Download Physiology of GI tract and Nutrition

Physiology of GI tract and
Nutrition
Main functions of the GI tract
• Mechanical activity (chopping, mixing, forwarding,
blocking of reflux, storing, delaying)
• • Secretory/chemical functions (secretion of the
gastrointestinal juices, enzymatic breakdown of the
nutrients)
• • Absorbtion
• • Coordination (fitting the mechanical, chemical and
absorbtive activities)
• • Adaptation (to the status of the body and to the
external conditions)
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Mechanical, chemical and absorbtive functions at
individual parts of the GI tract
Localisation
Mechnical
function
Chemical function
(digestion)
Absorption
Chopping,
mixing
(chewing)
Negligible
Speciális cases
Pharynx,
esophagus
Forwarding
(swallowing)
None
None
Stomach
Mixing,
forwarding,
storing
Proteins
Alcohol
Smal intestine
Mixing,
forwarding
All nutrients
All nutrients
Large intestine
Forwarding
None
Water,
electrolytes
Rectum
Forwarding,
defecation
None
Water,
electrolytes
Mouth
Mechanical (motor) activity of the GI
tract
Esophagus (swallowing)
- oral or voluntary phase of swallowing
- pharyngeal stage of swallowing (involuntary part)
- esophageal phase of swallowing (involuntary part)
Stomach
- pacemaker zone generates slow gastric
contractions
- stomach movements can be detected even in
case of empty stomach
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Vomiting
Vomiting p is forceful expulsion of stomach and proximal small intestine contents
Vomiting caused by intracranial diseases p immediate, without nausea
Vomiting caused by peripheral diseases
p preceded by
• feeling of nausea
- common sensation of gastric upset,
- reduced gastric motility,
- increased secretions
• rapid, irregular heartbeat,
• dizziness,
• sweating,
• pallor,
• pupillary dilation
Mechanical (motor) activity of the GI
tract
Small intestine
- segmentation contraction (circular muscle),
- peristaltic contraction (longitudinal muscle),
- pacemaker cells
- f ibers of chyme are necessary to maintain the stretch of gut wall
Large Intestine
- mass peristalsis: brief forcible peristaltic movements that move the contents
through long segments of the large intestine
- defecation reflex: activated by the mechanoreceptors of the rectum wall
(stretching)
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Secretory function of GI tract
Composition
Function
Saliva
-water & electrolytes
- amylase
- lysosim
- antibodies (IgA)
- calcium-binding protein
- mucin
- pH: basic
- keeping the oral cavity moist (speech)
- facilitating swallowing
- lubrication of food to aid its movement
- bactericid effects
- defense of teeth
- digestion (in the stomach)
- dilution and buffering of ingested foods
Gastric juice
- HCl
- ware & electrolytes
- pepsinogen
- mucin
- intrinsic factor
- pH: acidic
- protein denaturation & digestion
- bactericid effect
- defense of the stomach against self-digestion
- stress p mucin secretion p ulcer
Secretory function of GI tract
Composition
Bile
- water & electrolytes
- bile salts
- phospholipids
- metabolic waste products
Function
- facilitation of fat digestion (emulsification)
- facilitation of lipid absorption (micelles)
- detoxication
Intestinal juice
- water & electrolytes
- enzymes (amylase, lipase, nuclease)
- pH: basic
- enzymatic digestion of all nutrients
- neutralization of gastric HCl content
(ensuring pH optimum)
Pancreatic juice
- water & electrolytes
- proenzymes (tripsinogen)
- enzymes (amylase, lipase, nuclease)
- pH: basic
- enzymatic digestion of all nutrients
- neutralization of gastric HCl content of
chyme (ensuring pH optimum)
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The most important hormons of GI tract
• Gastrin
- increases the HCl production in the stomach
• Cholecystokinin
- stimulates the emptying of gall bladder
- stimulates pancreatic juice secretion
- reduces the emptying of stomach
• Secretin
- increases the secretion of bile
- increases the secretion of pancreatic juice
Nutrients:
Everything serving as raw material and
energy, plus all other molecules required
for their utilization (trace elements, water,
ions and vitamins).
