Regulation of HCl Secretion in Sympathetic Nervous System
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Regulation of HCl Secretion in Sympathetic Nervous System

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Questions and Answers

Match the following respiratory system processes with their descriptions:

Pulmonary ventilation = Air in and out of lungs External respiration = Gas exchange between lungs and blood Transport = Transportation of O2 & CO2 Internal respiration = Gas exchange between blood and tissues

Match the following respiratory system organs with their functions:

Nose = When we inhale, air moistens and warms Pharynx = Includes the nasopharynx (nose area), oropharynx (mouth area), and laryngopharynx (lower throat area) Lungs = Respiratory zone where gas exchange happens Alveoli = Part of the respiratory zone, where gas exchange happens

Match the following respiratory system muscles with their descriptions:

Diaphragm = Involved in the process of pulmonary ventilation External intercostal muscles = Assist in expanding the thoracic cavity during inhalation Internal intercostal muscles = Assist in compressing the thoracic cavity during exhalation Smooth muscle = Present in the bronchioles

Match the following respiratory structures with their corresponding types of epithelium:

<p>Oropharynx = Stratified squamous Laryngopharynx = Stratified squamous Trachea = Pseudostratified ciliated columnar Bronchi = Simple columnar epithelium</p> Signup and view all the answers

Match the following respiratory volumes with their definitions:

<p>Tidal volume (TV) = Amount of air moved in one cycle (regular breathing cycle) Inspiratory reserve volume (IRV) = Air that can be forced in beyond the tidal volume Expiratory reserve volume (ERV) = Air that can be evacuated from lungs after tidal expiration Residual Volume (RV) = The air left even after forcing as much air out after exhalation</p> Signup and view all the answers

Match the following respiratory processes with their corresponding pressure changes:

<p>Inhalation (Inspiration) = Volume increases, Pressure decreases Exhalation (Expiration) = Volume decreases, Pressure increases Intrapulmonary pressure = Pressure within the alveoli (lungs) Intrapleural pressure = Pressure within the pleural sac (between the visceral and parietal pleura)</p> Signup and view all the answers

Match the following cells in the alveoli with their characteristics:

<p>Type 1 Cells = Simple Squamous Type 2 Cells = Simple Cuboidal, Secrete a surfactant</p> Signup and view all the answers

Match the following organs with their key features:

<p>Liver = 4 lobes Large Intestine = 4 areas Stomach = Peristalsis - waves of contraction that move bolus/food forward Rectum = Inferior half of sacrum</p> Signup and view all the answers

Match the following digestive processes with their definitions:

<p>Ingestion = Food entering mouth deglutition/swallowing Propulsion = Movement of food through GI tract Peristalsis -&gt; major means of movement Digestion = Broken down into physical and chemical breakdown of food Mechanical digestion -&gt; movement oriented (chewing, segmentation etc) Chemical digestion -&gt; complex molecules broken down into chemical components Absorption = Transport of nutrients into bloodstream</p> Signup and view all the answers

Match the following sphincters with their control:

<p>Internal Sphincter = Control over external but not internal sphincter External Sphincter = Control over external but not internal sphincter</p> Signup and view all the answers

Match the following phases of gastric secretion with their descriptions:

<p>Cephalic Phase = Preparation for food entry P. symp nervous system (vagus) controls this (+) Sight, smell, taste or thought of good (-) depression, loss of appetite Gastric Phase = Once food enters - enhanced secretion (+) chemoreceptors -&gt;peptides, caffeine, rising pH (+)Stomach distension-&gt; stretch receptors (+) neural -&gt; plexuses (+) hormonal -&gt; secretion of gastrin (-) pH lower than 2 (-) emotional upset overriding p.</p> Signup and view all the answers

Match the following gas laws with their descriptions:

<p>Dalton's Law = Total pressure exerted by a mixture of gases is the sum of the pressure of the individual gases Henry's Law = The more pressure you exert on gas over a solution/liquid, the gas will dissolve proportionately into the liquid to its own partial pressure Fick's Law = Describes the factors that affect the rate of diffusion of gases Hemoglobin Saturation Curve = Shows the relationship between partial pressure of oxygen and the saturation of hemoglobin</p> Signup and view all the answers

