digestive system Flashcards
overview of abdomen
The anatomical location for the abdomen is from the diaphragm to the pelvic inlet/ lower limbs
It is enclosed by the abdominal wall and the inner large peritoneal cavity
Functions of the abdominal cavity
. breathing = The abdominal wall relaxes to allow the thoracic cavity to expand and contracts to reduce the thoracic cavity (forcibly when coughing or sneezing)
. It contains and protects the major organs
. Increasing abdominal pressure = contraction of the abdominal wall assists in mictuation defecation and childbirth
Peritoneum
• This is the innermost layer of the abdominal wall
• It is a closed sac for men, unclosed in women (there is an opening for the uterine tubes)
It is a
• Continuous serous membrane
• Layer of simple squamous epithelium
• Supported by connective tissues
There are 2 layers names by its role / location
• Parietal – lines the abdominal wall / peritoneal cavity
• Visceral (serosal) – covering the organs
Peritoneal cavity
• The cavity only contains minimal serous fluid – 5-20ml
• Fluid has an important role in peritoneal homeostasis
• It is divided into 2 parts
greater sac - most of the space
lesser sac - smaller area
omenta
2 layers which connect the stomach / first part of the duodenum to the other organs
Mesenteries
Surround and support loops of bowel, connecting to the posterior abdominal wall
It allows for some movement of bowel
The digestive system
• It converts food into energy and absorbs nutrients
main processes =
ingestion
propulsion
digestion (mechanical and chemical)
absorption
elimination
structure of GI tract
There are 4 basic tissue layers
• Mucosa
• Sub-mucosa
• Muscularis
• Serosa
Nerve supply of the GI tract
• There is intrinsic and extrinsic innervation
• All of the digestive system is innervated by the autonomic nervous system
Parasympathetic
• Increases secretions and motility
• Mostly the vagus nerve and sacral nerve
Sympathetic
• Decreases secretions and motility
• This is your spinal nerves along the spine
What is the aim of digestion?
• To break down food in preparation for absorption
It is mechanical
• There is movement along the GI tract
• Breaking down the food increases the surface area for absorption
• As the food passes through it mixes with chemicals / secretions
Chemical enzymes
• Amylase – carbohydrates (salivary glands and
pancreas)
• Proteases (pancreas) and hydrochloric acid (stomach) – proteins
• Bile (pancreas) and lipases (pancreas)- fats
tongue
main functions
- mastication
- swallowing
- speech
The role of the tongue in digestion
- grips food and positions it between the teeth
- mixes food with saliva
- forms a bolus of food
- intiates swallowing
saliva
• Food is mixed with saliva which contains enzymes
• The enzymes are only activated in liquid and help to dissolve chemicals in food to aid taste
• Salivation is controlled by the autonomic nervous system.
• Parasympathetic –continuous secretion
• Sympathetic – works during stress or dehydration – dry mouth / thirst
• Chemicals in food stimulate the receptors in taste buds which result in secretion
• After eating there is a flow of saliva for cleaning and diluting any remaining chemicals
swallowing
3 stages according to location of bolus; takes around 4-8 seconds (1 for fluid)
stomach
c/j shaped
15-25 cm long
stomach layers
Serosa
• Serosa is continuous with the visceral peritoneum
• 3 muscle layers which allow churning and mixing
stomach layers - mucosa
. Made up of simple columnar epithelium
• Contains mucus cells
• Has a protective alkaline layer to protect from acids and enzymes
• Gastric juices are secreted from gastric glands – up to 2-3l a day
mechanical dogestion in the stomach
- there are peristaltic waves every 15-20seconds
- food is macerated
- it is mixed with secretions to form chyme
- the fundus secrion is mainly for storage - less movement
- the rugae allow dor expansion and increase the surface area
chemical digestion in the stomach
- The food may be in the fundus for more than an hour before churning begins but the salivary amylase continues to work
- Food is mixed with acidic gastric juices
- Very small amounts of nutrients are absorbed
- The epithelial cells are impermeable to most materials
- Some water is absorbed
- some drugs are absorbed
• Aspirin
• Alcohol
• The stomach empties 2-4 hours after eating
• Carbohydrate rich food is the quickest
• Fatty food is the slowest
• Each wave moves approximately 3mm of chyme through the sphincter into the duodenum
Some drugs are absorbed
small intestine
• Food is prepared in the small intestine so it can enter the cells of the body
• The small intestine is a muscular tube approx. 7m long from the pyloric sphincter to the ileocaecal sphincter
• Longest segment of digestive tract
small intestine - divisions
Duodenum - 25cm long (5%)
Jejunum - 2.5m long (40%)
Ileum -3m long (55%
duodenum structure
• Surrounds the head of the pancreas
• Receives
Gastric chyme from the stomach
Digestive juices from the pancreas
Bile from the live
Mechanical digestion in the small bowel.
