Ch 25- Digestive System

Question 1

Digestive System

Answer 1

-food must be broken down into molecules that are small enough to enter body cells, a process called digestion

• digested food that passes through cells that line the stomach and intestine and into blood or lymph is call absorption

-organs that accomplish digestion and absorption are called digestive system

Question 2

Digestive tract (gastrointestinal (GI)

Answer 2

muscular tube that extends from the
mouth to the anus consisting of Mouth, pharynx, esophagus,
stomach, small intestine and
large intestine

-Accessory digestive organs –
organs that assist in digestion.
- Teeth, tongue, salivary glands,
liver, gallbladder and
pancreas.

Question 3

Digestive Function

Answer 3

Ingestion: intake of food

Digestion: mechanical and chemical breakdown of food thats useful for a body

• Absorption: molecules into cells of the digestive tract and then into the blood and lymph
• Compaction: absorbing water and indigestible into feces
• Defecation: elimination of feces

Question 4

layers of the Digestive Tract

Answer 4

Mucosa- includes:
-Digestive epithelium: cells that protect ,secrete, absorb
-Lamina propria: capillaries route for nutrients, protection, thin layer called mucosae

Submucosa-binds the mucosa to
the muscularis, includes:
-vessels and glands
-network of neurons from ENS that coordinates digestive system

Muscularis- main layer, includes:
-Skeletal muscle- voluntary, eg swallowing and pooping
-Smooth muscle- involuntary
-muscles help break down food, mix food, push along tract
-Serosa – superficial layer, lines the digestive tract

Question 5

Serous Membranes

Answer 5

peritoneum- divided in two parts:
-visceral- outer digestive tube
-parietal- lines abdominopelvic cavity

-space between called peritoneal cavity filled w fluid

Question 6

Peritonitis

Answer 6

inflammation of the
peritoneum that can
be caused by wounds or ruptured appendix

Question 7

the oral cavity

Answer 7

-first part of digestive tract
-three structures involved in digestion:
tongue- processes food by compression and distortion, assists in sewing and initiates swallowing

-salivary glands- releases saliva in the mouth (mostly water) and other enzymes like amylase and lysozyme(controls bacteria), lubricates, breaks down carbs, for tasting, begins digestive reaction, buffers

-teeth- hardest structures in the body, calcified

Question 8

Extrinsic Salivary Glands

Answer 8

-parotid gland
-submandibular gland
-sublingual gland

Question 9

Mechanical digestion of the oral cavity

Answer 9

from mastication (chewing), where food is manipulated by the tongue, broken down by the teeth and mixed with saliva, food becomes soft and then swallowed called bolus

Question 10

chemical digestion of the oral cavity

Answer 10

-based on two enzymes
-Salivary amylase –breakdown of polysaccharides (e.g., starch,
glycogen) into disaccharides (e.g., maltose).

 Lingual lipase – initiates the breakdown of triglycerides into fatty acids and monoglycerides.
o It works over a broad range of pH (3.0-6.0), so it can remain active longer
than amylase in the acidic environment of the stomac

Question 11

absorption of oral cavity

Answer 11

-no nutrient absorption from ingested foods occurs in the oral cavity.

-under tongue can absorb lipid soluble drugs

Question 12

Stages of swallowing

Answer 12

-deglutition (swallowing)

three steps:
-Oral stage – the
tongue compresses the bolus and forces into oropharynx
- Pharyngeal stage –
involuntary passage of bolus
through the pharynx into the
esophagus, the epiglottis folds and pushes into esophagus
-Esophageal stage – involuntary
passage of bolus through the
esophagus into the stomach, lower esophageal prevents it from coming back up

Question 13

what happens if lower esophageal fails to keep food down

Answer 13

-heartburn
-acid reflux

Question 14

chronic acid reflux is called what

Answer 14

gastroesophageal reflux disease (GERD)

-acid reflux
-regurgitation
-chest pain

Question 15

The Stomach

Answer 15

-The stomach is a J-
shaped digestive tract that connects the esophagus to the small intestine
-accommodate large amounts of food