Match the following terms related to gas exchange with their definitions:

<p>Ventilation = Amount of gas reaching alveoli (lungs) Perfusion = The amount of blood flow reaching the alveoli (lungs) Partial Pressure Gradients = The difference in partial pressure of gases that drives their diffusion across membranes Hemoglobin Saturation = The percentage of heme groups in hemoglobin that have oxygen bound to them</p> Signup and view all the answers

Match the following equations with the correct gas exchange process:

<p>$CO2 + H2O \rightarrow H2CO3 \rightarrow H+ + HCO3-$ = Carbon dioxide transportation in blood $PO2 = 760mmHg \times 0.21$ = Partial pressure of oxygen in air $PO2 = 100mmHg \rightarrow 40mmHg$ = Partial pressure of oxygen change in external respiration $PO2 = 40mmHg \rightarrow 100mmHg$ = Partial pressure of oxygen change in internal respiration</p> Signup and view all the answers

Match the following factors with their effects on the affinity of hemoglobin for oxygen:

<p>$pCO2$ = Increase decreases the affinity for oxygen Temperature = Increase decreases the affinity for oxygen $H+$ = Increase decreases the affinity for oxygen DPG = Increase decreases the affinity for oxygen</p> Signup and view all the answers

Match the following respiratory terms with their correct descriptions:

<p>Hyperventilation = Increased depth and rate of breathing to assist in flushing CO2 Hypoventilation = Slow and shallow breathing to assist in retaining CO2 Hypoxic drive = When pCO2 levels are chronically high, the chemoreceptors get desensitized and body relies on pO2 levels as respiratory stimulus Arterial pH = Changes in arterial pH can modify respiratory rate</p> Signup and view all the answers

Match the following parts of the digestive system with their correct descriptions:

<p>Oral cavity = Includes hard &amp; soft palates, and uvula that triggers epiglottis Esophagus = Continuation of the pharynx and carries solids and liquids to stomach Stomach = Includes cardia, fundus, body, pylorus, and rugae Small Intestine = Includes duodenum, jejunum, ileum, and ileocecal sphincter</p> Signup and view all the answers

Match the following stomach cells with their correct secretions:

<p>Mucous neck Cells = Mucus Parietal Cells = HCL and intrinsic factor Chief cells = Pepsinogen Enteroendocrine cells = Gastrin, histamine, cholecystokinin</p> Signup and view all the answers

Match the following small intestine structures with their correct descriptions:

<p>Plicae circulares = Circular folds of the mucosa Villi = Fingerlike projections for mucosa Microvilli = Villi on each individual cell Lacteals = Lymphatic vessel of the small intestine</p> Signup and view all the answers

Match the following respiratory control components with their descriptions:

<p>Medullary Respiratory DRG = Sets basic breathing rate VRG = Involved in forced breathing (inspiration and expiration) Pontine Respiratory Group = Smoothes breathing Central Chemoreceptors = Monitor levels of pCO2 in CNS</p> Signup and view all the answers

Match the following effects with their definitions:

<p>Haldane Effect = Removing O2 from Hemoglobin increases the ability of hemoglobin to then go and pick up CO2 and CO2 generated H+ Bohr Effect = At the tissue level, as more CO2 enters blood, more O2 dissociated with hemoglobin Pulmonary irritant reflexes = Irritants promote reflexive constriction of airways Respiratory Control center = Signals to the body to increase ventilation</p> Signup and view all the answers

Match the following chemical reactions with their descriptions:

<p>$CO2 + H2O \rightarrow H+ + HCO3^-$ = CO2 links up with H2O and kicks off the fancy formal resulting in H+ and HCO3 $H+ + CO2 \rightarrow Respiratory Control Center$ = H+ and CO2 bind to the Central Chemoreceptor on the medulla (through the CSF) which then sends a signal to the Respiratory Control center $Increase arterial pCO2 \rightarrow Decrease in pH$ = Increase in arterial pCO2 leads to a decrease in pH $Increase ventilation \rightarrow Decrease in CO2 in body$ = Increase in ventilation leads to a decrease in CO2 in the body</p> Signup and view all the answers