•Contraction of circular muscle into segments
•Muscle fibres in middle of each segment contract –
dividing segment further
•First fibres relax -> large segment again
•Repeats – chyme sloshed back and forth
•Most rapid in duodenum
•After most of food absorbed segmentation stops and peristalsis begins
•Peristalsis migration reaches end of ileum in 90 –
120 minutes
•Chyme remains in small intestines 3 – 5 hours
duodenum
The mucosa has villi to increase the surface area
Its function is to breakdown food using enzymes
It uses hormones to regulate the rate of stomach emptying
jejunum
Has villi
• Has large circular folds to increase surface area of
mucosa
• Main function is to absorb previously digested food from the duodenum
ileum
• There isn’t an obvious junction between the
jejunum and ileum
• Has smaller and thinner walls than the jejunum
• Function
Absorb B12 and bile salts
Absorb remaining products not absorbed in the
jejunum
Large bowel
• Large because it has a larger diameter
• 1.5m long
• Differing diameters – 6-9cm
• No villi on the mucus membrane as there is no chemical digestion
• There are no structural alterations to increase surface area
• There are goblet cells with produce mucus to ease the passage of faeces
Caecum and appendix
• Caecum – 6cm long
• Receives chyme from the ileum
• Has the appendix hanging from it
Mechanical digestion in the large bowel
•Chyme enters cecum via ileo-caecal sphincter (Usually slowly)
•Gastro-colic reflex:
• Food entering stomach stimulates release of Gastrin into blood
•Gastrin plays a part in ileo-caecal sphincter relaxation
•Allows chyme to enter caecum from ileum
•Faeces in caecum triggers mass movement
Mass movement of faeces
When caecum becomes distended the contraction of the ileocaecal sphincter increases
Chyme fills caecum and accumulates in ascending colon
Haustral churning –distended by contents, walls contract moving contents to next haustrum
Peristalsis also occurs but slower 2 – 3 contractions per minute
Mass peristalsis – strong peristaltic wave from mid transverse colon
Drives faeces into rectum
Occurs after meals – 3 – 4 times per day
Chemical digestion in the large bowel
No enzymes secreted
Final stage of digestion – activity of bacteria in lumen
Bacteria:
Ferment any remaining carbohydrate
Releases hydrogen, CO2 and methane gas
Flatus – which becomes flatulence if excessive
Breakdown remaining proteins and amino acids
Decompose bilirubin to simpler pigments results in brown colour
Absorption in the large bowel
Water
• Most water is absorbed in the large bowel
• The large bowel is important in maintaining homeostasis
Bacterial products
• Including vitamins – B and K
Defaecation
•Elimination of indigestible residue
•When faeces into rectum by mass movement
defecation reflex initiated
•Spinal reflex:
• Causes walls of sigmoid colon and rectum to
contract
• Anal sphincters relax
• Faeces in anal canal messages to brain
• Voluntary decision to open external sphincter
• If not contraction ends and walls relax
• Next mass movement initiates new reflex
What are the functions of the liver?
digestive
haematological
metabolism of nutrients
detoxification
mineral and vitamin storage
bile production
absorbs iron and vitamin K
liver divisions
• It is divided into 4 lobes
Left lobe
Right lobe
• Subdivided into the caudate and quadrate lobes
Blood supply to the liver
A large amount of blood is needed for metabolic functions
Hepatic artery – 400-500 ml/min 25%
Hepatic portal vein 1000-1200 ml/min 75%
hepatic veins return blood to the IVC
Hepatocytes
metabolise proteins lipids and vitamins
the gallbladder
• Sac like organ
• Situated on the inferior surface of the liver
• It stores and concentrates bile
• Bile passes from the liver to the gallbladder via the right and left hepatic ducts into the common hepatic duct
• The bile passes into the gallbladder via the cystic duct
How does the gallbladder work
• Approx. 30 minutes after eating the gallbladder contracts - empties bile
• This forces bile through the cystic duct into the common bile duct
• The sphincter of Oddi relaxes
• Bile passes into the duodenum via the major duodenal papilla
The pancreas
• Approx. 20cm long
• It has a head, neck, body and tail
• The head, neck and body are retroperitoneal
• The head sits in the curve of the duodenum, the tail touches the spleen
• The body sits behind the stomach
Functions of the pancreas exocrine function
• Exocrine function
Has cells that secrete enzymes and alkaline pancreatic juices
These cause the gallbladder to contract and
release bile into the duodenum
Endocrine function
• There is secretion of
Insulin – lowers blood glucose
Glucagon – raises blood glucose
Regulation of blood glucose rising blood glucose level
Glucagon, a peptide hormone secreted by the pancreas, raises blood glucose levels. Its effect is opposite to insulin, which lowers blood glucose levels. When it reaches the liver, glucagon stimulates glycolysis, the breakdown of glycogen, and the export of glucose into the circulation.
Regulation of blood glucose declining blood glucose level
low blood glucose level is detected by glucagon whoch releases cells of pancreas. glucagon releasing cells of pancreas are stimulated to release glucagon into the blood and to pass to the liver. liver breaks down glycogen stores and releases glucose to the blood. blood glucose level rises to set point which stimulates for glucagon release and body returns to homeostasis
