Absorption of Digested Products & Disorders of Digestive System | Biology for Grade 11 PDF Download

Absorption of Digested Products (Food)

The process through which the foodstuff diffuses through the intestinal mucous membrane and reaches the blood is termed as absorption. The process of absorption in different parts of the alimentary canal takes place in the following manner:

• Absorption in Buccal Cavity: No absorption of food takes place in the oral and the oropharyngeal cavity. Only some chemicals/ medicines and alcohol are absorbed in the oropharyngeal cavity.
• Absorption in Stomach: In the stomach, absorption of water, some salts, alcohol, glucose and few drugs like Aspirin takes place, complete absorption of alcohol takes place in the stomach.
• Absorption in Duodenum: Iron & calcium ion are absorbed in the duodenum.
• Absorption in Jejunum: Maximum absorption takes place in the jejunum.

Summary of Absorption in Different Parts of Digestive System

• Millions of microscopic folds or finger like projections are present in the lumen of gut which are called villi, villus is unit of absorption.
• These villi are supplied with a network of blood capillaries and Lymphatic capillaries. Largest of which is central Lacteal. The cells that line the surface of villi numerous microscopic bristle like projections are called microvilli or brush border. These further increase the surface area for the absorption of the nutrients/digested food.
• On the surface of the mucous epithelium are billions of single-cell (Unicellular) mucous glands called mucous or goblet cells. These cells mainly secrete mucus that acts as a lubricant and protects the epithelial surface from damage and digestion.
• The lining cells of the villi are columnar epithelial cells called enterocytes. On the surface of enterocytes, numerous microvilli are found, they increase the surface area of the mucous membrane.
  
  Movement of absorbed nutrients into the blood and lymph

Digestion and Absorption of Carbohydrate

• The principal carbohydrate of our food is usually starch (from rice or wheat) which is broken down by pancreatic amylase. Disaccharides are broken down to their monosaccharide by enzymes of the succus-entericus.

• Monosaccharides are absorbed via the capillary blood within the villus to finally reach into portal vein.

Note:

Absorption of glucose molecules occurs along with Na⁺ by active symport (Co-transportation) and Fructose is absorbed through Facilitated diffusion because the concentration of glucose is higher in cells whereas the concentration of fructose is low in cells.

Digestion and Absorption of Amino Acid

• All these proteins are exposed to pepsin, trypsin, chymotrypsin, carboxypeptidases etc and as a result, they are converted into tri and dipeptides or free amino acids.
  Amino acid are of two types: 
  (i) L-amino acid  
  (ii) D-amino acid

• The L-amino acids are naturally occurring & are absorbed by an active process against the concentration gradient while D-amino acid is absorbed passively by diffusion.

• Di and tripeptide enter the enterocytes where they are hydrolyzed to amino acids by peptidases and then absorbed via portal blood.

Digestion and Absorption of Fat 

• One molecule of triglyceride is hydrolyzed into one molecule of monoglyceride and two molecules of fatty acids by pancreatic lipase.

• After hydrolysis, the bile salt, monoglyceride and fatty acid together produce a complex called a mixed micelle. These are water-soluble & enter in the enterocytes. Monoglyceride and fatty acid are resynthesized within enterocyte to form a molecule of triglyceride (TG). TG combines with a small amount of protein and the resultant complex is called chylomicron (150mm, white). Chylomicron enters the lacteal.

• Fat-soluble vitamins are absorbed along with dietary fat whereas water-soluble vitamins are absorbed by passive diffusion. Vitamin B12 is absorbed with intrinsic factor by forming a complex.

• In ileum, Vitamin B12 & Bile salt are absorbed. In the colon, only water is absorbed.

• All lymph capillaries coming out of the alimentary canal unite to form Lymph vessels. All lymph vessels coming from the alimentary canal open into the Left Thoracic Lymph Duct. This duct now opens into the Left Subclavian vein. Through the blood, fats reach the heart and from here it is distributed throughout the body.

