NTA Level 4 • Semester 1 • PST04103

Introduction to Gastrointestinal System

Human Anatomy and Physiology • Source Session/Topic 13

Full source-text version: all educational wording from the extracted learning source is retained; only presenter/tutor metadata and web-layout noise are removed, while formatting is improved for readability.

Session 13: Introduction to Gastrointestinal System

Total Session Time: 120 minutes + 60 minutes assignment

Prerequisites

• None

Learning Tasks

By the end of this session students are expected to be able to:

• Define Gastrointestinal System

• Explain Gastrointestinal System Overview

• Explain Functions of the Gastrointestinal System

• Describe Structure of the Oral Cavity

• Describe Structure and Functions of the Tongue

• Explain Constituents of Salivary Glands

• Explain Mechanism of Swallowing

Resources Needed:

• Flip charts, marker pens, and masking tape

• Black/white board, chalk and whiteboard markers

• Overhead Projector and Transparencies or Slide Projector/LCD and Computer

• Handout 13.1: The overview of alimentary canal

• Handout 13.2: General structure of the alimentary canal

• Handout 13.3: The Teeth

• Handout 13.4: The Tongue

• Handout 13.5: The Salivary glands

SESSION OVERVIEW

SESSION CONTENTS

STEP 1: Presentation of Session Title and Learning Tasks (5 minutes)

READ or ASK students to read the learning tasks and clarify

ASK students if they have any questions before continuing

STEP 2: Definition and Overview of Gastrointestinal System (20 minutes)

|Activity: Brainstorming (5 minutes) |

| |

|Ask students to brainstorm on the following question: |

| |

|What is digestive system? |

|What are the organs of digestive system? |

| |

|ALLOW few students to respond |

| |

|WRITE their responses on the flip chart/ board |

| |

|CLARIFY and SUMMARISE by using the content below |

• Digestive system consists of the digestive tract(alimentary canal) which

is a tube extending from the mouth, pass through the thorax, abdomen and

pelvis and ends at the anus and its associated accessory organs

• Organs of the digestive tract include:

o The mouth or oral cavity, which has salivary glands and tonsils as

accessory organs

o The pharynx, or throat , with tubular mucous glands

o The oesophagus, with tubular mucous glands

o The stomach, which contains many tube like glands

o The small intestine, consisting of the duodenum, jejunum and ileum,

with the liver, Gallbladder and pancreas as major accessory organs

o The large intestine, including the cecum, colon, rectum and anal

canal, with mucus glands

o The anus

• The digestive system also consists of accessory organs which include the

teeth, tongue, salivary glands, liver, gallbladder, and pancreas

• Teeth aid in the physical breakdown of food, and the tongue assists in

chewing and swallowing.

• The other accessory digestive organs produce or store secretions that

flow into the GI tract through ducts to aid in the chemical breakdown of

food

[pic]

Figure 13.1: Alimentary

Canal and Accessory Organs

[pic]Refer students to Handout 13.1: The Overview of Alimentary Canal

The gastrointestinal tract is made of four layers of tissues:

o Mucosa is the innermost layer made up of three layers

▪ The inner epithelium

▪ Lamina propria

▪ Muscularis mucosae

o Submucosa this layer is composed of connective tissue, it contains

numerous small glands, blood vessels, and parasympathetic nerves that

form the submucosal plexus

(Meissner plexus)

o Muscular is thick layer of smooth muscle tissue which consists of

inner circular layerand outer longitudinal layer

o Between the two layers of muscles there is a nervous plexus called

myenteric plexus (Auerbach plexus)

o Serosa is the outermost layer of made up loose connective tissue

(visceral peritoneum)

• Layers of the GI tract have various modifications to enable it to perform

various functions

[pic]Refer students to Handout 13.2: General Structure of the Alimentary

Canal

STEP 3: Functions of the Gastrointestinal System (15 minutes)

|Activity: Brainstorming (5 minutes) |

| |

|Ask students to brainstorm on the following question: |

| |

|What are the functions of the digestive tract? |

| |

|ALLOW few students to respond? |

| |

|WRITE their responses on the flip chart/ board |

| |

|CLARIFY and SUMMARISE by using the content below |

Overall, the digestive system performs six basic processes:

• Ingestion. This process involves taking foods and liquids into the mouth

(eating)

