6.4 Homeostasis Flashcards
Define homeostasis in mammals
Involves physiological control systems that maintain the internal environment within restricted limits.
What does negative feedback do
Restores systems back to their original levels
What does negative feedback use to return levels to optimum point
Corrective mechanisms
What is positive feedback
Enhancing an effect further which results in even greater deviation from the normal
With negative feedback, what provides a greater degree of control
The possession of separate mechanisms which controls the departure in different directions from the optimum point
What are the 2 control systems
- Nervous system
- Endocrine system
How are responses communicated in the endocrine system
By chemicals in the blood steam
How are response communicated in the nervous system
By electrical impulses through neurones and synapsesf
Is hormonal or nervous coordination, more wide spread
Hormonal
Is hormonal or nervous coordination more localised
Nervous coordination
What is the name of the group of cells in the pancreas that contain alpha and beta cells
Islet of Langerhans
What secrete insulin
Beta cells
In response to what do Beta cells secrete insulin
In response to increased glucose concentrations
What secretes glucagon
Alpha cells
In response to what, do alpha cells secrete glucagon
In response to lowered glucose concentration
What is meant by the term glycogenesis
Forming glycogen from glucose
What is meant by glycogenolysis
The hydrolysis of glycogen into glucose
What is meant by gluconeogenesis
Synthesis of glucose from molecules that are not carbohydrates such as amino acids and fatty acids
What detects the increase in glucose levels
Beta cells
What are the 4 things that homeostasis controls
- Core body temperature
- Blood glucose concentration
- Blood pH
- Blood water potential
After what activity will your blood glucose concentrations increase
After ingestion of food or drink containing carbohydrates
After what activity will your blood glucose concentrations decrease
Following exercise or if you have not eaten food or drink containing carbohydrates
What is the organ that detects the change in blood glucose levels
The pancreas
What affect does insulin have on blood glucose levels
Decreases
What affect does glucagon have on the blood glucose levels
Increases
Where is adrenaline released from
The adrenal glands
What affect does adrenaline have on the blood glucose concentration
Increases
Why does adrenaline increase blood glucose concentration
As more glucose is being released from the hydrolysis of glycogen in the liver
What 3 effects arise as a result of insulin binding to glycoprotein receptors
- Increase in the number of glucose carrier proteins in the cell’s membrane
- Changes in the tertiary structure of glucose carriers so they open and allow uptake of glucose by faciliatated diffusion
- Activation of enzymes that convert glucose to glycogen and fats (Glycogenesis)
List the steps that happen when the blood glucose levels increase
- Detected by beta cells in the Islets of Langerhans
- Beta cells release insulin
- Liver cells become more permeable to glucose and enzymes are activated to convert glucose to glycogen
- Glucose is removed from the blood and stored as insoluble glycogen in cells
- So the normal blood glucose levels have been restored
List the steps that happen when the blood glucose levels decrease
- Detected by alpha cells in Islets of Langerhans
- Alpha cells release glucagon and adrenal glands release adrenaline
- Second messenger model occurs to activate enzymes to hydrolyse glycogen into glucose
- More glucose is released back into the blood
- Normal blood glucose levels are restored
What are the 3 actions of glycagon
- Attaches to receptors on the surfaces of liver cells
- Once bound to receptors a protein is activated enzymes involved in glycogenolysis
- Activates enzymes involved in gluconeogenesis
What are 3 main sources when glucose enters the blood
- Absorption from the gut after digestion
- Hydrolysis of stored glucose
- Conversion of non carbohydrates into glucose
What happens after glucagon has bound to the receptors on target cells
The protein changes shape
After the glucagon-receptor complex has formed, what is activated
Adenyl cyclase
What reaction does Adenyl cyclase catalyse
Converts ATP to cyclic AMP
What is the name of the enzyme that cAMP activates
Protein kinase
What reaction does protein kinase catalyse
Conversion of glycogen to glucose, glycogenolysis
Glucagon also causes the production of glucose from other sources, name 2 examples
Glycerol and amino acids
Does adrenaline and glucagon effect the cells directly
No
What effect do adrenaline and glucagon have on the cell they bind to
The binding causes a cascade of reactions
What is the enzyme that acts as the secondary receptor
