Lecture 37 11/15/23 Flashcards
What are the functions of the GI system?
-ingestion, digestion, and absorption of food/nutrients
-ecological niche for commensals
-prevent pathogens from penetrating epithelial barrier
-eliminate waste
Which species have a simple stomach?
-humans
-dogs
-cats
-pigs
What are the characteristics of foregut fermenters?
-multi-chambered stomachs which allow for fermentation
-4 compartments in ruminants
-3 compartments in pseudoruminants
Which species are foregut fermenters?
even-toed ungulates
What are the characteristics of hindgut fermenters?
-monogastric stomach
-extensive cecum and colon
Which species are hindgut fermenters?
-odd-toed ungulates
-rabbits
-guinea pigs
Which section of the brain serves as the control center for appetite regulation?
hypothalumus
What are the two centers of the hypothalamus?
-appetite center: increases hunger
-satiety center: decreases hunger
What are the short term signals for appetite regulation?
-neuronal signals
-blood levels of nutrients
-GI hormones
What are orexigenic neurons?
neurons that send signals that increase hunger
What are anorexigenic neurons?
neurons that send signals that decrease hunger
How does the oral cavity play into appetite regulation when eating?
-taste receptors distinguish between acceptable and unacceptable foods
-acceptable foods encourage intake
How does the stomach play into appetite regulation when eating?
-stretch-sensitive mechanoreceptors detect distension
-neuronal input relays info. to hypothalamus via vagus nerve
How do the intestines and colon play into appetite regulation when eating?
-chyme triggers release of hormones
-CCK, peptide YY, and insulin have important roles
What is the short-term regulator of appetite when fasting?
Ghrelin, an orexigenic hormone that stimulates appetite/food intake
What is the long-term regulator of appetite?
Leptin, an appetite suppressant produced by adipose tissue
What are the five categories of taste?
-sour (H+ ions)
-salty (sodium)
-sweet (organic comp.)
-bitter (organic comp./alkaloids)
-umami (L-glutamate)
What are the types of GI function regulation?
-intrinsic: within GI system walls
-extrinsic: outside GI system walls
What is the role of the enteric/intrinsic nervous system?
controls localized GI functions
Which ganglionated plexuses make up the enteric nervous system?
-myenteric plexus
-submucosal plexus
What are the characteristics of the myenteric plexus?
-between muscle layers of GI system
-controls GI movements
What are the characteristics of the submucosal plexus?
-under submucosal layer of GI tract
-controls local secretion, absorption, and blood flow
What is the function of enteric neuron varicosities?
allow the neurons to activate a wider area
What are the sources of input for enteric sensory neurons?
-mechanoreceptors (sensing stretch)
-chemoreceptors (sensing chemical conditions)
What are the characteristics of enteric motor neurons?
-supply gut muscle, vascular muscle, and glands
-may be inhibitory or stimulatory
-secrete various neuropeptides
What are the characteristics of enteroendocrine cells?
-“taste buds” of gut
-scattered throughout mucosal layer
-largest endocrine organ
-senses components of chyme to determine secretions
How can GI peptides act, hormonally?
-endocrine (released in circulation)
-paracrine (diffuse short distances)
-autocrine (act on same cell)
-neurocrine (released from nerve endings)
What are the characteristics of parasympathetic innervation of the GI system?
-stimulatory
-mediated by acetylcholine
-innervation through vagus and pelvic nerves
What are the characteristics of sympathetic innervation of the GI system?
-inhibitory
-mediated by norepinephrine
-innervation through splanchnic nerves
What are the characteristics of aldosterone?
-mineralocorticoid hormone
-produced by adrenal glands
-functions in H2O and Na reabsorption and K excretion
Which organs are involved in splanchnic circulation?
-GI tract
-pancreas
-liver
-spleen
How does blood flow through splanchnic circulation?
-blood from GI tract/pancreas/spleen dumps into portal vein
-portal vein carries blood to liver
-blood passes through liver sinusoids
-blood leaves through hepatic veins which dump into caudal vena cava
What is the role of reticuloendothelial cells in the liver sinusoids?
remove bacteria and potentially harmful substances from the blood
How does blood flow change within the GI system?
-blood flow increases for a few hours following a meal
-sympathetic NS can reduce blood flow for short periods
What are the characteristics of the microvasculature of intestinal villi?
-counter-current system
-arterioles and venules diffuse oxygen to each other
-80% of oxygen and nutrients bypass the tips of the villi
