Chapter 23 digestive system Herlihy

The four functions of the digestive system:

Ingest food

Digest food

Absorb nutirents

Excrete waste

Digestive tract:

Also called the alimentary canal or the gastrointestinal tract is a hallow tune extending from the mouth to the anus.

Parts of the digestive system:

Mouth

Pharynx

Esophagus

Stomach

Small intestine

Large intestine

Rectum

Anus

Accessory organs

Salivary glands empty their secretions into the:

Mouth

The liver, gallbladder, and pancreas empty their secretions into the:

Small intestine

Digestion:

The process where food is broken down into smaller particles suitable for absorption. Digestion takes place in the digestive tract.

Absorption:

The process where the end-products of digestion move across the walls of the digestive tract into the blood and lymph for distribution throughout the body.

Two types of digestion:

Mechanical and chemical

Mechanical digestion:

The breakdown of large food particles into smaller pieces by physical means. This is usually done by chewing and by mashing actions of the muscles in the digestive tract.

Chemical digestion:

The chemical alteration of food. For example a protein is chemically digested into amino acids. Digestive enzymes, stomach acid and bile accomplish chemical digestion.

Accessory organs of the digestive system include:

Salivary glands

Teeth

Liver

Gallbladder

Pancreas

The wall of the digestive tract has four layers:

Mucosal layer

Submucosal layer

Muscle layer

Serosal layer

The Mucosa layer function:

The innermost layer of the digestive tract

Consists of the mucous membrane, small amount of connective tissue and smooth muscle. The mucosa is concerned with digestion and absorption.

Submucosa:

A thick layer of loose connective tissue, the submucosa lies beneath the mucosa. The submucosa contains blood vessels, nerves, glands and lymphatic vessels.

Muscle layer:

The third layer of the digestive tract. The muscle layer enables the digestive tract to mix mash and move food through the tract; the mixing and mashing are achieved by segmentation while the forward movement of food from mouth to anus is caused by peristalsis.

The function and structure of teeth:

Part of the oral cavity

The purpose of teeth is to chew food and to begin mechanical digestion

Teeth: mastication

The process of chewing

During this process the teeth break down larg pieces of food into smaller pieces. Once moist by the secretions of the mouth the small pieces of food are easily swallowed.

Decisions teeth:

Aka baby teeth

There are usually 20 baby teeth

They start to show up at 6 months

Generally in place by 2 1/2 years old.

Between 6-12 years old these teeth are pushed out and replaced by permanent teeth.

Permanent teeth:

There's usually 32

Three parts of a tooth:

-crown

-neck

-root

The function and structure of the tongue:

The tongue is a muscular organ that occupies the floor of the mouth and serves two major roles in the digestive process.

1. It facilitates chewing and swallowing by continuously repositioning the food in the mouth. As swallowing begins, the tongue pushes the food (which is molded into a ball like mass called a bolus) toward the pharynx.

2. The tongue has taste buds that allows us to taste the food.

Medications are easily absorbed under the tongue because of the rich blood supply.

The three pairs of salivary glands:

Parotid glands

(the largest/and lie below and anterior to the ears)

Sibmandibular glands

(Located on the floor of the mouth)

Sublingual glands

(Located under the tongue/are the smallest of the salivary glands)

These glands secret their content into the mouth.

The Hard and Soft Palates:

Form the roof of your mouth

There's 2(anterior hard palate and posterior soft palate)

Anterior hard palate:

Separates the oral cavity from the nasal passages.

Posterior soft palate:

Separates the oral cavity from the nasopharynx.

Uvula:

Prevents food and water from entering the nasal passages during the act of swallowing.

palatine tonsils:

Are masses of lymphatic tissue located along the sides of the posterior oral cavity.

The three parts of the pharynx:

Nasopharynx (not part of digestive tract)

Oropharynx (part of digestive tract)

Laryngopharynx (part of digestive tract)

The act of swallowing directs food from the pharynx(throat) into the esophagus;a long tube that empties into the stomach.

Structure of the esophagus:

The food tube that carries food from the pharynx to the stomach.

The esophagus is 10inches in length

Descends through the chest cavity and penetrates the diaphragm.

The location and purpose of LES

The les closes the base of the esophagus, thereby preventing reflux or regurgitation of acidic stomach contents back into the esophagus.

The two esophageal sphincters:

Pharyngo esophageal sphincter (Located at the top of the esophagus)

Gastroesophageal/lower esophageal sphincter(Located at the base of the esophagus)

Functions of the stomach:

-mixes the food with gastric juice and mashing it into a paste called CHYME.

-gastric juice has the secretions from the gastric glands: mucus pepsinogen(protease) HCI intrinsic factor and a hormone called gastrin.

-regulates the rate of gastric emptying

-generates peristaltic waves that squeeze the food toward the pylorus.

Parts of the stomach

Fundus

Body

Pylorus

Pyloric sphincter

Lesser curvature

Greater curvature

Rugae

Muscles of the stomach:

Longitudinal

Oblique

Circular

Mixing and mashing chyme

Peristalsis

Stomach structure of the mucosa:

Mucous cells

Parietal cells

(HCI , intrinsic factor)

Chief cells

(Digestive enzymes)

Three small parts of the small intestine:

-duodenum(most of the digestion and absorption happens here)

-jejunum

-ileum

Function of the small intestines:

Digests, absorbs, secretes hormones and digestive enzymes.