“You Are What You Eat”The Digestion System

Jade BennettJade HoayunKarla Burnett

Worryin’ Bout What Dey Eat And How Dey Eat, You Nosy

Three Dietary Categories:Herbivores – An heterotrophic animal that eats plantsCarnivores- eats other animals Omnivores- heterotrophic animal that consumes both meat and plant material

Four Main Feeding Mechanisms:Suspension Feeders-sifts small food particles from the waterSubstrate Feeders- an organism that lives in or on its food source, eating its way through the foodFluid Feeders- suck nutrient rich food from the living hostBulk Feeders- an animal that eats relatively large pieces of food

Guess Who’s Comin’ To Dinner

Herbivore

Carnivore

Omnivore

The Importance Of Being Homeostasis

Nearly all ATP generation is based on the oxidation of organic fuel molecules—carbohydrates, proteins, and fats—in cellular respiration.

If more calories taken in than can be used for ATP production, excess used to fuel biosynthesis

Example of homeostasis: glucose regulationBody tends to store surplus energyIf body’s store of glycogen is full and caloric intake exceeds expenditure, excess is stored as fatIf expenditure exceeds intake then fuel is taken out of storage

Caloric imbalanceUndernourishment- a diet that is chronically deficient in caloriesOvernourishment- a diet that is chronically excessive in calories

Gimme Gimme More(Homeostasis cont’d)

ObesityA major health problem for humansActually beneficial in some species such as petrelLeptin:

One of several hormones that helps regulate body weightAs adipose tissue (fat) decreases, leptin levels fall, and appetite increases

Inheritance also plays large factor in obesityEvolution of obesity

Natural selection could have favored those with a physiology that induced them to eat rich, fatty food on the rare occasion they were availableAlso, those with genes enabling them to better store high-energy molecules may have been more likely to survive famines.

Mo’ Supply and DemandFuel as well as organic precursors (carbon skeletons) are needed as material for biosynthesis

However, some materials (Essential nutrients) must be obtained in preassembled form because the animal’s cells can’t make them from any raw materialsAn animal whose diet is missing 1 or more essential nutrients is said to be malnourished. 4 classes of essential nutrients: essential amino acids, essential fatty acids, vitamins, and minerals.

Essential NutrientsAn essential amino acid cannot be synthesized by the animal and must be obtained from food

Eight amino acids are essential in most animals’ diet.Insufficient amounts of 1 or more essential amino acids causes a protein deficiency

Ex. KwashiorkorMeat products are able to provide all essential amino acids

Animals can synthesize most of the fatty acids they need. The essential fatty acids, the ones they cannot make, are certain unsaturated fatty acids

Ex. Linoleic acidThe diets animals generally furnish ample quantities of essential fatty acids, and thus deficiencies are rare.

Essential Nutrients: VitaminsVitamins are organic molecules required in the diet in very small amountsTwo categories: water-soluble vitamins and fat-soluble vitamins

Water-soluble vitamins – Vitamins B and C; excesses of these are excreted in urine so moderate overdoses are harmlessFat-soluble vitamins – Vitamins A,D,E, and K; excesses of these are deposited in body fat, so overdose may lead to toxic level build up

The subject of vitamin dosage has aroused debate

Betta Get Dem Vitamins

Essential Nutrients: MineralsMinerals are simple inorganic nutrients, usually required in small amountsIngesting an excess of salt or several other minerals can upset homeostatic balance and cause toxic side effects

Most people ingest too much salt (sodium chloride)

Too much sodium is associated with high blood pressure

Also, excess Iron can cause liver damage

Betta Get Dem Minerals

The Main Stages of Food Processing

Organic material in food consists largely of proteins, fats, and carbohydrates in the form of starch and other polysaccharidesAnimals cannot use these macromolecules directly for two reasons (IB- Explain why digestion of large food molecules is essential)

First, polymers are too large to pass through membranes and enter the cells of the animalSecond, the macromolecules that make up an animal are not identical to those of its food

For these reasons food processing involves four stages: ingestion, digestion, absorption, and elimination

Put It In Yo Mouth: Ingestion

Ingestion – The act of eating, is a mechanical fragmentation of the food, such as chewingBreaking food into smaller pieces increases the surface area exposed to digestive juices containing hydrolytic enzymes

DigestionDigestion- food is broken down into molecules small enough for the body to absorbMacromolecules are cleaved into component monomers, which the animal uses to make its own molecules or for ATP production

Polysaccharides and disaccharides are split into simple sugars, fats are digested to glycerol and fatty acids, proteins are split into amino acids, and nucleic acids are cleaved into nucleotides

Enzymatic hydrolysis is the process in digestion that splits macromolecules by the enzymatic addition of water.

