Rest and digest physiology Flashcards
What is digestion
process by which is broke down mechanically and chemically into absorbable units
What forms the small intestines
duodenum, jejunum, ileum
What forms the large intestines
caecum, acending transverse and descending colon and rectum
What are herbivores
animals who feed on plants
what are carnivores
animals who feed on meat
what are omnivores
animals who regularly feed on both plants and meat
What are cows and sheep stomachs shaped and why
4 chambers to breakdown plant fibre (cellulose)
How do horses intestinal tract differ from other animals
developed large caeca and colons
What are levels of salivary amylase in carnivores like
low or not any at all, as food not in mouth long
What are monogastric
animals who only have 1 stomach like carnivores and also included are hind gut fermenters like horses and rabbits
what are ruminants
have a four chambered stomach and perform rumination such as cows, sheep, goats, giraffes and deer
What are pseudo-ruminants
animals who don’t ruminate but have 3 chambered stomachs such as alpacas, llamas, camels and hippopotami (some people also include hind gut fermenters in this group)
What is the avian digestive system stomach like
specialized stomachs called proventriculus (where chemical digestion occurs) and gizzard(where mechanical digestion occurs)
What are the 3 layers of mucosa
innermost-epithelium
middle- lamina propria (connective tissue that contains blood and lymphatic vessels as well as mucosa associated lymphoid tissue)
Final- muscularis mucosa which causes the mucosal membrane of the stomach to fold creating the rugae
Prehension for cows and other ruminants
Use protrusible tongue and mandibular incisors
What is prehension
obtaining food in oral cavity
Prehension for horses
upper lip, tongue and incisors
Prehension for carnivores
grasp prey with forelimbs and teeth and take into mouth by movements of head and jaw
what is mastication
breaks food down to increase its surface area for better enzymatic digestion
How does body detect food for mastication
presence of food in oral cavity stimulates sensory branches of trigeminal, facial and glossopharyngeal nerves then efferent input via trigeminal nerve activates masticatory muscles
Masticatory muscles in herbivores
masseter and pterygoid
Masticatory muscles in carnivores and omnivores
temporalis
Mastication movement herbivores
lateral movement of lower jaw
Mastication movement carnivores
shear their food with minimal side to side movement
What helps mastication and how
saliva into the ingesta
coat with mucus and depending on species start chemical digestion
also lubricating the ingesta is important for species that don’t have teeth to chew such as birds
What is deglutition
swallowing
what is swallowing
deglutition which is a complex reflex with its nervous control center situated in the medulla
nervous control for swallowing/deglutition
Starts as voluntary act with tongue pushing ingesta caudally then turns into involuntary reflex when pharyngeal pressure receptors stimulate the deglutition centre(medulla) to initiate swallowing reflex
what muscles and nerves involved in swallowing
muscles of tongue pharynx, oesophagus and controlled by lower motor neuron, vagus (X), hypoglossal (XII) , glossopharyngeal (IX) and efferent parts of trigeminal (V) nerve
Describe what happens when swallowing
At the beginning breathing stops as soft palate elevated to close nasopharynx and glottis is pulled under epiglottis to ensure block of laryngeal opening
Once all opening are closed the muscle contractions along wall of pharynx pushes ingesta towards oesophageal opening
What is peristalsis
wave-like smooth muscle contractions that take place throughout the GI tract and propel the ingesta aborally (away from mouth)
What does the adaptive relaxation properties of proximal stomach mean the stomach does
it is in a state of continuous weak contraction so when as it fills the stomach relaxs allowing for dilation without increase of intraluminal pressue
What does the adaptive relaxation feature mean the proximal stomach can do
capability to store food facilitating the accommodation large volumes
What does the distal stomach facilitate
grinding by intense, slow-wave activity with frequent muscular contractions
what happens when wave of peristalsis nears pylorus
it constricts blocking most of gastric exit, only allowing particles about 2mm or less to pass through
What size of food that can pass through a constricted pylorus
2mm or less
What is chyme
finely ground, partially digested and liquid material passes through to the duodenum after stomach
what happens if ingesta is not small to pass through pylorus gastric exit
it is propelled back for further griding until it is chyme
Gastric emptying time for liquid and solid
liquid- 30 mins
solids- 3-4hours
what is aborally
away from mouth
Dogs speed circular contraction of peristatic waves in duodenum, jejunum and ileum
duodenum-12cm/s
jejunum- 4-7cm/s
ileum- 0.7-0.8cm/s
4 types of small intestine motility patterns
peristatic waves (circular contractions)
stationary contractions
cluster of contraction
migrating motor complexes
what are stationary contractions