Match the following components with their roles in respiration:

<p>Respiratory centers = Activate respiratory muscles Phrenic and intercostal nerves = Used by DRG &amp; VRG to communicate actions Cerebral motor cortex = Responsible for voluntary breathing, ex holding breath Limbic system = Controls breathing during emotional situations, ex having anxiety</p> Signup and view all the answers

Match the following parts of the digestive system with their functions:

<p>Large Intestine = Absorb water and electrolyte, compact remaining material to feces Stomach = Relax ileocecal sphincter allows chyme to move to large intestine Rectal Walls = Distention stimulates contraction of rectal walls Enteric Nervous System = Largest and most complex unit of the peripheral nervous system containing the GI tract</p> Signup and view all the answers

Match the following types of control with their descriptions:

<p>Intrinsic Control = Stimulus (food, stretch etc) -&gt;receptors (chemo-mechano etc) -&gt;local enteric nerve plexus-&gt;smooth muscle or glands create response -&gt; response is contraction or secretion Extrinsic Control = Stimulus (seeing/smelling food) -&gt;CNS -&gt;local nerve plexus -&gt; smooth muscle or glands create response -&gt; response is contraction or secretion Local Mechanisms = Respond to changes in pH, physical and chemical stimuli Neural &amp; Hormonal = Coordinate glands to enhance or inhibit smooth muscle Digestion &amp; Absorption of nutrients</p> Signup and view all the answers

Match the following types of reflexes with their functions:

<p>Gastroileal reflex = Relax ileocecal sphincter allows chyme to move to large intestine Mechanoreceptors and chemoreceptors = Detect stimulus: Stretch, osmolarity, pH, presence of substrate, end products Enteric Nervous System = Controls GI tract motility Intrinsic (short/local) reflexes = Initiate reflexes that activate or inhibit digestive glands</p> Signup and view all the answers

Match the following hormones with their roles in the digestive system:

<p>Gastrin = Relax ileocecal sphincter allows chyme to move to large intestine Intrinsic Hormones = Activate or inhibit digestive glands GI hormones = Influence smooth muscle Extrinsic Hormones = Arise from outside the GI tract like CNS</p> Signup and view all the answers

Match the following gastrointestinal hormones with their functions:

<p>Gastrin = Increase secretion of HCl and pepsinogen, enhance gastric motility, help maintain digestive tract lining Secretin = Stimulate pancreatic duct cells to produce NaHCO3, stimulate liver to produce NaCO3 rich bile, inhibit gastric emptying, inhibit gastric secretion CCK (cholecystokinin) = Inhibit gastric motility and secretion, stimulate pancreatic acinar cells to secrete pancreatic enzymes, contract the gallbladder GIP (Glucose-dependent Insulinotropic Peptide) = Stimulate insulin release, inhibit gastric activity</p> Signup and view all the answers

Match the following organs with their functions:

<p>Liver = Produce bile, process blood-borne nutrients, store fat-soluble vitamins, detoxify Gallbladder = Store and concentrate bile, release bile via cystic duct Pancreas (Endocrine Functions) = Maintains blood glucose levels, release insulin to bring BGL down, release glucagon to bring BGL up Pancreas (Exocrine functions) = Digestion, secrete enzyme-rich pancreatic juice, secrete bicarbonate-rich pancreatic juice</p> Signup and view all the answers

Match the following regulation mechanisms with their descriptions:

<p>HCL secretion regulation = HCl is low if only 1 ligand binds to parietal cells, HCl is high if all 3 ligands bind to parietal cells Gastric emptying regulation = Gastric emptying controlled by enterogastric reflex &amp; enterogastrone, carb-rich food moves fast through duodenum, fat-rich food digested more slowly in stomach Bile release regulation = Fatty &amp; acidic chyme signals to duodenum to secrete CCK and secretin, secretin and bile salts stimulate liver to produce more bile, CCK stimulate vagus nerve causing gallbladder contraction Pancreatic secretion regulation = Secretin and CCK released when fatty &amp; acidic chyme enters duodenum, CCK helps pancreas secrete enzyme-rich pancreatic juice, Secretin helps pancreas secrete bicarbonate-rich pancreatic juice</p> Signup and view all the answers

Match the following hormones with their stimulants:

<p>Gastrin = Stimulated by protein Secretin = Stimulated by presence of acid in duodenum CCK (cholecystokinin) = No specific stimulant mentioned in the text GIP (Glucose-dependent Insulinotropic Peptide) = No specific stimulant mentioned in the text</p> Signup and view all the answers

True or false: The respiratory system consists of four separate processes.

<p>True</p> Signup and view all the answers

True or false: External respiration occurs between the lungs and the blood.

<p>True</p> Signup and view all the answers

True or false: The nose functions to moisten and warm the air we inhale.

<p>True</p> Signup and view all the answers

True or false: The oropharynx is lined with stratified squamous epithelium.

<p>True</p> Signup and view all the answers

True or false: The larynx is responsible for producing vocal sounds.

<p>True</p> Signup and view all the answers

True or false: The trachea is lined with pseudostratified ciliated columnar epithelium.

<p>True</p> Signup and view all the answers

True or false: Boyle's law states that pressure and volume of gas are directly proportional.

<p>False</p> Signup and view all the answers

Peripheral chemoreceptors sense changes in pCO2 and pH, but not pO2.

<p>True</p> Signup and view all the answers

Hyperventilation assists in flushing CO2 out of the body.

<p>True</p> Signup and view all the answers

Hypoventilation occurs in response to respiratory acidosis.

<p>True</p> Signup and view all the answers

The pharynx is a common passageway for food and air.

<p>True</p> Signup and view all the answers

True or false: Dalton's Law states that the total pressure exerted by a mixture of gases is the sum of the pressure of the individual gases?

<p>True</p> Signup and view all the answers

True or false: CO2 is 20 times more soluble than Oxygen according to Henry's Law?

<p>True</p> Signup and view all the answers

True or false: Tissue surface area and tissue thickness affect the rate of gas diffusion according to Fick's Law?

<p>True</p> Signup and view all the answers

True or false: Vasoconstriction occurs when alveolar CO2 is high and O2 is low?

<p>True</p> Signup and view all the answers

True or false: Carbonic acid is split into H2O and CO2 in the alveoli.

<p>False</p> Signup and view all the answers

True or false: Removing O2 from Hemoglobin increases the ability of hemoglobin to pick up CO2.

<p>True</p> Signup and view all the answers

True or false: As more CO2 enters the blood, more O2 dissociates with hemoglobin at the tissue level.

<p>True</p> Signup and view all the answers

True or false: The Medullary Respiratory DRG sets the basic breathing rate.

<p>True</p> Signup and view all the answers

True or false: The release of gastrin stimulates the secretion of HCl and pepsinogen.

<p>True</p> Signup and view all the answers

True or false: Secretin stimulates the production of NaHCO3 by the pancreas.

<p>True</p> Signup and view all the answers

True or false: CCK inhibits gastric motility and secretion.

<p>True</p> Signup and view all the answers

True or false: Bile salts emulsify fat and facilitate fat absorption.

<p>True</p> Signup and view all the answers

True or false: The liver has four lobes: left, right, caudate, and quadrate.

<p>True</p> Signup and view all the answers

True or false: The common bile duct is formed by the merging of the common hepatic duct and the cystic duct.

<p>True</p> Signup and view all the answers

True or false: The large intestine has four areas: ascending, transverse, descending, and sigmoid.

<p>True</p> Signup and view all the answers

True or false: The rectum is located in the superior half of the sacrum.

<p>False</p> Signup and view all the answers

True or false: The main function of the large intestine is to absorb water and electrolytes.