-

Question 16

mechanical digestion of the stomach

Answer 16

-As food enters the stomach, it is stored briefly, while digestion by salivary amylase and lingual lipase
continues
-minutes after food enters the stomach, mixing waves pass over the stomach every 15-25 seconds, and reduce it to a soupy liquid called chyme
-mixes chyme with acidic gastric
juice, inactivating salivary amylase while lingual lipase remains
active until the pH becomes very acidic
-Each wave forces a small amount of acidic chyme through the pyloric sphincter and into the duodenum

Question 17

glands of the mucosa in the stomach

Answer 17

-pyloric gland
-gastric gland

Question 18

chemical digestion of the stomach including infants

Answer 18

-stomach lining cells secrete 1.5 L of gastric juice a day. Cells found in depressions called gastric pits which include:

-Parietal cells secrete: (HCL)-acidic, kills bacteria, denatures protein, alkaline mucus cells protects lining from acidity, if that fails then ulcers form, intrinsic factor- glycoprotein that absorbs B12 across lining

-chief cells- inactive enzyme pepsinogen converts to pepsin from HCL in stomach and digests large proteins into smaller chains, works best at low pH

-G cells- gastrin secreted into blood, produces more secretions from P and C cells, stimulates contractions to stir contents in stomach

infants:
-also produce additional enzymes for milk digestion (rennin and gastric lipase)

Question 19

control of gastric activity (phases)

Answer 19

-cephalic phase: vagus nerve stimulates gastric secretion even before food is swallowed (prepares stomach for food arrival)

-gastric phase: food stretches stomach, activates reflexes that stimulate gastric secretion

-intestinal phase: briefly stimulates the stomach (not to much at one time) secretin, CCK allow digestion into intestine, controls rate of chyme entry into duodenum

Question 20

how many hours for stomach to empty contents into duodenum, absorption, and vomiting

Answer 20

2-4 hours

-carbs digest faster then protein

-absorption: Very little absorption occurs in the stomach,digestion not completed by the time chyme leaves the stomach

-Vomiting - forcible expulsion of the contents of the upper digestive tract
through the mouth

Question 21

pancreas

Answer 21

pancreas produces pancreatic juice (about 1L daily), which helps digestion in the small intestine. It contains:

Sodium bicarbonate – Neutralizes stomach acid, creates the right pH for digestion, and stops pepsin.

Enzymes:
-Pancreatic amylase – Breaks down carbohydrates.
-Pancreatic lipase – Breaks down fats.
-Nucleases – Break down DNA/RNA.
-Trypsinogen (inactive) → Trypsin (active) – Helps digest proteins.

Pancreatic juice is released into the duodenum along with bile to aid digestion

Question 22

Liver and Gallbladder

Answer 22

The liver makes 1L of bile daily, which helps digest fats.
-Bile salts break large fat globules into tiny droplets so enzymes can digest them.
- The gallbladder stores and concentrates bile until it’s needed in the small intestine

Question 23

Gallstones

Answer 23

-form when there aren’t enough bile salts or too much cholesterol, causing crystals that turn into stones.

• These can block bile flow, leading to pain and digestion issues.

-Treatments include medications, surgery

-Without the gallbladder, bile still flows but isn’t stored or concentrated.

Question 24

The small intestine

Answer 24

-major site of digestion and absorption

-length and folds provide a large surface area for digestion and absorption

Question 25

walls of small intestine that increase large surface area

Answer 25

Plicae (circular folds) – Permanent ridges that make chyme spiral, increasing contact with the intestine for better absorption. Villi – Small finger-like projections containing blood and lymph vessels that absorb nutrients. Microvilli – Tiny hair-like structures that increase surface area and contain brush-border enzymes for digestion

Question 26

mechanical digestion of small intestine

Answer 26

two main movements: segmentation- brings food into contact with mucosa for absorption -peristalsis- contractions that move chyme along (remains in SI for 3-5 hours)

Question 27

chemical digestion of small intestine

Answer 27

-When chyme enters the small intestine, it contains partially digested carbs, proteins, and fats. -Digestion is completed using pancreatic juice, bile, and intestinal juices (from the brush border). -The small intestine produces 2L of intestinal juice daily to aid digestion.

