Summary HAP-30306 - Nutritional Physiology - Overview

HAP-30306
NUTRITIONAL
PHYSIOLOGY
EXTENSIVE SUMMARY




Iris Pelgrim

, LECTURE 1 – M ASS FLOW OF NUTRIENTS

INTRODUCTION

Signalling systems are activated before, during and after ingestion of the meal by sensory inputs
- sight
- smell
- taste of the food
- mechano- and chemoreceptors in the stomach or gut wall.
The integrated response to a meal represents a complex set of regulated gastrointestinal (GI) behavior
responses
- secretory  induce secretion of water, ions, digestive enzymes, and bile salts
- motor  induce movement of the food, storage, mixing, and grinding
These responses result in assimilation of the nutrients from (solid as well as liquid) meals by the GI tract. The
meal is converted by both chemical and physical means to a mixture of nutrients that can be absorbed by the
gut epithelium.
1. The meal is ingested as boluses of food. A bolus is a mouthful of food ready for swallowing after
chewing and addition of saliva.
2. The bolus is transported to the stomach via the esophagus. Motor behaviors such as mixing and
grinding convert the bolus in the stomach to a suspension of small particles: chime.
3. This chime enters the small intestine where water, ions, bile salts and enzymes are added. The
chime particles are further digested to macromolecules and then to oligo- and monomeric nutrients
that can be absorbed across the GI epithelium into the blood circulation. Also the water, ions and
other secreted components are absorbed into the blood circulation for reuse. Unabsorbed and
undigested matter is eliminated.
The assimilation of nutrients requires thus the conversion of those nutrients (polymers) to an aqueous
solution of small molecules (oligo- and monomers).  digestion and propagation of chime in the GI tract is
controlled by a combined action of the motor activity of the sphincters and the gut wall.
Many organs are involved in the response to a meal.
- sensors (eyes, nose, ears)
- responders (salivary glands, gallbladder, pancreas)
- both sensing, signalling, and responding (stomach wall distension due to entry of the meal activates
a pathway to the brain by way of the vagus nerve, upon which the brain causes relaxation of the
stomach wall, gallbladder contraction and secretions of the stomach and pancreas.)
 Complex interrelationship between the many organs involved in the response to meal  response
becomes an integrated response with specific roles for each of the organs involved.

NUTRITIONAL INPUT VS PHYSIOLOGICAL OUTPUT

Nutritional Input ↔ Metabolism ↔ Physiological Output
Metabolism links nutritional input with physiological output and keeps it in balance. Metabolism needs to
adapt to input and output in order to have adequate ATP production and adequate heat production.
Nutritional input : total daily intake (kJ), meal size, meal pattern, nutrient composition
Physiological output : physiological status, health status, environment
Metabolism : ∆ metabolic pathways, ∆ energetic pathways, ∆ body composition – waste products
DIETARY COMPONENTS – NUTRIENTS
- Macronutrients (carbohydrates, proteins, fat) provide us with energy. Fermentation may provide us
with energy, but it can never provide us with amino acids.
- How do these macronutrients move through the body?
o Translocation
o Transformation
- How are these movements regulated?

, o Neural system
o Endocrine system
- You have hardly any influence on the fate of the food after swallowing. There is increasing interest in
feeding strategies aimed to influence the fate of the food.
- There are three pathways that food can follow :
o Digestion and absorption
o Storage
o Utilization
Why does the digestive system not digest itself?
- Activity restricted to presence of food
- Regulation (local, distal, proximal)
- Enzymes stored as inactive pro-enzymes (zymogens)
- Non-digestible mucus coats the walls
- High replacement rate (turnover) of mucosal cells
All these components have influence on metabolic settings.
Settings of metabolism
Settings of metabolism need to adjust to release enough heat to keep your body temperature (by substrate
cycling f.e.).
- Digestion to and absorption of monomers
- Intermediary metabolism -
The sum of all metabolic reactions between uptake of foodstuffs and formation of excretory products.
o Interconversions of absorbed monomers
o Anabolic reactions  synthesis of body constituents
 formation of glycogen from glucose (glycogenesis)
 formation of fat from fatty acids (lipogenesis)
 formation of protein from amino acids (protein synthesis)
o Catabolic reactions (energy / ATP / heat)  release of
energy from food or body constituents
 glycogenolysis
 lipolysis
 proteolysis
o Unavoidable waste products
- Time scale of events
o Post-prandial phase (PP)
o Post-absorptive phase (PA)
- Physiological adaptation Figure 1 - Input vs. Output

METABOLIC CHANGES
Table 1 - Body composition
Component Male Female
Water 64% 54%
Proteins 15% 13%
Storage fat 12% 19%
Essential fat 3% 9%
Minerals 6% 5%
Post prandial (PP) phase - the period during which nutrients are being absorbed from the intestine
- Digestion  absorption  storage
- Input > needs  anabolic or catabolic disposal (storage, interconversion, oxidation)  net anabolic
metabolism (but both anabolic as well as catabolic metabolism takes place)
- Diet-induced thermogenesis (DIT) – thermogenic effects of a meal (you always have heat
production directly following a meal)
o PP metabolism increases heat production (5 – 20% ingested ME)  caused by absorption
and deposition (for which you need ATP, and therefore you also produce heat).