Physiology II, Quiz 1

Mastication

Grinding and shearing actions of the teeth

Prehension in horses

lips

Prehension in dogs and cats

Teeth

Prehension in ruminants

tongue

Prehension in sheep/goats

The tongue, incisor and lips

Prehension in pigs

The tongue, incisor, lips and propulsive movement of the head

Hypsodent teeth

The teeth emerge from the gums at continuous rate as the animal ages

Brachydont teeth

• Teeth wear and are not replaced.

• Molars are covered entirely on the occlusal surface by the enamel

Primary peristalsis

• Begins in the pharynx and spreads into the esophagus

• During pharyngeal stage of swallowing

Secondary peristalsis

Generated within the esophageal musculature by distension of the esophagus by the retained food.

Esophagus layers

• Muscle

• Submucosa

• Mucosa

Anatomical divisions of the stomach

• Cardia

• Fundus

• Corpus

• Pylorus

Layers that make up the stomachs mass

• Inner lining mucosa

• Submucosa

• Muscularis

• Adventitia

Three glandular regions in non ruminant stomachs

• Cardiac: cardiac glands

• Fundus: gastric gland proper

• Pyloric: pyloric glands

The intrinsic nervous system

• Gastrointestinal movements

• One plexus located in the submucosa

• The second plexus between the longitudinal and circular muscles layers

Anatomic innervation of GIT

• Parasympathetic system increases activity

• Sympathetic system inhibits activity

The parasympathetic to the GIT

• Vagus nerve contains motor and sensory fibers.

• The sensory fibers register the condition of the gut and its contents

• The motor fibers enhance digestive activities via intrinsic nervous system

Phasic contractions

• periodic contractions and relaxations

• occur in esophagus, antrum of stomach, and small intestines

Tonic contractions

• Constant contraction without regular relaxation

• Occur in cardiac sphincter, orad region of the stomach, iliocecal sphincter, and internal anal sphincter

Stomach and hunger contractions in monogastric

• Adaptive relaxation

• Peristaltic contraction

• Terminal Antral Contraction

Glossopharyngeal Nerve (CN IX)

sensory input for the posterior part of the tongue and throat.

Vagus Nerve (CN X)

• responsible for swallowing and enzymatic digestive organs

• parasypathetic (only one)

Facial Nerve (CN VII)

responsible for mastication and salivary glands' function

Trigeminal Nerve (CN V)

responsible for the sensory input and motor control of the muscles involved in chewing

Slow waves depolarization phase

• Cyclic opening of Ca2+ channels

• Inward Ca2+ current

Outer longitudinal muscularis externa depolarization and contraction

reduce segment length

Slow waves repolarization phase

• Cyclic opening of K+ channels

• Outward K+ current

Inner circular muscularis externa depolarization and contraction

reduce segment diameter

General GIT motility

• Unitary smooth muscle with electrical coupling via gap junctions.

• Exceptions: Pharynx, upper esophagus, and external anal sphincter (striated muscle)

Flavors detected by the tongue

salty, sour, sweet, bitter, and umami tastes

Control of gastric emptying

• Duodenum stimulation by CCK release

• The vagovagal reflex controls the contraction of GI muscles in response to distension from food.

• Local enterogastric reflexes (vomiting)

• Hormones

Inhibition of emptying of stomach contents into the small intestine

• duodenal acidic pH, distension, and hypertonicity

• sympathetic stimulation

• pain

• increased gastric chyme osmolarity

Small intestine segments

• Duodenum

• Jejunum

• Ileum

Small intestinal mucosa

• Crypts of Lieberkuhn

• Plicae circulares

• Villi

Structures of the small intestine

• The inner wall is covered by plicae circulare.

• Plicae circulare are covered in villi and microvilli,

• Nutrients are circulated blood capillaries and lacteals.

Law of the small intestine

• Peristalsis is only in the direction of the large intestine

• Not towards the stomach

Mucosa Cell

secretes mucus

Three stages of deglutition

• Oral/voluntary stage

• Pharyngeal stage

• Esophageal stage

Oral/Voluntary Stage

• Initial eating and bolus formation.

• Increased saliva production.

• Involves tongue motor coordination.

Pharyngeal Stage

• Closure of nasopharynx and oropharynx.

• Increased pressure in the throat.

• Depression of the esophageal sphincter.

Esophageal Stage

Esophageal sphincter opens to allow food passage.

Ileum

• Ileocecal sphincter or valve

• Gastro-ileac reflex

• Ileogastric reflex

The large intestine

• Cecum, colon, and rectum

• Water, ion, fatty acids, vitamins, and electrolyte absorption

• Vat for indigestible materials

• Microbial fermentation

Endopeptidases

attack peptide linkages involving specific amino acids in the interior of a polypeptide.

