Digestion and Absorption Processes

• The digestive system encompasses dental, oral, and craniofacial anatomy, and physiology for patient management

Session Goals

• Describe the digestive system's organs
• Explain the functions of the major organs in digestion
• Label the different tissues and linings of digestive organs
• List the function of gastric juices
• Summarize the chemical digestion of food

Curriculum Context

• Understanding the digestive system's structure and function aids dental hygienists and therapists

Initial Knowledge Check

• Five main digestive system activities include Ingestion, Propulsion, Digestion, Absorption, and Elimination

Alimentary Canal Parts

• The mouth is the beginning of the process
• Salivary glands produce saliva to begin chemical digestion
• The gall bladder, the liver, the pancreas, the small intestine, the oesophagus and the stomach aid the digestive process
• The large intestine absorbs water
• The rectum eliminates solid waste

Alimentary Tract

• It's a tube extending from the mouth to the rectum
• As food passes through, it gets ground and mixed with digestive juices
• Food turns into small nutritional molecules through absorption and circulation
• Unused residue gets excreted

Alimentary Tract Function

• Part of the immune system
• Achieved through low pH, mucus (IgA), lysozyme, and enzymes (saliva, bile)

Digestive System Components

• These include the Mouth, Oesophagus, Stomach, Gut (small and large intestines), and Rectum

Accessory Organs

• These include the Salivary glands, Liver, Pancreas, and Gall bladder

General Structure

• It is composed of Mucosa and Submucosa
• Also composed of Circular and Longitudinal muscle layers
• The Peritoneum is also part of the general structure

Digestive Tract Walls

• Made of four key layers
• Adventitia/Serosa: the outer connective tissue
• Muscularis: smooth muscle for contractions (peristalsis); has longitudinal and circular layers
• Submucous: loose connective tissue with blood vessels, lymphatic vessels, nerves, and glands
• Mucosa: epithelial lining coated with mucus

The Mouth

• Mechanical breakdown occurs here via the teeth which physically tear and chew food into smaller pieces and create a bolus
• The Uvula prevents food or liquid from entering the nasal cavity
• The Tongue, a voluntary muscular structure, aids mastication and deglutition

Chemical Process in the Mouth

• Salivary amylase (ptyalin) breaks polysaccharides in bolus into maltose
• Starch cannot be absorbed into the small intestine
• Taste buds allow food appreciation and detect hazards

The Bolus

• Food forms a round or oval mass in the mouth after chewing
• Grinding and crushing of food occurs by teeth, also known as mastication
• Salivary glands secrete saliva (containing mucin) which makes the food moist and easy to swallow
• Enzymes that help with digestion are also released here

Salivary Glands (3 Pairs)

• Submandibular glands: They are located at the angle of the jaw and contribute 70% of saliva
• Sublingual glands: Found in front of the submandibular pair and contribute 5% of saliva
• Parotid glands: Located below the external acoustic meatus; contribute 25% of saliva
• Saliva is 99.5% water, and 0.5% is mucus and salivary amylase

Swallowing Phases

• Involves coordinated activity of tongue, soft palate, pharnyx, and oesophagus
• Phase 1: Voluntary, bolus is forced into the pharynx
• Phase 2: Reflex action
• Tongue blocks mouth, soft palate closes nose, and larynx rises so that epiglottis closes off trachea
• Food enters the pharynx and moves onward by peristalsis

Oesophagus

• Swallowed bolus travels from mouth to stomach by this muscular tube
• First part of the digestive tract proper, about 25cm long
• Lined with a mucous membrane
• Smooth muscle wall contracts to propel food towards the stomach

Peristalsis

• Rhythmic contractions of smooth muscles propel contents along the digestive tract
• Circular contraction occurs behind the bolus to prevent backwards movement
• Longitudinal smooth muscles push bolus forward
• At the end of the process, the bolus enters the stomach as chyme

More Digestive Tract Movements

• Segmentation happens in the small Intestine
• It presents as muscular movement, and a periodic constriction of segments moving backwards or forwards
• This is a mixing rather than a propulsive movement
• Propulsion comes from abdominal muscular contraction; therefore, in vomiting the peristalsis does not reverse in the oesophagus

The Stomach

• It is a hollow and muscular J-shaped organ within the left side of the abdominal cavity
• It is divided into three distinct regions
• Contains a highly acidic environment

Stomach Structure

• Parietal cells: They produce hydrochloric acid that denatures proteins
• Chief cells: They produce pepsin for protein digestion to begin
• Mucus cells: They produce mucus protecting from hydrochloric acids

Stomach Lining

• Forms deep pits with glands
• Hormones like gastrin increase HCl secretion and motility
• The stomach epithelium forms deep pits which creates glands
• The absorption of water, lipids , caffeine and alcohol occurs here
• Glands secrete enzymes, hormones and mucus
• Enzymes such as pepsinogen act as the catalyst to protein digestion

Functions Of The Stomach

• Temporary storage area for food for 3-4 hours
• Churning of food by muscular layers to form chyme, a creamy substance voided via pyloric sphincter to duodenum
• Muscles aiding mechanical breakdown relax and contract here
• surface area is increased by rugae
• The pyloric sphincter controls for emptying of chyme from stomach into small intestine

Small Intestine

• Consists of Duodenum, Jejunum, and Ileum
• Majority of digestion happening here
• Longest part of digestive system
• Usually sterile

