Lecture 9 - Fatty Acid Metabolism

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Advanced Physiology(part 1, Digestive system)
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By A. Riasi (PhD in Animal Nutrition
Physiology)
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• Introduction

• The primary function of digestive system
• Intracellular and extracellular process in
  digestive system
• Three specific regions in most animals digestive
  system
• Foregut
• Midgut
• Hindgut

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• Introduction

• Digestive systems perform four basic digestive
  process
• Motility
• Propulsive movements
• Mixing movements
• Secretion
• Digestion
• Absorption

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• Introduction

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• Introduction

• The digestive system of animals consists of
• The digestive tract (gastrointestinal tract)
• Accessory digestive organs

• Additional function of the digestive tract
• Osmoregulation
• Endocrine secretion
• Immune function
• Elemination of toxins

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• Introduction

• Regulation of digestive function is complex and
  synergetic
• The smooth muscle cells of digestive system are
  single unit type
• The nervous system control digestive system
  function
• Intrinsic nerve plexuses
• Extrinsic nerves

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• Introduction

The four layers are the same from esophagus to
anal canal
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• Introduction

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• Introduction

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• Introduction

The enteric nervous system of a rats stomach
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• Introduction

• Receptor activation alters digestive activity
  through neural reflexes and hormonal pathways
• Three different types of sensory receptors
• Chemoreceptors
• Mechanoreceptors (pressure receptors)
• Osmoreceptors

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• Different parts of digestive tract and the
  functions

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• Mouth

• Obtaining and receiving food

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• Mouth

• Taste buds are composed of groups of about 40
  columnar epithelial cells bundled together along
  their long axes.

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• Salivary glands

• Acini is a secretary unit of salivary gland
• Each acini secrete a fluid into collecting ducts
• Water
• Electrolytes
• Mucus
• Enzymes

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• Salivary glands

• Three major parts of salivary glands
• Parotid glands
• Submaxillary glands
• Sublingual glands

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• Salivary glands

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• Salivary glands

In the histological sections of salivary gland
shown above, the cells stained pink are serous
cells, while the white, foamy cells are
mucus-secreting cells.
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• Control of salivary secretion

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• Salivary secretion in sheep

Salivary glands Total salivary volumes (L d) Characteristics Site of reflexogenic stimuli
Parotids Inferior molars Palatine, buccal, pharyngeal Submaxillary Sublingual, labial 3-8 0.7-2 2-6 0.4-0.8 0.1 Serous, isotonic, strongly buffered Serous, isotonic, strongly buffered Isotonic, strongly buffered Mucous, hypotonic, weakly buffered Very mucous, hypotonic, weakly buffered Mouth, esophagus, ruminoreticulum Mouth, esophagus, ruminoreticulum Mouth, esophagus, ruminoreticulum Mouth during feeding, not cudding Mouth
Total volume 6-16
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• Swallowing

• Eating and swallowing are complex neuromuscular
  activities consisting essentially of two stages
• Oropharyngeal stage
• Esophageal stage

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• Esophagus

• Anatomically and functionally, the esophagus is
  the least complex section of the digestive tube
• It contains the crop in poultry

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• Esophagus

• There are two physiologic sphincters
• Upper and lower esophageal sphincters.
• In ruminants, a nasopharyngeal sphincter is
  present.

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• Esophagus in birds

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• Stomach

In monogastric mammals, the stomach is divided
into three section
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• Stomach

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• Stomach

• Microscopic anatomy of the stomach
• Muscularis has an additional oblique layer
• Epithelial lining composed of goblet cells
• Gastric pits contain gastric glands

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• A remarkable ability for significant changes in
  volume

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• Stomach

• Two distinct areas for secretion of gastric
  digestive juice
• Oxyntic mucosa (contain three type of cells)
• Mucous cells
• Chief cells
• Parietal cells or oxyntic cells
• Pyloric gland area (PGA)
• Mucous cells
• Chief cells

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• Gastric secretion cells

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• Gastric secretion cells
• Exocrine cells
• Paracrine cells
• Endocrine cells

