PHYSIOLOGICAL ADAPTATIONS FOR SURVIVAL
HOMEOSTASIS Homeostasis means staying similar or unchanging and refers to the constant internal environment or steady state of an organism. It also includes the processes by which this internal environment is maintained, usually within narrow limits. When deviations occur within in the internal environment of a healthy organism, mechanisms usually act to restore values to the normal state. Homeostasis is critical to the survival of an organism.
Homeostasis continued A see-saw, a human and a eucalypt forest are all examples of homeostasis. See-saw: : If a child jumps on a see-saw, one side of it will rise and the other will fall but when he/ she jumps off again, it will return to its balanced position. Eucalypt forest: : A bushfire may devastate a eucalypt forest but 1 year later the forest will be on the way to its former balanced (steady) state.
Homeostasis continued 3. Human: : The human body is capable of maintaining a constant internal environment whatever the external environment. Eg. Blood sugar remains close to 90mg/ 100ml blood, body temp is approx 37 degrees Celcius and blood ph must be within the range 7.38-7.42. Refer to Table 10.1, page 300 of text for other examples of major variables that are subject to homeostasis in humans.
Homeostasis continued Various mechanisms (called feedback mechanisms) ) monitor conditions inside the body and when change is detected, body systems react to restore the balance. Consider the example of a self-regulating non- living system such a laboratory water bath. The required temp is set on a thermostat Water bath is switched on. a sensitive thermometer (detection system) detects changes in the temp of the water and sends info or feedback (current temp) to the thermostat (control centre) In the thermostat, the temp is compared with the set temp. It then activates the water heater (a regulating device) so that the required temp is achieved.
Homeostasis continued If the temp is LESS than the set temp, the thermostat switches ON the water heater. If the temp is GREATER than the set temp, the thermostat switches OFF the water heater. All the time the thermometer is sampling and relaying information (feedback) to the control centre.
Homeostasis continued Therefore, the essential parts of a non-living self- regulating system are: A system in which a set value must be maintained A detector device, which sends feedback to a control centre A control centre,, which responds to the feedback A regulator,, which is operated by the control centre to correct any deviations from the set value. Deviations from the set value activate the system, which then returns the original conditions
Homeostasis continued How homeostasis in living systems resembles a non- living self-regulating system is as follows: The maintenance of homeostasis involves a receptor, control centre and an effector to keep the set point or desired value relatively constant. The receptor (or detector) is constantly monitoring the internal environment, which may reflect the external environment. The control centre monitors the information passed on from the receptor and compares it with the set point. The effector ( or regulator) carries a message from the control centre, which restores the set point to its desired value. Homeostasis is a dynamic state that is constantly responding to environmental changes by maintaining a narrow range of desired values in some metabolic variable (such as body temp).
Homeostasis continued In the human organism (as an example), cells form tissues and systems (except reproductive) that play an essential role in homeostasis. The endocrine (hormonal) and nervous systems are the major systems responsible for the control and coordination of homeostasis. In addition, various types of behaviour contribute to the maintenance of homeostasis.
NERVOUS SYSTEM STRUCTURE OF THE NERVOUS SYSTEM The nervous system is made up of the central nervous system (CNS) which comprises the brain and spinal cord,, and the peripheral nervous system (PNS) which is composed of all the nerve cells that connect the CNS to the rest of the body.
Nervous system continued Parts of the Neuron (nerve cell) Dendrite group of fine branches that receive messages from receptors and other neurons and convey nerve signals to the cell. Cell body contains a nucleus which supplies energy and nutrients for the activity of the nueron Axon a long structure through which the nerve (electrical) impulses pass from the cell body. There are axon branches at the end of each axon. Myelin sheath an electrically insulated substance covering the axon. Many neurons joined end-to-end form a nerve.
Label the parts of this neuron and indicate the direction of impulse
AXON Nervous system continued DENDRITE Take info away from the cell body Smooth surface Generally only 1 axon per cell No ribosomes Usually has myelin sheath Branch further from the cell body Bring info to the cell body Rough surface (dendrite spines) Usually many dendrites per cell Have ribosomes No myelin sheath Branch near the cell body
Nervous system continued Types of Neurons Affector (sensory) neurons may have one or more receptors that detect change in either the external or internal environment. Information detected is transmitted as an electrical impulse to the CNS by the affector neuron. Effector (motor) neurons carry impulses away from the CNS to muscle cells or glands and cause them to respond. Connecting (interneuron) neurons are typically located in the CNS and link sensory and effector neurons.
Copy and label the diagram of neurons interconnecting on page 302 of text. Indicate direction of electrical impulse.
Nervous system continued REFLEX ARC Some of the body s reactions are very fast and we have no time to think about them. WHY?? Such reactions are known as reflex arcs. The example given below is when the hand is quickly retracted after touching something hot.
ENDOCRINE SYSTEM The hormonal (endocrine) system is the other major controlling system in the body. It produces hormones hat help maintain homeostasis. Hormones are chemical messages produced in special structures called endocrine glands Also called ductless glands because they are secreted directly into bloodstream. They are transported around to other parts of the body through the bloodstream and act on other organs and tissues.
HYPOTHALAMUS As a control centre for homeostasis, the hypothalamus has the following features: A change in the external or internal envts is detected by receptor cells. Receptors are connected to neurons which relay the change to the hypothalamus. The hypothalamus controls regulatory organ/s or endocrine glands the restores the original set value within a limited range
HOMEOSTASIS Homeostasis is maintained by feedback mechanisms. Negative feedback acts to counteract any changes in the cell or tissue. Positive feedback operates by re- enforcing the changes in the cell or tissue environment.