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Homeostasis - Coggle Diagram
Homeostasis
Homeostasis:
maintaining a constant internal environment for cells in the body
Internal environment:
conditions inside the body that help cells to optimally function
blood glucose concentration
low glucose concentration:
respiration stops, meaning cells don't have an energy source
high glucose concentration:
water osmoses out of cell, disrupting metabolic reactions
blood pH
low pH:
enzymes cannot function optimally
high pH:
enzymes are denatured
internal temperature
low temperatures:
slow down metabolic reactions
high temperatures:
denature enzymes and other proteins
blood water potential
decreased water potential:
water osmoses out of cells causing metabolic reactions to slow or stop
increased water potential:
water osmoses into cells causing them to swell up and burst
metabolic waste levels
concentration of respiratory gases in blood
Negative feedback mechanism:
when the body detects fluctuations of the internal environment, it initiates reactions to reverse the change and restore the conditions to where they should be
step 1:
the stimulus are detected by receptors (i.e. thermoreceptors for heat, chemoreceptors for pH)
step 2:
the receptors send input to a central control in the CNS (brain or spinal chord)
step 3:
the CNS sends output to effectors, telling them to carry out corrective actions
step 4:
the receptors continue monitoring the factor as it fluctuates around its set point
Positive feedback mechanism:
when the body detects a fluctuation of the internal environment, it initiates reactions to amplify the change
Control of glucose concentration
glucose concentration is maintained by hormones secreted by the islet of Langerhans in the pancreas
insulin is produced by beta cells
glucagon is produced by alpha cells
Increase in glucose concentration
step 1:
blood that contains high glucose levels passes through the pancreas, and the alpha and beta cells detect the imbalance
step 2:
the alpha cells stop secreting glucagon, and the beta cells secrete insulin into the blood plasma
step 3:
the insulin is carried around the body and binds to receptors in the cell surface membranes of cells
step 4:
the insulin signals glucose transporter proteins (GLUT) in the cell to fuse with the cell membrane so that glucose can diffuse into the cell. It also signals the cell to increase the use of glucose in cellular respiration and the rate of glycogenesis
Decrease in glucose concentration
step 1:
blood that is low in glucose passes through the pancreas, and the alpha and beta cells detect the imbalance
step 2:
the beta cells stop producing insulin, and the alpha cells secrete glucagon into the blood plasma
step 3:
the glucagon binds to receptors in the cell membrane if liver cells, which causes a conformational change in the receptor protein that activates a G-protein
step 4:
the G-protein activates the enzyme adenylyl cyclase in the cell membrane, which catalyses the conversion of ATP to cyclic AMP (cAMP)
step 5:
the cAMP is a second messenger that activates protein kinase A enzymes in the cytoplasm, and these enzymes activate phosphorylase kinase enzymes by adding a phosphate to them, and then these activate glycogen phosphorylase enzymes
step 6:
glycogen phosphorylase enzymes catalyse glycogenolysis, which forms glucose that is secreted into the blood to restore the glucose concentration
Control of water content (osmoregulation)
water potential of the blood is controlled by specialised sensory neurones in the hypothalamus called osmoreceptors
decrease in water potential
step 1:
the osmoreceptors detect the decrease in water potential and send nerve impulses along the neurones to the posterior pituitary gland
step 2:
the nerve impulses stimulate the release of ADH (antidiuretic hormone) into the capillary blood to be carried around the body
ADH
ADH targets the collecting ducts of nephrons. It makes the membranes of the collecting ducts more permeable to water
to make the membranes more permeable ADH increases the number of aquaporins in the membranes
step 1:
ADH binds to receptors in the membrane that stimulate the production of cAMP, which leads to a series of enzyme reactions that phosphorylate the aquaporin molecules
step 2:
the vesicles containing the phosphorylated (activated) aquaporin molecules move towards and fuse with the cell membrane, increasing the permeability of the membrane to water
step 3:
water moves out of the fluid in the collecting duct and into the concentrated tissue fluid and blood plasma in the medulla of the kidney