The Respiratory System 

Anaerobic cellular respiration: series of chemical reactions that occur in the cell that provide energy and consume oxygen

• Brings oxygen in

• Removes carbon dioxide

cellular respiration formula: glucose + oxygen → carbon dioxide + water + energy 

64% for thermal energy, 36% stored in adenosine triphosphate molecules 

1. cellular respiration occurs to produce energy

2. The energy produced is used to produce adenosine triphosphate through phosphorylation 

3. When cells need energy, ATP reacts w/ other molecules releasing energy and breaking down into ADP (adenosine diphosphate) and Pi ( a free phosphate group) 

   1. That energy moves muscles, sends nerve signals, pumps substances in and out of cells and more 

4. Carbon dioxide and most water produced during cellular respiration get disposed to the environment as waste products 

Phosphate group: a small, energy-carrying part of a molecule that helps store and transfer energy in cells—especially in molecules like ATP.

• It’s what gets added to ADP to make ATP.

• When a phosphate group is removed from ATP, energy is released for the cell to use.

Breathing: movement of gases

Respiration: supplying oxygen to cells

Where does gas exchange occur? Body cells and alveoli

What are the 4 important features of mammals’ respiratory  system?

• Thin permeable respiratory membrane = diffusion can occur 

• Large surface area for gas exchange

• Good supply of blood

• Breathing system for bringing oxygen rich air into the respiratory membrane

Key parts of the respiratory system

• Nose (nasal cavity)

• Air enters through here 

• Detects smells 

• The nose contains 

  • Nose hair: clears out and stops dirt from entering the the trachea

  • Sinuses: warms air 

  • Sinuses and mucus: warms air

• Pharynx: takes air from nose to trachea

• Larynx: the voice box, where your vocal cords are found 

• Epiglottis: A flap of cartilage at the top of the larynx (voice box), covers glottis 

• Glottis: The opening between the vocal cords inside the larynx, allows air into trachea and lungs 

• Trachea (windpipe)

• Consists of rings of cartilage (keep airway open)

• Filters air

• Contains mucus which traps unnecessary particles 

• Travels from here to the bronchi

• Bronchi

• Two branches of trachea

• Lined with cilia (filter air)

• Bronchioles: Smaller airways that divide off from the bronchi

• Alveoli:

• Like tiny air bags

• Fill with air when we breathe in

• Place of gas exchange

• Kept moist because gases must be dissolved in liquid 

  • Diffusion occurs by carbon dioxide entering the thin alveoli membranes and oxygen exiting into the thin membranes of capillaries

    • The CO2 travels up through the respiratory system and gets exhaled out

• Lungs 

• Two lungs 

• Right lung has 3 lobes 

• Left lung has 2 lobes (to make space for the heart)

• Pleural membrane: A thin, double-layered tissue that surrounds the lungs and lines the chest cavity, helping reduce friction during breathing.

  • Space between pleural membranes is the pleural cavity – it is filled with fluid so membranes don’t separate and can slide easily

• Red blood cells (RBC)

• Carry oxygen to various body cells 

• Carry CO2 from various parts of the body back to lungs to be exhaled 

• Deoxygenated = dark red

• Oxygenated = bright red 

• Diaphragm 

• A sheet of muscles at the bottom of chest cavity

• Separates chest from abdominal area

When it:

• Contracts: oxygen pulled into lungs, moves down = breathing in

• relaxes:  carbon dioxide pumped out of lungs, moves up = breathing out

Mechanisms of ventilation

based on principal of negative pressure - air always flows from high to low pressure

Inhalation: 

• Brain causes diaphragm to contract

  • Shortens and flattens diaphragm

  • External intercostal muscles move rib cage up and out 

• Increase in volume of thoracic cavity, reduced pressure in lungs = air entering rushes to lungs to equalize pressure

• Lungs expand like balloons

Exhalation:

• Diaphragm relaxes and moves up to regular position

• external intercostal muscles relax and rib cage moves down and in

• Air pressure in lungs is greater than outside, air rushes out of lungs

• Lungs return to resting size

Partial pressures

The pressure of each individual gases that make up the total pressure of mixed gases 

• Depends on the surface area of alveoli and differences in concentration of gases across the membrane 

• Air is most dense at sea level

• lower air pressure the higher you go

• Less air pressure = the harder it is for oxygen to enter and diffuse into your bloodstream = why its harder to breathe at high altitudes

• The higher the pressure difference between outside and inside, the easier it is to get oxygen and remove carbon dioxide but there can also be too much

• In your lungs, gases like oxygen and carbon dioxide move (diffuse) across membranes (like alveoli) from high partial pressure to low partial pressure.

