Feeding and Digestive System Flashcards
(76 cards)
1
Q
What are the components of the mammalian digestive system?
A
Buccal cavity (mouth)
Salivary Gland
Oesophagus - a muscular tube for contractions
Stomach - gastric juice for digestion
Liver - regulation of blood glucose, production of bile, deamination and detoxification
Bile duct
Pancreas - produces pancreatic juice (digestive enzymes)
Duodenum - part of small intestine. Secrete digestive enzymes
Colon - part of large intestine. Absorb water and mineral salt. No digestion
Ileum - part of small intestine. Digestion
Rectum - temporary store of faeces.
2
Q
What is suspension-feeding (filter-feeding)?
A
Filter small particles (alive or dead, depending on species) out of water column
3
Q
What is suction-feeding?
A
Open mouth, suck in food
4
Q
What is ram-feeding?
A
Open mouth, swim over food
5
Q
What is inertial feeding?
A
Inertia of food is used to move it in oral cavity
6
Q
What is transport (feeding)?
A
Movement of food within oral cavity (by water currents in aquatic vertebrates or tongue in tetrapods)
7
Q
What is mastication?
A
Physical reduction of food size by chewing
8
Q
What are the two key patterns in the evolution of feeding?
A
Shift from water transport to tongue (tetrapoda)
Inertial feeding, mastication (Amniota)
9
Q
What was feeding like (before specific evolution)?
A
- Intraoral prey transport by water currents
- Gape constant prior to fast opening
- Mouth opening caused by both lower jaw depression and head elevation
- Recovery phase present
- Hyoid retraction coincident with fast opening
10
Q
What evolved in feeding in early tetrapoda?
A
- Tongue-based intraoral transport
11
Q
What evolved in feeding in amniota?
A
- Short slow-open phase (SO) just prior to fast opening
- Recovery phase absent
- Inertial feeding present
- Four-stage masticatory cycle for intraoral food
- Gape increases mostly by lower jaw depression
12
Q
What are teeth (think vertebrate)?
A
The vertebrate innovation
13
Q
What did teeth come from?
A
Bony armour in early vertebrates (ectodermal)
As jaws evolved and ectodermal margin of jaws moved inside the mouth, teeth moved inwards as well.
But: Conodonts
Pharyngeal teeth?
14
Q
What is the inside out theory regarding teeth?
A
Teeth originated in pharynx (endodermal) and progressed forward in mouth
15
Q
How are teeth useful?
A
Initiate mechanical digestion
Increase surface area for chemical digestion
Grip food (friction)
Puncture food for enzyme activity (insectivores; venomous animals)
Mineral reservoir
16
Q
What is polyphyodont?
A
Multiple generations of tooth replacement (most vertebrates)
17
Q
What is diphyodont?
A
Two sets of teeth: Milk and permanent (most mammals, incisor, canine and pre molar teeth are replaced)
18
Q
What is monophyodont?
A
A single set of teeth (e.g. cetaceans)
19
Q
What is homodont?
A
Teeth of similar shape along the jaw (ancestral)
20
Q
What is heterodont?
A
Teeth of different shape along the jaw (crocodylia, mammalia)
21
Q
What are tooth plates?
A
Fused teeth (rare)
22
Q
What are the three tooth attachment types?
A
Acrodont
Pleurodont
Thecodont
23
Q
What is acrodont?
A
Tooth bottom loosely attached to jaw
24
Q
What is pleurodont?
A
The tooth is loosely attached to the jaw at the side
25
What is thecodont?
Tooth is deeply set in a socket attached to the jaw
26
What do we know about evolution of tooth forms: Early vertebrates?
Homodont
Polyphodont
Acrodont
27
What do we know about evolution of tooth forms: Amniotes?
Independent origins of thecodonty in archosaurs, e.g. crocodiles, dinosaurs, even early birds and synapsids/mammals; some lizards = pleurodonts
28
What do we know about evolution of tooth forms: Mammals?
Heterodont
Diphyodont
(+ Secondary exceptions)
29
What are the types of teeth in a puppy?
(back to front)
Premolars
Canines
Incisors
30
What are the types of teeth in an adult dog?
(Front to back)
Molars
Premolars
Canines
Incisors
31
What are the components of a tooth?
