Chapter 40

Question 1

Ingestion

Answer 1

The process of taking food into the mouth, starting on its journey through the digestive tract

Question 2

Digestion

Answer 2

A group of processes that break complex nutrients into simpler ones, thus facilitating their absoption

Question 3

Mechanical

Answer 3

Physically breaks large chunks of food into smaller bits and pieces

Question 4

Chemical

Answer 4

Breaks molecules apart; chemically changes food

Question 5

Mechanical digestion caused by

Answer 5

Caused by ‘movements’ of the digestive tract.
Changes ingested food from large particles into tiny particles, facilitating chemical digestion
Churns contents of the GI lumen to mix with digestive juices and ensure contact with the surface of the intestinal mucosa, facilitating absorption
Propels food along the alimentary tract, eliminating digestive waste from the body

Question 6

Mechanical digestion involves

Answer 6

Mastication (chewing)
Deglutition (swallowing)
Peristalsis and Segmentation
Regulation of motility
Intestinal Motility

Question 7

Chewing and swallowing

Answer 7

Mastication (chewing): reduces size of food particles and mixes food with saliva to prepare it for deglutition
Deglutition (swallowing): a complex process involving several stages (See Figure in Textbook):
Oral stage
Pharyngeal stage
Esophageal stage

Question 8

Oral stage

Answer 8

Mouth-> oropharynx

under voluntary control
food bolus is formed, pushed against palate by tongue, then moved back into the oropharynx

Question 9

Pharyngeal stage

Answer 9

Oropharynx -> esophagus

Involuntary
Requires blockage of mouth, nasopharynx and larynx
Accomplished by contractions & gravity

Question 10

Esophageal stage

Answer 10

Esophagus -> stomach

Involuntary
Accomplished by contractions and gravity

Question 11

Peristalsis and segmentation are

Answer 11

two main types of motility produced by smooth muscle of the GI tract.

Question 12

Peristalsis

Answer 12

wave-like ripple of the muscle layer of a hollow organ that moves matter forward in the GI tract (See Figure in Textbook). Triggered by the presence of food.

Question 13

Segmentation

Answer 13

: a forward-and-backward mixing movement within a single segment of the GI tract. Helps breakdown food, mixes food with digestive juices and brings it in contact with the intestinal mucosa where absorption takes place (See Figure in Textbook)

Question 14

Gastric (STOMACH) mobility

Answer 14

Food in stomach is churned and mixed (via peristaltic contractions called propulsion and retropropulsion) with gastric juices to form chyme , which exits the stomach about every 20 seconds. Emptying of stomach after a meal takes about 2 to 6 hours and is controlled by:
Hormonal mechanisms – the presence of fat in the duodenum stimulates a hormone that slows down the passage of chyme into the duodenum
Nervous mechanisms – presence of acid and distention picked up by receptors in duodenal mucosa  impulses travel through vagus nerve  inhibits gastric peristalsis

Question 15

Intestinal motility

Answer 15

Includes peristalsis and segmentation

Question 16

Segmentation

Answer 16

O ccurs in duodenum and 1st part of jejunum; mixes chyme with digestive juices from pancreas, liver, & intestinal mucosa

Question 17

Peristalsis

Answer 17

moves chyme through rest of small intestine  large intestine.
Takes 5 hours for chyme to travel through length of small intestine
Regulated by stretch reflexes and the hormone CCK (cholecystokinin)

Question 18

Chemical changes in food result from

Answer 18

Hydrolysis

Question 19

Digestive enzymes

Answer 19

Function in lumen of digestive tract (extracellular enzymes)
All digestive enzymes = hydrolases  breakdown food molecules using water
Specific in action (lock-and-key)
Require specific pH and temperature for optimal function
Digestive enzyme reactions do not go in reverse!
Continually synthesized since they are continually destroyed or eliminated from body – even though they are not used up in the reaction they catalyze/assist
Most are sythesized and secreted as inactive proenzymes

Question 20

Carbohydrates

Answer 20

Saccharide compounds

Begins in the mouth (salivary amylase)

None occurs in stomach

Most occurs in small intestine

Question 21

Polysaccharides are hydrolzed by

Answer 21

Amylase to form disaccharides

Question 22

Carbohydration digestion happens in the

Answer 22

Small intestine

Question 23

Maltose

Answer 23

Glucose + glucose

Question 24

Sucrose

Answer 24

Glucose + fructose

Question 25

Lactose is

Answer 25

Glucose + galactose

Question 26

Proteins

Answer 26

Amino acids Begins in stomach; completed in small intestine Main proteases are: Pepsin: Gastric juice, partially digests proteins Trypsin and chymotrypsin: Pancreatic enzymes, continue digestion of proteins Peptidases: Intestinal enzymes, complete digestion of protein  amino acids

