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Exam 3: The Digestive System

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created 3 years ago by kelss_taylor
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Comparative Vertebrate Anatomy

updated 3 years ago by kelss_taylor

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1

What are the three divisions of the embryonic vertebrate tract? What happens to each of these as development proceeds?

1. Midgut: contains yolk or attached yolk sac

2. Foregut: oral cavity, pharynx, esophagus, stomach, small intestine

3. Hindgut: large intestine and cloaca

2

How and why is the oral cavity of mammals specialized? What is a primary palate, secondary palate? How is it known that vertebrate teeth are derived from “dermal armor” of early vertebrates?

- Oral cavity of mammalian mouth is specialized by the suckling and masticatory organ (with muscular cheeks)

- Primary palate: internal nares lead into the oral cavity anteriorly

- Secondary palate: nasal passages are located above the secondary palate and open at the end of the oral cavity

- Vertebrate teeth are derived from "dermal armor" of early vertebrates, we know this because of placoid scales, composition of teeth, and variations in evolution

3

What is the roof of the buccal cavity?

- Primary palate

4

What is the anterior part of the secondary palate called?

- Hard palate

5

What are the bony contributions of the secondary palate?

- Premaxilla and maxilla

6

What are the placoid scales?

- Show gradual transition to teeth at the edge of the jaw

7

What is the composition of teeth?

- Primarily dentin surrounded by enamel

8

How do variations in vertebrates affect "dermal armor"?

- Vary among vertebrates in number of distributions in oral cavity, degree of permanence, mode of attachment, and shape

9

What are the main constituents of teeth? In which groups of vertebrates are found species without teeth? What is the relative abundance and distribution of teeth in fish, early tetrapods, crocodilians, toothed birds, and mammals?

- Enamel, Dentin, Cementum, Root Canal (Dental pulp)

- Toothless vertebrates are found in every class and include agnathans, sturgeons, some toads, birds, turtles, and baleen whales

- Fish: teeth are numerous and widely distributed in the oral cavity and pharynx

- Early tetrapods: widely distributed on the palate; most amphibians and some reptiles still have teeth of the vomer, palatine, and pterygoid bones

- Crocodilians, toothed birds, and mammals: teeth are limited to the jaws

10

What is enamel?

- Hardest substance of the body and forms the surface of the crown

11

What is dentin?

- Resembles bone in chemical composition but it is harder

12

What is cementum?

- Like bone; cellular and acellular regions; grows in layers on the surface of the roots

13

What is the root canal (dental pulp)?

- Supports blood vessels and nerves that enter the tooth

14

What is the general trend among vertebrates in terms of numbers of teeth, distributions of teeth within the oral cavity, and degree of permanence? What are the two sets of teeth found in mammals?

- Have tended toward reduced numbers & distribution

- Most vertebrates (through reptiles) have succession of teeth

- Most vertebrates (except mammals) replace teeth in ‘waves’ (back to front; every other tooth)

- Mammals generally develop two sets of teeth: milk (deciduous) teeth & permanent teeth

15

What is homodont dentition and which groups exhibit such dentition? What is heterodont dentition and which groups exhibit such dentition? What are the various types of teeth found in groups that exhibit heterodont dentition and what is the general function of each type of tooth?

- Homodont dentition: dentition in which the teeth are similar in general appearance throughout the mouth - fish, amphibians, and reptiles

- Heterodont dentition: dentition in which the teeth are different in general appearance throughout the mouth - mammals

- Incisors, canines, premolars, and molars

16

What is the general function of each type of tooth?

- Incisors: cutting

- Canines: piercing and tearing

- Premolars/Molars: crushing and grinding of food - macerating

17

What is the primary tongue and which groups possess such a tongue? What is the glandular field and lateral lingual swelling?

- Primary tongue is a simple crescent-shaped elevation in the floor of the oral cavity caused by the underlying hyoid skeleton

- Gnathostome fish, most amphibians, reptiles, and mammals

- Glandular field is tuberculum impar

- Lateral lingual swelling is more hypobranchial muscle

18

Characterize the tongues of amphibians, reptiles, birds, and mammals. How “mobile” is the tongue of turtles, crocodilians, whales, snakes, lizards, birds, and mammals? What is frenulum? What are the various functions of vertebrate tongues?

