3.6.4 Homeostasis Flashcards
What is homeostasis?
Maintenance of a stable internal environment despite varying conditions in the external environment
What do homeostatic systems involve ?
Sensing systems involving various types of receptors. Control systems that may be use either the nervous sytem or endocrine system or both. Effector systems that respond to keep the internal environment within narrow limits, keeping the environment in a state of dynamic equilibrium
What is a negative feedback mechanism?
The mechanism that restores the level back to normal. It maintains systems within narrow limits. It only works within certain limits
Why do chemoreceptors detect a drop in blood pH during exercise?
More CO2 is produced by respiration. This reacts with water to form carbonic acid (the enzyme carbonic anhydrase speeds this up) which then dissociates to release H+ ions that decrease blood pH.
What is a typical human response to high body termperture (hyperthermia)
Sweating, flushed skin as blood flow to capillaries in the skin increases. Hairs on body lie flat
What is a typical human response to low body termperture (hypothermia)
Shivering, paler skin as blood flow is diverted away from skin. Hair on body stand up (nb. This reponse doesn’t do much in humans but does in other mammals with more hair)
What is a positive feedback mechanism?
Amplifies the change from the normal level. It does not keep the internal environment stable so is not involved in homeostasis
Give examples of positive feedback used in biology
- Childbirth, where contractions stimulate oxytocin release, which stimulates stronger contractions. 2 Fever, where the temperature increases in response to infection. Both responses will ultimately finish when the initiating stimulus dissapears (eg due to birth or destruction of pathogen)
Compare the hormonal and nervous system
Hormonal control - chemical transmission via blood, slower acting, blood carries the hormones to all cells but only target cells can respond, widespread and long lived response. The nervous system is faster, using electrical impulses (action potentials) and generally provides a short lived and targetted response
What is a hormone?
Chemical messengers that are released from glands and travel in the blood
How are hormones secreted ?
When a gland is stimulated. Glands can be stimulated by a change in concentration of a specific substance or by electrical impulses
What is a gland?
Group of cells that are specialised to secrete a useful substance such as a hormone. (Endocrine glands release hormones into the blood, exocrine glands release substances exteranlly such as digestive enzymes, sweat etc)
Describe how arenalin works as part of a 2nd messenger system
Adrenalin binds to receptor site on membrane, causing adenyl cyclase to be activated inside the cell which converts ATP to cAMP, which activates protein kinase enzyme. This causes more glycogenolysis
Where is insulin produced and when?
In the Beta cells of the islets of langerhans in the pancreas. Produced when blood sugar levels are high
Where is glucagon produced and when?
In the Alpha cells of the islets of langerhans in the pancreas. Produced when blood sugar levels are low
Explain how an increase in blood glucose causes insulin release by beta cells
Define gluconeogenesis
When glucose is made from sources other than carbohydrtate e.e. glycerol/amino acids.
Define glycogenolysis
When glycogen is hydrolysed into glucose
Define glycogenosis
When glucose is converted into glycogen
Describe what happens when your blood glucose level is too high
B cells of the islets of langerhans in the panreas release insulin which binds to body cells causing - more glucose to move into cells by facilitated diffusion (more glucose transport proteins in the cell membrane) and more glucose to be converted into glycogen and fats
Desrcibe what happens when blood glucose is too low
A cells of the islets of langerhans in the pancreas release glucagon which binds to liver cells causing glycogen to be converted to glucose and amino acids and glycerol to be turned into glucose
What is the suspected cause of type 1 diabetes
We think there is a genetic risk that is then triggered in early childhood by infection with an unkown pathogen. This causes an autoimmune reaction which kills beta cells
What’s the difference between type 1 and type 2 diabetes?
type1 - can’t produce insulin (so need injections). Type 2 - cells don’t respond to insulin (can be controlled with diet/exercise)
what is the main cause of type 2 diabetes?
A high sugar diet or obesity is the main cause although some groups of people appear genetically predisposed to developing the condition
Describe the structure of the kidney
Medulla - inner region with loops of Henle, collecting ducts and blood vessels. Cortex - outer region with bowman’s capsules, convoluted tubules and blood vessels. Renal artery and vein and Ureter
Describe ultrafiltration of blood in the kidney
Water, glucose and mineral ions are squeezed out of the capillary in the glomerulus due to the high hydrostatic pressure through fenestrated capillaries. Blood cells and protein cannot pass into the capsule as they are too large and cannot pass through the basement membrane. Podocyte cells hold the membrane in place around the capillaries.
Which substances form the glomerular filtrate and which do not?
Water glucose and mineral ions leave the blood. Large proteins and blood cells do not.
What happens in the proximal convuluted tubule?
Sodium ions are actively transported out of the cells into the blood, creating a concentration gradient. More sodium ions diffuse in from the lumen of the tubule by co-transport - bringing glucose, amino acids, chloride ions with them. This reduces the water potential of the PCT cells and blood so water also follows via osmosis.
Describe what happens in the loop of Henle
Sodium ions actively transported out of the ascending limb creating a low water potential in the medulla. Water moves out of the descending limb (ascending limb is impermeable), water is carried away in blood. Filtrate continues to lose water as it moves down the collecting duct. The loop of henle serves as a hairpin countercurrent multiplier system to provide a salty and low water potential environment within the medulla.
What happens when osmoreceptors detect a decrease in blood water potential?
Hypothalamus releases ADH to the pitutitary gland and into the capillaries. ADH increases the permeability of the distal convuluted tubule and collecting duct as aquaporin proteins are added into the membrane. Hence more water can move out of the filtrate and into the blood. So less water is present in urine and more stays in the blood. Urine produced would be darker in colour.
