The Gastronintestinal System (GIT) Etc Lectures 8.1-11.1 Flashcards
What are the two parts of the gastrointestinal tract? `
Gastrointestinal Tract- a continious tube from mouth to anus consisting of:
*mouth, pharynx, oesophagus, stomach, small intestine, large intestine and the anus
Accessory digestive organs:
*salivary glands, exocrine pancreas and biliary system (liver and gallbladder)
What is the primary function of a GIT tract?
Transfer nutrients, water + electrolytes from ingested food into the body’s internal environment
What are the six digestive processes?
-ingestion
-propulsion
-mechanical digestion
-chemical digestion
-absorption
-defecation
What are the 4 major tissue layers?
-mucosa
-submucosa
-muscularis externa
-serosa
What is the function of the mucosa?
-inner epithelial layer
*protects and transports substances
What is the function of the submucosa?
-connective tissue
*supports and contains nerve plexus
What is the function of the muscularis externa?
-contraction
*inner circular smooth muscle
*outer longitudinal muscle layer
What is the function of the serosa?
-connective tissue
*protects the tissue
Swallowing/ deglutition
-transportation of food from mouth —> stomach
-involves voluntary and involuntary control
-divided into oral, pharyngeal + oesophageal phases
-controlled in the brainstem (unconscious part of the brain)
What does swallowing involve that moves food along the GIT?
A series of wave-like contractions (peristalsis)
-begins in the oesophagus when a bonus of food is swallowed
What is the functional anatomy of the stomach divided into?
-divided into 3 sections;
*fundus, body and antrum
What is the rugae of mucosa?
Rugae = folds in stomach lining
-allows the stomach to expand and stretch to accommodate food- receptive relaxation
*empty volume= 50mL
*full volume= 1000-4000mL
What are the 3 main functions of the stomach?
-stores food until it can be emptied into the small intestine
-secretes HCl + enzymes that begin protein digestion
-mixing movements -> converts pulverised food to chyme
What does the pyloric sphincter (valve) serve as?
-serves as a barrier between the stomach and small intestine
HCl secretion in a parietal cell;
Explain the cephalic (head) phase:
-secretion of HCl + pepsin before food reaches the stomach
-gastrin is released from G-cells in pyloric gland area + increases HCl and pepsin
HCl secretion in a parietal cell;
Explain the gastric phase:
-begins when food reaches the stomach
-presence of protein increases HCl and pepsin secretion
HCl secretion in a parietal cell;
Explain the intestinal phase:
-inhibitory phase: inhibits gastric juices as chyme begins to empty into the small intestine
What is the function of the gastric mucosal barrier?
-enables the stomach to contain acid without injuring itself
*luminal membranes; impermeable to H+ so HCl cannot penetrate cells
*cells are joined by tight junctions= preventing penetration of HCl
*muscles coating over the gastric mucosa= offers further protection
Gastric emptying- peristaltic waves in the stomach
-contractile rhythm
-set by pacemaker cells
Occurs every 3 mins
What is gastric emptying time?
The time to empty the stomach after a meal can take 4-6 hours
*Increases fluidity - time decreases
*Increases fat content- increases time it takes
What do fats in the duodenum allow?
secret CCK (cholecystokinin) that in turn stimulates the gallbladder to contract and release stored bile that helps to break down fats
What does stomach acid in the duodenum stimulate?
stimulates the pancreas to release bicarbonate ions to neutralise the acid
The small intestine;
What is its function?
absorption by increasing surface area
Structures of the small intestine:
-circular folds
-villi= ‘finger like’ projections
-microvilli= projections of plasma membrane
-finger-like shape
-crypt: different types of cells; intestinal stem = constantly regenerate the epithelial layer
-epithelial layer is always regenerated= new layer is always been formed
What is hydrolysis?
Hydrolysis is a reaction involving the breaking of a bond in a molecule using water
How does glucose exit the intestinal cell?
passively by a glucose transport protein
What are dietary lipids?
