Digestive 2

Question 1

How long is the oesophagus and where is it located?

Answer 1

In the thoracic cavity, extending from the pharynx to the stomach (a muscular tube 25 cm long)
- It travels posterior to the trachea

Question 2

What prevents food from going into the trachea?

Answer 2

The epiglottis

Question 3

How does the oesophagus normally appear?

Answer 3

Normally empty with its lumen collapsed. It expands to accommodate food/water

Question 4

Functions of the oesophagus:

Answer 4

1. Transport (travel time five seconds for food and one second for fluid due to peristalsis)
2. Protection (from abrasive foods)
3. No absorption, little secretion (mucous), no digestion

Question 5

Which of the four layers of the gut tube is specialised in the oesophagus?

Answer 5

Epithelium of the mucous membrane
External muscle
Serosa

Question 6

Epithelium in oesophagus:

Answer 6

Thick with many layers (stratified squamous), with sacrificial outer layers for protection against abrasive fragments of food

Question 7

What is the turnover rate of epithelium in the oesophagus?

Answer 7

The entire epithelium is renewed every 7 days

Question 8

Direction of epithelial cell replacement in the oesophagus:

Answer 8

Cells are replaced by division in the basal layers, then slow migration outwards. Old cells are shed from the surface

Question 9

External muscle in oesophagus:

Answer 9

contains in addition to the usual smooth muscle, there is also skeletal in the upper third of the oesophagus.

Question 10

Why is there additional skeletal muscle in the external muscle of oesophagus?

Answer 10

To allow rapid contraction and voluntary control of swallowing

Question 11

Serosa in oesophagus:

Answer 11

Lacks a serosa, instead is covered with a fibrous adventitia which attaches it to neighbouring organs e.g. trachea

Question 12

Structure of the stomach:

Answer 12

J shaped bag on the left side, an enlargement of the gut tube

Question 13

What is the capacity of the stomach?

Answer 13

About 1.5 litres

Question 14

Primary function of the stomach?

Answer 14

Storage (food can be eaten more quickly that it can be digested and absorbed)

Question 15

What are the four regions of the stomach?

Answer 15

1. Cardia (mostly mucous glands)
2. Fundus (secrete acid, enzymes, and mucous)
3. Body (secrete acid, enzymes, and mucous)
4. Pylorus (mostly mucous glands)

Question 16

What is the pyloric sphincter?

Answer 16

A well developed muscular sphincter at outlet in which the inner circular muscle keeps the stomach shut when food is stored inside

Question 17

Why is the chyme?

Answer 17

Semi-liquid mixture of partially digested food moving through the stomach

Question 18

Stomach epithelium + external muscle characteristics

Answer 18

Epithelium of mucosa - forms many pits lined with mucous secreting cells + gastric glands which open into the pits

External muscle - three layers rather than two (addition of innermost oblique layer)

Question 19

What are the 3 layers of muscle in the stomach?

Answer 19

1. Longitudinal muscle
2. Circular muscle
3. Oblique muscle

Question 20

Purpose of oblique muscle in the stomach?

Answer 20

Peristalsis (contract and squeeze) but also specifically provide a churning action

Question 21

Functions of the stomach:

Answer 21

1. Storage
2. Secretion of acids, enzymes, mucous (2-3 L per day)
3. Chyme = food + gastric juice
4. Digestion of proteins by pepsin (enzyme secreted as inactive form)
5. Absorption of water, ions, some drugs (aspirin, alcohol)
6. Protection (against its own secretions and microbes)
7. Transport (mixing waves every 20 seconds)

Question 22

What sections is the mucosa of the stomach divided into?

Answer 22

1. Gastric pit (invaginations)
2. Neck
3. Gastric glands

Question 23

Purpose of surface mucous cells in the mucosa of the stomach:

Answer 23

Secrete insoluble alkaline mucus which protects the mucosa from acid and pepsin

Question 24

Purpose of parietal cells in the mucosa of the stomach:

Answer 24

Secrete HCl (H+ and Cl- separately) which kills microbes and living cells. Also secretes intrinsic factor which is vital for B12 absorption

Question 25

Purpose of mucous neck cells in the mucosa of the stomach:

Answer 25

Secrete soluble acid mucous at mealtimes

Question 26

Purpose of chief cells in the mucosa of the stomach:

Answer 26

Secrete pepsinogen and gastric lipase pepsinogen secretes as inactive form and then converted to protein splitting enzyme pepsin by acid in the lumen Gastric lipase aid in a very small amount of fat digestion

Question 27

How to distinguish between chief cells and enteroendocrine cells?

Answer 27

Chief - granular cells face IN to the lumen enteroendocrine - granular cells face OUT

Question 28

Purpose of enteroendocrine cells in the mucosa of the stomach:

Answer 28

Secretes gastrin which enters the blood stream as a hormone

Question 29

Function of gastrin:

Answer 29

1. Stimulates secretion of acid and pepsinogen 2. Increases muscular contractions of stomach 3. Relaxes the pyloric sphincter

Question 30

What is the liver?

Answer 30

An enormous gland made of epithelial cells called hepatocytes

Question 31

Where are hepatocytes derived from?

Answer 31

Embryonic endoderm

Question 32

Function of hepatocytes?

Answer 32

More than 500 metabolic functions - glycogen/glucose storage and release - recycling of red blood cells - bile synthesis and secretion - synthesis of plasma proteins - removal of toxins from blood

Question 33

What does each hepatocyte require?

Answer 33

1. Access to nutrient laden blood drained from the intestinal wall 2. Access to oxygenated blood from the systemic circuit 3. Access to ducts which drain bile to the gall bladder

Question 34

Purpose of fenestrated endothelial cells of liver sinusoid:

Answer 34

Act as a filter and allow passage of the watery part of the blood (lymph) but exclude red blood cells

Question 35

What forms liver lobules?

Answer 35

Plates of hepatocytes stacked together form liver lobules

Question 36

Shape + size of liver lobules:

Answer 36

Each lobule is hexagonal in cross-section 2mm long by 1 mm wide

Question 37

How does blood leave the lobule?

Answer 37

Via central vein