Biological pressure
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Circulatory system, respiratory system and Aquatic systems. Biological Pressure. Biological Pressures. Bladder pressure Hydrocephalus: Cerebrospinal pressure Glaucoma: Pressure in the eye Heart burn: Pressure in the gastrointestinal cavity. BLOOD PRESSURE. The silent killer!!!!.

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Biological Pressure

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Biological pressure

Circulatory system, respiratory system and Aquatic systems

Biological Pressure

Biological pressures

Biological Pressures

  • Bladder pressure

  • Hydrocephalus: Cerebrospinal pressure

  • Glaucoma: Pressure in the eye

  • Heart burn: Pressure in the gastrointestinal cavity

Blood pressure


  • The silent killer!!!!

The blood vessels and the cardiovascular system

The Blood Vessels and the Cardiovascular System

Figure 15-1: Functional model of the cardiovascular system

Blood pressure bp measurements

Blood Pressure (BP): Measurements

  • "Blood pressure"

    • Systolic over diastolic

    • About 120/80 mmHg

  • Sphygmomanometer

    • "Estimation of pressure"

    • Korotkoff sounds

Blood pressure bp measurements1

Blood Pressure (BP): Measurements

Figure 15-7: Measurement of arterial blood pressure

More blood pressures pulse and mean arterial pressures

More Blood Pressures: Pulse and Mean Arterial Pressures

Figure 15-5: Pressure throughout the systemic circulation

Pressure respiratory

Pressure Respiratory

Respiration involves 3 processes

  • Ventilation/ breathing- bulk movement of air into and out of lungs

  • Gas exchange between air in lungs and blood

  • Gas exchange between blood and tissues



  • Alveoli- small air sacs

  • So numerous that the walls are little more than a succession of alveoli

  • Alveolar ducts end into alveolar sacs- chambers connected to about 3 alveoli

  • 300 million alveoli in each lung


Pleural cavities

Pleural Cavities

  • Lungs are in thoracic cavity

  • Lungs are surrounded by pleural cavity

  • Cavity lined with serous membrane called pleura- 2 parts

  • Parietal pleura- thorax, diaphragm, mediast.

  • Visceral pleura- covers surface of lung

  • Pleural cavity- between pleurae, filled with pleural fluid, lubricate and stick pleurae together



  • 2 phases of ventilation

  • Inspiration- inhalation

  • Expiration- exhalation

  • Due to changes in thoracic volume- changes in air pressure in lung

Changing thoracic volume

Changing Thoracic Volume

  • Muscles of inspiration- diaphragm, external intercostals, others

  • Diaphragm- dome shaped muscle separating thoracic cavity from abdominal

  • Muscles of expiration- internal intercostals, abdominals

Pressure changes

Pressure Changes

  • Flow of air is governed by 2 principals

  • Changes in volume= changes in pressure

  • Air flows from high to low pressure- greater the difference, the faster the flow

Lung recoil sa

Lung Recoil SA

  • During quiet expiration- recoil of lungs and thoracic wall

  • Lung recoil- due to elastic fibers and surface tension of fluid in alveoli

  • Two things prevent lung collapse

  • Surfactant

  • Pressure in pleural cavity



  • Mixture of lipoproteins produced by epithelium

  • Forms a thin layer inside lungs

  • Reduces surface tension

  • Reduces tendency of lungs to collapse



  • There are three important pressure in respect to breathing:

  • atmospheric pressure-  the pressure of the air around us.  At sea level the atmospheric pressure is 760 mmHg, at higher altitudes the pressure is lower.  

  • intrapleural pressure-  the pressure within the potential pleural space between the parietal and visceral pleura.  Intrapleural pressure is always slightly below atmospheric pressure.  This is called negative pressure because the elastic lungs are always tending to collapse and pull the visceral pleura away from the parietal pleura.  The serous fluid, however, prevents separation of the pleural membranes.

  • intrapulmonic pressure-  the pressure within the bronchial tree and alveoli.  This pressure fluctuates below and above atmospheric pressure during each cycle of breathing.

Gas exchange partial pressure

Gas Exchange – partial pressure

  • Diffusion of gases between alveoli and pulmonary capillaries

  • Does not occur in bronchioles, bronchi and trachea = dead space

  • Diffusion is dependant upon the partial pressure of that gas

  • Partial pressure is very similar in concept to concentration

Fig 15 13

Fig. 15.13

Carbon dioxide

Carbon dioxide

  • Plays a vital role in pH balance

    CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-

Chemical control

Chemical control

  • Increase in pH = decrease in CO2 = decrease in ventilation = increase in CO2 = decrease in pH

  • Decrease in pH = increase in CO2 = increase in ventilation = decrease in CO2 = increase in pH

Aquatic system

Aquatic system

  • Gas solubility

    • CO2 higher solubility

    • O2 low solubility

  • Temperature

    • High temp – low solubility

    • Low temperature – high solubility

Metabolic functions

Metabolic functions

  • How can we measure indirectly the rate of photosynthesis?

  • How can we indirectly measure the rate of respiration?

Aquatic system1

Aquatic System

  • Photosynthesis and Respiration

    • Plants – higher rate of photosynthesis high concentration of DO and low dissolved CO2

    • Plants – higher rate of photosynthesis lower concentration of DO and low dissolved CO2

  • Global warming and partial pressures of gas

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