PHYSIOLOGY COPY Flashcards
what is the alimentary canal
series of hollow organs running from mouth to anus (oral to aboral) that are separated by sphincters, controlling movement
what is the function of mouth and pharynx
chops and lubricates food, starts carbohydrate digestion, delivers food to oesophagus
what is the function of the oesophagus
propels food to the stomach
what is the function of the stomach
stores and churns food continues carbohydrate, initiates protein, digestion regulates delivery of chyme to duodenum
what is the function of the small intestine
(duodenum, jejunum and ilium) principal site of digestion and absorption of nutrients
what is the function of the large intestine
(caecum, appendix and colon). Colon reabsorbs fluids and electrolytes, stores faecal matter before delivery to recutum
what is the function of the rectum anal canal and anus
regulated expulsion of faeces
what are accessory structures to the alimentary canal
salivary glands, the pancreas, the liver and gall bladder (hepatobiliary system)
what are the generalised structures of the digestive tract wall (4)
- mucosa
- submucosa
- muscularis externa
- serosa
what are the 3 layers in the mucosa
- mucous membrane
- lamina propria
- muscularis mucosae
what are the structures in the submucosa
- connective tissue
- larger blood and lymph vessels
- glands
- submucosa plexus (neurone network)
what are the structures in the muscularis externa
- circular muscle layer
- myenteric plexus (neurone network)
- longitudinal muscle layer
what are the 4 major functions of the alimentary canal
- motility
- secretion
- digestion
- absorption
what does the function of motility entail
mechanical activity mostly involving smooth muscle (skeletal at mouth, pharynx, upper oesophagus and external anal sphincter)
what does the function of secretion entail
into the lumen of the digestive tract occurs from itself and accessory structures in response to the presence of food, hormonal and neural signals. Required for digestion, protection and lubrication
what does the function of digestion entail
chemical breakdown by enzymatic hydrolysis of complex food stuffs to smaller, absorbable units
what does the function of absorption entail
transfer of the absorbable products of digestion from the digestive tract to the blood or lymph
what does circular muscle contraction cause
lumen becomes narrower and longer
what does longitudinal contraction cause
intestine becomes shorter and fatter
what happens when the muscularis mucosae contracts
change in absorptive and secretory area of mucosa (folding), mixing activity
what are the function of gap junctions between smooth muscle cells in the GI tract
Electrically couple adjacent cells (allow slow wave of depolarisation to spread across muscle sheet).
- synchronous wave (ie single unit smooth muscle)
what are Interstitial cells of Cajal (ICC)
Pacemaker cells located largely between the circular and longitudinal muscle layers. They form gap junctions with each other and smooth muscle cells electrically coupling them. Slow waves in ICC drive slow waves in the smooth muscle cells coupled to them. Some ICCs form a bridge between nerve endings and smooth muscle cells.
when does contraction in the intestines only occur
Contraction in the intestines occurs only if the small wave amplitude is sufficient to reach a threshold to trigger smooth muscle cell calcium action potentials
- Depolarising slow waves do not necessarily result in smooth muscle contraction
what are slow waves
Slow waves, also known as the basic electrical rhythm (BER), vary in frequency along the length of the GI tract eg stomach, 3 min-1, small intestine, 8-12 min-1
whether a slow wave amplitude reaches threshold depends on: (3)
- neuronal stimuli
- hormonal stimuli
- mechanical stimuli
(generally act to depolarise smooth muscle cells rather than influence slow waves directly - depolarisation shifts slow wave peak to threshold)
explain the autonomic innervation of the GI tract by the parasympathetic system
pre ganglionic fibres (releasing ACh) synapse with ganglion cells within the enteric nervous system
- excretory influences = increased gastric, pancreatic and small intestinal secretion, blood floe and smooth muscle contraction
- inhibitory influences = relaxation of some sphincters, receptive relaxation of stomach during feeding
explain the autonomic innervation of the GI tract by the sympathetic system
pre ganglionic fibres (releasing ACh) synapse in the pre vertebral ganglia. Post ganglionic fibres ( releasing noradrenaline) innervate mainly enteric neurones but also other structures
- excretory influences = increased sphincter tone
- inhibitory influences = decreased motility, secretion and blood flow
what is the enteric nervous system
The enteric nervous system (ENS) is a large division of the peripheral nervous system (PNS) that can control gastrointestinal behaviour independently of central nervous system (CNS) input
what does the myenteric (Aurbachs) plexus regulate
mainly regulates motility and sphincters
what does submucosus (Meissners ) plexus
