Digestive system

Know and understand the functions of the digestive system overall

Ingest, transport, and digest food. (Mechanical: peristalsis & segmentation & chemical). Absorbs nutrients into blood. Expels the waste products from the body. Two separate categories of organs (Digestive & accessory digestive organs). And collectively make up the gastrointestinal tract (digestive tract)

Peristalsis

Longitudinal wave like contractions that propel along bolus in gi tract wall

Segmentation

Circular fibers of smooth muscles contract and pinches off tube like sphincters closing and opening repeatedly mixing the bolus and breaking it up to smaller boli

GI Tract Organs

Oral cavity, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus. GI tract is a continuous tube about 30 feet from mouth to anus

Functions of GI tract

include protecting against corrosive effects of digestive enzymes and acids. Defense against swallowed pathogens, and mechanical stresses.

Know the tunics of the digestive system, and respective anatomy and functions, and their order from deep to superficial

From the esophagus through the large intestine is a tube composed of four concentric layers (Tunics)

Mucosa

Epithelium, connective tissue, smooth muscle, glands. May have folds to increase surface area and expansion

Submucosa

Superficial of mucosa. Connective tissue, glands, blood vessels.

Muscularis

Superficial of submucosa. Two layers of smooth muscle (Circular and longitudinal), sphincters. Mechanical processing, propulsion, parasympathetic & sympathetic innervation.

Adventia

Superficial-most tunic. Serous membrane, protective outer layer

Oral cavity

The entrance to the GI tract. Initial site of mechanical digestion and chemical digestion. Vestibule is the space between the cheeks, lips, and gums

Tongue

Manipulates material inside the mouth that leads to swallowing. Papilla, skeletal muscle, lingual frenulum, lingual tonsils.

Palates

Function is when swallowing, the soft palate and uvula elevate to close of the opening of the nasopharynx

Hard palate

Anterior two thirds, maxilla & palatine bones

Soft palate

Posterior one third, is soft and muscular

Uvula

extends inferiorly from the posterior part of the soft palate

Palatine tonsils

Lateral walls of oral cavity

Salivary glands

Moistens ingested food, turns into bolus. Moistens and cleanses the oral cavity structures. Contains antibodies and an antibacterial element that help inhibit bacterial growth

Three pairs of salivary glands

Parotid, submandibular, and sublingual glands. Watery medium into which food molecules are dissolved so taste receptors can be stimulated. Volume secreted daily ranges from 1-1.5 liters. Most is produced during mealtime.

Parotid

Largest salivary glands, anterior and inferior to ear, partially overlying the masseter muscle. Produces around 25-30% of the saliva. And secretes fluid rich in amylase to break down carbs

Submandibular

Inferiorly to the body of the mandible. A duct from each gland opens on the lateral sides of the lingual frenulum. Produces most of the saliva (60-70%). And secretes semi-viscous fluid.

Sublingual

Inferior to the tongue. Each gland extends multiple tiny ducts that open onto the inferior surface of the oral cavity. Contributes about 3-5% of total saliva. And secretes thick, stringy mucous

Teeth

Responsible for mastication, the first part of the mechanical digestion process. A tooth has an exposed crown, a constricted neck, and one or more roots that anchor it in the jaw. Roots of the teeth fit tightly into alveoli, within the alveolar processes of both the maxillae and the mandible

Gomphosis joint

The roots, alveoli, and ligament (that binds the roots to the alveolar processes)

Types of teeth

Incisors, cuspids/canines, bicuspids/premolars, and molars

Pharynx

Passageway for food, air and liquids. Pharyngeal muscles initiate swallowing of bolus

Esophagus

Long muscular tube. Posterior to trachea, goes into the peritoneal cavity, and empties into the stomach.

Stomach

Located in the upper left quad of abdominal cavity. Acts as temporary storage for food with limited amount of absorption. Mechanical breakdown of food, digestion of proteins aided by gastric juices (hydrochloric acid ph2.0) and digestive enzymes. Lined by simple columnar epithelium and renewed every 3-6 days

Regions of stomach

Cardia, fundus, body, pylorus, rugae, pyloric sphincter. Bolus becomes chyme in the pyloric sphincter.

