Lecture 13 - Digestion and Intestinal Absorption]

Question 1

What are the 3 primary macronutrients that get broken down to produce energy

Answer 1

Carbohydrates
Fats
Protein

Question 2

What are the sections of the gastrointestinal tract

Answer 2

Mouth
* Pharynx
* Oesophagus
* Stomach
* Small Intestine
* Large Intestine

Question 3

What are accessory organs Salivary Glands

Answer 3

Salivary Glands
* Liver
* Gallbladder
* Exocrine Pancreas

Question 4

What are the layers to a gastrointestinal wall

Answer 4

Lumen
Mucosa
Submucosa
Muscular externa
Serosa
Enteric Nervous System

Question 5

What makes up the mucosa

Answer 5

Mucous membrane
Lamina Propria
muscuoaris Mucosae

Question 6

What are parts of the muscular externa

Answer 6

Circular muscle
Longitudinal muscle

Question 7

What are the parts of the enteric nervous system

Answer 7

Submucosal plexus
Myenteric plexus

Question 8

What is laminate propia

Answer 8

Loose connective tissue in the GIW

Question 9

What does the muscularis mucosa do

Answer 9

Layer of smooth muscle

Question 10

What do epithelium do in the mucosa in the GIW

Answer 10

Contain both endocrine and exocrine cells

Question 12

what are in the submucosa

Answer 12

Blood and lymphatic vessels– Penetrate the layers above
and below
Submucosal Plexus– A network of neurons for control of
muscular activity

Question 13

what are the functions of the composites of the muscular externa

Answer 13

Circular muscle– Contraction produces narrowing of lumen
Myenteric plexus– Innervated from autonomic nervous system,
also connected to submucosal plexus
Longitudinal muscle – Contraction shortens the tract

Question 14

What does the serosa do

Answer 14

Connective tissue surrounding outer surface of the tract
Sheets of connective tissue connect serosa to the abdominal wall
and hold GI tract in place

Question 15

What is the Cephalic phase

Answer 15

Brain’s anticipation of food:
sight, smell or thought
Saliva production increases - parasympathetic
nervous system activity
Stimulation of gastric juice secretion & insulin
secretion

Question 16

What does the mouth do

Answer 16

Mechanical breakdown of food
Mixing of food with saliva
Initiate chemical digestion of carbohydrates (salivary
amylase)
Antibacterial action

Question 17

What does saliva do

Answer 17

Bicarbonate – neutralise acid
Mucus – lubricates & protects from abrasion
Salivary amylase – breakdown CHO
Lysozyme – destroys certain bacteria (prevent tooth
decay)

Question 18

What does Salivary amylase do

Answer 18

Begins CHO digestion
Starts starch hydrolysis
Limited: <5% of starch digestion…
…unless chewing is prolonged

Question 19

What does the pharynx do

Answer 19

Conducts food into the oesophagus

Question 20

What does the oesophagus do

Answer 20

Conducts food into the stomach

Question 21

What do the epiglottis do

Answer 21

closes to prevent aspiration into trachea

Question 22

What do the sphincters at the bottom of the pharynx do

Answer 22

Sphincters at bottom of Pharynx and opening to
stomach prevent movement of air and stomach
contents entering oesophagus

Question 23

What is peristalsis

Answer 23

Food moves towards stomach due to
progressive muscular contraction
This “wave” compresses the lumen
and forces food along
If a particularly large bolus does not
reach the stomach then reflexes
initiate repeated waves of activity
Known as ”secondary peristalsis”

Question 24

What are the parts of the small intestine

Answer 24

Duodenum
Jejunum
Ileum

Question 25

What does the stomach do

Answer 25

Mechanical breakdown of food (and mixing -> chyme) Secretion of acid (HCl) – kill bacteria Pepsin (secreted as pepsinogen) – begin protein digestion Gastric lipase Storage