Note:

• Besides fats, other substances of the digested food like sugars, amino-acids, vitamins, minerals-salts after being absorbed, enter the blood capillaries. 

• All blood capillaries coming out of the alimentary canal, join together to form the Hepatic portal vein. This vein takes the digested food material into the liver. From the liver, the Hepatic vein and the superior post - caval vein takes them to the heart. Heart distributes them throughout the body. Liver performs some necessary and important actions on the digested food.

• Maximum water absorption occurs from upper part of small intestine passively.

Absorption in Colon

• The colon absorbs water from the undigested food. Due to Haustra, the water-absorbing surface of the colon increases and it efficiently increases the absorption of water.

• The excreta of the rabbit is given out of the body in the form of small Pellets. The process of removal of undigested food from the body is termed as Defecation. The process of Defecation is involuntary in rabbit, though it is voluntary in most animals.

• Symbiotic bacteria is found in the colon. Bacterias synthesise vitamin-K, B1, B2 etc.

• Undigested food goes into the rectum where it gets converted into faeces contains water and solid matter. Solid matter contains dead bacteria 30%, fat 10-12%, proteins 2-4% and others. These faeces ejected outside through the anus.

• In the morning the excreta of rabbit is in the form of semi-solid pellets. It has more amount of undigested cellulose in it. Cellulose is a colloid substance, Colloids have the capacity to bind water on their surface, so complete absorption of water is not possible in the intestine, to completely digest the cellulose rabbit again ingests the semi-solid excreta so again digestion of cellulose takes place in the caecum.

• In the evening the excreta of rabbit is in the form of solid, dry pellets. These have less amount of undigested cellulose in them. This nature of rabbit to eat is own excreta is termed as Coprophagy or Caecotrophy or also Pseudorumination. Double circulation of food through the alimentary-canal is termed as Caecotrophy.

• The food of rabbit mainly consists of cellulose so this activity is necessary for rabbits.

• The brown colour of the excreta is due to 2 pigments - Stercobilin and Urobilin. Both of them are formed due to the degradation of Bilirubin. The foul smell of the excreta is due to Indole, Scatole and Tryptophan, CH₄, NH₃, H₂S. These are found in the colon due to the decomposition of amino-acids by bacteria.

• Pellets of rabbit don't have a foul smell because it has a minimum amount of protein in its diet. Carnivores have an excess protein-rich diet so their excreta is highly foul-smelling.

Compound Stomach / Ruminant Stomach

The stomach of Ruminant animals made of 4 chambers:

1. Rumen (paunch) → Largest
2. Reticulum (honeycomb) → Smallest
3. Omasum (psalterium)
4. Abomasum (Rennet) →  True stomach
   Ruminant Stomach

• Gastric juice is secreted by Abomasum. So it is called the true stomach. The inner surface of the Rumen and Reticulum is lined by a Keratinised epithelium. Symbiotic bacteria found is in Rumen and Reticulum. 
• Voluntary muscles are found in Rumen and Oesophagus. Hence reverse peristalsis is found in the Rumen and oesophagus which is controlled by the will power of the animal. Omasum is absent in Camel and Deer.

Calorific Value

• The amount of heat liberated from complete combustion of 1 gm food in a bomb calorimeter (a closed metal chamber filled with O₂) is its gross calorific value or gross energy value (G.C.V.).

• The actual amount of energy liberated in the human body due to the combustion of 1 gm of food is the physiologic value (P.V.) of food.

Assimilation of Absorbed Food

• Amino acids are not stored but are taken up by the cells in connection with the synthesis of proteins. Proteins are used for growth, repair, etc. Excess amino acids can be converted into glucose and then fat and are thus stored. This is an irreversible reaction. Assimilation of Absorbed Food

• Amino acids can also be converted to glucose and used as fuel for the cell. During their conversion to glucose, the amino acids are deaminated (removal of amino groups –NH₂). 