segmental contractions at single sites; enables mixing of luminal contents
What are peristaltic waves
circular contractions propagating aborally
what are cluster of contractions
several short repetitive contractions; enables mixing of luminal contents
what are migrating motor complexes
cyclic motor pattern exhibited during inter-digestive state consisting of cluster of contractions divided into 4 phases that propagate over a longer intestinal segment
4 phases of migrating motor complexes
Phase 1- does not involve contractions
phase 2- random contractions occur
phase 3- rapid contractions with high amplitude and duration
phase 4- amplitude and duration of contractions decrease
MMC are disrupted when animals ingest feed
overall definition of large intestines
fermentation chambers and absorb vast amount of water from the digesta producing faeces
what is digesta
chyme that has been broken down further in the small intestine
name the most common contractile patterns in the large intestine
peristaltic and antiperistaltic waves
aborally propagating giant contractions
What are peristaltic and antiperistaltic waves
happens in caecum and proximal colon, the waves are of shallow circular constriction followed by low retropulsion
What are aborally propagating giant contractions
large amplitude, long duration, slower propagation of velocity
what is defecation
act of expelling material that could not be used in form of faeces out of digestive tract through the anus
what species have a cloaca and not anus
birds, reptile and amphibians
What is emesis
the forceful oral expulsion of gastrointestinal contents due to contractions of the sotmach and proximal intestions together with the thoracoabadominal musculature
Neurones and brain part involed in emesis
Vomiting centre is in medulla oblongata and receives inputs from the GI tract, the vestibular apparatus, the chemoreceptor trigger zone and the cerebral cortex
What is vomiting/emesis used fro
defence act to remove toxins, drugs and pathogens from body
What cant and why cant they vomit
rabbits, hares and rodents as they lack the vomiting reflex and their oesophageal sphincters and very strong
What is Myogenic control for GI function
electrical activity of GI smooth muscles is initiated from the interstitial cells of cajal which surround circular and longitudinal smooth muscle layers
What are Interstitial cells of cajal (ICC)
resembles purkinje cells with rhythmic, oscillating, slow wave properties
so called pacemakers of the guts
What is neural control of GI function
GI tract is innervated by the enteric nervous system and the autonomic nervous system
How does the sympathetic system affect GI muscles and glands
Inhibitory to GI muscles and glands
What makes up parasympathetic system in GI tract
Comprises vagus ( oesophagus, stomach, pancreas, cranial large intestine) and pelvic nerves ( caudal large intestine, rectum and anus)
What is hormonal control for GI function
system uses several hormones such as cholecystokinin, gastrin and secretin as part of the GI control
4 major salivary glands
zygomatic, parotid, mandibular, sublingual
What is saliva made of
mostly mucus and water but also has antibiotic activity, enzymes and chemicals
Saliva antibiotic activity
antibodies and lysozymes in saliva keeps oral flora in check
What is present in omnivorous animals in saliva
salivary amylase but in carnivores this enzymes is usually absent
Saliva fat digesting enzymes
lingual lipase more commonly present in young animals such as calves while on milk diet
What does ruminant saliva have high concentrations of
bicarbonate and phosphate and high pH which are necessary for neutralising acids formed by fermentation in the rumen
What regulates salivary glands
parasympathetic system- autonomic, parasympathetic nerve fibers of facial and glossopharyngeal nerves stimulate salivary gland cells through cholinergic receptors
How much saliva a day in adult cow
100-200 L
so this is why digestive diseases can be important and lead to hypovolemic shock quickly
What happens to majority of digestive secretions produced by the body
reabsorbed
Cephalic phase of gastric secretion
ACh release by the ENS in response to parasympathetic vagal impluses from anticipation of eating
ACH stimulates G cells (gastrin producing) present in gastric mucosa of distal stomach to produce gastrin which increases secretion of HCL and gastric contractions
ACh also stimulates parietal cells to secrete HCL causing high concentrations of acid to lower pH of stomach
Gastric phase of gastric secretion
Initiated by distention of stomach causing changes to stretch receptors providing afferent stimulation to ENS
Food buffers the pH in stomach, raising the pH and removing inhibiting effect of acid on G cells further stimulating the secretion of gastrin
How does gastrin secretion depend on
Gastric pH - when it to about pH 2 , gastrin secretion is suppressed and at pH 1 gastrin secretion is stopped completely
Within mucosa of stomach and gastric pits name the 3 main type of cells
surface mucus cells
chief cells
parietal cells
what are surface mucus cells of stomach and where found
found in all parts of stomach and secrete mucus to lubricate food and protect stomach wall from mechanic injury due to to the griding activity and from autodigestion( damage by digestive enzymes)
