CH 22~The Digestion System

All Quick Checks in the BIO 202 A&P presentation

set of organs that breaks down food items into nutrients that can be delivered by bloodstream to cells in body

Digestive system

Digestive system consists of two types of organs. What are those two organs

1. alimentary canal (gastrointestinal (GI) tract or digestive tract)

2. accessory organs

continuous tube through which food passes directly

Alimentary canal

list organs that belong to Alimentary canal

• Mouth

• pharynx

• esophagus

• stomach

• small intestine

• large intestine.

not part of alimentary canal but assist in digestion in some way

Accessory organs

list organs that belong to Accessory organs

• Teeth

• tongue

• salivary glands

• liver

• gallbladder

• pancreas.

Describe the major functions of the digestive system.

• Ingestion and Digestion of food

• fluid and electrolytes

• acid-base homeostasis

• vitamins and minerals

• producing hormones and excreting metabolic wastes

Describe the six basic processes of the digestive system.

• ingestion

• secretion

• propulsion

• digestion

• absorption

• defecation

Food and water are brought into digestive system

• Occurs via mouth under normal conditions

ingestion

digestive organs contain both endocrine and exocrine glands that secrete a variety of substances—such as mucus, enzymes, acid, and hormones—to aid other digestive processes

Secretion

Ingested food and liquids pass from one digestive organ to next by process; is accomplished largely by rhythmic contractions of smooth muscle of alimentary canal called peristalsis

• aided by mucus secreted by multiple organs

propulsion

Food breakdown occurs by process of

• Mechanical - chewing and mixing

• Chemical - enzyme breakdown

digestion

Once food particles are digested, they move through wall of alimentary canal into blood or lymphatic vessels by a process called _____

absorption

such materials continue their transit through alimentary canal until they exit body as feces through _____.; also provides body with a way to eliminate certain metabolic wastes

defecation

Briefly explain regulation of motility by the endocrine and nervous systems.

• Nervous system: ANS and ENS control digestive movements.

• Endocrine system: Hormones regulate digestive activity and motility.

Describe the peritoneal membranes and the peritoneal cavity

• Parietal peritoneum: Lines abdominal wall.

• Visceral peritoneum: Covers organs.

• Peritoneal cavity: Space between layers containing serous fluid.

Organs located entirely within peritoneal cavity; Inside cavity.

Intraperitoneal

partly or completely outside peritoneal cavity

retroperitoneal

Visceral peritoneum folds over on itself around certain organs, particularly small intestine, to form structures

Mesenteries

Discuss the basic functions of the oral cavity, the teeth, and the tongue.

• Oral cavity: Ingestion, digestion, and swallowing.

• Teeth: Chew food.

• Tongue: Forms and moves food for swallowing.

These organs turn ingested food into a moist, chewed mass called _____.

bolus

posterior oral cavity, pharynx, and esophagus then deliver bolus to stomach through process of swallowing.

deglutition

chew, ingested food, grinding it into smaller pieces.

masticate

List the two types of cells in a salivary gland

• serious cells

• mucus cells

explain what product each produces and when

serious cells - produce watery enzyme-rich secretions

mucus cells - produce mucus

List the three pairs of salivary glands.

• Parotid

• submandibular

• sublingual glands.

describe the composition of saliva

• Water

• electrolytes

• mucus

• salivary amylase

• lysozyme

• IgA

• bicarbonate.

describe the functions of saliva

• Lubricates food

• cleans mouth

• begins carbohydrate digestion; mechanical and chemical digestion

• helps taste.

Describe the role of the pharynx in regards to digestion.

Passageway that moves the bolus from the mouth to the esophagus during swallowing.

Describe the structure and functions of the esophagus including the roles of the upper esophageal sphincter and the gastroesophageal sphincter.

Muscular tube that carries food to the stomach.

• Upper esophageal sphincter: Controls entry into esophagus.

• Gastroesophageal (lower esophageal) sphincter: Controls entry into stomach and prevents reflux.

Explain the process of deglutition, including the three phases.

• Voluntary phase: Tongue pushes bolus backward.

• Pharyngeal phase: Bolus moves through pharynx; airway closes.

• Esophageal phase: Peristalsis moves bolus to stomach.

Secrete mucus to protect the stomach lining.

Mucous cells

Secrete hydrochloric acid (HCl) and intrinsic factor.

Parietal cells

Secrete pepsinogen (inactive protein-digesting enzyme).

Chief cells

Secrete hormones such as gastrin.

Enteroendocrine cells

Semi-liquid mixture of partially digested food and gastric secretions.

chyme

• Food sight, smell, taste, or thought stimulates acid secretion.

• Food enters the stomach, causing increased acid secretion.

• Food enters the small intestine, reducing stomach acid secretion.

Define these phases

• cephalic phase

• gastric phase

• intestinal phase

A reflex that slows stomach activity and gastric emptying when the small intestine becomes full or receives acidic chyme.

