The Digestive System BIO 117... · Digestive System • Alimentary canal or Gastrointestinal (GI) tract: continuous tube, mouth anus • Key structures of the Alimentary Canal: mouth,

The Digestive System

Chapter 23

Learning Objectives

• Describe the alimentary canal• Functions of alimentary canal• Digestive pathway!• Sphincters• Major Accessory Organs and

their functions• Digestion v Absorption

Overview

• Digestive system deals with food, water, drugs, etc.

• Breaks down food (digestion) and absorbs the nutrients (absorption) and water in specific areas of GI tract

• Eliminates waste (non-digestible)• Accessory organs help break down

food mechanically and chemically

Digestive System

• Alimentary canal or Gastrointestinal (GI) tract: continuous tube, mouth anus

• Key structures of the Alimentary Canal: mouth, pharynx (3 parts), esophagus, stomach, small and large intestine, rectum, and anus

• Digestion: process by which food is broken down into smaller molecules for absorption

• Absorption: bringing the small molecules from the GI tract into the blood

• *Digestion and absorption happen in key areas along the way*

Digestive System

Alimentary CanalAccessory Organs

• Salivary glands

• Teeth• Liver• Gallbladder• Pancreas

Layers to Alimentary CanalLayers to the Alimentary Canal:• Mucosa (Innermost)• Submucosa• Muscular, “peristalsis”

– rhythmic muscle movements

• Serosa (Outermost)Innervation? • Parasympathetic “Rest

and Digest”

Draw it Out!

• Doodle our Digestive Pathway in your notes as we go• Pay attention to: • Enzymes• Absorption, Digestion, or both• Where will food go next?• Different names for food

depending on the area where its found!

The Oral Cavity (Mouth)

Contains:• Teeth: mechanical

digestion – 20 deciduous teeth, – 32 permanent teeth– incisors, cuspids,

premolars, molars

• Tongue: – forms a bolus – contains taste buds

• Salivary glands

Salivary Glands3 pairs of salivary glands:1. Parotid – anterior to

ears2. Submandibular –

located below the mandible

3. Sublingual – located below the tongue

Secretes saliva, contains Salivary Amylase, which digests carbohydrates

The Pharynx (Throat)

Divided into 3 regions1. Nasopharynx:

“nasal part”2. Oropharynx: “oral

part”3. Laryngopharynx:

“near the Larynx” Which parts of the pharynx receives food? Air?

Swallowing

The Esophagus

• 10 inch muscular tube

• Connects pharynx to the stomach

• Transports food– Peristalsis – voluntary or

involuntary?

• No digestion or absorption—Just transportation

The Stomach• “Pouch-like organ”• Turns food into

chyme• Regions of the

Stomach:a)Fundusb)Bodyc)Pylorus • Does Mechanical and

Chemical digestion– Churning and mixing

movements

The Stomach

Stomach secretions:1.Mucus2.Hydrochloric

Acid3.Pepsin4.Intrinsic Factor

The Small Intestine

Connects stomach to the large intestine3 regions:1. Duodenum2. Jejunum3. Ileum• “Dow Jones

Industrial”• “Don’t Judge It”

The Small Intestine1. Duodenum:– Absorption and

Digestion– receives chyme -

digests carbs, proteins, and fats

2. Jejunum: – Absorption Either

into bloodstream or lymphatic system

3. Ileum: – immune function

The Large IntestineMultiple segments:

1.Cecum: – has appendix

2.Ascending colon:– “going up”

3.Transverse colon: – “going across”

4.Descending colon:– “going down”

5.Sigmoid colon: – S-shaped

6.Rectum: – stores feces, passes

through anus

Sphincters

• Muscle that “guards” opening of tube• 6 sphincters• 5 are made of smooth

muscle• 1 is made of skeletal muscle

Sphincters1. UES: between pharynx and esophagus2. LES: between esophagus and stomach3. Pyloric: between the stomach and small

intestine4. Ileocecal Valve: between the small

intestine and large intestine5. Internal Anal Sphincter: between rectum

and anus = smooth muscle!6. External Anal Sphincter: between rectum

and anus = skeletal muscle (means what?)

PRACTICE

Labelling

Major Accessory Organs

Chapter 23

The LiverFunctions:1. Produce bilirubin and

bile2. Converts ammonia to

urea. 3. Make plasma proteins4. Detox5. Glycogen6. Metabolism of carbs,

proteins, and fats• Location• Blood supplies?

The Gallbladder• Location• Stores and releases bile into the

duodenum• What does bile do?a)Emulsify fats (think washing

dishes)b)This helps another enzyme digest

the fat

The PancreasBoth exocrine and endocrine glands!• Releases the following into

the duodenum:1.Bicarb: neutralize chyme

coming from stomach2.Pancreatic Lipase: “fats”3.Pancreatic Amylase:

“carbs”4.Proteases: “proteins”

Recap

• We digest: carbs, proteins, and fats. Remember where?

A.Oral cavityB.The StomachC.The Small

Intestine

Final Digestion and Absorption

Make the small molecules even smaller• Table 23-1• Absorption happens

in the duodenum and jejunum

• Absorb monosaccharaides, amino acids, and fatty acids where?

Group Activity