homeostasis

• Communication is essential for the survival of organisms as they must detect and respond to changes in both their internal and external environments
• In multicellular organisms, changes necessary for survival are triggered by nervous and endocrine systems
• Cell signalling involves communication between cells through electrical signals carried by neurones or hormones
• Neuronal cell signalling is faster and short term, while chemical signalling is slower and long term
• Endocrine signalling is used for long-distance signalling, paracrine signalling occurs between close cells, and autocrine signalling stimulates a cell's own receptors
• Homeostasis maintains a constant internal environment despite external changes, involving factors like temperature, water potential, pH, and blood glucose level
• Negative feedback in homeostasis counteracts changes in internal conditions to restore optimum conditions, involving sensory receptors and effectors
• Positive feedback, less common than negative feedback, increases the original change in conditions, like dilation of the cervix during childbirth
• Ectotherms regulate body temperature with external sources, while endotherms maintain a constant body temperature independently
• Endotherms control body temperature through actions like shivering, sweat production, hair position on skin, and arteriole dilation/constriction
• The liver breaks down excess amino acids through deamination, converting them to ammonia and organic acids
• Ammonia is converted to urea in the ornithine cycle in the liver, then released into the blood and filtered out by the kidneys to produce urine
• The main role of the kidneys is the excretion of waste products, such as urea in the form of urine
• Blood enters the kidney through the renal artery, passes through the capillaries in the cortex, and undergoes ultrafiltration in the glomerulus
• Selective reabsorption occurs in the proximal convoluted tubule, reabsorbing useful substances back into the blood through tubules in the medulla
• Substances to be excreted pass through the tubules, ureter, and bladder to be disposed of as urine, while filtered blood exits the kidneys through the renal vein
• In dehydration, less water is reabsorbed into the blood by osmosis from the loop of Henle, distal convoluted tubule, and collecting duct
• In cases of dehydration, where the water content of blood is too low, less water is reabsorbed into the blood by osmosis from the loop of Henle, the distal convoluted tubule, and collecting duct, leading to the production of more concentrated urine
• Hormones play a crucial role in controlling the reabsorption of water, with osmoreceptors in the hypothalamus detecting low water content in the blood, leading to the release of antidiuretic hormone (ADH) from the posterior pituitary gland to increase water reabsorption from the tubules into the blood
• The balance of the water potential of the blood is maintained through osmoregulation, ensuring that essential processes like respiration of brain cells are maintained
• Blood glucose regulation involves insulin secretion by beta cells in the pancreas to stimulate the conversion of glucose into glycogen or fats for storage and subsequent use for respiration when blood glucose concentration is too high
• Adrenaline triggers physiological changes like pupil dilation, increased heart rate, and increased metabolic rate through the second messenger model, where cAMP acts as a secondary messenger to activate protein kinase A for energy production
• In plants, stomatal aperture is regulated to balance carbon dioxide uptake for photosynthesis and water conservation, with guard cells controlling the opening and closing of stomata by inflating or deflating based on environmental conditions and water potential changes