Interactive learning

• Lecture

• Rapid answers

• Small group discussions

• Class discussions

• Hands-on projects

Participation is key!

Homework

• Read Nijhout 1981 by next Friday (January 18th). Come to class with your written summary and ready to discuss it.

• Remote sites will receive it by e-mail.

Organization of Organisms

Whole Organism

Systems

Organs

Tissues

Cells

Organization of Organisms

Whole Organism

Systems

Organs

Tissues

Cells

What are the basic systems that insects need?

• Cells can only survive over a relatively small range of physiological conditions.

• Cells function best over an even smaller range of physiological conditions

• Cells can only survive over a relatively small range of physiological conditions.

• Cells function best over an even smaller range of physiological conditions.

• Therefore, multicellular organisms regulate their internal environment to optimize cell survival and function.

• This tendency of organisms to regulate their bodies to maintain internal stability is called ?????????

• Cells can only survive over a relatively small range of physiological conditions.

• Cells function best over an even smaller range of physiological conditions.

• Therefore, multicellular organisms regulate their internal environment to optimize cell survival and function.

• This tendency of organisms to regulate their bodies to maintain internal stability is called HOMEOSTASIS.

Some environments are unsuitable because of fluctuations.

• Animals survive a small range of conditions, and cells perform best under an even smaller range of conditions.

• However, not all animals have the same range of conditions for survival or optimal function. Deinocerites cancer – Florida crabhole mosquito

• Animals fall into two categories with respect to their physical environment.

1. Conformers – allow their internal conditions to reflect the external conditions.

2. Regulators – maintain internal stability even as external conditions change.

• How do regulators maintain a constant internal condition?

• Use a feedback system!

• What are the components necessary in a feedback system?

• Design a feedback system for an osmoregulator placed in a solution that is more dilute than it’s body fluids. (e.g., crab hole mosquito after rain)

• Start out by asking what kind of components would a feedback system need and then asking in what order they should interact. Try to produce a list of components and a flowchart of their interactions.

• Two types of feedback systems– 1. Negative Feedback – 2. Positive Feedback

Both have the following components arranged in similar ways

- Sensor – monitors internal conditions

- Integrating Center – compares internal conditions to a set point.

- Effector – causes changes to compensate for the deviation from set point.

- Response – return to set point.

Most biological processes involve negative feedback.

Negative feedback systems are critical for homeostasis.

Imagine a crabhole mosquito larva whose water osmolarity changes.

Decrease in water solute concentration

Decrease in extracellular fluid solute concentration

Nervous system senses deviations from normal and signals the brain/CNS

CNS responds by releasing more diuretic hormone

Increased filtration and urine output

Compensation for lower environmental solute concentration.

• Many aspects of the internal environment are controlled by multiple effectors.

• Often these effectors have an antagonistic effect, one moving the system in one direction and the next moving the system in another direction.

• These antagonistic interactions between multiple effectors can achieve a greater degree of control than a system with a single off/on effector.

•Simple one-effector negative feedback system.

•Useful and robust, but can easily overshoot particularly if conditions change.

Antagonistic feedback regulates the temperature in my incubators.

Exercise Eating•Maintaining appropriate blood sugar levels is critical.

•Levels too low (hypoglycemia), leads to inadequate fuel supply, decreased cellular function and ultimately death.

•Levels too high (hyperglycemia), leads to osmotic and other problems which affect cell and organ function (diabetes).

•Therefore, blood sugar is controlled by two antagonistic hormonal systems.

Winter dormancy and fat regulation

Larvae

Early 3rd Late 3rd Wandering Day 5

% F

at C

onte

nt

2

3

4

5

6

7

8

9

10

Diapause

Non-Diapause

Pupae

Diapause-destined individuals accumulate more fat than non-diapause individuals.

There is a clear change in the liporegulatory set point!

Other examples in insects or humans?

• Positive feedback systems where the stimulus drives the system even farther from the set point also occur.

• Not involved in homeostasis, but many other examples.

• Can you think of one in insects?

Positive feedback helps to escalate ecdysis behavior to get the insect out of it’s previous larval cuticle. Process keeps escalating until the stimulus of the old cuticle is removed, kind of like human birth.

• Homeostasis is a complex process with many layers which involves multiple interacting systems.

• Many aspects of whole organism homeostasis are studied in isolation from other systems for simplicity’s sake.

• Important to remember that there are multiple physiological demands on an organism that must be solved simultaneously.