b5 homeostasis

• Brain

  • Part of the CNS
  • Made of billions of interconnected neurones
  • Controls complex behaviours eg eating sleeping breathing
• Regions of the brain

  • Cerebral cortex - controls language, intelligence, memory and consciousness
  • Cerebellum - controls muscle coordination
  • Medulla - controls unconscious activities
• Methods to study the brain

  • Studying patients with brain damage - the effect on the damaged part of the brain can tell you about what this part does
  • Electrical stimulation - pushing a small electrode into brain tissue and zapping it
  • Observing electrical stimulation gives an idea of what that certain tissue does
  • MRI scans - produces detailed pictures of the brain and can be used to see which parts of the brain are active during activities eg listening to music
• Issues with studying the brain

  1. Brain is delicate and complex - investigating is difficult
  2. Can physically damage brain
  3. Increased problems with brain function eg difficulties with speech
• The eye = a sense organ that contains receptors sensitive to light intensity and colour
• The eye‘s role is to focus light
• Case study : Phineas Gage

  • An iron rod was driven through his skull
  • Most of the frontal lobe was destroyed
  • Experienced complete personality and behaviour change
  • So it can be inferred that the frontal lobe controls personality
• Structures of the eye

  • Cornea - transparent outer layer that refracts light into the eye
  • Iris - contains muscles that allow it to control pupil diameter (controls amount of light that enters the eye)
  • Pupil - a hole in the middle of the iris
  • Lens - focuses light onto the retina
  • Retina - at the back of the eye, contains receptors which are sensitive to light intensity and colour
• Structures of the eye

  • Ciliary muscles and suspensory ligaments - control size and shape of the lens (help focus on objects)
  • Sclera - tough supporting wall of the eye
  • Optic nerve - a type of sensory neurone that carries EI from receptors on the retina to the brain (helps to form an image)
  • Fovea - specialised region of the retina, produces sharpest vision and greatest colour discrimination
• The iris reflex in bright light

  • Bright light - circular muscles contract and radial relax (CCRR)
  • Protects retina from damage
  • Pupil constricts to allow less light in
• The iris reflex in dim light

  • Dim light - circular muscles relax and radial contract
  • Protects retina from damage
  • Pupil dilates to allow more light in
• Reflex arc in the eye

  • Stimulus = light intensity
  • Receptors found in retina
  • Info about light travels as EI along the optic nerve
  • Brain processes info and creates a response which is sent along the motor neurone
  • Effector = circular and radial muscles in the iris
  • Response = pupil constricts or dilates depending on light intensity
• Iris reflex involves the circular and radial muscles in the iris
• Accommodation involves the ciliary muscles and suspensory ligaments
• Accommodation = changing the shape of the lens to focus on near or far objects
• Looking at near objects

  • Ciliary muscles contract
  • Loosens suspensory ligaments
  • Lens becomes fat and curved
  • Amount of light refracted increases
• Looking at far away objects

  • Ciliary muscles relax
  • Tightens suspensory ligaments
  • Lens becomes thin and narrow
  • Amount of light refracted decreases
• Vision defects - hyperopia (long-sighted)

  • Unable to focus on near objects
  • Images are brought into focus beyond the retina
  • Causes = lens is the wrong shape so doesn’t refract light enough, eyeball is too short
  • Solutions = convex lens (rays converge inwards together)
• Vision defects - myopia (short-sighted)

  • Unable to focus on far away objects
  • Images are brought into focus before the retina
  • Causes = lens is the wrong shape so refracts light too much, eyeball is too long
  • Solutions = concave lens (rays diverge outwards)
• Treatments for vision defects - laser eye surgery

  • Laser is used to vaporise tissue and changes the shape of the cornea
  • Light will now be refracted differently by the cornea
  • + Completely corrects vision - surgeon can precisely take off tissue
  • — Risk of infection
  • — Eye reaction could worsen vision
• Treatment for vision defects - replacement lens surgery

  • Treats long-sightedness
  • Natural lens is removed, replaced with an artificial lens
  • + Corrects long sightedness
  • — Possible retinal damage
  • — Loss of sight
• Treatment for vision defects - contact lenses

