Pharynx. Muscles of Pharynx

Transcription

1

2 Pharynx A funnel shaped fibromuscular tube that extends from the base of the skull & continues below with the esophagus at the level of C6 in the neck. It is divided into 3 parts: (1) Nasal: nasopharynx; (2) Oral: oropharynx; (3) Laryngeal: laryngopharynx. Muscles of Pharynx They are 6 muscles. 3 main constrictors: superior constrictor, middle constrictor and inferior constrictor. They run more or less in a posteriosuperior circular direction & attached posteriorly to a fibrous ligament called pharyngeal raphe. The successive contractions of these muscles produce the action of swallowing or deglutition. They overlap each other from inferior to superior; the inferior constrictor will cover the middle one, and the middle constrictor will cover the superior one. The inferior constrictor is the largest muscle and in fact it is subdivided into two muscles according to their anterior attachments to laryngeal cartilages: 1. Thyropharyngeus muscle superiorly: which originates from the thyroid < Greek: thyreoeidḗs; shield-shaped, equivalent to thyre (ós); oblong shield + -oeidēs; -oid > cartilage (the largest cartilage in the larynx). P a g e 1

3 2. Cricopharyngeus muscle inferiorly: which originates from the cricoid < Greek: krikoeidḗs; ring-shaped, equivalent to krikos; ring + -oeidēs; -oid > cartilage. NOTE: CARTILAGE )الغضروف( IS AN UNCALCIFIED, UNOSSIFIED TISSUE THAT IS A LITTLE BIT SOFTER THAN THE BONE. IT IS A STAGE BEFORE THE FORMATION OF THE BONE (ENDOCHONDRAL OSSIFICATION). Most of the constrictors fibers pass in a posterior-superior direction, so upon contraction they will close the pharynx and push it downwards. This is applied to the superior constrictor, middle constrictor and the thyropharengues part of the inferior constrictor. These three muscles function in swallowing, pushing the food bolus to the esophagus. Cricopharyngeus fibers however run in a horizontal direction carrying out a sphincter-like function to prevent the regurgitation of food; physiologically it is called the upper esophageal sphincter for its function as a valve; which is a physiological sphincter not anatomical one because it is part of the pharynx. The difference in the orientation of fibers between the two parts of the inferior constrictor separates the muscle and creates a gap that is discovered by the founder of the bronchoscopy 'Gustav Killian' therefore it is named Killian's dehiscence (area of weakness). During swallowing, there is an increase in the pressure inside the pharyngeal cavity, if this pressure exceeds the physiological limit it will produce Pharyngeal Pouch; which is an outpouching ب) (تجي of pharyngeal mucosa in the region of Killian dehiscence between the thyrophryngeus & cricopharynengeus parts of the inferior constrictor muscle. It is also called Pharyngoesophageal diverticulum or Zenker's diverticulum Friedrich Zenker is the pathologist who discovered it- and it mainly affects older adults due to muscles weakness and atrophy at this age. Although it may be asymptomatic, it could be manifested by: (1) dysphagia difficulty in swallowing. (2) Regurgitation reappearance of the food in the oral cavity because it will be accumulated in the pouch above the cricopharengeus muscle (sphincter). And (3) cough. This pouch can be radiographically visualized after a simple barium sulfate meal for the diagnosis. No treatment is needed if it is small and asymptomatic, P a g e 2