Bioactive substances: in the absence of these, the metabolic
processes would proceed towards undesired directions, and
diseases would develop (e.g. dietary fibres, flavonoids, etc.).
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The well-balanced diet
• Isodynamic diet; applicable with certain restritions only,
because:
– Loss of amino acids
– Fat soluble vitamines
– The digesting and absorbing capacities of the GI tract
• Recommendation for a healthy adult - The total amount of
energy consumed should have the following composition:
– Fats: < 30%
– Proteins: 10-15%
– Carbohydrates: > 55%
Nutrient Molecules 1
Water, inorganic salts, trace elements
maintaining of membrane potential,
regulation of cell volume,
fluid balance of body
Nucleic acids
every cell can produce them for simple precursors,
hence they are NOT essential from nutritional
perspective (!!)
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Nutrient molecules 2
Carbohydrates
• Direct or indirect sources of energy
• When bound to proteins (glycoproteins) structural function
(e.g. surface antigens, mucin ...... )
• Dietary fibres (pektin, cellulose, .....)
– delay the absorption of glucose and lipids from gut
– reduce the blood cholesterol levels
– have important roles in weight-control as well as in reducing the
incidence of colon cancers
• Recommendation:
- 55-60% of the total energy uptake should be provided by carbohydrates.
- The recommended amount of dietary fibres is 30 g/day (about 0.5-1 kg
fresh vegetables and fruits; or consumption of 56-84 g oat meal).
Nutrient Molecules 3
Lipids
• concentrated energy stores
• a structural elements of membranes and certain other organelles
• Essential fatty acids: (linolenic and linoleic acid ...)
• Fat storage is practically limitless, the lipid surplus is transported and
accumulated in the adipose tissue
• The metabolic value of the fat is more than twice as great as that of the
carbohydrates – it is easy to consume more than required
Recommendation:
- Lipids should provide less than 30% of the daily total energy intake.
- At most 10% of the daily energy intake should be provided by saturated
fatty acids
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Nutrient Molecules 4
Proteins and amino acids
• essential components of the tissues and enzymes,
•
(enzymes, transport and storage proteins, structural proteins,
protective proteins, hormones, contractile proteins,)
• may serve as energy sources
• essential amino acids (e.g. Threonine, Methionine, Valine, ...)
• biological value of the dietary proteins depends on the the proportion of
proteins that can be utilized for the biosynthesis of the „own” proteins after
absorption. E.g..:
Mother milk, whole egg: 100
Cow milk: 88-95
Beef: 88-92
Fish: 80-92
Soya beans: 74-78
Corn flour: 49
Nitrogen balance
• The protein catabolism takes place in our bodz even in case of fasting
• This is when a person’s daily intake of nitrogen from proteins equals
the daily excretion of nitrogen
– If + : The protein content of the body increases
– If ̶ : The protein content of the body reduces
Recommended daily protein intake
absolute minimum:
protein degradation during starvation
20 g/day
physiological minimum:
protein intake required for nitrogen balance 40 g/day
hygienic minimum:
protein intake required for health
80-100 g/day
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Nutrient Molecules 5
Vitamins:
• they are required in small quantities
• they are available in the food or provided by bacteria of
the gut
• they do not give energy but they act as cofactors or
enzymes
• characteristic deficiency symptoms are seen
• these symptoms can be treated by the application of the
appropriate vitamin
Vitamin A (Retinol)
Formation of visual pigments
maintenance of epithelial structures
Hemeralopia
Skin lesions
Birth defects
Sources: meet, egg, milk, colorful vegetables
(carrot, tomato etc. )
Recommendation : 0.8 mg/day
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Vitamin E (Tocopherol)
Maintenance of RBCs
