GIT Physiology (struc) Flashcards
GIT - overview
Main Functions GI Tract
Transportation of ?
Digestion of food into ? particles
Absorption of ? components and transport into the ?
Regulation of ? and ? balance
? barrier (GALT – Gut Associated Lymphoid Tissue)
GIT - overview
Main Functions GI Tract
Transportation of food
Digestion of food into absorbable particles
Absorption of food components and transport into the blood
Regulation of water and electrolyte balance
immunologic barrier (GALT – Gut Associated Lymphoid Tissue)
Comparative anatomy
Why do animals have different GIT anatomy?
GIT anatomy and function - mammals
Esophagus
? (glandular/non glandular areas)
Small ? (duodenum, jejunum, ileum)
Large intestine (cecum (like the appendix in humans), ?, ?)
see pic:
Comparative anatomy
Why do animals have different GIT anatomy?
GIT anatomy and function - mammals
Esophagus
stomach (glandular/non glandular areas)
Small intestine (duodenum, jejunum, ileum)
Large intestine (cecum (like the appendix in humans), colon, rectum)
GIT- anatomy and function
comparative anatomy and behavior
?: the process of getting food into the mouth (diff. in dogs and cows)
? (also diff. in dogs and cows)
Lips
Tongue
Teeth
? (swallowing)
? palate
?
?
? sphincter
Mastication
Carnivores: sparsely, ? movements, jaws move like ? blades
Herbivores: short or long? time masticating, ? movements, large chewing ?
GIT- anatomy and function
comparative anatomy and behavior
Prehension: the process of getting food into the mouth (diff. in dogs and cows)
Mastication (also diff. in dogs and cows)
Lips
Tongue
Teeth
Deglutition (swallowing)
soft palate
tongue
epiglottis
esophageal sphincter
Mastication
Carnivores: sparsely, vertical movements, jaws move like scissor blades
Herbivores: long-time masticating, horizontal movements, large chewing surfaces
CONTROL OF DIGESTION
Gut function is regulated by:
? nervous system (ENS) (direct regulation)
gastrointestinal (GI) ? system (direct reg.)
? nervous system (CNS)
-> Influence on the gut is mediated through ? effects on the * ? * and
* ? * systems
CONTROL OF DIGESTION
Gut function is regulated by:
enteric nervous system (ENS) (direct regulation)
gastrointestinal (GI) endocrine system (direct reg.)
central nervous system (CNS)
-> Influence on the gut is mediated through indirect effects on the * enteric nervous sytem (ENS) * and
* GI endocrine * systems
ENS - enteric nervous system
An independent, ? enteric nervous system lies within the ? of the gut
The “little ?” within the gut
Extensive and highly sophisticated, containing as many neurons as the ? cord
Consists of:
? (mechanoreceptors - senses stretch, within muscular layer
and chemoreceptors within the mucosa layer)
? neurons
? neurons
? neurons
all of which lie within the ? wall
ENS - enteric nervous system
An independent, intrinsic enteric nervous system lies within the wall of the gut
The “little brain” within the gut
Extensive and highly sophisticated, containing as many neurons as the spinal cord
Consists of:
receptors (mechanoreceptors - senses stretch, within muscular layer
and chemoreceptors within the mucosa layer)
sensory neurons
interneurons
motor neurons
all of which lie within the gut wall
Communication with CNS
The parasympathetic and sympathetic nervous systems form the link between the ? nervous system (CNS) and the ?
In general
parasympathetic (receptors involved: nictonic, muscarinic) stimuli are ? (acetylcholine) i.e., they ? gut blood flow, motility, and ? secretion
sympathetic stimuli are ? (epinephrine)
CNS works in a coordinated manner with the ? in the regulation of gut function
? neurons (splanchnic) signal the presence of pathological conditions:
* ? of the gut wall
I.e., equine ?, gastric distention and ? in dogs
* ?
