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The Digestive System

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DIGESTIVE SYSTEM

• Collective name used to describe– The alimentary canal– Some accessory organs– A variety of digestive processes

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• Ingestion

• Mechanical processing/Propulsion

• Digestion

• Secretion

• Absorption

• Excretion

Functions of the digestive system

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The Components of the Digestive System

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• Gastrointestinal (Gl) tract (Alimentary canal)– Tube within a tube

– Direct link/path between organs

– Structures• Mouth

• Oral Cavity

• Pharynx

• Esophagus

• Stomach

• Small intestine

• Large intestine

• Rectum and anal canal

Digestive System Organization

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Digestive System Organization

• Accessory structures– Not in tube path– Organs

• Teeth• Tongue• Salivary glands• Liver• Gall bladder• Pancreas

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The Structure of the Digestive Tract

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The Wall of the Digestive Tract

The digestive tract wall has four layers:

Mucosa (mucous membrane – secretes digestive enzymes and mucus),

Submucosa (loose connective tissue – houses blood and lymph vessels),

Muscularis (two layers of smooth muscle - for peristalsis), and

Serosa (serous membrane – secretes serous fluid to prevent sticking).

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MOUTH

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Adult mouth

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Mouth

• The mouth opens into the oral or buccal cavity

• Its functions include:– Analysis of material before swallowing– Mechanical processing by the teeth,

tongue, and palatal surfaces– Lubrication– Limited digestion

Lips and cheeks enclose the mouth.

Taste buds on the tongue provide the sense of taste; skeletal muscle in the tongue allows it to move.

The roof of the mouth is formed by the hard and soft palates that separate it from the nasal cavities.

The soft palate ends in a finger-shaped projection called the uvula.

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TONGUE

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Functions Of Tongue

• Mastication (Chewing)

• Deglutition ( Swallowing)

• Speech

• Taste

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TEETH

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Structure of tooth

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Adult mouth

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SALIVARY GLANDS

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The Major Salivary Glands

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Structure of salivary gland

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PHARYNX

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Pharynx• Divided into 3 parts for descriptive

purpose

Nasopharynx– Important for respiration

Oropharynx

Laryngopharynx– Passages common for both respiratory and

digestive system

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Pharynx

• Food passes from the oral cavity into the pharynx and then to oesophagus below

• Walls of pharynx consist of 3 layers of tissue

1. The lining membrane (mucosa)

2. The middle layer – fibrous tissue

3. The outer layer –involuntary muscles

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Pharynx

• Lined with stratified squamous epithelium

• Pharyngeal muscles assist in swallowing– Pharyngeal constrictor muscles– Palatal muscles

Esophagus

• 25cm long

• 2cm in dia

• Front of vertebral column

• Behind the trachea

• Continuous with pharynx

• Joints the stomach

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Esophagus• Compressed form -arch of aorta - left brochi - left attrium• Surrounded by

– SNS plexus– Blood vessels

• Functions– Secrete mucous– Transport food

No chemical digestion occurs in the esophagus.

The entrance of the esophagus to the stomach is marked by a constriction, called a SPHINCTER;

----the sphincter must relax in order for food to enter the stomach.

The sphincter prevents food from backing up into the esophagus.

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- four layers of tissue

-Adventia layer consist of elastic fibrous tissue

Attaches the oesophagus to the surrounding structures

Bolus formation• Bolus formed is pushed into pharynx (by

action of voluntary muscles of tongue and cheeks

• Muscles of pharynx contract n propels the bolus-----to esophagus -- stomach

• Epiglottis prevents entry into trachea

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Formation of bolus

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Stomach

• Usually “J” shaped• Left side, anterior to the spleen• Mucous membrane

– G cells – make gastrin– Goblet cells – make mucous– Gastric pit – Oxyntic gland – Parietal cells – Make

HCl– Chief cells – Zymogenic cells

• Pepsin• Gastric lipase

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Anatomy of the Stomach

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Stomach

• 3 muscle layers– Oblique– Circular– Longitudinal

• Regions– Cardiac sphincter– Fundus– Antrum (pylorus)– Pyloric sphincter

• Vascular• Inner surface thrown into folds

– Rugae• Contains enzymes that work best at

pH 1-2

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Gastric Juice

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obesity

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Stomach

• Functions– Mix food– Reservoir– Start digestion of

• Protein• Nucleic acids• Fats

– Activates some enzymes– Destroy some bacteria– Makes intrinsic factor – B

12 absorption– Destroys some bacteria

– Absorbs• Alcohol

• Water

• Lipophilic acid

• B 12

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Small Intestine

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Small Intestine

• Histology– Intestinal glands – Intestinal enzymes– Duodenal glands – Alkaline mucous– Paneth cells – Lysozyme– Microvilli– Lacteals– Plica circularis– Smooth muscle– Lymphatic tissue – GALT– Vascular

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Small Intestine

• Absorbs– 80% ingested water– Electrolytes– Vitamins– Minerals– Carbonates

• Active/facilitated transport

• Monosaccharides

– Proteins• Di-/tripeptides• Amino acids

– Lipids• Monoglycerides

• Fatty acids

• Micelles

• Chylomicrons

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Structure of the Villi in the Small Intestine

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Small Intestine

• Secretes digestive enzymes– Peptidases– Sucrases– Maltase– Lactase– Saccharidases

