Heterotrophic nutrition

 

·         This is a mode of nutrition in which organisms take in already manufactured complex food substances such as carbohydrates, proteins and lipids.

·         Heterotrophs are organisms that feed on already manufactured food substances.

·         These substances are broken down in the bodies of the Heterotrophs into simple soluble food substances that can be absorbed and be utilized by the cells.

Modes of Hetero-trophism

There are four main heterotrophic modes on nutrition:

•           Holozoic- Where organisms ingest, digest and assimilate solid complex food substances.

•           Saprophytism – Where organisms feed on dead decaying matter causing decomposition.

•           Parasitism- a feeding association in which one organism (parasite) feeds on or obtain nutrients on another organism, the host.

•           Symbiosis/Mutualism- An association where two organisms live together and mutually benefit from each other.

a)         Parasitism

There are two main types of parasites:

Endo parasites- Live inside the host

Ecto-parasites- Found on the external surface of the host.

The parasite benefits but the host does not. Some of the parasites cause diseases to the hosts and damage their tissues thereby weakening them.

b)         Symbiosis

In saprophytism, both organisms benefit:

Symbiotic r/ships include

›Rhizobium and leguminous plants: rhizobium fixes nitrogen for the legume while the bacteria obtains manufactured food from the legumes.

›Lichen: association of fungi (absorbing water and nutrients) and algae (manufacturing food for the association.

›Catalase digesting bacteria and ruminants

 

DENTITION

Large animals depend on complex manufactured food substances. These food substances once ingested must be broken down to simpler forms that can be utilized by the cells. The breakdown is both physical and chemical.

Most of the large animals have teeth to enhance physical breakdown of the complex food substances.

Dentition refers to the description of types of teeth, their arrangement and specialization.

Types of Dentition

Homodont dentition: Teeth arrangement and description where an organism has teeth of the same size and shape. Fishes and birds are homodont dentition.

Heterodont dentition: where an organism has teeth of different sizes and shapes that is incisors, canines, premolars and molars. Heterodont dentition is common with mammals and reptiles.

 

a)         Incisors

Are flat and chisel shaped with sharp ridged edges for cutting and biting food.

They have one root.

a.         Canines

Are conical teeth with sharp pointed edges modified for seizing and tearing prey among carnivores.

They have one root

b.         Premolar and molar

They have cusps on their surface to suit their grinding action. Premolars have two roots.

Molars have either two or three roots.

 

 

Classes of Holozoic Heterotrophs

Holozoic heterotrophs are classified according to the type of food they consume.

These are:

a)         Herbivores: heterotrophs that exclusively feed on vegetation.

b)         Carnivores: heterotrophs that exclusively feed on flesh.

c)         Omnivores: heterotrophs that feed on both flesh and vegetation. Dentition of heterotrophs is based on the kind of food they consume.

Dental Formula

This is the description of the number, type and position of teeth in the jaws of animals.

 

Number of teeth recorded represents half the total teeth in the upper and lower jaws.

The teeth names are abbreviated as

a)         i-incisors.

b)         c-canines.

c)         pm-premolars.

d)         m-molars.

Question:

An animal was found to have no incisors and canines on the upper jaw. It had six premolars and four molars on the upper jaw. On the lower jaw, it had eight incisors, no canines, six premolars and six molars.

a)         Write down its dental formula.

b)         State its mode of feeding.

c)         Give a reason.

Herbivores

•           Most do not have upper incisors. Instead they have a horny pad against which grass is pressed and cut by the lower incisors.

•           They have a long tongue that assists in the cutting and moving food.

•           They have a gap in the lower jaw separating canines from premolars known as diastema which allows the tongue to manipulate food.

•           Herbivore teeth have open enamel which allows for continuous growth to replace worn out surfaces due to grinding.

•           Their incisors are wedge shaped to cut grass and vegetation together with the horny pad

•           The jaws have movable joints to allow the sideways movement of lower jaw to facilitate grinding of grass.

 

 

 

 

Carnivores

•           Their incisors are chisel shaped and closely fitting to seize the prey.

•           Their canines are long, conical and curved to hold, kill and tear the prey.

•           Some of their premolars in the lower and upper jaw are modified into specialized carnassial teeth which have smooth sides and sharp edges to slice through flesh and crush bones

•           Premolars and molars are broad with cusps for crushing bones.

•           Their jaws are attached to powerful muscles that move the jaws up and down

•           Carnivores are adapted to fast running by possessing well developed leg muscles.

Dental Diseases

a)         Dental Carries

•           Caused by lack of hard food, too much sweet or sugary food, lack of calcium in diet, lack of vitamin D, lack of cleaning teeth and general ill- health. The bacteria in the mouth break down the sugars to form energy and organic acids. The acids corrode the enamel.

b)         Periodontal Diseases

•           Caused by lack of vitamins A and C, lack of massage of the gums and imperfect cleaning of gums.

