Physiology II
Gastroinstestinal System
Lecture 2
Dr Than Kyaw
30 April 2012
Ruminant and monogastric Digestion
•
•
•
•
•
Ruminant digestion
Monogastric digestion
Enzymes and hormones
Digestion products
Absorption and utilization
Compound stomach
(multichambered , polygastric, ruminant stomach)
• Consume fibrous foods
- forages (grasses)
- roughages
- other fibrous food sources
Cellulose and
semicellose
• Plant materials other simple stoach animals are unable to
digest.
• Fermented in the rumen with the help of microbes
(microflora)
To valuable products
4 compartments
Rumen (paunch)
- Bacterial and chemical breakdown of fiber (anaerobic)
- Occupy most of the left-side of the abdomen
- Has thick, muscular wall
- Papillae on walls: up to 1 cm. in length, bacteria more
concentrated
- Rumen capacity
- 50 to 65 gallons (dairy cattle)
- 5 to 10 gallons (sheep)
Dorsal
coronary
groove
Dorsal sac
Posterior Dorsal
blind sac
Posterior ventral
blind sac
Ventral
coronary
groove
Ventral sac
Right
longitudinal
grove
Papillae in Rumen
Papillae in Rumen
Interior surface of rumen
- numerous papillae
- vary in shape and size
- short and pointed to long and
foliate.
4 compartments
Reticulum (honey combs)
- interior surface – looks like honeycomb
- helps to remove foreign matter from the food
material.
Reticulum - full
Epithelium of reticulum
- thrown into folds that form
polygonal cells
- honey-comb appearance
- Numerous small papillae
Reticulum - cleaned
4 compartments
Omasum (book stomach)
- round and muscular
- “Grinds” the food material and prepares the food
material for chemical breakdown.
Omasum - full
Inner surface of omasum
- Broad longitudinal folds or leaves (lay term - 'book').
- Omasal folds - packed with finely ground ingesta
- Estimated to be 1/3 of the total surface area of the forestomachs.
4 compartments
Abomasum – inside view
Abomasum (true stomach)
• very similar to the stomach of non-ruminants
• the majority of chemical breakdown of food
material occurs.
• mixes in digestive enzymes (pepsin)
Size of young and adult ruminants
Important to know the
development of ruminant
stomach for feeding young
and adult
Compartment size of young and
adult ruminants
% of Total Stomach
Newborn Calf
Adult Cow
Rumen
25%
80%
Reticulum
25%
6%
Omasum
10%
3%
Abomasum
40%
11%
Capacities of digestive tract of mature sheep
Compartment
Capacity
Reticulum
Rumen
Omasum
Abomasum
1.2 to 2.0 quarts
5.0 to 10.0 gallons
0.5 to 1.0 quarts
2.0 to 3.0 gallons
Small intestines
2.0 to 2.5 gallons (80 ft)
Large intestines
1.5 to 2.0 quarts
Rumen microbes (micro flora)
-
Bacteria: Over 60 spp
- digest sugars, starch, fiber, and protein for the cow.
-
Protozoa: About 35 spp (size: 20 – 200 μ)
- some spp swallow and digest bacteria, starch
granules, and some fiber.
-
Bacteria and protozoa
– differ greatly in size, shape, and structure
Rumen microbes (micro flora)
- Fungi
- very small fraction
- important in splitting plant fibers open to provide
easy digestion by bacteria
Protozoa of rumen
A Protozoan
A fungal spore
A Protozoan dividing into two
Bacteria attaching under side of the
protozoan
A Protist found in rumen
Some protozoan and
bacteria have symbotic
relationship
Protozoan covered with
chains of bacteria
Bacteria attacking a strand of
Fiber taken from a cow’s rumen.
Rumen microbes (micro flora)
- One trilion microbes/oz of ruminal fluid
- multiply in double in 11 minutes
- Almost all rumen microbes – anaerobic
- 2/3 of feed digestion
- 90% of fiber digestion
In rumen
Rumen microbes (micro flora)
- Rumen bacteria – good source of protein for the host
- Microbes - 55% of protein and may provide up to half of total
dietary need
- Urea – can be utilized by microbes (synthesis of microbial protein)
- Vitmins K and B-complex synthesis
- adapted to a pH between roughly 5.5 and 6.5
- Abomasum pH: 2 to 4
- 3 primary zones based on their specific gravity
- Gas rises to fill the upper regions
- Grain and fluid-saturated roughage ("yesterday's hay")
sink to the bottom
- Newly arrived roughage floats in a middle layer.
