Heterotrophic Nutrition Flashcards
Define nutrition.
Nutrition is the process of acquiring energy and materials for cell activities
Define heterotrophic nutrition.
Heterotrophic nutrition is the process of obtaining energy metabolic raw materials from organic materials made by other organisms.
What are heterotrophs?
These are organisms that feed on organic sources of carbon. Their survival is dependent directly or indirectly on the autotrophs.
What are the types of heterotrophic nutrition?
(a) Holozoic nutrition
(b) Saprotrophic nutrition (Saprophytic nutrition)
(c) Symbiosis:
(i) Parasitism
(ii) Mutualism
(iii) Commensalism
What is holozoic nutrition?
This is the type of nutrition in which complex organic food is taken in and broken down inside the body of an organism into simple soluble molecules which are then absorbed and assimilated.
What is digestion?
This refers to the process of reducing large complex food materials into simpler soluble materials.
What is absorption?
This is the process of taking the soluble molecules from the region of
digestion into the tissues of the organism.
Define assimilation.
This is the process of using the absorbed nutrients for a particular purpose in the organism’s body.
What are the characteristic processes involved in holozoic nutrition?
- Ingestion; is the taking in of food.
- Digestion. Is the breakdown of large organic molecules into smaller and simpler molecules.
- There are two types of digestion namely;
• Mechanical digestion, involves mechanical or physical break down of food for example by
teeth.
• Chemical digestion. Involves the activity of enzymes which carry out chemical breakdown
of food by hydrolysis. Digestion can also be intracellular (inside the cell) or extracellular
(outside the cell) - Absorption. This is the uptake of the soluble molecules from the digestive region across a membrane into the body tissues. The food may pass directly into the cells or first into blood stream to be transported other regions of the body.
- Assimilation. This is the process of using the absorbed molecules to provide either energy or materials to be incorporated into the body.
- Egestion. This is the elimination from the body of undigested waste food materials.
Define saprophytic nutrition.
This is a type of nutrition where organisms feed on dead decaying organic matter.
Organisms which undergo this form of nutrition are called saprotrophs/saprophytes/ saprobionts mainly fungi such as yeast, mucor, and Rhizopus; and bacteria.
- Nucleotidases: catalyse hydrolysis of nucleotides into phosphoric acid, nitrogenous bases and pentose sugars.
- Maltase: catalyses hydrolysis of maltose into glucose molecules, thereby completing starch digestion.
- Sucrase (invertase): catalyses hydrolysis of sucrose into glucose and fructose molecules
- Lactase: catalyses hydrolysis of lactose into glucose and galactose molecules
- Intestinal lipase: catalyses hydrolysis of lipids into fatty acids and glycerol.
- Intestinal amylase: catalyses hydrolysis of starch into maltose.
What is another name for succus entericus?
Intestinal juice
Define food absorption
It is the process by which soluble food substances are absorbed across the gut epithelium into blood circulatory system or lymphatic system to be carried to all body cells.
How does saprophytism proceed?
These organisms secrete enzymes into their food where it is extracellulary digested.
The soluble end-products are then absorbed assimilated by the saprotrophs.
How do Rhizopus feed?
Their hyphae (wire-like structures) penetrate the food on which they grow and secrete hydrolyzing enzymes from their tips.
These enzymes then carry out extracellular digestion of starch to glucose and proteins to amino acids respectively.
The thin, branching nature of the mycelium (a mass of hyphae), provides a large surface area for absorption.
Glucose is then used during respiration to provide energy for the organism’s metabolic activities.
More glucose and amino acids are used for growth and repair.
Excess glucose will be converted to glycogen and fats, and excess amino acids to protein granules and stored in the cytoplasm.
Extracellular digestion in a common bread mould (Rhizopus stoloninfer)
Define symbiosis.
This refers to the process by which two or more organisms of different species form a close relationship involving living together.
What is mutualism?
This is a relationship between two organisms of different species in which both partners benefit
What is parasitism?
A relationship between two organisms of different species in which one partner benefits and causes harm to the other
What is commensalism?
A relationship between two organisms of different species in which one partner benefits but the other receives no harm or benefit.
What are examples of mutualistic relationships?
