Wk 7 Revision Deck:

what are the functions of the digestive system?

• takes in food

• breaks food down into nutrient molecules

• absorbs nutrient molecules into the bloodstream

• rids the body of the indigestible remains

the digestive system falls into 2 main groups, what are they?

• alimentary canal or gastrointestinal (GI) tract

• accessory digestive organs

what is some characteristics of the alimentary canal or gastrointestinal (GI) tract? what does it do?

• a continuous muscular digestive tube that winds through the body

• since it is open to the external environment, it is considered to be outside of the body

• it digests food and absorbs it through its lining into the blood

what are the accessory digestive organs?

organs that aid in the digestive process

what are all the organs and structures involved in the digestive system?

• mouth

• salivary glands

• pharynx

• oesophagus

• stomach

• pancreas

• liver

• gallbladder

• small intestine

  • duodenum

  • jejunum

  • ileum

• large intestine

  • cecum

  • appendix

  • colon

  • rectum

  • anal canal

• anus

the process of food by the digestive system involves six essential activities, what are they?

• ingestion

• propulsion

• mechanical digestion

• chemical digestion

• absorption

• defecation

what is ingestion?

the process of taking food or substances into the mouth to begin the digestive process

what does ingestion involve?

• chewing (mastication)

• swallowing (deglutition)

• passage of food into the digestive tract

• further breakdown and absorption

what is propulsion?

the movement of food and other substances through the digestive tract

what is peristalsis?

involuntary muscular contractions which propel the contents forwards along the length of the gastrointestinal (GI) tract with waves of contraction and relaxation, each wave starts distal to previous

what does peristalsis help with?

mixing and churning the contents of the GI tract while also aiding in the transportation of food from one digestive organ to another

what does a peristaltic contraction involve?

a single ring of contraction that travels down a segment of the GI tract, pushing its contents along

where is peristalsis most notable?

• oesophagus

• stomach

what is mechanical digestion?

when food is physically broken down into smaller particles, facilitating the subsequent chemical digestion and absorption of nutrients

what are 3 primary locations of mechanical digestion?

• mouth

• stomach

• small intestine

what is the mechanical digestion happening in the mouth?

• mastication (chewing and mixing with saliva)

  • increases the surface area for enzymatic action

what is the mechanical digestion happening in the stomach?

• muscular contractions that churn and mix the food with gastric juices

  • breaks down food into chyme, aiding in nutrient absorption

what is the mechanical digestion happening in the small intestine?

• segmentation and peristalsis that further breaks down food and mixes it with digestive enzymes, facilitating nutrient absorption

  • moves contents toward ileocecal valve

what is chemical digestion?

breakdown of complex food molecules into simpler molecules through the action of enzymes and other digestive substances

what is chemical digestion for?

it allows nutrients to be absorbed and utilised by the body

what are the 3 places where chemical digestion occurs?

• mouth

• stomach

• small intestine

what chemical digestion occurs in the mouth?

the action of enzymes like amylase which breaks down carbohydrates into simpler sugars

what chemical digestion occurs in the stomach?

secretion of gastric juices containing hydrochloric acid and enzymes like pepsin work to break down proteins into amino acids

what chemical digestion occurs in the small intestine?

enzymes from the pancreas and bile from the liver further breakdown carbohydrates, proteins and fats into their component molecules:

• simple sugars

• amino acids

• fatty acids

• glycerol

what happens after the chemical digestion in the small intestine is complete?

the nutrients are then absorbed through the intestinal lining into the bloodstream and transported to cells throughout the body for energy, growth and repair

where does the majority of chemical digestion occur?

in the small intestine

what is absorption?

the process by which digested nutrients, along with water and electrolytes, are taken up from the GI tract into the bloodstream or lymphatic system for distribution throughout the body

what is a characteristic of the lining of the small intestine?

