Topic 6: Homeostasis Flashcards
Define homeostasis
Homeostasis is the maintenance of a constant internal environment via physiological control systems.
Define negative feedback
When there is a deviation from the normal values and restorative systems are put in place to return this back to the original level. This involves the nervous system and often hormones.
Why must the following be kept within set limits in the body?
Blood glucose:
Glucose is needed for respiration, so a lack of glucose in the blood could result in cell death. If blood glucose levels are too high, then this will lower the water potential of the blood and water will leave surrounding cells by osmosis and prevent normal cell function. If the water potential of the blood is too low, water will move into cells by osmosis and can cause them to burst (lyse).
Why must the following be kept within set limits in the body? Temperature
If body temperature is too low there will be insufficient kinetic energy for enzyme-controlled reactions, and if body temperature is too high then enzymes will denature. Either way, metabolic reactions could slow to the point that cells die. Alterations in blood pH will also result in enzymes denaturing.
What is the role of the pancreas?
Detects changes in the blood glucose levels and contains endocrine cells in the Islets of Langerhans which release the hormones insulin and glucagon to bring blood glucose levels back to normal.
Why do type I and type II diabetes result in the body being unable to control blood glucose?
Type I diabetes is due to the body being unable to produce insulin, it starts in childhood and could be the result of an autoimmune disease where the beta cells were attacked. Treatment involves an injection of insulin.
Type II diabetes is due to receptors on the target cells losing their responsiveness to insulin, which usually develops in adults because of obesity and poor diet. It is controlled by regulating the intake of carbohydrates, increasing exercise and insulin injections.
Insulin is secreted by the Beta cells when blood glucose levels are too high. Explain how insulin helps bring this back within the normal limits.
- Attaching to receptors on the surfaces of target cells. This changes the tertiary structure of the channel
proteins resulting in more glucose being absorbed by
facilitated diffusion. - More protein carriers are incorporated into cell
membranes so that more glucose is absorbed from the
blood into cells. - Activating enzymes involved in the conversion of
glucose to glycogen. This results in glycogenesis in the liver.
Glucagon is secreted by the alpha cells when blood glucose levels are too low. Explain how glucagon helps bring this back within the normal limits.
1.Attaching to receptors on the surfaces of target cells (liver cells).
2.When glucagon binds, it causes a protein to be activated into adenylate cyclase which converts ATP into a molecule called cyclic AMP (cAMP). cAMP activates an enzyme, protein kinase, that can hydrolyse glycogen into glucose.
- Activating enzymes involved in the conversion of glycerol and amino acids into glucose.
Which two hormones can trigger the second messenger model?
Glucagon and adrenaline
Adrenaline is secreted by the adrenal glands when blood glucose levels are too low. Explain how adrenaline helps bring this back within the normal limits.
- Adrenaline attaches to receptors on the surfaces of target cells. This causes a protein (G protein) to be activated and to convert ATP into cAMP.
- cAMP activates an enzyme that can hydrolyse glycogen into glucose.
- This is known as the second messenger model of adrenaline and glucagon action because the process results in the formation of cAMP, which acts as a second messenger.
Label and draw the diagram of the nephron.
check sheets or booklet
Describe what occurs at each part of the nephron:
- The Bowman’s (renal) capsule - Ultrafiltration occurs here as the afferent arteriole (entering the glomerulus) is wider than the efferent arteriole (leaving the glomerulus) creating high hydrostatic pressure. Small molecules and water are forced out of the capillaries into the renal capsule creating the glomerular filtrate. Large proteins and blood cells remain in the blood.
- Proximal convoluted tubule (PCT)- The walls are made of microvilli epithelial cells to provide a large surface area for the diffusion of glucose into the cells from the PCT.
- Glucose is then actively transported out of the cells into the intercellular space to create a concentration gradient. Glucose can then diffuse into the blood again.
- Loop of Henle- Sodium ions are actively transported out of the ascending limb into the medulla to create a low water potential. Water moves out of the descending limb and out of the distal convoluted tubule and collecting duct by osmosis due to this water potential gradient.
Describe what would happen if water potential of blood is too low. May draw a diagram
- Changes in the water potential of the blood are detected by osmoreceptors found in the hypothalamus. The hypothalamus is also where the antidiuretic hormone (ADH) is produced. ADH then moves to the posterior pituitary gland and from here it is released into capillaries and into the blood. ADH travels through the blood to its target organ, the kidneys.
- If the water potential of the blood is too low water leaves the osmoreceptors by osmosis and they shrivel. This stimulates the hypothalamus to produce more of the hormone ADH. If the water potential of the blood is too high water enters the osmoreceptors by osmosis. This stimulates the hypothalamus to produce less ADH.
- When ADH reaches the kidney it causes an increase in the permeability of the walls of the collecting duct and distal convoluted tubule to water. This means more water leaves the nephron and is reabsorbed into the blood, so urine is more concentrated.
Alport syndrome (AS) is an inherited disorder that affects kidney glomeruli of
both men and women. Affected individuals have proteinuria (high quantities of
protein in their urine).
(a) Suggest how AS could cause proteinuria. (2 marks)
- Affects/damages basement membrane
OR
More protein channels/carriers in basement membrane; - Proteins can pass into the (glomerular) filtrate/tubule;
Describe how ultrafiltration occurs in a glomerulus. (3 marks)
- High blood/hydrostatic pressure;
Ignore references to afferent and efferent arterioles
Ignore ‘increasing/higher blood pressure’ as does not
necessarily mean high - Two named small substances pass out eg water, glucose,
ions, urea;
Accept correct named ions
Accept mineral ions/minerals
Accept amino acids/small proteins
Ignore references to molecules not filtered - (Through small) gaps/pores/fenestrations in (capillary)
endothelium;
Accept epithelium for endothelium
- (And) through (capillary) basement membrane;
