H.2.1 State that digestive juices are secreted into the alimentary canal by glands, including salivary glands, gastric glands in the stomach wall, the pancreas and the wall of the small intestine.
Digestive juices are secreted into the alimentary canal by glands, including salivary glands, gastric glands in the stomach wall, the pancreas and the wall of the small intestine.
H.2.2 Explain the structural features of exocrine gland cells.
Exocrine glands are responsible for the release of digestive fluids. Exocrine glands secrete into ducts. Exocrine gland has a duct portion and a glandular portion. At the end of each branch is an acinus formed at secretory cells of two types: serous cells
H.2.3 Compare the composition of saliva, gastric juice and pancreatic juice.
saliva (from salivary glands) consists of: water, electrolytes, salivary amylase, mucus, lysozyme (which works as antibacterial fluid)
gastric juice (from stomach) consists of: water, mucus, enzymes (pepsin, rennin), HCl
pancreatic juice (from pancreas) c
H.2.4 Outline the control of digestive juice secretion by nerves and hormones, using the example of secretion of gastric juice.
The initial release of gastric juice occurs under nerve stimulation after sight or smell of food.
The sustained release occurs under the influence of gastrin secreted when food is in the stomach.
H.2.5 Outline the role of membrane-bound enzymes on the surface of epithelial cells in the small intestine in digestion.
Some of the enzymes are immobilized on the membranes of the intestinal epithelium cells. The active sites of the enzymes are oriented toward the lumen of the intestine. They remain functional even when epithelial cells have been sloughed off into the lume
H.2.6 Outline the reasons for cellulose not being digested in the alimentary canal.
Humans lack the digestive enzyme cellulase, the dietary cellulose remains undigested and is egested in the feces. In some animals the symbiotic relationship developed with cellulose-digesting bacteria.
H.2.7 Explain why pepsin and trypsin are initially synthesized as inactive precursors and how they are subsequently activated.
Pepsinogen and trypsinogen are inactive forms of enzymes. This is done to prevent self-digestion of the cells that produce those inactive enzymes (known as the zymogens).
Pepsinogen (in stomach) is converted into pepsin by the acidic conditions, the hydro
H.2.8 Discuss the roles of gastric acid and Helicobacter pylori in the development of stomach ulcers and stomach cancers.
A stomach ulcer is an open sore in the stomach wall, where digestive juices - mostly acid and the enzyme pepsin - have begun to eat away the stomach lining.
It is now recognized that about 80 per cent of ulcers are caused by infection from a bacterium cal
H.2.9 Explain the problem of lipid digestion in a hydrophilic medium and the role of bile in overcoming this.
Lipids tend to coalesce (lump together), in an aqeuous environment, due to their water insolubility. When the lipids clump it decreases the surface area-volume ratio, meaning the lipase have less surface to attach to. They can only bind to the lipids on t
H.3.1 Draw and label a diagram showing a transverse section of the ileum as seen under a light microscope.
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H.3.2 Explain the structural features of an epithelial cell of a villus as seen in electron micrographs, including microvilli, mitochondria, pinocytotic vesicles, and tight junctions.
Villi - provide a huge surface area for absorption
Epithelium cells - single layer of small cells, packed with mitochondria - the source of ATP (metabolic energy) for active uptake across the plasma membrane
Mitochondria - these organelles are present in
H.3.3 Explain the mechanisms used by the ileum to absorb and transport food, including facilitated diffusion, active transport and endocytosis.
Facilitated diffusion. Some substances need a little assistance to enter and exit cells. The transmembrane protein helps out by changing shape.
Active transport. Some substances need a lot of assistance to enter cells. Similar to swimming upstream, energy
H.3.4 List the materials that are not absorbed and are egested.
The materials that are not absorbed and are egested are cellulose and lignin from plant matter, the remains of intestinal epithelial cells, bile pigments, and bacteria.
H.4.1 Outline the circulation of blood through liver tissue, including the hepatic artery, hepatic portal vein, sinusoids and hepatic vein.
The liver is served by the hepatic artery, which delivers oxygenated blood, and it is drained by the hepatic vein. In addition, there is a portal vein, the hepatic portal vein that brings blood to the liver directly from the small intestine.
The blood bro
H.4.2 Explain the role of the liver in regulating levels of nutrients in the blood.
The normal level of blood glucose in humans is about 90mg per 100cm3(90mg 100cm-3). On arrival in the liver sinusoids, excess glucose is withdrawn from the plasma solution and used in metabolism or stored as glycogen. Glycogen reserves are also stored els
H.4.3 Outline the role of the liver in the storage of nutrients, including carbohydrate, iron, vitamin A and vitamin D.
When certain nutrients are in excess in the blood, hepatocytes absorb and store them, releasing them when they are at too low a level. For example, when the blood glucose level is too high, insulin stimulates hepatocytes to absorb glucose and convert it t
H.4.4 State that the liver synthesizes plasma proteins and cholesterol.
The liver is the site of synthesis of all the blood proteins, including globulins, albumin, prothrombin and fibrinogen. Also, most of the cholesterol required by the body on a daily basis is manufactured in the liver (but the remainder is taken in as part
H.4.5 State that the liver has a role in detoxification.
The liver detoxifies harmful substances such as alcohol (see below), or renders drugs and toxins that have entered the blood stream into harmless forms for excretion from the blood circulation in the kidneys. Drugs such as the antibiotics penicillin and e
H.4.6 Describe the process of erythrocyte and hemoglobin breakdown in the liver, including phagocytosis, digestion of globin and bile pigment formation.
Erythrocytes, also called red blood cells, have a fairly short lifespan of about 120 days. The plasma membrane becomes fragile and eventually ruptures, releasing the hemoglobin into the blood plasma. The hemoglobin is absorbed by phagocytosis, chiefly in
H.4.7 Explain the liver damage caused by excessive alcohol consumption.
Cirrhosis of the liver - a chronic inflammation of the liver in which liver cells are destroyed and replaced by fibrous or adipose (lipid-containing) connective tissue