GI System

6 functions of the digestive system

ingestion, mechanical digestion, chemical digestion, secretion, absorption, elimination

Ingestion

the oral cavity allows food to enter the digestive tract and have mastication (chewing) occurs, and the resulting food bolus is swallowed

Mechanical digestion

muscular movement of the digestive tract (mainly in the oral cavity and stomach) physically break down food into smaller particles

Chemical digestion

hydrolysis reactions aided by enzymes (mainly in the stomach and small intestine) chemically break down food particles into nutrient molecules, small enough to be absorbed

Secretion

enzymes and digestive fluids secreted by the digestive tract and its accessory organs facilitate chemical digestion

Absorption

passage of the end, products (nutrients) of chemical digestion from the digestive tract into blood or lymph for distribution to tissue cells

Elimination

undigested material will be release through the rectum and anus by defecation

Alimentary canal

GI tract or digestive tract, digestive tube that extends from the mouth to the anus, contains the small and large intestine, oral cavity, mouth, esophagus, stomach, oropharynx, rectum, anus
It's about 40 feet long and has 4 layers called outer serous layer of tissue, muscle layer, loose connective tissue, and mucus membrane

Accessory organs of digestion

teeth, tongue, salivary glands, liver, pancreas, gallbladder

1st way food is processed

Food is consumed and taken into the oral cavity

2nd way food is processed

Food is broken down into a small mass called the bolus by being chewed and mixed with saliva that is secreted by the salivary glands

3rd way food is processed

The tongue rises to the roof of the mouth, directing the bolus out of the oral cavity.

4th way food is processed

The bolus passes from the oral cavity to the pharynx and into the esophagus

5th way food is processed

Peristaltic waves move the bolus down the esophagus into the stomach

6th way food is processed

Gastric juices, produced in the gastric gland and containing hydrochloric acid and enzymes, digest food into chyme

7th way food is processed

Pancreatic juice enters the duodenum through the pancreatic ducts to aid digestion in the small intestine

8th way food is processed

Chyme travels through the small intestine, where nutrients are absorbed into the bloodstream

9th way food is processed

Chyme travels through the large intestine, where water and specific vitamins are absorbed and the remaining waste materials pass to the rectum

10th way food is processed

Solid waste is temporarily stored in the rectum before it is passed through the anal canal

How do nutrients get from the food we eat to the body tissues?

The small intestine is where the nutrients are absorbed like water (by osmosis) and fatty acids (by diffusion). Other ones are absorbed by active transport like glucose, amino acids and minerals are absorbed. The large intestine absorbs water, electrolytes, and some vitamins. It goes into the bloodstream and then the blood delivers the nutrients.

Small intestine

A long tube (22-24 ft), with a small diameter (about 1 inch), extending from pyloric sphincter to the ileocecal valve, digestive enzymes split molecules of sugars, proteins and fats
Regulation of small intestine secretions: secretion is stimulated by gastric juice, chyme, and reflex stimulated by distension of the small intestinal wall

Duodenum

First segment of the small intestine, about 10 inches long
Curves around the head of the pancreas
Site where the pancreatic duct and the common bile duct empty into the intestine
Pancreatic duct empties digestive juices of the pancreas
Common bile duct empties bile from the liver

Jejunum

About 8 feet long
The long, coiled mid-section of the small intestine
Mostly concerned with absorption of sugars, fatty acids, and amino acids

Ileum

About 6.5 feet long
The last part of the small intestine before the large intestine begins
Leaves through the ileocecal valve
Almost all of the absorption and assimilation have occurred, about 5% is left
Water will be absorbed in the large intestine
Absorbs vitamins, minerals, fat, and H2O

Large Intestine

The last segment of the GI tract about 5 ft long, with a large diameter (2-3 inches), extending from the ileocecal valve to the anus
6 sections: cecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum
Little or no digestive function, although it secretes mucus (format to feces and maintain alkaline condition)
Mechanical stimulation and parasympathetic impulses control the rate of mucus secretion
The large intestine only absorbs water, electrolytes and some vitamins
Many bacteria inhabit the large intestine, where they break down certain indigestible substances and synthesize Vitamin K and B12