The Final Two…Stages

In the third stage, absorption, the animal’s cells take up (absorb) small molecules such as amino acids and simple sugars from the digestive compartments And last but not least, elimination occurs, as undigested material passes out of the digestive compartments

Absorption versus Assimilation

Absorption occurs in the small intestine. During this process the food is truly inside the body .

Small finger-like projections called villi line the small intestine and are adapted to absorb food molecules

Assimilation occurs once food has been absorbed and becomes part of the tissues in the body.

Kitty

Nutrient moleculesenter body

cells

Undigested material!

Smallmolecules

Chemical digestion(enzymatic hydrolysis)

Piecesof food

Mechanicaldigestion

Food

Digestive CompartmentsTo avoid self-digestion animals process food in specialized digestive compartments

Two types: Intracellular Digestion and Extracellular Digestion

Intracellular digestion is the joining of food vacuoles and lysosomes (organelles containing hydrolytic enzymes) to allow chemical digestion to occur safely within the cytoplasm of a cell

Begins after phagocytosis or pinocytosis In most animals, at least some hydrolysis occurs by extracellular digestion- the breakdown of food outside cells

Occurs within compartments that are continuous with the outside of the animal’s bodySuch animal able to devour much larger prey than can be ingested by phagocytosis and digested intracellularly.

Some Like It Simple, While Some Like It Complicated There are two types of extracellular digestionAnimals with simple body plans such as cnidarians and flatworms have a gastrovascular cavity A digestive sac with a single opening, functions in both digestion and distribution of nutrients throughout the body Single opening functions as mouth and anus

Most animals have a digestive tube extending between two openings, called a complete digestive tract or an alimentary canal Because food moves along the canal in a single direction, the tube can be organized into specialized regions that carry out digestion and nutrient absorption in a stepwise fashionAbility to ingest additional food before earlier meals are completely digested

Cnidarians called hydras

Gastrovascularcavity

Food

EpidermisMesenchyme

Gastrodermis

Mouth

Tentacles

Mesenchyme

Food vacuoles

Gland cells

Flagella

Nutritivemuscularcells

Earthworm. The digestive tract ofan earthworm includes a muscular pharynx that sucks food in through themouth. Food passes through the esophagus and is stored and moistened in the crop. The muscular gizzard, whichcontains small bits of sand and gravel, pulverizes the food. Digestion and absorption occur in the intestine, which has a dorsal fold, the typhlosole, that increases the surface area for nutrient absorption.

Grasshopper. A grasshopper has several digestive chambers grouped into three main regions: a foregut, with an esophagus and crop; a midgut; and a hindgut. Food is moistened and stored in the crop, but most digestion occurs in the midgut. Gastric ceca, pouches extending from the midgut, absorb nutrients.

Bird. Many birds have three separate chambers—the crop, stomach, and gizzard—where food is pulverized and churned before passing into the intestine. A bird’s crop and gizzard function very much like those of an earthworm. In most birds, chemical digestion and absorption of nutrients occur in the intestine.

The process of digestion:

Foods processing in all animals follow the same general process so mammals will be representative.Consists of alimentary canal and accessory glands: salivary glands, liver, pancreas, and gallbladder.

