CHAPTER 4

HUMAN DIGESTION AND ABSORPTION

ORGANIZATION OF THE HUMAN BODY

• Chemical Level• Atoms combine to

form molecules• Cell Level• Molecules form

organelles• Use ATP

• Tissue Level• Similar cells make up

tissues

ORGANIZATION OF THE HUMAN BODY

• Organ Level• Different tissues

combine to form organs

• Organ System Level• Organs make up an

organ system• Organism Level• Organ systems make

up an organism

DIGESTIVE ORGAN SYSTEM

•GI tract•Mouth, esophagus, stomach, small intestine, large intestine

•Accessory organs: Liver, pancreas and gall bladder

DIGESTIVE ORGAN SYSTEM

DIGESTIVE SYSTEM OVERVIEW

•Digestion• Process of breaking down foods into a form

the body can use

•Absorption• Uptake of nutrients from the GI tract into

the blood or lymph

ANATOMY OF THE GI TRACT

• GI tract • Long hollow muscular canal. Nutrients pass

through the wall of the canal to be absorbed• Four layers (listed from inner most layer to

outermost layer)• Mucosa• Submucosa• Muscle• Serosa

GI MOTILITY

• Peristalsis• Contractions of the GI tract, mainly in esophagus,

stomach, and small intestine• Segmentation• Back and forth movement-happens in small

intestine so there is mixing with digestive juices•Mass movements• Slow peristalsis over widespread area- in large

intestine to help propel fecal matter to rectum• Elimination

Sphincters: Ring like muscles along the GI tract that control the flow of contents

ONE WAY STREET

MOUTH (ORAL CAVITY)

Chewing breaks up food and increases surface area. These smaller food particles are mixed

with saliva and forms a bolus.Saliva• Lysozyme• Break down bacteria

• Amylase• Break down starch

• Mucus• Lubricate and hold bolus together

TASTE AND SMELL

• Taste buds on the tongue and soft palate• Salty (from metal ions)• Sour (from acids)• Sweet (from organic compounds)• Bitter (many diverse compounds like

phytochemicals)• Umami or savory (from amino acids)

• Olfactory glands• Sense of smell (enhances sense of taste)

ESOPHAGUS

• Swallowing• Moves bolus from the mouth to the esophagus

• Epiglottis• Prevents food from lodging in the trachea• Covers the larynx

http://youtu.be/sM6uxd1uS6M

STOMACH

• Bolus goes through lower esophageal sphincter into stomach• Mixed with stomach secretions becomes chyme• Pyloric sphincter allows chyme into the small

intestine• Gastric inhibitory peptide (hormone) slows release of

chyme into the small intestine to allow time for acid neutralization and digestion (only one teaspoon is allowed into the SI at a time).

STOMACH SECRETIONS

Chief cells produce:•Pepsinogen (an inactive protein-digesting enzyme)Other secretions include, Gastric lipase •Gastrin•Hormone stimulated when food is in stomach; controls release of HCl and pepsinogen and stimulates motility•Mucus•Protects the stomach from being digested

STOMACH SECRETIONS

Parietal cells produce hydrochloric acid which: • Inactivates proteins• Destroys bacteria and viruses• Aids in mineral absorption (dissolves them)• Converts pepsinogen (protein digesting

enzyme) into pepsin (active form)

SMALL INTESTINE

Most digestion and absorption

occurs here

Sections:Duodenum, JejunumIleum

SMALL INTESTINE

Villi (finger like projections on interior of SI) that are lined with:• Goblet cells make mucus• Endocrine cells produce hormones• Cells (enterocytes) that produce enzymes for

absorption

HORMONES OF THE SMALL INTESTINE

• Gastrin• Also released by stomach, stimulates intestinal motility

• Cholecystokinin (CCK)• Stimulated by dietary fat in chyme, stimulates release

of pancreatic enzymes and bile• Secretin• Stimulated by acidic chyme, stimulates release of

pancreatic bicarbonate• Gastric Inhibitory peptide• Stimulates stomach to limit gastric juices, slows motility

ACCESSORY ORGANS: LIVER, GALLBLADDER AND PANCREAS

• Liver• Provides bile• Needed to emulsify fat (disperse into droplets and suspend

in water) so it can be absorbed

• Gallbladder• Bile storage• Pancreas• Produces sodium bicarbonate, lipases, proteases and

pancreatic amylase

ACCESSORY ORGANS: LIVER, GALLBLADDER AND PANCREAS

LARGE INTESTINE

Functions: Absorption of water and electrolytes, house bacterial flora, and form

and expel feces.•Colon• Cecum, ascending colon, transverse colon,

descending colon and sigmoid colon

•Rectum•Anus

LARGE INTESTINE

ABSORPTION

ABSORPTION

• Passive (fat, water, some minerals)• High concentration to low• Facilitated (ex. fructose)• High concentration to low + carrier protein• Active (amino acids, glucose)• Low concentration to higher + energy• Endocytosis (large proteins like immune

factors)• Engulfment

ABSORPTION

MOVING NUTRIENTS

• Cardiovascular System• Includes heart, blood

vessels and blood• Water-soluble nutrients

transported via capillaries in villi to portal vein, which leads to liver• Allows liver to process

nutrients before entering general circulation

• Lymphatic System• Includes lymph• Fat-soluble nutrients and

large particles transported via lacteals into the lymph vessels to thoracic duct, where it connects to the blood stream.

BACTERIAL FLORA

• Beneficial bacterial flora• Controls pathogenic bacteria• Synthesize Vitamin K and Biotin• Aid lactose digestion and fermentation• Pro-biotic• Live bacteria• Pre-biotic• Non digestible carbohydrates that promote the

growth of beneficial bacteria

PUTTING IT ALL TOGETHER

Be able to trace the pathway of food from when you first eat it until it is eliminated or

absorbed

Know the major function of each organ and if it secretes any major enzymes or hormones

DIGESTION GONE AWRY

Heartburn and Gastroesphogeal reflux (GERD)

Causes Overweight, alcohol, smoking, pregnancyFoods that increase reflux

Citrus, caffeine, chocolate, fatty foods, spicy foods, onion, garlic and tomato based foodsMedications include H2 blockers (blocks histamine formation) and proton pump inhibitors

DIGESTION GONE AWRY

Heartburn and Gastroesphogeal reflux (GERD)

DIGESTION GONE AWRY

UlcersCauses: H pylori, alcohol, aspirin and smoking (not stress)

Treatment:• Medications (abx, same as GERD)• Avoid foods that increase symptoms

DIGESTION GONE AWRY

• Gallstones• Food Intolerances• Lactose, gluten, MSG

• Intestinal Gas• Flatulence• Air and undigested CHO in large intestine

DIGESTION GONE AWRY

DIGESTION GONE AWRY

• Constipation• Fiber, fluid and exercise• Laxative use (bulk, osmotic, stimulants, softeners,

and lubricants)• Diarrhea• Replace fluid and electrolytes• Irritable bowel• Cause unknown, examine dietary factors• Hemorrhoids