Mesenteries

Stabilize position of attached organs, access for B.V., nerves and lymphatic

Lesser omentum

Between stomach and liver

Greater Omentum

Posterior to stomach, body wall to anterior surface of intestines

Adipose

Energy storage, insulation

Small Intestine

Finishes the chemical digestion process, responsible for absorbing most of the nutrients. Ingested nutrients spend at least 12 hours. Coiled, thin walled tube about 20 feet in length. Extends from the pylorus of the stomach to the cecum of the large intestine, occupies a significant portion of the abdominal cavity.

Duodenum

First segment of the small intestine, originates at the pyloric sphincter. Receives secretions from liver and pancreas, mostly fixed in position.

Jejunum

Middle region, lots of digestion & absorption, free moving

Ileum

Last region, ends at the ileocecal valve, free moving. Contains less villi than in jejunum

Circular folds

increase surface area and slow food down

Intestinal Villi

Increase surface area and aid in absorption & chemical digestion

Villi

Secretions of intestinal juices and mucus to help dissolve nutrients for absorption, buffer lining, and enzymes to aid in digest saccharides, peptides, and fats

Large Intestine

Absorbs water and electrolytes from the remaining digested material that compacts to form feces. Stores feces until the body is ready to defecate. Approximately 5 feet in length. Secretions are only mucus to lubricate and buffer chyme

Segments of Large Intestine

Composed of four segments, cecum, colon (ascending, transverse, descending, and sigmoid), rectum, anal canal (internal anal sphincter (involuntary) and external anal sphincter (voluntary)

Liver

Right and left lobe, separated by ligaments (Falciform, coronary, and round), surrounded by fibrous capsule. Highly vascular, reddish in color. Dual Blood Supply. Hepatic veins drain into inferior vena cava. Cells can regenerate

Hepatic Portal Vein

Blood from digestive tract brings newly absorbed nutrients to liver

Hepatic Artery Portal Vein

Brings oxygenated blood.

Functions of the liver

Produces bile that assists chemical digestion by breaking down fats, stored in gall bladder. Maintenance of normal blood glucose, amino acid, and fatty acid concentration. Removes toxic substances, detoxifies drugs, metabolites, and poisons. Storage of glycogen, lipid reserves, iron and vitamins A D E and K, and releases them when they are needed.

Blood Liver Functions

Synthesize blood plasma proteins such as albumins, globulins, and proteins required for blood clotting. Breaks down and recycles components of aged RBCs and other damaged formed elements. Phagocytic macrophages filter out foreign particles and damage RBCs

Gallbladder

Pear shaped sac located under the liver. Concentrates bile produced by the liver and stores until needed for digestion. Cystic duct connects the gallbladder to the common bile duct

Pancreas

Found beneath the stomach and associated with small intestine. Pancreatic duct runs through middle. Endocrine functions are performed by the pancreatic islets. Exocrine activity results in the secretion of pancreatic juices by pancreatic acini cells into the duodenum. Contains enzymes capable of digesting proteins, carbs, and fats

Know and understand the function and composition of bile, as well as the biliary apparatus. - Bile

assists chemical digestion by breaking down fats, stored in gallbladder. Water, bile salts, pigments, cholesterol and electrolytes. Salts are requires for normal lipid digestion and absorption, plus it helps with absorption of fat soluble vitamins and cholesterol. Other material help to dilute and buffer the chyme

Biliary apparatus

Bile drains from the left and right hepatic ducts into the common hepatic duct to the cystic duct. The cystic duct and common hepatic duct merge to form common bile duct

Sphincter list

Mouth, upper esophageal sphincter, lower esophageal sphincter (cardiac), pyloric sphincter, internal anal sphincter (involuntary), external anal sphincter (voluntary)