9 The Gastrointestinal System Flashcards
What’s the aka for the gastrointestinal tract?
aka alimentary canal
What are the accessory digestive organs?
- teeth
- tongue
- salivary glands
- liver
- gallbladder
- pancreas
What are teh functions of the gastrointestinal system?
- ingestion
- secretion
- mixing and propulsion
- digestion
- absorption
- elimination
What’s medical terminology for:
- chewing
- swallowing
- vomiting
- taste
- chewing: mastication
- swallowing: deglutition
- vomiting: emesis
- taste: gustation
What are the three major salivary glands?
- parotid: inferior and anterior to the ear, between the skin and the masseter
- submandibular glands: floor of the mouth
- sublingual glands: beneath the tongue
The wall of the GI tract from the lower esophagus to the anal canal has the same 4 layered arrangement:
- mucosa
- submucosa
- muscularis
- serosa
What’s the mucosa of the GI tract made of?
a mucous membrane consisting of:
- epithelium
- apithelial cells
- exocrine cells (secrete mucous, liguid)
- enteroendocrine cells (secrete hormone)
- lamina propria
- CT (areolar)
- blood and lymphatic vessels (for absorption)
- mucosa-associated lymphatic tissue (MALT) (for immune function/protection)
- muscularis mucosa
- a smooth muscle layer that creates folds in the mucosa (in some places, folds upon folds upon folds to increase surface area)
What’s the submucosa of the GI tract?
- a CT layer that binds the mucosa to the muscularis layer
- contains many blood and lymphatic vessels (for nutrient transport)
- contains neurons of the enteric nervous system for GI control
What’s the serosa of the GI tract?
- serous membrane
- outermost layer of teh organs in teh abdominal cavity
- aka visceral peritoneum
What are the layers of peritoneum, what’s its purpose, and what’s between the layers?
- visceral peritoneum (aka the serosa)
- parietal peritoneum
- purpose: contains large folds that bind organs to one another and to the walls of the abdominal cavity
- some organs (kidneys, ascending and descending colons, duodenum, pancrease) are covered by teh peritoneum on their anterior side only - they are called retroperitoneal
- between the two layers is the peritoneal cavity
How long does food mix in the stomach?
2-4 hours
The soupy mix of food in the stomach is called ___
chyme
How much absorption happens in the stomach?
little-no absorption (water, ions, some fats, medicatinos, alcohol)
Once food particles are small enough in the stomach, they pass through the ___ ___ into the small intestine
pyloric sphincter
The wall of the stomach has the same 4 layered arrangement as the rest of the GI tract with some additions:
- the mucosal layer has specialized cells that secrete:
- mucous (mucous neck cells)
- intrinsic factor and HCl (parietal cells)
- secretions from mucous, parietal and chief cells (Gcells not included) are collectively called gastric juice
- pepsinogen and gastric lipase (chief cells)
- gastrin (a hormone secreted by G cells)
- stimulates gastric juice production
- strengthens LES contraction
- increases stomach peristalsis
- relaxes the pyoloric sphincter
- secretions from mucous, parietal and chief cells (G cells not included) are collectively called gastric juice
- the muscularis has an additional (oblique) layer of smooth muscle to facilitate mixing
How long and wide is the small intestine?
~3m long and 2.5 cm diameter
What are the 3 regions of the small intestine?
- duodenum
- jejunum
- ileum
The mucosal layer of the small intestine has villi, and each villus is covered in epithelium. The cells of the epithelium are:
- absorptive cells (digestion/absorption)
- absorptive cells have microvilli (brush border)
- goblet cells (mucous)
- Paneth cells (kill bacteria)
- enteroendocrine cells (secrete hormones)
Each villus has an arteriole, a venule and a lacteal (e.g. lactase – lack of these results in some degree of lactose intolerance)
In the small intestine, absorbed nutrients pass into:
- either:
- the blood stream (carbohydrates, proteins, water, electrolytes, water-soluble vitamins) and go to the liver
- the lymphatics (lipids) via a lacteal
- generally speaking, fats get delivered to lymph, everything else to blood
- remaining food passes through the iliocecal valve/sphincter into the large intestine
Where is the Pancreas located and how does it function?