* presence of ? chemicals or substances in the gut lumen
Communication with CNS
The parasympathetic and sympathetic nervous systems form the link between the central nervous system (CNS) and the ENS
In general
parasympathetic (receptors involved: nictonic, muscarinic) stimuli are stimulatory (acetylcholine) i.e., they increase gut blood flow, motility, and glandular secretion
sympathetic stimuli are inhibitory (epinephrine)
CNS works in a coordinated manner with the ENS in the regulation of gut function
afferent neurons (splanchnic) signal the presence of pathological conditions:
* overdistension of the gut wall
I.e., equine colic, gastric distention and volvulus in dogs
* inflammation
* presence of noxious chemicals or substances in the gut lumen
hormone - GASTRIN
production - distal stomach
action
primary: stimulates and secretion from stomach glands
secondary: stimulates gastric motility, growth of stomach epithelium
release stimulus - the protein in the stomach; high gastric pH, vagal stimulation
SECRETIN
- production: Duodenum
- primary: stimulates bicarbonate secretion from the pancreas
- secondary: stimulates biliary bicarbonate secretion
- release stimulus: proteins and fats in the small intestine
CHOLECYSTOKININ (CCK)
- duodenum to the ileum, with the highest concentration in the duodenum
- primary: stimulates enzyme secretion from the pancreas
- second: inhibits gastric emptying
release stimulus: proteins and fats in the small intestine
** GASTRIC INHIBITORY POLYPEPTIDE (GIP) **
- duodenum and upper jejunum
- primary: inhibits gastric ? and ? activity
- secondary: stimulates ? secretion provided sufficient glucose is present; may be the most imp. action in many species
- release stimulus: ? and fat in the small or large? intestine
MOTILIN
- duodenum and jejunum
- primary: probably regulates motility pattern of the gut in the period between meals
- secondary: may regulate tone of lower esophageal sphincter
- release sphincter: acetylcholine
** GASTRIC INHIBITORY POLYPEPTIDE (GIP) **
- duodenum and upper jejunum
- primary: inhibits gastric motility (for time for food to be digested - carbohydrate) and secretory activity
- secondary: stimulates insulin secretion provided sufficient glucose is present; may be the most imp. action in many species
- release stimulus: carbohydrate and fat in the small intestine
PHASES OF DIGESTION
The processes of ?, secretion (enzymes and fluids), ?, and absorption take place throughout the entire length of the GIT in 3 overlapping stages:
1. ?
2. ?
3. ?
Cephalic phase
* ? of food
visual/olfactory stimulation → brain
* ? system
Vagal response (Ach) → “rest and digest”
PHASES OF DIGESTION
The processes of digestion, secretion (enzymes and fluids), motility, and absorption take place throughout the entire length of the GIT in 3 overlapping stages:
1. cephalic (brain)
2. gastric
3. intestinal
Cephalic phase
* anticipation of food
visual/olfactory stimulation → brain
* parasympathetic system
Vagal response (Ach) → “rest and digest”
sending Ach to the gastric area
Digestion - gastric phase
- motility of the esophagus propels food from the ? to the stomach
- food entering the stomach -> * ? receptors *(are mechanoreceptors) -> afferent stimulations ENS - more Ach which:
- stimulates * ? * secretion -> stimulates * ? cells * to secrete * ? * and pepsinogen (gets converted to pepsin and pepsin acts on pepsinogen for it to get converted to pepsin)
- the proximal stomach stores food awaiting further * ? processing in the ? stomach *
- the ? stomach grinds and sifts food before entering the small intestine
- control of ? motility differs in the proximal and distal stomach
Digestion - gastric phase
- motility of the esophagus propels food from the pharynx to the stomach
- food entering the stomach -> * stretch receptors *(are mechanoreceptors) -> afferent stimulations ENS - more Ach which:
- stimulates * gastrin * secretion -> stimulates * parietal cells * to secrete * HCl* and pepsinogen (gets converted to pepsin and pepsin acts on pepsinogen for it to get converted to pepsin)
- the proximal stomach stores food awaiting further * gastric processing in the distal stomach *
- the distal stomach grinds and sifts food before entering the small intestine
- control of gastric motility differs in the proximal and distal stomach
DIGESTION - GASTRIC PHASE
- At pH 1 – ? secretion is abolished (acid secretion is ?)
- Food passes the stomach ? sphincter (flow to duodenum) at a ? rate
The rate of ? emptying (e.g. CCK) must match the small intestine’s rate of digestion and ? - Gastric phase stimulates ? secretion (get the intestine ready for the arrival of ?)
