week 8 Flashcards
what does Hb bind to and carry
Hb binds and carries O2 from the lungs to the tissues (iron is required for O2 binding to the Heme group of hemoglobin)
Hb binds and carries CO2 from the tissues back to the lungs
the more O2 bound to 1 Hb molecule …
… the stronger the bond
once Hb loses its first O2, it changes shape and has a lower affinity for the remaining 3. The last O2 is the least tightly bound to Hb
factors that decrease the affinity of O2-Hb binding
increased temp, decreased pH, increased PCO2 in the blood
list the 3 methods of transport of CO2 in the blood
- dissolved in the blood plasma (7-10% of CO2)
- bound to hemoglobin: carbaminohemoglobin (20% of CO2)
- as HCO3- (bicarbonate) in the blood (70%)
what enzyme catalyzes the reaction of CO2 to HCO3-
carbonic anhydrase
HCO3- is reconverted to CO2 once it reaches the pulmonary capillaries
what is the pH of blood under normal conditions
7.34-7.45 - maintained by HCO3-
hyperventilation vs. hypoventilation effect on blood PCO2
more CO2 expired = low blood PCO2
less CO2 expired = high blood PCO2
describe eupnea
normal breathing, one of the most vital functions body carries out as absence of breathing leads to death
define chemoreceptors
specialized cells that respond to changes in concentration of specific chemical
what are central and peripheral chemoreceptors
specialized cells that detect changes in PCO2, PO2 and H+ in the blood and cerebrospinal fluid - in order to control the rate and depth of ventilation
where are central chemoreceptors found
in the medulla - they detect changes in PCO2 and in H+ by monitoring levels in the cerebrospinal fluid - signal sent to regulate rate and depth of breathing in order to return to levels of normal
where are peripheral chemoreceptors found
in the aorta and carotid arteries - they detect changes in PCO2, H+ and PO2 (<70mmHg) - signal sent to medulla to increase rate and depth of ventilation
where does digestion begin
the oral cavity
where does most digestion occur
the stomach
where does most nutrient absorption occur
the small intestine
what are macronutrients used for
used for fuel and as building blocks for many components in the body
- carbs
- fats
- protein
what are micronutrients used for
critical components in all physiological processes
- vitamins
- minerals
what is the primary goal of the digestive system
to break food down in order to get all nutrients into absorbable units
what is the role of the alimentary canal (gastrointestinal (GI) tract
- food moves through this continuous passage (a 9m tube)
- sphincters regulate flow from one compartment to the other
accessory organs
- assist in GI processes
- secretion into the lumen of the GI tract
define digestion
chemical and mechanical breakdown of food into absorbable units
define absorption
nutrients, water and electrolytes are moved from the GI lumen to circulation
define secretion
endocrine and exocrine glands secrete substances into the lumen
define motility
mvmt of material through the GI tract
what are the 4 layers of the wall of the GI tract
- inner epithelium (mucosa)
- the innermost component - a layer of epithelial cells: simple columnar epithelium, with many goblet cells (mucus coats the entire epithelium of the GI tract) - layer of connective tissue (submucosa)
- contains the submucosal plexus (nerve network) - layer of smooth muscle (muscularis externa)
- 2 layers of smooth muscle
- contains the myenteric plexus (nerve network) - outer layer of connective tissue (serosa)
how does the body maintain homeostasis in terms of digestion
in order to maintain homeostasis, the volume of fluid entering the GI tract by intake or secretion must equal the volume leaving the lumen
what are the basic functions of the digestive system (digestion, absorption, secretion and motility) regulated by?
they are regulated by endocrine and nervous systems - the autonomic nervous system and enteric nervous system (a branch of the ANS that is completely contained within the GI tract)
describe peristaltic contractions
peristaltic contractions occur when circular muscles contract just behind the bolus of food - there is a direction of movement
describe segmental contractions
segmental contractions occur when segments of smooth muscle alternatively contract and relax - there is no net forward movement
what are the 3 phases of regulation
- cephalic phase
- gastric phase
- intestinal phase
REVIEW SLIDE 12 (MAR 7)
describe the cephalic phase
- the cephalic phase is mediated by the vagus nerve which carries an output from higher order brain centers
- this phase prepares the GI tract in advance for incoming food
- it is activated in response to sight, smell, taste, and even thought of food
- it stimulates saliva production, gastric and pancreas secretions, and GI hormone release
describe the oral cavity and its role in digestion
main digestive functions:
- mechanical and chemical digestion, secretion, and propulsion
- chewing initiates the process of mechanical digestion
- saliva secretions moisten and soften food, and begin the process of chemical digestion
- propulsion of food from oral cavity to the pharynx (throat) to the esophagus through the process of swallowing
describe saliva as well as its role in digestion
there are 3 pairs of salivary glands that secrete saliva into the oral cavity:
1. parotid glands
2. submandibular glands
3. sublingual glands
saliva consists of: water, electrolytes, mucus, salivary amylase, lysozyme, antibodies, and bicarb ions
salivation is regulated by both the parasympathetic (mainly) and sympathetic divisions of the ANS
define salivary amylase
enzyme that starts the chemical digestion of carbs
what is the role of bicarbonate ions
to help neutralize the acid that may have escaped the stomach
outline the swallowing reflex
- voluntary phase
- the tongue pushes the bolus posteriorly towards the oropharynx - pharyngeal phase
- the bolus enters the oropharynx: the soft palate and epiglottis seal off the nasopharynx and larynx respectively - esophageal phase
- peristaltic waves move the bolus down the esophagus to the stomach
describe the esophagus and its roles in digestion
main functions: propulsion (peristalsis) and secretion (mucous)
top end: upper esophageal sphincter
bottom end: lower esophageal (gastroesophageal) sphincter
what are the 5 anatomical regions of the stomach
- cardia
- fundus
- body
- pyloric antrum
- pylorus (contains the pyloric sphincter which controls the flow between stomach and small intestine)
REVIEW SLIDE 20 (MAR 7)
what are the 3 main digestive functions of the stomach
- secretion
- HCl + intrinsic factor from parietal cells
- pepsinogen + gastric lipase from chief cells
- hormones from neuroendocrine cells - digestion
- mechanical digestion through mixing and churning
- chemical digestion of protein by the enzyme pepsin
- chemical digestion of fat by the enzyme gastric lipase - motility
- mixing and churning of contents: mechanical digestion and mixing of all the secretions with the food bolus - produces chyme
Why do our cells secrete an inactive
form of pepsin (pepsinogen)
to protect the cells of these secretory glands from strong protein digesting action of the enzyme
describe the gastric phase
distention of the stomach wall from incoming food triggers neurons of the enteric NS and sensory receptor that stimulate the vagus nerve
describe the intestinal phase
- triggered by the entry of partly digested protein into the duodenum
- followed by inhibition of HCl secretion via the enterogastric reflex.
- hormones that inhibit HCl secretion when released:
1. secretin
2. gastric inhibitory peptide
describe the motility of the stomach
- receives the bolus from the esophagus by relaxation of the gastroesophageal sphincter, fundus and body of the stomach
- mixing and churning of the food into chyme through waves of peristalsis and segmental contractions
- chyme released into the small intestine is regulated