antioxidant
Increased fragility of RBCs
Muscular dystrophies
Abortion
Sources: vegetable oil, vegetables, egg, fish, liver, meet
Recommendation : 10 mg/day
Vitamin K (Naphtoquinone)
synthesis of clotting
factors in liver
Failure of
coagulation
Sources: green vegetables (cabbige, brokkoli, bean, pear), milk, meet, liver
Recommendation : 0.08 mg/day
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Vitamin D (Calciferol)
Enhancement of Ca2+ and phosphate
absorption from gut
Bone and tooth formation
Rickets in children (defective
bone formation)
Osteomalacia in adults
Sources: fish oil, egg yolk, milk, butter,
liver (e.g. 250g calf's liver)
Recommendation: 5 μg/ day
Vitamin C (Ascorbic acid)
essential for all vital processes,
antioxidant
Scurvy
extravasations of blood into the tissues
failure to form connective tissue
Sources: fruits, vegetables , liver,
Recommendation: 75 mg/ day
( e.g. 133 g lemon or 1200 g apple or orange)
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Vitamin B family
vitamin
hatás
hiánytünetek
vitamin B1
(thiamine)
carbohydrate metabolism
(Kreb's cycle)
Beriberi, polyneuritis
vitamin B2
(riboflavin)
flavoprotein synthesis
fissuring the skin
inflammation of tounge
vitamin B6
(pyridoxine)
coenzyme of amino acid and
fatty acid metabolism
dermatitis,
nervous disorders
vitamin B12
red blood cell production
(Cyanocobalamine) nucleoprotein synthesis
pernicious anemia
vitamin Bx
(panthotenic acid)
essential for the health of skin
and hair (coenzyme A)
neurmotor and cardiovascular
disorders
biotin
protein and fatty acid synthesis
dermatitis,
muscle pain
folic acid
red blood cell production
"fetus protecting vitamin"
anemia,
neural tube defects
niacin
(vitamin B5)
coenzyme of hydrogen
transport
Pellagra
(Dermatitis, Diarrhoea Dementia)
Nutrient Molecules 6
Trace elements:
• they are required in minute quantities
• Iron (anemia) (haemochromatosis)
• Cobalt (B12, pernicious anemia)
• Iodine (thyroid hormones, hypothyroidism)
• Zinc (dermal ulcers, reduced immune response)
• Copper (anemia, impaired bone formation,)
• Chromium (insulin resistance)
• Fluoride (increased risk of caries)
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Thermoregulation
The aim of thermoregulation is to maintain
a constant core temperature
Heat lost = Heat gained
To understand thermoregulation one must
be aware of the various
heat losing and heat producing mechanisms
Heat losing mechanisms
Radiation (60%)
Direct
Indirect
Convection (15%)
Respiration
Evaporation (22%)
(Sweating)
Conduction (3%)
Proportions change with environmental temperature
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Heat producing mechanisms
• Shivering thermogenesis
(heat production may be 4-5-times higher than at rest!)
• Non-shivering thermogenesis
Metabolism (Sympathtic activity, thyroid hormones,
glucocorticoids, insulin, glucagon)
Exercise
Shivering is a high frequency (10-20 Hz) skeletal muscle
contraction, when no effective work is performed.
How does the hypothalamus work?
Terrible news Sir,
the core
temperature is more
than 37°C!!
SET POINT = 37°C
hypothalamus
Heat losing mechanisms ×
Heat producing mechanisms Ø
Vasodilatation
Sweating
Panting
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How does the hypothalamus work?
Terrible news Sir,
the core
temperature is less
than 37°C!!
Heat losing mechanisms Ø
Vasoconstriction
Piloerection
Curling up
SET POINT = 37°C
hypothalamus
Heat producing mechanisms ×
Shivering
Metabolic activity ×
Symp.activity, Thyroid hormons
Voluntary movements ×
How does the fever develop?
Endogen pyrogens
SET POINT = 40°C (!)
hypothalamus
Exogen pyrogens
Ø
Heat losing mechanisms
Vasoconstriction
Piloerection
Curling up
Heat producing mechanisms ×
Shivering
Metabolic activity ×
Symp.activity ×
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How is the fever terminated?
SET POINT = 40°C (!)
antipyretic drugs
SET POINT = 37°C (again)
hypothalamus
Heat losing mechanisms ×
Vasodilation
Sweating ×
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