• The liver is the chief site for deamination, i.e, a process by which the amino group is removed from the amino acid resulting in the production of ammonia. Ammonia is soon converted into urea, which is filtered from the blood in the kidney.

• The excess of the monosaccharides; glucose, fructose and galactose are usually stored in the liver and muscle cells in the form of glycogen(glycogenesis). Whenever there is a deficiency of glucose in the blood the glycogen is converted into glucose (glycogenolysis). 

• Muscle glycogen is utilized during muscle contraction. Glucose is utilized in the production of energy for various body activities. A considerable amount of glucose is converted into fat and stored as such.

• The fat is stored in the fat deposits of the body. Such as subcutaneous layers, mesenteries etc. The fat stored is a readily available source of fuel for the cells. 

• Fat has important insulating properties in connection with the conservation of heat and maintenance of body temperature. Fat also plays a protective role as filling or around packing material and between organs.

• In the liver, phospholipids are formed which are returned to the blood to be used by all the cells. In the liver cells, the fats are converted into amino acids and carbohydrates. Vitamins, salts and water are also useful for various metabolic processes.

Egestion or Defaecation

• The elimination of faeces from the alimentary canal is called egestion or defaecation.

• Peristalsis gradually pushes the indigestible materials of the small intestine into the large intestine or colon. Normally 1500 ml of chyme passes into the large intestine per day. The colon absorbs most of the water. It also absorbs electrolytes, including sodium and chloride from the chyme. The epithelial cells of the colon also excrete certain salts such as iron and calcium from the blood.

• Escherichia coli (bacterium) lives in the colon which feeds on the undigested matter. This bacterium, in turn produces vitamin B12 (cobalamin), vitamin K, vitamin B1, (thiamine), and vitamin B2 (riboflavin) that are absorbed by the wall of the colon. Consequently, the chyme is converted into semi solid faeces. 

• As the pellets of faeces enter the rectum, distension of rectal wall induces the feeling of defecation due to a defaecation reflex. This reflex initiates peristalsis in the last part of the colon (sigmoid colon) and the rectum, forcing the faeces towards anus.

• As the faeces reach the anus the anal sphincters relax to allow its discharge (defaecation). The external anal sphincter is under voluntary control whereas the internal anal sphincter is involuntary relaxation of the internal anal. 

• In infants, defaecation occurs by reflex action without the voluntary control of the external anal sphincter.

Disorders of Digestive System

Protein Energy Malnutrition (PEM)

(i) Kwashiorkor

• It is a protein deficiency disease. It commonly affects infants and children between 1 to 3 year of age.
• Symptoms: Underweight, stunted growth, poor brain development loss of appetite anaemia, oedema on lower leg and face.
• Cure: Proteins are necessary for growth, repair of tissue and body defence therefore adequate amount of proteins must be present in the diet.
• Daily Requirement: 1 gm protein per kg body weight in adults. 2 gm protein per kg body weight in growing children. Sources in food are cereals pulses, meat, fish, milk, groundnuts, peas, leafy vegetables etc. 
  Protein Energy Malnutrition Diseases

(ii) Marasmus

• It is caused by protein-energy-malnutrition(PEM) or deficiency of protein and total food caloric value. It mainly occurs in the age group of one year in newly born baby.

• Symptoms: Impairs physical growth, subcutaneous fat disappears, ribs become very prominent, limbs become thin and skin becomes dry, thin & wrinkled. There is no oedema on leg and face but loss of weight occurs.

• Cure: Diet with adequate proteins and proper caloric value should be given to the infants. Sources in food are the same as kwashiorkor. 

(iii) Hypercholesterolemia (Overnutrition)

• It is caused due to intake of excess of saturated fat such as butter, ghee, red meat, egg. Cholesterol level in the blood rises abnormally (hypercholesterolemia). This may cause thrombosis and heart attack.

(iv) Obesity (Overnutrition) 

• It is caused by excessive intake of high caloric nutrients such as sugar, honey and saturated fat. Fat accumulates in the tissue. This may cause high blood pressure, diabetes and heart diseases. 
• Regular exercise and taking of green leafy vegetables are recommended to such persons.

