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Topic 18: The Digestive System

� How does the gut develop?

� What are the parts of the digestive system?

� Tooth types, differentiation and diversity

� What are the modes of feeding and how do they

work?

� What are the functions of the digestive system and

how are the functions distributed among parts?

� Gut differentiation and specialization

How does the gut develop?

� _______________

� ______________

� Intraembryonic

� Foregut

� Midgut

� Hindgut

� Extraembryonic

� Yolk sac & allantois

� Umbilical cord

� Stomodeum

� Proctodeum

Liem et al. Fig. 16-1

What are the parts of the digestive system?

© Mader 1997

� Lips (mammals)

� Teeth

� Oral cavity

� Pharynx (oro, naso, laryngo)

� Esophagus

� Stomach

� Small intestine

� Colon

� Rectum

� Anus

� Cloaca

� Also salivary glands, liver, gall bladder, pancreas

Fore

gut

Mid

-

gut

Hin

dgut

What are the components of the foregut?

© doctorcaruana.org

� ______________� Suckling

� Keeping food in mouth

� ________� Prey prehension

� Prey mastication

� __________________� Initial breakdown of food

� ______________� Food manipulation

� Swallowing

� ______________� Nasopharynx

� Oropharynx

� Laryngopharynx (hypopharynx)

� ______________� Amylase – carbohydrate digestion

� Mucous – lubrication

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Functions of the foregut

� Prey processing

� _____________

� _____________

� _____________

� Formation of bolus

� _____________

� Tongue

� Esophagus

� What kind of muscles are involved?

L. Frolich

Teeth

� Primarily ___________

� _____________

� Erupted, chewing portion

� Capped with enamel

� _____________

� Portion in socket

� Lined with cement

� Molars

� Low-crowned: omnivores

� High-crowned: herbivores

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

Teeth

Liem et al. Fig. 16-4; Photos © save-our-sharks.org, KP Bergmann; PJB

Who else has a thecodont dentition?Teeth

� Homodont

� Can be variable in size

� Heterodont

� _______________

� Diphyodont

� Molars not replaced

� _______________

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?

� I:

� C:

� P:

� M:

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

� How is prey ingested?

� Aquatic modes rely on movement of water

� ____________ feeding

� Cilia move water through pharyngeal slits

� ____________ feeding

� 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

Feeding Modes

� Terrestrial

� Generally grasping of prey

� Specializations� _________________

� Inertial feeding

� _________________

� Tearing of prey

Herpetology Fig. 11-28; wikipedia; SM Deban; H Chittenden

What is a feeding cycle?

� Mouth ____________

� Epibranchial m.

� m. coracomandibularis

� m. coracohyoideus

� m. levator hyomandibulae

� Mouth ____________

� Adductor mandibulae

� m. levator palatoquadrati

� m. intermandibularis

� m. interhyoideus

Liem et al. Fig. 16-11

What are the phases of the tetrapod feeding cycle?

� Tetrapods have four phases:

� ______ opening

� Preparatory

� ______ opening

� Strike

� ______ closing

� Grasp

� ______ closing

� Powerstroke

� Prehension & mastication

� Muscles very similar

between slow & fast phases

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

Liem et al. Fig. 16-16

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

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Midgut: Stomach

� Fundus

� Body

� Pylorus

� Control of food movement

� Cardiac/esophageal sphincter

� Pyloric sphincter

� Function?

� ____________________

� ____________________

� 3 layers of smooth muscle

� ____________________

� Hydrochloric acid

� Pepsinogen � Pepsin

� ____________________

© WebMD.com

Midgut: Small Intestine

� _____________: Straight

� Digestion

� Products of liver

� Products of pancreas

� ___________: Convoluted

� Digestion & absorption

� ___________: Convoluted

� Absorption & digestion

© Mayo Foundation

Midgut: Small Intestine

� Digestion

� Liver produces bile

� Stored in gall bladder

� _________________

� Pancreas produces

� ________ – Carbohydrates

� ________ – Proteins

� Intestine produces

� Lipase – Fats

� Enterokinase – activates trypisn

wikispaces.org

Midgut: Small Intestine

� _____________� Villi with microvilli

� High Surface area for absorption

� _____________

� Glands

� Secrete digestive enzymes

� _____________

� Smooth muscle

� Moves material along

Liem et al. Fig. 17-1

Hindgut: Colon

� Functions

� Absorption

� Waste storage

� Caecum (appendix)

� Ascending colon

� Transverse colon

� Descending colon

� Rectum vs. Anus

wikispaces.org

Hindgut: Cloaca

� Mammals

� Lack a __________

� Separate openings for excretory,

digestive, and reproductivesystems

� Other tetrapods

� Everything opens into cloaca

� Turtle

Liem et al. Fig. 17-8

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Gut Evolution

� Esophagus

� Stomach

� Small Intestine

� Colon

� Cloaca/Anus

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

LampreyShark

FrogTurtle

Cat

How have gut

proportions

evolved and why?

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

� Tadpole vs. Adult frog

� How does the diet differ?

Source ??

Gut Evolution and Herbivory

� _____________________

� Subdivision of the stomach

� Rumen

� Reticulum

� Omasum

� Abomasum

� Typical stomach

� Pylorus

� Stomach may contain 300L of material!

� Bacteria and protistsproduce cellulase

Liem et al. Fig. 17-6

Gut Evolution and Herbivory

� Rumen

� Fermentation

� Regurgitation

� Rumination

� Swallowing

� Reticulum

� Absorption of starch

� Omasum, abomasum

� Protein digestion

� More absorption

Liem et al. Fig. 17-6

� ______________________� Elaboration of colon or caecum

� No repeated mastication

� 70% as efficient as foregut fermentation

� Horses, camels, antelopes

Gut Evolution and Herbivory

Liem et al. Fig. 17-7

Rhea Zebra Capibara