  • Lenses that sit on the surface of the eye - compensates for the fault in focusing
  • 2 types - hard and soft
  • + Lightweight
  • + More convenient than glasses
  • + Almost invisible
  • — Soft lenses = risk of eye infections
• Osmoregulation = control of water levels and mineral salts in the blood
• Osmoregulation

  • Protects cells by stopping too much water from entering or leaving them (keeps a balance)
  • If body cells gain or lose too much water by osmosis, they don’t function properly
• Osmoregulation - high water conc in blood and low conc in cell

  • Cells swell and burst
  • Water moves into the cell by osmosis
• Osmoregulation - low water conc in blood and high water conc in cell

  • Cells shrivel up
  • Water moves out of the cell and into the blood by osmosis
• The kidneys

  • Act as a filter to clean the blood
  • Stage 1 (Filtration) - unwanted substances (excess water or ions) and waste products (urea) are filtered out of the blood as it passes through the kidneys
  • Stage 2 (selective reabsorption) - Useful substances like glucose, ions and the right amount of water are absorbed back into the blood
• Filtration in the kidneys

  • Blood passes through the nephron in the kidneys (blood under high pressure which forces small molecules out of the blood, pass into the tubule)
  • Large molecules like blood proteins stay in the blood (too big to fit through capillary wall)
• Selective reabsorption in the kidneys

  • Kidneys selectively reabsorb molecules which are needed
  • All glucose
  • As much water as needed (to keep water levels constant in blood plasma)
  • As many ions needed (to keep mineral ions balanced in blood plasma)
• Formation of urine after selective reabsorption

  • Molecules that aren’t selectively reabsorbed continue along tubule as urine which passes to the bladder
  • Substances = urea, excess water and ions)
• Formation of urea

  1. Proteins are broken down by protease in stomach and SI into amino acids - some stay as excess
  2. Excess amino acids are sent to the liver to be deaminated - amino group is removed and forms ammonia
  3. Ammonia is toxic - converted into urea to make it safer
  4. Urea and water are released from liver and travel to kidneys where blood is filtered
  5. Urea is filtered out of blood, exits body as urine
• Hormones in the kidneys

  • ADH - Anti-diuretic hormone
  • ADH is made in the pituitary gland
  • ADH controls the concentration of urine
• Dialysis

  • The usual treatment for someone with kidney failure
  • Patients are connected to dialysis machine - acts as an artificial kidney
  • Removes urea and helps to maintain water and salt levels of the blood
  • Blood and dialysis fluid move in opposite directions to maintain a conc gradient for diffusion
• Dialysis fluid

  1. Healthy levels of water and ions - to restore normal levels
  2. Healthy levels of glucose
  3. No urea - low conc in fluid to make sure all urea leaves blood during diffusion
• Advantages of dialysis

  • Prolongs the life of someone with kidney failure
  • Allows time to find a donor
  • Temporarily low risk and effective - reduces levels of urea with no need to change glucose, ions or water unless needed
• Disadvantages of dialysis

  • Risk of infection due to needles reentering regularly
  • Not a cure for kidney failure - temporary treatment until transplant is available
  • Time-consuming - patient must go 3 times a week for hours
  • Negatively impacts QOL and finance
  • Risk of blood clots
  • Uncomfortable process
  • Costly to NHS
• Advantages of kidney transplant

  • More permanent treatment
  • Less time-consuming - dont have to spend hours at the dialysis machine
  • Cheaper in the long term - dialysis is costly especially if done regularly
• Disadvantages of kidney transplants

  • Recovery can be hard as its major surgery
  • Risk of infection
  • Risk of anaesthetic reaction
  • Risk of rejection - to prevent this, patients must take immunosupressant drugs which increases risk of disease
  • Long waiting list for suitable donors
• Basic concept of dialysis

  • Unwanted substances will diffuse into the fluid due to a conc gradient
  • Wanted substances will stay in the blood and be returned to the patient
• Tropism = turning and growth in response to a stimulus