Anatomy of the Digestive System Exercise 38 Anatomy of the Digestive System

Objectives Overall function Organs of alimentary canal Accessory digestive organs General functions of organs/structures Histological structure of alimentary canal wall Stomach and small intestine specializations Enzymes produced Deciduous and permanent teeth

Digestive System Provides body with nutrients, water, electrolytes essential for health Organs ingest (take in), digest (break down), & absorb (take into bloodstream) food, and eliminate the undigested remains

Alimentary Canal Hollow tube extending from mouth to anus (gastrointestinal tract or GI tract) Various accessory organs/glands empty into “Disassembly Line”

Alimentary Canal Histology Mucosa (mucous membrane) Inner layer, lines lumen; secretion of enzymes, absorption of nutrients, protection Surface epithelium: simple columnar Lamina propria: areolar connective Muscularis mucosa: smooth muscle—local movements of mucosa Lacteals: in villi (small fingerlike projections) of small intestine, lymphatic capillaries—transport fatty acids to bloodstream LUMEN OUTER surface

Lacteals will be in here ONE VILLUS Fig. 24-3

Alimentary Canal Histology Submucosa (superficial to mucosa; nutrition, protection) Blood, lymph vessels, nerve fibers Submucosal plexus is it’s intrinsic nerve supply Fig. 24-3

Alimentary Canal Histology Muscularis externa Bilayer of smooth muscle: Circular layer of muscle (deep) Longitudinal layer of muscle (superficial) Myenteric plexus = another intrinsic nerve plexus, controls these muscle layers  major controller of GI motility Fig. 24-3

Alimentary Canal Histology Serosa (visceral peritoneum) Outermost tunic Mesothelium, areolar connective tissue Reduces friction as GI organs slide across one another and cavity’s walls, protects and anchors organs also Fig. 24-3

Alimentary Canal Organs Fig. 24-1

Alimentary Canal Organs Oral cavity (mouth) Labia (lips) Hard palate (anterior roof of mouth) Soft palate (posterior roof of mouth) Uvula (fingerlike projection of soft palate) Tongue (floor of oral cavity)

Fig. 24-6

Pharynx Nasopharynx (behind nasal cavity) Oropharynx (behind oral cavity) Laryngopharynx (epiglottis to larynx) Fig. 24-6

Esophagus From pharynx through diaphragm to gastroesophageal sphincter at esophagus-stomach junction, controls food passage into stomach

STOMACH (left side of abdominal cavity) Cardiac region: upper region, through which food ENTERS stomach Fundus: superior & lateral to cardiac Body: middle portion, inferior to fundus Pyloric region: terminal part of stomach, continuous w/small intestine Pyloric sphincter: between stomach & small intestine

Alimentary Canal Organs Stomach (left side of abdominal cavity) Greater curvature: lateral, convex Lesser curvature: medial, concave Rugae: prominent folds in the mucosa when stomach’s empty

Fig. 24-12

SMALL INTESTINE ~2m long Duodenum: from pyloric sphincter around pancreas Jejunum: umbilical region of abdomen Ileum: terminal portion, joins lg intestine Plicae circularis: like rugae, deep folds Ileocecal valve: between small and large intestine

Fig. 24-16

Fig. 24-17

LARGE INTESTINE ~1.5m long Encircles the small intestine on 3 sides Cecum: 1st region, expanded pouch Appendix:  attached to cecum, ~3.5” long Ascending colon: up the right side Transverse colon: across the top Descending colon: down the left side

Fig. 24-23

LARGE INTESTINE Sigmoid colon: S-shaped curve (behind bladder) between descending colon and Rectum: last 6” of digestive tract Anus: exit of the anal canal Anal sphincter: muscle layers (2) surrounding the anus

Fig. 24-23

LARGE INTESTINE Teniae coli: 3 external longitudinal muscle bands of muscularis, shorter than rest of wall, cause it to pucker into Haustra: small pocketlike sacs

Fig. 24-23

ACCESSORY Digestive Organs Teeth Deciduous: appear 6 months-2.5 years; begin to lose teeth around 6 years old 20 teeth 2, 1, 0, 2 x 2 = 20 2, 1, 0, 2 Each SIDE of the jaw Upper: 2I, 1C, 0 PM, 2M Lower: 2I, 1C, 0 PM, 2M SIDES of the jaw

TEETH Permanent: gradually replaces the 1st set to age 12 32 teeth 2, 1, 2, 3 x 2 = 32 2, 1, 2, 3 Each SIDE of the jaw Upper: 2I, 1C, 2 PM, 3M Lower: 2I, 1C, 2 PM, 3M

Permanent Teeth For biting For chewing Central incisors Lateral incisors Canines (cuspids) 1st premolars (bicuspids) 2nd premolars (bicuspids) 1st molars 2nd molars 3rd molars For biting For chewing

Fig 24-9

Fig. 24-8

Teeth Anatomical crown: entire area of tooth covered by enamel Clinical crown: portion of tooth visible above the gum Root: inferior portion (base) of the tooth (below the gum)

Fig. 24-8

Teeth Enamel: “white” mineral (calcium salt) outer covering of crown Dentin: like bone, but no cells; under enamel, it’s most of the tooth Pulp, pulp cavity: interior chamber of the tooth—has blood vessels & nerves

Fig. 24-8

SALIVARY GLANDS Parotid glands: inferior to zyg. arch, lateral/posterior mandible Submandibular glands: floor of mouth, along inside of mandible Sublingual glands: floor of mouth, more anterior & under tongue

Fig. 24-7

LIVER Right, left, caudate, quadrate lobes Fig. 24-19

LIVER Falciform ligament: divides Rt/Lt lobes Fig. 24-19

LIVER Round ligament: thickened posterior part of falciform ligament Fig. 24-19

LIVER Hepatic ducts: right, left—collect bile (secreted by liver) from all bile ducts of lobes, unite to form the Common hepatic duct which leaves the liver…bile then flows to Cystic duct which leads to the gallbladder (stores/concentrates bile) ….OR goes to the Common bile duct which is formed by union of cystic and common hepatic ducts--empties into the duodenum (sm intest),

Fig. 24-21

PANCREAS Posterior to stomach, extends laterally off the duodenum toward the spleen Secretes digestive enzymes and buffers via the Pancreatic duct into the duodenum Accessory pancreatic duct branches off the larger pancreatic duct, also empties into duodenum Hepatopancreatic sphincter (muscle) controlling entrance of substances (from common bile duct, pancreatic duct) into duodenal ampulla

Fig. 24-18

Fig. 24-21

Microscope Work Stomach Gastric pits: shallow depressions, open onto gastric surface; mucous cells at base of each one mitotically active—shed into chyme (acidic “soup” of stomach secretions and food)

Fig. 24-13 Fig. 24-13

Microscope Work One VILLUS Small intestine Villi: fingerlike projections all over the plicae circulares One VILLUS Fig. 24-17

Microscope Work Large intestine (no villi in colon) Goblet cells (unicellular glands) abundant secrete mucus to help GI motility Fig. 24-24