- Transport across cell membranes RCN.com
- Wright EM et al, 2011, Biology of Human Sodium Glucose Transporters Physiological Reviews
- Endocytosis RCN.com
- Laterra J et al, 1999, Blood-brain barrier National Center for Biotechnology Information
- Hamilton JA et al, 2007, A model for fatty acid transport into the brain PubMed
- Edmond J, 2001, Essential polyunsaturated fatty acids and the barrier to the brain: the components of a model for transport PubMed
- Neuwelt EA, 1989, Implications of the Blood-Brain Barrier and Its Manipulation: Volume 1 Basic Science Aspects, pp. 119-127
- Pan Y et al, 2015, Fatty Acid-Binding Protein 5 Facilitates the Blood–Brain Barrier Transport of Docosahexaenoic Acid ACS Publications
- Vitali C et al, 2014 Cardiovascular Research
- Schaffer S et al, 2012, Do polyphenols enter the brain and does it matter? Some theoretical and practical considerations PubMed Central
- Turner RS et al, 2015, A randomized, double-blind, placebo-controlled trial of resveratrol for Alzheimer disease
PubMed Central - Rege SD et al, 2014, Neuroprotective effects of resveratrol in Alzheimer disease pathology PubMed Central
- 5-Hydroxy-DL-tryptophan PubChem
- Mishra S et al, 2008, The effect of curcumin (turmeric) on Alzheimer’s disease: An overview PubMed Central
- Brett KE et al, 2014, Maternal–Fetal Nutrient Transport in Pregnancy Pathologies: The Role of the Placenta
PubMed Central - Cetine I et al, 2009, Long chain fatty acids and dietary fats in fetal nutrition PubMed Central
The Transport of Nutrients Across the Cell Membranes
Nutrients can move in and out of the body cells by mechanisms described below.
1. Passive Diffusion
Passive diffusion (from the Latin diffundere = to scatter, spread out) is the free movement of nutrients across the cell membranes from the side with high to the side with low nutrient concentration. This is how certain nutrients, such as glycerol, short- and medium-chain fatty acids, and ethanol move from the bowel across the intestinal lining cells into the blood and from the blood to the tissue cells.
2. Facilitated Diffusion
Facilitated diffusion (from the French faciliter = to render easy) is the movement of nutrients with the help of certain carriers [1].
Mineral ions, such as sodium [Na+], potassium [K+], calcium [ Ca++] and chloride [ Cl-], and larger molecules, such as glucose, amino acids and long-chain fatty acids, move in and out of the cells down their concentration gradient with the help of substance-specific carriers (proteins), which form channels or “pores” in the cell membranes.
Transport of glucose into the tissues is facilitated by the hormone insulin.
3. Osmosis
Osmosis (from the Greek osmos = push) is the movement of water across the cell membranes from the solution with lower concentration (hypotonic solution) to the solution with higher concentration of solutes (hypertonic solution). Osmosis is the main mechanism of water distribution in the body [1].
When you drink usual beverages, like water and fruit juices, the fluid in your intestine will become less concentrated (hypotonic) in relation to the blood plasma, so it will move across the intestinal wall into the blood, by the principle of osmosis.
Osmosis can also cause problems:
When a person with lactose intolerance drinks a lot of milk, the unabsorbed lactose will build up in the intestinal fluid, which will become hypertonic in relation to the fluid in the intestinal wall, so the fluid will start to move from the intestinal wall into the intestine and thus cause diarrhea.
When a person drinks a large amount of water in a short time and consumes no or very little salt, the water absorbed from the intestine into the blood plasma will make blood plasma less concentrated (hypotonic) in relation to the fluid in the brain, so the water will move from the blood into the brain cells resulting in brain swelling. This is called water intoxication.
4. Cotransport
In cotransport, one nutrient helps to transport another nutrient across the cell membrane.
Sodium, which moves into the cells down its concentration gradient, helps glucose to enter the cells up its concentration gradient. This is called sodium-glucose cotransport [2].
5. Active Transport
Active transport is the movement of nutrients across the cell membranes with the help of pumps — the most known is the sodium/potassium pump [1]. Active transport requires energy produced by breakdown of highly-energetic molecules of adenosine triphosphate (ATP).
Sodium/potassium (Na+/K+) pumps in the cell membranes pump the sodium ions out and the potassium ions into the cells thus maintaining high sodium concentration outside and low sodium concentration inside the cells, and high potassium concentration inside and low potassium concentration outside the cells [1].
6. Endocytosis
In endocytosis, the cells engulf nutrients from the blood. Cholesterol and some other molecules enter the cells by endocytosis [3].
The Brain-Blood Barrier
The blood-brain barrier (BBB), which consists of the lining (endothelium) of the brain arteries, does not allow certain nutrients and drugs to enter the brain from the blood.
