6C Homeostasis Flashcards
Give two factors that can change your blood glucose concentration
Eating and exercise
Why must blood glucose concetration be carefully controlled?
All cells need a constant energy supply to work (glucose provides this)
What is the normal blood glucose conc.?
Normally around 90mg per 100cm^3 of blood
Which organ monitors blood glucose conc.?
The pancreas
When will blood glucose conc. rise?
After eating food containing carbohydrates
When will blood glucose conc. fall?
After exercising, as more glucose is used in respiration to release energy
What are the two hormones that control blood glucose conc.?
- Insulin
- Glucagon
Does the nervous system or the hormonal system control blood glucose conc.?
The hormonal system
Where do insulin and glucagon come from?
They’re secreted from islets of Langerhans, which are cells in the pacreas
How do insulin and glucagon travel around the body?
Travel in the blood
Where do insulin and glucagon travel to in the body?
To their target cells (effectors)
What are the two types of cells found in islets of Langerhans?
- Beta (β) cells
- Alpha (α) cells
What do Beta (β) cells in the pancreas do and where are they specifically found?
Secrete insulin into the blood
What do Alpha (α) cells in the pancreas do and where are they specifically found?
Secrete glucagon into the blood
What do insulin and glucagon act on?
Effectors, which respond to restore the blood glucose conc. to the normal level
What is the action of insulin?
It lowers blood glucose when it’s too high
What is glycogenesis activated by?
Insulin
What is glycogenolysis activated by?
Glucagon
What is gluconeogenesis activated by?
Glucagon
What is the action of glucagon?
It raises blood glucose conc. when it’s too low
What is another name for liver cells?
Hepatocytes
What are the two main roles of the kidneys?
- Excrete waste
- Regulate blood water potential
Give an example of a waste product that the kideney excrete
Urea
Describe the process of ultrafiltration
As blood passes through capillaries in the cortex (outer layer) of the kidneys, substances are filtered out of blood & into long tubules that surround the capillaries
Describe the process of selective reabsorption
(Comes after ultrafiltration)
Useful substances, such as glucose & the right amount of water are then reabsorbed back into the blood
What happens after useful substances have been selectively reabsobed in th kidneys?
Remaining unwanted substances pass along the bladder & are excreted as urine
Where is blood filtered in the kidneys?
At the start of the nephrons
Name the structures that make up the kidney
- Fibrous capsule
- Cortex
- Medulla
- Renal pelvis
- Ureter
- Renal artery
DONT NEED TO KNOW THIS IGNORE IT
- Renal vein
What is the Fibrous capsule (kidneys)?
An outer membrane that protects the kidney
What is the Cortex (kidney)?
A lighter coloured outer regionmade up of renal (Bowman’s) capsules, convoluted tubules & blood vessels
What is the Medulla (kidney)?
A darker coloured inner region made up of loops of Henle, collecting ducts and blood vessels
What is the Renal pelvis (kidney)?
A funnel shaped cavity that collects urine into the ureter
What is the Ureter (kidney)?
A tube that carries urine to the bladder
What is the Reanl artery (kidney)?
Supplies the kidney with blood from the heart via the aorta
What is the Renal vein (kidney)?
Returns blood to the heart via the vena cava
What is the Loop of Henle?
A long, hairpin loop that extends from the cortex to the medulla of the kidney & back again
It is surrounded by blood capillaries
What is the Distal convoluted tubule (DCT)?
A series of loops surrounded by blood capillaries
Its walls are made of epithelial cells, but its surrounded by fewer capillaries than the proximal tubule
What are the component of a nephron?
- Afferent arteriole
- Efferant arteriole
- Glomerular capillary
- Renal (Bowman’s) capsule
- Proximal convoluted tubule
- Loop of Henle (Ascending & descending limb)
- Blood capilaries
- Distal convoluted tubule
- Collecting duct
What is the Collecting duct?
A tube into which a no. distal convoluted tubules from a no. nephhrons empty
It is lined by epithelial cells & becomes increasingly wide as it empties into the pelvis of the kidney
What are the blood vessels found in each nephron?
- Afferent arteriole
- Glomerulus
- Efferent arteriole
- Blood capillaries
What is the Reanl (Bowman’s) capsule?
Closed end at the start of the nephron
It’s cup-shaped & surrounds a mass of blood capillaries known as the glomerulus
Inner layer of the renal capsule is made up of specialised cells called podocytes
What is the Proximal convoluted tubule?
A series of loops surrounded by blood capilaries
Its walls are made of epithelial cells which have microvilli
What is the Afferent arteiole?
