Ch 26 Learning Objectives

Digestive System

26.1.1 List the organs that make up the gastrointestinal (GI) tract.

GI tract:

• oral cavity, pharynx, esophagus, stomach, small intestine, large intestine, anal canal

Accessory organs:

• teeth, tongue, salivary glands, liver, gallbladder, pancreas

26.1.2 List the accessory digestive organs and structures involved in the digestive process.

Accessory organs:

• teeth, tongue, salivary glands, liver, gallbladder, pancreas

26.1.3 List and describe the six general functions of the digestive system.

Ingestion: introduction of solid and liquid nutrients in oral cavity

• first step of digesting & absorbing nutrients

motility: general term for voluntary (skeletal muscle) & involuntary (smooth muscle) muscular contractions

• for mixing & moving materials through GI tract

secretion: process of producing & releasing substances that facilitate digestion & movement of contents of GI

• secretions produced by accessory digestive glands

digestion: breakdown of food into smaller components

• mechanical digestion: breaking down of ingested material into smaller pieces without changing chemical structure

• chemical digestion: involves activity of specific enzymes to break down molecules into smaller molecules to be absorbed

absorption: membrane transport of digested molecules, minerals, vitamins, & water across epithelial lining of GI tract into blood/lymph

• primarily occurs in small intestine

elimination: getting rid of indigestible components through anal canal

26.1.4 List and describe the four tunics (layers) that make up the gastrointestinal wall.

mucosa: innermost layer

• protects GI tract, secretes mucus & digestive substances, absorbs nutrients

submucosa: contains blood vessels, lymphatic vessels, nerves, & connective tissue

• supports & nourishes mucosa

muscularis externa: contains smooth muscle layers that mix & move food through digestive tract

serosa: outermost protective layer

• reduces friction between organs & surrounding tissues

memory trick: M-S-M-S

26.1.5 Briefly explain the process of absorption.

absorption: moving digested nutrients from GI tract into blood/lymph

• occurs in small intestine

• sugars & amino acids enter blood capillaries

• most fats enter lymphatic vessels (lacteals)

• water & electrolytes are also absorbed

26.1.6 Distinguish the action of the muscularis mucosae of the mucosal tunic from that of the muscularis tunic.

muscularis mucosae: creates small, local movements of mucosa to help with secretion & absorption

muscularis externa: produces larger movements that mix & push food through GI tract

Muscularis mucosae = moves the inner lining.

Muscularis externa = moves and mixes the food.

26.1.7 Describe the general function of the enteric nervous system and autonomic nervous system in the regulation of the digestive system.

enteric nervous system: digestive tract’s own nervous system

• controls digestive activities, segmentation, & secretion

autonomic nervous system: controls digestion through sympathetic & parasympathetic divisions

• parasympathetic: stimulates digestion by increasing movement & secretions

• sympathetic: slows digestion by decreasing movement & secretion

Overall: The ENS controls local digestive functions, while the ANS adjusts digestive activity based on the body's needs.

26.1.8 Compare short reflexes and long reflexes that regulate the digestive system.

short reflexes: controlled entirely by ENS

• dont involve brain or spinal cord

• respond to changes within digestive tract (stretching/chem)

long reflexes: involve CNS (brain & spinal cord)

• signals travel through ANS

• can be trigged by food sights, smells, tastes, or stomach stretching

26.1.9 Describe the general function of hormones that regulate the processes of digestion.

Stomach hormones

• gastrin: stimulates stomach acid secretion & stomach activity

• somatostatin: inhibits release of gastrin & inhibits release of acidic secretions

small intestine hormones

• Cholecystokinin (CCK): stimulates pancreatic enzyme release & gallbladder contraction to release bile

• secretin: stimulates bicarbonate release from pancreas to neutralize stomach acid

• glucose dependent insulinotropic peptide (GIP): regulates release of insulin from beta cells

26.1.10 Describe the structure of the serous membranes associated with the GI tract.

peritoneum: serous membrane associated with abdominopelvic cavity

parietal peritoneum: lines inner surface of abdominal wall

visceral peritoneum: lines surface of internal organs within abdominal cavity

26.1.11 Distinguish between intraperitoneal and retroperitoneal organs.

intraperitoneal organs: almost completely covered by visceral peritoneum & usually suspended by mesenteries

• more mobile

• stomach, liver, spleen, jejunum, ileum, & transverse colon

retroperitoneal organs: located behind the parietal peritoneum, against posterior abdominal wall

• covered by peritoneum on their anterior surface

• kidneys, pancreas, duodenum, & ascending/descending colon

26.1.12 Explain the function of the mesentery, and describe the five individual mesenteries of the abdominopelvic cavity.

mesenteries: double layers of peritoneum that supports & stabilizes digestive organs from posterior abdominal wall

