Homeostasis and Feedback Mechanisms

• Maintaining a stable internal environment is essential for animals, regardless of external environmental changes.
• Even small changes in conditions around an animal cell can greatly affect its function, especially enzymes and hormones.
• Animals maintain a steady state around set points.

Homeostasis Explained

• It is the ability to maintain a relatively stable internal state despite external changes through:
  • Structural adaptations
  • Biochemical adaptations
  • Physiological adaptations
  • Behavioral adaptations

Components of a Control System

• Stimulus that creates a change
• Detector/receptor detects environmental changes
• Control center initiates and integrates corrective steps
• Effector carries out corrective mechanisms to bring the system back to normal
• Response

Negative Feedback

• It is the most common control mechanism, that produces an opposite effect when a change occurs.
• It counteracts changes of various properties from their set points.
• For example, with a body temperature that is too high, negative feedback brings it back down towards the set point of 98.6°F / 37.0°C.

Examples of homeostasis

• Blood Glucose level regulation
• Body temperature regulation
• Blood pH regulation
• Osmotic pressure of body fluid
• Concentration of various ions
• Hormone level regulation

Positive Feedback Loops

• Positive feedback loops amplify the initiating stimuli, moving the system away from its starting state, unlike negative feedback loops.
• These are usually found in the processes that needs to be pushed to completion, not when the existing state needs to be maintained.
• An example is childbirth, where the baby's head presses on the cervix, which activates neurons to the brain.

Oxytocin and Childbirth

• Neurons signal the release of oxytocin from the pituitary gland
• Oxytocin causes uterine contractions, increasing pressure on the cervix.
• Release of more oxytocin produced from the pressure that causes even stronger contractions.
• The positive feedback loop continues until the baby is born.

Temperature Regulation

• Temperature significantly constrains animals and requires a balance to maintain function.
• Biochemical activities are sensitive to the temperature.
• Enzymes have optimum temperatures; function is impaired if temperature either rises above or drops below optimum.
• Low temperatures slow metabolic processes and reduce available energy.
• High temperatures imbalance metabolic reactions; and destroy or hamper enzyme activities.

Factors Determining Temperature

• Many variables, including external, internal, and behavioral factors, influence body temperature of an animal.
• Body heat = heat produced + (heat gained – heat lost)
  • Simplified to: Body heat = heat produced + heat transferred

Heat Transfer Mechanisms

• Radiation: Heat transfer by electromagnetic radiation, like the sun, that transfers heat from hotter to colder bodies without direct contact.
• Conduction: Direct heat transfer between two objects that transfers energy from hotter to colder objects.
• Convection: Heat, external or internal, that transfers by movement of gas or liquid, due to density differences.
• Evaporation: Heat of vaporization (liquid → gas)

Other Factors Affecting Body Temperature

• Surface area, temperature difference and heat conduction mechanisms also significantly change body temperature.
• A larger surface area relative to mass increases heat conduction.
• Small organisms gain/lose heat more readily due to their larger surface area to mass ratio.
• If the difference of ambient temperature and body temperature is high, heat transfer is also high.
• High heat conductance leads to a body temperature close to the ambient temperature.
• Fur, feathers, and blubber help to lower the heat conductance

Ectothermy and Endothermy

• Ectothermic and endothermic are also known as: cold-blooded/poikilothermic and warm-blooded/homeothermic, respectively.
• Animals that regulate their body temperature about a set point are called homeotherms.
• Animals using metabolism to generate body heat and maintain their body temperature above the ambient temperature are called endotherms.
• Animals that allow their body temperature to conform to the environment are called poikilotherms.
• Animals with relatively low metabolic rates that conform to the ambient temperature without using metabolism to produce heat are called ectotherms.
• Endotherms tend to have a lower thermal conductivity due to insulating mechanisms.
• Ectotherms tend to have high thermal conductivity and lack insulation.

Adaptations for Temperature Regulation

• Animals will be less active during the day.
• Other adaptations include burrowing, basking, being nocturnal and changing color depending on color of surroundings.
• Additionally: evaporative cooling, muscular activity, and peripheral heat exchanging systems in limbs.

Other Temperature Adaptations

• Non-shivering thermogenesis
• Daily torpor
• Hibernation
• Staying together in herds/flocks
• Body covered with mud
• Thin surfaces in certain areas of the body

Organs Involved in Homeostasis

Regulation of Blood Glucose Levels

• Average person should maintain 80 mg/100ml.
• Less than 50 mg is hypoglycemia, and more than 150 mg is hyperglycemia, both lead to death.
• Above 180 mg, glucose appears in urine, indicating Diabetes Mellitus.
• The pancreas mainly controls blood glucose concentration and It is a paler gray gland, 12 – 15 cm long, situated in the abdominal cavity.
• It consists of a broad head a body and a narrow tail.
  • Its head is in in the curve of the duodenum
  • Its body is behind the stomach

Pancreas Physiology

• The pancreas functions as both an exocrine and endocrine gland.
• The exocrine pancreas consists of many acini-made lobules where the walls contain secretory cells.
• Each lobule has tiny ducts that form the pancreatic duct, which joins the common bile duct just before entering the duodenum.
• Its function is producing pancreatic juice.
• The endocrine pancreas contains specialized cells are called pancreatic islets/ islets of Langerhans throughout the gland.
• The islets lack any ducts and hormones diffuse directly into blood
• The endocrine pancreas secretes the insulin and glucagon hormones.
• Beta (β) and alpha (α) cells produce those

Glucose Regulation

• Blood glucose concentration is mainly controlled by Pancreas which contains endocrine cells -- Beta (β) and alpha (α) cells.
• Beta cells have glucose receptors which detect the fluctuation of glucose levels
• Beta-cells secrete insulin while alpha cells secrete glucogen.
• The two cells are antagonistic and work opposite each other.

Explore the critical reasons why animals maintain homeostasis and the components of homeostatic control systems. Learn about the types of feedback mechanisms involved in maintaining homeostasis. Understand behavioral adaptations that aid in maintaining body temperature.