Digestive System: Anatomy and Function

Digestive System Anatomy

• Consists of the gastrointestinal (GI) tract and accessory organs.
• The GI tract is a muscular tube from mouth to anus where food passes.
• Accessory organs produce or store secretions that flow into the GI tract via ducts.

Digestive System Functions

• Ingestion occurs when food and liquids enter the oral cavity.
• Mechanical digestion involves crushing food and mixing in the stomach.
• Chemical digestion involves the enzymatic breakdown of food into absorbable molecules.
• Secretion involves the release of water, acids, enzymes, buffers, and salts.
• Absorption involves nutrient movement across the digestive epithelium into the bloodstream.
• Defecation involves the compaction of indigestible waste into feces, which are eliminated.

Mechanical Digestion

• Includes mastication (chewing), swallowing, mixing, and peristalsis.
• Muscular contractions break down food by churning and propelling it along the GI tract.

Chemical Digestion

• It involves enzymes from accessory organs and the GI tract lining that break down food chemically.
• Hydrolysis is the main process, using water to break chemical bonds.
• Fats break down into fatty acids and glycerol.
• Carbohydrates break down into monosaccharides.
• Proteins break down into amino acids.

Major Organs and Functions

• The oral cavity processes food mechanically, moistens it, and mixes it with saliva.
• The pharynx propels food into the esophagus via muscular action.
• The esophagus transports materials to the stomach.
• The stomach chemically breaks down and mechanically processes food.
• The small intestine enzymatically digests and absorbs nutrients.
• The large intestine dehydrates and compacts indigestible materials.

Accessory Digestive Organs

• Salivary glands produce saliva containing mucins and enzymes.
• The gallbladder stores and concentrates bile secreted by the liver.
• The pancreas secretes buffers and digestive enzymes from exocrine cells.
• The pancreas secretes hormones from endocrine cells.
• The liver performs almost 200 known functions.

Layers of the GI Tract

• Four major layers include the mucosa, submucosa, muscular layer, and serosa or adventitia.
• The same basic layers are present from the esophagus to the anal canal.

Mucosa

• The inner lining/superficial layer has three components: epithelium, lamina propria, and muscularis mucosae.
• In the mouth, pharynx, esophagus, and anal canal, the epithelium is nonkeratinized stratified squamous for protection.
• In the stomach and intestines, the epithelium is simple columnar for secretion and absorption.
• The lamina propria is areolar connective tissue containing blood, lymphatic vessels, and mucosa-associated lymphatic tissue (MALT).
• MALT contains immune cells, protecting against disease.
• The muscularis mucosae is a thin smooth muscle layer.
• It creates folds to increase surface area, especially in the stomach and small intestine.

Submucosa

• A layer of dense irregular connective tissue.
• It contains blood and lymphatic vessels.
• It also contains exocrine glands in some regions.
• These glands secrete buffers and enzymes into the digestive tract.
• It features the submucosal (Meissner's) plexus, a network of neurons.

Muscular Layer

• Smooth muscle is arranged in two layers.
• An inner circular layer and an outer longitudinal layer exists.
• They are involved in mechanical processing and peristalsis.
• The myenteric (Auerbach's) plexus, another network of neurons, is located between the muscle layers.

Serosa

• The outermost covering of digestive tract organs in the abdominal cavity.
• It is also called the visceral peritoneum.
• The oral cavity, pharynx, esophagus, and rectum lack a serosa.
• These are covered instead by adventitia, which firmly attaches the tract to adjacent structures.

Peritoneum

• The largest serous membrane in the body.
• It is divided into the parietal peritoneum (lining the inner surface) and the visceral peritoneum (covering organs).
• The space between is the peritoneal cavity containing serous fluid
• The serous membrane continuously secretes peritoneal fluid into peritoneal cavity, which is about 7 liters/day secreted and reabsorbed.
• The volume at any one time is about 50 mL
• It allows sliding movements without friction or irritation.
• Liver, kidney disease, and heart failure can accelerate the rate of fluid moving into the cavity.
• Accumulation of peritoneal fluid can create abdominal swelling called ascites.

