The Mammalian Respiratory System

The Mammalian Respiratory System

Respiration is the process of obtaining sufficient oxygen from the environment to support cellular metabolic requirements.
Function: transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide to the outside. It is also the metabolic process by which an organism obtains energy by reacting oxygen with glucose to give water, carbon dioxide and ATP.


Breathing: the actual mechanism of gas exchange.

Types of Breathing :
Inspiration (Inhalation): air moves in.
Expiration (Exhalation): air moves out.
Types of Respiration:
External respiration: exchange of O2 and CO2 between air and blood.
Internal Respiration: exchange of O2 and CO2 between blood and cells of the surrounding tissues.
Cellular respiration chemical reactions in the mitochondria that yield ATP
O2 + C6H12O6 → CO2 + ATP + H2O

The upper respiratory tract:

•Nasal Cavity/ Nasal Passages
Vestibule – the area surrounding the anterior external opening to the nasal cavity.
Respiratory region – lined by a ciliated psudeostratified epithelium, interspersed with mucus-secreting goblet cells.
Olfactory region located at the apex of the nasal cavity. It is lined by olfactory cells with olfactory receptors.


Turbinate bones (conchae): The function of the conchae is to increase thesurface areaof the nasal cavity
Inferior meatus: Lies between the inferior concha and floor of the nasal cavity.
Middle meatus: Lies between the inferior and middle concha.
Superior meatus: Lies between the middle and superior concha.
Spheno-ethmoidal recess: Lies superiorly and posteriorly to the superior concha.

Openings

Paranasal sinuses (The frontal, maxillary and anterior ethmoidal sinuses).
Themiddle ethmoidal sinuses.
sphenoid sinus.
nasolacrimal duct.

Pharynx

tube at the back of the mouth and nasal cavities.
intersection of the oesophagus (digestive system) and the trachea (respiratory system)- the pharynx contains passageways for both food and air.
connects the mouth and nasal cavity to the larynx and the trachea/esophagus.


Epiglottis

protects the glottis (and ultimately the opening to the trachea).
flap-like piece of cartilage .
when food is swallowed, the epiglottis presses down and covers the opening to the trachea- this prevents food from going down your trachea (choking).
Glottis
the opening of the trachea.
conducts air to the lungs.
Larynx
located at the upper end of the trachea.
also known as the voice box.
contains two folded ligaments that stretch across the larynx, held in place by the cartilage on the larynx walls.
two ligaments are known as the vocal cords.
sound are produced when air is forced past the ligaments, they vibrate, and the pitch and volume of sound varies with the amount of tension on the vocal cords and the amount of air being forced by them.



Trachea
a long tube made up of cartilage that connects the nasal cavity/mouth/pharynx/larynx to the lungs.
usually about 10-12cm long.
often called the windpipe in mammals.
lined with epithelial cells that contain cilia, that produce mucus to traps foreign particles.
beating/waving of cilia help to propel material back into the nose and throat where it is expelled by a cough or a sneeze

Lower respiratory tract

Bronchi (plural is bronchi, if you talk about only one it is called a bronchus)
the bottom of the trachea branches into the left bronchus (for left lung) and the right bronchus (for right lung)
surrounded by a layer of smooth muscle- smooth muscle contraction and relaxation causes changes in air flow
lined with cilia/mucus to keep passageway clear and acts a filter
branching increases surface area
Bronchioles
passageways that branch from the bronchi into the separate lobes of the lungs
increase surface area
smallest tubes lined with cilia and mucus membranes.
divide into smaller and smaller and smaller passageways that carry air into all portions of the lungs.

