Lecture 27-29: Metabolism Flashcards Preview

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Flashcards in Lecture 27-29: Metabolism Deck (29):

Give a definition for the following
Essential nutrient
Non-essential nutrient

Nutrient = a substance used in an organisms metabolism of physiology
Essential nutrients are those that MUST be supplied in the diet
Non-essential nutrients are those that can be synthesised


List the major nutrients and give a brief description of each

1. Carbohydrates (55-60%) of total intake
-most common simple sugar is glucose
-used as an energy source in cells
Three main groups of carbohydrates are:
A) monosaccharides: eg glucose
B) disaccharides: eg lactose, maltose and sucrose
C) polysaccharides: eg starch, glycogen, fibre

2. Proteins: (10-20%)
-large complex organic molecules.
-we use 20 amino acids to build proteins, that are linked by peptide bonds
-we have obligatory diet requirement for 8 amino acids (essential aa) diets deficient lead to developmental defects and slower growth

3. Lipids (25-30%)
-large organic, hydrophobic molecules
-provides barrier function eg main part of cell membranes
-comprises of fatty acids which are stored as triglyceride in liver, muscle and adipose tissue
-fatty acids vary in chain length and number of double bonds (saturated have no double bonds.
-also have essential fatty acids

4. Vitamins: unrelated molecules with diverse functions, usually categorised based on solubility

5. Minerals: eg calcium, phosphorus, iron, copper, zinc
Serve a variety of functions:
-co-factors in enzyme-catalysed reactions
-regulation of acid-base balance
-nerve conduction
-muscle contraction
-structure ie skeleton

6. Water: 60% of what we consume is water
-it has no intrinsic energy value and acts as solvent for other nutrients
-we would die without water


What is digestion?

Breakdown of larger molecules into absorbable units (monomers) is achieved by mechanical and chemical digestion
Chemical breakdown = hydrolysis, because water molecule is added to each broken bond


What is absorption?
Also what are the enzymes which break each nutrient down?

Uptake into the body
-most nutrient absorption occurs in small intestine, with additional absorption of water, ions and some acids in large intestine

Convert complex macromolecules into forms that can be absorbed and processed
Amylases: breaks down polysaccharides into oligosaccharides
Proteases: breaks down proteins to shorter polypeptides
Lipases: release fatty acids from triglycerides and phospholipids
Nucleases: break down DNA into nucleotides


View slides 23 24 and 25 to see how each nutrient is broken down

Do it


Digestion and absorption: digestive enzymes
Lipid breakdown how?

-Digestion and import of lipids is complicated by hydrophobicity
-GI tract secretes chemicals like bile that emulsify lipids into small droplets
-transport of lipids depend on physical properties:
-in the blood without assistance eg short chain fatty acids and glycerol
-in lymph as complexes called chylomicrons: triglycerides, cholesterol


What is assimilation?
And egestion?

Assimilation: the sequential process of nutrient breakdown and absorption
Gastrointestinal tract: is continuous with the external environment
Egestion = elimination = expulsion of undigested food


Briefly what happens in the GI tract?

Mechanical breakdown of food: mouth--> pharynx --> esophagus
Acidic compartment: stomach
Most digestion and absorption: upper or small intestines
Reclamation of water: lower or large intestines
Release of indigestible material: anus
There are different digestive tracts due to variations in diet ie carnivor, herbivores etc


GI tracts: Food Quality

The quality of food influences digestion time
High quality foods: minimal energy to capture and eat
-higher rate of digestion
-releases lot of energy

Low quality food:
-more energy to capture and eat
-lower rate of digestion
-yields less energy


Gastrointestinal tracts: stomach
What are the 4 layers of the stomach and describe each of them

4 layers:
1. Mucosa: composed of columnar elithelial cells
-tight junctions preventing leakage
-mucous neck cells-secrete mucus
-parietal cells-secrete HCL acid
-chief cells- secrete pepsin (protease)
-enteroendocrine cells: secrete hormones into the blood
-enterocytes: absorptive cells with microvilli
-goblet cells-secrete mucus
-paneth cells-secrete anti microbial molecules

2. Submucosa
3. Circular
4. Longitudinal


Gastrointestinal tracts: the liver

Bile: solution of digestive chemicals and liver waste products
-produced in the liver and stored in the gallbladder
-phospholipids- aid in the uptake of lipids
-bile salts- emulsify fats


Gastrointestinal tracts: the pancreas
Pancreatic exocrine secretions contain digestive enzymes:
What are they?


Pancreatic endocrine secretions control blood glucose
Alpha cells secrete glucagon
Beta cells secrete insulin


Gastrointestinal tract: specialisations
Give an example

Physiology and anatomy of the digestive tract is matched to the chemical and physical nature if the diet
1. Ruminants/ foregut fermenters:
-ruminants have a fore-stomach with 4 chambers
-cellulose converted to volatile fatty acids by symbiotic bacteria, protozoa and fungi
2. Hindgut fermenters
-cellulose passes through into large intestine
-fermentation in large intestine: production of volatile fatty acids


Metabolism can be divided into absorptive state and post-absorptive state. Explain the two

Absorptive state: the period of time following a meal where products of digestion are being absorbed, used and stored (primary anabolic)
-during and immediately after following meal consumption
-glucose serves as major energy source following a meal
Post-absorptive state: the period of time when nutrients from a meal are no longer available (primarily catabolic)
-GI tract is emptied and energy is derived body reserves
-primary goal is to spare glucose
-endogenous stores ie fat and glycogen are used
-gluconeogenesis maintains blood glucose
-fat is mobilised as alternative energy source, proteins is mobilised for glucose formation


Describe the starvation response

-preserve glucose to protect glucose- dependent tissues eg nervous tissue
-muscle shift to lipid metabolism
-once lipid and glucose stores are depleted protein breakdown accelerates; amino acids can be converted to fatty acids and carbohydrates
-at this point degradation occurs because there are no proteins stores


What are the key tissues or organs that play different roles between these alternating states?

