Digestive System & Nutrition — the Complete Vitamins Table

Why This Chapter Matters

Digestion and nutrition together are worth 3-5 questions in almost every SSC CGL, CHSL, MTS and RRB NTPC paper, and the vitamins table alone has probably decided more Science marks than any other single topic in this book. Ask a hundred toppers which chapter they revised the night before the exam and most will say this one, because the questions are direct: which vitamin's deficiency causes scurvy, which enzyme breaks down starch, which organ is the largest gland in the body. You are not being tested on understanding here. You are being tested on recall speed.

Here is the shape of what is coming. We will walk the food's actual path through your body, mouth to rectum, naming the organ and the enzyme it releases at each stop. Then we will slow down for the liver and pancreas, which do more heavy lifting than any other digestive organs and get asked about constantly. After that comes nutrition itself: macronutrients, and then the vitamins table, built to be exam-perfect. The single biggest mistake aspirants make in this chapter is mixing up vitamin B1 (thiamine) deficiency with B12 (cobalamin) deficiency, or confusing rickets with osteoporosis. Both pairs sound similar under exam pressure and both get tested almost every year. We will build clear separators for exactly these traps.

The Digestive Tract: Organ by Organ

Your digestive system is one continuous tube, about 9 metres long in an adult, running from mouth to anus. Think of it as a food-processing assembly line at a factory: each station does one job and passes the product to the next.

Mouth. Digestion starts here, not in the stomach, a fact SSC loves to test. The salivary glands release saliva, containing the enzyme salivary amylase (also called ptyalin), which begins breaking down starch into simpler sugars. That is why a piece of plain roti or rice tastes faintly sweet if you chew it for a full minute: the amylase in your own saliva is already converting starch into sugar before it even reaches your stomach. Teeth do mechanical digestion, chewing food into a soft mass called a bolus. There are three pairs of salivary glands: parotid (the largest, near the ear), submandibular (under the jaw) and sublingual (under the tongue). Mumps, a viral infection, classically causes painful swelling of the parotid glands, another small fact worth filing away.

Pharynx and Oesophagus. The pharynx is a short shared passage for food and air, and a flap called the epiglottis closes over the windpipe every time you swallow so food does not enter the lungs. Choke on food and this is usually the mechanism that briefly failed. The oesophagus is a muscular tube, roughly 25 cm long, that pushes the bolus down to the stomach using peristalsis, a rhythmic wave of muscle contraction strong enough that you could technically swallow food while standing on your head; gravity is not what moves food down the gut, muscle is. No digestion happens in the oesophagus. It is pure transport, like a conveyor belt at a factory that adds nothing to the product but moves it reliably to the next station.

Stomach. A muscular, J-shaped bag that churns food and bathes it in gastric juice. Gastric glands secrete hydrochloric acid (HCl), which kills bacteria and activates the enzyme pepsin from its inactive form pepsinogen. Pepsin begins protein digestion, breaking proteins into peptides. The stomach also secretes rennin in infants, which curdles milk protein so it stays in the stomach long enough for digestion, which is why breastfed infants digest milk efficiently while an adult's stomach handles milk differently. Food leaves the stomach as a thick, acidic liquid called chyme. The stomach lining itself is protected from its own strongly acidic juice (pH around 1.5 to 3.5, acidic enough to dissolve a coin over time) by a thick layer of mucus; when that mucus layer breaks down, acid starts attacking the stomach wall itself, which is exactly how a peptic ulcer forms.

Exam trap: Students often think the stomach digests everything. It mainly works on proteins. Fat and starch digestion continue and largely finish in the small intestine, not the stomach.

Small Intestine. The real workhorse of digestion, about 6-7 metres long, divided into three parts: duodenum (the shortest section, curving around the pancreas), jejunum and ileum (the longest section, joining the large intestine). The duodenum receives bile from the liver and pancreatic juice from the pancreas, both loaded with enzymes that finish breaking down fats, proteins and carbohydrates into absorbable units: glucose, amino acids and fatty acids. The jejunum and ileum are lined with finger-like projections called villi (and even smaller microvilli sitting on each villus), which massively increase surface area for absorption, to the point that the small intestine's inner lining, if flattened out, would cover an area close to a badminton court. This is where nearly all nutrient absorption into the blood happens; each villus contains its own tiny blood capillaries and a lymph vessel to carry absorbed nutrients away.

Analogy: picture the small intestine as a long market street lined with thousands of tiny shopfronts, the villi, each one grabbing a bit of nutrient as it passes and handing it into the bloodstream. A smooth intestine would sell far less; the folding is what makes the business work.

