digestive system part 2 Flashcards
stomach, small and large intestine
size and shape of the stomach
C/J shaped
15 – 25cm long
Volume depends on the contents – up to 4L capacity
When empty the rugae collapse and fold in, shrinking the stomach
what is the position of the stomach
Inferior to the diaphragm
In the upper left quadrant / left epigastric and hypochondriac region
what are the 4 regions of the stomach
Cardia-s urrounds the cardio-oesophageal sphincter
Fundus- The section lateral to the cardia. sits above oesophageal sphincter, where gas sits.
Body- Mid portion, Narrows inferiorly- where most mixing and breakdown occurs.
Pylorus - Consists of the antrum and canal
Contains the pyloric sphincter which is continuous with the small intestine
stomach layers- serosa
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
some facts about mechanical digestion in the stomach
-There are peristaltic waves every 15-20 seconds
-Food is macerated
-It is mixed with secretions to form chyme
-The fundus section is mainly for storage- less movement
-The rugae allow for 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
-HCI acid
Kills microbes
Denatures proteins
Promotes flow of bile
-Gastrin
Increases mobility of stomach
Relaxes the pyloric sphincter
-Pepsin
Starts digestion of -protein
Breaks peptide bonds making smaller chains
what is the small intestine, and what are its main parts.
-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
parts- duodenum- 5cm peritoneal
rest of duodenum, jejunum, ileum are retroperitoneal,
small intestine divisions
Duodenum
25cm long (5%)
Jejunum
2.5m long (40%)
Ileum
3m long (55%)
duodenum
C shaped
Extends from the pyloric sphincter to the jejunum
Has 4 sections
1st – superior
2nd – descending
3rd – horizontal
4th - ascending
Surrounds the head of the pancreas
Receives
Gastric chyme from the stomach
Digestive juices from the pancreas
Bile from the liver
what is mechanical digestion in the small bowel
-localised mixing contractions
-the chyme mixes with digestive juices.
-food comes into contact with the mucosa, contents are not moved along.
what is the step by step process of 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 – 12 x per minute 8 x per minute in ileum
-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
what is the 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
what is the jejunum
Has villi
Has large circular folds to increase surface area of mucosa
Main function is to absorb previously digested food from the duodenum
what is the 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
features of the large bowel
-large diameter
-1.5m long
-differing diameters- 6-9cm
-runs from ileocaecal valve to anus
-no villi on mucous membrane as there’s no chemical digestion.
-goblet cells which produce mucus to ease the passage of faeces.
no structural alterations to increase surface area.
large bowel- teniae coli
Teniae coli
2 bands of smooth muscle
Runs from the caecum to the rectosigmoid junction
These contact lengthwise to produce haustra
This helps to move faeces through the large bowel
Do not have them in the rectum and anus
caecum and appendix
Caecum – 6cm long
Receives chyme from the ileum
Has the appendix hanging from it
colon
-ascending: 20 cm long, has hepatic flexure at distal end.
-transverse: has hepatic and splenic flexure at either end.
-descending: left side of pelvis
-sigmoid: s shaped, projects medially.
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
outline the process of 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
what are some features of the liver
-irregular wedge shaped organ
-largest gland in the body
-situated under the diaphragm in the right upper quadrant extending into the left upper quadrant.
-largely protected by the ribs and overlies the stomach
divisions of the liver
-4 lobes, left lobe and right lobe
right lobe- subdivided into the caudate and quadrate lobes.
-the 2 main lobes are divided by the falciform ligament.
-the falciform ligament attached the liver to the anterior abdominal wall.
the liver is covered by what?
fibroelastic capsule made up of:
-visceral peritoneum
-a Glisson capsule underneath which contains blood and lymph vessels and nerves.
what is the blood supply to the liver
A large amount of blood is needed for metabolic functions
Hepatic artery – 400-500 ml/min
Hepatic portal vein 1000-1200 ml/min
hepatic veins return blood to the IVC
what are hepatocytes
Liver cells are capable of regeneration – damaged or resected liver can regrow
the gallbladder
-Sac like organ
-Situated on the inferior surface of the liver
-It stores and concentrates bile (approximately 90mls)
-Bile passes from the liver to the gallbladder via the right and left hepatic ducts into the common hepatic duct
-There is resistance at the sphincter of Oddi – this controls flow into the duodenum and precents reflux
-The bile passes into the gallbladder via the cystic duct
How does the gallbladder work- overview
Approx. 30 minutes after eating the gallbladder contracts
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
detailed description of how the gallbladder works
1- acidic, fatty chyme entering duodenum causes release of cholecystokinin and secretin.
2- cholecystokinin and secretin enter bloodstream.
3-bile salts + secretin transported via blood stream stimulate liver to produce bile more rapidly.
4- stimulation causes weak contractions of gallbladder.
5-cholecystokinin causes gallbladder too contract and hepatopancreatic sphincter to relax: bile enters duodenum.
6- bile salts reabsorbed into blood
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
exocrine functions of the pancreas
Exocrine function
Has cells that secrete enzymes and alkaline pancreatic juices
These cause the gallbladder to contract and release bile into the duodenum
endocrine functions of the pancreas
Endocrine function
There is secretion of
Insulin – lowers blood glucose
Glucagon – raises blood glucose
regulation of blood glucose - declining level
stimulus- declining blood glucose
-low bg detected by glucagon releasing cells of pancreas
-glucagon releasing cells stimulated to release glucagon into blood- target is liver.
-liver breaks glycogen stores and releases glucose to blood.
bg level rises to set point, and body returns to homeostasis.
regulation of blood glucose- rising level
-high blood glucose level detected by insulin secreting cells of pancreas.
-insulin secreting cells of pancreas stimulated to release insulin into the blood.
-most body cells take up more glucose, liver takes up glucose and stores it as glycogen.
-blood glucose level declines to a set point: stimulus for insulin release diminishes and body returns to homeostasis.