mainly modulates epithelia and blood vessels
what neurones coordinate muscular, secretive and absorptive activities in the GI tract
sensory neurones , interneurones, effector neurones
what is peristalsis
A wave of relaxation, followed by contraction, that normally proceeds a short distance along the gut in an aboral direction - triggered by distension of the gut wall
what is the effect of altered activity of interneurones and hence motoneurons on the longitudinal and circular muscle in the propulsive segment and the receiving segment
- (oral) Longitudinal muscle relaxed (release of VIP and NO from inhibitory motoneurons). Circular muscles contract ( release of ACh and substance P from excretory motoneurons)
- (aboral) Longitudinal muscle contrasts ( release of ACh and substance P from excretory motor neurone). Circular muscle relaxes (release of VIP and NO from inhibitory motor neurone)
what is segmentation
mixing or churning movements- rhythmic contractions of the circular muscle layer that mix and divide luminal contents. It occurs in the small intestine ( in the fed state) and in the large intestine (where is it called haustartio)
what is colonic mass movement
powerful sweeping contraction that forces faeces into the rectum - occurs a few times a day
what is the migration motor complex
powerful sweeping contraction from stomach to terminal ilium
what are tonic contractions
- Low pressure - organs with a major storage function
- High pressure - sphincters
how many sphincters are in the GI tract
6 excluding the sphincter of odd
what do sphincters do
act as one way valves by maintaining a positive resting pressure relative to two adjacent structures
name the sphincters
Upper oesophageal sphincter Lower oesophageal sphincter Pyloric sphincter Ileocaecal valve Internal and external anal sphincter
what are the functions of each of the sphincters
- UOS = skeletal muscle relaxes to allow swallowing or closes during inspiration
- LOS relaxes to permit entry of food to the stomach or closes to prevent reflux of gastric contents to the oesophagus
- Pyloric sphincter = regulates gastric emptying and usually prevents duodenal gastric reflux
- Ilieocaecal valve = regulates flow from ilium to caecum or distension of ilium opens, distension of proximal colon closes
- Internal (smooth muscle) and external (skeletal muscle) anal sphincters = are regulated by the defection reflex
what is glycogenesis
synthesis of glycogen from glucose
what is glycogenolysis
breakdown of glycogen to form glucose catalysed by glycogen phosphorylase
- Rate limiting step of glycogenolysis. One glucose molecule is cleaved off the ends of glycogen at a time
what is gluconegenesis
de novo synthesis of glucose from metabolic precursors (lactate, amino acids, glycerol)
-It is not the verse of glycolysis due to the need to overcome energetically unfavourable steps, catalysed by a unique set of enzymes
what is the function of hexokinase in glycolysis
primer for glucose phosphorylation
what is the function of phosphoglucomutase in glycolysis
Targets glucose away from glycolysis and towards glycogen synthesis. It changes the position of the phosphate from 6 to 1
What is the function of UDP glucose pyrophosphorylase in glycolysis
Binds the UDP to the glucose
Simple precursors are first converted to activated intermediates
UDP glucose can be thought of an activated form of glucose. ATP and acetyl-CoA are activated forms of phosphate and acetate respectively
what is the function of glycogen synthase in glycolysis
attaches UDP glucose as a primed molecule to glycogen
what is the function of glycogen syntheses
synthesises glycogen from UDP glucose. Adds one glucose molecule to glycogen at a time. Can only extend the chains of glycogen ie cannot start new molecules. Cannot introduce branches. Rate limiting enzyme of glycolysis
what are the 4 liver enzymes required for gluconeogenesis
- Glucose-6-phosphate
- Fructose-1,6-bisphospahte
- PEP carboxykinase
- Pyruvate carboxylase
what is the cori cycle
Lactate is a precursor if gluconegenesis. Blood transports lactate to the lover. The liver converts lactate back ti glucose. Glucose released into bloodstream. Buys time and shifts metabolic burden form muscle to other organ
what is the structure of a triglyceride
glycerol and 3 fatty acids
what are the main natural fatty acids
Palmitic acid 16:0
Stearic acid 18:0
Oleic acid 18:1
what are the main products of fat digestion
Glycerol, fatty acids and monoglycerides
where is fat absorbed
Absorbed into mucosal cells of intestine. Short and medium length fatty acids enter portal blood. Longer chains FAs and monoglycerides are resynthesises to triglycerides
what is lipolysis
breakdown of lipids. Fat is stored in adipose tissue
before fatty acids can be oxidised to generate energy what do they have to be converted to
CoA derivatives
what is the carnitine shuttle
The carnitine shuttle represents a mechanism by which long-chain fatty acids, which are impermeable to the mitochondrial membranes, are transported into the mitochondrial matrix for the purpose β-oxidation and energy production.