1. Liver: primary role is maintaining blood glucose levels; stores glycogen, release glucose to blood, and gluconeogenesis.
2. Adipose tissue: main energy storage site; regulates fatty acids
3. Muscle: primary site of amino acid storage and major energy user; uses lipids for energy in long term fasting
4. Brain: relies primarily on glucose for fuel: uses ketone bodies after fatty acid oxidation in starvation


Metabolism: change of state
Eg python in between meals

Reduce energetic costs in between meals
-seen in pythons that eat very frequently
Between large meals:
-mucosa and submucosa degrade
-gut becomes thinner and brush boarder decreases
-smooth muscles and nerves are maintained
-following a meal, snake rebuilds GI


Look at the table on slide 68 and 69 for a summary of reactions and storage in fuel metabolism



Fuel for metabolism: role of hormones in release

For most animals the hormones insulin and glucagon regulate metabolism:
-in the FED state, insulin is the dominant hormone and the body undergoes net anabolism
-in the fasted state, glucagon is the dominant hormone and the body undergoes net catabolism

When these get out of whack diabetes can result:
Type 1: can't produce insulin
Type 2: insulin insensitivity


What are the 3 hormones that control appetite by binding to receptors in the hypothalamus

1. Leptin-white adipose tissue
2. Ghrelin- stomach
3. Peptide YY- colon


Energy balance exists between energy input and energy output:
Explain both ways it can slide

Positive energy balance is when the rate if energy assimilation if GREATER THAN energy output (gain weight, as fat)

Negative energy balance is when the rate if energy assimilation is LESS THAN energy output (lose weight)


Energy balance

75% of overall energy released from food (digestible energy) appears as heat or biological work eg
Transport, mechanical or chemical


Components of energy balance: energy expenditure
In animal nutrition, digestion and utilisation of energy is described in four stages. What are these stages

1. Gross energy (GE) = total energy content of a food
2. Digestible energy (DE) = energy contained in nutrients absorbed from digestive tract
3. Metabolisable energy (ME)= chemical energy available
4. Net energy (NE)= represents TRUE amount of energy available for maintenance, work, growth and reproduction


What has a higher metabolic rate? Smaller or larger animals?

Smaller animals usually have higher metabolic rates per unit of body mass than larger animals
Mass specific metabolic rate declines with increasing body mass


Relationship between body mass and metabolic rate

In mammals the metabolic energy requirements at maintenance = aW 0.75 (KJ/day) where
a= constant 525
W= body mass (Kleibers Law)


How do we directly measure the amount of energy in a food

A direct calorimetry
(A machine)
Amount of energy release from food:
Calorie: approximates the energy required to increase the temp of 1 gram of water by 1 degree
Amount of energy to increase kg of water by 1 degree is 4.184 kilojoules

Indirect calorimetry = consumption of O2 and/or production of CO2 is measured
-consuming 1 L of O2 is associated with releasing 21.1 kJ of carbohydrate, 19.8 kJ of fat etc
A average figure is 20./ KJ/L of oxygen


What is the basal metabolic rate and resting metabolic rates?

BMR: amount of energy expended while at rest in a neutrally temperate environment, in post-absorbtive state (12h fasting humans)
BMR is very restrictive, it assumes that the sympathetic NS is not stimulated
Resting metabolic rate- is a related, less restrictive measurement
BMR of RMR constitutes about 66% of total daily expenditure

Skeletal muscle-18%
Other organs-13%


Factors affecting BMR/ RMR
1. Age/gender
2. Body comp
3. Diet

1. Age and gender- BMR higher in maes than females (more muscle, less fat in males) decreases with age
2. Body composition- fat free mass explains 60-80% of the variation in RMR between individuals
-BMR/RMR increases with body mass
-muscle consumes more O2 than fat at rest -> increase muscle mass to increase BMR and lose weight
3. Diet- diet induced thermogenesis associated with digestion and absorption
-an increase in energy expenditure (via increased metabolic rate) occurs in response to food intake
-thermic effects of a meal (meal-induced thermogenesis) is about 10% of the meal consumed
-fats cause a relatively little diet-induced thermogenesis compared to proteins and dietary fiber.
4. Growth and reproduction
-eg lactation, growth, pregnancy
-energy required for these purposes must be ADDED to the MER for calculation of total energy requirements
5. Hormones and drugs
-thyroid hormones and catecholamines (adrenaline/noradrenaline) increase metabolic rate
-smoking, drugs, caffein can increase BMR through increased thermogenesis.
6. Physical activity level increases the metabolic rate over the basal rate-determined by amount/duration of the activity, type of activity, and intensity of activity


Specific dynamic action

Basically saying that O2 consumption increases after food consumption