Anatomy Topic 10

Functions of digestive system

ingest food, breakdown into nutrient molecules, absorb nutrients into bloodstream, remove indigestible remains from the body

Alimentary canal (GI) tract

muscular tube, mouth to anus (9m), mouth, pharynx, esophagus, stomach, small intestine, large intestine, anus

Accessory organs

teeth, tongue, gall bladder, digestive glands (salivary glands, liver, pancreas)

Digestive process - Ingestion (1)

taking in food/eating

Digestive process - Propulsion (2)

movement of food through the alimentary canal, voluntary (swallowing), involuntary (peristalsis)

Propulsion - Perstalsis

main route of propulsion of food, alternating waves of contraction and relaxation

Propulsion - Segmentation

constriction of intestine to allow mixing of food with digestive juices, continuous movement across intestinal wall, mechanical breakdown

Digestive process - Mechanical breakdown (3)

organs of the alimentary canal increases surface area for enzymatic breakdown (chewing - in the mouth using teeth), (churning - in the stomach when muscles squeeze food and churn it around)

Digestive process - Digestion (4)

mostly chemical

Digestive process - Absorption (5)

digested fragments from lumen of GI tract pass into the blood or lymph

Digestive process - Defecation (6)

indigestible part is eliminated through the anus as feces

Serous membranes

lined with moist serous membranes, parietal peritoneum, peritoneal cavity, visceral peritoneum

Mesenteries

formed by double layer of peritoneum, attaches intestine to posterior abdominal wall, support and stabilizes GI tract organs, store fat, contains blood and lymphatic vessels, nerves (supplies the digestive organs)

Greater and lesser omentum

dorsal mesenteries, greater holds the small intestine, lesser holds the stomach and liver

Proper mesentery

small intestine

Mesocolon

large intestine

Four tunics - Mucosa

secrete mucus, digestive enzymes, and hormones, absorb food, protection from infection, innermost layer

Mucosa - epithelium

stratified squamous (mouth, esophagus, anus)

simple columnar (rest of GI tract, mucus secretion)

innermost section of the mucosa

Mucosa - lamina propria

loose areolar connective tissue, lymphoid tissue

middle section of mucosa

Mucosa - muscular mucosae

smooth muscle, helps movement of mucosa, outermost layer of mucosa

Four tunics - submucosa

areolar connective tissue, nerves, lymphatic vessels, blood vessels, elastic fibers, second inner layer

Four tunics - muscular externa

inner layer is circular, outer layer is longitudinal, forms the sphincters, helps in peristalsis and segmentation, third innermost layer

Four tunics - Serosa

areolar connective tissue, visceral peritoneum, serosa in esophagus is called adventitia, outside layer of the tunics

Organs associated with the mouth

mouth, tongue, salivary glands, teeth, walls of mouth lined with thick stratified squamous epithelium to resist abrasion

Oral cavity - positions

Lips: anteriorly

Oropharynx: posteriorly

Cheeks: Laterally

Palate: Superiorly

Tongue: Inferiorly

Oral vestibule

area between lips and teeth

Labial frenulum

medial structure that joins lips to gum

Palate

roof of mouth

Hard palate

palatine bone

raphe: midline ridge that increases friction

Soft palate

uvula: fleshy extension at the end of soft palate

closes of nasopharynx when swallowing

Tongue

occupies floor of mouth, composed of criss-crossing bundles of skeletal muscles

Tongue functions

gripping and repositioning of food during chewing, formation of bolus (food and saliva), initiation of swallowing, speech, and taste

Parotid glands

anterior to ear, parotid ducts open through 2nd upper molar

Submandibular glands

along mandibular body, ducts open at base of sublingual frenulum

Sublingual glands

anterior to submandibular gland, ducts open along floor of mouth

Functions of saliva

mouth cleanser, dissolves food chemical for tasting, moistens food and forms bolus, enzymes in saliva begin chemical breakdown

Saliva chemical state

mainly water and slightly acidic, electrolytes, defensive proteins, and enzymes (amylase and lipase)

Teeth

lie in alveolar processes in mandible and maxilla, periodontal ligament forms gomphosis fibrous joint, hardest substance in body, covered by enamel, mineralized with calcium salts and hydroxyapatite crystals, mastication

Pharynx and Esophagus

food is swallowed (deglutination), bolus travels through pharynx and esophagus, esophagus is route for food from pharynx to stomach, passes through mediastinum of the thoracic cavity, epiglottis covers laryngeal opening, food in esophagus undergoes peristalsis/segmentation, connects to stomach through gastroesophageal sphincter

Stomach

physical and chemical degradation of food, mechincal breakdown, HCl acid denatures proteins, pepsin breakdown proteins, holds food, bolus converted to chyme in stomach

Stomach gross anatomy

cardia, fundus, body, pyloris, pyloric sphincter (smooth muscle connects to duodenum, gastric folds - rugae), greater and lesser curvature

Greater omentum

from greater curvature to transverse colon

Lesser omentum

from lesser curvature to liver

Stomach wall layers

mucosa, submucosa, muscularis externa, serosa, mucosal layer for secretions, has gastric pits

Stomach - mucosal layer

surface mucous cells made of simple columnar epithelium, mucus in alkaline, for protection

Stomach - mucous neck cells

produce acidic mucus

Stomach - parietal cells

contain HCl, lowers pH

Stomach - chief cells

acidic pH converts pepsinogen to pepsin (protein digestion)

Stomach - enteroendocrine cells

contains gastrin, maintains stomach secretion and motility

Small intestine - duodenum

curves around the pancreas, pyloric sphincter in stomach connects to duodenum, site for most absorption

Small intestine - jejunum

attached posteriorly by mesentery

Small intestine - ileum

attached posteriorly by mesentery, joins large intestine at ileocecal valve/sphincter

Small intestine - circular folds

force chyme down the lumen, increases absorption time

Small intestine - villi

fingerlike projections of muscosa

Small intestine - microvilli

cytoplasmic extensions of mucosal cells on villi

Large intestine

greater diameter than small intestine, shorter than small intestine, absorbs remaining water from small intestine, site for mutualistic bacteria that aids digestion, storage and elimination of undigested food, Vit. K absorption

Large intestine - ileocecal valve

connects to small intestine

Large intestine - cecum

blind pouch that connects to appendix

Large intestine - appendix

mass of lymphoid tissue

Large intestine - colon

longest part, ascending, transverse, descending, sigmoid

Large intestine - rectum

rectal valve in rectum, stops feces from being passed with gas

Large intestine - anal canal

opens externally at the anus, internal sphincter, external sphincter

Liver

right lobe, caudate lobe, qaudrate lobe, left lobe

Liver functions

produce bile for digesting fats, stores nutrients (glucose/glycogen), detoxification

Hepatic portal circulation: connects veins from small intestine to heart

Gall bladdar

inferior to liver, concentrates and stores bile

cystic duct: connects gall bladdar to bile duct

Pancreas - exocrine functions

secretes digestive enzymes into ducts

Proteases (proteins)

Amylase (starch)

Lipases (fats)

Nucleases (nucleic acids)

Bicarbonate

Alkaline pH

Pancreas - endocrine functions

secretes into blood, produces insulin and glucagon in pancreatic islets

Bile and pancreatic secretion into small intestine

bile duct and pancreatic duct untie in the wall of duodenum, fuse together in hepatopancreatic ampulla (bulblike), entry in controlled by hepatopancreatic sphincter