Junctional communication of the large intestine

• Ileocecal junction

• Ileocecocolic junction

• Rectoanal junction

Gastric juice functions

• Solubility of non-water soluble food

• Necessary for activation of pepsin

• Disinfectant

• Stimulates duodenal cholecystokinin (CCK) secretion

Gastrin

• pyloric region of the stomach, upper small intestine, and pancreas

• stimulates gastric secretion

Villikinin

• Stimulates motility of intestinal villi

• aids in the transport of lymphatic fluid into the lymphatic duccts

Enterogastrone

decreases gastric emptying

Motilin

• Gastric mucosa

• Stimulates gastric motor activity

• gastric emptying

Pepsin in the presence of hydrochloric acid

brings about conversion of the inactive enzyme, pepsinogen, to the active enzyme pepsin

Gastric inhibitory peptide

It has enterogastrone-like activity

Enterocrinine

It has been shown to stimulate intestinal secretion

Exopeptidases

liberate end amino and carboxyl groups

Ribonuclease

is a type of nuclease that catalyzes the degradation of RNA into smaller components.

The enzymes contained in pancreatic juice

Are capable of digesting all three major types of food classes; proteins, carbohydrates, and fats

Gall bladder not found in:

Horse and Rat

Secretin

• Upper small intestine

• stimulates the secretion of bicarbonate and water from pancreas.

• It inhibits gastric secretion and motility

Gastric secretion during a meal can be divided into three phases

• Cephalic phase

• Gastric phase

• Intestinal phase

Pancreases

• large compound gland

• lies parallel to and beneath the stomach.

• secretes digestive enzymes and lots of sodium bicarbonates

Types of bile salts

• Cholic acid

• Deoxycholic acid

Vasoactive intestinal peptide

• Duodenum

• Gastric receptive relaxation

Cholecystokinin (CCK)

• Upper portion small intestine

• It stimulates pancreatic secretion

• Promots emptying of the gall bladder

Pancreatic Proteolytc Enzymes

• Split proteins into small peptides or amino acids:

  • Trypsin

  • chymotrypsin

  • carboxypeptidase

Carboxypeptidases

• Zinc-containing exopeptidases that remove single amino acids from the carboxyl end of oligopeptides

• Digestion of dietary proteins by pepsin, trypsin and chymotrypsin.

Bile

• secrete by the bile secreting hepatocytes

• transported through the bile cananiculi into the bile terminal duct

• contains no digestive enzyme

• Bile salts have digestive relevance

Bile salts

• emulsification of fat.

• exposes the fat molecules to lipase for maximum contact and digestion

• act on fats

  • most of them are reabsorbed by the ileum

• sodium bicarbonate keeps bile salts in solution within the bile.

Bile pigment

• called bilirubin, yellow in color

• product of haemoglobin catabolism

• transported in blood as a compound bound to albumin (unconjugated bilirubin)

• In the liver

  • incorporated in bile (conjugated bilirubin)

Bile is secreted continually by

• The liver

  • stored in the gallbladder

Rate of bile secretion is controlled by

• The concentration of circulating bile salt.

• Neural mechanism

• Hormonal mechanism

• Rate of blood flow

Obstructive jaundice

• yellow coloration of tissues

• blockage of free flow of bile from the gall bladder

Biliary Reflux

• duodenogastric reflux

  • Causes painful heartburn, nausea, and vomiting and inexplicable weight loss

secreations of the small intestine

• Papilla of vater: bile flow

• Brunner's glands: protects mucosa from HCL

• Goblet cells: mucus

Digestive enzymes of the small intestines

• Peptidases

• Sucrase, maltase, isomaltase, and lactase

• Lipase

• Secretin and cholecystokinin (CCK) enhance secretory potential of the intestinal secretory cells

Large intestinal functions

• Volatile fatty acid: the large intestines

• Urea: converted to ammonia in the large intestine

• Vitamin K, Vitamin B12, thiamin, riboflavin, biotin and folic acid formed and absorbed in the large intestine

The tongue

• Hypoglossal controls movement

• Temperature, touch, and pain is done via the trigeminal nerve (rostral 2/3rd)

• Sensation of taste is via facial (rostral 2/3rd) and glossopharyngeal (caudal 1/3rd) nerves controlled by their lingual branches

• Have various types of papillae with taste buds

Small intestinal motility

• Villous movement

• Segmentation movement (circular muscle)

• Peristaltic movement.