Retroperitoneal Organs

• Peritoneum covers only the anterior surface.
• These include kidneys, ascending and descending colon, duodenum, pancreas, and ureters.

Peritoneal Folds

• Three major peritoneal folds exists: mesentery, omenta, and falciform ligaments.

Mesentery

• Consists of double sheets of peritoneal membrane.
• Areolar tissue lies between mesothelial layers.
• It provides an access route for blood vessels, nerves, and lymphatics.
• It stabilizes attached organs and attaches to the posterior abdominal wall.
• It prevents entanglement of intestines.
• This includes the mesocolon, the mesentery of the colon.

Omenta

• There are two omenta, they are continuations of the mesentery: greater and lesser.

Greater Omentum

• It is attached to the stomach and transverse colon.
• It forms a large pouch extending inferiorly between the anterior body wall and the small intestine.
• It contains adipose tissue for padding and protection.
• It also contains blood vessels and lymphatic tissue.

Lesser Omentum

• It suspends the stomach and duodenum from the liver.
• Provides an access route for blood vessels entering/leaving the liver.
• It is the location of the hepatic portal vein, hepatic artery, and common bile duct.

Falciform Ligament

• Connects the liver to the anterior body wall, making the liver the only digestive organ attached to the anterior abdominal wall.
• It is a remnant part of the umbilical vein.

Nerve Plexuses

• Involved in local control of digestive activities.
• Parasympathetic stimulation increases digestive muscle tone and activity.
• Sympathetic stimulation decreases muscle tone and activity.
• Two major nerve plexuses exists: submucosal (Meissner's) and myenteric (Auerbach's).

Submucosal Neural Plexus

• Located in the submucosal layer.
• It innervates the mucosa and submucosa.
• Contains sensory neurons and autonomic nerve fibers.

Myenteric Plexus

• A network of sensory neurons and autonomic nerve fibers.
• Located in the muscularis externa.
• Works with the submucosal plexus to coordinate local control of digestive activity.

Enteric Nervous System

• The submucosal and myenteric plexuses make it up.
• It is an intrinsic set of nerves (the "brain of the gut").
• Neurons extending from esophagus to anus.
• It is quasi-autonomous, acting independently with some autonomic nervous system input.

Autonomic Nervous System

• It is an extrinsic set of nerves.
• The vagus nerve (CN X) supplies parasympathetic fibers to most of the GI tract.
• The last ½ of the large intestine is supplied from the sacral spinal cord.
• Parasympathetic stimulation increases secretion and motility by increasing the activity of ENS neurons.
• Sympathetic nerve supply arises from the thoracic and lumbar region of the spinal cord.
• Stimulation decreases secretions and activity by inhibiting ENS.

The Oral Cavity

• Space containing the tongue, teeth, and gums.
• It is lined by oral mucosa (stratified squamous epithelium).
• The thin mucosa inferior to the tongue allows for rapid absorption of lipid-soluble drugs.
• Little to no nutrients absorbed here.
• Digestion of carbohydrates and lipids begins here.

Oral Cavity Boundaries

• The hard palate is formed by the palatine processes of the maxillary bones and horizontal plates of the palatine bones.
• Its thick mucosa with ridges provides traction for compression of food by the tongue.
• The soft palate is muscular posterior to the hard palate.
• Cheeks form the lateral walls.
• They are supported by pads of fat and the buccinator muscles.
• Anteriorly, cheek mucosa is continuous with the labia.
• The labia or lips form anterior boundary.
• The tongue body is anterior and mobile, forming the inferior boundary.
• The uvula is a dangling process extending from the soft palate, which assists in preventing food from prematurely entering the pharynx.
• Palatine tonsils are located on either side of the oropharynx.
• The root of the tongue is fixed, projecting into the oropharynx.
• It is marked by a V-shaped line of vallate papillae.
• Lingual tonsils are located in the root of the tongue.

