Control Systems of the Body: Endocrine and Nervous Systems

These systems operate like control systems with sensory receptors that detect changes, such as temperature.
The system involves:
- Sensory receptors
- Input signal to an integrating center
- The integrating center controls information and determines the necessary response.
- Output signal

The nervous and endocrine systems work to keep body parameters balanced, including:
- Electrolytes
- Water levels
- pH
- Blood pressure
- Glucose levels
- Cholesterol
The input signal relays information to an integrating center, which then sends an output signal to produce a response.

Local controls: Occur within the cell or tissue.
Reflexive controls: Use long-distance loops, involving signals sent from one part of the body to another (e.g., touching a hot stove).

Response loops are modulated by feedback loops, starting with a stimulus and progressing sequentially through sensor, input signal, integration center, output signal, target, and response.
Example: Touching a hot stove
- Stimulus: Change in temperature
- Sensor: Thermal or temperature receptor
- Input Signal: Neuron sends a signal to the brain (integrating center).
- Output Signal: Brain sends a signal back via a nerve to a muscle (target).
- Response: Muscle contraction to move the hand away.

Negative feedback loops counteract the initial stimulus to stabilize conditions. They do not mean 'bad'.
Example: High blood pressure is lowered back to normal.

Positive feedback loops reinforce the initial stimulus, creating a domino effect.

These allow the body to anticipate changes and prepare in advance.
Example: Salivating at the sight or thought of food, preparing the body for digestion and nutrient absorption.

Homeostatic functions maintain a set point or normal value.
The body operates within a normal range of function, fluctuating around a set point.
Negative feedback turns the response loop off when conditions are within range and on when conditions are outside the range.
This creates constant adjustments to balance body conditions, influenced by factors like eating, moving, and metabolism.
Adequate sleep is essential for the body to repair itself and for feedback loops to rest.

Negative Feedback: The initial stimulus triggers a response that decreases the stimulus, leading to cutoff.
Positive Feedback: The initial stimulus triggers a response that increases the stimulus repeatedly.

As the baby grows, its head presses on the cervix, causing it to stretch (distend).
Cervical stretching stimulates the pituitary gland to secrete oxytocin.
Oxytocin stimulates uterine contractions, pushing the baby further onto the cervix, increasing oxytocin secretion.
This positive feedback loop continues until the baby is born.
During labor, OBGYNs check for:
- Dilation: Opening of the cervix (10 cm indicates readiness for birth).
- Effacement: Thinning of the cervix.

After eating sugary foods, glucose enters the bloodstream, increasing blood glucose levels.
The body uses mechanisms to bring blood glucose back down to its normal level (set point) to maintain homeostasis.

High Blood Glucose:
- Glucose enters beta cells in the pancreas.
- Beta cells release insulin.
- Insulin travels to liver cells, causing them to take in more glucose and convert it to glycogen (storage molecule).
- Blood glucose levels decrease, reducing insulin release.
Low Blood Glucose:
- Alpha cells in the pancreas release glucagon.
- Glucagon travels to liver cells, signaling them to break down glycogen into glucose.
- Glucose is released into the blood, increasing blood glucose levels, and reducing glucagon release.

Type 1: Beta cells are destroyed; no insulin is produced.
Type 2: Insulin is produced, but target cells don't respond to it.
In both types, blood glucose remains high because cells do not take up the additional glucose.

Biological rhythms, such as daily circadian rhythms, result from changes in set points.
Circadian rhythms are the body's responses to light and darkness, affecting body temperature and cortisol levels.
Body Temperature:
- Lowest right before sunrise (4-6 AM).
- Decreases during sleep.
- Spikes upon waking up.
Cortisol Levels:
- Highest around 9 AM.
- Sudden drop around noon.
Biological rhythms are affected by light and darkness.

Acclimatization: Natural adjustment to environmental conditions.
Acclimation: Adjusting in a laboratory setting, often using tools to assist with adaptation.

Living in Alaska with 24 hours of light: Using blackout curtains to simulate darkness and maintain a normal sleep cycle.
Living in Denver (Mile High City): The body produces more red blood cells due to low oxygen concentration in the atmosphere, leading to polycythemia.