Digestive System

What are the 6 functions of the digestive system?

ingestion, secretion, motility, digestion, absorption, defecation

What is the myenteric plexus?

controls GI tract motility

What is the submucosal plexus?

controls secretions

Parasympathetic nervous system affect on digestion

Stimulation increases secretion and activity by stimulating ENS

Sympathetic nervous system affect on digestion

Stimulation decreases secretion and activity by inhibiting ENS

What does the tongue do?

Participate in food manipulation for chewing, swallowing, and speech

What do papillae on the tongue contain?

taste buds

What is mastication?

Food is mixed with saliva, shaped into a bolus to be swallowed

What enzymes are in the mouth?

Salivary amylase and lingual lipase

Whats step one of swallowing? (Deglutition)

Voluntary movement of food through the oropharynx

What is step two of swallowing (Deglutition)

Involuntary movement through pharyngeal

What is step three of swallowing (Deglutition)

Involuntary progressive contractions of the muscularis push the bolus onward in the esophagus. (Peristalsis)

What is HCL

Secreted by parietal cells and kills bacteria and denatures proteins

What is pepsin

Begins the digestion of proteins by breaking them into peptides

What are peptides

Smaller strings of amino acids

What acid environment do peptides need?

pH of 2.0

What is gastric lipase?

Continues the digestion of triglycerides

What keeps pepsin from digesting the protein in stomach cells along with the food?

Pepsinogen and alkaline mucous

What is the intrinsic factor secreted by?

parietal cells

What is the intrinsic factor?

Its needed for vitamin b12 absorption and RBC formation

What substances are absorbed in the stomach?

Water, ions (salt), fatty acids, alcohol, and some drugs

Where does the small intestine start and end?

pyloric sphincter to ileocecal sphincter

What major events occur in the small intestine?

Digestion and absorption

What organs help the small intestine do its job?

Liver, pancreas, and the gallbladder

What is the pancreas connected to?

the duodenum via pancreatic duct and accessory duct

What do endocrine cells in pancreatic islets do?

produce hormones

What do pancreatic islets do?

Secrete hormones

Starch digestion in the small intestine is done by?

pancreatic amylase

What are proteins in the small intestine digested by?

Trypsin, chymotrypsin, and carboxypeptidase

What are fats digested in the small intestine by?

Pancreatic lipase

What are nucleic acids digested in the small intestine by?

Ribonuclease and deoxyribonuclease

Sodium bicarbonate function

Converts the acid stomach contents to a slightly alkaline pH (7.1-8.2)

Pancreatic juices affect on pepsin and pancreatic enzymes activity

It halts stomach pepsin activity and promotes pancreatic enzymes activity

What is the second largest organ in the body?

liver

What is bile produced by?

Hepatic cells

Where is bile transported to after it produced?

Transported to the gallbladder for concentration and temporary storage

What does it mean for something to be more concentrated?

Water is removed making it more concentrated

How would you describe bile?

It's partially an excretory product (containing components of worn-out red blood cells) and partially a digestive secretion

Bile function

emulsification of triglycerides

What are circular folds?

permanent ridges of mucosa and submucosa that cause chyme to spiral

What are villi

Finger like projections of mucosa, contain arteriole, venule, blood capillary, and lacteal

What are microvilli

Projects off apical membrane of absorptive cells and is brush border with brush border enzymes

What are the three mechanical digestion functions of the small intestine?

Segmentation, peristalsis, and spiraling

What are enzymes

specialized proteins have specific functions

What are carbohydrates absorbed as?

Monosaccharides

What enzyme do the intestinal mucosal cells fail to produce in people with lactose intolerance?

lactase

What happens to the body in response to the lactose in an intolerant person

diarrhea, gas, bloating, and abdominal cramps. the body wants to expel the lactose sugar

Where does protein digestion start?

in the stomach

What does the liver metabolize?

Carbohydrates, lipids, and proteins

What does the liver help remove from the blood?

Drugs and hormones

What does the liver excrete?

bilirubin

What does the liver store?

Vitamins and minerals

What vitamin does the liver activate?

Vitamin D

What immune response occurs in the liver?

Phagocytosis

What is carboxypeptidase?

