Homeostasis and Body Variables

Study Notes

The human body must maintain specific ranges for various variables to function properly.
These variables include fluid balance, body temperature, oxygen and carbon dioxide levels, blood pressure, pH, and plasma levels of substances like creatinine, urea, sodium, potassium, glucose, and amino acids.
Changes in the external environment can influence these variables.

Homeostasis is the process by which the body maintains a stable internal environment despite external changes.
It involves the maintenance of a constant internal environment, even when there are changes in the external environment.
The internal environment of the body is the extracellular fluid, which surrounds cells, facilitates nutrient exchange, and removes waste products.
Cells are the basic unit of life and require a constant internal environment to function.

The body utilizes various systems to maintain homeostasis, with the endocrine and nervous systems playing key roles.
The nervous system facilitates rapid responses and coordination of bodily functions, while the endocrine system regulates longer-lasting processes.

Receptor: Structures that sense changes in variables (stimuli). Example: Temperature receptors in the skin.
Afferent Pathway: Transmits information about the change from the receptor to the control center. Example: Sensory nerves carrying temperature information to the brain.
Control Center: Receives information, interprets it, and initiates responses. Examples: The brain and specific endocrine glands.
Efferent Pathway: Delivers messages from the control center to the effector organs/tissues. Examples: Motor neurons in the peripheral nervous system and hormones released by endocrine glands.
Effectors: Respond to the messages from the control center to bring back balance. Examples: Muscles, glands, and organs.

Part of the brain which is often the coordinating center for temperature, blood pressure and hunger control.
Receives messages from receptors.
Initiates hormonal and nervous system responses.

Negative Feedback: Response triggered by changed conditions reverses the change. Example: Increased body temperature causes vasodilation (widening of blood vessels) to release heat and lower temperature.
Positive Feedback: Response triggered by changed conditions reinforces the change and amplifies the stimulus. Example: During childbirth, oxytocin release stimulates uterine contractions, which pushes the baby further into the birth canal, leading to more oxytocin release and stronger contractions.

Condition: High blood sugar levels can lead to toxicity, while low blood sugar levels can prevent cells from meeting their energy needs.
Receptor: Glucose transporter molecules sense glucose levels.
Control Center: Beta cells in the pancreas release insulin when blood glucose levels are high, and alpha cells in the pancreas release glucagon when blood glucose levels are low.
Effector: Insulin promotes glucose uptake by muscle and fat tissue, reducing blood glucose levels, while glucagon stimulates the liver to break down glycogen into glucose, increasing blood glucose levels.

Positive feedback loop during breastfeeding.
Sensory detectors in the nipple sense baby suckling.
Message is relayed to the hypothalamus.
Hypothalamus signals the posterior pituitary to release oxytocin.
Oxytocin stimulates the mammary glands to produce milk, which the baby sucks, triggering the release of more oxytocin, further stimulating milk production.

Anticipates changes and initiates a response before the change occurs.
This allows the body to prepare for the change, minimizing the need for a large response once the change occurs.
Example: Increased heartbeat in advance of physical exertion.