Animal Physiology Homeostasis

BIO 2209 - Animal Physiology Homeostasis By: Dr. Dilani K. Hettiarachchi  At the end of the lesson you should be able to: 1. Explain what Homeostasis is and it’s importance to endothermic animals 2. Describe the mechanisms of blood glucose level regulatio...

BIO 2209 - Animal Physiology Homeostasis By: Dr. Dilani K. Hettiarachchi  At the end of the lesson you should be able to: 1. Explain what Homeostasis is and it’s importance to endothermic animals 2. Describe the mechanisms of blood glucose level regulation 3. Discuss different adaptations shown by animals to regulate body temperatures according to their environment  Even a very small change/ fluctuation in the conditions surrounding a cell of an animal can have great effect to its proper function  Especially due to the effect it can have on the enzymes and hormones  Thus it is essential for an animal to have a mechanism to maintain a stable internal environment regardless of the external environment changes  Accordingly they maintain themselves in a steady state, around set points What is Homeostasis? It is the ability to maintain a relatively stable internal state that persists despite changes in the world outside. - To maintain this steady environment;  Structural  Biochemical  Physiological  Behavioural adaptations are involved  Any control system have the following components; 1. Stimulus 2. Detector/receptor – they detect the changes in the environment 3. Control center – initiate and integrate suitable corrective steps 4. Effector – carryout the corrective mechanism to bring the system back to normal 5. Response  Negative feedback mechanism is the most common  When something changes the opposite effect is produced  Homeostasis typically involves negative feedback loops that counteract changes of various properties from their target values, known as set points For example, if your body temperature is too high, a negative feedback loop will act to bring it back down towards the set point, or target value, of 98.6 ∘ F / 37.0 ∘ C if you’re sitting in a cold room and aren’t dressed warmly, the temperature center in the brain will need to trigger responses that help warm you up. The blood flow to your skin decreases, and you might start shivering so that your muscles generate more heat. You may also get goose bumps—so that the hair on your body stands on end and traps a layer of air near your skin—and increase the release of hormones that act to increase heat production.  Examples of negative feedback mechanisms; 1. blood glucose level regulation 2. body temperature regulation 3. blood pH regulation 4. osmotic pressure of body fluid 5. concentration of various ions 6. hormone level regulation  In contrast to negative feedback loops, positive feedback loops amplify their initiating stimuli, in other words, they move the system away from its starting state.  Positive feedback loops are usually found in processes that need to be pushed to completion, not when the existing state needs to be maintained.  A positive feedback loop comes into play during childbirth.  childbirth, the baby's head presses on the cervix—the bottom of the uterus, through which the baby must emerge—and activates neurons to the brain. The neurons send a signal that leads to release of the hormone oxytocin from the pituitary gland. Oxytocin increases uterine contractions, and thus pressure on the cervix. This causes the release of even more oxytocin produces even stronger contractions. This positive feedback loop continues until the baby is born. Temperature regulation - Biochemical activities are sensitive to the temperature of the body. - All enzymes have an optimum temperature - Temperature above or below this optimum temperature enzymes function is impaired - Thus temperature is sever constraint for animals - When temperature drops too low; - metabolic processes are slowed - it reduce the amount of available energy - When the temperature increase; - metabolic reactions become imbalances - enzyme activities will be hampered or destroyed Temperature determining factors - Large number of variables influence the body temperature of an animal - These can be external factors, internal factors and behavioural factors Body heat = heat produced + (heat gained – heat lost) Simply; Body heat = heat produced + heat transferred - There are four mechanisms of heat transfer; 1. Radiation – transfer of heat by electromagnetic radiation such as sun. It does not require direct contact. Heat is transferred from hotter bodies to colder bodies 2. Conduction – direct transfer of heat between two objects. Energy is transferred from hotter objects to colder objects 3. Convection – transfer of heat brought about by movement of gas or liquid. This movement may be external caused (wind) or maybe due to density differences related to heating and cooling 4. Evaporation – heat of vaporization (liquid  gas) - Surface area, temperature difference and heat conduction mechanisms also have an effect on body temperature - Larger the surface area relative to overall mass, greater the conduction of heat - Small organisms have relatively larger surface area for their mass and they gain or lose heat more readily to the surroundings - Heat transfer is high if the difference of ambient temperature and body temperature is high - Animal with high heat conductance tend to have a body temperature close to ambient temperature - Some animals have substances that will help to lower the heat conductance such as fur, feather, and blubber Ectothermy and Endothermy - Other words are;  cold – blooded/poikilothermic ≈ Ectothermic  warm-blooded/ homeothermic ≈ Endothermic - There is a slight difference in the terms but are more similar - Animals that regulate their body temperature about a set point were called homeotherms - Animals that use metabolism to generate body heat and maintain their body temperature above the ambient temperature are called ENDOTHERMS -Those that allow their body temperature to conform to the environment were called poikilotherms - Animals with relatively low metabolic rate that do not use metabolism to produce heat and have a body temperature that conforms to the ambient temperature 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 Adaptation to regulate temperature - Some animals are less active during day time - Shows burrowing /fossorial - Basking - Being nocturnal - Color of the animal - Evaporative cooling - Muscular activities increase - There is a peripheral heat exchanging system in limbs Adaptations to regulate of temperature - Non-shivering thermogenesis - Daily tropor - Hibernation - Staying as a herd/flock - Cover the body with mud - Thin surfaces in certain areas of the body - Etc… Regulation of Blood Glucose levels - Main organ regulating blood glucose is the Pancreas - It is a pale gray gland - 12 – 15 cm long - Situated in the abdominal cavity - Consists of broad head, a body and a narrow tail - Head  lies in the curve of the duodenum - Body  is behind the stomach - Pancreas is both an exocrine and endocrine gland The exocrine pancreas - Consists of large number of lobules made up of acini - Acini walls contain secretory cells - Each lobule have tiny ducts and they together form the pancreatic duct - Just before entering the duodenum the pancreatic duct joins with common bile duct - Function of the exocrine pancreas is producing pancreatic juice The endocrine pancreas - Specialized cells called pancreatic islets/ islets of Langerhans are there - Distributed throughout the gland - Islets have no ducts - Hormones diffuse directly into blood - Endocrine pancreas secrete the hormones insulin and glucagon - Produced by β cells and α cells Regulation of Blood Glucose levels - Range a person should maintain is 80 mg/100ml - Less than 50 mg  Hypoglycemia  can lead to death -More than 150 mg  Hyperglycemia  can lead to death -Above 180 mg  glucose may appear in urine a condition known as Diabetes Mellitus -Blood glucose concentration is mainly controlled by Pancreas -Pancreas contains endocrine cells – β cells and α cells - β cells have glucose receptors which detect the fluctuation of glucose levels - α cells secrete glucogen - β cells secrete insulin - α cells and β cells are antagonistic  work opposite to each other Cross reference: - Filtration in the kidney - Osmoregulation of fishes, amphibians and birds