- sits posterior to the stomach
- has both endocrine and exocrine functions
- exocrine function: secretes pancreatice juice (water, salts, sodium bicarbonate, enzymes) into the duodenal lumen
- juices are secreted into the proximal duodenum via 2 main ducts:
- a common duct formed by the pancreatic duct joining the common bile duct from the liver/gallbladder
- accessory duct
Where is the liver located?
sits inferior to the diaphragm in the right upserior region of the abdominal cavity
(has 2 lobes: larger right and smaller left)
Where does the liver receive blood from?
- hepatic artery - oxygenated blood
- hepatic portal vein - deoxygenated blood containing absorbed nutrients, medications, microbes and toxins
Blood flows past hepatocytes (liver cells). What do the hepatocytes do?
- absorb oxygen, nutrients and toxins
- release nutrients (needed by other cells)
- hepatocytes also manufacture and secrete bile
Describe the liver function: carboydrate metabolism
- helps maintain blood sugar levels
- low blood sugar - hepatocytes break down glycogen and release glucose into the blood
- high blood sugar - hepatocytes remove glucose from the blood and store it (as glycogen and fats)
- can convert some amino acids, lactic acid, and other sugars into glucose
Describe the liver function: lipid metabolism
hepatocytes store fat, break it down (to make ATP), and make cholesterol
Describe the liver function: protein metabolism
- makes amino acids available for energy
- can convert amino acids into carbs or fats
- synthesizes most plasma proteins
Describe the liver function: drug and hormone processing
detoxifies/inactivates substances (drugs, alcohol, hormones)
How is the liver generally concerned with bilirubin, vitamins and minerals, and more specifically concerned with vit D?
- biliruben elimination (when, due to liver disfunction, this accumulates, it leads to yellow pigmentation – like jaundice)
- vitamin andmineral storage
- vitamin D activation
Where’s the gallbladder located, how is it shaped and what does it do?
- pear-shaped organ sitting in the posterior surface ofhte liver
- stores and concentrates bile (helps break down fats)
What’s bile, how is it made and what’s its function?
- a yellow/brown/olive liquid
- made by hepatocytes
- collects into larger and larger vessels
- function: emulsification (breakdown) of fats
From where does food enter the large intestine?
from the small intestine (ileum) through the ileocecal valve/sphincter
What are the 4 main regions of hte large intesting?
- cecum
- colon
- rectum
- anal canal
What are the functions of the large intestine?
- completion of absorption
- vitamin K production
- formation and elimination of feces
What’s the cecum and what’s attached to it?
- small pouch attached to the ileocecal valve
- contents move from the cecum into the colon
- attached tothe cecum is the appendix
What are the portions/divisions of the colon?
- ascending (to the hepatic flexure)
- transverse (to the splenic flexure)
- descending (to the left iliac crest)
- sigmoid (to the rectum at ~S3)
flexure = bend
How does food move through the colon?
- as food accumulates in the ascending colon, haustra fill up/distend which stimulates smooth muscle contraction and food moves into the next haustra
- regular peristalsis occurs, but more slowly than in the small intestine
- with each meal, mass peristalsis moves feces from the transverse colon into the rectum
What are the divisions of the GI tract?
- upper GI: mouth, pharynx, esophagus, stomach, duodenum
- reverse movement could be vomit
- lower GI: most of the intestines and the anus
- no reverse at this point, diarreah if there’s need to expel quickly
What are the 3 overlapping phases in the process of digestion?
- cephalic
- gastric
- intestinal
What happens in the cephalic phase of digestion?
- the thought, smell, sight, initial taste of food activates the NS
- salivary and gastric glands are stimulated to prepare the mouth and stomach for digestion
What happens in the gastric phase of digestion?
- once food reaches the stomach:
- stretch receptors are stimulated by the change in the stomach shape
- chemo receptors are stimulated by the change in stomach pH
- these changes:
- increase peristalsis and gastric juice production
- stimulate gastrin release (g cells release gastrin)
- small amounts of chyme pass through the pyloric sphincter into the duodenum
- food leaving the stomach decreases the volume of the stomach and removes some of the stimulus from stretch receptors
- food leaving the stomach allows the stomach to become more acidic
- decreasing stretch receptor stimulation and normalizing pH removes some of the stimulus for gastrin release (stops negative feedback loop; return to homeostasis)
What happens in the intestinal phase of digestion?