Question 26

What does the small intestine do

Answer 26

Chemical digestion all nutrients (pancreatic & brush border enzymes) Absorption of digestive end-products, water, ions and vitamins Secretion of hormones Secretion of bicarbonate-rich fluid

Question 27

What does the colon do

Answer 27

Absorption of ions and water Transformation of chyme into faeces Storage of faeces

Question 28

What does the rectum do

Answer 28

Stores faeces

Question 29

What do mucous cells do

Answer 29

Secrete mucous - Alkaline solution released along with mucus to protect the stomach lining

Question 30

What do parietal cells do

Answer 30

Secretes HCl and intrinsic factor - necessary for vitamin B12 absorption

Question 31

What do Chief cells do

Answer 31

Secrete pepsinogen - Inactive - activated by acidic environment

Question 32

What do Enteroendocrine cells do

Answer 32

Secrete Gastrin

Question 33

What do Entero-chromaffin-like cells (ECLs) do

Answer 33

Release histamine

Question 34

What do D cels do

Answer 34

Secrete somatostatin - important for H+ secretion

Question 35

What is potentiation

Answer 35

Action of 3 substances combined is greater than the sum of the individual effects Negative feedback

Question 36

What are the parts of the stomach

Answer 36

Antrum Sphincters main body

Question 37

What does the pancreas do

Answer 37

Secretion of pancreatic juice (bicarbonate) Proteases Pancreatic lipase

Question 38

What does the gall bladder do

Answer 38

Storage and concentration of bile

Question 39

TABLE OF ENZYMES AND JUICES

Question 40

What does the liver do

Answer 40

Secretes bile (bile salts and bicarbonate) Processes absorbed nutrients

Question 41

What are the bile components important for digestion

Answer 41

Bile salts Phospholipids HCO3-

Question 42

What are the bile substances removed from the blood

Answer 42

Cholesterol Bile Pigments Trace metals

Question 43

What are the incretin hormones

Answer 43

GIP (glucose dependant insulinotropic polypeptide) GLP-1 (glucagon-like peptide-1)

Question 44

What does GLP-1 do

Answer 44

Stimulated by nutrients in the small intestine Secreted by L-cells in the ileum Promotes insulin release Inhibits glucagon release Delays gastric emptying Suppresses appetite and energy intake

Question 44

What does GIP do

Answer 44

Stimulated by nutrients in small intestine Secreted by K-cells in duodenum and jejunum Stimulates insulin secretion

Question 45

HORMONES OF THE GI TRACT

Question 46

How are fats emulsified

Answer 46

Bile salts - lipid insoluble in water Lipase can only act of the surface of droplets Emulsification increases surface area

Question 47

What is micelle formation used for

Answer 47

Increasing fat absorption Constant turnover equilibrium of micelles and fattu acids

Question 48

How is fat turned into chylomicrons

Answer 48

1. Emulsified 2. Hydrolysed by lipase 3. Temporarily stored as micelles 4. Transported into epithelial cells 5. Re-esterified to TAG 6. Packaged as chylomicrons

Question 49

protein absorption ****

Question 50

What are the 2 main processes in small intestine

Answer 50

Peristalsis Segmentation More segmentation than peristalsis Rythmic contraction and relaxation of longitudinal muscles Greater mixing of material Net flow through small intestine

Question 51

What is the Gastroileal reflex

Answer 51

Segmentation increased in the ileum with gastric emptying Once the majority of the meal has been absorbed, segmentation is replaced with peristalsis

Question 52

What is the MMC -

Answer 52

migrating myoelectric complex (MMC) Movesundigested material to the large intestine Prevents bacteria from remaining in the small intestine too long

Question 53

What is the role of the large intestine

Answer 53

Primarily storage of material prior to defacation Some digestion of undigested material (via bacteria) Fluid absorption concentrates fecal matter

Question 54

What does the ileocecal sphincter do

Answer 54

Opens to allow chyme through when ileum contracts Closes when large intestine distends to prevent