Heterotrophic Nutrition

Define Nutrition

process of acquiring energy and materials needed for cell metabolism including repair of cells and maintenance and growth

Classes of organisms depending on how they obtain energy/carbon

1. chemoautotrophs co2 and synthesize energy through chemical reactions (nitrifying bact)

2. photoautotrophs; use photosynthesis

3. chemoheterotrophs; get carbon from organic substances and use chemical reactions to generate energy

4. photoheterotrophs; use light energy to synthesize organic matter from other organic material (purple non-sulfur bact)

3 ways in which heterotrophs obtain their food

• parasitic - get nutrients from other living organisms

• holozoic - complex food being broken down into smaller pieces to be absorbed

• saprophytic - feeding on dead organic remains of other organisms

Main way of how food is processed in all heterotrophs

1. digestion - breaking down of food into small pieces to be absorbed

2. absorption - taking up of the products of digestion into body tissues

3. assimilation - using the absorbed nutrients for a particular purpose

General Description of Saprophytic Nutrition

• secrete enzymes onto dead matter

• soluble products of extracellular digestion are absorbed and assimilated

• many of simple substances formed by breakdown of dead bodies are used by plants NOT the saprotroph

Explain Saprophytic Nutrition through Mucor and Rhizopus

• fungi

• hyphae penetrate the food and secrete hydrolyzing enzyme

• extracellular digestion

• carb and protease enzymes turn starch → glucose and protein → amino acids

• branched nature - large sa for absorption

• glucose - organism metabolic activities

• amino acids - synthesize proteins for growth and repair

• xs glucose is converted to glycogen and fat, amino acids in xs are stored as protein granules in the cytoplasm

Holozoic

• free-living animals which have a specialized digestive tract - alimentary canal

Holozoic Nutrition Involves

1. Ingestion

2. Digestion

3. Absorption

4. Assimilation

5. Egestion

Ingestion

• ingestive eaters - use a mouth to ingest food

• filter feeders - small organisms and particles from the surrounding water

• substrate feeders - eat the material they burrow through

• fluid feeders - piece the body of a plant or animal and withdraw fluid

• microphagous feeders - take in food in the form of relatively small particles

• microphagous feeders - take in food in the form of relatively large particles.

Digestion

• breakdown of large organic molecules into smaller soluble molecules

  • sac-like plans (gastrovascular cavities) - dual function of digesting and distributing digested products

  • tubular plan - food enters through one opening and waste leaving through another

• mechanical or chemical digestion

• intracellular digestion

  • cell englufs food

• extracellular digestion

  • digestion occurs in the lumen of digestive system

Absorption

uptake of soluble molecules from the gut

• directly into cells

• uptake into the bloodstream

Assimilation

• absorbed molecules are used to provide energy and materials to be incorporated into the body

Egestion

• elimination of undigested waste material

In humans where does digestion and absorption occur

• the alimentary canal /gut which is a coiled muscular tube extending from the mouth to the anus with several specialized compartments

Accessory Digestive Organs

• connected to the main system by a series of ducts

• produce compounds that contribute to digestion and release them into the gut

11 Main Parts of the Gut and their main functions

1. Buccal Cavity: ingestion, masticiation and digestion of starch starts

2. Pharynx; swallowing

3. Oesophagus; connects the pharynx to the stomach

4. Stomach; food storage and digestion of Proteins

5. Duodenum; digestion and absorption

6. Liver; production of bile to emulsify fats

7. Pancreas; digestion of proteins, fats carbs

8. Ileum; completes digestion and absorption

9. Colon; absorption of water

10. Rectum; storage and formation of faeces

11. Anus; egestion

Generalize Structure of the Human Gut

• mucosa

• submucosa

• muscularis externa

• serosa

Mucosa

→ mucosa is the major absorbing/secreting layer

1. Glandular Epithelium

   1. secretes mucus to lubricate food

   2. digestive enzymes

   3. brush border of microvilli - increase SA

   4. prevents digestion of the gut wall by its own enzymes

2. Lamina Propria

   1. connective tissue containing blood and lymph vessels (carry absorbed nutrients away)

   2. glands

3. Muscularis Mucosa

   1. smooth muscle - produces folds of mucosa and submucosa to increase SA

Submucosa

• its a layer of connective tissue containing nerves, lymph, blood vessels, collagen and elastin fibres

  • carries digestion and absorbed food away from ileum

  • nerves r sensory and regulatory

• in duodenum Brunner’s glands

  • secretion of mucus

• Meissner’s Plexus

  • nerve tissue which controls secretion from glands in the gut wall

Muscularis Externa

1. inner circular smooth muscle

   1. constricts the gut when they contract

2. Sphincters

   1. thickening of the circular muscle, control the movement of food from one part of the alimentary canal to the other