Type of secretary cell Product secreted Stimuli for secretion Function (s)
Exocrine cells
Mucous cells Alkaline mucus Mechanical stimulation by contents Protects mucous against mechanical, pepsin, and acid injury
Chief cells Pepsinogen Ach, gastrin When activated, begins protein digestion
Parietal cells HCl Ach, gastrin, histamine Activates pepsinogen, breaks down connective tissue, denatures proteins, kills micro-organisms
Endocrine/ paracrine cells
Enterochromaffin-like cells Histamine Ach, gastrin Stimulates parietal cells
G cells Gastrin Protein products, ACh Stimulates parietal , chief, and ECL cells
D cells Somatostatin Acid Inhibits parietal, G, and ECL cells

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• Mechanism of HCl secretion

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• Control of gastric secretion
• Cephalic phase (Mediated by vagus nerve and
  acetylcholin)
• Gastric phase (gastrin has the main effect)
• Intestinal phase (intestinal gastrin has the
  main effect)

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• The duodenal factors trigger either neural or
  hormonal responses

• Neural response is mediated through two reflexes

• Intrinsic nerve plexus (short reflex)

• Autonomic nerves (long reflex) (These reflexes
  are called the enterogastric reflex)

• The hormonal response involves the release
  duodenals several hormones

• Secretin
• CCK
• Gastric inhibitory peptide or glucose-dependent
  insulinotrophic peptide
• Avian pancreatic polypeptide (APP)

(These hormones are known as enterogastrones)
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• Gastric emptying and mixing

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• Factors that influence the rate of gastric
  emptying

A- Stomach factors

• Amount of chyme in the stomach (more effect)

• Vagus nerve

• Stomach hormone gastrine

• The degree of fluidity of the chyme

B- Duodenum factors

• Fat (more effect)

• Acid

• Hypertonicity

• Distention

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• Bird stomach

• Proventriculus-gizzard processes of digestion in
  birds
• There are two type of glands into the
  proventriculus
• Simple mucosal glands that secrete mucus
• Submucosal glands that secrete HCl and
  pepsinogen

Interestingly, unlike in mammals, both HCl and
pepsinogen are synthesized with in the same cell
(chief or oxynticopeptic cell)
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• Bird stomach

• The mucosal lining of the gizzard is covered by
  koilin
• In birds myoglobin content of the gizzard is
  approximately 100-fold greater than the breast
  muscle, and mitochondrial numbers are also
  elevated.

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• Ruminant stomach

• Rumen development

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• Ruminant stomach

• Pre-ruminant period

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• Ruminant stomach

• Absorptive surface area is enhanced by
  increasing
• Papillae length
• Papillae width
• Papillae density

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• Ruminant stomach

• Rumen development

Undeveloped Rumen
Developed Rumen
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• Ruminant stomach

• Rumen properties
• Largest compartment
• On left side of animal
• Contains micro-organisms
• Ferments cellulose
• Absorbs VFAs
• Divided into chambers
• Continually contracting
• Contains papillae
• Produces CO2 and CH4
• pH close to neutral (6 - 7)

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• Ruminant stomach

• The interior surface of the rumen forms numerous
  papillae

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• Ruminant stomach

• Absorption VFAs from the ruminal wall

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• Ruminant stomach

The 4 layers of the rumen epithelium stratum
corneum (SC), stratum granulosum (SG), stratum
spinosum (SS) and stratum basal (SB).
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• Ruminant stomach

Light micrographs of rumen papillae biopsied
during the high forage and high grain diets
(Adapted from Steele et al. 2009)
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• Ruminant stomach

• Rumination
• Rumination occurs in resting.
• The highest incidences of rumination occur
  during afternoon and in the middle of the night.

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• Ruminant stomach

• Rumination is centrally mediated by the "gastric
  centers".
• Tactile stimulation of the reticular and ruminal
  epithelia is a powerful stimulus for rumination.

