Homeostasis

Learning Objective Discuss the importance of homeostasis in mammals, and explain the principles of homeostasis in terms of receptors, effectors and negative feedback.

Think about the following: What happens if ....... Your body loses too much water? You eat a bag of sweets? You get too hot?

Homeostasis Waste products that need to be removed + how Homeostasis means “controlling internal conditions”: Waste products that need to be removed + how CO2 Urea Internal conditions that need controlling + how Temperature Ion content Water content Blood glucose Produced by respiration, removed via lungs Produced by liver breaking down amino acids, removed by kidneys and transferred to bladder Increased by shivering, lost by sweating Increased by eating, lost by sweating + urine Increased by drinking, lost by sweating + urine Increased and decreased by hormones

A Steady State In order to survive, an organism has to be able to keep its internal environment within tolerable limits. The internal environment of a multicellular organism is the tissue fluid bathing the cells. Keeping these conditions constant is called Homeostasis. The features of the environment which affect the functioning of the cell are: temperature, amount of water and amount of glucose. Q) How do you think these conditions affect the functioning of the cell? Write down your ideas.

Temperature Low temperatures slow metabolic reactions, while high temperatures cause denaturation of proteins, including enzymes.

Amount of Water Lack of water in the tissue fluid causes water to be drawn out of cells by osmosis, causing metabolic reactions in the cell to slow or stop, while too much water entering the cell may cause it to swell and burst.

Amount of Glucose Glucose is the fuel for respiration, so lack of it causes respiration to slow or stop, depriving the cell of an energy source, while too much glucose may draw water out of the cell by osmosis.

Negative Feedback Negative feedback is an important type of control that is found in homeostasis. A negative feedback control system responds when conditions change from the ideal or set point and returns conditions to this set point. There is a continuous cycle of events in negative feedback.

Stages in negative feedback

An example An increase in the internal body temperature causes the body to lose more heat; a decrease in body temperature causes the body to generate more heat.

Places where regulation takes place Blood Sugar Concentration – Insulin and Glucagon Osmoregulation – hypothalamus and pituitary gland Temperature regulation - hypothalamus

Task Hot Day Running a Marathon Lazy Day at Home Suggest how your fluid intake and urine output would vary under these different circumstances and why.