NTA Level 4 • Semester 1 • PST04103

Structure and Functions of Stomach and Intestines

Human Anatomy and Physiology • Source Session/Topic 14

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Session 14: Structure and Functions of Stomach and Intestines

Total Session Time: 120 minutes

Prerequisites

• None

Learning Tasks

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

• Identify structure and Functions of Pharynx and Oesophagus

• Describe Structure and Functions of the Stomach

• Describe Structure and Functions of the Small Intestines

• Describe Structure and Functions of the Large Intestines

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 14.1: The Oesophagus

• Handout 14.2: General Structure of Stomach

• Handout 14.3: Blood Supply to the Stomach

• Handout 14.4: The duodenum

• Handout 14.5: Structure of Small Intestine

• Handout 14.6: Large Intestine

• Worksheet 14.1: Large Intestine

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: Structure of the Pharynx and Oesophagus (15 minutes)

• Pharynx: A tube through which a bolus passes when moved from the mouth to

the oesophagus by the process of deglutition

• The pharynx is divided into three parts namely

o Nasopharynx

o Oropharynx

o Laryngopharynx

• The Oropharynx is important for digestive system

• The wall of the pharynx consists of three layers

• These are the Mucosa, Middle layer (Fibrous tissue) and Outer layer

consisting of Smooth muscles involved in swallowing

• When food enters the pharynx swallowing is no longer under voluntary

control

• The oesophagus is a narrow muscular tube about 25 centimetres long

diameter of 2cm, which starts at pharynx at the back of the mouth

• It passes through the thoracic diaphragm, and ends at the cardiac orifice

of the stomach

• It lies in the median plane in the thorax in front of the vertebral

column behind the trachea and the heart

• The oesophagus has 4 constrictions where adjacent structure produce

impression

o At the beginning approximately 15cm from the incisor teeth and caused

by the cricopharyngeus muscles – upper oesophageal sphincter

o Where it crossed by the arch of aorta 22.5cm from the incisor teeth

o Where it crossed by the left main bronchus 27.5cm from the incisor

o Where it passes through the diaphragm – lower oesophageal sphincter

• At the top of the oesophagus, is a flap of tissue called the epiglottis

that closes during swallowing to prevent food from entering the trachea

(windpipe)

• It has four layers; from outside:

o The adventitia

o Muscular layer; the muscles are striated (voluntary) in the upper

third and mixed (striated & smooth) in the middle and smooth

(involuntary) in the lower third

o There are two layers:

▪ The inner is circular

▪ The outer is longitudinal

o Sub-mucosa layer

o Mucosa layer which is made up of stratified squamous epithelium

• Arterial blood supply of the oesophagus is through oesophageal arteries,

branches of thoracic aorta, inferior phrenic arteries and the left

gastric branch of the celiac artery

• Venous drainage is through the azygos and hemiazygos veins

[pic]Refer students to Handout 14.1: The Oesophagus

STEP 3: Structure and Functions of the Stomach (25 minutes)

|Activity: Brainstorming (5 minutes) |

| |

|Ask students to brainstorm on the following question: |

| |

|What is a stomach? |

| |

|ALLOW few students to respond |

| |

|WRITE their responses on the flip chart/ board |

| |

|CLARIFY and SUMMARISE by using the content below |

• The stomach: The most dilated part of the gastrointestinal tract

• Has a J-like shape

• Positioned between the abdominal oesophagus and the small intestine, the

stomach is in the epigastric, umbilical and left hypochondrium regions of

the abdomen

• Its shape and size varies from person to person; even within the same

individual its size and shape change from time to time depending on its

food contents and the moisture of the body and in adult capacity range

from 1.0 to 1.5 litre

Structure of the Stomach

• The stomach is divided for descriptive purposes into four regions by

arbitrary lines drawn on its external surface which are

o The outlet of the stomach (pyloric orifice) is marked on the surface

of the organ by the pyloric constriction and surrounded by a thickened

ring of gastric circular muscle (the pyloric sphincter)

