6.4 Homeostasis Flashcards
What is homeostasis?
involves phsyiological control systems that maintain the internal environment within restricted limits
Why is it important to maintain core body temperature and pH?
enzymes will denature in extreme pHs and in high temps
in low temps - eznzyme activity is slowed
Why is it important to maintain blood glucose levels?
to maintain water potential of blood and supply glucose to cells as a respiratory substrate
water potential needs to be maintained in order to prevent cells loosing or gaining water by osmosis
What is negative feedback?
when deviations from the optimum level are detected by receptors, corrective mechanisms bring the factor back to optimum
What is positive feedback?
when a stimulus detected by a receptor brings about a response that enhances the effect further - so there is greater deviation from the optimum
What is the benefit of having separate mechanisms for different deviations from the optimum?
there is greater control over the system when a factor becomes too high or too low
What are the 3 ways glucose can enter the bloodstream?
absorption from the gut after digestion
hydrolysis of stored glucose
conversion of non carbohydrates into glucose
How do hormones bring about a response?
produced by glands which secrete hormones directly into the blood
carried in blood plasms to target cells with specific receptors
What are all the strcutures of the pancreas?
the pancreatic duct
the pancreas
acinar glands
islet of langerhans:
- alpha and beta cells
-capillary
What is the role of beta cells?
secrete insulin in response to increased glucose concentrations
What is the role of alpha cells?
secrete glucagon in response to lowered glucose concentrations
What is glycogenesis?
the formation of glycogen from glucose
What is glycogenolysis?
the hydrolysis of glycogen into glucose
What is gluconeogenesis?
the synthesis of glucose from molecules that are not carbohydrates - amino acids and fatty acids, glycerol
What triggers the release of insulin?
increased glucose levels detected by beta cells
vesicles containing insulin move to the cell surface membrane and release insulin into surrounding capillaires
How does insulin lower blood glucose concentrations?
- insulin binds to receptor proteins on the surface membrane of target cells
- glucose carrier proteins on the membrane allow for facilitated diffusion of glucose
- insulin changes the shape of carriers and causes more carrier proteins to join the cell surface membrane of target cell = increase rate of glucose uptake
- insulin activates an enzyme for glycogenesis
- also activates enzymes that manufactures fatty acids and glycerol which are stored as fat
negative feedback
What triggers the release of glucagon?
decreased glucose levels are detected by the alpha cells
vesicles fuse with membrane to release glucagon into surrounding capillaries
How does glucagon raise blood glucose concentration?
- binds to transmembrane protein of hepatocytes
- activates enzymes involved in glycogenolysis and gluconeogenesis = adenyl cyclase
Descibe the second messenger model with glucagon and adrenaline increasing glucose levels
- Glucagon/adrenaline bind to a transmembrane protein in the cell surface membrane of a liver cell
- the binding of the Glucagon/adrenaline causes an enzyme, adenyl cyclase, to change shape and become activated
- activated adenyl cyclase converts ATP to cyclic AMP - this acts as a secondary messenger
- the cAMP activates the enzyme protein kinase
- activated protein kinase catalyses glycogenolysis - glycogen –> glucose
apart from the second messenger model how can glucagon cause the production of glucose?
uses other sources when the supply of glycogen is exhausted - amino acids and glycerol = gluconeogenesis
What is the role of the liver in gluconeogensis?
the liver can produce glucose from non carbohydrates sources such as amino acids and glycerol
what triggers the release of adrenaline?
in times of stress and excitement it is produced by the adrenal glands
What is the role of Glucagon/adrenaline in the second messenger model?
the binding of Glucagon/adrenaline does not have a direct effect on the cells
but causes a series of chain reactions within the cells
What is the role of adenyl cyclase?
converts ATP to cyclic AMP - this acts as a secondary messenger
What is the role of cyclic AMP?
activates protein kinase enzyme
What is the role of protein kinase?
activated protein kinase catalyses glycogenolysis
What is diabetes?
the inability to control blood glucose levels
What are the 2 possible causes of Type 1 diabetes?
the body being unable to produce insulin
an auto immune response - immune system destroys the beta cells
What are the cause of Type 2 diabetes?
the glycoprotein receptors on the body cells being lost or becoming less sensitive to insulin
associated with obesity and unbalanced diet
How is Type 1 diabetes controlled?
injections of insulin to match the glucose intake
How is Type 2 diabetes controlled?
regulating intake of carbohydrate
improving exercise levels in response to diet
Why is fatigue a symptom of diabetes?
not enough glucose available to cells for respiration
Why is being thirsty a symptom of diabetes?
decreased water potential in the blood
where is the nephron located
is the functional microscopic structure found in the kidneys that is positioned within the cortex and medulla
What is the role of the kidneys?
