Physiology- Digestive system

Question 1

5 stages of digestion:

Answer 1

Ingestion
Digestion
Absorption
Assimilation
Egestion

Question 2

Ingestion definition:

Answer 2

Taking large pieces of food into the body

Question 3

Digestion definition:

Answer 3

Breaking down the food by mechanical and chemical means

Question 4

Absorption definition:

Answer 4

Taking up the soluble digestion products into the body

Question 5

Assimilation definition:

Answer 5

Using the absorbed materials

Question 6

Egestion definition: how is it different from excretion

Answer 6

Eliminating the undigested material from the body cavity

-excretion is elimination of metabolic waste from body cells

Question 7

What are the 3 glands in the gut (alimentary canal) that secrete enzymes?

Answer 7

• salivary gland
• liver
• pancreas

Question 8

What are the 4 layers in the lining of the alimentary canal?

Answer 8

Lumen

1) Mucosa
2) Submucosa
3) Muscle
4) Serosa

Question 9

What is the structure of the mucosa?

Answer 9

• It is the layer closest to the lumen, so is folded to increase surface area
• secretes digestive enzymes from glands
• epithelium is made from columnar epithelial

Question 10

What is the structure of columnar epithelial?

Answer 10

• Contains microvilli
• bilayer contains lots of membrane bound proteins for facilitated diffusion and active transport
• lots of mitochondria
• membrane bound enzymes

Question 11

What makes up the submucosa?

Answer 11

• Layers of blood vessels and the lymph vessels
• also contains glands secreting enzymes
• contains the nerves to control the longitudinal and circular nerves

Question 12

What is the structure of the muscle layer in the gut?

Answer 12

• layer of circular muscle
• layer of longitudinal muscle
  These 2 muscle work antagonistically so are able to push food through gut by peristalsis

Question 13

What is the serosa and its function?

Answer 13

• thin layer of tough connective tissue that holds the gut together
• attaches to the abdomen

Question 14

What 5 parts make up the alimentary canal?

Answer 14

Mouth
Oesophagus 
Stomach
Small intestine
Large intestine

Question 15

Describe what happens in the mouth when food is taken in by digestion:

Answer 15

• mastication to increase SA
• Salivary glands secrete saliva, containing water to dissolve soluble substances, mucus for lubrication, amylase and lysozyme to kill pathogens

Question 16

What occurs in the oesophagus?

Answer 16

This is a muscular tube connection the mouth to the stomach, no digestion occurs
- only peristalsis occurs in this

Question 17

Describe peristalsis:

Answer 17

Muscles are antagonistic so one works while other relaxes

• circular muscles contract while longitudinal muscles relax squeezing the tube
• this contraction occurs like a wave

Question 18

Describe digestion in the stomach

Answer 18

• expandable bag with layers of muscle to churn the food into a liquid (chime)
• chime is gradually released into small intestine by the sphincter valve
• inner wall lining (mucosa) has gastric glands that secrete gastric juices (mucus, HCL acid and protease)

Question 19

Describe the small intestines duodenum

Answer 19

A) First part of small intestine 30cm is the duodenum where most of digestion occurs, due to pancreatic juices and bile released through the pancreatic ducts and bile ducts from the pancreas and liver

Question 20

Describe the ileum part of the small intestine:

Answer 20

• this is the site of the remaining digestion and all absorption
• numerous glands in the mucosa and submucosa secreting enzymes, mucus and sodium hydrogen carbonate
  Epithelial contain microvilli
  Network of blood capillaries in the submucosa (short diffusion pathway and to maintain high conc gradient)

Question 21

How has the ileum adapted to maximise ficks law

Answer 21

1) large SA, epithelial cells have microvilli
2) short diffusion pathway, network of capillaries in submucosa, substances only have to diffuse across the mucosa
3) blood flow in capillaries ensures low conc of nutrients in blood, and contraction of lumen ensures high conc of nutrients in the lumen

Question 22

What is the large intestine?

Answer 22

Comprised of caecum, appendix, colon and rectum

- water is reabsorbed while faeces is released via the anal sphincter

Question 23

Where does digestion of starch occur?

Answer 23

Mouth-> salivary amylase
Duodenum -> pancreatic amylase
Also in the ileum by membrane bound enzymes

Question 24

How is glucose transported into the blood?

Answer 24

Cotransport with sodium ions

Question 25

Describe the process of cotransport of glucose and sodium into the blood

Answer 25

• sodium ions are pumped out of the cell and into the blood by active transport
• there is now a low conc. of sodium inside the cell
• sodium binds to the transport protein (glucose symporter)
• glucose also binds to the same protein, causing the shape of the protein to change transporting glucose and sodium through
• higher conc of glucose in blood, glucose goes into blood by facilitated diffusion

Question 26

What makes people lactose intolerant?

Answer 26

Inability to produce the lactase enzyme, to break down lactose which then remains in the poo, changing the water potential causing symptoms like farting

Question 27

How does cholera produce diarrhoea?

Answer 27

• cholera secretes the toxin CT into epithelial cells
• CT activates a chloride ion channel
• Chloride ions diffuse into the lumen
• lowers water potential of lumen
• water moves into the lumen to increase water potential again
• > water poo

Question 28

How is diarrhoea treated?

Answer 28

• Glucose and sodium is taken in equal quantities
• both are transported into the epithelial cell by cotransport
• this lowers the cell water potential
• water moves into the cells from the lumen by osmosis, so the cells are rehydrated