Large Intestine. About 1.5 metres long, made of the caecum, colon and rectum. It does not digest food. Its job is absorbing water and some salts from the leftover indigestible matter, and housing gut bacteria that produce certain vitamins, including some vitamin K. What remains, undigested fibre and dead bacteria, is compacted into faeces and stored in the rectum before elimination through the anus.

Exam trap: the appendix, a small tube attached to the caecum, is often asked about as a "vestigial organ" with no major digestive role in humans. Inflammation of the appendix is called appendicitis.

Liver and Pancreas: The Two Support Organs

These two glands do not lie directly in the food's path but pour their secretions into the duodenum, and exam papers ask about them constantly, sometimes trying to trick you into thinking they are part of the tube itself. They are not. They are accessory glands.

Liver. The largest gland in the human body (and the largest internal organ), sitting on the upper right side of the abdomen, weighing about 1.5 kilograms in an adult. Its digestive job is producing bile, a greenish fluid stored in the gall bladder and released into the duodenum when fatty food arrives. Bile contains no enzymes. Its role is emulsification: breaking large fat globules into tiny droplets so pancreatic lipase can act on far more surface area at once, the same way a bit of soap breaks a film of oil into tiny droplets in washing-up water rather than leaving one greasy sheet on top. Beyond digestion, the liver stores glucose as glycogen and releases it back into the blood when the body needs energy between meals, detoxifies harmful substances including alcohol and drugs, produces bile pigments (bilirubin) from the breakdown of old red blood cells, and manufactures several blood-clotting proteins. It is one of the few human organs that can regenerate a substantial part of itself after injury or partial surgical removal, which is why living-donor liver transplants are possible.

Exam trap: the gall bladder stores bile; it does not produce it. Bile is produced by the liver. This distinction is tested repeatedly.

Pancreas. A gland lying behind the stomach, and unusual because it does two completely different jobs, which makes it a favourite exam topic. As an exocrine gland, it releases pancreatic juice into the duodenum through the pancreatic duct, containing three major enzymes: trypsin (digests proteins), amylase (digests starch) and lipase (digests fats). This exocrine role means the pancreas is doing chemistry, breaking food down using enzymes carried through a duct, exactly like the salivary glands and stomach. As an endocrine gland, clusters of cells called the islets of Langerhans, discovered by and named after German scientist Paul Langerhans, secrete the hormones insulin and glucagon directly into the blood to regulate blood sugar. Insulin lowers blood glucose by helping cells absorb it; glucagon raises blood glucose by triggering the liver to release stored glycogen. The two work as opposites, like a thermostat's heating and cooling functions, keeping blood sugar in a narrow healthy band. Insulin deficiency or resistance causes diabetes mellitus, a disease now extremely common across urban India and a frequent general-awareness topic in its own right.

Memory hook: think "Pancreas Plays Two Roles" — Pancreatic juice (digestion, exocrine) and Producing insulin (blood sugar, endocrine). One gland, two completely separate jobs, and SSC papers test both sides.

Macronutrients: What the Body Needs in Bulk

Food gives the body three macronutrients, needed in large daily quantities, plus water.

Carbohydrates are the body's primary energy source, broken down into glucose. Found in rice, wheat, potato and sugar. One gram yields about 4 kilocalories.

Proteins build and repair body tissue, made of chains of amino acids. Found in pulses, milk, eggs, meat and soybean. One gram also yields about 4 kilocalories. Protein deficiency in children causes kwashiorkor (marked by a swollen belly, despite the child often looking otherwise fed) and, when combined with overall calorie deficiency, marasmus (severe wasting, the child looks visibly starved). This pair is a genuine favourite of SSC and RRB question-setters.

Exam trap: kwashiorkor is protein deficiency with adequate or near-adequate calories; marasmus is deficiency of both protein and calories together. Do not swap them.

Fats are the most concentrated energy source, at about 9 kilocalories per gram, more than double carbohydrates or protein gram for gram. They also form cell membranes and help absorb the fat-soluble vitamins A, D, E and K. Found in oils, ghee, nuts and butter.

Water, while not a calorie-giving nutrient, makes up roughly 60-70% of adult human body weight and is essential for every digestive, circulatory and excretory process. Chew any meal and notice how dry food becomes soft and swallowable only once saliva, which is mostly water, mixes into it; the same principle scales up through the whole gut, where digestive juices are overwhelmingly water-based.

Analogy: think of the three macronutrients as a household's monthly budget. Carbohydrates are the everyday cash you spend immediately for quick needs. Fat is the fixed deposit, a concentrated store you draw on when daily cash runs low, which is exactly why the body stores extra energy as fat rather than as sugar. Protein is not spending money at all; it is the raw material used to build and repair the house itself, muscle, skin, enzymes, and should not be burnt for quick energy except in genuine starvation.

