Homeostasis Flashcards
What is homeostasis?
The maintenance of a constant internal environment, despite changes to the external environment
What is hyperglycaemia and how can it be dangerous?
High blood glucose concentrations
Water potential of blood decreases, water moves by osmosis from cells into blood
Cells may be dehydrated and cannot carry out metabolic functions optimally
Blood pressure increases which may lead to cardio vascular disease
What is hypoglycemia and how can it be dangerous?
Decreased blood glucose concentrations
Water potential of the blood increases, water moves by osmosis into cells causing damage by osmotic lysis
Cells may not receive enough glucose to maintain a high metabolic rate
What pH does homeostasis maintain, and what happens if this is not maintained?
Between 7.35 and 7.45
If pH is higher or lower, the hydrogen bonds in the tertiary structure break, tertiary structure changes shape. Active site changes shape and no longer complimentary, so no enzyme substrate complexes can be formed and the enzyme is denatured. Can no longer act as catalysts
What temperature does homeostasis maintain in the body, and at what temperatures do hypothermia and hyperthermia occur?
Normal- 37
Hyperthermia- 38
Hypothermia- 35
What is negative feedback?
When a change from a set point are detected, and physiological mechanisms are used to return to the set point
Describe the process of negative feedback
A deviation from the normal set point is detected nay receptors. This can be an excess or deficiency of something.
Effectors are stimulated to initiate corrective mechanisms
The normal conditions are restored at the set point
What is positive feedback?
Where any change away from the normal set point stimulates more change to occur. This is therefore not a homeostatic mechanism
Positive feedback amplifies the change
What is the normal blood glucose level?
5 mmol dm-3
How does the pancreas respond to blood glucose levels increasing?
In the inglets of langerhans (in the pancreas), receptors on b cells detect the increase
The b cells secrete insulin into the bloodstream
Insulin binds to specific protein receptors on the membrane of its target cells
Once insulin is released by the pancreas, what are the four ways in which it reduces glucose levels?
1) in increases the uptake of glucose by cells. Insulin causes more specific channel proteins to be inserted into the cell membrane. This increase the permeability of the membrane, so more facilitated diffusion of glucose occurs.
2) glycogenesis- insulin activates enzymes that convert glucose into glycogen in olive and muscle cells. Glycogen can then be stored
3) activates enzymes which convert glucose into fats, to store in adipose tissue
4) increases respiration rates in cells
How does the pancreas respond to glucose levels decreasing?
In the islets of langerhans, receptors on a-cells detect the decrease
A-cells re;ease glucagon into the bloodstream. Glucagon binds to specific membrane receptors on the membranes of its target cells
Once glucagon is released by the pancreas, what are the two ways in which it increases blood glucose levels?
Glycogenolysis- activates enzymes that catalyse the conversion of glycogen to glucose
Glucogenogenesis activate enzymes that convert amino acids and glycerol top glucose
In which part of the pancreas does homeostasis of blood glucose levels take place?
In the islets of langerhans
What is the general action of hormones?
They are produced by endocrine glands
Transported in the blood to target cells in other organs
The target cells have specific receptor proteins in the plasma membrane or cytoplasm, that the hormones bind to with complimentary structures
Where is adrenaline secreted and when is it secreted?
Secreted in the adrenal glands when blood glucose concentrations are low, then bins to receptors on liver cels
How does adrenaline increase the blood glucose concentrations?
Binds to specific receptors on the cell membranes of livers
They active enzymes that cause glycogenolysis
Deactivate enzymes that cause glycogenesis
Describe the process of how adrenaline or glucagon cause glycogenolysis
They act via a second messenger.
- glucagon/ adrenaline (1st messenger) bind to the receptor sites on the liver cells. This activates the enzyme adenylate cyclase inside the membrane.
- adenylate cyclase converts ATP to cyclic AMP (cAMP), That then activates the enzyme protein kinase A.
- protein kinase A activates a chain of reactions that convert glycogen into glucose, to increase blood glucose concentrations.
What is diabetes mellitus?
A disease where the body cannot effectively control blood glucose levels.