• This is how oxygen enters your blood and carbon dioxide leaves it.

Oxygen transport and diffusion

• Oxygen has a lower partial pressure at alveoli than in stale air, the pressure is even lower in capillaries = movement of oxygen from alveoli to capillaries (specifically into the plasma)

• Oxygen is in constant use for cellular respiration

• When oxygen reaches body tissues, it diffuses into tissue fluid and then into tissue cells to be used

• When it leaves the plasma/rbc, the blood cell becomes deoxygenated and travels back 

• Alveoli has higher pressure than capillaries 

• Capillaries have higher pressure than body cells 

• Some oxygen remains in your veins as it moves back to your heart and lung = why you don't die when you hold your breath

Hemoglobin:

• Protein in RBC that binds to oxygen = forms oxyhemoglobin (what makes blood cells bright red)

• allows blood to carry up to 70 times more oxygen than plasma alone

• When oxygen is released, blood becomes deoxygenated, which is dark red.

Carbon dioxide transport and diffusion

• Cells constantly produce CO2, allow it to accumulate for a short while

• Moves from cells to tissue fluid to capillaries 

Pressure Differences:

• Atmospheric pressure decreases with altitude:

  • At 2000 m: about 80 kPa (higher pressure compared to higher altitudes).

  • At 7000 m: about 40 kPa (much lower pressure).

• Oxygen percentage stays the same (~20.9%), but because total pressure is lower at high altitudes, the partial pressure of oxygen (PO₂) is also lower.

• Low PO₂ at high altitude means there are fewer oxygen molecules in each breath → less oxygen available to your body.

RBC (Red Blood Cell) Count Adaptation:

• Due to low oxygen supply at high altitude, the kidneys release erythropoietin (EPO).

• EPO stimulates the production of more red blood cells.

• RBC count can increase from around 5,000,000 cells/mL (normal) to 7,000,000 cells/mL (at altitude).

• This increase allows your blood to carry more oxygen despite the low oxygen pressure.

• After returning to lower altitudes, the RBC count gradually returns to normal.

Controlling breathing

• Involuntary, controlled mainly by circulatory system and nervous system

• Respiratory centre in brain stem manages diaphragm movement and intercostal muscles

Rate of breathing is determined by:

• Demand for oxygen

• Need to eliminate CO2 

If there is an increase in cellular respiration, more CO2 is produced which lowers the pH of the blood so chemical receptors are sent to the brain to increase breathing rate + increase in heart rate 

• More focus on monitoring CO2 levels not oxygen

• Receptors in arteries monitor oxygen levels

• only triggers the respiratory center in the brain (to make you breathe faster or deeper) if oxygen drops significantly below normal.

Lung capacity

• total lung volume depends on sex, body type and lifestyle

• males, non-smokers and athletes have larger than females, smokers and non-athletes

Total lung capacity: max volume of air that can be taken into the lungs in a single breath, THAT CAN BE TAKEN AND HOLD, GREATER THAN VITAL CAPACITY 

Tidal volume: volume of air inhaled and exhaled in a normal, involuntary breath (small fraction of total lung capacity - about 0.5L in average adult) 

Inspiratory reserve volume: the extra amount of air that can be forcibly inhaled after a normal breath 

Expiratory reserve volume: the extra amount of air that can be forcibly exhaled after a normal exhalation

Residual volume: the amount of air that stays in the lungs after forced exhalation to keep them from collapsing 

Vital capacity: The maximum amount of air you can exhale after a maximum inhalation. This includes the tidal volume and reserve volumes 

• Physical activity is dependent on the amount of oxygen that can be supplied and how quickly it can be supplied 

• high maximum rate of oxygen (usage) indicates efficient respiratory system

VO₂ (Oxygen consumption rate):

• The rate your body uses oxygen, measured in millilitres of oxygen per kilogram of body weight per minute (mL/kg/min).

VO₂ max (Maximum oxygen uptake):

• The highest rate at which an individual can use oxygen measured in millilitres of oxygen per kilogram of body weight per minute (mL/kg/min).

• Can be calculated with a spirometer = measures volume of air that can be taken into the lungs also calculates rate at which oxygen is used by taking into account the breathing rate and body mass