The digestive system- 1 Flashcards
How does the digestive system contribute to homeostasis?
It transfers nutrients, water, electrolytes from external to internal environment. (This is also the function of the digestive system)
True or False:
The digestive system directly regulates concentration of internal constituents.
FALSE
Does the digestive system change water, nutrients or electrolyte uptake?
No
The digestive system optimizes conditions for:
Digestion and absorption
label
GI system = ?
Gastrointestinal system (digestive system)
What role does food play?
- Used by cells to generate ATP
- Source of building material for renewal and addition of body tissues
is eaten food ready to be used by cells?
NO,
- Food must be digested (broken down) into simple molecules.
- SImple molecules must then be absorbed from GIT
- Then distributed via circulation to cells.
What are the 4 main digestive processes?
- Motility (movement)
- Secretion (release)
- Digestion (breakdown)
- Absorption (uptake)
Name and describe the two types of basic motility
1. Propulsive movements:
-Propel/push contents forward through the digestive tract
-Rate of propulsion differs from one region to another
(esophagus vs small intestine)
2. Mixing movements:
- Mix food
- Facilitate absorption
What causes motility? are there any exceptions?
Smooth muscles, and yes…
Exceptions: Ends of GI tract- mouth and anus -Motility is caused by skeletal muscle
Why is the mouth and the anus (motility) controlled by skeletal muscle?
For voluntary and involuntary reflexes
Part of the respiratory passageway is located between the trachea and the pharynx. It keeps the airway open, prevents food from entering the airway, and produces sounds
The larynx
Visceral smooth muscle; contracts as a unit, electrically coupled, often has spontaneous action potentials.
unitary smooth muscle
Characteristic of smooth muscle to adapt to increased length and relaxation; stress-relaxation response
Plasticity
Explain the motility in the mouth
- The mouth receives food into the GI tract.
- Chewing tears and grinds food, reducing lumps to a size that can be swallowed.- also mixes ingested food with saliva, moistening it enough to be easily swallowed.
Summary:
Type- chewing
Function-
Mechanical breakdown of food particles
Mixing food with saliva
Chewing is part voluntary and involuntary…what sets the pattern and rhythm of chewing?
The cortex and brain stem centers
True or false:
The esophagus serves a digestive or absorptive function.
False, it is simply a conduit between the pharynx and stomach
What is the motility in the esophagus?
Peristalsis- a progressive wave of muscle contractions
What initiates primary peristalsis?
Swallowing
describe the motility of the esophagus
- Tongue separates a bolus
- Soft palate closes the nasopharynx
- The larynx rises and the glottis closes- to cover the trachea
- epiglottis falls to cover the closed glottis.
- Pharyngeal muscles contract and upper esophageal sphincters relax.
- Bolus enters the esophagus, and lower esophageal sphincters (LES) and stomach relax.
- Bolus moves toward the stomach
- Respiratory passages open ( everything reverts to normal)
- Bolus enters the stomach and LES closes-prevents regurgitation
what causes the variations of the force of peristaltic contractions?
the size of the bolus
stimuli from what is delayed to the CNS to modify the pressure generated by the esophageal muscles?
from the distention of the esophagus wall
What happens if a bolus of food doesn’t progress all the way to the stomach?
Secondary peristalsis
describe what happens during secondary peristalsis:
- The esophagus is distended
- Afferent signals are relayed to the CNS
- This leads to the second wave of peristaltic contractions.
Summarise what the motility is of the esophagus ( what it is and function)
-Primary and secondary peristalsis
Function=propel a bolus of food to the stomach
Name 3 functions of the stomach:
- It stores food
- Mixes food with gastric juice for digestion
- Empties chyme into duodenum
What allows for different movements (which serve each function) of the stomach?
The muscular structures of the stomach wall.
what happens in the stomach during a swallow?
- Receptive relaxation occurs in the fundus and body of the stomach.
- Relaxation occurs with each swallow and permits the stomach to accommodate a volume of at least 1L with little increase in pressure.
- Peristaltic contractions mix stomach contents and empty chyme into the duodenum.
- The frequency of gastric peristaltic contractions is 3-5/min
Peristaltic waves begin ____________, ripple over the body and become _______ over the muscular _________ and _______
Midstomach
Stronger
antrum and pylorus
What do antral contractions do?
They force chyme toward the duodenum and pulverize small lumps
Explain how food and gastric juice is mixed:
- Antral contractions squirts a small amount of chyme through the constantly contracted pyloric sphincter with each powerful antral contraction.
- As the contraction progresses, it closes the sphincter completely and most of the chyme is forced back into the stomach.
- This retropulsion mixes the food and gastric juice.
Why does the volume and contents of the stomach regulate the strength of contractions?
Because the frequency of peristaltic contractions are constant
-The greater the volume, the more rapidly the contents are emptied.
What are the functions of the duodenum?
- Regulates gastric emptying
- regulates fat, acid, and hypertonic solutions in the duodenum
- duodenal distention and slow gastric emptying
summarise the motility of the stomach:
Motility:
- Receptive relaxation
- Peristalsis
Functions:
- Relaxation- accommodates meals
- Peristalsis mixes and empties stomach content
What are the two types of secretion the digestive system produces?
exocrine and endocrine secretions
Specialized cells found in lining of GIT and accessory organs (pancreas)
release digestive juices when stimulated (neural or hormonal)
Exocrine glands
What are the digestive juices?
- Water
- Electrolytes
3. Enzymes
4. Mucus
5. Bile salts
-→ organ specific
What excretes enzymes
Exocrine glands
What excretes hormones
Endocrine glands
Describe exocrine glands
- Larger component
- Secretes 1.5-2L/day, rich in digestive enzymes
- Has alkaline pH due to its content of NaHCO3
- Produced by pancreatic acinar cells
Describe endocrine glands
- Smaller component
- COnsists of islets of Langerhans-4 cell types
- Secretes 4 hormones
what 4 hormones do endocrine glands release?