Ingesta flow
• Digestion
Compound stomach
Ruminal motility
- mix the ingesta
- aid in eructation of gas
- propel fluid and fermented foodstuffs into the omasum
- Supression of motility - ruminal impaction
- Cycles of contraction - 1 to 3 times/min
- During feeding - highest frequency
- During resting - lowest
Ruminal motility
Two types of contractions
Primary contractions
- Originate in the reticulum
- Pass caudally around the rumen
- Involves a wave of contraction followed by a wave of
relaxation, so as parts of the rumen are contracting, other
sacs are dilating
Secondary contractions
- occur in only parts of the rumen
- usually associated with eructation.
Rumination
Rumination (cud chewing)
- regurgitation of ingesta from the reticulum
- remastication
- resalivation and
- redeglutition (reswallowing)
Provides - effective mechanical breakdown of roughage
- increases substrate surface area to fermentative
microbes.
Rumination
Sequences
- Contraction of reticulum
- Relaxation esophageal sphincter
- Inspiratory movement with closed glottis
- Negative pressure in the thorax
- Dilation of thoracic esophagus and cardia
- Reverse peristalsis
Rumination time = about 8 h/d
1 circle of rumination = 1 min
Result
Flow of
ingesta
Roughage
+
Fluid
to mouth
Eructation
– Enormous quantity of gas by fermentation
– About 30-50 liters/h in adult cattle
5 l/h in a sheep or goat
- Eructation or belching
- continually get rid of fermentation gases
- eructation is associated with almost every secondary
ruminal contraction
- Eructated gas travels up the esophagus at 160 to 225 cm/s
Eructation
- Any interferences with eructation – life threatening
- Expanding rumen rapidly interferes with breathing
- Animals suffering ruminal tympany (bloat) die from asphyxiation.
Fermentation in the rumen
Carbohydrate fermentation
• Fibrous feed (cellulose, hemicellulose, xylans)
• Readily fermentable CHO (starch, sugars)
• Principle end products
- VFAs Volatile fatty acids
- CO2
- CH4
- Heat
Volatile Fatty Acids
Carbohydrates
Microbial Fermentation
VFA’s
×
Glucose
O
CH3
C
O
–
Acetic acid (2c)
- Rumen, cecum, colon
O
O
CH3
CH2
CH3
C
O
–
Propionic acid (3c)
CH2
CH2
C
O–
Butyric acid (4c)
VFA Formation
2 acetate + CO2 + CH4 + heat
1 Glucose
2 propionate + water
1 butyrate + CO2 + CH4
- VFAs absorbed passively from rumen to portal blood
- Provide 70-80% of ruminant’s energy needs
Uses of VFA
• Acetate
– Energy
– Fatty acid synthesis
• Propionate
– Energy
– Gluconeogenic – glucose synthesis
• Butyrate
– Energy
– Rumen epithelial cells convert to ketone
Proportions produced depends on diet
- Fibrous feed – less propionic/a
- carbohydrate feed – more propionic/a
Absorption of VFAs
•
•
No evidence for active transport
VFA metabolism in the rumen wall
– Cells use most of the butyrate
for their own energy needs
– Acetate and propionate are ‘exported’ to blood
Fermentation of plant protein
Plant proteins
Proteolytic
organisms
Amino/a
Ammonia
Organic acids
Resynthesized to
different microbial
proteins
Rumen microbes – also able to utilze non-protein nitrogens
- urea, biurets, amines
Fermentation of lipids
•
Plant contains limited amount of lipids
•
Lipids found in most plant = galactosyl diglycerides
•
Microbes do not alter lipids very much
•
Can synthesize some lipids
•
Cannot tolerate if dietary fat contains 5 – 7% of total diet
Digestion in simple stomach
Discussed in Lecture (1)
Stomach produces:
- HCl (stomach pH about 2, pareitel cell)
- pepsinogen (pepsin, Chief cell)
- gastric lipase (fat digestion)
- mucus (protect the stomach epithelium)
- gastrin (hormone – G-cell; stimulate gastric secrretions
- signals S/I to prepare for arrival of food)
Digestion in simple stomach
- Digest mainly protein to polypeptides
- Kill pathogens
Protein in
bolus
Pepsinogen
(Pro-enzyme/
Precursor of
pepsin)
HCl
pepsin
Peptide
- Liquids - removed quickly (about 30 m)
- Solid portion (chyme) - takes hours
Small intestine
3 parts
- Duodenum
- Jejunum
- Ileum.
