NBP Module 3: Digestive System

1

Mucosa

2

Submucosa

3

Muscularis Propria

4

Serosa

Serosa: Connective tissue

• Supports the intestine in the abdomen

• provides a route for blood vessels, lymphatic vessels, and nerves

Serosa: Squamous epithelial Cells

• secretes lubricating fluid reducing friction between organs

Serosa: Adventitia

• connective tissue layer that binds structures together

• Found outside the peritoneal cavity

Intraperitoneal

• organs suspended by the mesentery and almost completely enclosed in visceral peritoneum

• organs are mobile

Retroperitoneal

• Organs are partially covered by peritoneum

• “Outside peritoneum”

• Immobile or fixed organs

Muscularis propria (aka externa)

• Composed of two muscle layers (circular and longitudinal)

• regulates the movement of food through gut

Submucosa

• layer of connective tissue (supporting mucosa + submucosal nerve plexus)

Mucosa

• made of three basic layers (epithelium, lamina propria, muscularis mucosa)

Layers of Mucosa: Lamina Propria

connective tissue layer containing blood/lymph vessels and nerves

Layers of Mucosa: Muscularis Mucosa

helps squeeze and expel digestive enzymes out of gastric glands

Esophagus

• conducts food from the mouth to stomach

• mostly produces mucus

• no digestive enzymes

Muscular sphincter

at either end of the esophagus to prevent regurgitation

Stomach

churn/mix food mechanically and secretes digestive chemicals from gastic pits

rugae

folds in stomach that allow the stomach to expand

1

Lower esophageal sphincter

2

Cardia

3

Fundus and body

4

Antrum

5

Phylorus

1

Secretion Reservoir

2

Mixing and grinding

Where are gastric glands located?

Fundus and Antrum

Cells of the Gastric Gland: Chief Cell

stores pepsinogen Gastric lipase

Cells of the Gastric Gland: Parietal Cell

Secrete HCl to activate pepsinogen

Cells of the Gastric Gland: Mucus Cell

secretes mucus

Small Intestine

• Long with a small diameter

• Macromolecule digestion

• Site of major nutrient absorption

Large Intestine

• absorption of water/vitamins

• storage of waste and indigestible material

• propulsion of stool

Intestinal epithelial lining: Villi

• finger-like projections of epithelium and lamina propria

• Composed of: enterocytes, goblet cells, enteroendocrine cells

Intestinal epithelial lining: Crypts

• at the base of villi

• composed of: enterocytes, goblet cells, enteroendocrine cells, stem cells, paneth cells

Function of the small intestine: Duodenum

receives more digestive enzymes; more acidic than distal SI

Function of the small intestine: Jejunm

pH is more alkaline than duodenim, villi are much longer than duodenum or ileum

Function of the small intestine: ileum

absorbs vitamin B12, bile salts, products of digestion not absorbed by jejunum

1

Duodenum

2

Jejunum

3

ileum

5

Large intestine

6

Rectum

Cecum

the transitional structure between the small intestine and the large intestine

Rectum connects the ____ to the anus

colon

1

Small Intestine

2

Large Intestine

____ are absent in the large intestine making it seem flat

Villi

Microbiota

important for maintaining normal physiology and function (AKA: immune system, metabolism, brain/behavior)

Curvature of stomach: Omentum

a large fold of viscerak abdominal lining (peritoneum) that connects the stomach to other organs in the abdomen

Curvature of stomach: Vessels/Portals

running along the omentum

Curvature of stomach: lesser curvature

connected to the liver

Curvature of stomach: Greater curvature

drapes over small and large intestines, and loops back to attach to the transverse colon

Liver

Critical role in maintaining blood glucose

What is the liver important for?

• glycogen storage, gluconeogenesis

• Oxidation of fatty acids

• Deamination of amino acids

Blood supply to the liver comes from two sources:

• Hepatic artery

• Hepatic portal system

Hepatic artery

supplies oxygenated blood to the liver

Hepatic portal system

brings venous blood from the intestine to the liver for detoxification (nutrients)

What does every vertebrate have?

Pancreas

Pancreatic juices

are made in pancreatic acinar cells and released into the pancreatic duct, which terminates in the duodenum

Digestive enzymes:

• Trypsin (protein)

• Amylases (carbohydrate)

• Lipases (fat)

1

islet cells

2

Acinar cells

Definition: islet cells

specialized clusters of cells scattered throughout the pancreas that produce hormones to control blood sugar

Definition: Acinar cells

specialized exocrine gland cells that synthesize, store, and secrete digestive enzymes

1

Liver

2

Gallbladder

3

Cystic duct

4

common bile duct

5

pancreas

6

Pancreatic duct

Teeth tissues: Enamal

• Hardest substance in the body

• lines surface of tooth

Teeth tissues: Cementum

• like bone

• on surface of roots

Teeth tissues: Dentin

• Similar to bone but harder

• beneath enamel and cementum

Why do birds have no teeth?

ability to fly means to weigh as little as possible and beaks are lighter than teeth

Mammals tongues: Muscular

crucial for positioning and swallowing

Birds tongues: little musculature

mainly for swallowing and taste

Fish Tongues: No musculature

an angular elevation in the ventral oropharynx to direct food to esophagus

Oral glands: Mammals

Salivary glands on tongues to lubricate and partially digests food

Oral glands: Birds

Goblet cells and few (if any) digestive enzymes

Oral glands: Fish

No salivary glands, Goblet cells (oropharynx), and No digestive enzymes

Pharynx is in

birds and mammals

Function: Pharynx

separates breathing from swallowing

Fish esophagus

very short esophagus that is expandable for larger objects

Swim bladder (fish)

internal gas filled organ that is used to control buoyancy

Physostomic

Swim bladder connected to the esophagus

Physoclistic

swim bladder not conencted to esophagus

1

Gas bladder

2

stomach

3

Pneumatic duct

4

intestines

fish stomachs are commonly in what shape?

j shape

Bird stomach: Proventriculus

secretes digestive enzymes, acid

Bird stomach: Gizzard

thick musculature that grinds food using small stones that are deliberately swallowed

bird gizzards are coated by ____ ____ epithelium to protect from small rocks

Keratinous squamous

The intestines of ____ is similar to mammals bur with shorter intestines

birds

in ____ it is not possible to distinguish the small and large intestine

fish

Teeth modifications in herbivores: Hypsodont dentition

high crowned: worn down by plant material

Teeth modifications in herbivores: Rootless dentition

have unconstructed roots; grow continuously (beaver)

Ruminates have ____ stomach(s) with 4 compartments

one

Rumen

The largest stomach compartment

Rumination

food is ingested, swallowed, regurgitated, and swallowed again