digestive system

Question 1

The GI tract has

Answer 1

4 layers

Question 2

Mucosa

Answer 2

• Protective
• Epithelium
• Muscularis mucosae - thin layer of muscles, helps make folds in mucosa, more SA

Question 3

Submucosa

Answer 3

houses blood vessels and nerves

Question 4

Muscularis

Answer 4

• Very muscular
• Longitudinal and circular muscle

Question 5

Serosa

Answer 5

Outside
- connective tissues, nerves, fat cells, blood vessels.
- Slippery layer so GI tract can move freely
- If it touches another organ - adventitia

Question 6

Oral (buccal) cavity

Answer 6

accessory organs:
* Teeth
* Tongue salivary glands

Question 7

Tongue salivary glands

Answer 7

1. Parotid
   - Largest
   - Sits in front of ear
2. Submandibular
   - Lower jaw
3. Sublingual
   - Under tongue

Question 8

Pharynx

Answer 8

• Moves bolus to oesophagus
• Made up of skeletal muscles

Question 9

Bolus

Answer 9

chewed up food, in a ball

Question 10

Oesophagus

Answer 10

Propel bolus to stomach
Anatomy
* Muscular tube - (~25cm long)
* Upper - skeletal muscles
* Middle - mixed
* Lower - smooth muscle

Question 11

Anatomy of the stomach

Answer 11

j -shaped chamber
Very muscular
Rugae - ridges
4 main areas:
* Cardia, fundus, body, pylorus

Question 12

Muscular valves (sphincter) of stomach

Answer 12

ensure movement is only one way
Top: gastro-oesophageal sphincter
Bottom: pyloric sphincter

Question 13

Muscle layers of stomach

Answer 13

help with churning motion
1.Longitudinal layer
2.Circular layer
3.Oblique layer
Oriented diagonally

Question 14

Chyme

Answer 14

what food is called after digestion in the stomach

Question 15

function of the stomach

Answer 15

• Holding reservoir
• Mixing chamber (chyme)
• Secretion of gastric juices
• Secretion of gastrin

Question 16

Anatomy of Small intestine

Answer 16

3 regions
1. Duodenum (shortests)
2. Jejunum (2-2.5m) - bulk of where chemical digestion and absorption occurs
3. Ileum (3m) - at the end ileocecal sphincter (ensures chyme travels one way)
Joins large intestine at ileocecal sphincter

Question 17

At mucosa of small intestine

Answer 17

(at mucosa) Villi: finger-like projections of mucosa
Microvilli: hair-like projections of absorptive cells

Question 18

function of small intestine

Answer 18

• Receives pancreatic juice and bile
• Secretes intestinal juice
• Major site of digestion and absorption

Question 19

Pancreas

Answer 19

Endocrine cells releases insulin and glucagon
Exocrine cells release pancreatic juice

Question 20

Liver

Answer 20

Largest gland
Secretes bile

Question 21

Gallbladder

Answer 21

Store and concentrate bile

Question 22

Anatomy of Large intestine

Answer 22

4 major regions:
* caecum, colon, rectum, anal canal

Sphincters:
* Internal anal sphincter (involuntary)
* External anal sphincter (voluntary)

Question 23

Functon of the large intestine

Answer 23

• Absorption
• Production of certain vitamins
• Formation and elimination of faeces
• Housing microbes

Question 24

Mechanical digestion

Answer 24

involves the physical breakdown of food into smaller particles

Question 25

Chemical digestion

Answer 25

assisted via enzymatic activity to form absorbable compounds

Question 26

If we consume carbohydrates (mostly starches)

Answer 26

we can absorb Monosaccharides (mostly glucose)

Question 27

If we consume proteins

Answer 27

we can absorb amino acids

Question 28

If we consume lipids (mostly triglycerides)

Answer 28

we can absorb fatty acids

Question 29

Oral cavity

Answer 29

* **Saliva** (99.5% water, 0.5% solutes) * **Mucus** lubricates food * Immunoglobulin A (**IgA**) prevents microbes from attaching to epithelium * Mechanical digestion via mastication * Chemical digestion via action of two enzymes in saliva 1. **Salivary amylase** digests **starch** to maltose 2. **Lingual lipase** digests **triglycerides**

