Module 5

• Homeostasis is the maintenance of the internal environment through physiological control systems.
• Homeostasis keeps blood temperature, pH, glucose and water potential within set limits
• Homeostasis consists of negative and positive feedback loops
• Negative feedback is when the receptor detects a change in the internal environment and opposes the change to maintain the optimum working environment
• Negative feedback involves the nervous system and occasionally hormones
• Positive feedback is when a change in the internal environment is reinforced to trigger a response further from the set limits
• An example of positive feedback is during child birth, the baby's head presses on the cervix which causes oxytocin to be released.
• Ectotherms cannot regulate their internal temperature but can control their temperature by changing their behaviour
• Ectotherms within aquatic organisms do not have to regulate their body temperature as water has high specific latent heat capacity, therefore the temperature would not fluctuate that much
• Endotherms regulate their body temperature through their nervous system
• The peripheral temperature receptors in the skin detect a change in the temperature. This sends an impulse along a sensory neuron to the brain which causes the hypothalamus to coordinate an impulse. This triggers a response by glands in the skin.
• Endotherms sweat to allow heat loss. This is because water has a high specific latent heat capacity, so the water produced evaporates which gives a cooling effect
• Vasodilation increases heat loss by widening the blood vessels due to the muscles contracting to increase the volume and speed of blood flowing to and within the skin.
• Vasoconstriction is used to minimise heat loss by restricting the arterioles nearer to the skin. This causes more blood to flow to the capillaries carrying blood away from the skin.
• Shivering minimises heat loss by contracting and relaxing the muscles. This increases the rate of respiration which produces more heat energy
• Metabolic reactions produce waste products which can be toxic if they are not removed
• The removal of waste products is called excretion
• Carbon dioxide is a waste product formed from respiration; it is excreted from the lungs
• Nitrogenous waste is formed from excess amino acids in the diet. They are broken down from ammonia to urea. Urea is excreted by the kidneys.
• In multicellular organisms, change is triggered by the endocrine or nervous systems.
• Cell signalling involves the communication between the cells through electrical signals carried by the neurons
• Autocrine signalling is where the cell releases signals to stimulate its own receptors
• Negative feedback requires a nervous system to detect the change and an effector to produce a response.
• Liver cells are called hepatocytes
• Liver cells have a large nuclei, mitochondria and a golgi apparatus to enable a high metabolic rate.
• Hepatic vein carries deoxygenated blood away from the liver through the central vein.
• Hepatic artery supplies oxygenated blood to the liver
• Hepatic portal vein transports the bile duct to the gall bladder
• Sinusoids are a type of capillary that connects the central vein to the hepatic artery and the portal vein.
• Hepatocytes break down the toxic substances to the hepatic vein
• Sinusoids contain kupffer cells that break down old red blood cells and removes bacteria.
• Deamination is the removal of amine group from excess amino acids. This forms ammonia and organic acids. Then respiration occurs to produce ATP or the acids are converted to carbs like glycogen.
• Ammonia is converted to urea by the addition of carbon dioxide in the ornithine cycle. The urea is then released by the liver into the blood which is then filtered by the kidney to produce urine.
• Liver is involved in the detoxification process which is the removal of harmful substances like drugs and alcohol
• For example, the liver breaks down alcohol into ethanal which is further broken down into acetic acid.
• The role of kidneys is the excretion of waste products like urea in the form of urine
• Blood enters the kidney through the renal artery, where the blood passes through the capillaries into the cortex of the kidney. The waste products are filtered out of the blood when passing through the capillaries in the process of ultrafiltration
• Selective absorption is where useful substances like glucose is reabsorbed back through the tubules in the medulla.
• Waste products that need to be excreted are passed along the tubules through the ureter to the bladder where it is disposed as urine
• The renal vein passes the filtered blood from the kidneys