

Cell signaling

communication btwn cells using chemical messengers

coordinates cellular activity

important for maintaining homeostasis

Hormesis

Process where a low-moderate dose of a potentially harmful stress results in a beneficial adaptive response on the cell or organ system

Cell signaling pathways

promote cellular adaptation to exercise training

5 Cell signaling mechanisms

Intracrine, juxtacrine, autocrine, paracrine, endocrine

Intracrine signaling

Chemical messenger inside cell triggers response

Juxtacrine

Chemical messenger passed between two connected cells

Autocrine signaling

Chemical messenger acts on that same cell

Paracrine

Chemical messengers act on nearby cells

Endocrine

Chemical messengers (hormones) released into blood

affects cells with specific receptor to the hormone

Extracellular vesicles (EVs)

small membrane bound sacs that carry cargo of bioactive molecules (e.g. RNAs and proteins)

Where EVs are released and travel to

released from contracting skeletal muscles and other organs during exercise.

after release, they enter nearby target cells to be transported via the blood to enter cells around the body

What signaling type do EVs participate in?

paracrine and endocrine

Exercise-induced protein synthesis

improves ability of cells to maintain homeostasis

Resistance and endurance exercise

promote activation of different signaling pathways

Steps leading to exercise-induced protein synthesis

1) exercise activates cell signaling pathways

2) activates transcriptional activator molecule

3) transcriptional activator binds to gene promoter region

4) DNA transcribed to mRNA

5) mRNA leaves nucleus and binds to ribosome

6) mRNA is translated into protein