• Herbivorous ruminants contain very many cellulose-digesting bacteria and ciliates which can only survive in the anaerobic conditions of a ruminant’s alimentary canal. Bacteria and ciliates feed on the cellulose in host’s diet converting it into simple compounds for further digestion, absorption and assimilation by the ruminant.
• Formation of root nodules by Rhizobium bacteria. The bacteria which inhabit the nodules hence stimulating growth and division of parenchyma cells resulting into swellings (nodules). The bacteria gets sheltered by the plant as the plant benefits from nitrogen fixation done by the bacteria.
• Another example is a mycorrhiza. This is a symbiotic association between a fungus and a plant root. This association is the major route of entry of mineral nutrients into roots. The fungus receives organic nutrients mainly carbohydrates and vitamins from the plant and in return absorbs mineral salts and water which can pass in the plant root.
There are two forms of mycorrhizas are; Ectotrophic mycorrhizas, form a sheath around the root and penetrate the air spaces between the cells in the cortex. Endotrophic mycorrhizas, occurring in virtually all plants, forming an intercellular network and extend into the soil but appear to penetrate cells.
What are obligate parasites?
Organisms which live their entire life parasitically
What are facultative parasites?
Organisms which live as parasites for only a short period of their life cycle are termed facultative parasites
Give nutrition-related adaptations of parasites.
• Many endoparasites such as flat worms have no gut, since they can above pre-digested food through the cuticle.
• The large surface area to volume ratio of the flatworms means that no special internal system is required because materials can rapidly diffuse to all body parts.
• Endoparasites have no special sense organs like eyes, because they live in the dark, constant environments and do not need move looking for food.
• They also lack locomotory devices, since they live in a constant environment except free living flat worms.
• The nervous system of internal parasites is poorly developed compared with free-living ones, because they do not need coordination since they live in a constant environment.
• The ecto parasites have well developed sucking mouse parts such as proboscis, to such blood from their hosts.
• The internal parasites such as tape worms can withstand low oxygen levels of the gut and respire anaerobically, since they live in the gut where there is very little oxygen.
What is an example of commensalism?
- An egret bird and a grazing cow; the cow chases insects due its feeding method while the egret picks the exposed insects for food.
- In this case the cow (host) doesn’t intend to chase the insects for the egret (commensal) but they fly away from the grass being fed on by the cow.
Describe detritus feeding.
The term detritus refers to fresh or decaying organic matter commonly found at the soil surface.
What is a detritivore?
An organism specialized for feeding on detritus for example the earth worm.
Briefly explain how earthworms are significant in the maintenance of soil fertility.
The earthworm consumes fragments of detritus; pieces of food are torn off, moistened by alkaline secretions of pharynx and then swallowed.
Earthworms can also feed on organic material contained in soil which they swallow during burrowing activity.
Thus nutrients are recycled
What organs are a part of the alimentary canal?
- Mouth
- throat
- oesophagus
- stomach
- small intestine (duodenum, jejunum and ileum)
- large intestine (colon, caecum and appendix)
- rectum
- anus.
What structures are a part of accessory structures?
- Teeth
- tongue
- salivary glands
- liver
- gall balder
- pancreas
What are accessory structures?
These are organs, glands, and tissues that enable digestive processes, e.g. by secreting fluids /chemicals, but the food does not actually pass through them.
What are the secretions of the mucous cells, chief cells, and parietal cells known collectively as?
Gastric juice
What are the components of gastric juice?
- mucus
- pepsinogen
- hydrochloric acid
What do mucus cells secrete?
- Mucus
- Bicarbonate ions
What are the functions of the secretions of the mucus cells?
- Mucus is a physical barrier between the lumen and stomach lining
- Bicarbonate ions buffer gastric acid to prevent damage to the epithelium
What do chief/peptic/zymogenic cells secrete?
- Pepsinogen
- Prorennin
What are the functions of the secretions of the chief cells?
- Pepsinogen is converted to pepsin which digests protein, including collagen
- Gastric lipase: Digests lipids
- Prorennin is converted to Rennin which curdles soluble Caseinogen (milk protein) into insoluble casein whose slow flow enables digestion
What do parietal cells secrete?
