Respiratory tract

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Respiratory tract

In humans the respiratory tract is the part of the anatomy

Anatomy

Anatomy is a branch of biology that is the consideration of the body plan. It is a general term that includes human anatomy, animal anatomy and plant anatomy ....
that has to do with the process of respiration

Respiration (physiology)

In animal physiology, respiration is the transport of Oxygen from the outside air to the cells within Tissue s and the transport of carbon dioxide in the opposite direction....
.

The respiratory tract is divided into 3 segments:

The respiratory tract is a common site for infections. Upper respiratory tract infection

Upper respiratory tract infection

Upper respiratory tract infections, , are the illnesses caused by an acute infection which involves the upper respiratory tract: nose, Paranasal sinus, pharynx or larynx....
s are probably the most common infections in the world.

Most of the respiratory tract exists merely as a piping system for air to travel in the lungs; alveoli are the only part of the lung that exchanges oxygen

Oxygen

Oxygen no O2 produced; 2) O2 produced, but absorbed in oceans & seabed rock; 3) O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer; 4-5) O2 sinks filled and the gas accumulates]]...
and carbon dioxide

Carbon dioxide

Carbon dioxide is a chemical compound composed of two oxygen atoms covalent bond to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state....
with the blood

Blood

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Encyclopedia

In humans the respiratory tract is the part of the anatomy

Anatomy

Respiration (physiology)

Upper respiratory tract
Upper respiratory tract

The upper respiratory tract refers to the following parts of the respiratory system:* nose and paranasal sinuses* oral cavity * throat**pharynx...
: nose
Nose

Anatomically, a nose is a protuberance in vertebrates that houses the nostrils, or nares, which admit and expel air for Respiration in conjunction with the mouth....
and nasal passages, paranasal sinus
Paranasal sinus

Paranasal sinuses are air-filled spaces, communicating with the nasal cavity, within the bones of the skull and face....
es, and throat
Throat

In anatomy, the throat is the anterior part of the neck, in front of the vertebrae. It consists of the pharynx and larynx. An important feature of the throat is the epiglottis, a flap which separates the esophagus from the vertebrate trachea and prevents inhalation of food or drink....
or pharynx
Pharynx

FunctionsThe pharynx is part of the digestive system and respiratory system of many organisms.Because both food and Earth's atmosphere pass through the pharynx, a flap of connective tissue called the epiglottis closes over the trachea when food is swallowed to prevent choking or Pulmonary aspiration....
Respiratory airways: voice box
Voice box

Voice box could mean:* The larynx , colloquially known as the voicebox, is an organ in the neck of mammals involved in protection of the trachea and sound production....
or larynx
Larynx

The larynx , colloquially known as the voicebox, is an organ in the neck of mammals involved in protection of the vertebrate trachea and sound production....
, trachea
Vertebrate trachea

The traceartes, or windpipe, is a tube that has an inner diameter of about 20-25 mm and a length of about 10-16 cm in humans. It commences at the larynx and bifurcates into the primary bronchus in mammals, and from the pharynx to the syrinx in birds, allowing the passage of air to the lungs....
, bronchi
Bronchus

A bronchus is a caliber of airway in the respiratory tract that conducts air into the lungs.No gas exchange takes place in this part of the lungs....
, and bronchiole
Bronchiole

The bronchioles or bronchioli are the first airway branches that no longer contain cartilage. They are branches of the bronchi, and are smaller than one millimeter in diameter....
s
Lung
Lung

The lung is the essential respiration organ in air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located in the chest on either side of the heart....
s: respiratory bronchiole
Respiratory bronchiole

The respiratory bronchioles are the beginning of the respiratory segment of the airway and are just distal to the terminal bronchioles . The epithelium in this segment is simple cuboidal....
s, alveolar duct
Alveolar duct

Alveolar ducts are the tiny end ducts of the branching airways that fill the lungs. Each lung holds approximately 1.5 to 2 million of them. The tubules divide into two or three alveolar sacs at the distal end....
s, alveolar sacs, and alveoli

The respiratory tract is a common site for infections. Upper respiratory tract infection

Upper respiratory tract infection

Oxygen

Carbon dioxide

Blood

Blood is a specialized bodily fluid that delivers necessary substances to the body's Cell s ? such as nutrients and oxygen ? and transports waste products away from those same cells....
.

Moving down the respiratory tract starting at the trachea, the tubes get smaller and divide more and more. There are estimated to be about 20 to 23 divisions, ending up at an alveolus.

Even though the cross-sectional area of each bronchus or bronchiole is smaller, because there are so many, the total surface area is larger. This means there is less resistance at the terminal bronchioles. (Most resistance is around the 3-4 division from the trachea due to turbulence.)

General histology

The respiratory tract is covered in an epithelium

Epithelium

In biology and medicine, epithelium is a Biological tissue composed of cell s that line the cavities and surfaces of structures throughout the body....
, the type of which varies down the tract. There are gland

Gland

A gland is an Organ in an animal's body that synthesizes a substance for release such as hormones or breast milk, often into the bloodstream or into cavities inside the body or its outer surface ....
s and mucus

Mucus

In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. It is a viscous colloid containing antiseptic enzymes and immunoglobulins that serves to protect Epithelium in the respiratory,...
produced by goblet cell

Goblet cell

Goblet cells are glandular simple columnar epithelium Cell whose sole function is to secrete mucus. They use both apocrine and merocrine methods for secretion....
s in parts, as well as smooth muscle

Smooth muscle

Smooth muscle is a type of non-striated muscle, found within the tunica media layer of large and small arteries and veins, the urinary bladder, uterus, male and female reproductive tracts, gastrointestinal tract, respiratory tract, the ciliary muscle, and iris of the eye....
, elastin

Elastin

Elastin is a protein in connective tissue that is Elasticity and allows many tissues in the body to resume their shape after stretching or contracting....
or cartilage

Cartilage

Cartilage is a type of dense connective tissue. It is composed of specialized cells called chondrocyte that produce a large amount of extracellular matrix composed of collagen fibers, abundant ground substance rich in proteoglycan, and elastin fibers....
.

Most of the epithelium (from the nose to the bronchi) is covered in pseudostratified columnar ciliated epithelial cells, commonly called respiratory epithelium

Respiratory epithelium

Respiratory epithelium is a type of epithelium found lining the respiratory tract, where it serves to moisten and protect the airways. It also functions as a barrier to potential pathogens and foreign particles, preventing infection and tissue injury by action of the #mucociliary escalator....
. The cilia beat in one direction, moving mucus towards the throat where it is swallowed. Moving down the bronchioles, the cells get more cuboidal in shape but are still ciliated.

Cartilage is present until the small bronchi. In the trachea they are C-shaped rings, whereas in the bronchi they are interspersed plates.

Glands are abundant in the upper respiratory tract, but there are fewer lower down and they are absent from the bronchioles onwards. The same goes for goblet cells, although there are scattered ones in the first bronchioles.

Smooth muscle starts in the trachea, where it joins the C-shaped rings of cartilage. It continues down the bronchi and bronchioles which it completely encircles.

Instead of hard cartilage, the bronchi and brochioles have a lot of elastic tissue.

Summary: Upper respiratory tract - nose, pharynx & asscociates structures Lower respiratory tract - larynx, trachea, bronchi & lungs

Respiratory tract

General histology

See also