Enterogastric Reflex

define these functions

• Stomach relaxes and expands to store food.

• Muscular contractions mix food with gastric juices to form chyme.

• Small amounts of chyme are released through the pyloric sphincter into the duodenum.

• Receptive function

• Churning function

• Emptying function

 Describe the functions of the small intestine

• digestion

• absorption of nutrients.

increase surface area and slow movement of chyme

Circular folds (plicae circulares)

fingerlike projections that increase surface area for absorption.

villi

tiny projections on epithelial cells that form the brush border and further increase surface area for absorption and digestion.

Microvilli

migrating motor complexes move residual materials through the intestine.

motility in the small intestine during fasting

segmentation mixes chyme with digestive secretions, and peristalsis moves chyme toward the large intestine.

motility in the small intestine during eating

 Describe the functions of the large intestine

• Absorption of water and electrolytes, formation and storage of feces, and defecation.

discuss the histology of the large intestines.

•  Contains simple columnar epithelium with many goblet cells that secrete mucus; lacks villi.

 Describe the functions of the bacteria within the large intestines.

• Ferment undigested carbohydrates.

• Produce vitamins, especially vitamin K and some B vitamins.

• Help prevent growth of harmful bacteria.

 Describe roles of the proximal and distal portions of the large intestines

• Proximal large intestine: Absorbs water and electrolytes and forms feces.

• Distal large intestine: Stores feces until elimination.

• Includes haustral churning, peristalsis, and mass movements that move feces toward the rectum for defecation.

Motility

Describe the pancreas

• he pancreas is an accessory digestive organ.

• It secretes pancreatic juice into the duodenum.

list pancreas digestive functions.

• Bicarbonate ions to neutralize acidic chyme.

• Digestive enzymes that break down carbohydrates, proteins, fats, and nucleic acids.

Describe liver functions that pertain to digestion

• The liver's major digestive function is the production of bile.

Explain the role of bile

• Bile helps digest fats by breaking large fat globules into smaller droplets.

is the process of breaking large fat droplets into many small droplets, increasing surface area for lipase action.

Emulsification

Describe the other functions of the liver.

• Processes and stores nutrients.

• Stores glycogen, vitamins, and minerals.

• Removes toxins and drugs from the blood.

• Destroys old red blood cells.

• Produces plasma proteins.

• Helps regulate blood glucose levels.

Describe the function of the gallbladder

• the gallbladder stores and concentrates bile.

1. Liver produces bile.

2. Bile enters the right and left hepatic ducts.

3. Hepatic ducts join to form the common hepatic duct.

4. Bile travels through the cystic duct to the gallbladder for storage.

5. When needed, bile leaves the gallbladder through the cystic duct.

6. It enters the common bile duct.

7. It empties into the duodenum of the small intestine.

the pathway of bile to the small intestine.

Explain the two types of digestion

• Mechanical digestion: Physical breakdown of food into smaller pieces (chewing, churning, segmentation).

• Chemical digestion: Breakdown of food molecules by enzymes.

Water is added to nutrient molecules, breaking chemical bonds and producing smaller molecules that can be absorbed.

Enzymatic hydrolysis

Digestion

• Salivary amylase

• Pancreatic amylase

• Brush-border enzymes: maltase, sucrase, lactase

Absorption

• Monosaccharides (glucose, fructose, galactose) are absorbed into blood capillaries.

Carbohydrates

Digestion

• Pepsin (stomach)

• Trypsin

• Chymotrypsin

• Carboxypeptidase

• Aminopeptidase

• Dipeptidase

Absorption

• Amino acids are absorbed into blood capillaries.

Proteins

Digestion

• Lingual lipase

• Gastric lipase

• Pancreatic lipase

• Bile aids digestion by emulsifying fats.

Absorption

• Fatty acids and monoglycerides combine with bile salts to form micelles.

• Lipids enter intestinal cells, become chylomicrons, and move into lymphatic vessels.

Lipids

Digestion

• Pancreatic nucleases

• Nucleosidases

• Phosphatases

Absorption

• Nitrogenous bases, sugars, and phosphate groups are absorbed into the blood.

Nucleic Acids

A small spherical structure made of bile salts that transports fatty acids and monoglycerides to the intestinal epithelium.

Micelle

• Absorbed by osmosis through the intestinal wall.

water

• Sodium, potassium, chloride, calcium, phosphate, and iron are absorbed by diffusion or active transport.

electrolytes

Vitamins A, D, E, and K are absorbed with lipids through micelles and chylomicrons.

Fat-Soluble Vitamins

Vitamins B and C are absorbed by diffusion or active transport directly into the blood.

Water-Soluble Vitamins

what is the quick memory aid for carbs, proteins, lipids, nucleic acids, ADEK

• Carbs → Monosaccharides

• Proteins → Amino acids

• Lipids → Fatty acids + Monoglycerides

• Nucleic acids → Bases + Sugars + Phosphates

• ADEK = Fat-soluble vitamins