Micronutrients: Minerals in Brief

Minerals are needed in small quantities but their absence causes clear, named diseases that exams test directly. Calcium and phosphorus build bones and teeth; deficiency weakens bones and, combined with low vitamin D, worsens rickets and osteomalacia. Iron builds haemoglobin, the oxygen-carrying protein in red blood cells; deficiency causes anaemia, which shows up as fatigue and pale skin and is extremely common among women and children in India, another reason it is a frequent exam topic. Iodine is required by the thyroid gland to make its hormone, thyroxine; deficiency causes goitre, a visible swelling in the neck, and severe deficiency during pregnancy can cause a form of stunted physical and mental development in the child. This is precisely why India mandates iodised salt. Sodium and potassium maintain the body's fluid balance and let nerves and muscles fire correctly; severe imbalance can affect heart rhythm. Zinc supports immunity and wound healing. Keep this list light; the real micronutrient heavyweight, and the one exams return to again and again, is vitamins, covered next.

Vitamins: The Complete Table

This is the highest-yield table in the chapter. Learn it cold. Vitamins split into two families based on how the body stores them, and that split is itself a common exam question.

Fat-soluble vitamins (A, D, E, K) dissolve in fat, get stored in the liver and fatty tissue, and do not need to be eaten every single day. Memory hook: "ADEK stays and stores."

Water-soluble vitamins (B-complex and C) dissolve in water, are not stored in meaningful amounts, and must be replenished through diet regularly, since any excess is simply flushed out in urine.

Vitamin	Chemical Name	Deficiency Disease	Major Sources
A	Retinol	Night blindness, xerophthalmia	Carrot, milk, liver, papaya, spinach
B1	Thiamine	Beriberi	Whole grains, cereals, pulses
B2	Riboflavin	Ariboflavinosis (cracked lips, sore tongue)	Milk, eggs, green leafy vegetables
B3	Niacin	Pellagra	Groundnut, whole grain, meat
B5	Pantothenic acid	Fatigue, tingling in hands/feet	Meat, whole grains, broccoli
B6	Pyridoxine	Anaemia, skin disorders	Banana, meat, whole grains
B7	Biotin	Hair loss, dermatitis	Egg yolk, nuts, soybean
B9	Folic acid	Anaemia; neural tube defects in the unborn child	Green leafy vegetables, pulses
B12	Cobalamin	Pernicious anaemia	Liver, meat, milk, eggs (animal sources only)
C	Ascorbic acid	Scurvy (bleeding gums)	Amla, lemon, orange, guava
D	Calciferol	Rickets (children), osteomalacia (adults)	Sunlight, fish liver oil, egg yolk
E	Tocopherol	Infertility, muscle weakness	Vegetable oils, nuts, seeds
K	Phylloquinone	Delayed blood clotting	Green leafy vegetables, cabbage

Exam trap: vitamin B12 is the one water-soluble vitamin the body does store, in the liver, in enough quantity to last a few years. It is also the only vitamin found almost exclusively in animal foods, which is why strict vegans are specifically screened for B12 deficiency. Question-setters like to test this exception right after teaching the "water-soluble means not stored" rule, precisely because it breaks that rule.

Exam trap: rickets and osteomalacia are the same disease of poor bone mineralisation caused by vitamin D deficiency, just at different ages: rickets in growing children (bow-legs, soft skull), osteomalacia in adults (bone pain, weakness). Do not confuse either with osteoporosis, which is age-related bone thinning linked to low calcium and hormonal change, not a vitamin deficiency by itself.

Memory hook: for the numbering gaps in the B-complex (there is no B4, B8, B10 or B11 in the standard list), remember "1-2-3-5-6-7-9-12", read it once as a phone number and it sticks: one-two-three, five-six-seven, nine, twelve.

Analogy: think of vitamins as a construction site's small but essential supplies, nails, screws, glue. The bricks and cement (carbohydrates, proteins, fats) build the bulk of the structure, but without the small stuff nothing holds together properly, and the building develops specific, identifiable faults depending on exactly which small item ran out.

Vitamin naming history is a frequent one-mark question too: the term "vitamine" was coined by biochemist Casimir Funk in 1912, and vitamin A was the first vitamin to be identified and named, by American biochemist Elmer McCollum in 1913. Frederick Gowland Hopkins is remembered separately for his earlier work on "accessory food factors," the research that helped establish the wider concept of vitamins, for which he later shared a Nobel Prize with Christiaan Eijkman.

