✅16 - Homeostasis Flashcards
What is homeostasis?
The maintenance of an internal environment within restricted limits in organisms
What does homeostasis involve?
Trying to maintain the chemical make-up, volume and other features of blood and tissue fluid within restricted limits
What does homeostasis ensure?
That the cells of the body are in an environment that meets their requirements and allows them to function normally despite external changes
What are some examples of things maintained by homeostasis?
pH
Temperature
Water potential
What is the optimum point?
The point at which the system operates best
What is the optimum point monitored by?
A receptor
What is a coordinator?
Coordinates the information from receptors and sends instructions to appropriate effectors
What is a feedback mechanism?
The way by which a receptor responds to a stimulus created by the change to the system brought about by the effector
What is negative feedback?
When the change produced by the control system leads to a change in the stimulus detected by the receptor and turns the system off.
What is positive feedback?
When a deviation from an optimum causes changes that result i an even greater deviation from the normal
What is an example of positive feedback?
When a stimulus leads o a small influx of sodium ions in a neurone and the permeability of the neurone to sodium ions is increased.
Control systems normally have many…
…receptors and effectors
What are endotherms?
Animals which generate heat from inside their bodies
What are exotherms?
Animals which obtain a proportion of their body heat from sources outside their bodies
Where are hormones produced?
In glands, which secrete the hormone directly into the blood (endocrine glands)
What do hormones act on?
Target cells, which have specific receptors on the cell surface membrane that are complementary
What is the secondary messenger model?
One mechanism of hormone action, used by the two hormones in blood glucose regulation, adrenaline and glucagon
How does the secondary messenger model work for adrenaline and glucagon?
Adrenaline binds to a transmembrane protein receptor within the cell surface membrane of a liver cell
The binding causes the protein to change shape on the inside of the membrane
The change in protein shape leads to activation of an enzyme adrenal cyclase which converts ATP to cyclic AMP
The cAMP acts as a second messenger that binds to protein kinase enzyme, changing its shape and activating it.
The active protein kinase enzyme catalysed the conversion of glycogen into glucose which moves out of the liver cell by facilitated diffusion and into the blood, through channel proteins
What is the role of the pancreas in regulating blood glucose?
It produces enzymes for digestion and hormones insulin and glucagon for regulation of blood glucose
Which cells produce the hormones?
Islets of Langerhans
What do the islets of langerhans include?
Alpha cells and Beta cells?
What is the function of alpha cells?
Larger cells which produce glucagon
What is the function of Beta cells?
Smaller cells which produce insulin`
What is the role of he liver in regulating blood glucose?
The hormones produced by the pancreas take effect in the liver
What is glycogenesis?
Conversion of glucose into glycogen when glucose concentration is higher than normal
What is glycogenolysis?
The breakdown of glycogen to glucose, when blood glucose concentration is lower than normal
What is gluconeogenesis?
The production of glucose from sources other than carbohydrate such as glycerol and amino acids
What are the consequences if blood sugar falls too low?
Cells will be deprived of energy and die, as glucose is a substrate for respiration. Brain cells are especially sensitive
What happens if blood glucose concenration is too high?
It lowers the water potential of the blood and creates osmotic problems that can cause dehydration
What are the three sources of blood glucose?
Directly from the diet via hydrolysis of other carbohydrates
From the hydrolysis in the small intestine of glycogen (glycogenolysis)
From glconeogenesis
What is insulin?
A globular protein made up of 51 amino acids
How is insulin detected by cells?
Almost all body cells have glycoprotein receptors on their cell surface membrane which bind specifically with insulin
What happens when insulin binds with a receptor?
- change in tertiary structure of glucose transport proteins, causing them to change shape and open, allowing more glucose in
- increase in number of carrier proteins responsible for glucose transport in the cell membrane
- activation of enzymes that convert glucose into glycogen and fat
How are blood glucose concentrations lowered?
- by increasing the rate of absorption of glucose into cells, especially muscle cells
- by increasing the respiratory rate of cells, which therefore use up more glucose from the blood
- by increasing the rate of conversion of glucose into glycogen (glycogenesis) in liver and muscle cells
- by increasing the rate of conversion of glucose to fat
What actions does glucagon have?
- attaching to specific protein receptor son the cell membrane of liver cells
- activating enzymes that convert glycogen to glucose
- activating enzymes involved in the conversion of amino acids and glycerol to glucose (gluconeogenesis)
What is the role of adrenaline in regulating blood glucose levels?
- increase blood glucose concentration
- attaches to protein receptors on the cell membrane of target cells
- activating enzymes that causes the breakdown of glycogen to glucose in the liver
The hormones insulin and glucagon act in…
…opposite directions
What are the two types of diabetes?
Type 1 (insulin dependent) and Type 2 (insulin independent)
What is type 1 diabetes?
When the body is unable to produce insulin
What is type 2 diabetes?
When glycoproteins receptors on body cells are lost or lose their responsiveness to insulin, later onset around 40 years of age
What are the controls for type 1 diabetes?
Injections of insulin and use of biosensors to monitor blood glucose concentrations
What are the controls for type 2 diabetes?
Regulating the take of carbohydrate in the diet and matching this to the amount of exercise taken
What is osmoregulation?
The homeostatic control of the water potential of the blood
What are the parts of the kidney?
Fibrous capsule Cortex Medulla Renal pelvis Ureter Renal artery Renal vein
What is the fibrous capsule?
An outer membrane that protects the kidney
What is the cortex?