- chyme in the duodenum causes enteroendocrine cells to release hormones:
- cholecystokinin (CCK)
- secretin
- these hormones:
- stimulate the gallbladder to eject bile into the duodenum (CCK)
- secretin decrease gastric juice production (CCK/secretin)
- slows food coming through the pyloric valve (CCK/secretin)
- increases pancreatic juice secretion (CCK/secretin)
Describe the endocrine system:
- a system of glands and cells that secrete hormones to regulate and integrate body systems
- a control system
- endocrine glands: organs that secreete substances into the blood in resopnse to stimuli
- glands work slower than nerves (seconds to hours to days)
What’s a general description for hormones and how they work?
- chemical messengers (aka mediator molecules)
- don’t actually participate in a response, they simply activate it
- released into the interstitial fluid which then enters the bloodstream and via the circulation, have access to body cells
- they are released in one part of the body to regulate activity in another
What’s a general description of hormone receptors and how they work?
- to function (deliver their ‘message’), hormones must bind to receptors on the cell membranes of target cells/organs
- must have proper lock/key match
- when the hormone binds to the receptor, it changes the shape of the receptor
- changing the receptor’s shape activates pathways that modify cellular functions (i.e. the ‘message’ is delivered)
- one hormone can regulate several different body functions
- one body function can be regulated by several different hormones
What’s upregulation/down regulation where hormones are concerned?
- the increase/decrease in target cell receptors due to a lack/excess of circulating hormone
- this increases/decreases sensitivity to the hormone
What are the endocrine glands?
- pituitary
- thyroid
- parathyroid
- adrenal
- pineal
What are the ‘part time’ endocrine organs?
- hypothalamus
- thymus
- ovaries/testes
- pancreas
- kidneys
- stomach and small intestine
- heart
- adipose tissue
- placenta
- liver
- skin
The key overlap between the nervous and endocrine systems, these 2 regulate all aspects of growth, development, metabolism and homeostasis
hypothalamus and pituitary
Describe the functions of the hypothalamus
- the major integrating centre between the nervous and endocrine systems
- receives input/information from many different structures
- controls the ANS, regulates body temperature, thirst, hunger, some emotions
- hormonally, it regulates the synthesis and release of anterior pituitary hormones
- neurologically, it regulates the synthesis and release of posterior pituitary hormones
What’s the aka, location and structure of the pituitary gland?
- aka the hyphophysis
- a small gland that sits in the sella turcica (turkish saddle) of the sphenoid bone
- has 2 lobes:
- anterior lobe (aka adenohypophysis)
- posterior lobe (aka neurohypophysis)
What are the hormones released by the anterior pituitary?
- human growth hormone (hGH)
- thyroid stimulating hormone (TSH)
- adrenocorticotropic hormone (ACTH)
- luteinizing hormone (LH)
- follicle stimulating hormone (FSH)
- prolactin (PRL)
- melanocyte stimulating hormone (MSH)
What are the general functions of Human Growth Hormone (hGH)?
- stimulates tissue growth
- promotes healing and tissue repair
- increasses the use of lipids for energy
- decreases cellular uptake of glucose/elevates blood glucose levels
- hGH is released in bursts every few hours
What are factors that will promote the release of hGH?
- hypoglycemia
- deep sleep (stages 3 and 4 or nREM)
- increased SyNS (e.g. vigorous exercise)
- other hormones (glucagon, cortisol, insulin, estrogens)
What are factors that will inhibit the release of hGH?
- hyperglycemia
- REM sleep
- obesity
- low levels of thyroid hormones
- high levels of hGH in the blood (negative loop)
What’s adrenocorticotropic hormone?
- stimulates the release of cortisol from teh adrenal glands
- release increases with stress-related stimuli (e.g. injury, hypoglycemia), macrophage activity
What’s Luteinizing Hormone (LH)?
- females: triggers ovulation
- males: stimulates testes to release testosterone
What’s Follicle Stimulating Hormone (FSH)?
- females: triggers ovarian follicle development
- males: triggers sperm production in the testes
What’s Prolactin (PRL)?
- initiates and maintains milk production in the mammary glands
- just production, not necessarily release or uptake
What hormones can be released by the posterior pituitary?
- oxytocin
- antidiuretic hormone (ADH) (aka vasopressin)
What’s Oxytocin?