Question 28

breakdown of carbohydrates

Answer 28

mouth- salivary amylase stomach- new enzymes duodenum- pancreatic amylase brush border- maltase (into glucose), sucrase(into glucose and fructose), lactase (into glucose and galactose) -absorbed as monosaccharides -SGLT transported w Na+ into intestinal cells and diffuse into villi

Question 29

breakdown of proteins

Answer 29

mouth- no enzymes stomach- pepsin, large polypeptides into smaller duodenum- enzyme from pancreas that breakdown into peptides: trypsin, chymotrypsin brush border enzymes- aminopeptidase, dipeptidase -absorbed as amino acids into intestinal cells, Na + dependent, diffuse into villi

Question 30

lipid breakdown

Answer 30

-pH 3-6 mouth- lingual lipase stomach- lingual lipase until pH3, secrete gastric lipase in infant -duodenum- bile salts from gallbladder, break down fats pancreas- pancreatic lipase -absorbed as fatty acids and monoglycerides micelles- carry lipids to intestinal cells and diffuse into cell

Question 31

Chylomicron Formation

Answer 31

Eat, fat, break it down, pack it into chylomicrons, send it to the blood

Question 32

water absorption

Answer 32

Water is absorbed by osmosis into cells and then into blood capillaries. Nutrient absorption creates a gradient that helps pull in water. 9L of water enters the digestive tract daily (2L from food/drink, 7L from secretions). 85-90% (~8L) is absorbed in the small intestine, with 1L passing to the large intestine.

Question 33

hepatic portal system

Answer 33

Nutrients like enter the blood and travel to the liver through the hepatic portal system. This system directs blood from one capillary network to another via a portal vein, bypassing the heart initially. Nutrients absorbed into the lymph (like fats) eventually join blood circulation

Question 34

liver functions

Answer 34

Filters absorbed materials before they enter circulation via the hepatic veins. Regulates metabolism and blood levels of carbs, proteins, and fats. Stores glycogen, lipids, vitamins, and iron. Processes drugs and hormones. Produces bile, plasma proteins, and excretes bilirubin.

Question 35

large intestine

Answer 35

The final part of the digestive tract, from the ileocecal sphincter to the anus. The colon has pouches called haustra, giving it a puckered look. The anus has two sphincters: Internal sphincter (involuntary control). External sphincter (voluntary control).

Question 36

mechanical digestion of the large intestine

Answer 36

The ileocecal sphincter controls the passage of chyme into the large intestine. food fills the large intestine, the haustra stretch, and when they stretch enough, they contract to move the contents into the next haustrum Mass peristalsis moves contents from the second half of the colon into the rectum through strong peristaltic waves, usually occurring 2-3 times a day, especially after meals (leading to bowel movements).

Question 37

Chemical Digestion of Large intestine

Answer 37

-doesn’t produce enzymes; digestion comes from small intestine enzymes and bacteria. - Bacteria ferment carbs into gases, causing flatulence, and break down proteins into compounds like ammonia and hydrogen sulfide, which give feces their odor.

Question 38

Large intestine absorption

Answer 38

About 1.5L of material enters the large intestine daily, but only 150-200 mL becomes feces. The large intestine fine-tunes water absorption. Bile salts are reabsorbed and recycled by the liver. Some B vitamins and vitamin K are produced by bacteria and absorbed. After 3-10 hours, the chyme becomes solid or semisolid due to water absorption and is then called feces.

Question 39

Neural Control of Defecation

Answer 39

When the rectum stretches, the defecation reflex begins. Stretch receptors trigger a spinal reflex that causes the rectal muscles to contract, increasing pressure. This pressure opens the internal anal sphincter. Feces are expelled if the external anal sphincter is voluntarily relaxed; otherwise, it backs up into the sigmoid colon until the next mass peristalsis wave

Question 40

diarrhea and constipation

Answer 40

Diarrhea – Increased volume and fluid in feces due to faster motility and decreased absorption (chyme moves too quickly through the intestines). Constipation – Infrequent or difficult defecation caused by slower motility, leading to excessive water absorption, making feces hard and dry.

Question 41

primary site for water absorption in the GI tract

Answer 41

The small intestine