• Anti-peristaltic movement

Large intestinal motility

• Adaptive relaxation

• Antidromic (retrograde) peristaltic waves

• Haustrations

• Pendular

Phases of Digestion

• Luminal phase

• Membranous phase

Absorption

End of product of digestion blood capillaries or lymphatics of the villi

Transportation of absorbed Material

Materials absorbed into the capillaries are carried to the mesenteric veins and the portal veins

The opening of the biliary and the pancreatic duct into duodenum varies in different animals

• Cow and pig: the bile and pancreatic duct open into the duodenum separately

• Goat and sheep: the duct systems join prior to arrival at the duodenum

• Horse, cat, and dog: common pancreatic bile duct

Deoxyribonuclease

• Enzymes degrade DNA via phosphodiester backbone hydrolysis

• Cleaves single or double-stranded DNA, requiring metal ions

• yields 3'-hydroxyl and 5'-phosphorylated DNA products

Villi

• Surface epithelial projections for absorption

• The central vein carries waste and products

• Central lymphatic responsible for absorbing dietary fats and fat-soluble vitamins

Elastase

• Serine protease from the pancreas cleaves carboxyl groups on small hydrophobic amino acids

• Breakdown of elastin

Constipation

• Delayed peristalsis, infrequent and painful defecation

• Reduced large intestine motility leads to constipation

• Can be relieved by fiber which boosts fecal bulk, stimulating colon motility

GI hormones

• Mostly peptide hormones.

• Paracrine hormones come from intestinal lamina propria cells

• Intestinal endocrine hormones from specialized epithelial cells.

• Bind to specific receptors and create second messengers.

Biliary secretions and hepatic system

• Hepatocytes synthesize bile and secrete it into canaliculi

• Canaliculi combine into smaller bile ducts

• Ducts merge to form the main hepatic duct, then exiting the liver

Metabolic aspects of digestion

• Chemical digestion by enzymes: hydrolysis

• Glycosidic linkages: carbohydrates

• Peptide bonds: proteins

• Ester bonds: fats

• Phosphodiester bonds: nucleic acids

Lipid digestion

• Initiated by pancreatic enzymes like lipase.

• Act at the oil-water interface of the emulsion particles releasing a β-monoglyceride (beta) and long-chain free fatty acids from the dietary triglyceride.

• Chylomicrons: transport dietary lipids

Carbohydrate Digestion

Salivary amylase: absent in carnivores

Diarrhea and vomiting

• Hyper-secretion of the intestinal crypt cells

• Excessive and frequent loss of fluids and electrolytes: watery feces.

  • Sometimes caused by toxins of pathogens & increase in intestinal motility.

• Chloride: secreted into the lumen

• Sodium, chloride & water absorption is reduced

• Rapid delivery of chyme to colon leaves little time for absorption of water

• Defecation: frequent and feces is watery.

  • Anxiety, ingestion of certain foods, as well as microbial infections

• E. coli: implicated

• Osmotic diarrhea: ingestion of solutes that cannot be absorbed

  • overfeeding of young animals with milk

Monogastric digestion

• Three glandular regions of the stomach

• Gastric juices: flow through gastric pits on the gastric mucosa

• The glands proper in the submucosa

Parental cells

• HCL

• Intrinsic factor

• Found: glands within the fundus and body of the stomach

• largest cells

G cells

• synthesis and secretion of gastrin

• increases gastric contraction and emptying

• Found in the pyloric antrum

  • in the duodenum and the pancreas

Principles of GIT Slow waves

• Slow waves: smooth muscle

• oscillating depolarization and repolarization of membrane potential

• action potentials: "on top of" slow wave if depolarized to threshold

• Origin occurs at interstitial cells of Cajal

  • spontaneous

• Frequency of slow waves varies along the GIT

• stomach: 3 slow waves per minute

• ileum: 8-9 slow waves per minute

• duodenum: 12 slow waves per minute

Chief cells

• produce pepsinogen and hydrochloric acid

• gastric lipase

  • that cleave the proteins into smaller pieces

• Found in the fundic stomach

Gastric intrinsic factor and anemia

• Intrinsic factor is secreted: parietal cells.

• Achlorhydria: absence of hydrochloric acid

• Pernicious anaemia: Vitimin B12 deficiency

• Control of parietal cell acid secretion

• Histamine (H2 receptors)

• Gastrin flow through blood to act on gastrin receptors

• Vagus nerve (Ach via muscarinic receptors)

Functions of pancreatic enzymes

• Trypsin and chymotrypsin: inactive enzyme

• Trypsinogen is activated: by enterokinase.

• trypsin activates itself and converts chymotrypsinogen to its active form chymotrypsin

• Proteins: cleaved in the stomach under acidic pH conditions by pepsin into peptide fragments.

• small intestine: cleaved under alkaline conditions into oligopeptides and amino acids

• optimum pH range: pH 7 and pH 8

Enterohepatic circulation of bile

• Food reaches the duodenum, the intestinal endocrine cells: stimulated to secrete CCK

• Relaxation of the Sphincter of oddi and contraction of the gall bladder

• bile: forced into the duodenum.

• bile aids: digestion and absorption of fats in the jejunum

• ileum: the bile acids are absorbed and recirculated into hepatic portal vein

• reabsorbed in the liver

  • further re-secreted into bile duct to contribute in more bile formation