Introduction to Homeostasis 

Homeostasis Homeostasis maintaining internal balance in the body organism must keep internal conditions stable even if environment changes also called “dynamic equilibrium” or “steady state” example: body temperature humans: too cold = shiver too warm = sweat lizard: too cold = bask in sun too warm = hide in shade

Regulation How we maintain homeostasis nervous system endocrine system nerve signals control body functions endocrine system hormones chemical signals control body functions

Hormones Why are hormones needed? chemical messages from one body part to cells in other parts of body communication needed to coordinate whole body growth hormones

What do they do? Maintain homeostasis Start a new process Body Temperature Maintain homeostasis blood sugar level temperature control Start a new process growth fetal development sexual development

Homeostasis To maintain a steady state our body uses feedback regulation.

Homeostasis Our bodies contain several kinds of cells all with their own specific functions. For all of them to work cooperatively they require a relatively constant environment. Such things as pH, O2 concentration, glucose and chemical concentrations, and temperature must be maintained within a very narrow range (set points). Specific limits are necessary for survival.

Homeostasis Recall; the ongoing exchange between cells and their surrounding ECF (extra cellular fluid) Nutrients Gases Wastes Heat Cells are always attempting to maintain homeostasis so that they can function optimally.

Homeostasis Our ‘set points’ mark the upper and lower limits of our tolerance for survival. Feedback regulation – a regulatory mechanism whereby a biochemical pathway is regulated by the amount of the product produced by that pathway,

Positive Feedback Positive feedback loops are rare. They are usually associated with disease and abnormal functioning.

General Control System Afferent Carrying toward. Vein = blood toward the heart, Nerve that carries impulses toward the central nervous system Efferent Carrying away. Artery = blood away from the heart, Nerve that carries impulses away from the central nervous system

Positive Feedback Example: Labour (child birth) contraction – disturbance in normal body function they are maintained & prolonged by oxytocin (hormone) hypothalamus (in brain) releases oxytocin as long as the baby’s head is exerting pressure on the birth canal after birth, no pressure, therefore oxytocin is no longer released (slows) and contractions stop

Negative Feedback Response to changed body condition if body is high or low from normal level signal tells body to make changes that will bring body back to normal level once body is back to normal level, signal is turned off

Maintaining homeostasis hormone 1 gland lowers body condition high specific body condition low raises body condition gland Negative Feedback Model hormone 2

Example 1: Blood Sugar Body’s attempt to maintain a balance in glucose level high blood sugar levels stimulate the pancreas to release insulin into the blood, therefore glucose enters body cells & Liver (glycogen) now low blood sugar levels cause release of glucagon (from the pancreas) and glycogen (from the liver), therefore blood sugar levels rise again

Regulation of Blood Sugar Endocrine System Control Feedback Regulation of Blood Sugar islets of Langerhans beta islet cells insulin body cells take up sugar from blood liver stores glycogen reduces appetite pancreas liver high blood sugar level (90mg/100ml) low liver releases glucose triggers hunger pancreas liver islets of Langerhans alpha islet cells glucagon

Thermoregulation Thermoregulation is the maintenance of body temperature within a range that enables cells to function efficiently.

Thermoregulation Invertebrates and most fish, amphibians, and reptiles, are referred to as ectotherms. These animals depend on air temperature to regulate metabolic rates. Some of these animals have adapted specific habits like sunning themselves on rocks or hiding in the shade to help them regulate their temperature.

Thermoregulation Mammals and birds are referred to as endotherms; they are able to maintain a constant body temperature regardless of their surroundings. Endotherms adjust to decreases in environmental temperatures by increasing the rate of cellular respiration to generate heat.

Thermoregulation The hypothalamus is the body’s internal thermostat. The hypothalamus region of the vertebrate’s brain responsible for coordinating many nerve and hormone functions.

Controlling Body Temperature Nervous System Control Feedback Controlling Body Temperature nerve signals hypothalamus sweat dilates surface blood vessels high body temperature (37°C) low hypothalamus constricts surface blood vessels shiver nerve signals

Sending Signals Signals, in response to stimuli, can be sent in 2 different ways Fast – transient – via the nervous system Slow – persistant – via the endocrine system (hormones – chemical signals)

Negative Feedback Negative feedback every time body is high or low from normal level a signal tells the body to make changes that will bring body back body temperature control of blood sugar