Lecture 30. Digestion and Metabolism Flashcards
What are essential nutrients ?
Requires materials that an animal cannot assemble from simpler organic molecules
What are the four classes of essential nutrients ?
- Essential amino acids
- Essential fatty acids
- Vitamins
- Minerals
What is an essential precursor for phospholipids and prostaglandins ?
Linoleic acid converted by the enzyme fatty acid desaturase to y-linoleic acid
What is digestion ?
The process of breaking food down into molecules small enough to absorb
What is mechanical digestion ?
Chewing or grinding increases the surface area of food
What is chemical digestion ?
Splits food into small molecules that can pass through membranes that are used to build larger molecules
In chemical digestion, what splits bonds with the addition of water ?
Enzyme hydrolysis
What forms the mammalian digestive system ?
Organs specialised for sequential stages of food processing
What is the function of accessory glands ?
Secrete digestive juices through ducts into the alimentary canal
What are the mammalian accessory glands ?
- Salivary glands
- Pancreas
- Liver
- Gallbladder
Where does food processing begin ?
The oral cavity
What is saliva ?
Exocrine secretion from the salivary glands
What does saliva contain ?
Mucose
What is saliva mucous ?
A viscous mixture of water, salts, cells, amylase and glycoproteins
What is the function of the tongue ?
Shapes food into a bolus and help with swallowing
What does the esophagus do ?
Connects to the stomach
Where does the trachea lead to ?
The lungs
What does swallowing do ?
Causes the epiglottis to block entry to the trachea
What is the bolus guided by ?
The larnyx
Where is the larynx ?
The upper part of the respiratory tract
When does coughing occur ?
When the swallowing reflex fails and food/liquid reaches the trachea
How is food moved from the pharynx to the stomach ?
Peristalsis
What is peristalsis ?
The rhythmic contraction of muscles in the wall of the alimentary canal
Where does peristalsis occur through ?
Small and large intestine
What helps to regulate the movement of material between compartments ?
Valves called sphincers
What is the function of the stomach ?
Stores food and processes it into a liquid by mechanical churning and chemical secretions
What is chyme ?
The mixture of ingested food and gastric juice
What is the pH of gastric juice ?
2.2
What is the purpose of the low pH of gastric juice ?
Kills bacteria and denatures protein
What is gastric juice made up of ?
Hydrochloric acid and pepsin
What secretes hydrogen and chloride ions ?
Parietal cells
Where do paretial cells secrete hydrogen and chloride ions separately to ?
The lumen of the stomach
What secretes inactive pepsinogen ?
Chief cells
When is pepsinogen activated to pepsin ?
When mixed with hydrochloric acid in the stomach
What is the function of mucous in the stomach ?
Protects the stomach lining from gastric juices
What does cell division do to the epithelial layer ?
Adds a new epithelial layer every three days
What are gastric ulcers caused mainly by ?
Heliobacter pylori
How is gastric juice produced ?
- Pepsinogen and HCl introduced into lumen
- HCl converts pepsinogen to pepsin
- Pepsin activates more pepsinogen, starting a chain reaction
What is the longest compartment of the alimentary canal ?
The small intestine
Where does most enzymatic hydrolysis of macromolecules occur ?
The small intestine
What is the first portion of the small intestine called ?
The duodenum
What happens in the duodenum ?
Chyme from the stomach mixes with digestive juices from the pancreas, liver, gallbladder and the small intestine itself
What does the pancreas do ?
Produces the protease trypsin and chymotrypsin
Where are trypsin and chemotrypsin activated ?
Lumen of the duodenum
What is the solution of the duodenum and what is its function ?
Alkaline which neutralises the acidic chyme
What is the function of bile salts ?
Facilitate digestion of fats
What are bile salts a major component of ?
Bile
Where is bile made ?
Liver
Where is bile stored ?
Gallblader
What does bule destroy ?
Non functional red blood cells
How does the small intestine have a huge surface area ?
Due to villi and microvilli exposed in the intestinal lumen
What does the enormous microvillar surface create ?
A border that greatly increases the rate of nutrient absorption
What can transport across the epithelial cells be ?
Passive or active depending on the nutrient
Where is most of the water we ingest absorbed ?
In the small intestine via osmosis
What is the hepatic portal veins function ?
Carries nutrient rich blood from capillaries of the villi to the liver, then to the heart and onwards to all organs
What does the liver do ?
- Regulates nutrient distribution
- Interconverts many organic molecules
- Detoxifies many organic molecules
What is the function of epithelial cells ?
Absorb fatty acids and monoglycerides and recombine them into triglycerides
What are triglycerides coated with ?
Phospholipids, cholesterol and proteins
What do triglycerides form ?
Water soluble chylomicrons
Where are chylomicrons transported into ?
A lacteal
What is a lacteal ?
A lymphatic vessel in each villus
What is the function of lymphatic vessels ?
Deliver chylomicrons containing lymph to large veins that return blood to the heart
What enzyme breaks down triglycerides down to fatty acids and monoglycerides ?
Lipase
What does the alimentary canal end with ?
The large intestine
What does the large intestine include ?
- Colon
- Caecum
- Rectum
What does the colon lead to ?
The rectum and anus
What is the function of the caecum ?
- Fermentation of plant material
2. Connects where the small and large intestines meet
What is the extension of the human caecum called ?
Appendix
What does the colon complete ?
The recovery of water that begins in the small intestine
What is the waste of the digestive system ?
Feces
What happens to feces as they move through the colon ?
They become more solid
Where are feces stored ?
In the rectum
What controls bowel movement ?
The two sphincters between the rectum and anus
What is the digestive system regulated by ?
- Nervous system
2. Endocrine system
What does the nervous system control in digestion ?
Control of salivary secretion
What does the endocrine system control in digestion ?
Gastrin, CCK, secretin
What happens in the absorptive state ?
- Fed state
- Glucose is plentiful and serves as a major energy source
- Insulin is major hormone of absorptive state
What happens in the postabsorptive state ?
- Fasting state
- Endogenous energy stores are mobilised to provide energy
- Glucagon is major hormone of postabsorptive state
What is central to maintaining metabolic balance ?
Synthesis and breakdown of glycogen
What regulates the breakdown of glycogen into glucose ?
Insulin and glucagon
What is the site for glucose homeostasis ?
The liver
What can brain cells do that others cannot ?
They can take up glucose whether or not insulin is present
Where are glucagon and insulin produced ?
Islets of the pancreas
What makes glucagon ?
Alpha cells
What makes insulin ?
Beta cells
What is the central mechanism underlying the pathophysiology of insulin resistance and MetS ?
A chronic state of inflammation
Where is ghrelin secreted from ?
The stomach wall
What is the function of ghrelin ?
Triggers feelings of hunger before meals
What suppresses hormones ?
Insulin and PYY
Where is PYY secreted from ?
Small intestine
Where is leptin produced from ?
Adipose tissue
What is the function of adipose tissue ?
Suppresses appetite and plays a role in regulating body fat levels
