Download Digestive system

Digestive system
Digestive System Functions
•Ingestion: occurs when materials enter digestive tract via the mouth
•Mechanical processing: crushing and shearing; makes materials easier to propel along digestive tract
•Digestion: is the chemical breakdown of food into small organic fragments for absorption by digestive
epithelium
•Secretion: is the release of water, acids, enzymes, buffers, and salts by epithelium of digestive tract by
glandular organs
•Absorption: movement of organic substrates, electrolytes, vitamins, and water across digestive epithelium into
interstitial fluid of digestive tract
•Excretion: removal of waste products from body fluids
Alimentary Canal
•a hollow tube extending from mouth to anus
•Four main tissue layers
–Mucosa
–Submucosa
–Muscularis externa
–Serosa
•Foods must be broken down to their building blocks to be absorbed.
–Carbohydrate building blocks: simple sugars
–Protein building blocks: amino acids
–Fat or lipid building blocks: fatty acids and glycerol
Oral cavity
Functions of Oral Cavity
•Lubrication: mixing with mucus and salivary gland secretions
•Limited digestion: of carbohydrates and lipids
•Sensory analysis: of material before swallowing
•Mechanical processing: through actions of teeth, tongue, and palatal surfaces
Tongue
Salivary Glands
•Three pairs – parotid, submandibular, and sublingual
•Secrete saliva into the oral cavity
•Contains mucus and serous fluids
•The serous component contains salivary amylase
Teeth
•Two sets of teeth are formed.
•The first set consists of 20 deciduous teeth that begin to appear at 6 months of age and are lost by 12 years.
•Permanent teeth (32) begin to replace deciduous teeth around 7 years.
•A typical tooth consists of crown covered with enamel and root covered with cementum.
•Most of the tooth is bonelike dentin.
•The pulp cavity contains blood vessels and nerves
Types of Teeth
•Incisors – thin, sharp teeth that are best for cutting ( 8 total)
•Canines – teeth that aid in tearing ( 4 total)
•Premolars – grinding food ( 8 total)
•Molars – larger and also used for grinding (12 total)
Mastication: Also called chewing
•As you chew your food it mixes with saliva and becomes a round ball called a BOLUS.
Pharynx
•The pharynx is a muscular tube that provides passage way for both food and air.
•Regions of the Pharynx
–Nasopharynx
–Oropharynx
–Laryngopharynx
•Food passes through oropharynx and laryngopharynx to esophagus
Swallowing
•Swallowing has two phases:
–The buccal phase
•voluntary
•begins in the mouth
•the tongue pushes the bolus into the pharynx
–pharyngeal-esophageal phase
•involves the closing off of nasal and respiratory passages
•conduction of food to the stomach by peristalsis from the pharynx through the esophagus
Peristalsis
Esophagus
•A hollow muscular tube
•About 25 cm long and 2 cm wide
•Conveys solid food and liquids to the stomach
•Begins posterior to cricoid cartilage
Stomach
Functions of the Stomach
•Storage of ingested food
•Mechanical breakdown of ingested food
•Disruption of chemical bonds in food material by acids and enzymes
•Production of intrinsic factor: glycoprotein required for absorption of vitamin B12 in small intestine
Regions of the Stomach
Parts of the stomach
Stomach Anatomy
•C-shaped organ
•located on the left side of the abdomen beneath the diaphragm.
•Food enters it through the cardio-esophageal sphincter
•Food leaves to enter the small intestine through the pyloric sphincter.
4 Layers of the Stomach
•Serous Coat: covers most of the stomach
•Muscular Coat: churns food, three layers of muscles that run in different directions
•Mucous Coat: protects the inner lining of the stomach
•Submucosal Coat: connects the muscular and mucosal layers
Stomach Layers
Mechanical Digestion
•3 layers of muscularis layer
–Longitudinal
–Circular
–Oblique
•3 layers allow churning and mixing of food (mechanical digestion)
What happens in the stomach?
•Food enters and gastric secretions is stimulated by the vagus nerves and by gastrin
•HCL activates the protein digesting enzyme pepsin
•Food is mechanically broken down by churning of stomach muscles
Mucous Coat of Stomach
•Mucous cells secrete mucous that protect the cells lining the stomach and prevent the stomach from digesting
itself.
•When the stomach is empty, the walls are folded into rugae (stomach folds), which allow the stomach to
expand as more food fills it.
Stomach Digestion
•Peristaltic contractions (mechanical digestion) mix the bolus with strong digestive juices that the stomach
lining cells secrete (chemical digestion)
Stomach - Chemical Digestion
Carbohydrate digestion continues in the stomach.
