Digestive System - Intestinal Movements and Liver Function Flashcards
Describe the chewing reflex
Presence of food in the mouth initiates a reflex inhibition of the muscles of mastication allowing the lower jaw to drop
This initiates a stretch reflex of the jaw muscles that leads to rebound contraction, which raises the jaw to cause the teeth to close
This compresses the bolus of food against the lining of the mouth which inhibits the jaw muscles once again causing the jaw to drop
This process is repeated again and again (chewing)
Describe the oral phase of swallowing
The bolus of food is forced backwards with the tongue until pressure on the pharyngeal wall
initiates the swallowing reflex.
Coordinated by the swallowing centre in the
medulla oblongata
Describe the pharyngeal phase of swallowing
Involuntary and allows the food to pass through the pharynx to the oesophagus
The soft palate is deflected upwards, sealing off the nasal passages.
Muscle contraction pulls the larynx upwards, the glottis closes and the epiglottis deflects food away from the laryngeal opening
Describe the oesophageal phase of swallowing
Peristaltic wave of contraction drives the food into and along the oesophagus
Controlled by somatic nerves (glossopharyngeal) supplying the striated muscle in the upper GI tract
Also parasympathetic (vagus) nerves innervating smooth muscle in the lower oesophagus
List 3 vitamins stored in the liver
Vitamin A
Vitamin D
Vitamin B12
What is dyslipidemia and why it is a health risk?
Disturbances of lipoprotein metabolism
Result in abnormalities in plasma lipoprotein concentrations
Increase the risk of cardiovascular disease and atheroma
Explain the basic reflex arc involved in defecation and how it is influenced by higher centres
- Defecation is a bowel movement process regulated by the enteric nervous system (ENS) and higher brain centers.
- It begins with the filling of the rectum with feces, which stimulates stretch receptors in the rectal wall.
- These signals are sent to the spinal cord via pelvic and somatic nerves, forming the defecation reflex center.
- The spinal cord integrates sensory signals, causing efferent motor signals to be sent back to the rectum and colon.
- These signals cause relaxation of the internal anal sphincter, contraction of the rectum and sigmoid colon, and contraction of the abdominal muscles.
- Higher brain centers, particularly in the cerebral cortex, can modulate defecation patterns through voluntary control and learning and conditioning mechanisms.
Explain the basic reflex arc involved in vomiting and how it can be influenced by higher centres
- Nerve impulses are transmitted by both vagal and sympathetic afferent nerve fibres to multiple nuclei in the vomiting centre situated in the medulla oblongata
- Motor impulses are sent to the upper and lower GIT, through vagal and sympathetic nerves and through spinal nerves to the diaphragm and abdominal muscles
- Antiperistalsis
- Contractions of the abdominal muscles and diaphragm increase intra-abdominal pressure, forcing the contents of the stomach upward.
- Relaxation of the lower oesophageal sphincter allows the contents of the stomach to pass into the oesophagus
- Contractions of the pharyngeal muscles propel the vomitus out of the mouth
Explain how reflux from stomach to oesophagus is avoided
- Swallowing involves the stomach, which has different motility patterns for accommodation and gastric emptying.
- The orad and caudad parts relax during swallowing, allowing food to enter the bolus.
- Receptive relaxation occurs after swallowing, allowing large volumes to be accommodated with minimal intragastric pressure increase
List at least four major liver functions
Filtration and storage of blood
Metabolism of carbohydrates, fats, proteins, hormones and foreign chemicals
Formation of bile
Storage of vitamins and iron
Formation of coagulation factors
Explain the detoxification of toxins, drugs and hormones
The liver plays a crucial role in detoxification and removal of steroid hormones, protein metabolism by-products, ethanol, and drugs.
Protects the body by allowing toxic substances to pass through the liver before reaching the rest of the body.
The liver removes most ammonia produced by peripheral tissue via the urea cycle, releasing it into the systemic circulation.
Facilitates the conversion of ethanol into acetaldehyde and reduced nicotinamide adenine dinucleotide.
Drug metabolism, with some drugs designed to take advantage of its first pass effect
Describe protein metabolism in the liver
- Deamination of amino acids - forms ammonia and the resulting carbon skeleton is available for energy metabolism
- Urea formation - ammonia released during the deamination of amino acids is toxic and will be removed from the blood by the liver and converted to urea
- Formation of plasma proteins
- Conversion of amino acids into other amino acids and synthesis of other compounds from amino acids
- Formation of blood clotting factors
Describe lipid metabolism in the liver
Degrades fatty acids into energy-rich compounds
Synthesising triglycerides from carbohydrates and proteins
Synthesising cholesterol and phospholipids from fatty acids
Contains large quantities of cholesterol and phospholipids, which are lipid-soluble and used for structural purposes in cell membranes and intracellular membranes
The liver is also more capable of desaturating fatty acids than other tissues
What are the movements of the small intestine?
Segmentation contractions - muscle contracts simultaneously at regular intervals along the gut wall pushing the chyme in both directions
Peristalsis - main propulsive force in the small intestine, ensure that there is adequate time for digestion and absorption
Migratory motor complexes - when absorption is complete more powerful propulsive waves occur
What are the movements of the large intestine?
Proximal portion of the colon is responsible for the absorption of water and electrolytes
Distal portion stores faecal matter
Mass movement - sustained contraction of circular muscle
Mass movements force colonic contents into the rectum resulting in distension and initiating the defecation reflex