- during delivery, it anhances smooth muscle contraction of the uterus
- post-partum, it stimulates milk ejection (release of – as opposed to production)
- part of a positive feedback loop
Describe Antidiuretic Hormone (ADH)
- decreases urine production
- causes arteriolar vasoconstriction
What are some factors that will promote the release of ADH?
- dehydration
- pain/stress/anxiety/trauma
- nicotine
- some medications
What are some factors that will inhibit the release of ADH?
- increased blood volume
- alcohol
Where’s the thyroid gland, what does it produce, and what controls it?
- inferior to the larynx
- produces thyroid hormones and cacitonin
- activity is controlled by the hypothalamus-pituitary
What do Thyroid Hormones do?
- increase basal metabolic rate (base metabolic level)
- maintain body temperature
- stimulate protein synthesis
- increasse the use of glucose and lipids to generate ATP
- mobilize lipids and anhance cholesterol excretion
- enhance the actions of norepinephrine and epinephrine (= increased HR, increased heartt contractility, increased BP)
- with hGH and insulin, body growth accelerates
What does Calcitonin do?
decreases blood calcium levels by inhibiting osteoclast activity
What’s epinephrine?
adrenaline
Where is the Parathyroid Gland and what does it do?
- located on the posterior aspect of the thyroid gland
- secrete parathyroid hormone (PTH)
- increase blood calcium, magnesium, and phosphate levels by increasing the number and activity of osteoclasts
- also works on the kidneys to decrease their secretion of calcium and magnesium and to promote the formation of calcitriol (active form of vit D)
Each Adrenal Gland has an Adrenal Cortex and Adrenal Medulla. What do each release?
Adrenal cortex releases:
- aldosterone
- cortisol
- androgens
Adrenal medulla releases:
- epinephrine (adrenaline)
- norepinephrine (noradrenaline)
- both are released during stress and exercise – they increase the SyNS response)
(cortex = bark (outside); medulla is inside)
What does Aldosterone do?
- regulates sodium and potassium levels
- helps regulate blood pressure/volume
- helps in the elimination of H+ (acid)
- stimulates the kidneys to reabsorb sodium and water and stimulates arteriolar smooth muscle contraction
- released in response to dehydration, sodium deficiency, hemorrhage
What do Androgens do?
- during puberty: stimulate axillary and pubic hair growth
- males (after puberty): weak
- femails (after puberty): function in libido and are converted to estrogens
What does the Pineal Gland do?
- secretes melatonin to regulate sleep cycles
- increased secretion in darkness, decreased secretion in sunlight
What does the Thymus do?
hormones promote the maturation of T cells
What do Ovaries do?
- secrete estrogens and progesterone which (along with FSH and LH) regulate the menstrual cycle, maintain pregnancy and prepare the mammary glands for lactation
- they also initiate/maintain the 2o female sex charateristics
- with the placenta, they secrete relaxin which increases tissue/joint compliance in preparation for delivery
What do Testes do?
secrete testosterone which regulates sperm production and initiates/maintains the 2o male sex characteristics
Where is the Pancreas located?
located in the curve of the duodenum
Pancreatic islets (islets of Langerhans) are the endocrine cells which secrete:
- glucagon
- insulin
- somatostatin
What does Glucagon do?
- increases blood glucose levels
- stimulates hepatocytes to release glucose from their stores
- triggered by hypoglycemia, exercise
What does insulin do?
- decreases blood glucose levels
- it stimulates:
- body cells to take up glucose from the blood
- hepatocytes to uptake and store glucose (as glycogen)
- hepatocytes to slow their release of glucose
- triggered by hyperglycemia
- also triggered by hGH, ACTH, PaNS, some amino acids, and the GI tract
What does Somatostatin do?
- inhibits glucagon and insulin release
- may slow GI absorption
What hormones can the kidneys release and what do those hormones do?
- erythropoietin (EPO) stimulates RBC production
- calcitriol (active form of vidD)
What hormones can the stomach/intestine release?
- gastrin
- CCK
- secretin
What hormones can the heart release and what do those hormones do?
atrial naturetic peptide (ANP) decresase BP
What hormone can adipose release and what does that hormone do?
leptin suppresses appetite
What hormone can the placenta release and what does that hormone do?
human chorionic gonadotropin (hCG) helps maintain pregnancy
What hormone can the liver/skin release and what does that hormone do?
calcitriol (active form of vitD) – starts in skin, continues in liver, ends in kidneys
