Digestive System

Bio 211

Functions of digestive system

Breakdown foods, Release their nutrients, Absorb those nutrients, Eliminate wastes

2 parts of digestive system

Alimentary canal/Gastrointestinal Tract, and Accessory digestive organs

Alimentary canal/Gastrointestinal Tract

mouth, pharynx, esophagus, stomach, small and large intestines, and anus

Accessory digestive organs

critical to the function of the digestive system. Includes the teeth, tongue, salivary glands, the gallbladder, liver, and pancreas are all accessory organs

layers of Alimentary canal/Gastrointestinal Tract

mucosa, submucosa, muscularis, and serosa

mucosa of alimenatry canal

Epithelial tissue lining of the tract, Produces mucus for lubrication and protection, Contains a very thin smooth muscle layer called the *muscularis mucosa* (which is not the same as the muscularis layer) Is in direct contact with ingested food

submucosa of alimentary canal

Dense connective tissue serves as the location for blood vessels, lymphatic vessels, and glands. Also contains a dense branching network of nerves.

muscularis of alimenatry canal

made up of layers of smooth muscle (circular and longitudinal except where otherwise indicated), the contractions of which promote mechanical digestion and propulsion. contains sphincters, skeletal muscle curved fibers located at certain locations along the length of the canal that give voluntary control over swallowing and defecation. Contractions of the muscularis promote deglutition, churning,

peristalsis, and segmentation

serosa of the alimentary canal

is the outermost layer. terminology: instead of serosa, the mouth, pharynx, and esophagus have a dense sheath of collagen fibers called the adventitia. adventitia serves to hold the alimentary canal in place near the ventral surface of the vertebral column since these organs aren’t as moveable

as the latter organs

histology of mucosa (epithelium)

Of the mouth, pharynx, esophagus, and anus: stratified squamous (structure complements function!) Of the stomach, small intestines, and large intestines: simple columnar (structure complements function!)

histology of mucosa (lamina propria)

Made of areolar connective tissue, blood vessels, nerves. In the small intestine, contains MALT called Peyer’s Patches (review Chapter 21)

histology of mucosa (muscularis mucosa)

Smooth muscle creates constant tension on mucosa, creating folds. (What are these folds for?)

ENTERIC NERVOUS SYSTEM

a nervous system within another system

What is food detected by?

Food is detected by receptors from the ENTERIC NERVOUS SYSTEM – a nervous system within another system

What 2 plexuses are Enteric neurons grouped into?

The myenteric plexus and The submucosal plexus

nerve supply

Extrinsic innervation (from without) is provided by the autonomic nervous system: sympathetic activation restricts/inhibits the activity of enteric neurons (reduces digestion) parasympathetic activation activates/stimulates those neurons (promotes digestion)

The functions of blood vessels in digestive system

transport absorbed the protein and carbohydrate nutrients – (recall that lipids are absorbed via lacteals) supply the organs with the nutrients and oxygen needed to drive their cellular processes

BLOOD SUPPLY TO/FROM THE DIGESTIVE SYSTEM

The supply comes FROM: thoracic aorta►abdominal aorta►and celiac trunk, superior, and/or inferior mesenteric arteries. Nutrient-filled blood goes TO: the hepatic portal system from digestive

organs about one-fourth of the blood pumped with each heartbeat enters arteries serving the intestines.

Peritoneum

Squamous epithelial issue making up the membranes of the abdominal cavity. Parietal peritoneum

adheres to abdominal cavity. Visceral peritoneum adheres to the abdominal organs. Visceral peritoneum is folded into a number of specific structures (next slide)

Parts of the visceral peritoneum

Greater omentum, Falciform ligament, Lesser omentum, Mesentery, Mesocolon

Greater omentum

Apron-like fatty structure that lies superficial to the stomach, small intestine and transverse colon

Falciform ligament

Anchors the liver to the anterior abdominal wall and inferior border of the diaphragm

Lesser omentum

Connects the stomach to the liver

Mesentary

Vertical band of tissue anterior to the lumbar vertebrae and anchoring all of the small intestine except the initial portion (the duodenum) – Like spokes on a bicycle wheel

Mesocolon

Attaches two portions of the large intestine (the transverse and sigmoid colon) to the posterior abdominal wall