what are chief cells of stomach and where found
found in the fundus and secrete pepsinogen( precursor of pepsin which breaks proteins to peptides)
What are parietal cells of stomach and where found
found in the fundus and secrete HCL creating a low pH environment which denatures several proteins and enables pepsin to work effectively
general pH of stomach in herbivores
3-4
general pH of stomach in carnivores
1-2
What is the small intestine the major site for
enzyme digestion and absorption
especially in duodenum where both pancreas and live through gall bladder secrete their enzymes and other products
In dogs where do the pancreatic duct and common bile duct open into
duodenum in separate locations (but quite close together)
In cats how to the pancreatic duct and common bile duct open into the duodenum
they join before reaching the duodenum and form the ampulla of Vater/ hepatopancreatic ampulla
Which then passes through sphincter of oddi before opening into the major duodenal papilla in duodenum
What do 20% of cats have (accessory pancreatic duct)
an accessory pancreatic duct empties into the minor duodenal papilla
What is secretin and what activates it
hormone produced as a response to the passage of acidic chyme through the pyloric sphincter into the duodenum
what does secretin do and produced by
secretin is produced by the duodenum and primarily stimulates bicarbonate secretion from pancreas also stimulates biliary bicarbonate secretion and plays a role in neutralizing the acidic chyme arriving from the stomach
what is in the duodenal mucosa
structures called crypts of Lieberkühn where several different cell types live
What is apart of the crypts of Lieberkühn in duodenal mucosa
brunners glands- secrete alkaline-based mucus to protect the duodenal mucosa and secretin producing cells
other cells that produce- antimicrobial peptides, cholecystokinin, amylases, proteases and lipases
Function of somatostatin to do with gut motility
decrease gut motility and reduce secretion of digestive fluid
what secretes somatostatin
pancreas- endocrine portion
What does exocrine portion of pancreas release
digestive enzymes and bicarbonate into the duodenum via pancreatic duct.
what causes the pancreas to release its exocrine products
stimuli from ANS and secretion of cholecystokinin and secretin from duodenal wall plus gastrin from gastric wall
what does bicarbonate do
neutralizes the acidic pH and allows other enzymes to work
what is autodigestion
damage by digestive enzymes
what main enzymes does the pancreas release
proteases, lipases and amylases
most in precursor form to prevent autodigestion
what is trypsinogen
enzyme release by pancreas and converted to trypsin by enterokinase breaking down proteins to amino acids
what do lipases do
convert fats to fatty acids and glycerol
what does amylase do
acts on starch converting them to simpler sugars like maltose
what happens when the liver produces bile
stores in gall bladder and secretes into duodenum via common bile duct through major duodenal papilla
what happens when bile is secreter through major duodenal papilla but little to no food in the intestinal lumen
sphincter of oddi is closed and bile diverted into gall bladder
what happens to species without a gallbladder like horse and rat
sphincter of oddi no function and bile secreted into intestine during all phases of digestive cycle
What signals bile to be released into the intestine
when food especially fatty reaches the duodenum there is secretion of CCK
which relaxes the sphincter of oddi and contracts the gall bladder
What is needed for hepatocytes to form bile acids from cholesterol
amphipathic molecule with hydrophillc and hydrophobic attributes- a detergent
function of bile acids
emulsify dietary lipids and solubilize the products of fat digestion
what makes the colour of bile and what is the colour
yellow/green due to bilirubin produced from breakdown of old erythrocytes and further breakdown of bilirubin through digestion produces the pigment of faeces
what do bile salts do
emulsify fat globules so that they have a larger surface area on which enzymes can act and also activates lipases
where do bile acids act, where are they absorbed and what happens to them
act in jejunum
absorbed in ileum
return to liver via hepatic portal vein due to enterohepatic circulation and almost completely absorbed which is the reason biles acids are found in low concs in systematic circulation
What do large intestines have/ dont
dont have any villi or digestive galnds but do have goblet cells secreting mucus
What are the 4 histological layers of the GI tract in order starting from the lumen
Mucosa, submucosa, muscularis, serosa
What feature gives the stomach the ability to store large amounts of food
Adaptive relaxation
What is the main purpose of the numerous villi and microvilli in the small intestine
to increase surface area
what organ produces secretin
duodenum
stimulus of release secretin
acidic chyme
response of secretin
bicarbonate secretion from pancreas and biliary tract
Why are bile acids only found in low concentrations in the systemic circulation
because they are reabsorbed via the hepatic portal vein
