HOMEOSTASIS How does the body maintain body temperature, blood calcium or glucose levels, or the right amount of water?

Factors in the external environmental may change but body parts function best when internal conditions are maintained within a range Ex: Oxygen levels, glucose levels, pH, temperature Homeostasis - Maintenance of a stable internal environment (around a set point) In general, organ systems participate in a negative FEEDBACK LOOP designed to maintain the status quo of internal environment

3 Components of a feedback system: Receptor: provide information about specific conditions in the internal environment (e.g. body temperature)

3 Components of a feedback system: Control Center – Maintains a “Set Point”: Compare current value to set point value (normal body temp: 37ºC or 98.6ºF); Send message to correct.

3 Components of a feedback system: Effectors: cause responses that alter conditions in the internal environment (always a muscle or a gland – ex: muscles cause shivering/goosebumps or sweat glands release sweat)

Types of Feedback Loops 1) Negative feedback loop: maintains homeostasis! Prevents sudden, severe changes in the body Corrects the set point Causes opposite of bodily disruption to occur, i.e. the ‘negative’ of the disruption Most common type of feedback loop Examples: body temperature, blood pressure & glucose regulation

**Negative feedback maintains HOMEOSTASIS!** Change in internal environment Receptor Set point in Control Center Effectors Oxygen level in blood decreases due to exercise Cells in carotid artery detect levels of oxygen in blood Medulla (in the brain stem) recognizes that oxygen levels are too low Nerve impulses from medulla cause muscles surrounding lungs & diaphragm to contract more often so repiratory rate increases

Types of Feedback Loops 2) Positive feedback loop: (moves body away from homeostasis) Increases (accelerates) the actions of the body short-lived do not require continuous adjustments Examples: blood clotting and child birth

POSITIVE FEEDBACK Heightens or elevates a response Example of childbirth (body needs to achieve a heightened state of exertion… LABOR!) pressure  uterine  more  more  more etc. of baby’s contractions pressure contractions pressure head

A more complex feedback loop example: glucose, insulin, & glucagon You gain glucose through the food that you eat Digest carbohydrates into glucose and other sugars Amount of sugar in blood increases

Two Hormones Regulate Blood Sugar High blood sugar - Insulin (protein) stimulates sugar uptake by cells and converts extra glucose into glycogen (stored in your liver); insulin, therefore, decreases your blood sugar level Like a key that causes the glucose door to open so glucose can leave the blood and enter the cell Low blood sugar - Glucagon (protein) stimulates the conversion of glycogen back into glucose and therefore, raises your blood sugar level

Feedback cycle to control blood glucose levels: body cells & liver cells take up glucose cells secrete insulin blood glucose level drops High glucose level Blood Glucose Level (90 mg/100 mL) blood glucose level rises Low glucose level liver cells break down glycogen & release glucose Cells secrete glucagon

Is insulin/glucagon an example of positive or negative feedback? Homeostasis Video