Topic 3- Digestive system

Question 1

functions of the digestive system

Answer 1

Takes in food, breaks it down, absorbs the molecules and excretes the waste

Question 2

Difference between alimentary canal and accessory organs

Answer 2

GI: Continual digestive muscular tubes, alimentary canal

Accessory: Aid in digestive process

Question 3

Ingestion

Answer 3

Taking in food via mouth

Question 4

Propulsion

Answer 4

Aids in moving food along gastrointestinal tract

Involves the voluntary process of swallowing

Automatic process of perastalsis:

Involuntary

Alternating waves of contraction and relaxation

Each waves starts distal to previous

Where small remnants, bacteria and debris is moved from the small to the large intestine.

Travel time from duodenum to ileum is 2 hrs.

Question 5

Mechanical Digestion

Answer 5

Increase surface area of ingested food to physically prepare it for digestion by enzymes

Eg. Chewing in mouth, churning of food in stomach, segmentation along small intestine

Segmentation:

Mixes food with digestive juices

Enhances absorption

Moves contents toward ileocecal valve via alternating contracting smooth muscles at a rate slow enough for absorption and digestion to occur.

Question 6

Chemical digestion

Answer 6

Complex food molecules are broken down to their chemical building blocks by enzymes

Begins in mouth, and is completed in the small intestine

Question 7

Absorption

Answer 7

Passage of the digest end products along with vitamins, minerals and water from the lumen of the gastrointestinal tract to the blood or lymph

Major site of absorption is small intestine

Question 8

Defecation

Answer 8

Indigestible substances are eliminated from the body

Question 9

Mouth
composition, function and digestive process

Answer 9

Composition
Oral cavity:

-Bounded by lips, cheeks palate and tongue

Lips and cheeks:

-Core of skeletal muscle covered by skin

-Palate:

Hard palate

Soft palate

Function
Mechanical digestion

Digestive Processes

Ingestion

Mechanical digestion

Chewing (Partly voluntary and partly reflexive)

Chemical digestion

Propulsion

Question 10

Tongue
composition and function

Answer 10

composition=Skeletal Muscles

Function= Repositioning and mixing food during chewing

Formation of the bolus (compact mass of food)

Initiation of swallowing (pushing bolus into pharynx), speech and taste

Question 11

Salivary Glands function

Answer 11

Secretion:

Cleanses the mouth

Moistens and dissolves food chemicals

Aids in bolus formation

Contains enzymes that begin the breakdown of starch

Antimicrobials that protect against microbial invasion.

Question 12

Pharynx

Answer 12

function= (No digestive role)

Oropharynx and laryngopharynx

Allow passage of food, fluids and air

Stratified squamous epithelial lining

Skeletal muscles layers contract to propel food into the oesophagus

Digestive processes=Deglutition (swallowing)

-Buccal phase

——Voluntary

——-Forces food into oropharynx

-Pharyngeal-oesophageal phase

——–Food enters the oesophagus

——–Momentarily, respiration is inhibited

———8 seconds for solid food to reach stomach, 1-2 seconds for liquids.

Question 13

Oesophagus composition, function and digestive processes

Answer 13

composition=Flat muscle tubes from laryngopharynx to stomach. Esophageal mucosa contains stratified sqamous epithelium

Function= Esophageal glands in submucosa secrete mucus to aid in bolus movement

Question 14

Stomach composition and function

Answer 14

composition=Mucosal lining composted of:

Simple columnar epithelial cells

——-Secrete mucous

Gastric glands composed of

-Mucous neck cells

-Parietal cells (secrete HCl which makes stomach content acidic.

-Chief cells (secrete lipases which are fat digestive enzymes)

-Enteroendocrine cells (release chemical messengers that aid in digestion)

Function=Temporary storage tank (4L)

Physical digestion

Denaturation of proteins

Delivers chyme to the small intestine

Question 15

Regulation of gastric secretion

Answer 15

Stimuli acting 3 distinct sites being the head, stomach and small intestine provoke or inhibit gastric secretions.

there are 3 phases

Question 16

Phase 1 of the regulation of gastric secretion

Answer 16

Cephalic(reflex) phase
-triggered by the taste, sight, smell or thought of food
- prepares stomach for it’s digestive roles
- Hypothalamus receives signals from tastebuds, olfactory receptors and then stimulates the medulla, which transmits impulses by vagus nerves, which affects secretory and contractile activity of the stomach

Question 17

Phase 2 of the regulation of gastric secretion

Answer 17

Gastric phase
-Occurs once food enters the stomach
-Hormonal and neural stimuli

Question 18

Phase 3 of the regulation of gastric secretion

Answer 18

Intestinal phase
-Stimulatory: as food fills the duodenum (mucosal cells release gastrin)
-Inhibitory: enterogastric reflex prevent further food entry into small intestine which causes a decline in gastric secretory activity.

