Physiology and Nutrition

Amino acids: 22 found in animal tissue, 9 essential amino acids directly needed in the diet. 

  • Threonine, Methionine, Lysine, Valine, Leucine ect.

Non-essential- Formed 'endogenously' by 'transmutation reaction.'



Amino acids: 22 found in animal tissue, 9 essential amino acids directly needed in the diet. 

  • Threonine, Methionine, Lysine, Valine, Leucine ect.

Non-essential- Formed 'endogenously' by 'transmutation reaction.

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60-70% of the body composed of water. 

Temperature: Adults consume 2-2.5L/day 

--> Sweat = water loss

Salt: Intake average 9g - recommended 6g.

Age: Immune and system, retain water through joints and swelling. 

Altitude: dehydration 

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-Essential fatty acids include linoleic/ Alpha - Linolenic 

-Carriers of fat soluble vitamins A,E,D and K. 

Fat: Stored 

Water soluble: Vitamins B and C. 

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Carbohydrate (CHO)

40-75% - Dietary energy, the UK suggests no more than 50%.

Refined sugars --> sweets and sugary cakes 

Staple food at a low cost. 

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Micro-Nutrients (Vitamins)

Water soluble - B and C

Fat Soluble - A,D,E and K 

Function as co-enzymes and antioxidants (Fight disease) 

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-Inorganic (Naturally found) - Needed in small amounts for life (mg/ug) 

Needed for - Muscle contraction, neural control (mg), oxygen transport (fe), Nerve impulse conduction (Na,K) 

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Metabolic Rate

(Individual rate) 

Balanced (Being able to support.) Growth, reproduction and good ongoing - physical/ mental health.

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Energy is the capasity to do things. 

-Comes from the sun through photosynthesis light energy --> chemical energy. 

- Have to consume plants or animals that eat plants. 

-CHO+O2 +   H2O + CO2 +Energy (ATP)

Energy released due to the breakdown of organic substances (Cellular respiration) Energy then captured in ATP.

The Metabolic processes whereby certain organisms obtain energy from organic molecules. 

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Not substrate specific

KREBS CYCLE -  stream of protons for electron transport. 

Electron transport chain. 

Units of energy. 

- Joule - Used when a mass of 1kg is moved through 1m by a force of 1N (kJ/MJ)

-Calorie - Energy required to raise the temperature of 1g of water from 14.5 to 15.5◦C .

-Kcal - Used in relation to nutritional context. --> Metabolises energy. 

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Energy in Food

Bomb calorimeter : Energy measured this way - Gross energy (GE) 

Gross energy is not always available. 

1. Not all food is absorbed from the digestive tract. 

2. Protein not completley metabolised. 

Energy available after digestion - digestable energy (DE) - Urinary energy loss -- Metabolisable energy. (ME) 


PROTEIN  4         per gram (kcal) 

FAT        9 

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Determined using direct calorimetry. 

- Involves measurement of energy expenditure (EE) over a given period by measuring the heat emitted from the body. 

Indirect calorimetry 

- When food is oxidised 02 and  C02 produced in proportion to make heat generate.

- Formula calculated in human energy expenditure.     


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Components of EE

-Basal metabolic rate (BMR) - Lying at physical and mental rest, at least after the last meal 60-65%.

-Physical activity - Accounts for 25-35% (Depending on type/duration of activity.) 

-Ingestion of food - Causes an increase in EE (Post prandial thermogenesis PPT) - 10% of EE.

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Factors affecting EE.

Body size: The more cells the more energy is needed. 

Body coposition: Adipose tissue has a lower metabolic rate than other (ESP muscle tissues) 

Gender: Accounted for by difference in body size and coposition. 

Age: EE increases as the body grows to adult size, then decreases with advancing age. 

Diet: Overfeeding increases EE by 5-10%. / Underfeeding reduces EE by 5-10%. 

Genetic differences: EE varies upto 10% between individuals of the same age, sex, body weight and fat free mass. 

Hormonal state: EG. Hyperthyridism increases EE, hypothroidism decreases EE. 

Psychological state: Acute anxiety stimulates adrenaline secretion - increases EE. 

Pharmacological agents: Nictotene and caffine increases EE, Amphetamine increases EE. Some antideppresants decrease EE.

Disease Process: Can increase, metabolic rate, E.G. fever and burns to the skin. 

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The GI tract

Mechanical Processing: Movement, chewing, mixing. 

Secretion: Fluid, digestive enzymes and hormes, bile, alkali and mucus. 

Digestion: Breaking down food to absorbale units. 

Absorption: Through mucosa, into blood or lymph vessels. 

Elimination: Undigestable material eliminated. 

Motility of the GI tract. 

Peristalsis: Propels content through the GI tract.

Segmentation: Mixes content --> (Mixes up) 

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Enteric nervous system.

