6C: Homeostasis Flashcards
What is homeostasis?
In mammals involves physiological control systems that maintain the internal environment within restricted limits.
Why is it important to maintain the right core body temp?
If body temp is too high enzymes may become denatured.
= The enzyme’s molecules vibrate too much, which breaks the H bonds that hold them in their specific 3D shape, so they can no longer work as a catalyst –> makes metabolic rates less efficient
If it’s too low then enzyme activity will be reduced
Why is it important to maintain the right blood pH?
If blood pH is too high/low enzymes become denatured
What is the optimum body temp for the human body?
Around 37oC
Why is it important to maintain blood glucose conc.s?
If blood glucose conc. is too high the WP of blood is reduced to the point where molecules diffuse out of cells into the blood by osmosis = cells will shrivel up and die
If blood glucose conc. is too low, cells are unable to carry out normal activities because there isn’t enough glucose for respiration to provide energy
Describe what negative feedback is
Change in conditions are reversed + returned back to the set point in order to maintain optimum conditions.
What is a stimulus?
Deviation from optimum point
What is an optimum point?
The point at which a system operates best
Describe what positive feedback is
When the change detected is increased further away from optimum conditions, and does not lead to homeostasis
What is an endotherm?
Organisms that maintain body temp at a set point
- Generate heat through respiration
- Change cellular + physiological processes
What is an ectotherm?
Organisms that rely on external heat to maintain body temp
- Warm/cool their body by changing their behaviour in response to changing conditions
e. g basking in the sun, taking shelter…
Give 4 ways endotherms try to gain heat
- Vasoconstriction
- Shivering
- Raising of hairs
- Increased metabolic rate
Give 4 ways endotherms try to loose heat
- Vasodilation
- Increased sweating
- Lowering of body hair
- Behavioural mechanisms
Name 3 factors that affect blood glucose conc.
- Directly from diet
- Glycogen converted into glucose in the liver
- From gluconeogenesis
What organ monitors blood glucose levels?
The pancreas
What are the sections of tissue that detect blood glucose conc. in the pancreas called?
Islets of Langerhans
What 2 types of cells make up the islets of Langerhans
Alpha cells and beta cells
Describe alpha cells in the Islets of Langerhans, what is their function?
- Larger
- Detect low glucose conc.
- Secrete glucagon
Describe beta cells in the Islets of Langerhans, what is their function?
- Smaller
- Detect high glucose conc.
- Secrete insulin
What is glycogenesis?
Synthesis of glycogen from glucose
What is glycogenolysis?
Breakdown of glycogen into glucose
What is gluconeogenesis?
Synthesis of glucose from lipids, amino acids or nucleic acids
What is the synthesis of glycogen from glucose called?
glycogenesis
What is the breakdown of glycogen into glucose called?
glycogenolysis
What is the synthesis of glucose from lipids, amino acids or nucleic acids?
gluconeogenesis
Describe what happens when blood glucose conc. is too high.
- B cells in the islets of Langerhans detect & secrete insulin into the bloodstream
- Insulin binds to receptors on surface of either muscle or liver cells
- Muscle cells: Insulin controls uptake of glucose into cells (by regulating the activity of channel proteins in the surface membranes)
- Liver cells: Insulin activates enzymes that convert glucose into glycogen (Glycogenesis) - If excess glucose remains, it may undergo conversion into fat.
Describe insulin’s effect on muscle cells
Insulin binds to receptors on muscle cell surface. It controls the uptake of glucose by regulating the inclusion of channel proteins in the surface membrane.
What is insulins function?
To lower blood glucose levels back to normal (optimum)
Describe what happens when the blood glucose conc. is too low.
- Alpha cells in the islets of Langerhans detect & secrete glucagon into the bloodstream
- Glucagon binds to receptor on surface of liver cells:
- Activates enzymes to convert glycogen to glucose (glycogenolysis)
- Activates enzymes to convert glycerol + amino acids into glucose (gluconeogenesis
What is glucagons function?
To increase blood glucose levels back to normal (optimum)
How can glucagon and insulin be said to act?
They act antagonistically (in opposite directions)
What is the role of adrenaline
- attaching to receptors on the surfaces of target cells
- activating enzymes involved in the conversion of glycogen to glucose.
Describe the second messenger model
5 steps
- Adrenaline/glucagon bind to protein receptors on the cell surface membrane of target cells (liver)
- This binding causes a protein on the inside of cell to change shape
- This actives the enzyme adenylyl cyclase to convert ATP to cAMP
- cAMP acts as a second messenger that binds to protein kinase enzyme, changing its shape and activating it
- This activated enzyme catalyses the conversion of glycogen to glucose, which then moves out of the liver cell and into the bloodstream by facilitated diffusion
What is type 1 diabetes?
The body is unable to produce insulin
When does type 1 diabetes usually develop?
Childhood, rapid onset of symptoms
What are the symptoms of type 1 diabetes?
Frequent urination, glucose in urine, genital itching, weight loss, tiredness
What is type 1 diabetes thought to be caused by?
Autoimmune response, immune system attacks B cells in the islets of Langerhans
How is type 1 diabetes controlled?
- Insulin injections (dose is matched to glucose intake)
- Blood glucose is monitored by biosensors
What is type 2 diabetes?
Glycoprotein receptors are lost/lose responsiveness to insulin
- Can also be due to an inadequate supply of insulin from the pancreas
When does type 2 diabetes usually develop?
In people over 40 (obesity increases risk)
- develops more slowly than type 1
How is type 2 diabetes controlled?
- Regulating intake of carbohydrate in the diet
- Can also be supplemented by insulin injections / drugs that stimulate insulin production
What is osmoregulation?
The control of the water potential of the blood
What is excretion?
