GI physiology Flashcards
Steps of digestion (8)
- prehension
- mastication
- salivation
- swallowing
- stomach
- small intestine
- large intestine
- defecation
Prehension
the seizing and conveying of food to the mouth
Describe two different means of prehension
bipeds may use the upper limbs, quadrupeds may use the mouth/teeth/lips
Cow prehension
cattle utilize their mobile tongue to seize grass
cattle have a bony upper dental pad
no upper teeth, yes lower incisor
big molars for mastication
sheep prehension
utilize their mobile cleft lip
also have a dental pad, with no upper incisors
more selective/graze closer than cattle
horse prehension
mobile lip but NOT cleft
upper AND lower incisors
graze closer than cattle
avian prehension
no lips, no teeth
beak type is adapted to diet
mastication
vertical movement of the jaw that crushes food particles between the teeth
main purpose of mastication in carnivores
to make food small enough to swallow
main purpose of mastication in herbivores
need thorough mastication to reduce particle size enough to move through GI tract
What is special about ruminant mastication
form a bolus, swallow -> rumen, regurgitate, chew more
horses, unlike ruminants…
cannot regurgitate
salivation
the secretion and mixing of saliva with food
name the three paired salivary glands
- parotid (below ear)
- submandibular - either side of jaw
- sublingual - underneath tongue
Which diet type produces the most saliva? the least?
Carnivores - the smallest amount
omnivores - the middle amount
herbivores - the largest amount
Salivary composition (4)
- water
- mucin
- electrolytes
- salivary amylase (sometimes, NOT in cattle, dogs, cats or horses)
acinar cells, located in the salivary glands release…
HCO3 (bicarb), Na, Cl
Functions of saliva (7)
- lubrication
- solvent (dissolve food into solution, allow mixing with taste buds)
- cleans oral cavity/inhibits bacterial growth
- washes dental cavity
- buffer (NaCO3 in ruminants)
- nitrogen recycling (microbes utilize nitrogen)
- phosphorous source for ruminants
Is swallowing voluntary or involuntary?
first 1/3 is voluntary
last 2/3 is neural reflex
what is the name of the rhythmic muscle contractions that move food through the GI tract
peristalsis
What is the name of the sphincter that marks the end of the esophagus and the beginning of the stomach
the cardiac sphincter - failure causes heartburn
The cardiac sphincter is located at the ____ of the stomach, while the pyloric sphincter is located at the ______
top, bottom
Name the three regions of the stomach, from top to bottom
the fundic/cardiac region, the body or proper gastric region, and the pyloric region
What does the fundus produce?
mucus, HCl
what does the proper gastric region produce
HCl, pepsinogen
what does the pyloric region produce?
mucus, pepsinogen
What part of the intestines does the pyloric sphincter connect to?
the duodenum
What do the neck cells in the gastric pits produce?
mucus
what do the parietal cells in the gastric pits produce?
HCl
what do the chief cells in the gastric pits produce?
pepsinogen
What are the three types of cells in the gastric pits?
neck cells, parietal cells, and chief cells
How is HCl produced by parietal cells?
carbon dioxide and water are combined to make carbonic acid (H2CO3). The carbonic acid dissociates into H+ and HCO3. The bicarbonate is pushed out of the cell and into the bloodstream. The H+ moves into the lumen of the gut, along with a Cl from the bloodstream
what is the stomach of nonruminant animals called?
glandular stomach or true stomach
what is the ‘stomach’ of a chicken called?
the proventriculus
what is the stomach of a ruminant called?
the abomasum
how does mechanical digestion occur in the stomach? what is its purpose?
mechanical digestion occurs when the stomach contracts. it mixes digesta with enzymes (pepsin) and chemicals (HCl)
How does chemical digestion occur in the stomach? What is the purpose of chemical digestion?
