Homeostasis Flashcards
Can you describe the nature of homeostasis
Need to clarify but:
Maintenance of an internal environment within the restricted limits of an organism.
Why is homeostasis important? (4)
Ensures an organism is more independent of changes in external environment
Enzymes are sensitive to changes in ph and temperature - reduces rate/ denatures
Changes to WP of blood and tissue fluid may cause cells to shrink and expand.
Constant blood glucose concentration needed as a glucose source for respiration and ensuring a constant WP of blood.
Can you explain how control mechanisms work? (6)
An optimum point
Is monitored by a receptor
A co ordination transfers information to an effector
Effector brings changes to return to optimum point
Feedback mechanism occurs
Receptor responds to stimulus from effector
Explain negative feedback loops and an example (3)
Change produced by control system is detected by receptor and turns the system off
INHIBITS FURTHER CHANGE
Regulation of blood glucose
Can you explain what positive feedback loops are and give an example (3)
Deviation from optimum results in an even greater deviation from optimum
AMPLIFIES EFFECT
Labour contractions
Influx of Na+ into axon
Can you explain how hormones work? (4)
Hormones are secreted from endocrine glands directly into the bloodstream.
Some are steroid but most are proteins.
Are effective in low concentration but have long lasting effects
Specific target cells with specific and complementary cell - surface receptors
Why can steroid hormones enter the cell?
Lipid soluble, hence simple diffusion
Exocrine glands
Secrete substances (not hormones) into tubes or ducts
Endocrine glands
Secreted hormones directly into blood capillaries
Is the pancreas exocrine or endocrine? (3)
Both
Protease, lipase
Glucagon and insulin
Where are receptors found for water soluble hormones and steroid hormones
Water soluble can not pass by simple diffusion hence OUTSIDE cell
Steroid = lipid soluble = simple diffusion = INSIDE CELL
Islets of Langerhams contain
Alpha and Beta cells
Hyperglycemic
Too high blood glucose concentration
Hypoglycaemic
Too low blood glucose concentration
Is regulation of blood glucose concentration a positive or negative feedback loop?
Negative
4 ways blood glucose is lowered
Increase uptake of glucose increase in respiratory rate ( glucose is respiratory substrate)
Increased rate of glycogenesis - conversion from glucose to glycogen
Increased rate of conversion of glucose into adipose/fat.
Describe insulin action (6 includes 4 ways)
Insulin attaches to specific and complementary glycoprotein receptors on body cells.
Causes glucose transport channel proteins to change shape and open
Also rise in insulin results in fusion of vesicles with cell surface membrane. Vesicles contain many channel proteins, hence once fused more channel proteins available for glucose entry into cells
Glucose enters cells by facilitated diffusion p, which increases rate of absorption
Increases glycogenesis
Increases glucose conversion to fats in fat cells
What is glycogenesis
Conversion of glucose to glycogen
What is glycogenolysis
Conversion of glycogen to glucose
What is gluconeogensis?
Conversion of amino acids and glycerolinto glucose
Describe and explain regulation of an increase in blood glucose concentration (hyperglycaemia)
Receptor: Beta cells in Islets of Langerhams (pancreas) are stimulated to release
Regulator: insulin INTO BLOODSTREAM
Insulin attaches to specific and complementary glycoproteins receptors on body cells, which cause glucose transport channel proteins to change shape and open - also fusion of vesicles which contain many channel proteins so more entry points to cell for glucose.
Effector: body cells. Increased uptake of glucose. Increased rate of respiration because glucose is respiratory substrate. Increased rate of glycogenesis (glucose to glycogen). Increased rate of conversion of glucose into adipose/fats in fat cells.
Hence blood glucose concentration decreases.
4 ways an increase in blood glucose is regulated (hypoglycaemia)
Glucagon attaching to specific and complementary protein receptors on cell surface membrane of liver cells.
Activating enzymes for glycogenolysis ( glycogen to glucose)
Activating enzymes involved in gluconeogensis (converting amino acids and glycerol to glucose)
Fatty acids used in respiration instead of glucose, hence lowers uptake of glucose for aerobic respiration so higher glucose concentration in blood.
