The Digestive System

Or…What happens to that “Big Mac” once you take a bite!

What makes up a “Big Mac”?

• The six basic groups of nutrients are:1. Water2. Carbohydrates3. Fats4. Proteins5. Minerals6. Vitamins

Water

• Water is the most basic nutrient• You die first without it• If you lose 10% of your body water you are in

danger of dying –dehydration.• Water makes up 70% or more of your body

(depending on your age).• You are dehydrated before you actually

experience thirst.

Carbohydrates

• Made of carbon, hydrogen, and oxygen in the proportion of [CH2O]n.

• Nutritional carbs are of plant origin.• Function: provide energy.1. Simple sugars

-Monosaccharides (glucose, fructose, galactose, and mannose) C6H12O6 (isomers)

-Dissaccharides (2 monosaccharides combined by dehydration synthesis)

Sucrose (glucose + fructose)Lactose (glucose + galactose)Maltose (glucose + glucose)

2. Complex Carbohydrates (polysaccharides)-Starches (amylose, amylopectin, glycogen)-Cellulose -mammals have no cellulase –not digestible = FIBER

Isomers: same empirical formula, different structural formula

Something to think about!!!

Lipids (Fats)• Made of carbon, hydrogen, and oxygen.• Functions: stored energy, cell membranes,

insulation and padding, steroid hormones• Calorically dense. 2.54 calories / gram more

that carbs or protein• Triglycerides (LDL and HDL), Cholesterol• Basic component is fatty acids– Saturated –each carbon fully hydrated– Unsaturated –some double bonds

Generalized triglyceride structure

Cholesterol

Triglycerides

• Cylomicrons– Form of fat absorption from the intestines– More about it later

• HDL: High density lipoproteins– Good Cholesterol– Increased by cardiovascular exercise

• LDL: Low density lipoproteins – Bad Cholesterol

Essential Fatty Acids

• Essential: required in the diet for health, not made in adequate amounts by the body to sustain health.• Linoleic acid• Linolenic acid• Aracadonic acid

Proteins• Structure: chains of amino acids coded for on

DNA -C, H, O, N, and sometimes S.• Functions: structural, enzymatic, antibodies,

regulatory (some hormones), energy• Essential Amino Acids: PVT MATT HILL• Non-essential –made by the body.• Complete proteins –have the right combination

of essential amino acids• Incomplete proteins have an imbalance of

essential amino acids –at least one limiting aa.

Meat, milk, eggs, soy.Which is the best protein?

• What is protein quality?• How is protein evaluated?• What about vegetarians?• What is the difference between ouevo-

lacto and vegan?• What is a complementary protein?

Vitamins• Fat Soluble: ADEK1. Vitamin A -retinoic acid –eyesight (night

vision), epithelial tissue health2. Vitamin D –calcitrol –calcium absorption and

bone health. Deficiency disease =Rickets3. Vitamin E –α-tocopherol –antioxidant in fat

soluble tissues.4. Vitamin K – part of the clotting cascade.

Made by gut bacteria.

Water Soluble Vitamins• B vitamins:• B1 =thiamine TPP• B2 =riboflavin FAD -carries hydrogens• B3 =niacin NAD -carries hydrogens• B5 =Pantothenic acid• B6 =Pyridoxine transfers amino acids• B9 = Folic acid• B12 =carboxycobalamine -only one stored!

Animal products only

Vitamin C

• Ascobic acid• Water soluble• Deficiency disease is scurvy• Only required by primates (including humans),

guinea pigs, and fruit bats.• Important in the conversion of proline to

hydroxyproline to make collegen• Important in immune response. Increase

turnover in disease.• Anti-oxidant

Minerals

• Macro-minerals: required in percentage amounts in the diet

–structural: calcium, phosphorus, magnesium

-electrolytes: sodium, potassium, chlorineMicro-minerals: trace elements –ppm (1mg/kg)

-iron, copper, fluoride, iodine, selenium, manganese

Back to the “Big Mac”

• What is in a “Big Mac”• Dissect your burger into its

nutrients?• Explain the caloric effect of fat in the

burger or any food?

• Now what happens!!!

What is digestion?

• Digestion is the sum of the mechanical and chemical processes that convert food elements into small enough particle to be absorbed into the body.