Question 30

Oesophagus: motility

Answer 30

Propulsion of bolus via peristalsis

Question 31

Peristalsis

Answer 31

continuous waves of contraction and relaxation of muscles down the tract

Question 32

Stomach: Mechanical digestion, motility

Answer 32

Peristaltic contractions ~3/min push bolus towards pylorus (propulsion) 1. **Contractions **strengthen towards the pylorus grinding contents 2. Pylorus allows 1/10 of chyme it holds to **pass through pyloric valve** per contraction 3. Contractions also close pyloric value and remaining contents are propelled back (**retropulsion**)

Question 33

Gastric Pits in the Stomach consist of:

Answer 33

1. Pareital cell 2. Chief cell 3. Mucous cell 4. G cell

Question 34

Parietal cell

Answer 34

* secretes **HCl** - kills microbes, denatures proteins, converts pepsinogen to pepsin * Secretes **intrinsic factor** - needed for transportation & absorption of vitamin B12 in ileum

Question 35

Chief cell

Answer 35

* release **pepsinogen** (inactive enzyme) and active form (pepsin) and breaks **proteins into peptides** * Secretes **gastric lipase** - breaks **triglycerides** into *fatty acids* and *monoglycerides*

Question 36

Mucous cell

Answer 36

release **bicarbonate**-rich mucus * **lubrication, protects** stomach wall from protein digestion, corrosion

Question 37

G cell

Answer 37

releases **gastrin** (hormone) into bloodstream, *stimulates* **parietal** cells to secrete *HCl* and **chief** cells to secrete *pepsinogen*

Question 38

Bile secreted by liver

Answer 38

* Bile **salts**: emulsifies fats, facilitate absorption of **fat** and **cholesterol** * **Bilirubin**: pigment that is a waste product from the breakdown of red blood cells. * Gallbladder stores and concentrates bile by absorbing water and ions

Question 39

intestinal juice

Answer 39

* secretion *stimulated* by **acidic chyme** * 1-2 L/day * pH 7.4-7.8 * Water, mucus, enzyme-poor

Question 40

Pancreatic juice

Answer 40

* 1.2-1.5 L/day * Water * Bicarbonate ions: neutralizes HCl from stomach * Pancreatic proteases released in active form e.g. trypsinogen activated to trypsin * Pancreatic amylase, lipases, nucleases

Question 41

Small intestine: chemical digestion

Answer 41

* Largely occurs in the duodenum * All forms of organic compounds are digested in the small intestine * Most enzymes are transported from pancreas * Brush border enzymes: on plasma membrane of microvilli

Question 42

Optimal digestive activity relies on...

Answer 42

slow delivery of chyme from stomach * Regulate against hypertonicity of entering chyme * Allows low pH of chyme to be neutralised

Question 43

Small intestine: motility & absorption

Answer 43

Peristalsis moves chyme through intestinal tract, ~16 contractions/min **Segmentation** the most common motion in the jejunum * Localised contractions and relaxations move chyme back and forth a few centimetres * Promotes mixing, absorption of nutrients and water

Question 44

Small intestine: absorption

Answer 44

**Water-insoluble** products of lipid digestion, fat-soluble vitamins, cholesterol **form micelles** with **bile salts** * Components transferred to absorptive cells * Lipids would ‘float’ in chyme without micelles * Normally occurs in **ileum**

Question 45

large intestine: motility

Answer 45

**Haustral contractions** in ascending and transverse colon * Slow segmenting movements lasting ~1 min aids with mixing and water absorption * Occurs every 30min **Peristalsis** occurs 3-4 times/day * Allows for mass movement of content towards rectum

Question 46

Large intestine: digestion, absorption

Answer 46

Some digestion of **resident bacteria** - Insoluble carbohydrates broken down via **fermentation -> short-chain fatty acids** Absorbs remaining **water** and electrolytes (Na+, Cl -) Absorbs vitamins synthesised by resident bacteria (vitamin B complexes, vitamin K)