Common Digestive Disorders

Jaundice turns skin and eyes yellow due to excess bilirubin, usually from liver malfunction or bile duct blockage; you have likely seen a newborn treated for mild jaundice under blue light in a hospital nursery, a common and usually harmless version of the same underlying mechanism. Diarrhoea is frequent, watery stool, often from infection, and remains a leading cause of child mortality in India, which is why ORS (oral rehydration solution) awareness questions appear in general awareness papers too; ORS works by replacing the water and salts the body is losing faster than it can absorb them. Constipation is difficulty passing stool, often linked to low fibre and water intake. Peptic ulcer is a sore in the stomach or duodenum lining, now known to be commonly caused by the bacterium Helicobacter pylori rather than spicy food alone, a fact that has replaced older assumptions in recent exam-setting; the bacteria were identified by Australian scientists Barry Marshall and Robin Warren, who won a Nobel Prize for the discovery. Gastroenteritis is inflammation of the stomach and intestine lining, usually from infection, causing vomiting and diarrhoea together. Cirrhosis is long-term scarring of the liver, commonly from chronic alcohol use or hepatitis infection, and progressively reduces the liver's ability to do its many jobs, from detoxification to clotting-factor production. Piles (haemorrhoids) involve swollen veins around the anus, often linked to chronic constipation and straining.

You have now walked the entire path: mouth to rectum, the two accessory glands, the three macronutrients, and the full vitamin table. That is a complete, exam-ready map of this topic.

Quick Revision — One-Line Facts

1. Digestion begins in the mouth, not the stomach.
2. Salivary amylase breaks starch into simple sugars in the mouth.
3. Food moves down the oesophagus by peristalsis.
4. The stomach secretes HCl and pepsin to digest proteins.
5. Pepsinogen is the inactive form of pepsin, activated by HCl.
6. Food leaving the stomach is called chyme.
7. The small intestine has three parts: duodenum, jejunum, ileum.
8. Villi in the small intestine absorb digested nutrients into blood.
9. The large intestine mainly absorbs water, not nutrients.
10. The liver is the largest gland in the human body.
11. Bile is produced by the liver and stored in the gall bladder.
12. Bile emulsifies fat; it contains no digestive enzyme.
13. The pancreas is both an exocrine and endocrine gland.
14. Pancreatic enzymes: trypsin (protein), amylase (starch), lipase (fat).
15. Islets of Langerhans secrete insulin and glucagon.
16. Insulin deficiency or resistance causes diabetes mellitus.
17. Carbohydrates and proteins give about 4 kcal/gram; fats give about 9 kcal/gram.
18. Kwashiorkor is protein deficiency with near-normal calories; marasmus is protein plus calorie deficiency.
19. Iron deficiency causes anaemia; iodine deficiency causes goitre.
20. Casimir Funk coined the term "vitamin" in 1912.
21. Fat-soluble vitamins are A, D, E, K; they are stored in the body.
22. Water-soluble vitamins are the B-complex and C; they are not stored (except B12).
23. Vitamin A deficiency causes night blindness.
24. Vitamin B1 (thiamine) deficiency causes beriberi.
25. Vitamin B3 (niacin) deficiency causes pellagra.
26. Vitamin B12 deficiency causes pernicious anaemia and is found mainly in animal foods.
27. Vitamin C deficiency causes scurvy; richest natural source is amla.
28. Vitamin D deficiency causes rickets in children and osteomalacia in adults.
29. Vitamin K deficiency causes delayed blood clotting.
30. Helicobacter pylori bacteria commonly cause peptic ulcers.

Memory Tables

Table 1: Digestive Organs, Secretions and Their Jobs

Organ	Secretion / Enzyme	Main Job
Mouth	Salivary amylase	Starch digestion begins
Stomach	HCl, pepsin	Protein digestion, kills bacteria
Liver	Bile	Emulsifies fat
Pancreas	Trypsin, amylase, lipase, insulin, glucagon	Digests protein/starch/fat; regulates blood sugar
Small intestine	Completes digestion via villi	Absorbs nutrients into blood
Large intestine	None (no digestion)	Absorbs water, forms faeces

Table 2: Vitamins — Deficiency Disease Quick-Match

Vitamin	Deficiency Disease
A (Retinol)	Night blindness
B1 (Thiamine)	Beriberi
B2 (Riboflavin)	Ariboflavinosis
B3 (Niacin)	Pellagra
B6 (Pyridoxine)	Anaemia, skin disorders
B9 (Folic acid)	Anaemia, neural tube defects
B12 (Cobalamin)	Pernicious anaemia
C (Ascorbic acid)	Scurvy
D (Calciferol)	Rickets / Osteomalacia
E (Tocopherol)	Infertility
K (Phylloquinone)	Delayed blood clotting

