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What is homeostasis? It’s all about balance …

What is homeostasis? It’s all about balance …. Homeostasis defined:. The ability to maintain a relatively stable and balanced internal environment including when the external environment is changing. Homeostasis comes from the Greek and means “ staying the same ”.

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What is homeostasis? It’s all about balance …

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  1. What is homeostasis?It’s all about balance…

  2. Homeostasis defined: The ability to maintain a relatively stable and balanced internal environment including when the external environment is changing. Homeostasis comes from the Greek and means “staying the same”.

  3. The “Goldilocks principle” • Maintains ‘just right’ levels • Temperature • Water • Blood Pressure • Blood Glucose Levels • Heart Rate • Works by negative feedback: reverses the stimulus and restores it within equilibrium range.

  4. Body takes action Increase Decrease Normal Normal Body takes action Decrease Increase

  5. Too hot Normal Too cold

  6. Blood to skin surface Too hot Vasodilation Sweating Increased breathing rate Normal Blood to vital organs Vasoconstriction Too cold Goosebumps Shivering

  7. In rare instances, the body does not maintain homeostasis. • Positive feedback: intensifies the stimulus and pushes further away from equilibrium.

  8. Blood Pressure: a Model of Homeostasis • Has a normal (‘just right’) range • Within normal range • Higher pressure = more O2 + nutrients to cells • Lower pressure = less O2 + nutrients to cells • Outside of normal range • High blood pressure = life threatening • Low blood pressure = life threatening

  9. What is normal and abnormal? • Two numbers: • #1: Systolic BP: force applied by blood on walls of arteries when heart contracts • #2: Diastolic BP: when heart rests between contractions • 90/60 to 120/80 mm Hg =‘ Just right’ • Below 90/60 = ‘Hypotension’ • Not enough O2 • Light-headed, fainting, death • Above 140/90 mm Hg = ‘Hypertension’ • Damage to arteries in heart, brain, kidneys • Heart attack, stroke, kidney failure

  10. Measuring Blood Pressure • Inflate cuff to cut off blood flow • Slowly deflate cuff (5-10 mm/sec) • Note when tapping sounds start = systolic pressure • Note when tapping sounds stop = diastolic pressure

  11. Measuring Blood Pressure • Sounds are critical, but are hard to hear (a quiet room helps) • Artery completely closed or completely open = NO Sounds • Artery partially open = Tapping sounds (‘Korotkoff sounds’)

  12. Practice with Sounds + Pressure • Watch this video clip and listen carefully to the audio. What is the blood pressure? • Blood Pressure Practice 1 • 98/68 mm Hg • Watch this video clip and listen carefully to the audio. What is the blood pressure? • Blood Pressure Practice 3 • 94/62 mm Hg

  13. Practice with Sounds + Pressure • Watch this video clip and listen carefully to the audio. What is the blood pressure? • Blood Pressure Practice 4 • 92/68 mm Hg • Watch this video clip and listen carefully to the audio. What is the blood pressure? • Blood Pressure Practice 7 • 132/90 mm Hg

  14. Practice with Sounds + Pressure • Watch this video clip and listen carefully to the audio. What is the blood pressure? • Blood Pressure Practice 8 • 114/60 mm Hg • Watch this video clip and listen carefully to the audio. What is the blood pressure? • Blood Pressure Practice 9 • 112/76 mm Hg

  15. Blood pressure = cardiac output x peripheral resistance. BP = CO x PR • Cardiac output: blood volume/minute (changes with heart rate and blood volume) • Peripheral resistance: blood friction on arteries walls (changes with diameter of arteries and blood viscosity) video • To maintain BP homeostasis, need to regulate both CO and PR • When BP increases/decreases, baroreceptors (sensors in walls of arteries) sense it  they signal medulla oblongata in the brain  sends impulses to: • For CO: cardioinhibitory or cardioacceleratory center of the heart  they change heart rate. • For PR: muscles around arteries they vasodilate/vasoconstrict arteries and change their diameter.

  16. Blood Pressure Homeostasis Review • Try to write down the stimulus, receptors, set point, control center, effectors and response as they relate to blood pressure homeostasis. Draw a diagram if it helps. • Answer: is this an example of positive or negative feedback? Explain.

  17. Homeostasis + Negative Feedback • Additional examples of homeostasis + negative feedback that we will consider this year

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