Homeostasis Flashcards
Define homeostasis
Physiological control systems that maintain a constant internal environment
Why does a constant internal temperature need to be maintained?
- Metabolism is controlled by enzymes- Enzymes have an optimum temperature- Too hot = denatured enzymes- Too cold = slow rate of reaction
Why does a constant internal pH need to be maintained?
- Metabolism is controlled by pH- Enzymes have an optimum pH- Away from optimum pH rate of reaction decreases and then beyond a point enzymes denature
Why does a constant internal glucose concentration need to be maintained?
A minimum amount of glucose is needed as a respiratory substrate
What happens if glucose concentration is too high?
- Decreases water potential- Water moves out of cells by osmosis- Cells shrivel up
What is negative feedback?
- Receptors detect a change away from the normal/optimum and effectors activate mechanisms to return the body to normal/optimum- Control and regulation- e.g. blood temp, pH, glucose- Separate negative feedback systems give you more control
What is positive feedback?
- A response that results in the effectors further amplifying the change away from the normal - Rapid changes and responses- e.g. giving birth, hypothermia, blood clotting, depolarisation
What happens when there’s an increase to the blood glucose concentration
- Receptors in the pancreas detect an increase in blood glucose- Beta cells in the islets of Langahans (pancreas) secrete insulin- Insulin binds to receptors in liver + muscles- Increases permeability to glucose- More glucose absorbed by facilitated diffusion- Glycogenesis converts glucose into glycogen- Increases rate of respiration
What happens when there’s an decrease to the blood glucose concentration
- Receptors in the pancreas detect blood glucose is low - Alpha cells in the islets of Langahans (pancreas) secrete glucagon - Glucagon binds to receptors on liver cells- Decreases rate of respiration - Glycogenolysis (glycogen to glucose)- Gluconeogenesis (non carbs to glucose)
What is glycogenesis?
Makes glycogen and is promoted by insulin when blood glucose is high
What is glycogenolysis?
Splits glycogen to produce glucose when blood glucose is low, it is promoted by glucagon and adrenaline
What is glyconeogenesis?
Makes glucose from non carbs when blood glucose is low , is promoted by glucagon
What is glucagon secreted by?
Alpha cells in the islets of Langahans in the pancreas
When is glucagon secreted?
When blood glucose is low
What receptors does glucagon bind to?
Liver cells
What is the effect on blood glucose when glucagon binds to receptors on liver cells?
Blood glucose increases
What are the mechanisms of glucagon?
- decreases respiration- gluconeogenesis- glycogenolysis
What is adrenaline secreted by?
Adrenal glands
When is adrenaline secreted?
When blood glucose is low
What receptors does adrenaline bind to?
Liver cells
What is the effect on blood glucose when adrenaline binds to receptors on liver cells?
Blood glucose increases
What are the mechanisms of adrenaline?
- activates glycogenolysis by secretion of glucagon- inhibits glycogenesis
What is insulin secreted by?
Beta cells in the islets of Langahans in the pancreas
When is insulin secreted?
When blood glucose is high
What receptors does insulin bind to?
Liver and muscle cells
What is the effect on blood glucose when insulin binds to receptors on liver and muscle cells?
Blood glucose decreases
What are the mechanisms of insulin?
- increases respiration- glycogenesis- increases permeability of liver and muscle cells
How does insulin cause an increase in liver and muscle cell permeability?
- glucose carrier proteins are stored in vesicles inside liver and muscle cells - insulin binds with receptors on the cell membrane of the target cells- causes vesicles to fuse with cell membranes- carrier proteins join the membrane and glucose is absorbed by fascillitated diffusion
What is diabetes meilitus?
An illness where blood glucose levels are not controlled
What is hyperglycemia?
Dangerously high blood glucose concentration
What is hypoglycemia?
Dangerously low blood glucose concentration
What are the causes of type 1 diabetes?
Immune system kills beta cells in the islets of Langerhans therefore insulin cannot be made
What effect does type 1 diabetes have on blood glucose?
Hyperglycemia
What age groups are most effected by type 1 diabetes?
Children and young adults
What is the treatment for type 1 diabetes?
- insulin injections - avoid simple carbs- eat at regular intervals- regular exercise to use up glucose
What are the causes of type 2 diabetes?
- obesity - lack of exercise- poor diet - beta cells dont make enough insulin - liver + muscle cells stop responding to insulin
What effect does type 2 diabetes have on blood glucose?
Hyperglycaemia
What age groups are most effected by type 2 diabetes?
Adults/elderly
What is the treatment for type 2 diabetes?