4 but if it is large and symptomatic then it is treated by endoscopic stapling. 3 small vertical muscles: they help in the elevation of the pharynx during the action of swallowing. 1- Stylopharyngeus muscle: it originates from styloid < Greek: stuloeidēs; like a stylus. Stylus means a pencil > process of the skull, passes between the superior constrictor and the middle constrictor and inserts at the posterior border of thyroid cartilage. 2- Palatopharyngeus muscle: it is considered as a muscle of the palate or a muscle of the pharynx. First of all the soft palate is made of 5 muscles; 2 superior muscles, 2 inferior muscles and the musculus uvulae. The two muscles that come down from the soft palate are (1) palatoglossus muscle which originates from the soft palate towards the tongue. It is a unique muscle of the tongue since its innervation comes from the palate by pharyngeal plexus not from the tongue-. (2) Palatopharyngeus muscle -behind the Tonsillar artery (A branch from facial art.) palatoglussus- which originates from the palatine aponeurosis in the soft palate and inserts at the posterior border of thyroid cartilage. These two muscles are covered by a Palatoglossal fold mucus membrane, the mucus membrane will fold onto the palatoglossus muscle forming palatoglossal fold anteriorly if you cut the mucus Palatopharyngeal fold membrane by a scalpel, you will find the muscle beneath it-. The second folding; the mucus membrane will fold onto the palatopharyngeus muscle forming palatopharyngeal fold posteriorly. In between these two folds, there is the tonsillar bed where the palatine tonsils are located. So palatoglossus is an important muscle, it helps us to distinguish the location of palatine tonsils. 3- Salpingopharyngeus muscle: < Greek: salpingos; trumpet بوق > it is a small, totally insignificant muscle. It is a single bundle of muscle fibers that originates from the medial side of the "trumpet" which is the auditory tube or Eustachian tube and blends with the palatopharyngeus muscle. It s a common thing in the human anatomy that as the muscle gets smaller, it has a longer name; for instance, the longest name of a muscle consists of 6 words "levator labii superioris dilator alaeque nasi" and it is a very tiny muscle in the face that needs several hours of dissection to find it, while the largest muscle in our body is the gluteus maximus or simply 'the gluteus". P a g e 3

5 Important: (a common USMLE question) All muscles of the pharynx are innervated by the Vagus nerve (CN X) via the pharyngeal plexus except the stylopharyngeus muscle which is innervated by the glossopharyngeal nerve (CN IX). So, the superior constrictor, middle constrictor, inferior constrictor, palatopharyngeus and salpingopharyngeus muscles are innervated by the vagus nerve via the pharyngeal plexus While the stylopharyngeus muscle is innervated by the glossopharyngeal nerve. Pharyngeal plexus: is a network of nerves over the wall of the pharynx. It s formed mainly by the vagus, glossopharyngeal and accessory nerves. But the innervation of these 5 muscles comes from the vagus nerve. to sum up: Pharyngeal cavity Nasopharynx: Opening of auditory tube Adenoid It s located posteriorly to the nasal cavity, directly behind the conchae (bony shelves). So the nasal cavity ends at the posterior end of superior, middle and inferior conchae, where the nasopharynx starts. It is lined by Tubal tonsils respiratory epithelium (ciliated pseudostratified columnar epithelium) since it is behind the nasal cavity. Odontoid (dens) Salpingopharyngeal fold P a g e 4

6 It contains the opening of Eustachian tube on its lateral walls, which connects the nasopharynx with the middle ear. Each tube has an elevated ridge that is called the tubal elevation, if we cut the mucus membrane at this elevation we will see an aggregation of lymphatic nodules, this is another tonsil called tubal tonsil related to auditory tube-, but it is very small that's why it has no significance clinically. Furthermore, there is a fold called the salpingopharyngeal fold; which is a mucus membrane that covers the salpingopharyngeus muscle. Finally, there is a large aggregation of lymphatic nodules in the submucosa of the roof of the nasopharynx called adenoid or pharyngeal tonsil. Oropharynx It is located posteriorly to the oral cavity and opens to it through oropharyngeal isthmus. The palatoglossal fold marks the border between the oral cavity and the oropharynx. It is located at the level between C2 (axis) and C3. Its roof is made by the soft palate, while the floor is formed by the posterior 1/3 of the tongue [which is the lingual tonsil] and the valleculae (a depression between the tongue and epiglottis a part of the larynx-). It contains the palatine tonsils on its lateral walls, between the palatoglossal fold (covering the palatoglossus muscle) and the palatophryngeal fold (covering the palatopharyngeus muscle). Oropharyngeal isthmus is the separation between the oral cavity and the oropharynx. And its borders are: Roof: the junction between the hard palate and the soft palate. Lateral border: palatoglossal folds. Floor: sulcus terminalis (the sulcus separating the anterior 2/3 from the posterior 1/3 of the tongue) on the dorsum of the tongue. Relations of Palatine Tonsils: Anteriorly: palatoglossal fold Posteriorly: palatopharyngeal fold P a g e 5

