A2 Level OCR: Communication & Homeostasis

A2 Level OCR: Communication & Homeostasis

1. Hormonal System & Glands

   • Adrenal gland
     • Cortex (Outer)
       • Secretes steroid hormones e.g. glucocorticoids
     • Medulla (Inner)
       • Secretes catecholamine hormones e.g. adrenaline (when stresed)
     • Adrenaline
       • Secreted when blood glucose is low (e.g. when stressed)
       • Increases blood glucose
         • Glucose binds to receptors on cell membranes
           • Activates adenylate cyclase
             • Catalyses production of cyclic AMP inside cells
               • Causes cascade of enzymes, that makes glucose more available to cell
       • Cardiac muscle contracts faster & w/ more force, increasing heart rate
       • Diaphragm & Intercostals contract w/ more force, increasing rate & depth of breathing
       • Vasoconstriction at gut & skin, vasodilation at skeletal muscles, heart and lungs
       • Muscles in broncioles relax, airways widen, deeper breathing
       • Glycogen to glucose
   • Pancreas
     • Islets of Langerhans (endocrine)
       • Control blood glucose
       • Alpha cells secrete glucagon to increase blood glucose
         • Glycogenolysis
         • Gluconeogenesis
           • Glycerol + amino acids
         • Decrease rate of respiration of glucose
       • Beta cells secrete INSULIN
         • Glycogenesis
         • Increase rate of respiration of glucose
         • 1. Increased glucose = Increased ATP inside cell
         • 2. Increased ATP causes K+ channels to close
         • 3. K+ ions build up inside cell membrane. Membrane becomes polarised
         • 4. Ca2+ channels open, and Ca2+ diffuses into cell
         • 5. Vesicles fuse with cell membrane, insulin is secreted by exocytosis
     • Acinar cells (exocrine)
       • Secrete digestive enzymes into pancreatic duct
         • e.g. Amylase breaks down starch
         • Leads to duodenum

2. Control of body temperaure

   • Ectotherms
     • Cold blooded animals e.g. lizards
     • Can't internally control body temperature
     • Bask in sun to increase heat
     • Go to shade/underground to decrease heat
     • Activity level depends on internal temperature (therefore external temperature)
       • More active at high temperature
     • Don't generate much heat
     • Variable metabolic rate
   • Endotherms
     • Warm blooded animals e.g. humans
     • Relatively constant, high metabolic rate
     • Homeostasis used to maintain constant internal temperature
     • TOO HOT
       • Hairs lie flat
       • Vasodilation
         • More heat lost by radiation as more blood flow to skin surface
       • Sweating
         • Heat evaporates off skin
       • Change behaviour (e.g. strip)
     • TOO COLD
       • Shivering
         • Muscles release more energy from glucose, so heat released
       • Vasoconstriction
         • Less heat lost by radiation
       • Hairs become erect
         • Forms insulating layer of air above skin
           • Air is a poor conductor of heat
       • Less sweating
       • Hormones
         • Adrenaline & thyroxine increase metabolism, therefore more heat energy released
     • HYPOTHALAMUS
       • Thermoreceptors in hypothalamus detect internal temp.
       • Peripheral thermoreceptors detect external temp.
       • Receives impulses from sensory neurones, sends impulses to effectors via motor neurones

3. Diabetes

   • Type 1
     • Likely to be inherited
     • Auto-immune disease
     • Immune system attacks Beta cells in pancreas
     • Insulin not produced by body
     • Blood glucose remains high after eating
       • Can cause death if untreated
     • Treatment
       • Regular, controlled injections of insulin
       • Stem cells is a possibilty
   • Type 2
     • Linked w/ obesity
     • Body doesn't produce enough insulin, or cells don't react to insulin
       • Cells don't respond properly to insulin, so cells don't take up glucose
     • Treatment
       • Diet
       • Exercise
       • If diet & exercise not enough, can take glucose lowering tablets
   • GM Insulin
     • More effective than pig insulin, and less likely to be rejected by immune system
     • Cheaper than extracted insulin from pig pancreas
     • Larger quantities can be produced than pig insulin
     • Ethical issues
       • Vegetarians may object to use of animals
       • Some religions object to use of insulin from pigs

4. Control of Heart Rate

   • Rate at which SAN fires is unconciously controlled by cardiovascular centre in Medulla Oblongata
   • Internal stimuli
     • Baroreceptors (in Aorta, vena cava & carotid arteries)
       • Detect blood pressure
     • Chemoreceptors (in aorta, carotid arteries, and MOb.
       • Detect Oxygen level, Carbon dioxide level, & pH
   • High blood pressure
     • 1. Baroreceptors detect high pressure, send impulses to MOb. via sensory neurones
     • 2. MOb. secretes ACh
     • 3. ACh binds to receptors on heart, heart rate DECREASES
   • Low blood Oxygen
     • 1. Chemoreceptors detect stimuli
     • 2. MOb. secretes noradrenaline
     • 3. Noradrenaline binds to receptors on heart, heart rate INCREASES
   • Parasympathetic system
     • Acetylcholine (ACh)
   • Sympathetic system
     • Noradrenaline