- Gnathostome fish and primitive amphibians: tongue is a simple crescent shape; elevation in the floor of the oral cavity caused by the underlying hyoid skeleton called the primary tongue

- Most amphibians: primary tongue + glandular field

- Reptiles and mammals: primary tongue + glandular + lateral lingual swelling

- Birds: lateral lingual swellings are suppressed and intrinsic muscle is usually lacking

- Tongue Mobility:

  • Turtles, crocodilians, some birds, and whales: tongue is largely immobilized in the floor of the oral cavity and cannot be extended
  • Snakes, lizards, amphibians, and some birds: tongue is sometimes long and may move and out of the oral cavity
  • Mammals: tongue is attached to the floor of the oral cavity (via the frenulum) but can still be extended out of the oral cavity
  • Frenulum is a small fold or ridge of tissue that supports the motion of the part attached in particular a fold of skin beneath the tongue, or between the lip and the gum
  • Functions of tongues:

- Human speech, swallowing, grooming, capturing and gathering food, taste, thermoregulation, manipulate fluids and solids in oral cavity

19

What types of secretions are produced by oral glands and what are the functions of those secretions?

- Oral glands secrete a variety of substances: saliva, poisons, and anticoagulants

  • Saliva: oral hygiene, evaporative cooling, lubrication and binding (mucus to bolus), initiates starch digestion, provides alkaline buffer, and solubilizes dry food
  • Poisons: lizards, snakes, and some mammals
  • Anticoagulant: vampires bats
20

What is the pharynx? What is the glottis and epiglottis? Which groups possess an epiglottis and what is its function?

- Pharynx is part of digestive tract exhibiting pharyngeal pouches (at least in the embryo) that may give rise to slits

- Glottis is a muscular slit leading into the larynx

- Epiglottis sits above the larynx, and the trachea sits below it; flap of cartilage at the root of the tongue - which is depressed during swallowing to cover the opening of the windpipe

- Mammals: an epiglottis is positioned over the glottis so that, when a mammal swallows, the larynx is drawn forward against the epiglottis & the epiglottis blocks the glottis (which prevents food or liquids from entering the trachea)

21

What is the function of the esophagus? What is the crop and which groups have such a structure? What is the function of the crop? What is “pigeon milk” and how is it formed?

- Esophagus is a distensible muscular tube connecting the pharynx to the stomach

- Crop is a baglike expansion of the esophagus; found only in birds

- Crop function as a storage place for food

- Pigeon milk is a milky substance made from their crop that is fed to the young for the first few days after hatching

22

What is/are the function(s) of the vertebrate stomach? Characterize the stomach of cyclostomes, amphibians, reptiles, birds, and mammals.

- Stomach is a muscular chamber at the end of esophagus

- Functions of the stomach: Serves as storage, macerating site for ingested solids, and secretes digestive enzymes

Cyclostomes: weakly developed, similar to esophagus

Fish, amphibians, and reptiles: increasing specialization (more differentiated than esophagus

Birds: proventriculus (glandular stomach) and ventriculus (muscular stomach, or gizzard)

Mammals: well developed stomach

23

What are the components and functions of the avian stomach? What are the components and function of the ruminant stomach?

  • Avian stomach:
    • Glandular portion known as the proventriculus: secretes gastric juice to help digest the bolus
    • Muscular portion known as the gizzard: grinds large food into smaller pieces
  • Ruminant stomach:
    • Reticulo-rumen (reticulum and rumen): main fermentation vat where microorganisms attach and breakdown the ingestible feed components
    • Omasum: acts as a filter to sort liquid and fine food particles, may be site for absorption of water, minerals, and nitrogen
    • Abomasum: true stomach; only site on the digestive tract that produces gastric juices (HCl and the enzymes, pepsin and rennin)
24

What is(are) the function(s) of the vertebrate intestine? Characterize the intestine of fish and tetrapods. Which groups have a spiral valve and what is its function? What is the duodenum, jejunum, and ileum?

  • Vertebrate intestine functions: site for absorption and digestion
  • Fishes - relatively straight and short intestine in cartilaginous fishes and in primitive bony fishes (lungfish & sturgeon); however, the intestine of cartilaginous fishes has a spiral valve
  • Tetrapods: differentiated into a coiled small intestine and a short, straight large intestine that empties into a cloaca
  • Spiral valve is within the lumen of the alimentary canal is one way to increase the lengthy of the route through the digestive tract
  • Duodenum: receives chyme from the stomach and exocrine secretions primarily from the liver and pancreas
  • Jejunum and ileum: basis of histological features of the mucosal wall
25

What is(are) the role(s) of the liver, gall bladder, and pancreas in digestion? Which groups have a large intestine? What is the colon and rectum?

