This is due to low food calorie intake not due to protein deficiency. In developing countries like India, it is common in infants below one year of age. The causal factor may be due to early replacement of mother's milk by other foods of low protein and calorific value. This may happen if the mother has a second pregnancy when the older infant is still too young.

Pellagra is a vitamin deficiency disease most frequently caused by a chronic lack of niacin (vitamin B3) in the diet. It can be caused by decreased intake of niacin or tryptophan and possibly by excessive intake of leucine.

Protein should be supplied only for anabolic purposes. The catabolic needs should be satisfied with carbohydrate and fat. Protein catabolism involves the urea cycle, which is located in the liver and can easily overwhelm the capacity of an already damaged organ.

After being chewed and swallowed, the food enters the esophagus. It uses rhythmic, wave-like muscle movements (called peristalsis) to force food from the throat into the stomach. This muscle movement gives us the ability to eat or drink even when we are upside-down.

Vitamin E deficiency causes nerve problems due to poor conduction of electrical impulses along nerves due to changes in the nerve membrane structure and function.

The striated duct is well developed in the submandibular gland. The epithelium of the striated duct participates in ion and water transport and secretes kallikrein. A segment of this duct is lined by cuboidal-to-columnar epithelial cells with basal infoldings containing numerous mitochondria.

Low levels of  vitamin B9 can disrupt transmethylation reaction, leading to an accumulation of homocysteine (hyperhomocisteinemia) and to impaired metabolism of neurotransmitters (especially the hydroxylation of dopamine and serotonin from tyrosine and tryptophan), phospholipids, myelin and receptors. All of these can lead to the development of various disorders including depression.

The spleen breaks down both red and white blood cells that are spent. This is why it is sometimes known as the 'graveyard of red blood cells' . A product of this digestion is the pigment bilirubin, which is sent to the liver and secreted in the bile.

Unlike most of the other facial muscles, which are innervated by the facial nerve (or CN VII), the muscles of mastication are all innervated by the trigeminal nerve (or CN V). More specifically, they are innervated by the mandibular branch.

Epsilon cells are endocrine cells found in the Islets of Langerhans and produce the hormone ghrelin. They were recently discovered in mice.

Kupffer cell activation is responsible for early ethanol-induced liver injury, common in chronic alcoholics. Chronic alcoholism and liver injury deal with a two hit system. The second hit is characterised by an activation of the Toll-like receptor 4 (TLR4) and CD14, receptors on the Kupffer cell that internalise endotoxin (lipopolysaccharide or LPS).

Different phases of digestion take place including the cephalic phase, gastric phase and intestinal phase. The cephalic phase occurs at the sight, thought and smell of food, which stimulate the cerebral cortex. Taste and smell stimuli are sent to the hypothalamus and medulla oblongata.

The liver produces and excretes bile (a yellowish liquid) required for emulsifying fats and help the absorption of vitamin K from the diet. Some of the bile drains directly into the duodenum, and some is stored in the gallbladder.

The common hepatic duct joins the cystic duct coming from the gallbladder to form the common bile duct. The duct is usually 6–8 cm length and 6mm in diameter in adults.The hepatic duct is part of the biliary tract that transports secretions from the liver into the intestines. It carries more volume in people who have had their gallbladder removed.

Secretin is secreted in the duodenum and signals the secretion of sodium bicarbonate in the pancreas, and it stimulates the bile secretion in the liver. This hormone responds to the acidity of the chyme.

Gastritis is the inflammation of the lining of the stomach and has many possible causes. Common causes of gastritis are excessive alcohol consumption or prolonged use of non-steroidal anti-inflammatory drugs such as aspirin or ibuprofen.

As they are not specific for pernicious anaemia, GPC must be interpreted in conjunction with low serum vitamin B12 level.

Water and lipids are absorbed by passive diffusion throughout the small intestine.

Peyer's patches are covered by specialszed epithelium (follicle-associated epithelium). Some of these epithelial cells have surfaces, which seem folded under the scanning electron microscope. These microfold, or M, cells sample and actively transport particulate antigens from the lumen into the ‘dome’ area, where priming of both T and B lymphocytes occurs.

Very common in Asia and the far East as well as tropical Africa, where 35% of the population carry HBV whereas the rate is much lower in Northern Europe.

Contaminated water is the most common source.

On the contrary, ammonia is toxic to the mucosa.

Pancreatic amylase digests all the remaining starch in the duodenum. Amylase digests starch molecules from the ends of the chains in two-glucose units, forming the disaccharide maltose. Glycogen is also digested here.

Intrinsic factor antibodies are specific and rarely occur in the absence of latent or overt pernicious anaemia, although a low serum B12 level and a positive gastric parietal cell antibody allows a presumptive diagnosis of PA to be made.

Intraepithelial lymphocytes are T cells of various types, not B cells. CD19 is a B cell marker.