response and regulation

• Sensitivity is the ability to detect changes in the environment. These changes are called stimuli. Being able to respond to these stimuli helps the organism to survive. Organisms use two ways to respond, nerves or hormones.
• Sensitivity in Animals

  • rapid responses are brought about by nerves
  • it goes in this order stimulus > sense organ > coordinator > effector > response
  • the whole process is very quick and the time taken is called the reaction time
• Nervous system

  The nervous system is the control centre of the body. It consists of two parts

  • the central nervous system (C.N.S)
  • The Peripheral nerves
• The central nervous system

  • the spinal cord, which is protected by the backbone
  • the brain which is protected by the skull
• The Peripheral Nerves

  • These carry messages to the central nervous system. These messages are carried as electrical impulses called nerve impulses.
• The nerve cells

  The nervous system is made of nerve cells called neurones. Neurones transmit an impulse electrically.

  There are three types of neurones :

  1. sensory neurones - these takes messages from the receptors (sense organs) into the CNS
  2. relay neurone - these connect the sensory nerves to motar nerves, they are inside the CNS
  3. motor neurones - these carry impulses from the CNS to the effector (muscles and glands). The junction between two nerve cells is called a synapse. The impulse passes across a synapse as a chamical message.
• The reflex action is :

  • rapid
  • automatic response of the body to a stimulus
  • these are usually protective
• Homeostasis and Hormones

  Homeostasis means keeping the conditions inside the body constant. This is the way the animal is able to regulate its internal conditions by coordinating a response to changes. Homeostatis keeps conditions in animals bodies relatively constant and protected from harmful effects. This is often achieved using hormones which are chemical messengers. They are produced by glands; travel in the blood system to target organs where they have their effect. Humans control their body temperatures, pH, concentrations (e.g water) to allow enzymes to work at their optimum rates.
• Homeostatic processes always follow a sequence of events :

  • there is a normal level
  • the body may deviate from the normal level
  • the body detects this
  • the body uses some form of corrective mechanism to return to normal
  • when the body returns to normal the mechanism is switched off
  • this is called negative feedback
• Skin and temperature control

  • learn the following structures in the skin:
  • hair, erector muscle, sweat gland, sweat pore, sweat duct, blood vessels
• The skin has a number of functions. It acts as a barrier to infection, it has a number of receptor cells in it which detect stimuli, and it helps control our body temperature.
• Skin during hot conditions

  • sweat is produced which uses heat from the body to evaporate
  • hair lies flat. This traps only a thin layer of air, so there is less insulation
  • the blood vessels supplying the surface skin to get wider
  • this brings more warm blood to the surface of the skin
  • this is called vasodilation. More heat lost by radiation
  • no shivering
• Skin during cold conditions

  • little or no sweat produced
  • hair stands erect. This traps a thick layer of air. Air is a good insulator, which helps keep the body warm
  • the blood vessels supplying the surface skin get narrower. This brings less warm blood to the surface of the skin. This is called vasoconstriction. Less heat is lost by radiation
  • shivering occurs. The muscles contracting release heat energy into the body
• Glucose control and diabetes

  • sugar (glucose) is needed in the body as a source of energy. The cells need a constant supply of sugar.
  • but the level needs to be balanced, this is an example of homeostatis.
  • we take in sugar in our diets. It gets absorbed into the blood. Sugar can also be released into the body from glycogen stored in the liver.
  • sugar is used in respiration to release energy, used for movement and warmth.
  • the excess is stored in the liver.
• Diabetes

  • is a condition where we are unable to control blood glucose levels. There are two types of diabetes
  • type 1 diabetes which usually starts during teenage years, this is where the pancreas fails to make insulin. This is not caused by obesity, but is probably genetic. Treatment is by insulin injection.
  • type 2 diabetes is more common in the over 50's and is often linked with obesity. Here the pancreas makes insulin but it does not affect the liver. Treatment is by diet control.
• Diabetics need to balance their glucose intake and the amount of insulin that they inject. To do this they must know how much glucose is in their blood by:

  1. testing their blood glucose level using a blood test meter
  2. testing urine using clinistix or benedicts test. The presence of sugar in the urine indicates diabetes, as sugar is normally reabsorbed in the kidneys, but diabetics have such high glucose levels that not all of the sugar is reabsorbed
• Lifestyle choices

  • can have an effect on our health
• Obesity

  • can result from a combination of an unhealthy diet and a lack of exercise. It can cause heart disease, some cancers, high blood pressure and type 1 diabetes.
• Drug abuse

  • is a use of a drug (in excess) for no medical reason. It can have physical and mental effects on the body. Some drugs cause addiction, if you stop taking the drug unpleasant withdrawal effects occur.
• Examples and effects of drugs

  1. alcohol - slows down body processes and reaction times. Causes liver damage when exposure is prolonged and excessive. Can also lead to diseases of the kidney and stomach
  2. cannabis - dizziness, sickness, panic, hunger, psychological problems
  3. cocaine - addictive, increased heart rate, psychological problems, heart attacks
  4. steroids - build muscle, liver problems, heart disease and strokes, affects fertility and secondary sexual characteristics
  5. heroin - highly addictive, painkiller, slows the body down, psychological problems