      1. gastroesophageal - oesophagus/stomach

      2. pyloric - stomach/duodenum

      3. anal - anus

   2. Longitudinal Muscle

      1. shorten the gut

      2. the interaction between these two layers causes the persitaltic movements which also mix the food

   3. Auerbach’s Plexus

      1. nerve tissue which controls peristalsis

      2. sympathetic stops digestion and parasympathetic resumes digestion

Serosa

• outermost layer coat of the gut wall

  • lines abdominal cavity and forms mesenteries

• peritoneum

  • covers serosa - helps to reduce friction as peritoneum cells are moist

• mesenteries

  • double layers of peritoneum which contains nerves, blood vessels and lymph vessels that pass to and from the gut

  • attach stomach and intestines to the body wall

Buccal Cavity

• chamber inside the mouth where mechanical digestion takes place

• tongue mixes and moistens the food with saliva

Saliva

• contains salivary amylase or ptyalin

• lysozyme → kill bacteria

• mucus → lubricate food making it easier to swallow

• mineral ions such as chloride ions which activate the salivary amylase

• saliva is secreted via the salivary glands

Swallowing of Food

• bolus forms and is then pushed toward the pharynx by the tongue

• here a reflex is triggered where the larynx closes, soft palate moves up and the epiglottis covers the entrance of the trachea

Teeth

• located on the fixed upper jaw and the moveable lower jaw

• function is to masticate food - mechanical digestion, increases surface area for enzymes

• deciduous vs permanent teeth

Types of Teeth + Dental Formula

• up to 32 permanent teeth in humans

• 8 incisors, 4 canines, 8 premolars and 12 molars

Incisors

• located at the front of the buccal cavity

• flat and sharp edges

• cutting and biting food

Canines

• pointed teeth

• highly developed in carnivores

  • piercing, killing and tearing flesh

Premolars

• posses one or two roots

• 2 cusps

• crushing, grinding and in humans tearing food

Molars

• more then 1 root

• upper molars have 3 roots

• lower molars have 2 roots

• they have 4/5 cusps

• crush and grind food

The Oesophagus

• made of stratified squamous epithelium (abrasion) - also contains mucus glands

• entry of food stretches muscles in the muscularis externa triggering peristalsis

• contraction/shortening of circular and longitudinal muscles respectively causes the bolus to advance

  • passes through cardiac sphincter into the stomach

Function of cardiac sphincter

• prevent backflow of gastric juices

• causes heartburn if doesnt prevent backflow

Stomach

• muscular bag which can hold up to 5L of food

• has 3 layers of smooth muscle instead of 2

• mechanical digestion - churning which produces chyme

• dotted with gastric pits which lead to tubular gastric glands lined with gastric juice secreting cells

• contains endocrine cells which secrete GASTRIN

2 types of specialized cells in the gastric glands

1. parietal cells (oxyntic cells) - SECRETE HCL

2. Chief Cells (zymogen cells) - Secrete inactive enzymes pepsinogen and prorennin

Function of hcl secreted by parietal cells

1. kills many bacteria

2. alters 3’ structure of proteins - increasing surface area

3. acidic pH for enzymes to work

4. converts pepsinogen/prorennin into their active forms

5. hydrolysis of sucrose into fructose

6. loosens fibrous and cellular components of tissue - increases surface area

Function of Pepsin

• hydrolyses proteins into smaller polypeptides

• pepsin by POSITIVE FEEDBACK activates other pepsinogen molecules

Function of Rennin

• rennin coagulates casein (protein in milk) into insoluble calcium salts making it easier to digest

What can be absorbed directly through the stomach

• alcohol, caffeine, aspirin

Significance of sphincters

1. prevent uncontrolled exit of food

2. regulation of pyloric sphincter ensures the duodenum only works on small amounts of food at a time.

