Digestive system physiology

What is the role of the mouth in digestion?

Ingestion of food

What are the four functions of the tongue?

Mastification

Deglutition

Speech

Taste

What is the function of incisors and canines?

Cutting and biting off pieces of food

What is the function of premolars and molars?

Grinding and chewing

What are the five functions of saliva?

Chemical digestion

Lubrication

Cleaning

Antibodies

Taste

What happens to amylase past the mouth?

It reaches the stomach and is inactivated by gastric juices

How does saliva aid lubrication?

Moistens dry food to form semi solid bolus

How does saliva aid taste?

Food must be in solution before taste buds are stimulated by chemicals

What is Mastification?

Mechanical digestion and mixing of food with saliva

What is deglutition?

Swallowing

What are the three stages of deglutition?

Oral

Pharyngeal

Oesophageal

What happens at the oral stage of deglutition?

Tongue and cheeks push bolus into pharynx

What happens at the pharyngeal stage of deglutition?

Pharynx muscles push bolus into oesophagus

Soft palate blocks nose, tongue blocks mouth and epiglottis blocks trachea

What happens in the oesophageal stage of deglutition?

Bolus entering pharynx triggers peristalsis moving it into the stomach

What is peristalsis?

Contraction and relaxation of muscle layer to push food onward

What happens to the lower oesophageal sphincter ahead of a peristaltic wave?

Relaxes from guarding the stomach entrance

What are the six components of gastric juice?

Water

Mineral salts

Mucus

Hydrochloride acid

Intrinsic factor

Inactive enzyme precursors

What is the function of the intrinsic factor?

B12 absorption

What is the function of mucus?

Lubrication to prevent mechanical injury

Barrier between mucosa and gastric acid

What are the three functions of gastric juice?

Liquifies food

Digests food and deactivates amylase

Kills microbes

What are the three phases of gastric juice secretion?

Cephalic phase

Gastric phase

Intestinal phase

What happens in the cephalic phase of gastric juice secretion?

Gastric juice secretion caused by reflux stimulation of senses

What happens in the gastric phase of gastric juice secretion?

Prescence of food in stomach causes enteroendocrine cells to secrete gastrin

What is the function of gastrin?

Stimulation of gastric glands to produce more gastric juice

What happens in the intestinal phase of gastric juice secretion?

Food reaches small intestine causing enteroendocrine cells to release secretin and cholecystokinin

What is the function of secretin and cholecystokinin?

Slow gastric juice secretion and slow stomach motility allowing chyme to mix better

What are the nine functions of the stomach?

Food storage

Chemical digestion

Mechanical digestion

Some absorption

Microbe defence

Preparation of iron for absorption

Intrinsic factor production

Passage regulation into duodenum

Gastrin secretion

How does the stomach aid preparation of iron for absorption?

Acidic gastric juices solubilise iron salts

How does the stomach regulate the passage of contents in the duodenum?

Pylorus forcing chyme in small jets through pyloric sphincter

What are the two functions of bile?

Fat emulsification

Excretion of bilirubin

How is bile released from the gallbladder?

Enteroendocrine cells of the villi secrete secretin and cholecystokinin

What are the three functions of secretin and cholecystokinin?

Stimulate gall bladder contraction

Stimulate hepatopancrearic sphincter relaxation

Expels pancreatic juice through the duodenal papilla

What are the three main functions of the gallbladder?

Bile storage

Increasing bile concentration

Release of stored bile

How does the gall bladder increase bile concentration?

Absorption of water through the walls of the gallbladder

What are the two ways gallbladder contraction is stimulated?

Secretion of CCK

Prescence of chyme in the duodenum

What reflex response occurs when the gallbladder contracts?

Relaxation of the hepatopancrearic sphincter

What are the ten functions of the liver?

Carbohydrate, protein and fat metabolism

Reanimation and transanimation

Plasma protein synthesis

Detoxification

Microbe defence

Hormone inactivation

Heat production

Bile secretion

Vitamin storage

What is the livers role in heat production?

By-product of intense metabolic activities

What are the four components of pancreatic digestive juice?

Amylase

Lipase

Proteases

Bicarbonate

What are the six functions of the small intestine?

Peristalsis

Intestinal juice secretion

Chemical digestion

Protection of infection

Hormone secretion

Absorption

What are the four functions of the microvilli?

Increase surface area expanding the intestinal lining

Contain digestive enzymes

Absorb nutrients

Form brush border

What are the four functions of the large intestine?

Absorption

Microbial activity

Mass movement

Demarcation

What is the purpose of a heavily bacterial colonised large intestine?

Synthesise vitamin K and folic acid

Bacterial fermentation of unabsorbed dietary components

How does mass movement occur in the large intestines?

long intervals of strong peristaltic waves along the transverse colon

How does defecation occur?

nerve endings in rectal walls stretch

Involuntary contraction of rectal muscle

relaxation of internal anal sphincter