Mouth

Ingestion; with salivary glands, begins breakdown of carbohydrates

Pharynx

Propulsion

Esophagus

Peristalsis

Stomach

Churning, begins breakdown of proteins, secretes intrinsic facto

Small intestine

Peristalsis, Segmentation, Major site of absorption

Large intestine

Peristalsis, Segmentation, Absorption of water/vitamins, concentration of chyme

salivary glands

Secretion of amylase and lingual lipase, lubrication

Liver

Produces bile, detoxification, metabolism, storage

Pancreas

Secretion of digestive enzymes, insulin and digestive enzyme

Gall Bladder

Stores, concentrates and secretes bile

6 digestive processes in alimentary canal

Ingestion, Propulsion (2 types), Mechanical digestion (3 types), Chemical digestion, Absorption, Defecation

Ingestion

entry of food into the alimentary canal through the mouth, mastication and mixing with saliva occur just after via the teeth, tongue, and salivary glands

Propulsion

forward movement of food through the digestive tract, includes deglutition (voluntary and involuntary), includes peristalsis (involuntary), is NOT considered mechanical digestion as nothing is physically being broken apart by the process

Mechanical Digestion

is purely physical, makes the food smaller to increase both surface area and mobility, involves mastication (voluntary), Involves churning (involuntary), involves segmentation (involuntary)

Chemical Digestion

takes place in the mouth, stomach, and small intestine, digestive secretions break down complex food molecules into their chemical building blocks using hydrolysis, the secretions contain water, various enzymes, acids, and salts

Absorbtion

Majority occurs in the small intestine It is different for carbohydrates, proteins, and nucleic acids, versus lipids

Defecation

Undigested materials are removed from the body as feces

Regulatory mechanisms

There are two ways that the digestive system is controlled (regulated) Nerves, Hormones. These two ways alter the responses to stimuli (or lack of) to change mechanical and chemical digestion

What are the receptors located on the walls of GI tract?

baroreceptors, chemoreceptors, and osmoreceptors detect pressure/stretch, chemicals, and hydration concentration

Two types of reflexes serve the digestive system

long and short

Extrinsic nerve plexuses create “long reflexes”

central and autonomic nervous systems, respond to stimuli from OUTSIDE (external to) the digestive system

Intrinsic nerve plexuses create “short reflexes”

nerves found within the walls of the alimentary canal, regulate activities in the specific area of the digestive tract where they are found

What produces gastrin?

G- cells in stomach

What produces secretin?

Duodenum

What producesCholecystokinin (CCK)?

Duodenum

What produces Glucose-Dependent Insulinotropic Peptide (GIP)?

Duodenum

What produces Gastric Inhibitory Peptide (GIP)*?

Duodenum

Gastrin function

Stimulates gastric acid secretion and motility

secretin function

Stimulates release of bicarbonate from the pancreas

Cholecystokinin (CCK) function

Stimulates secretion of pancreatic enzymes, bile from the liver, concentrated bile from the gallbladder

Glucose-Dependent Insulinotropic Peptide (GIP) function

Stimulates insulin secretion

Gastric Inhibitory Peptide (GIP) function

Inhibits gastric acid secretion, slows gastric motility and emptying

parts of the mouth

Oral cavity (also called the buccal cavity), Labia (also called the lips), Labial frenulum, Oral vestibule, Fauces, Hard Palate, Soft Palate, Uvula

the tongue

facilitates ingestion, facilitates mastication, facilitates chemical digestion by producing lingual lipase (very minor aid for lipid digestion beginning in the stomach), contains papillae under which are receptors that aid in sensation of taste, texture, and temperature of food aid in swallowing aid in vocalization

What is number 1?

Lips

What is 2?

Hard palate

What is 3?

Soft palate

What is 4?

uvula

What is 5(opening)?

Fauces

What is 6?

Oropharynx

What is 7?

Laryngopharynx

What is 8?

Esophagus

What organ is this?

Stomach

What is 10?

Cardia

What is 11?

Pylorus

What is 12?

Fundus

What is 13?

Body

What is 14?

Pyloric sphincter

What is 15?

Rugae

What is 16?

Greater curvature

What is 17?

Lesser curvature

What is 18?

Cardiac sphincter

What organ are all the arrows pointing to?

Small intestine

What is 20?

Duodenum

What is 21(ridges)?

Plicae circulares

What is 22?

Jejunum

What is 23(valve)?

Ileocecal valve

What is 24?

Ileum

What is 25?

Duodenum

What is 26?

Ileum

What is 27?

Appendix

What is 28?

Cecum

What is 29?

Sigmoid Colon

What is 30?

Rectum

What is 31?

Anus

What is 32?

Ascending colon

What is 33?

Right (hepatic) colic flexure

What is 34?

Transverse colon

What is 35?

Left (hepatic) colic flexure

What is 36?

Descending colon

What is 37?

Haustra

What is 38?

Taenia coli

What is 39?

Tongue tip

What is 40?

Tongue body

What is 41?

Tongue root