5-12-14 Anat 304

Daily layout - Video -  Digestive system - Labeling worksheet

The Digestive System

The Cloaca   Art exhibit by Wim

Delvoye

  Artificial digestive system

  Feces at the end were sold

The food begins at a long, transparent mouth, travels through a number of machine-like assembly stations, and ends in hard matter which is separated from liquid through a cylinder.Delvoye collects and sells the realistically smelling output, suspended in small jars of resin at his Ghent studio. (Wikipedia)

Functions of the Digestive Tract (aka Gastrointestinal Tract)

  NOURISH the cells of the body

  PHYSICAL AND CHEMICAL breakdown of food

  Absorption of nutrients to the BLOODSTREAM

  Removal of SOLID wastes

The Digestive System

  Total length of the digestive tract in an adult human = 8m

Mouth (Oral cavity)   Entry place for food

  SALIVA secreted from SALIVARY GLANDS

  SALIVARY AMYLASE begins to break down STARCH to simpler sugars

  Saliva = water, electrolytes (Na+, K+, Cl-, HCO3-), MUCUS, salivary amylase, antimicrobial agents (ex. LYSOZYME)

  TEETH physically break food

  Tongue rolls food into a smooth lump-like mass BOLUS

  Tongue pushes bolus back during swallowing

The Pharynx, Epiglottis and Swallowing

  Food enters the PHARYNX

  Need to prevent food from entering the TRACHEA which leads to the lungs

  The EPIGLOTTIS is a flap of CARTILAGENOUS tissue

  Covers the trachea during SWALLOWING to ensure that food does not enter the RESPIRATORY SYSTEM

Esophagus   Tube that connects the

PHARYNX to the STOMACH

  MOTILITY down the esophagus is achieved by PERISTALSIS   two layers of smooth

muscle

The Stomach

  Physical and chemical DIGESTION occurs here

  Other purpose: STORAGE site for food

Stomach (cont.)   Entry to stomach

controlled by an ESOPHAGEAL SPHINCTER   A SPHINCTER is a ring-

like muscular structure

  The Esophageal Sphincter keeps the STOMACH closed (prevents acid from going up the esophagus HEARTBURN)

Stomach (cont.)  Has 3 MUSCLE

LAYERS (circular, longitudinal, and oblique layer

•  Foldings of stomach wall = RUGAE

•  RUGAE allow the stomach to expand for STORAGE

Stomach (cont.)   Gastric juice produced in GASTRIC

PITS   Hydrochoric acid HCl (aq) – pH of

1-3 – begins to break down PROTEINS and kills bacteria

  Pepsinogen – activated by the HCl to form PEPSIN – an ENZYME that breaks certain peptide bonds

  Mucus – protects the stomach EPITHILIUM from the ACIDITY of the stomach

Stomach (cont.)   The stomach MECHANICALLY

mixes the food, the GASTRIC juice, and saliva producing a thick liquid CHYME

  Very little ABSORPTION in the stomach (some water and salts, some medications and ALCOHOL) because most of the substances are not broken down enough to be absorbed

  Between the stomach and the small intestine is another SPHINCTER: The PYLORIC Sphincter – controls the flow of chyme into the first segment of the SMALL INTESTINE

http://www.youtube.com/watch?v=Mxlc0-okOR4&feature=related

The Small Intestine •  Main FUNCTIONS of the

Small Intestine : complete digestion and absorption of NUTRIENTS

  Length of 5.5-6m

  Has 3 regions: Duodenum, Jejunum, Ileum

  Is in fact 4 times longer than the large intestine

  Only mechanical digestion that occurs here is SEGMENTATION (contraction of circular muscles only)

The Small Intestine (cont.)   Throughout length of the Small intestine

there are VILLI to increase the SURFACE AREA and microscopic MICROVILLI to increase the SURFACE AREA even further

  The Villi have a CAPILLARY NETWORK

  ENZYMES produced to continue breakdown of macromolecules   Carbohydrases (sucrase, maltase,

lactase)   Peptidases (break down peptides even

further)

Microvilli of small intestine

Duodenum   There are cells that detect

the presence of ACIDIC chyme and FATTY chyme. They release hormones

  There are DUCTS that attach ACCESORY organs to the duodenum. These accessory organs are: LIVER, GALL BLADDER, and PANCREAS

The Liver and Gall Bladder   Liver

  Largest INTERNAL organ of the human body

  Digestive function: produces bile salts that are used to EMULSIFY fat

  Also METABOLIZES substances

  Storage of GLYCOGEN

  Gall Bladder   STORES bile   When fatty substances enter

the duodenum, the gall bladder contracts and the bile enters the DUODENUM

The liver and gall bladder (con’t)

The Pancreas   Creates PANCREATIC fluid that

contains ENZYMES used for digestion   Trypsin and Chymotrypsin :

proteases (breakdown proteins)

  Pancreatic Amylase: CARBOHYDRASE (breaks down starch)

  Lipase : digests FAT   Nucleases: digests

Nucleotides

  Pancreatic fluid also has bicarbonate (NaHCO3): NEUTRALIZES the stomach acid (HCl)

Pancreas

Jejunum   LONGER than

Duodenum

  Contains more FOLDS than the duodenum

  Continues to break down and ABSORB food

Ileum   Slightly LONGER

than the Jejunum

  Fewer and smaller VILLI

 Mostly just absorption of NUTRIENTS

The Large Intestine   SHORTER than small intestine

(1.5m)

  Function: to CONCENTRATE and ELIMINATE wastes

  Water and salts absorbed, FECES eliminated

  ANAEROBIC bacteria breakdown the undigested food

  Has 3 regions (caecum, colon, rectum) and 1 attachment (appendix)

Colon and Rectum

  Colon   SECOND region

  Absorption of water and salts

  Storage of BACTERIA   MUCOUS cells along

length (lubrication function)

  Rectum

  Storage of FECES until they are eliminated

  Even more mucous cells

Anus

  Opening to the exterior of the body for expelling feces

  Opening is controlled by 2 sets of muscular SPHINCTERS   One is INVOLUNTARY

(when rectum fills, signal is sent to move the feces out)

  Other is VOLUNTARY