D2 Digestion Flashcards
What mechanisms control the secretion of digestive juices? How?
Nervous and hormonal mechanisms
* nerves and hormones ensure resources are devoted to digestion only when needed
What does the smell, sight, thought of food causes to the brain?
Cause the brain to send nerve impulses via the vagus nerve from the medulla
What are gland cells in the stomach wall stimulated to do?
to secrete components of gastric juice
What do chemoreceptors and stretch receptors have to detect to send impulses to the brain?
Chemoreceptors in the stomach wall detect peptides in the stomach contents
Stretch receptors detect distension of the stomach
Where are chemoreceptors?
in the stomach wall
How does the brain respond to impuleses sent to the brain from chemoreceptors and stretch receptors?
respond by sending impulses via the vagus nerve to endocrine cells in the wall of the duodenum and the part of the stomach nearest to the duodenum, stimulating them to secrete gastrin
What does the hormone gastrin stimulate?
secretion of acid (HCL) and pepsinogen by two types of exocrine gland cell in the stomach wall
What 2 types of exocrine gland cell in the stomach wall is HCL and pepsinogen secreted by?
HCL: Parietal cells
Pepsinogen: Chief cells
What is secreted if pH in the stomach falls too low?
Secretin and somatostatin hormones are secreted to inhibit gastrin secretion
What is the alimentary canal?
the passage thorugh which food passes from mouth to anus
What is the alimentary canal?
the passage thorugh which food passes from mouth to anus
What do exocrine glands do?
Secrete digestive juices
What are examples of exocrine glands?
- salivary glands
- pancreas
- gland cells in the stomach and intestine wall
What is the difference between endo and exocrine glands?
Endo: secrete directly into the bloodstream
Exo: secrete into ducts
What is the arrangement of cells in an exocrine gland?
- secretory cells are in groups (acinus) around the duct branch
What is an acinus?
A group of secretory cells
What is an acinus?
A group of secretory cells
What are the features of an exocrine gland? (3)
- extensive endoplasmic reticulum for synthesis of enzymes
- numerous mitochondria to povide ATP for protein synthesis and other cell activities
- large numbers of secretory vesicles containing enzymes
When can the process of exocytosis be seen in progress in an exocrine gland?
When plasma membrane of vesicles containing enzymes is in contact with the duct
What are the features of a inner surface of the ileum?
- numerous folds
- each folds is covered in tiny projections called villi
Where does absorption take place?
through the epithelial cells covering each villus
What are the adaptations of the villus? (5)
- Tight junctions - between each epithelial cell covering the villus, which ensures that most materials pass into the blood vessels lining the villi through the epithelial cell
- microvilli - extensions that increased cell surface area of membrane on the intestinal lumen side. The collection of microvilli on the intestinal side of the epithelial cells is termed the brush border.
- Large numbers of mitochondria - high amount of ATP to drive active transport processes
- Large numbers of pinocytic vesicles - due to absorption of some foods by endocytosis
- Different types of proteins - on the apical and basal surface for material transport
What is the apical and basal surface?
Apical: the surface facing the lumen of the intestine
Basal: the surface facing the blood vessels
What is acid secreted by in the stomach?
Parietal cells