B5 Homeostasis and Response

• Homeostasis

  The maintenance of a constant internal environment
• Homeostasis - in the human body, these include control of

  • blood glucose concentration
  • body temperature
  • water levels
• Coordination centre

  A coordination centre (Brain) controls the internal environment by monitoring it and providing a response
• Stimulus

  • A stimulus is detected by a receptor
  • Information is processed by a central coordinator
  • Muscles and glands are called effectors and they bring about a response
• Nerve Pathway

  1. Stimulus (environmental change)
  2. Receptor (retinas in eyes)
  3. sensory neurone
  4. CNS (coordination centre)
  5. motor neurone
  6. effector (muscles, glands)
  7. response
• Sensory Neuron

  A) Dendron

  B) Receptor cells

  C) Cell body

  D) Axon

  
• Relay Neuron

  A) Dendrites

  B) Cell Body

  C) Axon

  
• Motor Neuron

  A) Dendrites

  B) Cell Body

  C) Myelin Sheath

  D) Axon

  E) Effector Cells

  
• Axon 


  The part of the cell that carries the impulse
• Response


  An action that happens due to a stimulus
• Sense Organ 


  An organ containing receptor cells
• Stimulus

  An external factor that is detected by receptors
• Reflexes are:

  • Fast
  • Automatic
  • Protective
  • Responses to stimulus

  They use the same nerve pathway but with the relay neurons in the CNS (no conscious thought)
• The Knee jerk

  • Ask the subject to sit on a stool and to cross their legs. Gently but firmly tap the subject just below the knee cap with the side of the hand. Observe the movement
  • Stimulus: contact with knee
  • Body's response: leg moving forward
  • Importance: protects muscle from overstretching
• The blink

  • Ask the subject to sit on a stool in a relaxed posture. Wave your hand in front of the face of the subject and note the response. (Be mindful of the subject's safety)
  • Stimulus: hand waving
  • Body's response: flinching and blinking
  • Importance: protects eye from potential danger
• Pupil response to light

  • Ask the subject to sit on a stool. Make a note or drawing of the relative size of the iris and pupil in the subject's eye. Shine a light towards the face, but not directly at the face. Observe the changes to the size of the pupil of the eye
  • Stimulus: light increased
  • Body's response: pupil gets smaller
  • Importance: protects retina/eye from excess light
• Pupil response to dark

  • Ask the subject to sit on a stool. Make a note or drawing of the relative size of the iris and pupil in the subject's eye. The subject covers their eyes for about 3-5 minutes. Immediately after they remove their eye cover, observe the changes to the size of the pupil of the eye
  • Stimulus: reduced light
  • Body's response: muscles cause the iris to get smaller, pupils dilate
  • Importance: allows more light to enter the eye, allowing the subject to see in poor light
• Ankle jerk reflex

  • Ask the subject to sit on a stool, and to cross their legs. Ask them to flex the elevated foot towards their shin. Then gently and firmly tap the Achilles tendon on the back of the ankle with your hand. Observe the movement.
  • Stimulus: tap on Achilles tendon, stretching muscle/tendon
  • Body's response: muscle contracts, extending foot
  • Importance: protects calf muscle from overstretching
• Synapse

  • A Synapse is a gap between 2 neurones
  • The electrical impulse passes along the first neurone.
  • When it reaches the pre-synaptic knob (the end of the neurone), it stimulates vesicles of neurotransmitter to move and fuse with the membrane
  • The neurotransmitter is released into the synapse and diffused across.
  • It binds to receptors on the second neurone and triggers a new electrical impulse

  
• Endocrine system

  • The endocrine system is composed of glands which secrete chemicals called hormones directly into the bloodstream.
  • The blood carries the hormones to a target organ where it produces an effect

  A) Pituitary gland

  B) Thyroid gland

  C) Pancreas

  D) Adrenal glands

  E) Testes

  F) Ovaries

  
• Pituitary gland

  • It secretes several hormones which trigger other glands to make other hormones
  • TSH: stimulates the thyroid gland
  • FSH: stimulates the ovary to make oestrogen or the testes to make testosterone
• Blood sugar level rises

  1. Stimulus: Blood glucose level rises above the norm.
  2. Detected by specific cells in the Pancreas
  3. Which triggers the release of insulin from the pancreas
  4. Insulin causes: Cells to increase their uptake of Glucose, Increased enzyme activity causing excess glucose to be stored as glycogen in the liver and muscles
  5. This all causes the blood glucose levels to decrease
  6. Which is detected and the pancreas stops making insulin. Negative Feedback control
• Blood sugar level lowers

  1. Stimulus: Blood glucose level falls below the set point
  2. Detected by specific cells in the pancreas
  3. Which triggers the release of glucagon from the pancreas
  4. Glucagon causes: Increased enzyme activity causing glycogen to be broken down into glucose
  5. This all causes the blood glucose levels to rise
  6. Which is detected and the pancreas stops making glucagon. Negative feedback control
• Type 1 diabetes

  • Cause: usually genetics
  • The pancreas fails to produce enough insulin
  • Treatment: Inject with insulin, dose depends on diet
• Type 2 diabetes

  • Causes: eating a high sugar diet, obesity, lack of exercise
  • The pancreas makes insulin but the cells don't respond to it
  • Treatment: control diet
• Adrenaline

  • Responding to stress: fight or flight
  • Increased heart rate, breathing rate
  • More Oxygen supplied to muscles, increased respiration, increased energy
• When we get too hot:

  • Sweat glands in the skin release more sweat. The sweat evaporates, transferring heat energy from the skin to the environment.
  • Blood vessels leading to the skin capillaries become wider - they dilate - allowing more blood to flow through the skin, and more heat to be lost to the environment. This is called vasodilation.
• When we get too cold:

  • Skeletal muscles contract rapidly and we shiver. These contractions need energy from respiration, and some of this is released as heat. Blood vessels become narrower, constrict which allows less blood to flow through the skin and conserve the core body temperature. (Vasoconstriction)
  • The hairs lie flat when we are warm, and rise when we are cold.
  • If we are too cold nerve impulses are sent to the hair erector muscles which contract. This raises the skin hairs and traps a layer of insulating air next to the skin.
• Negative feedback

  • Negative feedback systems work to maintain a constant state
  • If a factor in the environment changes, the system changes to reduce this back to normal
  • If a factor decreases, system changes this back to normal
• FSH (Follicle stimulating hormone)

  • Causes the egg to ripen
  • Triggers Oestrogen release
• Oestrogen

  • Causes the uterus lining to thicken
  • Triggers LH release
• LH (Luteinizing Hormone)

  • Causes ovulation (release of the egg)
  • Triggers progesterone
• Progesterone

  • Maintains the lining
  • Inhibits the pituitary gland hormones
• • Day 1: Period, where the lining of the uterus is lost
  • Day 4: the lining of the uterus starts to thicken again
  • Day 14: ovulation, an egg is released from one ovary
  • Day 28: when the lining of the uterus is maintained
• IVF

  • Give the woman FSH and LH to allow superovulation (several eggs to be released)
  • Collect the eggs
  • Mixed in a petri dish with sperm from the father
  • Fertilised eggs developed into embryos
  • When they are tiny balls of cells, embryos are inserted into the mother's uterus
• Motor neurone

  (electrical insulation restricts impulses to a single axon)

  A) Dendrites

  B) Cell body

  C) Myelin sheath

  D) Axon

  E) Effector Cells