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• Ruminant stomach

• The time spent ruminating by a given animal
  depends
• The texture of the food
• The amount of food ingested
• Cattle may ruminate from 35 to 80 minutes per
  kilogram of roughage consumed

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• Ruminant stomach

• The ruminal movements serve to
• Mix the ingesta
• Aid in eructation of gas
• Propel fluid and fermented foodstuffs into the
  omasum.
• A cycle of contractions occurs 1 to 3 times per
  minute.

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• Ruminant stomach

• Two types of contractions are identified
• Primary contractions
• Secondary contractions

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• Ruminant stomach

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• Ruminant stomach

• Rumen investigation and sampling

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• Ruminant stomach

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• liver acinus the unit supplied and drained by
  terminal branches of portal triad vessels

• Small intestine

• Three parts of small intestine
• Duodenum
• Jejunum
• Ileum

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• Small intestine

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• liver acinus the unit supplied and drained by
  terminal branches of portal triad vessels

• Small intestine

Adapted from http//www.ufrgs.br/imunovet/molecula
r_immunology/gastrointestinal.html)
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• liver acinus the unit supplied and drained by
  terminal branches of portal triad vessels

• Small intestine

Adapted from http//www.ufrgs.br/imunovet/molecula
r_immunology/gastrointestinal.html)
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• Small intestine

The Meckels diverticulum is found in birds small
intestine
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• Pancreas

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• Pancreas

• Exocrine functions

Enzyme Substrate Action
Trypsin, Chymotrypsin, Elastase Peptides Endopeptidases cleave bonds between amino acids
Carboxypeptidase and Aminopeptidase Peptides Exopeptidases cleave bonds at the terminus of a peptide
a - amylase Polysaccharides starch and glycogen Endoglycosidase cleaves bonds between carbohydrate monomers to produce maltose and short carbohydrate chains.
Pancreatic lipase Triacylglycerols and 1,2 - diacylglycerols Fatty acids, glycerol and 2 - monoacylglycerol
Adapted from wikivet (http//en.wikivet.net)
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• Pancreas

• Control of exocrine secretions

• Neural controls
• Endocrine controls
• Cholecystokinin
• Secretin
• Gastrin

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• Pancreas

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• liver acinus the unit supplied and drained by
  terminal branches of portal triad vessels

• Liver and gallbladder

• Liver is the largest and most important
  metabolic organ in the body
• The functions of liver
• Metabolic processing of the major categories of
  nutrients
• Detoxification or degradation of body waste
• Synthesis of plasma protein
• Storage of glycogen, fat, iron, copper, and many
  vitamin
• Removal of bacteria and worn-out red blood cells
• Excretion of cholesterol and bilirubin
• Synthesis of ascorbic acid
• Gluconeogenesis

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• liver acinus the unit supplied and drained by
  terminal branches of portal triad vessels

• Liver and gallbladder

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• liver acinus the unit supplied and drained by
  terminal branches of portal triad vessels

• Liver and gallbladder

• Liver blood flow
• 75 venous blood from the portal vein
• 25 from the hepatic artery

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• liver acinus the unit supplied and drained by
  terminal branches of portal triad vessels

• Liver and gallbladder

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• liver acinus the unit supplied and drained by
  terminal branches of portal triad vessels

• Liver and gallbladder

Adapted from http//www.ufrgs.br/imunovet/molecula
r_immunology/gastrointestinal.html)
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• Liver and gallbladder

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• Liver and gallbladder

• Lymph formation in liver

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• Liver and gallbladder

• Hepatic phagocytic system

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• Liver and gallbladder

• Two stage for bile secretion
• Hepatocytes secrete bile into canaliculi
• Bile modification in bile ducts

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• Liver and gallbladder

• Pattern and control of bile secretion
• Effect of cholecystokinin
• Effect of secretin

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• Large intestine

• Large intestine in vertebrate consist of
• Cecum
• Colon
• Rectum/cloaca

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• Large intestine

Adapted from http//www.ufrgs.br/imunovet/molecula
r_immunology/gastrointestinal.html)