Hemostasis

• Homeostasis


  The tendency of a system, primarily the physiological system of higher animals, to maintain internal stability, owing to the coordinated response of its parts to any situation or stimulus that tends to disturb its normal condition or function
• Homeostasis


  1. Receptors detect changes

  2. Control center processes information

  3. Effectors respond to maintain balance
• Homeostasis


  • Involves negative and positive feedback loops
  • Is a continuous process with no starting or finishing point
• Hormones are made of proteins; glands release them into the bloodstream where they reach target cells
• Positive feedback loop


  Amplifies the change in a system
• Negative feedback loop


  Reacts to reverse the change of direction in a system
• Homeostasis involves the nervous system and endocrine system
• Endotherms


  Mammals and birds that maintain body temperature through internal metabolic activity
• Ectotherms


  Amphibians, reptiles, and fish that rely on external factors to maintain body temperature
• Smaller animals have more surface area relative to body volume, so they must use more energy to maintain constant body temperature
• Behavioral responses to regulate temperature

  • Moving to a different environment
  • Changing body position
  • Changing fur/clothing weight, color, and composition
  • Using shelters like dens, burrows, and nests
• Shivering


  Muscle twitches that produce heat to warm the body
• Raynaud's disease


  Sudden spasms in arteries, particularly in fingers and toes, in response to cold
• Thyroid hormone increases metabolic activity to warm the body in response to cold
• Brown fat cells in infants and small animals are stimulated by the sympathetic nervous system to increase metabolic activity in response to cold
• Core temperature


  The temperature maintained for vital organs within the head and torso
• Hot flashes experienced by women during menopause are caused by disturbances in the body's ability to maintain average core temperature
• Temperature regulation involves a structural hierarchy of activity from the spinal cord to the hypothalamus, with increasing sensitivity to temperature changes at higher levels
• Solute


  Molecules dissolved in a fluid
• Electrolyte


  A solute that breaks into ions and dissolves
• Essential electrolytes


  • Sodium
  • Calcium
  • Potassium
  • Chloride
  • Magnesium
  • Bicarbonate
• Intracellular fluid


  About two-thirds of the body's water found within cells
• Extracellular fluid


  About one-third of the body's water found in the blood supply and interstitial fluid surrounding cells
• Extracellular fluid has higher concentrations of sodium and chloride, while intracellular fluid has higher potassium concentrations
• Isotonic


  Two solutions with equal concentrations of solutes
• Excess sodium and water are removed by the kidneys and excreted as urine
• We lose water through breathing, perspiration, evaporation, and defecation
• Humans need about 2.5 liters of water per day, which can be obtained from both beverages and food
• The sensation of thirst arises when the body's water supply drops
• Kidney filtration


  1. Blood is filtered through nephrons

  2. Impurities and excess water/sodium removed

  3. Filtered blood returns to circulation

  4. Kidney dialysis for kidney failure
• Thirst


  Sensation experienced when body's water supply drops
• Dry mouth is not the critical stimulus for thirst
• Osmotic thirst


  Occurs in response to cellular dehydration and drops in intracellular fluid volume
• Hypovolemic thirst


  Occurs in response to drops in blood volume
• Osmotic thirst is the more common mechanism for thirst
• Eating salty foods


  Increases blood sodium concentration, making blood hypertonic
• Untreated diabetes


  Causes blood to become hypertonic, leading to polydipsia and polyuria
• Hormonal regulation of fluid levels

  1. Osmoreceptors/baroreceptors stimulate pituitary to release ADH

  2. ADH signals kidneys to reduce urine production and release renin

  3. Renin converts angiotensinogen to angiotensin II

  4. Angiotensin II triggers aldosterone release to retain sodium
• Subfornical organ (SFO)


  Responds to angiotensin II, initiates drinking behaviour
• Median preoptic nucleus


  Receives input from SFO and solitary tract nucleus, communicates with lateral hypothalamus to initiate drinking