Other Features

• The oral vestibule is the space between the cheeks (or lips) and teeth.
• The frenulum attaches gums to the upper lip.
• The frenulum attaches gums to the lower lip.
• Gingivae (gums) surround the base of each tooth.
• The gingivae are firmly attached to the periostea of bone.

Tongue

• The tongue is an accessory digestive organ.
• Skeletal muscle covered by mucous membrane.
• Extrinsic muscles move the tongue, in and out, for chewing and swallowing.
• Intrinsic muscles originate in and insert into connective tissue in the tongue.
• The dorsum and lateral surfaces have papillae containing taste buds and touch receptors.
• The surface is flushed by secretions of small glands.
• Secretions contain water, mucins, and lingual lipase (digests lipids).
• It is attached to the floor of the mouth by the lingual frenulum.

Salivary Glands

• Release saliva into the oral cavity.
• When stimulated; secretion increases to lubricate and begin chemical digestion.
• Three pairs of major salivary glands secrete most of the saliva: parotid, submandibular, and sublingual.

Parotid Glands

• Lie inferior to the zygomatic arch, deep to skin, covering the mandible.
• They secrete saliva via the parotid duct.
• Produce serous secretions containing salivary amylase.
• They contribute ~25% of the total saliva.

Sublingual Glands

• Located beneath the tongue.
• Sublingual ducts open into the floor of the mouth.
• They produce mucous secretions acting as a buffer and lubricant.
• They contribute ~5% of the total saliva.

Submandibular Glands

• Located medial and inferior to the body of the mandible.
• Submandibular ducts enter the oral cavity lateral to the lingual frenulum.
• They secrete a mixture of buffers, mucins, and salivary amylase.
• Cells transport IgA antibodies into saliva, for protection against pathogens.
• They produce ~70% of the total saliva.

Saliva

• Mostly water (99.5%).
• Solutes (0.5%) - including ions, dissolved gases, urea, uric acid, mucous, immunoglobulin A, lysozyme, and salivary amylase.
• It constantly flushes oral surfaces.
• Buffers keep mouth pH near 7.0, preventing acid buildup by bacteria.
• Contains antibodies (IgA) and lysozyme to help control bacteria.
• Mixes with food to form a bolus.
• Lingual glands (Ebner's glands) secrete lingual lipase.

Salivation

• Controlled by the autonomic nervous system.
• Parasympathetic stimulation promotes secretion of a moderate amount of saliva.
• Sympathetic stimulation decreases salivation.
• The taste and smell of food are potent stimulators ("cephalic phase").

Teeth

• Teeth or Dentes are accessory digestive organs.
• Dentin forms the majority of the tooth and is harder than bone.
• Covered by enamel, which is even harder.
• Two dentitions: deciduous (baby) and permanent (secondary) teeth.

Components of a Tooth

• dentin: forms the bulk of each tooth, a mineralized matrix similar to bone (but no cells)
• pulp cavity: interior chamber
• enamel: covers the dentin of the crown, composed of calcium phosphate (requires calcium, phosphate, and vit D for formation and resistance to decay)
• root canal: narrow tunnel within the root of the tooth and opening into the root canal is the apical foramen

Regions of Tooth

• The crown projects into the oral cavity from the gums.
• The neck is the boundary between the crown and root.
• The root is below the gum line, sitting in alveolus.

Digestion in the Mouth

• It is the first place where digestion begins (mechanical and chemical).

Mechanical Digestion

• Chewing or mastication.
• Food is manipulated by the tongue, ground by teeth, and mixed with saliva.
• Forms a soft, flexible mass called a bolus.

Chemical Digestion

• Salivary amylase, secreted by salivary glands, acts on starches.
• Only monosaccharides can be absorbed into the bloodstream.
• It continues to act until inactivated by stomach acid.
• Lingual lipase, which is secreted by lingual glands, acts on triglycerides/fats.
• It becomes further activated in the stomach (acidic environments).