<p>True</p> Signup and view all the answers

True or false: The rectal walls contract when they are distended, leading to defecation.

<p>True</p> Signup and view all the answers

True or false: The enteric nervous system is the largest unit of the peripheral nervous system and controls GI tract motility.

<p>True</p> Signup and view all the answers

True or false: Extrinsic control of the digestive system is influenced by the autonomic nervous system and GI hormones.

<p>True</p> Signup and view all the answers

Study Notes

Respiratory System

  • The respiratory system consists of four separate processes: pulmonary ventilation, external respiration, transport, and internal respiration.

Organs Involved

  • Nose, nasal cavity, paranasal sinuses, pharynx, larynx, trachea, bronchi, bronchioles, lungs, and alveoli
  • Muscles involved: diaphragm, external and internal intercostal muscles, and smooth muscle

Conducting Zone

  • Nose to terminal bronchioles
  • 23 series of branching in bronchioles

Respiratory Zone

  • Surface area in lungs where gas exchange happens (respiratory bronchioles to alveoli)

Nose

  • Functions:
    • Deflects particulate to mucus surfaces
    • Houses nasal conchae (superior, middle, and inferior)
    • Houses nasal meatuses (grooves under each concha) to increase turbulence and surface area
  • Nasopharynx:
    • Pseudostratified ciliated columnar epithelium (respiratory mucosa)
    • Used to move mucus
    • Has some goblet cells
    • Cilia used to filter air and move contaminants to the back to be swallowed

Pharynx

  • Includes:
    • Nasopharynx (nose area)
    • Oropharynx (mouth area)
    • Laryngopharynx (lower throat area)
  • Mucosal lining changes along the length of the pharynx
  • Oropharynx: stratified squamous epithelium
  • Palatine and lingual tonsils
  • Laryngopharynx: stratified squamous epithelium
  • Passageway for food and air

Larynx

  • Produces vocal sounds via vocal folds/cords
  • The connection between the pharynx and the trachea
  • Upper half: stratified squamous epithelium
  • Lower half: pseudostratified ciliated columnar epithelium
  • Three big cartilages: thyroid cartilage (Adam's apple), epiglottis, and cricoid

Trachea

  • Descends into the mediastinum
  • Pseudostratified ciliated columnar epithelium
  • Carina: marks the division of the trachea into two primary bronchi

Bronchial Tree

  • Primary, secondary, tertiary, and bronchioles
  • Bronchi: simple columnar epithelium
  • Bronchioles and terminal bronchioles: simple cuboidal epithelium
  • Smooth muscle in bronchioles allows for widening when sympathetically stimulated and constricting under parasympathetic stimulation

Lungs

  • Anatomy: left has 2 lobes, right has 3 lobes
  • Cardiac notch: heart
  • Pleurae: parietal pleura and visceral pleura
  • Respiratory bronchioles: between terminal bronchioles and alveolar ducts
  • Alveolar sacs: clusters of alveoli
  • Alveoli: respiratory membrane made up of alveolar and capillary walls + their basal lamina (alveolar epithelium -> fused basement membrane -> capillary endothelium)
  • Type 1 cells: simple squamous
  • Type 2 cells: simple cuboidal
  • Secrete a surfactant to prevent attraction of liquid molecules/reduce surface tension
  • Surrounded by elastic fibers
  • Have alveolar pores

Pulmonary Ventilation

  • Physical air in and out of the lungs
  • Lung volume changes during inspiration and exhalation
  • Causes pressure change, which allows for gases to flow across the membrane to equalize pressure

External Respiration

  • Gas exchange between the lungs and the environment
  • Based on partial pressure gradients and gas solubility
  • Alveolar ventilation and pulmonary perfusion
  • Respiratory membrane structure

Dalton's Law

  • Total pressure exerted by a mixture of gases is the sum of the pressure of the individual gases
  • Partial pressure: the pressure of an individual gas from a mixture of gases

Henry's Law

  • The more pressure you exert on a gas over a solution/liquid, the more the gas will dissolve proportionately into the liquid to its own partial pressure
  • The amount also depends on how soluble the gas is

