Nutrition II: Micronutrients

Fat Soluble Vitamins
Vit A
Vit D
Vit E
Vit K

Water soluble vitamins
Vit C
Thiamine
Riboflavin
Niacin
Pantothenic acid
Pyroxidine
Biotin
Folate
Cobalamin

Minerals
Calcium
Zinc
Selenium
Magnesium
Iodine
Iron
Sodium
Potassium

Nutrition I: Macronutrients

Nutrients

1. Roles at cellular and molecular level

Types

Carbohydrates

• Important source of energy
• Provide energy to muscles- carbs have a protein-sparing action (prevent protein catabolising to provide glucose when carb levels are low and hence, can preserve muscle tissue)
• Allows protein to perform its function (development and maintenance of muscle mass)
• Healthy function of the CNS (CNS depends on glucose)
• Components of glycolipids, glycoprotein and nucleic acids
• Provide fiber: 
• Insoluble fiber increases stool weight, promoting regular elimination of waste and prevent constipation
• Soluble fibre: food source for gut bacteria
• Fermentation of soluble fiber results in release of short chain fatty acids and B vitamins
• Short chain FA block cholesterol synthesis in the liver
• Reduce cholesterol by enhancing hepatic control to bile acid
• Reduce postprandial rise in blood glucose
• Delay gastric emptying and increase satiation
• Provide desirable flavor and texture in food products

Health issues

• dental carries
• obesity
• CVD
• Colorectal cancer

Protein

• Growth and maintenance
• Cell structure
• Antibodies and hormone production
• Source of energy
• Maintenance of fluid balance

Fat

• source of energy
• Supply of EFA
• cell structure- PL
• Required for absorption of fat soluble vitamins
• increase palatability

Deficient of macronutrient

Carbs- increase in ketone bodies production, protein-tissue wasting

Protein- protein energy malnutrition- kwashiorkor and marasmus

Fat- weight loss, can't keep warm, lack of EFA and Vit ADEK

Excessive intake of macronutrient

Carbs- too much triglycerides in blood

Protein- proteins consumed in excess is deaminated, and the resulting carb skeletons are metabolised to provide energy/ acetyl CoA for fatty acid synthesis. Excess protein is eliminated form the body as urinary nitrogen, and is accompanied by increasing urinary calcium, leading to osteoporosis, gout etc

Fat- increased cholestrol levels leading to CVD

Fluid, Electrolyte and Acid-Base Balance III

pH: concentration of free hydrogen ions in a solution

Intracellular fluid has the lowest pH

Acidosis: When the pH of systemic arterial blood falls below the normal range

Alkalosis: When pH rises above the normal range

Respiratory acidosis: blood CO2 levels increase and blood pH drops due to low breathing rate

Metabolic acidosis: kidneys are unable to remove acid from the body; kidneys not functioning normally and is unable to remove H+ ions in urine

Respiratory alkalosis: blood CO2 levels drop and blood pH increases due to high breathing rate

Metabolic alkalosis: body lose large amounts of H+ (vommitting) or when large amounts of bicarbonate ions build up in body.

Ways to control pH

1. Chemical buffer systems (fastest)
2. Respiratory mechanisms
3. Renal mechanisms (slowest)

Buffer systems

1. Carbonic acid-bicarbonate buffer system
• ALL BODY FLUID COMPARTMENTS
2. Protein buffer system
• blood plasma fluid and intracellular fluid
• act as zwitterion
• haemoglobin as a buffer (deoxyhaemoglobin)
3. Phosphate buffer system
• intracellular fluid

Respiratory mechanisms

- Can regulate the pH of the blood using rate and depth of breathing due to carbonic acid-bicarbonate buffer system

Alkalosis- respiratory muscles contract and relax more slowly, decreasing the rate of breathing

- Increased acidity of blood (less CO2 is exhaled, more H2CO3 produced, which dissociates, liberating more H+)

Acidosis- respiratory muscles contract and relax more rapidly, increasing rate and depth of breathing

- More Co2 exhaled, less H2CO3 produced, resulting in lower concentration of H+.

Renal compensation

1. Na+/H+ antiporters
• Increasing body pH by pumping H+ ions out of tubule epithelial cells and into the filtrate within the tubule lumen and then excreted as urine
2. Reabsorption of bicarbonates
• Reabsorbed from the glomerular filtrate in the proximal convoluted tubule of the nephron in the kidney
• reabsorbed from intercalated cells at collecting ducts
3. Regulation of urine pH
• phosphate and ammonia

Fluid, Electrolyte and Acid-Base Balance II

Composition of fluid compartments

Highest in Interstitial fluid compared to blood plasma in ECF

1. Bicarbonate

2. Chloride

3. Sodium

Highest in blood plasma compared to interstitial fluid

1. Calcium

2. Protein anions

Same amount in both blood plasma and interstitial fluid

1. Magnesium

2. Phosphate

3. Potassium

4. Sulfate

Highest in ICF compared to ECF

1. Magnesium

2. Phosphate

3. Potassium

4. Sulfate

5. Protein anions

Highest in ECF compared to ICF

1. Bicarbonate

2. Calcium

3. Chloride

4. Sodium

5. Protein anions

These levels of electrolytes are measured using blood serum (with cells and clotting proteins removed). Fluctuations in protein levels can interfere with the result.

