Urinary system

• When analysing markets, a range of assumptions are made about the rationality of economic agents involved in the transactions
• The Wealth of Nations was written


  1776
• Rational


  (in classical economic theory) economic agents are able to consider the outcome of their choices and recognise the net benefits of each one
• Producers act rationally by


  Selling goods/services in a way that maximises their profits
• Workers act rationally by


  Balancing welfare at work with consideration of both pay and benefits
• Rationality in classical economic theory is a flawed assumption as people usually don't act rationally
• Marginal utility


  The additional utility (satisfaction) gained from the consumption of an additional product
• If you add up marginal utility for each unit you get total utility
• The key molecules that are required to build structures that enable organisms to function are: Carbohydrates, Proteins, Lipids, Nucleic Acids, Water
• Monomers


  Smaller units from which larger molecules are made
• Polymers


  Molecules made from a large number of monomers joined together in a chain
• Synthetic polymers


  • nylon, polyethylene, polyester, Teflon, epoxy
• Enzyme catalysis


  1. Substrate binding

  2. Transition state facilitation

  3. Catalysis

  4. Release
• Enzymes


  • They increase the rate of chemical reactions without themselves being consumed or permanently altered by the reaction
  • They increase reaction rates without altering the chemical equilibrium between reactants and products
• As temperature increases


  The rate of reaction increases
• The urinary system filters blood and excretes toxic metabolic wastes
• The urinary system regulates blood volume, pressure, and osmolarity
• The urinary system regulates electrolytes and acid-base balance
• The urinary system secretes erythropoietin, which stimulates the production of red blood cells
• The urinary system helps regulate calcium levels by participating in calcitriol synthesis
• The urinary system clears hormones from blood and detoxifies free radicals
• In starvation, the urinary system can synthesize glucose from amino acids
• Nitrogenous wastes


  • Urea
  • Uric acid
  • Creatinine
• Blood urea nitrogen (BUN)


  Level of nitrogenous waste in blood
• Azotemia is elevated BUN
• Uremia is a syndrome of diarrhea, vomiting, dyspnea, and cardiac arrhythmia stemming from the toxicity of nitrogenous waste, treated by hemodialysis or organ transplant
• Excretion is the process of separating and eliminating wastes from body fluids
• Body systems that carry out excretion

  • Respiratory system
  • Integumentary system
  • Digestive system
  • Urinary system
• The urinary system excretes many metabolic wastes, toxins, drugs, hormones, salts, and water
• The ureters are about 25 cm long and enter the bladder inferiorly, with a flap of mucosa acting as a valve to prevent urine from backing into the ureters
• The ureters


  • They have 3 layers: mucosa, muscularis, and adventitia, with the lumen containing transitional epithelium
  • They have peristaltic waves, not gravity, to move urine
• Urinary bladder


  A hollow, distensible organ that is collapsed when empty and spherical when full
• The bladder capacity is 700-800 mL
• The discharge of urine is called micturition
• When the bladder volume reaches 200-400 mL, stretch receptors signal the micturition center in the sacral spinal cord
• Urinary bladder


  • The inner mucosa is lined with transitional epithelium
  • The muscularis has three layers of smooth muscle
  • Sphincters control entry from the ureters and exit at the urethra
• The involuntary micturition reflex is controlled by the autonomic nervous system
• Involuntary micturition reflex


  1. Stretch receptors detect bladder filling and transmit afferent signals to the spinal cord

  2. Signals return to the bladder from spinal cord segments S2 and S3 via parasympathetic fibers in the pelvic nerve

  3. Efferent signals excite the detrusor muscle

  4. Efferent signals relax the internal urethral sphincter, causing urine to be involuntarily voided if not inhibited by the brain
• Voluntary control of micturition

  1. The micturition center in the pons receives signals from stretch receptors

  2. If timely to urinate, the pons returns signals to spinal interneurons that excite the detrusor and relax the internal urethral sphincter, causing urine to be voided

  3. If untimely to urinate, signals from the cerebrum excite spinal interneurons that keep the external urethral sphincter contracted, retaining urine in the bladder

  4. If timely to urinate, signals from the cerebrum inhibit sacral neurons that keep the external sphincter closed, allowing it to relax and urine to be voided
• The kidney has three main parts: the cortex, medulla, and pelvis