Sphingosine is an amino alcohol present in sphingomyelins (sphingophospholipids).  They do not contain glycerol at all.

Sphingosine is attached by an amide linkage to a fatty acid to produce ceramide. The alcohol group of sphingosine is bound to phosphorylcholine in sphingomyelin structure. .

Sphingomyelins are important constituents of myelin and are found in good quantity in brain and nervous tissues.

Nomenclature for stereoisomers: D and L designations are based on the configuration about the single asymmetric carbon in glyceraldehydes

For sugars with more than one chiral center, the D or L designation refers to the asymmetric carbon farthest from the aldehyde or keto group.

Most naturally occurring sugars are D isomers.

D & L sugars are mirror images of one another. They have the same name. For example, D-glucose and L-glucose

Other stereoisomers have unique names, e.g., glucose, mannose, galactose, etc. The number of stereoisomers is 2 ⁿ, where n is the number of asymmetric centers. The six-carbon aldoses have 4 asymmetric centers, and thus 16 stereoisomers (8 D-sugars and 8 L-sugars

An aldehyde can react with an alcohol to form a hemiacetal

Similarly a ketone can react with an alcohol to form a hemiketal

Pentoses and hexoses can cyclize, as the aldehyde or keto group reacts with a hydroxyl on one of the distal carbons

E.g., glucose forms an intra-molecular hemiacetal by reaction of the aldehyde on C1 with the hydroxyl on C5, forming a six-member pyranose ring, named after the compound pyran

The representations of the cyclic sugars below are called Haworth projections.

Fructose can form either: 

• a six-member pyranose ring, by reaction of the C2 keto group with the hydroxyl on C6
• a 5-member furanose ring, by reaction of the C2 keto group with the hydroxyl on C5.

Cyclization of glucose produces a new asymmetric center at C1, with the two stereoisomers called anomers, α & β

Haworth projections represent the cyclic sugars as having essentially planar rings, with the OH at the anomeric C1 extending either:

• below the ring (α)
• above the ring (β).

Because of the tetrahedral nature of carbon bonds, the cyclic form of pyranose sugars actually assume a "chair" or "boat" configuration, depending on the sugar

IRON

The normal limit for iron consumption is 20 mg/day for adults, 20-30 mg/day for children and 40 mg/day for pregnant women.

Milk is considered as a poor source of iron.

Factors influencing absorption of iron Iron is absorbed by upper part of duodenum and is affected by various factors

(a) Only reduced form of iron (ferrous) is absorbed and ferric form are not absorbed

 (b) Ascorbic acid (Vitamin C) increases the absorption of iron (c) The interfering substances such as phytic acid and oxalic acid decreases absorption of iron

Regulation of absorption of Iron

Absorption of iron is regulated by three main mechanisms, which includes

(a) Mucosal Regulation

(b) Storer regulation

(c) Erythropoietic regulation

In mucosal regulation absorption of iron requires DM-1 and ferroportin. Both the proteins are down regulated by hepcidin secreted by liver. The above regulation occurs when the body irons reserves are adequate. When the body iron content gets felled, storer regulation takes place. In storer regulation the mucosal is signaled for increase in iron absorption. The erythropoietic regulation occurs in response to anemia. Here the erythroid cells will signal the mucosa to increase the iron absorption.

Iron transport in blood

The transport form of iron in blood is transferin. Transferin are glycoprotein secreted by liver. In blood, the ceruloplasmin is the ferroxidase which oxidizes ferrous to ferric state.

Storage form of iron is ferritin. Almost no iron is excreted through urine.

Anemia

Anemia is the most common nutritional deficiency disease. The microscopic appearance of anemia is characterized by microcytic hypochromic anemia

The abnormal gene responsible for hemosiderosis is located on the short arm of chromosome No.6.

The main causes of iron deficiency or anemia are

(a) Nutritional deficiency of iron (b) Lack of iron absorption (c) Hook worm infection (d) Repeated pregnancy (e) Chronic blood loss (f) Nephrosis (g) Lead poisoning

Folate: Folic Acid, Folacin Folate, also known as folic acid or folacin, aids in protein metabolism, promoting red blood cell formation, and lowering the risk for neural tube birth defects. Folate may also play a role in controlling homocysteine levels, thus reducing the risk for coronary heart disease.

RDA for folate is 400 mcg/day for adult males and females. Pregnancy will increase the RDA for folate to 600 mcg/day.

Folate Deficiency

Folate deficiency affects cell growth and protein production, which can lead to overall impaired growth. Deficiency symptoms also include anemia and diarrhea.

A folate deficiency in women who are pregnant or of child bearing age may result in the delivery of a baby with neural tube defects such as spina bifida.

The Protein Buffer Systems

The protein buffers are very important in the plasma and the intracellular fluids but their concentration is very low in cerebrospinal fluid, lymph and interstitial fluids.

The proteins exist as anions serving as conjugate bases (Pr ⁻ ) at the blood pH 7.4 and form conjugate acids (HPr) accepting H⁺ .  They have the capacity to buffer some H₂CO₃  in the blood.

PHOSPHORUS

Serum level of phosphate is 3-4 mg/dl for adults and 5-6 mg/dl in children. Consumption of calcitriol increases phosphate absorption.

Functions of phosphorus
(a) Plays key role in formation of tooth and bone

(b) Production of high energy phosphate compounds such as ATP, CTP, GTP etc.,

(c) Synthesis of nucleotide co-enzymes such as NAD and NADP

(d) Formation of phosphodiester backbone structure for DNA and RNA synthesis

Hypophosphatemia is the condition which leads to decrease in absorption of phosphorus. it leads to hypercalcamia

Hyperphosphatemia, increase in absorption of phosphate was noticed. Hyperphosphatemia leads to cell lysis, hypocalcemia and thyrotoxicosis.