7 Superiorly: the soft palate Inferiorly: the lingual tonsils (posterior 1/3 or the pharyngeal part of the tongue) Medially: the cavity of oropharynx, so the palatine tonsils are located in the oropharynx and not in the oral cavity. Laterally: the tonsillar bed formed by the superior constrictor muscle. Clinical correlation: Tonsillitis: inflammation of any of these tonsils but in general the most common tonsils to be infected are the palatine tonsils that s why it clinically means inflammation of palatine tonsils. There are two forms of tonsillitis as following: Tonsillitis form Acute حاد Chronic duration More severe, lasts for 4-6 days Lasts for several weeks to months Causative agent Viral infection Bacterial infection enlarged, very reddish tonsils Massively enlarged tonsils with a Clinical features and no pus white-yellowish spots (pus) therapy NSAIDs NSAIDs + antibiotics* *antibiotic of preference: -after doing a culture and confirming the bacterial infection- Mainly it is amoxicillin, but in case of penicillin hypersensitivity it is erythromycin and in case of penicillin resistance it is azithromycin. Tonsillectomy: the removal of palatine tonsils surgically (ENT surgery). The rationale to carry out this procedure is recurrent tonsillitis which is continuous episodes of tonsillar infections. It's indicated in case of (1) 7 or more episodes of tonsillitis a year for one year, (2) 5 times a year for successive continuous 2 years and (3) 3 times a year for continuous 3 years. These guidelines can be changed according to the financial status and other factors. The procedure of tonsillectomy is easily done nowadays, due to the advanced technology of using what is called electrocautery procedure; a device that uses electric current to cauterize )يكوي( or burn the tissue, so it cuts the tissue and ligates the blood vessels at the same time, thus prevents hemorrhage and by that it removes the tissue in the best disinfection manner (burning). So nowadays we don t use the scalpel for tonsillectomy. The procedure: Check out this video of the procedure: First of all, the patient has to be under general anesthesia, so intubation is a demand. Since the physician is going to work inside the oral cavity, then the oral intubation is not beneficial, the nasal intubation is preferred instead. P a g e 6

8 Normal tonsils should have a smooth surface while the tonsils that are subjected to the tonsillectomy in the video- have a nodular appearance and a rough surface due to the continuous episodes of tonsillitis. The physician finds the tonsil (between the palatoglossal and the palatopharyngeal folds), grasps it using the forceps and burns the tissue using an electric current; he removes the tonsil from its root. At the same time, burning prevents bleeding from the tonsillar artery which is a branch of the facial artery. This procedure takes less than two minutes, but the time is consumed to prepare the patient; general anesthesia, giving the patient sedatives and IV fluids and intubation. After the surgery, the patient should be given sedatives and IV fluids again. Also he/she cannot eat after the surgery (Drinking water is allowed). The patient can practice his normal life the day after the surgery. Because of the simplicity of this procedure it became very common which rises an argument about it: (1) some argue that tonsillectomy is unnecessary surgery & may be dangerous because you remove a part of immunity, while (2) Others argue that chronically inflamed tonsils are a site of recurrent infections. Note: the inflammation of the pharyngeal tonsils is called adenoiditis. Laryngopharynx It extends from the tip of epiglottis down to the cricoid cartilage. It s located at the vertebral level of C4-C6. At the C6, the pharynx becomes the esophagus. The laryngopharynx continues as a digestive tract; so it is lined by non-keratinized stratified squamous epithelium, which is a strong lining and can resist the friction with food. And it is nonkeratinized because there should be a mucus production for lubrication. There is a small depression (recess) on each side of the laryngeal inlets posteriorly called piriform fossa. Piriform <like a pear fossae. Its function is to prevent swallowing sharp <(اجاص) objects (e.g. Fish bone) as following: As the sharp object goes down, it will stuck between these fossae stimulating a nerve that lies just beneath the mucus membrane of piriform fossae which is the internal laryngeal nerve, its activation will activate the vagus nerve that supplies the pharyngeal constrictors, thus produce their contraction in an inverted fashion, i.e. in P a g e 7

