Dr. VeipuJanuary 2015

Nutrition

Process by which organisms obtain and utilize their food.

There are two parts to Nutrition:1. Ingestion- Process of taking food into the digestive system so that it may be hydrolized or digested.

2. Digestion- The breakdown of food (either chemically or mechanically) in order to utilize nutrients

Types of Nutrients Micronutrients- vitamins, minerals, & water

Macronutrients- proteins, lipids, carbohydrates, etc…

Breakdown of the nutrients requires the coordination of several “enzymes” secreted from specialized cells within the mouth, stomach, intestines, and liver.

Major organs that coordinate digestion within the human body include the mouth, esophagus, stomach, small and large intestine, and liver.

Human Digestive System

Oral CavityMechanical biting and chewing of food using

Incisors (8), Canines (4), Premolars (8), Molars (12)

Oral Cavity / Mouth“Saliva” moistens the food by acting as lubrication

and source of enzymes

Three pairs of salivary glands help secrete saliva into the mouth1. Parotid Glands 2. Submandibular glands 3.

Sublingual Glands

Parotid gland located in front of the ear, drain saliva through its tubes

Submandibular gland located behind the lower jawSublingual secrete through many ducts in the floor

of the mouth

Oral Cavity / MouthSaliva contains an enzyme called “Amylase”

that helps digest Starch molecule into disaccharides and monosaccharides

Tongue moves food around manipulating it into a mass called “Bolus” or a ball-like structure to allow swallowing

Bolus is pushed into the throat ( pharynx) and into the esophagus

Ingestion

Mouthmechanical digestion

teeth breaking up food

chemical digestion saliva

amylase enzyme digests starch

mucin slippery protein (mucus) protects soft lining of digestive system lubricates food for easier swallowing

buffers neutralizes acid to prevent tooth decay

anti-bacterial chemicals kill bacteria that enter mouth with food

mouthbreak up fooddigest starchkill germsmoisten food

MouthChemical and mechanical digestion.

Food is chewed (masticated) mechanically.

A bolus (lump) is formed with saliva and the tongue.

Which type of digestion is the following?

1. Chewing a saltine? -

2. Saliva breaking the saltine down into molecules of glucose? -

3. Your tongue breaking pieces of a hamburger apart?

4. Pepsin (an enzyme) in your stomach breaking the hamburger into amino acids?

Alimentary TractPharynx --- Function in swallowing

Esophagus --- Transport of bolus

Esophagus is thick-walled muscular tube that transport the food by “Peristalsis” or muscular contractions that propel the food from pharynx to stomach

Located behind or posterior to the trachea (windpipe)

Epiglottis --- Flap of cartilage that closes the airways or trachea when swallowing

PharynxThe back of the throat.

Larynx- passage for air, closes when we swallow.

Is approximately 15cm long.

Swallowing (& not choking)

Epiglottis flap of cartilagecloses trachea (windpipe) when swallowingfood travels down esophagus

Peristalsis involuntary muscle contractions to move food

along

series of involuntary wave-like muscle contractions which move food along the digestive tract

Peristalsis

StomachFood is temporarily stored here.

Gastric juices are secreted.

Has layers of muscle that line the inside.

Mechanically and chemically breaks down food.

Stomach“Storage and churning of food”

Storage of digestive enzymes

Esophagus joins the stomach at “ Cardiac Sphincter”, a muscular valve

As food or bolus passes through, the cardiac sphincter relaxes and then closes

Structure Layers of stomach muscle contract and churn

food with gastric juices to form “Chyme”

Gastric JuicesSecreted by the stomach.Acidic (pH 2) (HCl or

Hydrochloric acid).

Pepsin- an enzyme that breaks down large proteins into amino acids.

Food is further broken down into a thin liquid called chyme.