Pharynx

• Membrane-lined cavity posterior to the nose and mouth (throat).
• The skeletal muscle wall plays a part in swallowing.
• Continuous with the esophagus.
• The common passageway for solid food, liquids, and air.
• Three regions: nasopharynx, oropharynx, and laryngopharynx.

Esophagus Function

• Actively moves food and liquids to the stomach.
• No enzymes are produced and no absorption takes place.

Esophagus Structure

• Hollow, muscular tube.
• Narrowest point at the beginning (posterior to cricoid cartilage).
• It descends posterior to the trachea.
• Enters the abdominopelvic cavity through the esophageal hiatus.

Esophagus Histology

• Mucosa: nonkeratinized stratified squamous epithelium for protection.
• Submucosa: areolar CT, blood vessels, and mucous glands.
• Muscularis externa: superior third (skeletal muscle), middle third (mix of skeletal and smooth muscle), and inferior third (smooth muscle).
• No serosa: adventitia connects the esophagus to the posterior body wall.

Control of Movement

• The upper esophageal sphincter prevents air from entering the esophagus.
• The lower esophageal sphincter, which is normally contracted, prevents backflow of stomach contents

Swallowing (Deglutition)

• Initiated voluntarily but proceeds automatically.
• Facilitated by secretions of saliva and mucus.
• It involves the mouth, pharynx, and esophagus.
• It has three phases: buccal, pharyngeal, and esophageal.

Buccal Phase

• Or voluntary phase.
• It begins with a bolus compression against the hard palate.
• The tongue forces bolus into the oropharynx.
• It also elevates the soft palate (sealing off nasopharynx).
• Entry into oropharynx triggers reflex response.

Pharyngeal Phase

• Begins with stimulation of tactile receptors in the uvula and palatine arches.
• Motor commands from the swallowing center coordinate muscle contraction in the pharyngeal muscles.
• The larynx is elevated, the epiglottis is folded, and the uvula and soft palate are elevated.
• Bolus is moved through the pharynx into the esophagus.

Esophageal Phase

• Begins as bolus is forced through the entrance to the esophagus.
• Bolus is pushed toward the stomach by peristalsis.
• The approach of the bolus triggers the opening of the lower esophageal sphincter.
• Bolus enters the stomach.
• It typically takes 9 seconds (liquids travel faster).
• A dry (poorly lubricated) bolus may require secondary peristaltic waves.

Peristalsis

• This is smooth muscle contractions that produce motility of the digestive tract.
• A wave of muscle contraction.
• Food enters the digestive tract in bolus form.
• Bolus is propelled along the tract by peristalsis.

Periodontal Disease

• Most common cause of tooth loss.
• Dental plaque forms between gums and teeth.
• Can cause gingivitis, tooth decay, eventual breakdown of periodontal ligaments, and surrounding bone.

The Stomach

• Connects the esophagus to the duodenum in the upper left quadrant.
• It serves as a mixing chamber and holding reservoir.
• Digestion of starch continues (briefly), protein digestion begins, and triglyceride digestion increases.
• Produces intrinsic factor.

Structure

• It is a muscular, expandable, J-shaped organ with three layers in the muscular layer.
• It has a highly variable shape depending on contents.
• Empty: muscular tube with constricted lumen.
• Full: can expand to contain 1 – 1.5 L of material (chyme) -- a viscous, highly acidic, soupy mixture formed from the combination of food, saliva, and gastric gland secretions.
• The lesser curvature forms the medial surface and is attached to the lesser omentum.
• The greater curvature forms the lateral and inferior surfaces and is attached to the greater omentum.

Stomach Regions

• The fundus is superior to the junction between the stomach and esophagus.
• The cardia is located in the superior, medial portion within 3 cm of gastroesophageal junction.
• The body is the largest region, between the fundus and pylorus.
• The pylorus is the sharp curve of "J" of the stomach, commonly changing shape with mixing and is made up of pyloric antrum, that is connected to stomach body and the pyloric canal which empties in the duodenum.
• Chyme leaving the stomach is controlled by the pyloric sphincter.