  • Liver and gall bladder:
    • liver produces bile which is stored in the gall bladder (cyclostomes, most birds, and some mammals, including cervids, have no gall bladder)
    • bile aids in digestion by emulsifying fats (breaking fats down into tiny particles that permits more efficient digestion by enzymes)
  • Pancreas - secretes pancreatic juice (bicarbonate solution to neutralize acids coming from the stomach plus enzymes to help digest carbohydrates, fats, and proteins) into the intestine
26

What is a cecum and what is the function of such structure? Which groups have ceca associated with their digestive tracts and where are ceca located? Which groups have a cloaca and what is its function?

  • Cecum: increases surface area
  • Ceca - blind diverticula that serve to increase the surface area of the vertebrate digestive tract
    • Fishes - pyloric & duodenal ceca are common in teleosts; these are primary areas for digestion and absorption (not fermentation chambers)
    • Tetrapods - ceca are present in some herbivores; may contain bacteria that aid in the digestion of cellulose
  • Cloaca: chamber at end of digestive tract that receives the intestine, & urinary & genital ducts, & opens to the exterior via the vent
    • shallow or non-existent in lampreys, ray-finned fishes, & mammals (except monotremes)
    • if no cloaca is present, the intestine opens directly to the exterior via anus
27

What is a bolus? What is peristalsis? What is chyme and digesta? What is the buccal cavity? What is the GI tract? What are cheek pouches and which groups have them?

  • Bolus: a lump of food in the mouth
  • Peristalsis: progressive waves of muscle contractions within the walls of a tubular structure, as within the walls of the digestive tract
  • Chyme/Digesta: the liquified bolus of partially digested food after it leaves the stomach and enters the intestine
  • Buccal cavity: mouth region of digestive tract
  • GI tract: stomach and intestines; most apply it to the whole digestive tract from buccal cavity to anus
  • Cheek pouches: small compartments in which gathered food can be temporarily held until it is chewed or carried to caches
  • Some rodents and monkeys have cheek pouches
28

What is the hard palate and soft palate? What are the functions of teeth? What are the three hard tissues composed of the tooth? What is the ‘role’ of each of these substances?

  • Hard palate: anterior part of secondary palate
  • Soft palate: posterior margin of the secondary palate
  • Functions of teeth:
    • Help catch and hold prey
    • Offer strong opposing surfaces that haws work to crush hard shells of prey
  • Enamel is the hardest substances in the body and forms surface of the tooth crown
  • Dentin: resembles bone in chemical composition but it is harder
  • Cementum: like bone; cellular and acellular regions; rests upon dentin and grows in layers on the surface of the roots
29

What is the advantage of recurved teeth and which vertebrates have such teeth? What are the four types of teeth found in mammals? What is the function of each type?

  • Recurved teeth are found in other vertebrates, such as snakes and sharks; hold the prey facilitate its swallowing
  • Incisors: cutting, Canines: for piercing, Premolars/Molars: matriculating food
30

What are carnassials? Which mammals have them and what is their function? What is lingual feeding and which groups exhibit such feeding behavior?

  • Carnassials: specialized sectorial teeth that slice against each other like scissors to cut sinew and muscle; deployed in fights between individuals or in defense
  • Mammals and some primates have carnassials
  • Lingual feeding is the capture of prey with the tongue
  • Many tetrapods, terrestrial salamanders, lizards, and woodpeckers use their tongues
31

What do woodpeckers use their tongue for? What is intraoral transport?

  • Woodpeckers use their long specialized tongues like a probe to obtain insects between cracks in tree bark or in holes they manufacture
  • Intraoral transport is the ability to transport captured prey, move prey through the buccal cavity to the back of the pharynx where it is swallowed
32

In adult vertebrates, what is the function of the pharynx? Which animals have stomachs that serve as storage compartments?

  • The pharynx is a little more than a corridor for passage of food and air
  • Carnivores have stomachs that serve as storage compartments
33

What is the predominate function of the stomach? What is gastric juice? How is the mucosa of the intestines distinctive?

  • Serves to churn and mix food mechanically and add digestive chemicals collectively called gastric juice
  • Gastric juice includes some enzymes and mucus but is primarily composed of hydrochloric acid released from the mucosal wall of the stomach
  • The mucosa of the intestines contain an epithelium whose free surface facing the lumen has many microvilli and include intestinal glands
34

What are the three successive parts of the small intestines (in some vertebrates)?