removes waste from the blood, mostly urea, and dilutes urea with water to excrete it as urine
Why do the Kidneys need a good blood supply?
so there is no build up of waste in the blood and the waste can be flushed away
Name all the structures in the kidney
fibrous capsule
renal cortex
medulla
nephrons
renal pelvis
ureta
renal vein
renal artery
What is the role of the fibrous capsule?
outer membrane of the kidney - thin layer of collagen
protects the kidney from injury
What is the role of the renal cortex?
the lighter region of the kidney = contains the bowmans capsule and convoluted tubules, where the nephron begins
What is the role of the medulla?
darker inner region = contains the loop of henle and the collecting duct
filters waste and balances electrolytes
What is the role of the ureta?
carries urine from the kidneys to the bladder
What is the role of the renal pelvis?
collects urine from the kidneys
What is the role of the renal artery?
oxy blood contains a high conc of urea
supplies blood to the glomerulus
What is the role of the renal vein?
carries deoxy blood with a low conc of urea away from the kidney (glomerulus)
What is the role of a nephron?
where blood filtration takes place, the functional unit
Name all the structures of a nephron starting from the beginning of the flow of blood
afferent artieriole
glomerulus
efferant arteriole
bowmans capsule
proximal convoluted tubule
blood capillaries (vesa recta)
loop of henle
distal convoluted tubule
collecting duct
What are the 3 stages of osmoregulation?
- ultrafiltration
- selective reabsorption
- estabilishing salt grad and water reabsorption
Explain the process of ultrafiltration
- high hydrostatic pressure is created in the glomerulus as the efferant arteriole is narrower than the afferant arteriole
- fenestrations in the endothelium of the capillaires allows small substances through
- the basement membrane acts as a filter only allowing small molecules through = water, glucose, amino acids, urea, ions
- the glomerular filtrate enters bowmans capsule
What type of cells line bowmans capsule?
epithelium cells
What type of cell is found between the bowmans capsule and the glomerulus?
podocytes
What are podocytes?
the inner wall of bowmans capsule
What is the glomerulus?
tight network of caplliaries in the bowmans capsule
What creates a high hydrostatic press in the glomerulus?
the efferent artierole lumen is narrower than the afferant arteriole = there is a greater flow rate of blood into the glomerulus than out of the glomerulus
What is the role of the afferant arteriole?
carries blood into the glomerulus
What is the role of the efferent arteriole?
carries blood away from the glomerulus
What is the role of podocytes?
forms a specialised and efficient barrier within the golmerulus, preventing larger proteins and blood cells into the filtrate
How does the podocytes create a filter and barrier?
has cytoplasmic extensions that wrap around the capillaries = creating filtration slits = gaps
How does the capillary fenerstrations and podocytes filtration slits create a free flow of filtrate?
fenerstrations align with filtration slits
molecules pass the basement membrane between the epithelial cells of the capillary and the podocytes
Describe the process of selective reabsorption
- sodium ions are actively transported out of the epithelial cells lining the proximal convoluted tubule into surrounding blood capillaries by a Na+/K+ pump
- Na+ conc in the epithelial cells is lowered
- Na+ diffuse down a conc grad from lumen of proximal tubule into the epithelial cells by facilitated diffusion
- glucose/ a.a is co transported by facilitated diff with the Na+
- the removal of Na+ from the lumen increases water potential in the PCT and so water moves into the cells out of the lumen by osmosis
- loss of water in the PCT increases the conc of urea in thr PCT, there is a conc grad between the PCT and capillary, leads to facilitated diff of urea
What are all the adaptations of the epithelial cells of the proximal convoluted tubule?
microvilli = increase SA
many carrier proteins = for rapid facilitated diff and for active transport (Na+/K+ pump)
many mitochondria for active transport
Describe sodium co-transport in terms of the PCT lumen and the tissue fluid
- Na+ actively transported out of the epithelial cells lining the PCT into the tissue fluid
- forms a conc grad of Na+ inside the epithelial cell, there is a lower conc in the cell than in the lumen of the PCT
- Na+ facilitated diffuse into the epithelial cell from the lumen of the PCT, glucose and a.a are actively transported (indirectly) into the epithelial cell
- facilitative diff of glucose out of the epithelial cell into the blood
Why is everything removed from the blood to then be returned back into the capillary?
only want to remove urea = remove everything to be able to remove all of the urea from the blood
What % of sodium ions are reabsorbed into the blood?
99%
What % of glucose is reabsorbed into the blood?
100%
What % of urea is reabsorbed into the blood?