cAMP
What are the causes of type 1 diabetes
Body being unable to produce insulin
What causes type 2 diabetes
Due to glycoprotein receptors on body cells being lost or becoming less sensitive to the presence of insulin
How is type 1 diabetes controlled
Injections of insulin to match the glucose intake
How is type 2 diabetes controlled
Regulating intake of carbohydrates and improving exercise levels
What is diabetes
Inability to control blood glucose concentrations
What process takes place in the kidneys
Osmosregulation
What is osmoregulation
The control of water potential in the blood
What is the name of the functional unit of the kidney
Nephron
What is the name of the beginning of the tubule that makes up the nephron
Bowman’s capsule
What is the name of the network of capillaries that surrounds the Bowman’s capsule
Glomerulus
What is produced in the first step of filtration of the blood in the nephron that takes place in the Bowman’s Capsule
Glomerular filtrate
What is the name of the artierole that flows into the Glomerulus
Afferent arteriole
What is the name of the arteriole that flows/ out of the Glomerulus
Efferent artierole
Does the afferent arteriole or the efferent arteriole have a wider lumen
Afferent arteriole
In the nephron, what does PCT stand for
Proximal Convoluted Tubule
What happens at the proximal convoluted tubule
Site of selective reabsorption
What 2 things are reabsorbed from the Glomerular filtrate through the PCT
- Glucose
- Water
The Loop of Henle produces a low water potential where in the kidney
In the medulla
What are the names of the 2 limbs that the Loop of Henle consist of
- Ascending limb
- Descending limb
The ascending limb is ____________ to water
Impermeable
The descending limb is _________ to water
Permeable
What is reabsorbed at the collecting duct
Water
If water potential of blood is low, is more or less water reabsorbed at the collecting duct
More water is absorbed
If water potential of blood is high, is more or less water reabsorbed at the collecting duct
Less water is absorbed
What creates the high hydrostatic pressure in the Glomerulus
The lumen width of the afferent arteriole being wider than the lumen width of the efferent arteriole
What does the high hydrostatic pressure in the Glomerulus result in
The blood plasma leaving the capillaries and entering the Bowman’s capsule
What is the name of the membrane in the capillary that stops larger molecules from leaving the capillary
Basement membrane
Due to the basement membrane, what remains in the capillary
- Large plasma proteins
- Blood cells
What is the name of the cells in the inner Bowman’s capsule membrane
Podocytes
What 5 things are inside the Glomerular Filtrate
- Water
- Amino acids
- Urea
- Glucose
- Inorganic ions
What does the renal artery supply blood to
The Glomerulus
What is the role of the ureter
Carries urine from kidney to bladder
What does the renal cortex contain
- Bowman’s capsule
- Convoluted tubules
What does the medulla of the kidney contain
- Loop of Henle
- Collecting duct
What is the role of the fibrous capsule
Protects kidney
At this card label a diagram of a nephron
Podocyte cells have long _________ extensions that _______ around the __________
- Cytoplasmic
- Wrap
- Capillary
What is the name of the gap between podocytes
Filtration slits
Where does selective reabsorption occur
In the proximal convoluted tubule
What is the first step in the selective reasborption process
The sodium ions are actively transported out of the epithelial cells lining the proximal convoluted tubule and into the surrounding blood capillaries
What is the effect of actively pumping sodium ions out of the cells lining the proximal convoluted tubule
The sodium ion concentration in the cells lining the PCT so a sodium ion concentration gradient is established
What happens once the sodium ion concentration gradient has been established in the PCT
Sodium ions diffuse down concentration gradient via facilitated diffusion through a carrier protein from lumen of PCT and into the epithelial cells
What is also transported into the epithelial cells with sodium ions in the PCT
- Glucose
- Amino acids
What happens to the glucose/ amino acids once they’re inside the cells lining the PCT
Move by facilitated diffusion into the blood stream
What decreases the water potential of the cells lining the PCT
Moving sodium ions from lumen
What does water do the counteract the decrease in water potential gradient in the cells lining the PCT
Move from the lumen of the PCT, into the cells lining the PCT via osmosis
What are 4 adaptations of the cells of the PCT
- Microvilli provide a large surface area
- Many carrier proteins for facilitated diffusion
- Many carrier proteins/ sodium ions-potassium ion pump for active transport
