Anat - Unit 6

Digestion (Mechanical vs Chemical)

Mechanical - breaks food down physically (chewing, mixing)

Chemical - enzymes break large nutrient molecules (proteins, lipids, carbohydrates) into smaller ones

Absorption of digestive system

Movement of end product (nutrients) move from lumen of alimentary canal (GI tract) to blood/lymphatic system

Propulsion (motility) + Peristalsis

Propulsion - Movement of ingested food through the alimentary canal (RESULT OF PERISTALSIS)

Peristalsis - wave-like movement to push the food forward (THE PROCESS)

Secretion of digestive fluids

GI tract & accessory glands (salivary glands, pancreas, liver) secret digestive fluids

Label the layers of GI tract

Peritoneum (serous membrane)

Visceral Peritoneum - covers many abdominal organs

Parietal Peritoneum - lines walls of cavity (abdomen)

Peritoneal cavity - space between layers, contains little serous fluid (reduces friction)

Peritoneal Fold - Anatomy and Physiology (Part 1)

1. Two fused layers of serous membrane

2. Supports:

• Organ nerves

• Blood vessels

• Lymphatic vessels

3. Extends from posterior abdominal wall to:

• Liver

• Stomach

• Spleen

• Most of small intestine

• Transverse colon

Types of Peritoneum Folds & function (Part 2)

1. Greater Omentum:

• gives insulation, storage for energy (fat, adipose)

2. Mesentery:

• supports sm intestines (holds in place)

3. Mesocolon:

• supports lg intestines (colon= large)

4. Lesser Omentum:

• supports stomach (smaller, pathway for hep.portal veins)

Major Divisions: Alimentary Canal vs Accessory Glands

Alimentary Canal - Digestive tract/ GI tract

• pathway from oral to anal opening

Accessory Glands - everything else of GI tract

• Chemical digestion helpers, no direct food contact

Mouth - Oral Cavity (Anatomy and Physiology)

Formed by: cheeks, tongue, hard & soft palate

Orbiculares oris in lips (changes shape for speech, closed mouth)

Buccinator mm in cheeks

Lined with stratified squamous epithelium (mucous membrane) for food

Oral Cavity - Label the Diagram

Salivary Glands - label the Diagram

Saliva (Anatomy & Physiology)

Secreted from small glands in oral mucosa

1000 - 1500 ml secreted/day (most from the “big 3”)

Cleanses, moistens mouth & pharynx

Saliva Composition

•water - dissolves food, facilitates taste

•mucus - lubricates food

•urea, uric acid - metabolic wastes

•Ab’s - inhibits bacterial growth

•lysozyme - kills bacteria

•salivary amylase - acts on starch → carbohydrates

•lingual lipase - acts on triglycerides

Salivation Control - stimulation & inhabitation

Stimulated by: sight, smell, sound, memory of food, mechanical stimulation

Inhibited (reduced) by: fear, anxiety (SNS)

Tongue (General Anatomy)

• Skeletal muscle

• Covered with mucous membrane

• Contains taste buds on surface

• Has papillae

Tongue (extrinsic muscle)

Attach to:

• Hyoid

• Mandible

• Hard palate

• Styloid process

Function:

• Move tongue:

  • In/out

  • Side-to-side

• Help chewing and swallowing

Tongue (Intrinsic muscle)

• Located within tongue (originate and insert to CT)

• Function:

  • Change shape and size

  • Aid speech and swallowing

Digestion in mouth (in dept)

• Mechanical digestion:

  • Mastication (breaksdown food)

  • Mixes with saliva to form bolus

• Chemical digestion: (breakdowns)

  • Salivary amylase → starch digestion (carbs)

  • Lingual lipase → triglycerides (fats)

Deglutition - name the 3 phases

Beginning of the end of voluntary portion of digestive system.

Three phases:

• Voluntary

• Pharyngeal (involuntary)

• Esophageal

Voluntary phase

Tongue pushes bolus to back of oral cavity (anterior to posterior)

Pharyngeal Phase

• Bolus stimulates receptors in oropharynx

• Signals to deglutition centre in brainstem

• Uvula & soft palate blocks nasopharynx

• Vocal cords close

• Epiglottis blocks glottis (vocals closed)

Esophageal phase - Start

• Upper esophageal sphincter relaxes

• Bolus enters esophagus (No more voluntary control)

Esophageal phase - End

• Lower esophageal/cardiac sphincter relaxes (prevents stomach acid from jumping to esophagus)

• Bolus enters stomach

Esophagus

• Moves ingested food by peristalsis

• From pharynx → thoracic cavity → stomach

Histology of Esophagus

• Mucosa

• Submucosa

• Muscularis:

  • Upper = skeletal

  • Lower = smooth

• Sphincters at both ends

• Adventitia

Stomach (Anatomy)

• J-shaped sac

• About 1.5 L capacity

• Located in left upper quadrant of abdominal cavity

• Inferior to diaphragm

• Anterior to pancreas

Label the stomach

Label the stomach (curvatures and sphincters)

Label the muscularis and its function

Gastric secretions

• Mucus:

  • Protects underlying tissue

• Pepsinogen:

  • Inactive protease (enzyme)

• Hydrochloric acid (HCl):

  • Activates pepsinogen → (converts to) pepsin

• Together = gastric juice

Gastric Physiology - Mechanical Digestion Process

• Bolus enters stomach

• Gentle mixing waves every 15–25 seconds

• Bolus + gastric juice → chyme (watery, acidic)

• More vigorous waves in body

• Intensify near pyloric part

• Few waves in fundus

• Each contraction:

  • Pushes 1–2 mL chyme to duodenum