What is an example of controlled secretion by nervous and hormonal mechanisms?
The volume and content of gastric secretion
How does the secretion of gastric juices work?
Sight and smell of food causes the brain so send nerve impulse via the vagus never from the medullla- gland cells in the stomach walls are stimulated to secrete components of gastric juice
Where do Exocrine glands secrete to?
salivary glands, the pancreas , gland cells in the stomach wall and the wall of the small intestine
To the surface of the body or the lumen of the gut
What do exocrine glands secrete into?
Ducts - secretary cells are in groups around the duct brunch- each group of cells is called an acinus
What do exocrine glands secrete
Structure of exocrine gland?
1) endoplasmic reticulum for syntheses of enzymes
2) mitochondria to provide ATP for protein synthesis and other cell activity
3) large number of secretory vesicles containing enzymes
The inner surface of the ileum has numerous folds- each of the folds is covered in tiny projections called villi- where does absorption take place??
Through the epithelial cells covering each villus
Each epithelial cell covering the villus adheres to its neighbours through tight junctions- what does this ensure?
That most materials pas into the blood vessels lining of the villi through the epithelial cell
The cell surface membrane on the intestinal lumen side has a number of extensions called the micro villi- what is the collection of micro villi on the intestinal side of the epithelial cells calledV what do they do?
The brush border
Function is to increase the surface area for absorption
What is the adaption of the epithelial cells regarding ATP
High amounts of ATP are needed to drive active transport - so epithelial cells have large numbers of mitochondria
Adaption of pinocytic vesicles (regards to epithelial adaptions)
Often present in large numbers due to absorption of some foods by endocytosis
What is the surface facing the lumen of the intestine referred to as? And the surface facing the blood vessels referred to as? What do they do?
Have different types of proteins involved in material transport
How and who discovered the role of gastric acids in digestion?
William Beaumont while observing the process of digestion in an open wound caused by a gun shot
What is acid secret by in the stomach?
The parietal cells
What does acid inthe stomach do?
Disrupts the extracellular matrix that holds cells together in tissues- it also leads to the denaturing of proteins, exposing the polypeptide chains so that enzyme pepsin can hydrolyse the bonds within peptides
Pepsin is released by chief cells in inactive pepsingon- acid condition me in stomach convert inactive pepsingon into pepsin- ensures that the cells that produce pensinogen are not digested at the same time as the protein in the diet
What are stomach ulcers caused by?
Open sores, caused by partial digestion of the stomach lining by the enzyme pepsin and hydrophilic acid in gastric juices - bacteria helicobacter shown to be more significant cause
Why is stomach acid bad sometimes?
Several diease conditions made worse by release of acid- stomach acid is corrosive so the body produces a natural mucus barrier which protects the lining of the stomach being attacked by the acid- and some people this barrier may be broken down allowing the acid to damage the stomach and cause bleeding- known as a ulcer
Other caused by stomach acids rather than just ulcer?
In others they may be a problem with the circular muscle at the top of the stomach that prevents fluid from escaping stomach- If the muscle is not functioning the acid escapes and irritates they oesophagus- this is called ‘acid reflux’ which can cause a symptom called heartburn
What is a production of the acidic environment in the stomach achieved by?
A proton pump- this pump uses one ATP molecule to exchange two protons from the cytoplasm for two potassium ions in the lumen- one therapy is prescribed proton pump inhibitors for gastric disease
What happens to materials that are not absorbed?
What are the excretory products and what are they egested as?
Water and undigested dietary fibres are egested as feces
What wre the two categories of dietary fibres?
Soluble and insoluble
Why does a healthy balanced diet contain fibre?
As it increases the bulk of material passing through the intestines and helps to prevent constipation as it draws water into the intestine
The higher the water content of the intestine the quicker the movement of fecal matter
What are other benefits of fibre in the diet?
Risk of various diseases of the large intestine may be reduced, including bowel cancer, hemorrhoids and appendicitis
Causes of cholera
Caused by infection by the bacterium Vibrio Cholrea- releases toxin that binds to receptors on intestinal cells A toxin is then brought into the cell by endocytosis- toxin triggered cascade of results that leads to reflux of CL and HCO into intestines- leads to watery diarrhoea because water is drawn up to replace fluid lost in intestines - can result in death
What do nervous and hormonal mechanisms control?
The secretion of digestive juices