- Between meals, the stomach is cleared of ? material (inter-digestive motility complex – housekeeping function)
Chyme is the ?-fluid mass of ? digested food that is expelled by an animal’s ?, through the ? valve, into the duodenum
DIGESTION - GASTRIC PHASE
- At pH 1 – gastrin secretion is abolished (acid secretion is reduced)
- Food passes the stomach pyloric sphincter (flow to duodenum) at a controlled rate
The rate of gastric emptying (e.g. CCK) must match the small intestine’s rate of digestion and absorption - Gastric phase stimulates pancreatic secretion (get the intestine ready for the arrival of ** chyme **)
- Between meals, the stomach is cleared of indigestive material (inter-digestive motility complex – housekeeping function)
- THUS need gap between meals as this would be prevented if no gap
Chyme is the semi-fluid mass of partly digested food that is expelled by an animal’s stomach, through the pyloric valve, into the duodenum
DIGESTION - INTESTINAL PHASE
- Chyme enters the ? → ? receptors + chyme (containing peptides, lipids, saccharides) in the ? intestine → stimulate secretion of ? (cholecystokinin)
- ? pH of chyme stimulates the secretion of ?
- As food is digested and absorbed and acid is ? → the stimuli for pancreatic secretion are ?
→ secretion of hormones is reduced to ? levels
[PIC: Absorption of nutrients in ? and ileum → monosaccharides, lipids (mixed micelle), and aa]
- The ? sphincter prevents movement of colon contents back into the ileum
- Motility of the colon causes mixing, ?, and propulsion of?
- The colon is an important site of ? (accumulation of ingesta) and ? (mostly water and electrolytes) in all animals
The anal opening is constricted by two sphincters:
an ? sphincter of smooth muscle
an ? sphincter of striated muscle (the one we can control)
recto ? reflex is important in defecation → entry of feces into the rectum is accompanied by the reflex relaxation of the internal anal sphincter, followed by peristaltic contractions of the rectum
DIGESTION - INTESTINAL PHASE
- Chyme enters the duodenum → stretch receptors + chyme (containing peptides, lipids, saccharides) in the small intestine → stimulate secretion of CCK (cholecystokinin)
*low pH of chyme stimulates the secretion of secretin - As food is digested and absorbed and acid is neutralized → the stimuli for pancreatic secretion are removed
→ secretion of hormones is reduced to basal levels
Absorption of nutrients in jejunum and ileum → monosaccharides, lipids (mixed micelle), and aa
- The ileocecal sphincter prevents movement of colon contents back into the ileum
- Motility of the colon causes mixing, retropulsion, and propulsion of ingesta
- The colon is an important site of storage (accumulation of ingesta) and absorption (mostly water and electrolytes) in all animals
The anal opening is constricted by two sphincters:
an internal sphincter of smooth muscle
an external sphincter of striated muscle (the one we can control)
recto sphincteric reflex is important in defecation → entry of feces into the rectum is accompanied by the reflex relaxation of the internal anal sphincter, followed by peristaltic contractions of the rectum
SECRETIONS OF THE GIT
The Salivary Glands
* Saliva moistens, ?, and ? digests food (which enzyme?, lingual lipase)
* Salivary glands are regulated by the ? nervous system.
* Ruminant saliva is a ?-phosphate buffer secreted in large quantities (100-200L saliva/day!)
Gastric Secretion
* The gastric mucosa contains different cell types:
? cells
? cells (secrete HCl) – stimulated by gastrin
and Ach
? cells (secrete pepsinogen) – stimulated by Ach and HCl
cells of the gastric glands: surface mucous cells
secretory products: ? in an alkaline fluid
- ? neck cells -> mucin in an acidic fluid
- parietal cells -> ? & intrinsic factor
- chief cells -> ? & lipase
- G cells/? cells -> ?
SECRETIONS OF THE GIT
The Salivary Glands
* Saliva moistens, lubricates, and partially digests food (amylase, lingual lipase)
* Salivary glands are regulated by the parasympathetic nervous system.
* Ruminant saliva is a bicarboante-phosphate buffer secreted in large quantities (100-200L saliva/day!)