It can be type 1 or type 2 diabetes
Describe the causes, effects and treatments of type I diabetes. What else is it known as?
Insulin dependent diabetes
Causes- B cells do not produce insulin, because they have been destroyed by the body due to an autoimmune response
Effects- hyperglycaemia, which can be fatal. The kidneys also do not reabsorb glucose so it may be lost in excretion
Treatments- monitor glucose levels regularly using glucose biosensors. Use insulin injections and manage diet and exercise to avoid hypoglycaemia
Why can insulin not be given to people with type 1 diabetes in a tablet?
Insulin is a protein, so will be hydrolysed in the stomach and small intestine by proteases. Or will be denatured in the stomach due to the low pH
What are causes and treatments of type II diabetes, what is it also known as?
Insulin independent diabetes
Causes- a gradual loss of target cells responsiveness to insulin, caused by receptor abnormalities. Usually linked with obesity, lack of exercise or poor diet. More common
Treatments- manage with a careful regulation of diet and exercise. Loose weight. Eventually insulin injections may be necessary
What are diagnostic features associated with type II diabetes?
High blood glucose levels
Kidney cannot reabsorb glucose to excreted in urine
Thirsty
Frequent urination
Craving of sweet foods
What are the health impacts and economic impacts of type II diabetes?
Health impacts- increased risk of cardiovascular disease, blindness, amputation, kidney disease and depression
Economic impacts- in 2018 the NSH spent £14 billion a year on treatment
Early retirement
Absences from work
How might food and drink manufacturers make their products healthier? Why might this not be beneficial?
Reduce portion size, low cal sweeteners, reduce sugar/salt/fat content. This all rescues caloric intake.
Change in formulation of products may alter taste so customers don’t buy. Not all customers a]want to be healthier
What is osmoregulation? Where does it take place?
The regulation of a constant water potential, controlled by the kidney
What are the two functions of the kidneys?
Excretion- filtration of blood to remove urea
Osmoregulation- maintaining a constant water potential
Describe the structure of the overall kidneys
Outer cortex
Medulla- which is organised into renal pyramids
The pelvis that leads to the ureta, which leads to the bladder. (The pelvis drains urine into the ureta)
The renal artery carries blood from the aorta to the kidneys
The rental veins carry blood away from the kidneys, to the vena cava
Each kidney is made of a million fine tubules called nephrons
What are nephrons?
Fine tubules that are surrounded by capillaries
The make up the kidneys and are divided into different functional regions
What are the features of a nephron?
The renal artery leads to the afferent arteriole (wider)
Glomerulus
Efferent arteriole (narrower)
The renal vein leads to the vasa recta, which surrounds the loop of henle
Bowman’s capsule leads to the proximal convoluted tubule, then to the loop of Henle, which leads to the distal convoluted tubule and then the collecting duct
In which regions of the kidneys are bowman’s capsule, PCT, loop of henle and the DCT found?
Bowman’s capsule- cortex
PCT- cortex
Loop of henle- both cortex and medulla
DCT- cortex
Describe the structure of the bowman’s capsule
The inner cell lining of the capsule is lined with cells called podocytes.
The podocytes have many finger like processes that have gaps between them, and fit closely with processes of adjacent podocytes with small filtration slits between them
The processes wrap round capillaries, separated by a mesh of fibres called the basement membrane.
Capillaries also have pores in their endothelial cells
This creates a filter
Describe the process of ultrafiltration, and where it takes place
Occurs in the bowman’s capsule
The afferent arteriole is wider than the efferent arteriole, creating a high hydrostatic pressure in the glomerulus.
Water and small molecules are forced out the capillary into the lumen of the bowman’s capsule, forming the filtrate.
The water molecules pass out the pores of the endothelial cells in the capillary, and through the basement membrane
Then through the filtration slots in the processes of the podocytes.