Accessory glands secrete digestive juices through ducts Peristalsis- rhythmic waves of contraction by smooth muscles that move food downSphincters- ring- like modified muscles that close up like drawstrings to modify the amount of material that passes through the chamber of the canal

IB Important!: mouth, esophagus, stomach, anus, liver, small intestine, large intestine, pancreas,

and gallbladder

IIeumof small intestine Duodenum of

small intestine

Appendix

Cecum

Ascendingportion of large intestine

Anus

Small intestine

Large intestine

Rectum

Liver

Gall-bladder

Tongue

Oral cavity

Pharynx

Esophagus

Stomach

Pyloricsphincter

Cardiacorifice

Mouth

Esophagus

Salivaryglands

Stomach

Liver

Pancreas

Gall-bladder

Large intestines

Small intestines

RectumAnus

Parotid glandSublingual gland

Submandibular gland

Salivaryglands

A schematic diagram of the human digestive system

Pancreas

Elements to Digest: Oral Cavity, Pharynx, and Esophagus

Physical and Chemical digestion begins in the mouthFood in the oral cavity triggers a nervous reflex that cause salivary glands to deliver saliva. Saliva important for mucin that lubricates food and protects inside of mouth from abrasion

Prevents tooth decay by neutralizing acids Kills off bacteriaSalivary amylase- hydrolyzes starch and glycogen which helps to break down carbohydrates for chemical energy

Swallowing moves food into a bolus and to back of oral cavity to the pharynx (throat) then to esophagus and trachea (windpipe) which has an opening called the glottis covered by the epiglottis The esophagus moves food from the pharynx to the stomach by peristalsis. Muscles at top are voluntary (striated) but become involuntary contractions

Let’s Begin (41.16)

Esophagus

Epiglottis down

Tongue

Pharynx

GlottisLarynx

Trachea

Bolus of food

Epiglottisup

To lungs To stomach

Esophageal sphinctercontracted

Glottis upand closed

Esophageal sphincterrelaxed

Glottisdown and open

Esophageal sphinctercontracted

Epiglottisup

Relaxedmuscles

Contractedmuscles

Relaxedmuscles

Stomach

Elements to Digest: StomachStores food and does the beginning steps of digestionLocated in upper abdominal cavity below diaphragm.Large and has elastic , accordion- like walls that can stretch it to 2 liters. Secretes gastric juice - has a high concentration of hydrochloric acid with a pH of 2

Breaks extracellular matrix that binds cells in meat and plantsKills most bacteria swallowed with foodPepsin- enzyme that begins the hydrolysis of proteinBreaks peptide bonds adjacent to specific amino acids, that cleave proteins into smaller peptides which are later digested to amino acids in small intestines Low pH of gastric juice unfolds the proteins that increase exposure of peptide bonds to pepsin

Elements to Digest: Stomach (Cont’d.)

Pepsin does not destroy the stomach due to pepsinogens that are an inactive form. In the gastric cell the chief cells produce pepsinogens while the parietal cells secrete hydrochloric acidThe acid converts the pepsinogens to the active form by removing a small part of the molecule and exposing it to the active siteThe two ingredients do not mix because they come from different cells and pepsinogen is not activated until they enter cavity (lumen) of stomach.Example of positive biofeedback (nerves). Once a bit of pepsinogens is activated, activation occurs rapidly because pepsin can activate itselfMucus also prevents self digestion A recent meal becomes acid chyme (nutrient- rich broth) that is regulated from the stomach to the small intestine by the pyloric sphincter.

A meal can take 2-6 hours to leave stomach

Get in Mah Belly: Stomach Lining (41.17)

Pepsin (active enzyme)

HCl

Parietal cellChief cell

Stomach

Folds of epithelial tissue

Esophagus

Pyloric sphincter

Epithelium

Pepsinogen

3

2

1

Interior surface of stomach.The interior surface of the

stomach wall is highly folded and dotted with pits leading

into tubular gastric glands.

Gastric gland. The gastric glands have three types of cells

that secrete different components of the gastric juice: mucus cells,

chief cells, and parietal cells.

Mucus cells secrete mucus,which lubricates and protects

the cells lining the stomach.

Chief cells secrete pepsino-gen, an inactive form of the

digestive enzyme pepsin.

Parietal cells secretehydrochloric acid (HCl).

