Digestive System Flashcards
The gastrointestinal (GI) tract is a series of hollow organs joined in a long, twisting tube from the mouth to the anus. It includes the following parts:
what are the accessory organs involved in digestion?
Gastronomical tract :
- Mouth
- Oesophagus
- Stomach
- Small intestine
- Large intestine
Accessory Organs:
* Pancreas
* Gallbladder
* Liver
Be able to label the digestive system
where does digestion begin?
In the Mouth.
Mastication (chewing) breaks down food and increases surface area, mixing it with saliva- Forms the food bolus (mass of chewed food mixed with saliva, ready to be swallowed).
what is 90% of saliva secreted by?
3 pairs of salivary glands:
– Sublingual (lingual = tongue)
– Submandibular (mandible = jaw)
– Parotid (otid = ear)
what is saliva made up of?
How much of it is produced?
what is it under the control of?
what is it secreted by? + DIAGRAM !
what makes saliva hypOtonic?
99.5% water and 0.5% electrolytes and proteins.
it is Continuously produced so around 1-2L per day.
under the control of the autonomic nervous system
Secreted by the acinar cells in the salivary glands:
- Serous – proteins in an isotonic fluid (watery fluid)
- Mucous – mucin proteins (thicker fluid)
Duct cells absorb NaCI to make solution hypotonic (low concentration of solutes-sugar/salts).
what are the 5 key functions of Saliva
Lubrication
– Mucus facilitates eating and speech
- Digestion
– Salivary amylase breaks down carbohydrate - Oral hygiene / Antimicrobial
– Washes away debris
– Lysozyme lyses/breaks down bacterial cell walls
*Taste
– Solvent to allow molecules to interact with taste receptors
*Buffering
– Neutralise acids to protect teeth
Diagram!
where is the pharynx located and what is its function?
Behind mouth and nasal cavity.
- Takes food to the oesophagus
- Takes air to the trachea.
- Divides the trachea from the oesophagus- epiglottis folds over as food passes through (swallowing).
what is swallowing?
- Complex reflex process
- Initiated voluntarily (you start with a conscious decision to swallow).
- Bolus passes to the back of throat and to oesophagus
oesophagus
what is it?
function?
what does it secrete?
Straight tube surrounded by smooth
muscle
Passes food bolus to the stomach using peristalsis (6-10 seconds).
Only secretion is mucus (no absorption)
what is peristalsis?
a wave of muscle contraction in a coordinated way to help push the food down the oesophagus.
where is the Gastroesophageal sphincter located and what is its funtion?
between the oesophagus and the stomach- its a ring of smooth muscle that prevents the content of the stomach from going back up the oesophagus.
When you swallow, the sphincter :
- relaxes to allow food and liquid to pass into the stomach
-tightens to keep the stomach contents from coming back up.
where is pyloric sphincter located and what is its function?
between the stomach and the small intestine- a ring of smooth muscle which controls the amount of chyme (partially digested food) entering the small intestine.
what helps churn (mix) food in the stomach?
Waves of peristaltic contractions -The rhythmic muscle contractions ensures the food is thoroughly mixed with digestive juices, to create semi-liquid form called chyme.
what does the stomach secrete?
Secretes 2 L/day of gastric juice:
– Water
– Mucus
– HCl
– Pepsinogen
– Hormones
what are the 3 key functions of the stomach.
Mixes and breaks down food into chyme.
Stores food (50ml to 1L) and releases into the
small intestine slowly
Begins protein digestion through secretion of
hydrochloric acid and enzymes (pepsinogen)
what creates the harsh/acidic environments in the stomach.
HCl
enzymes e.g. pepsinogen
gastric lipase - breaks down fatty acids
The stomach is the site of ——– NOT ——–.
The stomach is the site of Secretion NOT Absorption.
Secretions of the Stomach (Gastric Juice)- Exocrine Secretion:
- Mucous cells – secrete Mucus (protects stomach lining from acidic environment)
- Chief cells – secretes Pepsinogen (pre-cursor enzyme, digests proteins)
Parietal cells – secretes Hydrochloric acid and intrinsic factor (HCl activates pepsinogen, intrinsic factor aids vitamin B12 absorption).
Secretions of the Stomach (Gastric Juice)- Endocrine and Paracrine Secretions:
Enterochromaffin-like cells (ECL) – secrete Histamine to maintain the acidic environment in the stomach.
G cells - secrets Gastrin (a hormone)-
D cells - secretes Somatostatin ( a hormone)
what cells control eXOcrine secretion?
Enterochromaffin-like cells
G cells
D cells
Control of Stomach Secretions:
- Vagal Nerve Stimulation.
what is is activated by?
what does it release?
what cells does it stimulate?
part of the ANS- activated by sight, smell, taste, thought of food.
releases acetylcholine (Ach)
Stimulates:
– Chief cells (secrete pepsinogen)
– Parietal cells (secretes HCl and intrinsic factor)
– G cells (secretes gastrin)
– ECL cells (secretes histamine)
Control of Stomach secretions:
- Gastrin (endocrine)
what is it secreted by?
what does it stimulate (2)?
what does it help maintain?
