Dietary sources

All natural sources of vitamin A in the diet are derived ultimately from provitamin A carotenoids. For much of the world's human population, and particularly in parts of the developing world, vegetables and fruits provide the main dietary sources of vitamin A in the form of P-carotene and other provitamin carotenoids. In other parts of the world, milk, butter, cheese and eggs are important dietary sources of vitamin A. The liver of meat animals is a particularly rich source as this organ stores...

The bloodbrain bloodcerebrospinal fluid and placental barriers

3.2.1 The blood-brain and blood-cerebrospinal fluid barriers The brain must be protected from abrupt changes in the concentrations of circulating adrenaline and other neurally active substances which would interfere with synaptic communication, as well as from potentially toxic molecules that may find their way into the bloodstream. On the other hand, essential molecules such as glucose, amino acids and water-soluble vitamins must have access to the brain cells (neurons and glial cells). The...

Introduction the nervous endocrine and neuroendocrine systems

Anatomically, the nervous system can be divided into the central nervous system (CNS) and the peripheral nervous system. The CNS is composed of the brain and spinal cord located in the cranium and vertebral canal the peripheral nervous system includes all other nervous structures. The CNS receives all nervous impulses from the body (interoceptive) and all impulses following stimuli originating outside the body (exteroceptive). The peripheral nervous system serves to interconnect all other...

Key discussion topics

The human immune system has two components a ready-made innate immunity that relies largely on phagocytosis of pathogenic microorganisms, and a longer-term, more specific acquired immunity that has a 'memory'. Phagocytic leucocytes (e.g. neutrophils, monocytes and macrophages) internalize pathogenic microorganisms and kill them by the release of toxic products into cytoplasmic vacuoles. The acquired immune response is mediated by two main types of lymphocyte cytotoxic T lymphocytes combat...

Type II osteoporosis

Type II osteoporosis is a purely age-related syndrome, which affects men and women over 70 and is twice as common in women as in men. Bone loss increases gradually with aging, unlike the accelerated loss seen in type I osteoporosis. In both sexes, cancellous bone loss begins at about age 40 and continues into old age. Cortical bone loss commences five to ten years later but slows or ceases later in life (Riggs & Melton, 1986). In elderly women, type I and type II osteoporosis overlap and...

Vitamin A and cancer

Apoptosis is a tightly regulated natural process of cell death, which involves changes in the expression of distinct genes. The physiological role of apoptosis in cancer prevention is to eliminate DNA-damaged cells that would otherwise replicate and lead to mutations and possibly cancer. Retinoic acid induces apoptosis in many tumour cell types and therefore retinoids have potential use for cancer chemotherapy and prevention. According to Warrell et al. (1993), all-trans retinoic acid appears...

Stability and bioavailability of vitamins

Vitamin stability is an important issue when considering the nutritional value of a food. Processing and storage losses depend upon conditions such as pH, temperature and moisture content. Niacin and biotin are relatively stable, but the other water-soluble vitamins are labile to varying extents and under different conditions. Riboflavin is notoriously susceptible to decomposition by light. During domestic cooking the water-soluble vitamins are easily leached out into the cooking water or...

Hormones and cell signalling General principles

There are three general classes of hormones (1) peptide hormones, e.g. thyroid-stimulating hormone and adrenocorticotropic hormone (2) steroid hormones, e.g. oestrogens, testosterone and cortisol and (3) derivatives of the amino acid tyrosine, e.g. thyroxine and adrenaline (epinephrine). Peptide and amine hormones are stored in secretory vesicles until needed. Steroid hormones are not stored they are synthesized from intracellular stores of cholesteryl esters after a stimulus. Hormone action is...

General features of the immune system

Immunity refers to the body's resistance to invasive pathogens (viruses, bacteria, fungi, protozoa and multicellular parasites) or their toxic products, to allergens (pollen, animal hair, chemicals, etc.) and to unwanted cells or cell products arising within the body from cancer or autoimmune diseases. The immune system comprises (1) cellular defence mechanisms mediated by several types of leucocytes and (2) humoral defence mechanisms mediated by soluble proteins, so-called because they are...