Villi/Microvilli

Each villus contains blood capillaries and lymphatic capillaries to absorb nutrients, increase surface area for absorption, equivalent to 250 square meter area

Emesis

vomiting

Hematemesis

vomiting blood

Cholecystectomy

surgical removal of the gallbladder

Colostomy

surgical procedure to remove part of the colon and make an opening in the abdomen from wastes of digestion to exit the body

Esophagus

muscular tube connecting the mouth to the stomach, goes through diaphragm, ends at entrance of stomach (cardiac sphincter, esophageal)

Pharynx

food/air share this space, muscular tube

Cardiac esophageal sphincter

the sphincter that keeps food from reentering the esophagus

Pyloric sphincter

the sphincter that keeps food in the stomach until it is chime and ready to move one to the small intestine

Stomach

A pouch-like organ in the LUQ primarily designed for food storage (for 2-4 hours), some mechanical and chemical digestion also occur
Contains two sphincters at both ends to regulate food movement
Divided into 4 regions: cardiac stomach (or cardiac), fundus stomach (or funded), body of stomach, and pyloric stomach (or pylorus)
Contain thick folds called rugae at its layer, which help provide larger surface area for expansion, secretion, digestion, and some absorption

Salivary glands

3 pairs of salivary glands called parotid, submandibular, and sublingual gland secrete most of the saliva in the oral cavity, using salivary ducts
Saliva helps moisten food during mastication, dissolve the food in forming the bolus, and help cleanse the teeth

Peritoneum

Covers abdominal organs
Protects organs
Contains blood vessels
Skin to fat to muscle to peritoneum

Gallbladder

A small sac located on the inferior, visceral surface of the liver (RUQ)
Bile is produced in the liver
Gallbladder stores and concentrates bile (bile helps digest food)
The bile is sent to help breakdown chyme/continue digestion through the cystic duct and common bile duct to the small intestine (duodenum)

Liver

RUQ
Largest gland in body- 3 pounds
Smooth, dense
All absorbed nutrients pass through liver from portal vein for processing
Releases or stores glucose according to need
Deactivates drugs, alcohol

Functions of the liver

Carbohydrate metabolism where hepatic cells conduct glycogenesis (converting glucose into glycogen), and glycogenolysis (breaking glycogen down to glucose)
Lipid metabolism where hepatic cells produce bile, oxidize fatty acids, synthesize various forms of lipids, and convert glucose to fatty acids (lipogenesis)
Storage of glycogen, iron, and vitamins A, D, B12
Contains phagocytes to destroy damaged erythrocytes and foreign substances, using phagocytosis
Detoxifies harmful substances in the blood
Serves as a blood reservoir (contains 7% of blood volume)

Amylase

found in salivary glands, and pancreas, enzymes break down starch and glycogen into disaccharides
2 types: salivary( site of action in mouth), pancreatic (site of action in small intestine)

Pepsin

from gastric glands, begins protein digestion, site of action in small intestine

Maltase

found in small intestine, breaks down disaccharides like maltose into glucose, site of action in small intestine

Lactase

found in small intestine, breaks lactose into sugars called glucose and galactose, site of action in small intestine

Lipase

from gastric glands, begins fat digestion
from pancreas, breaks down fats into fatty acids and glycerol
site of action in small intestine

Nuclease

found in pancreas, breaks down nucleic acids into nucleotides

What does the pancreas produce

Most pancreatic enzymes are produced as inactive molecules, or zymogens, so that the risk of self- digestion within the pancreas is minimized
It secretes pancreatic juice and produces hormones like insulin and glucagon that regulate blood sugar and carbohydrate metabolism

The function of the muscle layer of the intestines

This layer enables the gut to contract and break apart larger food particles. It also stops food from moving in the wrong direction by blocking the more proximal end.

Salivary amylase

secreted in the mouth to begin digestion

Regulation of GI tract

Autonomic nervous system: parasympathetic nerves stimulate GI tract activities (ENS)- sympathetic nerves inhibit GI tract activities
Hormonal control- hormones from endocrine gland and from GI tract itself help regulate GI tract activities
Reflex mechanism- regions of the GI tract (especially the stomach and small intestine) use reflexes to stimulate or inhibit one another