• Di-• Tri-

– Lipase– Nucleases

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Small Intestine

• Requires pancreatic enzymes & bile to complete digestion

• Overview of digestive system

• Layers of digestive tract

• Structure of mouth

• Teeth

• Tougue

• Salivary glands

• Pharynx

• Oesophagus

• stomach

• Small intestines

• Large intestines

• Pancreas

• Liver

• Gall bladder

• Rectum,anal cannal

• Digestion and absorbtion of nutrients

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Absorption of nutrients in SI

• Diffusion

• Active transport: FASTER

monosaccharides ,a.a,fatty acids intestinal lumen villi capillaries

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Large Intestine

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Large Intestine

• 1.5meters long,width= 6.5cm• Extends from ileocaecal valve to anus• Regions

– Caecum –– Colon

• Ascending

• Transverse

• Descending,sigmoid

– Rectum– Anal canal

Layers

• 4 layers

• Mucosa: goblet cells ------more

• Submucosa: ----more lymphoid tissue

• Muscularis---longitudinal----3bands---taenia coli

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Anatomy of the Large Intestine

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functions• Absorption

• Immunity

• Mass movement(MM) and defecation

• Intestine distend

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MM increased

• Send efferent impulses

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• Afferent impulses relax the internal sphincter

• defecation occurs

• (can be controlled voluntarity by external sphincter

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• Commensals-- non pathogenic bacteria lines intestine

• prevents harmful bacteria to attach n invade intestine

• Synthesis of vitamin K--PREVENT BLEEDING

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functions

• ABSORPTION\

• IMMUNITY

• COMMENSALS: SYSTHESIS OF VITAMIN K

• MASS MOVEMENT

• DEFECATION

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• Intestine distend

• mass movement gastrocolic reflex

• send efferent impulses to higher centers

• afferent impulses

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• relax internal anal sphincter

• defecation reflex occurs

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• controlled by voluntarity by external anal sphincter

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Difference

Large I SMALL I

LENGTH 1.5m 6m

width 6.5cm 2.5cm

parts colon Duodeum,jejunum,ilieum

haustrations + -

Taenia coli 3 0

Fat epiploic appendages + -

region retroperitoneal intraperitoneal

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ANAL CANAL

• Two sphincter muscles control the anus

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Internal external--Smooth muscle ---skeletal muscle--autonomic nerves --voluntary controlsystem

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Large Intestine

• Histology– No villi– No permanent circular folds– Smooth muscle

• Taeniae coli

• Haustra

– Epiploic appendages– Otherwise like rest of Gl tract

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Large Intestine

• Functions– Mechanical digestion

• Haustral churning

• Peristalsis

• Reflexes – Gastroileal

– Gastrocolic

– Chemical digestion – Bacterial digestion

• Ferment carbohydrates

• Protein/amino acid breakdown

– Absorbs•More water•Vitamins

– B– K

– Concentrate/eliminate wastes

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Feces Formation and Defecation

• Chyme dehydrated to form feces

• Feces composition– Water– Inorganic salts– Epithelial cells– Bacteria– Byproducts of digestion

• Defecation– Peristalsis pushes feces

into rectum– Rectal walls stretch

• Control– Parasympathetic

– Voluntary

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Pancreas

• Intraabdominal /retroperitoneal

• 60grams

• 12-15cm

• Situation: epigastrium,umbilical,left hypochondriac regoin

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Endocrinal (islet cells)

Alpha beta delta gamma-glucagon insulin somatostatin pancreatic polypeptide

- reduce the rate at --which reduces appetite

which food is

absorbed

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Exocrine (Acinar cells)

• Secrete Pancreatic Juice

-water, mineral salts,enzymes

-Proteins:trypisinogen,chymotrypsinogen

Carbohydrate: pancreatic amylase

lipids: pancreatic lipase

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Liver

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Liver

• Location– R. Hypochondrium– Epigastric region

• Lobes– Left and Right-----functionally– Quadrate– Caudate anatomically

• Each lobe has lobules – Contains hepatocytes – Surround sinusoids – Feed into central vein

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R.Atrium of heart

• IVC

• blood leavin liver

hepatic vein

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• central vein

• • sinusoid blood in liver

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• Interlobular vein

85Portal veins-de oxygenated blood

Functions--Metabolism

- carbohydrate

-fats

-proteins

--Synthesis of plasma proteins

--Defense against microbes

--Detoxification of drugs

--Inactivation of hormones

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Gall Bladder

CARBOHYDRATE METABOLISM

• Glycogenesis(excess glucose)

• Glycogenolysis(low glucose)

• Glyconeogenesis(when glycogen stores are low)

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Liver

• Functions– Makes bile

• Detergent – emulsifies fats• Release promoted by:

– Vagus n.– CCK– Secretin

• Contains– Water– Bile salts– Bile pigments– Electrolytes– Cholesterol– Lecithin

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Liver– Detoxifies/removes

• Drugs• Alcohol

– Stores• Gycolgen• Vitamins (A, D, E, K)• Fe and other minerals• Cholesterol

– Activates vitamin D– Fetal RBC production– Phagocytosis

Gall bladder

• Pear shaped

• Attached to posterior surface of liver

• Parts

• fundus

• body

• neck

• 4 layers

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• Blood supply

• hepatic artery

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• cystic artery

• blood to GB

• Drained by cystic vein +portal vein

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functions

• Reservoir of bile

• Release of bile when stimulated by hormones cholecystokinin and secreatin

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Bile

• Secreted by liver

• Ph ; 8,100-500ml

• Greyish green

• Composition

water,mineral salts,bile salts,bile pigments,cholesterol

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The Organs and Positions in the Abdominal Cavity