Smooth m/s
- circular (segmental contraction)
- longitudinal (contract a wave-like action – peristalsis)
- further digestion and absorption of nutrients
- micro villi on the epithelium
Small intestine
Digesta pH
Functions
Duodenum
2.7 - 4
Enzymes
pH change
Flow rate regulation
very little absorption
Jejunum
4–7
Enzymes
Absorption
Ileum
7-8
Absorption
Limited fermentation
• Rate of pH increase through small intestine is faster in monogastrics.
Enhanced Surface Area for
Increased Nutrient Absorption
Intestinal villi
Note: provision of
Large surface areas
by the micro villi
for absorption
Gastrointestinal Hormones
• Gastrin
– Origin: stomach, abomasum
– Stimulus: food in stomach
– Function: stimulates HCl & pepsinogen secretion,
increases stomach motility
• Secretin
– Origin: duodenum
– Stimulus: acid
– Function: stimulates pancreatic secretions; slows
stomach motility and acid production
Gastrointestinal Hormones
• Cholecystokinin (CCK)
– Origin: duodenum
– Stimulus: fat & protein in duodenum
– Function: stimulates bile and pancreatic secretions
• Also regulates appetite and feed intake
• Gastric Inhibitory Protein (GIP)
– Origin: duodenum
– Stimulus: fats and bile
– Function: inhibit stomach motility and secretion of acid
and enzymes
Pancreas and its secretions
- long, thin delicate organ
- pinkish gray, glandular
Secretions of pancreas
- Exocrine
- enzymes and carbonates
- Endocrine
- hormones
Pancreas and its secretions
Enzymes
1. Amylase: -- carbohydrate digestion (starch, dextrin)
mainly to disaccharides (maltose)
-- amylase low in ruminants
2. Lipase: fat digestion
- triglycerides to monoglycerides and free fatty acids
Pancreas and its secretions
3. Proteases*: protein digestion
Trypsinogen - converted to trypsin (by enterokinase)
Chymotrypsinogen - converted to chymotrypsin (by trypsin)
Procarboxypeptidase - converted to carboxypeptidase (by trypsin)
4. Nucleases
Digest nucleic acids and nucleotides
5. Lecithinase
Lecithin to lysolecithin
Inorganic compound
NaH2CO3 – neutralize acids
Secretion - pH is 7.2-7.8
* Enzymes are ususally released in inactive forms in the source
organs. Why?
- They are capable of doing autodigestion.
Pancreas and its secretions
Endocrine
-
islets of Langerhans
insulin ( beta cells)
glucagon (alpha cells)
somatostatin (delta cells)
1. Insulin
Main functions
-- Fat Break down inhibited
-- promote fat deposition and glycogenesis
-- enhance glucose transport across cell
membrane and facilitate diffusion
Blood
Glucose
Amino
acids
uptake of
glucose
Insulin
uptake of
amino/a
Insulin
Muscle, Liver
(Stored as glycogen)
Used for protein
synthesis by all cells
- All essential amino/a (balanced ration) are needed
for protein synthesis
2. Glucagon
Opposite effect of insulin
Glycogen
Glycogenolysis
Fat
(Lipolysis)
glucagon
Blood glucose
glucagon
Blood glucose
3. Somatostatin
-- Act as a moderator to the metabolic effect s of insulin,
glucagon and growth hormone.
