B16- Homeostasis Flashcards
What is homeostasis?
Homeostasis is the regulation of internal conditions in cells or organisms to maintain optimal function despite internal and external changes.
What is negative feedback of glucose?
- Blood glucose levels are detected by α cells in the pancreas
- Glucagon is produced by these cells in response to low levels
- Liver hydrolyses glycogen
- Increased blood glucose level reduces the stimulus of α cells, glucagon production reduced
What is positive feedback?
amplifies the change however not part of homeostasis as doesn’t regulate.
How does adrenaline work?
- Adrenaline binds to its receptor on the target liver cell
- Receptor changes shape activating adenyl cyclase
- Activated adenyl cyclase converts ATP to cAMP
- cAMP binds to protein kinase, changes its shape, and therefore activates PK, which will convert glycogen into glucose. Glucose leave cells by facilitated diffusion
Role of pancreas?
The pancreas consists mainly of enzyme-producing cells, with hormone-producing cells (islets of Langerhans) scattered throughout. These islets contain:
- α cells: Larger cells that produce glucagon
- β cells: Smaller cells that produce insulin
Role of the Liver
- Glycogenesis: Converts glucose to glycogen for storage
- Glycogenolysis: Breaks down glycogen into glucose when needed
- Gluconeogenesis: Produces glucose from non-carbohydrate sources
What is the role of insulin?
Insulin binds to the receptors and signals transduction cascade
The number of GLUTs increase on the cell surface
Glucose transport carrier proteins are stored in vesicles
Vesicles move to cell surface where they fuse with the membrane
More GLUTs available for glucose transport
Enzymes which convert glucose to glycogen and fat are activated
How to test for diabetes?
Glucose tolerance test: Patient fasts for 8-12 hours, then drinks 75g glucose solution. Blood glucose levels are monitored every 30-60 minutes or after 2 hours
Rapid testing methods:
- Test strips for clinical/home monitoring
- Urine dipsticks to detect glucose
- “Pinprick” test using needle and test strip
Type 1 diabetes - T1D
Insulin dependent diabetes, the body is unable to produce insulin.
Lack of insulin results in:
- Less glycogen stored in the liver
- Dangerously high blood glucose level that can lead to serious organ damage
Type 2 diabetes - T2D
T2D is insulin independent diabetes and it is much more common than T1D.
The glycoprotein receptors on the cell surface lost their responsiveness to insulin. It can also be a result of inadequate insulin supply from pancreas.
What is osmoregulation
is the homeostatic control of the water potential of the blood.
What is the structure of the kidney?
- Cortex: The outer layer of the kidney, containing most of the nephrons’ renal corpuscles.
- Medulla: The inner region, composed of cone-shaped renal pyramids.
- Renal pelvis: A funnel-shaped structure that collects urine from the pyramids.
- Nephrons: The functional units of the kidney, extending from the cortex into the medulla.
- Renal artery and vein: Blood vessels that supply and drain the kidney.
- Ureter: The tube that carries urine from the renal pelvis to the bladder.
What is the Renal (Bowman’s) capsule
cup-shaped structure which surrounds the glomerulus (mass of capillaries). Inner layer is made up of podocytes.
What is the proximal convoluted tubule?
series of loops surrounded by capillaries, its walls are made of epithelial cells which have
microvilli.
What is the Loop of Henle (LoH)
hairpin loop spanning from cortex to medulla and back, surrounded by capillaries.
What is the Distal convoluted tubule (DCT)
series of loops surrounded by capillaries
What is the collecting duct
tube into which a number of DCT empty. These empty into the pelvis of the kidney.
Where does the blood travel
Renal Artery → Afferent Arteriole → Glomerulus →Efferent Arteriole → Blood Capillaries → Renal Vein
What is the role of the nephron
- Formation of glomerular filtrate
- Reabsorption of Glc and water
- Maintenance of a gradient of Na+ ions in the medulla
- Reabsorption of water
Formation of glomerular filtrate by ultrafiltration
Diameter of afferent arteriole is greater than of efferent - > hydrostatic pressure builds up in the glomerulus
Water, Glc and mineral ions are squeezed out of the glomerulus to form glomerular filtrate
Formation of Glomerular Filtrate by Ultrafiltration
Prodocytes with large spaces between them, filtrate passes between the cells. Endothelium of glomerulus has spaces between cells acting as a sieve. Connective tissue of fibrous material acts as a filter. (All designed to allow only water, amino acid, mineral ions, vitamins and urea through)
How is the PCT adapted
Increase surface area to allow for more absorption
How does amino acid and glucose reabsorb into the blood stream
Na+ ions actively transported into the blood stream, causing Na+ ions to move into the epithelium cell through facilitated diffusion with protein channels. Glucose/ Amino Acids move into the blood through diffusion.
How does the loop of henle work
- Na+ active transport in ascending limb
- Low Ψ in medulla between the 2 limbs
- H2O leaves by osmosis descending limb
- Filtrate progressively loses H2O until lowest Ψ in hairpin
- At the base of ascending limb Na+ diffuses out, further up active transport (see step 1)
- Decreasing Ψ gradient established
- H2O leaves collecting duct by osmosis
