digestive system and anatomy functions

Question 1

name and describe the different layers of the GI tract

Answer 1

1. Mucosa: faces the lumen of the GI tract. The lumen is inside the GI tract and therefore is in contact and absorbs these nutrients
   a. One single layer of enterocytes that form an epithelium
2. Submucosa: found underneath the mucosa. Contains the submucosal plexus it is where you find neurones and ganglion cells that control movement of GI tract
3. Muscularis propria: layer of smooth muscle (circular or longitudinal). They propel food through the gut
4. Serosa: outer layer of the GI tract and protects against extremal aggressions. Consists of outer mesothelium and a loose connective tissue

Question 2

What are the differences between the GI tract and the oesophagus?

Answer 2

1. There is no mesothelium or serosa
2. Muscularis propria, in the rest of GI tract the muscles are smooth which are for involuntary movements, however the smooth muscles in the oesophagus also have striated muscles are attached to the skeleton and used in voluntary movements

Question 3

why is the direction of the bolus unidirectional

Answer 3

1. Presence of 2 sphincters: first one avoids the food to go down the trachea and the second one is near the stomach to avoid acid reflux.
2. Movements within the oesophagus called peristaltic movements that pushes the bolus down. These are reflex contractions of the muscles of the muscularis propria

Question 4

what is bolus, chyme and faeces

Answer 4

Bolus: Food that has been masticated (chewed) going from oesophagus to stomach.

chyme: Bolus that is processed in the stomach, mixed with various juices. Exits stomach to the small intestine
faeces: Chyme leaves small intestine, becomes faeces in the large intestine which are semi-solid substance with very few nutrients

Question 5

what is the peristaltic reflex?

what is the propulsive segment and receiving segment?

Answer 5

A wave of muscular contractions and relaxations that go down one side of the gut wall. Regulated by ANS

Propulsive: The diameter of the gut is made smaller. Circular muscles contract to constrict the section of the gut wall. The longitudinal muscles relax. When relaxed they elongate and stretch easier, decreasing gut diameter. Propels bolus into the receiving segment

receiving: The gut wall must have a bigger diameter to accommodate for the size of the bolus. The longitudinal muscles contract and this shortens the tube. The circular muscles relax. The result is that the lumen (where bolus is) larger at that site

Question 6

what is the function of serotonin during the peristaltic reflex

Answer 6

1. Activates sensory afferent neurones in the myenteric plexuses
2. Inhibits its own production from epithelium

a. Why? Because we’d have continuous peristaltic movements without food

Question 7

what are the cells and their functions located within the stomach

Answer 7

Parietal cells: produce HCL which makes the stomach secretions acidic. Also secrete intrinsic factor that is important for Vit B12 to be absorbed

Neck cell: secrete bicarbonate to buffer the pH, secrete water and mucus to protect the lining of the stomach.

Pit cells: secrete gastric mucus

Chief cells: secrete digestive enzymes

Endocrine cell: secretion of ghrelin (food uptake) somatostatin (acid production)

Question 8

what are the three parts of the small intestine

Answer 8

• Duodenum
• Jejunum & Ileum
• Mesentery

Question 9

describe what the duodenum, Jejunum and Ileum and mesentery is

Answer 9

Duodenum: Wrapped around the pancreas, receives pancreatic secretions & bile from the gall bladder

Nutrients have all been broken down to their monomers.

Jejunum & Ileum: main site of nutrient absorption

Mesentery: Connecting membrane that is between the intestine and abdominal walls. Provides insulation
Supplies blood to the intestine

Question 10

how is the stomach vascularised

Answer 10

Blood in: Abdominal aorta (mesenteric artery), the vessels branch out of the artery to irrigate the intestine wall

blood out: Leaves via the superior mesenteric vein that connects to the portal vein.

Question 11

what are enterocytes

Answer 11

intestinal villi which are in contact with chyme, are covered by epithelium and they are Polarised.

Question 12

Describe what the brush boarder is and what the function of the brush boarder is?

Answer 12

enterocytes that face the chime are in contact with the apical membrane. Apical membrane is covered in microvilli which form the brush boarder.

there are enzymes are located on the brush boarder to help nutrient breakdown into their final monomer.

Question 13

why is there limited absorption in the colon

Answer 13

no vili

Question 14

where is the main site to reabsorb water and electrolytes

Answer 14

colon

Question 15

the liver is the site of what metabolism

Answer 15

protein, carbs and fat

Question 16

what are the functions of hepatocytes

Answer 16

• are 80% of liver volume and can regeneration.
• They have a very active metabolism

-Highly developed to provide
enzymes for high metabolism rate

-Synthesize cholesterol and primary bile acids derived from acid

Question 17

what is the difference between acinar cells and islet cells

Answer 17

acinar: represents 95% of the pancreas cells, exocrine function. They produce substances such as digestive enzymes
islet: have endocrine function, they secrete hormones

Question 18

what are the three types of islet cells within the pancreas. what are their functions?

Answer 18

1. alpha: secrete glucagon to increase blood glucose levels
2. beta: which secrete insulin to decrease glucose levels
3. delts cells: which secrete somatostatin which acts on glucagon and insulin to maintain a balance between the hormones