Digestive System Flashcards
list and describe the 5 functions of the digestive system
- prehension: the act of obtaining food
- mastication: chewing, mechanical breakdown
- digestion: chemical breakdown
- absorption: smaller components entering rest of body
- elimination of solid wastes: as feces
list the 4 layers of the wall of the digestive tract, from innermost to outermost
- mucosa
- submucosa
- muscularis
- serosa
describe the mucosa
inner layer, epithelia lining
list and give the locations and functions of the two types of epithelial linings of the mucosa
- stratified squamous epithelium: protective layer, prevents damage, mouth and esophagus
- simple columnar epithelium: more glandular for digestion and absorption
what tissue composes the submucosa?
loose areolar connective tissue
describe the two muscle types and their locations in the muscularis, plus the functions
- skeletal muscle: mouth and esophagus (chewing and swallowing)
- smooth muscle: rest of tract
circular and longitudinal layers allows for contraction in different directions and propulsion
describe the serosa, including an alternate name and tissue type
outer layer, also called visceral peritoneum, simple squamous epithelium
list the 3 components of the mouth
- labia/lips
- teeth
- tongue
describe the labia/lips of the mouth
entrance to mouth, major species variation
list and describe the 4 types of teeth from front of the mouth to the back
- incisors: cutting, prehension
- canines: tearing, mastication
- premolars: grinding, mechanical
- molars: fine grinding, mechanical
what is the dental formula?
indicated the number of upper and lower incisors (i), canines (c), premolars (pm), and molars (m) on one side of the mouth
how many upper incisors and canines do ruminants have?
zero!
list the 4 structures of teeth
- periodontal membrane
- dentin
- root
- enamel
describe the periodontal membrane
attaches tooth to underlying bone in a gomphosis joint, a fibrous joint made of dense regular connective tissue
describe dentin
mineralized substance that makes up the majority of the tooth
describe the root of a tooth
contains nerves and blood vessels
describe enamel
covers the crown, which is the part of the tooth visible above the gum, is the hardest substance in the body and mineralized
can enamel be resynthesized?
no, it can not be resynthesized once worn away
describe the tongue, including muscle type and epithelial type
skeletal muscle for voluntary movement, covered with stratified squamous epithelium, contains tastebuds which allow animal to distinguish between harmful and proper food
what happens in the pharynx?
contraction of the tongue will fold epiglottis over the larynx to direct food/water to the stomach
where is the esophagus?
extends from the pharynx to the stomach
what muscle and epithelium make up the esophagus?
skeletal muscle, stratified squamous epithelium
where is the cardiac sphincter and what muscle is it composed of?
smooth muscle, at the junction on esophagus and stomach
what is the role of the cardiac sphincter?
keeps food from returning to esophagus
is the cardiac sphincter present in ruminants? equines?
not present in ruminants due to regurgitation, so well developed in equines that it is almost impossible to vomit
what epithelium lines the stomach?
simple columnar
what muscle makes up the stomach?
smooth muscle
list and describe the 2 curvatures of the stomach
- lesser curvature: attached to liver
2. greater curvature: situated caudally, not attached to anything
what does the pyloric sphincter connect?
stomach to duodenum
what is the role of the pyloric sphincter?
keep contents of stomach from moving immediately into duodenum and keep contents of duodenum from returning to stomach
what muscle makes up the pyloric sphincter?
smooth muscle
list the 4 compartments of the ruminant stomach
- reticulum
- rumen
- omasum
- abomasum
where does the esophagus empty in ruminants?
into the space between the reticulum and rumen
describe the locations and insides of the reticulum
most cranial compartment, sits right against the diaphragm, honeycomb inside
describe the function and epithelium of the reticulum
lined with stratified squamous epithelium, traps foreign material
which is the largest ruminant stomach compartment?
the rumen, takes up the majority of the left side of the abdomen
what is the function, epithelium, and special thing about the rumen?
microbial fermentation, stratified squamous, has tiny papillae projections
what does the inside of the omasum look like?