Removes the waste products from metabolism (urea and creatine)
What are nephrons?
Long tubules along with the bundle of capillaries where blood is filtered - there are around one million in each kidney
What are the 2 main functions of the kidney?
- To excrete waste products e.g urea
- To regulate the water potential of blood
Briefly describe the process of ultrafiltration
As blood passes through capillaries in the cortex (outer layer) of the kidneys, substances are filtered out of the blood and into long tubules that surround the capillaries
Briefly describe the process of selective reabsorption
Useful substances, such as glucose and the right amount of water, are then reabsorbed (after ultrafiltration) back into the blood
What is a glomerulus?
(Inside the nephron) A bundle of capillaries looped inside a hollow ball called a bowman’s capsule
What process takes place in the glomerulus?
Ultrafiltration
Describe the role of the afferent arteriole
Takes blood into each glomerulus
Describe the role of the efferent arteriole
Takes the filtered blood away from the glomerulus
Where in the kidney are the nephrons located?
In the Medulla (loop of henle) and the cortex
Why is the blood in the glomerulus at high pressure?
Because the efferent arteriole is smaller in diameter than the afferent arteriole, so blood in the glomerulus is under high pressure
What does high pressure in the glomerulus result in?
The high pressure forces liquid and small molecules in the blood out of the capillary and into the Bowman’s capsule
- The liquid & small molecules pass through 3 layers to get into the Bowman’s capsule
Describe generally what ultrafiltration is?
Blood is filtered at the glomerulus and passes into the Renal Capsule (only small components are filtered)
Describe the process of ultrafiltration.
- High pressure is created in the glomerulus and forces water and small molecules to be filtered out of the blood and into the renal capsule
- High pressure is created as the diameter of the afferent arteriole is bigger than the diameter of the efferent arteriole.
Also:
The coiling of the capillaries in the glomerulus further restricts blood flow and so pressure
What is the solute potential like in the glomerulus? and why?
Low solute potential, because water is lost and plasma proteins stay behind
What are the 3 layers blood must pass through to be filtered?
- Glomerular capillary endothelium (pores)
- Basement membrane
- Renal capsule epithelium (podocytes have large filtration slits)
Describe the composition of glomerular filtrate
Smaller molecules e.g water make up the filtrate. While larger molecules e.g proteins and red blood cells, can’t pass through so they remain in the blood
What are the substances that can enter the Bowman’s capsule known as?
Glomerular filtrate
What is the solute potential like in the Bowman’s capsule?
High (because no plasma proteins)
Where does selective reabsorption take place?
As the glomerular filtrate flows along the proximal convoluted tubule (PCT), through the loop of Henle and along the distal convoluted tubule (DCT)
Briefly describe what selective reabsorption is.
Useful component of blood are reabsorbed, leaving behind waste products to be filtered.
What adaptations does the epithelium wall of the PCT have to aid absorption?
- Microvilli = increase SA for reabsorption of useful substances from the glomerular filtrate (in the tubules) into the blood (capillaries)
- Infoldings
- Mitochondria
Where does the glomerular filtrate go after its formed?
the tubules
What is absorbed by the PCT?
Useful substances e.g glucose are absorbed by the PCT by active transport and facilitated diffusion
Why does water enter the blood in selective reabsorption?
Water enters the blood by osmosis because the water potential of the blood is lower than that of the filtrate.
What is water potential?
The tendency of water to move down the WP gradient (from an area of higher WP to an area of lower WP).
What is urine made up of?
- Water and dissolved salts
- Urea
- Other substances e.g hormones and excess vitamins
What is the role of the DCT?
- Makes final adjustments
- Where toxic substances can be secreted into filtrate
- Water reabsorption
What is reabsorbed by the PCT?
- Water
- Ions
- Glucose
- Amino acids
- Small proteins
- Urea (passively)
Describe the process of selective reabsorption.
sodium ions
- Sodium ions are actively transported from PCT cells into the blood. The blood carries sodium ions away.
- Sodium ions diffuse into PCT cells from the lumen of the PCT by facilitated diffusion.
- Another molecule is carried with the sodium ions (glucose, or amino acids or chloride ions ect)
- The molecules then diffuse from the PCT into the blood.
What does urine not usually contain?
- Proteins and blood cells –> they’re too big to be filtered out of the blood
- Glucose because it’s actively reabsorbed back into the blood
What is the role of the loop of henle?
Make the medulla concentrated with ions, lowering the water potential and promoting the reabsorption of water by osmosis in the collecting duct
Describe the descending limb of the loop of henle.
- Permeable to water
- Impermeable to ions
Describe the aescending limb of the loop of henle.
- Impermeable to water
- Permeable to ions
Describe what happens to Na+ ions at the top of the ascending limb of the Loop of Henle
- Na+ ions pumper out via active transport into the medulla
- Water stays in the tuble (because its impermeable)
- Creates low WP in the medulla (because there’s a high ion conc.)
Describe what happens to water in the descending limb of the Loop of Henle
- Because there’s a lower WP in the medulla than the descending limb, water moves into the medulla by osmosis
= Filtrate becomes more concentrated (this limb is impermeable to ions)
What happens to water in the medulla?
It is reabsorbed into the blood by the capillary network
What happens to the Na+ ions at the bottom of the ascending limb of the Loop of Henle?
Na+ ions diffuse out into the medulla, further lowering the WP of the medulla
What happens to water in the distal convoluted tubule?
It moves out of the DCT via osmosis and is reabsorbed into the blood
Describe what happens to water in the collecting duct
- Ion conc of the medulla is very high, which lowers the WP
- Causing water to move out of the collecting duct by osmosis
= water is reabsorbed into the blood by the capillaries
