Digestion Lecture Notes Flashcards
Why do we need food?
To get organic molecules to the cells so they can be fed into the metabolic pathways for energy to create ATP
Replace body components: Lost in urine, metabolic breakdown, etc.
Grow new tissue
Gain energy sources
Ingestion
Take something into your digestive system
Food into your GI tract
Mastication
Chewing of the food in your mouth Physical breakdown; Doesn't break the bonds between the atoms Makes big clumps into smaller clumps Increases the surface area of the food
Digestion
Chemical breakdown
Need to break chemical bonds so you go through a complicated polypeptide protein to small fragments, or individual amino acids
Absorption
Uptake of small molecules by cells
Uptake process
Egestion
Eliminate the non-absorbable material
There is stuff you take in that you cannot absorb
Defecation or vomiting
Internal Nares
Opening of Pharynx
Epiglottis
Flap above Glottis
Sphincters
Bands of muscles that remain contracted
Hypopharyngeal Sphincter
Lies at the Esophagus
Do the sphincters remain opened or closed typically?
The sphincters remain closed unless there is food entering
What happens during the swallowing reflex?
As the food is swallowed, the larynx moves upwards, sphincters are relaxed
Peristalsis
Food moves down the esophagus via peristalsis action
Why produce saliva?
Produce saliva to give you watery fluid in order for chemical reactions to take place
Salivary glands produce water, and the digestive enzyme Amylase
Amylase
Breaks down amylose (plant starch)
Where does digestion begin?
Digestion begins in the mouth
Start carb digestion in the mouth and finish carb digestion in the small intestine
Chyme
The material that is working down the GI tract
When chyme enters the stomach, it is extremely acidic
The gastroesophegeal sphincter makes sure the acidic chyme cannot make its way back up into the GI tract
Heartburn
Movement of acid chyme upstream to esophagus and the gastroesophageal sphincter has failed doing its job
Epimere
Segmented throughout the GI tract
Mesomere
Forms kidneys and gonads
Segmented throughout the tract
Hypomere
Not segmented
Broad sheets
Dorsal and ventral mesentary
Outermost sheet known as parietal peritoneum
Inner sheet that surrounds gut tube = visceral peritoneium
Mesentaries
Connect to body wall
The place where two serous membranes come together and attach to body wall
Stomach
Organ of storage Layers of smooth muscles Circular band of muscles Top = esophagus Cardiac region = top of stomach
Chief cells
Secrete pepsinogen
Pepsinogen
An inactive digestive enzyme that is converted into pepsin (active enzyme) in the presence of high acid produced by parietal cells
Pepsin is a protease that breaks down proteins into protein fragments at specific peptide sites
Protease
Each one, catalyzes the cleavage of different amino acids
Each breaks down a different pair of an amino acid
Need a variety because there are a variety of peptide bonds
Zymogen
Inactive protease
Inactive forms are made so we do not eat ourselves
Pepsinogen
Inactive form of pepsin
Cells secrete pepsinogen which is then activated and becomes pepsin
It wants to be activated when it comes into contact with food
Parietal cells
Secrete HCl
Effects of HCL
HCL denatures proteins (unravels it so the amino acids are exposed);
If you eat a meal with a lot of protein, your pH can become very low due to HCl secretions
HCl activates pepsin;
Pepsinogen is converted into pepsin in the presence of HCl;
Its shape becomes active when in an active solution
Needs to be in contact with acid chyme
Kills many varieties of bacteria
The acidity from HCl will erode away the living cells that should not be destroyed
Globlet Cells
Secrete mucus
Mucus
Alkaline neutralizes the HCL
Coats the epithelial cells of the stomach to help protect them from HCL
Epithelial cells are replaced every 4 days
Gastric Ulcer
An erosion of the lining of the stomach
The stomach was eaten away by the chyme
Caused by an acid loving bacteria
Heliobacter Pylori
Can burrow underneath the mucus lining and they secrete toxins that will help erode the mucus lining allowing the chyme to get to the soft tissue and cause the ulcer
3 Regions of Small Intestine
Duodenum
Jejunum
Illium
Duodenum
Can’t be covered with mucus to protect it, because you need the lining for absorbtion
Neutralize chyme by adding HCO3-
Pancreas
Located on top of duodenum and secretes pancreatic juice
Pancreatic Juice produces: Bicarbonate ions, many digestive enzymes (most inactive form)
Pancreatic juice is added to chyme in the beginning of the duodenum; this avoids a duodenum ulcer and changes to pH
Segmentation of Small Intestine
Irregular contraction
Mixing the chyme
The rate of segmentation changes as you move through the regions of the small intestine
Surface area of small intestine
Huge surface area needed for membrane transport in absorbtion
Absorption in the Small Intestine
To Increase surface area:
Long tube, small intestine makes up most of the GI tract
Villi, finger-like projections; water soluble solutes enter blood in the capillaries; lipids enter lymphatic system via lacteals
Microvilli: extensions of the cell membrane, form brush border, greatly increase surface area to enhance rate of absorption
Large Intestine
Has bacteria living there
Bacteria lives on the material that you do not digest
The bacteria in your large intestine receive fragment of plant cell walls and other things that you can’t digest
Bacteria in large intestine can produce the enzyme cellulase
Cellulose
Most common carbohydrates
Animals can’t break down cellulose because we can’t produce it
Comes from plants; Cell wall that surrounds cytoplasm of the plant cell (inside, after cell wall, it digestible):
Digestive enzymes can’t break down cellulose to get to the inside –> we can physically break it down by chewing
Do harmful bacteria live in large intestine?