what is beta oxidation (in mitochondrial matrix)
Beta oxidation is a metabolic process involving multiple steps by which fatty acid molecules are broken down to produce energy. More specifically, beta oxidation consists in breaking down long fatty acids that have been converted to acyl-CoA chains into progressively smaller fatty acyl-CoA chains.
what are ketone bodies
(three related compounds produced during the metabolism of fats, two of which are used as a source of energy instead of glucose during a period of fasting or very low carbohydrate intake) They are formed in the mitochondria from acetyl-CoA from b oxidation. Diffuse into the blood stream and to peripheral tissues. Important molecules of energy metabolism for heart muscle and renal cortex- convert back to acetyl-CoA, which enters the TCA cycle.
what cells cover the oral cavity, oropharynx and larngopharynx
stratified squamous epithelium which is generally not keratinised
what cells are on the anterior 2/3 of the tongue
stratified squamous epithelium, thin on ventural surface, thick and with papillae of the dorsal surface
what cells are on the posterior 1/3 of the tongue
covered by smooth stratified squamous epithelium which, except for the circumvallate papillae, lacks papillae but does have substantial lymphoid aggregates in the submucosa
what are the 4 types of papillae on the tongue
Fungiform, Circumvallate, Foliate, Filiform
what are the 4 main layers from the digestive tract from the oesophagus to the anal canal
- Mucosa: 3 parts
- Epithelium (sits on basal lamina)
- Lamina Propria (loose connective tissue)
- Muscularis mucosa (thin layer of smooth muscle) - Submucosa (dense irregular connective tissue)
- Muscularis externa ( 2 thick layers of smooth muscle, an inner circular layer and an outer longnitudinal layer)
- Serosa or Adventitia (Outer layer of connective tissue that either suspends the digestive tract or attaches it to other organs)
what is the gastro-oesophageal; junction
abrupt transition from stratified squamous epithelium of oesophagus to the simple columnar epithelium of the cardia of the stomach
where would you find parietal cells and stem cells of the gastric gland
isthmus
where do you find neck mucous cells and parietal cells
neck
where do you find mostly chief cells with a few parietal cells and enteroendocrine cells
funds (base)
what is the function of chief cells
digestive enzyme secreting cell
what is the function of parietal cell
hydrochloric acid producing cell
what are the different stomach regions
- Cardia: deep gastric pits that branch into loosely packed, tortuous glands
- Body: shallow gastric pits with long straight gastric glands
- Pylorus: Deep gastric pits with branched, coiled gastric glands at a higher density than in the cardia
what are the 3 segments of the small intestine
- Duodenum = 25cm long
- Jejunum = 2m long
- Ilium = 2.75m long
compare the small intestine regions
- Duodenum contains Brunners glands in the submucosa
- Jejunum. Tallest villi, located on permenant circular folds of the mucosa and submucosa, the place circulars. Lymphoid follicles infrequent
- Ileum is characterised by shorter villi and aggregates of lymphoid follicles callers Peyer’s patches found in the submucosa and often extending into the lamina propria
what are enterocytes
the most numerous cells, they are tall columnar cells with a brush boarder and are the principle absorptive cell
what are goblet cells
produce mucin to protect epithelium and lubricate passage of material
what are paneth cells
found at the base of the crypts of lieberkuhn, there have a defensive function and have a role in regulating bacterial flora (secrete lysozyme and definsins)
what are enteroendocrine (neuroendocrine) cells
produce hormones that contribute to the control of secretion and motility
what are stem cells
found at the base of the crypts of lieberkuhn, they divide to replenish the epithelium
what occurs in the duodenum
Receives acidic, partly digested semifluid material called chyme from the stomach. It has glands located within the submucosa called Brunners glands and when stimulated by the presence of chyme they produce a thin, alkaline mucous to neutralise the chyme
what are Peyers patches
the numerous areas of lymphoid tissue in the wall of the small intestine which are involved in the development of immunity to antigens present there.