• There are 2 basic aspects of digestion:

• Chemical Processes –enzymatic• Physical process –mechanical like chewing and

mixing

Mouth: ProcessesMechanical digestion:Prehension: food gathering –lips, hands, etc.• Mastication: chewing, breaks food into smaller

pieces (greater surface area) to facilitate enzyme breakdown.• Ensalivation: coats food particles with saliva to

facilitate swallowing -lubrication Chemical digestion • Salivary amylase: breaks down starch (amylose)

into dextrins (6 carbon sugars).

Teeth

• Dental Formula– Set up like a fraction = ½ of the mouth– Numerator = the top of the jaw– Denominator = bottom jaw– Numbers are given in the following order– Incisors/canines/premolars/ molars– Human permanent teeth =– 2123/2123 X 2

Permanent teeth

Do all animals have the same teeth?

Swallowing

• Food is swallowed• Moves through the pharynx• Past the epiglottis

What is the purpose?

– Enters esophagus– Moves by peristalic movement (wave-like

movement)

Stomach: gastric phase

Gastric Activities

• Mixing movements• Gastric secretions: pH=2-3– Pepsinogen– HCl– mucous

• Hormone release: (gastrin and intrinsic factor)• Absorption

alcohol and water

Secretions

• Chief cells -secrete pepsinogen• Parietal cells –secrete HCl• HCl converts pepsinogen to pepsin

Functions of the Stomach

• 1. Break down of proteins into peptides• 2. Absorption of water –especially if

dehydration exists.• 3. Absorption of alcohol• 4. Absorption of acidic drugs (due to pH)• 5. Secretion of “rennin” in babies causes milk

proteins to form “curds” for digestion.

Intestinal Digestion

Small Intestine• Parts: No distinct bounderies.• Duodenum

-first 25 cm (10 inches)-primary area of digestion and absorption

• Jejunum– Continued digestion and absorption

• Ileummostly water

• Ileocecal junction: where SI joins the cecum and LI

Intestinal lining

Intestinal “juices”

ACTION ORIGIN• Sodium bicarbonate -neuralizes pH pancreas• Mucous – -protection

Brunner’s glands goblet cells.

• Chyme has a pH of____7_________.

Enzymes (all enzymes are proteins –coded for on DNA)

• ENZYME ACTION ORIGIN• Peptidase 1 breaks down proteins• Dissaccharidases convert dissacharides SI

to monosaccharides • Lipase breaks down triglicerices SI & P• Enterokinase breaks down proteins SI• Amylase Breaks down amylose SI & P • Chyme passes through the ileocecalvalve into the Large

Intestine

LARGE INTESTINE

• Cecum -in some animals (rabbits and horses) is very large and provides a fermentation vat.

• Vermiform appendix – function is a lymph node• Ascending colon• Transverse colon• Descending colon• Sigmoid colon• Rectum• Anus has 2 sphincters.

Lots of distance –little function

• The digestive function of the large intestine is absorption.

• Only mucous is secreted• Absorption of water.• Intestinal bacteria make: vitamin K, some

amino acids.

LI problems

• Diverticula: balloon like projections that form in the large intestine due to strain and weakness of the intestinal wall.• Diverticulitis= inflammation of the

diverticula–painful

Digestion of Fat:

• Bile emulsifies fat: O (droplets) + Bile o o o o o o • Emulsify means: the mixture of immiscible liquids

(like oil and water).• Lipase attaches to the glycerol of the triglyceride

and breaks off the fatty acids 1 and 3. Glycerol is absorbed into the bloodFatty acids pass through mucosal cells are combined with protein as cylomicrons the lymph system.

Chylomicron

–transport of fat coated with protein from intestines in lymphatics to thoracic duct. -Dumped into the vena cava. -Can go directly to muscle and adipose tissue or to the liver to be reprocessed. • LDL and HDL made by liver and

transport of fat in blood. HDL –happy cholesterol.

LIVER

• Largest gland in the body.• Many important functions:• Carbohydrate metabolism• -maintains blood glucose level• -converts excess glucose to glycogen for

storage.• -gluconeogenesis- breaks down glycogen to

glucose when blood sugar is low.

Lipid Metabolism

• -oxidation of fat• -converts cylomicrons to VLDL, LDL, and HDLs.• -bile formation and release.• Protein Metabolism• -deamination of amino acids• -formation of urea• Storage• -glycogen• -vitamins A, D, and B12• -iron