State the name of the model by which Glucagon and Adrenaline action occurs
Second Messenger model
Second messenger model with glucagon
Glucagon binds to specific and complementary glucagon receptor on cell surface membrane of liver and muscle cells
Causes an enzyme cascade reaction in cells
Adenylate cylase is activated
Active adenylate cylase causes ATP to become cyclic AMP, which acts as a second messenger
Causes protein kinase to become active
Active protein kinase causes glycogen conversion to glucose
Gluconeogenesis also occurs
Second messenger model with adrenaline
Adrenaline binds to specific and complementary adrenaline receptor on cell surface membrane of liver and muscle cells
Causes an enzyme cascade reaction in cells
Adenylate cylase is activated
Active adenylate cylase causes ATP to become cyclic AMP, which acts as a second messenger
Causes protein kinase to become active
Active protein kinase causes glycogen conversion to glucose
Gluconeogenesis also occurs
Describe and explain including glucagon action how low blood glucose concentration is regulated
Receptor: Alpha cells in islets of Langerhams in pancreas detect low blood glucose concentration, and stimulate the release of glucagon INTO BLOOD.
Regulator: glucagon binds to specific and complementary receptors on cell surface membrane of liver and muscle cells. Causes and enzyme cascade reaction. Causes adenylate cylase it become activated. Active adenylate cylase cause ATP to become cyclic AMP, which acts as a second messenger. Causes activation of protein kinase. Active protein kinase converts glycogen to glucose (glycogenolysis)
Gluconeogenesis also occurs
Effector: body cells and liver cells - glycogenolysis, gluconeogensis, fatty acids used in respiration instead of glucose hence lowers glucose uptake for respiration so HIGHER GLUCOSE CONC IN BLOOD
Can you explain roles of pancreas and liver in regulation of blood glucose concentration?
Pancreas -> islets of Langerhams cells are receptors
Liver -> effectors
Can you outline factors which influence blood glucose concentration? (3)
Diet = glucose absorbed following hydrolysis of other carbohydrates, directly consumed in diet Glycogenolysis = hydrolysis of glycogen (stored in liver and muscle cells) into glucose in SMALL INTESTINE Gluconeogenesis = conversion of amino acids and glycerol into glucose
How can efficiency of homeostatic models be judged?
How little change there is from the reference point and the speed with which they are restored after disturbance
Type 1 diabetes is insulin — and three background points
Dependent
Body’s inability to produce insulin
Generally from childhood
Autoimmune response where body attacks it’s own cells
Test for diabetes
High blood glucose concentration
Presence of blood glucose in urine
Signs of diabetes
Excessive need to urinate
Weight loss
Blurred vision
Symptoms of diabetes
Tiredness
Increased thirst and hunger
Type 2 diabetes is insulin — and six background points
Independent
Due to glycoproteins on body cells damaged or lose their responsiveness
Or inadequate supply of insulin from pancreas
Generally +40 years
Due to obesity and poor diet is now seen in adolescents
Control of type 1 diabetes (3 points)
Injections of insulin matched to glucose intake
Too much insulin injected causes too low blood glucose concentration and then lose consciousness
so biosensors used to control
Control of type 2 diabetes
Regulation of carbohydrate intake and more exercise
Some drugs slow absorption of glucose
Describe the structure of the mammalian kidney (6)
Fibrous capsule - outer membrane that protects the kidney
Cortex - lighter coloured outer region made up of Bowman/ Renal capsules
Medulla - made up of loops of Henle and collecting ducts
Renal Pelvis - funnel shaped cavity that collects urine into ureter
Renal artery - supplies blood to kidney
Renal Vein - returns blood to heart via vena cava
Describe the structure of a nephron (7)
Bowman’s/Renal capsule - contains GLOMERULUS (mass of blood capillaries). Inner layer made up of PODOCYTES
Proximal Convoluted tubule - epithelial cells in its walls which contain microvilli and surrounded by many blood capillaries
Loop of Henle
Distal Convoluted tubule - epithelial cell walls but no microvilli and less capillaries
Collecting duct
Afferent artieriole is THICKER to each nephron
Efferent arterioles
Which is on outside in cross section of kidney medulla or cortex? And what does it contain
Cortex (bowmans capsule on outside)
Draw and label diagram of nephron
Yes
Where, why and how is urea formed
In the liver
Ammonia is very soluble and toxic - urea is less soluble and less toxic
Deamination due to excess protein consumption releases NH2 (amine) which is converted into ammonia NH3. Ammonia is then converted into urea and CO2 in the liver.
Excretion is
Removal of toxic substances processed by cells eg: urea and CO2
Ejestion is
Removal of undigested matter
How is the liver involved with urea
Production
How are the kidneys involved with urea?
Removal
State term that describes the formation of glomerular filtrate
Ultrafiltration
What is the glomerular capillaries separated from lumen of bowmans capsule by?
Endothelium of capillary has fensters! Basement membrane (not an actual membrane) mesh of collagen and glycoproteins Epithelium of Bowmans capsule with specialised cells called podocytes
Podocytes structure and function
Many finger like projection
Extensions wrap aroudn glomukar capillaries and interlink with other podocyte extensions
Leave filtration slits for filtered fluid to pass through
Basement membrane structure and function
Mesh of fibres contains glycoproteins and collagen
Negative charges on fibres repel plasma proteins that pass through endothelium of capillary.