sheets
give the function and epithelium of the omasum
thin sheets filter by particle size, stratified squamous epithelium
what is the only ruminant stomach compartment not lined with stratified squamous epithelium, and what epithelium does line it?
the abomasum, simple columnar epithelium
what is the function of the abomasum?
same as the monogastric stomach, chemical digestion
what epithelium lines the small intestine?
simple columnar
list and describe the 3 parts of the small intestine
- duodenum: connected to stomach via pyloric sphincter; receives ducts from pancreas and gallbladder
- jejunum: longest part; site of digestion and absorption of digested nutrients
- ileum: connects to large intestine
what is the epithelial surface of the small intestine arranged into?
small projections called villi
what are microvilli?
projections on surface of each epithelial cell
what is the role of villi and microvilli?
to increase the surface area for absorption
what are all 3 components of the large intestine lined with?
simple columnar epithelium
what is the cecum?
the blind pouch where the large intestine and ileum join
list and describe the 3 parts of the colon
- ascending colon: runs back up cranially
- transverse colon: runs across body
- descending colon: runs down caudally
what is the anus? what epithelium lines it?
the external opening at the end of the digestive tract; stratified squamous
what is different about the avian mouth?
no teeth
what is different about the avian esophagus?
it enlarges into the crop, then reforms and leads to the proventriculus
what does the avian crop do?
stores and moistens food
what does the avian proventriculus do?
where chemical digestion starts
what does the avian gizzard do?
mechanical digestion; swallowed grit is their form of chewing here
are there species variations between mammalian and avian small intestine?
none
how does the avian large intestine differ from the mammalian?
paired ceca, small colon (no ascending, descending, or transverse
list 3 accessory components of all digestive tracts
- mesenteries
- lesser omentum
- greater omentum
describe and give epithelium of mesenteries
membranes continuous with visceral peritoneum, composed of simple squamous epithelium, holds intestines in place
describe what the lesser omentum connects an is attached to, and epithelial type
membrane that connects stomach to liver, attached to lesser curvature of stomach, simple squamous epithelium
describe what the greater omentum connects to, covers, and give connective tissue type
connected to greater curvature of stomach, covers ventral surface of abdominal cavity, composed of adipose tissue
how many pairs of and what is the function of the salivary glands?
3 main pairs, produce saliva
list and give location of the 3 main salivary glands
- parotid gland: ventral to ear; parotid duct runs under mandible to mouth
- mandibular gland: caudal to mandible
- sublingual gland: ventral to tongue
list and give the locations of 3 accessory glands of the digestive tract
- pancreas: alongside duodenum
- liver: largest gland in body, lobed, sits caudal to diaphragm
- gallbladder: dorsal side of liver
give the function of the gallbladder, and do horses have?
stores bile produced by liver, horses don’t have
list the 2 types of contraction/movement of the digestive tract
- peristalsis
2. segmentation
describe peristalsis
unidirectional waves of contraction that propel contents down digestive tract, contraction on cranial side to push down
describe segmentation
back and forth mixing of contents of digestive tract, alternating areas of contraction
what is prehension?
animals using lips, tongue, and/or teeth to obtain food/water
what is mastication?
when food is reduced to smaller pieces by chewing and mixed with saliva
what 3 things make up saliva?
water, mucus, enzymes
list and describe 2 enzymes in salive
- lysozyme: antibacterial
2. alpha amylase: starts to digest starch
is alpha amylase found in ruminants or carnivores?
no
what is deglutition?
the process of swallowing
list and describe the 3 steps of deglutition
- passage of food through the mouth: food is chewed and mixed with saliva and formed into a bolus, tip of tongue moves to roof of mouth, which pushes food bolus up and back towards pharynx
- passage through pharynx: contractions of the tongue fold epiglottis over trachea= no breathe while swallow, peristaltic contractions move food through pharynx
- passage through esophagus: peristaltic contractions propel food down esophagus and into stomach, very quick process
list and describe the 4 steps of rumination
- regurgitation: food bolus returns to mouth via reverse peristalsis
- remastication: food is thoroughly chewed
- reinsalvation: food is mixed with more saliva
- redeglutition: food returns to stomach
which steps of rumination occur at the same time?
