digestive system

Question 1

overview of abdomen

Answer 1

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

Question 2

Functions of the abdominal cavity

Answer 2

. 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

Question 3

Peritoneum

Answer 3

• 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

Question 4

Peritoneal cavity

Answer 4

• 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

Question 5

omenta

Answer 5

2 layers which connect the stomach / first part of the duodenum to the other organs

Question 6

Mesenteries

Answer 6

Surround and support loops of bowel, connecting to the posterior abdominal wall
It allows for some movement of bowel

Question 7

The digestive system

Answer 7

• It converts food into energy and absorbs nutrients
main processes =
ingestion
propulsion
digestion (mechanical and chemical)
absorption
elimination

Question 8

Nerve supply of the GI tract

Answer 8

• 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

Question 9

What is the aim of digestion?

Answer 9

• 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

Question 10

tongue

Answer 10

main functions
- mastication
- swallowing
- speech

Question 11

The role of the tongue in digestion

Answer 11

• grips food and positions it between the teeth
• mixes food with saliva
• forms a bolus of food
• intiates swallowing

Question 12

swallowing

Answer 12

3 stages according to location of bolus; takes around 4-8 seconds (1 for fluid)

Question 13

stomach

Answer 13

c/j shaped
15-25 cm long

Question 14

mechanical dogestion in the stomach

Answer 14

• 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

Question 15

chemical digestion in the stomach

Answer 15

• 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

Question 16

small intestine

Answer 16

• 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

Question 17

small intestine - divisions

Answer 17

Duodenum - 25cm long (5%)
Jejunum - 2.5m long (40%)
Ileum -3m long (55%

Question 18

duodenum structure

Answer 18

• Surrounds the head of the pancreas
• Receives
Gastric chyme from the stomach
Digestive juices from the pancreas
Bile from the live

Question 19

Mechanical digestion in the small bowel.

Answer 19

•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

Question 20

duodenum

Answer 20

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

Question 21

jejunum

Answer 21

Has villi
• Has large circular folds to increase surface area of
mucosa
• Main function is to absorb previously digested food from the duodenum

Question 22

ileum

Answer 22

• 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

Question 23

Large bowel

Answer 23

• 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

Question 24

Caecum and appendix

Answer 24

• Caecum – 6cm long
• Receives chyme from the ileum
• Has the appendix hanging from it

Question 25

Mechanical digestion in the large bowel

Answer 25

•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

Question 26

Mass movement of faeces

Answer 26

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

Question 27

Chemical digestion in the large bowel

Answer 27

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

Question 28

Absorption in the large bowel

Answer 28

Water • Most water is absorbed in the large bowel • The large bowel is important in maintaining homeostasis Bacterial products • Including vitamins – B and K

Question 29

Defaecation

Answer 29

•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

Question 30

What are the functions of the liver?

Answer 30

digestive haematological metabolism of nutrients detoxification mineral and vitamin storage bile production absorbs iron and vitamin K

Question 31

liver divisions

Answer 31

• It is divided into 4 lobes Left lobe Right lobe • Subdivided into the caudate and quadrate lobes

Question 32

Blood supply to the liver

Answer 32

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

Question 33

Hepatocytes

Answer 33

metabolise proteins lipids and vitamins

Question 34

the gallbladder

Answer 34

• 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

Question 35

How does the gallbladder work

Answer 35

• 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

Question 36

The pancreas

Answer 36

• 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

Question 37

Functions of the pancreas exocrine function

Answer 37

• Exocrine function Has cells that secrete enzymes and alkaline pancreatic juices These cause the gallbladder to contract and release bile into the duodenum

Question 38

Endocrine function

Answer 38

• There is secretion of Insulin – lowers blood glucose Glucagon – raises blood glucose

Question 39

Regulation of blood glucose rising blood glucose level

Answer 39

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.

Question 40

Regulation of blood glucose declining blood glucose level

Answer 40

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

Question 41

structure of gi

Answer 41

Mucosa • Sub-mucosa • Loose connective tissue to bindmucosa to the muscle layer • Contains neurovascular and lymphatic structures • Muscularis • Serosa • Fibrous outer layer in the thorax • Single serous layer membrane in the peritoneum