Naming of the vitamins

By 1915, Osborne and Mendel and also McCollum and Davis had between them distinguished two types of accessory factors based on their solubilities and called them 'fat-soluble A' and 'water-soluble B'. Fat-soluble A was present in butterfat and egg yolk a deficiency of this substance produced an infectious eye disease (xerophthalmia) and growth retardation in young rats. Water-soluble B was present in wheat germ and milk powder its deficiency produced the avian form of beriberi in pigeons. In...

Type I osteoporosis

This syndrome manifests in women typically between 50 to 75 years of age, and results from an acceleration of cancellous bone loss after the menopause. About one in five postmenopausal women will develop type I osteoporosis unless treated. Within the first 1 to 5 years after the onset of menopause, the rate of cancellous bone loss is two to six times the pre-menopausal rate of about 1 per year, but it gradually returns to the pre-menopausal rate about the 10th year after onset of menopause...

Experiments on formulated diets

In the meantime, research was under way into what constituted a physiologically complete diet. Lunin, a pupil of the Swiss biochemist Bunge, first showed in 1882 that laboratory animals failed to thrive when kept on an artificial diet comprising the then known constituents of food (fat, protein, carbohydrate, mineral salts and water) in purified form. Taking a similar approach of using isolated purified food ingredients, Pekelharing formulated a baked product containing only casein, albumin,...

Digestion absorption and transport of dietary fat

The plasma lipoproteins are a family of globular proteins, each of which consists of a core of neutral lipid (predominantly triglyceride or cholesteryl ester) surrounded by a coat of phospholipid and protein. These particles can be divided into four broad categories (1) chylomicrons, which primarily transport dietary triglyceride and cholesterol (2) very-low-density lipoproteins (VLDL), which primarily transport triglycerides that have been synthesized in the liver and two lipoproteins that...

Neuroendocrine modulation of immune responses

It has long been known that stressful conditions can suppress immune functions, reducing the ability of an individual to recover from infection. This can be explained by the fact that the neuroendocrine and immune systems are interconnected, forming an integrated system with common mediators and receptors. Cells of the immune system have receptors for many hormones, hormone-releasing factors and neurotransmitters - evidence that these molecules regulate immune responses. Moreover, immune cells...

Formation of Vldl Hdl and LDL

In the liver, the constituent lipids of chylomicron remnants are repackaged into HDL and VLDL particles (mainly the latter), which are released into the circulation. There is no direct synthesis of LDL in the liver. VLDL contain high concentrations of triglycerides and moderate concentrations of cholesteryl esters and phospholipids. The triglycerides are removed from VLDL by the action of lipoprotein lipase located on the endothelial surface of blood vessels in extrahe-patic tissues, enabling...

Early studies of nutritionally related diseases

For centuries in the past, certain populations in the world were subjected to the ravages of four particular diseases with well-characterized symptoms these diseases are beriberi, scurvy, pellagra and rickets. Progress in the aetiology of these diseases was hindered by the dogged belief that a disease must be caused by a positive factor, i.e. a microorganism or a toxin. The medical authorities could not envisage that a disease could be caused by a lack of something in the diet. Although the...

Nutritional vitamin deficiency

In countries where diets are unbalanced and inadequate, or where there are particular dietary customs, certain typical disease patterns have been shown to be due to vitamin deficiency. Examples of the most commonly observed diseases are xerophthalmia, rickets, beriberi, pellagra and scurvy, which result from deficiencies of vitamin A, vitamin D, thiamin, niacin and vitamin C, respectively. Deficiency of a single member of the vitamin B group is rare in humans because these vitamins are largely...

Definition and classification of vitamins

Vitamins are a group of organic compounds which are essential in very small amounts for the normal functioning of the body. Thirteen vitamins are recognized in human nutrition and these have been classified, according to their solubility, into two groups. The fat-soluble vitamins are represented by vitamins A, D, E and K also included are the 50 or so carotenoids that possess varying degrees of vitamin A activity. The water-soluble vitamins comprise vitamin C and the members of the vitamin B...