A lighter coloured outer region made up of renal (Bowman’s) capsules,convoluted tubules and blood vessels
What is the medulla?
A darker coloured inner region made up of loops of Henle, collecting ducts and blood vessels
What is the renal pelvis?
A funnels shaped cavity that collects urine into the ureter
What is the ureter?
A tube that carries urine to the bladder
What is the renal artery?
Supplies the kidney with blood from the heart via the aorta
What is the renal vein?
Returns blood to the heart via the vena cava
What are nephrons?
Tiny tubular structures that are the basic structural and functional units of the kidney
What are the parts of the nephron?
Renal (Bowman’s) capsule Proximal convoluted tubule Loop of Henle Distal convoluted tube Collecting duct
What is the Bowman’s capsule?
The closed end at the start of the nephron. Cup shaped and surrounds a mass of blood capillaries known as the glomerulus. The inner layer of the capsule is made up of specialised podocytes
What is the proximal convoluted tubule?
A series of loops surrounded by blood capillaries. Its walls are made of epithelial cells which have microvilli
What is the loop of Henle?
A long, hairpin loop that extends from the cortex into the medulla of the kidney and back again. It is surrounded by blood capillaries
What is the distal convoluted tube?
A series of loops surrounded by blood capillaries. It’s walls are made of epithelial cells, but it is surrounded by fewer capillaries than the proximal tube
What is the collecting duct?
A tube into which a number of distal convoluted tubules from a number of nephrons empty. It is lined by epithelial cells and becomes increasingly wide as it empties into the pelvis of the kidney
What is the afferent arteriole?
A tiny vessel that ultimately arises from the renal artery and supples the nephron with blood. 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 glomerular capillaries recombine to form the efferent arteriole
What is the efferent arteriole?
A tiny vessel that leaves the renal capsule. It has a smaller diameter than the afferent arteriole and so causes an increase in blood pressure within the glomerulus
What are the blood capillaries?
A concentrated network of capillaries that surrounds the proximal convoluted tubule, the loop of Henle and the distal convoluted tube and from where they reabsorb mineral salts, glucose and water
What are the stages of osmoregulation in the nephron?
The formation of a glomerular filtrate by ultrafiltration
Reabsorption of glucose and after b the proximal convoluted tubule
Maintenance of a gradient of sodium ions in the medulla by the loop of Henle
Reabsorption of water by the distal convoluted tubule and collecting ducts
Where does blood enter the kidney from?
The renal artery
What is the glomerular filtrate formed of?
Water, glucose and mineral ions squeezed out of the capillary
What is movement of filtrate out of the glomerulus resisted by?
Capillary epithelial cells
Connective tissue and epithelial cells of the blood capillary
Epithelial cells of the renal capsule
The hydrostatic pressure of the fluid in the renal capsule space
The low water potential of the blood in the glomerulus
What are the modifications made to reduce the barrier to flow of the filtrate?
The inner layer of the renal capsule is made up of highly specialised podocytes high allow the filtrate to pass beneath them
The endothelium of the glomerular capillaries has spaces up to 10nm wide between its cells
How much of the filtrate is reabsorbed back into he blood, and where?
Nearly 85%, by the proximal convoluted tubule
How are the epithelial cells in the proximal convoluted tubule adapted for reabsorption?
Microvilli provide a large surface area to reabsorb substance from the filtrate
Infolding at their bases to give a larger surface area to transfer reabsorbed substances into blood capillaries
A high density of mitochondria to provide ATP for active transport
What is the process of reabsorption of glucose through the proximal convoluted tubule?
Sodium ions are actively transported out of the cells lining the tubule into blood capillaries which carry them away. Sodium ion concentration of these cells lowered
Na+ now diffuse down a concentration gradient from the lumen of the PCT into epithelial lining cell through carrier proteins
Carrier proteins are specific types, each of which carries another molecule along its the sodium, cotransport
The molecules cotranported into cells them diffuse into the blood
What is the loop of Henle responsible for?
Water being reabsorbed front he collecting duct, concentrating the urine so that it has a lower water potential than the blood
What are the woe regions of the loop of Henle?
The descending limb
The ascending limb
What are the features of the descending limb?
It is narrow, with thin walls that are highly permeable to water
What are the features of the ascending limb?
It is wider, with thick walls that are impermeable to water
What does the water potential of the blood depend on?
The concentration of solutes like glucose, proteins, sodium chloride and other mineral salts
What may cause the water potential of the blood to lower?
To little water being consumed
Too much sweating
Large amounts of ions, eg sodium chloride, being taken in
What detects a fall in water potential?
Osmoreceptors in hypothalamus of the brain
When is ADH produced?
When water is lost and osmoreceptor cells shrink, causing the hypothalamus to produce ADH
What effect does ADH have on the kidneys?
It increases the permeability to water of the cell surface membrane of the cells making up the distal convoluted tubule and the collecting duct
What can cause the water potential of the blood to be increased?
Large volumes of water being consumed
Salts used in metabolism or excreted not being replaced in the diet
How does the body respond to an increase in water potential of the blood?
The osmoreceptors in the hypothalamus detect the rise in water potential and increase the frequency of nerve impulses to the pituitary gland to edge crease ADH release
Less ADH via the blood leads to a decrease in the permeability of the collecting ducts to water and urea
Less water is reabsorbed into the blood from the collecting duct
More dilute urine is produced and the water potential of the blood falls
When the water potential of the blood has returned to normal, the osmoreceptors in the hypothalamus cause the pituitary to raise its ADH back to normal levels