Tiny vessel that ultimately arises from the renal artery & supplies the nephron with blood
It enters the renal capsule of the nephron where it forms the glomerulus
What is the glomerulus?
A many-branched knot of capillaries from which fluid is forced out of the blood
The glomorular capillaries recombine to form the efferent arteriole
What is the efferent arteriole?
Tiny vessel that leaves the renal capsule
It has a smaller diameter than afferent arteriole & causes an increase in blood pressure within the glomerulus
Efferent arteriole carries blood away from the renal capsule & branches to form blood capillaries
What role do capillaries play in the nephron?
Concentrated network of capillaries that surround proximalCT, loop of Henle & distalCT & from where they reabsorb reabsorb mineral salts, glucose & water
Capillaries merge to form venules that merge to form the renal vein
What is homeostasis?
The maintenance of a stable internal environment
Changes in your internal environment can affect your internal environment
Why is homeostasis important?
Keeping you internal environment stabel is vital for cells to function normally & to stop them being damaged
What are some of the most important important things to be maintained in homestasis?
- Core body temp
- Blood pH
Because temperature & pH affect enzyme activity & enzymes control the rate of metabolic reactions
What happens if temperature is too high?
(e.g. 40 degrees) Enzymes may become denatured
The enzymes’s molecules vibrate too much, which breaks the hydrogen bonds that hold them in their 3D shape
Shape of enzymes’s active site is changed & it no longer works as a catalyst
Means metabolic reactions less efficient
What happens if body temp is too low?
Enzyme activity is reduced, slowing the rate of metabolic reactions
What temp is the highest rate of enzyme activity?
The optimum temp - 37 degrees
What happens if blood pH is too high/low?
(highly alkaline or acidic) The enzymes become denatured
The hydrogen bonds that hold them in their 3D shape are broken, so the of the enzyme’s active site is changed & no longer works as a catalyst
What pH is the highest rate of enzyme activity?
The optimum pH - usually around pH 7 (neutral)
Some enzymes work best at other pH’s e.g. enzymes found in the stomach
Why is it important to maintain the conc. of blood glucose?
Cells need glucose for energy
Blood glucose conc. also affects the water potential of the blood
What happens if the blood glucose conc. is too low?
Cells are unable to carry out normal activities as there isn’t enough glucose for respiration to provide energy
What happens if blood glucose conc. is too high?
The water potential of blood is reduced to a point where water molecules diffuse out of cells into the body by osmosis
This can cause the cells to shrivel up and die
How do homeostatic systems respond to a detected change?
By negative feedback
What do homeostatic systems involve?
- Receptors
- A communication system
- Effectors
What do receptors do in homeostasis?
They detect when a level is too high or low & the info is communicated via the nervour system or the hormonal system to effectors
What do effectors do in homeostasis?
They respond to counteract the change - bringing the level back to normal
What is the mechanism that restores levels back to normal in homeostasis?
Called a negative feedback mechanism
Can negative feedback work all the time?
Not all the time - it works within certain limits
If the change is too big, then the effectors may not be able to counteract it
e.g. a huge drop in body temp caused by prolonged exposure to cold weather may be too large to counteract
Why are there multiple negative feedback mechanisms in homeostasis?
Having more than one gives more control over changes in your internal environment
Means you can actively increase/decrease a level so it returns to normal - e.g. feedback mechanisms to reduce body temp & mechanisms to increase it
What would happen if you only had one negative feedback mechanism?
All you could do would be turn it on and off - you could only change the level in one direction so it returns to normal
e.g. it’s a bit like trying to slow down a car with only an accelerator - you can only take your foot off the accelerator
What do positive feedback loops do?
They amplify a change from the normal level
How do effectors act in a positive feedback loop?
They respond by further increasing the level away form the normal
What is positive feedback useful for?
It’s useful to rapidly activate something
e.g. a blood clot after an injury
How does positive feedback work to form a blood clot after an injury?
- Platlets become activated & release a chemical - this triggers more platelets to be activated & so on
- Platelets very quickly form a blood clot at the injury site
- The process ends with -ive feedback, when the body detects the blood clot has been formed
When in a bad situation does poitive feedback happen?
It can happen when a homeostatic system breaks down
e.g. if you’re too cold for too long
What sort of feedback happens in hypothermia?
Positive feedback
Explain how positive feedback causes hypothermia?
- Hypothermia is low body temp. (below 35 degrees)
- It happens when heat’s lost from the body quicker than it can be produced
- As body temp falls, the brain doesn’t work properly & shivering stops - this makes body temp fall even more
- +ive feedback takes body temp further away from the normal level & it continues to decrease unless action is taken
Is positive feedback involved in homeostasis?