50%
Why is only 50% of urea removed from the blood?
leaves the PCT by facilitated diffusion so an equilibrium will be reached eventually
Where is the loop of henle in the kidney?
in the medulla
What is the role of the loop of henle?
sets up a salt grad in the medullary tissue fluid to reabsorb water from urine by osmosis
What are the 3 parts of the loop of henle?
the descending limb
the hairpin - bottom loop
the ascending limb
How is water absorbed by the collecting duct?
a water potential grad is set up by the loop of henle so that water can be absorbed from the entire length of the collecting duct
What are the features of the wall of the descending limb?
thinner
permeable to water
relatively impermeable to NaCl
What are the features of the wall of the ascending limb?
thicker
not permeable to water
permeable to NaCl
Describe the water potential of the urine after passing through the collecting duct
it is hypertonic = has a lower water potential than the blood
why is the wall thicker at the top of the ascending limb?
there is lots of mitochondria here for the active transport of NaCl
Describe the entire process of establishing a salt grad in the loop of henle
- NaCl is actively transported out of the ascending limb, so the conc of NaCl in the filtrate inside the ascending limb decreases moving up the limb
- in the descending limb - a reduced water potential in the medullary tissue fluid surrounding the LOH, causes water to move out by osmosis = counter-current multiplier
therefore the NaCl conc down the descending limb increases - at the bottom of the LOH - the max conc of NaCl
- filtrate passes through the distal convoluted tubule to the collecting duct
- the collecting duct is permeable to water so water moves out into the medullary tissue fluid by osmosis, a water potential grad is maintained the entire length of the collecting duct
- hypertonic urine is formed at the collecting duct
What is the counter current multiplier?
filtrate flows down the descending limb in the opposite direction of the filtrate flowing in the ascending limb
it is an example of positive feedback = as more NaCl moves out of the As limb, more H2O moves out of the Ds limb
What is the role of the counter current multiplier?
ensures that there is always a water potential grad drawing water out of the tubule by osmosis
Why is the wall thicker at the top of the ascending limb?
the walls here have more mitochondria to provide energy for active transport of NaCl
Why is it important for the LOH to set up a water potential grad through the medullary tissue?
ensures a water potential grad between the collecting duct and tissue fluid is maintained for the entire length of the collecting duct - more water is absorbed into the blood plasma
What is the structural difference of a LOH of a mammel living in a dry environment?
they have an extended LOH
Explain the process of greater water absorption if a mammel has an extended LOH?
- there is more time for NaCl to move out of the ascending limb, and more time for water to move out of the descending limb
- there is a greater max conc of NaCl at the hairpin
- this leads to a more conc medullary tissue fluid - lower water potential in the medullary tissue fluid
- so more water is drawn from the collecting duct into the medullary tissue fluid = more water is conserved
Where does ADH act on in the nephron?
the collecting duct
What does ADH stand for?
anti-diuretic hormone
What systems does osmoregulation include?
the endocrine system and the nervous system
What is the role of ADH in osmoregulation?
it targets the epithelial cells in the wall of the collecting duct
more ADH makes the epithelial cells more permeable to water
What is the process of osmoreguulation if there is a decrease in water potential in the blood?
- decrease in water potential in the blood
- the change is detected by osmoreceptors in the hypothalamus
- more ADH is produced by the hypothalamus
- the posterior pituitary gland recieves a higher freq of impulses which causes it to release more ADH into the blood plasma
- ADH increases the permeability of epithelial cells in the wall of the collecting duct
- kidneys produces a small vol of conc urine
What is the process of osmoregulation if there is an increase in water potential in the blood?
- increase in water potential in the blood
- the change is detected by osmoreceptors in the hypothalamus
- less ADH is produced by the hypothalamus
- the posterior pituitary gland recieves a lower freq of impulses which causes it to release less ADH into the blood plasma
- less ADH decreases the permeability of epithelial cells in the wall of the collecting duct
- kidneys produces a large vol of diluted urine
What causes the water potential of the blood to decrease?
high salt intake
low water intake
sweating
What causes the water potential of the blood to increase?
high water intake
low salt intake
Describe how ADH increases the permeability of the epithelial cells in the collecting duct
- ADH in blood plasma binds to protein receptors in the cell membrane of the epithelials that line the wall of the collecting duct (& DCT)
- activates phosphorylase enzyme in cells which in turn triggers vesicle in cytoplasm containing aquaporins to move to and fuse with the apical cell membrane
- aquaporins incorporated with the cell membrane increasing the membranes water permeability
- increased osmosis of water from CD lumen into the epithelial cell down a water potential grad
- increase in water potential of the cell so water moves out across the basal membrane into the medullary tissue fluid to be absorbed by the capillaries