Small intestine

• carbs and protein digestion continues, and digestion of fats and absorption starts here

• first part is the duodenum - pancreatic and bile ducts

• leads to jejunum and ileum

• folded mucosa and submucosa

• goblet cells secrete mucus - lubricate food

What does the mucosa possess in the small intestine

• villi with many blood and lymph vessels

• able to contract/relax which brings them closer to the food

• many microvilli which increase surface area

• base of epithelium folds inwards to form the crypts of Lieberkühn

Purpose of Crypts of Lieberkühn

1. epithelial cells r produce to replace those being shed from villi

2. secrete intestinal juice - slightly alkaline - increases volume of fluid

3. paneth cells - secrete lysozyme

Duodenum secretes alkaline fluid - what is its function

• neutralize acid of stomach

• provides and optimum pH for enzymes of small intestine

Digestion of Fats

• bile is produced in the liver from cholesterol and stored in the gallbladder

• enters via bile ducts

• contains bile salts which EMULSIFY large fat globules into smaller ones

• pH of 7.6 - 8.6

• increase the surface area for lipase to work

• MECHANICAL DIGESTION - CHEMICAL DIGESTION INVOLVES HYDROLYSIS

Digestion of Proteins and Carbs

• through the pancreas

• secretes lipases, amylases and proteases such as trypsin, chymotrypsin and carboxypeptidases

• enter through pancreatic duct - joins w bile duct

• enzymes (proteases esp) are released as zymogens

• trypsinogen → trypsin by enterokinase

• trypsin activates more trypsinogen molecules and chymotrypsin

• pancreas also produces a secretion rich in bicarbonate ions (alkaline)

• small intestine also has enzymes immobilized on the microvilli

  • hydrolysis of disaccharides, dipeptides and tripeptides producing monosaccharides and amino acid

Saliva - source, enzyme, action, site of action and pH

1. salivary glands in buccal cavity

2. salivary amylase

3. starch → maltose

4. buccal cavity

5. 6.7-7.5

Gastric Juice - source, enzyme, action, site of action and pH

• gastric glands in the stomach

• rennin ; (prorennin) casein → insoluble salt of casein

• pepsin (pepsinogen) proteins → large peptides

• stomach

  • ph 2

Enzymes bound to microvilli - source, enzyme, action, site of action and pH

• microvilli

• amylase - starch → maltose

• maltase - maltose → glucose

• lactase - lactose → glucose + galactose

• sucrase - sucrose → glucose + fructose

• aminopeptidase - proteins → large polypeptides

• dipeptidase - dipeptides → amino acids

• enterokinase - trypsinogen → trypsin

• nuclease - nucleic acid → nucleotides

• site of action - duodenum

• ph - 8.5

Pancreatic Juice - source, enzyme, action, site of action and pH

• pancreatic glands in the pancreas

• pancreatic amylase; starch → maltose

• trypsin (trypsinogen); large peptides/proteins + small peptides and chymotrypsinogen → chymotrypsin

• chymotrypsin (chymotrypsinogen); large peptides/proteins → small peptides

• carboxypeptidase; small peptides → amino acids (attacks c-terminus)

• lipase; lipids → glycerol + fatty acid

• nuclease; nucleic acids → nucleotides

Endopeptidases + exopeptidases

• endo; hydrolysis of peptide bond in the interior of the polypeptide chain (trypsin, pepsin, chymotrypsin)

• exo; hydrolysis of single amino acids from the end of polypeptide chain (aminopeptidase, carboxypeptidase)

Absorption/Assimilation

• takes place in the villi of ileum (dense blood supply + microvilli (high sa))

• monosaccharides, amino acids, depeptides are absorbed via active transport or diffusion depending on conc gradient

• capillaries join to form hepatic portal vein, delivering the products of digestion to liver

• fatty acids and glycerol - diffuse into columnar epithelial cells → lipids → chylomicrons → lacteal by exocytosis (lymph vessel)

• chylomicrons → near heart where enter blood circulatory system, enzyme in blood lipids → fatty acids and glycerol and they r taken up by cells

• inorganic salts, vitamins + water r also taken up

• some bile is reabsorbed and return to liver

What is the point of chylomicrons

• so they dont clump up together in the water of the lymph/blood

• chylomicrons are coated with protein - lipoproteins

Large Intestine

• No digestion takes place here

• only absorption of water

• mucus lubricates faeces

• metabolic waste/inorganic substances r excreted here

• symbiotic bacteria exist here which synthesize amino acids and vitamin K which is absorbed into the blood stream

Appendix

• posses no function in humans

• if material gets trapped here - appendicitis

Faeces

• dead bacteria

• cellulose

• other plant fibres

• mucus

• cholesterol

• bile pigments and water

• dead epithelial cells

• stored for 36 hours in colon before being passed to rectum then anus

Anal Sphincters

• 1 smooth muscle - involuntary

• 1 straited muscle - voluntary

Control of Digestive System

• nervous/hormonal control

Mention Stimuli which control digestion through the NERVOUS SYSTEM

1. sight/smell/thought of food

2. Taste

3. Stretching of Stomach

4. Acidic Chyme in Duodenum

Sight Smell and Thought of Food

1. conditioned response

2. produces saliva

Food in contact with tastebuds - reflex and response

1. Unconditioned reflex

2. sends nerve impulse to the brain which stimulates the salivary glands to release saliva