It isn’t involved in homeostasis because it doesn’t keep your internal environment stable
Does insulin lower or raise blood glucose levels?
It lowers blood glucose conc. when it’s too high
Does glucagon lower or raise blood glucose levels?
It raises blood glucose conc. when it’s too low
Describe the process which insulin lowers blood glucose conc.
- Insulin binds to specific receptors on cell membranes of liver cells & muscle cells
- Increases permeability of muscle-cell membranes to glucose, so cells take up more glucose. This involves increasing the no. channel proteins in cell membranes
- Insulin also actives enzymes in liver & muscle cells that convers glucoes into glycogen
- Cells are able to store glycogen in their cytoplasm as an energy store
- Process of forming glycogenfrom glucose is called glycogenesis
- Insulin also increases rate of respiration of glucose, especially in muscles
Describe the process in which glucagon raises blood glucose conc.?
- Glucagon binds to specific receptors on the cell membranes of liver cells
- Glucagon activates enzymes in liver cells that break down glycogen into glucose
- The process of breaking down glycogen is called glucogenolysis
- Glucagon also activates enzymes that are involved in the formation of glucose from glycerol (a component of lipids) & amino acids
Why are responses produced by hormones slower and why do they last longer?
They travel in the blood to their target cells - these responses are slower than those produced by nervous impulses
Hormones are not broken down as quickly as neurotansmitters, so the effects last longer
Describe what happens when blood glucose levels are too high
- Pancreas detects blood glucose conc. is too high
- Beta cells secrete insulin, alpha cells stop secreting glucagon
- Insulin binds to receptors on liver & muscle cells
- Cells take up more glucose, glycogenesis is activated,, cells respire more glucose
- Less glucose in the blood
Describe what happens when blood glucose levels are too low
- Pancreas detects blood glucose conc. is too low
- Alpha cells secrete glucagon, beta cells stop secreting insulin
- Glucagon binds to receptors on liver cells
- Glycogenolysis is activated, gluconeogenesis is activated & cells respire less glucose
- Cells release glucose into the blood
What does insulin do to lower blood glucose conc.?
It makes glucose transporters availble for facilitated diffusion (e.g. GLUT4)
What is the glucose transporter found in skeletal & cadiac muscles?
GLUT4
What is the overall function of the kidneys?
Excrete waste and regulate blood water potential
What is ultrafiltration in the kidneys?
As blood passes through capillaries in cortex (outer layer) of kidney substances are filtered out of blood into long tubules that surround the capillaries
What is selective reabsorption in the kidneys?
- Occurs after ultrafiltration
- Useful substances (glucose and water) are reabsorbed back in the blood
What happens to remaining unwanted substances that don’t get reabsorbed?
They pass along the bladder and are excreted as urine
What are the long tubules along the bundle of capillaries called?
Nephrons (around 1 million in each kidney)
What is the process of blood filtration?
1) Blood from renal artery’s enters arteriolar in cortex
2) Each arteriole splits into the glomerulus (this is where ultrafiltration takes place)
3) The afferent arteriole takes blood into each glomerulus and the efferent arteriole takes filtered blood away from the glomerulus
4) High pressure in efferent arteriole forces molecules in blood out of capillary into Bowman’s capsule
5) Blood passes through 3 layers to get from capillaries to Bowman’s capsule
6) Large substances can’t pass through and substances that do are called the glomerular filtrate
7) Glomerular filtrate passed along rest of nephron and useful substances are reabsorbed
8) Filtrate flows through collecting duct and pass out of kidney though ureter
What does the efferent arteriole do?
Takes filtered blood away from the glomerulus
What does the afferent arteriole do?
Takes blood into each glomerulus
Why does the efferent arteriole have high pressure?
Smaller in diameter so high pressure forces liquid and small molecules in the blood out of the capillary
What are the 3 layers that molecules pass through form the capillary to Bowman’s capsule?
- Capillary wall
- Basement membrane
- Epithelium in Bowman’s capsule
Where does selective reabsorption take place?
As the glomerular filtrate flows along the PCT, through the loop of Henle, and along the DCT
How’s does selective reabsorption take place?
1) Useful substances leave the nephrons into the capillary network
2) Epithelium of the PCT has microvilli (larger SA) for reabsorption of useful materials from glomerular filtrate to the blood
3) Useful solutes (glucose) are reabsorbed along PCT by active transport of facilitated diffusion
4) Filtrate that remains is urine which passes along ureter to the bladder
What does urine usually consist of?
- Water and dissolved salts
- Urea
- Hormones and excess vitamins
How is the epithelium of the PCT adapted for reabsorption?
