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Lion Track icon Lion Den » A&P » AP2 Lec » Outlines » Respiration

Learning Outline

Respiratory System

A&P 2



Respiration from re- ("again") and -spiro- ("breathe")

Continuous breathing

Overall function

Gas exchange

Acid-base balance

Fluid balance

Functional anatomy

Overview of respiratory anatomy

Conducts air under relatively low pressure, thus requiring open (not collapsed) passages

General plan

Respiratory tract is two-way

Lined mostly with respiratory mucosa


Nose — nasal cavity

Held open by skull bones and cartilage activity

Divided into left and right nasal cavities by the nasal septum activity activity

Lateral walls have three bony shelves (superior, middle, and inferior nasal conchae) that curl downward and inward activity



Paranasal sinuses

Hollow spaces in skull connected to nasal cavity via membranous canals

Lined with nasal mucosa

Main purpose is to lighten the skull

Passages are required to allow air pressure inside to equilibrate with atmospheric air pressure


Pharynx — throat activity

Air passage held open by bone and muscle

Lined with respiratory mucosa

Three divisions of pharynx


Larynx — voice box

Held open by 9 pieces of cartilage that form a box with no bottom and hinged lid (epiglottis) activity

Front cartilages form a neck protrusion called the Adam's apple activity activity activity

Passageway for air activity

Vocal cords (vocal folds) activity activity activity


Trachea — windpipe

Low-pressure air passage to/from thoracic cavity

Held open by C-shaped cartilage rings slide activity

Lined with mucosa activity

cilia flow
Flow of cilia.
The "efficient" phase drives mucus forward, then the "inefficient" phase slides back under the mucus without moving it much.

Bronchial tree

Literally, "branched tree" (bronchus — "branch") (pl. bronchi)

Walls of bronchi and larger bronchioles supported by cartilage rings

Low-pressure airway

bronchiole structure

Bronchioles and alveoli


Alveoli (sing. alveolus) — literally "small space"

Microscopic air pouches at ends of bronchial tree activity

Thin wall coated with watery film

Contain macrophages that aid in tidying up the place (immunity)


Free A&P imagePaired organs — left and right lungs

Location: thoracic cavity (left and right pleural cavities) activity activity activity

Size: grow to fill available space activity activity

Apex is pointed top; base is broad bottom of each lung


Coverings — pleurae

Physiology of respiration

Overview of function

External respiration

Transport of gases — in the blood (to / from pulmonary tissues / systemic tissues)

Internal respiration

Overall regulation of respiration

respiration flow chart

The "big picture" of respiratory function

Click on image to enlarge it


Primary principle of ventilation

Boyle's Law — air pressure is inversely proportional to air volume tv icon

The respiratory cycle tv icon slide

Pip — intrapleural pressure (air pressure in intrapleural space)
PA — alveolar pressure (air pressure inside the alveoli)
PB — atmospheric [barometric] pressure (air pressure of the external environment [atmosphere])
PBJ — peanut butter & jelly

All P values are mm of Hg

Pulmonary volumes and capacities

Pulmonary volumes and capacities
Volume or capacity
Tidal volume (500 ml)   Volume moved during a normal quiet respiratory cycle Low TV may indicate a restrictive disorder; TV is high during exercise
Inspiratory reserve volume (3000 ml)   Extra volume that can be inspired (forcefully) beyond the tidal volume IRV decreases with increased tissue demand for oxygen, as in exercise
Expiratory reserve volume (1100 ml)  

Extra volume (beyond tidal volume) moved during a forced expiration

ERV is highly variable among normal persons; it decreases during exercise as the tidal volume approaches the vital capacity
Residual volume (1200 ml) RV = TLC - VC Volume of air that always remains in the respiratory tract, even after forced expiration. RV greater than one third of total lung capacity may indicate an obstructive disorder.
Dead space (160 ml)  

Anatomical dead space — volume of air in conductive areas of respiratory tract, unavailable for gas exchange.

