TOPIC 6

• RECEPTORS IN THE EYE?

  ROD CELLS

  • 120 million per eye, periphery of retina
  • black and white images (cannot distinguish different wavelengths of light)
  • poor visual acuity (clarity)
  • sensitive to low intensity light
  • only one type (rhodopsin)
  • demonstrate retinal convergence, multiple rod cells link to one bipolar cell
  • so more likely to exceed threshold and create a generator potential

  CONE CELLS

  • 6 million per eye, fovea
  • colour images (three types of pigment each receptive to different wavelengths of light)
  • good visual acuity
  • not sensitive to low intensity light (iodopsin)
  • no convergence, one cone cell links to one bipolar cell (separate impulses make easier to differentiate different wavelengths)
  • so less likely to exceed threshold and create a generator potential so only responds to high intensity light
• STRUCTURE OF PACINIAN CORPUSCLE?

  • capsule
  • blood capillary
  • layers of connective tissue with viscous gel between
  • neurone ending
  • neurone
• HEART RATE CONTROL?

  1. Wave of electrical excitation spreads out from SAN across both atria
  2. Atria contract
  3. Atrioventricular septum prevents wave crossing to ventricles
  4. Wave of excitation enters AVN
  5. Short delay
  6. AVN conveys wave of electrical excitation between ventricles along bundle of His
  7. Bundle of His conducts wave through atrioventricular septum to base of ventricles
  8. Bundle branches into smaller fibres of Purkyne tissue
  9. Wave released from tissue
  10. Ventricles contract quickly at same time from bottom
• CHANGING HEART RATE?

  • detect change
  • send impulses to medulla
  • more impulses to SAN
  • by sympathetic/ parasympathetic nervous system
• WHERE ARE DIFFERENT RECEPTORS FOUND?

  CHEMORECEPTORS: carotid artery walls

  BARORECEPTORS: carotid artery/ aorta walls

  OSMORECEPTORS: hypothalamus (posterior pituitary gland)
• REFRACTORY PERIOD?

  • inward movement of Na+ prevented as voltage-gated Na+ channels are closed
  • action potentials propagated in one direction only
  • discrete impulses
  • limits number of action potentials (detect stimulus strength)
• MUSCLE FIBRES?

  SLOW TWITCH

  • contract more slowly
  • less powerful
  • longer period
  • adapted to endurance and aerobic respiration
  • large myoglobin store
  • rich supply of blood vessels
  • numerous mitochondria

  FAST TWITCH

  • contract more rapidly
  • more powerful
  • shorter period
  • adapted to intense exercise and anaerobic respiration
  • thicker
  • more numerous myosin filaments
  • high concentration of glycogen
  • high concentration of enzymes required for anaerobic respiration
  • store of phosphocreatine
• NEUROMUSCULAR JUNCTION VS SYNAPSE?

  • NMJ excitatory, cholinergic excitatory or inhibitory
  • NMJ links neurones to muscles, cholinergic links neurones to neurones/ neurones to effector organs
  • NMJ only involves motor neurones, cholinergic involves motor/ sensory/ relay neurones
  • at NMJ action potential ends, at cholinergic a new action potential may be produced
  • at NMJ acetylcholine binds to receptors on sarcolemma, at cholinergic acetylcholine binds to receptors on post-synaptic membrane
• EVIDENCE OF SLIDING FILAMENT MECHANISM?

  changes occur to sarcomere:

  1. I band becomes narrower
  2. Z lines move closer together (sarcomere shortens)
  3. H zone becomes narrower
  4. A band stays same width
• FEEDBACK?

  NEGATIVE

  • change produced by control system
  • causing change in stimulus detected by receptors
  • turns system off

  POSITIVE

  • deviation from optimum
  • causing change leading to greater deviation from normal
• INSULIN?

  1. Binds to complementary insulin receptor
  2. Activates tyrosine kinase
  3. Stimulates GLUT4 protein vesicles to fuse with cell-surface membrane
  4. Inserted
  5. Glucose in blood enters by facilitated diffusion down concentration gradient
  6. Converted to glycogen via glycogenesis
  7. Stored as lipids
  8. Used in increased respiration
  9. Required to maintain concentration gradient
  10. Blood glucose concentration lowers and returns to normal (negative feedback)
• GLUCAGON?