• colds organs in place while allowing for movement

• provides pathways for blood vessels, lymphatic vessels, & nerves

• store fat & provides cushioning

greater omentum: large, fatty apron that hangs over intestines, protects organs & stores fat

lesser omentum: connects liver to lesser curvature of stomach & the first part of the duodenum

falciform ligament: attaches liver to the anterior abdominal wall & diaphragm

mesentary proper: anchors jejunum & ileum (small intestine) to the posterior abdominal wall

mesocolon: anchors portions of large intestine to posterior abdominal wall

26.2.13 Describe the components of the upper gastrointestinal tract and associated accessory digestive structures.

oral cavity & salivary glands: mechical digestion begins in oral cavity

• saliva is secreted & mixed with food to create a wet mass (bolus)

pharynx: bolus is moved into pharynx during swallowing

• mucus is secreted in saliva provides lubrication for swallowing

esophagus: bolus is transported from pharynx through esophagus into stomach

• mucus secreted by esophagus lubricates

stomach: bolus is mixed with gastric secretions as stomach muscles contract

• stomach releases digestive enzymes, HCI (hydrochloric acid), & mucin

• mixing continues as chyme is formed (acidic semifluid)

26.2.14 Identify and describe the anatomic structures of the oral cavity.

Lips: helps hold in food in mouth/assist in speech

cheeks: forms lateral walls of oral cavity & keeps food between teeth

vestibule: space between lips/cheeks & teeth/gums

oral cavity: space inside teeth

hard palate: bony anterior of roof of mouth; separates oral & nasal cavities

soft palate: muscular posterior roof; closes off nasopharynx during swallowing

uvula: small projection hanging from soft palate

tongue: skeletal muscle that moves food, assists in swallowing & contains taste buds

teeth: breaks food into smaller peices through mechanical digestion

salivary glands: produces saliva to moisten food & begin chem digestion

26.2.15 Explain how the release of saliva is regulated.

release of saliva is controlled by autonomic nervous system through salivary reflexes

26.2.16 Describe the process of mastication.

mechanical process of breaking food into smaller pieces

Food enters the mouth: The lips and cheeks help keep food inside.

Teeth break down food: Incisors cut, canines tear, and premolars/molars crush and grind.

Tongue moves food: The tongue positions food between the teeth for chewing.

Saliva mixes with food: Moistens food and begins chemical digestion.

Bolus forms: Food combines with saliva into a soft, rounded mass called a bolus.

Swallowing begins: The tongue pushes the bolus toward the pharynx.

26.2.17 Explain the growth and development of the teeth.

known as dentition,

deciduous teeth: 20, erupt between 6-30 months after birht

• are eventually lost

permanent teeth: 32,

incisors: in the front, made for slicing/cutting

canines: tearing food

premolars: crush/grind

molars: thickest, large, broad, for crushing/crinding

26.2.18 Describe the anatomy of the pharynx and esophagus and their complementary activities in the process of swallowing.

both work together to move food from mouth to stomach

Nasopharynx Upper region behind the nasal cavity; carries air only.

Oropharynx Middle region behind the oral cavity; carries both food and air.

Laryngopharynx Lower region; directs food toward the esophagus and air toward the larynx.

esophagus: connects pharynx to stomach

Upper esophageal sphincter (UES): Controls the passage of food from the pharynx into the esophagus.

Lower esophageal sphincter (LES): Controls the passage of food into the stomach and helps prevent stomach acid from flowing backward.

Muscular walls: Produce contractions that push food toward the stomach.

Stages of swallowing

Oral phase (voluntary) The tongue pushes the bolus toward the back of the mouth and into the pharynx.

2. Pharyngeal phase (involuntary) The soft palate closes the nasopharynx, the epiglottis helps protect the airway, and muscles push the bolus into the esophagus. Breathing temporarily stops.

3. Esophageal phase (involuntary) Peristalsis moves the bolus down the esophagus. The LES relaxes, allowing food to enter the stomach.

26.2.19 Identify and describe the gross anatomy and histology of the stomach.

26.2.20 Explain the two general functional activities of the stomach.

26.2.21 Describe the phases that regulate motility and secretion in the stomach.

26.3.22 Describe the three components of the lower gastrointestinal tract and the associated accessory digestive organs

26.3.23 Identify and describe the anatomy of the small intestine.

26.3.24 List the glands found in the small intestine and their secretions.

26.3.25 Explain motility within the small intestine.

26.3.26 List the accessory digestive organs associated with releasing secretions into the duodenum, and describe the ducts that deliver these secretions.

26.3.27 Identify and describe the liver, and explain how both blood and bile flow through the liver.

26.3.28 Identify and describe the pancreas, and explain its general function in digestion.

26.3.29 Explain the regulation of the accessory digestive glands associated with the small intestine.

26.3.30 Identify and describe the three major regions of the large intestine and four segments of the colon of the large intestine.

26.3.31 Explain the distinguishing histologic features of the large intestine.

26.3.32 Describe the bacterial action that takes place in the large intestine.

26.4.33 Name the three classes of carbohydrates.

26.4.34 Explain the processing in the oral cavity that initiates carbohydrate digestion and how it is completed in the small intestine.

26.4.35 Explain why the proteolytic enzymes of the stomach and pancreas are synthesized in inactive forms.

26.4.36 Describe the activation and role of pepsin in the initiation of protein digestion in the stomach.

26.4.37 Describe the activation of proteolytic enzymes and the chemical digestion of proteins that occurs in the small intestine.

26.4.38 Explain the role of bile salts in the mechanical digestion of lipids and the role of pancreatic lipase in the chemical digestion of triglycerides.

26.4.39 Discuss the process by which lipids are absorbed.

26.4.40 Describe the digestion of nucleic acids.

26.4.41 Describe the absorption of water, electrolytes, and vitamins.

26.4.42 Explain the details of vitamin B12 absorption.