Physiological dead space — anatomical dead space volume plus volume of air in respiratory areas of tract that can't exchange gases with pulmonary blood

Anatomical dead space usually equals physiological dead space. If physiological dead space is higher, then lungs may not be adequately perfused with blood. Or, inspired air is more than needed for adequate gas exchange.
Inspiratory capacity (3500 ml) IC = IRV + TV

The total capacity for inspiration, including both tidal volume and inspiratory reserve.

Low IC may indicate a restrictive disorder
Functional residual capacity (2300 ml) FRC = ERV + RV Volume of air remaining in tract after a normal expiration Overfilling of lungs, as in obstructive disorders, may cause a high FRC
Vital capacity (4600 ml) VC = IRV + TV + ERV Total volume moved by forced expiration, starting from the inspiratory maximum Low VC (with high flow rate) may indicate respiratory distress; High VC (with low flow rate) may indicate reduced gas exchange area in lungs
Total lung capacity (5800 ml)



Combined total of all four basic lung volumes: tidal volume, inspiratory reserve, expiratory reserve, residual volume High TLC is associated with obstructive disorders; low TLC is associated with restrictive conditions
Total minute volume (6000 ml/minute) TV x respiratory rate Volume of air moved per minute during normal, quiet breathing Low minute volume may indicate edema of the functional pulmonary tissues
Forced expiratory volume (FEV1 = 83% of VC) % VC expelled forcefully by end of interval x (sec) Volume (or % VC) expired forcefully during a given interval, beginning at the point of maximum inspiration Low FEV1 associated with obstructive conditions

Gas Exchange

Simple diffusion of gases dissolved in water

Gas fractions are expressed as partial pressures rather percent by volume

Pulmonary gas exchange — in lungs

Systemic gas exchange— in all other tissues tv icon

Transport of gases

Oxygen transport

Hb dissociation curve
Hemoglobin dissociation curve

The Bohr effect is named for Danish physiologist Christian Bohr (pictured) who first described it in 1904. He is the father of Neils Bohr, the atomic physicist for whom the Bohr model of the atom is named, and grandfather of atomic physicist Aage Bohr —each of whom won a Nobel Prize for his work. Free A&P image

Carbon dioxide transport

CO2 + H2O double arrow H2CO3 double arrow H+ + HCO3-

When carbon dioxide (CO2) dissolves in water, some remains dissolved and some forms carbonic acid (H2CO3). The H2CO3 may revert back to CO2 and H2O or it may dissociate into hydrogen ions (H+) and bicarbonate ions (HCO3-). Enzymes in the blood facilitate conversion of CO2 to bicarbonate (and vice versa).


CO2 + H2O right arrow H2CO3 right arrow H+ + HCO3-
right arrow
In systemic capillaries, the equilibrium tends to shift this way as CO2 moves into the blood


CO2 + H2O left arrow H2CO3 left arrow H+ + HCO3-
left arrow

In pulmonary capillaries, the equilibrium tends to shift this way as CO2 is lost to the air

The location of the original CO2 molecule is highlighted in red at each step of the conversion. This chemical equilibrium occurs elsewhere in the body. For example, it it used to make stomach acid and the bicarbonate in pancreatic juice and bile.

Carbon dioxide handling by the respiratory system affects acid-base balance (pH homeostasis)

Normal pH flow chart

Maintaining normal pH through respiratory mechanisms.

Click on image to enlarge it (and print it out)

Control of breathing

Many levels of control

Basic respiratory cycle

Affected by stretch reflexes in thorax that may help protect you from overinflating your lungs

Can be overridden by cerebral cortex

Respiration control flow chart

Role of medullary respiration centers in quiet and heavy breathing slide

Click image to enlarge it (and print it out)


This is a Learning Outline page.
Did you notice the EXTRA menu bar at the top of each Learning Outline page with extra helps?

This page updated on 23-sep-16