Homeostasis Flashcards
example of a positive feedback mechanism
At birth, Oxytocin causes the uterus to contract. when the foetus hits the surface of the cervix, this causes oxytocin to be released and so the uterus contracts even more.
name of liver cells
hepatocytes
what is the name for the point at which the system operates best
the optimum point
endocrine glands
produce hormones and then secrete them directly into the blood
Adrenaline effects
secreted by the Adrenal glands. This hormone will cause different effects in different cells including:
liver cells are stimulated to break down glycogen into glucose which is then released into the blood.
Smooth muscle cells are responsible for peristalsis in the alimentary canal are prevented from contracting so that glucose is not used on digestion and is instead used on more necessary processes.
Adrenalines effects specifically on the liver
Adrenaline binds to a transmembrane protein receptor within the cell surface membrane of the hepatocyte. This causes the protein on the inner membrane of the cell to change shape and causes the activation of Adenyl Cyclase. This converts ATP into cyclic AMP. cAMP is the secondary messenger hormone and binds to the enzyme protein kinase A which therefore changes shape and is activated. This catalyses the conversion of glycogen into glucose.
Glucagon action
Glucagon binds to a receptor and causes a conformational change in the intracellular domain of the receptor. This activates the enzyme Adenyl Cyclase A, which converts ATP into cyclic AMP. This is the second messenger, and activates Protein Kinase A (by binding to a site that isn’t the active site). Protein Kinase A activates the Glucagon phosphorylase enzyme, which converts Glycogen to Glucose.
cascade of enzyme reactions
amplification on the effect of the Glucagon hormone. This is because one enzyme can be reused multiple times and Glycogen itself is very branches so many enzymes can bind to it at once.
when insulin binds with a receptor what does it cause
- vesicles containing the protein which makes the glucose transport protein to fuse with the membrane thus increasing the number of glucose protein channels and so increasing the rate of uptake of glucose from the blood into the cells.
- Insulin causes a change in the tertiary structure of the glucose transport proteins allowing more glucose to enter the cell by facilitated diffusion.
- Activates the enzymes that convert Glucose into Glycogen and fat.
- rises the rate of respiration so increasing the rate go glucose uptake.
pancreas function
Endocrine: ductless as it secretes insulin and Glucagon into the bloodstream by exocytosis.
Exocrine: down the pancreatic duct secreting enzymes into the duodenum.
hyperglycaemia
high blood glucose levels
hypoglycaemia
low blood glucose levels
glycosuria
glucose in the urine
glycogenesis
conversion of glucose to glycogen
glycogenolysis
break down of glycogen
Gluconeogenesis
conversion of substrate such as amino acids into glucose (caused by Glucagon)
conversion of glucose to glycogen
glycogenesis
break down of glycogen
glycogenolysis
conversion of substrate such as amino acids into glucose (caused by Glucagon)
Gluconeogenesis
role of the kidney
responsible for both osmoregulation and excretion
3 layers of the kidney
- fibrous capsule (outermembrane that protects the kidney)
- the cortex (lighter coloured region made up of the renal corpuscle)
- Medulla (darker coloured inner region made up of loops of henle, collecting duct and blood vessels).
ureter
tube that carries urine to the bladder
renal copuscle
bowmans capsule, bowmans space and glomerulus.
3 layers of the filtration barrier separating blood in the glomerulus and bowmans space
- single celled capillary epithelium containing fenestrations
- basal lamina (non-cellular protein basement layer)
- single celled epithelium of the bowmans capsule consisting of single flattened cells called podocytes.
ultrafiltration
formation of filtrate:
1. blood enters the afferent arteriole from the renal artery
2. the lumen of the afferent arteriole is a lot wider than the lumen of the efferent arteriole and so there is a high hydrostatic pressure.
3. This pushes out water, urea, salts and glucose but no proteins.
The blood leaves the glomerulus out of the efferent arteriole into the Vasa Recta.
what type of cells are the proximal convoluted tubules cells
cuboidal
adaptations of the proximal convolute tubule
- microvilli
- long length of the tubule increases the surface area and allows more space for channel proteins and sodium/potassium pumps
- in foldings at the base of cells gives a large SA for the transferring substances to capillaries.
- high density of mitochondria to provide ATP for active transport.
- squamous endothelium of the capillary gives a short diffusion distance.
- continuous flow of both filtrate and the blood maintains a concentration gradient
proximal convoluted tubule
Reabsorption.
Water: osmosis from filtrate into the cells. Then enters the blood through aqua porins.
Glucose and Amino acids: pass from the filtrate into the cells of the PCT by co-transport (requires ATP).
the loop of henle
purpose is to make the medulla salty.
descending limb of the loop of henle
permeable to water but not salts (although some salts can diffuse in but not out).
The water leaves by osmosis into the very salty medulla (by aquaporins) and is then reabsorbed into the vasarecta.
ascending limb of the loop of henle
is impermeable to water and transports salts out:
1. Sodium ions are actively transported out of the top section and diffuse out lower down. They move into the interstitial space.
2.
loop of henle adaptations
the longer the loop of henle, the more time there is for salts to be pumped out in the ascending limb, and so theres a greater concentration gradient and so more water is reabsorbed by the vasarecta.
Countercurrent multiplier:
the filtrate in the collecting duct with a lower water potential meets the interstitial fluid that has an even lower water potential. This ensures that a concentration gradient exists throughout the whole collecting duct.
distil convoluted tubule
made up of cuboidal cells with microvilli and many mitochondria.
Its role is to Mae any final adjustments to the water and salts that are reabsorbed. It also controls the pH of the blood by selecting which ions to reabsorb.
where is ADH synthesised
the hypothalamus
