DIGESTION

What does the previous slide suggest?

Digestion leads to the breakdown of the important substances needed by the body to grow and develop…..– Protein– Carbohydrates– Fats– Nucleic acids

• Why does the plant need to eat a fly when it can undergo photosynthesis?

Plant nutrition

• Plant are producers, they are ________.• Animals are _______, they are heterotrophic.– Heterotrophs are opportunistic feeders

Digestion as an evolutionary evidence

• Compartmentalization• Mode of feeding• Mutualistic relationship

– Also presence of fats, why?

Intracellular, extracellular and everything in between…..

• Intracellular– Food vacuoles, amoebocytes

• Extracellular– Incomplete vs complete digestive system

Incomplete digestive system bridges…..

• Differs from complete because……• E.g. gastrovascular cavity of cnidarians• Gastrodermis- with specialized digestive cells

• HYDROLYSIS OF MACROMOLECULES IS INTRACELLULAR

Gastrovascular cavity

Complete

• Specialized compartment• Exit and entrance are different• Extracellular hydrolysis of food• Complexity varies

Modes of Feeding

• Suspension feeders• Substrate feeders• Fluid feeders• Bulk feeders

Symbiosis is nice…..

Evolution of symbiotic relationship with other organisms in processing food…. why is this needed?

The four-chambered stomach of cows

Four stages of food processing

• Ingestion– Large oral cavity

• Digestion– Mechanical vs chemical

• Absorption• Elimination

The oral cavity or in short the mouth

• What is the mouth for?• Why do we need to produce saliva?• What is an enzyme and how does it help in

the digestion of food?

Mechanical Digestion, what is it for?

Pharynx

• Crossroad of food and air• Where bolus enters the esophagus• Epiglottis- flap that covers the entrance of air

when swallowing

Epiglottis in action

The esophagus

• Presence of striated and smooth muscle• Moves the bolus from pharynx to the stomach– peristalsis

• Presence of goblet cells

Peristalsis

• Wave-like motion responsible for the movement of digested food in the alimentary canal

The stomach

• Storage and digestion of food• Sphincters- regulate movement of bolus and

chyme• Which one has a larger stomach, a carnivore

or an herbivore? (pound-for-pound)

Still on stomach…..

• Chief cells vs parietal cells• Pepsinogen and HCl follows a positive

feedback mechanism

Ouch, my stomach hurts….

• Rapid mitotic activity• Activation of pepsin• Goblet cells

Ouch, my heart burns!!!!

• Heart burn is not caused by the devil or your evil exes burning your heart, it is the result of the loosening of the valves

Small intestine

• Main organ of digestion and absorption• Why is it the longest?• Divided into the duodenum, jejunum, ileum

Absorption

• Villus- folds found in the small intestine

• Microvillus- microscopic fingerlike projections that increases the absorption of materials

• Each villus is connected to a capillary (BV) network and lacteals(Lymphatic system)

RECITATION ON THE DIGESTION OF THE FOUR MACROMOLECULES

• Protein• Carbohydrates• Fats• Nucleic acids

Hormones that regulate digestion

• Gastrin-stimulated by gastric juices– Inhibited by low pH– stimulates secretion of gastric juice

• Enterogastrones- group of enzymes found in the duodenum• Cholecystokinin (CCK)- stimulated by fats and amino acids

– Stimulates gall bladder to release bile• Secretin- stimulated by the acidic chyme

– Stimulates pancreas to release bicarbonates

– If chyme is rich in fats, it stimulates the duodenum to release other enzymes to slow down digestion in the stomach

Large Intestine

• Also called the colon• Cecum – small pouch that has different fxns• Appendix- small cecum found in man• Rectum- portion of the large intestine that

temporarily stores feces• Main fxn of colon is to reabsorb water• Feces- waste that was formed after digestion

• Compactness depends on water that was reabsorbed

Large Intestine

• Intestinal Bacteria- common example is E. coli

• Have mutualistic relationship with host

• Generate methane or hydrogen sulfide

• Some produce vitamins that are needed by the body

Nutrition

• Nutritionally adequate diet– composed of:• fuel (chemical energy)• organic raw materials (carbon skeletons)• essential nutrients (substances the

animal cannot make)

Balancing the fuel

• Homeostatic mechanism balances the animal’s fuel

• ATPs that were produced are budgeted depending on the energy requirements

• Fats have the highest amount of ATP• Glucose conversion is an example of

homeostatic mechanism

Caloric Imbalance

• Undernourishment– Calorie deficiency

• Overnourishment– Excessive calorie intake- results to obesity

• Malnourishment– Deficient in any essential nutrients

Essential Nutrients

• Essential Amino Acids• Essential Fatty Acids• Vitamins• Minerals

Essential Amino Acids

• Tryptophan, methionine, Valine, Threonine, Phenylalanine, Leucine, Isoleucine, Lysine, Histidine (infants)

• Deficiency in one of these may result into protein deficiency

Essential Fatty Acids

• Essential Fatty Acids belong to the unsaturated fatty acid groups

• An example is linoleic acid• Deficiencies are rare

Vitamins

• Organic molecules that are required relatively in small amount

• Two types:– Water-soluble• B vits, C

– Fat-soluble• A, D, E, K

Minerals

• Inorganic nutrients that are required in small amounts

• E.g. Calcium, Phosphorous, Sodium, etc.

Balance diet

• what enters= what leaves• It is easier to take in calories in the body than

to burn it• The food pyramid serves as a guide in the kind of foods that should be taken in