Endothelium of capillary structure and purpose for ultrafiltration in kidney
Festers that allow small molecules to pass (plasma proteins too!) but not RBC
Describe and explain ultrafiltration to produce glomerular filtrate
Diameter of afferent ARTERIOLE is greater than diameter of the efferent arteriole resulting in build up of hydrostatic pressure, which forces small molecules out through 3 layers: endothelium of capillary, basement membrane and then epithelium of capillary.
Endothelium of capillary has fensters that prevent RBC not plasma proteins
Basement membrane has negative charges that repel plasma proteins.
Epithelium of bowmans capsule contains podocytes with finger like extensions that interlink with each other leaving filtration slits allowing filtered fluid to enter renal capsule.
As water AND water soluble substances leave blood, water potential decreases hence osmosis back into capillary HOWEVER hydrostatic pressure is greater than osmotic pressure so net movement of fluid from glomerulus into renal capsule
Damage to filtration process due to high BP. Causes and how damage affects filtration process.
High BP damages capillaries, widens podocyte slits and damages the basement membrane hence allows plasma proteins and RBC to enter bowmans capsule
Diabetes Stress Obesity CHD Cholesterol -> narrows artery
Glomerular filtration rate is affected by two things
Damage to filtration process
Osmosis the wrong way but hydrostatic pressure is greater than osmotic.
Glomerular filtrate contains? What is left behind in capillary?
Water Amino acids Glucose Urea Mineral ions
Left = RBC, plasma proteins, some H2O
When looking at microscopic image/diagram of cortex of kidney what to look out for?
Glomerulus cluster of many tiny cells surrounded by capsule
Outside is bowmans capsule
Proximal convoluted tubules cells have microvilli
Distal convoluted tubules don’t have microvilli
Small round circles = may be capillaries
Five adaptations of proximal convoluted tubules and explain
Microvilli provide a large surface area for efficient absorption (by Fick’s law) of WANTED MOLECULES
Numerous mitochondria - AEROIBIC RESPIRATION producing ATP needed for Na+/K+ pump.
Closeness of blood capillaries - short diffusion PATHWAY; increases efficiency by Fick’s law
Contains co - transport carrier proteins - carries TWO molecules via FCAILLITATED DIFFUSION; one Na+ and one glucose/ amino acid
Cells tightly packed together means that no fluid can pass between cells and all substances reabsorbed must pass through PCT epithelial cells
How does solute concentration affect water potential in glomerulus and Bowmans capsule?
Resulting movement of water is?
Plasma proteins are repelled by negative charges of basement membrane and hence stay in capillaries.
Solute concentration in blood plasma is higher than that of filtrate in Bowmans capsule
Water potential of blood plasma is lower than that of filtrate
Hence water into capillaries BUT HYDROSTATIC PRESSURE GREATER THAN OSMOTIC PRESSURE SO NET MOVEMENT OF FLUID INTO BOWMANS CAPSULE
Where is most water re- absorbed in the nephron?
Proximal convoluted tubule
What is selectively re-absorbed in the proximal convoluted tubule?
Water Na+ K+ Cl- 50% urea
Why is urea selectively re-absorbed in the proximal convoluted tubule
Small molecule hence passes through plasma membrane even though urea is polar.
Concentration of urea in filtrate is higher than capillaries causing diffusion back into blood from Bowmans capsule
Purpose of tight junctions in epithelial cell of proximal convoluted tubule
Prevents water and mineral ions from escaping to adjacent cells
Describe and explain re-absorption in cells of the proximal convoluted tubule
Sodium ions actively transported out of cells into tissue fluid via Na+/K+ pump in BASAL membrane, which creates a deficit of Na+ ions in PCT cell allowing for
Co - transport of sodium and glucose or amino acids. Sodium ions diffuse down concentration gradient via facilitated diffusion. Creates an electroptoential gradient which pulls in glucose or amino acid molecule at the same time against its concentration gradient. One Na+ and one glucose/amino acid enter epithelial cell of PCT from PCT lumen.
Increase in glucose and amino acid inside cell increases solute concentration and hence lowers water potential compared to lumen of PCT so water enters cell via osmosis.
Glucose and amino acid then leave epithelial cell by facilitated diffusion through a channel protein into capillaries.
What is the function of the loop of Henle?
