Homeostasis & Feedback all images generated by Microsoft Clip Art Gallery

What is homeostasis? Process that occurs in all living things All organ systems work together to achieve homeostasis Ability of an organism to maintain its internal environment, despite changes to its internal or external environment Life Sciences-HHMI Outreach. Copyright 2009 President and Fellows of Harvard College. http://en.wikipedia.org/wiki/File:Tightrope_artist_Cologne_1.jpg all images generated by Microsoft Clip Art Gallery

How does homeostasis work? Feedback pathways A cellular relay race! Specific organs and structures must communicate with each other in response to changes in the body Keeps levels of certain processes within a normal range http://en.wikipedia.org/wiki/File:Southern_12_stage-02_1988.jpg all images generated by Microsoft Clip Art Gallery

What things in your body need to be kept within a range? Body Temperature Blood pressure Blood pH O2 and CO2 concentration Osmoregulation-Water balance Blood glucose Ion levels Hormone levels all images generated by Microsoft Clip Art Gallery

Cellular Relay Race Stimulus Receptor Integrating center Effector Response Reverses the stimulus all images generated by Microsoft Clip Art Gallery

Feedback Loops: Types Negative feedback loop Positive feedback loop original stimulus reversed most feedback systems in the body are negative used for conditions that need frequent adjustment Positive feedback loop original stimulus intensified/amplified seen during normal childbirth

Negative Feedback Loop

Homeostasis – Negative Feedback Loop Blood glucose concentrations rise after a sugary meal (the stimulus), the hormone insulin is released and it speeds up the transport of glucose out of the blood and into selected tissues (the response), so blood glucose concentrations decrease (thus decreasing the original stimulus).

Homeostasis of Blood Pressure Baroreceptors in walls of blood vessels detect an increase in BP Brain receives input and signals blood vessels and heart Blood vessels dilate, HR decreases BP decreases

Thermoregulation (Regulation of Body Temperature) Ectothermy (cold-blooded animals) body temperatures vary with that of the environment e.g. reptiles, fish, amphibians Endothermy(warm-blooded animals) keep body temperature constant even in winter by increasing metabolic rate e.g. birds, mammals

Ectotherm vs Endotherm

Advantages Disadvantages Endothermy Maintains stable body temp Cooling & heating the body cooling and heating the body high levels of aerobic metabolism sustains vigorous activity for much longer than ectotherms Long distance running Flight Disadvantages Greater food consumption to meet metabolic needs Human metabolic mate at 200C & at rest 1,300 to 1,800 kcal per day. American alligator metabolic rate at 200C & at rest 60 kcal per day at 200C.

Mechanisms for thermoregulation Insulation Fur Hair Feathers Fat Blubber Evaporative cooling sweating, panting, bathing Shivering Nonshivering thermogenesis & brown fat Circulation adaptations Countercurrent exchange Vasodilatation (cooling) Vasoconstriction (heat conservation) Behavioral responses

Regulating Body Temp in Humans

Some ectotherms that experience subzero body temperatures protect themselves by producing “antifreeze” compounds (cryoprotectants) that prevent ice formation in the cells. In cold climates, cryoprotectants in the body fluids let overwintering ectotherms, such as some frogs and many arthropods and their eggs, withstand body temperatures considerably below zero. Cyroprotectants are also found in some Arctic and Antarctic fishes, where temperatures can drop below the freezing point of unprotected body fluids (about -0.7oC).

Cells can often make rapid adjustments to temperature changes. For example, marked increases in temperature or other sources of stress induce cells grown in culture to produce stress-induced proteins, including heat-shock proteins, within minutes. These molecules help maintain the integrity of other proteins that would be denatured by severe heat. These proteins are also produced in bacteria, yeast, and plants cells, as well as other animals. These help prevent cell death when an organism is challenged by severe changes in the cellular environment.

Positive Feedback during Childbirth Stretch receptors in walls of uterus send signals to the brain Brain induces release of hormone (oxytocin) into bloodstream Uterine smooth muscle contracts more forcefully More stretch, more hormone, more contraction etc. Cycle ends with birth of the baby & decrease in stretch

Lactation in Mammals Suckling by an infant stimulates sensory neurons in the nipples, generating signals in the nervous system that trigger the release of the neurohormone oxytocin In response to the oxytocin, the mammary gland secrete milk. Milk release leads to more suckling and more stimulation.

Role of Body Systems in Homeostasis

Control of Homeostasis Homeostasis is continually being disrupted by External stimuli heat, cold, lack of oxygen, pathogens, toxins Internal stimuli Body temperature Blood pressure Concentration of water, glucose, salts, oxygen, etc. Physical and psychological distresses Disruptions can be mild to severe If homeostasis is not maintained, death may result

Alteration in the mechanisms of feedback often results in deleterious consequences Diabetes mellitus Response to decreased insulin Cannot absorb glucose out of the blood Dehydration Response to decreased antidiuretic hormone (ADH) Grave’s disease (hyperthyroidism) imbalance of metabolism caused by overproduction of thyroid hormone which control the way that every cell in the body uses energy (metabolism). Blood clotting

Life Sciences-HHMI Outreach Life Sciences-HHMI Outreach. Copyright 2009 President and Fellows of Harvard College.

Plant responses to water limitations When plants under water stress, they close their stomata and decrease their transpiration rates (water loss that occurs when stomata open to get carbon dioxide for photosynthesis) Life Sciences-HHMI Outreach. Copyright 2009 President and Fellows of Harvard College.

Operons in gene regulation An operon is a cluster of coordinately regulated genes.  It includes structural genes(generally encoding enzymes), regulatory genes(encoding, e.g. activators or repressors) and regulatory sites(such as promoters and operators).

Ripening of Fruit First fruit that starts to ripen releases ethylene gas that stimulates other fruits to ripen and create more ethylene gas