D3.3 :

• Homeostasis :


  Ability to maintain optimal conditions for suvival & equilibrium.
• Variables maintained by homeostasis in humans :

  Blood pH.

  Internal body temperature.

  Ventilation rate.

  Blood glucose concentration.
• + feedback :


  Mechanism where a system responds to the change in internal/external environment by reversing the direction of the change - maintain homeostasis.
• — feedback :


  Mechanism where a system responds to the change in internal/external environment by amplifying the direction of the change - cascade of events.
• Examples of — feedback :

  Heart rate.

  Blood pH.

  Blood glucose concentration.
• Examples of + feedback :

  Blood clotting triggering further clotting.

  Cancer cells trigger more cancer cells.

  Fruit rippening triggers more fruit around it to rippen.
• — feedback loop pathway :

  Stimulus triggers a receptor to signal the change to the control centre (brain).

  Brain signals to an effector to carry out a response -> creates a response to amplify/reverse the initial signal.
• Systems involved in homeostasis :

  Nervous & Endocrine system work together to ensure homeostasis occurs through signalling.
• Glucose within the body :

  Glucose is monosaccharide -> broken down to produce ATP.

  Carbohydrates are eaten & converted into glucose in digestion -> absorbed into bloodstream via facilitated diffusion.

  Transported within blood to other cells as it’s water-soluble & polar -> pass through membrane.
• Concentration of blood glucose :

  Kept within narrow limits as hypo(low)/hyper(high) glycemia is detrimental.

  Maintained by balancing amount of glucose removed from blood with glucose added to it.

  • Hypoglycemia : Seizure, Coma, Death.
  • Hyperglycemia : Heart disease, Stroke, Kidney damage.
• Organs involved in Blood glucose homeostasis :

  Receptor -> Chemoreceptor proteins in catReceptor -> Chemoreceptor proteins in cat

  Control centre -> Hypothalamus detects changes in blood glucose concentration & triggers release of hormones from pancreas.

  Effectors :

  • Pancreas -> secretes hormones (insulin & glucagon)
  • Liver -> responds to hormones by storing/releasing glucose.
• Pancreas (Blood glucose concentration) :

  In pancrea, islet of Langerhans are endocrine tissues -> produce & secrete hormones.

  Exocrine tissue in pancreas produces enzymes for digestion.
• Blood glucose rises above normal range :

  Typically occur after eating.

  If blood glucose rises -> beta cells secrete insulin -> blood glucose levels fall :

  • Glucose absorbed by body cells -> facilitated diffusion.
  • Glucose enters liver & muscle cells -> convert into glycogen.
  • Glucose enters fat cells -> convert into fats
• Blood glucose falls below normal range :

  Typically occurs when starving.

  If blood glucose falls below normal range -> alpha cells secrete glucagon -> blood glucose levels rise :

  • Stimulates liver/muscle fat cells to hydrolyse glycogen into glucose.
  • Stimulate fat cells to hydrolyse lipids into glucose.
• Type 1 diabetes :

  Autoimmune disease where immune system attacks beta cells of pancreas (inhibits insulin production).

  Typically occurs in children/young adults.

  Treatment : Insulin therapy by monitoring levels.

  Symptoms :

  • Excessive thirst -> compensate fluid loss.
  • High blood glucose.
  • Vaginal yeast infections -> yeast thrive on glucose.
  • Blurriness -> affect lens.
• Type 2 diabetes :

  Body cells no longer responds to insulin as they once did -> insulin resistance.

  Typically occur with older people.

  Due to resistance, beta-cells secrete more insulin.

  Treatment : Reduction in weight & dietary changes or antidiabetic drugs to stimulate insulin production.

  Symptoms :

  • Excessive thirst.
  • Increased hunger -> glucose not effectively used.
  • Bluriness -> affect lens.
• Cause of Type 1 diabetes :

  High blood glucose levels -> no insulin secreted due to no beta cells.

  No insulin -> no activation signal transduction cascade -> glucose-transporter proteins are not activated.

  Glucose transporter channels never activated -> glucose cannot enter cells -> blood glucose levels stay high.
• Cause of Type 2 diabetes :

  High blood glucose levels -> insulin secreted -> insufficient/non-function insulin receptors -> insulin unable to active -> signal transduction to not occur.

  Glucose transporter proteins not activated -> glucose transporter channel not open -> blood glucose levels to be high.
• Risk factors :


  Family history.

  Body weight -> overweight/obesity.

  Lifestyle.

  Diet.

  Age.
• Thermoregulation :

  Process of maintaining a core body temperature despite fluctuations in external temperature by balancing heat generation & loss.

  Has a - feedback loop.
• Ectothermic :


  Internal temperature equalises with environment.
• Endothermic :


  Internal temperature is higher than environment -> excess nutrients.
• Process of thermoregulation :

  Receptor : Thermoreceptors proteins detect changes in temperature -> nerve endings of sensory neurons transmit this to CNS.

  Control centre : Hypothalamus -> senses & responds to changes in body temperature.

  Effectors :

  • Pituitary gland.
  • Thyroid gland.
  • Muscle.
  • Adipose tissue.
  • Blood vessels.
  • Sweat glands.
• Pituitary gland :


  Release hormone (TSH) that stimulate thyroid gland to release thyroxin.
• Thyroid gland :

  Release Thyroxine that changes the basal metabolic rate -> increases.

  Endocrine gland located in the front of the neck.

  2 lobes that sit at the trachea connected by tissue.
• Adipose tissues :

  Fat cells generate heat through uncoupled cellular respiration.
• Blood vessels :


  Vessels constrict/relax to cause less/more blood towards different regions of the body.
• Muscle :


  Causes contraction (shivering - generates heat through cellular respiration).

  Changes to ventilation rate.

  Hair to erect -> causes insulating layer of air to be trapped.
• Sweat glands :

  Activate sweating to cause heat loss -> reduces body temperature as sweat evaporates it causes some heat to be lost.
• Thermoreceptors :


  Ion channel proteins in specific sensory neurons.

  Help detect changes in temperature.

  Change in temperature -> depolarisation -> action potential being generated -> electrical impulse to travel to brain & cause a response.

  Found in skin & core of body.
• Hypothalamus :


  Region in brain recieves information from receptors & compares it to an internal set point.

  Sends nerve impulses to effectors to change the conditions to normal.
• Pituitary glands :


  Hypothalamus communicates to pituitary glands which responds by increasing/decreasing TSH depending on change needed.
• Thyroxine :


  Binds to type II intracellular receptor -> activates genes for higher metabolic rate -> more heat to be produced.
• Brown adipose tissue :

  Located in neck, chest cavity & shoulder regions.

  Contain lots of mitochondria -> Thyroxine increases heat production through uncoupled cellular respiration.
• Shivering :


  Involuntary reflex occuring when body temperature drops.

  Causes skeletal muscle rapidly contracts & relax -> generates heat through hydrolysis of ATP.
• Blood :


  Distributes heat energy through metabolism -> circulation of blood causes it to be absorbed from metabolically active tissue to colder areas.
• Body temperature too hot :


  Thermoreceptors detect the temperature -> Hypothalamus activates response -> blood vessels dilate & sweat glands activate.
• Body temperature too cold :

  Thermoreceptors detect the temperature -> Hypothalamus activates defense -> more heat generated & less heat lost -> blood vessels constrict, shivering activated & metabolism increases.