Unit 3 - Digestive System Functional Anatomy

darl swartz

I. Functional Anatomy Pt. 1

Alimentary canal is tube through body from mouth to anus

• Lip

• Oral Cavity

• Oropharynx

• Laryngopharynx

• Esophagus

• Stomach

• Small intestines

• Large intestines

• Anus

Accessory digestive organ secrete substances into the canal

• Salivary glands

• Pancreas

• Liver

• Gallbladder

I. Functional Anatomy Pt 2

The purpose of alimentary canal and accessory digestive organs is to convert food into nutrients for absorption and transfer via the cardiovascular system for use and storage

I. Functional Anatomy Pt 3

There are several steps that occur along the alimentary canal

• Ingestion → mouth (lips, teeth, oral cavity)

• Mechanical Breakdown → oral cavity (chewing) and stomach (churning)

• Propulsion → swallowing; peristalsis (moves food from mouth to anus)

• Digestion → The stomach and small intestine break down macromolecules

• Absorption → small intestine (main site), large intestine (water and ions)

• Defecation → removal of indigestible waste (feces) via the anus

I. Functional Anatomy Pt 4

Digestive organs are located in the head, neck, thorax, and abdominopelvic cavity

• Head/neck: oral cavity → esophagus

• Thorax: esophagus (through mediastinum)

• Abdominopelvic cavity: stomach, liver, pancreas, intestines

I. Functional Anatomy Pt 5

Abdominopelvic organs suspended in/adjacent to peritoneum membrane

• Peritoneum = serous membrane

  • Parietal: lines the abdominopelvic wall

  • Visceral: covers organs

  • Peritoneal cavity: fluid-filled space between the two

• Serous membranes folded to form double layer called mesentery (folded peritoneum) with several functions

  • Functions: Anchors organs to wall, carries vessels/nerves, and stores fat

• Mesentery attaches to abdominal wall

  • Dorsal Attachment: most organs

  • Ventral Attachment: liver and stomach

• Most organs are within mesentery while others are not

  • WITH MESENTERY

    • Intraperitoneal: fully enclosed (most organs)

  • WITHOUT MESENTERY (covered only on one side by serous membrane)

    • Retroperitoneal: behind peritoneum (e.g. pancreas, duodenum, part of large intestine)

• Infection of peritoneum = peritonitis

II. Four layers of the Alimentary Canal

Alimentary canal made of four laters with sublayers, each containing different levels of each tissue type.

1. Mucosa

   • Epithelium

     • Stratified squamous = protection (e.g. esophagus)

     • Simple columnar = secretion/absorption (e.g., intestines)

   • Lamina propria

     • loose CT (fibroblast, collagen fibrils)

     • immune cells

     • capillaries (fenestrated blood, lymphatic)

   • Muscularis mucosa

     • thin smooth muscle layer and orthogonal layers (circular + longitudinal)

2. Submucosa

   • Loose CT (fibroblast, immune cells, collagen fibers, elastin fibers)

   • Rich in blood vessels, lymphatics, submucosal plexus

   • Nerve plexi (Meisner’s)

   • Seromucous glands

3. Muscularis externa

   • Inner circular muscle layer

   • Outer longitudinal muscle layer

   • Myenteric plexus (Auerbach’s) in between

4. Serosa/Adventitia

   • Serosa = visceral peritoneum (in abdominal cavity)

   • Adventitia = CT layer (outside peritoneum like esophagus)

III. Motor Control of Digestive Tract Pt. 1

Motor responses invovle muscle and secretion

Muscles motor responses mediated mostly by smooth muscles throughout alimentary canal EXCEPT AT THE ENDS

• Skeletal muscle (voluntary):

  • oral cavity, upper esophagus, anus

• Smooth muscle (involuntary):

  • lower esophagus to rectum

  • moves food via peristalsis (waves) and segmentation (mixing)

III. Motor Control of Digestive Tract Pt. 2

Control Systems

• Intrinsic control: Enteric Nervous System (like “gut brain”)

  • Short reflexes

• Extrinsic control: Autonomic system CNS (brain and spinal cord)

  • Long reflexes (involve vagus nerve, sympathetic/parasympathetic)

III. Motor Control of Digestive Tract Pt. 3

Organized as two or more sheets/fascicles around the lumen to mix and move digesta

1. Orthogonal (90 degrees) layers

   • Circular layer that shortens to decrease diameter of the tube

   • Longitudinal layer that shortens to decrease the length of the tube

2. Peristalsis moves digesta along the tube

   • Coordinated waves of circular and longitudinal muslces shortening

   • Wave of circular layer contraction to form valve/pinch off tube

   • Wave of longitudinal shortening to move digesta along tube

3. Segmentation mixes the digesta within a region of the tube

   • Circular layers in different regions shorten to form segments

   • DIFFERENT REGIONS AT DIFFERENT TIMES

III. Motor Control of Digestive Tract Pt. 4

Control of the smooth muscle along the alimentary canal involves the enteric nervous system

1. Enteric nervous system intrinsically controls motor activity

   • Akin to intrinsic control system of heart and lung

   • Can be overridden by autonomic system

2. Has ganglia and nerve plexi (meshwork) within the walls

   • Ganglia contain pace-maker-like cells

   • Neurons and fibers within submucosa = submucosal/Meissner’s plexi

   • Neurons and fiber between the muscularis externi layers = myenteric/Auerbach’s plexi