Inner pulp (living, softer)
Middle cementum (~living; bone-like, layered)
Outer dentin(e) (harder)
Outermost enamel (doesn't grow after tooth erupts; only ectodermal part; 95% inorganic)
Self-sharpening properties
- From wear patterns when teeth rub together
32
Describe mammalian teeth in brief:
Dental formula (upper/lower)
- Incisors, canines, premolars, molars
Brachydont (ancestral) = low-crowned
Hypsodont (derived) = high-crowned, deep-rooted, related to grazing
33
What are the two parts of a tooth (top and bottom)?
Root
Crown
34
What are the occlusal surfaces on mammalian teeth?
1. Bunodont:
Rounded peaks, generalised (ancestral)
2. Lophodont:
Cusps into drawn-out ridges. Rodents and perissodactyls; elephants
3. Selenodont:
Crescent-shaped cusps. Artiodactyls
35
What are the three main parts of the buccal cavity?
Lips
- Fleshy, muscular in mammals, suckling milk etc; cheeks
-Vs. beaks, keratinous: Birds, turtles
Palate
- Vertebrates ancestral hard palate (which bones? Skull!!!)
Secondary palate
- Evolved convergently in mammals, crocodylia and sea turtles
36
What is the jaw mechanism in early actinopterygia?
Epaxial muscles open upper jaw
Hypaxial muscles open lower jaw
Adductor muscles close jaw
Similar throughout early vertebrates incl. amphibia
37
What is the difference in jaw mechanisms between carnivores and herbivores (mammalia)?
Bite force:
- Differently produced, mainly by temporalis in carnivore; masseter in herbivore
- Note only lower jaw opens/closes
38
How do snakes exhibit kinesis?
Snakes swing their fangs forward for striking using very mobile joints of the upper and lower jaws
39
What do we know about digestive system anatomy (generally)?
One-way (normally!!) flow of ingesta through gut
Mechanical and digestive processing
Absorption
Excretion
40
What are the components of the turtle digestive system?
Buccal cavity
- Oral glands
Pharynx
Alimentary canal
- Oesophagus
- Liver
- Stomach
- Gallbladder
- Pancreas
- Small intestine
- Large intestine
- Urinary bladder
- Cloaca
- Cloacal opening
41
What are the accessory digestive glands?
Salivary
Pancreas
Liver
42
What do the salivary glands do?
Salivary glands release saliva into mouth; amylase breaks down carbohydrates
43
What does the pancreas do?
Secretes a variety of enzymes into small intestine
44
What does the liver do?
Help emulsify fats
45
What is venom?
Modified saliva
46
What do you know about the evolution of venom in Squamata?
Surprise discovery
Venom is ancient for many lizards
"Toxicofera" hypothesis
Increased venom enzymes in snakes, venomous lizards
47
What do we know about rear-fanged snakes?
Ancestral trait
48
What do we know about front-fanged snakes?
Novel trait in elapid and viper snakes
49
What is the epiglottis?
Flap of cartilage at root of tongue, depressed during swallowing to cover opening to trachea and ensure food is delivered to the oesophagus
50
What does a stomach do?
Mechanical and chemical digestion = primary
Specialised lineages: More separation of functions (glandular/muscular stomachs)
Hydrochloric acid, gastric juices and microbiome all contribute to the breakdown of food
What is gut microbiome?
Mechanical breakdown of food via churning
Secondary functions: Absorption of water, salts and vitamins; storage
51
What are the components of the stomach?
Smooth muscle layers
Rugae (increased surface area, like villi)
Pylorus
- Sphincter
- Canal
- Antrum
Fundic gland
Parietal cell
Chief cell
Gastric pit
Muscularis mucosae
Submucosa
Smooth muscle layer
52
What do the ridges in the stomach, the rugae, do?
Create gastric pit
- Increase surface area
53
What is an adaptation of the small intestine?
Increased surface area via microvilli (up to several thousand per epithelium cell)
54
What are the functions of the small intestine?
Peristalsis
Enzyme secretions
Selectively absorb final products of digestion (amino acids, carbohydrates, fatty acids)
55
What is the caecum?
At juncture of small and large intestine in some species (e.g. mammals)
56
What is the role of the large intestine?
To reabsorb water
57
What are the gross components of the small intestine?
Peyers patch
Serosa
Longitudinal muscle
Circular muscle
Circular fold (plica circularis)
58
What are the components of the vili of the small intestine?
Peyers patch
Villi
Mucosa
Submucosa
Central lacteal
Intestinal gland
Goblet cell
Absorptive epithelial cell
Artery
Vein
59
What do you know about the diversity of non-mammalian intestines?