1. Bicarbonate
•  carbonic acid-bicarbonate buffer
• regulated by kidneys by intercalated cells
2. Sodium
• fluid and electrolyte regulation & production of action potentials
• regulated by Renin-aldosterone-angiotensin mechanism, ADh and ANP
3. Chloride
• balance level of anion and HCl production
• regulated in the same way as Na+
4. Potassium
• production and propagation of nerve impulses along an axon
• regulate pH
• regulated by aldosterone. When K+ is too high in blood, aldosterone is secreted to stimulate principal cells along renal tubule to secrete more K+ to be released in urine
5. Magnesium
• Co-factor for many enzymes
• Needed for Neural and myocardial activity
• Secretion of parathyroid hormone
• Regulated by kidneys
6. Phosphate
• strengthen skeleton
• important pH buffer
• produce ATP
• Regulated by parathyroid hormone; when too low, parathyroid hormone released to promote release of phosphate from bone to blood. Calcitriol stimulates absorption from blood to bone from food; calcitonin vice versa
7. Calcium
• blood clotting
• neurotransmitter release
• muscle activity
• strengthen bone and teeth
• Regulated by parathyroid hormones
• When too low, parathyroid hormone is released to stimulate release of Calcium from bone to blood. When too high, parathyroid hormone 
• increases the reabsorption of Calcium from urine in renal tubules in the kidneys 
• stimulate the secretion of calcitriol, that increases the rate of calcium uptake from ingested food. 
• Calcitonin, produced by thyroid gland when calcium level is too high in blood, opposes effects of parathyroid hormone. It
• inhibits release of calcium from bone
• reduce reabsorption of calcium from kidneys
• inhibit calcium uptake from food
8. Sulfate
• maintenance of cell membrane
• regulated by kidneys (reabsorption)

Fluid, Electrolyte and Acid-Base Balance I

Major fluid compartments separated by barriers:
2/3 - Intracellular Fluid
1/3 - Extracellular Fluid
            - Blood plasma
            - Interstitial fluid


The barriers separating these compartments are:
- Plasma membrane (between ICF and interstitial fluid) - selectively permeable
- Blood vessel walls (blood and interstitial fluid) - exchange occurs in the capillaries


Regulation of water balance

1. Water intake= water output
2. Regulation of water gain (e.g. thirst) via negative feedback loop!
• When the water content in the body is decreased, this decreases plasma volume. As a result, there is a decrease in blood pressure, stimulating the juxtaglomerular cells in the kidneys to release and begin the renin-angiotensin-aldosterone system. Via a signalling cascade, the production of angiotensin II (a potent vasoconstrictor) is increased. This change is noted by the hypothalamus.
• When the water content in the body is low, this increases plasma osmolality, which decreases saliva production and activates the osmoreceptors in the hypothalamus. Dryness in the mouth will subsequently be detected by the sensory receptors. This change is noted by the hypothalamus. 
• This creates a conscious perception of thirst and leads to drinking water. 
• As a result, blood volume is increased, blood osmolality is decreased and increase hydration levels of the mouth. All these restores normal water balance.
3. Regulation of water loss controlled by 3 hormones
• Na+ and Cl-: main determinant of body fluid volume!
• Renin-angiotensin-aldosterone hormones (renin)
• Decrease in blood volume/ pressure activates this mechanism. Renin is released and via intermediary steps, leads to increased production of angiotensin II (a potent vasoconstrictor). It causes 
• The vasoconstriction of the glomerular afferent arteries, decreasing the glomerular filtration rate.
• Stimulate the activity of Na+/H+ antiporters (cotransporters) in the renal tubules
• Secretion of aldosterone from adrenal cortex cells
• As a result, there is an increased reabsorption of Na+ and Cl- from the tubular filtrate back to the blood, leading to osmosis and increasing blood volume
• Aldosterone
• Increase water retention by acting on the kidney to increase reabsorption of Na+ and Cl- at the loop of Henle back into the blood. 
• Increase secretion of K+ into the tubular filtrate by altering Na+/K+ ATPase activity in principal cells located on the distal convoluted tubule and collecting ducts.
• Antidiuretic hormone/ vasopressin
• Increases water retention.
• When osmolarity of blood plasma and interstitial fluid increases above set point, osmoreceptors of hypothalamus are stimulated and send nerve impulses to the neurohypophysis (posterior pituitary gland), leading to the ADh secretion 
• ADh increase water permeability of principal cells lining the collecting ducts. Adh stimulates the insertion of aquaporin-2 water channels in the apical membrane of these cells. As a result, water permeability is increased and more water is reabsorbed. Blood volume is retained, producing a lower volume of more concentrated urine
• Atrial Natriuretic peptide
• Increase water loss
• When blood vol increases, the atria of the heart are stretched, and cells release ANP.
• ANP 
• causes relaxation of the glomerular mesangial cells, increasing capillary surface area, leading to an increase in gfr.
• inhibit reabsorption of Na+ and water in the proximal convoluted tubule and collecting duct
• inhibit secretion of aldosterone and ADh.