secretion Flashcards
What are the two types of secretions, what are the types of glands that produce them, and what are the factors that cause the glands to secrete stuff
2 types of secretion: mucus and digestive enzymes
types of glands: epithelial glands (single cell goblet cells), submucosal glands (small intestines-crypts of Lieberkuhn), deep tubular glands (glands in stomach producing acid and pepsinogen), complex glands emptying into GI tract (salivary, pancreatic, liver glands)
Factors causing glands to secrete products: direct contact (mucus), ENS (tactile stimulation, chemical irritation, gut digestion), ANS (parasympathetics increase secretion, sympathetics alone cause a slight increase in secretion but decreases blood flow via vasoconstriciton)
Salivary glands
Parotid, submandibular, sulingual
Produce 2 types of proteins:
- Ptyalin (alpha amylase) that digests starches (serous glands)
- mucus
Types of glands and products
Parotid: serous
submandibular: serous and mucous
sublingual: serous and mucous
Fomation and secretion of saliva via submandibular gland
Primary secretion via acini:
produces ptyalin, mucus, extracellular fluid
As the saliva moves slowly through the salivary ducts it is modified via: Na active absorption, Cl passive absorption, K active secretion, HCO3- secretion
during maximal salivation there is less time for modification therefore saliva is closer to ECF
Nervous regulation of saliva production:
Parasympathetic controlfrom salivary nuclei in brainstem Taste stimui (particularly acid), Tactile stimuli (particularly smooth objects
Parasympathetic NS also leads to production of kallikrein by salivary gland (precursor to brady kinin) dialates blood vessels
Other areas in CNS such as sight and smell. Gastric and Sm intestine stimulate the salivary glands to neutralize irritating substances
Esophageal secretion
ONLY MUCUS, MUCUS MUCUS cause it lubricates the passage of food and prevents mucosal damage
Gastric secretion
mucus glands- lubricates and protects gastric mucosa against the effects of acid
Oxyntic/gastric glands- most glands located in proximal stomach:
oxyntic/pareital cells-secret acid and intrinsic factor
chief cells- secrete pepsinogen
enterochromaffin-like cells (ECL)- secrete histamine
Pyloric glands: secrete mucus, Gastrin and somatostatin located at the antrum (end of stomach)-
Gastrin produced by G cells in the response to proteins (controlls gastric acid production)
Somatostatin produced by D cells and inhibits gastrin in response to low pH
acid production
Stimuli for acid secretion: histamine (H receptors), Ach- from vagus and ENS (parasymp M cells), gastrin (CCK receptors)
Parietal cell:
Active counter transport of H into the lumen, K into the cell
Cl passive transport into the lumen with H20
Duodenal factors affecting gastric secretion: ENS (gastric secretion inhibited by distension irritation, acidity, in duodenum). Fats and proteins breakdown products and altered osmolarity in duodenum results in release of Secretin which mostly acts on pancreas, but secondary effect is decreasing gastric secretion
Pepsinogen and intrinsic factor
Stimuli for pepsinogen secretion: Ach from para symp, ENS, gastric acid
pepsinogen: secreted by chief cells, activated to pepsin by HcL, begins protein digestion by hydrolizing collagen
intrinsic factor: necessary for vitamin B12 absorption in terminal ileum
Phases of gastric secretion
total gastric secretion: 1500 ml
Cephalic 20% (sight smell, thought of food), originates in cerebral cortex and appetite centers of amygdala and hypothalamus and transmitted to stomach via vagus
Gastric: 70% (vagovagal reflexes from stomach to brain and back to stomach, local enteric reflexes, Gastrin mediated while food is in stomach)
Intestinal phase: minimal ( small amounts due to duodenal production of Gastrin)
Pancreatic secretion
is both exocrine and endocrine Phases of pancreatic secretion: Cephalic 20%- mostly digestive Gastric 5%- mostly digestive Intestinal 75%- increased amount of water (secretin)
CCk is released in response to proteins
Regulation of pancreatic secretion: acid from stomach releases secretin from duodenal wall. fats and amino acids cause the release of CCK. Vagal stimulation releases enzymes into acini, secretin causes lots of pancreatic secretion and bicarbonate. CCK causes secretion of enzymes. then secretin and CCK is absorbed back into the blood stream
Pancreatic secretion stimuli: ACh- acini, CCK- acini, secretin- pancreatic duct epithelium (prosecretin converted to secretin in low pH)
Proteins
trypsin, chymotrypsin and carboxypolypeptidase (secreted in inactive forms). Trypsin further activates trypsinogen and activates carboxytrypsin and chymotrypsin
Full proteins get get broken down into big chunks via pepsin then those chunks get further broken down by trypsin, chymotrypsin ets and then peptidases break up into AAs
Carbohydrates
mainly amylases break down:
Starches get broken down in saliva (ptyalin 20-40%) and pancreatic amylase (50-80%)
Then maltose and 3-9 glucose polymers get broken down to glucose by maltase, dextrase, lactose and sucrase. Lactase and sucrase also make a galactase and fructose respectively
Fat digestion
Fat-> emulsified via bile and agitation
emulsified fat-> FAs andTGs via pancreatic lipases
bile salts form micelles and remove monoglycerides and FAs and transport them to brush border for absorbtion
Bicarbonate secretion
in ductule cells CA takes Co2 and H20 and makes it into bicarb and H
Bicarb and NA (with h20) get secretd in lumen) via secreten
Hepatic histology
Hepatic artery bring in 1/3 of blood, 2/3 of blood is braught in by portal vein.
At every corner of every lobule of the liver receives a branch of the portal vein, hepatic artery. All those branches from both the hepatic artery and the portal vein drain into the central vein of each lobule
At each corner of the lobule, the hepatic artery and the portal vein combo drain into a common Sinusoid. Sinusoids have a fenestrated lining made of Kupffer cells. The basement side of the Kupffer cells are the hepatocytes. The space between the Kupffer cells and the hepatocytes is the space of Disse. The space of Disse is where the hepatocytes input the good proteins and takes out the bad stuff via lymphatics.
the hepatocytes also form a tube that makes bile, where the bile can flow from the center out at each corner into a bile duct
Kupffer cells are macrophages that eat up bad stuff in the sinusoids
in the space of disse- there is a stellate ito cell that produces collagen (in stress)
Zonation (as you get closer and closer to the central veins 1-3 you get less blood supply)