- Many mitochondria produce ATP for active transport
Where does the Loop of Henle dips down into in the nephron
Into the medulla
What is the Loop of Henle responsible for
Setting up a salt (NaCl) gradient
What are the names of the 2 limbs in the loop of Henle
- Descending Limb
- Ascending Limb
Which limb of the Loop of Henle is permeable to water
The descending limb
Which limb in the Loop of Henle is relatively permeable to salt (NaCl)
The ascending limb
In which limb of the Loop of Henle does water leave as the water potential of the tissue fluid decreases
Descending limb
What is the bottom of the Loop of Henle called
Hairpin
Where in the Loop of Henle, is the concentration of salt (NaCl) the highest
In the hairpin
By what process, does water leave the descending limb of the Loop of Henle
Osmosis
Where is water that is lost from the Loop of Henle taken
Reabsorbed into the blood in the surrounding capillaries via osmosis
What diffuses out of the ascending limb of the Loop of Henle
Sodium ions and chloride ions
By what process do sodium ions and chloride ions leave the ascending limb at the top of the limb
Active transport
Why at the top of the ascending limb, are sodium and chloride ions transported by active transport
Since the concentration of these ions in the filtrate has decreased and the concentration in the medullar tissue fluid has increases, so a concentration gradient isn’t there
Further down into the medulla, does the water potential increase or decrease and why
Decrease as there is a higher concentration of salt in the medulla tissue fluid
What does the filtrate pass through to reach the collecting duct from the ascending limb
Distal convulated tubule
What is the collecting duct permeable to
Water
What process occurs in the collecting duct, when water leaves
Osmosis
How does osmosis occur down the entire collecting duct
As the salt concentration increases deeper into the medulla, so the water potential is lower in the medullar tissue fluid compared to the collecting duct, so water potential gradient is maintained, so osmosis occurs
Is the urine that leaves the kidney hypotonic or hypertonic
Hypertonic
Does the urine that leaves the kidney have a higher or lower water potential than the blood
Lower water potential than the blood
Why is water reabsorbed in the collecting duct
To conserve water to prevent dehydration
What type of system operates in the Loop of Henle
Countercurrent multiplier system
What 3 steps are involved in the countercurrent multiplier system
- As filtrate moves down the collecting duct, it loses water, which lowers the water potential
- However, due to the pumping of ions out of the ascending limb, the water potential of surrounding tissues in the medulla is even lower than in the collecting duct
- Allowing water to continue to move out of the filtrate down the whole length of the collecting duct
Why does water not move from the tissue fluid into the ascending limb down a very large water potential gradient
The cells lining the ascending limb of the Loop of Henle are impermeable to water
Why do cells in the ascending limb of the Loop of Henle have a large number of mitochondria
- NaCl needs to be actively transported out of the ascending limb by active transport which requires energy in the form of ATP which is provided by mitochondria
Explain the term counter current multiplier
Counter-current = Filtrate flowing down the descending limb of the Loop of Henle in the opposite direction to filtrate in ascending limb
Multiplier= NaCl leaves ascending limb which lowers the water potential of the MTF so water moves out of the descending limb which in turns results in more NaCl leaving- and so on, positive feedback
Why is it necessary for the Loop of Henle to set up a water potential gradient through the medullary tissue fluid
So water potential gradient between collecting duct and tissue fluid is maintained along the entire length of collecting duct so the maximum water reabsorbance is reached so water is conserved
Why would a mammal living in a dry environment have an extended loop of Henle
- Greater maximum concentration of NaCl at the hairpin
- More concentrated medullary tissue fluid
- Lower water potential gradient of the medullary tissue fluid
- More water drawn from collecting duct into the medullary tissue fluid and into the blood
- So more water is conserved
What does ADH stand for
Anti-diuretic hormone
What are the target cells for ADH
The epithelial cells of the collecting duct and the distal convoluated tubule
What effect does ADH have on the target cells
Increases the cells permeability to water
What system(s) are involved in osmoregulation
- Endocrine
- Nervous
What may cause a decrease in blood water potential
- Sweating
- Not drinking enough water
- Too much salt in the diet
What detects a change in the blood water potential
