GIT Physiology (struc) Flashcards

1
Q

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)

A

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)

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2
Q

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:

A

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)

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3
Q

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 ?

A

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

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4
Q

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

A

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

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5
Q

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

A

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

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6
Q

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

A

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

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7
Q

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

A

** 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

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8
Q

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”

A

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

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9
Q

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
A

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
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10
Q

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

A

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

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11
Q

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

A

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

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12
Q

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 -> ?
A

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
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13
Q

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 ?

A

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

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14
Q

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) **
A

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) **
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15
Q

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)

A

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

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16
Q

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

A

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)

17
Q

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)

A

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)

18
Q

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

A

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

19
Q

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

A

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