Introduction to Homeostasis

• Homeostasis


  process by which organisms maintain a constant internal environment despite external factors

  
• Normal internal environment for humans


  37° Celsius, 0.1% blood sugar, 7.35 blood pH
• Dynamic Equilibrium


  when conditions remain stable within fluctuating limits

  
• Blood sugars when exercising

  decreases because glucose is needed to create ATP for energy
• Blood sugars when eating

  increases, food containing carbohydrates gets broken down into glucose and absorbed into the bloodstream
• Body temperature when exercising


  increases because muscles create heat when exercising
• Body temperature when sleeping


  decreases, core temperature drops during sleep
• Systolic blood pressure during exercise

  increases because the heart needs to beat faster, so blood pressure is higher
• Systolic blood pressure during sleep


  decreases because the body is at rest, so the heart beats less
• blood pH when exercising

  increases, because more CO2 is released, so blood releases bicarbonate ions as a buffer system, which give the blood slightly basic properties
• blood pH when eating

  decreases
• 2 types of feedback loops

  positive and negative

  
• positive feedback loop


  when a system continues to reinforce the change

  
• example of a positive feedback loop


  childbirth, oxytocin is released to create and intensify contractions in the uterus, leading to stronger and continuous contractions and pressure until the child comes out of the uterus. once the baby is released, oxytocin is no longer released

  
• negative feedback loop


  when the system responds to change by bringing the body back within an acceptable range

  
• example of a negative feedback loop

  blood pressure, when blood pressure drops, the medulla sends a nerve signal to the heart to constrict arterioles, leading to the heart rate increasing and blood pressure rising, and the cycle repeats

  
• thermoregulation


  system that maintains body temperature, controlled by hypothalamus which also controls nerve and hormones

  
• What happens when the body has a high internal temperature?

  the hypothalamus sends a signal for sweat glands to produce sweat and for blood vessels on the skin to dilate, these processes releases heat and body temperature decreases

  
• What happens when the body has a low internal temperature?

  the hypothalamus signals muscles to contract (shivering) to produce heat and for blood vessels to constrict to reduce heat loss and blood flow. this leads to an increase in body temperature and warm blood is drawn to the internal organs

  
• water freezing in cells


  sharp ice crystals are formed in the cell, destroying cell membranes, which leads to frostbite
• what happens when cells thaw after freezing?

  water is collected in the cell and it expands until it eventually bursts
• why do some animals not die from being frozen?

  because some have proteins or glucose that act as anti-freeze
• systems involved in homeostasis

  nervous system, endocrine system, muscular system, integumentary system, excretory system, reproductive system

  
• parts of nervous system

  brain, spinal cord, peripheral nerves

  
• parts of endocrine system

  pancreas, adrenal

  
• parts of muscular system

  smooth muscle, skeletal muscle, cardiac muscle

  
• parts of intergumentary system

  skin, sweat glands

  
• parts of excretory system

  kidneys, bladder

  
• parts of reproductive system


  ovaries, testes

  
• water balance in homeostasis


  the body must maintain a constant volume, solute concentration, and temperature of extracellular fluid
• how is balanced in extracellular fluid maintained?

  through osmotic and hydrostatic pressure
• water toxicity


  too much water in the body
• what if extracellular fluids aren't balanced?

  the cells will either rupture or shrivel
• what causes the cell to rupture?


  when the cells lack water and more water is outside of the cell, so water diffuses into the cell which leads it to expand and burst
• what causes the cell to shrivel?

  when there is too much water in the cell, so water diffuses out of the cell which makes it shrivel
• osmoregulation

  actively regulating osmotic pressure of bodily fluids

  
• concentration of water and solutes both inside and outside the cell have to be ______ (fill in the blank)

  balanced
• excretion of waste


  the removal of ions and toxic compounds to maintain homeostasis
• how do lungs eliminate waste?

  CO2 is exhaled

  
• How do intestines eliminate waste?

  eliminates solid waste as feces (digestible byproducts and indigestible material