- Duodenum, jejunum, and ileum

35

Where is the ileocolic valve located and what is its function? What are the functions of the intestines?

- A sphincter between the ileum of the small intestine and the large intestine

- Function of ileocolic valve: regulates movement of food into the large intestine

- Functions of intestines: peristalsis of food, add secretions to food, lubricate food, absorb products of digestions – amino acids, fatty acids, carbohydrates, water is absorbed

36

What is the cloaca? Which groups have no cloaca?

- Cloaca is a common chamber for digestive, urinary, and reproductive products to empty

- In some fishes and most mammals, the cloaca is absent

37

What are some specializations of the alimentary canal that prolong passage of digesta? What is the rectal gland and which groups have such a gland?

- Structural modifications accommodating specialized diets, expansions or extensions of the canal may develop to accommodate specialized diets, differentiation of the canal may occur through regionalization

- Rectal gland opens into the cloaca; eliminates excess salt ingested during feeding

- Rectal glands are found in elasmobranchs and coelacanths

38

What are pyloric ceca? Which group has them and what is their function?

- In most bony fishes, pyloric ceca opens into the duodenum form at the junction between the stomach and the intestine

39

What are the four chambers of the ruminant stomach? Know the material in Box Essay 13.5 – The “Spare” Appendix (p. 497). What are the functions of the liver?

  • The four chambers are rumen, reticulum, omasum, and abomasum
  • Rumen receives food after it is clipped by teeth and swallowed
  • Reticulum is a small accessory chamber with honeycombed texture
  • Omasum is lined with esophageal epithelium; folded into overlapping leaves
  • The abomasum is an actual derivative of the stomach; true stomach
  • Functions of the liver
    • Production of RBC, destruction of old blood cells
    • Detoxifies and removes toxic substances from blood
    • Bile is manufactured here and releases into the intestine to emulsify fats or break them up into smaller droplets
    • Carbohydrates, proteins, and fats are stored and metabolized in the liver
40

What is the ‘exocrine’ product of the liver and what is its function? Where is bile stored in most vertebrates? What is pancreatic juice and where does it enter the digestive tract?

- Bile is the ‘exocrine’ product; bile serves to emulsify fats

- In most vertebrates, bile is stored in the gall bladder

- Pancreatic juice is an alkaline exocrine product; composed of enzyme trypsinogen

41

Where does absorption of food begin and what is absorbed? Where are the end products of digestion usually formed and absorbed? What does the appearance of a long, distinct large intestine correlate with?

  • Absorption of food begins in the stomach
  • Water, salts, and simple sugars are absorbed
  • End products of digestion are usually formed and absorbed in the intestine
  • Appearance of a long, distinct large intestine in terrestrial vertebrates correlates with greater requirements to conserve water
42

Why does the large intestine retain digesta? What is coprophagy and which groups exhibit such behavior?

  • Large intestine retains digesta so that the electrolytes and water secreted in the upper digestive tract can be resorbed by the body
  • Coprophagy is the process of eating of feces
  • Tinamous, a family of neotropical birds, and rabbits, hares, many rodents, and even gorillas eat their feces
43

What is the purpose of mechanical manipulation of food?

- To improve the access of digestive enzymes

44

What is mastication and what group is this characteristic of? How are different types of foods chewed?

  • The mastication process reduces a large bolus to smaller particles so that digestive enzymes can work on more surface area
  • Mammals is the group of mastication
  • Compressing, grinding, sliding, and cutting
45

Which vertebrates are able to produce cellulases? What microorganisms break down cellulose in the digestive tracts of host vertebrates? What is fermentation? What is foregut fermentation?

  • Many herbivores depend on it as a major energy source, yet, no vertebrate is able to manufacture cellulases
  • Symbiotic microorganisms, bacteria, and protozoans produce cellulases to break down cellulose from ingested plants
  • Fermentation is the microbial process of breaking down cellulose; yields organic acids that are absorbed and utilized in oxidative metabolism
  • Foregut fermentation (gastric fermentation): process in which microorganisms digest food in a specialized stomach
46

In which groups does foregut fermentation occur? What is hindgut fermentation and which groups are examples of hindgut fermenters?

- Birds, mammals, ruminants, sloths, monkeys, elephants, and many rodents

- Hindgut fermentation (intestinal fermentation) is process in which microorganisms digest food in the intestines

- Rabbits, pigs, horses, and koalas are examples of hindgut fermenters


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