15. Mouth, teeth, pharynx/ Fig. 16.1

15. Mouth, teeth, pharynx/

Fig. 16.1

Liem, Bemis, Walker & Grande.

In Deuterostomes, mouth forms where the archenteron meets the stomodeum (a fold in ectoderm).

The pharynx forms just posterior to that point.

Early in ontogeny and phylogeny it has associated gill structures.

Pharynx performsrespiratory and digestive system functions

The pharynx is the major respiratory structure in early vertebrates.

Water high in O2 and low in CO2 enters pharynx via mouth and / or

spiracle

This water is forced across gills and out external gill slits

Blood low in O2 and high in CO2 is pumped into gills where gas

exchange takes place

What mechanism makes gases move from water to

blood or blood to water?

Diffusion gradient

Walker and Homberger

The pharynx is highly vacularizedTo allow it to function in respiration.

a primary palate – primitive condition for Choanata

a primary palate – Still present in Dermochelys

Crocodilians evolveA long secondary Palate, as in Alligator

a short secondary

palate ispresent in

Some turtles

Synapsids evolveA long secondary Palate, as in Homo and Canis

Surrounds Internal nares

13 = hard palate

28 = soft palate

palate separatesrespiration from ingestion

24 = oral cavity

but systemscross pathsin the pharynx

8= esophagus

33= trachea

27 = nasal cavity

21= vomero-nasal opening

Walker and Homberger

Fig. 7-20

Muscles of the pharyngeal region

Walker and Homberger

(thyroid cartilage)

Fig. 10-20 Walker and Homberger – The larynx of the cat

A. Longitudinal section

B. Lateral view of the laryngeal and tracheal cartilages

C. Lateral view of the laryngeal muscles

Marieb

Tongue – modified hypobranchial muscle anchored by hyoid apparatus

Tongue function:

1- food handling

2- taste buds

3- move scent tovomeronasal organ4- prey capture

5- grooming

6- speech

Lingual or glossal refers to tongue

Genio refers to chin

= Adam’s apple

Seven openings into pharynx

1 – oral cavity

2+3 – paired internal nares

4– esophagus

5– trachea

6+7 – paired eustachian tubes

Marieb

Superioresophagealsphincter

Superioresophagealsphincter

Function of epiglottis

Basic Terms Used for Feeding Mechanisms of Vertebrates

1. Suspension-feeding (= filter-feeding) - filter small particles (alive or dead, depending on species) out of water column

2. Suction-feeding - open mouth, suck in food

3. Ram-feeding - open mouth, swim over food

Ram-Suction Index - compares movement of food relative to movement of feeder

4. Inertial-feeding - inertia of food is used to move it in oral cavity

5. Transport - movement of food within oral cavity (by water currents in aquatic vertebrates or tongue in tetrapods)

6. Mastication - physical reduction of food size by chewing

Liem, Bemis, Walker & Grande.

Mastication requires teeth

Primitively homodont, and non-occlusal

With a variety of tooth attachment types

and tooth replacement modes

Some Important Terms for Teeth

Polyphyodont - multiple generations of tooth replacement (most vertebrates)

Diphyodont - two sets of teeth: milk and permanent (most mammals; incisor, canine and premolar teeth are replaced)

Monophyodont - a single set of teeth (e.g., cetaceans)

Homodont - teeth of similar shape along jaw

Heterodont - teeth of different shape along the jaw

Tooth plate or Toothplate - at least two uses are common:1. Many individual teeth fused together at their bases; separate cusps are still visible (e.g., in pharynx of fishes)2. Fusion of individual teeth during ontogeny: separate cusps may not still be visible (e.g., lungfishes, chimaeras)

Liem, Bemis, Walker & Grande.

Types of Mammalian Teeth and Dental Formulae

Incisor teeth (I), typically these are replaced

Canine teeth (C), typically these are replaced

Premolar teeth (P), typically these are replaced

Molar teeth (M), typically these are not replaced

Formulae are expressed as type # in upper jaw/# in lower jaw

I 5/4, C 1/1, P 2/2, M 4/4 = opossum

I 2/2, C 1/1, P 2/2, M 3/3 = humansLiem, Bemis, Walker & Grande.

Heterodonty has produced four tooth types:

Fig. 16.6Carnassial Pair: P4-M1

Liem, Bemis, Walker & Grande.

“Montre moi vos dents,et je vous dit que vous est”

Cleft Palate

The problems created by a cleft palate can extend from a simple fissure in the soft palate to a fissure into the hard palate, creating an opening between the nasal cavity and the mouth. This disorder has many variations and may be unilateral, bilateral, lip only, palate only, or both lip and palate. The septum (dividing wall) between the nostrils may be absent, and the teeth at the cleft site may be malformed or absent.

Suspected causes include environmental factors such as maternal diseases, chemotherapy, radiation, alcohol, excess retinoic acid, anticonvulsant medications and other teratogens, and genetic factors. There are greater chances of congenital malformations in teenage pregnancies and in pregnancies in women over age 35.

A cleft palate can limit a child’s sucking ability which may lead to malnutrition. The child may also require oral or maxillofacial surgery, speech and language therapy, plastic surgery, dental surgery, and orthodontic treatment.

A cleft palate is a fairly common congenital disorder (a problem occurring during gestation - in this case during the fourth or tenth week) when the medial, lateral, and maxillary nasal processes on either left, right or both sides of the forming craniofacial complex do not fuse completely. This creates a fissure in the mouth that affects about 1 in 700 people every year.

Andrew – cleft palate