Homeostasis notes #1 (copy)

Homeostasis

• Maintenance of a relatively constant internal state, regardless of external changes; this dynamic equilibrium is crucial for cellular functions.

• Optimal metabolic efficiency requires efficient and coordinated chemical reactions, which depend on stable internal conditions.

• Enzymes are highly sensitive to temperature, pH, and substrate concentrations; deviations can impair their function.

• In mammals, the nervous and endocrine systems work in tandem to maintain homeostasis through feedback mechanisms.

• Variables such as body temperature, blood glucose, and pH are maintained within a narrow range, known as tolerance limits, around a set point to ensure optimal physiological function.

Negative Feedback System

1. Detecting change: Receptors, such as thermoreceptors or chemoreceptors, detect a stimulus that deviates from the set point.

2. Counteracting the change: Effectors, which can be muscles or glands, reverse the change to restore the body to its set point.

• The control center, often the hypothalamus, maintains fluctuations around the set point to prevent drastic changes.

• The hypothalamus is a critical control center that links the nervous and endocrine systems, coordinating responses to maintain internal balance.

• Negative feedback counteracts the stimulus, reducing or removing the initial trigger to stabilize the internal environment.

Thermoregulation

• Thermoreceptors in the skin and hypothalamus detect temperature changes, initiating appropriate responses.

Cooling the Body

• Increase in body temperature detected by anterior hypothalamus triggers cooling mechanisms.

• Vasodilation: Blood vessels dilate to release heat through increased blood flow to the skin's surface.

• Sweat glands activate to secrete sweat, removing heat through evaporation, which has a cooling effect.

• Thyroid gland reduces thyroxine production to lower metabolism and decrease heat production.

Warming the Body

• Decrease in temperature detected by posterior hypothalamus initiates warming responses.

• Vasoconstriction: Blood vessels constrict to conserve heat by reducing blood flow to the skin's surface.

• Contraction of hair erector cells traps warm air near the skin, providing insulation.

• Pituitary gland releases TSH, increasing thyroxine production by the thyroid gland, which boosts metabolism and heat generation.

• Shivering generates heat through rapid muscle contractions.

Internal Coordination Systems

• Nervous and endocrine systems coordinate to maintain homeostasis through rapid neural signals and slower hormonal responses.

• Receptors detect stimuli outside tolerance limits, triggering responses to restore balance.

• Interoceptors detect internal stimuli and are named according to the type of energy they detect (e.g., mechanoreceptors, chemoreceptors).

• Thermoreceptors detect temperature changes, crucial for thermoregulation.

• Chemoreceptors detect chemical concentrations, such as blood glucose or oxygen levels.

• Osmoreceptors detect osmotic pressure changes, important for maintaining fluid balance.

The Nervous System

• Neural pathways are provided by the nervous system, with the CNS and PNS facilitating rapid communication.

• CNS: Brain and spinal cord; PNS: Nerves throughout the body, connecting the CNS to limbs and organs.

• Nerves transmit electrochemical impulses, enabling quick responses to stimuli.

Neurons

• Cell body: Contains nucleus and organelles (grey matter), essential for neuron function.

• Dendrites: Receive impulses and conduct them towards the cell body, branching extensively to increase surface area.

• Axon: Carries messages away from the cell body (white matter), often covered in myelin for faster transmission.

Types of Neurons

• Sensory neurons: Carry impulses from PNS to CNS, transmitting information about the environment.

• Motor neurons: Transfer messages from CNS to effectors (muscles or glands), initiating responses.

• Interneurons: Link sensory and motor neurons within the CNS, facilitating complex reflexes and higher-level processing.

• Synapse: Gap between neurons where impulses are transferred via neurotransmitters.

Transmission of Nerve Impulses

• Action potential: Change in electric potential of the cell membrane, allowing rapid signal transmission.

• At rest: Neuron attempts to balance ion concentrations, maintaining a resting membrane potential.

• Stimulus causes a change in ion concentrations, leading to depolarization and initiation of an action potential.

• Action potential involves depolarization and repolarization, creating a rapid electrical signal.

• Neurotransmitters transfer messages across the synapse, stimulating action potential in the next neuron, propagating the signal.

Central Nervous System

• The brain controls homeostasis through various centers and nuclei, integrating sensory information and coordinating responses.

• The hypothalamus links the nervous and endocrine systems, regulating numerous physiological processes.

• The spinal cord conducts nerve impulses and coordinates reflex actions, enabling quick responses to stimuli without brain involvement.

The Endocrine System

• The endocrine system regulates body activity via hormones, which are slower but have longer-lasting effects.

• Hormones are transported by the bloodstream to target cells, binding to receptors and triggering specific responses.

• The pituitary gland regulates other glands, acting as a central control point for the endocrine system.

• The hypothalamus controls the anterior pituitary through hormones, while nerve impulses control the posterior pituitary, which secretes hormones directly.

• Pancreatic islets (alpha and beta cells) regulate glucose levels by producing insulin and glucagon, maintaining blood sugar balance.

Adaptations in Endotherms

• Endotherms maintain body temperature within a narrow range, independent of external temperatures.

• Adaptations increase survival and reproduction by optimizing physiological functions.

• Thermoregulation is the regulation of body temperature, crucial for maintaining metabolic efficiency.

Behavioural Adaptations

• Changing body position, such as huddling for warmth or stretching out to cool down.

• Seeking shade to avoid overheating or basking in the sun to warm up.

• Nocturnal activity to avoid high daytime temperatures.

• Migration to more favorable climates during seasonal changes.

Structural Adaptations

• Insulation (fur, hair, feathers, blubber) reduces heat loss by trapping air and providing thermal resistance.

• Surface area to volume ratio is important for temperature regulation; smaller animals lose heat more rapidly.

Physiological Adaptations

• Altering metabolic activity to maintain body temperature, such as increasing metabolism during cold exposure.

Mechanisms to Maintain Water Balance in Plants

Reducing Internal Temperature

• Waxy or leathery cuticles prevent water loss by reducing evaporation from the leaf surface.

• White hairs reflect sunlight to reduce temperature, minimizing heat absorption.

Reducing Exposure of Transpiring Structures

• Leaf orientation, such as vertical positioning to reduce direct sunlight exposure.

• Reduced surface area, such as small or compound leaves, to minimize water loss.

• Loss of leaves during dry seasons to prevent transpiration.

Other Adaptations

• Reduced leaf size, reduced flower size, shedding leaves, and leaf orientation to conserve water.

• Regulating stomata opening and closing, controlling gas exchange and water loss.

• Succulents store water in fleshy stems or leaves, providing a water reserve.

• Woody fruits reduce water loss when dispersed, protecting seeds from