Gastric Secretion
* The gastric mucosa contains different cell types:
mucous cells
parietal cells (secrete HCl) – stimulated by gastrin
and Ach
“ch”ief cells (secrete pepsinogen) – stimulated by A”ch” and “HC”l
cells of the gastric glands: surface mucous cells
secretory products: mucin in an alkaline fluid
- mucous neck cells -> mucin in an acidic fluid
- parietal cells -> HCL & intrinsic factor
- chief cells -> pepsinogen & lipase
- G cells/? cells -> Gastrin
SECRETIONS OF THE GIT
The Pancreas (exocrine or endocrine? pancreas)
* Pancreatic exocrine secretions digest ?, protein and ?
? cells secrete digestive enzymes
? cells and duct cells secrete sodium bicarbonate (H2CO3) (raise pH so digestive enzymes of pancreas can work well)
- Pancreatic fluid is a ?-rich ? fluid that neutralizes the ? arriving in the duodenum from the stomach
- Pancreatic cells have cell surface ? stimulated by acetylcholine (muscarinic receptors), cholecystokinin, and secretin
(recall: muscarinic receptors are GPCRs)
BILE SECRETION
* Contains ?, cholesterol, bile acids (detergent), and ? (green pigment produced during the normal process of red blood cell turnover)
* The ? stores and concentrates bile during the periods between feeding
* Bile secretion is initiated by the presence of food in the ? and stimulated by the return of bile acids to the ?
SECRETIONS OF THE GIT
The Pancreas (exocrine pancreas)
* Pancreatic exocrine secretions digest carbohydrates, protein and lipids
acinar cells secrete digestive enzymes
centroacinar cells and duct cells secrete sodium bicarbonate (H2CO3) (raise pH so digestive enzymes of the pancreas can work well)
- Pancreatic fluid is a bicarbonate-rich alkaline fluid that neutralizes the chyme arriving in the duodenum from the stomach
- Pancreatic cells have cell surface receptors stimulated by acetylcholine (muscarinic receptors), cholecystokinin, and secretin
(recall: muscarinic receptors are GPCRs)
BILE SECRETION
* Contains phospholipids, cholesterol, bile acids (detergent), and bilirubin (green pigment produced during the normal process of red blood cell turnover)
* The gallbladder stores and concentrates bile during the periods between feeding
* Bile secretion is initiated by the presence of food in the duodenum and stimulated by the return of bile acids to the liver
HEPATIC PORTAL SYSTEM
Is the system of veins that transports blood from the ? tract to the liver
* The system extends from the lower portion of
the ? to the upper part of the ? canal
- Includes ? drainage from the spleen, pancreas and ? fat
** The liver also receives some blood directly from the ? through the ? artery (oxygenated blood) **
HEPATIC PORTAL SYSTEM
Is the system of veins that transports blood from the digestive tract to the liver
* The system extends from the lower portion of
the esophagus to the upper part of the anal canal
- Includes venous drainage from the spleen, pancreas and visceral fat
** The liver also receives some blood directly from the aorta through the hepatic artery (oxygenated blood) **
HEPATIC PORTAL SYSTEM
First pass metabolism
- nutrients absorbed from the ? tract are delivered directly to the liver -> to be metabolized (drug), transformed for ? or allowed to pass into the ? circulation
-after passing the liver, blood enters the ? ? and returns to the heart (now deoxygenated)
- ? drainage from the gut ? the liver, entering the bloodstream through the thoracic duct
what is the implication of the first-pass effects ond drugs?
- ? or activate the drug
- other administration routes (sublingual, ?, rectum)
HEPATIC PORTAL SYSTEM
First pass metabolism
- nutrients absorbed from the gastrointestinal tract are delivered directly to the liver -> to be metabolized (drug), transformed for storage or allowed to pass into the systemic circulation
-after passing the liver, blood enters the vena cava and returns to the heart (now deoxygenated)
- lymphatic drainage from the gut * bypasses * the liver, entering the bloodstream through the thoracic duct
what is the implication of the first-pass effects ond drugs?
- deactivate or activate the drug
- other administration routes (sublingual, transdermal, rectum)
so as seen in pic,
-> Lymphatics go directly from the intestine to the heart
-> The blood vascular system goes from the intestine to the liver and then to heart
DIGESTION
OVERVIEW OF THE FERMENTATIVE PROCESS
Fermentation = ? action of microorganisms
The microbes responsible for fermentative digestion include:
bacteria
?
?
above 3 are major types of microorganisms
Cooperation among the species of microbes give rise to a * ? ecosystem * in the forestomach and hindgut
The forestomach and hindgut provide an * ? environment * for the fermentative process:
pH
?