Question 19

Gastric contractile activity

Answer 19

After a meal, peristalsis begins near the gastropharyngeal sphincter.

As contractions approach pyloric sphincter, contractions become stronger retropulsion occurs at pyloric valve where food is broken up due to the backwards and forwards motion of the chyme between the duodenum and the stomach

The stomach usually empties completely within 4 hours after a meal

Question 20

Liver digestive function, liquid produced each day

Answer 20

Produce bile for export to the duodenum (first part of small intestine

Bile:

Alkaline solution containing:

Bile salts:

Emulsifies fats

Yellow green solution

Approx 900ml

Question 21

Pancreases digestive function and liquid produced each day

Answer 21

Enzyme production that breaks down all food stuffs

Pancreatic juice:

-Drains from the pancreas to duodenum
-pH8 and neutralises chyme

Enzymes:
-Amylase, lipases and nucleases
——–Secreted in active but require ions or bile for optimal activity
-Proteases (protein digesting enzymes) are secreted in inactive form
———–They are activated in the duodenum

1.5L daily
water, electrolytes, enzymes

Question 22

Gall bladder digestive function

Answer 22

Stores bile

Concentrates it by absorbing water and ion

Question 23

Small intestines info?

Answer 23

Major organ of digestion and absorption

All of the foodstuffs

805 of the electrolytes

Most of the water

Up to 4 metres in length

Question 24

Layers of small intestines

Answer 24

1.Mucosa

2.Innermost layer

3.Three parts:

-Epithelium: secretes mucous, digestive enzymes and hormones
-Lamina propria: contains capillaries for nourishment and absorption
-Muscularis mucosa: smooth muscle that produces local movements of the mucosa

4.Submucosa
-External to mucosa
-Rich supply of blood
-Lymphatic vessels and follicles
-Nerve fibres
-Muscularis externa
-Responsible for segmentation and peristalsis of the small intestine
-Serosa
-Protective outermost layer

 

Question 25

Divisions of small intestines

Answer 25

Duodenum -Receives bile from the liver -Receive pancreatic juice from the pancreas Jejunum Ileum

Question 26

Motility

Answer 26

Motility of the small intestine There are two motility patterns in the small intestine After a meal - segmentation --------Ensures that the chyme is thoroughly mixed with bile, pancreatic and intestinal juices ---------Ensures that the absorbable products of digestion comes into contact with the mucosa of the small intestine for absorption Between meals - peristalsis ------Migrating motor complex (form of peristalsis) -------Sweeps contents down to large intestine In order for contents to pass into the large intestine: -The ileocecal sphincter (b/w small and large intestine) relaxes by: ---------Gastrolieal reflex enhances force of segmentation in ileum -------------------------Triggerd by stomach activity ----------V Gastrin increases motility of ileum

Question 27

Modifications of the small intestines

Answer 27

increased surface area for nutrient absorption -Circular folds: deep permanent folds of the mucosa and submucosa It forces the chyme to slowly spiral through the lumen Villi: finger-like extensions of the mucosa -Largest in the duodenum (where absorption) -Narrow and shorten along the length of the intestine Microvilli- brush border -Found on enterocytes -Contain enzymes that complete digestion of carbs and proteins

Question 28

Small intestines digestion and absorption

Answer 28

Digestion and absorption in the small intestine requires: -Slow delivery (3-6 hours) of chyme which contains: -------------Partially digested carbohydrates and proteins --------------Undigested fats -Delivery of bile, enzymes and bicarbonate --------------From the liver and pancreas -Mixing Absorption of: -All of the foodstuffs -80% electrolytes -Most of water (95%)

Question 29

Function of Large intestines

Answer 29

Absorb remaining water, vitamins and electrolytes from indigestible food residues -Temporarily store the residues -Eliminate residues from the body (propulsion of faeces towards the anus) -*also absorbs metabolites produced by resident bacteria as they ferment carbs not absorbed in the small intestine

Question 30

Motility of Large intestines

Answer 30

Haustral contractions -Slow segmenting movements Gastrocolic reflex -Initiated by presence of food in stomach -Activates three to four slow powerful peristaltic waves per day in colon (mass movements)

Question 31

Defecation Large Intestines

Answer 31

Mass movements force faeces toward rectum Muscles of rectum contract to expel faeces Distension initiates spinal defecation reflex Assisted by Valsalva's maneuver -Closing of glottis, contraction of diaphragm and abdominal wall muscles leads to increased intra-abdominal pressure -Levator ani muscles contracts -> anal canal lifted superiorly -> faeces leave body