StomachCells lining the stomach secrete three important

substances:

1. Mucus2. Hydrochloric acid3. Pepsin

Mucus protects the stomach lining from acids and enzymes

Hydrochloric acid secreted by “Parietal cells” in the stomach lining. Produces acidic environment for Pepsin

Pepsin digests large proteins into amino acids

Stomach

Pepsin:

Gastric glands called “Chief Cells” secrete Pepsinogen

Pepsinogen is converted to Pepsin in the presence of hydrochloric acid

StomachFunctions

food storagecan stretch to fit ~2L food

disinfect foodHCl = pH 2

kills bacteria

chemical digestionpepsin

enzyme breaks down proteins

But the stomach is made out of protein!What stops the stomach from digesting itself?

mucus secreted by stomach cells protects stomach lining

stomachkills germs break up fooddigest proteinsstore food

sphincter

sphincter

mouthbreak up fooddigest starchkill germsmoisten food

Sphincters close off the stomach at both ends, and opens only when a bolus arrives

Occasionally, however a person experiences “ACID REFLUX”, backflow of chyme from stomach into the lower esophagus. Resulting in Irritation!! Or Heartburn

Small IntestineAlimentary tract or GI tract ‘s longest

compartment

20 feet long or 6 meters

First compartment is the DUODENUM, where chyme from stomach mixes with digestive juices from pancreas, liver, and gall bladder.

Accessory Organs

LiverPancreasGall Bladder

Spleen

Liver Multiple Functions

Produces bile

Bile stored in gallbladder until needed

Breaks up fats act like detergents to breakup fats into small droplets

bile contains “Bile Salts”, acts as emulsifiers (detergents) aid in digestion and absorption of lipids

bile contains “Bile Salts”, acts as emulsifiers (detergents) aid in digestion and absorption of lipids

LIVERStores glucose as glycogen & breakdown of

glycogen to glucose when needed (Blood glucose regulation)

Detoxifies toxic materials (E.g. drugs)

Stores vitamins and minerals

Amino acid metabolism in which ammonia is produced and converted to less toxic substance, urea

Destroys old red blood cells, converting hemoglobin from RBC into bilirubin and its end products pigment Jaundice = Bile pigments or bilirubin accumulate

in skin

BILEBile “emulsifies” lipids (physically breaks

apart FATS)

Bile is a bitter, greenish-yellow alkaline fluid, stored in the gallbladder between meals and upon eating is discharged into the duodenum where it aids the process of digestion

Bile consists of water, bile salts, phospholipids, cholestrol, bilirubin

Gall Bladder Pouch structure located near the liver which

concentrates and STORES bile

Bile duct – a long tube that carries BILE. The top half of the common bile duct is associated with the liver, while the bottom half of the common bile duct is associated with the pancreas, through which it passes on its way to the intestine.

Pancreas An organ which secretes both digestive enzymes

(exocrine) and hormones (endocrine)

** Pancreatic juice digests all major nutrient types.

Nearly all digestion occurs in the small intestine & all digestion is completed in the SI.

Pancreas Exocrine Gland (Acinar cells)Digestive enzymes (Breakdown fat, protein

and carbohydrates Digest proteins

TRYPSIN, Chymotrypsin, ProteasesDigest starch

AmylaseDigest Triglyceride

Lipases

• Digest Nucleic Acid• Nucleases

Buffers == Sodium Bicarbonateneutralizes acid from stomach

Pancreas

Endocrine Gland (Islets of Langherans) -Produces “Insulin and Glucagon” that maintain sugar level in blood

pancreasproduces enzymes to digest proteins & starch

stomachkills germs break up fooddigest proteinsstore food

mouthbreak up fooddigest starchkill germsmoisten food

liverproduces bile

- stored in gall bladderbreak up fats

Pyloric Sphincter

Small IntestineMost chemical digestion

takes place here.Simple sugars and

proteins are absorbed into the inner lining.

Fatty acids and glycerol go to lymphatic system.

Lined with villi, which increase surface area for absorption, one cell thick.

Small intestineFunction

chemical digestion major organ of digestion & absorption

absorption through lining over 6 meters! small intestine has huge surface area = 300m2

(~size of tennis court) Structure

3 sections duodenum = most digestion jejunum = absorption of nutrients & water ileum = absorption of nutrients & water

Duodenum 1st section of small intestines

acid food from stomach mixes with digestive juices from: pancreas

liver gall bladder

stomachkills germs break up fooddigest proteinsstore food

mouthbreak up fooddigest starchkill germsmoisten food

pancreasproduces enzymes to digest proteins & starch

Absorption in the Small Intestine Much absorption is thought to occur directly through

the wall without the need for special adaptations

Almost 90% of our daily fluid intake is absorbed in the small intestine.