-- Inhibit the secretion of insulin and glucagon
-- As a moderator – it also inhibit the secretion of –
gastrin, secretin, cholicystokinin, pancreatic exocrine
secretion and gastric acid
4. Pancreatic polypepitides
-- secretion stimulated by -- ingestion of protein
-- exercise
-- fasting
Control of insulin and glucagon secretion
Insulin sensitivity
Brain
Kidney
Intestine
Erythrocytes
Little response
to insulin
Liver
Muscle
Adipose tissue
Leucocytes
readily response
to insulin
Normal blood glucose value of animals (mg/dl)
Horse
60-110
cow
40-80
sheep
40-80
Blood glucose level lower
than other animals
Pig
80-120
dog
70-120
chicken
130-270
Large Intestine (Colon)
• Absorption o f VFAs
• Absorption of ammonia-N
– About 30 to 40% of the net transport of N into body fluid
– Absorbed N may be used for:
• Synthesis of nonessential amino acids
• Recycling of N to the rumen
– Important on low protein diets
– Regulated by:
• Increased by increasing N concentration of diet
• Decreased by increasing the amount of carbohydrate fermented
in the large intestine
• Mineral absorption
• Water absorption
– 90% of water entering the LI is absorbed
Note: No enzymatic digestion
fermenting micro-organisms are not digested; voided with feces.
Nutrient absorption
2 types
Passive transport (by concentration gradient)
- Diffusion: freely movable through lipid bilayers of cell
membrane - especially smaller molecules e.g. O2, CO2
- Facilitated diffusion – molecule diffusion facilitated by
the help of transport protein, e.g glucose, amino acids
Active transport – use of transport protein,
– need energy
– e.g. N+-K + pump, glucose and amino acid
absorption in GIT
Nutrient absorption
Transporter protein
Avians Digestive System
Digestive Tract - Poultry
Gall bladder
Gizzard
Liver
Cecum
Esophagus
Crop
Proventriculus
Cloaca
Pancreas
Large intestine
Duodenum
Small intestine
(jejunum, ileum)
Avians (Poultry)
Mouth
•
•
No teeth, rigid tongue
Poorly developed salivary glands
– Saliva contains amylase
•
Beak - adapted for prehension and
mastication
Avians (Poultry)
Esophagus
– Has an enlarged area called crop
• Ingesta holding and moistening
• Location for breakdown of carbohydrate by
amylase
• Fermentation
Proventriculus (stomach)
• Release of HCl and pepsin (gastric juices)
• Ingesta passes through very quickly (14 seconds)
Avians (Poultry)
Gizzard (ventriculus)
– Muscular area with a hardened lining reduces
particle size
• Muscular contractions every 20-30 seconds
• Includes action of grit
• HCl and pepsin secreted in proventriculus
Small intestine
– Similar to other monogastrics
Avians (Poultry)
Ceca and large intestine
– Contain two ceca instead of one as in other
monogastrics
– Large intestine is very short (2-4 in) and
empties into cloaca where fecal material will
be voided via the vent
• Water resorption
• Fiber fermentation by bacteria
• H2O soluble vitamin synthesis by bacteria
compound
Simple
Avian
mouth
mouth
mouth
esop
esop
esop
reticulum
Rumen
omasum
abomasum
Salivary
glands
Rumen microbes
fermentation
stomach
crop
Rumen microbes
proventriculus
Gastric secretion
gizard
Grinding, mixing
S/I
S/I
S/I
Digestion, absorption
cecum
cecum
cecum
fermentation
colon
colon
colon
Absorption of water
summary
(RUMEN)
Telephone Cord
Traumatic reticulitis in cow
Wire
Sponge taken from digestive
system of an animal
End of Lecture
Major Gastrointestinal Hormones
Honnone
Production
Action
Release
stimulus
Gastrin
Distal stomach
Primary: Stimulates acid secretion from
stomach glands
Secondary: Stimulates gastric motility,
growth of stomach epithelium
Protein in
stomach; high
gastric pH;
vagal stimulation
Secretin
duodenum
Primary: Stimulates bicarbonate
secretion from pancreas
Secondary: Stimulates biliary
bicarbonate secretion
Acid in
duodenum
Cholecystokinin (CCK)
Duodenum to
Primary: Stimulates enzyme secretion
ileum, with highest from pancreas
concentration in
Secondary: Inhibits gastric emptying
duodenum
Proteins and fats
in small intestine
Major Gastrointestinal Hormones
Gastric
inhibitory
polypeptide
(GIP)
Duodenum and
upper jejunum
Primary:
Inhibits gastric motility and
secretory activity
Secondary:
Stimulates insulin secretion
provided sufficient glucose is
present; may be most important
action in many species
Carbohydrate and
fat in small instine
Motilin
Duodenum and
jejunum
Primary: Probably regulates motility
pattern of the gut in period between
meals
Secondary:
May regulate tone of lower esophageal
sphincter
Acetylcholine