Question 32

Carbohydrates

Answer 32

Intestine can only absorb monosaccharides; therefore carbs must be broken down -Only monosaccharides (glucose, galactose, fructose) can be absorbed as they are -The more complex carbs (lactose, starch, glycogen) need to be broken down into monosaccharides before they can be absorbed Digestion of starch -In mouth with salivary amylase -Continues via secretions from the pancreas --------Pancreatic amylase -Is completed by intestinal brush border enzymes Eg. Lactase, maltase, sucrase

Question 33

Protein

Answer 33

Begins in stomach -pepsin -rennin(infants only) Continues via secretions from the pancreases -pancreatic protease(e.g Trypsin) Is completed by the brush border enzymes - Eg. Aminopeptidases, carboxypeptidases and dipeptidases Lipids Begins in the mouth -Lingual lipase Continues in the stomach -Gastric lipase Emulsification occurs in the small intestine -Bile salts Digestion into fatty acids and monoglycerides -Via pancreatic lipases   Primary site of lipid digestion is the small intestine Emulsification by bile salts -Pre-treatment step to break large fat globules into small fat droplets Digestion -Lipases split triglycerides into fatty acids and monoglycerides Micelle formation -Fatty acids + monoglyceride + bile salts Diffusion -Lipids leave the micelles by simple diffusion Chylomicron formation -Smooth ER converts the lipids back into triglycerides, which combine with other lipids to form chylomicrons Chylomicron transport -Enter the lymph

Question 34

Nucleic Acids

Answer 34

Occurs in the small intestines - enzymes -------Pancreatic ribonuclease and deoxyribonuclease -> nucleotide monomers ---------Brush border enzyme nucleosidases and phosphatases -> free bases, pentose sugars, phosphate ions

Question 35

Anabolic

Answer 35

Anabolic: synthesizing larger molecules

Question 36

Catabolic

Answer 36

Catabolic: degrading larger molecules into smaller ones

Question 37

What to metabolic controls act to equalize

Answer 37

Metabolic controls act to equalize the balance between the absorptive state (when you've eaten) and postabsorptive state (when you haven't eaten in a long time) Amino acids can only be used as energy when converted to a carbohydrate intermediate (ketoacid) Carbohydrates can be directly oxidised to produce cellular energy  

Question 38

Absorption state

Answer 38

Anabolism exceeds catabolism The absorptive state is the fed state -Time during each meal -And for four hours after that meal Dietary amino acids and fats are used to remake degraded body protein or fat and small amounts of these are used to provide ATP Excess metabolites are transformed to fat (if not used for anabolism)

Question 39

Carbohydrates

Answer 39

Delivered to the liver Fructose and galactose are converted to glucose -Glucose is converted in liver to glycogen or fat ---------Is the major energy fuel

Question 40

Triglycerides

Answer 40

Most glycerol and fatty acids converted to triglycerides for storage Triglycerides used in adipose tissue, liver, and skeletal and cardiac muscle as primary energy source - Excess fats stored in adipose tissue

Question 41

Amino Acids

Answer 41

Excess amino acids are used for ATP synthesis or stored as fat in liver Most amino acids used in protein synthesis

Question 42

Hormonal Control

Answer 42

Absorptive state primarily controlled by Insulin secretion stimulated by increase in BGL -Insulin binds to membrane receptors of target cells -GLUT4 transporter moves to plasma membrane ----------------Enhances uptake of glucose into target cells (eg. Muscle and adipose cells

Question 43

Postabsorptive state

Answer 43

GI tract is empty - occurs late arvo, all night, etc. Catabolism of fat, glycogen and proteins exceeds anabolism Goal is to maintain blood glucose between meals -Makes glucose available to blood -Promotes use of fats for energy -Glucose sparing - save glucose for organs that need it most ----------Brain uses blood glucose -----------Other organs use fatty acids

Question 44

Sources of blood glucose:

Answer 44

Glycogenolysis: stores in liver -Stores in skeletal muscle must be converted to pyruvic acid/lactic acid because the enzyme required to break glycogen to glucose is not present Lipolysis: adipose tissues and liver -Glycerol used for gluconeogenesis in liver ----------Making glucose from non-carb sources Catabolism of cellular protein -Major source during prolonged fasting

Question 45

Hormonal controls

Answer 45

Post-absorptive state triggered by decreased insulin release as blood glucose levels drop Glucagon released: -Declining blood glucose -Rising amino acid levels Glucagon promotes: -Glycogenolysis and gluconeogenesis in the liver -Lipolysis