Digestive System Functions

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Questions and Answers

What is the primary function of the mouth in the digestive process?

Regulation

Mechanical digestion

Chemical digestion

Ingestion (correct)

What type of muscle contractions move food through the digestive tract?

Involuntary (correct)

Rhythmic

Voluntary

Reflexive

Which process breaks down complex molecules into simpler molecules?

Ingestion

Chemical digestion (correct)

Mechanical digestion

Absorption

What is the main function of the small intestine?

Absorption Signup and view all the answers

Which organ releases bile?

Gallbladder Signup and view all the answers

What is the process of eliminating indigestible substances and waste products from the body?

Defecation Signup and view all the answers

Which of the following is NOT an accessory organ?

Kidneys Signup and view all the answers

What is the process of mixing food with digestive juices in the stomach?

Churning Signup and view all the answers

Which of the following is an example of chemical digestion?

Saliva breaking down carbohydrates Signup and view all the answers

What is the term for the rhythmic contractions of the intestines that mix food with digestive juices?

Segmentation Signup and view all the answers

Which layer of the digestive tract contains epithelium, lamina propria, and muscularis mucosae, and is responsible for secretion, absorption, and protection?

Mucosa Signup and view all the answers

What is the primary function of the muscularis externa?

Peristalsis and segmentation Signup and view all the answers

What is the function of the submucosal plexus?

All of the above Signup and view all the answers

What is the term for the process of chewing food?

Mastication Signup and view all the answers

What is the name of the membrane that covers abdominal organs?

Peritoneum Signup and view all the answers

What is the location of the myenteric plexus?

Between the layers of the muscularis externa Signup and view all the answers

What is the function of the lower esophageal sphincter?

To prevent acid reflux Signup and view all the answers

What is the function of gastric glands in the stomach?

All of the above Signup and view all the answers

What is the term for the wave-like muscle contractions that move food through the digestive tract?

Peristalsis Signup and view all the answers

What is the term for the act of swallowing?

Deglutition Signup and view all the answers

What is the function of pepsinogen?

To begin protein digestion when activated Signup and view all the answers

What is the role of mucus neck cells?

To secrete mucus that protects the stomach lining Signup and view all the answers

What is the function of parietal cells?

To secrete HCl and intrinsic factor Signup and view all the answers

What is the definition of chyme?

A semi-liquid mixture of partially digested food and gastric juices Signup and view all the answers

What is the function of the mucosal barrier?

To protect the stomach lining from self-digestion Signup and view all the answers

What is the function of the small intestine?

To digest and absorb nutrients Signup and view all the answers

What is the function of Peyer's patches?

Immune surveillance and response in the small intestine Signup and view all the answers

What is the function of the large intestine?

To absorb water and electrolytes, and form and store feces Signup and view all the answers

What is the function of the gallbladder?

To store and concentrate bile Signup and view all the answers

What is the function of pancreatic lipase?

To digest fats into fatty acids and glycerol Signup and view all the answers

Study Notes

Functions of the Digestive System

Ingestion: The process of taking in food and liquids through the mouth.
Propulsion: The movement of food through the digestive tract, including swallowing and peristalsis.
Mechanical Digestion: The physical breakdown of food into smaller pieces, including chewing, churning, and segmentation.
Chemical Digestion: The breakdown of complex molecules into simpler molecules by enzymes, which occurs in the mouth, stomach, and small intestine.
Absorption: The process of taking nutrients into the bloodstream or lymphatic system from the digestive tract, primarily in the small intestine.
Defecation: The elimination of indigestible substances and waste products from the body in the form of feces.
Secretion: The release of digestive juices and enzymes by various organs, such as saliva from salivary glands, gastric juice from the stomach, bile from the liver, and pancreatic juice from the pancreas.
Regulation: Coordination of the digestive process through neural and hormonal signals to ensure efficient digestion and nutrient absorption.

Organs of the GI Tract and Their Accessory Organs

GI Tract Organs:
- Mouth
- Pharynx
- Esophagus
- Stomach
- Small intestine (duodenum, jejunum, ileum)
- Large intestine (cecum, colon, rectum, anal canal)
Accessory Organs:
- Salivary glands (parotid, submandibular, sublingual)
- Liver
- Gallbladder
- Pancreas

Layers of the Alimentary Canal

Mucosa: Innermost layer, contains epithelium, lamina propria, and muscularis mucosae. Functions in secretion, absorption, and protection.
Submucosa: Connective tissue layer containing blood vessels, lymphatics, and nerves. Supports the mucosa and allows it to move flexibly during peristalsis.
Muscularis Externa: Layers of smooth muscle (circular and longitudinal). Responsible for peristalsis and segmentation.
Serosa (or Adventitia): Outermost layer. The serosa is the visceral peritoneum, and the adventitia is a connective tissue layer (in regions not covered by the peritoneum).

Mechanical vs. Chemical Digestion

Mechanical Digestion: Physical breakdown of food into smaller pieces, such as chewing, churning, and segmentation.
Chemical Digestion: Breakdown of food by enzymes into simpler molecules that can be absorbed, such as amylase breaking down starch into sugars.