Nutrients that can readily cross the BBB:
- Water [7-p.122]
- Minerals [4]
- Vitamins [4]
- Glucose, mannose, galactose [7-p.127]
- Amino acids (most) [4]
- 5-hydroxytryptophan [13]
- Fatty acids:
- Essential [5]: alpha-linoleic, linolenic
- Non-essential [8]: docosahexaenoic acid (DHA), oleic, palmitic
- Ketones (produced from fatty acids) [4]
- Ethanol [4]
- Phytonutrients: resveratrol [11,12], curcumin [14]
Nutrients that can cross the BBB slowly/in small amounts:
- Fructose [4]
- Amino acids alanine, glycine, proline and γ-aminobutyric acid (GABA) [4]
Nutrients that cannot cross the BBB:
- Disaccharides (sucrose, maltose, etc.)
- Oligosaccharides, such as raffinose
- Polysaccharides, such as starch
- Triglycerides
- Some nonessential fatty acids [6]
- Cholesterol [6,9]
It is not yet known if these nutrients can cross the BBB:
- Polyphenols (flavonoids, tannins) [10,12]
Transport of Nutrients across the Placenta
Nutrients that can cross the placenta [15]:
- Water
- Minerals
- Vitamins
- Glucose
- Amino acids
- Fatty acids (but not triglycerides) [16]
- Cholesterol
- Ethanol
Alcohol
- Alcohol chemical and physical properties
- Alcoholic beverages types (beer, wine, spirits)
- Denatured alcohol
- Alcohol absorption, metabolism, elimination
- Alcohol and body temperature
- Alcohol and the skin
- Alcohol, appetite and digestion
- Neurological effects of alcohol
- Alcohol, hormones and neurotransmitters
- Alcohol and pain
- Alcohol, blood pressure, heart disease and stroke
- Women, pregnancy, children and alcohol
- Alcohol tolerance
- Alcohol, blood glucose and diabetes
- Alcohol intolerance, allergy and headache
- Alcohol and psychological disorders
- Alcohol and vitamin, mineral and protein deficiency
- Alcohol-drug interactions
- Fructose
- Galactose
- Glucose
- Isomaltose
- Isomaltulose
- Lactose
- Maltose
- Mannose
- Sucrose
- Tagatose
- Trehalose
- Trehalulose
- Xylose
- Erythritol
- Glycerol
- Hydrogenated starch hydrolysates (HSH)
- Inositol
- Isomalt
- Lactitol
- Maltitol
- Mannitol
- Sorbitol
- Xylitol
- Fructo-oligosaccharides (FOS)
- Galacto-oligosaccharides (GOS)
- Human milk oligosaccharides (HMO)
- Isomalto-oligosaccharides (IMO)
- Maltotriose
- Mannan oligosaccharides (MOS)
- Raffinose, stachyose, verbascose
- SOLUBLE FIBER:
- Acacia (arabic) gum
- Agar-agar
- Algin-alginate
- Arabynoxylan
- Beta-glucan
- Beta mannan
- Carageenan gum
- Carob or locust bean gum
- Fenugreek gum
- Galactomannans
- Gellan gum
- Glucomannan or konjac gum
- Guar gum
- Hemicellulose
- Inulin
- Karaya gum
- Pectin
- Polydextrose
- Psyllium husk mucilage
- Resistant starches
- Tara gum
- Tragacanth gum
- Xanthan gum
- INSOLUBLE FIBER:
- Cellulose
- Chitin and chitosan
- FATTY ACIDS
- Saturated
- Monounsaturated
- Polyunsaturated
- Short-chain fatty acids (SCFAs)
- Medium-chain fatty acids (MCFAs)
- Long-chain fatty acids (LCFAs)
- Very long-chain fatty acids (VLCFAs)
- Monoglycerides
- Diglycerides
- Triglycerides
- Vitamin A - Retinol and retinal
- Vitamin B1 - Thiamine
- Vitamin B2 - Riboflavin
- Vitamin B3 - Niacin
- Vitamin B5 - Pantothenic acid
- Vitamin B6 - Pyridoxine
- Vitamin B7 - Biotin
- Vitamin B9 - Folic acid
- Vitamin B12 - Cobalamin
- Choline
- Vitamin C - Ascorbic acid
- Vitamin D - Ergocalciferol and cholecalciferol
- Vitamin E - Tocopherol
- Vitamin K - Phylloquinone
- Curcumin
- FLAVONOIDS:
- Anthocyanidins
- Flavanols: Proanthocyanidins
- Flavanones: Hesperidin
- Flavonols: Quercetin
- Flavones: Diosmin, Luteolin
- Isoflavones: daidzein, genistein
- Caffeic acid
- Chlorogenic acid
- Lignans
- Resveratrol
- Tannins
- Tannic acid
One Response to "The Transport of Nutrients Across the Cell Membranes"