RESPIRATORY SYSTEM

•Vertebrate respiratory organs

•Human (mammalian) respiratory process

Catalin Bogdan

bcatal@uic.edu

Wednesday, Friday 8am-12pm

http://www2.uic.edu/~bcatal1

What is respiration ?

• Chemical and physical processes by which animals and plants obtain oxygen and use it to release energy from food molecules

• Essential to life

Phases of respiration• EXTERNAL • Delivery of Oxygen to

each cell of body• Removal of Carbon

Dioxide (gaseous by-product)

• In animals with lungs, breathing represents external respiration

• INTERNAL• Occurs in every cell of

body• Involves chemical

reactions that liberate energy from food

• Food molecules are usually combined w/ Oxygen and Carbon Dioxide is released

External Respiration• In lower animals external respiration is

simply an exchange of O2 and CO2 across cell membranes along concentration gradients

• Inside the body the concetration of O2 is lower than that of surrounding water/air while the concentration of CO2 is greater

• Oxygen difuses into the organism while Carbon dioxide difuses out

• Examples: sponges

• Complex animals require more oxygen than it can be obtained via diffusion thru body surfaces

• Specialized gas exchange structures evolved:

• GILLS – aquatic

• LUNGS – terrestrial

Fish• Aquatic animals have

gills• Gills consist of several

gill arches on each side

• Each gill arch has 2 rows of gill filaments further subdivided into lamelllae (thin)

• Area of gills is proportional to how active the fish is

• Fish gills exhibit an important characteristic: countercurrent flow

• Efficiency is increased as blood flows in opposite direction to that of water over the gills

• Water movement over gills is accomplished via a dual pumping system

• Pressure Pump – fish opens & closes mouth

• Suction Pump – opening & closing “beating” of opercular flaps

• When swimming at high enough speeds (> 0.5 m/s) some fish change to RAM Ventilation

• Keep mouth open, water flows in thru the mouth and out between the gills

• All other kinds of respiration stop

• More energy efficient due to overall lower Oxygen consumption

Air Respiration - LUNGS• Most terrestrial animals have them

• Are located inside the body

• Have no direct contact with air – so they can stay moist

• There is however need for an elaborate circulatory system to transport oxygen in the body

• Why are gills NOT suited for air respiration ?

Why are gills NOT suited for air respiration ?

• Gills are poorly suited to air respiration because they cannot keep moisture

• They collapse and stick together• Some fish can breathe thru gills if air is cool

and moist though (lung fish)

• So then what are the advantages of using lungs for respiration ?

So then what are the advantages of using lungs for respiration ?

• Oxygen concentration in air is several orders of magnitude higher than in water

• Oxygen diffuses much more readily in water than in air

• Less energy is expended by respiratory process because air is much easier to move than water

Amphibians• Lungs are thin walled,

connected to mouth via glottis.

• Lung surface is increased by inner partitions richly innervated by blood vessels

• Amphibians ventilate their lungs via a mechanism called pressure pump

• Frog inflates its lungs by fillings its mouth with air, then closing the mouth, opening the glottis and pushing the air into the lungs by raising the floor of its mouth pressure pump

• Lungs are however too small to sustain high levels of activity

• Frog’s skin serves as supplementary organ of gas exchange. It is well vascularized but must remain moist

• Summer, Hot, High Metabolism (high O2 consumption) Lungs and skin

• Winter, Cold, Low Metabolism (low O2 consumption) Skin mainly

Reptiles

• Skin of reptiles is dry and scaly so it cannot be used for gas exchange

• Lungs are more efficient, higher surface area, better vascularization

• Lung ventilation is dependant on a new mechanism called suction pump

Lung Ventilation by Suction Pump

• Lungs are inflated and deflated by repeated expansion and contraction of the thoracic cavity

• Reptiles, Birds, Mammals• Pressure difference – in the closed thoracic

cavity during inhalation the air pressure is lower than outside

• Ventilation (Inhalation / Exhalation) is usually aided by the muscles of the thoracic cavity, rib cage (intercostals) muscles, and diaphragm muscle

Mammalian Respiratory System

• Air is drawn thru nose or mouth into the pharynx (throat)

• Pharynx opens to both esophagus (to stomach) and trachea (to lungs)

• Position of epiglottis – a tissue flap above the larynx – will determine which passage is open

• Usually one does not breathe while one is swallowing food or he’d choke.