  1. Binds to complementary glucagon receptor
  2. Activates adenyl cyclase
  3. ATP converted to cAMP
  4. Stimulates phosphorylation of enzymes to activate them, e.g. protein kinase A
  5. Cascade of enzyme reactions
  6. Glycogen converted to glucose via glycogenolysis
  7. Glycerol and AAs converted to glucose via gluconeogenesis
  8. Glucose moves out cell down concentration gradient via facilitated diffusion
  9. Blood glucose concentration increases and returns to normal (negative feedback)
• ADRENALINE?

  1. Binds to complementary adrenaline receptor
  2. Activates adenyl cyclase
  3. ATP converted to cAMP
  4. Stimulates phosphorylation of enzymes to activate them, e.g. protein kinase A
  5. Cascade of enzyme reactions
  6. Glycogen converted to glucose via glycogenolysis
  7. Glucose moves out cell down concentration gradient via facilitated diffusion
  8. Blood glucose concentration increases and returns to normal (negative feedback)
• REGULATING BLOOD GLUCOSE?

  PANCREAS: Islets of Langerhans (hormone-producing cells)

  • alpha = glucagon
  • beta = insulin

  LIVER: hepatocytes

  • glycogenesis
  • glycogenolysis
  • gluconeogenesis
• DIABETES?

  TYPE 1

  • unable to produce insulin
  • immune system attacks beta cells
  • insulin injections

  TYPE 2

  • glycoprotein receptors on body cells lose responsiveness to insulin
  • or inadequate supply of insulin from pancreas
  • regulating carbohydrate intake in diet, match to exercise
  • supplementary insulin injections
• NEPHRON?

  • afferent arteriole into, efferent arteriole out (narrower)
  • cortex: outer region, convoluted tubules and blood vessels (top)
  • medulla: inner region, loop of Henle, collecting ducts, blood vessels (bottom)
• ULTRAFILTRATION?

  PROCESS

  1. Blood enters Bowman's Capsule
  2. Build up of hydrostatic pressure in glomerulus
  3. Water, mineral ions and glucose squeezed out glomerular capillary = glomerular filtrate
  4. RBCs and large proteins too large to pass across into renal capsule

  RESTRICTED BY

  • connective tissue and endothelial cells of blood capillary
  • epithelial cells of renal capsule
  • hydrostatic pressure of fluid in renal capsule space
  • low water potential of blood in glomerulus

  REDUCED BY

  • podocytes (inner layer of renal capsule, highly specialised cells with gaps between them)
  • capillary endothelium (gaps)
• REABSORPTION OF GLUCOSE?

  1. Na+ actively transported out of epithelial cells lining PCT
  2. Concentration gradient
  3. Na+ diffuse down concentration gradient from PCT lumen into epithelial lining cells (facilitated diffusion, co-transporter proteins)
  4. Co-transporters carry glucose/ AAs too into cells of PCT
  5. Diffuse into blood by facilitated diffusion
• LOOP OF HENLE?

  DESCENDING LIMB

  • thin walls
  • permeable to water, not ions

  ASCENDING LIMB

  • thick walls
  • impermeable to water, only ions

  DETAILS

  • countercurrent multiplier
  • opposite directions

  
  

  STAGES

  1. Na+ and Cl- actively transported out ascending limb into interstitial fluid = concentration gradient in medulla
  2. Water cannot move out of ascending limb (impermeable to water)
  3. Water moves out of descending limb via osmosis
  4. Filtrate concentration increases
  5. At base of loop, filtrate it very concentrated so Na+ diffuse out at ascending limb
  6. Filtrate at top of ascending limb is dilute again
  7. Water can be reabsorbed in DCT
  8. Filtrate drains into collecting duct, which flows back through concentrated medulla
• ROLE OF LOOP OF HENLE?

  • create low water potential in medulla
  • so more water can be reabsorbed from fluid in collecting duct
• HOW DO MUSCLES ACT?

  in antagonistic pairs against an incompressible skeleton
• REGIONS OF SARCOMERE?

  • M LINE: middle
  • Z LINES: end of actin
  • A BAND: both actin and myosin
  • H ZONE: just myosin
  • I BAND: just actin
• HOMEOSTASIS?

  involves physiological control systems that maintain the internal environment within restricted limits