DIGESTIVE SYSTEMDIGESTIVE SYSTEM

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INTRODUCTION

DIGESTIVE SYSTEM Digestive system is a system which involve in digesting

or broken down the food and liquid portion that we ate into smaller molecules of nutrients

Digestive system is made up of the digestive tract or gastrointestinal tract and accessory digestive organs.

Digestive tract : mouth-pharynx-esophagus-stomach-small intestine-large intestine-rectum and anal canal-anus

Accessory organs : salivary glands, exocrine glands, liver, pancreas, gallbladder.

There are 4 primary layers in digestive system: mucosa, submucosa, muscularis, serosa

MOUTH ( ORAL CAVITY ) Covered by stratified squamous epithelium and mucous membrane Produce saliva and digest food become bolus Oral cavity includes:

Lip3 layer: outer skin layer, middle muscle layer and inner mucosa layer

Hard and soft palate Hard lined by keratinized type of

stratified squamous epithelium Soft lined by non-keratinized type of

stratified squamous epithelium Tongue

Covered by non-keratinized type of stratified squamous epithelium

Uvula Teeth

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PHARYNX Lympatic tissue area present

called tonsils such as palatine tonsile, lingual tonsile and pharyngeal

Divided into 3:1. Nasopharynx Pseudostratified columnar

epithelium2. Oropharynx Stratified columnar epithelial3. Laryngopharynx Stratified squamous epithelium

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ESOPHAGUS Contains 4 layers:

1. Mucosa Stratified squamous epithelium

which contains mucous glands2. Submucosa

Collagen and elastic fibres network Mucosa and submucosa hold together

called longitudinal fold3. Muscularis

Consists of inner circular layer ( the fibres are circular) and outer

longitudinal layers ( fibres are longitudinal)

4. Adventitia Loose fibrous tissue http://

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STOMACH Contains 4 layers:

1. Mucosa -lamina propia ( loose CT)

inside lamina propia : colagen and reticular fibres, cells such as fibroblasts, lymphocytes, mast cells, eosinophils and a few plasma cells

2. Submucosa Dense irregular connective tissue

with abundant of collagen and elastic fibres.

3. Muscularis Smooth muscle tissue which is divided into 3 coats such as circular, oblique, and longitudinal muscle layer.

4. Serosa http://images.google.com.sg/imgres?imgurl=http://www.bu.edu/histology/i/10801loa.jpg

SMALL INTESTINE Length: 5 – 7 m Intestinal wall has 4 layers: Serosa,Muscularis,Sub

mucosa,Muscularis mucosa

1. Duodenum : 25cm in length, surrounded by incomplete serosa, contain Brunner’s gland in submucosa and leaf-like shaped villi

2. Jejunum: movable segment suspended by a mesentery, has long finger-like vilii

3. Ileum: contains lymphoid nodules in mucosa and submucosa & shorter villi

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Length : 1.5 – 2 m Width : 6.5 cmContains 3 segments: Caecum with appendix

attached : 1st part located in the right lower abdomen

Ascending, descending, transverse, sigmoid colon

Rectum consists of 2parts : rectum proper and anal canal which is controlled by sphincters

LARGE INTESTINE

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ACCESSORY ORGANS Salivary gland: connected with

oral cavity through excretory ducts; consists of minor gland and 3 main parts : parotid, sublingual, submandibular glands

Liver: largest gland surrounded by a collagen elastic fiber and made up of hepatocytes,

Gall bladder: ovoid sac covered by muscular wall _tall columnar epithelium for absorption

Pancreas: located behind stomach and contains pancreatic endocrine and exocrine cells

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Functions of Digestive System The primary function is to break down the materials into

smaller parts so the body can use them to build and nourish cells and provide energy

Can be viewed as a series of integrated steps that consists of Ingestion, Mechanical processing, Digestion, Secretion, Absorption, and Excretion

It begins in the mouth, following with pharynx, esophagus, stomach, small intestines, large intestines, anus

Functions of Digestive System

Ingestion: Process that occurred when food enter the digestive tract via the mouth. It is an active process that involves conscious choice and decision making such as biting, sucking and filtering

Mechanical processing: flattening and cutting to make the materials easier to propel along the digestive tract

Digestion: breakdown of food chemically into smaller organic pieces to make it suitable for absorption

Functions of Digestive System

Secretion: the released of a substance, like water, acids, enzymes, buffers, and salts by the epithelium of the digestive tract and by glandular organs

Absorption: movement of organic substrates, electrolytes (inorganic ions), vitamins, and water across the digestive epithelium and into the adjacent blood and lymphatic vessel of the digestive tract

Excretion: removal of waste products from body fluids into the anus.