•           The gums become flabby and soft so they do not support the teeth. Common in adults than children

•           Are of two types:

a)         Gingivitis- Characterized by reddening of gums, bleeding and pus in the gums.

b)         Pyorrhea- The teeth become loose due to infection of the fibres holding the teeth in the sockets.

 

Dental Hygiene

Proper teeth care requires:

·         Regular cleaning or brushing teeth after every meal Avoid eating too much sugary foods.

·         Eating hard foods e.g. raw carrots, cassava, yams, sugar cane.

·         Eating diet rich in calcium, phosphate and vitamins A, C and D. Teeth should be used for their correct purpose.

·         Regularly visit the dentist if necessary.

DIGESTION

·         The process through which complex food substances is broken down physically and chemically into simpler food substances that can be absorbed by body cells.

·         However, small molecules like those of vitamins, mineral salts and water are directly absorbed into the bloodstream without undergoing digestion.

·         Digestion occurs in the mouth, stomach, duodenum and ileum.

·         There are glands also associated to the digestive system. These include the pancreas, gall bladder, salivary glands.

  

Digestion in the mouth

·         At the mouth both physical and chemical digestion takes place.

·         The food is mechanically broken down by the teeth through grinding and chewing. This process is called mastication.

·         Mastication reduces the food into small size to increase the surface area for enzymatic action.

·         The tongue helps in manipulation of the food as it mixes the food with the saliva secreted from the salivary glands. The salivary glands are:

 

a)         Sublingual salivary gland; beneath the tongue

b)         Sub mandibular gland: under the jaw

c)         Parotid gland: Found in the cheeks in front of the ears.

·         All the glands have ducts through which saliva is directed to the mouth.

·         The tongue also rolls the food into small round masses called boluses. The boluses are then pushed to the back of the mouth to initiate the swallowing process. The boluses are then moved to the stomach via oesophagus. Movement is facilitated by a wave of muscular contractions of longitudinal and circular muscles of the oesophagus known as peristalsis.

·         There is a flap of cartilage, epiglottis which closes the wind pipe (trachea) during swallowing.

Digestion in the stomach

·         Upon swallowing, the boluses move down the gullet to the stomach. The boluses enter the stomach via the cardiac sphincter (a muscular valve).

·         The stomach has thick circular and longitudinal muscle layers which contract and relax to produce movements that mix the contents of the stomach. The mixing process is known as churning and results in formation of a fluid called chyme

·         Arrival of food in the stomach stimulates secretion of the hormone gastrin which stimulates the gastric glands in the stomach walls to secrete gastric juice which contains:

·         Pepsinogen-This is activated to pepsin which breaks down proteins to peptides.

·         Rennin- Digests caseinogens protein in milk to casein (curd).

·         Hydrochloric acid- This:

•                    Activates pepsinogen to pepsin

•                    Provides a favorable medium for action of the enzymes rennin and pepsin

•                    Kills some bacteria ingested with food.

·         Mucus- Forms a protective barrier to the stomach wall against corrosion by the HCl. Mucus is secreted by goblet cells in the epithelial membrane of the alimentary canal.

Duodenum

·         The chyme then passes down to the duodenum through the pyloric sphincter. Duodenum is the first section of the small intestine. In humans it measures about 25-38 cm. the chyme is let down into the duodenum in small quantities.

·         Secretions that contribute to digestion at the duodenum are received from:

a)         Gall bladder in the liver- Secretes bile.

b)         Pancreas- Secrete hormones and digestive enzymes.

·         Arrival of food in the duodenum stimulates secretion of

i.          Secretin hormone from the pancreas: Secretin stimulates secretion of pancreatic juice into the duodenum

ii.         Cholecystokinin from the duodenal wall: This stimulates secretion of bile from the gall bladder.

·         Pancreatic juice contains:

a)         Pancreatic amylase- This facilitates breakdown of the remaining starch into maltose

b)         Trypsin-  Digests proteins into peptides.

c)         Pancreatic juice-Digests lipids into fatty acids and glycerol

d)         Sodium hydrogen carbonate- This:

•           Provides alkaline medium for activity of the duodenum enzymes.

•           It also neutralizes the acidic chyme.

 The bile juice contains bile salts that include sodium glycocholate and sodium taurocholate. These salts:

i.          Aid in emulsification (breakdown of fat molecules into tiny fat droplets to increase surface area for digestion).

ii.         The salts also provide a suitable alkaline medium for action of the duodenal enzymes.

iii.        In addition they neutralize the acidic chyme.

 

Digestion in the ileum

·         Ileum is the final part of the small intestine.

 

·         The inner cells contain secretory cells some of which secrete mucus while some secrete an alkaline fluid known as succus entericus (intestinal juice). The arrival of chyme in ileum stimulates secretion of intestinal juice which contains:

a)         Maltase: speeds up breakdown of maltose to glucose

b)         Sucrase: speeds breakdown of sucrose to glucose and fructose

c)         Peptidase: speeds breakdown of peptides to amino acids

d)         Lipase: speeds breakdown of lipids to fatty acids and glycerol.

e)         Lactase: speeds breakdown of lactose to glucose and galactose.

f)         Polypeptidase: speeds breakdown of plypeptides into amino acids

Note:

·         The mucus secreted by the goblet cells lubricates food along the alimentary canal and also protect the canal from being digested by enzymes.