what are the 2 main types of cells in the large intestine epithelium
- Absorptive cells for the removal of salts and thereby water
- Goblet cells for the secretion of mucus to lubricate the colon
what is the appendix
A blind ending hollow extension of the cecum
what is the structure of the appendix
the structure of the appendix is similar to the rest of the colon, but the crypts are far less abundant sonf there is typically a circular arrangement of lymphoid tissue in the submucosa and often the lamina propria
what cells are along the long anal canal
continuous with the keratinised stratified squamous epithelium of the surrounding skin
what is the digestive tracts own nervous system
Enteric nervous system.
where does the enteric nervous system receive input from
autonomic nervous system, but is capable of coordinating gut motility locally
what is a neuron living outside the brain and spinal chord called
ganglion
what cell composes the parenchyma of the liver and pancreas
glandular epithelial cells
what is the structure of the liver
Made up of segments called lobules. Each lobule is approximately hexagonal and has a branch of the hepatic vein called the centrolobular even at its centre and portal triads at each corner
what are portal triads
Branches of the vessels which enter at the aorta hepatis, that is the hepatic artery and hepatic portal vein. There is a third tube called the bile duct
what are the main cells of the liver
hepatocytes
what is the space of Disse
The sinusoids are lined by endothelial cells and there is a narrow space between these lining cells and the hepatocytes. The space is called the space of Disse
what are hepatic stellate cells
They are scattered in the space of Disse. They are modifies fibroblasts and make connective tissue. They also store vitamin A within fat droplets in their cytoplasm. In some pathological conditions they transform into myofibroblasts and produce scar tissue in the liver
what are Kupffer cells
They are resident macrophages scattered within the sinusoids. These cells remove particulate matter from the blood and help remove worn out RBCs
what is bile
bile is an alkaline solution containing water, ions, phospholipids, bilirubin and bile salts.
what is bilirubin
A pigment which results from the breakdown of haemoglobin in the spleen, and when excreted in the bile, is the principal cause of the brown colour of feces
what are bile salts needed for
They are necessary for emulsification of fats in the digestive tract.
how is bile produced
All hepatocytes produce bile in the liver
what are bile canaliculi
they are small channels formed by tight junctions in the cell membranes of adjacent hepatocytes
what does the exocrine pancreas produce
Digestive juices, lipase to break down lipids, nucleases to breakdown DNA and RNA, amylase to breakdown starch. These enter the duodenum via the pancreatic duct
The cells in the exocrine pancreas are very basophilic because they contain large amounts of RER in the basal part. In the apical part its very eosinophilic due to the presence of zymogen granules
what does the endocrine pancreases do
the endocrine pancreas consists of small scattered islands of tissue called islets of langerhans which produce a number of hormones including insulin and glucagon
what is the function of the enzymes produced from the exocrine pancreas
the enzymes produced are produced as proenzymes. Once the pancreatic secretion arrives at the duodenum an enteropeptidase converts the inactive proteolytic enzyme trypsinogen into the active form trypsin
what is trypsinogen
an inactive substance recreated by the pancreas, from which the digestive enzyme trypsin is formed in the duodenum
what is trypsin
enzyme that helps digest protein
what is the structure and function of the gall bladder
the gall bladder is a muscular sac which is lined by columnar epithelium backed by lamina propria of loose connective tissue rich in blood vessels and lymphatic vessels, a coat of smooth muscle and an outer collagenous layer of adventitia. The gall bladder stores bile and modifies the bile within it. It has a folded mucosa when empty
what hormone causes contraction of the gall bladder
cholecystokinin
what is cholecystitis
Inflammation of the gall bladder is not uncommon. Here gall stones have obstructed the cystic duct leading expansion of the gall bladder, thickening of the muscle layers and inflammation
what is the absorption of water in the GI tract largely driven by
absorption of Na+
what are the principle mechanisms in the absorption of water in the GI tract
- Na+/glucose co transport
- Na+/ amino acid co-transport
- Na+/H+ exchange
- Parallel Na+/H+ and Cl-/HCO3- exchange
- Epithelial Na+ channels (ENaC )