Specific functions in digestive system

Mouth/Oral cavityMechanical processing, moistening, and mixing with saliva

Salivary glandSecretes saliva to break down carbohydrates

Pharynx/ThroatTransfer food from mouth to esophagus

Specific functions in digestive system Esophagus

Connects pharynx to stomach

Liversecretes bile for lipid digestion, storing nutrient, detoxifying drugs

StomachChemical processing and breaking down of protein by using hydrochloric acid and enzymes

Specific functions in digestive system

GallbladderStores and concentrates bile

PancreasExocrine tissues: synthesizes and secretes pancreatic juices that contains digestive enzymesendocrine tissues: secretes hormones

Small intestineDigests by enzymes and absorbing nutrients

Specific Specific functions in digestive system in digestive system

Large intestine

Absorbs the remaining water from the waste and preparing it for elimination

Anus

Excretes the waste out from the body

Nerves in Digestive system

1. Mouth

• Parasympathetic nerves releases acetylcholine which increases salivary secretion and vasoactive intestinal polypeptide which expands the salivary gland blood vessels

• Sympathetic nerves causes secretion of small amounts of saliva, rich in protein and glycoprotein

2. Esophagus

• Between two smooth muscles lies the nerves and nerve cells of the myenteric nerve plexus which controls peristalsis movements

Nerves in Digestive system

3. Swallowing Cranial nerves : excites muscles Intercostals nerves : inhibits diaphragm and intercostals

muscles Vagus nerves to myenteric nerves : peristalsis waves of

contraction to move the food down to stomach

4. Stomach Once messages from hypothalamic feeding centre from

brain reaches medulla, autonomic nervous system activates reaction

5. Pancreas

• Vagus nerves releases small quantity of gastrin which stimulates functions within

6. Gall bladder

• Vagus nerves causes bile to be expelled out into small intestine

7. Small intestine•Myenteric nerve plexus found in outer Serosa of

peritoneum controls peristalsis movements•Extrinsic nerve causes parasympathetic stimulation to

increase contractions and sympathetic stimulation to decrease motility

•Submucous nerves plexus, stimulated by intestinal hormones, causes movements of villi, to absorb nutrients

Nerves in Digestive system

8. Gut wall

• Myenteric nerves in smooth muscle layers coordinates secretory and muscular activities

9. Intestinal secretions• Intrinsic nerve plexuses causes stimuli to secrete intestinal juice• Cholinergic nerves stimulates secretion of mucus but it is inhibited by sympathetic nerves

Nerves in Digestive system

10.Gut wall of large intestine

• Intrinsic nervous system : myenteric and sub mucous plexus for controlling gut movement

• Types of neurons found : postganglionic parasympathetic, secretory, sensory ( chemoreceptor and mechanoreceptors), interneuron

• Extrinsic autonomic nerves : sympathetic decreases and parasympathetic (pelvic and pudendal) increases gut movement and secretion

• Acetylcholine released by parasympathetic stimulation contracts gut muscles and relaxes sphincters

Nerves in Digestive system

Blood system in digestive system

1. Stomach / pancreas

Humoral control: chemical messages are carried via blood stream to gastric glands

• In gastric phase, gastrin from G cells are released when blood leaves stomach / pancreas

• Arterial blood returns to stomach / pancreas to stimulate secretion of juices rich in acid and pepsinogen (enzyme digesting protein)

• In intestinal phase, chyme is broken down by (GIP) ,leaves through blood circulation

• Arterial blood returns to stomach / pancreas to inhibit formation of bile and decrease acidity and motility

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2. Gall bladder

•Humoral intestinal phase : products of fat disgestion stimulate duodenal (small intestine) mucosa to secrete cholecystokinin (CCK)

• This enters venous blood and via portal circulation, arterial blood causes contraction of gall bladder

3. Liver

•It receives 1/3 arterial blood from hepatic artery

•Remainder venous blood from hepatic portal vein which begins from capillaries of esophagus, stomach ,small intestine and most from large intestine

•Blood leaving liver re enters via inferior vena cava

Blood system in digestive system

What happens when we age?

1.1. The rate of epthelial stem cell division declinesThe rate of epthelial stem cell division declines Digestive cells more prone to damage and stomach ulcers Digestive cells more prone to damage and stomach ulcers

occurs most likelyoccurs most likely

2.2. Smooth muscles tone decreasesSmooth muscles tone decreases Motility decreases and pancreatic contraction weakensMotility decreases and pancreatic contraction weakens

3.3. Cancer rate increasesCancer rate increases

4.4. Changes in other systems have direct or indirect effects on Changes in other systems have direct or indirect effects on digestive systemdigestive system

For e.g. : reduce in bone mass and calcium content of For e.g. : reduce in bone mass and calcium content of skeleton can cause tooth lossskeleton can cause tooth loss

Decline in olfactory and gustatory sensitivity can lead to Decline in olfactory and gustatory sensitivity can lead to dietary changesdietary changes

References

Fox, S. I.,1999. Human physiology. 6th ed. U.S.A: The McGraw Hill Companies.

Kierszbaum, A. L., 2002. Histology and cell biology : an introduction to pathology. USA: Mosby.

Mackenna, B. R., 1997. Illustrated physiology. 6th ed. Singapore: Longman Singapore Publisher.

Martini, F. H., 1998. Fundamentals of anatomy and physiology. 4th ed. New Jersey: Prentice Hall International.

Martini, F.H., 2006. Fundamental of anatomy & physiology. 7th ed. San Francisco: Daryl Fox.

MDIS. 2005. Anatomy course study booklet. Singapore: MDIS.

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DONE BY:

Farhath Jabien, Nishachand Vohreh, Felly, Ensy Caroline, Melisa and Ton Nu Thien An