Osmoreceptors
Where are osmoreceptors found
In the hypothalamus
Where is ADH produced
In the hypothalamus
Where is ADH released from
The posterior pituitary gland
If there’s a low blood water potential, does the posterior pituitary gland receive a higher or lower frequency of impulses from the osmoreceptors
Higher frequency
What does a higher frequency of impusles from the osmoreceptors cause the posterior pituitary gland do
Release more ADH into blood plasma
When there’s a high concentration of ADH, what is the urine concentration and volume like
- Small volume
- Concentrated
What detects a change in blood water potential
Osmoreceptors
When there’s an increase in blood water potential, what is the frequency of impulses from osmoreceptors like to the posterier pituitary gland
Lower frequency of impulses
What is the effect of a lower frequency of impulses from osmoreceptors to the posterior pituitary gland
Less ADH is released into blood plasma
What effect does less ADH in blood plasma have on the epithelial cells of the collecting duct
Less permeable to water
What is the volume and concentration of urine like when there’s an increase in blood water potential
- Large volume
- Dilute urine
Once ADH has reached the capillary by the epithelial cells of the collecting duct, what happens to ADH
ADH diffuses through tissue fluid between capillary and the epithelial cell and binds to an ADH protein receptor on the basal membrane
What is the effect of ADH binding to ADH protein receptor
The binding triggers vesicles to move towards the apical membrane
What is the name of the proteins in the apical membrane and the basal membrane where water flows through
Aquaporins
What do the vesicles in the epithelial cell of the collecting duct contain
Contain aquaporins
How does ADH increase the permeability of the epithelial cells of the collecting duct
By increasing the number of aquaporins in the epithlial membrane
What are primary messengers
Messengers that don’t enter cells
What are examples of primary messengers
Hormones
What do primary messengers bind to
Receptors on the cell surface membrane
What is the name of the enzyme that converts ATP to cyclic AMP
Adenylate cyclase
Explain why a change in the amino acid sequence of insulin prevents insulin binding to its receptors (2 marks)
- Changes tertiary structure;
- No longer complementary (to receptor);
Explain why glucose is found in the urine of a person with untreated diabetes (3 marks)
- High concentration of glucose in blood/filtrate;
Accept tubule for filtrate. - Not all the glucose is (re)absorbed at the proximal convoluted tubule;
- Carrier/co-transport proteins are working at maximum rate
OR
Carrier/co-transport proteins/ are saturated;
Describe the role of glucagon in gluconeogenesis (2 marks)
- (Attaches to receptors on target cells and) activates/stimulates
enzymes; - Glycerol/amino acids/fatty acids into glucose;
Explain how increasing a cell’s sensitivity to insulin will lower the blood glucose concentration (2 marks)
- (More) insulin binds to receptors;
- (Stimulates) uptake of glucose by channel/transport proteins
OR
Activates enzymes which convert glucose to glycogen;
Explain how inhibiting adenylate cyclase may help to lower the blood glucose concentration (3 marks)
- Less/no ATP is converted to cyclic AMP/cAMP;
- Less/no kinase is activated;
- Less/no glycogen is converted to glucose
OR
Less/no glycogenolysis;
Give 2 reasons why pancreas transplants are not used for treatment of type 2 diabetes
- (Usually)Type II produce insulin;
- Cells / receptors less sensitive / responsive (to insulin)
OR
Faulty (insulin) receptors; - (Treated / controlled by) diet / exercise;
Give 2 ways in which people with type 1 diabetes control their blood glucose concentration
- Treat with insulin (injection/infusion);
- (Control) diet/control sugar intake;
Describe how ultrafiltration occurs in a glomerulus (3 marks)
- High blood/hydrostatic pressure;
- Two named small substances pass out eg water, glucose,
ions, urea; - (Through small) gaps/pores/fenestrations in (capillary)
endothelium; - (And) through (capillary) basement membrane;
Explain why the concentration of fluid in the tubule remains constant in the PCT (1 mark)
Water is also reabsorbed
Give the location of the osmoreceptors in the body of a mammal
Hypothalamus
Explain why, when a person is dehydrated the cell volume of an osmorecptor decreases (2 marks)
- Water potential of blood will decrease;
- Water moves from osmoreceptor into blood by osmosis
Describe and explain how the secretion of ADH affects urine produced by the kidneys (4 marks)
- Permeability of membrane / cells (to water) is increased;
- More water absorbed from / leaves distal tubule / collecting duct;
- Smaller volume of urine;
- Urine becomes more concentrated.