Fick's Law

  • Law of diffusion
  • Factors that affect the rate of diffusion:
    • Tissue surface area
    • Tissue thickness
    • Diffusion coefficient of the gas
    • ΔP (difference in partial pressure)

Internal Respiration

  • Gas exchange between the blood and body tissues

Transport of Oxygen

  • Hemoglobin: 98% saturated (never higher) if healthy
  • 2% dissolved in plasma
  • Males: 201 ml O2/Liter
  • Females: 174 ml O2/Liter
  • A saturated hemoglobin: all four heme groups have an O2 molecule
  • Partially saturated: 1-3 heme groups have an O2 molecule
  • Rate of hemoglobin binding and releasing O2 affected by:
    • pO2 (partial pressure of O2)
    • pCO2 (partial pressure of CO2)
    • Temperature
    • Blood pH (H+)
    • DPG (2,3-bisphosphoglycerate)
  • Hemoglobin saturation curve: normal curve, pO2 40mmHg = 75% saturation, pO2 100mmHg = 98% saturation

Transport of Carbon Dioxide

  • Transported in the blood via:
    • Dissolved in plasma (7-10%)
    • Bound to hemoglobin (20%)
    • Bicarbonate in plasma (most - 70%)
  • CO2 diffuses into RBCs and combines with water to form carbonic acid, which dissociates to hydrogen and bicarbonate ions
  • Chloride shift: bicarbonate quickly diffuses out of the RBC and into the plasma, and chloride ions move into the RBC for balance

Control of Respiration

  • Medullary Respiratory DRG (Dorsal Respiratory Group)
    • Sets basic breathing rate
    • Controls muscles of inspiration and stops neural impulses during exhalation
  • VRG (Ventral Respiratory Group)
    • Involved in forced breathing (inspiration and expiration)
  • DRG and VRG use phrenic and intercostal nerves to communicate actions (efferent pathway)
  • Pontine Respiratory Group: smooths breathing

Central Chemoreceptors

  • Chemoreceptors in the medulla monitor levels of pCO2 in the CNS

  • Signal to make sure enough pH isn't too much

  • Rise of pCO2: the original stimulus, but the rate of breathing is actually dependent on the H+ ion concentration in the cerebrospinal fluid

  • H+ and CO2 bind to the central chemoreceptor on the medulla, which then sends a signal to the respiratory control center

  • Drop in pH results in pulmonary respiration### Intestinal Phase

  • Partially digested food enters the duodenum, releasing hormones that control the rate of gastric emptying

  • The presence of partially digested food, distension of the duodenum, low pH, and fatty, acidic, or hypertonic chyme inhibit gastric emptying

  • Irritants in the duodenum also inhibit gastric emptying

Regulation of HCl Secretion

  • HCl is stimulated by ACh, histamine, and gastrin through a G-protein coupled receptor (GPCR) 2nd-messenger system
  • HCl is low if only one ligand binds to parietal cells
  • HCl is high if all three ligands bind to parietal cells

Regulation of Gastric Emptying

  • Gastric emptying is controlled by the enterogastric reflex and enterogastrone (hormonal mechanism)
  • The enterogastric reflex inhibits gastric emptying in response to distension of the duodenum
  • Hormonal mechanisms (enterogastrone) involve the secretion of hormones into the bloodstream to stop gastric emptying
  • Carbohydrate-rich foods move quickly through the duodenum, while fat-rich foods are digested more slowly in the stomach

Gastrointestinal Hormones

  • Gastrin is stimulated by protein and functions to increase HCl and pepsinogen secretion, enhance gastric motility, and help maintain the digestive tract lining
  • Gastrin is inhibited by the accumulation of acid
  • Secretin is stimulated by the presence of acid in the duodenum and functions to stimulate pancreatic duct cells to produce NaHCO3, stimulate the liver to produce NaCO3-rich bile, inhibit gastric emptying, and inhibit gastric secretion
  • Secretin is also trophic to the exocrine pancreatic glands
  • CCK (cholecystokinin) functions to inhibit gastric motility and secretion, stimulate pancreatic acinar cells to secrete pancreatic enzymes, and contract the gallbladder
  • GIP (glucose-dependent insulinotropic peptide) functions to stimulate insulin release, inhibit gastric activity, and inhibit gastric secretion