• When you inhale, air moves into trachea• Trachea branches into two bronchi, each leading to a lung• Each lung is surrounded by a pleural membranes and

protected by the rib cage• Visceral Pleura covers the lung while the Parietal Pleura

lines the thoracic cavity walls

• Inside each lung, air moves into finer and finer branching called bronchioles

• A bronchiole terminates in a grape-like cluster of sacs called alveoli

• Alveoli are very thin and are surrounded by capillaries equally thin

• Thus gases diffuse rapidly in both directions

• Ventilation of lungs consists of two stages inhalation and exhalation

• Ventilation of lungs is NOT constant nor is it unidirectional it is tidal (in & out)

• Tidal breathing limits the concentration difference Tidal breathing limits the concentration difference that drives oxygen diffusion in bloodthat drives oxygen diffusion in blood

• Fresh air is not moving into the lungs during half Fresh air is not moving into the lungs during half the respiration cyclethe respiration cycle

Facts and Numbers• Lung Volume ~ 5% of total body volume,

regardless of body size

• Mammalian lung surface area ~ 120 m square

• Alveolar and capillary walls have a combined thickness of just ~ 0.5micrometres

• Cost of breathing

• @ rest ~1.2% of total oxygen consumption

• @ heavy exercise ~ 3%

• Trachea and bronchi and larger bronchioles have incomplete cartilage rings that prevent collapse

• Terminal Bronchioles and alveolar ducts and alveoli do NOT have such cartilage rings

• These terminal airways collapse during exhalation

Lung capacitiesTidal Volume ~ 500

mLAmount of air inhaled/exhaled at rest

Vital Capacity

Male

~4.5 L Maximum volume in/exhaled during forced breathing

Vital Capacity

Female

~3.4 L Maximum volume in/exhaled during forced breathing

Residual Volume

~1.2 L Always present; this air cannot be forcefully exhaled; reduces Oxygen partial pressure in lungs

In regards to epithelial lining of major airways…

• Cilia (always beating upwards towards the pharynx)

• Mucus for trapping dust, pollen. Mucus is pushed upwards towards pharynx thru beating of cilia then passed into esophagus [mucociliary escalator]

• Particles may also be phagocytized by macrophages and removed via lymphatic system (alveoli do not have cilia)

•Material such as inhaled toxic substances and small particles will enter bloodstreamThe only way to truly remove particles (smoke, dust, fumes) are sneezing (nasal) & coughing (lungs)ex. Emphysema (smoking) lungs become stretched and inelastic

Ventilation of Lungs

Review ?• Lungs are located in thoracic cavity

• Lungs are covered by visceral pleura

• An intrapleural space exists between lungs and the the parietal pleura which covers the thoracic wall

• Volume of thoracic cavity is determined by the contractions of the diaphragm muscle and of the intercostals muscles

Inhalation• Rib cage volume increasesthru outward & upward

expansion (intercostals) and downward expansion (diaphragm)

• Lung volume increases• Air pressure inside the

lung is less than pressure outside

• Air flows from HI LO pressures

• Inhalation is an active process

Exhalation• Rib cage volume decreasesthru inward & downward

movement of ribs and upward movement of diaphragm

• Lung volume decreases• Air pressure inside the lung

is higher than pressure outside

• Air flows from HI LO pressures

• Exhalation is usually a passive process

• Exhalation @ rest is a passive process and occurs thru the relaxation of the muscles of inhalation (external intercostals, diaphragm)

• Forced inhalation & exhalation require more muscles

• Forced Inahalation scalenus & sternocleidomastoid

• Forced Exhalation (active) external oblique, rectus et transversus abdominis

Airflow thru airways… ?

• Amount of air entering the lungs is also dependent on airway resistance & lung elasticity

• Airway resistance resistance to the passage and flow of air thru a “pipe”

• High diametre Low resistance

• Histamine (allergic rxns) constrict airways

• Asthma

• Epinephrine expands airway diametre

• Lung Elasticity ease with which lungs expand

• Dependant on elastin fibers (elastic…duh connective tissue)

• Fibrosis (caused by asbestos) increases amount of inelastic fibers

• Surfactant substance in alveoli which reduces the surface tension that opposes the expansion of lungs. Without it, alveoli would simply collapse.

• Lack of surfactant: Respiratory Distress Syndrome , often in newborns

…He annoyed us so far yet he forgot to talk about BIRDS…

Don’t they breathe too ?

Yeah they breathe…so what ?

Birds• Birds are endothermic animals (warm blooded)

with body temperature ~40-41 degrees

• Most birds are very active (flying) Need of lungs with high gas exchange

efficiency

• Bird lung ventilation is similar to mammalian ventilation with one exception: the presence of air sacs

Air sacsNo gas exchangeReduce bird density

Avian Respiratory System• Small lungs + 9 air sacs

• Air sacs permit unidirectional flow of air thru the lungs

• Air sacs not directly involved in gas exchange

• Unidirectional flow means that air moving thru bird is always fresh and with higher partial pressure of oxygen

• What other class of vertebrates had another unique feature for respiration? … You guessed it right… FISH (countercurrent flow)

Blood flow in bird lung is actually crosscurrent NOT Countercurrent (as in fish) as drawn here. Still, there isan improved gas exchange compared to mammals.

Air flow thru avian lungs and air sacs• 1 - On first inhalation, air flows through the

trachea & bronchi & primarily into the posterior (rear) air sacs

• 2 - On exhalation, air moves from the posterior air sacs & into the lungs

• 3 - With the second inhalation, air moves from the lungs & into the anterior (front) air sacs

• 4 - With the second exhalation, air moves from the anterior air sacs back into the trachea & out