secretion

Examples of secretion in the following topics:

• Type III and Type IV Secretion

  • Effector molecules secreted include proteins, enzymes or toxins.
  • The mechanisms by which pathogenic bacteria secrete proteins involve complex and specialized secretion systems.
  • The type IV secretion systems can either secrete or receive molecules.
  • The type IV secretion system utilizes a process similar to this.
  • This specific secretion system can transport both DNA and proteins.

• Tubular Secretion

  • This secretion is caused mainly by active transport and passive diffusion.
  • Usually only a few substances are secreted, and are typically waste products.
  • Urine is the substance leftover in the collecting duct following reabsorption and secretion.
  • The mechanisms by which secretion occurs are similar to those of reabsorption, however these processes occur in the opposite direction.
  • It is the tubular secretion of H+ and NH4+ from the blood into the tubular fluid is involved in blood pH regulation.

• Cephalic Phase

  • The cephalic phase of gastric secretion occurs even before food enters the stomach via neurological signals.
  • The cephalic phase of gastric secretion occurs even before food enters the stomach, especially while it is being eaten.
  • This phase of secretion normally accounts for about 20 percent of the gastric secretion associated with eating a meal.
  • Cephalic phase causes ECL cells to secrete histamine and increase HCl acid in the stomach.
  • Chemical stimuli (i.e., partially digested proteins, caffeine) directly activate G-cells (enteroendocrine cells) located in the pyloric region of the stomach to secrete gastrin; this in turn stimulates gastric glands to secrete gastric juice.

• Gastric Phase

  • About two-thirds of gastric secretion occurs during this phase .
  • ACh is secreted by parasympathetic nerve fibers of both the short and long reflex pathways.
  • Histamine is a paracrine secretion from the enteroendocrine cells in the gastric glands.
  • The chief cells secrete pepsinogen in response to gastrin and especially Ach, and ACh also stimulates mucus secretion.
  • During the gastric phase, gastrin is secreted.

• Epithelial Membranes

  • The mucous membranes are linings of mostly endodermal origin, covered in epithelium, which are involved in absorption and secretion.
  • These mucus membranes are involved in absorption and secretion.  
  • The term "mucous membrane" refers to where they are found in the body; not every mucous membrane secretes mucus.
  • Secreted mucous traps the pathogens in the body, preventing any further progression of  microbes.
  • Submucosal glands consist of exocrine glands that secrete mucus.

• Hormones of the Digestive System

  • Secretion of gastrin is stimulated by food arriving in the stomach.
  • The secretion is inhibited by low pH.
  • Secretin is in the duodenum and signals the secretion of sodium bicarbonate in the pancreas and it stimulates the bile secretion in the liver.
  • This hormone is secreted in response to fat in chyme.
  • Another function is to induce insulin secretion.

• Control of Hormone Secretion

  • The endocrine system relies on feedback systems to regulate hormone production and secretion.
  • Briefly, neurons in the hypothalamus secrete thyroid releasing hormone which stimulates cells in the anterior pituitary to secrete thyroid stimulating hormone.
  • When these drop below the ideal value the hypothalamus is signalled to begin secreting thyroid releasing hormone again.
  • During birth as the baby moves through the birth canal pressure receptors within the cervix signal the hypothalamus to stimulate the pituitary to secrete oxytocin.
  • Describe the manner in which hormone secretion in the endocrine system is controlled

• Other Hormone-Producing Structures

  • Secretion of gastrin is stimulated by food arriving in stomach.
  • The secretion is inhibited by low pH.
  • Secretin - is in the duodenum and signals the secretion of sodium bicarbonate in the pancreas and it stimulates the bile secretion in the liver.
  • This hormone is secreted in response to fat in chyme.
  • Another function is to induce insulin secretion.

• Glandular Epithelia

  • Functions of epithelial cells include secretion, selective absorption, protection, transcellular transport, and detection of sensation.
  • Secretion is one major function of epithelial cells .
  • Endocrine glands secrete their product into the extracellular space where it is rapidly taken up by the blood vascular system.
  • The exocrine glands secrete their products into a duct that then delivers the product to the lumen of an organ or onto the free surface of the epithelium.
  • The sebaceous glands are microscopic glands in the skin that secrete an oily/waxy matter, called sebum, to lubricate and waterproof the skin and hair of mammals.

• Pancreas

  • As a digestive organ, the pancreas secretes pancreatic juice containing digestive enzymes that assist the absorption of nutrients and the digestion in the small intestine.
  • They are relatively difficult to distinguish using standard staining techniques, but they can be classified by their secretion: α cells secrete glucagon (increase glucose in blood), β cells secrete insulin (decrease glucose in blood), delta cells secrete somatostatin (regulates/stops α and β cells), and PP cells or gamma cells, secrete pancreatic polypeptide.
  • It secretes pancreatic fluid that contains digestive enzymes that pass to the small intestine.