(v) Hypervitaminosis (Overnutrition)  

• It is caused by excessive intake of vitamins. Such as excess of vitamin D causes deposition of calcium in soft tissue. Excess of vitamin A causes lack of appetite, itching rash etc. Hypervitaminosis of 'D'-Nausea, anorexia, hypercalcaemia, hyperphosphatemia, calcification of soft tissue.

(vi) Fluorosis 

• It is caused by excessive intake of fluorine. It is characterised by mottled (brownish discolouration) teeth.

(vii) Constipation 

• Because of the slow reaching of excreta into the large-intestine, hard and dry excreta deposits in the colon.

(viii) Diarrhoea 

• The fast and rapid removal of excreta from the large-intestine is called Diarrhoea. It may be due to viral or bacterial infection in the intestine.

Vitamins: Uses & Diseases caused by their Deficiency

• The study of vitamins is called vitaminology.

• Vitamins were discovered by "Lunin".

• The term "Vitamin" was given by "Funk" and "Hopkins" (B1 from unpolished rice- 1912).

• Vitamins are micronutrients, biological regulators and metabolic regulators (Vitamin theory).

• Vitamins are important to maintain health, but cannot synthesize in the body.

• The earliest known vitamin is Vitamin 'C' (James Lind – Scottish naval surgeon – 1747).

• The earliest extracted vitamin is Vitamin B₁.

Vitamins are of the following types:

1. Fat-soluble vitamin
2. Water-soluble vitamin

1. Fat-Soluble Vitamin

(a) Vitamin - 'A' (Retinol) 

• The isomers of vitamin 'A' are:
  (i) A1 – Retinol for vision.
  (ii) A2 – Dehydro retinol which is essential for epithelial lining, glands and tears production.
• Source: A good source is carrot, other sources are Guava, papaya, mango, spinach etc.
• Deficiency Diseases:
  (i) Night blindness: Due to deficiency of A1 It is also known as Nyctalopia (Inability to see in dark).
  (ii) Xeropthalmia: Due to deficiency of A2 Tear formation is absent. In this disease conjunctiva & cornea become dry due to keratinization of conjunctiva & cornea. It is the main problem of blindness in children throughout the world.

(b) Vitamin - 'D' (Calciferol) 

• It is also known as the "Sunshine Vitamin" or "Anti Ricket" vitamin.
• Synthesized in the skin from cholesterol by UV light.
• It is necessary for bone & teeth. 
• Deficiency Diseases: Rickets in children and osteomalacia in adult.
• Source: Good source cod liver oil and shark liver oil for both 'A' & 'D'. Other sources are meat, liver, egg, milk etc.

(c) Vitamin - 'E' (Tocopherol) 

• It is also known as "antisterility" vitamin or "beauty" vitamin.

• This vitamin removes scar & wrinkles from the skin.

• Deficiency Disease: Sterility

• Source:  Egg, meat, cotton, seed oil.

(d) Vitamin - 'K' (Naphthoquinone) 

• It is also known as the "antihaemorrhagic" vitamin.

• Essential for the synthesis of prothrombin.

• Menadione is an important source of synthetic vitamin K.

• Deficiency Disease: Bleeding or delayed blood clotting.

• Source: Carrot, tomato, liver, cabbage etc.

2. Water-Soluble Vitamin

(a) Vitamin B1 (Thiamine)  

• It is also known as the "anti-beri-beri" factor or antineuritic factor.

• Beri-Beri affects the peripheral nervous system, alimentary canal & cardiovascular system.

• Deficiency Disease: Beri-Beri, Wernicke's encephalopathy.

• Source: Rice, wheat, egg and fish etc.

(b) Vitamin B2 (Riboflavin) 

• It is also known as vitamin 'G' or lactoflavin or yellow enzyme.

• It is essential for the formation of FMN & FAD. 

