The Digestive System Chapter 23
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