9 Internal laryngeal n. swallowing, the superior constrictor contracts, then the middle one and lastly the inferior one, while in this case the inferior constrictor will contract first, then the middle one and after that the superior one producing a gag reflex "اععع" which prevents the entry of the sharp object into the esophagus. Pharynx innervation Sensory: based on the nerve that supplies the cavity anterior to the pharyngeal part Nasopharynx: Maxillary nerve. Oropharynx: Glossopharyngeal nerve. Laryngopharynx: Vagus nerve (CN X) Gag reflex Motor: Vagus nerve via pharyngeal plexus except for the stylopharyngeus muscle. Waldeyer's tonsillar ring: Pharyngeal Tonsil: single, in the roof of the nasopharynx. Tubal Tonsils: on the lateral walls of the nasopharynx. Palatine Tonsils: on the lateral walls of the oropharynx. Lingual Tonsil: single, in the floor of the oropharynx. So, they are all located in the pharynx neither in the nasal cavity nor in the oral cavity. P a g e 8

10 Esophagus A muscular tube that lies posteriorly to the trachea & extends from the neck (C6) to the stomach (at the level of T12 L1). It is ~ cm long. It passes through esophageal opening of the diaphragm at the vertebral level of T10 [Inferior vena cava penetrates the diaphragm at the level of T8, and aorta passes through the aortic hiatus at the level of T12]. Its function is to transport food to the stomach. Histology of Esophagus The alimentary canal (from esophagus to anal canal) wall consists of 4 histological layers; 1- Mucosa: is made up of epithelium (cells) attached to a basal lamina that is called the lamina propria (the proper plate) األساسية(,)الصفيحة it acts as a tape to support the epithelial cells. The type of the epithelium changes as we move downwards; it is stratified squamous in the esophagus, to tolerate the friction with the food. In the stomach, the epithelial cells have many secretions and as the cell becomes more active it becomes larger; so it is lined by simple columnar epithelium. In the intestines, the cells of epithelium are also very active, not in secretion but in absorption/reabsorption; so they have to be rich in organelles such as mitochondria, so it is lined by simple columnar epithelium. 2- Submucosa: is composed of dense irregular connective tissue that contains irregular collagen fibers. It provides a framework for the vasculature of the canal wall, i.e. the nutrients reach the mucosa by filtration via the interstitial fluid. 3- Muscular layer: any hollow tube in our body must have a smooth muscle layer in its wall to control its diameter i.e. there is trachealis muscle in the trachea, tunica media in blood vessels and muscularis layer in the GI tract. P a g e 9

11 The unique feature of esophagus is the transitional state from the constrictors in the pharynx to the stomach that has smooth involuntary muscles, and in our body there cannot be an abrupt change in structures -it should be a gradual change-, so the upper 1/3 of esophagus muscular layer is composed mainly of striated muscles which are voluntary muscles without bony attachments, in the middle 1/3 there is an inner layer of smooth muscles and outer layer of striated ones and in the inferior 1/3 they are completely smooth muscles. The function of muscularis layer is the production of the peristaltic movements. 4- Adventitia: it is the "paint" of the tract that protects it and gives it its appearance. It is made of loose areolar connective tissue. Edited by: Yasmeen Kefah DONE! P a g e 10