• Deficiency Diseases: Cheliosis (Cracked lips at the corner of the mouth) sore mouth and ulceration, digestive disorder, Pellegra like beriberi.

• Source: Cow's milk, egg, liver, yeast etc.

(c) Vitamin B3 (Pantothenic acid) 

• It is derived from the Greek word, panthothen = everywhere.
• It is also known as yeast factor or chick antidermatitis factor.
• It helps in the formation of acetylcholine and Coenzyme A.
• Deficiency Diseases: Burning feet syndrome, fatigue & paralysis of muscles.
• Source: Kidney, liver, yeast, milk, egg, meat etc.

(d) Vitamin B5 (Niacin or Nicotinic acid)

• It is also known as "antipellagra" factor or vitamin PP (Pellagra preventing factor). 
• It forms an essential component of NAD & NADP 
• Deficiency Diseases: Pellagra in human beings (diarrhoea, dermatitis, dementia) and black tongue (hyperpigmentation) disease in dogs.
• Source: Kidney, liver, milk, yeast, egg etc.

(e) Vitamin B6 (Pyridoxine) 

• Function as co-enzyme. It is also known as the rat antidermatitis factor.
• Deficiency Diseases: Dermatitis, Anaemia, nervousness.
• Sources: Liver, meat, yeast, egg etc.

(f) Vitamin B7 (Biotin) 

• It is also known as vitamin 'H' or anti egg white injury factor (egg white contain avidin protein which is an antagonist to vitamin B7 – dermatitis, hair loss, nervous symptom).
• It is essential for fat synthesis. 
• Deficiency Disease: Dermatitis
• Sources: Vegetables, yeast, wheat egg etc.

(g) Vitamin B12 (Cyanocobalamin)  

• An extrinsic factor of the castle. It is also known as the "anti pernicious anaemic" factor or "RBC maturing" factor. It promotes DNA synthesis & Maturation of RBCs.
• Deficiency Disease: Pernicious anaemia.
• Sources: Meat, liver etc.

(h) Folic Acid 

• It is also known as folacin or Vitamin M.
• It is needed for the formation of RBC & synthesis of DNA. 
• Deficiency Disease: Anaemia.
• Sources: Green foilage of plant - cabbage, cauliflower. 

(i) Vitamin 'C' (Ascorbic Acid) 

• It is also known as"anti-scurvy" or anti-viral, anti-cancer vitamin.
• It is necessary for the healing of the wound. 
• Deficiency Disease: Scurvy (deficient formation of collagen fibres).
• Sources: Amla, Tomato, Orange, Guava, Lemon (citrus fruit).

Winning Stroke

• Citrin is also known as vitamin 'P' and controls vascular permeability.
• Vitamin B17 is a recently discovered anti-cancer vitamin.
• Vitamin Q helps in blood clotting.
• Vita B15 is also known as pogonic acid, deficiency causes disorder in liver.
• Vitamin B6 is also used in the treatment of tuberculosis.
• Thecodont teeth are also found in crocodile.
• One pair of vomerine teeth is found in the palate of the frog.
• Fangs are the poison teeth of snakes, these are the maxillary teeth.
• Upper incisor teeth are modified in tusk in elephant.
• Upper canine teeth are modified in tusk in walrus.
• Homodont type dentition is found in the toothed whale.
• Enamel is absent in Sloth and Armadillo.
• Salivary glands are absent in whale.
• The tongue is non-motile in the whale.
• Gall bladder is absent in lamprey, whale, rat and horse.
• The main pancreatic duct is also known as the duct of wirsung while the accessory pancreatic duct is known as the duct of santorini.
• Antinueritic Vitamins - A, E and C.
• Nature's most potent antioxidant - vitamin E, which is maximum in the liver.
• Vitamin B12 is absent in plants. However, it is considered that Spirulina (an alga) contains B12.
• Anticancer vitamins - A, B17, C etc.

Minerals: Uses & Diseases caused by their Deficiency