- HCl
What are the functions of the secretions of the parietal cells?
- HCl activates pepsinogen to pepsin, Prorennin to rennin
- HCl kills bacteria in the stomach
What do G-cells secrete?
- Gastrin hormone
What are the functions of the secretions of the G-cells?
- Gastrin stimulates secretion of gastric juice
- Gastrin Increases contractions of gastro-intestinal tract
- Gastrin hormone relaxes the pyloric sphincter.
What do D cells produce?
- HCl
What are the functions of the secretions of the D cells?
- HCl activates pepsinogen to pepsin, Prorennin to rennin
- HCl kills bacteria in the stomach
What do VIP-producing cells secrete?
Vasoactive intestinal peptide
What is the use of the secretions of VIP-producing cells?
- Vasoactive Intestinal Peptide induces smooth muscle relaxation
- It Inhibits gastric acid secretion
- It Stimulates pepsinogen secretion by chief cells
Define digestion.
Digestion is the process by which large food molecules are broken down into small soluble molecules which can be absorbed and assimilated into the tissues of the body.
What are the two types of processes involved in digestion?
- Mechanical processes; these include the chewing and grinding of food by the teeth and also the churning and mixing of the contents of the stomach to expose more surface area to the enzymes that finish the digestive process.
- Chemical processes; which include hydrolysis action of digestive enzymes, bile, acids.
Describe the process of digestion in the mouth.
- It starts with chewing (mastication), which breaks food into pieces small enough to be swallowed
- Chewing also increases the surface area of food to digestive enzymes.
- The sight, taste, smell and thought of food induces salivary glands to secrete saliva.
- During chewing, saliva mixes with food and the different saliva components perform different functions:
(i) Salivary amylase (ptyalin) enzyme catalyses the breakdown of amylose of cooked starch into maltose.
(ii) Water in saliva moistens food and binding it together for swallowing
(iii) Mucin binds and lubricates food; to enable swallowing.
(iv) Chloride ions activate salivary amylase
(v) Lysozymes kill bacteria in the buccal cavity.
True or false:
Amylase is usually absent in the saliva of carnivores because of absence of cooked starch in the diet.
True
Describe the process of swallowing in man
- Swallowing is a reflex action, which lasts less than 10 seconds.
- The tongue contracts to push the bolus towards the throat, forcing the soft palate upwards to close the nasopharynx
- Larynx and hyoid bone move anteriorly and upwards.
- Epiglottis bends downwards to close larynx (trachea entrance) to prevent food from entering the trachea.
- However, any food that enters into trachea is expelled out by coughing reflex.
- Breathing briefly stops due to closure of glottis.
- Pharynx shortens.
- Upper oesophageal sphincter relaxes, to allow the bolus enter into oesophagus
- In oesophagus the food bolus moves by peristalsis, a sequence of wave-like contractions that squeeze food down the oesophagus.
- Lower oesophageal sphincter (cardiac sphincter) relaxes to allow food into stomach.
Describe digestion of food in the stomach.
- Arrival of food in the stomach stimulates secretion of gastrin hormone from G-cells into the blood stream
- Gastrin stimulates the gastric glands to secrete gastric juice, whose components include: mucus, pepsinogen, hydrochloric acid.
- The components of gastric juice are secreted by different cells and perform different roles as follows:
- Mucus cells secrete mucus which forms a barrier at the stomach lining, to prevent tissue digestion.
- Mucus cells also secrete bicarbonate which buffers gastric acid to prevent damage to epithelium
- Chief cells secrete pepsinogen, prorennin and gastric lipase.
- When pepsinogen is activated to pepsin it digests proteins to polypeptides
- Prorennin is activated to rennin which coagulates soluble milk protein Caseinogen into insoluble casein in babies, whose slowed flow enables digestion.
- Gastric lipase digests lipids to fatty acids and glycerol
- Parietal / oxyntic cells secrete Hydrochloric acid this;
- Activates pepsinogen to pepsin, Prorennin to rennin
- Kills most bacteria in the stomach.
- Provides optimum acidic pH for pepsin to hydrolyse proteins into polypeptides.