It is very difficult for harmful bacteria to live in large intestine because there is already naturally occurring bacteria living there
If you have a bacterial infection and are taking antibiotics, it can effect the bacterial population in your intestines
Cecum
Storage chamber for bacteria at the start of the large intestine
Found in other animals
Not in dogs because they don’t eat plants
Appendix
Cecum
This is why we can remove it and be fine
Filled with lymphoid material
May be a site of vitamin B production
Liver
Purpose: Metabolic Intraconversions
Has 1 digestive impact; regulates glucose levels, metabolic regulation (non digestive functions)
Glycogenesis
Implies “creation” [creation of glycogen from glucose]
Creates glycogen (polymer of glucose molecules)
How we store our carbohydrates
Glycogenolysis
Production of glucose by catabolizing glycogen
Liver will take stored glycogen and make glucose molecules to enter the blood for use
Gluconeuogenesis
Conversion of non-carbohydrates into glucose
Lipogenesis
Forms triglycerides for storage
Purpose of Liver in digestion
Creates bile
How does blood go to the liver
Standard artery (oxygenated blood) Hepatic vein (deoxygenated blood)
Hepatic-sites
Liver Cells
Bile contains
Bile salts
Bilirubin
Bile Salts
Job is to emulsify lipids
Emulsification
No bonds are broken
Breaks big clumps into little clumps, nothing is digested
Digestion
Breaking bonds to make big molecules into smaller molecules
Bilirubin
Break down product of heme (from hemoglobin)
The hold heme is converted to bilirubin which is dumped into bile
Travels to the duodenum, where it is screened and passed through
Bacteria makes bilirubin convert into urobilinoen
How does bilirubin convert into urobilinoen
This is done by bacteria in the large intestine
Either passes out with the feces or is digested along the walls of the large intestine and leaves with the urine
What is another function of the liver
Detoxifies things; ex: alcohol, hormones
Where ammonia is converted into urea
Pancreatic Juice
Contains Bicarbonate ions
Inactive digestive enzymes
Neutralizes the pH and allows all the other digestive enzymes to work fine; HCL & digestive enzymes made from the small intestine
The Pancreas secretes
Protease
Lipases
Nucleases
Amylases
Starch Digestion
Start: Amylase in the saliva
Stops once it gets to the stomach because it is too acidic
Continues in the pancreas where amylase is secreted
Amylose (starch) is a disaccharide = fragments
The fragments must be broken down into smaller things
Monosaccharides are made and they can now be absorbed
Absorption of Glucose
Enters via active transport
Absorption of Galactose
Enters via active transport
Absorption of Fructose
Enters via facilitated diffusion
Intrinsic Control of Gastric Function
Contraction of smooth muscles
a. Via pacemaker action
b. Stretching will increase contractions
c. If you eat a meal, and distend your stomach (stretch muscle cells) it will contract more rapidly
Extrinsic Control of Gastric Function
Controlled by the brain= Cephalic Phase
Autonomic NS at work
a. Parasympathetic NS at work
i. Vagus Nerve
b. Increase blood flow to the stomach
You smell food cooking –> begin salivating and stomach starts secreting
Increase blood flow to stomach by dilating arterioles
Gastric Phase
When food enters the stomach Protein fragments cause 1. G cells to create gastrin 2. Parietal cells to create HCL 3. Chief cells to create pepsinogen
Positive Feedback in Gastric
- The more pepsinogen you secrete, the more fragments you get, the more digestion occurs, etc.
- More fragments→more gastrin→more secretion→more fragments (it’s a loop)
Gastrin
Isn’t secreted in the lumen
Is secreted by G cells into the blood
Is a hormone that circulates throughout your body
Target for gastrin are the chief cells and parietal cells for the stomach
Acts on the stomach to increase the secretion of HCL and pepsinogen
a. Very potent at doing this
b. Is driving this secretion
Gastrin is inhibited by low pH (acid)
Intact proteins buffer pH of chyme
Intestinal Phase
Neural reflex to inhibit gastric secretion and emptying
Gastric Inhibitory Protein (GIP)
a. Inhibits gastric secretion and emptying of the stomach
What turns on the secretion of GIP and natural reflex?