Villi - increase the surface area of the small intestines, thus providing better absorption of materials

All EXCEPT Fat products take a different path, “Chylomicrons” (Transport triglyceride, cholestrol, and phospholipids) through blood and into LACTEAL (lymph)

Absorption by Small IntestinesAbsorption through villi & microvilli

finger-like projectionsincrease surface area for absorption

Large IntestineCecum (Important in animals that ingest plant

material eg. Cellulose)

Colon (Ascending, Transverse, Descending)

Rectum

Note: Appendix – Pouch or Finger-like extension of Cecum. Minor role in immunity

Large intestines (colon)Function

re-absorb water use ~9 liters of water every

day in digestive juices > 90% of water reabsorbed

not enough water absorbed diarrhea

too much water absorbedconstipation

Large IntestineSolid materials pass

through the large intestine.These are undigestible

solids (fibers).Water is absorbed.Vitamins K and B are

reabsorbed with the water.

Rectum- solid wastes exit the body.

You’ve got company!Living in the large intestine is a

community of helpful bacteriaEscherichia coli (E. coli)

produce vitamins vitamin K; B vitamins

generate gases by-product of bacterial metabolism methane, hydrogen sulfide

AppendixVestigial organVestigial organ

Rectum Last section of colon

(large intestines)eliminate feces

undigested materialsextracellular waste

mainly cellulose from plants

roughage or fiber masses of bacteria

Digestive Homeostasis DisordersULCERS – erosion of the surface of the

alimentary canal generally associated with some kind of irritant

Digestive Homeostasis Disorders

CONSTIPATIONCONSTIPATION – a condition in which the large intestine is emptied with difficulty.

Too much water is reabsorbed

and the solid waste hardens

Lack of Fiber

Digestive Homeostasis DisordersDIARRHEA – a gastrointestinal

disturbance characterized by decreased water absorption and increased peristaltic activity of the large intestine.

This results in increased, multiple, watery feces.

This condition may result in severe dehydration, especially in infants

Digestive Homeostasis Disorders

APPENDICITIS – an inflammation of the appendix due to infection

Common treatment is removal of the appendix via surgery

Digestive Homeostasis Disorders

GALLSTONES – an accumulation of hardened cholesterol and/or calcium deposits in the gallbladder

Can either be “passed” (OUCH!!) or surgically removed

Digestive Homeostasis Disorders

ANOREXIA NERVOSA - a psychological condition where an individual thinks they appear overweight and refuses to eat.

Weighs 85% or less than what is developmentally expected for age and height

Young girls do not begin to menstruate at the appropriate age.

Digestive Homeostasis Disorders

HEART BURN – ACID from the stomach backs up into the esophagus.

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Disorders of the Digestive System

Intestinal obstruction Mechanical obstructions

Adhesions, tumors, or foreign objectsNonmechanical obstruction

Halt in peristalsis TraumaIntestines touched during surgery

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Disorders of the Digestive SystemInflammatory bowel disease

Inflammation of intestinal wall Crohn’s disease Ulcerative colitis

Viral hepatitisJaundice and flu-like symptoms Major types – A, B, C, and G

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Disorders of the Digestive SystemCystic Fibrosis and the Pancreas

Pancreatic ducts become blocked with mucus Clogged ducts prevent pancreatic juices from

entering small intestine Leads to malabsorption of fats and other nutrients

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Embryonic Development of the Digestive System

Alimentary canal formed in week threeEncloses tubular portion of yolk sac

Vitelline ductLandmark dividing into three regions

Forgut Midgut Hindgut

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Embryonic Development of the Digestive System

Figure 22.30a, b

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

The Digestive System in Later Life

Middle age – gallstones and ulcers Old age – activity of digestive organs decline

Fewer digestive juices and enzymes producedAbsorption is less efficientDehydration of fecal mass leads to constipationDiverticulosis and cancer of digestive organs