Has microvilli to provide a large surface area
How does the second messenger process work?
- Receptors for adrenaline & glucagon have specific tertiary structures, make them complementary in shape to their respective hormones
- Adrenaline & glucagon bind to their receptors & activate the enzyme adenylate cyclase
- Activated adenylate cyclase converts ATP into a chemical signal called a ‘second messenger’
- The second messenger is called cyclic AMP (cAMP)
- cAMP activates an enzyme called protein kinase A - Protein kinease A activates a cascade that breaks down glycogen into glucose
What other hormone can increase blood glucose conc.?
Adrenaline
Just like glucagon, it also helps to increase blood glucose conc.
Where is adrenaline secreted from?
The adrenal glands, which are located above the kidneys
When is adrenaline secreted?
When there’s a low conc. of glucose in your blood, when you’re stressed & when you’re exercising
What effect does adrenaline have on blood glucose concentrations?
Adrenaline binds to receptors in the cell membrane of liver cells
- It activates glycogenolysis (breakdown of glycogen to glucose)
- It inhibits glycogenesis (synthesis of glycogen from glucose)
What is glycogenolysis?
The breakdown of glycogen to glucose
What is glycogenesis?
The synthesis of glycogen from glucose
What hormones does adrenaline control for blood glucose conc.?
It activates glucagon secretion & inhibits insulin secretion
This increases glucose conc.
How does adreanile affect the body?
It gets the body ready for action by making glucose availble for muscles to respire
How do adrenaline and glucagon act?
Via a second messenger
Do adrenaline and glucagon bind to the inside or the outside of the cell?
They bind to receptors on the outside of the cell
They can activate glycogenolysis inside a cell via a second messenger
What regulates the water potential of the blood?
Kidneys
Why does water potential of the blood need to be kept constant?
Water is essential to keep the body functioning
What ways to mammals lose water?
- During excretion
- Sweating
What is osmoregulation?
Kidneys regulating water potential in the blood
What happens when the water potential of blood is too low?
- More water is reabsorbed by osmosis into the blood from the tubules of nephrons
- Urine is more concentrated (less lost during excretion)
What happens when the water potential of blood is to high?
- Less blood is reabsorbed by osmosis into the blood from the tubules of the nephrons
- Urine is more dilute (less lost during excretion)
Where does regulation of water mainly take place?
- Loop of Henle
- DCT
- Collecting duct
What is the function of the Loop of Henle?
Maintains a sodium ion gradient
Where is the loop of Henle located?
In the medulla (inner layer) of the kidneys
What is the loop of Henle made up of?
- Descending limb
- Ascending limb
How does the Loop of Henle control blood water potential?
1) At top of ascending limb Na+ are pumped into medulla by active transport, it’s not permeable to water so water stays inside (lowering water potential in medulla)
2) Because of this water in descending limb moves into the medulla by osmosis (not permeable to ions)
3) Water in medulla the reabsorbed into blood through capillary network
4) Near bottom of ascending limb Na+ diffuse out into medulla (further lowering water potential in medulla)
5) Water moves out of DCT by osmosis and reabsorbed into the blood
6) As ion concentration in medulla is high water moves out of the collecting duct by osmosis
What are features of the ascending limb?
- Ions are permeable
- Water is not permeable
What are features of the descending limb?
- Permeable to water
- Not permeable to ions
What cells monitor water potential in the blood?
Osmoreceptors (part of brain called hypothalamus
How do osmoreceptors respond when the water potential of blood decreases?
1) Water moves out of osmoreceptors by osmosis causing them to decrease in size
2) This sends signal to posterior pituitary gland which releases a hormone called ADH
3) ADH makes walls of DCT and collecting duct more permeable
4) More water is reabsorbed from these into medulla and into blood (small amount of concentration of urine produced)
Why does blood ADH levels fall when your hydrated?
1) Water content of blood rises, so water potential increases
2) Detected by osmoreceptors
3) Posterior pituitary gland releases less ADH into blood
4) Less ADH means DCT and collecting duct become less permeable (less water reabsorbed)
5) Large amount of dilute urine is produced and more water is lost
Where is ADH released?
Posterior pituitary gland
How does the second messenger process work?
- Receptors for adrenaline & glucagon have specific tertiary structures that make them complementary in shape to their respective hormones
- Adrenaline & glucagon bind to their receptors & activate an enzyme called adenylate cyclase
- Activated adenylate cyclase converts ATP into a chemical signal called a ‘second messenger’
- The second messenger is called cyclic AMP (cAMP)
- cAMP activates an enzyme called protein kinase A
