Lecture 4 digestion and nutrition 2nd sem 2008-2009

Lecture 4. Digestion and Nutrition

Major Nutritional ModesMode of Nutrition Energy

SourceCarbon Source Examples

Autotrophs

Photoautotrophs Light CO2 Photosynthetic prokaryotes, including cyanobacteria; plants; certain protists

Chemoautotrophs Inorganic chemicals

CO2 Certain prokaryotes (i.e. Sulfolobus)

Heterotrophs

Photoheterotroph Light Organic compounds

Certain prokaryotes

Chemoheterotrophs Organic compounds

Organic compounds

Many prokaryotes and protists; fungi; animals; parasitic plants

1. Herbivores

Dietary categories

2. Carnivores

Dietary categories

3. Omnivores

Dietary categories

4. Saprophagous

Dietary categories

Woodlice (Trachelipus ratzeburgii)

deer fly (Chrysops callidus)

red ant (Formica pallidefulva )hermit beetle (Osmoderma eremita)

Suspension feeder – sifts through food particles in the water

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Baleen whale

Feeding Adaptations

• bivalve molluscs use their gills as feeding devices

• herring and other suspension-feeding fishes use gill rakers to strain plankton

• whalebone whales filter out plankton, mainly large crustaceans called krill, with whalebone or baleen

krill

Deposit feeder – eats its way through dirt or sediments and extract partially decayed organic material (detritus) consumed along with the soil or sediments

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Feeding Adaptations

Substrate feeder – lives in or on its food source, eating its way through the food

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Leaf miners

Feeding Adaptations

Fluid feeder – sucks nutrient-rich fluids from a living host and is considered a parasite

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin CummingsMosquito

Feeding Adaptations

Bulk feeder – eats relatively large pieces of food

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Python

Feeding Adaptations

Cephalopod molluscs have beak-like jaws which serve as tearing devices

• chewing mouthparts adapted for seizing and crushing food

• mandibles are strong, toothed plates whose edges can bite or tear

• maxillae hold the food and pass it toward the mouth

• birds lack teeth

• bills are often provided with serrated edges

• In some, the upper bill is hooked for seizing and tearing prey

Four types of teeth found in mammals:• incisors, for biting, cutting, and stripping• canines, for seizing, piercing, and tearing• premolars, for grinding and crushing• molars, for grinding and crushing

• an elephant’s tusk is a modified upper incisor

• used for defense, attack, and rooting

• a male wild boar has modified canines that are used as weapons

Paramecium Hydra

• Incomplete – there is only one opening; no anus

Types of Digestive System

• Complete – there is a mouth opening and an anus

Types of Digestive System

• Ingestion – the act of eating

• Digestion – breaking food down into molecules small enough for the body to absorb

• Absorption – small molecules are taken in by the animal’s cells

• Elimination – undigested material passes out of the digestive compartment

Four Main Stages of Food Processing

• digestion is entirely intracellular in protozoa and sponges

• radiates, turbellarian flatworms, and ribbon worms (nemerteans) practice both intracellular and extracellular digestion

• in extracellular digestion, certain cells lining the lumen of alimentary canals form digestive secretions; other cells function in absorption

• for arthropods and vertebrates digestion is almost entirely extracellular

• alternate constriction of rings of smooth muscle of the intestine

Gut movement

• constantly divide and squeeze contents back and forth

• for mixing of food

• waves of contraction of circular muscle behind the gut and relaxation in front of bolus

• sweeps food down the gut

Salivary glands

Human Digestive System

•Food is called bolus if it passes through the esophagus

Human Esophagus

Human Stomach

•Food is called chyme after it passes through the stomach

• trypsin, chymotrypsin, and carboxypeptidase are secreted in inactive form by the pancreas

– the intestinal enzyme, enteropeptidase, converts inactive trypsinogen into active trypsin

– active trypsin then activates the other two

Human Small Intestine• Made up of three regions:

1. duodenum - Nearest to the stomach; 26 cm in length - With Bruner’s glands

- produce mucus-rich alkaline secretion with bicarbonates to

- protect the duodenum from the acidic content of chyme;

- provide alkaline condition for the intestinal enzymes to be active; and

- lubricate the intestinal walls

2. jejunum - Next to duodenum; 2.5 m in length

Human Small Intestine• Made up of three regions:

3. ileum- Last segment of the small intestine; 3.5 m in length - Contains Peyer’s patches

- Organized lymphoid tissues- Protects the intestinal lumen from pathogenic

bacteria

•Food is called chyle once it is in the small intestine

• the colon recovers water that has entered the alimentary canal as the solvent to various digestive juices

• the large intestine harbors a rich flora of mostly harmless bacteria

• the terminal portion of the colon is called the rectum, where feces are stored until they can be eliminated

Human Large Intestine

Regulation of Digestion

CCK - cholecystokinin

• the length of the vertebrate digestive system is also correlated with diet

• ruminants (deer, cattle, and sheep) have the most elaborate adaptations for a herbivorous diet

• A nutritionally adequate diet satisfies three needs: – fuel (chemical energy) for all the cellular work of the

body – organic raw materials animals use in biosynthesis

(carbon skeletons to make many of their own molecules)

– essential nutrients

Nutritional Requirements

– If the diet of a person or other animal is chronically deficient in calories, undernourishment results

– an animal whose diet is missing one or more essential nutrients is said to be malnourished

– marasmus, general undernourishment from a diet low in both calories and protein

– kwashiorkor, protein malnourishment from a diet adequate in calories but deficient in protein

– overnourishment or obesity results from excessive food intake

• in mammals, a hormone called leptin, produced by adipose cells, is a key player in a complex feedback mechanism regulating fat storage and use

• ghrelin (stomach wall)– triggers feelings of hunger as mealtimes approach

• leptin (adipose tissue)– suppresses appetite

• PYY or peptide-tyrosine-tyrosine (small intestine)– after meals– appetite suppressant; counters ghrelin

• insulin (pancreas)– a rise in blood sugar level after a meal– suppresses appetite by acting on the brain

Appetite-regulating hormones

• animals require 20 amino acids to make proteins• essential amino acids must be obtained from

food in prefabricated form

– eight amino acids are essential in the adult human (phenylalanine, lysine, isoleucine, leucine, valine, methionine, tryptophan, and threonine) with histidine and arginine essential for normal growth of children

• protein deficiency from a vegetarian diet can be avoided by eating a combination of plant foods that complement each other to supply all essential amino acids

• vitamins are organic molecules required in the diet in small quantities

• 13 vitamins essential to humans have been identified

• water-soluble vitamins generally function as co-enzymes

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• Minerals are simple inorganic nutrients, usually required in small amounts– humans and other vertebrates require large

quantities of calcium and phosphorus for the construction and maintenance of bone

– iron is a component of the cytochromes and of hemoglobin

– while sodium, potassium, and chloride have a major influence on the osmotic balance between cells and the interstitial fluids, excess consumption of salt (sodium chloride) is harmful