Homeostasis & Excretion

• The neuronal system uses neurones to carry signals very rapidly through the body to produce short-term responses
• The hormonal system uses blood carry hormones from endocrine glands to target cell with the specific receptors. This usually produces long-term responses
  • Peptide hormones are made of amino acids and must bind to receptors on the cell surface, activating second messengers which control transcription
  • Steroid hormones are formed from lipids and soluble in the plasma membrane, therefore enetering cells and binding to proteins to enter the nucleus and have an effecr on the DNA

• Homeostasis is the maintenance of a constant internal environment despite internal or external changes 
• Receptors detect a change; coordinators transmit the infomation and effectors bring about a response
• Negative feedback is the body's mechanism for reversing a change so that it returns back to the optimum which causes changes resulting in a even greater deviation from the norm. This is  usually harmful due to the large, unstable change in the body

• Kidney disease hypertension, diabetes, infection or heart disease
• Kidney failure can be assessed by measuring the glomerular filtrate rate, whic is the volume of fluid passing into the nephrons every minute
• One treatment is renal dialysis, which is a mechanism utilised to artificially regualte the concentrations of solutes in the blood
  • Haemodialysis- blood is removed and passed through a machine containing an artifical dialysis membrane, which allows countercurrent sibstance exhange. Heparin stops blood clots
  • Peritoneal dialysis- dialysis fluid is inserted into the abdomen; echange occurs across the peritoneum
• Kideney transplant can treat kidney failure but requires the use of immunosupressants because of the risk of rejection
• Pregnancy tests work by detecting the hormone human chorionic gonadotrophin (hCG) in urine
• Coloured monoclonal antibodies complementary to hCG form a complex. Which moves up the ***** and binds to immonbolised antibodies complementary to hCG resulting in the presence of a blue line, indicating preganancy

• Internal body temperature needs to be regulated to ensure reactions can happen as efficiently as possible without denaturation of proteins
• Ectotherms are organisms that rely on external sources of heat to regulate its body temperature
  • If its too cold, they can move into the sun, move to a warm surface or expose more surface area to the sun
  • If its too hot, they can, move into the shade, move underground or expose less surface area to the sun
• Endotherms are organisms that rely on metabolic reactions to regulate its own body temperature
  • If its too cold, they can shiver, increase their respiration rate, vasoconstrict and erect hairs or feathers
  • If its too hot, they can sweat, pant, vasodilate
• Endotherms can be activein colder habitats however they need more food and use more energy than ectotherms

Amino acid + Oxygen -----------------------> Keto acid + Ammonia

• Osmoregulation is maintaining a constant water potential of the blood, despite changes in the level of water and salt intake
• The kidneys are made of nephrons which help filter the blood. The blood undergoes ultrafiltration at the glomerulus due to the smaller diameter of the efferent arteriole than the afferent arteriole, creating high hydrostatic pressure
• The filtrate passes into the bowman's capsule and travels aorund the entire nephron
  • where ions and water are reaborbed into the blood whilst the remaining filtrate is excreted as urine
• Sodium is actively transported out of the promimal convoluted tubule and into the blood
• Glucose and amino acids are co-transported out of the proximal convoluted tubule via sodium ions diffusing into the epthelial cells

• The hypothalamus contains osmoreceptors which signal to specialised neurosecretory cells. A fall in water potential causes the release of antidiuretic hormone (ADH) from the posterior pituitary gland
• ADH travels in the blood to the kidneys, attaching to ADH receptors, activating the intracellular enzyme phosphorylase. This causes vesicles containing aquaporins to fuse with the plasma membrane, reducing water loss by increasing the permeability of the collecting duct and distal convoluted tubule

• Excretion is the removal of metabolic waste products from the body
• The main waste products are carbon dioxide, bile pigments and nitrogen containing compounds
• Amino acids are deaiminated, so the keto acid can be used in respiration, while the toxic amino group can be ecreted as urea
• The liver has three main blood vessels
  • Hepatic artery- carry oxygenated blood from the heart to the liver
  • Hepatic portal vein- carries deoxygenated blood away from the small intestine to the liver
  • Hepatic vein- carries deoxygenated blood away from the liver towards the heart
• Hepatocytes remove excess substances and wastes, and secrete substances back into the blood to maintain their concentration within it, while it travels down the sinusoids
• Bile travels down the bile canaliculi to the gall bladder
• Kupffer cells are present within the sinsoids to protect the liver from disease and break down red blood cells
• Other liver functions include
  • Glycogen storage
  • Detoxification and detoxification of alcohol
• Excessive alcohol consumption can lead to cirrhosis as NAD is used to detoxify alcohol instead of breaking down fatty acids, which are stored as lipids in hepatocytes