• excessive folding

  • to increases surface area of peak absroption

• has villi and microvilli

  • more absorption

what nutrients are absorbed at the small intestine?

the following through simple and facilitated diffusion as well as active transport:

• glucose

• amino acids

• fatty acids

• water

• electrolytes

what is the absorption of water and electrolytes crucial for?

maintaining fluid balance and electrolyte levels in the body

what is defecation?

the process of expelling indigestible waste, bacteria, and other substances from the body through the anus

what is faeces?

the remaining indigestible material which consists of food particles, bacteria, cellular waster and water

what are the steps of defecation?

1. faeces accumulate in the rectum

2. nerve signals trigger the relaxation of the internal anal sphincter

3. faeces moves into the anal canal

4. the external anal sphincter, which is under voluntary control, then relaxes

5. expulsion of faeces from the body

there are several processes that regulate digestive activity, what are they?

• neural regulation

• mechanical & chemical stimuli

• hormones

what is neural regulation in terms of regulating digestive activity?

the GI tract has its own enteric nervous system, sometimes called the “gut brain”

what are the 2 types of reflexes that occur in the enteric nervous system?

• intrinsic

  • short reflexes

• extrinsic

  • long reflexes

what do intrinsic reflexes respond to?

• stimuli within the GI tract

  • mechanical and chemical stimuli, regulating local digestive functions.

the intrinsic nerve plexus of the digestive system is collectively called the “enteric nervous system” consists of 2 plexus. What are they and what do they control?

• myenteric plexus

  • controls the contraction of smooth muscle in the digestive system

• submucosal plexus

  • controls the secretions in the digestive system

what do extrinsic reflexes respond to?

• respond to stimuli inside or outside the GI tract

  • sight, smell, taste or thought of food

what do extrinsic reflexes involve?

• CNS centers

• autonomic nerves

  • both sympathetic and parasympathetic nerves

what can extrinsic nerves alter?

• activity of intrinsic nerves

• hormone secretion

• can directly stimulate or inhibit smooth muscles and glands

how do mechanical and chemical stimuli regulate digestive acitivity?

• mechanoreceptors and chemoreceptors respond to changes

  • initiates reflexes that

    • activate or inhibit digestive glands

    • stimulate smooth muscle to mix and move lumen content

how do hormones regulate digestive activity?

endocrine cells in the epithelium of the stomach and small intestine can secrete hormones for digestion

what is the role of lips and cheeks for digestion?

help keep food between the teeth when we chew

what is the palate?

the roof of the mouth

what are the 2 parts of the palate and what are their different roles/functions?

• hard palate

  • forms the rigid surface where food is forced during chewing

  • slightly corrugated to help create friction against the tongue

• soft palate

  • closes off the nasopharyngeal during swallowing

what is the role of teeth in digestion?

mastication and grinding food to break it into smaller pieces

what is the role of the tongue in digestion?

• one of the accessory organs of digestion

• taste buds for taste information within papillae on the tongue’s surface

• gripes the food and constantly re-positions it between the teeth

• mixes food with saliva to form a bolus

• initiates swallowing

  • pushing the bolus into the pharynx

what is deglutination?

the process of digestion from intake of food to the bolus entering the stomach

how long does it take solif food to reach the stomach?

8 seconds

how long does it take liquids to reach the stomach?

1-2 seconds

what are the 4 phases of deglutination?

• ingestion

• buccal phase

• pharyngeal phase

• oesophageal phase

what happens in the ingestion phase of deglutination?

• intake of food

• mechanical digestion

  • teeth

• chemical digestion

  • salivary amylase

  • lingual lipase

what happens in the buccal phase of deglutination?

• propulsion of the bolus into the oropharynx and then laryngopharynx

• skeletal muscle layers contract to propel the food

what happens in the pharyngeal phase of deglutination?

• epiglottis closes off larynx

• bolus moves from larynx to oesophagus by peristalsis

how long is the oesophagus?

25 cm

what happens in the oesophageal phase of deglutination?

• bolus moves from oesophagus to stomach by peristalsis

• lower oesophageal sphincter opens to allow the bolus to pass into the stomach

what are the functions of the stomach?