Apart from age and gender, give 2 factors that could affect the concentration of creatinine in the blood
Muscle / body mass
Ethnicity
Exercise
Kidney disease
Explain how the binding of insulin leads to an increase in the rate of respiration in cells (2 marks)
- (Insulin) leads to more transport proteins / channel (proteins) / carrier (proteins) for glucose;
- More glucose (for respiration / glycolysis) enters cell;
Give the location of the receptors that detect a decrease in blood pressure
- Aorta
OR
Carotid artery/sinus;
Explain how the release of ADH will affect blood pressure
- (ADH) increases (re)absorption of water;
- Increases volume of (blood) and pressure
increases
OR
Increases volume of (blood) and pressure
returns to normal;
Describe the role of epithelial cell membranes in the PCT in the reabsorption of glucose
- Sodium ions are actively transported out of the PCT epithelial cells into the blood via the sodium/potassium pump, lowering the sodium ions concentration inside the cell
- Sodium ions diffuse back into the PCT epithelial cells from the filtrate via co-transport proteins, bringing glucose with them
- Glucose moves from the epithelial cells into the blood via facilitated diffusion through a specific carrier protein
- The epithelial cell membranes have microvilli, which increase the surface area for absorption, ensuring maximum reabsorption of glucose
Describe the role of epithelial cell membranes in the collecting duct in the reabsorption of water
- ADH binds to specific receptors on the epithelial cell membranes of the collecting duct
- This stimulates the insertion of aquaporins into the membrane, increasing its permeability to water
- Water moves out of the collecting duct epithelial cells into the surrounding MTF by osmosis, down a water potential gradient
- The surrounding MTF has a very low water potential due to ion concentration, maintaining the gradient. Reabsorbed water then enters blood capillaries, preventing dehydration and maintaining blood volume
Describe the role of liver cell membranes in the regulation of blood glucose
Glucagon binds to specific receptors on the liver cell membranes, initiating the activation of an enzyme pathway
- This stimulates the activation of enzymes like adenyl cyclase, leading to an increase in cAMP levels within the liver cell
- The elavated cAMP activates protein kinases, which promote the breakdown of glycogen into glucose through glycogenolysis
- The glucose produced is then released from the liver cells into the bloodstream, raising blood glucose levels
Explain the importance of regulating blood glucose concentration
- Maintaining a stable blood glucose concentration ensures a constant supply of the primary respiratory substrate, especially in the brain and muscles
- If blood glucose levels are too high, it can cause damage to tissues and organs as cells lose water and dehydrate, while too low can lead to insufficient energy for celluar activities
- The regulation of blood glucose concentration is essential for homeostatsis
Explain the importance of regulating blood water potential
- Regulating blood water potential ensures that cells maintain their shape and function by preventing excessive water loss or intake
- Maintaining blood water potential helps control the osmotic balance, which is essential
- Proper regulation of water potential also contributes to maintaining blood volume and pressure, supporting overall circulatory function
The scientists repeated the investigation using much higher doses of STZ. This led to destruction of pancreatic cells. The scientists concluded that these rats would not be
suitable for studying type II diabetes.
Give two reasons why the scientists made this conclusion (2 marks)
- (Type II) still produce/release insulin;
- (Type II) cells/receptors less/not
responsive/sensitive to insulin; - Pancreatic cells not destroyed (in type II
diabetes); - Damage to pancreatic cells may affect
processes/reactions (in the body);
Name the part of the body which releases antidiuretic hormone (ADH) into the blood
Posterior pituitary;
Alcohol decreases the release of ADH into the blood.
Suggest two signs or symptoms which may result from a decrease in ADH. (2 marks)
- Dehydration/thirst;
- Frequent urination
OR
Increase in volume of urine;
3.Less concentrated urine
OR
Dilute urine
OR
Urine paler/lighter in colour;
Describe the effect of ADH on the collecting ducts in kidneys (3 marks)
- (Stimulates) addition of channel proteins into
membrane; - Increases permeability to water
OR
(More) water (re)absorbed; - By osmosis;
Give 2 reasons why a weight-loss programme could be used to treat type II diabetes but not type I diabetes (2 marks)
- Type I do not produce insulin
- Type II receptors less sensitive to insulin
- Weight not linked to type I diabetes