Chemical digestion occurs via HCl, produced in the parietal cells of the gastric glands. HCl denatures proteins, kills bacteria, activates pepsinogen to pepsin, and maintains the low pH of the stomach
What is enzymatic digestion? What is its purpose?
Enzymatic digestion occurs when enzymes do work on digesta. Proteases digest proteins. pepsin is a protein, secreted as pepsinogen by the chief cells in the gastric pits. It cleaves proteins to be shorter chains. Rennin is a protease that acts on milk protein, coagulating it in the stomach and slowing the milk down as it passes through the digestive system. Rennin production wanes with age.
What is rennin?
protease that coagulates milk to slow it down as it moves through the digestive system
Functions of the stomach
- storage - the stomach allows animals to eat quickly and store larger amounts of food than could be passed through the digestive system if there were no stomach
- metering - doses out digesta from the stomach so as not to overload the small intestine
How does the stomach keep from digesting itself
- mucin - secreted by cells lining the stomach, provides a protective coating
- HCl is diluted in the stomach by saliva/digestion
- urease - an enzyme that breaks down urea/acts as a buffer
- enzymes are secreted in their inactive form - preventing cells from digesting themselves
What is an inactive form of an enzyme called?
zymogen
Name the three segments of the intestine, in order from pyloric sphincter to rectum
- Duodenum
- Jejunun
- Ileum
The duodenum is the primary site of…
Digestion
The jejunum is the primary site for…
Absorption
The ileum is the secondary site of…
Absorption
What are the 3 substances mixed with chyme to neutralize it?
- Bile acids
- Pancreatic juice
- Duodenal juice
What are the 2 functions of bile acid
- Detergent (solubilizes lipids)
- Complexes with fatty acids
What are the main enzymes in pancreatic juice (5) what are the main buffers? (2)
- Trypsin/chymotripsin
- Carboxypeptidases
- Aminopeptidases
- Intestinal lipase
- Amylase
- HCO3
- NaCO3
What are the components of duodenal juice? What is important about them?
Trypsinogen is activated into trypsin via the enzyme ENTEROKINASE!!!!!
Also other digestion for proteins and CHO
What happens in the cecum/colon in terms of digestion and absorption?
- Some microbial crude fiber digestion in monogastrics depending on diet type (herbivores-a lot, carnivores-very little)
The only digestion that occurs here is microbial
- Absorption is limited to VFAs, water and electrolytes
Characteristics of monogastric herbivore large intestine/cecum
- LARGE cecum - almost as large as a rumen
- Huge large intestine
Hind gut fermentation is not as efficient as rumination because…
- The site of digestion in hind gut fermentation (LI) is downstream from the site of absorption (SI).
- most commensal microbes are in the large intestine and cecum because that is where fermentation occurs
- The beneficial products of the commensal microbes (microbial protein, vitamins) cannot be absorbed by the small intestine :^(
- Thus, monogastrics such as herbivores need to eat higher quality food than ruminants because their digestion is less efficient
Monogastrics miss out on mco b vitamins, bacterial protein
How do monogastric herbivores compensate for less efficient digestion?
Coprophagy - think rabbits
-soft feces not fully processed, lots of vitamin b and bacterial protein
-hard, pelleted feces are fully processed
Omnivore monogastric large intestine
In between carnivore and herbivore
Some fiber digestion (dependent of time spent in LI), some vitamin synthesis , water/electrolyte absorption
Defecation
Discharge of excrement from rectum or cloaca
Two sets of muscles involved in defecation and their purpose
Internal anal sphincter
External anal sphincter
Prevent continuous defecation
The defecation reflex is initiated by…
The distension of the rectum by feces
5 components of fecal material
- Water
- Undigested food
- Residues of digestive enzymes
- Sloughed cells
- Bacteria
3 components of urine
- Water
- Minerals
- Nitrogenous compounds
-urea (mammal)
-uric acid (birds)
-ammonia - Glucose occasionally
Substances in urine are waste products of….
Metabolism
Substances in feces are waste products of…
Digestion