• The pyloric orifice is just to the right of midline in a plane that

passes through the lower border of vertebra LI (the trans pyloric plane)

• Other features of the stomach include:

o The greater curvature, which is a point of attachment for the gastro

splenic ligament and the greater omentum

o The lesser curvature, which is a point of attachment for the lesser

omentum

o The cardial notch, which is the superior angle created when the

oesophagus enters the stomach

o The angular incisure, which is a bend on the lesser curvature

• The stomach is lined with simple columnar epithelium

• The epithelium forms numerous tube like gastric pits, which are the

opening of the gastric glands

• The epithelial cells of the stomach are of five types

• The first type is surface mucous cells which produce mucus, is on the

surface and lines the gastric pits

• The remaining four cell types are in the gastric glands

• They are mucous neck cells which produce mucus; parietal (oxyntic) cells

which secrete hydrochloric acid and intrinsic factor needed for vitamin

B12 absorption; Chief (zymogenic) cells which produce pepsinogen and

endocrine cells, which produce regulatory hormones

[pic]Refer students to Handout 14.2: General Structure of Stomach

• Blood supply of the stomach; a rich arterial supply, arise from the

celiac trunk and its branches.

• Most of the blood is supplied by anastomoses formed along the lesser

curvature by the right and left gastric arteries and, along the greater

curvature, by the right and left gastro omental artery (gastroepiploic

artery)

• The fundus and upper body of stomach receive blood from the short and

posterior gastric arteries branches of the splenic artery

• Venous drainage is through gastric veins parallel the arteries in

position and course

[pic]Refer students to Handout 14.3: Blood Supply to the Stomach

Functions of the Stomach

• Reservoir for food until it is partially digested and moved further along

the GI tract

• Secrete gastric juice to aid in digestion of food

• Breaks food into small particles and mixes them with gastric juice

• Secrete intrinsic factor

• Carries limited absorption

• Produces gastrin hormone

• Helps protect body from pathogenic bacteria swallowed with food

STEP 4: Structure and functions of the Small Intestines (30 minutes)

|Activity: Brainstorming (5 minutes) |

| |

|Ask students to brainstorm on the following question: |

| |

|Where is small intestines found? |

|What are the functions of small intestines? |

| |

|ALLOW few students to respond? |

| |

|WRITE their responses on the flip chart/ board |

| |

|CLARIFY and SUMMARISE by using the content below |

• The small intestine extends from the pyloric sphincter to the ileocecal

valve

• It is highly adapted for digestion and absorption

• Its glands produce enzymes and mucus

• The walls of small intestine are composed of four layers of tissues and

there are some modifications of the peritoneum and mucous membrane

• The surface area of the mucosa is greatly increased by permanent circular

folds, villi and microvilli

• Villi are tiny finger like projections of the mucosa layer into

intestinal rumen about 0.5 too 1mm long, the function of villi is for

absorption

• It consists of three parts:

o The duodenum

o The jejunum

o The ileum

• Duodenum is the first section of the small intestine

• It begins with the duodenal bulb and ends at the ligament of Treitz

o The duodenum also regulates the rate of emptying of the stomach via

hormonal pathways; Secretin and cholecystokinin which are released

from cells in the duodenal epithelium in response to acidic and fatty

stimuli present there when the pylorus opens and releases gastric

chyme into the duodenum for further digestion

o The duodenum is divided into four sections for the purposes of

description

o The first three sections curve in a "C" loop concavity in which the

head of the pancreas lies

o Only the first 2 cm of the superior part is mobile (not covered by

peritoneum), the distal 3cm of the first part along with the rest of

the duodenum is retroperitoneal (immobile)