Cuts an amino acid off the end, specifically the carboxy end

What is aminopepidase?

Breaks off last amino acid on the amino-terminal end

What is dipeptidase?

Splits dipeptides to amino acids

What are the different methods of absorption in the small intestine?

Diffusion, active transport, facilitated diffusion, and osmosis

Where do absorbed products go?

blood or lymph

How are monosaccharides absorbed?

Into blood capillaries in the villus by active transport or facilitated diffusion

How are amino acids, dipeptides, and tripeptides absorbed?

By active transport processes into the blood capillaries in the villus of duodenum and jejunum

How are dietary lipids absorbed

simple diffusion

How are long-chain fatty acids and monoglycerides absorbed?

Absorbed as part of micelles, resynthesizes as triglyceride, formed into protein-coated masses called chylomicrons, taken up by lacteals of villus, enters the lymphatic system and then passes into the cardiovascular system, finally it goes to the liver or adipose tissue

Why is a chylomicron helpful?

Fatty acids and monoglycerides are insoluble and combining with the lipoproteins which are transporters make them soluble

What is an electrolyte?

compound that separates into ions when dissolved in water

What are examples of electrolytes?

Calcium, sodium, and chloride

How are electrolytes absorbed and why?

active transport because charged ions can't enter the cell membrane easily

How are fat soluble vitamins absorbed?

absorbed with lipids in micelles and then absorbed by simple diffusion

How are water-soluble vitamins absorbed?

Absorbed by simple diffusion

How is vitamin b12 absorbed

Combines with intrinsic factor and then the combo is absorbed in the ileum

How is water absorbed?

Osmosis

What does water absorption depend on?

the absorption of electrolytes and nutrients

Whats the goal of water absorption?

Maintain osmotic balance with the blood

What is haustral churrning

haustra remains relaxed until the distention by chyme, the walls will then contract and move contents to next haustra

What is peristalsis?

The normal rhythmic contraction of the digestive tract

What is mass peristalsis?

A strong peristaltic wave that begins at mid transverse colon, pushes colonic contents towards the rectum, occurs 3-4 times a day

How does chemical digestion occur in the large intestine?

Through action of bacteria

Whats absorbed in the large intestine?

Water, electrolytes (mostly sodium and chloride), and some vitamins

What does feces contain?

Water, inorganic salts, sloughed-off epithelium, bacteria, products of bacterial decomposition, and undigested parts of food

What is the large intestine important for?

Maintaining the body's water balance

What is the defecation reflex aided by?

Voluntary contractions of the diaphragm and abdominal muscles

Whats the external anal sphincters' role in defecation?

Voluntarily controlled to allow or postpone defecation

What causes diarrhea?

increased motility of the intestine

What does diarrhea lead to?

Dehydration and electrolyte imbalance

What causes constipation?

Decreased motility in the intestine

What is gastric secretion regulated by?

Hormonal and nervous mechanisms

What is the cephalic phase initiated by

consists of reflexes initiated by sensory receptors in the head and the sight, smell, taste, or thought of food

What does the cephalic phase stimulate?

Stimulates gastric secretion and motility-pepsinogen, hcl, and gastrin

When does the gastric phase begin?

When food enters the stomach

Why does ph increase during the gastric phase?

Proteins have entered the stomach and buffered some of the stomach acid

What happens during the gastric phase

Stomach walls are distended and waves of peristalsis along with continual flow of gastric juice occurs

What triggers the enterogastric reflex

partially digested food

What does the enterogastric reflex do?

inhibits gastric emptying

What hormones are involved in the intestinal phase?

Gastric inhibitory peptide, secretin, and cck,

What is secretin?

Stimulates pancreatic juice

What is cck

Stimulates the gallbladder

What stimulates gastric emptying?

Stomach distention, partially digested proteins, alcohol, and caffeine

What happens during gastric emptying?

Gastrin and nerve impulses from the parasympathetic nervous system stimulate contraction from the lower esophageal sphincter and relaxation of pyloric sphincter and increases stomach motility

Whats the order of macromolecules leaving the stomach?

Carbohydrates leave the earliest, followed by proteins and then fats

When does food leave the stomach after ingestion?

2-6 hours