• Secretion. Each day, cells within the walls of the GI tract and accessory

digestive organs secrete a total of about 7 litres of water, acid,

buffers, and enzymes into the lumen (interior space) of the tract

• Mixing and propulsion. Alternating contractions and relaxations of smooth

muscle in the walls of the GI tract mix food and secretions and propel

them toward the anus

• This capability of the GI tract to mix and move material along its length

is called motility

• Digestion. Mechanical and chemical processes break down ingested food

into small molecules

o In mechanical digestion the teeth cut and grind food before it is

swallowed, and then smooth muscles of the stomach and small intestine

churn the food

o As a result, food molecules become dissolved and thoroughly mixed with

digestive enzymes

o In chemical digestion the large carbohydrate, lipid, protein, and

nucleic acid molecules in food are split into smaller molecules by

hydrolysis

o Digestive enzymes produced by the salivary glands, tongue, stomach,

pancreas, and small intestine catalyse these catabolic reactions. A

few substances in food(vitamins, ions, cholesterol, and water).can be

absorbed without chemical digestion

• Absorption. The entrance of ingested and secreted fluids, ions, and the

products of digestion into the epithelial cells lining the lumen of the

GI tract is called absorption.

• Defecation. Wastes, indigestible substances, bacteria, cells sloughed

from the lining of the GI tract, and digested materials that were not

absorbed in their journey through the digestive tract leave the body

through the anus in a process called defecation and the eliminated

material is termed faeces

STEP 4: Structure of the Oral Cavity (20 minutes)

• The oral cavity or mouth is that part of the digestive tract bounded by

the lips anteriorly, the fauces throat; opening into the pharynx

posteriorly, cheeks laterally, the palate superiorly, and a muscular

floor inferiorly

• The oral cavity is lined throughout with mucus membrane consisting of

stratified

squamous epithelium containing small mucus secreting glands.

• The oral cavity is divided into two regions:

o The Vestibule; part of the mouth between Gums and Cheeks

o The oral cavity proper; which lies medial to the alveolar processes

(gums)

Structure of the Oral Cavity (The Buccal Cavity)

• Lips:

o Are muscular structure formed mostly by the orbicularis oris muscles

o They are covered externally by skin and internally by mucous membrane

o The junction between skin and mucous membrane is highly sensitive

o When lips are closed, line of contact is oral fissure

o Cheeks

o The cheeks are formed in large part by buccinator muscles covered by

adipose tissue

o They form the lateral boundaries of the oral cavity, they are continuous

with lips and lined by mucous membrane

o They contain mucus secreting glands which are placed between mucous

membrane and buccinator muscle

o Their ducts open opposite the last molar teeth

• Hard and soft palates; forms the roof of mouth consists of two parts:

o The anterior bony part the hard palate consists of portions of four

bones, two maxillae

and two palatine bones

o The posterior non bony part the soft palate forms partition between

the mouth and nasopharynx and is made of muscles arranged in an arch

▪ Suspended from midpoint of the posterior border of the arch

is the uvula

▪ The opening from the mouth into the oropharynx is called

fauces

Teeth

• The teeth are hard conical structures set in the dental alveoli (tooth

sockets) of the upper and lower jaws and are used in mastication

(chewing) and assisting in articulation

• These are organs of mastication

• Humans have two generations of teeth:

o The deciduous (primary) dentition

o The permanent (secondary) dentition

Deciduous Teeth

• They are temporary teeth, twenty in number, and ten on each jaw

• They start to emerge at 6 months after birth

• They should all be present at 24-36 months

Permanent Teeth

• They are thirty two in number, they begin to replace deciduous teeth at 6

years of age, and become complete when the third molars erupt at 18 – 24

years of age

• Of these 32 teeth there are 8 incisors, 4 canines, 8 Premolars and 12

Molars

• Incisors and Canines are for cutting and Premolars and molars for

grinding of food

o There are two incisors, a central and a lateral, in each half jaw or

quadrant

o Behind each lateral incisor is a canine tooth with a single cusp

o Distal to the canines are two premolars, each with a buccal and

lingual cusp

o Posterior to the premolars are three molars whose size decreases

distally

• A typical tooth has the following parts:

o Crown; exposed portion of a tooth, covered by enamel; ideally suited

to withstand abrasion during mastication

o Neck; narrow portion that joins the crown to the root; surrounded by

the gingiva

o Roots fits into the socket of the alveolar process and is suspended by

fibrous

o periodontal membrane

o In the centre of the tooth there is pulp cavity containing blood

vessels, lymph vessels and nerves

o Surrounding the pulp cavity there is hard ivory like substance called

dentine

o Outside the dentine of the crown is the thin layer of the very hard

substance called enamel

o The root of the tooth on the other hand is covered by substance

resembling the bone called the cement which secures the tooth in its

socket

Refer students to Handout 13.3: The Teeth

STEP 5: Structure and Functions of the Tongue (15 minutes)