- drugs to increase sensitivity to insulin, make more insulin, reduce amount of glucose released - eat healthy- lose weight - regular exercise- insulin injections
What is the mechanism by which cAMP acts as a second messenger?
- A hormone (first messenger), such as adrenaline or glucagon, is complimentary to the receptor protein on the cell membrane of the target cell (liver cell)- This activates adenyl cyclate (enzyme)- Adenyl cyclate connects ATP to form cAMP- cAMP activates protein kinase A by altering its tertiary structure allowing glycogenolysis to take place
In what part of the nephron is the glomerus?
Cortex
In what part of the nephron is the bowmans capsule?
Cortex
In what part of the nephron is the proximal conviluted tubule?
Cortex
In what part of the nephron is the loop of henle?
Medulla
In what part of the nephron is the distal conviluted tubule?
Cortex
In what part of the nephron is the collecting duct?
Medulla
Compare the afferent arteriole and the efferent arteriole
Upon entering the glomerus the afferent arteriole has a considerably larger surface area when comparing it to the efferent arteriole (by which the blood leaves the glomerus and the bowmans capsule). This allows for the mechanism of ultrafiltration
What happens at the proximal conviluted tubule?
Most of reabsorption from the filtrate that passes trough the glomerus, this is supported by numerous microvilli (increase the surface area). Most of reabsorption takes place through active transport, therefore the proximal conviluted tubule contains many mitochondria
What happens at the distal convoluted tubule?
Reabsorption of Na+ ions and osmoregulation
What happens after the collecting duct?
Urine passes to the ureter, bladder and finally the urethra
What happens at the collecting duct?
Osmoregulation
What is the order of the parts in a nephron?
1 - Glomerus2 - Bowmans capsule3 - Proximal conviluted tubule4 - Descending limb of the loop of henle5 - Ascending limb of the loop of henle6 - Distal conviluted tubule7 - Collecting duct
What does the nephron have?
A really good blood supply
How does ultrafiltration take place?
High hydrostatic pressure forms due to the change in width from the afferent arteriole to the efferent arteriole, this forces small molecules into the bowmans capsule (which form the filtrate). Larger molecules will not fit throgh the gaps in the capillary wall, basement membrane and the podocytes
Why does ultrafiltration take place?
To filter the blood
Where does ultrafiltration take place?
At the glomerus which is surrounded by the Bowmans capsule
What is the filtrate made up of?
- Water- Glucose- Amino acids- Ions (Sodium and chloride)- Urea
What molecules are too big to filter out of the blood and into the filtrate?
Red blood cells and other proteins
What is the role of the basement membrane and the podocytes in the process of ultrafiltration?
They prevent large molecules entering the filtrate
What is selective reabsorption?
Useful products are reabsorbed from the glomerular filtrate mostly by the proximal convoluted tubule but also by the distal convoluted tubule, the loop of Henle and the collecting duct
What is ultrafiltration and what does it produce?
The process of filtering under pressure to produce the glomerular filtrate
What is the process of selective reabsorption?
Useful molecules are absorbed into the epithelial cells lining the PCT from the lumen of the nephron where they can be transported into the surrounding capillaries
What part of the nephron does the most selective reabsorption?
The proximal convoluted tubule
How is the PCT adapted for selective reabsorption?
- Microvilli increase SA- Mitochondria provide ATP for active transport
What does urine contain?
- Water- Ions- Urea- Excess vitamins- Glucose if diabetic
What happens at the descending limb of the loop of Henle?
- Permeable to water- Water moves out by osmosis - Water absorbed by capillaries- Increases conc of urine
What happens at the ascending limb of the loop of Henle?
- Sodium and chlorine ions pumped out- Using ATP- Decreases water potential of the medulla- Impermeable to water (Water cannot move in or out)
What effect does ADH have on the collecting duct?
- ADH changes the collecting ducts permeability to water- More ADH = less piss
What happens if you have a longer loop of Henle and what is an example of mammals with a longer loop of Henle?
- Longer loop of henle = more concentrated medulla - More water reabsorbed by the capillaries- More concentrated urine- Dessert animals such as camels
How is dehydration detected by the body and dealt with?
- Low water potential of the blood is detected by the osmoreceptors in the hypothalimus - The posterior pituitary secretes antidiuretic hormone which is carried in the blood stream - ADH binds to specific receptor proteins on the collecting duct (and DCT)- Increases permeability to water- Water moves out of collecting duct (and dct) by osmosis (medulla now has a lower water potential) and more water is reabsorbed into the blood
What happens when there is more ADH?
- Collecting duct wall more permeable to water- More water moves out of collecting duct by osmosis- Less piss