▪ The first (superior) part begins as a continuation of the

duodenal end of the pylorus

▪ The second (descending) part of the duodenum begins at the

superior duodenal flexure

▪ It passes inferiorly to the lower border of vertebral body L3,

before making a sharp turn medially into the inferior duodenal

flexure

▪ The third (inferior/horizontal) part of the duodenum begins at

the inferior duodenal flexure and passes transversely to the left,

crossing the inferior vena cava, aorta and the vertebral column

▪ The fourth (ascending) part passes superiorly, either anterior

to, or to the right of, the aorta, until it reaches the inferior

border of the body of the pancreas

▪ Then, it curves anteriorly and terminates at the duodenojejunal

flexure where it joins the jejunum

[pic]Refer students to Handout 14.4: The Duodenum

• The jejunum is the middle section of the small intestine

o In adult humans, the small intestine is usually between 5.5-6m long,

2.5m of which is the jejunum

o The inner surface of the jejunum, its mucous membrane, is covered in

projections called villi, which increase the surface area of tissue

available to absorb nutrients from the gut contents

o The epithelial cells which line these villi possess even larger

numbers of microvilli

o The villi in the jejunum are much longer than in the duodenum or ileum

o The jejunum contains very few Brunner's glands (found in the duodenum)

or Peyer's patches (found in the ileum)

o It has many large circular folds in its submucosa called plicae

circulares which increase the surface area for nutrient absorption

• The ileum is the final section of the small intestine

• It is separated from the cecum by the ileocecal valve

o The function of the ileum is mainly to absorb vitamin B12 and bile

salts and whatever products of digestion which were not absorbed by

the jejunum

o The wall itself is made up of folds, each of which has many tiny

finger-like projections known as villi on its surface

o In turn, the epithelial cells which line these villi possess even

larger numbers of microvilli.

o Therefore the ileum has an extremely large surface area both for the

adsorption (attachment) of enzyme molecules and for the absorption of

products of digestion

o There is no line of demarcation between the jejunum and the ileum

o There are, however, subtle differences between the two

▪ The ileum has more fat inside the mesentery than the jejunum

▪ The ileum is a paler colour, and tends to be of a smaller caliber

as well

▪ While the length of the intestinal tract contains lymphoid

tissue, only the ileum has abundant Peyer's patches, un-

encapsulated lymphoid nodules that contain large amounts of

lymphocytes and other cells of the immune system

[pic]Refer students to Handout 14.5: Structure of Small Intestine

STEP 5: Structure and Functions of the Large Intestine (35 minutes)

• The large intestine extends from the ileocecal valve to the anus

• Its subdivisions include the cecum, colon, rectum, and anal canal

• The mucosa contains numerous goblet cells and the muscular is consists of

taeniae coli

• The large intestine is the second to last part of the digestive system,

the final stage of the alimentary canal is the anus

• It starts in the right iliac region of the pelvis, just at or below the

right waist, where it is joined to the bottom end of the small intestine

• From here it continues up the abdomen, then across the width of the

abdominal cavity, and then it turns down, continuing to its endpoint at

the anus

• Its length is about 1.5 metres long, which is about one-fifth of the

whole length of the intestinal canal

• The following are the parts of the large intestine:

o The cecum or caecum (from the Latin caecus meaning blind), is a pouch,

connecting the ileum with the ascending colon of the large intestine

o It is separated from the ileum by the ileocecal valve is considered to

be the beginning of the large intestine

o It is also separated from the colon by the cecocolic junction

o The ascending colon is smaller in caliber than the cecum, with which

it is contiguous

o It passes upward, from its commencement at the cecum, opposite the

colic valve, to the under surface of the right lobe of the liver, on

the right of the gall-bladder, here it bends abruptly forward and to

the left, forming the right colic flexure (hepatic)

▪ Hepatic (or the right colic) flexure is the sharp bend between

the ascending and the transverse colon

▪ The right colic flexure is adjacent to the liver, and is

therefore also known as the hepatic flexure

▪ The left colic flexure is also known as the splenic flexure (as

it is close to the spleen)