Gut nervous system. 

- A collection of nerve cell bodies within the wall of the GI tract. 

- Consists of two basic regions - Regulates motility/ secretion of the GI tract. 

- Vital component of reflex pathways. 

Secretion and digestion 

- Salivary glands produce secretion and amylase. 

- Stomach - stores ingested food, produces mucus, HCI and pepsinogen. HCI converts pepsinogen into pepsiri, pepsin digests proteins into peptide fragments. 

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Acid Secretion

1. Cephalic Phase- (controlled in the brain) - sight and smell of food. 

2. Gastric Phase - In the stomach. 

3 Intestinal phase - Triggers release of hormones (Cholecystokinin.) 


Pancreas secretes a range of digestive enzymes. Liver has a variety if actions (role in digestion in bile production.) 

Pancreatic Secretion 

1. Mostly stimulated by the intestinal phase. 

2. Bicarboncite stimulated by seretin (H+ in lumen.) 

3. Enzyme secretion stimulated by CCK - Fatty acids in the lumen. 

4. Partly controlled by the parasympathetic system. 

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CARBOHYDRATES - Digests carbohydrate 

PROTEASES - digests protein 

LIPASES - digests fat. 


- Epithelia of intestines are specialised in different ways to faciliate absorption. 

- Small intestine: Specialised for the absoroption of nutrients. 

- Large intestines: Specialised for re - uptake of water. 

- Little absorption in the stomach - absorbed in the small intestine. 

Fat: Chylomicrons passed in lacteal system. 

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Liver Functions

-Metabolic processing of nutrients.

-Detoxification of  chemicals.

- Synthesis of plasma proteins 

- Storage of glycogen, fat, iron, copper and vitamins. 

- Activation of Vitamin D.

- Excretion/re-uptake of cholesterol/

-Secretion of bile salts. 

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Micro nutrients

There are 3 main types of micro nutrients. 

Macronutrients (Needed in large amounts.) 

- Protein.




- Essential fatty acids - synthesis (4kcal/g) 

- 10-15% - total energy expenditure

- Cellular component. 

- Formation of hormones, coenzymes, nucleic acids and neurotransmitters. 

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Essential fatty acids (- synthesis of hormones and key bioactive molecules - energy provider - (9kcal/g) 

Linoleic (Linoleic) - Omega 6 - Cardiovascular 

Linolenic (Linolenic) - Omgea 3. 

Structure and Function 

- Important in maintaing cellular and membrane - integrity. 

- Needed in production. 

Saturated Fats 

Hard to break down - body stores instead. 

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Carbohydrate (CHO)

Provides energy (4kcal/g) made in liver from fat and protein. 

- 40-85% TDEI (DRV: no more than 50%) 

- Polysaccharides starch - Multiple sugar units joined together - starch is the storage CHO of cereal grains. Root vegetables (e.g. protein.) 

2 main forms - Amylose (Unbranched) / Amylopectin (Branched) 

- Most abundant CHO is a complex - CHO.

Non starch Polysaccharides (NSP) 

AKA - fibre/roughage - indigestable. 

- Derived mainly from plant cells walls.

CLASSIFIED AS: Soluble: hemicellulose, pectin

                            Insoluble: Cellulose 

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NSP - Delays gastric emptying, reduces speed and overall transit time. 

- Some are broken down by fermentation in the large intestine. 

- Produces SCFA'S - Short chain fatty acids. 

- Binds cholesterol in bile and carries it out the body -> Reduces overall cholesterol levels. 

Simple CHO'S - Sugars are mono or disaccharides 

- Oligosaccharides - A few.

Glucose, Fructose, Galactose are monomers combined to form: 

Sucrose -  Table sugar - Glucose + fructose 

Lactose- Milk sugar - glucose + galactose. 

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- Non - essential 

- No recommended units. 

Pint, ml, units,

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Classification of Vitamins

Fat soluble A,D,E and K

Stored in fat depot (Adipose tissue/ Liver) 

Fat soluble vitamins only absorb in the presence of fat. 

Water soluble vitamins- absorption only occurs by simple diffusion. 

Water soluble  B and C. 

Limited storage, found in all tissues. 

Pro vitamins 

- Compounds - function as vitamins only after they have undergone a chemical change. 

E.G. carotenes - Vitamin A (In intestinal way) 

Pro- vitamin D - (Subcut fat) - vitamin D by irradition. 

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-Inorganic elements required as major minerals or trace minerals. 

- Both are vital. 

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Glucostatic theory.

Glucose = the brains primary fuel 

- This is a stimulas for hunger and decreases in the level of blood glucose below a set point. 

The glucostat= a neuron that detects the level of blood glucose. 

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Lipostatic Theory

This focuses on the storage of fats in the adipocytes and ciculating free fatty acid (FFA) levels. 

