Topic 18: the Digestive System How Does the Gut Develop?

Home , Cloaca (embryology), Foregut, Hindgut, Midgut, Proctodeum, Stomodeum

1/10/2013

Topic 18: The Digestive System How does the gut develop?

______ How does the gut develop? ______ What are the parts of the digestive system? Intraembryonic

Foregut Tooth types, differentiation and diversity Midgut What are the modes of feeding and how do they Hindgut work? Extraembryonic Yolk sac & allantois What are the functions of the digestive system and Umbilical cord how are the functions distributed among parts? Stomodeum Gut differentiation and specialization Proctodeum

Liem et al. Fig. 16-1

What are the parts of the digestive system? What are the components of the foregut?

Lips (mammals) ______ Suckling Teeth Keeping food in mouth Oral cavity ______ Pharynx (oro, naso, laryngo) Prey prehension

Foregut Prey mastication Esophagus ______ Stomach Initial breakdown of food gut

Mid- Small intestine ______ Colon Food manipulation Swallowing Rectum ______ Anus Nasopharynx

Hindgut Cloaca Oropharynx Laryngopharynx (hypopharynx) Also salivary glands, liver, ______gall bladder, pancreas Amylase – carbohydrate digestion © Mader 1997 Mucous – lubrication © doctorcaruana.org

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Functions of the foregut Teeth

Prey processing Primarily ______ ______

______ ______ Erupted, chewing portion Capped with enamel ______

Formation of bolus ______ Portion in socket ______ Lined with cement Tongue

Esophagus What kind of muscles Molars are involved? Low-crowned: omnivores High-crowned: herbivores

L. Frolich Liem et al. Fig. 16-3, 16-9

Teeth Who else has a thecodont dentition? Teeth

Homodont Can be variable in size Heterodont

______ Diphyodont Molars not replaced ______

Liem et al. Fig. 16-4; Photos © save-our-sharks.org, KP Bergmann; PJB Liem et al. Fig. 16-5; Photos © wikipedia, N Jaquet, M Thompson, GF Maxwell

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Heterodont Teeth

Occlusion for proper function Differentiation ______ ______ ______ ______

Formula is # of teeth in upper & lower jaw

Human: I2/2, C1/1, P2/2, M3/3

What is the formula for this insectivore?

Liem et al. Fig. 16-7

Tooth Diversity

Tooth morphology depends on diet

Raptorial vs. durophagous sharks

What are some specializations we saw in lab?

Photos: Wikipedia

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Feeding Modes Feeding Modes

How is prey ingested? Terrestrial Generally grasping of prey

Aquatic modes rely on movement of water Specializations ______ ______feeding Inertial feeding Cilia move water through pharyngeal slits ______ ______feeding Tearing of prey

Sudden opening of mouth

Water rushes in ______feeding

Swimming with mouth open

Forces water with prey in ______feeding

Relies on grasping of prey

Independent of water movement © C Arenz, N Kley Herpetology Fig. 11-28; wikipedia; SM Deban; H Chittenden

What is a feeding cycle? What are the phases of the tetrapod feeding cycle?

Mouth ______ Tetrapods have four Epibranchial m. phases: m. coracomandibularis ______opening m. coracohyoideus Preparatory m. levator hyomandibulae ______opening Strike ______closing Mouth ______ Grasp Adductor mandibulae ______closing m. levator palatoquadrati Powerstroke

m. intermandibularis Prehension & m. interhyoideus mastication Muscles very similar between slow & fast phases

Liem et al. Fig. 16-11 Liem et al. Fig. 16-15

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Feeding Mechanics

How the jaw works influences lever arms and size of muscles Temporalis & masseter are the major jaw-closing muscles in mammals

What is main degree of freedom? How big are the in-levers? How big are the muscles?

Liem et al. Fig. 16-16

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Midgut: Stomach Midgut: Small Intestine

Fundus Body ______: Straight Pylorus Digestion Control of food movement Products of liver Cardiac/esophageal sphincter Products of pancreas Pyloric sphincter Function? ______ ______: Convoluted ______ Digestion & absorption 3 layers of smooth muscle ______

Hydrochloric acid ______: Convoluted Pepsinogen Pepsin Absorption & digestion ______

Midgut: Small Intestine Midgut: Small Intestine

Digestion ______ Villi with microvilli Liver produces bile High Surface area for absorption Stored in gall bladder ______ ______ Glands Pancreas produces Secrete digestive enzymes ______– Carbohydrates ______– Proteins ______ Smooth muscle Intestine produces Moves material along Lipase – Fats Enterokinase – activates trypisn wikispaces.org Liem et al. Fig. 17-1

Hindgut: Colon Hindgut: Cloaca

Mammals Functions Lack a ______ Absorption Separate openings for excretory, Waste storage digestive, and reproductive systems Caecum (appendix)

Ascending colon Other tetrapods Transverse colon Everything opens into cloaca Descending colon Turtle

Rectum vs. Anus

wikispaces.org Liem et al. Fig. 17-8

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Esophagus Stomach How have gut Small Intestine proportions Gut Evolution Colon evolved and why? Cloaca/Anus

Frog Turtle Shark Cat Lamprey

Liem et al. Fig. 17-2, 17-3, 17-4

Gut Evolution in Response to Diet

Which parts are longer in the koala?

Which parts are longer in the coyote?

Why?

Campbell, Fig. 37-17

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Gut Evolution in Response to Diet Gut Evolution and Herbivory

______ Subdivision of the stomach Rumen Tadpole vs. Reticulum Adult frog Omasum Abomasum

How does the Typical stomach diet differ? Pylorus

Stomach may contain 300L of material! Bacteria and protists produce cellulase

Source ?? Liem et al. Fig. 17-6

Gut Evolution and Herbivory Gut Evolution and Herbivory

______ Rumen Elaboration of colon or caecum Fermentation No repeated mastication Regurgitation 70% as efficient as foregut fermentation Rumination Horses, camels, antelopes Swallowing

Reticulum Absorption of starch

Omasum , abomasum Protein digestion More absorption

Rhea Zebra Capibara Liem et al. Fig. 17-6 Liem et al. Fig. 17-7