PT18: Digestive System

Digestive system

consists of organs and other structures responsible for process of digestion

Digestion

breakdown of food into small pieces until it can be absorbed and incorporated into the body

Where does the digestive system begins?

oral cavity

Where does the digestive system end?

rectum and anus

Gastrointestinal (GI) tract

primary part of digestive system; passageway from mouth to anus

GI tract pathway

oral cavity -> pharynx -> esophagus -> stomach -> small intestine -> large intestine -> rectum and anus

Accessory organs

secondary part of digestive system; aid in digestion

Accessory organs are...

pancreas, liver, gallbladder

Proximal part of digestive system

oral cavity and pharynx

Oral cavity

consists of mouth, teeth, jaws, and tongue to initiate digestion

Saliva

secretes digestive enzymes in mouth

Mastication

muscles that is used for chewing

Pharynx

semicylindrical tube formed by muscle and fascia; in between oral cavity and esophagus

Esophagus

muscular tube that connects pharynx to stomach

What vertebral level does the esophagus pass through the diaphragm?

T10

Esophagus location in thorax

anterior to vertebral column and posterior to trachea

Stomach

a dilated, J-shaped oran that is between the esophagus and small intestine

Stomach function

secretes gastric acid and digestive enzymes to aid in digestion

Fundus of stomach

area located above and to left of opening of esophagus

Cardia of stomach

area surrounding opening of esophagus into stomach

Body of stomach

centrally-located and largest region of stomach

Pylorus of stomach

distal end of stomach; connects to small intestine

Pyloric syphincter

regulates passage from stomach to small intestine

Small intestine

organ between stomach (proximally) and large intestine (distally); longest part of GI

Small intestine function

most of absorption of chemicals

Small intestine parts

duodenum -> jejunum -> ileum

Duodenum

first part of small intestine; C-shaped concave portion and adjacent to head of pancreas

Large intestine

located distally to small intestine; relatively short with wider diameter than its counterpart

Large intestine function

produces feces (by absorbing water and salt) and excretes it from body

Large intestine parts

cecum -> ascending colon -> transverse colon -> descending colon -> sigmoid colon -> rectum and anus

Appendix

short extension of cecum

Pancreas

accessory organ that secretes pancreatic juice into duodenum to aid in digestion

Pancreatic juice

a combination of enzymes and bicarbonate to neutralize acid

How much pancreatic juice is produce by the pancreas per day?

200-800 mL

Head of pancreas

located with C-shaped concavity of duodenum

Neck of pancreas

located left of head; posterior to pylorus of stomach

Body of pancreas

elongated portion of pancreas; posterior to body of stomach

Tail of pancreas

narrow extension of pancreas on left side; distal end is adjacent to spleen

Bile duct

conveys bile from liver/gallbladder; formed by common hepatic duct and cystic duct

Hepatopancreatic ampulla

formed by junction of main pancreatic duct and bile duct in head of pancreas; mixes bile with pancreatic juice

Main pancreatic duct

begins in tail of pancreas, continues through body, neck, and into head of pancreas

Duodenal papilla

raised area in duodenum where hepatopancreatic ampulla enters

Liver

an accessory organ located primarily on right side of abdominal cavity; inferior to diaphragm

Liver functions

detoxification of venous blood (via portal system) and production of bile

Bile

a substance that aids in digestion of fat

Liver lobes

right, left, caudate, and quadrate

Right lobe of liver

largest lobe of liver; occupies most of the right side

Left lobe of liver

second largest lobe of liver; occupies most of left side

Falciform ligament

separates right and left lobes on anterior side of liver

Quadrate lobe of liver

located on posterior surface of liver adjacent to gallbladder

Caudate lobe of liver

located on posterior surface of liver adjacent to inferior vena cava

Where is bile collected from the liver?

right and left hepatic ducts

What do the right and left hepatic ducts form?

common hepatic duct

Gallbladder

a pear-shaped sac located between right and quadrate lobes of liver

Gallbladder function

stores and concentrates bile produced by liver before it is delivered to duodenum

Neck of gallbladder

narrow ending leading to cystic duct

Fundus of gallbladder

rounded inferior end of gallbladder

Body of gallbladder

largest/main portion of gallbladder

Cystic duct

bidirectional duct that carries bile from common hepatic duct to gallbladder

Common bile duct

formed by common hepatic duct and cystic duct to carry bile to hepatopancreatic ampulla

Foregut-derived organs

stomach, duodenum (prox half), liver, gallbladder, pancreas, spleen

Midgut-derived organs

duodenum (distal half), jejunum, ileum, cecum/appendix, ascending colon, 2/3 of proximal transverse colon

Hindgut-derived organs

1/3 of distal transverse colon, descending colon, sigmoid colon, rectum, anus

Foregut blood supply

celiac trunk

Midgut blood supply

superior mesenteric artery

Hindgut blood supply

inferior mesenteric artery

Celiac trunk major branches

left gastric a., common hepatic a., and splenic a.

Celiac trunk

branches from abdominal aorta by superior part of L1 vertebra, inferior to aortic hiatus

Superior mesenteric artery branches

middle colic a., right colic a., ileocolic a., jejunal a., and ileal a.

Superior mesenteric artery

branches from abdominal aorta at inferior part of L1 vertebra, inferior to celiac trunk and posterior to pancreas

Inferior mesenteric artery major branches

left colic a., superior rectal a., and sigmoid arteries

Inferior mesenteric artery

branches from abdominal aorta by body of vertebra L3, posterior to small intestine

Portal system

drains all blood from abdominal viscera and delivers it to liver, where it is filtered/detoxified before returned to heart

Portal vein

final, common pathway of venous blood portal system before it enters liver

Splenic vein

venous drainage from foregut-derived viscera

What forms the portal vein?

splenic and superior mesenteric veins

Superior mesenteric vein

venous drainage from midgut-derived viscera

Inferior mesenteric vein

venous drainage from hindgut-derived viscera; drains into splenic vein

Sympathetic foregut innervation

greater splanchnic nerves

Parasympathetic foregut innervation

vagus nerve (CN X)

Sympathetic midgut innervation

lesser splanchnic nerves

Parasympathetic midgut innervation

vagus nerve (CN X)

Sympathetic hindgut innervation

lumbar splanchnic nerves

Parasympathetic hindgut innervation

pelvic splanchnic nerves