anatomy test 4 part I digestive

What are the general functions of the digestive system? 

Ingestion, Motility, Digestion, Absorption, Elimination, and Secretion

Ingestion

Introduction of solid and liquid nutrients into the oral cavity

• First step in process of digesting and

absorbing nutrients

Motility

Voluntary and involuntary muscular contractions

• Mixes and moves materials through the GI tract

Secretion

Process of producing and releasing fluid products facilitating digestion

• e.g., digestive enzymes, acid, bile

Digestion

Breakdown of ingested food into smaller structures

Absorption

Transport of digested molecules, electrolytes, vitamins, water

• Move from GI tract into blood or lymph

Elimination (Defecation)

Expulsion of indigestible components that are not absorbed

What are the 4 layers of the digestive tract? 

Mucosa, Submucosa, Muscularis, and Serosa/adventitia

Mucosa

the deepest layer of the digestive tract.

• touches food

Submucosa

This is the second layer of the digestive tract.

• support layer

Vascular connective tissue (many blood & lymphatic vessels)

Muscularis externa

Responsible for motility (peristalsis/segmentation).

Peristalsis

Alternating contraction sequence of inner and outer layers propelling ingested materials through the tract

Mixing (Segmentation)

“back-and-forward” motion that lacks directional movement blends ingested materials with secretions

What are the 2 layers of Muscularis externa?

Inner circular and Outer longitudinal

Inner circular muscle layer:

smooth muscle wrapped around the GI tract; contracts to constrict/narrow the lumen.

Outer longitudinal muscle layer:

smooth muscle running lengthwise; contracts to shorten the tube.

SEROSA/ADVENTITIA

The outermost layer of the digestive tract.

• Serosa = visceral peritoneum (covers organs in the abdominal cavity)

• Adventitia = connective tissue that anchors organs (ex, esophagus)

Why do we have 2 distinct types of muscle in the muscularis? 

circular + longitudinal

• The GI tract can create different types of movement to push and mix food.

Peritoneum

the double-layered membrane that lines the abdominopelvic cavity and suspends abdominopelvic organs.

Circular muscle

contracts to squeeze/narrow the lumen, pushing and mixing food.

Longitudinal muscle

• contracts to shorten the tube, helping move the bolus forward.

What other organs participate, but are not a direct part of the tract? 

• Salivary glands, Liver, Gallbladder, and Pancreas

What are the sections (folds) of the peritoneum?

Falciform ligament, Greater omentum, Lesser omentum, Mesentery, and Mesocolon

falciform ligament

attaches the liver to the anterior abdominal wall

greater omentum

is the largest peritoneal fold

• fatty apron

lesser omentum

suspends the duodenum and stomach from the liver

mesentary

attaches the small intestine to the posterior wall.

mesocolon

attaches the large intestine to the posterior wall.

Where are the peritoneum folds attached?

abdominal organs to each other and/or to the abdominal wall

What purpose does the upper esophageal sphincter serve? 

• Purpose: prevents air from entering the esophagus + prevents reflux back into the throat

• Control: mixed (mostly voluntary when swallowing, otherwise involuntary tone) 

What purpose does the lower esophageal sphincter serve? 

• Purpose: prevents stomach acid from refluxing into the esophagus

• Control: involuntary

What purpose does the pyloric sphincter serve? 

Purpose: controls the movement of chyme from the stomach → duodenum

Control: involuntary

Salivary glands:

add saliva to the mouth

Liver:

 produces bile

Gallbladder:

 stores and concentrates bile

Pancreas:

releases digestive enzymes + bicarbonate into the small intestine 

What are the three phases of swallowing?

Buccal Phase (voluntary), Pharyngeal Phase (involuntary), and Esophageal Phase (involuntary)

Buccal Phase (voluntary)

• Food is in the mouth

• tongue pushes the bolus toward the pharynx

2. Pharyngeal Phase (involuntary)

• Food is in the pharynx (throat)

• The epiglottis closes the airway to prevent choking

Esophageal Phase (involuntary)

• Food is in the esophagus

• Peristalsis pushes the bolus to the stomach

What purpose does saliva serve? 

moistens food for swallowing, begins chemical digestion, cleans the mouth and protects teeth, and helps taste (dissolves chemicals)

What is saliva composed of?

 salivary amylase (digests starch)

lysozyme (kills bacteria)

What purpose does Bile serve?

emulsifies fats (breaks fat into small droplets)

Makes fat digestion easier for enzymes

What breaks down sugars/proteins/fats in the digestive tract?

Carbohydrates (sugars/starch), Proteins: pepsin (stomach), and Fats: bile emulsifies fat (small intestine)

What is the cephalic phase of digestion (before food enters the stomach)?  

Purpose: prepares the stomach for food (gets digestion ready)

Signals: sight, smell, taste, thought of food

What happens: the brain stimulates the stomach to release acid and enzymes

What is the gastric phase (food in the stomach)?

• Purpose: boosts stomach digestion and mixing

• Signals: stomach stretching + presence of proteins

What happens: stomach releases more HCl and enzymes + stronger churning

What is the intestinal phase (food in the small intestine)? 

Purpose: regulates digestion in the small intestine and slows the stomach down

Signals: chyme entering the duodenum (especially acidic or fatty chyme)

What happens: hormones are released to slow gastric emptying and stimulate the pancreas/liver

Which phase of digestion opposes the others? 

Intestinal phase (it slows the stomach down to protect the small intestine)

What do mucous cells do? 

• Secretes mucus + bicarbonate

• protects the stomach lining from acid 

What do chief cells do?

Secretes pepsinogen, which becomes pepsin (digests proteins)

What do parietal cells do? 

• secrete HCl (stomach acid)

• secreted intrinsic factor (needed for vitamin B12 absorption) 

What do enteroendocrine cells (ex, G cells) do? 

Release hormones like gastrin,

which stimulate acid secretion and stomach activity

o Are the epithelial cells responsible for exocrine release? 

No

• What are the numerous ways the small intestines expand surface area?

Circular folds (plicae circulares)

Villi (fingerlike projections)

Microvilli (tiny projections on epithelial cells = brush border)