The Clinical Anatomy and Physiology of the Ear, Nose and Throat.

Transcription

1 C H A P T E R The Clinical Anatomy and Physiology of the Ear, Nose and Throat. 1 1 The term upper respiratory tract refers to the ears, nose and throat. The ears, nose and throat are all connected and infections pass easily from one to the other. Before discussing some common problems affecting the ears, nose and throat, the anatomy and physiology of each is explained and how these structures elate to each other. This chapter covers the following: c The outer, middle and inner ear. c The nose and the sinuses. c The throat, the pharynx and the larynx. The clinical anatomy and physiology of the ear. In this section the following questions are answered: c How are sounds heard? c How do ears function? c How are sounds transmitted from the outside environment by the ear and finally interpreted by the brain. Pinna External auditory canal Bone in middle ear Tympanic membrane (eardrum) Eustacian tube Hammer or malleus Outer Ear Middle Ear Inner Ear Below is a diagram of the anatomy the ear.

2 Notice that the ear has three parts: c the outer ear c the middle ear c the inner ear. The outer ear is made up of the following: c The pinna is the part of the ear that you can see. It is the skin and the cartilage that sticks out from the side of the head. c The external auditory canal leads from the pinna to the eardrum. The canal is not completely straight. It has bends in it. To examine the canal, gently pull the pinna upwards and backwards. This makes the canal straight, and easier to look at with an otoscope (auroscope). c The walls of the canal are covered by skin. This skin produces wax, which helps to protect the ear against dust and insects. Usually the wax gathers in the canal. The wax dries out and falls out of the canal. Wax can become hard and compacted - this can cause discomfort and hearing problems. c The skin inside the canal is fixed tightly to the cartilage and bone. This means that even slight inflammation and swelling can cause quite severe pain. People with infection of the outer ear often present at clinics complaining of pain inside the ear. Pinna Tympanic membrane Hammer or malleus External auditory canal View through an otoscope Cross-section of tympanic membrane and inner ear The eardrum is also called the tympanic membrane. It divides the outer ear and the middle ear. The eardrum can be seen with an otoscope. It is usually a shiny grey-white colour. If you shine a light on the membrane with an otoscope, you will see that the eardrum reflects some of the light. This is called the light reflex.

3 The middle ear The middle ear lies behind the eardrum. It is a space inside the skull. This space is filled with air. The middle ear contains : c The osicles. Inside the middle ear are three tiny bones or osicles. They are the smallest bones in the body. Sound travels to the inner ear along these bones. If these bones get damaged in any way, then the patient will suffer a loss of hearing. c One of these bones is call the hammer or malleus. You can see the handle of the hammer if you look at the eardrum with an otoscope. The handle is attached to the top part of the eardrum. c The Eustachian tube. There is a very thin tube which connects the middle ear to the throat. This is called the Eustachian tube. Air can move through these tubes between the throat and the middle ear. The middle ear is connected to the throat by the Eustachian tube. If air can travel between the throat and the middle ear so can infection. Infection can move up and down the tubes from the throat to the ear, and from the ear to the throat. For this reason it is important to examine the ear and the throat. Always examine the throat when treating an ear infection. The middle ear lies inside the skull. There is only a very thin layer of bone between the middle ear and the brain. Infection can spread from the middle ear to the lining of the brain. The membranes lining the brain are also called the meninges. If this happens, the patient gets inflammation of the meninges or meningitis. c The mastoid bones lie at the base of the skull, directly behind the ears. They are not required for hearing. The mastoid bones are full of air spaces. These air mastoid area spaces are connected to the middle ear. This means that it is possible for infection to spread from the middle ear to the mastoid area. The illustration on the right shows the area where the mastoid bone lies. The inner ear. The inner ear lies deep inside the skull. There are nerves in the inner ear that carry the sound to the brain. If the nerves get damaged, then the patient will suffer from loss of hearing or loss of balance. It is not possible to look at the inner ear during clinical examination. The function of the inner ear can be tested by testing hearing and balance.

4 Clinical anatomy and physiology of the nose and sinuses Septum Nostril The nose. When we breathe through the nose, the nose cleans, warms and moistens the air before it goes down into the lungs. The nose is lined with mucous membrane which helps to clean and moisten the air. Front Underview of Nose Back Cross-section of Nasal Passage The nose is divided into a left side and a right side by the nasal septum. The septum has a lot of blood vessels close to the surface. The nose can bleed easily from this surface. The nose is divided into a front and back section. The front section (also called the anterior section) is really the part of the nose that sticks out the face. The back section (also called the posterior section) is inside the skull, and leads into the throat (naso-pharynx). The nose is connected to the nasal passage sinuses via small ducts and to the eye via the tear duct. The sinuses. The sinuses are air-filled hollows in the bones of the face. They are lined with mucous membranes. All the sinuses drain into the nose. There are sinuses in the following areas: c below the eyes c on each side of the nose c above the eyes c in the forehead c behind and above the nose. Note the position of the sinuses within the face,

5 The clinical anatomy & physiology of the throat or pharynx. The throat is divided into three sections. The throat is also called the pharynx. The naso-pharynx is the part of the throat that lies behind the nose. The oro-pharynx lies at the back of the mouth. It goes from the tonsils backwards. The oro-pharynx is the only part of the throat that you can see just by looking down the mouth. The laryngo-pharynx. The larynx is the upper part of the airways, and lies in front of the oesophagus. The vocal cords are part of the larynx. Vocal cords Epiglottis Trachea Naso-pharynx Oro-pharynx Laryngopharynx Oesophagus Anatomy of the pharynx There are a number of organs in the throat that can be affected by throat infections. Below is a brief description of each of these: The tonsils and the adenoids. Inflamed tonsils and adenoids are common conditions in children. The tonsils and the adenoids are masses of lymphoid tissue in the pharynx. They are part of the defence system that the body uses to fight off infections. Upper respiratory tract infections often cause the tonsils and the adenoids to be inflamed and swollen. Adenoids Tongue Tonsils Adenoids Tonsils Uvula Adenoids Tongue Wooden spatula Cross-section of head showing the Adenoids and Tonsils Frontview Diagrams showing a cross-section of the head and looking inside the mouth with a wooden spatula

6 The tonsils can be found on each side of the entrance to the oro-pharynx. In young children the tonsils can seem to be quite enlarged. Tonsils grow to their largest size when children are about five years old. After that they become smaller. Health workers often think that a child s tonsils are abnormal, when there is nothing wrong with them. This is because they look so big. If you see a child with large tonsils but no sign of infection, there is nothing to be concerned about. The adenoids are situated in the naso-pharynx. The Eustachian tubes, which come from the middle ear, open into the pharynx very close to the adenoids. The adenoids, may enlarge when inflamed. This can block the opening of the Eustachian tubes. When this happens, and infection develops in the middle ear. Children often get infections of the middle ear (otitis media) because their adenoids are frequently inflamed. The vocal cords are used to make the sounds when speaking. They are situated in the larynx. They can only be seen with the help of a laryngoscope. The epiglottis is a flap of cartilage that covers the larynx when we swallow. This guides food away from the opening of the top of the airway. Together they prevent food and saliva from entering the airways which will cause choking. If the epiglottis gets infected, it can swell up and block the airways, making it difficult, or impossible to breathe. Large tonsils often occur in children. Unless you find infection there is no need to treat them.