Set point for body fat: Deviations - compensatory adjustments in food intake to maintain energy stores. 

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What happens during a meal.

Mouth= Forward feed mechanism oesophageal fistula - a tempory reduction in hunger. 

Stomach= Forward feed mechansim temporary reductions in hunger. 

Stretch receptors= in the stomach wall signal distension (in presence of food )

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What happens during a meal.

Hormones released as food enters the duodenum. 

What happens after a meal 

Food is absorbed. Hepatic and CNS receptors sensitive to circulating macronutrients. 


Factors initiating eating 

- Low blood glucose, hunger hormones.

Events during a meal 

- Forward feed and post absorptive

Events after a meal 

Circulating nutrients. 

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Neurotransmitters and food intake

Neurotransmitters known to influence food eating. 

- Serotonin - This leads to an reduction in food intake. - e.g. CHO

-Noradrenaline leads to a rise in food intake - e.g. CHO 

These effects promote a cycling of preference between CHO and Fats and protein. 

Ensures a steady supple of energy and essential nutrients from different food groups.

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Physiology of starvation 

- 25% weight loss is dangerous 

Death occurs between 25%- 55% body weight loss.

Autopsy - Little adipose tissue left muscle is atrophied (Skeletal and heart.) GI walls are thin and dysfunctional. 

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This is the starvation and not the same as pathological ketoacidosis of diabetes. 

Syndromes in children. 

Kwashiorkor - The failure to grow, skin lesions, fatty liver, oedema, irritability. 

Marasmus - Generalized wasting, stunting, lethargy. 

Undernutriton of phychological cause. 

Anorexia nervosa is a serious psychological illness that kills many of those that are affected.

10:1 ratio of females to male sufferers. 

Peak on set - 12-18 years. 

Frequent association with with exercise.

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Other symptoms

Metal illness. 



Drug abuse 


Cashexia - The general state of wasting. 

Decrease in food intake and increase in energy expenditure also due to circulating immune products e.g. cytokines - TNF, Cashectin, interleukins. 

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Under-nutrition Summary

Physiology of undernutrition 

Glucogenolysis - Gluconegenesis - protein sparing 

Undernutrition in developing countries

Famine - Kwashiorkor - marasmus 

Undernutrition in developed world



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Nutritional assessment

Dietary: Food intake over time 

Anthropometry: Body dimensions and composition. 

Biochemical: Body chemistry

Functional: Function of body systems 

Clinical: Clinical appraisal. 

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Body Mass index

Underweight: <18.5

Normal weight: 18.5-24.9 

Overweight: 25.0-29.9 


Muscuclar function, metabolic, immune function, biochemical pathway. 

Functional assesment 

Grip strength is a better indicator of likelihood of post-operative complication than weight loss or loss of subcataneous fat. 


Tests are used primarily to detect subclinical deficiency states.

Procedures can be used to supplement other methods - enabling specific nutritional problems to be indentified. 

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Some routine biochemical tests of nutritional stat

-Glucose fasting 

-CHolesterol total: HDL:LDL 

-Iron: Serum iron Hb 

Electrolytes (Na,K) 

Dietary assessment 

Methods can be classified into 2 groups 

1) Recall - includes 24hr recall (or longer)

2) Record - Consists of records (e.g. food diary)

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Recall methods

Advantages - 

Low repondent burden. 

Disadvantages - 

Memory dependant, many errors. 

Unsuitable for children and the elderly, 

May not reflect the normal eating pattern - alcohol often left out. 

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Caused by energy in - energy out. 

Changes that occur - 

Hypertrophy - of existing adipocytes

Hyperplasia - develepment of new adipocytes. 

Genetic factors 

- Obese parents frequently have obese children and pets. 

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Health risks of obesity

- Risk in developing serious diseases. 

- Main causes of premature death is CVD.

-Insulin insensitivity - e.g. type two diabeties. 

Metabolic syndrome 

Central obesity, high blood pressure, Low HDL - cholesterol , insulin resistance. 

Health risks of obesity 

- Gallstone formation - Bile - supersaturated with cholesterol - gallstones. 

- Risk of cancers - colon, prostate, breast, cervix, ovary 

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Nutritional Supplements.

Various formations 

- Single: e.g. calcium 

-Combined e.g. calcium and vitamin D 

- Multi - vitamins and minerals. 

Specific - cure deficiciency or disease 

Precise- e.g. folate dose - 0.4mg. 

Therapeutic does upto 10x the RDA of a nutrient.

Why use supplement 

Improves nutritional status of specific groups. - Dieters, vegetarians, elderly, pregnancy ect. 

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Why use supplements

Zinc/iron/vitamin c - improves immune function. 


- High doses of: 

Vitamin A - Death 

Vitamin C - abdominal cramps 

Vitamin B6 - Nerve damage .

Vitamin D - Abnormal tissue calcification. 

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