o The transverse colon the longest and most movable part of the colon,

passes with a downward convexity from the right hypochondrium region

across the abdomen, opposite the confines of the epigastric and

umbilical zones, into the left hypochondrium region, where it curves

sharply on itself beneath the lower end of the spleen, forming the

splenic or left colic flexure

o Toward its splenic end there is often an abrupt U-shaped curve which

may descend lower than the main curve

o The descending colon passes downward through the left hypochondrium

and lumbar regions, along the lateral border of the left kidney

o At the lower end of the kidney it turns medial-ward toward the

lateral border of the psoas muscle, and then descends, in the angle

between psoas and quadratus lumborum, to the crest of the ilium,

where it ends in the sigmoid colon

o It is smaller in caliber and more deeply placed than the ascending

colon

o The sigmoid colon (pelvic colon; sigmoid flexure) is the part of the

large intestine that is closest to the rectum and anus

o It forms a loop that averages about 40 cm. in length, and normally

lies within the pelvis, but on account of its freedom of movement it

is liable to be displaced into the abdominal cavity

o It begins at the superior aperture of the lesser pelvis, where it is

continuous with the iliac colon, and passes transversely across the

front of the sacrum to the right side of the pelvis (The name

sigmoid means S-shaped.)

o It then curves on itself and turns toward the left to reach the

middle line at the level of the third piece of the sacrum, where it

bends downward and ends in the rectum

o The rectum (from the Latin rectum intestinum, meaning straight

intestine) is the final straight portion of the large intestine and

terminating in the anus

o Its length is about 12 cm long

o Its caliber is similar to that of the sigmoid colon at its

commencement, but it is dilated near its termination, forming the

rectal ampulla

▪ The rectum intestinum acts as a temporary storage site for

faeces

▪ As the rectal walls expand due to the materials filling it from

within, stretch receptors from the nervous system located in the

rectal walls stimulate the desire to defecate

▪ If the urge is not acted upon, the material in the rectum is

often returned to the colon where more water is absorbed

▪ If defecation is delayed for a prolonged period, constipation

and hardened faeces results

▪ The rectum shortens as material is forced into the anal canal

and peristaltic waves propel the faeces out of the rectum

▪ The internal and external sphincters allows the faeces to be

passed by muscles pulling the anus up over the exiting faeces

o The anus is an opening at the opposite end of the digestive tract

from the mouth

o Its function is to control the expulsion of faeces, unwanted semi-

solid matter produced during digestion

o Flow of substance through the anus is typically controlled by the

anal sphincter muscle

• The peritoneum covers the ascending and descending colon on the anterior

surface and sides, and therefore they are described as retroperitoneal

• The transverse colon and sigmoid colon are intraperitoneal

[pic]Refer students to Handout 14.6: Large Intestine

|Activity: Individual Assignment (10 minutes) |

| |

|PROVIDE each student with a Worksheet 14.1: Large Intestine. |

| |

|ASK the students to work on the following assignment |

| |

|Label the diagram present on worksheet 14.1 |

| |

|REVIEW with them the correct answers using Handouts of this session. |

STEP 6: Key Points (5 minutes)

• The stomach is the most dilated part of the gastrointestinal tract and

has a J-like shape.

• The small intestine extends from the pyloric sphincter to the ileocecal

valve.

• Small intestine consists of three parts the duodenum, the jejunum and the

ileum.

• Subdivisions of large include the cecum, colon, rectum, and anal canal.

STEP 7: Evaluation (5 minutes)

• What are the parts of the stomach?

• What are the parts of the small intestine?

• What are the functions of the stomach?

• What are the functions of pharynx and oesophagus

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 14.1: The Oesophagus |

| | |

[pic]

Source: Standring, S., 200

|[pic] |Handout 14.2: General Structure of Stomach |

[pic]

Source: Standring, S., 2008.

|[pic] |Handout 14.3: Blood Supply to the Stomach |

[pic]

Source: Standring, S., 2008.

|[pic] |Handout 14.4: The Duodenum |

[pic]

Source: Standring, S., 2008.

|[pic] |Handout 14.5: Structure of Small Intestine |

[pic]

Source: Medical-Look

[pic].

[pic]

Source: Standring, S., 2008

|[pic] |Handout 14.6: Large Intestine |

[pic][pic]

Source: Standring, S., 2008.

|[pic] |Worksheet 14.1: Large Intestine |

[pic]

Source: Standring, S., 2008.

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