– Secreted into blood from G cells
– Stimulates parietal cells – increases HCl
– Stimulates chief cells – increases pepsinogen
– Maintains gastric mucosa (mucous membrane layer of the stomach).
Control of Stomach Secretions
- Histamine (paracrine)
what is it released by?
what does it stimulate?
- Released by ECL
– Stimulates parietal cells to increase HCl
Control of Stomach Secretion
- Somatostatin (paracrine)
what is is released by? in response to what?
what does it INHIBIT?
what is the effects of these inhibitions?
Released by D cells
-Negative feedback in response to low pH
– Inhibits:
* Parietal cells- reduces the secreion of HCl
- G cells- reduces HCl PRODUCTION.
- ECL cells- reduces secretion of HCl
Functions of Stomach acid: (4)
break/pepsin/proetin/anti
what does stomach acid NOT do?
Breaks down connective tissue
Activates pepsinogen to pepsin
Denatures protein
Antimicrobial
DOES NOT DIGEST PROTEIN.
How is Stomach Acid Secreted.
- When stimulated, parietal cells insert H+/K+ ATPase into the luminal membrane which cause canaliculi to form (increase surface area)
- Carbonic anhydrase is abundant and
causes CO2 to react with H2O to form carbonic acid (H2CO3) - Carbonic acid dissociates to H+ and HCO3-
- H+ is actively pumped into lumen via H+/K+ ATPase.
5.Bicarbonate ions (HCO3-) exchanged for
Cl- at the basolateral membrane
- Cl- PASSIVELY diffuses out of the luminal
membrane via chloride channels - HCl formed in the stomach lumen
what does the indigestion treatment Omeprazole do?
block the proton pump (H+/K+) to reduce acid production
what are the symptoms of indigestion?
Burning sensation in chest
Bad taste in mouth
Cough, hiccups, bad breath, nausea, bloating etc
what is acid reflux?
Acid reflux can occur when the stomach contents passes through the gastroesophageal
sphincter.
what are the two indigestion treatments?
Gaviscon
semiticone
Gaviscon
what does it treat? How?
treats acid reflux.
Gaviscon (sodium alginate, sodium bicarbonate and calcium bicarbonate)
- Sodium alginate
– Derived from seaweed
– Reacts with acid to form a gel – prevents reflux - Sodium bicarbonate and calcium bicarbonate
– Neutralises the acid
Simeticone
what does it treat? How?
- Simeticone
* Treats bloating/trapped wind
* Silicon surfactant – reduces the surface tension of bubbles causing them to coalesce and more easily disperse
what does the pancreas secrete ? to where?
Secretes:
1. Pancreatic juice into the duodenum:
– Alkaline fluid
– Enzymes
(amylase/lipase/peptidases)
- Hormones into the bloodstream:
– Insulin
– Glucagon
what does the biliary system consist of :
and what are there functions?
1= 4
2= 2
Liver:
* Processes fats, carbohydrates and proteins once
they are absorbed at duodenum
* Secretes bile
* Detoxification of waste
* Synthesis of plasma proteins
Gall bladder:
* Stores bile before release into the duodenum
* Bile emulsifies fats
what are the 4 layers of the digestive tract:
Four layers:
- Serosa/mesentery
– Secretes fluid for lubrication
– Supports digestive system - Muscularis externa
– Smooth muscle
- mixing/propulsion(pushes) food - Submucosa
– provides Flexibility/elasticity - Mucosa
– Lines luminal surface
– Produces mucus to protect lining
– Highly folded in small intestine- increases surface area for ABSORBPTION.
what is the main function of the small intestine?
what are the main components of the small intestine:
CHECK DIAGRAM
to digest and absorb nutrients from the food.
- Duodenum
– 20-25cm
– Receives chyme, pancreatic
enzymes and bile - Jejunum
– 2.5m
– Major area of nutrient absorption - Ileum
– 3m
– Absorption of vitamin B12 and bile
what does the small intenstine have on their folds?
what do they secrete? (3). TO WHERE?
Are digestive enzymes secreted?
what breaks down carbydrayes?
what breaks down proteisn and where is it found?
Villi / Microvilli / brush border- to increase surface area for absorption.
- Secretes succus entericus INTO THE LUMEN:
– Water
– Salts
– Mucus - No digestive enzymes secreted directly into the lumen:
– Fat broken down by bile
– Membrane-bound enzymes complete carbohydrate and protein digestion.
EXTRA!
(The cells lining the small intestine have enzymes (e.g. maltase, lactase, etc) attached to them which break down carbohydrates into simple sugars such as glucose. Other enzymes in called peptidases in the site of nutrient absorption, break down proteins into amino acids, making the digestion process very efficient)
Large Intestine- what are the 4 parts.
what is the main function of the large intestine?
4 parts of the colon:
* Ascending colon
* Transverse colon
* Descending colon
* Sigmoid colon
Main functions:
* Water and salt reabsorption from indigestible food.
* Storage of indigestible material (waste).