• The tongue is a highly muscular organ of deglutition, taste and speech

• It is made up of skeletal muscles covered by a mucous membrane

• It has the root, tip and the body

• It is attached by its base to the hyoid bone and by the lingual frenulum

to the floor of the mouth

• There are two types of muscles forming the tongue;

o Intrinsic muscles; they originate and insert in the tongue itself

o An example of the intrinsic muscles includes Genioglossus

o They are responsible for changing the shape of the tongue such as

flattening and elevating the tongue during drinking and swallowing

o Extrinsic muscles are those muscles that insert into the tongue but

originate from mother structures such as hyoid bone

o An example of the muscles includes hyoglossus

o They are responsible for protruding and retract the tongue, move it

from side to side and change its shape

• The dorsal mucosa is covered by numerous papillae; tiny projections, some

of which bear taste buds

• There are three types of papillae; vallate, fungiform and filariform

o Circumvallate papillae, arranged in an inverted V shape at the base of

the tongue are the largest papillae

o Fungiform papillae; are situated mainly at the tip ad the edge of the

tongue

o Filiform papillae; are the smallest of all three

o numerous on the surface of the anterior two-thirds of the tongue

[pic]Refer students to Handout 13.4: The Tongue

There are four basic taste sensations

o Sweetness; apex (tip)

o Saltiness; lateral margins

o Sourness; posterior part of the tongue

o Bitterness; posterior part of the tongue

• Although it is commonly stated that particular areas of the tongue are

specialized to detect these different tastes, evidence indicates that all

areas of the tongue are responsive to all taste stimuli

• Each afferent nerve fibre is connected to widely separated taste buds and

may respond to several different chemical stimuli

• Some respond to all four classic categories, others to fewer or only one

• Blood supply of the tongue is by lingual branch of the external carotid

artery and venous drainage is by lingual veins, which joins the internal

jugular vein

• Nerve innervations of the tongue is through:

o The hypoglossal nerve (12th cranial nerves)

o The lingual branch of the mandibular nerves

o The facial and glossopharyngeal nerves (7th and 9th CN) the nerves of

taste

o The parasympathetic innervation of the various glands of the tongue is

from the chorda tympani branch of the facial nerve

o The postganglionic sympathetic supply to lingual glands and vessels

arises from the carotid plexus

STEP 6: Salivary Glands and its Constituents (10 minutes)

• Salivary glands are compound, tubulo- alveolar exocrine glands, whose

ducts open into the oral cavity

• They secrete saliva, a fluid which lubricates food to assist deglutition,

moistens the buccal mucosa, which is important for speech, and provides

an aqueous solvent necessary for taste and a fluid seal for sucking and

suckling

• They also secrete digestive enzymes, e.g. salivary amylase and

antimicrobial agents e.g.

IgA, lysozyme and lacto ferrin, into saliva

• Conditions where there is a significant decrease in the production of

saliva (xerostomia) may result in periodontal inflammation and dental

caries

• Three pairs of compound tubulo-alveolar glands secrete approximately 1

litre of saliva each day

• The major salivary glands are the paired parotid, submandibular and

sublingual glands

• In addition, there are numerous minor salivary glands scattered

throughout the oral mucosa and submucosa

o Parotid glands – largest of the paired salivary glands produce watery

saliva containing enzymes

o Submandibular glands – compound glands that contain enzymes and mucous

producing element

o Sublingual glands – smallest of the salivary glands produce a mucous

type of saliva

o Buccal glands are important for hygiene and comfort of oral tissue

• In the unstimulated state, the parotid gland contributes 20%, the

submandibular gland 65%, and the sublingual and minor salivary glands 15%

of the daily output of saliva

• When stimulated, the parotid contribution rises to 50%

[pic]Refer students to Handout 13.5: The Salivary Glands

STEP 7: Mechanism of Swallowing (15 minutes)