- Both occur when there is an increase in osmotic concentration of chyme in the duodenum
- Stretching of duodenum
- Presence of fat in the duodenum
a. There are sensors in the duodenum that are triggered when there is a high fat content; This means that you are not done digesting
Gastric Inhibitory Peptide
Secreted from the duodenum
Stimulated by stretching, high fat, high osmotic concentration
CCK
Cholestokin
Lipids in duodenum causes CCK to be produced
Acts on pancreas to produce digestive enzymes
Secretin
Stimulated by low pH and stretching
When the duodenum experiences low pH (when it gets acidic chyme) it causes it to secrete secretin
Acts on the pancreas to stimulate HCO3-
Secretin and CCK
Nervous input from stretching
Act on the liver to produce bile
Nervous input feeds back to the gall bladder, causing it to contract
Does the pancreas secrete hormones?
Yes, the pancreas also secretes hormones
The pancreas is both an exocrine and endocrine organ because it has its own hormones to secrete as well as others
Exocrine: organ/tissue
i. Secretes via a duct to a specific location
Endocrine:
i. Insulin
ii. Glucagon
Can we make essential amino acids?
No
We get them from animals
What do Glucagon and Insulin regulate?
Regulate the circulating levels of glucose and amino acids in the body
After a meal, increase glucagon and insulin levels
If fasting, decrease levels
Need to maintain levels during fasting
a. Want to make glucose, and dump it into the blood
b. Can make it by breaking down glycogen storage and through glucogenesis (making glucose out of other things)
Glucagon
From alpha cells in the pacreas (in the islets of Langerhaus)
Insulin
From beta cells in the pancreas (in the islets of Langerhans)
Somatostatin
From delta cells in the pancreas
Hormone which acts on your brain and inhibits growth hormone
After a carbohydrate meal
Glucose concentrations rise
This causes insulin to be secreted and the inhibition of glucagon
a. Insulin is responsible for the uptake of glucose by the metabolizing cells
b. This reduces high blood glucose levels because cells are taking it away (ex: nervous tissue uses glucose for fuel, muscle cells turn it into glycogen to store it, the liver stores glycogen as well, fat cells use it to make triglycerides)
Glucagon causes the break down of glycogen into glucose (dumped into the blood from the liver)
a. This is why glucagon is inhibited
After a protein meal
If you just eat protein, you will produce insulin in response to the amino acids;
Insulin causes the uptake of amino acids and glucose (even though you did not have any glucose in your meal)
Uptake of glucose will cause a decrease in blood glucose levels
a. This is why glucagon has to be secreted because there is an initial drop in glucose
Glucose levels
After a meal: Glucose levels rise
up to about 170 mg%
During fasting: Glucose falls down to 50 mg%
Too high of glucose levels can damage the cells
Diabetes mellitus
Too high glucose concentration in the blood
Why would you have too high glucose concentration in the blood or diabetes mellitus?
Don’t produce enough insulin
a. Insulin causes glucose to be taken up into metabolizing cells
Make insulin, but target cells do not respond
a. Target cells may not have the receptors
Type 1 diabetes
Beta cells do not produce enough insulin
Beta cells are destroyed by the immune system or virus invaded beta cells on the pancreas
Usually occurs in childhood
Only way to get by: need regular insulin injections
Type 2 diabetes
Later onset, develops with age
May be genetic predisposition
It is much more prevalent in inactive, overweight people
Can be prevented by losing weight and exercising
Triglyceride
Glycerol + Fatty Acids
With big carb meals, your liver and adipose tissues will convert glucose to triglycerides causing you to gain weight
Glucose Sparing
Occurs during a fast
Glucagon rises as insulin falls
Glucagon causes glycogen in the liver to be broken down into glucose to enter the blood and fuel the nervous system
During a fast:
1. Initially lose fat, then you lose muscle mass
During a fast, decrease glucose concentration in blood
1. Glucagon is secreted
Acts on the liver in two ways:
i. Glycogen is converted into glucose
ii. Fatty acids are converted into ketones
Acts on adipose tissue
i. Lipolysis
1. Glycerol
2. Fatty acids
Glucose is fuel for
The Nervous System
Ketones and Fatty Acids are fuel for
Other tissues
Epinephrine
From Adrenal Medulla Effects were similar to glucagon: 1. Lipolysis produced 2. Gluconeogenesis produced 3. Increased substrates in the blood to fuel the stress (the fast)
Glucocorticoids
From Adrenal Cortex
Hormones cortisol, corticosterone, etc.
They stimulate the cells to promote lipolysis and ketogenesis
Stimulate liver to make enzymes for gluconeogenesis
Stimulate skeletal muscles to break down proteins into amino acids
Thyroxine
From Thyroid gland is secreted
Secreted in inactive form and then converted into active form
Increases cellular metabolism
Causes ion pumping by the cells
Stimulates Na+/K+ pumps (BMR increases_; need to make more ATP to maintain
Acts on DNA to increase protein synthesis
Mental retardation is linked to low levels of thyroxine
Hyperthyroidism
You produce too much thyroxine
Somatotrophin
Growth hormone
Stimulates by increase in amino acid concentration in blood after protein meal
Inhibited by increase glucose concentration in the blood
Growth hormone is stimulated after a protein meal and during a fast
