Further Human physiology Flashcards
Example of a hormonal steroid
Oestrogen - Increase thickness of uterine lining
Hormonal steroids: Enter cells and result in a modification in cell protein synthesis within the cells.
Example of a hormonal peptide (protein)
Insulin - Promote glucose uptake by body cells
Hormonal proteins: They do not enter cells. They bind to a receptor protein on the cell membrane surface.
Example of hormonal tyrosine derivative
Thyroxin - Increases metabolic rate
How do hormonal steroids function?
They enter cells and result in a modification in cell protein synthesis within the cells.
How do hormonal peptide (proteins) function?
Peptide hormones (protein hormones) do not enter cells. They bind to a receptor protein on the cell membrane surface.
Mode of action peptide hormone
a) Attachment to plasma membrane receptor ( Glycoprotein)
(b) Receptor-Hormone complex: A receptor protein binding with a hormone forms a hormone- receptor complex.
(c) Stimulation of secondary messenger in cytoplasm which alters the action of the cell.
Mode of action steroid hormone
(a) Pass straight through the plasma membrane
Directly affect the expression of genes (protein —–synthesis)
Relationship between hypothalamus and pituitary gland
The hypothalamus controls the hormonal secretion to the pituitary.
The hypothalamus has many receptors for changes of internal conditions and serves as a link between the nervous system and the endocrine system (pituitary).
What is secreted by the gastric glands into the alimentary canal?
Gastric glands: Secrete mucus, hydrochloric acid and pepsinogen from the inner lining of the stomach. Starts protein digestion.
What is secreted by the liver (liver is a gland) into the alimentary canal?
The liver: Secretes bile into small intestine. Bile comes from liver or gall bladder. It emulsifies lipids and increases surface area of lipids for the action of lipase.
Explain the structural features of exocrine gland cells
Exocrine gland cells: Secrete product into a duct to be transported to a specific location.
The exocrine gland cells (secretory cells) surround the end of a ‘‘small branch’’ which is a ductile. The secretory cells secrete digestive enzymes into the ductile by vesicles. This ductile then leads to a larger duct which leads to the pancreatic duct ‘‘stem of the tree’’. Exocrin gland cells have a lot of mitochondria because exocytosis require ATP. THey go thorough the entire process, transcription, translation at R.E.R, synthesis in golgi apparatus (cis to trans side, through cisternae) and then vesicle formation for exocytosis.
One ‘‘branch’’ is called acinus.
State the composition of Saliva
The solvent is water
Enzyme is amylase
Contains mucus
State the composition of Gastric Juice
The solvent is water
Enzyme is pepsin (inactive form is pepsinogen)
Contains hydrochloric acid which removes Pepsin from Pepsinogen and makes it active
Contains mucus
The control of digestive juice secretion by nerves and hormones
Pre - ingestion
The sight and smell of food triggers a reflex reponse in which gastric juice is secreted from gastric pits in the stomach wall. This ensures that gastric juice is in the stomach by the time food is consumed.
Post - ingestion
Food entering the stomach causes distension, which is detected by stretch receptors (nerves) in the stomach lining. Impulses are then sent to the brain, which triggers the secretion of gastrin from its lining the stomach wall. Gastrin in its turn causes the sustained release of gastric juice, particularly its acid component. When the pH drops too low, gastrin secretion is inhibited by hormones. Gastric juice lowers the pH (hydrochloric acid).
Why can we humans not digest cellulose in the alimentary canal?
Cellulose is a polysaccharide carbohydrate which is digested by cellulase which is produced by mutualistic microorganisms. We do not have a relationship with the type of bacteria that produces cellulase thus we cannot digest cellulose.
How is Pepsin activated from its inactive precursor Pepsinogen?
Pepsin is primarily synthesized as a primary structure with 44 other amino acids (pepsinogen). When it is exposed to hydrochloric acid the other amino acid are removed and only pepsin remains and thus becomes activated.
The role of bile in lipid hydrolysis and digestion
Lipase can only catalyse the hydrolysis of the lipids on the outer part of the lipid globule, which means that the interior is mostly inaccessible to the enzyme. Bile produced by the liver have both hydrophobic and hydrophilic end. They insert themselves between lipid molecules and prevent them from coalescing into larger globules. Thus bile is an emulsifier that beaks up relatively large accumulations of lipids into smaller droplets.
This increases the lipid surface area!
Lipase is also both polar and non-polar. ‘
List the materials that are not absorbed and are egested
Some substances cannot be digested thus never absorbed. They become a part of the solid waste or faeces.
They include: Cellulose Lignin (component of plant wall cells) Bile pigments Bacteria Intestinal cells
Main function of the Hepatic Artery
Hepatic artery: branch from the aorta (oxygenated blood) to the liver capillaries (sinusoids).
Main function of the Hepatic Portal Vein
Hepatic portal vein: carrier deoxygenated blood absorbed with nutrients from intestines to liver capillaries (sinusoids). Low pressure.
What are sinusoids?
Sinusoids: Capillaries in liver
Main function of the Hepatic Vein
Hepatic vein: Drains sinusoids deoxygenated blood to venae cava and right atrium of heart. This blood does not have much nutrients.
How can hepatocytes regulate levels of nutrients in blood
The body produces certain hormones which causes the hepatocytes to add or remove these substances from the blood to keep the solute concentration within the normal range.
E.g. insulin causes hepatocytes to convert glucose to glycogen lowering glucose concentrations in blood and glucagon from the pancreas causes the glycogen to be converted back to glucose to increase the concentration.
Function of sinoatrial node
This node contains modified cardiac muscle cells which send out action potentials across both atriums causing them to undergo systole. The action potential also reaches the atrioventricular node.
Approximately 0.1 seconds after receiving the first action potential this node sends out its own action potential through the septum between the ventricles eventually branching out to conducting fibres going around the thick cardiac muscle tissue of both ventricles causing them to undergo a much more powerful systole.