-triglycerides (90%)
= composed of 3 fatty acids; joined to a glycerol back bone
-cholesterol
-phospholipids
-fat soluble vitamins
What is the key role of bile salts; bio surfactants?
-Prepare the surface of fat globules
-act as detergents
-amphillic
Triglyceride (TG) hydrolysis:
-hydrolysed to monoglycerides (MGs) + free fatty acids (FAs) by pancreatic lipase
-rate of hydrolysis is strongly dependant on surface area of the lipid-water interface
What does monoglycerides and free fatty acids associate with?
Bile salts and phospholipids to form micelles
Transcellular lipid movement;
Where are intracellular fatty acids and MGs transported to?
transported to ER for synthesis into TGs
Once intracellular FAs and MGs are transported what are they packaged into and where are they transported?
Packaged into chylomicrons and transported to basal membrane in exocytotic membranes = extruded
Motility in the small intestine;
What is segmention initiated by?
Initiated by pacemaker cells in the small intestine= produces basic electrical rhythm (BER)
What are the functions of the circular smooth muscle?
-Mixing chyme with digestive juices secreted into small intestine lumen
-Exposing all chyme to absorptive surfaces of small intestine mucosa
Motility in the small intestine;
What does migrating motility complex do?
Sweeps intestines clean between meals
What are the features of the large intestine?
-drying and storage organ
-contents consist of indigestible food, residues, unabsorbed biliary components and water
What is the function of the colon?
Extracts more water and salt from contents and the feces remains to be eliminated
What is the function of the taenia coil?
Longitudinal smooth muscle bands in the colon wall
Facilitates efficient contraction of the circular muscle
What is the function of the haustra?
Ponches or sacs + actively changes location as a result of contraction of circular smooth muscle layer
What are haustral contractions initiated by?
Initiated by autonomous rhythmicity of colonic smooth muscle cells
Defection reflex;
What is mass movements?
Massive contractions move colonic contents into distal part of the large intestine
What is the defecation reflex?
Initiated when stretch receptors in rectal wall are stimulated by distension
Causes internal anal sphincter= relax and return + sigmoid colon to contract more vigorously
When does defecation reflex occur?
If the external anal sphincter is relaxed
What is the smallest function unit of skeletal muscle?
Sarcomere
What is the arrangement of the thick and thin filaments and what appearance does it give?
Arrangement of actin and myosin gives skeletal muscle its microscopic striated appearance and creates functional units = sarcomeres
How are sarcomeres viewed under electron microscopy?
Sarcomeres are arranged longitudinally and include the: M line, Z line, H band, A band and I band
What is the M line?
Central-most line of the sarcomeres where myosin filaments are anchored together through binding sites within the myosin filament
What is the H band?
The H band contains the M line and is the central region of the sarcomere that contains only myosin filaments
What is the I band?
The I band covers the terminal regions of two adjacent sarcomeres and contains only actin filaments
-shortens with muscle contraction
What is the A band?
The A band is a larger portion of the sarcomere that *contains the entirety of the myosin fibres and includes regions of actin and myosin overlap. *It does NOT shorten with contraction
What is the Z disc?
-start and end point of the sarcomere
-coin shaped; cutting through the cell
*alpha actin
*anchors the actin thin filaments
In the sliding filament theory what is the look of actin and myosin?
Actin: thin
Myosin: thick
Each actin: reacting with 3 myosin’s
Each myosin: reacting with 6 actin
Function of the Z disc in the sliding filament theory?
-Z discs coming closer together
-shortening
-myosin motors are pulling towards each other= contraction
-shape changes = thick and thin filaments slide part each other= increases the area of overlap
What is the myosin cross-bridge?
-each head has 2 binding sites; one for actin and one for ATP molecule
-hydrolysis of ATP is related to generation of force e.g. myosin head undergoes ‘shape’ change
What are the two shapes/ conformations of the myosin cross bridge?