·         At the end of digestion in the ileum, the resulting watery emulsion is called chyle; it contains soluble end products of digestion ready to be absorbed.

ABSORPTION

•           This is the process through which the soluble end products of digestion diffuse into the cellular lining of the villi.

•           Absorption of micronutrients such as water soluble vitamins, mineral salts and alcohol are absorbed at the stomach. Alcohol is equally absorbed here without undergoing digestion.

•           Most absorption of end products of digestion occurs in the ileum.

•           Molecules of amino acids and glucose pass through the epithelial lining and capillary walls into the blood system by active transport.

•           The capillaries drain into the hepatic portal vein where the absorbed products are transported to the liver before they are circulated to other body parts.

•           The fatty acids are absorbed into the lacteals of the villi which drain into the lymphatic vessels. The lymphatic vessels later join the blood circulatory system which transports them to other body parts.

 

•           The ileum is adapted to absorption in many ways

a)         It is long to provide a large surface area for absorption

b)         It has a narrow lumen so as to bring the digested food into close contact with the walls of the ileum for easier absorption

c)         It is highly coiled to slow down movement of food thus allowing more time for digestion and absorption of food.

d)         The inner surfaces have numerous villi and microvilli to increase surface area for absorption of end products of digestion.

e)         The epithelial lining is one cell thick to reduce the distance through which digested food diffuses.

f)         Has a dense network of blood capillaries into which digested food materials diffuse to increase transport and thus maintain a steep concentration gradient.

g)         Have lacteal vessels in the villi for absorption of fatty acids and glycerol.

 

Egestion

This is the process through which the undigested and indigestible food substances are eliminated from the body.

Caecum and Appendix

While these have no roles in man, they play vital roles in the ruminant animals and other herbivores. They contain some bacteria which secrete cellulose enzyme. These enzymes digest cellulose since most digestive systems cannot secrete cellulose digesting enzyme. The bacteria and the herbivores are in a symbiotic relationship.

Assimilation

This is process of incorporation of the end products of digestion into the cell metabolism. It involves utilization of the end products of digestion into various uses.

a)         Glucose

Oxidized to release energy

Excess glucose is stored under the skin to provide heat insulation Glucose is used to synthesize complex polysaccharide such as cellulose that is an important structural compound in plants.

b)         Fatty acids and glycerol

Oxidized to release energy

Combine to form neutral fats stored under the skin to provide heat insulation

Used to build structures

c)         Amino acids

Used to synthesize proteins for general body growth Oxidized during starvation to release energy

Vitamins

·         These are organic chemical compounds that are essential for a healthy body.

·         Some are synthesized in the body through the action of some microorganisms while some are also obtained in fresh fruits and vegetables.

·         Vitamins are destroyed when foods are excessively cooked. They are required in small quantities.

·         They play vital roles in metabolic reactions. Some act as co-enzymes while some influence the intake of certain substances. In particular, vitamin C influences uptake of iron while vitamin D influences absorption of calcium ions in the gut.

·         Lack of vitamins in the body results into abnormities that manifest through various deficiency diseases. These deficiency diseases can be corrected by inclusion of the deficient vitamins in the diet or taking the vitamin supplements.

·         There are two classes of vitamins owing to their solubility:

a)         Fat soluble vitamins- They dissolve in fats and are often stored in the liver. Include Vitamins A, D, E, K.

b)         Water soluble vitamins- Dissolve in water. Include vitamins B1, B2, B5, B12 and C.

 

Mineral salts

·         These are important inorganic compounds containing elements required for essential body functioning. Depending on body requirements, mineral salts are of two classes:

a)         Macro-nutrients: Nutrients required in large quantities. These include nitrogen, sulphur, phosphorous, calcium, sodium, iron and magnesium.

b)         Micro-nutrients: Nutrients required in small quantities. Include copper, manganese, boron, iodine and cobalt.

Roughages

·         This is the indigestible material in food. Mainly composed of cellulose from plant cell walls.

·         They are found in full cereals, fresh fruit fibres like lemons, oranges, mangoes and vegetables.

Importance of roughage:

a)         It rubs against the walls of the alimentary canal stimulating secretion of digestive enzymes and mucus to lubricate the epithelial lining.

b)         Roughage enhance peristalsis since as they rub against the walls of the alimentary canal, they stimulate contraction and relaxation of the muscles.

c)         Roughage is an absorbent; it extracts water from the alimentary canal making the fecal matter bulky and moist hence can be easily propelled by peristaltic movements. This prevents constipation.

Factors affecting energy requirements in humans

Discuss how the following factors affect energy requirements in humans:

›           Basal metabolic rate

›           Occupation

›           Health of an individual

›           Age

›           Sex

›           Body size

›           Environmental temperature