• intake of food from the oesophagus

• temporary storage tank

• physical digestion

• desaturation of proteins

• delivers chyme to the small intestines

what is the mucosal lining of the stomach composed of?

simple columnar epithelial cells that secrete mucous

what are gastric glands composed of?

• mucous neck cells

• parietal cells

• chief cells

• enteroendocrine cells

what is the role of the mucous neck cells in a gastric gland of the stomach?

its role is unknown

what is the role of the parietal cells in a gastric gland of the stomach?

secrete HCl

what is the role of the chief cells in a gastric gland of the stomach?

secrete lipase - fat digesting enzymes

what is the role of the enteroendocrine cells in a gastric gland of the stomach?

release chemical messengers that aid in digestion

there are 3 phases in the regulation of gastric secretion, what are they?

• cephalic (reflex) phase

• gastric phase

• intestinal phase

what triggers the cephalic phase?

taste, sight, smell or thought of food

what are the steps in the cephalic phase?

• hypothalamus receives info from taste buds/olfactory receptors

• medulla stimulated

• medulla transmits impulses via vagus nerve

• impluses affect secretory and contractile activity of the stomach

what kind of stimuli does the gastric phase have?

• hormonal stimuli

• neural stimuli

when does gastric phase occur?

once food enters the stomach

what are the 2 parts of the intestinal phase?

• stimulatory

• inhibitory

when does the stimulatory intestinal phase happen?

as food fills the duodenum

what happens in the stimulatory intestinal phase?

• food starts coming into the duodenum

• stimulates the mucosal cells in the stomach to secrete gastrin

• gastrin encourages the gastric glands to continue their secretory activity

what happens in the inhibitory intestinal phase?

• enterogastric reflex

  • decreases gastric activity

what are the 3 types of gastric contractile activity?

• propulsion

• grinding

• retropulsion

what is propulsion in terms of gastric contractile activity?

peristaltic waves move from the fungus toward the pylorus

what is grinding in terms of gastric contractile activity?

the most vigorous peristalsis and mixing action occur close to the pylorus

what is retropulsion in terms of gastric contractile activity?

the pyloric end of the stomach acts as a pump that delivers small amounts of chyme into the duodenum, simultaneously forcing most of its contained material backward into the stomach

what are 3 accessory organs associated with the small intestine?

• liver

• gall bladder

• pancreas

what is the liver’s function?

to produce bile

what is bile?

a yellow-green solution that contains bile salts and phospholipids which aid in the digestion process

what is the role of the gallbladder?

to store bile and concentrate it by absorbing water and iron

where is bile exported?

the duodenum

what do the bile salts in bile do?

emulsify fats and facilitate fat and cholesterol absorption

what does the pancreas produce?

enzymes that break down all categories of food stuff

what is the name of the exocrine product of the pancreas?

pancreatic juice

what does pancreatic juice contain?

• amylases

• lipases

• nucleases

• proteases

what do amylases break down?

carbohydrates

what do lipases breakdown?

lipids

what do nucleases breakdown?

nucleic acids

what do proteases breakdown?

proteins

what else does the pancreas secrete apart from pancreatic juice?

alkaline bicarbonate to balance the HCl produced in the stomach

what are the 4 main layers of the small intestine?

• mucosa

• submucosa

• muscularis external

• serosa

what is the mucosa of the small intestine?

the innermost layer

the mucosa of the small intestine consists of 3 parts what are they?

• epithelium

• lamina propria

• muscularis mucosae

what does the epithelium of the mucosa of the small intestine do?

secretes mucous and digestive enzymes and hormones

what does the lamina propria of the mucosa of the small intestine do?

contains capillaries for nourishment and absorption

what does the muscularis mucosae of the mucosa of the small intestine do?

smooth muscle that produces local movements of the mucosa

what are some characteristics of the submucosa of the small intestine?

• external to the mucosa

• has a rich supply of blood

• location of lymphatic vessels & follicles & nerve fibres

what is the muscularis external of the small intestine responsible for?

segmentation and peristalsis

what is the serosa of the small intestine?

the protective outermost layer