Human Body, Systems and Homeostasis

Homeostasis: The tendency of the body to maintain a relatively constant internal environment.
- Critical for survival: Essential for the cells and systems in the body to function properly.
- The human body can only survive within a narrow range of conditions.

The importance of healthy glucose levels represented through a time graph showing fluctuations:
- Spike: An increase in glucose level.
- Crash: A drop in glucose level after a spike.

Homeostasis Disturbance: Homeostasis is continuously disturbed by internal and external changes.
- The body constantly monitors internal changes.
- Maintains homeostasis through feedback systems.
- Feedback systems are composed of three main components:
- Sensor: Maintains and detects changes in the internal environment.
- Control Centre: Sets the range of values within which a variable should be maintained.
- Effector: Responds to signals from the control centre to effect change in a variable.

Definition: The output of a system reverses a change in a variable, bringing the variable back to within normal range.
Example: Body Temperature Regulation
- Vasodilation: Occurs when the hypothalamus detects overheating; the body cools down through increased sweat secretion (diaphoresis) and blood vessel dilation.
- Vasoconstriction: Occurs during cooling; the hypothalamus signals the body to shiver and constrict blood vessels to conserve heat.

Insulin: Hormone secreted by the pancreas that stimulates glucose uptake by cells and glycogen formation in the liver.
Normal Glucose Level: Generally maintained around 90 mg/100 ml.
Glucagon: Hormone that stimulates glycogen breakdown when blood glucose levels fall, returning glucose levels to normal range.
Balance and Imbalance:
- IMBALANCE: When blood glucose levels rise above or fall below the normal range.
- Normal function of glucose control is crucial for metabolic homeostasis.

The Hypothalamus releases Gonadotropin-Releasing Hormone (GnRH).
Positive Feedback (days 12-14):
- Increased secretion of Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH) from the anterior pituitary stimulates ovaries to produce estrogen and progesterone.
Negative Feedback: Dominates in most of the menstrual cycle, regulating hormonal levels to balance the cycle.

Baroreceptors: Detect changes in blood pressure. When stimulated:
- Cardioacceleratory centers are inhibited.
- Cardioinhibitory centers are stimulated to decrease cardiac output.
- Result: Vasodilation occurs leading to lower blood pressure.
Disturbance: Blood pressure can rise or fall outside the normal range, prompting adaptive reflex responses to restore homeostasis.

Definition: The output of a system strengthens or increases a change in a variable, resulting in less common loops that have definitive cut-off points.
Examples:
- Child Birth: Oxytocin release causes uterine contractions; baby pushes against the cervix leading to nerve impulses that signal the release of more oxytocin.
- Blood Clotting: Positive feedback amplifies the accumulation of platelets at a site of injury, rapid sealing of cuts in the blood vessels.
- Fruit Ripening: Ethylene gas produced by one ripening fruit prompts nearby fruits to ripen, increasing ethylene production further.

Responsive breastfeeding is vital for the maintenance of milk supply:
- Nursing stimulates nipple, releasing prolactin, leading to milk production in the mammary glands.
- Suckling further stimulates the hypothalamus causing the release of oxytocin, which ensures milk is ejected from the mammary glands.

The maintenance of body temperature within an optimal range ensuring efficient cellular function.
- Endotherms: Animals like mice that generate metabolic heat to maintain internal temperature (homeothermic).
- Ectotherms: Animals like snakes whose body temperature changes with environmental temperature (poikilothermic).

Conduction: Direct thermal energy transfer between molecules in contact.
Convection: Transfer of thermal energy within a fluid.
Radiation: Transfer of thermal energy in the form of electromagnetic radiation.
Evaporation: Loss of heat via the evaporation of water from surfaces, such as skin.

Torpor: A short-term state of decreased metabolic rate and body temperature.
Estivation: A similar state to torpor enabling survival through hot summers.
Hibernation: A prolonged state of decreased metabolic rate and activity allowing survival through cold winters.