Moisture
Oxidation-reduction ? and coenzymes
? patterns/time
DIGESTION
OVERVIEW OF THE FERMENTATIVE PROCESS
Fermentation = metabolic action of microorganisms
The microbes responsible for fermentative digestion include:
bacteria
fungi
protozoa
above 3 are major types of microorganisms
Cooperation among the species of microbes give rise to a * complex ecosystem * in the forestomach and hindgut
The forestomach and hindgut provide a * complex environment * for the fermentative process:
pH
temp.
Moisture
Oxidation-reduction enzymes and coenzymes
motility patterns/time
these enzymes are imp. for fermentation
(pic)
RUMINANTS (? fermentation)
sheep digestive system
goes into reticulum and then to omasum (mostly water is absorbed into omasum and then goes to the abomasum)
- chyme goes to small intestine
horse digestive system
FUNCTIONAL CECUM (? fermenters)
RUMINANTS (forestomach fermentation)
sheep digestive system
goes into reticulum and then to omasum (mostly water is absorbed into omasum and then goes to the abomasum)
- chyme goes to small intestine
horse digestive system
FUNCTIONAL CECUM (hindgut fermenters)
OVERVIEW OF THE FERMENTATIVE PROCESS
Substrates for fermentation:
* ? cell walls (cellulose, hemicellulose and lignin)
* Other ? (protein, other carbs, vitamin, minerals)
Pathway through the 4 chambers”
Food ingestion → fermentation in the ? (production of VFA and other byproducts)
Ingesta pass to ? → regurgitated into the mouth for rumination
Rumination (?-chewing) → ? → ? food particle size and stimulates ? secretion
Ingesta is re-? → small food particles pass into the ? → then ? (water absorption)
Ingesta pass into ? (? stomach) → digestive ? (aka ?)
? pass into small intestine (duodenum, jejunum and ileum) for further digestion and absorption
Continue the pathway through ? intestine to anal canal for excretion
vid:
https://www.sciencelearn.org.nz/videos/2057-cow-diet-and-digestion
OVERVIEW OF THE FERMENTATIVE PROCESS
Substrates for fermentation:
* plant cell walls (cellulose, hemicellulose and lignin)
* Other nutrients (protein, other carbs, vitamin, minerals)
Pathway through the 4 chambers”
Food ingestion → fermentation in the rumen (production of VFA and other byproducts)
Ingesta pass to reticulum → regurgitated into the mouth for rumination
Rumination (cud-chewing) → remastication → decrease food particle size and stimulates saliva secretion
Ingesta is re-swallowed → small food particles pass into the reticulum → then omasum (water absorption)
Ingesta pass into abomasum (TRUE stomach) → digestive enzymes (aka PROTEASES)
chyme pass into the small intestine (duodenum, jejunum and ileum) for further digestion and absorption
Continue the pathway through large intestine to anal canal for excretion
Anaerobic conditions in the rumen result in microorganisms’ ? activities leading to the production of ? fatty acids (VFAs)
important energy source for the host animal (cow)
Main VFA
? acid
? acid
? acid
VFAs → absorbed through the ? epithelium → transported in the blood to the ?
major energy ? (60-80% of energy needs)
Fermentative digestion of dietary protein results in the ? of a large portion of amino acids which leads to ->
Amino acids are deaminated to yield:
? (NH3) → source of nitrogen
? skeleton → source of energy
which leads to ->
Microbial protein
* Synthesized in the ? from nonprotein ?sources (ammonia, nitrate, urea)
* Digested in the ?/small intestine
Anaerobic conditions in the rumen result in microorganisms’ metabolic activities leading to the production of volatile fatty acids (VFAs)
important energy source for the host animal (cow)
Main VFA
acetic acid
propionic acid
butyric acid
VFAs → absorbed through the rumen epithelium → transported in the blood to the liver
major energy fuels (60-80% of energy needs)
Fermentative digestion of dietary protein results in the deamination of a large portion of amino acids which leads to ->
Amino acids are deaminated to yield:
ammonia (NH3) → source of nitrogen
carbon skeleton → source of energy
which leads to ->
Microbial protein
* Synthesized in the rumen from nonprotein nitrogen sources (ammonia, nitrate, urea)
* Digested in the abomasum/small intestine