To maintain a gradient of sodium ions in the medulla using a counter current multiplier- increases solute concentration in the interstitial region
Adaptations of loop of Henle (x2)
Cells contains lots of mitochondria for aerobic respiration to produce ATP used for Na+/K+ pump.
Many capillaries wind around loop of Henle for a shorter diffusion pathway, which by Fick’s law increases efficiency
Loop of Henle uses a — — — and why is it useful?
A counter current multiplier
Two limbs of loop run side by side with fluid moving in opposite directions enables maximum concentration gradients to be built up both inside and outside tube, hence a greater exchange if substances than if limbs contained fluid that flowed in the same direction
Which limb of the loop of Henle is permeable to salts and not water?
Ascending
Which limb of the loop of Henle is permeable to water but not to salts?
Descending
How is a concentration gradient of sodium ions maintained by the loop of Henle? (5)
Na+ and Cl- are actively transported out of ascending limb using ATP from mitochondria in cells of Henles wall.
This raises the concentration of solute in the interstitial region, and creates a lower water potential in this region. Due to thick water impermeable walls of ascending limb, very little if any water escapes from ascending limb.
Causes loss of water via OSMOSIS from descending limb (higher water potential to lower water potential in the interstitial region). Some Na+ and Cl-enters descending limb via diffusion. Water potential down descending limb decreases.
Hence Na+ and Cl- concentration increases at the bottom of descending limb.
Na+ and Cl- diffuse out of via facilitated diffusion at bottom of ascending limb as glomerulus filtrate is now concentrated. Due to diffusion of ions out of filtrate water potential of filtrate increases up the ascending limb.
Summary of water potential changes of filtrate up and down loop of Henle
Down descending limb water potential decreases
Up ascending limb water potential increases
What happens to concentration of filtrate and volume down descending limb of loop of Henle?
Concentration of glomerular filtrate increases (less water!) Volume decreases (less water!)
What happens to concentration of filtrate and volume up ascending limb of loop of Henle?
Concentration of glomerular filtrate decreases (ions move out!)
Volume is constant (no loss of water!)
Length of desert animals loop of Henle compared to humans and why?
Longer
Longer cross current multiplier
More concentrated glomerular filtrate formed
More water reabsorbed via osmosis into the bloodstream from loop of Henle
Briefly explain role of distal convoluted tubule and collecting duct in the reabsorption of water.
Very little but if necessary and regulated by ADH
State components and roles (brief) of osmoregulatory system?
Receptor - hypothalamus and posterior pituitary gland releases ADH into blood
Coordinator - ADH levels in blood
Effector - collecting ducts of kidney
Distal convoluted tubule
What to talk about when “how does ADH level affect urine”?
volume and concentration of urine
How does high ADH levels in blood affect urine?
Small volumes of concentrated urine produced
How does low ADH levels in blood affect urine?
Large volumes of dilute urine produced
High ADH levels in blood mean body wants to lose or retain water?
Retain
Low ADH levels in the blood mean body wants to lose or retain water?
Lose
Osmoregulation definition
Control of water potential of the blood
Process that occurs when low water potential of blood is detected. Include how it is detected and hormone actions and volumes and concentration of urine.
Receptor : Osmoreceptors in hypothalamus shrink and released ADH to posterior pituitary gland from which ADH is released into the blood.
Coordinator: ADH levels in blood increase
Mechanism: more ADH binds to specific and complementary receptors on plasma membrane of cells lining DCT and collecting tube.
Causes activation of phosphorylase enzyme
Phosphorylase causes vesicles containing aquaporins ( water permeable protein channels) to fuse with plasma membrane.
Hence plasma cells are more permeable to water as more aquaporins on plasma membrane.
Water can now move freely from collecting duct via osmosis through aquaporins into plasma membrane, down its water potential gradient and re-enter blood.
Effector: cells of DCT or collecting tube become more permeable, hence water enters blood stream via osmosis and small volume of concentrated urine formed.
Therefore INCREASE in water potential of blood
Why do osmorecpetors shrink when low water potential of blood is detected?
Osmorecpetor has a higher water potential, hence water leaves via osmosis into blood.
Water potential in blood may change due to
Little/more consumption of water
Sweating
Uptake of a large amount of ions
Process that occurs when high water potential of blood is detected. Include detection but not hormone mechanism. Include volume and concentration of urine.
Receptor: osmoreceptors in hypothalamus increase in volume and decrease release of ADH, which is released into bloodstream from the posterior pituitary.
Coordinator: ADH level in blood decreases, hence less binding to specific and complementary receptors on plasma membrane of cells lining DCT and collecting duct.
Effector: cells of DCT and collecting duct less permeable to water and hence a large volume of dilute urine is produced.
Therefore DECREASE in water potential of blood.
