Topic 6 Flashcards
(34 cards)
Purpose of Digestion
The main purpose of the digestive system is to break large molecules down into smaller subunits due to the fact that:
* Large molecules are typically chemically inert and need to be broken down and reassembled into usable products
* Large molecules are typically insoluble and cannot be easily absorbed into cells, whereas smaller subunits are soluble
Alimentary Canal (directly transfers food)
- Oesophagus – Food tract from mouth to stomach
- Stomach – Storage tank with low pH (protein digestion)
- Small intestine – Site of nutrient absorption
- Large intestine – Absorbs water and dissolved minerals
Accessory Organs (supports digestive processes)
- Salivary glands – Moistens food bolus (starch digestion)
- Pancreas – Secretes key enzymes into small intestine
- Liver – Metabolises absorbed nutrients (produces bile)
- Gall bladder – Stores and secretes bile (emulsifies fats)
Peristalsis (Digestive Movement )
- Unidirectional movement of food along alimentary canal
- Caused by contraction of sequential longitudinal muscles
Segmentation (Digestive Movement )
- Bidirectional mixing of food within the small intestine
- Caused by contraction of non-sequential circular muscles
Mechanical Digestion
The breakdown of food via physical actions
* Chewing (grinding food using teeth)
* Churning (squeezing stomach contents)
* Segmentation (intestinal contractions)
Chemical Digestion
The breakdown of food via chemical agents
* Stomach acids (low pH environment)
* Bile (emulsification of fats into droplets)
* Enzymes (catalyse hydrolysis reactions)
What is starch composed of
Starch is composed of glucose monomers
* Is linear (amylose) or branched (amylopectin)
Amylase
(salivary or pancreatic) digests starch
* It digests amylose into maltose disaccharides
* It digests amylopectin into dextrin chains
What does the pancreases do
The pancreas regulates the uptake of glucose
* Insulin increases glucose uptake by cells
* Glucagon decreases glucose uptake by cells
What does the liver do
The liver is responsible for glucose storage
* Glucose is stored as glycogen (polysaccharide)
Absorption
involves the movement of fluids or dissolved substances (such as nutrients) across a cellular membrane
* The absorbed components then undergo assimilation within the cell in order to become fluid or solid parts of an organism
Nutrient absorption occurs within the small intestine, while water and mineral ions are absorbed within the large intestine
Secondary Active Transport
Glucose and amino acids are co-transported across the
epithelial membrane with sodium ions (Na+)
Facilitated Diffusion
Certain monosaccharides, vitamins and some minerals
may be transported by epithelial channel proteins
Simple Diffusion
Hydrophobic materials (e.g. lipids) are capable of freely diffusing across the epithelial membrane
Endocytosis
- Dissolved materials may be rapidly absorbed en masse via
the process of pinocytosis (cell ‘drinking’)
Villi
Villi are finger-like mucosal projections that
increase the surface area of epithelium over
which absorption is carried out
Key features of villi include:
* Microvilli (⇧ SA:Vol)
* Rich blood network
* Single layer epithelium
* Lacteals (absorb lipids)
* Intestinal crypts (exocrine)
* Membrane proteins
Dialysis tubing
can be used to model the
size-specific permeability of a membrane
* Large molecules cannot cross (e.g. starch)
* Smaller molecules can cross (e.g. glucose)
If large molecules are digested with enzymes,
the absorption of the smaller subunits can
then be measured in a number of ways:
* Via a change in fluid / meniscus levels
* Via the presence of specific materials
(identified via treatment with a reagent)
Who proposed the modern understanding of the circulatory system
William Harvey
According to Harvey:
- The major blood vessels (arteries & veins) are connected by a single network
- Blood flow is unidirectional (due to the presence of one-way valves)
- The heart is a central pump (arteries = from heart ; veins = to heart)
- Blood flows continuously and is not consumed by the body
Veins
- Transport blood to the heart
- Blood at low pressure (<15 mmHg)
- Walls are thin (with wider lumen)
- Have valves to prevent pooling
Arteries
- Transport blood from the heart
- Blood at high pressure (80-120 mmHg)
- Walls are thick (muscle and elastin)
- Walls stretch or contract with pulse
Capillaries
- Facilitate material exchange
- Blood at low pressure (~10 mmHg)
- Walls made of single layer of cells
- Extremely narrow lumen (~10 µm)
Capillaries may be categorised as:
* Continuous (intact basement membrane)
* Fenestrated (have endothelial pores)
* Sinusoidal (discontinuous membrane)
Blood contains three main elements:
- Red blood cells (transport oxygen)
- White blood cells (fight infections)
- Platelets (responsible for clotting)