remastication and reinsalvation
what does rumination allow ruminants to do?
obtain a lot of food quickly and then digest in safety
where does microbial fermentation occur?
in the rumen in ruminants and in the cecum in hindgut fermentors
what do microbes have to break down cellulose?
cellulase
what is cellulose?
the main fiber component of food
what do microbes release after breaking down cellulose? (2)
- volatile fatty acids: acetate, proprionate, and butyrate, which are absorbed via rumen wall
- gases: CH4 (methane), and CO2
what is eructation?
removes gases; belching
what is bloat? how to fix?
occurs when gases build up in rumen due to failure of eructation, pass a tube down the esophagus to fix
how do microbes alter fat?
by converting unsaturated fatty acids into saturated fatty acids
what do microbes do to protein?
break down protein and synthesize microbial proteins
list and describe the 3 phases of the stomach/abomasum secreting gastric juice
- cephalic phase: gastric juice secreted due to the smell, sight, or food entering the mouth in preparation for consumption
- gastric phase: juice secreted due to presence of food in stomach
- intestinal phase: duodenum secretes gastric inhibitory peptide, which inhibits gastric juice secretion
what is gastric juice?
a combination of the secretions of cells in the stomach
list and describe the 2 things that parietal cells in the stomach secrete for gastric juice
- HCl: very acidic, kills bacteria, denatures protein
2. Intrinsic factor: binds to vitamin B12 and allows for its absorption
list and describe the 3 things that chief cells in the stomach secrete for gastric juice
- gastric lipase: breakdown of fat
- pepsin (from pepsinogen: breaks down protein
- rennin: only found in young ruminants, coagulates milk for slower passage through tract for nutrient absorption
what is emesis?
the emptying of the stomach towards the mouth, a protective measure; species variations in ease/difficulty
can ruminants perform emesis?
they can, but it will be the contents of the abomasum entering the omasum and forward for neutralizing, won’t see outside of body
when does the duodenum secrete hormones?
when partially digested material enters
list and describe the 3 hormones the duodenum secretes
- gastric inhibitory peptide: inhibits gastric juice secretion
- secretin: acts on pancreas to secrete bicarbonate, which makes contents less acidic
- cholecystokinin (CCK): acts on pancreas to secrete digestive enzymes and on gallbladder to secrete bile
list and describe the 3ish enzymes released by the pancreas
- amylase: breaks down carbohydrates
- lipase: breaks down fat
- trypsin and chymotrypsin: break down protein
what is the function of bile?
emulsifies fat in small intestine, allows for digestion and free movement of fat in small intestine
what is bile made of and what does this mean?
a lipid material; won’t mix well with aqueous environment
where does absorption occur?
along the epithelial surface of jejunum
where are transporters for nutrients found in the jejunum?
along the intestinal villi
list and describe the 4 things that are absorbed in the jejunum
- glucose: major carbohydrate
- amino acids: from protein
- fatty acids: from fat digestion
- vitamins and minerals
which 3 of the things that are absorbed in the jejunum enter the hepatic portal system?
glucose, amino acids, vitamins and minerals
where do fatty acids go after absorption?
to the lymphatic system
describe the hepatic portal system
blood returning from the heart takes a pit stop at the liver first, and then reforms capillaries
what does the hepatic portal system allow the liver to do?
choose what happens with nutrients
what does the lymphatic system do with fatty acids?
causes fat to be pumped through body before entering bloodstream
what is the function of the colon in everyone except hindgut fermentors?
water absorption
what is the function of the colon in hindgut fermentors?
microbial fermentation to produce volatile fatty acids which are absorbed in the colon for use
give 3 examples of hindgut fermentors
horses, rabbits, guinea pigs
who do strong contractions of the descending colon do?
push contents into rectum, signaling the need to defecate
what does the relaxation of the anal sphincter and contraction of abdominal muscles result in?
defecation