Swallowing: A mechanism used to accomplish primary function of digestive

system

• Deglutition: A process for swallowing

o It is a complex process requiring coordinated and rapid movement

• Swallowing transports the chewed food into the oesophagus, passing

through the oropharynx and hypopharynx

• The mechanism for swallowing is coordinated by the swallowing center in

the medulla oblongata and pons

• The reflex is initiated by touch receptors in the pharynx as the bolus of

food is pushed to the back of the mouth

• This occurs in three stages after mastication is completed and the bolus

has been formed

• It is initiated voluntarily but completed by a reflex action

o Oral stage (mouth to oropharynx), voluntarily controlled

▪ Formation of food bolus in the middle of the tongue; The mouth is

closed, tongue presses bolus against the palate, and the voluntary

muscles of the tongue and cheeks push the bolus backwards into the

oropharynx

o Pharyngeal stage (oropharynx to oesophagus) involuntary contraction of

muscles of the pharynx

▪ Propels the bolus down into the oesophagus

▪ It begins with the elevation of the soft palate, which closes the

passage between the nasopharynx and oropharynx

▪ This is controlled by the medulla and lower pons in the brain

stem

▪ The presence of the bolus in the pharynx stimulates a wave of

peristalsis that propelsthe bolus through the oesophagus to the

stomach

▪ Movement; contractions and gravity moves bolus through oesophagus

and into stomach

▪ So the function of the oesophagus is to convey food from the

pharynx to the stomach

▪ The chewed food is pushed down the oesophagus to the stomach

through peristaltic contraction of these muscles

▪ It takes only about seven seconds for food to pass through the

oesophagus and no digestion takes place

▪ Peristalsis; wave like ripple of the muscle layer of a hollow

organ progressive motility that produces forward movement of matter

along the GI tract

STEP 8: Key Points (5 minutes)

• The gastrointestinal system is the portal through which nutritive

substances, vitamins,

• minerals, and fluids enter the body

• The gastrointestinal tract is made of four layers of tissues: the mucosa,

submucosa,

• muscular and serosa

• The tongue is a highly muscular organ of deglutition, taste and speech

• There are four basic taste sensation; sweetness, saltiness, sourness and

bitterness

• Teeth are organs of mastication and humans have two generations of teeth;

the deciduous and permanent

• The oesophagus has 4 constrictions where adjacent structure produce

impression

STEP 9: Evaluation (5 minutes)

• What is gastrointestinal system?

• What are the structures of the gastrointestinal tract?

• What are the functions of digestive system?

• What are the functions of salivary glands?

• What are the structure of the tongue?

Step 10: Assignment (10 minutes)

|Activity: Take Home Assignment (10 minutes) |

| |

|DIVIDE learners in groups or individual. |

| |

|ASK the learners to work on the following assignment |

| |

|Describe structure and function of the tongue |

| |

|ALLOCATE time for learners to do the assignment and submit |

| |

|REFER learners to recommended references |

References

Gastrointestinal tract image. (2015). Retrieved September, 27, 2015 from

http://www.freeed.

net/sweethaven/MedTech/NurseCare/fig91801.

Seeley, R. R., Stephens, T. D.& Tate, P. (2003). Anatomy and Physiology.

New York:

McGraw-Hill

Shier, A., Butler, J., & Lewis, R. (2004). Hole’s Human Anatomy &

Physiology. New York:

McGraw-Hill

Standring, S. (2008). Grays’s Anatomy The anatomical basis of clinical

practice. United

Kingdom: Churchill Livingstone Elservier.

Thibodeau, G. A., & Patton, K. T. (1999). Anatomy & Physiology. Saint

Louis: Mosby,

Von Hoffman Press, Inc.

Tortora, G.J & Derrickson, B (2009). Principles of Anatomy and Physiology

12th Edition,

USA, John Wiley & Sons Inc, USA

Waugh, A. & Grant, A. (2006). Ross and Willson Anatomy and physiology in

Health and

illness. United Kingdom: Churchill Livingstone Elservier

|[pic] |Handout 13.1: Overview of Alimentary Canal |

[pic]

Source: Sweet Haven, 2015

|[pic] |Handout 13.2: General Structure of the Alimentary Canal |

| | |

[pic]

Source: Standring, S., 2008.

|[pic] |Handout 13.3: The Teeth |

[pic]

Source: Standring, S., 2008.

[pic]

Source: Moore, K. L., & Agur, A. M. R. (2007)

|[pic] |Handout 13.4: The Tongue |

[pic]

Source: Standring, S., 2008

|[pic] |Handout 13.5: The Salivary Glands |

[pic]

Source: Standring, S., 2008.

[pic]

Source: Standring, S., 2008

← Previous Topic Next Topic →View all Human Anatomy and Physiology topics Open Complete Full Notes

PDF / OFFLINE NOTES

Unataka kutumiwa notes hizi kupitia WhatsApp?Kwa notes zilizopangiliwa vizuri kwa kusoma offline au PDF, bonyeza kitufe hapa chini. Ujumbe wenye Level, Semester, Module na Topic utaandaliwa moja kwa moja.TUMIWA NOTES WHATSAPP

WhatsApp: 255620339260