Alveoli (plural is alveoli, if you talk about only one it is called an alveolus),

grape like clusters of air sacs at the end of each bronchiole
always kept moist, site of gas exchange, diffusion of gases occurs here
wall of each cell is only one cell thick
each alveolus is surrounded by a capillary bed, gas exchange occurs via diffusion across the alveolus cell wall into the surrounding capillaries
oxygen from outside air → pulmonary venules →heart → pumped to body
carbon dioxide from pulmonary arterioles→ breathe out.
Elastic Connective Tissues- fill spaces between individual structures to keep the entire arrangement in position (like anchors)


•Lungs
located deep within the body, protected from water loss and damage by bone and muscles of the thorax/rib cage.
many folds and fine membranes, delicate, fragile
air moves from the external environment to the respiratory surface deep inside the mammal.
each lung is divided into lobes: Right Lung: 3 lobes, Left Lung: 2 lobes
each lobe is subdivided into lobules, each lobule has its own bronchiole.

Pleura (singular pleuron)

thin double membrane that surrounds the lungs, still allows them to expand and contract during breathing
each pleuron consists of two layers separated by a thin lubricating fluid

In thewater) moves acrossorgans and methods of obtaining oxygen.

Definitions
Tidal volume is the amount of air breathed in and out of the body during normal breathing.
Forced breathing, is the volume that is forced to change during exercise.
Vital capacity is the largest amount or volume of air that can be exhaled after the largest possible inhalation.
Residual volume is the amount of air that, even after as much air as possible has been exhaled, is left in the lungs.
Control of breathing
Control for rate and depth, by breathing control center which is two regions in the brain, medulla oblongata and pone.
Control of Co2 concentration, by aortic and carotid arteries sensors.


Comparative respiratory mechanisms
Mammalian respiration : Compared to other species, mammalian respiration is highly efficient; there is a very large surface area within the lungs which is maximized by the bubble like structure of the alveoli. The lungs also benefit from very thin membranes between the moist layer within the alveoli and the blood. The blood supply to the lungs is very great. Mammals have a sealed thoracic cavity, which is sealed by the diaphragm. In conjunction with the ribs, the two sets of muscles are able to control breathing. Normally, the diaphragms relaxed position recoils (decreasing the thoracic volume) whereas in the contracted position it is pulled downwards (increasing the thoracic volume). This process works in conjunction with the intercostal muscles connected to the rib cage. Contraction of these muscles lifts the rib cage, thus aiding in increasing the thoracic volume. Relaxation of the diaphragm compresses the lungs, effectively decreasing their volume while increasing the pressure inside them. The intercostal muscles simultaneously relax, further decreasing the volume of the lungs. This increased pressure forces air out of the lungs. Conversely, contraction of the diaphragm increases the volume of the (partially empty) lungs, decreasing the pressure inside, which creates a partial vacuum. Environmental air then follows its pressure gradient down to fill the lungs. The ventilation system of mammals is basically a suction pump.

Insects are able to obtain all the oxygen they need for cellular metabolism without lungs. Instead insects have a hard exoskeleton which contains valve like openings called spiracles. Typically there is one pair of spiracles per body segment. Air flow is regulated by small muscles that operate flap-like valves within each spiracle which contract to close the spiracle, or relax to open it.
Amphibians have lungs which they use to respire, but they are also able to obtain oxygen through their skin. As expected with a gaseous exchange surface, the skin is thin, moist and well vascularized. Oxygen is therefore able to dissolve in the moist layer of the skin and diffuse directly into the blood. When submerged beneath the water surface, amphibians obtain all their oxygen through their skin.
Fish live in predominantly aquatic environments however there are exceptions, such as the lung fish which are able to utilize lungs to obtain oxygen. Aquatic fish however use a set of respiratory organs known as gills. Gills are highly vascularized with a large surface area, short diffusion distance and an always moist surface.
Avian just like mammals, birds have ribs, although they lack a diaphragm to seal the thoracic cavity. The thoracic and abdominal cavities are thus not separated and this single large body cavity is known as the coelom.The lungs of the bird are connected to the wall of the coelom by connective tissue and are unable to enlarge themselves like mammalian lungs. Instead air is moved in and out of the bird by expanding the coelom; this enlarges air sacs connected to the coelom causing air to pass through the lungs and into the air sacs.










Biology-lecture 11-----------------------------------------------------------------Dr. Ahmed MA. Nazar