3. stimulates liver to release bile

4. stimulates stomach to release gastric juices

5. stimulates pancreas to release enzymes

Stretching of stomach by food

• stretch receptors in the stomach send a nerve impulse to meissner’s plexus

• this stimulates release of gastric juice

• nerve impulse travels to colon without going through CNS

• this stimulates stronger peristaltic conditions from stomach to large intestine - expulsion of faeces

presence of acidic chyme in duodenum

• sends nerve impulses to brain

• inhibits secretion of gastric juices

• slows release of chyme into duodenum

→ this is because the role of the stomach at this point is done, and we dont want to overload the duodenum.

Stimuli which control digestion through HORMONAL CONTROL

• stretching of stomach by food

• presence of chyme rich in partially digested fats and proteins in duodenum

  • presence of partially acidic chyme in duodenum

Stretching of Stomach By food - site of production, hormone, target, response

• produced in the lower mucosa of stomach

• gastrin

• stomach

• stimulates secretion of gastric juices in upper stomach mucosa

• increases movements (peristaltic movements) of the stomach

Presence of chyme with partially digested fats and proteins in duodenum - site of production, hormone, target, response

• duodenal mucosa

• CCK cholecystokinin

• stomach → inhibits stomach emptying

• pancreas → release of pancreatic juice and digestive enzymes

• gallbladder → contraction, stimulating release of bile

Presence of Acidic Chyme - site of production, hormone, target,response

• duodenal mucosa

• secretin

• stomach - inhibits secretion of gastric juices

• pancreas - increases production of hydrogen carbonate in pancreatic juice

• liver - more hco3- in bile, making it more alkaline

Fate of Absorbed Glucose

1. stored in the liver or muscle as glycogen

2. stored in adipose tissue beneath the skin

3. used in respiration or other functions

Fate of Absorbed Amino Acids

1. deaminated via the ornithine cycle in the liver

2. synthesis of enzymes, hormones and proteins needed for growth and repair

Fate of Absorbed Fats

1. stored in adipose tissue beneath the skin, around the heart/kidneys or around the mesenteries

2. incorporated into cell membranes as phospholipids

Dental formula of sheep

Adaptations of Herbivore Dentition (6)

1. No upper incisors or canines - instead there is a horny pad with which the lower incisors and canines bite when chopping grass

2. diastema (gap between front and cheek teeth) allows to manipulate grass keeping the fresh grass separate from that being chewed

3. Teeth have a broad grinding surface area (W and M shape which fit into each other)

4. open roots - teeth are constantly growing and therefore have to be worn down by the constant chewing

5. loose jaw - back,forward and side movement → w shaped ridges coming into close contact into grooves of m shaped - grind grass

6. large masseter muscle (grinding), small temporal muscle (biting)

Ruminant

• animal which has a stomach with several chambers to maximize the benefits of their endosymbiotic microorganisms

Chambers of a ruminant stomach

1. Rumen

2. Reticulum

3. Omasum

4. Abomasum

Rumen

1. microorganisms which breakdown cellulose by fermentation produce carboxylic acids, co2 and methane

2. provide source of protein for animal

3. carboxylic acids - respiration in animal

4. microorganisms get a source of energy and an ideal temperature

Reticulum

• microorganisms here too

• food is turned into pellets

• this is regurgitates and rechewed - CHEWEING THE CUD

• this is then swallowed again and undergoes fermentation

• - being properly chewed provides a large surface area for digestive enzymes

Omasum

• absorption of water - concentrating partially digested food (cud)

Abomasum

• HCL and proteases are secreted here

• microorganisms killed by the acid and digested by proteases

• in small intestine regular digestion by the usual mammalian digestive enzymes + absorption takes place

Hind-gut fermenters

• which have a single chambered stomach and microbial fermentation chambers in the caecum

What makes hind-gut fermenters digestive system inefficient

• since caecum empties into the large intestine absorption of nutrients produced by the microorganism is ineffective

• so they must re-ingest their faeces

• caecal material passes through the body once again and nutrients r absorbed producing a diff type of faeces which is discarded

Adaptations in carnivorous mammals

1. large carnassial teeth which allow for scraping of flesh off of bones

2. large temporal muscle used for biting, small masseter muscle used for grinding

3. incisors which meet and grip to rip flesh off of bones

4. large canines to grip and kill prey quickly

Why is herbivores digestive system longer?

• because plant material is more complex to digest - requires specialized stomachs and microorganisms

• protein is easier to digest and more nutrient dense so carnivores can go longer w out eating