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 performs respiratory and digestive system functions
The pharynx is the major respiratory structure in early vertebrates. Water high in O 2 and low in CO 2 enters pharynx via mouth and / or spiracle This water is forced across gills and out external gill slits Blood low in O 2 and high in CO 2 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 vacularized To allow it to function in respiration.
a primary palate – primitive condition for Choanata a primary palate – Still present in Dermochelys Crocodilians evolve A long secondary Palate, as in Alligator a short secondary palate is present in Some turtles Synapsids evolve A long secondary Palate, as in Homo and Canis Surrounds Internal nares
13 = hard palate 28 = soft palate palate separates respiration from ingestion 24 = oral cavity but systems cross paths in the pharynx 8= esophagus 33= trachea 27 = nasal cavity 21= vomero- nasal opening
Walker and Homberger Fig. 7-20 Muscles of the pharyngeal region
Marieb Superior esophageal sphincter Superior esophageal sphincter 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 = humans Liem, Bemis, Walker & Grande. Heterodonty has produced four tooth types:
Fig. 16.6 Carnassial 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.