Insulin
Glucagon
Pancreatic polypeptide
somatostatin
What are the 3 categories of energy-rich food?
Carbs
Proteins
Lipids
-Digestion is needed to break food down (from macromolecules)
What is the ratio of C:H:O in carbohydrates
1:2:1
How are most carbs classified as?
Mono-, di-, or poly-saccharide
Saccharide =?
Sugar
What are the building blocks (monomers) of all carbohydrates?
Monosaccharides
What are the three monosaccharides of carbohydrates?
Gluces
Fructose
Galactose
Which monosaccharide is the most abundant and what are some of its properties?
Glucose
- it is water soluble
- Easily transported through an organsm
- Energy source for cellular resp.
[Energy source for cells]
-
what is the main monosaccharide found in sugar of fruits?
Fructose
Galactose
Primary monosaccharide found in milk
What is the general monosaccharide formula?
C6H12O6
How are disaccarides forme?
When 2 monosaccharides are joined together via dehydration
-Forming glycosidic linkages
What are the three disaccharides?
Maltose
sucrose
lactose
Glucose + Glucose
Maltose= Malt sugar
Glucose + Fructose
Sucrose
=Table sugar
Glucose + Galactose
Lactose
=milk sugar
How are polysaccharides formed?
When glucose monomers link together to form long chains
What are polysaccharides ideal for?
Storing energy
Energy storage in plants
Amylose- straight chain
Amylopectin-Branched
Animal energy storage
Glycogen-highly branched chain
why is glycogen so branched?
To enable it to be broken down quickly to supply cells/tissue with energy
Polysaccharides which act as structural molecules?
Cellulose
chitin
peptidoglycan
Most abundant polysaccharide?
Cellulose
- straight chain
- found in cell walls of plants → adds strength
- it is a polymer of glucose, but it differs in configuration due to the bonds between each glucose unit.
- Most organisms cant break cellulose down, and thus, can’t use it as an energy source
Polysaccharide which forms exoskeleton of insects and crustaceans?
Chitin
-Unique properties is due to chitin having amino groups attatched to its sugar monomers
complex polysaccharides found in cell walls of bacteria
Peptidoglycan
- Flexible and rugged due to its structure
- each monomer has a peptide chain attatched to it
Carbohydrates can be refered to as….
Simple sugars or complex carbohydrates
Monosaccharides and disaccharides?
Simple sugars
Polysaccharides
Complex carbohydrates
Amino acid structure
- Carboxyl group [O=C-OH]
- Amino group [N-H2]
What makes amino acids unique?
R group-gives amino acids properties
Order of amino acids in polypeptide chain
Primary structure
Pleated sheet/ helix- due to H bonding or other chemical reactions between the R groups or other chemical reactions of nearby amino acids
secondary protein structure
The overall shape of a polypeptide
Tertiary structure
- Secondary structure folds and twists upon itself
- then referred to as proteins
Interaction of multiple proteins= large protein complexes?
Quaternary structure
Hemoglobin and sodium channels in the cell membrane
Quaternary structure protein
Hydrophilic biomolecules
lipids
long term energy storage
The primary function of lipids
Hormone precursors, key component of cell membranes, protection, insulation, and lubrication
Other functions of lipids
4 basic groups of lipids
- Triglycerides
- phospholipids
- Steroids
- waxes
What do all lipids have in common
All insoluble in water
Fats-solid at room temp, used by animals.
Oils-Liquid at room temp, used by plants for long term energy storage.
triglycerides
Subunits of triglycerides
Glycerol and 3 fatty acids
3 parts of fatty acid
Acid group (OH)
Hydrocarbon chain
Methyl group (C-H3)
Single C-C fatty acid
Saturated fatty acid
Double bonds result in what
Kinks in the fatty acid chain affects melting point of fat
animal fats
saturated fatty acids
Veg oils
unsatturated
Trans fatty acid
when H bonds are on opposite sides of double bond
How do triglycerides form?
Through dehydration sysnthesis
- Glycerol and 2 fatty acids
- Phosphate group attached to 3rd carbon of glycerol
Phospholipids
4 fused rings of carbon- to which different functional groups are attached
Steroids
Precursor for the synthesis of other steroids:
Such as testosterone, estrogen, vit D, cortisone
Cholesterol
stabilizes plasma membrane
Cholesterol
difference between estrogen and testosterone
Testosterone has =O
Estrogen has -H
Nonpolar fats and repel water, are found in the outer coating on leaves and outer surfaces of animals.
Waxes
Occurs in the small intestine- in the ileum
Digestion
Digestion is incomplete
False
Where are digested substances transferred to?
From GIT to blood or lymph
finger-like projections found on the inner wall of the ileum
villi
Lymph vessel found in the middle of villi which is surrounded by a network of capillaries
Lacteal
water-soluble vitamins and minerals are absorbed where? and how?
through the walls of the villi, by diffusion and active transport
How is water drawn into the blood during digestion?
The absorption of digested food into the blood increases the water potential of the content in the ileum, water is drawn into the blood by osmosis.
Enter the epithelium of the villus by diffusion
Glycerol and fatty acid
what happens after glycerol and fatty acid are diffused into the epithelium of the villi?
They recombine into fine lipid droplets, which then enter the lymph in the lacteal
Lipid soluble vitamins are also absorbed into the lacteal
Vitamins A and D
What happens after everything has been absorbed by the villi?
Everything is transported to the main lymph vessels and then to the blood stream