•Protein digestion begins in the stomach.
–Pepsinogen and HCL are secreted into the lumen of the stomach
–HCL converts pepsinogen to pepsin and contributes to the breakdown of the bolus into a liquid called
chyme.
–Pepsin begins the chemical digestion of proteins.
Stomach
•Stomach has stretch receptors to indicate to the brain when stomach is full.
•Food is digested in the stomach for several hours.
•Chyme is slowly transported from the pylorus (end of the stomach) through the pyloric sphincter into the small
intestine.
Stomach to small intestine
•Food moves through the pyloric sphincter into the small intestine
•Chyme – name given the partially digested food that moves into the SI from the stomach.
Small Intestine
•Tube-like suspended from the posterior body wall by the mesentery
•21 feet long
•Begins at the pyloric sphincter and ends at the cecum
•Food digestion and absorption are completed here
3 Parts of the small intestine
•The small intestine is subdivided into the duodenum, jejunum, and ileum.
Intestinal Movement
•SI moves food by peristalsis and mixes it by segmentation
•Peristalsis propels food through the intestine by waves
•Segmentation mixes food by sequential movement.
Peristalsis
Segmentation
Duodenum
•The first portion of the small intestine is the duodenum where acidic chyme from the stomach mixes with
–bile from the liver & gallbladder
–digestive juices from the pancreas & intestine itself.
Small Intestine: Chemical Digestion:
The pancreas and gland cells of the small intestine secrete digestive enzymes. Enzymes include
–Trypsin: protein digestion
–Amylase: carbohydrate digestion
–Lipase: lipid digestion
•Bile is created in the liver and stored in the gallbladder.
–emulsifies (breaks down) lipids (fats)
•like dish detergent with grease
Pancreas
•Secretion of pancreatic juice into the duodenum
•Pancreatic juice contains enzymes that digest carbs, fats, proteins, and nucleic acids
Liver
•Largest internal organ
•Liver is divided into two lobes
•Secretes a digestive fluid called bile, produced by the breakdown of dietary fats and old red blood cells
•Removes toxins and wastes from the blood
Gall Bladder
•Pear shaped sac on the inferior surface of the liver
•Stores bile from the liver
Digestion Ends
•Once food passes through the duodenum, digestion is complete.
Small Intestine: Jejunum and Ileum
•Chyme then passes into the jejunum and ileum.
Surface of Small Intestine
•Surface contains lymph vessels and small arteries and veins
•Millions of projections called villi increase surface area which aids in absorption of nutrients
Food Absorption
•Food molecules enter the bloodstream through intestinal walls
•Capillaries absorb proteins and carbohydrates
•Lymph vessels absorb products of fat digestion that eventually lead to the bloodstream
Wall of Small Intestine
Intestinal villi
Large Intestine
•Once food has passed through the small intestine it is mostly undigestible material and water.
•Food now enters the large intestine
Large Intestine 6 parts
Cecum Ascending colon Transverse colonDescending colonSigmoid colonRectum
Colon
Cecum
•Pouch shaped beginning of the colon
•Appendix is attached to the bottom of the cecum
•Appendix intercepts pathogenic microorganisms and sometimes fecal matter
Large Intestine
•The rest of the large intestine absorbs water and turns chyme into feces
Rectum
•Final section of the large intestine
•Empty except just before and during defecation
Anus
•Contain two sphincters which act as valves during defecation
Disorders of the Digestive System
Hernia - A protrusion of an organ or body tissue out of the body cavity that it normally occupies.
Peptic Ulcer - Areas of eroded tissue in the lining of the stomach, esophagus, or duodenum
Liver Disease - Cirrhosis – scarring of the liver from alcohol abuse
Hepatitis - Inflammation of the liver
Gallstones- Solid accumulation of bile pigment and cholesterol
Cancer - Pancreatic and colon cancer
Hemorrhoids - Swollen veins in the lining of the anus; can be internal or external
Nutrition
Nutrients: Chemical substances supplied from the environment that an organism requires for survival
Metabolism: All chemical breakdown (catabolic) and building reactions (anabolic) needed to maintain life
Sources of major nutrients
 Carbohydrates
Organic compounds which include sugars and starches
One of the bodies main sources of energy
 Lipids
Organic compounds that include fats, oils, and fatlike substances.
The bodies other main source of energy
 Proteins
Long chains of amino acids that help with cell growth and repair
 Vitamins
Organic compounds required in small amounts.
Fat-soluble vitamins are A, D, E, and K
Water-soluble vitamins are B and C
 Minerals
Inorganic elements that are essential in human metabolism.
Most concentrated in bones and teeth and make up about 4% of our body weight