Digestion and Absorption in the Stomach

  • Preliminary digestion of proteins and carbohydrates occurs in the stomach
  • Very little nutrient absorption occurs in the stomach, except for lipid-soluble drugs like alcohol

Small Intestine

  • The glands of the duodenum function to moisten chyme, buffer acids, and maintain digestive material in solution
  • Hormones secreted in the small intestine include secretin, CCK, and GIP

Liver

  • The liver is composed of hepatocytes that produce bile, process blood-borne nutrients, store fat-soluble vitamins, and detoxify
  • Bile is a yellow-green alkaline solution containing bile salts, bile pigments, cholesterol, neutral fats, phospholipids, and electrolytes
  • Bile salts are cholesterol that emulsify fat and facilitate fat and cholesterol absorption

Regulation of Bile Release

  • Fatty and acidic chyme signals the duodenum to secrete CCK and secretin
  • Secretin and bile salts stimulate the liver to produce more bile
  • CCK stimulates the vagus nerve, causing gallbladder contraction
  • The hepatopancreatic sphincter relaxes, allowing bile to be released into the duodenum

Gallbladder

  • The gallbladder stores and concentrates bile by absorbing its water and ions
  • The gallbladder releases bile via the cystic duct and bile duct

Pancreas

  • The pancreas has endocrine functions, including maintaining blood glucose levels through the release of insulin and glucagon
  • The pancreas has exocrine functions, including digestion and secretion of pancreatic juice
  • Acini (secretory acinar cells) contain zymogen granules with digestive enzymes
  • Pancreatic juice enters the duodenum

Regulation of Pancreatic Secretion

  • Secretin and CCK are released when fatty and acidic chyme enters the duodenum
  • CCK helps the pancreas secrete enzyme-rich pancreatic juice
  • Secretin helps the pancreas secrete bicarbonate-rich pancreatic juice
  • Vagal stimulation helps release pancreatic juice

Digestion in the Small Intestine

  • When chyme enters the duodenum, proteins and carbohydrates are partially digested, and fat digestion has not started yet
  • Mixing starts to occur with the combination of juices
  • All nutrient absorption takes place in the small intestine

Control of Motility

  • Enteric neurons of the GI tract coordinate intestinal movements
  • Cholinergic neurons (from the parasympathetic nervous system) cause contractions and distension
  • The gastroileal reflex and gastrin relax the ileocecal sphincter, allowing chyme to move to the large intestine

Large Intestine

  • Barely any nutrients are left at this stage, as the rest are digested by bacteria
  • Main functions of the large intestine include absorbing water and electrolytes, compacting remaining material to feces, absorbing vitamins produced by bacteria, and storing feces
  • Defecation is regulated by distension in the rectal walls, which stimulates contraction of the rectal walls

Regulation of Digestion

  • Intrinsic control involves autonomous smooth muscle pacesetter cells, intrinsic nerve plexuses, and sensory receptors
  • Mechanoreceptors and chemoreceptors detect stimulus, such as stretch, osmolarity, pH, and presence of substrate or end products
  • Intrinsic control initiates reflexes that activate or inhibit digestive glands and mix lumen contents

Extrinsic Control

  • Extrinsic control arises from outside the GI tract, including the CNS, autonomic nervous system, and GI hormones
  • Stimulus from outside the GI tract, such as seeing or smelling food, triggers a response in the CNS, which then sends signals to the local nerve plexus
  • The local nerve plexus then creates a response, which is contraction or secretion of smooth muscle or glands

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Test your knowledge on the regulation of HCl secretion in the intestinal phase of the sympathetic nervous system. This quiz covers factors that stimulate or inhibit HCl secretion in the presence of partially digested food, low pH, and various chyme characteristics.

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