Question 27

Fat

Answer 27

Glycerol + fatty acids Fats must be emulsified by bile before being digested Bile - contains no enzymes but emulsifies fats Pancreatic lipase - changes emulsified fats to fatty acids and glycerol in small intestine

Question 28

Digestive secretions

Answer 28

``` T he release of various substances from the exocrine glands that serve the digestive system, e.g.: Saliva Gastric juice Pancreatic juice Bile Intestinal juice ```

Question 29

Saliva

Answer 29

``` secreted by salivary glands mucus + enzymes (mostly amylase) mucus lubricates and mixes with food main enzyme in saliva is amylase amylase functions best in an alkaline pH ```

Question 30

Gastric juice

Answer 30

Secreted by exocrine glands in stomach Pepsin – protease that begins digestion of proteins HCl – decreases pH of chyme to a level that activates and optimizes pepsin activity (See Figure in Textbook) Intrinsic factor – required for vitamin B12 absorption (See Figure in Textbook) Mucus & water – lubricate, protect, and help with mixing of chyme

Question 31

Pancreatic juice

Answer 31

Secreted by exocrine part of pancreas Secretes numerous enzymes: proteases, lipases, nucleases, amylase Secretes sodium bicarbonate Buffers stomach contents that enter duodenum Increase pH for optimum enzyme function Plays a role in maintaining blood pH

Question 32

Bile

Answer 32

Secreted by liver; stored by gallbladder Contains lecithin and bile salts which emulsify fat in preparation for digestion by lipases Unique property: hydrophobic and hydrophillic  micelles

Question 33

Release of bile

Answer 33

Initiated by the presence of fat in chyme Detection of fat in chyme stimulates release of the hormone cholecystokinin (CCK) from duodenum’s intestinal mucosa CCK contraction of GB bile into the duodenum

Question 34

Intestinal juice

Answer 34

Secreted by cells of intestinal exocrine glands Mucus and water - lubricate and aid with mixing of chyme Sodium bicorbonate increase pH to optimize enzyme function

Question 35

Salivary secretion

Answer 35

Controlled by reflex mechanism Chemical and mechanical stimuli from presence of food in the mouth Olfactory and visual stimuli also involved

Question 36

Three phases of gastric secretion

Answer 36

Cephalic Gastric Intestinal

Question 37

Cephalic phase

Answer 37

Sensations of thoughts of food are sent to the brainstem Parasympathetic signals are sent to the gastric mucosa via vagus nerve Gastric juice secretion is stimulated Gastrin secretion is stimulated

Question 38

Gastric phase

Answer 38

Presence of food in stomach  distention | Triggers reflexes that increase secretion of gastric juices and gastrin

Question 39

Intestinal phase

Answer 39

Occurs as food moves into/through duodenum | Presence of fats, carbs, proteins & acid stimulates hormonal and nervous reflexes that inhibit stomach activity

Question 40

Pancreatic secretion

Answer 40

Stimulated by several hormones released by intestinal mucosa Secretin  stimulates production of pancreatic fluid that is low in enzymes and high in bicarbonate CCK stimulates contraction of gallbladder

Question 41

Bile secretion

Answer 41

Continually secreted by liver; stored in GB (CCK stimulated GB to squeeze out bile)

Question 42

Intestinal secretion

Answer 42

Mechanism of regulation is uncertain

Question 43

Absorption

Answer 43

Movement of digested food molecules (amino acids, glucose, fatty acids, glycerol) from the mucous membrane of the intestine into blood or lymph. Occurs in: Small intestine: foods and most water Plicae – villi - microvilli – bumps! (See Figure in Textbook) Various nutrients are absorbed at different locations along digestive tract (See Figure in Textbook) Large intestine: Some water and vitamins synthesized in the large intestine

Question 44

Elimination/defecation

Answer 44

“Expulsion of feces from the digestive tract” Distention of rectum  receptors in rectal mucosa are stimulated  reflex It takes 3 to 5 days for fecal matter to pass through L.I. constipation – prolonged time in L.I. leads to more water being absorbed  feces becomes more solid, harder diarrhea – fecal matter rushes through the L.I. before the water is absorbed