Peristalsis

Definition: A series of wave-like muscle contractions that move food through the digestive tract.
Muscularis contractions move food through the digestive tract.

Myenteric and Submucosal Plexus

Myenteric Plexus: Located between the layers of the muscularis externa, controls gastrointestinal motility.
Submucosal Plexus: Found in the submucosa, regulates enzyme secretion, blood flow, and water and ion transport.

Covering of the Organs in the Abdomen

Peritoneum: Serous membrane covering abdominal organs.
Visceral Peritoneum: Covers the external surfaces of most digestive organs.
Parietal Peritoneum: Lines the body wall.
Small intestine has mesentary that keeps it in place.

Retroperitoneal

Definition: Organs located behind the peritoneum.
Examples: Kidneys, Duodenum, pancreas, ascending colon, and descending colon.

Mastication and Deglutition

Mastication: The process of chewing food, begins the mechanical breakdown of food.
Deglutition: The act of swallowing, voluntary phase, and involuntary phase.

Salivary Glands

Types:
- Parotid glands behind ears
- Submandibular glands under mandible
- Sublingual glands under lingual

Esophagus

Function: Transports food from the pharynx to the stomach using peristalsis.
Anatomy: A muscular tube lined with stratified squamous epithelium, containing the upper and lower esophageal sphincters.

Stomach

Functions:
- Stores food
- Mixes food with gastric juices to form chyme
- Begins protein digestion
- Secretes intrinsic factor for vitamin B12 absorption
- Regulates passage of food into the small intestine
Anatomy:
- Lower Esophageal Sphincter: Prevents acid reflux
- Body: Main part of the stomach
- Fundus: Upper part of the stomach
- Cardia: Area surrounding the opening of the esophagus
- Pylorus: Region leading to the duodenum of small intestine
- Rugae: Folds in the stomach lining that allow expansion
- Pyloric Sphincter: Regulates passage of food from stomach to duodenum

Gastric Juice

Components:
- Hydrochloric Acid (HCl): Lowers pH, kills bacteria, activates pepsin
- Pepsinogen: Inactive form of pepsin, begins protein digestion when activated
- Mucus neck cells secrete mucus, protects stomach lining from acid and digestive enzymes

Parietal Cells and Intrinsic Factor

Parietal Cells: Secrete HCl and intrinsic factor
Intrinsic Factor: Necessary for vitamin B12 absorption in the small intestine, needed for RBC production

Chief Cells

Secrete pepsinogen, which is activated to pepsin by HCl

Chyme

Definition: Semi-liquid mixture of partially digested food and gastric juices

Mucosal Barrier in Stomach

Protects stomach lining from self-digestion by HCl and enzymes

Small Intestine

Regions:
- Duodenum
- Jejunum
- Ileum
Functions:
- Major site of digestion and nutrient absorption
- Absorbs 90% of nutrients

Plica Circulares, Villi, and Microvilli

Increase surface area for nutrient absorption
PLICA: Folds of submucosa
Villi: Folds of mucosa, contains capillaries and lacteals for absorption of nutrients
Microvilli: Folds of cell membrane of mucosa for absorption across the microvilli, increases surface tension

Peyer's Patches

Location: Ileum
Function: Immune surveillance and response in the small intestine

Large Intestine

Functions:
- Absorbs water and electrolytes
- Forms and stores feces
- Houses gut microbiota
Parts:
- Cecum
- Appendix
- Ascending Colon
- Transverse Colon
- Descending Colon
- Sigmoid Colon
- Rectum
- Anal Canal
- Haustra: Pouches of the colon
- Internal and External Anal Sphincter: Control defecation

Accessory Organs of the Digestive System

Salivary Glands
Liver
Gallbladder
Pancreas

Role of Liver in Hepatic Portal Circulation

Processes nutrients and toxins from the digestive tract
Receives nutrient-rich blood from the digestive organs via the hepatic portal vein
Processes blood, filtering out toxins and storing nutrients, before releasing purified blood into the general circulation through the hepatic veins

Bile and Fat Digestion

Bile: Produced by the liver, stored in the gallbladder, emulsifies fats in the small intestine

Gallbladder

Stores and concentrates bile, releases it into the small intestine

Pancreas as Endocrine and Exocrine Gland

Endocrine: Secretes insulin and glucagon
Exocrine: Produces digestive enzymes and buffers (bicarbonate) to neutralize stomach acid

Pancreatic Secretions

Digestive Enzymes: Break down proteins, fats, and carbohydrates
Bicarbonate: Neutralizes stomach acid

Functions of Digestive Enzymes

Salivary and Pancreatic Amylase: Break down starch into sugars
Lingual, Gastric, and Pancreatic Lipase: Break down lipids
Pepsin: Breaks down proteins into smaller peptides
Nucleases: Break down nucleic acids (DNA and RNA) into nucleotides

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Test your knowledge of the digestive process, from the mouth to the small intestine, and the functions of different organs and muscles.