Rugae

• Wrinkles: prominent, temporary mucosal folds that allow gastric expansion by flattening as the stomach expands.

Histology

• The mucosa is composed of simple columnar epithelium.
• Epithelial cells produce a layer of alkaline mucus – protects epithelial cells against acid and enzymes in gastric lumen.
• The epithelial cells extend down into lamina propria, forming columns of secretory cells called gastric glands.
• Gastric glands secretions flow into gastric pits --> lumen.
• Gastric pits are shallow depressions opening onto the gastric surface.
• Active stem cells at the base of each pit replace superficial cells shed into the chyme.
• Each pit communicates with several gastric glands.
• Gastric glands in the fundus and body secrete most of the acid and enzymes.
• Gastric glands in the pylorus secrete mucus and hormones that coordinate and control digestive activity.
• Submucosa is composed of areolar connective tissue.
• The muscular layer has 3 layers of smooth muscle: outer longitudinal, middle circular, and inner oblique, which assists in mixing and churning to form chyme.
• The serosa visceral is peritoneum and from the lesser curvature, it forms the lesser omentum, and from its greater curvature it forms the greater omentum.

Cells of Gastric Glands

• The four main cell types: parietal, chief, mucous neck, and G cells.
• Parietal cells, or exocrine cells secrete intrinsic factor (a glycoprotein that aids in vitamin B12 absorption) and hydrochloric acid which activates pepsinogen & keeps stomach at a low pH.
• Chief cells, or exocrine cells secrete pepsinogen (activated by HCI to become pepsin, a proteolytic protein-digesting enzyme) and gastric lipase which digest fat.
• Mucous neck cells, or exocrine cells secrete mucus that protects epithelial layer from high acid contents.
• G cells, or endocrine cells secrete gastrin by the blood which regulates digestion.

Digestion in the Stomach

• Digestion continues in the stomach.

Mechanical Digestion

• Mixing waves are gentle, rippling peristaltic movements that create chyme.
• ~3mL of chyme is forced into the duodenum by each mixing wave, which is called gastric emptying.

Chemical Digestion

• Salivary amylase continues acting in the stomach only mixing with acidic gastric juices.
• Lingual lipase becomes more active in the stomach and digests triglycerides.
• Hydrochloric acid, secreted by parietal cells, kills many microbes, denatures proteins, and stimulates the release of hormones that promote flow of bile and pancreatic juice.
• Pepsin, secreted as pepsinogen by chief cells, becomes activated by contact with HCI for protein digestion.
• Gastric lipase, secreted by chief cells, splits triglycerides into fatty acids and monoglycerides.

Absorption in the Stomach

• Only a small amount of nutrient absorption occurs including water, ions, short-chain fatty acids, caffeine, certain drugs, and alcohol.
• Alcohol in the stomach has enzyme alcohol dehydrogenase.

The Small Intestine

• Plays a role in nutrient digestion and absorption.
• It absorbs 90% of nutrients and the remaining absorption occurs in the large intestine.
• The average overall length is 6m (20 ft).
• Three segments exists: duodenum, jejunum, ileum.

Segments of the Small Intestines

• The duodenum is the smallest in length and the segment closest to the stomach, called the mixing bowl.
• It receives chyme and digestive secretions from the liver, gallbladder, and pancreas.
• Duodenal glands produce alkaline mucous secretions and it has function to neutralize acidic chime with few circular folds and small villi.
• The jejunum is located between the duodenum and ileum -- the second longest portion, with majority of chemical digestion and nutrient absorption which contains circular folds and abundant long villi.
• The ileum is the final and longest segment which ends at the ileocecal valve.
• It has few circular folds.
• The submucosa contains aggregated lymphoid nodules.

