Homeostasis and Core Temperature

Core Temperature

• Humans have a normal temperature of around 36.2 to 37.2 degrees Celsius.
• Body temperature above normal indicates likely infection, as the body raises temperature to fight infection.
• Body temperature below normal indicates hypothermia, potentially causing cell damage and death if left untreated.

What is Homeostasis?

• Homeostasis is the body's attempt to maintain "normal" levels within the body.
• It's often referred to as a dynamic equilibrium, which is a mechanism to ensure all body systems function within acceptable ranges to sustain life.

Key Concept of Homeostasis

• Homeostasis is the regulation and maintenance of the internal environment.

Conditions Within the Body

• Homeostasis involves maintaining the internal environment within set ranges.

Homeostatic Control Systems

• Homeostatic control systems have three components: monitor, coordinating center, and regulator.
• The monitor detects changes in normal levels and sends a signal to the coordinating center.
• The coordinating center then sends messages to the regulator to restore balance.

Example: Household Thermostat

• A room temperature is set to 22 degrees Celsius.
• When temperature falls below 22 degrees, the thermostat switches on the furnace.
• When temperature rises above 22 degrees, the thermostat switches off the furnace.
• This is a negative feedback system.

Negative Feedback

• A system response by restoring conditions to their original state.
• Ensures that small changes don't snowball into larger problems.

Control Systems for Homeostasis

• Sensors: gather data (e.g., senses)
• Control Center: receives data, interprets information, and sends out messages (e.g., brain)
• Communication System: delivers messages to target organs/tissues, including the peripheral nervous system (e.g., motor neurons).
• Targets: respond to change (e.g., muscles, glands that release hormones).

Negative Feedback Loops in Homeostasis

• Feedback compares current conditions to comfort levels (set ranges)
• Negative feedback counteracts changes and brings the body back to homeostasis.
• Example: breathing rate changes to maintain O2/CO2 levels.

Homeostasis and Temperature Control

• Nervous system signals dermal blood vessels to dilate or constrict to regulate body temperature.
• Sweat glands secrete sweat to cool down the body, whereas blood vessels constrict to conserve heat.
• Hypothalamus in the brain is the body's temperature control center.

Positive Feedback

• Positive feedback increases change away from set points, needed for rapid body changes.
• Example 1: Torn blood vessels causing clotting to stop bloodflow.
• Example 2: Oxytocin stimulating mammary gland during childbirth and feeding.

Hormonal Regulation of Pregnancy

• Estrogen from placenta prepares the uterus for oxytocin response.
• Prostaglandins released by uterus enhance contractions.
• Sensory input to hypothalamus is enhanced by uterine contractions
• When the baby sucks at the nipple, it sends impulses to hypothalamus stimulating oxytocin secretion and milk production.
• Positive feedback loop of oxytocin release further stimulates uterine contraction during childbirth.

Systems Involved in Thermoregulation

• Muscular
• Integument (skin)
• Respiratory
• Circulatory
• Nervous (hypothalamus)
• Endocrine (hormones)

Responses to Heat/Cold Environments

• Hot: Vasodilation (blood vessels widen), Sweating (cooling via water evaporation), Pilorelaxation (hair flattened) and increased surface area.
• Cold: Vasoconstriction (blood vessels narrow conserving heat), Shivering (generating heat), and Piloerection (hair stands up for insulation).

Insulin & Glucagon

• Purpose: Regulate blood glucose levels for energy supply and metabolic balance.
• Insulin and glucagon are the two major player hormones.
• Insulin promotes glucose uptake into cells, converting excess glucose to glycogen for storage.
• Glucagon release glucose from stored glycogen when glucose levels decrease.

Insulin

• Source: Beta cells in the pancreas.
• Function: Decrease blood glucose levels, promote glycogen formation (glycogenesis), inhibit glycogen breakdown (glycogenolysis).
• Regulation: Increased secretion with high blood glucose, feedback loops of decreased glucose levels reduce stimulus for insulin secretion and maintain metabolic homeostasis.

Glucagon

• Source: Alpha cells in the pancreas.
• Function: Increase blood glucose levels, stimulates glycogen breakdown (glycogenolysis) promote gluconeogenesis from non-carbohydrate sources, and inhibit glycolysis.
• Regulation: Increased secretion with low blood glucose level.

Interaction (Insulin & Glucagon)

• Postprandial (After Eating): Insulin released to lower blood glucose levels.
• Fasting (Between Meals): Insulin secretion decreases while glucagon secretion increases to raise blood glucose levels.

Water & Electrolyte Balance

• Water Intake: Drinking, food, and metabolic processes.
• Water Loss: Urine, sweat, breathing, and feces.
• Kidney Regulation: Concentrated urine during dehydration, and diluted urine when excess water is present.

Water Regulation

• Too little: Hypothalamus detects low water level, pituitary gland releases more ADH, water reabsorbed by kidneys, less water lost in urine, and blood water levels return to normal.
• Too much: Hypothalamus detects excess water, pituitary gland releases less ADH, less water reabsorbed by kidneys, more water lost in urine, and blood water levels return to normal.
• Excess water leads to more diluted urine, while dehydration leads to more concentrated urine.

Renin-Angiotensin-Aldosterone System

• This system regulates blood pressure, which affects fluid and electrolyte balance.
• Low blood volume or blood pressure triggers the release of Renin which in turn activates a cascade process of hormones involved in regulating blood pressure.
• Aldosterone plays a significant role in reabsorbing sodium and water in kidneys to increase blood volume leading to maintaining blood pressure..