5.1 communication and homeostasis

• Communication is essential for the survival of organisms as they must detect and respond to changes in their internal and external environments
• In multicellular organisms, changes necessary for survival are triggered by the nervous and endocrine systems
• Cell signalling involves communication between cells through electrical signals carried by neurones or with the help of hormones
• Neuronal cell signalling is faster and short term, while chemical signalling is slower and long term
• Endocrine signalling can be used for long-distance signalling, carried by the circulatory system
• Examples of signalling include paracrine signalling between cells in close proximity and autocrine signalling where a cell releases signals to stimulate its own receptors
• Homeostasis ensures a constant internal environment despite changes in the external environment
• Homeostasis is maintained through negative feedback which counteracts changes in internal conditions
• Elements needed for negative feedback pathway: sensory receptors to detect changes, effectors like muscles and glands for response
• Positive feedback increases the original change in conditions, an example is dilation of the cervix during childbirth
• Ectotherms regulate body temperature with external sources, while endotherms maintain a constant body temperature
• Endotherms control body temperature through physiological or behavioural responses like shivering, sweat production, and changes in hair position
• Excretion is important to remove waste products like carbon dioxide or ammonia produced during metabolism
• The liver plays a crucial role in excretion by breaking down harmful substances and converting them into less harmful forms
• Liver lobules are composed of hepatocytes connected to the hepatic vein, hepatic artery, hepatic portal vein, and bile duct
• Liver detoxifies harmful substances like drugs and alcohol by breaking them down into less harmful forms
• Kidneys excrete waste products like urea in the form of urine
• Ultrafiltration in the kidneys involves the Glomerulus, Bowman’s Capsule, and selective passage of molecules through barriers
• Selective reabsorption in the proximal convoluted tubule reabsorbs glucose, amino acids, water, and salts back into the body
• Loop of Henle produces a low water potential in the medulla of the kidney through countercurrent multiplication
• Control of water potential in the blood involves osmoreceptors in the hypothalamus and release of antidiuretic hormone to increase water reabsorption
• Kidney failure can be caused by infections, high blood pressure, and can lead to toxic waste build-up and fluid accumulation
• Kidney failure can be treated with renal dialysis or kidney transplant as a long-term solution
• Haemodialysis and Peritoneal dialysis are two types of dialysis used to filter blood and remove waste products
• Kidney transplant is required to replace a damaged kidney and reverse kidney failure symptoms, matching blood and tissue types to minimize rejection risk
• Immunosuppressants are still required by patients to prevent rejection
• Patients may need to wait for a suitable donor with the same blood type and tissue type to minimize the risk of rejection
• In most cases, a family member is the donor due to the degree of similarity
• Urine samples can be used for diagnostic tests such as pregnancy testing using monoclonal antibodies to detect human chorionic gonadotropin
• Only one kidney is required for survival
• Urine samples can also be used to test for the presence of anabolic steroids
• Anabolic steroids are used to build muscle mass and are banned due to their dangerous side effects
• Detection of steroids in urine is done via gas chromatography
• Neurones play an important role in coordinating communication within the nervous system
• All neurones have a similar structure with a cell body containing the nucleus and organelles such as mitochondria
• Neurones have extensions called dendrites and axons
• There are three types of neurones: sensory, motor, and relay
• Motor neurones transmit electrical impulses from the central nervous system to muscles and glands
• Sensory neurones transmit impulses from receptors to the central nervous system
• Relay neurones are located within the central nervous system and transmit impulses from sensory neurones to motor neurones