The filtrate then flows from the bowman’s capsule into the proximal convoluted tube
After ultrafiltration, what will and wont be found in the filtrate? Why
Not in the filtrate-
Red blood cells, platelets, plasma proteins
They are too large to pass through the basement membrane
In the filtrate-
Water, urea, amino acids, glucose, sodium ions, fatty acids and glycerol
What process occurs in the proximal convoluted tubule? What occurs during this process
Selective reabsorption
Most filtrate is re absorbed into the blood, filtrate that is not reabsorbed continues through the nephrons and are excreted out the body as urine
Give adaptations of the proximal convoluted tubule and why they are important?
Many mitochondria- produces ATP for active transport
Microvilli- increases the surface area of the
Explain how glucose is reabsorbed into the blood in the proximal convoluted tubule
Using cotransport
Sodium ions are actively transported out the PCT cells into the lumen/filtrate. This maintains a concentration gradient
Glucose and sodium ions move into the PCT cells from the filtrate using specific co-transport carrier proteins
Glucose leaves the PCT cells by facilitated diffusion, into the blood flowing through the efferent arteriole
The movement of sodium ions and glucose into the PCT cells causes the water potential to decrease, so water ovens by osmosis from the filtrate into the cells.
Filtrate leaves the proximal convoluted tubule and enters the loop of henle
What is the function of the loop of henle?
To create a concentration of sodium ions, and therefore a water potential gradient, through the medulla. Therefore water can be reabsorbed from the collecting duct
Why is the loop of henle referred to as the countercurrent multiplier?
Fluids flow In opposite directions in two sides of the loop.
Multiplier because the deeper into the medulla the loop goes, the more concentrated the Na + is in the tissue fluid surrounding (and the lower the water potential)
Explain how the ascending and descending limbs in the loop o henle decrease the water potential of tissue fluid?
Ascending limb- carries filtrate through the medulla
Permeable to sodium ions, impermeable to water
At the top of the limb, sodium ions are actively transported out of the limb into the tissue fluid of the medulla
At the bottom, sodium ions move into the tissue fluid by facilitated diffusion
Conc. gradient of Na + down medulla- highest conc. at the top and lowest at the bottom. Therefore water potential gradient
Descending limb- carries filtrate down into the medulla
Permeable top water and impermeable to Na + ions
Water leaves filtrate by osmosis and enters tissue fluid in the medulla
Filtrate becomes more concentrated so water potential decreases.
Water in the medulla tissue fluid can then be reabsorbed into the vasa recta by osmosis
Filtrate leaves loop and enters the distal convoluted tubule
How do the distal convoluted tube and collecting ducts also reabsorbed water, after the loop of henle?
After the ascending limb, the concentration of Na+ in the tissue fluid of the medulla is high, so the water potential decreases. Therefore water moves out the filtrate in the collections duct into the tissue fluid by osmosis
The water is then reabsorbed by the vasa recta
How is having a thicker medulla beneficial?
Thicker medulla means the loop of henle is longer
More Na+ ions pumped out the ascending limp into tissue fluid. Conc. of Na+ is higher in medulla
More water moves out the collecting ducts also by osmosis, so more water can be reabsorbed by the vasa recta
What is ADH and explain its role in osmoregulation
Anti-diuretic hormone
- a peptide hormone
It is synthesised by the hypothalamus, and stored in the posterior pituitary
It is released into the bloodstream and acts on DCT and collecting ducts also cells, by a second messenger model
It makes the cells more permeable
Explain how ADH controls blood water potential y negative feedback, if the water potential decreases.
Osmoreceptors in the hypothalamus detect the decrease in water potential
The hypothalamus sends nerve impulses to the posterior pituitary gland, which is then stimulated top release more ADH into the blood.
ADH makes the cells of the DCT and collecting ducts also more permeable, so more water leaves by osmosis
More water reabsorbed by the vasa recta
Water potential decreases and a low volume of highly concentrated urine is produced
How does ADH increase the permeability of cells in the DCT and collecting ducts also walls?
It increases the transcription of genes that code for aquaporines
More aquaporines are produced and inserted into the mem,brands of cells making the wall.
More water can move out the filtrate into the medulla tissue fluid, and therefore into the vasa recta
(If less ADH is releases aquaporines are removed from the membranes to decrease permeability)
What are three symptoms that someone who lacks ADH would have
Low blood pressure
Thirst
Frequent need to urine