Histology

• The mucosa is a simple columnar epithelium.
• Absorptive cells digest and absorb (most abundant).
• Goblet cells produce mucus.
• Intestinal glands produce intestinal juice.
• Paneth cells produce lysozymes.
• Enteroendocrine cells secrete secretin (S cells), CCK (CCK cells), and GIP (K cells).
• The abundance of MALT has groups of lymphatic nodules called Peyer's patches that are present in the ileum.
• The submucosa has Brunner's glands that secrete alkaline mucus to neutralize gastric acid in chyme.
• The muscularis has outer longitudinal layer and inner circular layer.
• The serosa completely surrounds the small intestine except for duodenum.

Special Structures

• Plicae circularies are series of transverse folds along the intestinal lining which increase surface area for absorption.
• The Villi are small mucosal projections that increase surface area.
• Extensive Capillary networks carry absorbed nutrients to the hepatic portal circulation.
• Lymphatic Capillary transports proteins to venous circulation.
• Smooth muscle moves in the muscularis mucosae

Microvilli

• Projections of apical membrane of absorptive cells.
• Creates a brush border with brush border enzymes.
• The brush border is a carpet of microvilli that increase surface area with enzymes.
• Enzymes then digest the products.

The Pancreas

• Has endocrine and exocrine functions.
• The exocrine functions of the pancreas contribute to digestion.
• Retroperitoneal organ that lies posterior to the greater curvature of stomach.

Ducts

• The pancreatic duct delivers exocrine secretions to the duodenum, joining the common bile duct from the liver and gallbladder and enters duodenum as a common duct as the hepatopancreatic ampulla (Ampulla of Vater).
• Accessory pancreatic duct is branches from the pancreatic duct and empties separately into the duodenum.

Pancreatic Tissue

• Made up of small clusters of glandular epithelial cells
• 99% are Pancreatic Acini (exocrine): pancreatic acinar cells secrete pancreatic enzymes and buffers
• 1% are Pancreatic Islets (endocrine): secrete hormones

Pancreatic Juice

• About 1200 – 1500 mL of pancreatic juice are produced each day
• Mostly water and ions and exocrine secretions (enzymes and buffers)
• Sodium bicarbonate – buffers acidic stomach chyme
• Pancreatic juice is slightly alkaline which stops the action of pepsin
• Enzymes - Pancreatic amylase, Proteolytic enzymes, Pancreatic lipase, Nucleases, Trypsinogen.

Pancreas Enzymes

• Pancreatic Amylase: helps breaks down starches
• Pancreatic Lipase: main digesting fat
• Ribonuclease and Deoxyribonuclease helps break down RNA and DNA
• Proteolytic Enzymes: Secreted as inactive proenzymes and Activated in the duodenum (Trypsin, Chymotrypsin Carboxypeptidase, Elastase)

Trypsin

• Trypsinogen is released from pancreas and brush boarder enzymes will help breakdown and will activate other inactive enzymes

Liver

• Largest visceral organ and inferior to the diaphragm, Gallbladder which stores bile produced by the Liver.
• Surrounded by visceral peritoneum.

Liver Functions

• Carbohydrate and lipid metabolism
• Protein metabolism: Hepatocytes deaminate amino acids an will convert toxic ammonia to urea
• drug and hormonal processing
• bilirubin Excretion
• bile synthesis
• Vitamin d activation
• Phagocytosis and Vitamin Storage

Associated Structures

• Gallbladder
• Bile Ducts

Cells of the Liver

• Hepatocytes: Excretory product and digestive secretion
• Stellate Macrophages:Aka Kupffer cells, Immune function and Iron storage

Liver Ducts

• Bile Canaliculi: ducts between hepatocytes that lead to liver
• Hepatic Sinusoids: reciving oxygenated blood and converging to blood
• Portal Triad: contain three structures: A branch of the hepatic portal vein , A branch of the hepatic artery & A bile duct

Functional Anatomy of a Liver Lobule

• Blood enters the liver sinusoids from branches of the hepatic portal vein and hepatic artery proper
• Hepatocytes adjacent to the sinusoids regulate solute and nutrient levels by absorption and secretion
• stellate macrophages in the sinusoidal lining engulf pathogens and store iron
• Sinusoids drain into a central vein.