Duodenum

• First part of small intestine, 25 cms long
• Curves around the head of the pancreas and the entry of the common bile duct
• Chemical digestion of small amount of food controlled by the pyloric sphincter
• Enzymes secreted here aid with fat digestion

Ducts entering the Duodenum

• The Bile Duct, which drains the gall bladder, from the liver
• The Pancreatic duct, which drains the pancreas

Jejunum and Ileum

• Consists of 2 and 3 meters respectively
• The absorption of fats, carbohydrates, and protein occurs here
• Lining consists of a simple columnar epithelium
• Contains Villi, which are microscopic projections to absorbs proteins
• It has a large surface area for nutrient absorption

Villi Components

• Each has one Lacteal and one Capillary
• Lacteal absorbs fat into lymphatic system
• Capillaries absorbs everything else

Accessory Organs

• These include the Liver, the Gall Bladder, and the Pancreas

Liver

• This is the largest solid organ, and largest gland in the body
• Capillaries of small intestine drain fat and nutrient rich lymph through the hepatic portal system
• This organ is multifunctional
• It secretes the Bile
• Bile is an enzyme that accumulates in the Gall bladder between meals

Gall Bladder

• A pear shaped organ located underneath the liver
• Stores and concentrates Bile when fasting
• Alkaline based which allows pancreatic enzymes to take affect
• When fats move to small intestine it releases the cholecystokinin which in turn makes the gall bladder contract
• Cholesterol may cause hepatic ducts and bile ducts to cause pain and jaundice

Bile

• The liver secretes bile to the hepatic duct
• The cystic duct delivers to the gull bladder to be stored
• Bile is released via common bile duct at the opening around the duedenom
• Contains non iron hemogloblin and bilirubin which consist of bile salts and acids
• Bile salts and phospholipids are needed to aid emulsification of fats
• Large bile acids may be reabsorbed up to 95%

Pancreas

• Considered an endocrine and exocrine gland
• Exocrine glands help to enzymes digest components that aids the duodenum via pancreatic ducts
• Endocrine aids producing glucagon and insulin
• Exocrine pancreas has two functions which includes secreting digestive enzymes and secreting aqueous bicarbonate to help neutralize acids.

Pancreatic Fluid

• Contains Sodium Bicarbonate to neutralise acidity of contents arriving in stomach
• Pancreatic Amylase: Carbohydrates becomes simple sugars such as Maltose, Sucrose and Lactase
• Pancreatic Lipase: Lipids converts to fatty acids and glycerol
• Trypsin and Chymotrypsin: Proteins make amino acids
• Nucleases: The hydrolysis of Nucleic acids that are ingested (RNA/DNA) turns into nucleotides

The Large Intestine (Colon)

• Food is not broken down any more here
• Absorption of water remains from indigestible matter
• Some electrolytes and indigestible foods are left here
• Stores and eliminates waste
• Absorbs Vitamins, bacteria gut is produced, certain B and K

More on Colon

• Less muscular
• Goblet cells secrete Mucus
• No Villi
• Takes about 16 hours to complete processes
• Bacteria Fermentation of digested material
• Combination of mucus,chyme and stomach create faeces given bile and pigments
• Gut Bacteria synthesize vitamins

Rectum

• Stores solid waste which exist through the Anus for the body to move
• Las 13cms of Large intestine
• Peristaltic wave movement
• Sphincter relaxation happens voluntarily and involuntarily

Digestion

• Food is moved and mixed , chemical breakdown is activated which break smaller food portions with catabolism
• Nutrients are physically produced by the gut which creates unusable waste
• Exocrine and endocrine secretion are both activated to produce more secretion,
• A controlled movement through digestive tracts happens

Digestive Juices

• Stomach and small intestine produce a digestive juice
• Other digestive juices come from salivary glands , gallbladder and pancreas which exit through the alimentary canal
• The digestive juices contain digestive enzymes which are needed to breakdown foods

Digestive Enzymes

• Includes amylase which aid starch, maltose and glucose
• Protease helps aid enzymes to break proteins and amino acids
• Lipase enzymes break down lipids and glycerol

Digestion of Carbohydrates

• Digestion begins within the mouth with the Salivary Amylase
• Intestinal enzymes breakdown sugar and complex carbohydrates
• Monosaccharides that creates polysaccharides breakdown the maltose to the amylase through saliva
• The pancreatic creates amylase while maltose and sucrose help produce monosaccharides

Protein DIgestion

• Starts within the stomachs and ends in the small intestine
• Stomach enzymes and trypson enzymes produce juices which helps digestion
• Intestinal enzymes help digest protein to aid amino acids
• Pepsin enzymes create small poly peptides

Lipid Distestion

• Bile is produced by the liver and pushed through the duedenoum for the body to use.
• Also needs to emulsify.
• Pancreatic lipase split a lipid which helps fatty acids and glycerol form
• Bile helps create emulsified fat and allows lipids and fatty acids to function as enzymes

Absorption

• The stomach absorbs few substances
• Small intestine absorbs the water
• combination of simple diffusion , facilitated diffusion and active transports occurs
• The hepatic portal helps transport amino acids and glucose to the liver

More on ABsorption

• Jejunum and fatty duedemum helps support the intestinal processes by providing b12 and liquids to absorb bile salts

Explore the digestive system's crucial functions, covering the roles of the gallbladder, bile salts, and nutrient absorption in different parts of the small intestine. Understand lipid and protein digestion, the impact of cholecystokinin (CCK), and the hepatic portal vein's function.