Different lengths
Around 9 cm - 65 cm
Not very big
60
What do you know about the diverse intestines of mammals?
Very different lengths
Up to 850 cm in humans!!!
Ranges from fairly short ~40cm to extremely long ~850cm!!!
61
What happens in gut fermentation?
Microbiome to the rescue!!
Fermenting flora release CO2, methane
Break down complex ingesta (e.g. cellulose)
Enlarged gut chamber with greater surface area
62
What does foregut fermentation require?
Specialised stomach
63
What does hindgut fermentation require?
Specialised caecum
64
What do ruminants have (regarding fermentation)
Ruminants (Artiodactyls) have a rumen (stomach)
Grazers (cattle/sheep) and browsers (goats/deer)
65
What is ruminating?
Regurgitating for remastication
66
What are the components of a ruminant stomach?
Rumen
Gastroesophageal sphincter
Oesophagus
Ruminoreticular fold
Reticulo-omasal sphincter
Reticulum
Omasum
Abomasum (true stomach)
Pylorus
Glandular zone
Forestomach
Duodenim
Fermentation zones
67
What is the evolution of ruminants?
Fusion of cuboid and navicular in tarsus, etc.
Omasum (plus full rumination)
Parallel-sided astragalus
Complete distal metapodial keels (not in gelocids)
Fused metapodials with open metatarsal gulley
Fused metapodials with closed metatarsal gulley
Double lacrimal orifice
68
What adaptations are required for hindgut fermentation? Who needs it?
Extensive elongation of intesting and large caeca extend the volume available for fermentation
Rabbits, pigs, horses (perissodactyls), elephants, rodents, amphibians, reptiles and some birds
69
What is foregut vs hindgut fermentation?
Foregut fermentation is:
- Typically in larger species
- Very effective fermentation
- More mechanical breakdown via regurgitation
- Uses nitrogen as a resource; less wasted
- Camels re-use urea to conserve water
BUT
- Fermentation destroys many nutrients
- Microorganisms get digested to replace nutrients
- Slow fermentation
- Best with higher-quality food (not as good at grazing on grass)
- Large-bodied hindgut fermenters do very well
70
What kinds of digestive specialisations would an animal with a beak need, vs. a more typical toothed vertebrate? If it were herbivorous?
Muscular gizzard to grind material
Crop for storage and softening of food before it enters the stomach
71
What anatomical specialisations might inertial feeding require?
Cranial kinesis and flexible jaw
Strong neck
72
What functions does a tongue perform?
Food capture
Intraoral transport of food within the buccal cavity
Swallowing
Taste
73
How did the feeding and jaw mechanisms, tooth form and digestive system co-evolve from early vertebrates to amniotes?
Early vertebrates:
- Suction or filter feeding
- No true jaws or mineralised teeth
- Used a muscular pharynx and branchial arches to move food
- Simple gut, mainly passive and chemical
Jawed vertebrates:
- Jaws evolved from anterior pharyngeal arches, enabling biting and grasping
- First true mineralised teeth
- Still fairly simple digestion
Lobe-finned fish and early tetrapods:
- Transition from suction feeding in water to lingual and inertial feeding on land
- Muscular tongues play a role
- Labyrinthodont teeth and palatal teeth
- Early chewing behaviours
- Increasingly regionalised gut
Amniotes:
- Full diversification of feeding, lingual, chewing, swallowing, inertial feeding
- herbivory, carnivory, omnivory
- Heterodonty in mammals
- Occlusion development
- Temporal fenestration = stronger bite forces and jaw muscle expansion
- Highly regionalised and specialised digestive system
- Accessory glands
74
In what environments might foregut fermenters have advantages over hindgut fermenters of the same size?
Arid and semi-arid grasslands and savanna
- Extract more nutrients from grass
Nutrient poor woodlands
- Detoxify plant secondary compounds
Alpine or high-elevation meadows
- Slower and more complete extraction of energy in plants that may be high in cellulose and low in nutrients
75
How does the epiglottis exemplify a conflict between the feeding vs. respiratory systems?
Closes over the trachea when swallowing - prevents food from entering the lungs
76
Why might skull strength (e.g. bite force) and flexibility (e.g. kinesis) have tradeoffs?
Strength requires rigidity, demands a strong, fused skull
Flexibility requires mobility, so kinesis = less bone fusion = less strength