3. Contains sensory nerves within the wall and exposed to the lumen

   • Chemoreceptors in epithelium and lamina propria of mucosa

   • Mechanoreceptors in wall

III. Motor Control of Digestive Tract Pt. 5

4. Motor control involves short and long reflexes

   • Short reflexes mediated by enteric plexi along the tube

   • Control segmentation and peristalsis within regions of the canal (e.g, esophagus → stomach → small intestines → large intestines)

   • Long reflexes mediated by CNS with sensory input from enteric sensory nerves and CNS motor output to enteric motor nerves

     • Parasympathetic INCREASE activity

     • Sympathetic DECREASE activity

5. Receives input from the autonomic system to over-ride or modulate activity.

III. Motor Control of Digestive Tract Pt. 5

Sensory receptors

• Chemoreceptors detect pH, nutrients

• Mechanoreceptors detect stretch

• Stimuli trigger motor output to glands and muscles

IV. Oral Cavity Pt 1

Boundaries

• Anterior: lips

• Posterior: oropharynx

• Superior: hard/soft palate

• Inferior: tongue

• Lateral: cheeks

IV. Oral Cavity Pt 2

Epithelium

• Stratified squamous (keratinized in high friction areas like tongue and gums)

IV. Oral Cavity Pt 3

Lips/Cheeks

• Skeletal muscles move food

• Skeletal muscles: orbicularis oris (lips), buccinator (cheeks)

• Forms the oral vestibule (space between teeth and cheeks; puches for food)

Palate

• Roof of mouth to facilitate mastication (chewing)

• Hard palate: bone (palatine + maxilla)

• Soft palate: skeletal muscle

  • Closes nasopharynx when swallowing

  • Uvula hangs from it

  • Arches: palatoglosssal (anterior), palatopharyngeal (posterior)

• Oropharynx (throat) is the posterior-most and delimited by palatopharyngeal arches

IV. Oral Cavity Pt 4

Tongue

• Interlacing skeletal muscles giving a wide range of movement

• Intrinsic muscles are NOT attached to the skeletal structures and within the tongue proper.

  • Changes shape and rigidity NOT position

• Extrinsic muscles are attached to (origins) to bone

  • It moves the tongue during chewing and speech

  • Mandible, hyoid, and styloid process for named glossus muscles

• Anchored by lingual frenulum to floor of mouth

• Papillae cover the tongue for friction to move food about and house taste buds

  • Filiform - are most abundant and lack taste buds

  • Fungiform - scattered about and contain apical taste buds

  • Foliate - lateral; taste buds on side

  • Circumvalalate - large; posterior tongue; taste buds on side

• Posterior = no papillae; has lingual tonsils

IV. Oral Cavity Pt 5

Teeth

• Made of bone-like material and anchored into tooth socket by CT

• Tooth matrix (mineralized tissue) layers:

  • Outermost Crown Enamel

    • Acellular, hardest, made during development and maintained by salivary secretions upon eruption

  • Root outermost Cementum

    • Cellular, very bone-like but lacks vasculature (Havesian and Volkman’s canals)

  • Crown and Root Innermost Dentin

    • Cellular, with processes

    • More resilient/flexible than enamel

    • Maintained throughout life by odontoblasts

• Crown = Exposed Portion

• Neck = Region of crown covered by gums

• Gingival sulcus = space b/w base of crown and gum down to cementoenamel junction

• Gingival = gums

• Internal pulp: blood vessels and nerves

• Periodontal ligament anchors tooth to socket

• Dental formulas:

  • Primary (deciduous): 20 total (4 incisors, 2 canines, 4 molars per jaw)

  • Permanent: 32 total (add premolars + extra molars)

V. Salivary Glands

A. Functions of Saliva

• Clean mouth

• Protect enamel

• Fight microbes

• Dissolve taste chemicals

• Lubricate food

• Start digestion (enzymes)

B. Secretory Cells

• Serous cells: protein enzymes, watery secretion (organized in acini)

• Mucous cells: glycoproteins/mucus (tubular shape)

C. Saliva Composition

• Water, electrolytes (K⁺, Na⁺, Cl⁻, etc.)

• Waste (urea, uric acid)

• Enzymes: amylase (starch), lipase (fatty acid release)

• Mucins, lysozyme, IgA, defensins

D. Types of Glands

• Intrinsic: in tongue and soft palate

• Extrinsic (major pairs):

  1. Parotid: anterior to ear, serous only

  2. Submandibular: under mandible, mixed (serous + mucous)

  3. Sublingual: under tongue, mucous mostly

E. Control of Salivation

• Parasympathetic: increases secretion (e.g., smelling food)

• Sympathetic: decreases flow, thicker (mucous) saliva

VI. Esophagus & Swallowing

A. Esophagus Anatomy

• Runs behind larynx & trachea

• Passes diaphragm via esophageal hiatus

• Enters stomach at cardiac orifice

  • Valve-like sphincter prevents reflux

B. Esophagus Layers

• Mucosa: stratified squamous

• Submucosa: mucous glands

• Muscularis: skeletal (upper), smooth (lower), plus sphincters

• Adventitia: outer CT layer

C. Swallowing (Deglutition)

1. Buccal phase (voluntary)

   • Tongue forms bolus, pushes to oropharynx

   • UES (upper esophageal sphincter) closed initially

2. Pharyngeal-esophageal phase (involuntary)

   • Soft palate closes nasopharynx

   • Epiglottis closes glottis

   • UES opens → bolus enters esophagus

   • Peristalsis carries bolus to stomach

   • Lower esophageal sphincter opens briefly then closes to prevent reflux