Gastrointestineal System 

Tuesday, January 3rd

Function of digestive tract

Ingestion: mouth

Digestion: starts in mouth

mechanical and chemical breakdown of food

Mechanical: crushing by teeth, mixing of food in stomach and intestines

Chemical: enzymatic breakdown of food in mouth, stomach and primarily small intestines

Absorption: uptake of digested nutrients into blood and lymph vessels mostly small intestines some in stomach and large intestines (and mouth)

Six Functions of the Digestive System

Ingestion

Mechanical processing

Digestion

Secretion

Absorption

Excretion

Alimentary Canal: Tube that extends from mouth to anus: considered external

Digestive tract: mouth pharynx, esophagus, stomach small intestine, large intestine, rectum, anus

Accessory organs (not part of alimentary canal): teeth, tongue, salivary glands, liver, gallbladder, pancreas

Oral cavity

Upper and lower labial frenula

Lingual frenulum

Hard and soft palate- roof of mouth (hard palate: palatine process of maxillary bone and palatine bones)

Fauces- entrance to pharynx

Uvula- helps to close the entrance to the nasopharynx during swallowing

Palatine tonsils

Lingual tonsils are located on the posterior aspect of the tongue

Esophagus

From C6/cricoid cartilage to T7- enters stomach passes through diaphragm at the esophageal hiatus, then continues 3-4 cm to stomach cardiac orifice / lower esophageal sphincter (aka gastroesophageal sphincter)

Deglutition: (swallowing) 22 muscles

swallowing center- paired nuclei in medulla oblongata CN V, VII, IX, XII

Stomach

Cardia

Fundus

Body

Pylorus

Antrum

Canal

Sphincter

Greater curvature

Lesser curvature

Wall of the stomach with gastric pits

Glands of the Stomach: Gastric Pits \n Gastric Pits: contain 2-3 tubular glands \n Cardiac and pyloric glands in cardia and pylorus regions: mainly mucus-secreting (protect esophagus and duodenum) \n Gastric glands in body and fundus: secrete HCl, enzymes, hormones… \n Mucous neck cells \n Parietal cells: HCl, intrinsic factor (B12 absorption) \n Chief cells: pepsinogen (converted to active form in presence of HCL → pepsin) \n Enteroendocrine cells: hormones - gastrin (stimulates parietal cells to secrete HCl), others

Stem cells to replace epithelial cells (3-6 days)

Small intestine: digestion, absorption

Three parts: duodenum, jejunum, ileum

Epithelium is simple columnar with microvilli → the cells are called enterocytes

Enterocytes absorb digested material and secrete some digestive enzymes



Surface Area

3 levels of folds in the wall of the small intestines increase surface area (not found in colon)

Plicae circularis aka circular folds are visible with the naked eye (small intestine)

Villi are upwards foldings of the epithelium (small intestine)

Microvilli (small and large intestines) are projections on the surface of individual enterocytes (cells of the intestinal epithelium)





Villi

Finger-like projections of the epithelium into the lumen of the small intestines - up to 1.0mm long

*only found in the small intestines



Electron micrograph of an enterocyte.

Microvilli increase the surface area of the small intestines by 20 times.



Duodenum

First part of the small intestine: distal to the stomach (~10 inches)

distal ⅘ of duodenum is retroperitoneal



Function: protect mucosa of duodenum from acid in chyme.



Jejunum (NEED TO KNOW)

~40% of small intestine distal to duodenum

site of most digestion and nutrient absorption

NO GASTRIC GLANDS



Ileum

Distal 60% of of small intestines

contains Peyer’s patches - clusters of lymphatic tissue

Connected to large intestine at the ileocecal junction



Large Intestines --- aka Colon

Main functions:

Reabsorb water and electrolytes

Compaction of intestinal contents into feces

Storage of fecal material

Expulsion of fecal material (anus)

Colon

Longitudinal muscularis externa muscles form the 3 taeniae coli**:** because they are shorter than the colon, they cause the colon to sacculate and form pouches called haustra



Anus

Rectum → anal canal → anus

Epithelium of end of anal canal = stratified squamous epithelium

Epithelium of anus = keratinized stratified squamous epithelium (skin)

Inner circular layer of muscularis forms sphincters of the anus

Internal anal sphincter: smooth muscle

External anal sphincter: skeletal muscle





Thursday, January 5th



Wednesday, January 11th



Thursday, January 19th



Wednesday, January 25th



Friday, January 27th



Monday, Febuary 6th

Gastrointestinal System Review

What are the 6 functions of the gastrointestinal system? Be able to describe each

Ingestion (In The Mouth)

Digestion (Starting In The Mouth From Enzymes In The Saliva)

Absorpion (Of Nutirents Absorbed Into The Blood

Mechanical Processing (Teeth Physically Breaking Down Food)

Secretion (Saliva, Mucus, and Bile)

Extcretion (Get Rid Of Soild Waste The Body Can’t Digest)

Know the alimentary canal and the functions of each part

Alimentary Calnal: Tube That Extends From The Mouth To The Anus

Mouth (Mechanical Processing And Digestion)

Pharynx (Carries Food And Fluid Down From The Mouth)

Esophagus (Transport Food Through The Mouth And Stomach)



Stomach (Digestion And Secreation)

Small Intestine (Digestion)

Large Intestine (Absorbtion)

Recutum (Excretion)

Anus (Extcretion)

Know the accessory organs and their functions

Pancreas (

Gallbladder (

Salivary Glands (

Liver (

Teeth (

Tounge (

Glandular Organs (

Where does the esophagus begin



The Esophagus Begins In The C6/cricoid cartilage to T7 (OR Pharyngoesophageal Junction)



Muscles for swallowing (#)



Deglutition (Swallowing) Requires 22 Muscles

What are the 3 parts of both the large and small intestines



Large: Cecum, Rectum, Anal Cavity



Small: Duodenum, Jejunum, Ileum

Distinguish between internal and external sphincters



Internal- Involuntary Smooth Muscle Located Distally To The GI Tract.



External- Voluntary Muscle Around The Anal Cavity and Anal Opening.

Know the enzymes that are in saliva and their functions



Amylase-Breaks Down Starches Into Sugars Which Are Easily Digestable



Lingual Lapase- Breaks Down Fats

What is the purpose of bile



To Carry Away Waste And Break Down Fats

How long are the intestines



Large: Five Feet



Small: Twenty Feet

What is the reasoning for the size



So There Is Maximum Amount Of Space For Nutirents To Be Absorbed.

What is the name of the substance once it is chewed



A Bolus

What is the name of the substance once it is leaving the stomach



Chyme

What is the muscular contraction that the esophagus uses to move food



Peristalsis

Function of pancreatic juices



Break Down Fats, Sugar, and Starches

How is surface area increased in the intestines



The lineing is in small folds that form small peaks called Villi that help absorb nutirents.

Know medical terminology surrounding the GI system

Vomiting_

Nausea

Diarrhea

Constipation

Drugs used in the GI system disorders

Hernia (2 types

GERD

Celiac Disease

Crohns

eliac Disease

Crohns