*in the low energy; conformation the cross bridge (head) is tilted BACKWARDS
*in the high energy; conformation the cross bridge (head) is tilted UPWARDS
When the cross bridge ‘shape’ changes, thin filament is approx 10nm = power stroke of muscle contraction
Myosin
-each myosin head cycles approx 5x per second
-100-110 angstroms per cycle
-when hundreds of heads are interacting with the same actin filament= myosin MAY MOVE at 80,000 angstroms per second relative to actin
Titin
-34,350 amino acids
-largest human protein
-a molecular spring and scaffold protein= aiding myofibrillar assembly
Cross bridge cycle
Page 18 lecture 10.1
What is the function of the sarcoplasmic reticulum?
-a system of membranous tubules surrounding each myofibril
-function= release and secrete Ca2+
What is the function of T tubules?
-invaginations of the sarcolemma that run between the terminal cisternae of the SR
Function= allow the electrical stimulus to be delivered quickly to deep cell regions
Excitation contraction coupling;
How long does it take?
Active transport of calcium back into the SR TAKES TIME
^although the AP is very brief, the contraction phase of the muscle fibre lasts MUCH LONGER
Excitation contraction coupling;
What does the release of Ca2+ from SR provide?
Provides link between muscle excitation and contraction
Summary;
skeletal muscle is voluntary and must be stimulated by a motor neuron to contract
-skeletal muscle fibres are; *long, *striated and *multinucleate
-myofibrils are the contractile elements and consist of the regular arrangement of actin and myosin = how the skeletal muscle gets its striated appearance
-SR is a system of membranous tubules and functions to release and sequester calcium ions
-sliding filament model describes how the cross bridge (myosin head) activity of the thick filaments pulls the thin filaments towards the sacromere centre
-regulation of skeletal muscle contraction involves generating and transmitting an AP along the sarcolemma an excitation contraction coupling
Skeletal muscle;
Muscle contraction
What does a motor unit consist of?
Consists of a motor neuron and all the muscle fibres it innervates
Skeletal muscle;
Muscle contraction
How do motor units vary in the number of muscle fibres?
-finger muscles; 10-100 muscle fibres=allowing fine adjustments of movement
-leg muscles; up to 1000 muscles= allowing larger adjustments in force
Skeletal muscle;
Muscle contraction
What is a skeletal muscle fibre innervated by?
By a branch of a motor axon
-the AP arrives at the synapse (NMJ) and an AP is then generated in the muscle fibre membrane which causes contraction of the muscle fibre
Skeletal muscle;
Muscle contraction
What 3 phases does a muscle twitch have?
Latent period
Period of contraction
Period of relaxation
Explain the latent period:
-1-3 ms following stimulation when E-C coupling is occurring
-cross bridges are being formed but tension is not yet detectable
Explain the period of contraction;
-cross bridges are active up to the peak of tension development
-myogram trace rises to a peak
-lasts 10-100 ms
Explain the period of relaxation:
-initiated by re-entry of Ca2+ into SR
-muscle tension decreases to zero
-if muscle has shortened during contraction= returns to its original length
-lasts 10-100ms
What are graded muscle responses?
-Healthy muscle contractions are relatively smooth and vary in strength as different demands are placed on them
-variations are necessary for proper control of skeletal muscle= referred to as graded muscle responses
What does the size of muscle contraction depend on?
Number of motor units activated= achieved by changing the strength of the stimulus
Frequency of stimulation= increasing frequency of stimulation allows the contractions to be added together
What are the effects of stimulus intensity?
-sub threshold stimulus= no discernible contraction
-above threshold= increases stimulus strength= increases contractile strength
-illustrates an increase in motor unit recrutionent?
What is the size principle regarding motor units?