Bile

• Hepatocytes secrete 800 – 1000 mL of bile daily
• Bile salts play role in emulsification and aid in absorption of lipids
• The Fat will brake down mechanically but it will stay as fat and not change

The Gallbladder

• Hollow, pear-shaped organ located in the depression on the right lobe of the liver posterior surface
• Mucosa layer consists of simple columnar epithelium that makes rugae
• Pulls water out of the mile to make the bile more effective and powerful
• The Gallbladder Stores Bile that gets produced in the LIVER

Path of Bile

• Bile flows from the common hepatic duct to the to liver and goes to the duodenum: The cystic duct for gallbladder storage and enters Hepatopancreatic ampulla

Functional Relationship between the Liver and Gallbladder

• Liver produces about 1 L of bile per day and release from CCK TRIGGERS: dilate hepatopancreatic sphincter and contraction of gallbladder

Intestinal Juice

• Secreted by glands of the small intestine.
• Contains water, mucus, and is slightly alkaline.
• Provide liquid aid absorption and to move contents around

Brush Boarder Enzymes

• Inserted onto of cell on he membrane- some digested occurs surface
• Carbs: A-dextrinase, Maltase, Sucrase & Lactase
• Proteins: Aminopeptidase and Dipeptidase
• Nucleosides: Nucleosidases & Phosphatases

Digestion in the Small

• Mechanical Digestion: segmentation localized, mixing which mixes chyme with digestive juices Chemical Digestion Carbs: need break down- salivary amayse that continues in pancreases that brake down more and is he Brush border enzymes break to mono Small break down big 1: A-dextrinase 2: Sucrase 3: Lactase 4: Maltase and most digestion that happens in small I

Lactose Intolerance

• Mucosal cells of the small intestine fail to produce lactase if there is no lacatse causes water to be retained in the colon
• symptoms: diarrhea and gas

Chemical Digestion: Proteins and Lipids

• Proteins: proteins have been broken down into smaller peptide molecules in the stomach by – Pepsin and Help complete it - 1: Trypsin 2: Chymotrypsin 3: Carboxypeptidase 4:Elastase Brush boarder and Aminopeptidase
• Lipids: fats come form:1.Lingual lipase - tongue 2. Gastric lipase - stomach & Pancreatic lipase - Triglyceride: Most important in triglyceride digestion - Bile salts – emulsify fats that help enzymes

Absorption in the Small

• point is to have small molecules that need to be absorbed through the epithelial
• Monosaccharides, single amino acids and fatty acids
• Absorbing depends on the molecule - Diffusion, facilitated diffusion, osmosis, and active transport
• About absorbs occurs - 90% in and 10% in small/large i

Absorption- Mono and Amoino

• Mono: facilitated diffusion or active transport into the cell + facilitate diffusion by capillarys
• Animno: absorbed as amino acids by – Active transport into cell

Absorption Lipids

• Absorption: Lipids. All by Simple diffusion to the Cell Short Can: direct with no problems Long Chain: Micelles that take the stuff where bile cell make micelles where the Cell needs to get to then triglycerides where an end zone called chylomicrons come so the product act on tryg

Absorption MicroNutrience

• Electrolytes- active transport some vitamins: Simple and is transported in lipids with micelles Water comes from Total amount of digestion of enzymes is 20

Large Intestine

• Also known as large bowel which 1. reabsorption of water 2. vitamin produce 3. storing fecael material
• Starts in the ileum

Cecum

• Expanded pouch distal for collecting and storing
• Appendix attached
• The Colon : Ascending colon, Transverse colon, Descending colon & Sigmoid colon

Descending Rectum

• Expandable for storage
• To Exit a and anus
• the Interanal sphincter is under no voluntary

Histology Of the large Colon

• Has distinctive cell more mucus cells but less surface area and more enzymes

Mucluaris

• Not much digestion which occurs but there is some for the bacteria

Digestion:

• Bacteria acts to : Ferment any remaining carbohydrates Decomposes bilirubin and vitamins water gets absorbs And acocunts for absoprtion