1 Pepsinogen and HCIare secreted into thelumen of the stomach.

2 HCl convertspepsinogen to pepsin.

3 Pepsin then activatesmore pepsinogen,starting a chainreaction. Pepsinbegins the chemicaldigestion of proteins.

5 µm Small

intestine

Cardiac orifice

Elements to Digest: The Small Intestine

Name from diameter. More than 6 m in humans so it is longest part of alimentary canalDuodenum: 1st 25 cm, acid chyme mixes with digestive juices from the liver, gallbladder, and pancreas, and glass cells of wall Liver creates bile that has digestive enzymes and bile salts that aid digestion and absorption of fatsAs peristalsis moves the chime and digestive juices along the small intestine, enzymatic digestion is completedMost of the process is completed in the duodenum; the jejunum and ileum absorb nutrients and waterHormones help coordinate the secretion of juices Most absorption of nutrients occurs here- some still occurs in stomach and large intestineTransport across epithelial cells can be passive like sugar fructose with facilitated diffusonSmall peptides, amino acid, vitamins, and glucose are some examples of nutrients that are pumped against the concentration gradient by epithelial membranes.Active transport helps intestine absorb a higher amount of proteinsVilli help a lot…

When acid chyme and digestive juices get together… (41.19)

Liver Bile

Acid chyme

Stomach

Pancreatic juice

Pancreas

Intestinaljuice

Duodenum of small intestine

Gall-bladder

Oral cavity,pharynx,esophagus

Carbohydrate digestion

Polysaccharides(starch, glycogen)

Disaccharides(sucrose, lactose)

Salivary amylase

Smaller polysaccharides,maltose

Stomach

Protein digestion Nucleic acid digestion Fat digestion

Proteins

Pepsin

Small polypeptides

Lumen of small intes-tine

Polysaccharides

Pancreatic amylases

Maltose and otherdisaccharides

Epitheliumof smallintestine(brushborder)

Disaccharidases

Monosaccharides

Polypeptides

Pancreatic trypsin andchymotrypsin (These proteasescleave bonds adjacent to certainamino acids.)

Smallerpolypeptides

Pancreatic carboxypeptidase

Amino acids

Small peptides

Dipeptidases, carboxypeptidase, and aminopeptidase (These proteases split off one amino acid at a time, working from opposite ends of a polypeptide.)

Amino acids

DNA, RNA

Pancreaticnucleases

Nucleotides

Nucleotidases

Nucleosides

Nucleosidasesandphosphatases

Nitrogenous bases,sugars, phosphates

Fat globules (Insoluble inwater, fats aggregate asglobules.)

Bile salts

Fat droplets (A coating ofbile salts prevents small drop-lets from coalescing intolarger globules, increasingexposure to lipase.)

Pancreatic lipase

Glycerol, fattyacids, glycerides

What happens in the small intestines (doesn’t) stay in the small intestines

Villus: The Importance Of Structure

Increases the surface area from which food is absorbed

Microvilli also serves this purpose

The epithelium is one thin layer of cells- easy to pass throughProtein channels have rapid absorption because of active transport and facilitated diffusionATP is provided by mitochondria in the epithelium cellsBlood capillaries are close to the epithelium (small distance)A lacteal

Elements to Digest: Large Intestines

From the liver, blood travels to the heart, which pumps the blood and nutrients to all parts of the body. RECLAIMING WATER IS A MAJOR FUNCTION OF THE LARGE INTESTINE.The large intestine, or colon, is connected to the small intestine at a T-shaped junction where a sphincter controls the movement of materials. A major function of the colon is to recover water that has entered the alimentary canal as the solvent to various digestive juices. Living in the large intestine is a rich flora of mostly harmless bacteria.Feces contain masses of bacteria and undigested materials including cellulose. The terminal portion of the colon is called the rectum, where feces are stored until they can be eliminated.

Large Intestine is the Colon

Evolutionary Adaptations In Digestive Systems In Vertebrates

Dental adaptationsCarnivores generally have pointed teeth to kill prey and rip fleshHerbivores generally have teeth with broad ridged surfaces to grind plantsOmnivores are a combination of both

Stomach and intestinal adaptationsCarnivores usually have large, expandable stomachs so they can eat as much as possibleHerbivores and omnivores generally have longer alimentary canals to give more time for digestion of plants and more surface area for absorption of nutrients

Symbiotic adaptationsSymbiotic bacteria and protists in the fermentation chambers of the alimentary canals are a way for herbivores to break down celluloseRuminants- an animal such as a cow, or sheep, with an elaborate compartmentalized stomach specialized for a herbivorous diet