- Stops the working of salivary amylase enzyme
- Due to churning by the stomach wall, VIP-producing cells are stimulated to secrete the hormone called vasoactive intestinal peptide, which causes relaxation of pyloric sphincter muscle to allow the semi solid chyme flow from the stomach into the duodenum, after a maximum of about four hours.
Describe the mechanism of HCl secretion in parietal cells.
- Hydrochloric acid is produced by parietal cells through a complex series of reactions.
- Catalysed by the enzyme carbonic anhydrase, carbon dioxide (which diffused from capillaries) reacts with water to form carbonic acid, which dissociates into bicarbonate ion and hydrogen ion.
- Bicarbonate ion is transported into the blood stream by an ion exchange molecule in plasma membrane which exchanges bicarbonate ions exiting parietal cells for chloride ions entering.
- Hydrogen ions are actively pumped into the duct of gastric gland and the negatively charged chloride ions diffuse with the positively charged hydrogen ions.
- Potassium ions are counter pumped into the parietal cell in exchange for hydrogen ions.
- The net result is production of hydrochloric acid in the parietal cells and its secretion into the duct of gastric gland.
Describe the process of digestion in the duodenum.
- Arrival of partially digested, acid food mixture (chyme) in the duodenum stimulates endocrine cells in duodenal walls to secrete the hormones: Secretin, Enterogastrone, Cholecystokinin (CCK) Villikinin and Enterocrinin.
- Secretin hormone secretion is stimulated by presence of acid chyme in duodenum
- Secretin stimulates the liver to secrete bile into the gall bladder.
- It Stimulates pancreatic secretion of (hydrogen carbonate ions) from acinar cells.
- Hydrogen carbonate ions neutralise the acid from the stomach to provide an alkaline pH optimum for pancreatic enzymes.
- Secretin also inhibits secretion of HCl by parietal cells as chyme leaves the stomach.
- Enterogastrone hormone reduces stomach motility
- It inhibits oxyntic cells from secreting hydrochloric acid in order to provide an optimum pH for pancreatic enzymes.
- Signals the stomach to empty slowly when fat is present, allowing much time for digestion of fat already emptied.
- Cholecystokinin hormone (CCK) stimulates contraction of gall bladder to release bile into duodenum.
- Bile salts emulsify fats i.e. fats physically break into droplets which increases their surface area
- CCK also Stimulates the pancreas to secrete pancreatic enzymes
- Pancreatic amylase which catalyses the hydrolysis of starch into maltose
- Enterokinase which activates Trypsinogen to Trypsin.
- Trypsinogen, which is activated by enterokinase to Trypsin.
- Trypsin: Catalyses hydrolysis of polypeptides to peptides.
- Villikinin increases peristalsis in the small intestine and ileum villi movements, in duodenum preparation for incoming food.
True or false
High fat diets stimulate enterogastrone production
True
This prolongs food stay in the stomach, and is therefore useful in treating duodenal ulcer.
Why are all proteolytic (protein digesting) enzymes along the gut secreted in inactive (precursor) form?
To prevent autolysis (self-digestion) of gut tissues, which are protein in nature.
What does the churning action of duodenal walls turn the semi-solid Chyme into?
Chyle
A thin, milky-looking alkaline fluid
Describe the process of digestion in the ileum
- Distention of the small intestine by food stimulates the secretion of intestinal juice (Succus entericus)
- This consists of a mixture of substances from crypts of Lieberkühn and Brunner’s glands.
- Some of the components of Succus entericus include the following enzymes:
- Peptidases: catalyse hydrolysis of peptides into amino acids,thereby completing the digestion of proteins.
- Nucleotidases: catalyse hydrolysis of nucleotides into phosphoric acid, nitrogenous bases and pentose sugars.
- Maltase: catalyses hydrolysis of maltose into glucose molecules, thereby completing starch digestion.
- Sucrase (invertase): catalyses hydrolysis of sucrose into glucose and fructose molecules
- Lactase: catalyses hydrolysis of lactose into glucose and galactose molecules
- Intestinal lipase: catalyses hydrolysis of lipids into fatty acids and glycerol.
- Intestinal amylase: catalyses hydrolysis of starch into maltose.
