Homeostasis and Body Temperature

• Why polar bears and arctic fish don't freeze, the use of saline for IV medications, and why dogs pant on hot days are important questions related to body temperature and homeostasis

Homeostasis

• It is the maintenance of a dynamic equilibrium within the body
• Key variables in an organism's internal environment are maintained within a tolerable range, around a set point
• Examples of these variables are blood glucose levels, water levels, pH, ion concentration, and body temperature

Internal Conditions

• Organisms regulate internal conditions such as:
  • Core body temperature
  • Levels of metabolic waste products like CO2 and N wastes
  • Blood pH
  • Blood glucose concentration
  • Blood osmolarity
  • Blood pressure
• Dogs maintain a body temperature of around 38°C, regardless of the external temperature
• Dogs pant to cool off and maintain homeostasis when their body temperature rises
• Shivering can bring the temperature back up when a dog's body temperature falls

Conformers

• They allow their internal conditions to become similar to that of the external environment
• This has the advantage of lower energy expenditure
• This has the disadvantage of being less functional in certain environments
• Regulation and conformation are on opposite ends of conformity
• Most animals fall somewhere between those two extremes

Importance of Homeostasis

• It maintains stable internal environments to maximize enzyme efficiency
• Affects membrane permeability and how quickly solutes diffuse
• Freezing of water inside a cell can damage tissues

Homeostatic system components

• Sensor detects/senses the variable
• Integrator evaluates incoming sensory data and determines required response to achieve homeostasis.
  • Hypothalamus in mammals
• Effector is the structure/behavior that restores the internal condition

Thermoregulation in Animals

• Effectors change body temperature to return it to the set point
• Blood vessels near the skin dilate, sweat glands are stimulated and respiratory centers are stimulated
• When body temperature is above the set point it produces heat loss
• External stimuli like heat are recorded as temperature by temperature receptors.
  • These receptors are found in the skin, spinal cord, and hypothalamus
• The integrator compares sensor input with the set point to give instructions

Thermoregulation if Cold

• Blood vessels near skin constrict
• Shivering generates heat in muscles
• Chemical signals stimulate increase in cellular respiration and heat production

Heat Transfer

• Conduction is the direct transfer of heat between two bodies in contact
• Convection is a heat exchange between a solid and a moving liquid/gas
• Radiation is a transfer of heat between two not in direct contact
  • The sun radiates heat, so does your body
• Evaporation happens when a liquid becomes a gas, losing heat

Animal Thermoregulation

• Endotherms produce heat
  • Byproduct of chemical reactions that warms the body
• Ectotherms absorb heat
  • Heat comes from the environment
• Homeotherms keep their body heat constant
• Poikilotherms allow their body temperature to rise/fall depending on conditions

Japanese Honeybees

• They exhibit poikilothermy defending from hornets by raising the swarm's temperature to ~117°F
• They produce heat through endothermy

Endotherms vs Ectotherms

• Examples of endotherms are mammals and birds
• Insulation helps to retain heat
• Enzymes are maintained at a constant temperature
• Endotherms can remain active during winter and at night
• The high metabolic rate allows them to sustain high levels of aerobic activity
• Endotherms must consume large quantities of energy-rich food
• Energy used to make heat cannot be used for growth, reproduction, and other processes
• Examples of ectotherms are: amphibians, fish, invertebrates, reptiles
• Ectotherms survive on little food
• Have a greater proportion of energy going to reproduction
• Ectotherms temperature-dependent chemical reactions slow down as body temperature drops
• Molecular activities are slower in cold environments
• Ectotherms areOverall less successful at inhabiting cold environments

Afterwards

• There will be a discussion on osmoregulation in fishes
• There is a reading assignment but no pre-lecture
• The kangaroo activity needs to be completed on Achieve