Human Form & Function 2
Organisation of the Gastrointestinal Tract,
Salivary Glands and Swallowing Reflex
Dr. Neil Docherty
My Teaching Objec/ves •  Highlight 4 key phenomena in GI tract namely: motility, secretion,
digestion and absorption.
•  Outline tissue organisation of the GI tract and how its key
functions are coordinated by extrinsic and intrinsic nerves and
peptide hormones.
•  Explain the processing of food in the mouth and the role of
autonomic reflexes in governing the quantity and quality of
salivary gland secretions.
•  Outline the stages of the swallowing reflex and oesophageal
motility
Digestive System
Origin, Regions and Maturation
End of fourth week of development
Foregut
Midgut
Alimentary canal
and accessory
glandular tissues and
organs
Hindgut
The cartoon illustrates the structure of
the distal part of the foregut, the duodenum
With a number of specialised features
However general wall structure has
Significant commonality from oesophagus
to rectum.
General Features of Digestive Tract Wall
What the GI Tract Contributes to The Body
ROLE IN NUTRITION AND EXCRETION
(focus of these lectures)
-Mechanical and secretory promotion of
digestion
-Specialised pathways for the absorption of
macronutrients and micronutrients.
-Excretion of digestive waste and metabolic
waste products from around the body
ROLE IN DEFENCE
Gut associated lymphoid tissue protects against
harmful microorganisms and actively promotes
tolerance to commensal microorganisms and
dietary antigen.
-FLUID HOMEOSTASIS
Plays a role in whole body fluid & electrolyte
balance (ALDOSTERONE)
*Remember aldosterone, what causes its
release and what it does when you cover renal
physiology
Functional Anatomy of the GI Tract:
A Useful Analogy Regarding Nutritive
Function
We will revisit this analogy at the end of the lectures and you might find it
a useful primer during your study
Motility
Muscular contractions that mix and move forward the
contents of the digestive tract
•  Propulsive movements
–  Push contents forward through the digestive tract
•  Mixing movements
-Mixing food with digestive juices promotes
digestion of foods
-Facilitates absorption by exposing all parts of
intestinal contents to absorbing surfaces of
digestive tract
Secretion, Digestion & Absorption
• Secretions act on dietary substrate for digestion
• Secretions derive directly from cells lining the
digestive tract and from the associated organs liver
and pancreas
• Membrane bound enzymes in the small intestinal
epithelium complete digestion (carbohydrates)
• Absorption of macronutrient is is achieved using solute
carriers mainly in the small intestinal epithelium
Carbohydrates
Proteins
Fats
monosaccharides
amino acids
glycerol and fatty acids
DIGESTION
SECRETION
(enzymatic + non-enzymatic components)
MEMBRANE
BOUND ENZYME
ABSORPTION
-blood
-lymph (lipid)
Control of Motility and Secretion
-Central Role of Neural and Endocrine
Pathways
Four important factors 1)  Intrinsic nerves 2)  Extrinsic Nerves 3)  Gastrointes:nal Hormones Later you can fit gastric and intes:nal mo:lity and secre:on to this model Pre-processing of the Bolus in the Mouth
1, Sensory analysis of material before swallowing
2. Mechanical processing (teeth, tongue, palate)
3. Lubrication (mucus, and salivary gland secretions)
4. Sterilisation (lysozyme)
4. Neutralisation (bicarbonate)
4. Beginning of digestion (amylase, lipase)
PAROTID-amylase
EBNER’S-lipase
SUBMANDIBULAR
-mucus, amylase
SUBLINGUAL
-mucus
-1-1.5 litres per day (0.5ml/min-5ml/min)
-99.4% water, 0.6% salts, mucus, other proteins
Salivary Secretion
Key Points
Simple (mechanical)
and conditioned (cephalic)
responses
Arc to salivary centre in
brainstem
Autonomic inputs not
antagonistic
Dual Autonomic Input
Into Salivary Secretion
PARASYMPATHETIC
SYMPATHETIC
Ensures/Modifies
Quality and Quantity
Swallowing Reflex
-The Oropharyngeal Stage
Tongue moves bolus to back of mouth
and pharynx
Brain stem arc activation of swallowing
muscles
net effect
Uvula-(connective tissue at end of
soft palate) prevents nasal flux
Larynx elevated and vocal folds closed
Over glottis. Epiglottis covers glottis
-prevents tracheal flux
The Oesophagus and Oesophageal Phase
Muscular tube 25cm long 2 cm wide
Takes the food to the stomach
Sphincters at either end
Transverse
section
Your Learning From Today Should focus on being able to
•  Identify and list the 4 key phenomena occurring in the GI tract
in relation to nutrient assimilation and waste excretion.
•  Describe tissue organisation in the GI tract and how its key
functions are coordinated by extrinsic and intrinsic nerves and
peptide hormones.
•  Describe processing of food in the mouth and autonomic
rcontrol of salivary gland secretions.
•  List and describe the stages of the swallowing reflex and
oesophageal motility