Table 3: Protein-Energy Malnutrition Pair

Disease	Cause	Key Sign
Kwashiorkor	Protein deficiency, near-normal calories	Swollen belly
Marasmus	Protein and calorie deficiency together	Overall body wasting

Practice MCQs

Q1. Which enzyme present in saliva begins the digestion of starch? (a) Pepsin (b) Trypsin (c) Salivary amylase (d) Lipase

Q2. The hormone insulin is secreted by which part of the pancreas? (a) Duodenum (b) Islets of Langerhans (c) Gall bladder (d) Acinar cells only

Q3. Which organ produces bile? (a) Gall bladder (b) Pancreas (c) Liver (d) Stomach

Q4. Deficiency of vitamin C causes which disease? (a) Rickets (b) Scurvy (c) Beriberi (d) Pellagra

Q5. Which of the following is the largest gland in the human body? (a) Pancreas (b) Thyroid (c) Liver (d) Pituitary

Q6. Vitamin B1 is chemically known as: (a) Riboflavin (b) Thiamine (c) Niacin (d) Pyridoxine

Q7. The main function of bile in digestion is to: (a) digest proteins (b) emulsify fats (c) digest starch (d) kill bacteria

Q8. Which vitamin deficiency is most directly linked to poor blood clotting? (a) Vitamin K (b) Vitamin A (c) Vitamin B6 (d) Vitamin E

Q9. Chyme refers to: (a) saliva mixed with food in the mouth (b) the semi-digested acidic food leaving the stomach (c) bile stored in the gall bladder (d) waste matter in the large intestine

Q10. Which of these vitamins is stored in the human body despite being water-soluble? (a) Vitamin C (b) Vitamin B1 (c) Vitamin B12 (d) Vitamin B6

Q11. Kwashiorkor disease results primarily from a deficiency of: (a) carbohydrates (b) protein, with near-normal calorie intake (c) vitamin D (d) iron

Q12. Which bacterium is commonly associated with causing peptic ulcers? (a) Escherichia coli (b) Helicobacter pylori (c) Salmonella typhi (d) Vibrio cholerae

Q13. Rickets in children and osteomalacia in adults are both caused by deficiency of: (a) Vitamin A (b) Vitamin C (c) Vitamin D (d) Vitamin K

Q14. Which of the following correctly lists the three parts of the small intestine in order from the stomach? (a) Ileum, jejunum, duodenum (b) Duodenum, jejunum, ileum (c) Jejunum, duodenum, ileum (d) Duodenum, ileum, jejunum

Q15. The scientist credited with coining the term "vitamin" in 1912 was: (a) Edward Jenner (b) Casimir Funk (c) Frederick Hopkins (d) Louis Pasteur

Answer Key

Q	Answer	Reason
1	(c)	Salivary amylase (ptyalin) starts starch digestion in the mouth; pepsin and trypsin act on protein, lipase on fat.
2	(b)	Islets of Langerhans are the endocrine clusters in the pancreas that release insulin and glucagon into the blood.
3	(c)	The liver produces bile; the gall bladder only stores and releases it, a distinction exams test repeatedly.
4	(b)	Vitamin C deficiency causes scurvy, marked by bleeding gums; rickets is vitamin D, beriberi is B1, pellagra is B3.
5	(c)	The liver is the largest gland (and largest internal organ); the pancreas is far smaller despite its dual role.
6	(b)	Vitamin B1's chemical name is thiamine; its deficiency disease is beriberi.
7	(b)	Bile emulsifies fat into small droplets for enzymes to act on faster; it contains no digestive enzyme itself.
8	(a)	Vitamin K is essential for the blood-clotting cascade; its deficiency causes delayed clotting and easy bleeding.
9	(b)	Chyme is the thick, acidic, partly digested food mass that leaves the stomach and enters the duodenum.
10	(c)	Vitamin B12 is unusual among water-soluble vitamins because the liver stores enough to last a few years.
11	(b)	Kwashiorkor is protein deficiency with near-adequate calories, causing a swollen belly; marasmus adds calorie deficiency too.
12	(b)	Helicobacter pylori is the bacterium now known to cause most peptic ulcers, replacing the old "spicy food" assumption.
13	(c)	Vitamin D deficiency causes rickets in growing children and osteomalacia in adults; both are poor bone mineralisation.
14	(b)	The small intestine runs duodenum, then jejunum, then ileum, in that order from the stomach to the large intestine.
15	(b)	Casimir Funk coined "vitamine" in 1912; Elmer McCollum is credited with identifying and naming vitamin A the following year.