-small motor units= recruited first as they are controlled by smallest most excitable motor neurons
-recruitment of large motor neurons = increases the contractile force
-largest motor units= 50x more contractile force than smaller ones
^controlled by the largest least excitable neuron and are activated only when powerful contraction is necessary
What is the effect of frequency of stimulation?
Muscle force sums to higher levels when APs stimulate the muscle at higher rates —> reaching a tetanus
What is tetanic contraction?
It is the result of repeated stimuli at such short intervals that the muscle fibre doesn’t have time to fully relax before it is needed to contract again
Why is size principle important?
-It increases the force of weak contraction to occur in small steps
-muscle force can be progressively greater when large amounts of force are required
-motor units are commonly activated asynchronously
*at a given instant some are in tetanus = prolongs a strong contraction by preventing/delaying fatigue
What is isotonic?
Same tension, change in length
What is concentric?
Muscle shortens as it does work
What is eccentric?
Muscle lengthens while contracting
*50% more forceful than concentric contractions
*causes delayed onset muscle soreness
*all jumping and throwing activities involved both types of contraction
What is isometric?
Same length, increasing tension
Explain the interactions of skeletal muscles:
As muscles shorten, the insertion (attachment on the moveable bone) moves towards the origin (its fixed immovable point of attachment
Whatever one muscle group ‘does’ there is another group that ‘undoes’ that action
What is the classification of muscles?
4 groups:
1. Agonists= prime movers
2. Antagonists= e.g. triceps in elbow flexion
-when man agonist is active, the antagonist is relaxed/stretched
-can regulate degree of movement by contracting eccentrically
-pairs are always located on the opposite side of joints
3. Synergists= assist the agonist= add extra force
4. Fixators= reduces the undesirable movements when the synergist immobilises a bone or joint, they are fixators
What are fast twitch and slow twitch glycolytic fibres?
*fast-twitch glycolytic fibres are LIGHT YELLOW
-fewer mitochondria
-rely on glycolysis
*slow-twitch oxidative fibres are DARK RED
-rich in myoglobin
-rich blood supply= lots of mitochondria
Metabolic characteristics
Page 20- lecture 11.1
What are the differences between slow oxidative fibres and fast glycolytic fibres?
Slow oxidative fibres;
-depends on oxygen delivery
-thin cell- allows more rapid diffusion of oxygen and nutrients from the blood
-fewer myofibrils- less powerful
-many mitochondria
-rich in myoglobin
-rich in capillary supply
Fast glycolytic fibres;
-depend on glycogen reserves rather than glucose delivered through the blood
-reduced demand for oxygen
-few mitochondria
-low capillary density
-larger cell- more
Differences between all 3 types?
Type I= slow oxidative
Type IIA= fast oxidative
Type IIB= fast glycolytic
Men vs Women;
Men- average= faster than women when it comes to sprinting and marathoning
-as endurance races get longer, the gap between the women’s and men’s finishing time shrinks
Individual differences?
-everyone’s muscles contain all 3 types
-some have more of one type than others
-differences are predominantly genetic
-can be modified by training
Oestrogen in a skeletal muscle
In a skeletal muscle oestrogen increases the expression and protein content of peroxisome proliferation activator receptors
-skeletal muscles of women have higher intracellular lipid content than male muscles
Do men or women have more slow twitch fibres with better blood supply?
-women have a higher percentage of slow twitch oxidative muscle fibres than men
-estrogen receptors are expressed in type I muscle fibres
-higher capillary density of muscle fibres increases substrate availability
Force-velocity relationship of muscle?
? Page 21- lecture 11.1
Summary of motor units;
-Motor unit consists of a motor neuron and the muscle fibres it innervates
-muscle twitch’s have 3 phases: latent, contraction + relaxation phases
-size of muscle contraction depends on: number of activated motor units
-increased by:
*changing the strength of the stimulus
*increases the frequency of stimulation so contractions are added together= force summation
Agonist and agonistic muscle pairs:
-agonist and agonistic muscle pairs move joints?
-page 21
